Bearing Industry

Bearings are widely used in major equipment fields such as mining machinery, precision machine tools, metallurgical equipment, heavy equipment and high-end cars, and emerging industries such as wind power, high-speed rail and aerospace. The bearings produced in China are mainly medium and low-end bearings and small and medium-sized bearings, which are characterized by low-end surplus and high-end lack. Compared with foreign countries, there is a big gap between high-end bearings and large bearings. China's high-speed railway passenger car special wheelset bearings need to be imported from abroad. In the key bearings used in aerospace, high-speed railway, high-end cars and other industrial fields, there is a big gap between China's bearings in terms of service life, reliability, Dn value and carrying capacity. For example, the service life of foreign automobile gearbox bearings is at least 500,000 kilometers, while the domestic similar bearing life is about 100,000 kilometers, and the reliability and stability are poor.Aviation aspectAs a key component of the aero engine, the second generation of aerospace engine bearings with a thrust ratio of 15-20 is being developed abroad, and is ready to be assembled into the 5th generation aircraft by 2020. In the past 10 years, the United States has developed the second generation of bearing steel for aerospace engines. The representative steel grades are high-strength corrosion-resistant bearing steel CSS-42L resistant to 500 °C and high-nitrogen stainless steel bearing bearing X30 (Cronidur30) resistant to 350 °C. The development of bearings for the second generation of aerospace engines is underway.Car aspectFor automotive wheel bearings, the first and second generation of hub bearings (ball bearings) are widely used in China, and the third generation of hub bearings has been widely used in Europe. The main advantages of the 3rd generation of hub bearings are reliability, short payload spacing, easy installation, no adjustment, and compact structure. At present, most of the imported models in China use this lightweight and integrated structural wheel bearing.Railway vehicleAt present, China's railway heavy-duty train bearings are made of domestic electroslag remelting G20CrNi2MoA carburized steel, while foreign high-purity bearing steel (EP steel) vacuum degassing smelting technology, inclusion homogenization technology (IQ steel) Long life steel technology (TF steel), fine heat treatment technology, surface super-hardening treatment technology and advanced sealing lubrication technology are applied to the production and manufacture of bearings, which greatly improves the life and reliability of bearings. China's electroslag bearing steel is not only of low quality, but also costs 2000-3000 yuan/ton higher than vacuum degassed steel. In the future, China needs to develop ultra-high purity, fine-grained, homogenized and stable quality vacuum degassing bearing steel to replace the current Electroslag bearing steel used.Wind power energyFor wind power bearings, China is currently unable to produce spindle bearings and speed increase bearings with high technical content, basically relying on imports, and the localization of bearings for wind turbines above 3MW has not been solved. In order to improve the strength, toughness and service life of wind power bearings, a new special heat-treated steel SHX (40CrSiMo) was adopted. For yaw and pitch bearings, the surface hardness, surface hardness, soft belt width and width of the hardened layer were controlled by surface induction hardening heat treatment. Surface crack; carbonitriding for the gearbox bearings and spindle bearings, resulting in more stable residual austenite volume fraction (30%-35%) and a large number of fine carbides and carbonitrides on the surface of the part, improving the bearing Service life under contaminated lubrication conditions.In order to improve the service life and running accuracy of the rolling mill bearings, it is necessary to carry out research and development of ultra-high-purity vacuum degassing and smelting of bearing steels such as GCr15SiMn and G20Cr2Ni4 for rolling mills and large austenite volume control heat treatment of bearing surfaces. Japan's NSK and NTN Bearing Company have developed surface austenite strengthening technology, which has developed TF bearings and WTF bearings by increasing the surface austenite content, thereby increasing the bearing life by 6-10 times.In the future, the research and development direction of China's bearing steel is mainly reflected in four aspects:First, the economic cleanliness: under the premise of considering economics, further improve the cleanliness of steel, reduce the oxygen and titanium content in the steel, and achieve the mass fraction of oxygen and titanium in the bearing steel are less than 6×10-6 and 15 respectively. The level of ×10-6 reduces the content and size of inclusions in the steel and improves the uniformity of distribution.Second, organizational refinement and homogenization: through the application of alloying design and controlled rolling and controlled cooling process, further improve the uniformity of inclusions and carbides, reduce and eliminate network and ribbon carbides, reduce average size and maximum particle size. Dimensions, reaching the target of an average carbide size of less than 1 μm; further increasing the grain size of the matrix structure to further refine the grain size of the bearing steel.The third is to reduce the low-fold tissue defects: further reduce the center looseness in the bearing steel, the center shrinkage hole and the center component segregation, and improve the uniformity of the low-fold structure.The fourth is the high toughness of bearing steel: through the new alloying, hot rolling process optimization and heat treatment process research, improve the toughness of bearing steel.

The service life of the bearing is affected by many parameters that are not controlled by the bearing manufacturers. For example, bearing mounting, temperature, exposure to external environment, lubricant cleanliness and electrical currents through bearings etc. High frequency PWM inverters can induce currents in a bearing, which can be suppressed by use of ferrite chokes.The temperature and terrain of the micro-surface will determine the amount of friction by the touching of solid parts.Certain elements and fields reduce friction, while increasing speeds.Strength and mobility help determine the amount of load the bearing type can carry.Alignment factors can play a damaging role in wear and tear, yet overcome by computer aid signaling and non-rubbing bearing types, such as magnetic levitation or air field pressure.

L10 life Bearings are often specified to give an "L10" life (outside the USA, it may be referred to as "B10" life.) This is the life at which ten percent of the bearings in that application can be expected to have failed due to classical fatigue failure (and not any other mode of failure like lubrication starvation, wrong mounting etc.), or, alternatively, the life at which ninety percent will still be operating.The L10 life of the bearing is theoretical life and may not represent service life of the bearing. Bearings are also rated using C0 (static loading) value. This is the basic load rating as a reference, and not an actual load value. Plain bearingsFor plain bearings, some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear.Flexure bearingsFlexure bearings rely on elastic properties of material.Flexure bearings bend a piece of material repeatedly. Some materials fail after repeated bending, even at low loads, but careful material selection and bearing design can make flexure bearing life indefinite.Short-life bearingsAlthough long bearing life is often desirable, it is sometimes not necessary. Tedric A. Harris describes a bearing for a rocket motor oxygen pump that gave several hours life, far in excess of the several tens of minutes life needed.Composite bearingsDepending on the customized specifications (backing material and PTFE compounds), composite bearings can operate up to 30 years without maintenance.Oscillating bearingsFor bearings which are used in oscillating applications, customized approaches to calculate L10 are used.

Plain bearing consisting of a shaft rotating in a hole. There are several specific styles: bushing, journal bearing, sleeve bearing, rifle bearing, composite bearing. Rolling-element bearing in which rolling elements placed between the turning and stationary races prevent sliding friction. There are two main types Ball bearing in which the rolling elements are spherical balls Roller bearing in which the rolling elements are cylindrical,taper and spherical rollers Jewel bearing a plain bearing in which one of the bearing surfaces is made of an ultrahard glassy jewel material such as sapphire to reduce friction and wear Fluid bearing a noncontact bearing in which the load is supported by a gas or liquid Magnetic bearing in which the load is supported by a magnetic field Flexure bearingin which the motion is supported by a load element which bends.

A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. Rotary bearings hold rotating components such as shafts or axles within mechanical systems, and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the plain bearing, consists of a shaft rotating in a hole. Lubrication is often used to reduce friction. In the ball bearing and roller bearing, to prevent sliding friction, rolling elements such as rollers or balls with a circular cross-section are located between the races or journals of the bearing assembly. A wide variety of bearing designs exists to allow the demands of the application to be correctly met for maximum efficiency, reliability, durability and performance.

The bearing industry uses different materials for the production of the various bearing components. The bearing materials are processed to achieve desirable properties to maximize bearing performance and life. The materials described here are the most commonly used. Bearings Made of Chrome Steel - SAE 52100The most common material used to produce the load carrying components in precision ball bearings, roller bearings, and tapered roller bearings is 52100 chrome steel. These components are the bearings inner and outer rings, balls and rollers. The chemical composition of this steel has high carbon and about 1.5% chromium content. Using controlled processing and heat-treating methods the finished bearing components have high strength to resist cracking and a hard surface to resist subsurface rolling contact fatigue. The typical surface hardness for bearing components made from this material ranges from 60- 64 on the Rockwell hardness C scale (Rc).Extra clean 52100 chrome steel bearingsThe raw steel used to produce high precision miniature bearings is processed with additional melting steps. The result is a type of steel with very uniform fine grain material structure, the bearing contact surfaces can be super finished very smooth so the bearing is very quiet.The most common heat treating method for chrome steel is to thru harden the steel in a controlled atmosphere furnace. Bearings manufactured from chrome steel can operate at continuous temperatures up to 120°C.Where higher temperatures are encountered, it is possible to Heat Stabilize the bearing components. By varying the heat treating process, bearings can be produced so they are capable of operating at temperatures of 220°C, and higher. For these applications, the components must be subjected to a tempering treatment at a higher temperature corresponding to the service temperature. This elevated tempering treatment has a detrimental effect on the hardness of the material and the load carrying capacity of the bearing is reduced.SAE 52100 is an excellent general purpose bearing steel. Due to its excellent hardness and wear resistance, it exhibits good fatigue life in rolling element bearings. However, the corrosion resistance of chrome steel is poor because of the low chromium content. The surfaces of the bearings must be protected with a coating of rust inhibitor or oil to stop oxidation.