RU2487907C1 - High-temperature sealing material and method for production thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed material contains the following components, wt %: inorganic fibre 20-40, rubber 3-12, low-molecular weight polyisobutylene 0.1-1.0 and foamed vermiculite with packed density of 28-80 g/l, obtained by treating the starting vermiculite with hydrogen peroxide with concentration of not less than 35% - the balance. Also disclosed is a method of producing said material, wherein foamed vermiculite is mixed with inorganic fibre and water to obtain a first mixture. The rubber and the low-molecular weight polisobutylene are then mixed to obtain a second mixture. The first and second mixtures are mixed to obtain a mixture from which the material is formed.

EFFECT: improved sealing properties of the material and high operating temperature of the material.

14 cl, 5 tbl

Description

The invention relates to high-temperature sealing materials and their preparation and can be used in mechanical engineering and energy, in particular for the production of seals used in combined cycle power plants.

Currently, there is an urgent need to develop new materials for sealing high-temperature installations. The demand for high-temperature sealing materials in the energy sector is associated with the transition of this industry from steam-powered (operating temperature 550 ° C) to significantly more efficient combined-cycle plants (operating temperature up to 1100 ° C). Most commonly used graphite or paronite seals are unsuitable for long-term operation on this equipment and their frequent replacement significantly reduces its energy efficiency.

The obvious solution to this problem is to use oxide materials with elastic properties as an elastic component. One of such materials is vermiculite, a mineral of the hydrobiotite type mica group, which has a layered structure that provides elastic properties and can expand at high temperatures, which makes it possible to use small amounts of elastomeric binders as additional compaction ingredients, the volume of which as polymers burn out will take up foaming vermiculite.

Vermiculite in sealing products may be present in both non-foamed and foamed states.

So, for example, from the patent RU 2182918 a flexible sealing insulating material is known, which is used in catalytic converters of exhaust gases of automobile engines. This material contains, in wt.%: Unexpanded vermiculite with a particle size of 0.3-1.0 mm 40-60; acrylate rubber latex 6-14; aluminosilicate and / or silica fiber 30-54.

The material is prepared as follows. A mixture is prepared from a fibrous filler and a binder - latex acrylate rubber, then vermiculite is introduced into the mixture. A fibrous sheet material (fiber mat) is formed from the resulting mass, which is subjected to heat treatment, after which the material is ready for use.

In the patent it is reported that when operating under high temperatures, vermiculite foams, thus significantly increasing the volume of the material, and the use of the specified acrylate rubber as a latex binder and the experimentally selected ratio as a whole contribute to a more uniform distribution of filler particles and, thus, provide reliable fixation material in a fixed gap and the required operational properties.

However, the use of non-foamed vermiculite in the material creates serious limitations when using the invention. So, for effective expansion of vermiculite, sharp heating (thermal shock) to high (600-800 ° temperatures) is necessary. If these temperatures are not achieved or a smooth heating of the product is realized, then the expansion of vermiculite (especially enclosed in a polymer matrix) occurs slightly to ensure proper sealing properties of the sealing material. Another negative side of the use of unexpanded vermiculite is the low integrity of the composite material obtained according to the formulation claimed by the authors of the patent, which is associated with the high stiffness of the grains of unexpanded vermiculite. The insufficient mechanical strength of the sealing material obtained in this way limits its scope to minor pressures during sealing.

More promising for obtaining sealing materials is the use of foamed vermiculite as an elastic component of the sealing material.

Moreover, in the generally accepted classification of foamed vermiculites, chemically foamed and gas-foamed vermiculites are distinguished.

Chemically foamed vermiculite is understood to mean such vermiculite that can be obtained by treating the vermiculite raw material with a chemical reagent and subsequent foaming in the presence of water. In particular, vermiculite can be treated with a sodium chloride solution to exchange magnesium ions for sodium ions, and then treated with n-butylammonium hydrochloride to replace sodium ions with nC ₄ H ₉ NH ₃ ⁺ ions. Subsequent washing with water causes foaming. Foaming of vermiculite leads to intensive splitting of particles to obtain a superthin suspension with a particle size of vermiculite less than 50 microns.

The disadvantages of these materials include the fact that harmful organic substances are used in the processing of vermiculite, which worsens the environmental situation.

By gas foamed vermiculite is meant vermiculite foamed with gas.

Gas can be generated thermally and in this case the product is called "thermally foamed vermiculite." It can be obtained by quickly heating mineral vermiculite at 750-1000 ° C. At this temperature, water (free and bound) in vermiculite quickly evaporates and ionic forces repel silicate layers from each other, from which the starting material is formed. Thus, the expansion of vermiculite is achieved 10-20 times perpendicular to the plane of the layers. In this case, the formed granules have a chemical composition that is almost identical to the composition of the raw material (except for the loss of water).

Gas-foamed vermiculite can also be obtained by treating the vermiculite raw material with a liquid chemical, for example hydrogen peroxide, which penetrates between the silicate layers, and then gas (oxygen) is released during its decomposition, which causes the decomposition of vermiculite.

Chemically foamed vermiculite sealing materials are manufactured by Flexitallic Ltd under the trademark Termiculite and Victor Reinz under the trademark Xtreme®.

Flexitallic material compositions typically contain a fibrous component in the form of, for example, mineral fiber, a rubber component, and chemically foamed vermiculite (see, for example, WO 2006075149 (A1)).

A method of obtaining these materials involves obtaining a mixture of chemically foamed vermiculite and the fibrous component in the form of a wet paste and subsequent calendering of the paste.

To date, these materials have had the best range of consumer properties, and the temperature of use of such sealing materials is up to 980 ° C.

Sealing materials based on gas foam vermiculite are not as widespread as materials based on chemically foamed vermiculite, however, these materials are also presented in patent documents.

So, in the international publication WO 8001576 disclosed sheet sealing material, which is the closest to the claimed and used in high-temperature seals. The material includes 1-30 wt.% Organic fibers, 70-99 wt.% A mixture of foamed vermiculite with an inorganic filler (for example, glass fiber) with a particle size of this mixture from 45 to 180 microns and 3-30 wt.% Binder. The content of foamed vermiculite in the mixture is from 25-70% (optimally 25-35%), and various rubbers can be used as a binder, including natural rubber, acrylonitrile rubber and styrene butadiene rubber, as well as phenolic resins.

Gas-foamed vermiculite was obtained using the traditional foaming technology - vermiculite is heated to 650 ° C, which causes evaporation of water from interplanar cavities and splitting of vermiculite.

Sealing material is obtained by mixing all components in calculated amounts with water in a pulp. A paper is obtained from the pulp by papermaking technology, which is dried, and then passed through a calender to obtain the resulting sealing sheet material with a given density.

The disadvantages of this technical solution include the use of organic fibers, which significantly limits the temperature range of application of the claimed sealing material due to the rapid thermal degradation of the fibers at high temperature and, as a result, a significant loss of their reinforcing ability, as well as low elastic properties inherent in traditional gas-foam vermiculite.

The objective of the invention is to eliminate the inherent disadvantages of the known technical solution.

The problem is solved by high-temperature sealing material, including inorganic fiber, rubber and foamed vermiculite, according to which it contains foamed vermiculite with a bulk density of 28 g / l to 80 g / l, obtained by treating the original vermiculite with hydrogen peroxide with concentrations of at least 35 % and additionally contains low molecular weight polyisobutylene in the following ratio of components, wt.%:

Inorganic fiber 20-40 Rubber 3-12 Low molecular weight polyisobutylene 0.1-1.0 Foamed Vermiculite Rest.

In private embodiments of the invention, the problem is solved by a material that additionally contains 2.0-5.0 wt.% Phenol-formaldehyde epoxy

The material may also optionally contain 1.0-3.0 wt.% Rosin.

In other embodiments of the invention, the material as an inorganic fiber contains silica and / or kaolin fiber.

The material according to claim 1, characterized in that it contains foamed vermiculite obtained from the original vermiculite with a particle size of from 0.5 to 2.0 mm

The material may be made in the form of a sheet.

The material can be made in the form of a sheet laminated at least on one side with a protective layer of heat-resistant metal or metal alloy.

In this case, it is most desirable that the protective layer be made of a perforated sheet or stainless steel mesh.

The problem is also solved by the method of obtaining high-temperature sealing material, in accordance with which foamed vermiculite with a bulk density of from 20 to 80 g / l and a particle size of from 0.5 to 2 mm is mixed with water to obtain the first mixture, rosin, rubber and low molecular weight polyisobutylene mixed to obtain a second mixture, then the first and second mixtures are combined and mixed to obtain the resulting mixture, the resulting resulting mixture is dried, and then the material is formed from it

In particular embodiments of the invention, the material is extruded.

In other particular embodiments of the invention, the material is formed by rolling.

In the latter case, it is advisable to carry out rolling in a roll calendar.

The invention consists in the following.

The choice of the basis of the sealing material for foamed vermiculite with a density of 20-80 g / l, obtained by treating the initial vermiculite with hydrogen peroxide from concentrations of at least 35% (the optimal concentration range is 45-50%) due to the following. Vermiculite during its treatment with concentrated hydrogen peroxide increases in volume by 25-43 times, and its density immediately after processing and foaming is not more than 30 g / l (see RU 2296725). This vermiculite is characterized by high values of specific surface area and, as a consequence, greater ability to penetrate the polymer binder into the interlayer spaces of vermiculite, which provides the best elastic and strength properties of the claimed material. During the storage of such vermiculite, its density may increase by 10-20% due to moisture, but the features of its structure are preserved.

Table 1 shows data on the dependence of elastic properties on the bulk density of gas-foamed vermiculite (densities of more than 80 g / l were obtained on thermally foamed vermiculite). As follows from the data presented, the declared densities of gas-foamed vermiculite demonstrate the best values of elasticity

It is desirable that the particle size of the original vermiculite, which is exposed to concentrated hydrogen peroxide, be from 0.5 to 2 mm, since the use of vermiculite with larger particles reduces the strength of the sealing material, the use of smaller fractions is impractical from the point of view of the technology for producing the sealing material, because grades with a particle size of less than 0.5 mm are not commercially available, and their preparation requires a separate technological stage

To increase the elastic properties (recoverability) of the developed material, chopped inorganic fiber was used.

Table 2 shows data on the dependence of elastic properties on the content of inorganic fibers. As follows from the presented data, the content of inorganic fibers in the material should be from 20 to 40%, which, in combination with gas-foamed vermiculite with the claimed density, allows to obtain the best elastic properties.

It is most advisable to use silica and kaolin fibers as a fibrous filler, due to their availability.

The binder of the present invention is rubber.

As rubber, both natural rubber and styrene butadiene, nitrile butadiene, polyfluorosiloxane rubbers can be used.

Table 3 shows the data on the dependence of the sealing properties on the rubber grade at the optimum bulk density of gas-foam vermiculite.

As follows from the above data, the composition of the rubber is not critical, it is important that its content meets the declared.

With a rubber content of less than 3 wt.%, The integrity of the material is lost (strength decreases), and with a content of more than 12 wt.%, The efficiency of using the sealing material at high temperatures is reduced due to the compensation of the increase in the elastic properties by a significant loss in mass of the material due to thermal degradation of the polymer (void formation, material strength).

The composition contains low molecular weight polyisobutylene, which together with rubber improves the integrity of the sealing material, increases its bending strength, as well as crack resistance. If you go beyond the declared limits of the content of low molecular weight polyisobutylene, these properties fall.

It is extremely important for the implementation of the invention is the fact that the technical result can be achieved only if all of the claimed components are within the stated limits, since only together all of these components realize their functions.

As an optional additive to improve the creep resistance of the material, rosin in an amount of 1 to 3% by weight and / or phenol-formaldehyde resin is introduced into the material formulation, which helps to maintain the shape of the gaskets of the claimed material during operation at high temperatures. An increase in the content of these components in excess of the declared leads to an increase in this effect, and a decrease in the content below the declared values does not allow to achieve this effect.

The material in accordance with this composition can be obtained in the form of sheet material.

To prepare it, two mixtures are prepared, the first of which is a mixture of foamed vermiculite and fiber with water, and the second is a solution of rubber and polyisobutylene in an acceptable solvent. Then both mixtures are mixed, and sheet material is formed from the resulting mixture.

The sheet material can be molded in two stages - at the first stage receive on some media, for example on a plastic sheet, a flat blank, which is dried to such an extent that it could not spread during subsequent molding, which is carried out by pressing or rolling.

Rolling is possible both in a traditional rolling mill and in calender rolls.

In some cases, it is advisable to clad the declared sheet material with a metal material in order to further protect the surface from mechanical stress and high-temperature oxidation.

In the latter case, it is advisable to use some heat-resistant metal or alloy. The most available for creating a protective layer is stainless steel.

In this case, the dried billet is placed on a perforated stainless steel sheet and they are jointly rolled or pressed. Perforation provides better adhesion of the elastic sheet and steel due to the protruding edges of the holes.

An example embodiment of the invention.

At room temperature, 59 g of chemically foamed vermiculite of grade 60 and 29 g of silica fiber were added to 180 ml of water with continuous stirring, the mixture was stirred for 0.5 h. A previously prepared second mixture of 6 g was added to the resulting mixture at room temperature with vigorous stirring. natural rubber, 0.7 g of low molecular weight polyisobutylene of grade P 20.3.7 g of resin of grade 101 K and 1.6 g of rosin dissolved in 40 ml of nefras. The resulting mixture was stirred to homogeneity for 0.5 h, dried to a state in which the resulting mixture could be pressed and placed in a mold with a diameter of 8 cm. Then, pressing was performed at a pressure of 2.0 atm. The molded mass was placed in a drying oven and dried to constant mass at a temperature of 80 ° C (for ~ 1 h).

Table 4 shows the compositions of the material prepared in accordance with this example, as well as other compositions of the material, and in table 5 - the resulting properties.

As follows from the above data, it has good sealing properties: compressibility 35-46%, recoverability from 12 to 16%, maximum operating temperature - 1100 ° C, which exceeds the properties of the best foreign analogues (sealing material "Thermiculite 815" by Flexitallic, Ltd : compressibility 33-42%, recoverability from 10 to 13%, maximum working temperature - 950-980 ° С).

Table 1. No. The density of gas foam vermiculite, g / l Compressibility,% Recover
bridge,% Elasticity,% Note one 140 - - - No continuity 2 120 21 four 2,5 Low strength 3 80 * 31 10 4.8 Moderate strength four 60 * 47 7 4,5 Moderate strength 5 40 * 57 3 4.0 Moderate strength twenty* 60 3 4.1 Moderate strength * treatment for foaming with hydrogen peroxide with a concentration of from 35 to 5%

table 2 No. The density of gas foam vermiculite, g / l Type of fiber Containing
dragging
by wt.% Compressibility,% Recover
bridge,% Elasticity,% one 80 Kaolin twenty 22 twenty 5 2 60 Kaolin 25 46 9 6 3 60 Kaolin 33 35 fourteen 6 four 60 Kaolin 60 23 eighteen 5 5 60 Silica 25 48 eleven 7 6 60 Silica 33 41 fourteen 9 60 Silica 40 40 fourteen 9

Table 3 No. Chemically Foamed Vermiculite Density Type of polymer The polymer content, wt.% Compressibility,% Recovery,% Elasticity,% one Brand 60 Natural rubber 6 40 12 8 2 Brand 60 Styrene butadiene rubber 6 38 fourteen 8 3 Brand 60 Natural rubber 10 34 19 10 four Brand 60 Styrene butadiene rubber 10 32 22 10 Note: silica fiber was used in the samples, the ratio of foamed vermiculite - fiber 2: 1 by weight.

Table 4 Component Name Composition,% by weight one 2 3 four Silica fiber 29th twenty - - Kaolin fiber - twenty 40 25 Natural rubber 6 - - - Styrene butadiene rubber - 3 - - Nitrile butadiene rubber - - 6 12 Low molecular weight polyisobutylene P 20 0.7 0.1 1,0 0.5 Phenolic resin 101 K 3,7 - - 5,0 Rosin 1,6 - 3.0 - Gas-foamed vermiculite with a density of 60 g / l rest

Table 5 Material Composition Material properties Compressibility,% Rebuilt
rentability,% Upru
the guest, % Tensile strength, MPa Density, g / cm ³ Thickness Mach working tempera
the tour Chemical resistance, pH one 41 12 9.0 1.3 1,0 1.4 1100 1-14 2 39 fourteen 8.5 1.5 1.1 1.4 1100 1-14 3 37 fifteen 8.7 1.7 1.1 1.4 1100 1-14 four 40 13 9.0 1.4 1.2 1.4 1100 1-14

Claims (14)

1. High-temperature sealing material, including inorganic fiber, rubber and foamed vermiculite, characterized in that it contains foamed vermiculite with a bulk density of 28 g / l to 80 g / l, obtained by treating the original vermiculite with hydrogen peroxide at a concentration of not less than 35% and additionally contains low molecular weight polyisobutylene in the following ratio of components, wt.%:
Inorganic fiber 20-40 Rubber 3-12 Low molecular weight polyisobutylene 0.1-1.0 Foamed Vermiculite Rest 2. The material according to claim 1, characterized in that it further comprises 2.0-5.0 wt.% Phenol-formaldehyde resin. 3. The material according to claim 1, characterized in that it further comprises 1.0-3.0 wt.% Rosin. 4. The material according to claim 1, characterized in that the inorganic fiber contains silica and / or kaolin fiber. 5. The material according to claim 1, characterized in that it contains foamed vermiculite obtained from the original vermiculite with a particle size of from 0.5 to 2.0 mm 6. The material according to claim 1, characterized in that it is made in the form of a sheet. 7. The material according to claim 4, characterized in that it is made in the form of a sheet laminated at least on one side with a protective layer of heat-resistant metal or metal alloy. 8. The material according to claim 7, characterized in that the protective layer is made of perforated sheet or stainless steel mesh. 9. A method of obtaining a high-temperature sealing material in accordance with any of the preceding claims 1 to 8, characterized in that foamed vermiculite with a bulk density of from 20 to 80 g / l, obtained by treating the original vermiculite with hydrogen peroxide with concentrations of at least 38%, mixed with inorganic fiber and water to obtain a first mixture, rubber and low molecular weight polyisobutylene are mixed to obtain a second mixture, then the first and second mixtures are combined and mixed to obtain the resulting mixture, from which mold the material. 10. The method according to claim 9, characterized in that in the process of obtaining the second mixture, novolac phenolic resin and / or rosin are additionally added. 11. The method according to claim 9, characterized in that the material is molded at 120-200 ° C. 12. The method according to claim 9, characterized in that the material is molded by pressing. 13. The method according to claim 9, characterized in that the material is formed by rolling. 14. The method according to item 13, wherein the rolling is carried out in a roll calender.