Workshop for the production of asbestos-cement sheets. Coursework: Production of asbestos-cement products and characteristics of JSC Belgorodasbestcement Technology of asbestos-cement products
INTRODUCTION
Asbestos-cement production is a fairly strong source of air pollution, since asbestos is one of the main components for the production of asbestos-cement slate. According to the degree of impact on the human body, asbestos is classified as hazard class III.
A large number of scientific studies are carried out in the world on the subject of the effect of asbestos on the human body and the environment. The abundance of conflicting data sometimes baffles both consumers and producers.
The most common and widely used asbestos is chrysotile asbestos. The unique combination of high mechanical strength of the fiber, significant adsorption capacity, fire and heat resistance, alkali resistance and the ability to form stable compositions with various inorganic and organic binders made chrysotile asbestos indispensable in the production of more than 3000 types of industrial products.
The relevance of this work is obvious. Since no substitutes with unique properties of chrysotile asbestos have been found in the world yet. And artificial mineral fibers, used as substitutes, are obtained at the cost of high energy costs required to melt the raw stone. The only way to reduce the harmful impact on the natural environment and make people healthier is to modernize the treatment facilities at the enterprise. And it is even possible to introduce innovative technologies that prevent the formation of harmful gaseous substances and dust particles into the atmospheric air.
RAW MATERIALS FOR THE PRODUCTION OF ASBESTOCEMENT SHEETS
The technological process for the production of all types of materials and products is determined by the properties of the raw materials used and those requirements that apply to the produced materials and products.
The main raw materials for the manufacture of asbestos-cement sheets are three components: asbestos, cement and water. The raw mix (based on dry matter weight) contains on average 85% cement and 15% asbestos.
CHRYSOTYL-ASBESTOS
Asbestos is a group of minerals that have a fibrous structure and, under mechanical stress, are capable of breaking down into the finest fibers. Chrysotile asbestos is used in the production of asbestos-cement sheets. The chemical composition of chrysotile asbestos is expressed by the formula 3MgO-2Si02-2H20. In terms of chemical composition, asbestos minerals are hydrous silicates of magnesium, iron, calcium and sodium.
The industrial value of asbestos minerals is determined by their following properties: fiber length, elasticity, strength, ability to break down into thinnest fibers under mechanical action, chemical resistance when exposed to acids and alkalis, ability to withstand high temperatures without significant changes in physical properties.
Asbestos has a high adsorption capacity. And in a mixture with Portland cement, when wetted with water, it retains well on its surface the products of cement hydration that bind asbestos fibers.
The length of the asbestos fibers has a great influence on the quality of products. This is the main sign of dividing asbestos into grades. For the production of asbestos-cement products, short-fiber asbestos-3, 4, 5 and 6 grades with a fiber length from 10 mm to several hundredths of a mm are used. Sometimes part of the asbestos (10-15%) is replaced with basalt or slag mineral wool.
Table 1 - Grades and grades of asbestos used for the production of asbestos-cement products
Asbestos with a longer fiber length is not used, since in a bucket mixer it is twisted into bundles, thereby reducing the reinforcing ability of asbestos fibers.
Figure 1 - Chrysotile asbestos fibers (X-ray spectral analysis)
PORTLANDCEMENT M400
As a binder in the production of asbestos-cement sheets, special Portland cement is used for asbestos-cement products. In this case, Portland cement M400 is used. Such a cement is characterized by: a rapid increase in strength, both at the beginning and in the subsequent periods of hardening, a slow onset of setting (not earlier than 1.5 hours) and a sufficiently large fineness of grinding necessary in order to create a significant adhesion surface between the cement and finely fluffed asbestos fibers. This cement should not contain mineral additives (except gypsum).
The increase in the strength of the product must occur quickly enough for the transition of the semi-finished product to the finished product. The amount of additives in cement is set with the consent of the consumer, but not more than 3% (with the exception of gypsum). Gypsum is added to regulate the setting time in an amount of not less than 1.5% and not more than 3.5% of the mass of cement.
WATER
In the production of asbestos-cement sheets, water is consumed to prepare the asbestos-cement mixture and rinse the cloths and mesh cylinders of the forming machine. The water used for the production of asbestos-cement products should not contain clay impurities, organic substances and mineral salts. Clay particles, deposited on the surface of asbestos fibers, reduce their adhesion to cement, complicate the filtration of asbestos-cement slurry and reduce the mechanical strength of products.
The production of asbestos-cement sheets is associated with high water consumption. The waste water contains a significant amount of asbestos and cement, therefore it is returned to the technological cycle back. Working with recycled process water not only avoids environmental pollution, but also provides advantages. The saturation of the circulating water with Ca ions prevents the gypsum from leaching out and prevents premature setting, the absence of CO 2 in it eliminates the clogging of the meshes with calcium carbonate.
When asbestos is mixed with Portland cement and water, the asbestos fibers are evenly distributed in the mass of cement, with each fiber being surrounded by cement paste. By adsorbing calcium hydroxide and other products of cement hydration released during cement hardening, asbestos reduces their concentration in the solution. As a result, the setting and hardening of the cement is accelerated, it is firmly bound to the asbestos fibers. Due to the further crystallization of cement hydration products, the bond strength of asbestos fibers with cement stone in asbestos-cement products increases.
DELIVERY OF RAW MATERIALS TO THE WAREHOUSE
PORTLANDCEMENT M400
Delivery of cement from under-rail warehouses to the warehouse of the enterprise is delivered by a cement truck.
A cement truck is a tank with equipment for transporting cement. According to GOST 27614-93, these machines, depending on the method of loading and unloading cement, are divided into two types: auto cement trucks with pneumatic unloading and auto cement trucks with pneumatic unloading and pneumatic unloading. Also, cement trucks, depending on the weight of the transported cargo, are divided into standard sizes: 11; 13.5; 14.7; 15; twenty; 25; 30 t. For each standard size, excess of the weight of the transported cargo is allowed up to 1 t.
The cement truck has the following device. A semi-trailer tank is installed at an angle of 7 - 9 degrees on a tractor vehicle. The inclination of the tank ensures a better supply of cement to the unloading device. The front part of the tanker rests on the tractor's fifth wheel, the rear, through the bracket and springs, on the axle of the running wheels. The tank has a cylindrical or elliptical shape with specific bottoms. On the outside of the tank, there are support posts, a system of air ducts, a moisture-oil separator, wings of traction wheels, a ladder and a platform for service.
In the upper part of the tank there are two hatches for loading cement; inside the tank there is equipment for pneumatic unloading of cement.
Figure 5 - Cement truck (a) and its tank (b)
1 - semi-trailer; 2 - compressor; 3 - tractor; 4 - support post; 5 - service area; 6 - stairs; 7 - loading hatch; 8 - etook; 9 - air passage; 10 - plug valve; 11 - unloading branch pipe; 12 - air supply hose to the purge nozzle; 13 - check valve; 14 - moisture-oil separator; 15 - air duct to aerial trays; 16 - drain cock; 17 - pressure equalization pipe.
CHRYSOTYL-ASBESTOS
Currently, the asbestos-cement industry is organizing the supply of asbestos pre-calibrated in certain grades and compressed into small briquettes. The use of laminated briquette asbestos makes it possible to fully mechanize the loading and unloading operations and automate the technological processes of the procurement departments.
The transportation of batches of bags with asbestos is carried out by an onboard KamAZ-43118 with a carrying capacity of 11 tons. The bags must be carefully covered with tarpaulin or film. A pallet fixing device is provided inside the machine.
Figure 6 - KamAZ-43118 onboard. dimensions
UNLOADING RAW MATERIALS
PORTLANDCEMENT M400
Pneumatic unloading provides for the supply of air through a pipe under pressure to the aerial trays. The airway is a perforated steel sheet on which wire mesh and fabric are located. Coming under the lower part of the airlift, compressed air passes through the holes in the steel sheet, seeps through the fabric in streams and saturates the lower layer of cement. Mixing with compressed air. The cement becomes fluid and moves to the unloading device. Under pressure, cement can be transported to another container located at a height of 15-20 m.
Figure 7 - Scheme of unloading of a cement truck
1 - auto cement truck; 2 - bunker for cement (silo); 3 - device for dispensing cement.
To unload the cement, a sleeve is attached to the nozzle that directs the cement into the container, and the plug valve is opened. The aerated cement passes through the plug valve and, with the help of a blowing nozzle, which creates a vacuum at the plug valve, enters a stream of compressed air, which is fed into the container. Cement is poured onto the airways using slopes made of sheet steel and installed at an angle of 45-50 degrees to the horizontal plane.
To create the required air pressure, a rotary compressor is installed on the tractor chassis. To clean the pumped air from moisture and oil, a moisture-oil separator is installed on the compressor.
This way of unloading eliminates the loss of cement that occurs during manual loading and improves working conditions.
CHRYSOTYL-ASBESTOS
Asbestos is delivered to the enterprise in an on-board KamAZ. Unloading is carried out with a universal forklift TVEKS VP-05.
A universal forklift (auto-forklift) is used for unloading, transportation over short distances and stacking.
Figure 8 - Forklift universal TVEKS VP-05
Figure 9 - Overall dimensions of TVEKS VP-05
Table 2 - Specifications. Loader VP-05
RAW WAREHOUSE
PORTLANDCEMENT M400
When stored in large containers, cement, especially if it contains even a small amount of moisture, cakes, and often forms arches during unloading. These vaults make it difficult to unload the containers and, moreover, can cause an accident in the event of a collapse.
Therefore, during unloading, the cement is aerated, that is, air is introduced into it. This eliminates the possibility of vaults forming. The air, slowly flowing between the cement grains, makes them more mobile, and the aerated cement becomes fluid. In addition to ensuring that no arches are formed, aeration allows the silo to be completely unloaded. The cement from the silo is sent by pneumatic transport to the supply bins of the asbestos cement plant.
Figure 10 - Silo for storage of cement
Figure 11 - Scheme of a cement silo warehouse
1 - silo container; 2 - bottom unloader; 3 - pipeline (for unloading cement into the supply hopper); 4 - a hose that directs cement to the silo.
During storage, cement absorbs water vapor from the air and slowly hydrates. This process is more intense when the cement is freely washed with air or stored in a damp room. If the cement is in such conditions, then it cannot remain active for a long time.
CHRYSOTYL-ASBESTOS
Briquetted asbestos is produced in two grades - slate and pipe. The storage of the specified grades of asbestos can be organized in silos or bunkers. When using batch asbestos, dosing it will consist only in weighing a portion without compiling a batch.
The stock of asbestos at the enterprise must be calculated, depending on the distance from the asbestos deposit, from two weeks to one and a half months need for it. A closed warehouse is used for its storage.
The asbestos warehouse is adjacent directly to the asbestos fluffing and asbestos-cement mass preparation departments (preparation department).
RUNNERS
The most common apparatus in the first stage of fluffing is the runners. The wet method is more effective, since water, penetrating into the micro-crevices, has an unsticking effect. In addition, the elasticity of the fibers increases.
Runners are two rollers rolling in a horizontal bowl. Under the pressure of rollers moistened with water, the fibers are crumpled, split and mixed.
Figure 21 - Runners
1 - machine base; 2 - bowl; 3 - skating rink.
Dust collectors are installed above the receiving part of the conveyors for supplying asbestos to the runners, connected to devices for air purification
GOLLENDER
The final fluffing of asbestos is carried out in a gollender.
The gollender bath is filled to about 50% of its capacity with water clarified by recuperators. Then a certain weight portion of asbestos is loaded into it, which is gradually distributed throughout the entire volume of water. Since this asbestos has already been treated by the runners, as a result of this treatment, the bond between the fibers in the untreated asbestos bundles is drastically weakened. Gollender has to break these bundles into the finest filaments.
Figure 22 - Scheme of the working part of the gollender without auxiliary parts
1 - bath; 2 - partition; 3 - shaft; 4 - drum; 5 - pulley; 6 - channel; 7 - channel; 8 - removable casing; 9 - "slide"; 10 - "bar"; 11 - cast iron plug; 12 - branch pipe; 13 - steel scissors.
It consists of a cast-iron bath 1, divided in the middle by a partition 2. This partition divides the middle part of the bath into two channels 6 and 7. In channel 6 of the bath, a drum 4 is installed on the shaft 3 with steel knives reinforced along its generatrix 13. The drum is driven into a fast rotation through the pulley 5 of the belt drive using an electric motor. In the lowest part of the day of the bath, a branch pipe 12 is installed, closed with a cast-iron plug 11, through which the mass is poured out after the end of the process. From the outlet to the drum, the bottom of the bath goes with a certain rise, then it rises steeply around the drum, and after that it is steep at first, and then slowly descends to the outlet. The raised part of the 9th bottom is called a "slide". Its purpose is to increase the speed of movement of the contents of the bath in channels 6 and 7. To prevent the mass from being sprayed by the rotating drum, it is closed with a removable casing 8. Under the drum in the bottom of the bath there is a frame with steel knives 10, located at a slight angle to the drum knives. This knife frame is called a "bar". The edges of the knives facing the drum create a surface concentric with the surface formed by the knives of the drum.
Shaft bearings 3 are suspended on rods, which can be raised and lowered by a screw mechanism, changing the size of the gap between the knives of the drum and the bar.
MIXER
Figure 22 - Mixer of parallel type
1 - electric drive; 2 - metal vat with a conical bottom; 3 - nozzle for loading cement; 4 - cylindrical diffuser; 5 - three-bladed propeller; 6 - branch pipe for asbestos suspension; 7 - rotating shaft; 8 - electric motor; 9 - automatically opening valve; 10 - branch pipe for water from the working recuperator; 11 - branch pipe for draining the finished asbestos-cement mass.
BUCKET MIXER
Apparatus currently used in the asbestos-cement industry for the preparation of asbestos-cement mass are mainly of periodic action, and the forming machines must be fed with such a mass continuously. To create a stock of asbestos-cement mass, a bucket mixer is installed.
Figure 23 - Bucket mixer (vertical section)
1 - drive; 2 - vat; 3 - blades; 4 - crosses; 5 - hatch for cleaning and changing buckets; 6 - bucket wheel; 7 - receiving box; 8 - hatch for flushing the mass and rinsing the vat; 9 - shaft.
The bucket mixer consists of a metal vat 2, which has the shape of a truncated cone (with a small angle at the top), somewhat narrowing towards the drive of the mixing device. A shaft 9 is installed along the axis of this vat, which is driven into rotation through a drive 1 by an electric motor. On the shaft are mounted crosses 4 with blades 3. At the front end of the vat has a narrow bell-shaped cavity in which a frame circle with buckets 6 fixed on it rotates, called a bucket wheel. In the end wall of the vat, adjacent to the bucket wheel, a receiving box 7 is installed on its inner side, the drain from which goes out. Wheel buckets scoop up the asbestos-cement mass from the vat and pour it into the receiving box. The hatch 5 is used for cleaning and changing the buckets, and the hatch 8 is for draining the mass and rinsing the vat.
The mixer should not be replenished when there is a lot of mass in it, since the mass "grows old" with prolonged use. the cement grains are covered with a hydrated gel containing a lot of water. This increases the water-cement ratio in the formed products and their porosity after hardening.
From the mixer, the asbestos-cement mass is channeled into the baths of the mesh cylinders of the forming machine. The concentration of the mass in the mixer is slightly higher than it is necessary for the operation of the cylinder-vane machine.
To obtain the mass of the required concentration, water taken from the lower part of the recuperators is continuously introduced into the gutter supplying the asbestos-cement mass to the forming machine.
SM-943A
Figure 24 - Diagram of a three-cylinder cylindrical machine
The mesh part of the machine has three baths 1 with mesh cylinders 2 located in them. Between the ends of the cylinders and the sides of the baths, there are tape seals that prevent the suspension from leaking from the bath into the cylinders. Sealing tapes are fixed on stops 3. The baths have paddle mixers 4 that mix the asbestos-cement suspension entering the bath through compartment 6, separated by a partition 7, which protects the layer formed on the surface of the cylinder from flushing. In the bottom of the baths there are hatches for their washing and emergency drainage of the suspension. On the sheet-forming machine CM-943, mesh cylinders have a diameter of 1000 mm and a length of 1400 mm. They are a frame structure consisting of a shaft, spokes and rings on which steel strips located along the generatrix of the cylinder are supported. Between the strips, there are 10 mm wide slots for discharging the filtrate, the cross-sectional area of which is 65% of the entire surface of the cylinder. Two nets are put on the cylinders with tension - the lower one is made of brass and the upper one is made of phosphor bronze. The lower mesh is attached to the cylinder frame with wires, and the ends of the upper mesh are butt-welded or overlapped. The immersion depth of the mesh cylinders in the suspension is about 70% of their diameter. To flush the mesh of the cylinders, sprinkler tubes are installed 5. To the surface of the mesh cylinders by squeezing shafts 8 installed on the frame 12, the cloth 11 is pressed against the mesh cylinder. The pressure of the shafts on the mesh cylinder is created by their own mass and hydraulic cylinders 9. In front of the squeezing rolls there are water-separating rollers 10, which prevent spreading on the cloth of water squeezed out by the shafts.
Figure 25 - Diagram of a three-cylinder cylindrical machine Mesh cylinder and bath
Baths and mesh cylinders are numbered along the course of the cloth: the first bath and cylinder receive the cloth, and above the third cylinder, the cloth goes around the squeezing roller and moves to the vacuum box 13.
A centering device 14 is installed behind the vacuum box, which automatically holds the felt in the working position so that the axis of the felt coincides with the axis of the machine.
After the vacuum box, the felt moves to the formatting drum 25 and goes through three stages of squeezing: additional press rolls 16, 17 and the main press roll 18. The pressure between the press rolls and the formatting drum is created by hydraulic cylinders 19.
Bending around the main press roll, the felt comes to the felt-cleaning device, consisting of the accelerating roll 20, the swatter 21 and the washing tubes 22. The washed wet cloth moves to the tensioner 23, then it is wrung out between the rollers 15 and goes to the first vat to start a new working cycle.
The movement of the machine is reported by the main drive connected to the main press roll 19. The latter transfers rotation to the formatting drum 25 in contact with it, and this, in turn, to the press rolls 16 and 17.
The technical cloth, sandwiched between the formatting drum and the main press roll, acts as a driving belt that drives the mesh cylinders and the squeezing rolls lying on them.
The sheet forming machine works as follows. At idle, with the washing tubes turned on, the cloth is soaked, its tension is adjusted, and the serviceability of individual machine units is checked. Then the machine is stopped, the drives are turned on, rotating the agitators in the baths, and the asbestos-cement mass is fed into the baths. After it fills the baths to the working level, which is 10-12 cm from the sides, the machine is started working. Asbestos cement is filtered through the mesh of the cylinders under the influence of the difference in levels in the bath and in the cavity of the cylinders. Water and fine fractions of asbestos cement (up to 10% by weight of raw materials) pass through the mesh, and the bulk of asbestos-cement particles is deposited on the surface of the mesh cylinder in the form of a wet layer. This layer is formed on the working cylinders and is removed from their surface with a cloth. Simultaneously with the removal of the layers, they are also compacted due to the pressure of the squeezing rollers. The moisture content of the layer decreases. The layers removed from the three mesh cylinders are transported by felt to the vacuum box.
The last stages of compaction and dewatering of the layer of asbestos cement lying on the felt are carried out by a format drum and press rolls. The pressure between the sizing drum and the press rolls will build up. As a result of compaction, the moisture content of asbestos cement decreases. The layer is removed from the surface of the felt onto the surface of the sizing drum. The layers removed from the felt are wound onto a sizing drum until the thickness of the asbestos cement on its surface reaches the specified sheet thickness. Then, by a signal from the thickness gauge 26, the cutter 24 is automatically turned on, the roll-off while the machine is moving is cut along the generatrix and removed from the sizing drum onto the conveyor of the cutting device, and layers for the next roll are wound on the sizing drum.
Having given the asbestos cement to the format drum, the cloth is washed from dirt under the influence of the rotating rollers of the swatter 21 and the water flowing out under pressure from the tubes 22. The squeezing of the soaked cloth by rollers 15 is very effective for removing dirt.
Table 3 - Specifications. Cylindrical sheet-forming machine SM-943A
SCISSORS CUTTING CM-1162
Cutting scissors SM-1162 are intended for transportation of asbestos-cement roll from the sheet-forming machine to the shears, cross cutting of roll on workpieces, dumping of cross cuttings, transporting workpieces to the corrugator.
Figure 26 - Cutting scissors SM-1162
1 - rack; 2 - receiving conveyor; 3 - discharge conveyor; 4 - scissors; 5 - feeding conveyor; 6 - scissors drive; 7 - conveyor drive.
Shears for cutting have a receiving and feeding conveyors, rotary shears. They are controlled from the general electrical equipment and electrical automation system of the automated complex.
Figure 27 - Rotary scissors
1 - discharge conveyor; 2 - spring knife; 3 - cross knife;
4 - roller; 5 - circular knife; 6 - conveyor; 7 - drum transporting sheet; 8 - bed.
The sheets removed from the sizing drum of the sheet-forming machine are cut into specific sizes using rotary shears. In fig. shows a longitudinal section of these scissors. They consist of a frame 8, on the front of which a conveyor drum 6 is mounted on bearings, which feeds an asbestos-cement sheet removed from the format drum of the sheet-forming machine to the rotary shears. In the middle part of the frame, on sliding bearings, a transporting sheet drum 7 is installed, which receives an asbestos-cement sheet coming off the conveyor 6 and brings it to the shears' knives. First, the sheet comes to the circular shears 5, which cut off the side edges at the roll and cut it in the longitudinal direction, and then the drum 7 moves the sheet, already cut in the longitudinal direction, to the transverse knives 3, cutting it in the transverse direction.
An asbestos-cement sheet, cut into formats of the required dimensions, removes a shooting spring knife 2 from the surface of the drum, after which the formats are fed to a discharge conveyor 1, which brings them to the next apparatus. To prevent sliding of the cut sheet relative to the surface of the drum 7, two rollers 4 are installed, the surface of which is covered with a layer of rubber. These rollers press the asbestos-cement sheet against the drum 7.
The feed conveyor 6, drum 7, disc knives 5 and rollers 4 are in continuous motion during the operation of the sheet-forming machine, the peripheral speed of the drum 7 and rollers 4 is equal to the speed of movement of the conveyor belt 6. As a result, all parts of the sheet are told the same speed of movement, which protects the sheet from deformations.
The circular knives cut the longitudinal edges and cut it longitudinally into two strips. On a sheet-forming machine that produces corrugated sheets, three knives are installed, of which two of the outer ones are used to trim the longitudinal edges, and the middle one cuts the sheet in the longitudinal direction into two strips. So that the blades of the circular knives are not dull, narrow annular grooves are machined on the surface of the drum 7, into which the cutting edges of the knives enter to a certain depth.
The knives for cross-cutting the sheet are periodically set in motion by means of a special engagement clutch. The shaft, on which the hub with transverse knives is installed, turns on only when the front edge of the sheet approaches the knives, and it rotates until it has passed the entire sheet.
Table 4 - Technical characteristics. Cutting scissors SM-1162
SWEEPER SMA-233A
Rippler SM-233A is designed to give a wavy shape to flat workpieces coming from the feeding conveyor of the shears for cutting reel, calibration, slitting of folded sheets and their delivery to the stacker table.
Figure 28 - Roper СМА-233А
1 - wave section; 2 - calibration section; 3 - edge-shaped device; 4 - drive.
The main components of the ripper are the grooving section, the sizing section and the drive.
The ripper control is from the general electrical equipment and electrical automation system of the automated complex.
The corrugating section is a chain conveyor with eight profiled upper and lower chains. The working branches of the lower chains are the upper branches, of the upper chains - the lower branches. The lower chains are arranged in a horizontal plane in a fan-like manner so that at the exit from the section the chains are spaced relative to each other by a step equal to the step of the leaf wave. At the entrance to the section, the step between the circuits corresponds to the step of the wave sweep. Above the lower chains, the upper chains are coaxially and fan-shaped.
Due to the fan-shaped arrangement of the chains, the points of the workpiece, corresponding to the tops of the waves of the folded sheet, gradually come closer. In this case, the sections of the workpiece between the fixed points under their own mass gradually descend, forming wave troughs.
Thus, due to the transportation of the raw flat billet by the working branches of the lower and upper profile chains, the rolled sheet comes out of the section. When corrugated in this way, the sheet is practically not subjected to tensile forces in the transverse direction.
From the corrugating section, the sheets directly enter the calibration section, in which the lower profile chains are located between the upper profile chains with weighted linings.
The longitudinal edges of the sheet do not undulate from the extreme crests of the waves. When the sheet moves in the calibration section, its longitudinal edges fall under the circular knives, which cut them perpendicular to the sheet surface.
Table 5 - Specifications. Rippler SM-233A
STACKER SMA-260
The stacker СМА-260 of asbestos-cement sheets is intended for transferring the folded raw asbestos-cement sheets from the stacker table to the carts of the hardening conveyor.
Figure 29 - Stacker СМА-260
1 - frame; 2 - table; 3 - lever; 4 - rack; 5, 12 - chain drives; 6 - telescopic branch pipe; 7 - vacuum box; 8 - shock absorber cylinder; 9 - air duct; 10 - vacuum fan unit; 11 - spool.
The stacker СМА-260 for asbestos-cement sheets includes a stacker table, stacker, stacker drive, vacuum system drive.
The stacker table, designed to receive folded sheets from the calibrating section of the rounder to the sheet pick-up position and to dump damaged sheets onto the scrap cleaning conveyor, consists of a frame, a drive and driven shafts, a clutch engaging mechanism, a pusher installation and two crimping devices (right and left) ...
The stacker, which transfers the sheet from the stacker table to the hardening conveyor carriage, consists of two cast sidewalls, an assembled crosshead and a vacuum box.
The paver's drive, designed for turning the traverse with a vacuum box, has a part-turn hydraulic motor, two hydraulic shock absorbers and a control unit.
The control unit consists of axial throttles, mechanically controlled hydraulic valves, limit switches, roller levers, cam sectors and a flag. The block ensures that the stacker vacuum box stops at the required positions.
The drive of the vacuum system is designed to create a vacuum in the cavity of the vacuum boxes when removing the sheet from the stacker table and when transferring it to the hardening conveyor trolley, ”as well as to create excess pressure in the cavity of the vacuum box at the time the sheet is placed in the trolley. The drive of the vacuum system consists of a fan with an engine, pipelines and a spool, with the help of which, when the vacuum box is operating in vacuum mode, the suction cavity of the fan is connected to it, and when operating in the pressurization mode, the cavity of the blower is connected.
Table 6 - Specifications. Stacker СМА-260
CONVEYOR OF HARDENING SM-1158
The hardening conveyor SM-1158 is designed for curing corrugated asbestos-cement sheets in a vapor-air environment on special trolleys for a time sufficient for curing.
Picture 30 - СМ-1158 hardening conveyor
1, 2 - head and rear sections; 3 - frame; 4 - lubrication system; 5, 6 - front and rear wheel drive.
The hardening conveyor SM-1158 is a two-tier, double-chain, cart conveyor with a plane-parallel movement of the cart from one branch to another. It consists of a head and rear section, a frame, trolleys, front and rear section drives, a lubrication system and a hardening chamber.
Asbestos cement is an artificial stone material obtained by hardening a mixture of cement, asbestos and water.
Cement stone has good resistance to compressive and poor tensile loads. The introduction of a small amount (10 ... 20%) of fine-fiber asbestos into the cement, which has a high tensile strength, significantly changes the physical and mechanical properties of the cement stone. Such material has a sufficiently high strength, fire resistance, durability, low water permeability, thermal conductivity and electrical conductivity, but it is fragile and prone to warping when the humidity changes.
Nomenclature of asbestos-cement products, produced in the USSR, has over 40 items. They can be divided into the following main groups: profiled sheets - corrugated and semi-corrugated for roofs and wall cladding; flat slabs - ordinary and textured or painted for wall cladding; roofing and wall panels with a heat-insulating layer; pressure and non-pressure pipes and couplings to them; special products (architectural, sanitary, electrical, etc.).
In terms of the volume of production of asbestos-cement products, the Soviet Union ranks first in the world. More than half of the world production of asbestos-cement products is produced in our country.
Asbestos-cement products made from three main components: asbestos, cement and water. The raw mix (based on dry matter weight) contains on average 85% cement and 15% asbestos.
Asbestos refers to naturally occurring fine-fibrous inorganic masses, consisting mainly of hydrous or anhydrous magnesium silicates, and some varieties of calcium and sodium silicates. Chrysotile asbestos (3MgO 2SiO2 2H2O) is of the greatest importance in industry, the deposits of which in the USSR are the largest in the world.
When machining asbestos it is relatively easy to split into thin fibers (up to 0.0005 mm), which have flexibility, high mechanical strength (up to 600 ... 1000 MPa), fire resistance. In a fluffed state, asbestos is light, has low thermal conductivity and high electrical insulating properties.
Chrysotile asbestos has a high alkali resistance, but it is easily destroyed by acids.
As a result of asbestos fluffing, the surface of the fibers increases sharply, which contributes to its high adsorption activity in relation to cement.
Commercial chrysotile asbestos consists of a mixture of fibers of various lengths and their aggregates. Aggregates of asbestos with undeformed fibers, the size of which is more than 2 mm in diameter, are conventionally called "lumpy" asbestos, and less than 2 mm - "needles". "Fluffy" refers to asbestos in which the fibers are thin, deformed and entangled. Particles of the accompanying rock with a particle size of more than 0.25 mm are called "gal", and less than 0.25 mm - dust.
The length of the asbestos fibers has a great influence on the quality of products. This is the main sign of dividing asbestos into grades. The longer the average fiber length, the higher the grade. For the production of asbestos-cement products, short-fiber asbestos-3, 4, 5 and 6 grades with a fiber length from 10 mm to several hundredths of a mm are used, and their content is 50 ... 24% by weight, the remaining 50 ... 76% are to the share of dust and other non-fibrous particles. Sometimes part of the asbestos (10 ... 15%) is replaced with basalt or slag mineral wool.
As a binder in the production of asbestos-cement products, special Portland cement is used for asbestos-cement products. Such cement is characterized by a rapid increase in strength both at the beginning and in the subsequent periods of hardening, a slow onset of setting (not earlier than 1.5 hours) and a sufficiently large fineness of grinding necessary to create a significant adhesion surface between the cement and finely fluffed asbestos fibers. ... This cement contains at least 52% 3CaO · SiO2 and no more than 8% ЗСаО · А12Оз, it should not contain mineral additives (except for gypsum).
In the case of autoclaving of products, sandy Portland cement is used, which makes it possible to reduce the consumption of Portland cement clinker.
In the manufacture of asbestos-cement products, special white and colored cements are also used for facing.
When asbestos is mixed with Portland cement and water, the asbestos fibers are evenly distributed in the mass of cement, with each fiber being surrounded by cement paste. By adsorbing calcium hydroxide and other products of cement hydration released during cement hardening, asbestos reduces their concentration in the solution. As a result, the setting and hardening of the cement is accelerated, it is firmly bound to the asbestos fibers. Due to the further crystallization of cement hydration products, the bond strength of asbestos fibers with cement stone in asbestos-cement products increases.
To improve the technological properties of asbestos-cement slurry and freshly formed sheets, chemical additives are used, for example, as a plasticizer - LST
Water for the production of asbestos-cement products must be clean and slightly heated (up to 30 CC). You should not use swamp, peat, sea and other mineralized water.
Waterproof enamels and varnishes based on synthetic resins (glyphthalic, perchlorovinyl, nitrocellulose, etc.) are used for finishing asbestos-cement products.
Asbestos cement is an artificial stone material obtained as a result of hardening a mixture of cement, water and asbestos, which in asbestos cement reinforces the cement stone, providing high tensile and bending strength of products. Asbestos is a group of minerals that have a fibrous structure and, under mechanical stress, are capable of breaking down into the finest fibers.
Asbestos cement is a composite material. Thin asbestos fibers, uniformly penetrating the mass of hydrated cement, increase its tensile strength. The cement stone acts as a matrix. The introduction of reinforcement into the matrix leads to the production of a new material, the main mechanical properties of which differ from the properties of the matrix and reinforcement taken separately.
Asbestos cement has high mechanical strength in bending, low density, low heat and electrical conductivity, resistance against leaching by mineralized waters, high fire resistance, water resistance and frost resistance. The disadvantages of asbestos cement are reduced strength when saturated with water, brittleness and warpage when changing humidity.
General information and classification of asbestos-cement productsThe main raw materials for the production of asbestos-cement products are chrysotile asbestos and Portland cement. Depending on the type of products, as well as the quality of the used asbestos, its content in products is 10–20%, and in Portland cement, respectively, 80–90%.
In the production of colored asbestos-cement products, along with asbestos and cement, dyes are used, as well as colored varnishes, enamels and resins. To reduce gas leakage, the inner surfaces of asbestos-cement gas pipes are coated with resins.
Today the industry produces several dozen types of asbestos-cement products: sheets, pipes, panels and plates, shaped parts. They differ in shape, size, type of finish, manufacturing method and purpose.
Asbestos-cement materials are widely used for industrial, residential, civil and rural construction roofing products. In industrial construction, roofing products are used for non-insulated and insulated coatings. For non-insulated coatings in hot shops and unheated warehouse buildings, corrugated and semi-corrugated large-sized sheets with shaped parts are used. Hollow and tray slabs are used for insulated coatings. Hollow slabs are two profiled asbestos-cement sheets connected by aluminum rivets and having a mineral wool gasket inside. Tray slabs are asbestos-cement trays filled with thermal insulation material. Corrugated sheets of periodic profile are used for the construction of wall fences of buildings for various purposes.
Asbestos-cement corrugated sheets unified profile UV-7.5 most often they are used for the device of attic, as well as insulated roofs and wall fences of industrial and agricultural buildings and structures. These sheets are produced in lengths of 1750, 2000 and 2500 mm, 1125 mm wide and 7.5 mm thick. They have a high bending strength of at least 20 MPa, and a density of at least 1700 kg / m and frost resistance F50. Such sheets are produced on automated lines in an unlined way.
Unified asbestos-cement corrugated sheets profile UV-6 are produced in lengths of 1750, 2000 and 2500 mm, width of 1125 mm and thickness of 6 mm, with a wave step of 200 mm and an ordinary wave height of 54 mm, ultimate strength in bending of at least 18 MPa, density of 1700 kg / m and frost resistance of at least F25. UV-6-1750 sheets used for attic roofs of residential and public buildings, UV-6-2000 sheets - for overhangs of attic roofs and wall fences of industrial buildings and UV-6-2500 - for wall fences of buildings and structures.
Asbestos-cement corrugated sheets profile SV-40 used for roofing in mass housing construction, as well as for wall enclosing structures of industrial and agricultural buildings and structures. They are produced with a length of 1750 and 2500 mm, a width of 1130 mm and a thickness of 5 and 6 mm, with a wave pitch of 150 mm and a height of 40 mm.
Asbestos-cement facing slabs coated with polyester asbestos-plastic used for interior cladding of buildings. They are distinguished by a peculiar decorative surface, which cannot be obtained by conventional methods of painting and outlining. Coating asbestos-cement slabs with asbestos-plastics increases their impact strength and reduces water absorption. Double-sided coating with asbestos-plastic films increases the mechanical strength of the facing boards in bending by about 30%. The surface of the facing boards can be glossy or matte; depending on the composition of the pigments and the method of coating - monochromatic or marble-like, various shades and a wide variety of patterns.
Asbestos-cement flat facing slabs are intended for cladding the walls of the lobbies of metro stations, shops, as well as for the manufacture of finishing architectural details and other elements of buildings. They are produced both with ordinary gray and colored enamels, with a relief pattern. For painting, perchlorovinyl, organosilicon, water o-emulsion and other enamels, facade paints and varnishes are used. Plates should be painted in special workshops by spraying, filling or electrostatic methods. According to the production method, the slabs are made pressed and unpressed.
Asbestos-cement flat sheets They are used for the production of wall panels, slabs of coatings, plumbing cabins, partitions, installation of transport galleries, ventilation shafts, suspended ceilings, for interior and exterior cladding of residential and public buildings. Pressed and non-pressed sheets can be produced smooth and embossed, depending on the purpose - edged and unedged.
Asbestos-cement wall products are produced for external and internal wall cladding, as wall panels and partitions. For external wall cladding, gray and colored embossed products, colored pressed tiles are used; for interior cladding, sheets are used in which the front side is painted with waterproof colored enamels and varnishes.
Unified asbestos-cement wall slabs are a lightweight three-layer structure with the fastening of the facade colored asbestos-cement sheets to the wooden frame with aluminum layouts, and to the inner asbestos-cement cladding made of gray sheets - with screws "in the hole"; glass wool slabs are used as insulation. Wall panels are made up to 6000 mm long, 3300 mm wide and 140–170 mm thick.
Asbestos-cement pipes subdivided into pressure, gravity and ventilation; they are used for water supply and heating networks, oil and gas pipelines. Currently, the domestic industry produces asbestos-cement pipes with gas-tight coatings made of polymer materials. These pipes are the most economical and reasonably reliable substitutes for steel pipes. Asbestos-cement pipes with polymer coatings have high water-, petrol- and oil resistance, sufficient mechanical strength, good adhesion to asbestos cement. Asbestos-cement water pipes according to the maximum working pressure are divided into classes: up to 0.6 MPa - class VT6, up to 0.9 MPa - class VT9, up to 1.2 MPa - class VT12, up to 1.5 MPa - class VT15, up to 1, 8 MPa - class VT18. Gas pipes according to their maximum working pressure are subdivided into grades: GAZ-ND - for low-pressure gas pipelines (up to 0.005 MPa), GAZ-SD - medium pressure (up to 0.3 MPa).
Asbestos-cement boxes of rectangular cross-section are intended for ventilation of the air of industrial, auxiliary and domestic premises, industrial, residential and civil buildings. Seamless boxes without sockets are made from thin-walled pipes of special winding, freshly formed on pipe-forming machines. To give the freshly formed pipe a rectangular shape, a wooden core is inserted into it, consisting of three wedge-shaped parts. Then the boxes are stacked and kept for 1–2 days, after which the cores are removed, and the boxes are folded for further hardening. The boxes are made with a length of 4000 mm with an internal section of 150x300, 200x200, 200x300 mm and a wall thickness of 9 mm. Such boxes have high strength, bending strength at least 16 MPa, density - 1600 kg / m.
Asbestos-cement electrical arc-resistant boards (ACEID) are used for the manufacture of parts, panels, shields and bases of electrical devices and machines exposed to high temperatures and electrical discharge. Asbestos-cement rolls (blanks) for ACEID are made on sheet-forming machines and cut into formats of specified length, width and thickness. The formats are placed on metal spacers and pressed at a pressure of up to 20 MPa. After that, the boards on the gaskets harden for 10-16 hours, then they are separated from the gaskets, cut off and stored.
Special asbestos-cement products are also produced from asbestos cement. These include large-sized figured sheets used for vaulted roofs, cooling towers, grain dryers, etc.
Materials for the production of asbestos-cement productsPortland cement is used as a binder for the production of asbestos-cement products. It should hydrate quickly, but set relatively slowly. For the transition of a semi-finished product into a finished product, the increase in the strength of the product must occur quickly enough.
The setting and hardening of cement is carried out under specific conditions. Initial hydration occurs at a very high water-cement ratio. In the process of suction of the liquid phase, part of the neoplasms and small grains of clinker are filtered and, in addition, the physicochemical effect of asbestos on the hardening of cement in the composition takes place. For the production of asbestos-cement products, a special Portland cement with a specific surface area of 2200–3200 cm / g is used. The amount of additives in cement is set depending on the purpose, but not more than 3% (with the exception of gypsum). Gypsum is added to regulate the setting time in an amount of not less than 1.5% and not more than 3.5% of the cement mass, counting as S0.
According to the mineralogical composition, Portland cement should be alite (with a tricalcium silicate content of at least 52%), providing high productivity of molding machines and an intensive increase in the strength of asbestos cement. The content of tricalcium aluminate is limited, since it gives low strength of asbestos-cement products and low frost resistance; the content of free calcium oxide in cement should not exceed 1%, and magnesium oxide - 5%. Forming of asbestos-cement products takes longer than concrete products. In this regard, the beginning of setting for cement for asbestos-cement products should occur somewhat later than for ordinary Portland cement - not earlier than 1.5 hours from the moment of mixing with water, and the end - no later than 10 hours after the start of mixing.
The quality of asbestos-cement products largely depends on the quality of asbestos and the fineness of cement grinding and is characterized by the following indicators: texture (degree of fiber fluff), average fiber length, elasticity, moisture, degree of dust contamination. The greatest influence on the quality of such products is exerted by the length of asbestos fibers, therefore it is the main feature by which asbestos is divided into grades and grades. Depending on the length of the fibers, eight grades of chrysotile asbestos have been established, which, as already mentioned, is used for the production of asbestos-cement products. Asbestos with the longest fibers (more than 18 mm) is classified as grade 0 and 1, and with the shortest (less than 1 mm) - grade 7. For the production of asbestos-cement products, grades 3, 4, 5 and 6 are used with fiber lengths from 10 mm or less to several hundredths of a millimeter.
Water in the production of asbestos-cement products is necessary for the preparation of the asbestos-cement mixture and washing the felts and mesh cylinders of the forming machine. It should not contain clay impurities, organic substances and mineral salts. Clay particles, deposited on the surface of asbestos fibers, reduce their adhesion to cement, complicate the filtration of asbestos-cement slurry and reduce the mechanical strength of products. Organic impurities slow down the hydration of the binder.
Paints are used to paint wall tiles and sheets. Colored cements or alkali-resistant mineral pigments are also used that have high coloring ability, light and weather resistance and do not interact with the products of cement hydration: redoxide (artificial iron oxide), red lead, natural mummy, ocher, chromium oxide, ultramarine, manganese peroxide, etc. Sheets intended for cladding walls and panels of sanitary units and kitchens are coated with waterproof enamels and varnishes based on polymers (glyphthalic, perchlorovinyl, nitrocellulose).
Production of asbestos-cement productsCurrently, there are three methods for the production of asbestos-cement products: wet way - from asbestos-cement suspension, semi-dry - from asbestos-cement mass and dry - from dry asbestos-cement mixture. The most widespread method is the wet method, while the other two are used only in experimental installations.
The technological scheme for the production of asbestos-cement products by the wet method consists of the following main processes: storage and storage of basic materials; drawing up a mixture of asbestos from several grades and grades, fluffing up a mixture of asbestos, preparing an asbestos-cement mass, ensiling (storage), forming asbestos-cement products (facing sheets and roofing tiles are additionally pressed), preliminary hardening of molded products, mechanical processing of products, hardening of products, storage.
Colored asbestos-cement productsThe asbestos-cement industry produces the following main types of painted products: colored sheets molded from colored asbestos-cement slurry; sheets with a colored face obtained by forming on a sheet-forming machine; textured sheets and plates, the front surface of which is covered with colored enamels. When painting products over the entire thickness, prefabricated colored Portland cement or pigment is used, which is loaded into the apparatus at the same time as the cement. It should be noted that products painted with a pigment have a high cost (due to the high consumption of the dye), reduced mechanical strength and are inferior in decorative terms to products made on colored cement.
For the production of sheets with a colored front surface, dyeing is used in the molding process. To apply a colored layer of asbestos cement to the front surface of the sheets, an additional mesh cylinder is installed on the sheet-forming machine, in the bath of which there is a painted asbestos-cement suspension, or colored cement is sprinkled on the primary layer of asbestos cement, before the layer fits in a vacuum box (loose method). It will not be possible to obtain an intensely colored surface with this method, since the gray bulk of the sheet shines through through a thin colored layer. It is used only for flat sheets, since when bending, a network of tiny cracks forms on the colored layer not reinforced with asbestos fibers. For flat sheets, an intensely colored front surface is obtained. The application of the paint layer can also be done using a spray gun or by marking - rolling on rolls, on the surface of one of which a pattern is engraved.
To protect the facing sheets from warping, their front surface is painted with paints or colored enamels. These sheets must be compressed and have a smooth, even surface. Color the sheets through
3-4 weeks after molding. With a moisture content of more than 7%, they are dried at a temperature of 50-60 ° C. The front surface is pre-coated with a glyphthal primer, and then painted with nitroenamels, perchlorovinyl and other enamels. For a higher resistance of the cladding sheets against warpage when moistened, their back side is also coated with a primer. The temperature resistance of the enamels is low (70 ° C), but they are all waterproof and alkali-resistant. Asbestos-cement sheets coated with enamels are used for cladding the walls of kitchens, sanitary facilities, store lobbies, etc.
The main properties of asbestos-cement productsThe properties of asbestos-cement products are determined by the following factors: the quality of cement, the brand of asbestos, their quantitative ratio by weight, the degree of asbestos fluff, the location of asbestos fibers in the product, the degree of compaction of the mass, the conditions and duration of hardening, as well as the moisture content of asbestos cement. Asbestos-cement products are highly resistant to tearing, bending and compression.
Unpressed asbestos-cement products have tensile strength of 10-17 MPa, bending strength of 16-27 MPa, and pressed asbestos-cement products have tensile strength of 20-25 MPa, and bending strength of 27-42 MPa.
Over time, the mechanical strength and density of products increase. Asbestos cement is easy to saw, drill and grind. Products made from it have high frost resistance and water resistance, do not corrode under the influence of moisture, therefore they can be used without painting. Compared to steel and cast iron, they have several times less thermal conductivity and (3.5-4 times) density. Asbestos cement has high electrical insulating properties. Asbestos-cement pipes are almost impermeable when transporting gas, especially if the gas pipeline is laid in moist soils. The disadvantages of asbestos-cement products are low impact resistance and warpage.
FEDERAL EDUCATION AGENCY
Belgorod State Technological University named after V.G. Shukhova
Department of SMiK
COURSE WORK
By discipline:
"Technology of insulating building materials and products"
"Asbestos-cement roofing materials"
Is done by a student
Groups PS-41
Semenkov P.E.
Received: Ph.D., Assoc.
Alfimova N.I.
Belgorod 2011
CONTENT
introduction ……………………………………………………… ............. …… .3
Classification of asbestos-cement products ....................... 5
production methods ................................................ .........................eight
TECHNOLOGY FOR PRODUCTION OF ASBESTOSEEMENT LEAF .............................................. ................eleven
Materials for the production of asbestos-cement products ................ 11
Production technology of asbestos-cement products ...................... 15
Characteristics of finished products ............................................... .......... 23
Quality control of raw materials and finished products ................ 26
Industrial safety .............................. 29
Literature................................................. .................................................. .... 32
Introduction
Asbestos cement is a composite material. It is made from cement, asbestos and water. It has high physical and mechanical properties due to the reinforcement of cement stone with thin asbestos fibers: high mechanical strength in bending, low density, low thermal conductivity, resistance to leaching by mineralized waters, low water resistance and high frost resistance. The disadvantages of asbestos cement are a decrease in strength when saturated with water, brittleness and warpage with changes in humidity and toxicity. The main raw materials for the production of asbestos-cement products are asbestos of 3-, 4-, 5- and 6th grades (10 ... 20% by mass), and Portland cement of grades 300, 400, 500 (80 ... 90%). In the production of colored asbestos-cement products, along with asbestos and cement, dyes are used, as well as colored varnishes, enamels and resins.
Today in Russia there are more than a dozen enterprises producing slate. These companies are located in various cities of the country, they have different equipment - if some enterprises continue to operate old Belarusian-made equipment, then other factories have been using modern European technological lines for a long time. Naturally, in terms of quality, the latter will win.
Domestic slate of a new generation is currently produced by six out of ten plants in Russia - these are Volna Combine, JSC, Krasny Stroitel Combine, JSC, Sebryakovsky Plant of Asbestos-Cement Products, JSC, LATO JSC, and BelATSi JSC.
Low price, wide range of colors and competitive consumer qualities make it especially popular, and today such slate can be safely called a quality roofing for economy class.
Most of the supplies of imported slate to Russia are carried out from China. Chinese slate is characterized by good quality, however, in terms of its consumer characteristics, it is often inferior to domestic counterparts, and in price it exceeds.
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1. Classification of asbestos-cement products
More than 40 types of asbestos-cement products are produced. They are classified into sheets, pipes, panels and slabs, shaped parts. Sheets are produced different in shape, size, type of finish, manufacturing method and purpose. In terms of shape, they distinguish between flat and profiled sheets, and profiled ones are divided into wavy, double curvature and curved. Corrugated sheets are of low, medium and high profile, up to 2000 mm long - small-sized and more than 2000 mm - large-sized. Depending on the purpose, roofing, wall, facing, for elements of building structures and electrical engineering are distinguished. Asbestos-cement pipes are available pressure and non-pressure, round and rectangular cross-section, and depending on the purpose - water, gas, sewer, ventilation, casing and couplings. Panels and slabs are classified by purpose, manufacturing technology and design. According to their purpose, panels and slabs are subdivided into roofing (coverings and suspended ceilings), wall and partitions; they are produced both integrally molded and from individual elements - prefabricated, and by design - non-insulated, insulated and acoustic.
Roofing products are widely used for industrial, residential, civil and rural construction. In industrial construction, roofing products are used for non-insulated and insulated coatings. For non-insulated coatings in hot shops and unheated warehouse buildings, wavy (Fig. 1) and semi-wavy large-sized sheets with shaped parts are used.
Fig. 1 Corrugated sheet of ordinary VO profile:
1 - covering edge; 2 - edge to be covered.
Hollow and tray slabs are used for insulated coatings. Hollow slabs are two profiled asbestos-cement sheets connected by aluminum rivets and having a mineral wool gasket inside. Tray slabs are asbestos-cement trays filled with thermal insulation material.
Corrugated sheets of a periodic profile are used for the construction of wall fences of a building for various purposes.
Asbestos-cement corrugated sheets of the unified profile UV-7.5 are used for the installation of attic, as well as insulated roofs and wall fences of industrial and agricultural buildings and structures. They are produced in lengths of 1750, 2000 and 2500 mm, width of 1125 mm and thickness of 7.5 mm. These slabs have a high bending strength of less than 20 MPa and a density of at least 1700 kg / m 3, frost resistance F50. They are made on automated lines in a non-layered way.
Asbestos-cement corrugated sheets of the unified profile UV-6 are produced with a length of 1750, 2000 and 2500 mm, a width of 1125 mm and a thickness of 6.0 mm, with a wave step of 200 mm and an ordinary wave height of 54 mm, a bending strength of at least 18 MPa, density 1700 kg / m 3 and frost resistance not less than F25. UV-b-1750 sheets are used for attic roofs of residential and public buildings, UV-b-2000 sheets are used for overhangs of attic roofs and wall fences of industrial buildings and UV-b-2500 for wall fences of buildings and structures.
Asbestos-cement corrugated sheets SV-40 are used for roofing in mass housing construction, as well as for wall enclosing structures of industrial and agricultural buildings and structures. They are produced with a length of 1750 mm and 2500 mm, a width of 1130 mm and a thickness of 5 and 6 mm, with a wave pitch of 150 mm and a height of 40 mm.
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2. Production methods
The production of asbestos-cement products includes the following operations:
1) splitting (fluffing) asbestos into thin fibers;
2) preparation of asbestos-cement suspension;
3) filtration of thin sheets from liquid asbestos-cement mass;
4) molding of products from it: corrugated (roofing) and flat sheets, pipes, ventilation ducts, etc.; giving products the required density and shape by pressing, bending, cutting (required dimensions);
5) hardening of products in steaming chambers, water basins, autoclaves and keeping them in insulated warehouses until the desired strength is obtained.
Asbestos is fluffed up first on the runners and then in the gollender. Gollender is a reservoir, inside of which a drum with knives rotates. Cement, asbestos and water are mixed in a gollender. From the gollender, the resulting mass goes to the bucket mixer, and then it enters the molding machine (Fig. 2). The working part of the sheet-forming machine consists of a bath with asbestos-cement suspension and a hollow frame drum covered with a metal mesh. When the drum rotates on a metal mesh, a racing layer of asbestos cement is filtered out, which removes the endless years of technical cloth and transfers it to a metal format drum winding concentric layers of asbestos-cement mixture ..
Fig. 2 Forming machine diagram:
1 - stirrer; 2
- bath; 3
- partitions; 4
- mesh cylinder; 5, 13, 15
- flushing tubes; 6
- press shaft; 7
- cloth; 8
- upper vacuum box; 9
- metal format cylinder; 10
- supporting (driving) shaft; 1 - guide rollers; 12 -
lower vacuum box; 14
- bump roller; 16
- squeezing rolls; F 1
,
F 2
,
F 3 - pressures created by weights, springs or hydraulic cylinders.
When the layer of asbestos cement on the sizing drum reaches the required thickness, it is cut along the generatrix of the cylinder. The resulting raw asbestos-cement sheet goes to the conveyor for further processing: it is cut to the required dimensions, pressed under a pressure of 30-40 MPa, and to obtain profiled sheets it is waved. Asbestos-cement sheets SV and HC have one lowered wave (Fig. 3), which, when installing the roof, must be covered by a wave of the normal height of the adjacent sheet. In addition to the described "wet method" of forming asbestos-cement products, semi-dry and dry methods are used. With the semi-dry method, products are formed from a concentrated (creamy) mass with a moisture content of 30-35% on special machines for non-layer molding of products with strong compaction.
Fig. 3 Asbestos-cement corrugated sheets of a unified profile a- sheet profile; b - details of the profile.
With the dry molding method, asbestos is fluffed and mixed with cement and ground sand in a dry state. Then this mixture, moistened to 14-16%, is compacted on a conveyor line under a press or rolls.
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3. Technology for the production of asbestos-cement sheets
3.1 Materials for the production of asbestos-cement products
Portland cement is used as a binder for the production of asbestos-cement products. It should hydrate quickly, but set relatively slowly. The increase in the strength of the product must occur quickly enough for the transition of the semi-finished product to the finished product.
The setting and hardening of cement is carried out under specific conditions. Initial hydration occurs at a very high water-cement ratio. In the process of suction of the liquid phase, part of the neoplasms and small grains of clinker are filtered and, in addition, the physicochemical effect of asbestos on the hardening of cement in the composition takes place. To meet the requirements of GOST 9835-77 for the production of asbestos-cement products, a special Portland cement with a specific surface area of 2200 ... 3200 cm 2 / g is used. The amount of additives in cement is set with the consent of the consumer, but not more than 3% (with the exception of gypsum). Gypsum is added to regulate the setting time in an amount of not less than 1.5% and not more than 3.5% of the cement mass, counting as S0 3.
According to the mineralogical composition, Portland cement should be alite (with a tricalcium silicate content of at least 52%), providing high productivity of the molding machines and an intensive increase in the strength of asbestos cement. The content of tricalcium aluminate is limited, since it gives low strength of asbestos-cement products and low frost resistance; free calcium oxide in cement should not exceed 1%, and magnesium oxide - 5%.
Forming of asbestos-cement products lasts longer than of concrete products. In this regard, the beginning of setting for cement for asbestos-cement products should occur somewhat later than for ordinary Portland cement - not earlier than 1.5 hours from the moment of mixing with water, and the end - no later than 10 hours after the start of mixing.
Asbestos is a group of minerals that have a fibrous structure and, under mechanical stress, are capable of breaking down into the finest fibers. Chrysotile asbestos is used in the production of asbestos-cement products. The world production of chrysotile asbestos is 95%, and the entire group of acid-resistant asbestos is no more than 5%. Chemical composition of chrysotile asbestos. (theoretical) is expressed by the formula 3MgO * 2SiCO 2 * 2H 2 O, that is, it is magnesium hydrosilicate.
Asbestos molecules are firmly bound to each other only in one direction, while the lateral bond with neighboring molecules is extremely weak. This property explains the very high tensile strength of asbestos along the fibers and good fluffiness - splitting across the fibers. Chrysotile asbestos fiber diameter ranges from 0.00001 to 0.000003 mm, practically chrysotile asbestos fluffs up to an average fiber diameter of 0.02 mm; therefore, such a fiber is a bundle of a huge number of filaments. On average, the tensile strength of asbestos fibers is 3000 MPa, but since when fluffing asbestos fibers are subjected to compressive, shock and other influences, the strength of the fibers after fluffing decreases to 600 ... 800 MPa, which corresponds to the strength of high-quality steel wire.
Asbestos has a high adsorption capacity. in a mixture with Portland cement, when wetted with water, it adsorbs, i.e. well retains on its surface the products of cement hydration, which bind asbestos fibers, therefore, asbestos cement is, as it were, a finely reinforced cement stone. Chrysotile asbestos is non-combustible, but at a temperature of 110 ° C it begins to lose adsorption water, the tensile strength decreases to 10%, and at 368 ° C all adsorption water evaporates, which leads to a decrease in strength by 25 ... 30%. After cooling, asbestos restores lost moisture and previous properties from the air. When asbestos is heated to a temperature of more than 550 ° C, chemically bound water is removed, elasticity and strength are lost, asbestos becomes brittle, and after cooling, its properties are not restored. At a temperature of about 1550 ° C, chrysotile asbestos melts. Asbestos has low thermal and electrical conductivity, high alkali resistance and weak acid resistance.
The quality of asbestos-cement products largely depends on the quality of asbestos and the fineness of cement grinding. In accordance with GOST, the quality of chrysotile asbestos is characterized by the following indicators: texture (degree of fluff of fibers), average fiber length, elasticity, moisture, degree of dust contamination.
The length of asbestos fibers has the greatest influence on the quality of products, therefore it is the main feature by which asbestos is divided into grades and grades. Eight grades of chrysotile asbestos have been identified, depending on the length of the fibers. Asbestos with the longest fibers (more than 18 mm) is referred to as 0 and 1 grades, and with the shortest fibers (less than 1 mm) - to 7th grade. For the production of asbestos-cement products, 3, 4, 5 and 6 grades are used with a fiber length from 10 mm or less to several hundredths.
Water in the production of asbestos-cement products is consumed for the preparation of the asbestos-cement mixture and washing the felts and mesh cylinders of the forming machine. The water used for the production of asbestos-cement products should not contain clay impurities, organic substances and mineral salts. Clay particles, deposited on the surface of asbestos fibers, reduce their adhesion to cement, complicate the filtration of asbestos-cement slurry and reduce the mechanical strength of products. Organic impurities slow down the hydration of the binder.
The production of asbestos-cement products is associated with high water consumption. The waste water contains a significant amount of asbestos and cement, therefore it is returned to the technological cycle. Working with recycled process water not only avoids environmental pollution, but also gives advantages. The saturation of circulating water with Ca 2+ and S0 4 2- ions prevents gypsum leaching and prevents premature setting, the absence of CO2 in it eliminates the clogging of the meshes with calcium carbonate. The most favorable temperature is 20 ... 25 ° С. At temperatures below 10 ° C, the productivity of the molding units decreases, and the hardening of products slows down. Too high a water temperature can cause the cement to set quickly.
Paints are used to paint wall tiles and sheets. Colored cements or alkali-resistant mineral pigments are used that have high coloring ability, light and weather resistance and do not interact with cement hydration products. This is a redoxide (artificial iron oxide), red iron, natural mummy, ocher, chromium oxide, ultramarine, manganese peroxide, etc. Sheets intended for cladding walls and panels of sanitary units and kitchens are covered with waterproof enamels and varnishes, based on polymers (glyphthalic, perchlorovinyl, nitrocellulose).
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3.2 Technology of production of asbestos-cement products
Currently, there are three methods for the production of asbestos-cement products: wet method - from asbestos-cement slurry, semi-dry - from asbestos-cement mass and dry - from dry asbestos-cement mixture. The wet method is the most widely used. The other two are used only in experimental installations.
The technological scheme for the production of asbestos-cement products by the wet method consists of the following main processes: warehousing and storage of basic materials; making up a mixture of asbestos from several grades and brands, fluffing up a mixture of asbestos, preparing an asbestos-cement mass, ensiling (storing) asbestos-cement mass, forming asbestos-cement products (facing sheets and roofing tiles are additionally pressed), preliminary hardening of formed products, mechanical processing products, product hardening, warehousing.
Asbestos is delivered to factories in paper bags in railroad cars. At the factory, they are stored in a closed warehouse on a wooden floor in separate compartments for different brands and varieties. If asbestos entered warehouse in a container, then it can be stored in stacks. Above each compartment or stack, the grade and grade of asbestos is indicated.
For the manufacture of products, the composition of the mixture of asbestos is established. So, for asbestos-cement corrugated sheets used to cover the roofs of residential buildings, the asbestos mixture is set as follows: 50% of grade 5 asbestos, 50% of grade 6 asbestos, and the total content of soft texture should not exceed 50%, including the content of asbestos M-60-40 in the mixture should not be more than 15%. Asbestos grades and their percentage in the mixtures used are standardized with special technological maps.
Asbestos fluffing determines the quality of products to a large extent. There are three types of fluff: dry, wet and semi-dry.
With the wet method of fluffing (Fig. 4), asbestos is soaked in water for 3 ... 5 days, then the mixture is kneaded on runners.
Rice. 4 Schemes for wetting asbestos: 1 - asbestos warehouse; 2 - a site for making up a mixture of asbestos; 3 - dispenser; 4 - runners with asbestos humidification; 5 - gollender.
Water penetrates into micro-crevices and has a wedging effect, as a result of which the fibers fluff more easily and better. Moistening the asbestos increases the elasticity of the fibers, which increases the resistance to kink when handling on runners.
At present, a roller machine is becoming more and more widespread for crimping asbestos (Fig. 5). Unlike runners, this machine produces high quality crushed asbestos in a continuous flow.
Rice. 5 Mechanized installation for mixing, humidifying and crimping the mixture of asbestos: 1 - asbestos bunker; 2 - feeder; 3 - pre-jam; 4 - mixer-humidifier; 5 - leveling device; 6 - leveling roller; 7 - roller machine; 8 - freely rotating rolls; 9 - pneumatic device; 10 - driven rolls.
Finally, asbestos is fluffed in a gollender, and then cement and water are added to it and mixed until a homogeneous asbestos-cement mass is obtained. Gollender (Fig. 6) is a metal or reinforced concrete bath, divided in the middle by a longitudinal partition that does not reach the edges.
Rice. 6 Batch Gollender:
1, 7 - channels; 2 - bath; 3 - partitions; 4 - drum shaft; 5 - knife drum; 6 - pulley; 8- removable casing; 9 - slide; 10 - a frame with knives; 11 - valve; 12 - branch pipe; 13 - knives.
In one half of the bath there is a drum equipped with steel knives. A cast-iron box is placed under the drum at the bottom of the bath, in which there is a comb located at an angle of 1.5 ... 2.5 ° to the axis of the drum. The bath is half-filled with water, then pre-fluffed asbestos is fed. When the drum rotates (180 ... 240 min -1), the mixture is carried away into the gap between the drum knives and the comb, thrown over the hill, passes along the bath and again falls under the drum. The circulation of the mixture lasts up to 10 minutes, the degree of fiber fluff should be 90 ... 95%. Then cement is loaded, water is added and additional mixing is carried out. By the end of mixing, almost all of the cement is adsorbed on the asbestos fibers. The dosage of the components of the asbestos-cement mass is: asbestos - 10 ... 18%, cement - 82 ... 90%; for the production of pipes: water - 97%, and sheet asbestos-cement materials - about 95%.
Gollender is a batch-type apparatus. For continuous feeding of the molding machine, it is necessary to create a supply of asbestos-cement mass in a bucket mixer (vat), which would be periodically replenished from a gollender. Mixing of the mass in it is carried out with a cross with blades. On the same shaft with the crosspiece there is a frame circle - "bucket elevator". Buckets scoop the mass out of the vat and feed it into the receiving box of the sheet-forming or pipe-forming machine.
At present, the enterprises have introduced continuous gollenders (Fig. 7) of high productivity. Water and asbestos are continuously loaded into the bath from one end of the gollender, and the finished asbestos slurry is poured out from the other end. The capacity of a continuous gollender is the same as that of a roller heapler.
When using a gollender and a continuous roller machine, the asbestos-cement mass is prepared in a continuous flow. Mixing of continuously supplied asbestos-cement slurry with cement slurry is carried out in a screw mixer, and from there the asbestos-cement mass enters the bucket mixer or directly into the bath of the molding machine.
Rice. 7 Gollender of continuous operation;
1-intake of asbestos; 2 - water supply; 3 - exit of asbestos suspension.
Molding is the most important process in the production of asbestos-cement products. Products are formed on sheet-forming and pipe-forming machines. A sheet-forming machine (Fig. 1) consists of a metal bath, into which a liquid asbestos-cement mass is continuously fed through a chute. A hollow frame drum (mesh cylinder) covered with a metal mesh is placed in the bath. A conveyor belt is pressed against the surface of the mesh cylinder by the shaft. The drive support shaft drives a belt that rotates the mesh cylinder. The asbestos-cement mass is deposited in a thin layer on the surface of the drum's metal mesh, partially dewatered on it due to water filtration through the mesh and is removed from the drum during rotation, evenly placed on the moving belt. The asbestos-cement mass, moving on the belt, passes through a vacuum box, where it is dewatered, then goes to a rotating format drum, is wound on it in concentric layers and compacted.
In the manufacture of sheet asbestos-cement products, a mass of a certain thickness wound on a format drum is cut and removed from the drum. The resulting sheets are cut into sheets of a specified size and fed to the steaming chambers. The sheets intended for corrugation, after being removed from the sizing drum, are cut into formats and placed in molds on metal corrugated spacers.
In order to obtain increased mechanical strength and density, asbestos-cement sheet products are pressed on hydraulic presses under pressure up to 40 MPa. To acquire the products in the shortest possible time, they are steamed or kept first in air at normal temperature, and then in pools with warm water.
The hardening of asbestos-cement sheet products made on Portland cement occurs in two stages. The first is preliminary hardening in batch-type steaming chambers (pit or tunnel) at a temperature of 50 ... 60 ° C for 12 ... 16 hours. After steaming, sheet products are freed from metal gaskets and subjected to mechanical processing (trimming edging, punching, etc.). The finally formed sheets are sent to an insulated warehouse, where the second stage of hardening takes place for at least 7 days. Asbestos-cement products made on sandy Portland cement, after molding, are sent to autoclaves for steaming at a temperature of 172 ... 174 ° C and an operating pressure of up to 0.8 MPa.
Upon reaching the required strength, the product is subjected to mechanical processing.
Currently, a new set of equipment for the technological line for the automated production of large-panel asbestos-cement sheets based on a flat-mesh machine has been developed (Fig. 8.21). The technological line consists of two sections: a blank section, in which the asbestos-cement mass is prepared, and a sheet-forming section, in which the products are formed. For the preparation of the asbestos-cement mass, the asbestos mixture is fed from the warehouse to the asbestos feeder bunker, then weighed by the batcher by weight and enters the mixer-humidifier, in which the asbestos is mixed and moistened to 33%. The moistened asbestos mixture is fed into a roller machine for crushing asbestos with counter-rotating smooth rollers, and from there it enters the machine for hydraulic fluffing, where the required amount of water is simultaneously supplied to obtain an asbestos suspension. The prepared asbestos suspension and the cement tared by the doser by weight are fed into the mixer of the asbestos-cement mass. Mixing of asbestos with cement in the mixer takes place in a vertically downward flow of asbestos suspension with the simultaneous action of rotating and stationary blades. The prepared asbestos-cement mass enters the bucket mixer, which feeds the flat mesh sheet forming machine. The productivity of the equipment of the procurement department is 60 m 3 / h of asbestos-cement mass of 18% concentration, which provides the output of 12 thousand conv. pl / h
The flat-mesh sheet forming machine provides continuous dispensing of asbestos-cement slurry onto the machine mesh, dewaters the slurry, forms asbestos-cement tape, compaction and additional dewatering of the asbestos-cement sheet. The formed asbestos-cement tape is additionally compacted on a press, and then sent to cutting the raw asbestos-cement tape into sheets of specified sizes. The latter are subjected to corrugation, then placed in the feet and placed for 3.5 ... 4 hours in special pre-hardening chambers at a temperature of 40 ... 60 ° C and a humidity of 90 ... 95%.
The considered method of production of asbestos-cement slabs reduces the cost of production by 7% in comparison with the existing ones. The degree of automation of this method reaches 98% with 100% mechanization on the main technological lines.
^
3.3 Characteristics of finished products
The properties of asbestos-cement products are determined by the following factors: the quality of cement, the brand of asbestos, their quantitative ratio by mass, the degree of asbestos fluff, the location of asbestos fibers in the product, the degree of compaction of the mass, the conditions and duration of hardening, as well as the moisture content of asbestos cement. Asbestos-cement products are highly resistant to tearing, bending and compression. Asbestos-cement unpressed products have tensile strength of 10 ... 17 MPa, bending 16 ... 27 MPa, and pressed asbestos-cement products have a tensile strength of 20 ... 25 MPa, and in bending - 27 ... 42 MPa. With age, the mechanical strength and density of products increase. Asbestos cement is easy to saw, drill and grind. Products made of asbestos cement have high frost resistance and water-tightness, do not corrode under the influence of moisture, therefore they can be used without painting. Compared to steel and cast iron, they have several times less thermal conductivity and (3.5 ... 4 times) density. Asbestos cement has high electrical insulating properties. The disadvantages of asbestos-cement products are low impact resistance and warpage.
Appearance:
Sheets and parts can be produced painted and unpainted.
Sheets and parts should not have spalls, holes and through cracks.
Minor defects are allowed:
Separate tears with a length of no more than 100 mm in any direction;
Separate cracks on one side of the sheet (part) no more than 15 mm in size in the direction perpendicular to the edge of the product. The total size of the cracks, measured along the edge of the product, should not exceed 60 mm;
Separate superficial tears no more than 100 mm long and 2 mm wide.
The total number of minor defects on one sheet (part) in any combination should not be more than three, and the number of sheets (parts) with such defects in the sample should not be more than one third of its volume.
The color of the painted sheets and parts and the intensity of their coloring must correspond to the standard samples approved by the manufacturer.
The surface of sheets and parts must be uniformly colored, without efflorescence and stains visible at a distance of 10 m. The painted surface of sheets and parts must be resistant to abrasion. The strength of the colored coating, measured by the amount of quartz sand consumed during abrasion, must be at least 3 kg.
Physical and mechanical properties of sheets and parts must correspond to those indicated in table 1.
Table 1
^ 4. Quality control of raw materials and finished products
One of the main stages of the finishing materials manufacturing technology is control over the quality of incoming raw materials, over all technological operations, as well as control over finished products. The quality control of raw materials is as follows: each batch of raw materials entering the plant must be supplied by the supplier with a passport, and the factory laboratory, which checks their appearance, is directly monitored, samples are taken for each type of raw material, tests are carried out and the compliance of the property indicators with the requirements GOST.
Control methods - according to GOST 8747-88 and GOST 30340-95:
1. The length of the parts is measured as follows:
Ridge and simplified ridge parts - along the axis of the socket part;
Equal corner piece - along one of the side edges;
Tray part - along the axis of the part.
2. The width of the ridge and simplified ridge parts is measured once in the middle of the part using rectangular stops; the width of the isosceles corner piece and the chute piece - at both end edges at a distance of 30 - 50 mm from the edge.
Each measurement must be within the tolerance limits.
3. The height of each ordinary wave and overlapping waves of the ridge parts is measured from the end side of the wavy part.
4. Testing with a concentrated die load should be carried out for sheets:
Profile 40/150 - according to the scheme with two spans with a distance between the supports l equal to (750 ± 5) mm in the axes;
Profiles 54/200 - according to the scheme with one span with a distance between the supports l equal to (1500 ± 5) mm in the axes.
5. The value of the ultimate strength in bending of an individual specimen should not be lower than the standard, by more than 10%.
The laboratory reports the results of testing and analysis to the technical control department, which gives permission for the transfer of raw materials to production or rejects it, i.e. returns raw materials, always with their test results, to the supplier.
The tasks of monitoring technological processes include checking the sequence and correctness of the operation, the consumption of raw materials and the compliance of the recipe, the consumption of electricity, steam, air, the dimensions of the cross-section of the manufactured products, their appearance, etc.
The parameters of all technological processes are set by the factory laboratory, controlled by the technical control department, as well as by shop laboratories. All measuring and weighing devices are periodically checked in accordance with the regulations.
The quality of finished products for compliance with the requirements of GOST or TU is controlled by the factory laboratory. To characterize the appearance of the material, determine the size, shape, as well as conduct physicochemical and mechanical tests, a certain amount is taken from each batch, then the required number of samples is made from the selected material sample in the prescribed manner and subjected to all tests regulated by GOST, after which gives a conclusion about its quality.
The test results are included in the passport document that accompanies each batch of products shipped to the customer and satisfies its compliance with the requirements of the standard.
In addition to the test results, the passport indicates the name, address of the manufacturer, the brand and grade of the product, the main external features, the weight or number of products in the batch, the date of manufacture and the retail price.
^
5. Industrial safety
As you know, some finishing materials, binders and other components of plastics (except for mineral fillers and pigments) have sufficient toxicity and fire hazard.
Toxic polymers can cause illness in the people who process them. These materials, as well as the products of their decomposition, which are formed during the production of finishing materials, getting into the ground, water of rivers and lakes, poison the natural and animal world.
Most plasticizers are also toxic and flammable; many hardeners and stabilizers have a harmful effect on the human body. Most solvents, acetone, benzene, which are widely used in the production of paints and mastics, are toxic and explosive. Plants producing polymer composite materials are characterized by the following labor protection and fire safety rules:
Storage and transportation of toxic raw materials only in tightly closed containers;
Moving parts of mechanisms and machines, various production capacities are fenced: bunkers, tanks, etc .;
Reliable thermal insulation of installations and units operating at elevated temperatures;
Providing general ventilation of all working rooms, including local ventilation for each machine and unit, during the operation of which harmful substances are emitted;
Grounding of all electric motors, starters and assemblies to prevent the formation of static electricity and sparks;
Placement in isolated rooms of technological lines associated with toxic emissions of substances and dust.
Workers must be instructed in a timely manner on safety and fire-fighting techniques, strictly observe the rules of personal hygiene, in addition, workers are provided with special clothing and additional protective equipment. Also, what should be paid attention to, the work premises should be supplied with materials for medical assistance to the injured.
In order to protect the environment from pollution, all ventilation emissions and wastewater must be subjected to special cleaning, which would exclude the ingress of any pollutants into the air, soil and water bodies.
CONCLUSION
Asbestos-cement roofing has a number of excellent qualities. Slate is highly waterproof, resistant to high and low temperatures, and can easily endure sudden thermal drops and drops in humidity. Also, asbestos-cement corrugated sheets, having a relatively low weight, are able to withstand significant snow loads. An important advantage of slate is its high fire resistance, which favorably distinguishes asbestos-cement slabs from many other roofing coatings. It is worth noting the low cost of this material, which makes it available to a wide range of consumers. An important quality of asbestos cement is its thermal insulation properties. In addition, when installing slate, there is no need to lining a vapor barrier, since condensation practically does not form under it.
Unfortunately, with all its advantages, asbestos-cement roofing has a number of minor disadvantages. Over time, a roof made of slate can become covered with lichens, the outer surface swells in places, cracks and chips appear, which leads to a decrease in its waterproof qualities. In this case, it is possible to carry out simple roof repairs without special material costs.
Despite some minor drawbacks of asbestos-cement roofing, the excellent consumer qualities of the slate coating have made it a truly popular and popular building material.
Literature
GOrchakov V.I.... Building materials: Textbook. for universities / Gorchakov V.I., Bazhenov Yu.M. - M .: Stoyizdat, 1986 .-- 688 p.
Komar A.G. Building materials and products: Textbook. for engineer-econom. specialist. builds. universities / Komar A.G. - 5th ed., Rev. and add. - M .: Higher. shk., 1988. - 527 p.
Technology of insulating building materials and products: guidelines for the implementation of coursework for full-time and part-time students of the specialty 270106 (290600) / comp. A. N. Kharkhardin. N.I. Alfimova. - Belgorod: Publishing house of BSTU, 2010 .-- 23 p.
GOST 30340-95 "Asbestos-cement corrugated sheets".
Asbestos cement- an artificial stone material obtained by hardening a mixture of Portland cement, asbestos (15 ... 20% of the mass of cement) and water. Asbestos adheres well to hardening cement, and due to its high tensile strength, asbestos fiber reinforces the material throughout the entire volume, i.e., dispersed-reinforced concrete (fiber concrete) is obtained.
Asbestos cement with a relatively low density (1600 ... 2000 kg / m 3) has high strength indicators (ultimate strength in bending up to 30 MPa, and under compression up to 90 MPa, impact strength in the range of 1800-2500 J / m 2). It is durable, frost-resistant (after 50 freeze-thaw cycles it loses no more than 10% of its strength) and is practically waterproof.
Asbestos-cement products are mainly produced by casting a liquid-viscous mass on a frequent metal mesh, followed by dehydration and molding. Thus, flat and corrugated sheets and pipes are obtained.
Another method of forming asbestos-cement products is also used - extrusion - extrusion of plastic mass, as in the production of bricks. Thus, molded products are obtained: window slabs, channels, hollow slabs and panels.
Asbestos-cement products
Slate
Corrugated Roofing Sheets("Slate" from the German. Schiefet- roofing slate) - the main type of sheet asbestos-cement products. Slate is widely used as a roofing material (its share in the total production of roofing materials is about 50%). They are used to cover the roofs of open warehouses, commercial stalls, stalls, pavilions, bicycle sheds, garages, city and intercity transport stops.
Roofing sheets are produced in 6 standard sizes: length 1.2 ... 2.5 m; width 0.69 ... 1.15 m; thickness 5.5 ... 7.5 mm.
Initially, slate was produced in the form of flat sheets measuring 40 × 40 cm.
In addition to the usual ones, they produce sheets painted with weather-resistant paints, both in bulk and from the surface. Recently, the production of flat sheets with curly edges, imitating small-piece tiles, has begun. The durability of asbestos-cement roofs is up to 50 years.
Application advantages:
Slate roofs are several times cheaper than shingles and tin;
Quite low costs for roof maintenance;
Slate is resistant to biological effects (rotting, harmful mycelium);
Does not rust, does not burn;
Low thermal conductivity;
High frost resistance;
High strength (withstands significant snow load);
Resists strong gusts of wind, absorbs the noise of rain and gusts of wind in inclement weather;
Waterproof;
Easy to machine;
Provides almost unlimited service life;
Installation of the roof can be carried out all year round, it does not require high qualifications of performers and large labor costs;
The erection of roof structures is carried out fairly quickly;
Possibility of completing with plastic and metal finishing elements (corners, stripes, visors);
Simplicity of roof repair with the possibility of restoring local damage is possible without disturbing the overall coverage;
Competitive cost;
Durability.
Roofing made of painted slate blends well with the facades of houses, harmoniously blends into the surrounding landscape. A wide range of colors will ensure the harmony of any architectural ensemble.
Asbestos-cement flat sheets(flat slate) pressed and unpressed, intended for the manufacture and cladding of building structures of a wide profile - sanitary cabins, flooring of industrial premises, partitions, ventilation shafts, boxes, window boards, window lintels, formwork, as elements of sprinklers for cooling towers at power plants ...
They are used for external and internal cladding of residential, public and industrial buildings, hinged ventilated facades. They are used for the installation of sandwich-type wall panels, which allows you to effectively insulate buildings (you can lay a layer of insulation up to 200 mm.), In the construction of various complexes, pavilions, stalls, as well as a floor slab, partitions, fences for balconies, loggias , when arranging a cellar, etc.
Gardeners and truck farmers use flat sheets for arranging gazebos, beds, aviaries, paths, small outbuildings (toilet, shower, various sheds for household needs), in the construction of fences.
Produced in accordance with the requirements of GOST 18124-95 with dimensions in terms of 3500x1500, 1500x1000 with a thickness of 6, 8, 10, 12, 16, 20, 25, 30, 35, 40 mm.
Application advantages:
· Have high strength indicators;
· Resistant to aggressive environments and soils;
· Fireproof (belong to the group of non-combustible building materials);
· Reliable and durable;
· Easily amenable to mechanical processing using a circular saw or hacksaw, which allows you to make various architectural decisions;
· Quick installation;
· Installation of flat sheets does not require high qualifications of performers and large labor costs;
· Decorating the sheet (paint, various finishing materials can be applied to a flat sheet);
· Possibility of completing with plastic and metal finishing elements (corners, stripes, visors);
· Competitive cost;
· Durability.
ACEID
Asbestos-cement electrical arc-resistant boards(ACEID), are intended for the manufacture of electrical distribution boards, parts and bases of electrical machines and apparatus, as well as housings of arc-extinguishing chambers, gaskets and plates of induction furnaces, fences for electric furnaces, etc. They are used where protection and work at high voltages is required, and also used as structures, which are subject to increased strength requirements in comparison with asbestos-cement sheet.
It is used in the manufacture of spark-extinguishing partitions in electrical equipment. It is used as a structural building material (floors, sill boards, partitions), characterized by high strength and fire safety. In the case of use as building structures for buildings of medical and prophylactic, children's and other institutions where systematic wet disinfection is required, the boards should be covered with 2-3 layers of oil paint or other coatings that can withstand the action of disinfectants.
Produced in accordance with the requirements of GOST 4248-92 with dimensions in terms of 3500x1500, 1500x1000 with a thickness of 6, 8, 10, 12, 16, 20, 25, 30, 35, 40mm.
Application advantages:
· High mechanical strength;
· Possesses arc resistance;
· Increased electrical strength;
· Use at high temperatures;
· Resistance to aggressive environments;
· Fire safety;
· Environmental friendliness;
· Reliability and durability;
· The installation process can be carried out year-round;
· Installation of sheets does not require high qualifications of performers and large labor costs;
· Simplicity of object repair, if it is necessary to restore local damage, it is possible without disturbing the general coverage;
· Decorating the sheet (paint, various finishing materials with various textures can be applied to the sheet) - the possibility of completing with plastic and metal finishing elements (corners, stripes);
· Competitive cost.
Pipes
Asbestos cement pipes- a very promising type of pipes of the widest use, possessing a set of valuable properties. They do not corrode like metal ones, they are much lighter and are not prone to fouling. Due to the low thermal conductivity of asbestos-cement pipes, there are fewer problems with freezing. Asbestos-cement pipes are connected using couplings.
Asbestos-cement pipes are products of the widest use with a set of valuable properties:
3 times lighter than metal pipes;
Do not rust, do not burn, do not freeze;
Not prone to "overgrowth";
They do not need protection from stray currents and groundwater;
The friction of water along the walls is less than that of metal pipes, which increases their throughput and reduces energy consumption for pumping liquids;
The cost of construction and installation work is reduced by 50-60% (the cost-effectiveness of laying heating and hot water supply systems with pipes increases with an increase in the diameter of the pipeline);
Minimum construction time;
The cost of thermal insulation is reduced to a minimum (it is a heat insulator, the thermal conductivity of asbestos is 60 times less than the thermal conductivity of steel);
Not electrically conductive;
Fireproof;
Exposure to water (hot or cold) gives them additional strength;
Long service life 30-35 years.
Asbestos-cement pipes are produced free-flow and pressure-free, differing in thickness and strength characteristics.
Non-pressure pipes.
Produced according to requirements GOST 1839-80 for pipes with a diameter of 100 mm and 150 mm, and for pipes with a diameter of 200, 250, 300, 400 and 500 mm, use TU 5786-006-00281594-2002.
They are used for the device of external pipelines of free-flow sewerage (sewer pipes), chimneys (chimneys), air ducts, gas ducts, garbage pipes in residential buildings, when laying drainage collectors (drainage pipes), for drainage through roads and crossings, telephone cables and electric cables, instead of metal and wooden posts for fences, for replacing bricks in the construction of cellars, for covering the roofs of garages and industrial buildings, for the construction of columnar foundations for one-story or prefabricated panel garden houses.
Pressure pipes.
Produced in accordance with the requirements of GOST 539-80 class VT-6, VT-9 and VT-12.
They are used for laying pressure networks of drinking and industrial water, for pressure water supply, amelioration and irrigation systems, for pressure sewerage (sewer pipes), heating mains, ventilation, for drainage collectors (drainage pipes), chimneys (chimneys), air ducts, gas ducts, for thermal insulation in thermal units, in oil pipelines, for foundations in wetlands, for the device of drainage through roads and crossings, for poles and fences, as casing pipes for wells, wells, for the manufacture of durable trays-feeders for livestock, for the manufacture of garage floors, gutters ...
Couplings-rings.
To connect free-flow asbestos-cement pipes:
Asbestos-cement couplings;
Polyethylene couplings.
To connect asbestos-cement pressure pipes are:
Asbestos-cement couplings, type CAM
To seal the coupling joints, rubber rings are used to seal the butt joint.
Method of joining asbestos-cement pipes using polyethylene couplings:
1) pushing couplings onto the end of one pipe
2) pushing the end of the second pipe into the coupling
After being at a temperature below 5 ° C, rubber rings must be kept at a temperature of (23 + 5) ° C for at least 24 hours before installing the coupling joint. It is allowed to mount the rings at temperatures from minus 20 to plus 50 о С without direct exposure to solar irradiation for no more than 7 hours. Mounting of rings should be carried out without distortions, twisting and mechanical damage.
The pipes are supplied with couplings and rubber rings, the number of couplings must be equal to the number of pipes, and the number of rubber rings must be twice the number of couplings.
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