JP5214158B2 - Sintered friction material - Google Patents

Description

  The present invention relates to a sintered friction material as a friction material for a brake used in a braking device for an automobile, a motorcycle, a railway vehicle, an industrial machine or the like.

  Conventionally, as a sintered friction material for brakes, copper is the main component, and tin or a metal to which iron, nickel, zinc, antimony, chromium, lead, etc. are added, 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.

  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.

  As another example of the sintered friction material, an iron-based sintered friction 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. 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.

  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 above-mentioned additives such as copper, tin, iron, nickel, zinc, antimony, chromium, lead and other metal base materials and ceramics, lubricants, etc., which have been used as raw materials for sintered friction materials. Materials other than ceramics and graphite are set as PRTR-designated chemical substances, and it is hoped that they will not be used as much as possible.

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 sintered friction materials mainly composed of iron-based materials that do not use copper or tin as the main component until now, ceramics as a grinding material, graphite as a lubricant, and metal powder are used as a compounding material. Therefore, during sintering, graphite of the lubricant is dissolved in ferrite, which is a base structure of reduced iron powder and has a high melting point, to form pearlite with increased hardness. As a result, there is a phenomenon in which the amount of wear of the friction material and the amount of wear of the mating material (for example, brake discs, mainly made of iron-based materials such as ordinary cast iron, low alloy steel, stainless steel) greatly increase during braking. The required coefficient of friction cannot be ensured. In addition, materials such as aluminum, magnesium, and titanium that are not specified chemical substances in the PRTR method other than ferrous materials have many problems as the main component of sintered friction materials, and practical application of sintered friction materials excellent in environmental protection is quite easy. It was difficult. 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 (for example, Japanese Patent Application No. 2005-300817). . However, in the evaluation under high load conditions, it has been found that it has not reached the same level as the copper-based sintered friction 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 raw materials for sintered friction materials, not only hexavalent chromium compounds, which are the specified first class designated chemical substances of the PRTR method, but also zinc, antimony, copper, tin, lead, molybdenum, which are the first class designated chemical substances. As much as possible, this contributes to environmental protection, maintains the base structure of the sintered friction material in a mixed structure of ferrite and heat-resistant austenite with excellent high-temperature characteristics and corrosion resistance, and iron. There is a problem to be solved in terms of reducing the wear amount of the counterpart material by preventing the same kind of friction.

  The object of the present invention is to reduce the inclusion of PRTR-designated chemical substances as much as possible, which is preferable in terms of environmental protection, and keeps the base structure of the sintered friction material in a mixed structure of ferrite and austenite. It is intended to provide a sintered friction material that has excellent performance and corrosion resistance, and has excellent performance at the time of brake braking, such as reducing the amount of wear of the counterpart material by reducing the aggressiveness to the counterpart material such as a brake disk.

  In order to solve the above-mentioned problems, the sintered friction material according to the present invention is sintered by adding nickel or manganese as an austenite forming element and a graphitization accelerating element to a high melting point reduced iron powder as a main component, This consists of the base structure being kept in a mixed structure of austenite and ferrite.

  According to this sintered friction material, the main component is an iron-based material, and the other compounding materials are ceramics as an abrasive, graphite as a lubricant, and metal powder. Therefore, the base structure of the reduced iron powder during sintering, the graphite of the lubricant is dissolved in ferrite having a high melting point to form pearlite. Although pearlite increases in hardness, the melting point decreases and heat resistance decreases. A part of the base structure is kept in austenite by adding nickel or manganese, which are austenite forming elements, alone or in combination. Furthermore, by adding an element having a large graphitization tendency (Al> Si> Ti> C), a part of the base structure is kept in the ferrite. As a result, the base structure becomes a heat-resistant mixed structure of austenite and ferrite, so that the melting point of the main component is not lowered. Furthermore, the austenite and ferrite forming the mixed structure are softer than pearlite in which graphite is dissolved.

In this sintered friction material, as the austenite forming element , 2 to 10 vol% in total can be added in the range of 0 to 10 vol% of nickel and 0 to 8 vol% of manganese. With this addition of the austenite-forming element, a portion of the matrix structure can be kept austenite.

  In the sintered friction material, 2 to 8 vol% of aluminum can be added as the graphitization promoting element. Aluminum as a graphitization accelerating element is an element having a large tendency to graphitize. By adding such aluminum, solid solution of graphite in the lubricant can be prevented and a part of the matrix structure can be maintained as ferrite.

  In the sintered friction material, the mixed structure of the austenite and ferrite is preferably present in the matrix structure at 80% or more. The abundance of austenite and ferrite (percentage of [austenite + ferrite] / [base structure]), which is a base structure that is low in melting temperature, excellent in high-temperature properties, and relatively soft, is low in attacking the counterpart material. By setting it to 80% or more, which is a part, even if pearlite due to partial solid solution is present due to sintering, a decrease in heat resistance is reduced, which is preferable.

In the sintered friction material, fine alumina (average particle size: 0.3 to 2 μm) is 0 to 15 vol%, magnesia (average particle size: 50 to 250 μm) is 0 to 10 vol%, and alumina (average particle size: 5) ˜20 μm) can be added in the range of 2 to 10 vol% (however, magnesia + alumina is in the range of 5 to 15 vol%), and graphite can be added in the range of 30 to 45 vol%.
Here, the reason for setting the range of each component is that if the reduced iron is less than 20 vol%, the friction material wear amount rapidly increases due to insufficient binding force in the friction material, and if it exceeds 40 vol%, other components are insufficient and there is a problem. Arise. When magnesia + alumina is less than 5 vol%, the friction coefficient decreases, and when it exceeds 15 vol%, the increase in the wear amount of the mating material becomes significant. Since the particle size of alumina is small, even with alumina (5-15 vol%) alone, the aggressiveness is suppressed and the friction material and the counterpart material (iron-based material) wear during braking are reduced. It becomes easy to achieve both the securing of the coefficient and the suppression of the opponent material attack. 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. Each austenite forming element and graphitization accelerating element for keeping the base structure in austenite and ferrite cannot keep the base structure in austenite and ferrite below the respective lower limit addition amounts, and carbides containing additive metals above each upper limit addition amount Is generated.

  In the sintered friction material described above, it is preferable that the relative density as a percentage of the sintered body density after sintering by a pressure sintering method such as discharge plasma sintering or hot press is 80% or more. Using a pressure sintering method such as spark plasma sintering or hot pressing, the relative density after sintering (percentage of sintered body density / true density) should be 80% or more, so that the bonding between iron-based materials Strength is strengthened.

Since the sintered friction material according to the present invention is configured as described above, the main component is an iron-based material, but a part of the base structure can be obtained by adding nickel or manganese, which are austenite forming elements, alone or in combination. In addition, by adding an element having a large graphitization tendency (Al>Si>Ti> C), a part of the base structure is kept in ferrite, so that the base structure is a mixture of austenite and ferrite. Become an organization. That is, since the formation of pearlite in the reduced iron powder is suppressed by the additive metal, the melting point of the main component does not decrease compared to pearlite having a solid solution and a low melting point, and is excellent in high temperature characteristics and corrosion resistance. Since it is softer than pearlite, a sintered friction material can be obtained in which austenite and ferrite with a small amount of wear of the counterpart material form a matrix structure.

In addition, in order to keep the base structure in austenite, when the total of both is added in the range of 0 to 10 vol% of nickel which is an austenite forming element and 0 to 8 vol% of manganese, the base structure should be kept in austenite. Can do. Each austenite-forming element cannot keep the base structure in austenite below each lower limit addition amount, and generates carbide containing the added metal above each upper limit addition amount.

  In addition, in order to keep the base structure in ferrite (base structure of reduced iron powder), when adding 2 to 8 vol% of aluminum which is a graphitization promoting element, solid solution of graphite in the lubricant is prevented and the base structure is kept in ferrite. Can do. Aluminum that is a graphitization accelerating element cannot prevent the solid solution of graphite below the lower limit addition amount, so the base structure cannot be maintained in ferrite, and if it exceeds the upper limit addition amount, carbide containing the added metal is generated. End up.

  When the austenite and ferrite abundance (percentage of [austenite + ferrite] / [base structure]) is 80% or more, there is pearlite that is partly solid solution by sintering, but most of the base structure. By maintaining the austenite and ferrite, it is possible to take advantage of the high temperature characteristics and corrosion resistance, and the fact that there is little mating wear on the mating material.

  In addition, by determining the range of blending ratios for reduced iron, magnesia, alumina, magnesia + alumina, and graphite powder, it is possible to achieve both the ensuring of the friction coefficient and the suppression of the friction material wear amount and the counterpart material wear amount. it can. Also for the graphite powder, if the amount is less than the lower limit, the lubrication effect is reduced, so both the friction material and the wear amount of the counterpart material are increased, and if the upper limit is exceeded, the friction coefficient is greatly decreased. For each austenite forming element and graphitization accelerating element for keeping the base structure in austenite and ferrite, the base structure cannot be kept in austenite and ferrite below each lower limit addition amount, and in each upper limit addition amount or more, the added metal is not added. Carbide containing is produced.

  Furthermore, when using the pressure sintering method and the relative density after sintering (percentage of sintered body density / true density) is 80% or more, the bonding force between the iron-based materials is enhanced, 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, as a raw material, reduced iron powder having an average particle size of about 160 μm, aluminum powder having an average particle size of about 12 μm, fine alumina powder having an average particle size of about 1.2 μm, magnesia powder having an average particle size of about 190 μm, Natural graphite powder having a particle size of about 170 μm, artificial graphite powder having an average particle size of about 240 μm, alumina powder having an average particle size of about 12 μm, nickel powder having an average particle size of about 12 μm, and manganese powder having an average particle size of about 45 μm were prepared. . Aluminum powder is blended as a graphitization promoting element. Nickel powder and manganese powder are blended as austenite forming elements.

  After weighing each of the above raw materials into each of the blends C shown in Table 1, add 4% methanol to the mixture and mix for 10 minutes in order to prevent segregation during mixing using a stirring grinder (Ishikawa Factory). A mixed powder was prepared. As a comparative material, a mixed powder of a copper-based sintered material A and a mixed powder of a representative example B having a base structure made of pearlite were also prepared.

  Each mixed powder is filled into a graphite mold having a cavity of 23 mm × 35 mm, and using a discharge plasma sintering apparatus (manufactured by Sumitomo Coal Industry, model SPS-515S), the pressure is 14 MPa, the heating rate is 10 to 20 ° C./min, Sintering was also performed at a pressure of 0.7 MPa, and compared with that sintered by a discharge plasma sintering apparatus.

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. Moreover, the high-temperature brake performance test of 500 degreeC and 600 degreeC was implemented, and the friction coefficient and the other party material abrasion amount were calculated | required. 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. Brake performance test using our own 1/10 scale tester testing machine temperature of partner material 500 ℃ ・ 600 ℃, deceleration 5.88m / s 2s2.6.86m / s2, initial speed 120km / h → 0km / h The braking was performed 20 times. Table 1 shows the sintering conditions (temperature ° C, pressure MPa, production category), relative density (%), hardness (HRS), average friction coefficient in brake performance test, mating material wear (μm), and other than pearlite. The area ratio (%) is shown.

  In order to observe the base structure, etching with nital (5% nitric acid + ethanol 10 sec) was performed. The area ratio shown in Table 1 ([area of ferrite or ferrite + austenite in base structure] / [area of base structure]) is an average value of 10 fields of view.

  FIG. 1 is a photomicrograph showing the base structure of the material C2 of the present invention, and FIGS. 2 and 3 are photomicrographs obtained by etching the material C3 of the present invention with nital and etching with picric acid / hydrochloric acid / ethanol, respectively. FIG. 4 and 5 are photomicrographs showing the base structures of the comparative material B1 and the comparative material B2, respectively.

  As can be understood from Table 1 and the drawings, it was confirmed that in the comparative material B1 (FIG. 4), the ferrite in the white part was present in an area ratio of 61% and the pearlite in the colored part was present in an area ratio of 39%. Further, it was confirmed that for the comparative material B2 (FIG. 5), [ferrite + austenite] in the white part was present at an area ratio of 73% and pearlite in the colored part was present at an area ratio of 27%.

  In the present invention materials C1 to C8, nickel or manganese, which is an austenite forming element, is added in the formulation shown in Table 1, and aluminum, which is a graphitization promoting element, is also added in the formulation shown in Table 1. Inventive material C2 showing the base structure in FIG. 1 has [ferrite] or [ferrite + austenite] in the white part in an area ratio of 83%, and is present in a higher ratio than the area ratio in the case of the comparative material. . Further, as shown in FIG. 2, the material C3 of the present invention is hardly corroded by nital. Therefore, etching with a caustic solution (30 sec) of picric acid (1 g) + hydrochloric acid (15 cc) + ethanol (100 cc) was performed, and as shown in FIG. 3, austenite in the white part and ferrite in the colored part were confirmed. In this case, it was confirmed that the area ratio of the tissue other than pearlite was 95%. Similarly, the present invention materials C1 and C4 were confirmed to have an area ratio of 80% or more.

It is a microscope picture which shows the base structure | tissue of this invention material C2. It is the microscope picture which gives etching by the nital of this invention material C3. It is a microscope picture which gives etching by picric acid / hydrochloric acid / ethanol of this invention material C3. It is a microscope picture which shows the base structure | tissue of comparative material B1. It is a microscope picture which shows the base structure | tissue of comparative material B2.

Claims (2)

High melting point reduced iron powder 20-40 vol%,
As an austenite forming element, in the range of nickel 0-10 vol%, manganese 0-8 vol%, the total of both is 2-10 vol%,
2-8 vol% aluminum as a graphitization promoting element,
As the remainder, 0-15 vol% of fine alumina (average particle size: 0.3-2 μm), 0-10 vol% of magnesia (average particle size: 50-250 μm), and 2 (alumina particle size: 5-20 μm) are 2 -10 vol% (however, magnesia + alumina is in the range of 5-15 vol%), graphite is added in the range of 30-45 vol%, and is sintered.
A sintered friction material, wherein 80% or more of the base structure of the reduced iron powder is maintained in a mixed structure of austenite and ferrite. Relative density (apparent density of sintered body / true density of sintered body) as a percentage of sintered body density after sintering by pressure sintering method such as spark plasma sintering and hot press is 80% or more The sintered friction material according to claim 1, comprising:

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