JP2551170B2 - Friction material and heat treatment method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a friction material containing metal fibers, and particularly to a friction material suitable for improving the fade resistance of a brake pad for an automobile, and a friction material. The heat treatment method of

<< Prior Art >> Conventionally, a brake pad for an automobile uses a friction material in which a metal fiber, a glass fiber, a ceramic fiber or the like is used as a base material and a filler and a binder are mixed with the base material.

The heat treatment method for this friction material is 400 to 1 in a non-oxidizing atmosphere.
Heat treatment is performed under the heat treatment condition of 000 ° C to partially carbonize the binder of thermosetting resin, preferably phenol resin, and form a thermally stable carbon-based substance with a small amount of decomposition products at high temperature. There is a way to do it.

According to this heat treatment method, it is possible to eliminate the cause of the reduction of the friction coefficient of the friction material and prevent the phenomenon of the reduction of the braking force due to the deterioration of the friction material at high temperature and high load, that is, the so-called fade phenomenon from occurring. Further, this heat treatment method reduces the generation of squeal during braking at low speed and enhances the friction characteristics at high temperature (see Japanese Patent Laid-Open No. 59-113038).

<Problems to be Solved by the Invention> However, when the resin mold disc brake pad is heat-treated in a non-oxidizing atmosphere, the metal fiber as the base material is deteriorated by the heat, so that the strength of the friction material is lowered. .

In order to solve such a problem, an object of the present invention is to provide a friction material having excellent mechanical strength and fade resistance, and a heat treatment method thereof.

<< Means for Solving the Problems >> In order to achieve the above object, the invention of claim 1 mixes metal fiber, a filler such as graphite and inorganic powder, and a binder made of a thermosetting resin such as phenol resin. Then, the molded body is subjected to a heat treatment in a low oxygen concentration field with an oxygen concentration of 0.1% to 10% at a temperature of 250 ° C or higher and lower than 1250 ° C and a treatment time of 15 minutes or longer and lower than 4 hours. Characterize.

Further, the invention of claim 3 is such that after the metal fiber, the filler such as graphite and inorganic powder and the binder made of thermosetting resin such as phenol resin are mixed and molded, the oxygen concentration is 0.1% to 10%. In the low oxygen concentration field of 250 ℃ or more 1250 ℃
And the heat treatment is performed by setting the treatment time to 15 minutes or more and less than 4 hours.

Further, the inventions of claims 2 and 4 are characterized in that, in the inventions of claims 1 and 3, the metal fibers are steel fibers.

The metal fibers according to the invention of claims 1 and 3 are materials used for conventional friction materials, for example, steel fibers, aluminum fibers,
The base material is a copper fiber, a brass fiber, a zinc fiber, a nickel fiber, a chromium fiber, or the like, and a metal fiber whose strength is increased by oxidation. On this base material, graphite, a filler with inorganic powder,
A phenolic resin, NBR, or other thermosetting resin binder is mixed and molded, and this molded body is used as a friction material before heat treatment. Then, this friction material is subjected to heat treatment in a low oxygen concentration field of 0.1-10% oxygen concentration with a treatment temperature condition of 250 ° C. or higher and less than 1250 ° C.

By such a method, during the heat treatment, the friction material is reinforced by the oxide film due to the oxidation reaction of the base fiber of the friction material, so that the carbonization of the binder will proceed without deterioration of the fiber. .

Accordingly, in the inventions of claims 1 and 3, since the oxide film is formed around the metal fiber as a reinforcing material, the mechanical strength is excellent, and the thermosetting resin is partially carbonized to improve the high resistance. A friction material having a fade property and a heat treatment method thereof are obtained.

In addition, in the inventions of claims 2 and 4, since the steel fiber is used as the metal fiber, the friction coefficient of the friction material is stable under high temperature conditions.

Example An example of the friction material and the heat treatment method thereof according to the present invention will be described below.

First, a steel fiber as a base material, a phenol resin as a binder, graphite and other fillers were compounded according to the volume ratio (%) shown in the table, and this was uniformly kneaded.

Next, the above-mentioned composite material was filled in a mold and compression-molded at a temperature of 150 ° C. and a pressure of 500 kg / cm ² . The obtained molded product was subjected to after-curing under predetermined conditions at 200 ° C. for 4 hours. In this case, the oxygen concentration set as the heat treatment condition for the friction material is 0.1% or more and less than 10%, more preferably 1% or more and 5%.
Less than was optimal.

Treatment temperature is 250 ℃ or more and less than 1250 ℃, more preferably 350
Optimally, the temperature is not less than 800 ° C and less than 800 ° C, and the treatment time is less than 4 hours, more preferably 30 minutes or more and 2 hours or less.

Here, the oxygen concentration, which is the set temperature, is 0.1% or more 10
The reason for setting the content to be less than 10% is that when the oxygen concentration exceeds 10%, the oxidation reaction of the phenol resin, which is the binder, begins to occur remarkably and the strength of the friction material becomes weak. On the other hand, the oxygen concentration is 0.1%
This is because in the following cases, the oxidation reaction on the surface of the steel fiber occurs only slightly and it becomes impossible to improve the strength.

In addition, the reason why the treatment temperature is set to 250 ° C or higher and lower than 1250 ° C is that if the temperature exceeds 1250 ° C, the phenol resin undergoes rapid thermal decomposition, so the gas generated inside the friction material cannot escape to the outside, causing blisters and cracks. It tends to occur. On the other hand, if the temperature is 250 ° C. or lower, even if the heat treatment is carried out for a long time of 4 hours or more, the phenol resin as the binder is only slightly thermally decomposed, and it becomes impossible to improve the fade resistance.

Furthermore, the reason why the treatment time is set to less than 4 hours is that even if the treatment is performed for 4 hours or more, qualitative changes in the treated portion hardly occur.

In the above examples, in order to confirm the effect of improving the strength of the friction material, as a specific example thereof, the oxygen concentration is from 0% to 21%.
%, A heat treatment temperature of 400 ° C., a heat treatment time of 1 hour, the characteristics of the friction pads of the disc brake were examined. As a result, the relationship shown in FIG. 1 was obtained between the oxygen concentration and the bending strength. As is clear from FIG. 1, the friction pad treated in the oxygen concentration range of 1% to 10% has higher bending strength and lower oxygen content than the friction pad treated in the non-oxidizing atmosphere (oxygen concentration 0%). The strength improvement due to the heat treatment effect in the concentration field was fully demonstrated.

Furthermore, in order to confirm the effect of improving the fade resistance,
As a specific example, the heat treatment temperature in a 5% oxygen concentration field
The characteristics of the friction pad which was heat-treated at 400 ° C. for 1 hour was examined.

This heat-treated friction pad is used as JASO C 406-82.
Based on the above, a relationship as shown in FIG. 2 was obtained between the friction coefficient and the number of brakings when continuously braking every 35 seconds.
A curve A in this figure shows the characteristic of the specific example subjected to the heat treatment, and a curve B shows the characteristic of the conventional example of the ordinary heat treated product, that is, the characteristic of the heat treated at 200 ° C. for 4 hours in air. .

The curve A has a stable friction coefficient of 0.43 with respect to the initial wear when the number of braking times n is 10 or less, and shows a remarkable difference as compared with the curve B. That is, it was proved that the fade resistance due to the heat treatment effect in the example of the curve A was sufficiently higher than that of the conventional example of the curve B.

<< Effects of the Invention >> As is clear from the above description, according to the inventions of claims 1 and 3, by oxidizing the atmosphere during the heat treatment of the friction material, the atmosphere is reduced to oxidize the surface of the metal fiber. Since the film is formed, the metal fiber is reinforced, the strength of the friction material is improved, and the thermal decomposition of the binder at high temperature is carbonized in advance by heat treatment, thereby providing a friction material having excellent fade resistance and a heat treatment method thereof. Can be obtained.

Further, according to the inventions of claims 2 and 4, since the steel fiber is used as the metal fiber, the friction coefficient of the friction material is stabilized particularly at a high temperature, and the friction material is resistant to sudden braking from a high speed. It is possible to suppress the ignition phenomenon due to the pyrolysis gas generated during braking without lowering the coefficient, and further it is possible to prevent squeaking during braking.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between bending strength and oxygen concentration in a heat treatment atmosphere of a friction material in an example of the present invention, FIG.
The figure is a characteristic diagram showing the relationship of the friction coefficient with respect to the number of braking times of the friction material in the present example and the conventional example.

Claims (4)

(57) [Claims] 1. A metal fiber, a filler such as graphite or inorganic powder, and a binder made of a thermosetting resin such as phenol resin are mixed and molded, and the molded body is reduced in oxygen concentration from 0.1% to 10%. A friction material characterized by performing heat treatment at a temperature of 250 ° C or higher and lower than 1250 ° C and a treatment time of 15 minutes or longer and shorter than 4 hours in an oxygen concentration field. 2. The friction material according to claim 1, wherein the metal fiber is a steel fiber. 3. A metal fiber, a filler such as graphite or inorganic powder, and a binder made of a thermosetting resin such as a phenol resin are mixed and molded, and then this is mixed with a low oxygen concentration of 0.1% to 10%. A heat treatment method for a friction material, which comprises performing heat treatment at a temperature of 250 ° C or higher and lower than 1250 ° C and a treatment time of 15 minutes or longer and shorter than 4 hours. 4. The heat treatment method for a friction material according to claim 3, wherein the metal fiber is a steel fiber.