Abstract: The development and application of self-lubricating bearings are reviewed. The manufacture and characteristics are analysed and the application eriteria to automobles and other machines are given for reference.
Key words：ant-i friction material；plain bearing；chauge；characteristic；application
The powder metallurgy self-lubricating bearing material system consists of two parts: the matrix material and the lubricating material. The matrix materials include iron based, copper based, aluminum based, and metal based materials. There are three types of lubricating materials: fluid (mainly oil), lubricating grease (semi solid), and solid lubricant. The temperature ranges applicable to oil lubrication and grease lubrication are relatively narrow, ranging from -60 ℃ to+350 ℃ and -70 ℃ to+370 ℃, respectively; Solid lubrication is suitable for a wide temperature range from low temperature to over 1000 ℃. Powder metallurgy, with its unique process technology, replaces the friction surface between oil and grease isolation bearings and shafts through thin films or composite materials, and can be used for lubrication under increasingly harsh operating conditions of various machinery.
This article briefly introduces the transformation and application overview of commonly used powder metallurgy self-lubricating bearings, their characteristics, and their selection principles (or reference basis) in the design of automotive and other main engines.
1. Transformation and application overview of powder metallurgy self-lubricating bearings
Powder metallurgy self-lubricating bearings appeared in the United States in 1870. It was the initial pressed copper lead alloy bearing. The modern powder metallurgy sintered bronze bearing was proposed in a German patent in 1910 by General Electric Company of the United States, which successfully transformed it into a Cu-13S-i10Pb-4C material with an oil content of 5% (mass fraction) and obtained a US patent in 1916.
The powder metallurgy self-lubricating bearings that emerged from the early 1930s to the late 1940s include:
Sintered bronze graphite self-lubricating bearings were born. Chrysler Automotive Company manufactured sintered bronze graphite bearings using powder metallurgy around 1930. It is a dry friction (without the need for lubricating oil) bearing suitable for medium load and high speed working conditions.
Sintered iron based oil bearing appeared in Germany in the late 1930s. By the 1950s, the development of sintered iron based oil bearing in various countries was rapid. Due to its low cost and excellent performance, it has been widely used in industries such as automobiles both domestically and internationally and has begun to replace bronze graphite bearings.
Sintered metal steel three-layer metal composite bearings were introduced in the 1940s. It is composed of a three-layer metal composite of steel, sintered copper nickel alloy, and babbitt alloy, which is the beginning of the development of sintered metal composite materials.
After the 1950s, the main developments in process technology of powder metallurgy self-lubricating bearings at this stage were:
Modified plastic sintered bronze steel backed three-layer composite material bearings DU and DX were born. In the early 1950s, Glacier Metal Company in the UK developed this three-layer composite material, which was cut and rolled into thin-walled composite bearings (trade name DU). This is another major breakthrough in dry friction composite bearing technology. In the 1960s, the company also developed another three-layer composite material bearing (product name DX), which is a boundary friction (boundary lubrication) composite bearing that can be used for self-lubricating bearings in automobiles. Dongfeng Motors, such as EQ1092 series cars, have been widely used in vehicles since the 1980s.
Sintered copper lead alloy steel backed bimetallic bearing shells were born in the 1960s. This is a new development in powder metallurgy self-lubricating bearing technology. Compared with three-layer composite bearings, it can withstand higher loads and can be used as sliding bearings for heavy-duty diesel engines and chassis, as well as small end bearing shells for engine connecting rods. It is widely used in the EQ1141 series of Dongfeng heavy-duty trucks.
Sintered aluminum based oil bearing was born. In 1966, the United States broke through the difficulty of aluminum based sintering technology and developed sintered aluminum based oil bearing. It has the characteristics of light weight, excellent performance, and low cost, and is widely used in industries such as aviation and automobiles. In recent years, it has been widely installed and used on Dongfeng light vehicles.
The emergence of sintered aluminum lead alloy steel backed bimetallic bearings. In the early 1970s, the United States developed this type of bearing (bearing shell), which was later developed and produced by Britain, France, Japan, Germany, the former Soviet Union, and other countries. It is widely used in medium and light load engines, and has obvious technical and economic benefits compared to using copper based bearings.
2. Introduction to the manufacturing process of powder metallurgy self-lubricating bearings
Powder metallurgy self-lubricating bearings are made from metal powder (such as iron powder, copper powder, aluminum powder, etc.) and lubricant components (such as metal, non-metal, etc.) through processes such as batching, mixed pressing, forming, and sintering. Immersing lubricating oil in sintered porous metal materials can produce oil bearing; Spreading copper alloy powder on the treated steel back, loose sintering, and rolling can produce bimetallic material bearing shells (bearings); A layer of modified plastic can be reheated onto a loosely sintered but not rolled bimetallic plate (strip), and then rolled to produce a three-layer composite material. Through cutting and rolling, a three-layer composite material bearing (such as DU, DX, etc.) can be made. 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, and other industries.
3. Characteristics of self-lubricating bearings manufactured by powder metallurgy method
Compared with traditional casting and forging dense materials, it has the following characteristics:
Various solid lubricants (such as graphite, sulfur, sulfide, lead, molybdenum disulfide, calcium fluoride, etc.) can be added during mixing to improve the friction reduction performance of the material;
The porous nature of sintered materials can be used to impregnate various lubricating oils, fill solid lubricants, or modify plastic strips by hot pressing and rolling, making the materials more self-lubricating and excellent in reducing friction;
Its excellent self-lubrication enables it to be used in areas where lubricants are difficult to reach and where refueling is difficult or not desired (such as in industries such as medicine, food, textiles, etc.) to achieve safety and oil pollution free effects;
It is easier to produce bimetallic materials such as copper lead alloy steel back and aluminum lead alloy steel back without segregation and with large metal density differences;
The material has porous properties that can absorb vibration and reduce noise;
Flexibility in material composition selection, such as metal and alloy, non-metal, compound, and organic material polymer, can be added and used to achieve ideal friction reduction performance;
Special purpose antifriction materials such as air bearings, hydraulic bearings, corrosion-resistant bearings, etc. have further demonstrated the characteristics of powder metallurgy antifriction materials.
4. Selection principles in the design and manufacturing of automotive and other main engines
In the design and manufacturing of domestically produced automobiles, motorcycles, etc., in addition to understanding the characteristics and production process of powder metallurgy materials and parts, comprehensive analysis and comparison should also be conducted based on the stress state, working conditions (working conditions), performance and other special requirements of the materials and parts to be selected, as well as technical and economic benefits. The selection should be made according to the following principles.
4.1 Selection of self-lubricating bearing material matrix
(1) Iron based sintered metal oil bearing can be selected for operating conditions with high load and low speed. Iron resources are abundant and readily available, with low costs. Alloying or additives can improve the strength and friction reduction performance of the matrix, and it has higher wear resistance and load-bearing capacity than copper based bearings.
Aluminum based sintered metal oil bearing can be selected for higher speed and lower load conditions. Aluminum has become a promising lightweight material due to its low density, high modulus, and corrosion resistance through alloying; Alternatively, bronze based oil bearing copper can be chosen, which has high friction reduction performance, thermal conductivity, and corrosion resistance, but its price is higher than that of iron based or aluminum based bearings.
For working conditions with high accuracy and significant changes in working temperature, iron based sintered metal oil bearing should be selected. Because its linear expansion coefficient is close to the dual steel axis.
Copper or aluminum based sintered metal oil bearing with good corrosion resistance and no magnetism should be selected for working conditions in humid working environments and alternating magnetic fields.
From the perspective of domestic resources and economy, iron based sintered metal oil bearing should be selected as much as possible to reduce costs, provided that its performance can meet design requirements.
4.2 Selection of component material strength
The pores of sintered oil bearing can vary between 10% and 30%, and the pores are oil storage holes. But its pores have a significant impact on the density and strength of the material. The strength of the material increases with the decrease of porosity (i.e., the increase of density). Therefore, in order to ensure the strength of the sintered material, the density can be appropriately higher (i.e., the porosity can be appropriately lower) in working conditions with high stress; On the contrary, the porosity can be higher to improve the self-lubricating performance of the part material.
4.3 Selection of wear resistance of component materials
(1) Generally, when the hardness of the material is high, its wear resistance is good;
The material with a high content of pearlite in its metallographic structure has good wear resistance;
The high wear resistance of materials containing lubricants such as graphite and molybdenum disulfide significantly improves;
Surface treatment (such as steam treatment, vulcanization, carburization, carbonitriding, etc.) can improve the wear resistance of materials; (5) The presence of an appropriate amount of dispersed hard point phases (such as carbides) in the matrix can significantly improve the wear resistance of the material.
4.4 Selection of lubrication conditions for parts
(1) Working conditions with poor lubrication conditions require regular replenishment of lubricating oil or grease; For areas where lubricating grease is difficult to reach, bearings with high self-lubricating performance should be selected;
For those with good lubrication conditions (such as pressure lubrication, circulating oil circuit, etc.), materials with lower porosity can be selected to improve the strength of the material.
4.5 Addition of alloy elements
Sometimes it is necessary to improve the comprehensive properties such as strength, hardness, wear resistance, and allowable PV value of self-lubricating friction reducing materials, and appropriate addition of alloy elements such as C, Cu, Mo, Ni, P, S can be considered.
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