JP2007107066A - 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 more excellent in a friction coefficient, strength, wear resistance and brake performance such as low attackability to the mating material using an iron based material as the main component. <P>SOLUTION: In the sintered friction material using a metallic material as a matrix and comprising a lubricant and abrasives, as the metallic material, reduced iron powder is used. The main component is iron based reduced iron powder, and the other blending materials are the lubricant and abrasives, thus a sintered friction material can be obtained without using chemical substances designated in the PRTR Act at all. Since the reduced iron powder which is soft because of its low carbon content is used as the metal main component composing the matrix to form into the skeleton of the sintered friction material, the sintered friction material excellent in the points of friction properties at high temperature and low attackability to the mating material can be obtained. Further, by interposing aluminum as a different kind of material between sliding faces, the reduction of the friction amount is achieved. <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 type of sintered friction material is heavier and more expensive than resin-based friction materials, and there are important improvements such as the possibility of brake noise. However, the friction material is more severe than resin-based friction materials. Even under braking conditions, there is an advantage that stable performance is obtained without causing a fade phenomenon (the friction coefficient during braking at a high temperature is greatly reduced), and the strength and wear resistance are excellent. Many brakes are required to have high friction performance even below.

  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.

  An example of a copper-based 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 configured as a matrix component, stabilizes the coefficient of friction during braking, forms a hard copper oxide film on the surface due to heat generation with the mating material, water fade phenomenon and heat It is resistant to the fade 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). By sintering in the absence of alkaline substances and forming the body of the perforated friction material, the absolute strength of the friction material can be secured without being hindered by alkaline substances, and then the rust prevention effect Rust prevention is improved by fixing a highly alkaline substance in the hole.

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 demand to contribute to environmental protection by not using materials such as lead and molybdenum at all. The present applicant has invented an iron-based sintered friction material based on cast iron powder, and has obtained performance equivalent to that of a copper-based sintered friction material. However, there is a strong demand for further improvement in characteristics, and there is a problem to be solved in terms of meeting this demand.

  The object of the present invention is that it is preferable in terms of environmental protection because it does not contain any PRTR-designated chemical substance instead of the friction material mainly composed of conventional copper powder, and compared with cast iron powder as a main component. By providing a soft iron-based material with a higher melting point, it is possible to provide a sintered friction material that is superior in brake braking performance, such as coefficient of friction, strength, wear resistance, and low aggressiveness to the mating material. That is.

  The sintered friction material according to the present invention is formed by using reduced iron powder as a metal material in a sintered friction material including a metal material as a matrix and a lubricant and an abrasive.

  The main component is iron-based reduced iron powder, the other compounding materials are lubricants and abrasives, and a sintered friction material can be obtained without using any specified chemical substances specified by the PRTR method. . The main component of the metal that constitutes the matrix that forms the framework of the sintered friction material is changed from cast iron powder to soft reduced iron powder because the melting point is about 300 ° C higher than cast iron powder and low carbon, so friction at high temperatures An excellent sintered friction material can be obtained in terms of characteristics and low attack on the mating material.

  In this sintered friction material, an aluminum powder can be further included as a matrix metal material. This sintered friction material is based on powder formed from reduced iron powder, but 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 frictional sliding of the same type of iron. It has been found that if different materials are interposed between the frictional sliding surfaces, the function as a solid lubricant works and the amount of wear can be reduced. Therefore, by blending aluminum powder, a thin aluminum film is always formed on the surface of the sintered friction material, and the same kind of friction between iron in the friction material and iron in the counterpart material is avoided.

  In this sintered friction material, the content of reduced iron powder is 26 to 53 vol%, the content of aluminum powder is 5 to 20 vol%, and the total content of reduced iron powder and aluminum powder is 46 to 58 vol%. It is preferable that If the total content of the reduced iron powder and aluminum is less than 46%, the bonding force between the metal powders may be reduced, and the strength as a sintered friction material may be reduced. On the other hand, when the total content exceeds 58%, it becomes difficult to secure an effective amount of other blending components.

  In the sintered friction material containing aluminum described above, 2 to 10 vol% of fine alumina having an average particle diameter of 0.3 to 2 μm can be included as an aluminum reinforcing material. Sintered friction material containing reduced iron powder as the main component can achieve the same performance as copper-based sintered friction material, but it was found that it was not as good as copper-based sintered friction material in the evaluation of high load conditions. did. This is thought to be due to the fact that the heat-resistant strength is reduced because low melting point aluminum is contained. Therefore, by adding fine alumina with a high melting point with an average particle size of 0.3-2 μm, the aluminum is thermally strengthened to contribute to the improvement of the heat resistance strength, thereby improving the wear resistance under high load conditions. be able to.

  This sintered friction material may contain 10 vol% or less of magnesia having an average particle size of 50 to 250 μm. Magnesia is a ceramic that is an oxide of magnesium and not high hardness, and is blended for the purpose of improving wear resistance and ensuring a friction coefficient. Magnesia as an abrasive can ensure a coefficient of friction without damaging the mating material by blending a relatively soft material having a Mohs hardness of 6 or less.

  In the sintered friction material containing magnesia, 2 to 10% by volume of alumina having an average particle diameter of 5 to 20 μm can be further included as an abrasive. Since magnesia is a material with low hardness, alumina with higher hardness can be contained for the purpose of securing 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. At this time, the total content of magnesia and alumina is preferably 5 to 15 vol%.

  By containing 25 to 40 vol% of the graphite as a lubricant in a larger amount than usual, the aggressiveness of the counterpart material can be further reduced. Furthermore, by pressure-sintering the blended powder, the powder is densely formed and the strength of the product when sintered can be ensured. The relative density of the sintered friction material can be 80% or more. The relative density indicates the actual density of the sintered body as a relative ratio (percentage) when the theoretical density is 100. By using a pressure sintering method such as spark plasma sintering or hot pressing, and adjusting the temperature and pressure, the sintered friction material has a comparable strength by setting the relative density of the sintered body to 80% or more. Can be obtained.

Since the sintered friction material by this invention is comprised as mentioned above, there exist the following effects. That is, the main component of the present invention is reduced iron powder, the other compounding materials use lubricants and abrasives, and no PRTR-designated chemical substances are used. A friction material excellent in terms of environmental protection can be provided.
As the main component, the reduced melting point is approximately 300 ° C higher than cast iron powder and low carbon and soft reduced iron powder is used, so that a sintered friction material with excellent friction characteristics at high temperatures and low attack on the mating material is obtained. be able to.
Moreover, by adding aluminum, a thin film of aluminum is formed at the friction interface, and the same kind of friction between 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.). Can be prevented. With the above synergistic effect, a necessary friction coefficient can be secured, and wear mats of the friction material and the counterpart material can be reduced. When adding aluminum, by adding fine alumina with a high melting point with an average particle size of 0.3-2 μm, it contributes to the improvement of the heat resistance strength of the low melting point aluminum and improves the wear resistance under high load conditions. be able to.
In addition, as an abrasive material as another compounding material, an average particle diameter of about 50 to 250 μm and a magnesia that is not so hard as ceramics (Morse hardness 6) are used, so that a friction material and a counterpart material ( The amount of wear can be reduced without damaging the iron-based material, and a high coefficient of friction can be secured. Furthermore, when using hard alumina with a mean particle size of about 5 to 20 μm, which is considerably smaller than magnesia (Mohs hardness 9), the alumina particle size is small, so that only the alumina (range of 5 to 15 vol%) suppresses aggressiveness. The friction material and the counterpart material (iron-based material) wear during braking can be reduced. By combining and using two types of magnesia and alumina, it is easy to ensure a high coefficient of friction and to reduce the amount of wear by suppressing the friction material and the counterpart material aggression during braking.
Furthermore, by containing a large amount of the graphite of the lubricant, it is possible to reduce the attack of the counterpart material despite the fact that the main component is an iron-based material. Since the lubricant contains a large amount of graphite, the metal component that acts as a binder is reduced, but the sintering conditions can be adjusted by adjusting the temperature and pressure using a pressure sintering method such as spark plasma sintering or hot pressing. By appropriately setting, it becomes possible to ensure a relative density after sintering (percentage of sintered body density / true density) of 80% or more, so that the bonding force between iron-based materials is strong, A sintered friction material having excellent wear resistance can be obtained.

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

  First, reduced iron powder having an average particle size of about 160 μm, magnesia powder having an average particle size of about 190 μm, alumina powder having an average particle size of about 12 μm, natural graphite powder having an average particle size of about 170 μm, and an average particle size of about An artificial graphite powder of 240 μm and an aluminum powder having an average particle size of about 22 μm were prepared.

  Next, after weighing each of the above-mentioned raw materials into the composition indicated by sample symbols C1 to C3 in Table 1 (the cast iron powder was changed to reduced iron powder, the equivalent amount of graphite contained in the cast iron powder was increased). In order to prevent segregation during mixing, a mixed powder was prepared by adding 4% methanol to the mixture and mixing for 10 minutes using a stirring grinder (produced by Ishikawa Factory). In addition, the mixed powder of the copper-type sintered material A currently mass-produced as a comparison material and the mixed powder of the representative example B of the mixing | blending which used cast iron powder as a base material were also 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 the compounding material of the copper-based sintered material A is produced under the same conditions as the mass-produced material, it is also sintered in a batch-type sintering furnace (temperature increase rate: 10-20 ° C./min, pressure: 0.7 MPa), It was compared with that sintered by a discharge plasma sintering apparatus.

  After sintering, measure the relative density of each sintered body (apparent density of sintered body / percentage of true density of sintered body) and hardness, select a representative sample from them, and perform a brake performance test. The friction coefficient, the friction material and the wear amount of the counterpart material were determined. 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 with the S scale (HRS) 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 composition of typical samples, 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.

The friction coefficient of the present invention products C1 to C3 mainly composed of reduced iron powder is lower than that of the comparative material B mainly composed of cast iron powder, but is equivalent to the current copper-based sintered material A. The amount of wear of the counterpart material was less than B.
Judging from the effects of blending on the friction test results, the appropriate ranges for each component of the blended powder are as follows.
Reduced iron powder: 26-53 vol%,
Aluminum: 5-20 vol%
(However, reduced iron + aluminum: range of 46-58 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%
Here, the reason for setting the range of each component is that if the reduced iron is less than 26 vol%, the friction material wear amount rapidly increases due to insufficient binding force in the friction material, and if it exceeds 53 vol%, other components are insufficient and there is a problem. Arise.

  When the magnesia powder exceeds 10 vol%, the wear amount of the counterpart material increases. When the graphite powder is less than 30 vol%, the lubrication effect decreases, so both the friction material and the counterpart material wear amount increase, and when it exceeds 45 vol%, the friction coefficient decreases greatly. If the aluminum content is less than 5 vol%, the same kind of friction avoidance is insufficient, and the wear amount of the friction material and the mating material increases. If the aluminum content exceeds 20 vol%, the friction coefficient significantly decreases.

  An example in which fine alumina is added as a reinforcing material for aluminum on the basis of Example 1 will be described below as Example 2. First, in addition to the raw material prepared in the case of Example 1, fine alumina powder having an average particle size of about 1.2 μm was prepared as a raw material.

  The weighing of each raw material and the production of the mixed powder by mixing are the same as in Example 1. The sintering of the produced mixed powder is the same as that in Example 1 including the sintering conditions. The measurement of the relative density and hardness of the friction material obtained by sintering, the friction coefficient, the wear amount of the friction material and the counterpart material, and the conditions of the brake test are the same as in the case of Example 1.

  The sintered friction material according to Example 2 is for sample numbers C4 to C8, and the blending of raw materials, sintering conditions, and characteristic values are shown. The friction coefficient of the present example products C4 to C8 to which fine alumina is added is higher than that of the copper-based current sintered material A and the reduced iron powder base materials C1 to C3, and the friction material wear amount is the copper-based current sintered material. Sintered material B equivalent to material A and less than sintered material B based on cast iron and reduced iron powder base materials C1 to C3. It was less than the material B and the reduced iron powder bases C1 to C3.

Judging from the effects of blending on the friction test results, the appropriate ranges for each component of the blended powder are as follows.
Reduced iron powder: 26-53 vol%,
Aluminum: 5-20 vol%,
Fine alumina (average particle size 0.3-2 μm): 2-7 vol%
(However, reduced iron + aluminum + fine alumina: range of 46-60 vol%),
Magnesia (average particle size 50-250 μm): 0-10 vol%,
Alumina (average particle size 5-20 μm): 2-10 vol%
(However, magnesia plus 10 alumina: a range of 5 to 15 vol%),
Graphite: 30-45 vol%
The sintered friction material obtained by sintering this blended powder has a high friction coefficient, and can reduce the wear amount of the friction material and the counterpart material (iron-based material) during braking. Moreover, since fine alumina (2-7 vol%) having an average particle size of about 0.3-2 μm is added, the friction material and the counterpart material (iron-based material) wear during braking can be reduced. .

Claims (8)

  A sintered friction material comprising a metal material as a matrix, a sintered friction material comprising a lubricant and an abrasive, wherein reduced iron powder is used as the metal material.   The sintered friction material according to claim 1, further comprising aluminum powder as the metal material.   The content of the reduced iron powder is 26 to 53 vol%, the content of the aluminum powder is 5 to 20 vol%, and the total content of the reduced iron powder and the aluminum powder is 46 to 60 vol%. The sintered friction material according to claim 2, comprising:   The sintered friction material according to claim 2 or 3, comprising 2 to 10 vol% of fine alumina having an average particle diameter of 0.3 to 2 µm as the aluminum reinforcing material.   The sintered friction material according to claim 1, comprising 10 vol% or less of magnesia having an average particle diameter of 50 to 250 μm as the abrasive.   The sintered friction material according to claim 5, further comprising 2 to 10 vol% of alumina having an average particle diameter of 5 to 20 μm as the abrasive, and a total content with the magnesia of 5 to 15 vol%.   The sintered friction material according to claim 1, wherein the powder mixture comprising the reduced iron powder, the lubricant and the abrasive is subjected to pressure sintering.   The sintered friction material according to claim 7, wherein a relative density of the sintered friction material is 80% or more.