JP2007107068A - Sintered friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered friction material which does not comprise chemical substances designated in the PRTR (Pollutant Release and Transfer Resister) Act, and is excellent in a friction coefficient, strength, wear resistance and performance upon breaking such as low attackability to the mating material. <P>SOLUTION: The sintered friction material uses a metallic material as a matrix and comprises a lubricant and abrasives. By the incorporation of either or both of an iron/aluminum composite material and an aluminum/alumina composite material as a component, aluminum is compounded into the surface of iron powder, and, by the composite material, the friction of the same kind between iron in the friction material and iron in the mating material (an iron based material, mainly, of common cast iron, low alloy steel and stainless steel) can be prevented. Then, by the compounding of fine alumina into aluminum, aluminum is thermally reinforced, so as to improve its thermal strength. Thus, the sintered friction material having improved wear resistance can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a brake friction material used in a braking device for automobiles, two-wheeled vehicles, railway vehicles, industrial machines and the like.

  Conventionally, as a sintered friction material for brakes, copper is the main component, and tin or sometimes a metal added with iron, nickel, zinc, antimony, chromium, lead, etc. is used as a base material, and alumina, mullite, zirconia, etc. Ceramic friction materials and sintered friction materials to which lubricants such as graphite and molybdenum disulfide are added are used. This kind of sintered friction material is heavier than resin-based friction material, is expensive, and has the points to be improved such as the possibility of generating brake noise. Even under low conditions, it does not cause fade phenomenon (a phenomenon in which the friction coefficient during braking is greatly reduced at high temperatures), provides stable performance, and has excellent strength and wear resistance. However, it has been widely used for brakes that require high friction performance.

  However, in recent years, the PRTR Law (Act on the Promotion of Improvement in Management and Management of Specific Chemical Substances Emissions from the Environmental Protection Perspective) has been enacted, and materials used as brake friction materials are also considered for environmental protection. However, it has been demanded not to use designated chemical substances stipulated by the law. However, among the materials used as raw materials for sintered friction materials so far, materials other than iron, ceramics, and graphite are set as designated chemical substances of the PRTR method, and it is hoped that they will not be used in the future. It is rare.

  Against this background, research and development have been carried out on sintered friction materials having a formulation that uses as little PRTR-designated chemical substances as possible. However, in the case of a sintered friction material mainly composed of an iron-based material without using copper or tin as the main component until now, the wear amount of the friction material due to brake braking or the counterpart material (for example, brake disc, mainly. There is a problem that the amount of wear of iron-based materials such as ordinary cast iron, low alloy steel, and stainless steel) greatly increases, and the required coefficient of friction cannot be ensured. In addition, materials such as aluminum, magnesium, and titanium that are not designated PRTR chemicals other than ferrous materials have many problems as the main components of sintered friction materials, and it is difficult to put sintered friction materials with excellent environmental protection into practical use. Met. The present applicant has invented an iron-based sintered friction material based on cast iron powder or reduced iron powder, and has obtained performance equivalent to that of a copper-based sintered friction material. However, it was found that the evaluation under high load conditions did not reach the same level as the copper-based sintered friction material.

  An example of a bronze-type dry sintered friction material that aims to stably obtain a high friction coefficient has been proposed (Patent Document 1). This dry-sintered friction material is 60-80% copper, 3-20% tin, 3-20% alumina and / or silica, 3-10% graphite, 1-5% molybdenum disulfide and 15 manganese. %, Which is composed as a matrix component, stabilizes the friction coefficient during braking, forms a hard copper oxide film on the surface by heat generation with the mating plate, water fading phenomenon and heat It has resistance to fading phenomenon and aims to obtain a stable friction surface. Alumina and silica are added for the purpose of withstanding high loads and high-temperature frictional sliding. Graphite and molybdenum disulfide are added for the purpose of improving lubricity. Manganese reduces and oxidizes oxide films of other metals during sintering. It is added for the purpose of improving the properties.

  Further, as another example of the sintered friction material, an iron-based sintered material having a perforated main body portion made of an iron-based sintered body and an alkaline substance in which an aqueous solution fixed in the hole of the main body portion exhibits alkalinity. A friction material has been proposed (Patent Document 2). The metal base material used as the skeleton of the friction material is a material mainly composed of iron, and can be a general iron-based metal such as stainless steel or cast iron, a mixture thereof, or a mixture with other metals. Examples of the lubricant include graphite and molybdenum disulfide.

As another example of the sintered friction material, a sintered friction material containing copper or a copper alloy as a matrix and containing 2 to 20% by weight of stabilized zirconia has been proposed (Patent Document 3). According to this sintered friction material, by adopting stabilized zirconia in copper-based or iron-based sintered friction material, adaptability to a wide range of braking conditions is good, a stable friction coefficient is obtained, and wear resistance is improved. We aim to obtain a sintered friction material that is good in heat resistance and heat resistance, and has little attack on the mating material.
Japanese Examined Patent Publication No. 63-15976 (second column, second line to fourth column, first line) JP 2002-181095 A (paragraphs [0022] to [0026]) Japanese Patent No. 2958493

  Therefore, as a raw material of the sintered friction material, not only hexavalent chromium compounds and nickel compounds which are specified first class designated chemical substances of PRTR method, but also first class designated chemical substances zinc, antimony, copper, tin, There is a problem to be solved in that it does not use any material such as lead, molybdenum, etc., and contributes to environmental protection, and the main component is iron-based material and aluminum is included in the form of a composite material to prevent the same kind of iron friction. is there.

  The object of the present invention is that it does not contain any PRTR-designated chemical substances, which is preferable in terms of environmental protection, and performance during braking, such as friction coefficient, strength, wear resistance, and low aggressiveness against the mating material. It is also to provide an excellent sintered friction material.

  The sintered friction material according to the present invention is a sintered friction material that includes a metal material as a matrix and includes a lubricant and an abrasive, and is composed of one or both of an iron / aluminum composite material and an aluminum / alumina composite material. Consists of including.

  This sintered friction material is based on a powder made of iron, here reduced iron, instead of a friction material mainly composed of conventional copper powder. Since the iron-based sintered friction material is the same material as the counterpart material such as a brake disk, the amount of wear tends to increase due to the same type of friction friction sliding when the brake is applied. In such a case, it is known that if a different material is interposed between the friction sliding surfaces, the function as a solid lubricant works and the amount of wear can be reduced. Then, aluminum is compounded on the iron powder surface by including one or both of an iron / aluminum composite material and an aluminum / alumina composite material as a component of the friction material. This composite material can prevent the same kind of friction between iron in the friction material and iron in the counterpart material (mainly iron-based material such as ordinary cast iron, low alloy steel, stainless steel, etc.).

  In this sintered friction material, the iron / aluminum composite material may contain 21 to 46 vol% reduced iron and 3 to 20 vol% aluminum, and the total content thereof may be 26 to 58 vol%. Since the main component is reduced iron powder having a high melting point, the friction characteristics at high temperatures are excellent.

  In the sintered friction material, when the iron / aluminum composite material is used, the aluminum content including aluminum in the iron / aluminum composite material can be 5 to 25 vol%.

  In this sintered friction material, the abrasive material contains 10 vol% or less of magnesia having an average particle diameter of 50 to 250 μm, and the total with alumina having an average particle diameter of 5 to 20 μm is 5 to 15 vol%, and graphite as the lubricant 30-45 vol% can be included. Magnesia is a ceramic that is an oxide of magnesium and not high hardness, and is blended for the purpose of ensuring a coefficient of friction without damaging the counterpart material. In the sintered friction material containing magnesia, alumina having a particle diameter of 5 to 20 μm may further be included as the grinding component. Since magnesia is a material with low hardness, alumina having higher hardness can be contained for the purpose of further ensuring a friction coefficient. In this case, since the particle size of alumina is smaller than the particle size of magnesia, it is possible to reduce the aggressiveness to the counterpart material.

  In the present sintered friction material, the aluminum / alumina composite material contains aluminum in an amount of 12 to 20 vol% and alumina in an amount of 2 to 8 vol%, and the total content thereof can be in a range of 18 to 22 vol%.

  In this sintered friction material, the abrasive material contains 10 vol% or less of magnesia having an average particle diameter of 50 to 250 μm, and the total with alumina having an average particle diameter of 5 to 20 μm is 5 to 15 vol%, and graphite as the lubricant 30-45 vol% can be included. Since magnesia is a material with low hardness, for the purpose of further ensuring a friction coefficient, alumina having higher hardness but smaller than the particle size of magnesia can be contained. In this case, since the particle size of alumina is smaller than the particle size of magnesia, it is possible to weaken the aggressiveness to the counterpart material. Furthermore, the graphite as the lubricant can be further reduced in attacking the counterpart material by containing a larger amount than usual.

  In the present sintered friction material, the total content of the iron / aluminum composite material 26 to 58 vol% and the aluminum / alumina composite material 18 to 22 vol% can be 40 to 65 vol%.

  In the sintered friction material, the abrasive contains 10 vol% or less of magnesia having an average particle size of 50 to 250 μm, and the total with alumina having an average particle size of 5 to 20 μm is 5 to 15 vol%, and graphite as the lubricant 30-45 vol% can be included.

Since the sintered friction material by this invention is comprised as mentioned above, there exist the following effects. First of all, the product of the present invention is mainly composed of an iron-based material, and the other compounding materials use aluminum for preventing the same kind of friction of iron, graphite for lubricant, and magnesia for abrasive. Since no chemical substance is used, this sintered friction material can provide an excellent friction material in terms of environmental protection.
Moreover, by using an iron / aluminum composite material, an aluminum thin film is formed at the friction interface, and iron in the friction material and iron in the counterpart material (mainly iron-based materials such as ordinary cast iron, low alloy steel, stainless steel, etc.). The same kind of friction between each other can be prevented. In particular, when iron-based material is reduced iron powder and aluminum is combined on the surface of reduced iron powder by heat treatment, this composite material can be used for iron in the friction material and the counterpart material (mainly ordinary cast iron, low alloy steel, stainless steel, etc.) The same kind of friction between irons in the iron-based material) can be prevented.
Moreover, in order to improve the heat resistance and wear resistance of aluminum contained in the composite material, the wear resistance is improved by using an alumina (Al2O3) composite material for the sintered friction material. That is, aluminum that prevents the same kind of friction of iron has a low melting point of 660 ° C. By combining high melting point fine alumina with MA (mechanical alloying), the heat resistance of aluminum can be improved. Since this composite material uniformly distributes the high melting point fine alumina inside the aluminum, the heat resistance strength of the aluminum can be improved efficiently.
Further, by using the iron / aluminum composite material and the aluminum / alumina composite material in combination, the wear resistance can be further improved compared to the use of each.

  Hereinafter, the sintered friction material according to the present invention will be described in more detail with reference to examples.

  First, magnesia powder having an average particle size of about 190 μm, fine alumina powder having an average particle size of about 12 μm and an average particle size of about 1.2 μm, natural graphite powder having an average particle size of about 170 μm, and an average particle size of about 240 μm. Of artificial graphite powder, reduced iron powder having an average particle size of about 160 μm, and aluminum powder having an average particle size of 22 μm. As a composite material, a material obtained by heat-treating aluminum powder to reduced iron powder and an average of aluminum powder A material made of MA made of fine alumina powder having a particle size of about 1.2 μm was prepared.

  Next, after weighing each of the above raw materials into the blend C shown in Table 1, 4% methanol was added to the mixture to prevent segregation at the time of mixing using a stirring crusher (made by Ishikawa Factory). And mixed for 10 minutes to prepare a mixed powder. In addition, the mixed powder of the copper-based sintered material A currently mass-produced as a comparative material and the mixed powder of the representative example B in which fine alumina is added to the base of reduced iron powder as invented by the present applicant Prepared.

  Further, each mixed powder is filled into a graphite mold having a cavity of 23 mm × 35 mm, and a discharge plasma sintering apparatus (manufactured by Sumitomo Coal Mining Co., Ltd., model SPS-515S) is used. Sintering was performed under conditions of a sintering temperature of 800 to 1150 ° C. and a holding time of 5 minutes. In addition, since A compound material is produced on the same conditions as mass production material, it sinters also with a batch-type sintering furnace (temperature increase rate 10-20 degreeC / min, pressurization 0.7MPa), and it is a discharge plasma sintering apparatus. Compared to the sintered one.

  After sintering, the relative density (apparent density of sintered body / percentage of true density of sintered body) and hardness of each sintered body were measured. In addition, a brake performance test was conducted to determine the friction coefficient, the friction material, and the wear amount of the counterpart material. The apparent density of the sintered body was calculated from the weight in the air and water, and the true density was calculated from the true density of the raw materials and the blending ratio. Hardness was measured on the S scale (HR.S) of a Rockwell hardness tester. The brake performance test was conducted using a 1/10 scale tester tester owned by our company.

Table 1 shows the sintering conditions, relative density, hardness and average friction coefficient in the brake performance test, and the wear amount of the friction material and the counterpart material. Samples of this example are indicated by sample symbols C1 to C5. The darker hatched part represents an iron / aluminum composite, and the thinner hatched part represents an aluminum / alumina composite.

Judging from the effect of blending on the friction test results, the appropriate ranges for each component were as follows.
The iron / aluminum composite material for preventing the same kind of friction between irons is in the range of reduced iron powder: 21-46 vol%, aluminum: 3-20 vol% (however, reduced iron powder + aluminum: 26-58 vol%). is there.
In this case, the blended powder is
Iron / aluminum composite: 26-58 vol%
Aluminum: 5 to 25 vol% (including aluminum in Fe / Al composite)
Fine alumina (average particle size: 0.3-2 μm): 2-7 vol%
(However, iron / aluminum composite material + aluminum + fine alumina: range of 28-60 vol%)
Magnesia (average particle size 50-250 μm): 0-10 vol%
Alumina (average particle size 5-20 μm): 2-10 vol%
(However, magnesia + alumina: in the range of 5-15 vol%)
Graphite: 30-45 vol%
Within this range, a sintered friction material with a small amount of wear between the friction material and the counterpart material can be obtained.

Moreover, the aluminum / alumina composite material for improving the heat resistance and wear resistance of aluminum is aluminum: 12-20 vol%, fine alumina: 2-8 vol% (however, aluminum + alumina: range of 18-22 vol%). It is a range.
In this case, the blended powder is
Aluminum / alumina composite: 18-22 vol%
Reduced iron: 26-53 vol%
Magnesia (average particle size 50-250 μm): 0-10 vol%
Alumina (average particle size 5-20 μm): 2-10 vol%
(However, magnesia + alumina: in the range of 5-15 vol%)
Graphite: 30-45 vol%
Within this range, a sintered friction material with a small amount of wear between the friction material and the counterpart material can be obtained.

Furthermore, when using both the above composite materials,
Iron / aluminum composite: 26-58 vol%
Aluminum / alumina composite: 18-22 vol%
(However, iron / aluminum composite material + aluminum / alumina composite material: range of 40 to 65 vol%)
Magnesia (average particle size 50-250 μm): 0-10 vol%
Alumina (average particle size 5-20 μm): 2-10 vol%
(However, magnesia + alumina: in the range of 5-15 vol%)
Graphite: 30-45 vol%
Range.

Claims (8)

  A sintered friction material comprising a metal material as a matrix and containing one or both of an iron / aluminum composite material and an aluminum / alumina composite material in a sintered friction material comprising a lubricant and an abrasive.   2. The sintered friction material according to claim 1, wherein the iron / aluminum composite material includes 21 to 46 vol% reduced iron and 3 to 20 vol% aluminum, and the total content thereof is 26 to 58 vol%.   The sintered friction material according to claim 2, wherein when the iron / aluminum composite material is used, the content of aluminum including aluminum in the iron / aluminum composite material is 5 to 25 vol%.   The abrasive contains 10 vol% or less of magnesia having an average particle size of 50 to 250 μm, and the total with alumina having an average particle size of 5 to 20 μm is 5 to 15 vol%, and contains 30 to 45 vol% of graphite as the lubricant. The sintered friction material according to claim 3, comprising:   The aluminum / alumina composite material comprises 12 to 20 vol% of aluminum and 2 to 8 vol% of fine alumina having an average particle diameter of 0.3 to 2 µm, and the total content thereof is 18 to 22 vol%. The sintered friction material described in 1.   The abrasive contains 10 vol% or less of magnesia having an average particle size of 50 to 250 μm, and the total with alumina having an average particle size of 5 to 20 μm is 5 to 15 vol%, and contains 30 to 45 vol% of graphite as the lubricant. The sintered friction material according to claim 5, comprising:   The sintered friction material according to claim 1, wherein the total content of the iron / aluminum composite material 26 to 58 vol% and the aluminum / alumina composite material 18 to 22 vol% is 40 to 65 vol%.   The abrasive contains 10 vol% or less of magnesia having an average particle size of 50 to 250 μm, and the total with alumina having an average particle size of 5 to 20 μm is 5 to 15 vol%, and contains 30 to 45 vol% of graphite as the lubricant. The sintered friction material according to claim 7, comprising: