Technologically, the vulcanization process is the transformation of "raw" rubber into rubber. As a chemical reaction, it involves the integration of linear rubber macromolecules, which easily lose stability when exposed to external influences, into a single vulcanization network. It is created in three-dimensional space due to cross chemical bonds.

Such a kind of "cross-linked" structure gives rubber additional strength characteristics. Its hardness and elasticity, frost and heat resistance improve with a decrease in solubility in organic substances and swelling.

The resulting mesh has a complex structure. It includes not only nodes that connect pairs of macromolecules, but also those that unite several molecules at the same time, as well as cross chemical bonds, which are like “bridges” between linear fragments.

Their formation occurs under the action of special agents, the molecules of which partially act as a building material, chemically reacting with each other and rubber macromolecules at high temperature.

Material properties

The performance properties of the resulting vulcanized rubber and products made from it largely depend on the type of reagent used. These characteristics include resistance to exposure to aggressive environments, the rate of deformation during compression or temperature rise, and resistance to thermal-oxidative reactions.

The resulting bonds irreversibly limit the mobility of molecules under mechanical action, while maintaining high elasticity of the material with the ability to plastic deformation. The structure and number of these bonds is determined by the method of rubber vulcanization and the chemical agents used for it.

The process is not monotonous, and individual indicators of the vulcanized mixture in their change reach their minimum and maximum at different times. The most suitable ratio of physical and mechanical characteristics of the resulting elastomer is called the optimum.

The vulcanizable composition, in addition to rubber and chemical agents, includes a number of additional substances that contribute to the production of rubber with desired performance properties. According to their purpose, they are divided into accelerators (activators), fillers, softeners (plasticizers) and antioxidants (antioxidants). Accelerators (most often it is zinc oxide) facilitate the chemical interaction of all ingredients of the rubber mixture, help reduce the consumption of raw materials, the time for its processing, and improve the properties of vulcanizers.

Fillers such as chalk, kaolin, carbon black increase the mechanical strength, wear resistance, abrasion resistance and other physical characteristics of the elastomer. Replenishing the volume of feedstock, they thereby reduce the consumption of rubber and lower the cost of the resulting product. Softeners are added to improve the processability of processing rubber compounds, reduce their viscosity and increase the volume of fillers.

Also, plasticizers are able to increase the dynamic endurance of elastomers, resistance to abrasion. Antioxidants stabilizing the process are introduced into the composition of the mixture to prevent the “aging” of rubber. Various combinations of these substances are used in the development of special raw rubber formulations to predict and correct the vulcanization process.

Types of vulcanization

Most commonly used rubbers (butadiene-styrene, butadiene and natural) are vulcanized in combination with sulfur by heating the mixture to 140-160°C. This process is called sulfur vulcanization. Sulfur atoms are involved in the formation of intermolecular cross-links. When adding up to 5% sulfur to the mixture with rubber, a soft vulcanizate is produced, which is used for the manufacture of automotive tubes, tires, rubber tubes, balls, etc.

When more than 30% sulfur is added, a rather hard, low-elastic ebonite is obtained. As accelerators in this process, thiuram, captax, etc. are used, the completeness of which is ensured by the addition of activators consisting of metal oxides, usually zinc.

Radiation vulcanization is also possible. It is carried out by means of ionizing radiation, using electron flows emitted by radioactive cobalt. This sulfur-free process results in elastomers with particular chemical and thermal resistance. For the production of special rubbers, organic peroxides, synthetic resins and other compounds are added under the same process parameters as in the case of sulfur addition.

On an industrial scale, the vulcanizable composition, placed in a mold, is heated at elevated pressure. To do this, the molds are placed between the heated plates of the hydraulic press. In the manufacture of non-molded products, the mixture is poured into autoclaves, boilers or individual vulcanizers. Heating rubber for vulcanization in this equipment is carried out using air, steam, heated water or high-frequency electric current.

The largest consumers of rubber products for many years remain automotive and agricultural engineering enterprises. The degree of saturation of their products with rubber products is an indicator of high reliability and comfort. In addition, parts made of elastomers are often used in the production of plumbing installation, footwear, stationery and children's products.

The control method relates to the production of rubber products, namely, to methods for controlling the vulcanization process. The method is carried out by adjusting the vulcanization time depending on the time to obtain the maximum shear modulus of the rubber mixture during vulcanization of the samples on the rheometer and the deviation of the tensile modulus of rubber in finished products from the specified value. This allows you to work out the disturbing effects on the vulcanization process according to the characteristics of the initial components and the regime parameters of the processes of obtaining a rubber mixture and vulcanization. The technical result consists in increasing the stability of the mechanical characteristics of rubber products. 5 ill.

The present invention relates to the production of rubber products, namely, to methods for controlling the vulcanization process.

The process of production of rubber products includes the stages of obtaining rubber compounds and their vulcanization. Vulcanization is one of the most important processes in rubber technology. Vulcanization is carried out by keeping the rubber mixture in presses, special boilers or vulcanizers at a temperature of 130-160°C for a specified time. In this case, the rubber macromolecules are connected by transverse chemical bonds into a spatial vulcanization network, as a result of which the plastic rubber mixture turns into highly elastic rubber. A spatial network is formed as a result of heat-activated chemical reactions between rubber molecules and vulcanizing components (vulcanizers, accelerators, activators).

The main factors affecting the vulcanization process and the quality of finished products are the nature of the vulcanization environment, the vulcanization temperature, the duration of the vulcanization, the pressure on the surface of the vulcanized product, and the heating conditions.

With the existing technology, the vulcanization regime is usually developed in advance by calculation and experimental methods, and a program is set for the vulcanization process in the production of products. For the punctual implementation of the prescribed regime, the process is equipped with control and automation tools that most accurately implement the prescribed rigid program for the vulcanization regime. The disadvantages of this method are the instability of the characteristics of the manufactured products due to the impossibility of ensuring full reproducibility of the process, due to the limitation of the accuracy of automation systems and the possibility of shifting modes, as well as changes in the characteristics of the rubber mixture over time.

A known method of vulcanization with temperature control in steam boilers, plates or mold jackets by changing the flow rate of heat transfer fluids. The disadvantages of this method are the large variation in the characteristics of the resulting products due to the shift in operating modes, as well as changes in the reactivity of the rubber mixture.

There is a known method for controlling the vulcanization process by continuously monitoring the process parameters that determine its course: the temperature of the heat carriers, the temperature of the surfaces of the vulcanized product. The disadvantage of this method is the instability of the characteristics of the resulting products due to the instability of the reactivity supplied to the molding of the rubber mixture, and obtaining different characteristics of the product during vulcanization under the same temperature conditions.

There is a known method for adjusting the vulcanization mode, including determining the temperature field in the vulcanized product from controlled external temperature conditions on the vulcanizing surfaces of products by calculation methods, determining the kinetics of non-isothermal vulcanization of thin laboratory plates by the dynamic modulus of harmonic shift in the found non-isothermal conditions, determining the duration of the vulcanization process, at which optimal set of the most important properties of rubber, determination of the temperature field for multilayer standard samples simulating a tire element in terms of composition and geometry, obtaining the kinetics of non-isothermal vulcanization of multilayer plates and determining the equivalent vulcanization time according to the previously selected optimal level of properties, vulcanization of multilayer samples on a laboratory press at a constant temperature in during the equivalent vulcanization time and analysis of the obtained characteristics. This method is much more accurate than the methods used in industry for calculating the effects and equivalent vulcanization times, but it is more cumbersome and does not take into account the change in the instability of the reactivity of the rubber mixture supplied for vulcanization.

There is a known method for regulating the vulcanization process, in which the temperature is measured at the vulcanization process-limiting sections of the product, the degree of vulcanization is calculated from these data, when the specified and calculated degree of vulcanization is equal, the vulcanization cycle stops. The advantage of the system is the adjustment of the vulcanization time when the temperature fluctuations of the vulcanization process change. The disadvantage of this method is a large spread in the characteristics of the resulting products due to the heterogeneity of the rubber mixture in terms of reactivity to vulcanization and the deviation of the vulcanization kinetics constants used in the calculation from the real kinetic constants of the processed rubber mixture.

There is a known method for controlling the vulcanization process, which consists in calculating the temperature in the controlled shoulder zone on the R-C grid using boundary conditions based on measurements of the surface temperature of the molds and the temperature diaphragm cavity, calculating the equivalent vulcanization times that determine the degree of vulcanization in the controlled area, when implementing the equivalent time vulcanization on the real process the process stops. The disadvantages of the method are its complexity and a wide spread of characteristics of the resulting products due to changes in the reactivity to vulcanization (activation energy, pre-exponential factor of the kinetic constants) of the rubber mixture.

Closest to the proposed one is a method for controlling the vulcanization process, in which, synchronously with the real vulcanization process, according to the boundary conditions, based on temperature measurements on the surface of a metal mold, the temperature is calculated in the vulcanized products on a grid electric model, the calculated temperature values ​​are set on a volcameter, on which parallel to the main During the vulcanization process, the kinetics of non-isothermal vulcanization of a sample from a processed batch of rubber mixture is studied, when a given level of vulcanization is reached, control commands are generated on the vulcameter for the product vulcanization unit [AS USSR No. 467835]. The disadvantages of the method are the great complexity of implementation on the technological process and the limited scope.

The objective of the invention is to increase the stability of the characteristics of manufactured products.

This goal is achieved by the fact that the vulcanization time of rubber products on the production line is corrected depending on the time to obtain the maximum shear modulus of the rubber mixture during vulcanization of samples of the processed rubber mixture in laboratory conditions on the rheometer and the deviation of the rubber tensile modulus in the manufactured products from the specified value.

The proposed solution is illustrated in Fig.1-5.

Figure 1 shows a functional diagram of the control system that implements the proposed control method.

Figure 2 shows a block diagram of the control system that implements the proposed control method.

Figure 3 shows a time series of tensile strength of the Jubo coupling, produced at OJSC "Balakovorezinotekhnika".

Figure 4 shows the characteristic kinetic curves for the moment of shear images of the rubber mixture.

Figure 5 shows the time series of changes in the duration of the vulcanization of samples of the rubber mixture to 90 percent level of achievable shear modulus of the vulcanizate.

On the functional diagram of the system that implements the proposed control method (see figure 1), the stage of preparation of the rubber mixture 1, the stage of vulcanization 2, the rheometer 3 for studying the kinetics of vulcanization of samples of the rubber mixture, the mechanical dynamic analysis device 4 (or tensile machine) to determine rubber stretching module for finished products or samples of satellites, control device 5.

The control method is implemented as follows. Samples from batches of the rubber compound are analyzed on a rheometer and the values ​​of the vulcanization time at which the rubber shear moment has a maximum value are sent to the control device 5. When the reactivity of the rubber mixture changes, the control device corrects the vulcanization time of the products. Thus, perturbations are worked out according to the characteristics of the initial components that affect the reactivity of the resulting rubber mixture. The tensile modulus of rubber in finished products is measured by dynamic mechanical analysis or on a tensile testing machine and is also fed to the control device. The inaccuracy of the correction obtained, as well as the presence of changes in the temperature of heat carriers, heat exchange conditions and other disturbing influences on the vulcanization process, are worked out by adjusting the vulcanization time depending on the deviation of the rubber tensile modulus in the manufactured products from the specified value.

The block diagram of the control system that implements this control method and is presented in Fig.2 includes a direct control channel control device 6, a feedback channel control device 7, a vulcanization process control object 8, a transport delay link 9 to take into account the length of time for determining the characteristics of rubber of finished products , a feedback channel comparator 10, an adder 11 for summing adjustments to the vulcanization time via the forward control channel and the feedback channel, an adder 12 for taking into account the effects of uncontrolled perturbations on the vulcanization process.

When changing the reactivity of the rubber mixture, the estimate τ max changes and the control device corrects the vulcanization time in the process by the value Δτ 1 via the direct control channel 1.

In a real process, the vulcanization conditions differ from the conditions on the rheometer, so the vulcanization time required to obtain the maximum torque value in the real process also differs from that obtained on the device, and this difference varies with time due to the instability of the vulcanization conditions. These disturbances f are processed through the feedback channel by introducing a correction Δτ 2 by the control device 7 of the feedback loop, depending on the deviation of the rubber module in the manufactured products from the set value E ass.

The link of the transport delay 9, when analyzing the dynamics of the system, takes into account the influence of the time required to analyze the characteristics of the rubber of the finished product.

Figure 3 shows the time series of the conditional breaking force of the Juba coupling, manufactured by Balakovorezinotekhnika OJSC. The data show the presence of a large scatter of products for this indicator. The time series can be represented as the sum of three components: low-frequency x 1 , mid-frequency x 2 , high-frequency x 3 . The presence of a low-frequency component indicates the insufficient efficiency of the existing process control system and the fundamental possibility of building an effective feedback control system to reduce the spread of finished product parameters in terms of their characteristics.

Figure 4 shows the characteristic experimental kinetic curves for the moment of shear during the vulcanization of samples of the rubber mixture, obtained on the rheometer MDR2000 "Alfa Technologies". The data show the heterogeneity of the rubber compound in terms of reactivity to the vulcanization process. The spread in time to reach the maximum torque ranges from 6.5 minutes (curves 1.2) to more than 12 minutes (curves 3.4). The spread in the completion of the vulcanization process ranges from not reaching the maximum value of the moment (curves 3.4) to the presence of the overvulcanization process (curves 1.5).

Figure 5 shows a time series of vulcanization times to the 90% maximum shear moment level obtained by studying the vulcanization of rubber compound samples on the Alfa Technologies MDR2000 rheometer. The data shows the presence of a low frequency change in the cure time to obtain the maximum shear moment of the vulcanizate.

The presence of a large variation in the mechanical characteristics of the Juba coupling (figure 3) indicates the relevance of solving the problem of increasing the stability of the characteristics of rubber products to improve their operational reliability and competitiveness. The presence of instability of the reactivity of the rubber mixture to the vulcanization process (Fig.4,5) indicates the need to change the time in the process of vulcanization of products from this rubber mixture. The presence of low-frequency components in the time series of the conditional breaking force of finished products (figure 3) and in the vulcanization time to obtain the maximum shear moment of the vulcanizate (figure 5) indicates the fundamental possibility of improving the quality indicators of the finished product by adjusting the vulcanization time.

Considered confirms the presence in the proposed technical solution:

The technical result, i.e. the proposed solution is aimed at increasing the stability of the mechanical characteristics of rubber products, reducing the number of defective products and, accordingly, reducing the specific consumption rates of the initial components and energy;

Essential features, consisting in adjusting the duration of the vulcanization process, depending on the reactivity of the rubber mixture to the vulcanization process and depending on the deviation of the rubber tensile modulus in finished products from the specified value;

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Vulcanizeation-- the technological process of interaction of rubbers with a vulcanizing agent, in which the rubber molecules are crosslinked into a single spatial grid. Vulcanizing agents can be: sulfur, peroxides, metal oxides, amine-type compounds, etc. To increase the rate of vulcanization, various accelerator catalysts are used.

During vulcanization, the strength characteristics of rubber, its hardness, elasticity, heat and frost resistance increase, the degree of swelling and solubility in organic solvents decrease. The essence of vulcanization is the combination of linear rubber macromolecules into a single "crosslinked" system, the so-called vulcanization network. As a result of vulcanization, cross-links are formed between macromolecules, the number and structure of which depend on method B. During vulcanization, some properties of the vulcanized mixture do not change monotonously with time, but pass through a maximum or minimum. The degree of vulcanization at which the best combination of various physical and mechanical properties of rubber is achieved is called the optimum vulcanization.

Vulcanization is usually a mixture of rubber with various substances that provide the necessary performance properties of rubber (fillers, such as soot, chalk, kaolin, as well as softeners, antioxidants, etc.).

In most cases, general-purpose rubbers (natural, butadiene, butadiene-styrene) are vulcanized by heating them with elemental sulfur at 140-160°C (sulphuric rubber). The resulting intermolecular cross-links are carried out through one or more sulfur atoms. If 0.5-5% sulfur is added to rubber, a soft vulcanizate is obtained (car tubes and tires, balls, tubes, etc.); the addition of 30-50% sulfur leads to the formation of a hard inelastic material - ebonite. Sulfur vulcanization can be accelerated by adding small amounts of organic compounds, the so-called vulcanization accelerators - captax, thiuram, etc. The effect of these substances is fully manifested only in the presence of activators - metal oxides (most often zinc oxide).

In industry, sulfur vulcanization is carried out by heating the vulcanized product in molds under high pressure or in the form of non-molded products (in "free" form) in boilers, autoclaves, individual vulcanizers, and continuous vulcanization apparatus. etc. In these devices, heating is carried out by steam, air, superheated water, electricity, high-frequency currents. The molds are usually placed between heated hydraulic press plates. Sulfur vulcanization was discovered by C. Goodyear (USA, 1839) and T. Gancock (Great Britain, 1843). For the vulcanization of special-purpose rubbers, organic peroxides (for example, benzoyl peroxide), synthetic resins (for example, phenol-formaldehyde), nitro and diazo compounds, and others are used; the process conditions are the same as for sulfur vulcanization.

Vulcanization is also possible under the influence of ionizing radiation - g-radiation of radioactive cobalt, a stream of fast electrons (radiation vulcanization). The methods of sulfur-free and radiation bleaching make it possible to obtain rubbers with high thermal and chemical resistance.

In the polymer industry, vulcanization is used in the extrusion production of rubber.

Vulcanization at prepairetires

The technological process of tire repair consists of preparing damaged areas for applying repair materials, applying repair materials to damaged areas and vulcanizing repaired areas.

Vulcanization of repaired areas is one of the most important operations in tire repair.

The essence of vulcanization lies in the fact that when heated to a certain temperature, a physical and chemical process occurs in unvulcanized rubber, as a result of which the rubber acquires elasticity, strength, elasticity and other necessary qualities.

When vulcanizing two pieces of rubber glued together with rubber glue, they turn into a monolithic structure and the strength of their connection does not differ from the adhesion strength of the base material inside each piece. At the same time, to ensure the necessary strength, the pieces of rubber must be pressed - pressed under a pressure of 5 kg / cm 2.

In order for the vulcanization process to take place, it is not enough to produce only heating to the required temperature, i.e., to 143 + 2 °; the vulcanization process does not take place instantly, so heated tires must be held for a certain time at the vulcanization temperature.

Vulcanization can also occur at temperatures lower than 143°C, but this takes longer. So, for example, when the temperature drops by only 10 ° against the indicated one, the vulcanization time should be doubled. In order to reduce the time for preheating during vulcanization, electric cuffs are used that allow heating simultaneously from both sides of the tire, while reducing the vulcanization time and improving the quality of the repair. With one-sided heating of tires of large thickness, overvulcanization of rubber sections in contact with the vulcanization equipment occurs, and undervulcanization of rubbers on the opposite side. The vulcanization time, depending on the type of damage and the size of the tire, ranges from 30 to 180 minutes for tires and from 15 to 20 minutes for tubes

For vulcanization in car fleets, a stationary vulcanization apparatus model 601, manufactured by the GARO trust, is used.

The working set of the vulcanization apparatus includes corsets for sectors, tightening of corsets, tread and side profile linings, clamps, pressure pads, sandbags, mattresses,.

At a steam pressure in the boiler of 4 kg / cm 2, the required surface temperature of the vulcanization equipment is 143 "+ 2 °. At a pressure of 4.0-4.1 kg / cm 2, the safety valve must open.

Vulcanizing devices must be inspected by a boiler supervisor before being put into operation.

Internal damage to tires is vulcanized on sectors, external damage on slabs using profile linings. Through damage (in the presence of electric cuffs, they are vulcanized on a plate with a profile lining, in the absence of electric cuffs separately: first from the inside on the sector, then from the outside on a plate with a profile lining.

The electrocuff consists of several layers of rubber and an outer layer of rubberized chafer, in the middle of which is placed a spiral of nichrome wire for heating and a thermostat to maintain a constant temperature (150 °).

vulcanization industry tire repair

Rice. 4. Stationary vulcanizing apparatus GARO model 601: 1 - sector; 2 -- board plate; 3 - boiler-steamer; 4 - small clamps for cameras; 5 -- bracket for cameras; 6 - pressure gauge; 7 - clamp for tires; 8 - firebox; 9 - gauge glass; 10 -- manual plunger pump; 11 -- suction tube

Before vulcanization, the boundaries of the repaired area of ​​the tire are marked. To eliminate sticking, powder it with talc, as well as a sand bag, an electrocuff and vulcanization equipment (sectors, profile linings, etc.) in contact with the tire.

When vulcanizing on a sector, crimping is achieved by tightening the corset, and when vulcanizing on a plate, using a sandbag and a clamp.

Profile linings (tread and bead) are selected in accordance with the repaired part of the tire and its size.

The electrocuff during vulcanization is located between the tire and the sandbag.

The time of the beginning and end of vulcanization is marked with chalk on a special board installed at the vulcanization equipment.

Repaired tires must meet the following requirements:

1) tires should not have unrepaired places;

2) on the inner side of the tire there should be no swelling and traces of delamination of patches, undervulcanization, folds and thickenings that impair the operation of the chamber;

3) the sections of rubber applied along the tread or sidewall must be completely vulcanized to a hardness of 55-65 Shore;

4) sections of the tread over 200 mm in size restored during the repair must have a pattern identical with the entire tread of the tire; the "All-terrain vehicle" type pattern must be applied regardless of the size of the retread area;

5) the shape of the tire beads must not be distorted;

6) thickenings and depressions that distort the outer dimensions and surface of the tire are not allowed;

7) repaired sections should not have backlogs; it is allowed to have shells or pores up to 20 mm 2 in area and up to 2 mm deep in the amount of not more than two per square decimeter;

8) the quality of tire repair should ensure their guaranteed mileage after repair.

Vulcanization at prepairecameras

Similar to the tire repair workflow, the tube repair workflow consists of preparing damaged areas for patching, patching, and curing.

The scope of work on preparing damaged areas for patching includes: identifying hidden and visible damage, removing old unvulcanized patches, rounding edges with sharp corners, roughening the rubber around the damage, cleaning the chambers from roughing dust.

Rice. 5. Sector for vulcanization of tires: 1 - sector; 2 - tire; 2 - corset; 4 -- puff

Rice. 6. Vulcanization of onboard tire damage on the side plate: 1 - tire; 2 - side plate: 3 - side lining; 4 -- sandbag; 5 -- metal plate; 6 -- clamp

Visible damage is detected by external examination in good light and outlined with an indelible pencil.

To detect hidden damage, i.e., small punctures that are invisible to the eye, the chamber in the inflated state is immersed in a bath of water, and the puncture site is determined by the emerging air bubbles, which is also outlined with a chemical pencil. The damaged surface of the chamber is subjected to roughening with a carborundum stone or a wire brush at a width of 25–35 mm from the damage boundaries, preventing rough dust from entering the chamber. Rough areas are cleaned with a brush.

Repair materials for the repair of chambers are: unvulcanized chamber rubber 2 mm thick, rubber of chambers unsuitable for repair, and rubberized chafer. Raw, unvulcanized rubber seals all punctures and tears up to 30 mm in size. Rubber for cameras repairs damages of more than 30 mm. This rubber should be elastic, without cracks and mechanical damage. Raw rubber is refreshed with gasoline, coated with glue with a concentration of 1: 8 and dried for 40-45 minutes. The chambers are roughened with a wire brush or carborundum stone on a roughening machine, after which they are cleaned of dust, refreshed with gasoline and dried for 25 minutes, then coated twice with glue with a concentration of 1: 8 and dried after each spread for 30--40 minutes at a temperature 20--30°. The chafer is smeared once with glue of a concentration of 1: 8, then dried.

The patch is cut out in such a way that it covers the hole by 20–30 mm from all sides and is 2–3 mm less than the boundaries of the roughened surface. It is superimposed on the repaired section of the chamber with one side and gradually rolled with a roller over the entire surface, so that there are no air bubbles between it and the chamber. When applying patches, make sure that the surfaces to be bonded are completely clean, free from moisture, dust and grease.

In cases where the chamber has a gap greater than 500 mm, it can be repaired by cutting out the damaged piece and inserting in its place the same piece from another chamber of the same size. This repair method is called camera docking. The width of the joint must be at least 50 mm.

External threads damaged in valve bodies are restored with dies, and internal threads with taps.

If it is necessary to replace the valve, it is cut out together with the flange and another valve is vulcanized in a new place. The location of the old valve is repaired as normal damage.

Vulcanization of damaged areas is carried out on a model 601 vulcanization apparatus or on a GARO vulcanization apparatus for vulcanizing chambers. Curing time for patches is 15 minutes and for flanges 20 minutes at 143+2°.

During vulcanization, the chamber is pressed with a clamp through a wooden lining to the surface of the plate. The overlay should be 10-15 mm larger than the patch.

If the repaired area does not fit on the slab, then it is vulcanized in two or three successive installations (rates).

After vulcanization, the influxes on the non-roughened surface are cut off with scissors, and the edges of the patches and burrs are removed on the stone of the roughing machine.

Repaired cameras must meet the following requirements:

1) a chamber filled with air must be airtight both along the body of the chamber and at the place where the valve is attached;

2) the patches must be tightly vulcanized, free of bubbles and porosity, their hardness must be the same as that of the tube rubber;

3) the edges of patches and flanges should not have thickenings and delaminations;

4) the thread of the valve must be intact.

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The determination of vulcanization kinetics is of great importance in the manufacture of rubber products. The vulcanizability of rubber compounds is not identical to their ability to scorch, and to evaluate it, methods are needed that allow one to determine not only the beginning (by decreasing fluidity), but also the optimum vulcanization upon reaching the maximum value of some indicator, for example, the dynamic modulus.39

The usual method for determining vulcanizability is to make several samples from the same rubber compound, differing in the duration of the heat treatment, and test them, for example, in a tensile tester. At the end of the test, a vulcanization kinetics curve is plotted. This method is very laborious and time consuming.39

Rheometer tests do not answer all questions, and for greater accuracy, the results of determining the density, tensile strength and hardness must be processed statistically and cross-checked with curves vulcanization kinetics. At the end of the 60s. In connection with the development of control of the preparation of mixtures using rheometers, the use of larger closed rubber mixers began to be used and mixing cycles were significantly reduced in some industries, it became possible to produce thousands of tons of refills of rubber compounds per day.

Significant improvements have also been noted in the speed at which material moves through the plant. These advances have led to a backlog of test technology. A plant that prepares 2,000 batches of mixes daily requires that a test be carried out for about 00 control parameters (Table 17.1), assuming at 480

Definition of kinetics rubber vulcanization mixtures

When designing thermal modes of vulcanization, simultaneously flowing and interconnected thermal (dynamic change in the temperature field along the product profile) and kinetic (formation of the degree of rubber vulcanization) processes are simulated. As a parameter for determining the degree of vulcanization, any physical and mechanical indicator for which there is a mathematical description of the kinetics of non-isothermal vulcanization can be chosen. However, due to differences in the vulcanization kinetics for each417

The first part of Chapter 4 describes the existing methods for assessing the effect of the curing action of time-varying temperatures. Approximation of the simplifying assumptions underlying the assessment accepted in the industry becomes apparent in the light of consideration of the general patterns of changes in the properties of rubber during vulcanization (vulcanization kinetics for various indicators of properties determined by laboratory methods).

The formation of rubber properties during vulcanization of multilayer products proceeds differently than thin plates used for laboratory mechanical tests from a homogeneous material. In the presence of materials of different deformability, the complex stressed state of these materials has a great influence. The second part of Chapter 4 is devoted to the mechanical behavior of materials of a multilayer product in vulcanization molds, as well as methods for evaluating the achieved degrees of vulcanization of rubber in products.7
It should also be noted that when determining vulcanization kinetics according to this property, the test mode is not indifferent. For example, standard rubber made of natural rubber at 100°C has a different optimum, plateau and distribution of tear resistance indicators than at 20°C, depending on degree of vulcanization.

As follows from the consideration of the dependence of the basic properties of rubber on the degree of its cross-linking, carried out in the previous section, the assessment of the kinetics and degree of vulcanization can be done in various ways. The methods used are divided into three groups: 1) chemical methods (determination of the amount of reacted and unreacted vulcanization agent by chemical analysis of rubber) 2) physicochemical methods (determination of thermal effects of the reaction, infrared spectra, chromatography, luminescent analysis, etc.) 3) mechanical methods (determination of mechanical properties, including methods specially developed for determining the kinetics of vulcanization).

Radioactive isotopes (labeled atoms) are easy to detect by measuring the radioactivity of the product that contains them. To study the vulcanization kinetics, after a certain reaction time of rubber with radioactive sulfur (vulcanization agent), the reaction products are subjected to cold continuous extraction with benzene for 25 days. The unreacted curing agent is removed with the extract, and the concentration of the remaining bound agent is determined from the radioactivity of the final reaction product.

The second group of methods serves to determine the actual kinetics of vulcanization.

GOST 35-67. Rubber. Method for determining kinetics vulcanization of rubber compounds.

The development in recent years of new polymerization methods has contributed to the creation of rubber types with more advanced properties. Changes in properties are mainly due to differences in the structure of rubber molecules, and this naturally increases the role of structural analysis. The spectroscopic determination of 1,2-, cis-, A-, and 1,4-grain structures in synthetic rubbers is of the same practical and theoretical importance as the analysis of the physicochemical and performance characteristics of a polymer. The results of quantitative analysis make it possible to study 1) the effect of the catalyst and polymerization conditions on the structure of rubber 2) the structure of unknown rubbers (identification) 3) the change in the microstructure during vulcanization (isomerization) and the kinetics of vulcanization 4) the processes occurring during oxidative and thermal degradation of rubber (structural changes when drying rubber, aging) 5) the effect of stabilizers on the stability of the rubber molecular framework and the processes occurring during grafting and plasticization of rubber 6) the ratio of monomers in rubber copolymers and, in this regard, to give a qualitative conclusion about the distribution of blocks along the lengths in butadiene-styrene copolymers ( separation of block and random copolymers).357

When selecting organic rubber vulcanization accelerators for industrial use, the following should be taken into account. The accelerator is chosen for a certain type of rubber, because depending on the type and structure of rubber, a different effect of the accelerator on the vulcanization kinetics is observed.16

To characterize the kinetics of vulcanization at all stages of the process, it is advisable to observe the change in the elastic properties of the mixture. As one of the indicators of elastic properties during tests carried out in a stationary loading mode, the dynamic modulus can be used.

Details about this indicator and methods for its determination will be discussed in Section 1 of Chapter IV, devoted to the dynamic properties of rubber. As applied to the problem of controlling rubber compounds by the kinetics of their vulcanization, the determination of the dynamic modulus is reduced to the observation of the mechanical behavior of a rubber compound subjected to multiple shear deformation at an elevated temperature.

Vulcanization is accompanied by an increase in the dynamic modulus. The completion of the process is determined by the cessation of this growth. Thus, continuous monitoring of the change in the dynamic modulus of the rubber compound at the vulcanization temperature can serve as the basis for determining the so-called optimum vulcanization (modulo), which is one of the most important technological characteristics of each rubber compound.37

In table. 4 shows the values ​​of the temperature coefficient of the rate of vulcanization of natural rubber, determined from the rate of binding of sulfur. The temperature coefficient of the vulcanization rate can also be calculated from the kinetic curves of changes in the physical and mechanical properties of rubber during vulcanization at different temperatures, for example, by the modulus value. The values ​​of the coefficients calculated from the kinetics of modulus change are given in the same table.76

The method for determining the degree of vulcanization (T) on the product section limiting the vulcanization process. In this case, methods and devices for optimal control of the vulcanization modes of products are distinguished, in which the kinetics of non-isothermal vulcanization is determined 419

Place of definition (T). Methods and devices are known that allow determining the kinetics of non-isothermal vulcanization 419

The kinetic curves obtained using the described methods are used to calculate such parameters as rate constants, temperature coefficients and activation energy of the process in accordance with the equations of formal kinetics of chemical reactions. For a long time, it was believed that most kinetic curves are described by a first-order equation. It was found that the temperature coefficient of the process is equal to an average of 2, and the activation energy varies from 80 to kJ/mol, depending on the vulcanization agent and the molecular structure of rubber. However, a more precise determination of the kinetic curves and their formal kinetic analysis carried out by W. Scheele 52 showed that in almost all cases the reaction order is less than 1 and equals 0.6-0.8, and the vulcanization reactions are complex and multistage.

Curometer model VII by Wallace (Great Britain) determines the kinetics of vulcanization of rubber compounds under isothermal conditions. The sample is placed between plates, one of which is displaced at a certain angle. The advantage of this design is that there is no porosity in the sample because it is under pressure, and the possibility of using smaller samples, which reduces the warm-up time.499

The study of the kinetics of vulcanization of rubber compounds is not only of theoretical interest, but also of practical importance for assessing the behavior of rubber compounds during processing and vulcanization. To determine the modes of technological processes in production, the indicators of the vulcanizability of rubber compounds should be known, i.e. their tendency to premature vulcanization - the beginning of vulcanization and its speed (for processing), and for the actual vulcanization process - in addition to the above indicators - the optimum and plateau vulcanization, reversion area.

The book was compiled on the basis of lectures given to US rubber engineers at the University of Akron by leading American researchers. The purpose of these lectures was a systematic presentation of the available information about the theoretical foundations and technology of vulcanization in an accessible and fairly complete form.

In accordance with this, at the beginning of the book, the history of the issue and the characteristics of changes in the basic properties of rubber that occur during vulcanization are presented. Further, when presenting the kinetics of vulcanization, chemical and physical methods for determining the speed, degree and temperature coefficient of vulcanization are critically considered. The influence of the dimensions of the workpiece and the thermal conductivity of rubber compounds on the rate of vulcanization has been discussed.8

Instruments for determining the kinetics of vulcanization usually operate either in the mode of a given amplitude value of displacement (volcameters, viscurometers or rheometers), or in the mode of a given amplitude value of the load (curometers, SERAN). Accordingly, the amplitude values ​​of the load or displacement are measured.

Since samples 25 are usually used for laboratory tests, prepared from plates with a thickness of 0.5-2.0 mm, which are vulcanized almost under isothermal conditions (Г == = onst), the vulcanization kinetics for them is measured at a constant vulcanization temperature. On the kinetic curve, the duration of the induction period, the time of the onset of the vulcanization plateau, or optimum, the magnitude of the plateau, and other characteristic times are determined.

Each of them corresponds to certain vulcanization effects, according to (4.32). Equivalent vulcanization times will be those times which at a temperature of 4kv = onst will lead to the same effects as at variable temperatures. Thus

If the vulcanization kinetics at T = onst is given by equation (4.20a), in which t is the time of the actual reaction, the following method can be proposed definitions of kinetics non-isothermal vulcanization reaction.

Operational control of the vulcanization process allows the implementation of special devices for determining the kinetics of vulcanization - vulcanometers (curometers, rheometers), continuously fixing the amplitude of the shear load (in the mode of a given amplitude of harmonic shift) or shear deformation (in the mode of a given amplitude of shear load). The most widely used devices are vibration type, in particular Monsanto 100 and 100S rheometers, which provide automatic testing with obtaining a continuous diagram of changes in the properties of the mixture during vulcanization according to ASTM 4-79, MS ISO 3417-77, GOST 35-84.492

The choice of curing or vulcanization mode is usually carried out by studying the kinetics of changes in any property of the cured system of electrical resistance and dielectric loss tangent, strength, creep, modulus of elasticity under various types of stress state, viscosity, hardness, heat resistance, thermal conductivity, swelling, dynamic mechanical characteristics , refractive index and a number of other parameters, -. The methods of DTA and TGA, chemical and thermomechanical analysis, dielectric and mechanical relaxation, thermometric analysis and differential scanning calorimetry are also widely used.

All these methods can be conditionally divided into two groups: methods that allow you to control the speed and depth of the curing process by changing the concentration of reactive functional groups, and methods that allow you to control a change in any property of the system and set its limiting value. The methods of the second group have the common drawback that one or another property of the curing system is clearly manifested only at certain stages of the process, so the viscosity of the curing system can be measured only up to the gelation point, while most of the physical and mechanical properties begin to clearly manifest themselves only after the gelation point. On the other hand, these properties strongly depend on the measurement temperature, and if a property is continuously monitored during the process, when it is necessary to change the reaction temperature in the course of the reaction or the reaction develops essentially non-isothermally to achieve the completeness of the reaction, then the interpretation of the measurement results of the kinetics of property change in such a process becomes already quite complex.37

A study of the kinetics of copolymerization of ethylene with propylene on the VO I3-A12(C2H5)3C1e system showed that its modification with tetrahydrofuran makes it possible, under certain conditions, to increase the integral yield of the copolymer. This effect is due to the fact that the modifier, by changing the ratio between the rates of chain growth and termination, promotes the formation of copolymers with a higher molecular weight. The same compounds are used in a number of cases in the copolymerization of ethylene and propylene with dicyclopentadiene, norbornene, and other cyclodienes. The presence of electron-donating compounds in the reaction sphere during the preparation of unsaturated terpolymers prevents the subsequent slower reactions of cross-linking of macromolecules and makes it possible to obtain copolymers with good vulcanization properties.45

Kinetics of sulfur addition. The kinetic Weber curves, as can be seen from Fig. , have the form of broken lines.

Weber explained this type of curves by the fact that at certain moments of vulcanization, various stoichiometric compounds of rubber with sulfur are formed - sulfides of the composition KaZ, KaZr. Ka33, etc. Each of these sulfides is formed at its own rate, and the formation of a sulfide with a certain sulfur content does not begin until the previous stage of formation of a sulfide with a smaller number of sulfur atoms has ended.

However, later and more thorough research by Spence and Young led to the simpler kinetic curves depicted in Fig. and. As can be seen from these302

The results of determining the structural parameters of the vulcanization mesh using the sol-gel analysis, in particular, the data on the kinetics of changes in the total number of mesh chains (Fig. 6A), show that the most important feature of dithiodimorpholine vulcanizates is a significantly lower reversion and, as a consequence, a smaller decrease in the strength properties of vulcanizates with an increase in curing temperature. On fig. 6B shows the kinetics of the change in the tensile strength of mixtures at 309

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Kuznetsov A.S. 1 , Kornyushko V.F. 2

1 Postgraduate student, 2 Doctor of Technical Sciences, Professor, Head of the Department of Information Systems in Chemical Technology, Moscow Technological University

PROCESSES OF MIXING AND STRUCTURING OF ELASTOMER SYSTEMS AS CONTROL OBJECTS IN A CHEMICAL-TECHNOLOGICAL SYSTEM

annotation

In the article, from the standpoint of system analysis, the possibility of combining the processes of mixing and structuring into a single chemical-technological system for obtaining products from elastomers is considered.

Keywords: mixing, structuring, system, system analysis, management, control, chemical-technological system.

Kuznetsov A. S. 1 , Kornushko V. F. 2

1 Postgraduate stadent, 2 PhD in Engineering, Professor, Head of the department of Informational systems in chemical technology, Moscow State University

MIXING AND STRUCTURING PROCESSES AS CONTROL OBJECTS IN CHEMICAL-ENGINEERING SYSTEM

Abstract

The article describes the possibility of combining on the basis of system analysis the mixing and vulcanization processes in the unified chemical-engineering system of elastomer’s products obtaining.

keywords: mixing, structuring, system, system analysis, direction, control, chemical-engineering system.

Introduction

The development of the chemical industry is impossible without the creation of new technologies, an increase in output, the introduction of new technology, the economical use of raw materials and all types of energy, and the creation of low-waste industries.

Industrial processes take place in complex chemical-technological systems (CTS), which are a set of devices and machines combined into a single production complex for the production of products.

Modern production of products from elastomers (obtaining an elastomer composite material (ECM), or rubber) is characterized by the presence of a large number of stages and technological operations, namely: preparation of rubber and ingredients, weighing solid and bulk materials, mixing rubber with ingredients, molding a raw rubber mixture - semi-finished product, and, in fact, the process of spatial structuring (vulcanization) of the rubber mixture - blanks for obtaining a finished product with a set of specified properties.

All processes for the production of products from elastomers are closely interconnected, therefore, exact observance of all established technological parameters is necessary to obtain products of proper quality. Obtaining conditioned products is facilitated by the use of various methods for monitoring the main technological quantities in production in the central factory laboratories (CPL).

The complexity and multi-stage nature of the process of obtaining products from elastomers and the need to control the main technological indicators imply considering the process of obtaining products from elastomers as a complex chemical-technological system that includes all technological stages and operations, elements of analysis of the main stages of the process, their management and control.

1. General characteristics of mixing and structuring processes

The receipt of finished products (products with a set of specified properties) is preceded by two main technological processes of the system for the production of products from elastomers, namely: the mixing process and, in fact, the vulcanization of the raw rubber mixture. Monitoring compliance with the technological parameters of these processes is a mandatory procedure that ensures the receipt of products of proper quality, intensification of production, and prevention of marriage.

At the initial stage, there is rubber - a polymer base, and various ingredients. After weighing the rubber and ingredients, the mixing process begins. The mixing process is the grinding of the ingredients, and is reduced to a more uniform distribution of them in the rubber and better dispersion.

The mixing process is carried out on rollers or in a rubber mixer. As a result, we get a semi-finished product - a raw rubber compound - an intermediate product, which is subsequently subjected to vulcanization (structuring). At the stage of the raw rubber mixture, the uniformity of mixing is controlled, the composition of the mixture is checked, and its vulcanization ability is evaluated.

The uniformity of mixing is checked by the indicator of plasticity of the rubber compound. Samples are taken from different parts of the rubber mixture, and the plasticity index of the mixture is determined; for different samples, it should be approximately the same. The plasticity of the mixture P must, within the limits of error, coincide with the recipe specified in the passport for a particular rubber compound.

The vulcanization ability of the mixture is checked on vibrorheometers of various configurations. The rheometer in this case is an object of physical modeling of the process of structuring elastomeric systems.

As a result of vulcanization, a finished product is obtained (rubber, an elastomeric composite material. Thus, rubber is a complex multicomponent system (Fig. 1.)

Rice. 1 - Composition of the elastomeric material

The structuring process is a chemical process of converting a raw plastic rubber mixture into elastic rubber due to the formation of a spatial network of chemical bonds, as well as a technological process for obtaining an article, rubber, elastomeric composite material by fixing the required shape to ensure the required function of the product.

1. Building a model of a chemical-technological system
   production of products from elastomers

Any chemical production is a sequence of three main operations: the preparation of raw materials, the actual chemical transformation, the isolation of target products. This sequence of operations is embodied in a single complex chemical-technological system (CTS). A modern chemical enterprise consists of a large number of interconnected subsystems, between which there are subordination relations in the form of a hierarchical structure with three main steps (Fig. 2). The production of elastomers is no exception, and the output is a finished product with desired properties.

Rice. 2 - Subsystems of the chemical-technological system for the production of products from elastomers

The basis for building such a system, as well as any chemical-technological system of production processes, is a systematic approach. A systematic point of view on a separate typical process of chemical technology allows developing a scientifically based strategy for a comprehensive analysis of the process and, on this basis, building a detailed program for the synthesis of its mathematical description for the further implementation of control programs.

This scheme is an example of a chemical-technological system with a serial connection of elements. According to the accepted classification, the smallest level is a typical process.

In the case of the production of elastomers, separate stages of production are considered as such processes: the process of weighing ingredients, cutting rubber, mixing on rollers or in a rubber mixer, spatial structuring in a vulcanization apparatus.

The next level is represented by the workshop. For the production of elastomers, it can be represented as consisting of subsystems for supplying and preparing raw materials, a block for mixing and obtaining a semi-finished product, as well as a final block for structuring and detecting defects.

The main production tasks to ensure the required level of quality of the final product, the intensification of technological processes, the analysis and control of mixing and structuring processes, the prevention of marriage, are carried out precisely at this level.

1. Selection of the main parameters for the control and management of technological processes of mixing and structuring

The structuring process is a chemical process of converting a raw plastic rubber mixture into elastic rubber due to the formation of a spatial network of chemical bonds, as well as a technological process for obtaining an article, rubber, elastomeric composite material by fixing the required shape to ensure the required function of the product.

In the processes of production of products from elastomers, the controlled parameters are: temperature Tc during mixing and vulcanization Tb, pressure P during pressing, time τ of processing the mixture on the rollers, as well as vulcanization time (optimum) τopt..

The temperature of the semi-finished product on the rollers is measured by a needle thermocouple or a thermocouple with self-recording instruments. There are also temperature sensors. It is usually controlled by changing the flow of cooling water for the rollers by adjusting the valve. In production, cooling water flow regulators are used.

The pressure is controlled by using an oil pump with a pressure sensor and appropriate regulator installed.

Establishment of the parameters for the manufacture of the mixture is carried out by the roller according to the control charts, which contain the necessary values ​​of the process parameters.

The quality control of the semi-finished product (raw mixture) is carried out by the specialists of the central factory laboratory (CPL) of the manufacturer according to the passport of the mixture. At the same time, the main element for monitoring the quality of mixing and evaluating the vulcanization ability of the rubber mixture are vibrorheometry data, as well as the analysis of the rheometric curve, which is a graphical representation of the process, and is considered as an element of control and adjustment of the process of structuring elastomeric systems.

The procedure for evaluating the vulcanization characteristics is carried out by the technologist according to the passport of the mixture and the databases of rheometric tests of rubbers and rubbers.

Control of obtaining a conditioned product - the final stage - is carried out by specialists of the department for technical quality control of finished products according to the test data of the technical properties of the product.

When controlling the quality of a rubber compound of one specific composition, there is a certain range of values ​​of property indicators, subject to which products with the required properties are obtained.

Findings:

1. The use of a systematic approach in the analysis of the processes of production of products from elastomers makes it possible to most fully track the parameters responsible for the quality of the structuring process.
2. The main tasks to ensure the required indicators of technological processes are set and solved at the workshop level.

Literature

1. Theory of systems and system analysis in the management of organizations: TZZ Handbook: Proc. allowance / Ed. V.N. Volkova and A.A. Emelyanov. - M.: Finance and statistics, 2006. - 848 p.: ill. ISBN 5-279-02933-5
2. Kholodnov V.A., Hartmann K., Chepikova V.N., Andreeva V.P. System analysis and decision making. Computer technologies for modeling chemical-technological systems with material and thermal recycles. [Text]: textbook./ V.A. Kholodnov, K. Hartmann. St. Petersburg: SPbGTI (TU), 2006.-160 p.
3. Agayants I.M., Kuznetsov A.S., Ovsyannikov N.Ya. Modification of the coordinate axes in the quantitative interpretation of rheometric curves - M .: Fine chemical technologies 2015. V.10 No. 2, p64-70.
4. Novakov I.A., Wolfson S.I., Novopoltseva O.M., Krakshin M.A. Rheological and vulcanization properties of elastomer compositions. - M.: ICC "Akademkniga", 2008. - 332 p.
5. Kuznetsov A.S., Kornyushko V.F., Agayants I.M. \Rheogram as a process control tool for structuring elastomeric systems \ M:. NXT-2015 p.143.
6. Kashkinova Yu.V. Quantitative interpretation of the kinetic curves of the vulcanization process in the system of organizing the workplace of a technologist - a rubber worker: Abstract of the thesis. dis. … cand. tech. Sciences. - Moscow, 2005. - 24 p.
7. Chernyshov V.N. Theory of systems and system analysis: textbook. allowance / V.N. Chernyshov, A.V. Chernyshov. - Tambov: Tambov Publishing House. state tech. un-ta., 2008. - 96 p.

References

1. Teoriya sistem i sistemnyj analiz v upravlenii organizaciyami: TZZ Spravochnik: Ucheb. posobie / Pod red. V.N. Volkovoj i A.A. Emel'yanova. - M.: Finansy i statistika, 2006. - 848 s: il. ISBN 5-279-02933-5
2. Holodnov V.A., Hartmann K., CHepikova V.N., Andreeva V.P.. Sistemnyj analiz i prinyatie reshenij. Komp'yuternye tekhnologii modelirovaniya himiko-tekhnologicheskih sistem s material'nymi i teplovymi reciklami. : uchebnoe posobie./ V.A. Holodnov, K. Hartmann. SPb.: SPbGTI (TU), 2006.-160 s.
3. Agayanc I.M., Kuznecov A.S., Ovsyannikov N.YA. Modifikaciya osej koordinat pri kolichestvennoj interpretacii reometricheskih krivyh – M.: Tonkie himicheskie tekhnologii 2015 T.10 No. 2, s64-70.
4. Novakov I.A., Vol'fson S.I., Novopol'ceva O.M., Krakshin M.A. Reologicheskie i vulkanizacionnye svojstva ehlastomernyh kompozicij. - M.: IKC "Akademkniga", 2008. - 332 s.
5. Kuznecov A.S., Kornyushko V.F., Agayanc I.M. \Reogramma kak instrument upravleniya tekhnologicheskim processom strukturirovaniya ehlastomernyh sistem \ M:. NHT-2015 s.143.
6. Kashkinova YU.V. Kolichestvennaya interpretaciya kineticheskih krivyh processa vulkanizacii v sisteme organizacii rabochego mesta tekhnologa – rezinshchika: avtoref. dis. …cand. technology science. - Moscow, 2005. - 24 s.
7. Chernyshov V.N. Teoriya sistem i sistemnyj analiz: ucheb. posobie / V.N. Chernyshov, A.V. Chernyshov. – Tambov: Izd-vo Tamb. gos. technology un-ta., 2008. - 96 s.