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INTRODUCTION

Asbestos-cement production is a fairly strong source of air pollution, since one of the main components for the production of asbestos-cement slate is asbestos. According to the degree of impact on the human body, asbestos is classified as hazard class III.

A large number of scientific research on the impact of asbestos on the human body and the environment. The abundance of conflicting data sometimes baffles both consumers and manufacturers.

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 substitutes with unique properties of chrysotile asbestos have not yet been found in the world. And artificial mineral fibers used as substitutes are obtained at the cost of high energy costs required to melt stone raw materials. The only way to reduce harmful effect on the environment and a healthier person is the modernization of the treatment plant at the enterprise. And perhaps even an introduction innovative technologies, preventing the formation of harmful gaseous substances and dust particles in the atmospheric air.

RAW MATERIALS FOR THE PRODUCTION OF ASBESTOS CEMENT 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 the requirements that apply to the finished 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 the mass of dry matter) contains an average of 85% cement and 15% asbestos.

CHRYSOTILE-ASBESTOS

Asbestos is a group of minerals that have a fibrous structure and, under mechanical action, are capable of disintegrating into the finest fibers. In the production of asbestos-cement sheets, chrysotile asbestos is used. Chemical composition chrysotile asbestos is expressed by the formula 3MgO-2Si02-2H20. According to the chemical composition, asbestos minerals are hydrous silicates of magnesium, iron, calcium and sodium.

The industrial value of asbestos minerals is determined by the following properties: the length of the fibers, elasticity, strength, the ability to decompose into the thinnest fibers under mechanical action, chemical resistance when exposed to acids and alkalis, the 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 well retains cement hydration products on its surface that bind asbestos fibers.

The length of asbestos fibers has a great influence on product quality. This is the main sign of the division of asbestos into grades. For the production of asbestos-cement products, short-fiber asbestos-3, 4, 5 and 6 varieties are used with fiber lengths from 10 mm to several hundredths of a mm. 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 it is twisted into bundles in a ladle mixer, thereby reducing the reinforcing ability of asbestos fibers.

Figure 1 - Chrysotile asbestos fibers (X-ray spectral analysis)

PORTLAND CEMENT М400

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 cement is characterized by: a rapid increase in strength, both at the beginning and in subsequent hardening periods, a slow onset of setting (not earlier than 1.5 hours) and a sufficiently large grinding fineness necessary to create a significant adhesion surface between the cement and finely fluffed asbestos fibers. This cement must not have mineral additives(except plaster).

The increase in the strength of the product must occur quickly enough for the transition of the semi-finished product into 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% by weight of cement.

WATER

In the production of asbestos-cement sheets, water is consumed for the preparation of an asbestos-cement mixture and for washing the felts and mesh cylinders of the molding machine. Water used for the production of asbestos-cement products should not contain clay impurities, organic substances and mineral salts. Clay particles, settling on the surface of asbestos fibers, reduce their adhesion to cement, make it difficult to filter the asbestos-cement suspension 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, so it is returned back to the technological cycle. Working with recycled process water allows not only avoiding environmental pollution, but also provides advantages. Saturation recycled water Ca ions and prevents washing out of gypsum and prevents premature setting, the absence of CO 2 in it eliminates clogging of 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 a cement paste. By adsorbing calcium hydroxide and other cement hydration products 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 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

PORTLAND CEMENT М400

Delivery of cement from under-rail warehouses to the warehouse of the enterprise is brought by a cement truck.

A cement truck is a tanker 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: cement trucks with pneumatic unloading and cement trucks with pneumatic unloading and pneumatic self-unloading. Also, cement trucks, depending on the mass of the transported cargo, are divided into standard sizes: 11; 13.5; 14.7; 15; 20; 25; 30 tons. For each standard size, it is allowed to exceed the weight of the transported cargo up to 1 ton.

The cement truck has the following device. A tank-semi-trailer is installed on a tractor vehicle at an angle of 7 - 9 degrees. The inclination of the tank provides better supply of cement to the unloader. The front part of the tank rests on the truck tractor, the rear, through the bracket and springs, on the axles of the running wheels. The tank has a cylindrical or elliptical shape with specific bottoms. On the outer side of the tank, support posts, an air duct system, a moisture-oil separator, traction wheel wings, a ladder and a service platform are mounted.

In the upper part of the tank there are two hatches for loading cement, equipment for pneumatic unloading of cement is mounted inside the tank.

Figure 5 - Cement truck (a) and its tank (b)

1 - tank-semi-trailer; 2 - compressor; 3 - tractor; 4 - support post; 5 - platform for maintenance; 6 - ladder; 7 - loading hatch; 8 - otook; 9 - air tray; 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 the air trays; 16 - drain valve; 17 - pipe for pressure equalization.

CHRYSOTILE-ASBESTOS

At present, for the asbestos-cement industry, the supply of asbestos pre-buried into certain grades and pressed into small briquettes is being organized. The use of laminated briquette asbestos allows you to fully mechanize loading and unloading operations and automate technological processes preparation departments.

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 a tarpaulin or film. Inside the machine there is a device for fixing pallets.

Figure 6 - KamAZ-43118 airborne. dimensions

UNLOADING RAW MATERIALS

PORTLAND CEMENT М400

Pneumatic unloading involves supplying air through a pressurized pipe to the air trays. The air tray is a perforated steel sheet on which a wire mesh and fabric are located. Entering under the bottom of the air tray, compressed air passes through the holes in the steel sheet, seeps in streams through the fabric and saturates the bottom layer of cement. Mixed with compressed air. Cement acquires fluidity and moves to the unloading device. Under pressure, cement can also be transported to another container located at a height of 15-20 m.

Figure 7 - Scheme of unloading cement truck

1 - cement truck; 2 - cement hopper (silo); 3 - device for issuing cement.

To unload the cement, a sleeve is attached to the pipe, directing 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 purge nozzle, which creates a vacuum at the plug valve, enters the jet of compressed air, which is supplied to the container. Cement is poured onto the air trays using slopes made of sheet steel and set at an angle of 45 - 50 degrees to the horizontal plane.

To create the necessary air pressure, a rotary compressor is installed on the chassis of the tractor car. To clean the forced air from moisture and oil, a moisture-oil separator is installed on the compressor.

This method of unloading eliminates the loss of cement that occurs during manual loading, and improves working conditions.

CHRYSOTILE-ASBESTOS

Asbestos is delivered to the enterprise in an onboard KamAZ. Unloading is carried out by a universal forklift truck TVEKS VP-05.

The universal forklift (forklift) is used for unloading, transporting over short distances and stacking.

Figure 8 - Universal forklift TVEKS VP-05

Figure 9 - Overall dimensions of TVEKS VP-05

Table 2 - Specifications. Loader VP-05

WAREHOUSE OF RAW MATERIALS

PORTLAND CEMENT М400

When stored in large containers, cement, especially if it contains even a small amount of moisture, cakes, and often forms vaults during unloading. These vaults make it difficult to unload the containers and, in addition, they can cause an accident if they collapse.

Therefore, cement is aerated during unloading, that is, air is introduced into it. This excludes the possibility of formation of vaults. Air, slowly flowing between the cement grains, gives them greater mobility, and the aerated cement acquires fluidity. In addition to guaranteeing the formation of arches, aeration allows you to completely unload the silo. Cement from the silo is sent by pneumatic transport to the supply bins of the asbestos-cement plant.

Picture 10 – Cement storage silo

Figure 11 - Scheme of the cement silo

1 - silo capacity; 2 - bottom unloader; 3 - pipeline (for unloading cement into the feed hopper); 4 - a sleeve directing cement into the silo.

During storage, cement absorbs water vapor from the air and slowly hydrates. This process proceeds more intensively 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.

CHRYSOTILE-ASBESTOS

Briquetted asbestos is produced in two grades - slate and pipe. Warehousing of the specified grades of asbestos can be organized in silos or bunkers. When using laminated asbestos, its dosing will consist only in weighing a portion without compiling a charge.

The stock of asbestos at the enterprise should be calculated, depending on the distance from the asbestos deposit, from two weeks to one and a half months. For its storage use a closed warehouse.

The asbestos warehouse adjoins directly to the departments of asbestos fluffing and preparation of asbestos-cement mass (preparation department).

RUNNERS

The most common apparatus in the first stage of fluffing is runners. The wet method is more effective, since water, penetrating into the microcracks, has a sticking effect. In addition, the elasticity of the fibers is increased.

Runners are two rollers rolling in a horizontal bowl. Under the pressure of rollers moistened with water, the fibers are crushed, split and mixed.

Figure 21 - Runners

1 - machine base; 2 - bowl; 3 - ice rink.

Above the receiving part of the conveyors for feeding asbestos into the runners, dust collectors are installed, connected to air purification devices.

GOLLENDER

The final fluffing of asbestos is carried out in a gollender.

The hollender 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 processed by runners, as a result of this processing, the connection between the fibers in the bundles of untreated asbestos is sharply weakened. The gollender must break these bundles into the thinnest fibers.

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 part by a partition 2. This partition divides the middle part of the bath into two channels 6 and 7. In the channel 6 of the bath, a drum 4 is installed on the shaft 3 with steel knives 13 fixed along its generatrix. rotation through the pulley 5 of the belt drive by means of an electric motor. In the lowest part of the day of the bath there is a branch pipe 12, which is closed with a cast-iron plug 11, through which the mass is poured after the completion of the process. From the outlet to the drum, the bottom of the bath goes with a slight rise, then it rises steeply around the drum, and after that, at first steeply, and then slowly decreases to the outlet. The elevated part of the 9th bottom is called the "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 splashed by the rotating drum, it is covered 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 frame with knives is called the "bar". The edges of the blades facing the drum create a surface concentric with the surface formed by the blades of the drum.

Shaft 3 bearings are suspended on rods, which can be raised and lowered by a screw mechanism, changing the gap between the knives of the drum and the bar.

MIXER

Figure 22 - Parallel type mixer

1 – electric drive; 2 - a metal vat with a conical bottom; 3 - branch pipe 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 heat exchanger; 11 - 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 is mainly of periodic action, and forming machines must be fed continuously with such a mass. To create a stock of asbestos-cement mass, a ladle mixer is installed.

Figure 23 - Bucket mixer (vertical section)

1 - drive; 2 - tub; 3 - blades; 4 - crosses; 5 - hatch for cleaning and changing buckets; 6 - bucket wheel; 7 - receiving box; 8 - a hatch for flushing the mass and washing the vat; 9 - shaft.

The ladle mixer consists of a metal vat 2, which has the shape of a truncated cone (with a small angle at the top) somewhat tapering towards the drive of the mixing device. A shaft 9 is installed along the axis of this vat, which is driven into rotation through the drive 1 by an electric motor. Crosses 4 with blades 3 are fixed on the shaft. At the front end, the vat has a narrow socket cavity in which a frame circle with buckets 6 mounted on it, called a bucket wheel, rotates. 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 outside. The wheel buckets scoop up the asbestos-cement mass from the vat and pour it into a receiving box. Hatch 5 is used for cleaning and changing buckets, and hatch 8 is for draining the mass and washing the vat.

The mixer should not be replenished when there is a lot of mass in it, since the mass “ages” with a long stay, i.e. grains of cement 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 directed by a chute into the baths of the mesh cylinders of the molding machine. The mass concentration in the mixer is somewhat higher than is necessary for the operation of a circular mesh machine.

To obtain a mass of the required concentration, water taken from the lower part of the recuperators is continuously introduced into the chute supplying the asbestos-cement mass to the forming machine.

SM-943A

Figure 24 - Scheme of a three-cylinder circular mesh 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 leakage of the suspension from the bath into the cylinders. The sealing tapes are fixed on stops 3. The baths have paddle mixers 4, which mix the asbestos-cement slurry entering the bath through compartment 6, separated by a partition 7, which protects the layer formed on the surface of the cylinder from flushing. At the bottom of the baths there are hatches for washing them and emergency draining the suspension. On the SM-943 sheet-forming unit, 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 rest. Slots are left between the slats for discharging the filtrate with a width of 10 mm, 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 soldered end-to-end or overlapped. The immersion depth of the mesh cylinders in the suspension is about 70% of their diameter. To flush the mesh of cylinders, sprinkler pipes 5 are installed. The cloth 11 is pressed against the surface of the mesh cylinders by squeezing shafts 8 mounted on the frame 12. The pressure of the shafts on the mesh cylinder is created by their own mass and hydraulic cylinders 9. In front of the squeezing shafts, water-removing rollers 10 are installed that prevent spreading on the cloth of water pressed by the shafts.

Figure 25 - diagram of a three-cylinder circular mesh machine Mesh cylinder and bath

Baths and mesh cylinders are numbered along the felt: the first bath and cylinder receive the cloth, and above the third cylinder the cloth goes around the wringer roll and moves to the vacuum box 13.

Behind the vacuum box, a centering device 14 is installed, which automatically holds the cloth in the working position so that the axis of the cloth coincides with the axis of the machine.

After the vacuum box, the cloth moves to the sizing drum 25 and goes through three stages of squeezing: by additional press rolls 16, 17 and the main press roll 18. The pressure between the press rolls and the sizing drum is created by hydraulic cylinders 19.

Bypassing the main press roll, the cloth approaches the cloth cleaning device, which consists of an accelerating shaft 20, a cloth churn 21 and wash tubes 22. The washed wet cloth moves to the tension device 23, then is squeezed between the 15 rollers and goes to the first bath to start a new working cycle.

The movement of the machine is reported by the main drive connected to the main press roller 19. The latter transmits rotation to the format drum 25 in contact with it, and it, in turn, to the press rollers 16 and 17.

The technical cloth, sandwiched between the sizing drum and the main press roller, acts as a drive belt that drives the mesh cylinders and the wringer rollers lying on them.

Sheet-forming machine works as follows. At idle, with the wash tubes turned on, the cloth is soaked, its tension is adjusted, and the serviceability of individual machine components is checked. Then the machine is stopped, the drives are turned on, rotating the mixers in the baths, and the asbestos-cement mass is fed into the baths. After it fills the baths to a working level that is 10-12 cm from the sides, the machine is started up. Asbestos cement is filtered through the meshes of the cylinders under the influence of the level difference 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 grids, and the bulk of asbestos cement particles are 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, their compaction occurs due to the pressure of the squeezing shafts. The moisture content of the layer is reduced. The layers removed from the three mesh cylinders are transported by the felt to the vacuum box.

The last stages of compaction and dehydration 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 rollers 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 format drum. The layers removed from the felt are wound onto a format drum until the thickness of the asbestos cement on its surface reaches the specified thickness of the sheet. Then, at the signal of the thickness gauge 26, the cutter 24 is automatically turned on, the reel on the machine is cut along the generatrix and removed from the sizing drum onto the conveyor of the cutting device, and layers are wound on the sizing drum for the next reel.

Having given the asbestos cement to the format drum, the cloth is washed from contamination under the influence of the rotating rollers of the 21 cloth churn and the water flowing under pressure from the tubes 22. Squeezing the soaked cloth with rollers 15 is very effective for removing contamination.

Table 3 - Specifications. Sheet-forming circular mesh machine SM-943A

CUTTING SHEARS SM-1162

Cutting shears CM-1162 are designed for transporting asbestos-cement rolling from a sheet-forming machine to shears, transverse cutting of rolling into blanks, dropping transverse trimmings, transporting blanks to a waver.

Figure 26 - Cutting shears SM-1162

1 - rack; 2 - receiving conveyor; 3 – outfeed conveyor; 4 - scissors; 5 - feeding conveyor; 6 – scissor drive; 7 - conveyor drive.

Cutting shears have receiving and feeding conveyors, rotary shears. They are controlled from a common system of electrical equipment and electroautomatics of the automated complex.

Figure 27 - Rotary shears

1 - outfeed conveyor; 2 - spring knife; 3 - transverse knife;

4 - roller; 5 - disk knife; 6 - conveyor; 7 - conveying sheet drum; 8 - bed.

The sheets removed from the format drum of the sheet-forming machine are cut into certain formats by rotary shears. On fig. shows a longitudinal section of these scissors. They consist of a frame 8, on the front part of which a conveyor drum 6 is mounted on bearings, which feeds an asbestos-cement sheet taken from the format drum of the sheet-forming machine to the rotary shears. In the middle part of the frame, a conveying sheet drum 7 is installed on plain bearings, which receives an asbestos-cement sheet descending from the conveyor 6 and brings it to the shear blades. First, the sheet comes to the disk shear 5, which cuts the side edges at the reel and cuts 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.

The asbestos-cement sheet, cut into formats of the required dimensions, removes the shooting spring knife 2 from the surface of the drum, after which the formats are fed to the outfeed 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, circular knives 5 and rollers 4 are in continuous motion during the operation of the sheet-forming machine, the circumferential speed of the drum 7 and rollers 4 is equal to the speed of the conveyor belt 6. As a result, all parts of the sheet are given the same speed of movement, which protects the sheet from deformations.

Circular knives trim the longitudinal edges and cut it longitudinally into two strips. Three knives are installed on a sheet-forming machine that produces corrugated sheets, of which the two extreme ones serve 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 do not become 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.

Knives for transverse cutting of the sheet are set in motion periodically by means of a special switching clutch. The shaft, on which the hub with transverse knives is installed, is turned on only when the front edge of the sheet approaches the knives, and it rotates until it passes the entire sheet.

Table 4 - Technical characteristics. Cutting shears CM-1162

WAVER CMA-233A

The waver SM-233A is designed to give a wavy shape to flat blanks coming from the feeding conveyor of the shears for cutting the reel, sizing, slitting the waved sheets and issuing them to the stacker table.

Figure 28 - CMA-233A waver

1 - wave section; 2 – calibration section; 3 - edge-shaped device; 4 - drive.

The main components of the waver are the wave section, the calibration section and the drive.

The control of the waver is from the general system of electrical equipment and electroautomatics of the automated complex.

The wave section is a chain conveyor, the working canvas of which is eight profile upper and lower chains. The working branches of the lower chains are the upper branches, the upper chains are the lower branches. The lower chains are fan-shaped in the horizontal plane so that at the exit from the section the chains are located relative to each other by a step equal to the step of the sheet wave. At the entrance to the section, the step between the chains corresponds to the wave sweep step. 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 corrugated sheet, gradually approach each other. In this case, the sections of the workpiece between the fixed points under their own weight 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, a corrugated sheet comes out of the section. When waved in this way, the sheet is practically not subjected to tensile forces in the transverse direction.

From the corrugated section, the sheets directly enter the sizing section, in which the lower profile chains are located between the upper profile chains, which have weighted overlays.

The longitudinal edges of the sheet from the extreme crests of the waves do not wave. 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. Waver SM-233A

STACKER SMA-260

Stacker SMA-260 of asbestos-cement sheets is designed for transferring waved raw asbestos-cement sheets from the stacker table onto hardening conveyor trolleys.

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 - cylinder-shock absorber; 9 - air duct; 10 - vacuum fan installation; 11 - spool.

Stacker СМА-260 of asbestos-cement sheets includes a stacker table, stacker, stacker drive, vacuum system drive.

The stacker table, designed to receive wavy sheets from the sizing section of the waver to the position of taking the sheet and to dump damaged sheets onto the trimming conveyor, consists of a frame, drive and driven shafts, a clutch engagement mechanism, pusher installation and two crimping devices (right and left) .

The stacker, which transfers the sheet from the stacker table to the hardening conveyor trolley, consists of two cast sidewalls, a crosshead assembly and a vacuum box.

The stacker drive, designed to rotate the vacuum box traverse, has a part-turn hydraulic motor, two hydraulic shock absorbers and a control unit.

The control unit consists of axial throttles, hydraulic valves with mechanical control, limit switches, levers with rollers, sectors with cams and a flag. The unit ensures that the stacker's 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 box when the sheet is removed from the stacker table and when it is transferred to the hardening conveyor trolley, as well as to create excess pressure in the cavity of the vacuum box at the time of laying the sheet into the trolley. The drive of the vacuum system consists of a fan with a motor, pipelines and a spool valve, with the help of which, when the vacuum box is operating in a rarefaction mode, the suction cavity of the fan is connected to it, and when operating in the boost mode, the fan discharge cavity is connected.

Table 6 - Specifications. Stacker СМА-260

HARDENING CONVEYOR CM-1158

Hardening conveyor SM-1158 is designed to hold corrugated asbestos-cement sheets in a steam-air environment on special trolleys-forms for a period of time sufficient to gain strength.

Figure 30 - Conveyor hardening CM-1158

1, 2 - head and rear sections; 3 - frame; 4 - lubrication system; 5, 6 - front and rear drives.

Hardening conveyor CM-1158 is a two-tier, two-chain, trolley with plane-parallel movement of the trolley from one branch to another. It consists of head and rear sections, frame, bogies, front and rear section drives, lubrication system and curing chamber.

Production technology of asbestos-cement sheets

Currently, there are three methods for the production of asbestos-cement products: a wet method - from an asbestos-cement suspension, a semi-dry one - from an asbestos-cement mass and a dry one - from a dry asbestos-cement mixture. The wet method is the most widely used. The other two are used only in pilot plants.

The production process of asbestos-cement sheets consists of the following main technological operations:

Cement is transported by pipeline to closed bunkers

and is dosed strictly by weight by weight dispensers. Asbestos is stored according to grades and grades indoors. The dosage of asbestos is also carried out by weight according to the given charge.

Asbestos is delivered to factories in paper bags in railway cars. At the factory, they are stored in a closed warehouse on a wooden floor in separate compartments for different brands and grades. If asbestos entered the warehouse in a container, then it can be stored in piles. Above each compartment or stack indicate the grade and grade of asbestos.

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 mixture of asbestos is as follows: 50% asbestos of the 5th grade, 50% of asbestos of the 6th grade, and the total content of soft texture should not exceed 50%, including the content in a mixture of asbestos M-60-40 should not be more than 15%. Varieties of asbestos and their percentage in the mixtures used are normalized by special technological maps.

Further, asbestos on special pallets is fed by an electric forklift to the site and loaded into feed bins separately by groups and grades. From them, asbestos is fed along inclined conveyors to weighing batchers, where the finished asbestos charge is collected. On command from the control panel, the charge is poured out of the batchers and, with the help of transfer and inclined conveyors, it enters the distributing conveyor, from where it enters the runners, where the charge is subjected to primary processing (moistening, sticking). Simultaneously with the loading of asbestos into the runners, it is moistened with clarified recuperation water, using a special measuring device in an amount of at least 5 liters per 1 kg of dry asbestos. Duration of asbestos processing in runners is 12-15 minutes, asbestos humidity is not less than 28-80%.

At the end of the treatment, the asbestos is discharged from the runners without any residue. Further, the asbestos is processed in hydraulic fluffers in the presence of a large amount of water for the purpose of good fluffing. Processing time 8 - 10 min. Asbestos fluffing not less than 80 - 90%. Asbestos fluff determines to a large extent the quality of products. There are three types of fluff: dry, wet and semi-dry.

With the dry method, fluff is produced on runners and pushers. Asbestos bundles are kneaded in the runners, the connection between the fibers is broken, and in the pusher (disintegrator), the mashed bundles are further split into separate fibers. Asbestos fibers are finally fluffed up in the apparatus for preparing asbestos-cement mass - a hollender. With the wet method of fluffing, asbestos is soaked in water for 3-5 days, then the mixture is kneaded on runners. Water penetrates into micro-crevices and has a wedging effect, as a result of which the fibers fluff up easier and better. Wetting the asbestos increases the elasticity of the fibers, which increases the fracture resistance when processed on runners. At present, the roller machine is becoming more and more common for asbestos crushing. Unlike the runners, this machine releases high quality crumpled asbestos in a continuous stream.

At the end of the fluffing, the asbestos slurry is pumped to the turbomixer, where it is mixed with cement. The amount of cement loaded per batch into the mixer is 600-800 kg.

Cement is loaded into the mixer gradually in uniform portions from the supply hopper through a weight batcher. At the end of the cement loading, the asbestos-cement mass is mixed for 45 minutes. The finished mass flows by gravity into a ladle mixer designed for uninterrupted power supply. The mass in the mixer is continuously mixed. From the bucket mixer, the asbestos-cement mass enters the shafts of the mesh cylinders of the sheet-forming machines (LFM), on which the asbestos-cement layout of the semi-finished product is molded. Forming of sheets is carried out on a universal round-mesh three-cylinder machine SM 943. Asbestos-cement rolling is automatically removed from the forming drum of the machine upon reaching the specified thickness by a cutter. The stripped roll is fed by belt transport to the guillotine shears, which are cut into formats of 1750 * 10 mm in size.

The sheets are fed by the outlet and feed conveyors to the waver, where they are waved on the mechanized line of lineless molding CM 115 and SMA 170 using accelerated hydrothermal hardening. Currently, units are used for the automatic production of corrugated sheets and their stacking.

Sheets after profiling, having external defects, are dumped onto a standing conveyor to agitator scraps for processing.

1. pre-hardening in the conveyor;

2. hardening in a humidifier;

3. final hardening in a warm warehouse.

After the humidifier, the sorter picks up stacks of 80 sheets of UV 7.5 and 100 sheets of UV 6. The final hardening of the products is carried out in the finished product warehouse and then in open areas. In the warehouse, the sheets are kept for seven days, after which the finished products are received by the QCD and the batches are tested in accordance with GOST 16233 70.

Types of finished products and their areas of application

The range of asbestos-cement products includes over 40 items. They can be divided into the following main groups: profiled sheets - wavy and semi-wavy for roofing and wall cladding; flat slabs - ordinary and textured or painted for wall cladding; roofing and wall panels with heat-insulating layer; pressure and non-pressure pipes and couplings to them; special products (architectural, sanitary, electrical insulating, etc.).

Asbestos-cement sheet structures are used in all climatic zones of Russia and the volume of their production meets the needs of construction. The volume of production of prefabricated asbestos-cement structures satisfies only 6-7% of the demand for them.

Further industrialization of construction, reduction of labor and material intensity, increase in the durability and reliability of asbestos-cement structures require an increase in the size of corrugated sheets up to 6 m, the organization of the production of painted and reinforced sheets, flat pressed sheets, molded elements for panel frames.

Profiled sheets are made from asbestos cement wavy (ordinary and reinforced profile) and semi-wavy.

Wavy sheets have the shape of a rectangle with six (eight) waves, the direction of the ridges of which coincides with the direction of the large side of the rectangle. The length of the corrugated sheets of an ordinary profile (VO) is 1200 mm, the width is about 700 mm and the thickness is 5.5 mm. Reinforced profile wavy sheets (VU) are somewhat thicker, which allows them to be produced in large sizes. Their length is 2800 mm, width - about 1000 mm and thickness - 8 mm. IN last years a new type of asbestos-cement corrugated sheets has been developed - SV-40-250 with a size of 2500x1150x6 mm. Compared to previously produced VO sheets, these sheets have a large usable area and lower consumption of asbestos cement per 1 m2 of usable area.

Profiled sheets must be strictly rectangular in shape, without cracks and spalls. Profiled asbestos-cement sheets are used for roofing, wall cladding, balcony railings, etc. Flat facing asbestos-cement slabs are produced unpressed and pressed with increased strength, 4-10 mm thick, up to 1600 mm wide and up to 2800 mm long. In the process of molding, their front surface is finished, depending on the purpose, with a decorative asbestos-cement layer, painted with waterproof enamels, polished, and also made in relief, imitating glazed ceramic tiles. Plates painted with waterproof enamels, in Lately successfully used for facing panels, ceilings, walls of sanitary facilities and kitchens of residential and public buildings.

Asbestos-cement slate is inexpensive, easy to install and one of the best known roofing materials. Wavy asbestos-cement sheets (slate) are the most common roofing material. Until recently, their dimensions were relatively small: sheets of an ordinary VO profile had a size in terms of 1200X680 mm and a mass of about 9 kg. At present, their production has been almost universally discontinued and the production of large-sized corrugated asbestos-cement sheets has begun.

The most popular for rural housing construction are asbestos-cement sheets of UV with a size in terms of 1750 * 25 mm. Each of them covers about 1.5 m2 of the roof and, compared to a small-sized VO sheet, has 2 times fewer joints.

Modern asbestos-cement roofing sheets - slate, are painted to increase their decorative properties and increase their service life. Staining is carried out with silicate or phosphate-based paints, using various pigments. In the past, asbestos-cement sheets (slate) had either a featureless, gray tint, or could be red or green. At present, slate is produced in a variety of colors: red-brown, chocolate, brick red, yellow (ocher), blue, etc. The paint that is used to cover finished slate sheets forms a protective layer that protects the product from destruction, reduces its water absorption and increases frost resistance. Such a protective layer reduces the volume of asbestos emissions into the surrounding air and increases the service life of the slate by 1.3 - 1.5 times.

Flat slate is already moving away from the consumer market, its disadvantages still overcame its advantages: laying is complicated due to its small size (400x400 mm) and is limited to a slope angle of 30 °. But also appearance a flat slate roof leaves much to be desired, it is easier to replace it with elegant tiles and its interpreters (metal tiles and bituminous tiles) that are optimal for such slopes.

Introduction
1. Historical background

3. Raw materials



Conclusion
Literature

Introduction

1. Historical background

2. Classification of asbestos cement products

sheathing made of gray sheets - with sunken screws; glass wool plates are used as a heater (Fig. 2). Wall panels are produced up to 6000 mm long, 3300 mm wide and 140..170 mm thick.
Asbestos-cement flat roofing tiles (Fig. 3) are intended for low-rise rural buildings and individual construction. The most used size is 400x400 mm with two cut corners. The cut corners of the tiles make it possible to form a dense roof covering with their minimum consumption (10 pieces per 1 m). When using tiles without cut corners, the roof can only be formed with a two-layer coating. Tiles are laid on a solid or sparse crate with galvanized nails and an anti-wind button. The tensile strength of tiles in bending is 24 MPa, and frost resistance is 50 cycles

Rice. 3. Asbestos-cement roofing tiles:
a) ordinary; b) edge, c) ridge detail
Extruded panels and plates - products up to 6 m long, up to 750 mm wide and 60-180 mm high are made with and without insulation and are used as wall structures and partitions (Fig. 4). Semi-rigid mineral wool boards are used as insulation.

Rice. 4. Asbestos-cement extruded partition panels: a) corner; 6) transitional
Exterior asbestos-cement wall panels on a wooden frame with insulation are designed for exterior walls of the above-ground part of prefabricated residential buildings and houses made of monolithic concrete, and in brick houses - for loggia walls.
The dimensions of the panels are 2980 and 5980 mm in length and 2780 mm and 3280 mm in height. Panel thickness 160 and 210 mm. The outer surfaces of the sheets can be smooth or embossed, have a natural gray or white color, as well as a color created by a protective and decorative coating.
Asbestos-cement pipes produce pressure, non-pressure and ventilation; 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 polymeric materials.
These pipes are the most economical and fairly 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. Some water pipes are divided into classes according to the maximum working pressure: up to 0.6 MPa - class VT6, up to 0.9 MPa - class VT9, up to 1.2 MPa - class VT 12, up to 1.5 MPa - class VT 15, up to 1.8 MPa - class BT 18.
Gas pipelines are divided into grades according to the maximum working pressure: GAZ-ND - for low pressure gas pipelines (up to 0.005 MPa), GAZ-SD - medium pressure (up to 0.3 MPa).
Rectangular asbestos-cement boxes are designed for air ventilation in industrial auxiliary and domestic premises, industrial, residential and civil buildings. Seamless boxes without sockets are made from thin-walled pipes of special winding, freshly molded 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 box is made 4000 mm long with an internal section of 150X 300, 200 X 200, 200 X 300 mm and a wall thickness of 9 mm. The boxes have high strength, flexural strength not less than 16 MPa, density 1600 kg/m3.
Special asbestos-cement products are produced from asbestos cement. These include large-sized figured sheets used for vaulted roofs, cooling towers, grain dryers, etc.

3. Raw materials

4. Main technological processes and equipment for the production of asbestos-cement products

Rice. 5. Asbestos fluffing schemes:
a - wet method: 1 - asbestos warehouse; 2 - site for the preparation of a mixture of asbestos, 3 - dispenser; 4 - runners with asbestos moistening, 5 - gollender;
b- dry method 1 - asbestos warehouse. 2 - site for the preparation of a mixture of asbestos; 3 - runners; 4 - disintegrator (fluffer), 5 - exhauster, 6 - chambers of fluffed asbestos, 7 - dispenser, 8 - gollender
Rice. 6. Mechanized plant for mixing, moisturizing and crushing asbestos mixture: 1 - asbestos bunker, 2 - feeder, 3 - dispenser; 4 - mixer-moisturizer, 5 - leveling device, 6 - leveling roller; 7 - roll machine, 8 - freely rotating rolls; 9 - pneumatic device; 10 - drive rolls

At present, the roller machine is becoming more and more common for crushing asbestos (Fig. 6). Unlike the runners, this machine releases high quality crumpled asbestos in a continuous stream.
Rice. 7. Gollender of periodic action: 1, 7-channels, 2 - bath, 3-partitions, 4 - drum shaft, 5 - knife drum; 6 - pulley; 8 - removable casing, 9 - slide; 10 - frame with knives, 11 - valve; 12 - branch pipe; 13 - knives

Asbestos is finally fluffed up in a gollender, and then cement and water are added to it and mixed until a homogeneous asbestos-cement mass is obtained. Gollender (Fig. 7) is a metal or reinforced concrete bath, divided in the middle by a longitudinal partition that does not reach the edges. 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 served. When the drum rotates (180 ... 240 min-1), the mixture is carried away into the gap between the drum knives and the comb, is thrown over the hill, passes through the bath and again falls under the drum.
The circulation of the mixture lasts up to 10 minutes, the degree of fluffing of the fiber in this case should be 90 ... 95%. Then load the cement, add water and produce additional mixing. By the end of mixing, almost all of the cement is adsorbed onto the asbestos fibers. The dosage of the components of the asbestos-cement mass is equal to: asbestos - 10 ... 18%, cement - 82 ... 90%; for the production of pipes: water - 97%, and sheet asbestos-cement materials - about 95%. Gollender - apparatus of periodic action. For continuous supply of the molding machine, it is necessary to create a stock of asbestos-cement mass in the ladle mixer (vat), which would be periodically replenished from the gollender. The mixing of the mass in it is carried out by a cross with blades. On the same shaft with the cross there is a frame circle - a "bucket elevator". The ladles scoop up the mass from the vat and feed it into the receiving box of the sheet-forming or tube-forming machine.
Molding is the most important process in the production of asbestos cement products. Products are molded on sheet-forming and pipe-forming machines. The sheet-forming machine (Fig. 8) 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 with a shaft. The drive support shaft drives the belt, which rotates the mesh cylinder. The asbestos-cement mass is deposited in a thin layer on the surface of the metal mesh of the drum, partially dehydrated on it due to water filtration through the mesh and, during rotation, is removed from the drum, evenly placed on the moving belt. The asbestos-cement mass, moving on a belt, passes through a vacuum box, where it is dehydrated, then transferred to a rotating sizing drum, wound on it in concentric layers and compacted.

Rice. 8. Diagram of molding machine:
1 - mixer; 2 - bath; 3 - partition, 4 - mesh cylinder; 13, 15 - washing tubes; 6 - pressure shaft; 7 - cloth; 8 - upper vacuum box; 9 - metal format cylinder; 10 - support (drive) shaft; 11 - guide rollers; 12 - lower vacuum box; 14 - impact roller; 16 - squeezing shafts; F1 F2, F3 - pressures created by weights, springs or hydraulic cylinders.

In the manufacture of sheet asbestos-cement products, a mass of a certain thickness wound onto a format drum is cut and removed from the drum. The resulting sheets are cut into sheets of a specified size and fed into the steaming chambers. After being removed from the sizing drum, the sheets intended for wave formation are cut into formats and placed in the 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. In order to acquire the necessary strength in the shortest possible time, the products are steamed or kept first in air at normal temperature, and then in pools with warm water.
Hardening of asbestos-cement sheet products made on Portland cement occurs in two stages. The first is pre-hardening in intermittent 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 (edge ​​trimming, punching and so on.). 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 a working pressure of up to 0.8 MPa. Upon reaching the required strength, the products are subjected to mechanical processing.
At present, a new set of equipment has been developed for the technological line for the automated production of large-panel asbestos-cement sheets based on a flat mesh machine. This method production of asbestos-cement slabs reduces the cost of production by 7% compared to existing ones. The degree of automation of this method reaches 98% with 100% mechanization on the main production lines.

5. Main properties of asbestos-cement products

6. Technical and economic indicators