Production of asbestos-cement products. Abstract asbestos-cement products Workshop plan for the production of asbestos-cement products

The technological scheme for the production of asbestos-cement products includes: reception, storage and supply of cement and asbestos to production; accumulation of process water, its recovery; preparation of the mixture, crushing and fluffing of asbestos, preparation of asbestos-cement mass with its accumulation in an intermediate container; molding of sheet blanks (rolls) or pipes from asbestos-cement mass; cutting sheet blanks into formats and giving them a given shape; thermal and moisture treatment of asbestos-cement products during their hardening; mechanical processing of hardened products and quality control of products to submit to the production of raw materials - cement, asbestos of various grades, water. Then make a mixture of asbestos of various grades, knead and fluff, and then prepare a portion of the asbestos-cement mass from the asbestos mixture, cement and water and give it to an intermediate container - a drive for feeding molding machines. The technological scheme for the preparation of asbestos-cement mass is given in Fig. 4.19.

Figure 4.19.

1 - asbestos receiving hopper; 2 - water dispenser; 3 - asbestos feeder;
4 - asbestos dispenser; 5 - runners; 6 - receiving bunker of runners; 7 - crushed asbestos feeder; 8 - crushed asbestos dispenser; 9 - mixer; 10 - disintegrator; 11 - turbomixer; 12 - cement dispenser; 13 - cement bunker; 14 - dosing water tank; 15 - collection of clarified water; 16 - recuperator

According to this scheme, asbestos is fed into the receiving hopper 1 and further - to the feeder bunkers 3. From the bunkers, asbestos is periodically dispensed into dispensers 4 for weighing the mixture. The prepared portion of the mixture enters the runners 5, where from the dispensers 2 water is supplied. Crumpled portion of asbestos through the receiving hopper 6 enters for intermediate storage in the bunker of one of the feeders 7. The feeder periodically issues asbestos to the weight batcher 8. A weighed portion of crumpled asbestos and water in a given amount enter one of the mixers in turn 9 for the preparation of an aqueous suspension of asbestos. From the mixers, a portion of the suspension passes through the disintegrator 10 into one of the turbomixers 11, where from the bunker 13 with a dispenser 12 a weight portion of cement is supplied, and from the tank 14 - portion of water. The asbestos-cement mass prepared in the turbomixer is periodically discharged into the ladle mixer (not shown in the diagram).

Schemes without intermediate accumulation and storage of asbestos are used. Asbestos of different grades in a given weight quantity is poured into the mixer receiving hopper, mixed, and a portion of the mixture enters the runners for crushing, where water is supplied to moisten the asbestos.

A crumpled portion of asbestos is dispensed from the runners into the mixer, where water is supplied in a given amount. The aqueous suspension of asbestos prepared in the mixer is pumped to the gollender, where a weight portion of cement is fed from the dispenser.

The prepared portion of the asbestos-cement mass is discharged into a ladle mixer for intermediate accumulation and continuous supply to sheet-forming machines.

Weight batcher CM-593 is used for weight dosage of asbestos. The dispenser (Fig. 4.20) has a frame 1 with a weight mechanism installed on it, to which the bunker is suspended 2. Bunker straight

Rice. 4.20.

rectangular cross-section, with a bottom in the form of a double-leaf shutter 3, closed and opened by mechanism 4. The shutter mechanism is controlled by a pneumatic cylinder 5 through a spool 9. Asbestos is fed into the bunker by a belt conveyor. The bunker itself with a shutter mechanism and a pneumatic cylinder is suspended from a lever system 6.7, Jun 11 weight mechanism. To ensure free movement of the hopper with a weighing mechanism system, air from the spool 9 fed into the pneumatic cylinder 5 by flexible hoses 8. Under the action of the weight of the loaded asbestos, the hopper is lowered and through the system of levers and rods of the weight mechanism acts on the rod 13 dial pointer 14 weighing device. When the set weight is reached, the thrust 13, moving, turns off the limit switch 12, which stops the conveyor feeding asbestos into the bunker.

The twin-shaft mixer SM-923 is used to prepare a mixture of asbestos (Fig. 4.21), has a trough 6 with two paddle shafts 9 and 10, rotating in opposite directions. Shaft 9 driven by an electric motor 1 through the clutch 3 and reducer 2. From the gear 8, mounted on a shaft, rotation is transmitted through a gear 4 shaft 10.

Rice. 4.21.

blades 11 located at some angle to the axes of the shafts, which ensures the movement of asbestos along the mixer while mixing it. When changing the angle

As the blades change, the rate of passage of asbestos through the mixer changes. Asbestos is fed into the loading funnel 5 and unloaded through the hatch 7.

Fluff stages. The fluffing of asbestos is carried out in two stages, it is a cylinder with a conical bottom, in which a propeller fluffing device is installed. In addition, the hydraulic gunner is equipped with a pumping unit, with the help of which the asbestos suspension is repeatedly pumped through the pipeline and hits the ribbed plates under pressure, which accelerates the fluffing of asbestos.

Asbestos is mixed with cement in a gollender or turbo mixer. The turbomixer is a cylindrical container with a conical bottom. It has a vertical propeller-mixing device. If the turbo mixer is installed above the ladle mixer, then the asbestos-cement mass enters it by gravity, if below the mixer, then with the help of a pump.

The bucket mixer is used to create a stock of asbestos-cement mass, which ensures uninterrupted power supply to molding machines.

The SMA-82 bucket mixer (Fig. 4.25) is a metal case 5 in which the bucket wheel is located 9 and mixing device 8.

Rice. 4.25.

1 - drive; 2 - bearing; 3 - branch pipe; 4 - crosses; 5 - body;

B - blades; 7 - shaft; 8 - mixing device; 9 - bucket wheel; 10 - inspection hatch; 11 - bucket; 12 - receiving box; 13 - bracket;

The agitator body has the shape of a truncated cone, turning into a cylinder at a large diameter. Pipe branch 3 serves to supply asbestos-cement mass to the mixer, hatch 14 - for lowering, if necessary, asbestos-cement mass. receiving box 12 serves to supply asbestos-cement mass to the forming machine. mixing device 8 consists of three crosses 4 With

two rows of blades 6, arranged in a spiral. In the cylindrical part of the body there is a bucket wheel 9 with buckets 11.

In the production of asbestos-cement products by extrusion, it is necessary to prepare a plasticized asbestos-cement mass. Asbestos fluff is produced in two stages; the first is usually carried out in runners, the second in a dry fluffer.

An aqueous solution of plasticizing additives (when using methylcellulose) is prepared in a reactor using hot and cold water.

Weighed portions of fluffed asbestos and cement are fed into a working mixer of dry components SLU-2000 (Fig. 4.26). In it, the mixture is mixed for 4-5 minutes. To prevent the dry mixture from heating up, the mixer body is continuously cooled with water.

Rice. 4.26.

1 - rack; 2 - cover; 3 - plug; 4, 9 - hatches; 5 - body; 6 - mixer; 7 - engine; 8 - reducer

The prepared portion of the dry asbestos-cement mixture is fed into the mixer by an elevator. After 2.5-3 minutes after the start of the dry asbestos-cement mixture, a portion of the solution of plasticizing additives is fed into the mixer.

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.

INTRODUCTION

CHAPTER 1. GENERAL PART

1 Technological scheme for the production of asbestos-cement flat sheets

2 Raw materials used for the production of asbestos-cement flat sheets

2.1 Asbestos

2.2 Cement

CHAPTER 2. DESCRIPTION OF THE TECHNOLOGICAL SCHEME FOR THE PRODUCTION OF ASBESTOS-CEMENT FLAT SHEETS8

1 Asbestos treatment

2 Cement processing

2.3 Formation of sheets

CHAPTER 3. BRIEF DESCRIPTION OF THE EQUIPMENT

1 Asbestos treatment in runners

2 Fluffing in the hydraulic gun

3 Turbomixer

4 sheet forming machine

CHAPTER 4. PROPERTIES OF ASBESTOS CEMENT FLAT SHEETS

CHAPTER 5 SAFETY AND FIRE-FIGHTING MEASURES IN THE ROOFING INDUSTRY

CONCLUSION

LIST OF USED LITERATURE

INTRODUCTION

In modern construction<#"563595.files/image001.gif">

Fig.1 Flat asbestos-cement sheets. Specifications.

To get acquainted with the production technology of asbestos-cement flat sheets using the wet method.

a) Analysis of the used literature;

b) Consider the technological scheme for the production of asbestos-cement flat sheets by the wet method;

c) Describe the technological scheme for the production of asbestos-cement flat sheets by the wet method;

d) Tell about the properties of asbestos-cement flat sheets;

e) Talk about safety and fire prevention measures at the roofing industry;

g) Conclusion.

1. GENERAL

1.1 Technological scheme for the production of asbestos-cement flat sheets by the wet method

1.2 Raw materials used for the production of asbestos-cement sheets

asbestos cement sheet turbo mixer

Asbestos-cement sheets are made from three main components: asbestos, cement and water. The raw mix (based on the mass of dry matter) contains an average of 85% cement and 15% asbestos

1.2.1 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. Asbestos molecules are strongly bonded to each other in only 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. The diameter of the chrysotile asbestos fiber ranges from 0.00001 mm to 0.000003 mm.

Asbestos has a high adsorption capacity. And in a mixture with Portland cement, when wetted with water, it well retains cement hydration products that bind asbestos fibers on its surface, so asbestos cement is, as it were, a thinly reinforced cement stone.

Chrysotile asbestos does not burn, but at a temperature of 0°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 former properties from the air. When asbestos is heated to a temperature of more than 550 ° C, all 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, but it is easily destroyed by acids.

The length of asbestos fibers has a great influence on product quality. This is the main sign of the division of 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 are used with fiber lengths from 10 mm to several hundredths of a mm, and their content is 50-24% by weight, the remaining 50-76% are pulverized and other non-fibrous particles. Sometimes part of the asbestos (10-15%) is replaced with basalt or slag mineral wool.

Asbestos with undeformed fibers, the size of which is more than 2 mm in diameter, is conventionally called "lump" asbestos, and less than 2 mm - needles. Fluffy is called asbestos, in which the fibers are thin, deformed and entangled. Particles of accompanying rock with a particle size of more than 0.25 mm are called gales, and less than 0.25 mm are called dust.

1.2.2. Cement

As a binder in the production of asbestos-cement sheets, special Portland cement is used for asbestos-cement products.

The grade of cement is determined by determining the flexural strength of sample beams 4x4x16 cm in size during compression of their halves, made from a plastic (B / C \u003d 0.4) cement mortar with a composition of 1: 3 with normal sand and tested after 26 days (table 1 )

Grade of cement	Tensile strength, MPa, not less than
	When bending		When compressed
	After 7 days	After 28 days	After 28 days

Table 1. Strength properties of cement

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 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 cement and finely fluffed asbestos fibers. . This cement contains at least 52% 3CaO-SiO2 and no more than 8% 3CaO-A12Oz, it should not contain mineral additives (except for gypsum). The increase in the strength of the product must occur quickly enough for the transition of the semi-finished product into the finished product. To meet the requirements of GOST 9835-77, special Portland cement with a specific surface area of 2200-3200 cm2/g is used for the production of asbestos-cement sheets. 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.

The molding of asbestos-cement products lasts 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.

In the manufacture of asbestos-cement sheets, special white and colored cements are also used.

Water in the production of asbestos-cement sheets 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 of recycled water with Ca ions prevents washing out of gypsum and prevents premature setting, the absence of CO2 in it eliminates clogging of meshes with calcium carbonate. The most favorable temperature is 20-25°C. At temperatures below 10°C, the productivity of the molding units drops, and the hardening of the products slows down. Too high a water temperature can cause the cement to set too quickly. 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. Paints are used for painting asbestos-cement sheets. Colored cements or mineral alkali-resistant pigments are also used, which have a high coloring power, light and weather resistance and do not interact with cement hydration products. These are redoxside (artificial iron oxide), iron minium, natural mummy, ocher, chromium oxide, ultramarine, manganese peroxide, etc. Sheets intended for lining walls and panels of sanitary facilities and kitchens are covered with waterproof enamels and varnishes, which are obtained on the basis of polymers.

2. DESCRIPTION OF THE TECHNOLOGICAL SCHEME FOR THE PRODUCTION OF ASBESTOS-CEMENT FLAT SHEETS BY THE WET METHOD

The technological scheme for the production of asbestos-cement flat sheets by the wet method consists of the following main processes: warehousing and storage of basic materials; preparation of an asbestos mixture from several grades and grades, fluffing of an asbestos mixture, preparation of an asbestos-cement mass, ensiling (storage) of an asbestos-cement mass, molding of asbestos-cement products (facing sheets and roof tiles are additionally pressed), preliminary hardening of molded products, mechanical processing of products, hardening of products, storage .

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. At the end of the fluffing, the asbestos slurry is pumped to the turbomixer, where it is mixed with cement.

2.2 Cement processing

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 guillotine shears, which are cut into formats 17501x0 mm in size.

2.3 Sheet forming

The principle of forming asbestos-cement products on these machines is as follows. The asbestos-cement suspension is subjected to filtration on a rotating mesh cylinder, as a result of which a thin, water-saturated asbestos-cement layer is formed on its surface. This layer is further dehydrated by vacuum and compacted by rolling on a sizing drum. Since the layers filtered on the mesh cylinder have a relatively small thickness (0.2-0.3 mm), in order to obtain an asbestos-cement product of a given thickness (sheets 5520 mm, pipes 8-50 mm), they are formed from layers (films) wound on top of each other . As a result, the product has a layered structure. To speed up the process of forming a product of a given thickness, the asbestos-cement suspension is filtered not on one, but on several mesh cylinders. For example, for the manufacture of sheet products, three- and four-cylinder sheet-forming machines are used. Products made in this way are of high quality. This is due to the fact that during the preparation of the suspension, asbestos in the aquatic environment quickly splits into thin fibers and is quite evenly mixed with cement. The product is molded in the form of elementary layers of small thickness, in which the maximum degree of use of the reinforcing ability of asbestos fiber is ensured. The freshly formed semi-finished product has plasticity, which makes it possible to manufacture products of various shapes from it by profiling.

3. BRIEF DESCRIPTION OF THE EQUIPMENT

3.1 Asbestos treatment in runners

Runners have two cast-iron rollers with a diameter of 1400 mm; and a width of 400 mm; weighing 2800 kg; the axes of which are connected to a vertical shaft rotating at a speed of 12-16 rpm. To mix asbestos, scrapers are installed in the bowl of runners on their vertical ox. The height of the scrapers and the angle of their inclination to the direction of travel can be adjusted.

3.2 Fluffing in hydraulic guns

The hydraulic gun has a cylindrical tank with a volume of 4.1 m3 (working volume 3.6 m3), in which a vertical mixer with a propeller with a diameter of 500 mm, rotating at a speed of 480 rpm, is installed. The propeller is enclosed in a cylindrical diffuser. The mixer drive is carried out through a V-belt transmission from an electric motor with a power of 40 kW

3.3 Turbomixer

Designed for mixing asbestos slurry with cement and obtaining a homogeneous asbestos-cement slurry. The design of the turbomixer is similar to the design of the hydraulic gun. The difference lies in the absence of a fluffing knot. The turbomixer is a cylindrical vessel with a conical bottom. It has a vertical propeller-washing device.

3.4 Sheet-forming machine

Forming of sheets and other asbestos-cement products in a wet way is carried out on a round-mesh forming machine (or semi-dry - on a filter belt). The principle of forming products is to filter water from the layers of asbestos-cement mass under the influence of hydrostatic pressure to the required compaction. For this purpose, a hollow frame-type cylinder 2 is located in a metal bath 1 filled with asbestos-cement suspension, covered with a metal mesh (mesh drum). On the grid, the mass is deposited in a thin layer and partially dehydrated due to water filtration through the grid. Water from the drum is first diverted to thickeners (recuperators) to separate and return to production the non-settled part of the asbestos, and then it is used to wash the mesh and cloth and liquefy the asbestos-cement mass in the gutter. A layer of asbestos-cement mass is removed from the surface of the drum with an endless cloth tape 5. Having passed a vacuum box 6 on the tape (with a vacuum of about 300 mm Hg), the pre-dehydrated asbestos-cement mass is transferred to a metal format drum 7, which removes the mass from the cloth tape and winds it onto its surface in concentric layers, while it is compacted between rotating metal cylinders. When the asbestos-cement layer on the drum reaches the required thickness, it is cut along the generatrix of the cylinder, and the raw sheet is removed. The pressure of the press part of the sheet-forming machine is usually 0.2-0.4 MPa, for the second compression shaft 10.0-12.0 MPa, for the press shaft - up to 40.0 MPa. As a result of compression, the moisture content in the sheet is significantly reduced and reaches 25%

4. PROPERTIES OF ASBESTOS CEMENT FLAT SHEETS

The main properties of sheet asbestos-cement products are evaluated by a complex of such indicators as density, static and impact strength, frost resistance, temperature and humidity deformations and warping, as well as bearing capacity.

Hardened asbestos cement consists of several components that differ in density: cement clinker grains hydrated from the surface; cement stone; asbestos fibers; particles of asbestos-containing rock in the form of dust, hali. The density of asbestos cement will depend on the density and relative content of these components. In addition to cement hydration, an increase in the mass of asbestos cement over time causes carbonization of the lime present in the hardening cement stone due to the addition of carbon dioxide and air. The density of asbestos cement depends on the amount of porosity.

The porosity of asbestos cement is 35-40% for non-pressed sheets of products, and 25-30% for pressed sheets. The presence of porosity explains the ability of asbestos cement to absorb a significant amount of moisture, which is characterized by the amount of water absorption.

The static strength of asbestos-cement products is estimated by the flexural strength in kgf / cm2. VO corrugated sheets have a tensile strength of at least 160 kgf / cm2, UV and SV-40 - 160-190 kgf / cm2.

Bearing capacity - the amount of load that an asbestos-cement product must withstand without permission.

Impact strength (or impact strength) is an indicator that characterizes the brittleness of a material, which is estimated by the amount of work that needs to be spent on the destruction of the material. For asbestos cement, this indicator ranges from 1.5-2 to 4-5 kgf / cm2.

Frost resistance is the ability of a material saturated with water to withstand alternate freezing and thawing without destruction and loss of strength. The strength of asbestos cement after freezing decreases on average by 10% at an average density of 1.57 g/cm3 after 25 cycles, 1.65 g/cm3 after 50 cycles, and 1.8 g/cm3 after 100 cycles.

The amount of warping decreases with an increase in the density, thickness of the product, and an increase in the content of asbestos in it. The absolute values of the warping arrow, depending on the indicated factors, range from 0.125 to 0.52 mm.

Humidity deformations, in which the hardened asbestos cement swells when moistened, and shrinks when dried, significantly decrease with an increase in the density of asbestos cement.

Acids are dangerous for asbestos cement, including the acidic environment formed in the pores when gases containing SO3 are exposed to the material; aggressive media are less dangerous for high density asbestos cement.

5. SAFETY AND FIRE-FIGHTING MEASURES IN FINISHING INDUSTRY PLANTS

As you know, some finishing materials, binders and other components of plastic masses (except for mineral fillers and pigments) have sufficient toxicity and fire hazard.

Toxic polymers can cause illness in people who process them. These materials, as well as their decomposition products, which are formed during the production of finishing materials, getting into the soil, water of rivers and lakes, poison the natural and animal world.

Most plasticizers are 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:

-1 storage and transportation of toxic raw materials only in tightly closed containers;

−3 moving parts of mechanisms and machines, various production capacities are fenced: bunkers, reservoirs, etc.;

−4 reliable thermal insulation of installations and units operating at elevated temperatures;

-5 provision of general ventilation of all working premises, including local ventilation for each machine and unit, during the operation of which harmful substances are emitted;

-6 grounding of all electric motors, starting devices and units to prevent the formation of static electricity and sparks;

−7 placement in isolated rooms of technological lines associated with toxic release of substances and dust.

Workers must be instructed in a timely manner on safety and fire fighting equipment, strictly observe the rules of personal hygiene, in addition, workers are provided with special clothing and additional protective equipment. Also, what you should pay attention to, the working premises should be provided with materials for medical assistance to the victims.

In order to protect the environment from pollution, all ventilation emissions and wastewater must be subjected to special cleaning, which would exclude any pollutants from entering the air, soil and water bodies.

CONCLUSION

Experts believe that with the wet method of fluffing asbestos, the length of the fiber is preserved and the technological scheme for the production of asbestos cement is simplified. This method, compared to others, is less energy intensive, but is associated with the consumption of large amounts of water. Also, the main advantage of the wet method for the manufacture of asbestos-cement products using low-concentration suspensions is that it provides high-quality asbestos-cement products.

As a disadvantage of the wet method for the production of asbestos-cement products, it should be noted the need to use a large amount of water at the initial stage of the technological process for fluffing asbestos, preparing asbestos-cement mass.

Bibliography

The starting materials for the production of asbestos-cement products are asbestos, Portland cement and water.

Asbestos– fibrous material serves as a reinforced material, has high fire resistance, high tensile strength of 600-800 MPa. The density of asbestos cement is 1500-1950 kg/m3.

Asbestos is obtained from fine-fiber natural material, which is split into flexible and thin fibers up to 0.0005 mm thick, mainly "chrysotile asbestos" - hydrous magnesium silicate. The length of the fibers from 1mm (lowest grade) to 18mm (highest grade) of asbestos greatly affects the quality of the material.

Asbestos cement is a hardened cement stone reinforced with asbestos. Cement M 300 and above has a compressive strength of 90 MPa, in bending up to 30 MPa.

Today, asbestos is less commonly used in construction. turned out to be a carcinogenic material and its service life is not high - only 25 years.

There are several varieties of asbestos: chrysotilasbest, crocidolite, amosite, etc. Chrysotilasbest (hydrous magnesium silicate) is of the greatest importance in industry. This is explained by the fact that its fibers are more durable and elastic than those of other types of asbestos; they are less connected to each other and fluff (break apart) easily. In addition, the natural reserves of chrysotilesbestos significantly exceed the reserves of other types of asbestos taken together.

Enriched asbestos, that is, separated from rocks (asbestos ores) and partially fluffed, enters the factories of asbestos-cement products. Enrichment of asbestos consists in crushing asbestos ore (in this case, pieces of ore are split along the planes of asbestos bonding and including rocks), extracting asbestos from it and separating it into grades.

Asbestos of mechanical enrichment is a mixture of small aggregates of fibrous structure (fiber bundles) and individual fibers of various lengths (from fractions of a millimeter to 40 mm depending on core thickness).

Since the length of the asbestos fiber has a great influence on the quality of asbestos materials and products, the grade of asbestos is set depending on the length of its fibers: the longer the average fiber length, the higher the grade. For the production of asbestos-cement products, short-fiber asbestos of at least the fifth grade is used.

Asbestos has a high adsorption capacity. When mixed with Portland cement and water, asbestos absorbs calcium oxide hydrate released during cement hardening and other products of hydration of clinker minerals, intensively contributing to the acceleration of hardening and increasing the strength of asbestos-cement products. Asbestos also performs a reinforcing role in the cement stone, perceiving mainly tensile stresses. The production of asbestos-cement products is based on the high adsorption capacity of asbestos and its reinforcing role.

Chrysotilesbest does not burn, but at +368°C, when all the adsorption water evaporates, the strength of asbestos decreases by 20-35%.

For the production of asbestos-cement products, special Portland cement is used, which is produced by joint fine grinding of clinker of a normalized composition and the required amount of gypsum.

Production of asbestos-cement products

The areas of application and the range of asbestos-cement products are very extensive and diverse. Roofing products are made from asbestos cement (flat pressed tiles, profiled sheets, various roofing parts), water and sewer pipes and couplings, facing sheets, ventilation ducts, etc.

The technological process for the production of asbestos-cement products is carried out in the following sequence:

1) fluffing of asbestos and preparation of asbestos-cement mass;

molding (roofing tiles and facing sheets are additionally pressed);

pre-hardening of molded products;

mechanical processing of products;

hardening in an insulated warehouse.

Enriched asbestos entering the asbestos-cement plants is fluffed. Fluffing it is first done on runners in dry and wet ways. The wet method provides a fine fluff of asbestos fibers with less sophisticated equipment; in addition, better conditions for the work of maintenance personnel are created (dust formation is reduced). On the runners, the fibrous bundles of asbestos are kneaded, and the relationship between the fibers is disrupted; completely fluffs up during further processing in gollenders (rolls). In the production of sheet materials, the wound mass (of the required thickness) is cut, removed from the drum and further cut into sheets of the required size. In the manufacture of flat tiles, the sheets are fed to a hydraulic press and under a pressure of 300-400 kg/cm 2 pressed. Upon receipt of profiled sheets, the mass is not pressed, but placed in a metal mold and rolled out using rolling pins.

The molded products are placed in steaming chambers for 12-16 h, after which the mechanical processing of products is carried out (cutting edges, punching holes in tiles for attaching them to the roof, etc.).

From asbeto-cement material are made:

Asbestos-cement sheets - profiled (wavy, double curvature, curly), flat (pressed and non-pressed) are intended for walls, roofs, finishes and structural elements with a thickness of 5-10 mm, wavy with dimensions of 1000x2800 mm, flat 1600x2800 mm.

Asbestos-cement panels

Asbestos-cement pipes and boxes with a diameter of 100-500 mm, length 3; 4 and 6 m.

In the production of pipes, pipe-forming machines are used with removable format drums, the diameter of which determines the inner diameter of the pipe. Such a drum is called a format rolling pin.

The layers of asbestos-cement mass wound on a format rolling pin are evenly compacted from above with rollers and pressed into a monolithic mass. The wall of the pipe can be made of any thickness, controlled with great precision by special devices.

At the end of the winding process, the rolling pin with the pipe is removed and a new one is installed. To take out the format drum, the pipe is expanded and sent to the pre-hardening sites. Three-meter pipes of all diameters come to the site along with format drums, pipes of greater length - with wooden cores. Drums and cores are removed from pipes after 2-6 h, and the pipes withstand 1-2 days, after which they are sent to water basins or steaming chambers to accelerate hardening. After keeping in water or steaming, the pipes are dried and subjected to mechanical processing (cutting off the ends, turning the ends of water pipes, etc.).

In order for the pipes to acquire final strength, they are kept in an insulated warehouse for at least 13-18 days. To accelerate the hardening of asbestos-cement products in recent years, autoclave processing has been used (hardening of products in autoclaves).

Profiled sheets are made of wavy ordinary and reinforced profile, as well as semi-wavy. They may be unpainted or dyed. Sheets of an ordinary profile have a length of 120 cm, width about 70 cm and thickness up to 6 mm. Reinforced profile sheets are somewhat thicker (8 mm), which allows to produce them in large sizes: 175 and 200 long cm and about 100 wide cm. Semi-corrugated sheets have dimensions of 120x55 cm, 80x55 cm and thickness 6 mm.

Profiled sheets must have a strictly rectangular shape without cracks and spalls. The flexural strength of semi-corrugated sheets and corrugated ordinary profiles must be at least 160 kg/cm 2 , and reinforced profile - not less than 180 kg/cm 2 . Water absorption of sheets is allowed no more than 32% (by weight).

When tested for frost resistance, sheets must withstand 25-50 cycles of alternating freezing and thawing at temperatures provided by the standard.

Profiled sheets are used to cover the roofs of residential and civil buildings, as well as for wall fencing of workshops with excessive heat release or for roofing of temporary buildings. Corrugated profile sheets have significant rigidity and can be laid on a sparse crate, thereby reducing the cost of coating.

Asbestos-cement roofing does not rust and does not require painting; they are fireproof, weather resistant, durable and lightweight, which is also very important.

Significant disadvantages of all asbestos-cement products are brittleness, low impact resistance.

Flat facing slabs produced under the brands NP unpressed and P - pressed. Plates can be painted with various dyes.

Dimensions of non-pressed boards: length from 60 to 120 cm, width 30-80 cm, thickness 6-10 mm. Pressed plates have a length (Yu-160 cm, width 30-120 cm and thickness 4-10 mm. Water absorption of non-pressed boards should not exceed 25%, pressed - 18% (by weight). Bending strength of non-pressed slabs must be at least 160 kg/cm 2 , and pressed - over 250 cpsm" 2 ; their frost resistance should be at least grade 25.

Asbestos-cement flat facing slabs are used for external and internal cladding of solid and frame walls of various buildings, partitions and ceilings. For lining panels and walls of sanitary facilities, kitchens and other rooms with high humidity, flat slabs are produced, covered with a waterproof layer of synthetic polymers.

In large sewers made on site from concrete, asbestos-cement slabs are used to line the bottom of the collector (tray).

Sheet asbestos-cement products are stored indoors or under a canopy. Before transportation, the plates are laid horizontally in stacks and fixed so that they do not hit each other and the walls of vehicles. It is not allowed to hit such plates and drop them from a height.

In recent years, asbestos-cement panels have been used to erect the walls of buildings. Such a panel is a three-layer structure with two asbestos-cement sheets and a middle layer of insulation (polystyrene, foam glass, etc.).

The thickness of the panels, depending on the type of insulation, can be 12-20 cm, her weight is up to 200 kg, which is significantly less than the weight of other large wall materials, with the exception of aluminum panels with plastic insulation. Window drains and window sills are also made from asbestos cement.

Asbestos-cement pipes used for the installation of water pipelines (for plain, mineralized and sea water), sewerage of waters of various compositions (domestic, atmospheric and industrial), as well as for the installation of oil and gas pipelines, drainage, smoke and ventilation ducts, garbage chutes, laying telephone, telegraph, lighting and other cables, etc.

Water pipes made of asbestos cement are intended for the installation of water pipes with a working hydraulic pressure of 3, 6, 9 and 12 am Asbestos-cement pipes in service conditions in underground water supply and sewer networks are much more durable than cast iron and steel pipes. Such pipes are not subject to destruction caused by currents wandering in the ground, which sharply accelerate the process of corrosion of metal pipes. Pipes made of asbestos cement are more resistant than metal pipes against the action of sea, mineralized and other waters. The coefficient of friction of the liquid on the smooth surface of asbestos-cement pipes is less than on the surface of metal pipes, which increases their throughput and reduces the consumption of electricity for pumping liquids.

Asbestos cement, compared with cast iron and steel, has several tens of times lower thermal conductivity, and the walls of asbestos-cement pipes are 2.5-3 times thicker than those of cast iron pipes. Therefore, the heat-shielding capacity of the walls of an asbestos-cement pipeline is approximately 100 times greater than that of a cast-iron one. This makes it possible to lay asbestos-cement pipes at a shallower depth than cast iron pipes, saving on the amount of earthwork.

Asbestos-cement pipes have high crushing resistance and can withstand working hydraulic pressure up to 12 am, since asbestos fibers, which have high tensile strength, are usually located not along the pipe, but along its circumference.

They are made from special Portland cement grades 400-500 and asbestos fibers, which strengthen the structure of the cement stone.

In addition to products based on mineral binders, a wide range of asbestos-cement, gypsum, gypsum concrete, silicate and magnesia products are used in construction.

They are obtained in the same way as concrete products by shaping and subsequent hardening on the basis of appropriate binders and aggregates.

Questions for SRS

Asbestos-cement products are produced mainly by the wet molding method. Semi-dry and dry molding methods are used much less frequently. The latter - in the manufacture of only flat sheets and tiles.

The wet method of technology begins with the preparation of a mixture of several grades of asbestos in order to ensure high filtering capacity, density and water retention during molding. After that, asbestos fibers are fluffed. Fluffed asbestos is thoroughly mixed with cement in water until a homogeneous mass is obtained. The latter is diluted with an additional amount of water, resulting in an asbestos-cement slurry, into which, if required, additional substances (additives) can be introduced. In asbestos-cement suspension, the mass of water is more than 10 times the mass of cement. The finished suspension is sent to the molding of asbestos-cement products - sheets or 1 rub. In this case, most (over 96%) of free water is filtered out and removed. Sheets give the necessary size and shape. Facing sheets and roof tiles are additionally pressed. The hardening of the binder, under the influence of which asbestos-cement products acquire the required mechanical strength, occurs in warehouses or in autoclaves (with sandy Portland cement). Finished products can be given the required external surface by painting and facial processing.

To date, more or less definite compositions (mixtures) of asbestos from different deposits have been established in the production of asbestos-cement products. They are standardized by special technological maps.

The operation of fluffing asbestos largely determines the quality of the product. At the first stage of mechanical treatment on runners, the bond between the finest asbestos fibers weakens within 12-15 minutes. At the second stage - in a gollender-pusher or other apparatus (6-8 minutes) the asbestos is separated into the finest fibers. It is generally preferable to loosen the wet method, i.e. on the runners in the presence of water. A gollender, i.e. a metal tank inside which a drum equipped with knives rotates, is always a hydraulic fluff, since the asbestos crushed by runners is separated into fine fibers in the pockets between the drum knives as a result of the action of fast vortex movements of water jets. The apparatus is usually carried out and the mixing of fluffed asbestos with cement in an aqueous medium. Water is added simultaneously with the loading of cement from the bottom of the recuperator (collector of waste water).

The asbestos-cement mass relatively quickly (in 8-10 minutes) acquires sufficient uniformity, since the smallest grains of cement, which carry a high negative electric charge on the surface, are quickly deposited and firmly held on the developed surface of fine-fiber asbestos, which also carries a high, but positive charge in water and alkaline environment. If sandy cement is used, then the smallest particles of dispersed sand are also deposited on the asbestos fibers, although with a longer mixing of the suspension (12-13 minutes). To obtain a mobile suspension is required for 1 wt.h. dry asbestos-cement mixture add at least 4-5 wt.h. water, which is specified by calculation depending on the grades of asbestos in the mixture.

The produced asbestos-cement mass enters the bucket mixer to obtain a certain stock of mass in order to maintain the continuity of the molding machine. From the mixer, the mass is directed along the chute into the metal baths, which are part of the sheet-forming machine. At the same time, recuperative water, taken from the lower part of the recuperator, continuously enters the chute, which makes it possible to maintain the required consistency of the mass. The asbestos-cement slurry entering the mesh cylinder baths of the sheet-forming machine usually consists of 8-10% dry matter in 90-92% water. But there are other sheet-forming machines that use an asbestos-cement suspension of a higher concentration, for example, up to 40-45% dry matter (it contains up to 15% asbestos, up to 85% cement).

Forming of sheets and other asbestos-cement products by the wet method is carried out on a round-mesh molding machine (or semi-dry - on a filter belt). The principle of forming products is to filter water from the layers of asbestos-cement mass under the influence of hydrostatic pressure until the required compaction. To this end, in a metal bath , filled with asbestos-cement suspension, there is a hollow frame-type cylinder covered with a metal mesh (mesh drum). On the grid, the mass is deposited in a thin layer and partially dehydrated due to water filtration through the grid. Water from the drum is first diverted to thickeners (recuperators) to separate and return to production the non-settled part of the asbestos, and then it is used to wash the mesh and cloth and liquefy asbestos-cement mass in the gutter. A layer of asbestos-cement mass is removed from the surface of the drum with an endless cloth tape. Having passed a vacuum box on the tape (with a vacuum of about 300 mm Hg), the pre-dehydrated asbestos-cement mass is transferred to a metal format drum, which removes the mass from the cloth tape and winds it onto its surface in concentric layers, while it is compacted between rotating metal cylinders. When the asbestos-cement layer on the drum reaches the required thickness, it is cut along the generatrix of the cylinder, and the raw sheet is removed. The pressure of the press part of the sheet-forming machine is usually 0.2-0.4 MPa, for the second compression shaft 10.0-12.0 MPa, for the press shaft - up to 40.0 MPa. As a result of reductions, the moisture content in the sheet is significantly reduced and reaches 25%.

In the manufacture of flat small products, the sheet is additionally cut into tiles, which are pressed in stacks under high pressure (up to 40 MPa) on a hydraulic press. If fibrous sheets are made, then the wave is produced on special machines of the skalchaty type of periodic action. There are continuous machines that are used in all automated lines.

Products harden in steaming chambers at a temperature of 50-60°C, relative humidity of 90-95% for 10-14 hours, and then 5-7 days in an insulated warehouse. Hardening occurs faster in an autoclave under the action of steam at a pressure of 0.8 MPa, which allows the use of sandy cement and eliminates the keeping of products in the factory warehouse.

In the production of pipes, the forming principles remain the same, but special pipe-forming machines with removable format drums (rolling pins) are used. Pipe and sheet forming machines do not have fundamental differences in the design of mesh cylinder baths, vacuum dewatering devices and felt cleaning devices.

At the end of the process of winding asbestos-cement layers, the format rolling pin is removed and a new one is installed. To make it easy to remove the rolling pin, the diameter of the pipe is slightly increased. For this purpose, the mesh at the ends is slightly stretched with the help of metal wedges and the pipe is expanded on a special calender.

The dry method of forming asbestos-cement sheets involves fluffing asbestos and mixing it with cement and sand in a dry form. For subsequent moistening, 12-15% water is added, and the mass is compacted on a conveyor belt with rollers or under a press. Harden products, which mainly include floor tiles and cladding, in autoclaves. The dry method allows the use of short-fiber asbestos, mainly of the 6th grade.

Read also