JP2009001613A - Sintered friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered friction material favorable in aspects of environmental protection because of no designated chemical substance by the PRTR (Pollutant Release and Transfer Register) law contained at all and capable of avoiding production of friction of the same kind in a high-temperature region, preventing deterioration of friction coefficient, raising lubricity and preventing the occurrence of a large amount of sparks. <P>SOLUTION: The sintered friction material is prepared by regulating the total metal content of an iron-based component containing reduced iron or cast iron and a graphitization promoting element (aluminum, silicon or titanium) to 18-26 vol.% and the content of graphite having high lubricating effects to 45-65 vol.%. As a result, since the content of the metal causing friction of the same kind is smaller than that in the conventional metallic sintered friction material, the deterioration of the friction coefficient caused by the friction of the same kind can be prevented. The graphite is contained in a larger amount than that in the conventional metallic sintered friction material and the occurrence of the large amount of sparks can be prevented by raising the lubricating effects. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sintered friction material as a friction material for brakes used in braking devices for automobiles, motorcycles, 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.

  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.

  In recent years, the PRTR Law (Act on the Promotion of Improvement of Management and Management of Specific Chemical Substances Emissions to the Environment) has been enacted from the viewpoint of environmental protection, and the materials used as friction materials for brakes are also considered environmental protection. There has been a demand for not using designated chemical substances stipulated by the law. However, among the above-mentioned metal materials such as copper, tin, iron, nickel, zinc, antimony, chromium, lead, etc., ceramics and graphite, which have been used as raw materials for sintered friction materials, other than iron, ceramics and graphite These materials 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 a sintered friction material mainly composed of an iron-based material that does not use copper or tin, which has been used as a main component until now, the wear amount of the friction material or the counterpart material (for example, brake disc. In other words, the wear amount of a low-alloy steel, stainless steel, or other iron-based material is greatly increased, and 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, Patent Document 4). Further, according to the base material retaining the ferrite structure, the present applicant has obtained a result that the friction characteristics in the high temperature range exceed the above performance (Japanese Patent Application No. 2006-228358). In the iron-based sintered friction material in which the base structure is controlled, a friction material having a friction characteristic up to 600 ° C. is superior to that of the copper-based sintered friction material. However, it has been found that at the severer rotor maximum temperature of 900 ° C., the same kind of iron friction becomes prominent, resulting in a problem that the friction coefficient is reduced and a large amount of sparks are generated.
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 JP 2007-107068 A

  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, Contributes to environmental protection by using iron-based friction materials without using any material such as lead or molybdenum, and also focuses on the amount of metal and graphite to solve the above problems at high temperatures. There is a problem to be solved in terms of points.

  The object of the present invention is not to include any PRTR-designated chemical substances, which is preferable in terms of environmental protection, avoids the generation of the same type of friction in a high temperature range, prevents the friction coefficient from decreasing, and improves lubricity. An object of the present invention is to provide a sintered friction material that can be increased to prevent the generation of a large amount of sparks.

  The applicant of the present invention has made extensive studies and improved the present invention in order to further improve the high temperature frictional characteristics. That is, the sintered friction material by this invention is comprised including the metal amount: 18-26vol% and the graphite amount: 45-65vol%.

  According to this sintered friction material, the amount of metal causing the same kind of friction is set to 18 to 26 vol%, and the amount of graphite having a high lubricating effect is set to 45 to 65 vol%. Compared with the sintered friction material, the amount of metal is small, and the reduction of the friction coefficient due to the same kind of friction is prevented. Further, by increasing the lubricity, a large amount of sparks is prevented during braking.

  In this sintered friction material, one or more elements selected from the element group of aluminum, silicon, and titanium can be added as a graphitization promoting element. The graphitization tendency is from the largest to aluminum, silicon, titanium, and carbon.

  In this sintered friction material, reduced iron powder or cast iron powder can be included as the main component of the metal. The reduced iron powder and cast iron powder are preferably used in combination.

  The component range for producing the above effect is 18 to 26 vol% in total including the amount of metal including reduced iron: 3 to 8 vol% and cast iron powder: 10 to 20 vol% and aluminum, titanium and silicon, Graphite: Fine alumina (average particle size: 0.3 to 2 μm): 3 to 10 vol%, magnesia (average particle size: 50 to 250 μm): 2 to 10 vol% and alumina as components to be added in addition to 45 to 65 vol% (Average particle diameter: 5 to 20 μm): 2 to 20 vol% is preferable.

  In order to obtain the above effect, the relative density of the sintered body density to the true density is preferably 80% or more as a percentage. By setting the relative density after sintering to 80% or more as a percentage, the bonding force between the iron-based materials becomes strong, and a sintered friction material excellent in strength and wear resistance can be obtained. As the sintering method, a pressure sintering method can be used.

  In the sintered friction material according to the present invention, the amount of metal causing the same kind of friction is 18 to 26 vol%, and the amount of graphite having a high lubricating effect is 45 to 65 vol%. In comparison, the amount of metal is suppressed to prevent a reduction in the coefficient of friction due to the same kind of friction, and the increase in the amount of graphite increases the lubricity to prevent the generation of a large amount of sparks. Yes. Therefore, according to the present invention, it is possible to provide a sintered friction material that suppresses a decrease in friction coefficient, an increase in wear amount, and generation of sparks in a high temperature range.

  Moreover, in this sintered friction material, a part of the matrix structure can be kept in ferrite by adding an element having a large graphitization tendency (Al> Si> Ti> C). By keeping a part of the base structure in ferrite, a friction material excellent in high temperature characteristics and corrosion resistance can be obtained with little decrease in the melting point of the main component iron. Since ferrite is softer than (Fe, C) in which graphite is dissolved, there is little attack on the counterpart material.

  Moreover, in this sintered friction material, it can be set as the base material which utilized the characteristic of each iron powder by using reduced iron powder and cast iron powder in combination. Specifically, since reduced iron powder has a high melting point and is relatively soft, it can be expected to improve heat resistance, wear resistance, and attack of the counterpart material. Cast iron powder has a lower melting point than reduced iron powder, but is cementite. Since it is relatively hard due to its presence, an improvement in the coefficient of friction can be expected.

  Further, in this sintered friction material, the total amount of metal including reduced iron: 3 to 8 vol%, cast iron powder: 10 to 20 vol%, and aluminum, titanium, and silicon includes 18 to 26 vol%, and graphite: In addition to 45 to 65 vol%, fine alumina (average particle size: 0.3 to 2 μm): 3 to 10 vol%, magnesia (average particle size: 50 to 250 μm): 2 to 10 vol%, and alumina (average particle size: 5 to 20 μm): 2 to 20 vol% can be added. The reason for this blending is that the blending amount of cast iron is larger than the blending amount of reduced iron in order to ensure a high temperature coefficient of friction, and the graphitization promoting element (aluminum) to keep the iron component and the base structure in ferrite.・ If the total amount of titanium and silicon is less than 18 vol%, it is difficult to ensure the strength. If it exceeds 26 vol%, the friction coefficient decreases due to the same kind of iron friction at high temperatures. This is because it cannot be suppressed. The amount of graphite is added in order to increase the lubrication effect, but if it is more than 65 vol%, the other components are insufficient, and if it is less than 45 vol%, the lubrication effect is not fully exhibited.

  Furthermore, the pressure sintering method is used, and the relative density after sintering (percentage of sintered body density / true density) is 80% or more, and the bonding strength between ferrous materials is strong. Are better.

Hereinafter, examples of the sintered friction material according to the present invention will be described in more detail.
First, reduced iron powder with an average particle size of about 160 μm as raw materials, cast iron powder with an average particle size of about 85 μm (powder obtained by pulverizing and sieving FC250), and an average that is a graphitization promoting element for keeping the base structure in ferrite Aluminum powder having a particle size of about 20 μm, silicon having an average particle size of about 24 μm, titanium powder having an average particle size of about 10 μm, two types of alumina powders having an average particle size of about 12 μm and an average particle size of about 1 μm, an average particle size There were prepared magnesia powder having an average particle size of about 190 μm, natural graphite powder having an average particle size of about 170 μm, and two types of artificial graphite powder having an average particle size of about 240 μm and an average particle size of about 700 μm.

As shown in Table 1, A1 to A6, which are sintered friction materials (invention materials) according to the present invention, has a reduced iron content in the range of 3 to 6 vol%, while a cast iron content in the range of 11 to 10%. It is 17 vol%, and is increasing gradually in the order of the sample symbol. As elements having a large tendency to graphitize, 2 vol% of aluminum, 0.5 vol% of titanium, and 0.5 vol% of silicon are added. The total metal amount of the iron-based component and the graphitization accelerating element gradually increases from 18 to 26 vol% in the order of A1 to A6. On the other hand, 45 to 62 vol% of graphite is added, and further, fine alumina is added to 5 to 9 vol%, magnesia is 5 to 8 vol%, alumina is 10 to 18 vol%, and graphite: 45 to 65 vol% is added. ing.

  Next, after weighing each of the above-mentioned raw materials into the formulations shown in Table 1 (invention materials A1 to A6) and comparative materials (B1 to B5), using a stirring crusher (made by Ishikawa Factory), segregation during mixing is performed. To prevent this, 4% methanol was added to the mixture and mixed for 10 minutes to produce a mixed powder.

  Furthermore, each mixed powder is filled in 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, pressure is 14 to 25 MPa, heating rate is 100 ° C./min. Sintering was performed under the conditions of a sintering temperature of 1000 to 1025 ° C. and a holding time of 5 minutes.

After sintering, the relative density of each sintered body (apparent density of the sintered body / percentage of the ratio calculated by the true density of the sintered body) and hardness were measured. In addition, a high-temperature brake performance test at 900 ° C. was performed, and 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. For the brake performance test, using our own 1/10 scale tester and 1/5 scale tester tester, the mating material temperature is 500 ° C, the deceleration is 5.88 m / s ² , and the initial speed is 120 km / h. Braking was performed 20 times to 0 km / h (stop), the counterpart material temperature was 900 ° C., the deceleration was 0.39 m / s ² , and the initial speed was 120 km / h to 0 km / h (stop). Table 1 shows the sintering conditions, relative density, hardness, and friction coefficient, friction material wear amount, and counterpart material wear amount in the brake performance test.

  Comparative material B1 was a composition outside the structure of the present invention such that the amount of metal was 16 vol%, and the target physical property value was not obtained because the amount of metal was small, and a brake performance test could not be performed. Comparative material B2 is a composition outside the structure of the present invention such that the amount of metal is 28 vol%, and has a lower coefficient of friction during the 900 ° C. test than the present invention material, and the wear amount of the friction material and the counterpart material Many. Further, for B3 to B5 in which the amount of metal was increased, the friction coefficient during the 900 ° C. test was high, but the wear amount of the friction material and the counterpart material was greatly increased.

  The inventive materials A1 to A6 have a high friction coefficient at the time of the 500 ° C. and 900 ° C. tests, and have a good balance of friction characteristics such that the friction material and the counterpart material have a small amount of wear. Among them, the inventive materials A2 and A3 (metal content 20 vol%) were found to have a particularly high friction coefficient and a good blend with a small amount of wear between the friction material and the counterpart material.

Claims (5)

  A sintered friction material comprising a metal amount: 18 to 26 vol% and a graphite amount: 45 to 65 vol%.   The sintered friction material according to claim 1, wherein one or more elements selected from the group consisting of aluminum, silicon, and titanium are added as a graphitization promoting element.   The sintered friction material according to claim 1 or 2, wherein a main component of the metal amount is reduced iron powder or cast iron powder.   The amount of the metal is 18 to 26 vol% in total including reduced iron: 3 to 8 vol% and cast iron powder: 10 to 20 vol% and aluminum, titanium, and silicon, and fine alumina (average particle diameter: 0.3 ˜2 μm): 3 to 10 vol%, magnesia (average particle size: 50 to 250 μm): 2 to 10 vol%, and alumina (average particle size: 5 to 20 μm): 2 to 20 vol% Item 4. The sintered friction material according to any one of Items 1 to 3.   The sintered friction material according to any one of claims 1 to 4, wherein the relative density of the sintered body density with respect to the true density is 80% or more as a percentage.