Development characteristics of powder metallurgy self-lubricating bearings and selection principles in main engine manufacturing

Powder metallurgy self-lubricating bearing material is composed of base material and lubricating material. Matrix materials include iron-based, copper-based, aluminum-based and metal-based. There are three kinds of lubricating materials: fluid (mainly oil), grease (semi-solid) and solid lubricant. Oil lubrication and grease lubrication are suitable for a narrow temperature range? They are -60 °C ~ +350 °C and -70 °C ~ +370 °C respectively; solid lubrication is suitable for a wide temperature range? From low temperature to above 1000 °C. With its unique process technology, powder metallurgy can add different types of solid lubricants to various types of substrates? Make them in the form of solid powder, film or composite materials? Replace oil and grease to isolate the bearing and the shaft in contact with each other. Friction surface? It can be used for lubrication under increasingly severe operating conditions of various types of machinery. This paper briefly introduces the transformation and application of commonly used powder metallurgy self-lubricating bearings, their characteristics, and their selection principles (or reference basis) in the design of main engines such as automobiles.

1 Overview of the revolution and application of powder metallurgy self-lubricating bearings Powder metallurgy self-lubricating bearings appeared in the United States in 1870. It was the original pressed copper-lead alloy bearing. The modern powder metallurgy sintered bronze bearing was proposed in a German patent in 1910. It was successfully manufactured by the General Electric Company of the United States. Its material composition is Cu-13S-i10Pb-4C? The oil content is 5% (mass fraction)? And in 1916 received a US patent.

From the early 1930s to the late 1940s, the powder metallurgy self-lubricating bearings that appeared were:

(1) Sintered bronze-graphite self-lubricating bearings were born. The Chrysler Automobile Company of the United States manufactured the burnt bronze-graphite bearing by powder metallurgy around 1930. It is a dry friction (neither need to add lubricating oil) bearing? It is suitable for medium load and high speed conditions.

(2) Sintered iron-based oil-impregnated bearings appeared in Germany in the late 1930s. By the 1950s? Sintered iron-based oil-impregnated bearings in various countries developed rapidly. Because of its low cost and good performance, it is widely used in domestic and foreign industries such as automobiles and begins to replace bronze-graphite bearings.

(3) Sintered metal-steel 3-layer metal composite bearings came out in the 1950s. It is composed of steel – sintered copper-nickel alloy – babbitt alloy 3-layer metal composite? This is the beginning of the development of sintered metal composite materials.

After the 1950s? At this stage? The main development of powder metallurgy self-lubricating bearings in process technology is:

(1) Modified plastic-sintered bronze-steel backed 3-layer composite bearings DU and DX were born. Glacier Metal Company in the United Kingdom developed this 3-layer composite material in the early 1950s. It was cut and rolled into a thin-walled composite bearing (trade name DU)? This is another example of dry friction composite bearing technology. A major breakthrough. The company also developed another 3-layer composite bearing (trade name DX) in the 60s? It is a boundary friction (boundary lubrication) composite bearing? Self-lubricating bearings that can be used in automobiles, etc.? Dongfeng Motors such as EQ1092 series Cars, etc. have been used in large quantities since the 1980s.

(2) Sintered copper-lead alloy-steel-backed bimetallic bearing bushes were born in the 1960s. This is a new development of powder metallurgy self-lubricating bearing technology. Compared with the 3-layer composite bearing, it can withstand higher loads. It can be used as a sliding bearing and a small end bearing of the starting connecting rod for heavy-duty diesel engines and chassis. It is widely used in Dongfeng heavy truck EQ1141 series vehicles.

(3) Sintered aluminum-based oil-impregnated bearings were born. In 1966, the United States broke through the difficulties of aluminum-based sintering technology and developed sintered aluminum-based oil-impregnated bearings. It has the characteristics of light weight, excellent performance and low cost. It is widely used in aviation, automobile and other industries. In recent years, it has been used in batch loading on Dongfeng light vehicles.

(4) The emergence of sintered aluminum-lead alloy-steel back bimetal bearings. In the early 1970s, after the United States developed this kind of bearing (bearing bush), the United Kingdom, France, Japan, Germany, the former Soviet Union, etc. have also successively developed and produced it. It is widely used in medium-load and light-load engines. Bearings have obvious technical economy.

2 Introduction to the manufacturing process of powder metallurgy self-lubricating bearings

Powder metallurgy self-lubricating bearings are made of metal powder (such as iron powder, copper powder, aluminum powder, etc.) and lubricant components (such as metal, non-metallic, etc.) through batching, mixing, pressing and sintering. . Impregnating lubricating oil in sintered porous metal materials can make oil-impregnated bearings; spread copper alloy powder on the treated steel back? After loose sintering and rolling, bimetallic bearing bushes (bearings) can be obtained; Loading sintered but not rolled bimetal plate (strip) material? Reheating and compounding a layer of modified plastic? After rolling, a 3-layer composite material can be obtained? A 3-layer composite material can be made by blanking and rolling Bearings (eg DU, DX, etc.). Since the 1950s, these bearings have been widely used as sliding bearings for automobiles and motorcycles, household appliances, agricultural machinery, light industrial machinery, machine tools, etc.

3 The characteristics of self-lubricating bearings manufactured by powder metallurgy are compared with those of traditional casting and forging dense materials? It has the following characteristics:

(1) Various solid lubricants (such as graphite, sulfur, sulfide, lead, molybdenum disulfide, calcium fluoride, etc.) can be added during mixing to improve the antifriction performance of the material;

(2) Using the porosity of the sintered material, it can be impregnated with various lubricating oils, or filled with solid lubricants, or hot-compressed and rolled modified plastic belts, etc., to make the material more self-lubricating performance and excellent anti-friction performance;

(3) Excellent self-lubricating properties? It can be used in places where lubricants are difficult to reach, and where it is difficult to add oil or do not want to be refueled (such as medicine, food, textile and other industries) to achieve the effect of safety and no oil pollution;

(4) It is easier to obtain bimetallic materials such as copper-lead alloy-steel back, aluminum-lead alloy-steel back, etc. without segregation and with large metal density difference;

(5) The material has porous characteristics, which can absorb shock and reduce noise; (6) The flexibility of material composition selection is great, such as metals and alloys, non-metals, compounds and organic materials, polymers, etc. Ideal anti-friction performance;

(7) Anti-friction materials for special purposes, such as air bearings, hydraulic bearings, corrosion-resistant bearings, etc., also exert the characteristics of powder metallurgy anti-friction materials.

4 Selection principles in the design and manufacture of main engines such as automobiles In the design and manufacture of domestically produced automobiles, motorcycles, etc.? In addition to understanding the characteristics and production process characteristics of powder metallurgy materials and parts, it is necessary to select materials according to the requirements. The stress state, working conditions (working conditions), performance and other special requirements and technical economy of the parts? After comprehensive analysis and comparison? Choose according to the following principles.

4.1 Selection of self-lubricating bearing material matrix

(1) Operating conditions with large load and low speed? Iron-based sintered metal oil-impregnated bearings can be selected. Iron resources are abundant and easy to obtain, low cost, and through alloying or additives, the strength and anti-friction properties of the matrix can be improved, and it has higher wear resistance and load-carrying capacity than copper-based bearings.

(2) For the working conditions with high speed and low load, aluminum-based sintered metal oil-impregnated bearings can be selected. The density of aluminum is small? It has the characteristics of high strength, high modulus and corrosion resistance after alloying? Therefore, it has become a promising lightweight material; or bronze-based oil-impregnated bearings can be selected? Copper has high antifriction performance and thermal conductivity. performance and corrosion resistance? But its price is higher than that of iron-based and aluminum-based ones.

(3) For working conditions with high precision and large working temperature changes, iron-based sintered metal oil-impregnated bearings should be selected. Because its linear (expansion) coefficient is close to that of the dual steel shaft.

(4) The working conditions in the humid working environment and in the AC magnetic field? The copper-based or aluminum-based sintered metal oil-impregnated bearings with good corrosion resistance and non-magnetic properties should be selected.

(5) Considering domestic resources and economy, if its performance can meet the design requirements, iron-based sintered metal oil-impregnated bearings should be selected as far as possible to reduce costs.

4.2 Selection of material strength of parts The pores of sintered oil-impregnated bearings can vary within the range of 10% to 30%? The pores are oil storage pores. But its porosity has a great influence on the density and strength of the material? The strength of the material increases with the decrease of porosity (that is, the increase of density). Therefore, in the case of large working force, in order to ensure the strength of the sintered material, the density can be appropriately higher (that is, the porosity is appropriately lower); otherwise, the porosity can be higher to improve the self-lubricating performance of the part material. .

4.3 Selection of wear resistance of parts material

(1) Generally, when the hardness of the material is high, its wear resistance is good;

(2) The metallographic structure of the material has good wear resistance with high pearlite content;

(3) The high wear resistance of materials containing lubricants (such as graphite, molybdenum disulfide, etc.) is significantly improved;

(4) Surface treatment (such as steam treatment, vulcanization, carburizing, carbonitriding, etc.) can improve the wear resistance of the material;

(5) The presence of an appropriate amount of dispersed and distributed hard point phases (such as carbides, etc.) in the matrix can significantly improve the wear resistance of the material.

4.4 Selection of lubrication conditions for parts

(1) In working conditions with poor lubrication conditions, lubricating oil or grease needs to be added regularly; in places where lubricating grease is difficult to reach, bearings with high self-lubricating performance should be selected;

(2) The lubrication condition is good (such as pressure lubrication, circulating oil circuit, etc.)? The material with lower porosity can be selected to improve the strength of the material.

4.5 The addition of alloying elements sometimes needs to improve the strength, hardness, wear resistance and allowable PV value of the self-lubricating anti-friction material. Alloys such as C, Cu, Mo, Ni, P, S can be added as appropriate. element.

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