Powder metallurgy is an industry that uses special materials to make various parts. It uses reduced iron powder or electrolytic copper powder as raw materials to make various castings, forgings, gears, bearings and standard parts. It is widely used in transportation machinery, Industrial machinery and electrical machinery, etc.
Powder metallurgy bearings are one of the fields, also called oil-impregnated bearings or sintered bearings. They are mainly used in micro motors, such as electroacoustic devices, household appliances, electronic computers and other motors. They are made of iron powder and copper powder through mold pressing, high-temperature calcination, Made by high pressure polishing. The product has a certain degree of porosity. The biggest difference from ordinary bearings is that it can contain oil itself, and there is no need to replenish oil during use. The oil content of oil-containing bearings is generally controlled at no less than 18% (volume fraction, the highest can reach 22% to 24%). %). This kind of lubricating oil in the bearing is called powder metallurgy bearing lubricating oil. According to the metallurgical powder material of the bearing, powder metallurgy bearings are mainly divided into copper-based and iron-based. Copper-based bearings are generally used in motors with higher speeds (such as 20000r/min The above motors), iron-based bearings are mostly used in relatively low-speed motors (500-2500r/min) (there are also a small number of motors above 10000r1min), so the corresponding powder metallurgy bearing lubricants are used for high-speed copper-based bearings oil and low-speed iron-based bearing lubricants.
1. Development status at home and abroad
The powder metallurgy industry developed earlier abroad, starting in the 1880s. At that time, the products were mainly mechanical parts, friction materials, current collecting materials, etc. Bearing products were produced in the 1930s, among which Japan developed the fastest, in 1956 The total annual output of bearing products was 494t (copper-based 317t, iron-based 177t), which increased to 1586t (copper-based 978t, iron-based 608t) in 1963, an increase of three times. The corresponding lubricating oil also increased from the initial average Antioxidants were added to mineral oil, which later led to special oils for powder metallurgy bearings. The performance of special oil has also developed from general lubricating oil to high viscosity index lubricating oil with anti-oil throwing properties, antioxidant properties, anti-wear properties and anti-rust properties.
Domestically, it started in the mid-to-late 1950s. In the 1980s, when demand was strong, copper-based bearings began to be produced. Later, due to the low cost of iron-based, iron-based bearings began to be developed in large quantities. Most of the products produced were used in gears and machine tools. General motors for machinery. With the development of the electronics industry and the advent of micro motors, supporting micro bearings have begun to be produced. The lubricating oil used is mainly mechanical oil, followed by No. 68 and No. 100 ordinary hydraulic oil, generally based on the requirements of the motor manufacturer. Use, export products use internal combustion engine oil (Mobil1# is commonly used in export products in Hong Kong, Macao and southern regions), so the use of powder metallurgy bearing lubricating oil is relatively scattered in China, and there is no national standard or special oil production.
2 Characteristics of powder metallurgy bearings and lubricants
Bearings are generally divided into two categories: rolling bearings and sliding bearings. The impact of lubrication conditions on rolling bearings is not obvious, but it has a direct impact on the performance of sliding bearings. Sliding bearings are divided into dry bearings and powder metallurgy bearings. Dry bearings are solid lubricants (such as graphite, MoS2, Pb, etc.) dispersed in a bronze matrix. They have a high friction coefficient and are suitable for high temperature working conditions, while powder metallurgy bearings are suitable for In the boundary lubrication zone, the corresponding load is low and the friction coefficient is small - 3J. It has several characteristics: because it contains lubricating oil, it does not need to be replenished frequently (general pumps) or not replenished (micro motors); it is easy to make and can be directly pressed into bearings of various shapes; In the case of oil, the service life is not less than 1000h, and the micro motor is generally not less than 2000h, which is very helpful for equipment in the home appliance industry; in addition, the production cost is lower than that of ordinary metal bearings, and it is suitable for mass production.
Due to the particularity of its manufacturing process, the lubrication structure and lubrication mechanism of powder metallurgy bearings are different from ordinary metal bearings. Figure 1 shows the structures of oil-containing bearings (powder metallurgy bearings) and ordinary metal bearings respectively.
In general, when the shaft of a metal bearing starts to rotate, the lubricating oil accumulated in the upper space that does not bear the load adheres to the upper part of the shaft. As the shaft rotates, the oil is gradually sent into the slit in the lower part of the shaft to separate the shaft from the bearing. Acts as lubrication. As for oil-containing bearings, when the shaft is not rotating, the contact surface between the shaft and the bearing at the bottom of Z is isolated by a thin layer of lubricating oil connected to the gap of the oil-containing bearing. The action structure is shown in Figure 2. When the shaft rotates, under the influence of the uneven surfaces of the shaft and the bearing, frictional heat is generated, which increases the temperature of the bearing surface, reduces the viscosity of the lubricating oil contained in the bearing itself, and accelerates its seepage from the gaps in the oil-containing bearing. The isolation shaft and bearings provide lubrication. The characteristic of oil-impregnated bearing lubrication is that the lubricating oil flows from the unloaded side to the loaded side through the gap between the shaft and the bearing, while the opposite is true inside the bearing. The lubricating oil flows from the loaded area to the unloaded area.
Figure 1 Lubrication structure diagram of powder metallurgy bearings and general metal bearings
Figure 2 Lubrication structure diagram of powder metallurgy bearing at rest
3. Requirements for lubricating oil for powder metallurgy bearings
3.1 Appropriate PV value and friction performance
For general bearings, the load P, speed V and their product PV are the most basic factors in bearing load. For powder metallurgy bearings, the load P and allowable speed V must be considered when selecting bearing materials. In Japan and the United States, there are regulations on the load and speed of iron-based and copper-based oil-impregnated bearings and their product PV.
The lubrication of powder metallurgy bearings belongs to boundary lubrication. When it is first started, due to the metal friction, the friction coefficient is high, about 0.15 to 0.30; but as it runs, the oil in the oil-containing bearing gaps slowly forms an oil film, the metal friction decreases, and the friction coefficient Reduced, about 0.05 to 0.10, which is equivalent to fluid lubrication. Different PV values have different friction coefficients. Generally, the friction coefficient gradually decreases as the PV value increases. When the PV value is constant (that is, a metallurgical material is selected) the friction coefficient is related to the viscosity of the lubricating oil used. If the viscosity is too high, the oil film will be thick, and the oil will not be easily absorbed into the bearings; if the viscosity is too small, the oil film will be thin, and the oil will easily overflow from the bearings and seep out of the motor when the motor is running. Therefore, if the oil viscosity is too high or too low, the bearing friction may increase. . Therefore, appropriate viscosity and high viscosity index are important factors for oil bearings.
3.2 Appropriate viscosity and high viscosity index
Motors equipped with powder metallurgy bearings generally do not replenish oil during use. Insufficient or no oil in the bearings will cause wear of the shaft and bearings, friction sound, and burning of the bearings. Therefore, in addition to the general lubricating oil properties of powder metallurgy bearing oil, it is required that the lubricating oil in the bearing will not leak out of the motor with the high-speed operation of the motor (that is, the oil's anti-oil throwing properties) under the condition of high-speed operation of the motor. It has a higher viscosity index and better adhesion ability. When the loss of extravasated oil reaches 50%, it will affect the service life of the motor. The oil content of powder metallurgy bearings (test method GB5165) is closely related to the viscosity of the oil. Low-viscosity oil has a high oil content, High viscosity oil has a low oil content. When the motor is running at high speed, the oil temperature rises, which can easily cause the oil viscosity to drop and the light components to evaporate, resulting in a reduction in the oil content in the bearing. Therefore, the oil is required to have less light components, that is, the oil viscosity cannot be high. If it is too low, it must have appropriate viscosity and a high viscosity index to keep the oil content in the bearing at about 18%.
3.3 Anti-oil throwing characteristics
There are a large number of pores in the oil-containing bearing body that communicate with the outside world. Therefore, during use of the high-speed motor, frictional heat is generated due to the relative sliding of the bearing and the shaft, causing the lubricating oil in the oil-containing bearing to seep out or be thrown out, resulting in oil on the outside of the motor. Due to the loss of lubricating oil in the bearing, the friction increases, the noise increases, and the bearing may even seize the motor and burn out, affecting the service life of the motor. Therefore, additives of anti-oil throwing components must be considered in powder metallurgy bearings.
3.4 Other performance
In addition to the above properties, powder metallurgy bearing oil must also have good oxidation resistance. The acidic substances and sludge produced by the oxidation of the oil will block the bearing gaps, causing the shaft and bearing to contact without oil, causing wear and motor burnout. At the same time, for iron-based bearings, they are easy to rust when in contact with water in the air. The powder metallurgy bearing oil is required to have excellent anti-rust properties. In addition, it also needs to have certain wear resistance and non-toxicity when used in food grinder motors (food level) and other properties.
4. Market situation of powder metallurgy bearing lubricants
According to incomplete statistics, there are currently no less than 600 units producing powder metallurgy bearings in China, including some well-known manufacturers such as Shenzhen Factory. Their output is generally between 100 and 500t/a. These manufacturers, Zhendecang Motor Co., Ltd. and Yangzhou Baolaide Powder Metallurgy Bearings, are mainly concentrated in Guangdong, Shenzhen and Southeast Yan Co., Ltd. and Xinyi City, Guangdong Province, where the economy is developing rapidly. Powder metallurgy products area.
Judging from the oil usage in the market, most bearing manufacturers use mechanical oil, No. 68 or No. 100 ordinary hydraulic oil, and some use Mobil1#, Mobil1130 or Japanese Idemitsu brand No. 68 hydraulic oil according to the requirements of the motor manufacturer. However, there are A common problem is: oil leakage occurs during the effective use period of the motor. However, Yangzhou Baolaide Powder Metallurgy Bearing Co., Ltd. uses special oil specified by Japanese bearing manufacturers to prevent oil leakage.
From the powder metallurgy bearing market and current oil usage, we can see that the powder metallurgy bearing lubricating oil market is huge. It is expected that all the current bearing manufacturers with an annual output of more than 100t will use the supporting special oil for powder metallurgy bearings, and the amount of this oil will be greater than 100t.
5 Conclusions and suggestions
(1) Powder metallurgy bearing lubricating oil is a lubricating oil that must be added during the production of powder metallurgy bearings. Due to the special structure of powder metallurgy bearings, powder metallurgy bearing lubricating oil is required to have characteristics that match its performance, such as appropriate viscosity, viscosity, etc. temperature characteristics, anti-oil dump characteristics, etc.
At present, powder metallurgy bearings account for an increasing share of the domestic bearing market, but the lubricating oil used is still only in the mechanical oil stage, and oil leakage in motors is common. We have developed copper-based special oil for use at high speeds and iron-based lubricants with anti-rust capabilities for normal speeds, which have certain market potential and technological content.
2024 February 4th Week Marginal Product Recommendation:
MG-1A Aluminum matrix composite bearings：
MG-1A is a composite material of PTFE compound tape on aluminum shell, the PTFE is tape up to 0.20 mm thickness, enabling the bearing can be sized after being fixed, meanwhile the thick PTFE layer isolates noise. The bearing is widely applied in OA machinery, shock absorber for light design bicycle.
https://www.marginalbearings.com/aluminum-matrix-composite-bearing/mg-1a-aluminum-matrix-composite-bearing.html
