Production of gypsum and improvement of its quality properties with the help of additives. Gypsum business

Gypsum is widely used in construction in the production of various products and mortars. Gypsum is a white or white with a gray tint substance that hardens very quickly, but has very low water resistance. The technology for the production of gypsum is reduced to firing natural gypsum in industrial kilns, and the resulting gypsum gypsum stone crushed.

The composition of the article:

♣ Gypsum production technology in rotary kilns.

♣ Production of gypsum by the method of combined grinding and firing of gypsum.

♣ Production of gypsum in digesters.

Gypsum is a fast-acting and quick-setting air binder. Gypsum binders are divided into:

♦ High-strength gypsum,

♦ Building plaster,

♦ Anhydrite binder.

Gypsum binders are made from gypsum stone CaSO4 * 2H2O, CaSO4 anhydrite and some chemical industry wastes that contain anhydrous or dihydrate calcium sulfate. Natural gypsum usually does not contain impurities of clay, limestone, sand and other substances. Gypsum is obtained by firing at a high temperature of two-water natural gypsum, as a result of the reaction CaSO4 * H2O \u003d CaSO4 * 0.5H2O + 1.5H2O.

Building plaster.

♦ In natural gypsum, there are usually impurities of the following rocks: sand, limestone, clay, which reduce the strength and quality building plaster. Therefore, to obtain high-quality gypsum, which can be used in construction, medicine and other areas, it has to be processed thermally. To date, gypsum is processed in several ways, which differ in the method of firing in furnaces.

Gypsum is fired:

1. In shaft furnaces, ring, chamber and rotary furnaces. After firing, the resulting gypsum stone is crushed.

2. In digesters with preliminary grinding of gypsum stone.

3. Simultaneously with grinding in one apparatus.

Picture 1. Technological scheme for the production of building gypsum in rotary kilns

1-chute feeder, 2-gypsum bin, 3-belt conveyor, 4-hammer crusher, 5-elevator.

6 - screws, 7 - gypsum crushed stone bin, 8 - plate feeders, 9 - coal bunker, 10 - furnace, 11 - rotary kiln of dryer drum type.

12-bunker of burnt crushed stone, 13-dust settling chamber, 14-fan, 15-bunker of finished gypsum, 16-ball mill.

Depending on the size of the pieces of the feedstock (gypsum stone), as well as on the size of the required sizes of the pieces sent to the kiln for the purpose of firing, crushing of the raw material is carried out according to single-stage scheme or by two-stage scheme in crushers-4. To do this, the raw material is loaded into the gypsum stone bunker-2, then, with the help of a tray feeder-1, the raw material is continuously fed to the belt conveyor-3, which directs it to the crusher-4.

Crushers can be hammer or jaw and they crush the original gypsum stone into crushed stone with particle sizes from 0 ... 20-35 mm.

The gypsum crushed stone obtained in this way (if necessary) is subjected to screening in order to obtain fractions 0 ... 10; 10…20; 20…35 mm. After screening, the gypsum crushed stone fractions are sent further to the gypsum crushed stone bunker-7 located above the firing furnace-11. Crushed stone of various fractions is fired separately because each fraction requires a separate, appropriate firing mode.

From the bunker -7 crushed gypsum stone is continuously fed into the rotary kiln by means of a plate feeder. Depending on the design of the rotary kiln, gypsum crushed stone can be fired in two ways:
1. In direct contact with hot gases that are formed during the combustion of fuel.
2. Or due to external heating of the walls of the drum of a rotary kiln.
Dryer-type gypsum stone rotary kilns can be operated with liquid, gaseous or solid fuels. Depending on the type of fuel used, firing technologies are also developed. For example, at the entrance to the furnace, the temperature of the gases in the forward flow is -950 ... 1000 ° C, in the counter-current - - 750 ... 800 ° C. When leaving the furnace, the temperature of the gases in the forward flow is 170 ... 220 ° C, in the counter flow - 100 ... 110 ° C.

Burnt gypsum crushed stone comes further from the dryer drum (from the kiln) to the burnt crushed stone hopper -12 using an elevator or, depending on the design, service bins can be located directly under the dryer drum. Uniform feeding of the ball mill is provided by a tray-type feeder-8, which is located under the burnt crushed stone hopper-12.

Burnt crushed stone enters the ball mill with a temperature of 80 ... 100 ° C. In the ball mill -16, the burnt gypsum crushed stone is ground and the material composition of the gypsum is leveled due to the transition of overburning and underburning into hemihydrate. Further, from the ball mill, the finished product is sent to the finished gypsum hopper -15 using an elevator.

From the finished gypsum bin, the product is sent to storage bins or for packaging. During the production of gypsum stone, dust settling chambers -13 are used, which provide high air purification from dust.

Building plaster production technology

♦ It is believed that the most perfect method of obtaining building gypsum, which is based on the method of combined grinding and firing of gypsum stone, allows mechanizing the production process.

Figure-2. Scheme of combined grinding and firing of gypsum

With combined grinding and firing of gypsum, gypsum raw materials are crushed in one or two stages. Figure -2 shows a diagram of the combined grinding and firing of gypsum, where the gypsum stone goes through two stages of crushing. At the beginning, gypsum raw materials are loaded into the hopper -2 from where the feeder continuously feeds the gypsum stone to the jaw crusher -21, where the material is crushed for the first time to a fraction of 20-60 mm.

In a hammer mill, crushed gypsum stone is crushed a second time, until desired faction for example, 10-20 mm. Next, using the elevator -3 crushed gypsum crushed stone enters the feed hopper -17, from where with the feeder -16 continuously fed into the tube mill 15 .

In a tube mill, fine grinding and drying of gypsum stone occurs due to gases that, through the underflow -4 according to the principle of co-current or counter-current are fed with a temperature of 600-700 C. During the rotation of the tube mill -15, the raw material moves along its entire length, is dried and crushed. During the firing of gypsum stone, its dehydration occurs with the formation of beta hemihydrate.

Next, the crushed calcined product is fed into the in-line separator -5 , where the largest unburned gypsum particles are separated and then returned back to the mill for re-treatment through the air chute - 14 . Separated to a residue of no more than 2-5% on a sieve No. 02, crushed gypsum powder is carried out by a dusty air flow into the dust settling system -6 and 10.

The gas-dust mixture after leaving the tube mill through the separator passes into the system of dust settling devices -6 and 10, where the final dehydration of the crushed mixture takes place. The movement of gases in the system is forced and is carried out due to the work centrifugal fans -9. Passing through a system of dust precipitation devices (cyclones, electrostatic precipitators, bag filters), the crushed product is fed using a screw conveyor -11 into the receiving bunker -12. Next conveyor -13 the crushed product enters the elevator -8, which directs it to the receiving bunker finished products-7.

Gypsum production technology in digesters

with preliminary grinding of gypsum stone.

The boiler is designed for dehydration of two-water ground gypsum into semi-aqueous gypsum and is a vertical steel cylinder with a vertical bottom-2 (see figure -3). The boiler is assembled from cast iron elements and the joints between them are sealed with asbestos mass. The boiler is heated through the bottom and its side surface.

Figure-3. Gypsum boiler

In order to increase the heating surface, a metal jacket is suspended inside the boiler, which is also a casing for the screw.
In the horizontal direction, four flame tubes-3 pass through it, located in two rows (one above the other). The boiler body-4 rests on three cast iron supports with a concrete foundation under them.

The slide gate -9, located inside the boiler, allows closing the window in the casing. The window serves to unload the finished gypsum through the chute. The shutter is equipped with an electric drive that opens and closes it as needed. The top of the boiler is used to create a steam space. The top of the boiler is a cylinder consisting of two halves and closed with a lid.

On the cylinder cover there are two branch pipes for connecting loading augers-8 to them, as well as a branch pipe for connecting a steam outlet pipe, two level gauges, two inspection hatches for maintenance and inspection inner space boiler and two load sensors installed on the inlet pipes used to control the supply of gypsum to the boiler.

At the bottom end vertical shaft four blades are installed that serve to move the gypsum mass during the cooking process. The rotation of the blades of the vertical shaft is carried out by means of an electric motor through a gearbox. The technological process of the boiler operation takes place in a continuous automated mode.

Fresh gypsum powder continuously enters the boiler during the entire processing process. Due to this, a high degree of saturation of the material with air and water vapor is constantly maintained, which leads to an improvement in the properties and modification composition of the final gypsum product.

The technological process for the production of gypsum based on a gypsum boiler can be described in the following way:

1. First, gypsum stone is fed into the jaw crusher in large pieces by means of a transport system. In the crusher, it is crushed into crushed stone of a fraction of 20-60 mm. The size of the fraction of the final product - gypsum gravel can be adjusted depending on the design of the crusher.
2. Further, the crushed gypsum stone, passing through the iron separator, enters the fine grinding mill, where the mill turns crushed gypsum stone into powder. Mills can be used in different ways, such as ball, hammer, roller-beam, shaft and others. In the mill, the material is crushed into powder and also heated and dried by hot gases.

The fineness of the grinding material and the performance of the mill play important role and depend on the speed of the gas flow that is fed into the mill. Flue gases from gypsum boilers are used as a heat carrier. Depending on the gypsum chosen during firing thermal regime flue gases are supplied with a temperature ranging from 300 to 500 °C.

In the mill, crushed and separated gypsum to a residue on sieve No. 02 of no more than 2-5% is carried out into the dust precipitation system by a dusty air stream. As in the method described above, after leaving the mill, the gas-dust mixture passes through a system of dust-collecting devices (cyclones, bag filters, and so on).

The movement of gases in the system is forced and is carried out due to the operation of centrifugal fans. Passing through a system of dust settling devices (cyclones, electrostatic precipitators, bag filters), the crushed product is fed into the feed hopper. The temperature of the powder depends on the temperature of the gases at the outlet of the mill (85...105 °C) and can vary from 70...95 °C.

3. In the boiler, gypsum powder is boiled at the expense of flue gases having a temperature of 800-900 °C. Hot gases are supplied through the flame tubes and external channels created by the boiler lining. The heat carrier can be natural gas or another type of fuel. In the process of gypsum cooking, the gypsum mixture is constantly mixed with the help of blades and lasts 1 ... 2 hours or more. In the digester, gypsum does not come into direct contact with hot flue gases, and its temperature can vary from 100-180 °C. Combustion of gaseous or liquid fuels takes place in a special boiler heating furnace.

In the first period, the operating temperature in the boiler reaches 110...120°C. Gypsum powder is heated up to 110…120°C, respectively, and intensive dehydration of gypsum occurs. Then comes the second period when the water of hydration evaporates and the process of dehydration begins, or as it is also called mass boiling. In the third period, there is a rapid rise in temperature and a sharp decrease in the intensity of the dehydration reaction. As the density increases and the vaporization of the resulting dehydration products ceases, the gypsum mass becomes denser and its mass in the boiler decreases.

This stage is called the first precipitation of the powder.
The second settling of the gypsum powder occurs in the last cooking period when the dehydrated calcium sulfate hemihydrate turns into anhydrite. Further, the finished product is unloaded from the boiler into the receiving hopper and transferred to the silos using mechanical or pneumatic transport.

Designation of the plant

Equipment for building gypsum production is intended to obtain a binder that meets the requirements of GOST 125-79: Gypsum binders. Specifications.

Thermal unit at production of building gypsum on our installation is a gypsum boiler TOS165.

Depending on the compressive strength of the finished product in the gypsum boiler, building gypsum of the following grades can be obtained: G-4, G-5, G-6, G-7.

By adjusting the technological parameters of gypsum cooking, it is possible to obtain quick-hardening gypsum with index A, the beginning of setting no earlier than 2 minutes, the end no later than 15 minutes, and normal hardening B, the beginning of setting no earlier than 6 minutes, the end no later than 30 minutes.

Depending on the degree of grinding, gypsum of medium grinding with a 0.2 mm sieve residue of no more than 14% and fine grinding with a 0.2 mm sieve residue of no more than 2% can be obtained.

Upon receipt of a product with a fine grinding of less than 2%, the productivity of the equipment decreases.

plant productivity by production of building gypsum with an average grinding of 5-8% residue on a 0.2 sieve is 8 t/h.

Plant equipment according to production of building gypsum is placed on a technological shelf inside an unheated production premises.

During the construction of a new plant for the production of gypsum binder, sandwich panels are used as the enclosing structures of the production building.

The dimensions in terms of the production rack may differ depending on the technical specifications of the customer and the available free space. The standard dimensions are 4.5 x 30 m and 9.0 x 18 m in plan. The maximum height of the equipment inside the production room is 16 m.

Outside the dimensions of the production shelter, as a rule, they take out equipment for the crushing and transportation of gypsum stone and silo cans designed for storing and languishing the finished gypsum binder.

Requirements for the source material - gypsum stone

Occurs with the use of gypsum stone meeting the requirements of GOST 4013-82 grade 1 with a CaSO4 x 2H2O content of at least 95% and grade 2 gypsum stone with a CaSO4 x 2H2O content of at least 90%. A high-quality binder in a gypsum boiler of at least G4 grade can be obtained using grade 3 gypsum stone with a CaSO4 x 2H2O content of at least 80% on a hard gypsum stone.

To obtain a gypsum binder in a gypsum boiler, a gypsum stone of a fraction of 60 - 300 mm is used. The coarse stone is the cleanest without inclusions of foreign material. There are more inclusions of non-gypsum rock in fine crushed stone of a fraction of 0-60 mm, which reduces the properties of the finished gypsum binder when cooking gypsum.

Building plaster production technology

Technology production of building gypsum with a gypsum boiler TOS165 consists of three main technological stages: 1 - Crushing of gypsum stone, 2 - Drying and grinding of gypsum gravel, 3 - Cooking of building gypsum in a gypsum boiler TOS165.

Crushing gypsum stone

Crushing of gypsum stone with a fraction of 60 - 300 mm takes place in a jaw crusher.

The stone is loaded into the crusher's receiving hopper with a front-end or clamshell loader from the accumulation warehouse.

For trouble-free operation gypsum production a 15-day supply of raw materials should be stored in the warehouse.

The gypsum stone is fed into the jaw crusher by a swinging feeder.

The size of the crushed gypsum fraction after the crusher is regulated by the size of the crusher's exit gap. After the crusher, gypsum gravel is fed for further processing to the grinding department and drying along the belt conveyor.

The crushing department is usually located outside the closed production room, in which drying, grinding and cooking of gypsum is carried out.

The crushed material after passing the iron separator is fed into the hammer axial mill.

Axial hammer mill is designed for fine grinding of crushed gypsum stone of medium hardness with its simultaneous drying. The material is fed into the mill by a swinging feeder from the supply hopper.

Gypsum powder ground and dried in a mill in a stream of hot gases enters the dust and gas cleaning system. Hammer axial mills belong to the group of high-speed hammer mills. The crushed stone is fed into the mill in the direction of rotation of the rotor. As a result of blows, the crushed stone is crushed into powder. The fineness of grinding material depends on the feed rate, the volume of the ventilating agent and on the angle of installation of the blades of the built-in separator. Exhaust flue gases of the gypsum boiler are used as a heat carrier and a ventilating agent.

The temperature of the flue gases at the entrance to the mill, depending on the selected thermal regime of gypsum firing in the boiler, can vary from 250 to 500 0 С.

Crushed, dried and separated to a residue of no more than 5-8% on a sieve No. 02, gypsum powder is carried out in a dusty air stream to the dust settling system. Cyclones are used as the first stage of purification, two-section TOS 3.8 bag filters are used as the second stage of purification. To eliminate the hanging of the material in the hopper of the cyclone, pneumatic impact devices are installed. The cyclone and the bag filter are thermally insulated.

Regeneration of the bag filter is carried out by back blowing the bags with compressed air when one of the sections is turned off by the automation system. As a fabric for the sleeves, a fabric of the "Metaaramid" type is used. Fabric withstand operating temperature up to 230 0С. In the event of an unplanned increase in the temperature of the outgoing heat carrier above the specified temperature, the dilution damper installed in front of the filter opens automatically and outdoor air enters the suction system. Compressed air is supplied with a temperature exceeding the dew point temperature by at least 5-10 0 С.

As a traction unit, a smoke exhauster Dn is used.

The powder caught by cyclones and filters by hose conveyors by screw conveyor system enters the heat-insulated raw meal bunker. Sluice gates are used to eliminate suction in cyclones and bag filters.

Building gypsum cooking - dehydration of gypsum powder occurs in a gypsum boiler with flue gases with a temperature of 600-950 0 C, supplied through external channels created by the boiler lining and flame tubes. The heat carriers in these passages are the products of combustion. gaseous fuel in the combustion chamber adjacent to the lining.

The coolant, passing through the channels in the boiler lining and flame tubes with a temperature of 250-500 0 C, without contact with the material, is taken out of the boiler. Gypsum in the digester does not directly come into contact with gases, its temperature is 121-160 0 C. The process of roasting gypsum is accompanied by an intensive release of water of crystallization. During this period, boiling of gypsum powder is observed.

The gypsum boiler is a vertical steel drum equipped with a stirrer and closed with a lid on top, equipped with nozzles for loading powder and removing a mixture of steam with gypsum particles.

The residence time of the material is regulated by the mode of loading and unloading, depending on the required temperature of the material inside the boiler. The material is fed into the boiler by a screw conveyor from the raw meal hopper. Loading performance is controlled by changing the number of revolutions of the screw conveyor. In continuous mode, raw gypsum is loaded continuously above the material level in the boiler through a nozzle installed on the boiler cover. The vertical discharge chute placed inside the boiler is open at the bottom.

The material is unloaded continuously by overflow from the top of the discharge chute. To improve the transport of gypsum from the bottom of the discharge chute to the top, lower part supply compressed air with a pressure of 2 atm

Vacuum in smoke channels the boiler is created by a smoke exhauster, which is also the traction unit of the axial hammer mill. Water vapor and gypsum particles formed during gypsum hydration in the boiler, as well as excess dust-air mixture of the languishing hopper are removed from the boiler. The semi-aqueous gypsum obtained in the gypsum boiler is unloaded into the languishing bunker.

Automated control system

Automated control system building gypsum production ensures the operation of all elements of technological equipment in automatic, semi-automatic and manual modes to ensure technological process production of building gypsum.

The system is a complex of hardware and software that jointly perform the task of managing the process.

System architecture

The control system can be conditionally divided into three levels:

The lower (field) level is represented by sensors and actuators. As sensors in the system, there are temperature sensors, pressure sensors, level indicators, motor current control devices, inductive sensors, limit position indicators and additional contacts signaling the status and mode of operation of the engines.

The actuators of the system are motors with contactors for direct starting, motors with variable speed, controlled by frequency-controlled drives, electromechanical positioners for controlling the throttle valves of smoke exhausters and a switch for the direction of gypsum supply to the silos.

At the middle level, the system is represented by a programmable logic controller (PLC) with input-output modules for analog and discrete signals. The PLC is responsible for receiving signals from sensors and issuing control signals to actuators in accordance with the program embedded in it.

At the top level, the system is represented by a human-machine interface device. This is a computer connected to a controller industrial network, and with specialized software installed on it.

Controller equipment, switching and ballasts are supplied mounted in cabinets industrial use. The instrument is supplied separately in its original packaging.

All ballasts, circuit breakers, contactors and VFDs manufactured by Siemens.

Programmable Logic Controller

The system uses a Siemens Simatic S7 300 controller as a PLC with a set of discrete and analog inputs and outputs, sufficient to connect all sensors and actuators, and with a reserve determined at the design stage.

The controller must be mounted in a cabinet, which must be installed in a switchboard room with a temperature regime of 0-50 °C.

A brief description of the algorithms embedded in the controller will be discussed below.

Human Machine Interface

As a human-machine interface system, an operator station (OS) with an installed operating system Microsoft Windows XP and Siemens Simatic WinCC SCADA system. This station is connected to the PLC industrial network MPI to obtain information about the flow of the process.

The main functions of the OS are:

• Displaying the state of the technological process and equipment in the form of mnemonic diagrams, tables, trends and messages on the computer monitor.
• Providing the operator with the opportunity to adjust the technological modes of operation of the installation.
• Manual control of some elements of the installation.
• Display and archiving of emergency and service messages.
• Storage of historical data about the process with the ability to view them.

Depending on the natural mining and geological factors, the production and extraction of gypsum is carried out underground or open way.

The production of gypsum, or rather the process of processing natural rocks to a gypsum material that meets the technical parameters, is carried out by qualified personnel at special enterprises. As a rule, industrial facilities are built in the area of ​​gypsum deposits.

Open pit mining and production of gypsum

The open-pit mining method is characterized by high labor productivity, which, against the background of minimizing the loss of gypsum raw materials, is indisputable advantage process. The technological focus of production is based on the extraction, transportation and grinding of gypsum stone.

Gypsum production technology is provided by work in several stages:

• Crushing of gypsum rocks. To date, at this stage of work, the explosive method is used.
• Grinding Achieved by grinding gypsum to the desired consistency, which contributes to convenient use material in the future.
• Drying and roasting. The final stage of production associated with the heat treatment of the material.

Open-pit mining of material is carried out with the help of continuous mining miners, which crush gypsum with a rotating cutting drum. The mechanism of the device consists of segments fixed with bolts and holders with built-in cutters, which are equipped with durable hard alloy inserts.

The supply of the mined gypsum stone to the combine with the subsequent transportation of the material to the primary conveyor is provided by segments arranged in the form of an auger. Adjustment of the size of the loaded pieces of rock, the size of which should not exceed 300 mm, is carried out thanks to design features drums for mining combines.

The operation of the mechanism is based on the principle of a free arrangement of segments, coupled with a different configuration and size of the teeth. The leader among manufacturers is the German engineering concern Wirtgen.

The dimensions of the gypsum stone after the first stage of crushing are 30-50 mm. AT further material crushed to the state of cereals. It is worth noting that in recent times Hammer crushers are widely used, thanks to which the process of grinding gypsum is carried out in one stage.

The next stage in the production of gypsum is the transformation of gypsum gravel into powder, which takes place in roller-pendulum mills. Due to the impossibility of processing wet gypsum, drying of the material occurs at this stage. The adjustable speed of the gas flow from the flue boilers makes it possible to grind gypsum with high precision. At the same time, an increase in the flow rate makes the material coarser and vice versa. Gypsum is subjected to heat treatment for 1-3 hours at a temperature of 130-160 °C.

Underground mining and production of gypsum

Despite the fact that open-pit mining is carried out at most gypsum deposits, more than half of the total amount of material obtained is provided by enterprises whose activities are based on the underground mining method.

The technology of the underground method in the extraction and production of gypsum is based on the extraction of minerals from the rock formation by autonomous chambers with the maintenance of the roof. Cleaning activities are provided by core drills, scraper winches, deep hole drilling machines, dump trucks and self-propelled trolleys. Excavated cavities are used to store various materials.

As a rule, a useful layer of gypsum deposits is a heterogeneous and heterogeneous layer, often containing various impurities of clay, sand or carbonate rocks. Therefore, during processing, it is necessary to enrich the material. The method is a variant of selective grinding, which is based on different degrees of crushing of strong and weak components.

The most efficient selective grinding process occurs in impact mills and crushers. The advantage of this method is to ensure the maximum difference between the energy costs for crushing weak mineral components and strong crushed materials. The main parameter of the selective crushing process is the speed of the working rotor of the crusher or mill.

Raw gypsum is loaded into the boiler using a screw conveyor. Water vapor is expelled through special pipes. As a result of grinding and drying, gypsum enters the bunker. The final and ready-to-use material is a binder that is used as a component in.

An important factor in the production of gypsum is the installation of a multi-stage cleaning system. This is a mandatory requirement for any plant whose personnel work in conditions harmful to the lungs of dust emitted during the processing of the material.

The photo below shows a gypsum adit near Moscow. The volume of production is so great that all the tunnels of the adit are several times larger than the Moscow metro.

GYPSUM

(gypsum binder) - binder construction material, which can be obtained from natural gypsum dihydrate (CaSO 4 ∙ 2H 2 O), called gypsum stone, natural CaSO 4 anhydride and some industrial wastes (phosphogypsum, as well as calcium sulfate formed during chemical cleaning flue gases from sulfur oxides using limestone).

Depending on the temperature of heat treatment of raw materials, gypsum binder is divided into two groups:

• low-annealing (up to 250 ° C)
• high annealed (over 450 o C)

BUILDING GYPSUM

Building gypsum is made by annealing gypsum rock in digesters with preliminary grinding. At the same time, it loses part of the chemically bound water, turning into hemihydrate calcium sulfate CaSO 4 ∙ 0.5H 2 O [β - modification (β-hemihydrate). The main problem and disadvantage of building gypsum (β-hemihydrate) is the presence a large number free water in hardened gypsum.

The fact is that for the hydration of gypsum * you need about 20% of water from its mass, and to obtain a plastic gypsum dough 50-60%. Accordingly, after hardening of such a solution, 30-40% of free water remains in it (by weight of gypsum). This volume of water forms pores temporarily occupied by water, and this, in turn, affects the strength characteristics of the material. To increase the strength (1.5-2 times), the finished gypsum products are dried.

Our company offers its customers building gypsum produced by: Peshelansky gypsum plant (G6 BII), Samara gypsum plant, Gypsum concrete (Vidnoye, Moscow region), Ust-Dzhegutinsky gypsum plant (G5 BII grade) .

* Gypsum hydration- gypsum curing process

High-strength gypsum is obtained by heat treatment high-grade gypsum stone in sealed apparatus under steam pressure (autoclave). In this case, the problem of reducing the water demand of gypsum is solved, and, accordingly, during hardening, a less porous and more durable stone is formed. The gypsum obtained in this case has another crystalline modification of hemihydrate gypsum (α-hemihydrate) with a water demand of 35-40%.

Currently, in Russia and the CIS, the leader in the production of high-quality high-strength gypsum is CJSC Samara Gypsum Plant (SGK). Produced grades: gypsum GVVS-13, gypsum GVVS-16, Plaster for artistic stucco molding ( GVVS-19).

In addition, SGK produces specialized products based on high-strength gypsum gypsum mixes SCULPTOR and STONE MAKER. These are compositions where as binder material high-strength gypsum with the addition white cement, as well as a certain amount of mineral filler and chemical additives to improve the consumer properties of these mixtures and the technical characteristics of finished products.

OOO "GeoStil" is the main distributor in the Moscow region for the distribution and sale of gypsum products of CJSC "Samara gypsum plant".

In addition, as a kind of alternative for high-strength gypsum, we offer gypsum brand G-19 produced by LLC « CherkesskStroyProduct.

Molding gypsum is obtained by a certain mechanical "refinement" of building gypsum, subjecting it to additional grinding and sieving. As molding gypsum, we offer our customers gypsum for pouring molds produced by LLC Peshelansky gypsum plant (grade G6 BIII) and CJSC Ust-Dzhegutinsky gypsum plant (grade G5 BIII).

The name of this gypsum contains the possibility of its use for medical purposes. These are dentistry (temporary prostheses and casts) and traumatology (fixing plaster bandages). The main requirement for medical gypsum is its purity (absence of impurities), and therefore only 1st grade gypsum stone is used for the production of such gypsum (the content of impurities in the rock should not exceed 5%). And so, in fact, both construction and molding or high-strength gypsum can act as medical gypsum. The only question is obtaining the appropriate permits from certification bodies. Due to the rather expensive cost of these procedures and the relatively small volume of consumption of this product, many gypsum factories are not engaged in obtaining such certificates.

At the same time, normally hardening (the beginning of setting - from 6 minutes) molding and high-strength gypsums of fine grinding are most convenient for medical use.

We offer our Customers one of the highest quality Russian medical gypsum - medical gypsum for traumatology and dentistry produced by ZAO Samara Plaster Plant.

Gypsum brand

The grade of gypsum is determined by a compression and bending test of standard beam samples 4x4x16 cm 2 hours after their molding. During this time, hydration and crystallization of gypsum ends. According to GOST 129-79, 12 grades of gypsum are installed in terms of strength from G2 to G25 (the figure shows lower limit compressive strength of a given grade, unit of measure MPa).

Setting time

For a gypsum binder, the determining factors are: the beginning and end of setting. According to these parameters, gypsum is divided into three groups (A, B, C).

Fineness of grinding

According to the fineness of grinding, determined by the maximum residue of a gypsum sample when sifted on a sieve with 0.2 mm holes, gypsum binders are divided into 3 groups:

Colour

The color of gypsum depends on the presence of impurities in it, in particular iron oxide.

Density

True density 2650-2750 kg/m 3

Bulk density 800-1100 kg/m 3

Density of hardened gypsum stone 1200-1500 kg/m 3

Normal Density

Normal density is expressed as a percentage.

Marking

The marking of gypsum binder is carried out according to three main indicators - setting speed, fineness of grinding and strength, for example:

Gypsum binder G7 AII - fast hardening (A), medium grinding (II), compressive strength of at least 7 MPa.

For the preparation of a homogeneous mass of creamy consistency, in cold water gradually add gypsum and mix quickly. Depending on the type of gypsum, the following amount of water is used per 1 kg of gypsum binder.

It is allowed to increase the amount of water up to 10% by weight of the binder.

The best quality of work is achieved when applying the solution before setting. Strongly hardened mass cannot be re-diluted with water and used for work. The extension of the setting time of the solution is achieved by adding to the water before mixing: a solution of glue (carpentry, wallpaper), sulfate-alcohol stillage (SSB), technical lignosulfonates (LST), keratin retarder, boric acid, borax and polymer dispersions (eg PVA). To reduce the setting time of the solution can be used in a small amount salt. The amount of additives is determined empirically. It all depends on the type of binders, their normal density and the desired result.

Comparative characteristics of the technical parameters of gypsum

Building gypsum is called an air binder, consisting mainly of semi-aqueous gypsum and obtained by heat treatment of gypsum stone at a temperature of 150-160 ° C. In this case, CaSOi > 2H2O contained in gypsum stone is dehydrated by the reaction: CaSO4 2H2O - "- CaSOi 0, 5H2O + 1.5H2O - q.

The production of building gypsum consists of crushing, grinding and heat treatment (dehydration) of gypsum stone

There are several technological schemes for the production of building gypsum; according to some, preliminary drying and grinding of raw materials into powder precedes firing, according to others, grinding is carried out after firing, and according to the third, grinding and firing are combined in one apparatus. The last way called firing in a suspended state.

Heat treatment of gypsum stone can be carried out in digesters, drying drums, shaft or other mills. The choice of one or another roasting apparatus depends on the scale of production, raw materials, the required quality of the finished product and a number of other factors. The most common technology system with the use of boilers.

Gypsum stone entering the plant in large pieces is first crushed in jaw, cone or hammer crushers, then crushed in a mill with simultaneous drying. It is advisable to combine the process of drying and grinding in one apparatus, for example, in a shaft, air crusher or ball mill. The most widely used shaft mill (consisting of a hammer mill and a shaft located above it with a height of 12-15 m. Gypsum stone in the form of crushed stone 3-4 cm in size is fed into the mill by a pan feeder through a chute in the upper part of the chamber, meets rapidly rotating beaters of the mill on its way and is crushed into a fine powder.In the mill, some of the water of crystallization is removed from the gypsum.

The digester of periodic action (33) is a steel drum lined with bricks / with a spherical bottom 2, with its convex side turned into the cylinder. To mix gypsum in the boiler, there is a stirrer 3, driven by an electric motor 4. Hot flue gases heat the bottom and walls of the boiler, and also pass through the 5 flame pipes inside the boiler and are removed in a cooled state. chimney. The duration of cooking is 90-180 minutes, and holding for 3-4 hours at 140-150 ° C helps to reduce the water demand of gypsum and increase its strength. Water demand is significantly reduced when it is cooked with the addition of table salt. The resulting semi-aqueous gypsum is discharged from the boiler through hatch 6 into the holding bunker, where it is cooled and its quality is slightly increased, and then the gypsum is delivered to the finished product warehouse. When cooking in a boiler, gypsum does not come into contact with flue gases, which. allows you to get clean products, not contaminated with fuel ash. In the drying drums of rotary kilns (34), gypsum is obtained by firing gypsum stone in the form of crushed stone with a grain size of up to 20 MAI..

The firing part of the drying drum is an inclined steel cylinder with a diameter of up to 2.5 and a length of up to 20 m, mounted on roller bearings and continuously rotating. Gypsum crushed stone is fed into the drum from its raised side and moves down when the drum rotates. Hot flue gases with a temperature of 600-700 ° C enter the drum from the furnace, which are removed by a fan from the opposite side of the drum with a temperature of about 100 ° C. When moving along the drum, the gases meet the gypsum stone and burn it. Calcined gypsum is crushed in one- or two-chamber ball mills, obtaining building gypsum, which is usually stored in round silos with a diameter of 6-10 m.

When firing gypsum in a suspended state, two operations are combined - grinding and firing. According to this scheme (35), the sequence of operations is as follows. The gypsum stone coming from the warehouse is first crushed in a jaw crusher, and then in a hammer crusher until grains of 10-15 mm in size are obtained. The crushed material is fed by the elevator through the supply hopper to the ball mill, in which the joint grinding and firing of crushed gypsum stone is carried out. Flue gases with a temperature of 600-700 ° C enter the ball mill from a special furnace. The gypsum particles formed during grinding are entrained from the mill by a stream of hot flue gases, dehydrate in this stream to a semi-aqueous modification and enter through the separator into dust settling devices. In the separator, large grains of gypsum are separated, which are returned to the mill for additional grinding. In dust settling devices, dehydrated gypsum is separated from the gas stream and sent to the finished product bunker, while the purified gases are released into the atmosphere. The production of gypsum during combined grinding and roasting differs mainly in the types of mills and crushers, and also in the fact that sometimes the mills operate with the recirculation of gases that have passed through the dust precipitators.

Building gypsum is used for the production of gypsum and gypsum-concrete building products for internal parts buildings: - partition boards, panels, dry plaster, for the preparation of gypsum and mixed mortars, as well as the production of decorative and finishing materials such as artificial marble

Magnesian binders.

Varieties of magnesian binders are caustic magnesite and caustic dolomite.

Caustic magnesite is obtained by roasting rock magnesite MgCO3 in shaft or rotary kilns at 700-800 ° As a result, magnesite decomposes by the reaction MgCOe-^MgO + CO, the decomposition of MgCO3 is reversible, therefore, when firing magnesite, it is necessary to intensively remove CO2 from the furnace using natural or artificial draft. The remaining solid, magnesium oxide, is ground into a fine powder and packed into metal drums. Calcined magnesite is advisable to grind in a ball mill with a separator.

Caustic magnesite hardens relatively quickly: its setting should occur no earlier than 20 minutes, and the end - no later than 6 hours from the moment of mixing. Grades of caustic magnesite according to SNiP 1-V.2g62 according to the indications of the compressive strength of cube samples from a hard rammed mortar with a composition of 1: 3 by weight after 28 days of air hardening are set to 400, 500 and 600.

Caustic dolomite MgO CaCO3 is obtained by roasting at 650-750 ° C natural dolomite MgCO3 CaCO3, followed by fine grinding of the product. At the firing temperature, CaCO3 does not decompose and remains inert as ballast, which makes the binding activity of caustic dolomite lower than that of caustic magnesite.

Caustic dolomite contains a significant amount of calcium carbonate: it must contain at least 15% magnesium oxide and no more than 2.5% calcium oxide, so its quality is lower than that of caustic magnesite and its grade is only 100-300.

\ Magnesia binders are closed not with water, but with aqueous solutions of salts of sulfate or magnesium chloride. Magnesium chloride solution MgCb is the most common thickener, as it provides greater strength. Magnesia binders weakly resist the action of water, and they can only be used when curing in air with a relative humidity of not more than 60%. Caustic magnesite easily absorbs moisture and carbon dioxide from the air, resulting in the formation of magnesium oxide hydrate and magnesium carbonate. Therefore, it must be stored in a tight hermetic container.

On the basis of magnesia binders, xylolite (a mixture of binder with sawdust) is used for flooring, fibrolite and others. thermal insulation materials. Magnesia binders are also used in the manufacture of products for interior cladding premises, production of foam concrete, foundations for clean floors, sculptural products.

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