CS245693B1 - Asbestos-free friction material - Google Patents

Abstract

The solution relates to asbestos-free friction material, especially for dry work of synthetic resins, refractory fibers and a silicon carbide micropowder.

Description

(54) Asbestos-free friction material

The present invention relates to an asbestos-free friction material, in particular for dry working, consisting of synthetic resins, refractory fibers containing alumina and silicon carbide micro-powders.

The object of the invention is to provide an asbestos-free friction material, particularly suitable for working with and dry with the opposite friction surface.

Known friction materials represent a complex complex in approximate composition by weight%:

up to 50% chrysolite asbestos cl. 4 to 6 to 40% inorganic fillers powdered materials (limestone, kaolin, barite) powdered oxides (ferric, aluminum) and carbides (silicon) up to 15% organic fillers - friction powder (fine grain condensed resin) up to 20 16 metal fillers - powder , fine granules, machining chips (iron, brass, aluminum) up to 25% organic binder - resin (usually phenol-formaldehyde) and rubber with sieving resp. vulcanization (usually by a sulfur system).

Asbestos fibers form on the one hand and the organic · resin · binder · the backbone, on the other hand act as a filler and thus contribute to the frictional properties of the whole.

Their advantage is high thermal stability desirable in friction segments, especially disc brakes. The inorganic fillers also have the character of glidants to prevent seizure and undesirable increase in the abrasiveness of the friction material.

Organic fillers are predetermined as additives increasing and stabilizing the coefficient of friction.

Metal fillers are used for rapid heat dissipation so as to avoid enormous temperature increases on the contact surface due to the high insulating properties of the asbestos fibers, whereby the temperature gradient to the subsurface layer achieves undesirable values leading to disruption of the lining surface and cracking due to exceeding the resistance of organic binder. Maintaining the necessary mechanical properties, high coefficient (friction and acceptable abrasion resistance at the lowest possible abrasiveness) is a matter of selecting individual components and harmonizing their relative proportions.

A disadvantage of current asbestos friction materials is the discovery that sprayed asbestos particles from worn linings pollute the environment and have carcinogenic effects. per human population. There is a greater risk for workers in mining, industry, friction production, but above all in repair and service centers for long-term use (work and brake units adhering to the asbestos particle). For these reasons, in many industrialized countries around the world Another serious adverse event is the rapidly declining reserves of natural asbestos in the world and their mining, and at the same time incurring costs, while maintaining the current consumption trend, the remaining reserves are estimated to be several decades.

A significant disadvantage of the existing types of friction asbestos materials, especially as brake linings, is the presence of non-ferrous metal particles which are released from the linings during braking, by mechanical pressure of the linings on the brake cast iron disk. These then significantly accelerate the depth corrosion of the brake discs, especially in winter, when air humidity and deteriorated operating conditions due to chemical scattering agents cause an inorganic electrolyte aerosol to enter the brakes, causing internal electrolysis of the material on said local galvanic cells.

A number of solutions have already been proposed to overcome the shortcomings of asbestos fiber materials. For example, known asbestos-free friction materials using carbon fibers are known. These fibers are characterized by high heat resistance with unchanged basic physical properties. This solution, although relatively one of the most widely used, has the drawback of using carbon fibers, which are technologically demanding and expensive to manufacture.

Also known are embodiments replacing asbestos fibers with plastic, steel or combinations thereof.

The advantage of all these solutions is the formation of the friction material support frame, however, as the asbestos fibers also have frictional properties, as they have the disadvantage that the friction materials thus produced do not fully achieve the properties of the asbestos and the stability of the friction coefficient regardless of temperature.

It is an object of the invention to provide an asbestos-free friction material with high utility properties.

The present invention provides a non-asbestos-based synthetic resin friction material containing 20 to 30% by weight of alumina refractory fibers in combination with 20 to 40% haotmoati microparticle of silicon carbide having a particle size of up to 10 µm. The alumina refractory fibers resist high temperatures with unchanged strength.

According to the invention, the use of these fibers also provides for the substitution of asbestos fibers, the micro-powder and the silicon carbide, to increase and stabilize the coefficient of friction and to replace the additives of the metal particles. The particle size of the micropowder with particles up to 10 µm ensures greater homogeneity of the material and resistance to release of the filler from the material.

The advantage of combining alumina-based fibers with silicon carbide micro-powders as a filler is the high and stable friction coefficient value and good thermal conductivity that provides desirable heat dissipation from the contact friction zone. This additive also replaces metal fillers, increases thermal conductivity, stabilizes the coefficient of friction to an acceptable high value in the absence of asbestos fibers, and worn particles are completely inert to the formation and course of corrosion.

Further advantages of this friction material are sufficient strength, good abrasion resistance and also low abrasiveness. These properties are assured under both short and long term thermal loads, on the one hand alumina-based fibers, which form a sufficiently strong skeleton adequate to the asbestos fibers, and on the other hand contain silicon carbide micro-powder, which positively affects the friction process.

The method of producing the proposed material is essentially the same as that used in the manufacture of asbestos friction linings.

An exemplary selection of a base fiber skeleton and other ingredients includes the following composition by weight:

2 & up to 30% alumina fibers up to 40% silicon carbide micropowder size 10/7 µm up to 20% inorganic filler (limestone powder, barite, kaolin, alumina, iron oxide) up to 35% binder - phenol-formaldehyde resin powder up to 4% graphite, ie glidants up to 3% plasticizer (eg ethyl alcohol)

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Within the abovementioned ranges of contents of the individual components, the abrasive and friction characteristics of the resulting friction material can be slightly modified.

The friction material according to the invention is described in connection with the use as a brake lining of the friction pads of disc brakes. Obviously, the same effect of replacing asbestos fibers with alumina can be achieved in brake linings intended for drum brakes or other types of friction materials, e.g. in clutch linings.

Claims (1)

OBJECT OF THE INVENTION Asbestos-free friction material with a high coefficient of friction, in particular for dry friction, consisting of synthetic resins with a backbone of refractory inorganic fibers and a filler, characterized in that it contains 20 to 30% by weight of alumina-based fibers and 20 to 40% silicon carbide micro-powder With particle sizes up to 10 fxa.