RU2269550C2 - Composition for preparing composite sealing material - Google Patents

Abstract

FIELD: polymer materials.

SUBSTANCE: invention relates to polymeric materials science and is designed for use in mechanical engineering, in particular in compressor engineering and vacuum mechanical engineering to manufacture sealing articles for static and mobile sealants. Composition comprising polytetrafluoroethylene and carbon-containing filler further contains nano-dispersed modifier selected from group consisting of sodium titanate, ultradispersed ceramics, and carbon-containing detonation synthesis product, and also fluorine-containing oligomer.

EFFECT: increased wear resistance of composite, increased strength, reduced imperfection, and reduced coefficient of friction when operated without lubricant.

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Description

The invention relates to polymer materials science and can be used in mechanical engineering, in particular compressor engineering and vacuum engineering, for the manufacture of sealing products for static and mobile (tribotechnical) seals.

Composite sealing materials based on polytetrafluoroethylene (PTFE) are known that are used for the manufacture of sealing parts for technological equipment - vacuum equipment, equipment for chemical production, etc. Due to the unique combination of strength, thermophysical, and other service characteristics, polytetrafluoroethylene is widely used as a sealing material for fixed sealing units. To ensure its high wear resistance, various fillers and modifiers are introduced into the composition of PTFE. The most widely used as fillers for PTFE are powdered particles of metal oxides, silicates, graphite, molybdenum disulfate, etc. with sizes of 10-100 microns [1]. The introduction of fillers can significantly increase the wear resistance of PTFE, increase its hardness, strength, which ensures an increase in the operational range of application.

However, along with an increase in wear resistance and strength, materials based on PTFE and dispersed nanofillers have increased porosity, which reduces the effectiveness of their use for the manufacture of sealing products. This is due to the poor wettability of the filler surface with a highly viscous polymer melt. In this regard, one of the leading trends in the development of sealing materials is the decrease in the number of fillers. Low-filled compositions contain no more than 5 wt% fillers, therefore, they have less defectiveness with a sufficiently high wear resistance [1]. However, such materials have relatively low strength and deformation characteristics.

The prototype of the invention is a composite material based on PTFE containing carbon-graphite fiber (10-40 wt.%) And dry lubricant (1-5 wt.%) As a functional filler. Such materials are commercially available under the trademark "Flubon" [2]. The materials of "Flubon" have a wear resistance that exceeds the wear resistance of the original polytetrafluoroethylene more than 100 times.

The disadvantages of the prototype are insufficient high wear resistance in combination with the defectiveness of products made of composite material, a relatively high coefficient of friction, especially when operating the sealing assembly without lubricant.

The objective of the invention is to increase the wear resistance of the composite material; increased strength and reduced defectiveness; reduction of the coefficient of friction during operation without lubrication.

The problem is solved in that the composition for producing a composite sealing material, including polytetrafluoroethylene and a carbon-containing filler, further comprises a nanodispersed modifier selected from the group comprising sodium titanate or ultrafine ceramic Sialon, or a carbon-containing detonation synthesis product, and additionally contains a fluorine-containing oligomer of the Epil brand "or" Foleox "in the following ratio of components, wt.%:

specified nanodispersed modifier 0.01-0.1 the specified fluorine-containing oligomer 0.1-1.0 carbon filler 1,0-40,0 polytetrafluoroethylene rest

The invention consists in the following. Treatment of the carbon fiber filler with a fluorine-containing oligomer of the Epilam or Foleox brand leads to an increase in the strength and heat resistance of single monofilaments. As a result of this, when the fiber is dismembered, a fraction is formed predominantly, which provides the optimal combination of physicomechanical and tribological characteristics of the material. In addition, the oligomeric component chemisorbed on the surface of the metal counterbody and contributes to the formation of a stable transferred layer, providing high wear resistance and low coefficient of friction of the material.

An additional introduction of nanodispersed carbon particles or other substances (sialons, titanates, etc.) into the polymer matrix ensures the formation of an ordered matrix structure by the polarization orientation mechanism. As a result of this, a significant increase in the strength and wear resistance of PTFE is observed. The effect is manifested in the claimed ratio of components. With an increase in the content of the nanomodifier over the declared limits, agglomeration of nanoparticles with the formation of defective low-strength regions in the composite is observed. A decrease in the content of the nanomodifier below the declared limits does not allow to obtain the structure of PTFE with optimal characteristics. A fluorine-containing oligomer, when exceeding the declared limits, plasticizes the polymer matrix, reducing its strength. When the oligomer content is less than the declared limit, the effect decreases, because no transferred film is formed on the counterbody. The molecular weight of the oligomer is in the range of 2000-5000 units. and structure do not significantly affect the properties of materials, because the mechanism of action of oligomers is the same.

Thus, the claimed composition to obtain a composite sealing material in the stated ratios of the components provides the optimal combination of physico-mechanical and tribotechnical characteristics, exceeding the similar combination of characteristics of the prototype.

The inventive material can be used for the manufacture of sealing parts (cuffs, gaskets, stuffing box packing, etc.) used in static and dynamic (tribological) systems.

Compositions for obtaining a composite sealing material of a specific implementation are presented in table 1.

As a polymer matrix, powdered polytetrafluoroethylene grade F-4 with a particle size of 50 ÷ -100 μm was used. The carbon-containing filler was carbon fiber of the Wiskum brand manufactured by Svetlogorsk Production Association “Khimvolokno” and colloidal graphite.

The carbon-containing detonation synthesis product (charge: 60% diamond and 40% graphite) manufactured by Sinta CJSC, ultrafine sialon ceramics (Si _6-x Al _x O _x N _8x , x = 0.8; 4.2) was used as a nanodispersed modifier ) and sodium titanate. The size of single nanodispersed particles ranged from 3-10 nm (charge) to 50-100 nm (sialons), and the clusters of these particles were 30-150 nm. The specific surface area of these particles was from 50 to 350 m ² / g.

As a component of the compositions used fluorine-containing oligomers sold under the trade names "Epilam" and "Foleoks", representing perfluorinated carboxylic acid or its derivatives. The oligomer "Epilam" has the structural formula:

Epilam grade 6SFK-180-05 or grade SFK-180-20 is produced according to TU 6-02-1229-82. They are a solution of perfluoric acid 6MFK-180 (TU 6-02-2-610-80) in freon 113 (GOST 23844-79). The concentration of the active substance in a solution of 0.5 and 2.0 wt.%, Respectively. The molecular weight of Epilam is 2194 units, the number of links n = 12.

The oligomer "Foleox" is produced according to TU 38.03.1.013,

Oligomers "Foleoks" of other brands F-2, F-3, F-6, F-8, F-14 are derivatives of perfluoric acid. The composition of the oligomer "Foleox" or "Epilam" (brand) does not fundamentally affect the properties of the composite material, because the purpose of this component is to plasticize the particles of the matrix.

Used diluted (0.5-2.0) solutions of oligomers in freon of the following grades F-1 (R _F -COOH), F-14 (R _F -R _F ), F-3 (R _F -CONH ₂ ), F -8 (R _F —COOH), F-6 (R _F —COOR), F-2 (R _F —COOCH ₃ ). The molecular weight of oligomers of the F-1, F-14, F-3, F-6, F-2 brands is 2200 units, and the F-8 brands are 5000 units. The above structural formulas apply to the Foleox fluorine-containing oligomers. Brands F-1, F-14 are issued in some cases under the trade name "Epilam". Fluorine-containing oligomers under the trademarks "Foleoks", "Epilam" are produced in the Russian Federation.

Currently, oligomers based on various solvents are produced - alcohols, water, freons, etc.

The technology for producing composite sealing materials of the claimed compositions and prototype is as follows.

Prototype. 200 g of viscometric carbon fiber type Viscum was pulverized in a dismembrator mill for. 20 minutes. The obtained filler, graphite and polytetrafluoroethylene grade F-4 in predetermined proportions were mixed for 30 minutes in a paddle mixer to obtain a homogeneous composition. Mixing quality was determined by bulk specific gravity.

The resulting material was processed using a two-stage technology. At the first stage, blanks were made by cold pressing at a specific pressure of 40-60 MPa. The obtained preforms were sintered in a heating cabinet in the temperature range 280-350 ° С for τ = (0.5 ÷ 1) а, where τ is the time in min and a is the thickness of the preform in mm The thickness of the preform was 40 mm, the sintering time was 40 minutes. After sintering, the preforms were cooled together with the furnace. Samples were prepared from the obtained blanks, which were tested for tensile strength, Brinell hardness, friction coefficient, and wear resistance. The tribotechnical test scheme is “finger-drive”. The disk is made of carbon steel St45 with a surface roughness after quenching and grinding of 0.8 ÷ 1.1 μm. Sliding speed 1 m / s; specific load 5-20 MPa.

The inventive compositions (options II-IV, VI, VII).

Carbon fiber type Viscum is dried at a temperature of 90 ± 5 ° C for 2 hours to remove moisture and low molecular weight components.

The dried fiber was treated with 2 wt% oligomer of the desired grade and composition. Then it was dried until the solvent was completely removed and ground in a disinfecting mill. The chopped fiber was mixed with powdered nanomodifier and polytetrafluoroethylene in paddle mixers. The finished composite material was processed into the product according to the modes similar to those of the prototype.

The characteristics of the composite sealing materials of the prototype and the claimed compositions are shown in table 2.

As follows from the data of table 2, the claimed compositions exceed the prototype in strength and tribological characteristics. In this case, the effect is retained for various types of nanomodifiers and fluorine-containing oligomers used.

Information sources.

1. A.A. Okhlopkova. Physicochemical principles for the development of tribotechnical materials based on polymers and ultrafine ceramics. Abstract. Diss.doc. Sciences, Gomel, 1999 - p. 25.

2. G.A.Sirenko. Antifriction carboplastics. Kiev. "Technics", 1985. - P.195 - prototype.

Claims (1)

Settling to obtain a composite sealing material, including polytetrafluoroethylene and a carbon-containing filler, characterized in that it further comprises a nanodispersed modifier selected from the group comprising sodium titanate or ultrafine ceramic Sialon, or a carbon-containing detonation synthesis product, and additionally contains an Epilam fluorine-containing oligomer or "Foleox" in the following ratio of components, wt.%: Specified nanodispersed modifier 0.01-0.1 The specified fluorine-containing oligomer 0.1-1.0 Carbon filler 1,0-40,0 Polytetrafluoroethylene Rest