Technology of Plastic Sliding Bearing and its Application in the Automotive Industry

Bearings can be divided into rolling bearings and sliding bearings from the working principle. The rolling friction pair is formed when the rolling bearing works and the sliding friction pair is formed when the sliding bearing works. This determines that the friction coefficients of rolling bearings and sliding bearings differ by at least 10 orders of magnitude. Under a certain load and speed without lubrication, the size of the friction coefficient of the rolling bearing basically depends on the manufacturing accuracy of the balls, the inner and outer rings of the bearing, and the mutual clearance between them. The friction of rolling bearings is not directly related to the bearing material itself. Rolling bearings generally require regular lubricants. Under the same load and speed without lubrication, the friction coefficient of the sliding bearing mainly depends on the self-lubricating performance of the bearing material itself. The sliding bearing material itself has good self-lubricating properties and can work for a long time without or with little oil. The sliding bearing takes advantages of the self-lubricating technology, achieves self-lubricating and maintenance-free feature for bearings. So that more and more engineering designers adopt the sliding bearings.

Mechanism of sliding bearing lubrication and its limit PV value

When the sliding bearing works, a lubricant film can be formed on the surface of the sliding bearing to separate the surfaces of the moving pair. It reduces the sliding friction greatly after short-term operation. There is no direct contact between the surfaces of the moving pairs that avoids abrasion of the sliding bearings. The large bearing capacity and the high rotation precision of the sliding bearing, along with the anti-impact effect of the lubricating film formed during the movement lead to a widely used of sliding bearings in engineering projects. The formation of the lubricating film is the basic condition for the normal operation of the sliding bearing. The factors that affect the formation of the lubricating film are the lubrication method, the relative speed of the motion pair, the physical properties of the lubricant and the roughness of the surface of the motion pair. An important measure of sliding bearing performance is the maximum PV value that the bearing can reach. “P” refers to the load of the bearing and “V” refers to the linear velocity while bearing operates. The greater the limit PV value of the sliding bearing, the better performance and the longer life of the bearing. The main factors that affect the limit PV value of the sliding bearing are the self-lubricating performance, load bearing and temperature resistance of the bearing material itself. The external factors that affect the actual PV value of the sliding bearing are mainly the load, operating speed, ambient temperature and quality of fit. Generally speaking, the larger the limit PV value, the better for the design of sliding bearing manufacturing; while the smaller the PV value of the bearing, the better for the design of sliding bearing application which is beneficial to prolong the service life. The design of the sliding bearing generally determines the structural type and the geometric parameters of the bearing and selects the appropriate material according to the working conditions.

Technology of Sliding bearing and the R&D direction

Sliding bearings can be divided into metallic sliding bearings and non-metallic sliding bearings according to materials. Metal sliding bearings can usually be divided into composite sliding bearings, metal-based sliding bearings and so on; non-metallic sliding bearings can usually be divided into engineering plastic sliding bearings, filament-wound bearings, etc….

Composite sliding bearings are generally composed of three layers: substrate layer + copper powder layer + anti-friction layer. Part of the lubricating material will be transferred to the surface of the grinding shaft slowly during operation. It realizes the establishment of a friction pair between the friction layer of the bearing and the lubrication film on the surface of the grinding shaft. The wear rate of the bearing decreases as the friction coefficient decrease between the bearing and the grinding shaft. Metal-based sliding bearings can be divided into solid lubricant inlaid sliding bearings (CSB650 series), bimetallic sliding bearings (CSB800 series) and integral sliding bearings.

Non-metallic sliding bearings are the current research and development direction of sliding bearing technology. There are high polymer engineering plastic bearings (CSB-EPB series) and filament-wound bearings (CSB-CR series). The development of high polymer engineering plastic bearing technology has almost covered all polymer modification technologies. It can be divided into molded sintered plastic sliding bearings and injection molded plastic sliding bearings from the manufacturing process. Molded sintered sliding bearings are generally restricted by low efficiency and low manufacturing accuracy. So the development is limited and not suitable for mass production.

At present, high polymer engineering plastic modification technology and injection molded plastic sliding bearing technology have been rapidly developed globally. China CSB Company has been studying the self-lubricating modification technology of engineering plastics for more than 20 years. CSB uses advanced polymer modification technology to fill special lubricants and high-functional fibers in high-performance polymers as a wear-resistant base material. Special lubricants reduce the coefficient of friction, and fibers and fillers enhance the compression resistance and wear resistance. The body material of engineer plastic sliding bearings is self-lubricating modified materials, so it is superior to metal composite bearings in terms of friction performance and service life (the friction materials of metal composite bearings are only about 0.03mm thick on the surface). Some of CSB’s engineering plastic bearings as follow: 1. CSB-EPB5 bearings, which can be used for a long time in environments with temperatures up to 250°C and can resist almost all chemical media; 2. CSB-EPB4 bearings, which have extremely low water absorption and high anti-corrosion that can operate under water for a long time; 3. CSB-LIN linear bearing sliding module, has a very low coefficient of friction, the maximum allowable operating speed is 10m/s. Currently, the most widely used in the automotive industry is CSB-EPB general-purpose plastic sliding bearings and CSB-EPB3 enhanced plastic sliding bearings.

The new type of high-load non-metallic sliding bearings CSB-CR series filament-wound bearings take high-strength glass fiber and reinforced high-temperature epoxy resin as the carrier layer, and special fibers and PTFE fibers as the lubricant layer. That the bearing has excellent wear resistance and low friction coefficient under high load and low speed conditions.

Application technology of sliding bearing in automotive industry

Sliding bearing has been fully applied in the automotive industry due to its superior self-lubricating properties. At present, the sliding bearings of CSB are applied to almost every automobile manufacturer in the world. Especially the application of high polymer engineering plastic sliding bearings is extensively widely taken in the automobiles. The engineering plastic bearings can be used in various parts of automobiles. Applications are from the simplest automotive door hinge system to complex mechanical and demanding components, such as: steering gears in automotive steering systems, gear shifts in transmission systems, etc…. The cost of engineering plastic sliding bearings is extremely low as long as the excellent mechanical properties and the advantages of lubrication-free and dry operation availability itself. The CSB-EPB engineering plastic sliding bearings can be up to 50% cheaper than PTFE-coated metal sliding bearings.

The CSB-EPB3 enhanced series of plastic sliding bearings are used in the automobile door hinge system which overcomes the increase in the pulling force or noise caused by the rusting of the metal sliding bearings. It avoids the occurrence of instantaneous stuck when opening and closing the car door or trunk lid.

The sliding bearings used in automotive shock-absorption system are very strict in terms of wear resistance, impact resistance and fit accuracy. The  poor wear resistance of the sliding bearing will lead to increased wear on the outer seal ring. The hydraulic oil leaks if the seal ring fails and the shock absorption function of the shock-absorption system will fail. CSB-40 composite bearing (DP4 material) overcomes this harsh condition and is applied in various automotive shock absorbers successfully.

The CSB-RPM4 support sleeve is used in the automobile steering system makes the steering wheel runs smoothly during the entire steering process. It can ensure the steering system operates normally even in the poor road conditions. The excellent wear resistance and shock absorption of CSB-RPM4's have been verified in automotive steering systems.

The automobile is very stable during braking because of the application of CSB-EPB4 high-performance engineering plastic bearings in automobile braking system. The automobile can achieve fast and stable braking even in an emergency. It also ensures that the car is effectively braked whether the car is turning smoothly or suddenly. EPB4 engineering plastic bearings have high hardness and wear resistance and can achieve a long service life because of adding high-performance lubricants and functional fibers to the EPB4 material.

Generally speaking, the tolerance of the thickness of the sheet metal material used in the car seat system and the tolerance of the punching holes are relatively large. However, a minimum clearance is required to reduce noise as much as possible in the seat system. In order to solve this problem, CSB developed and produced EPB3 engineering plastic bearings and PCB plastic clamp bearings. Nowadays, more and more car seat design engineers use CSB's plastic bearings.

The application technology of sliding bearings is now developing rapidly with the continuous improvement of self-lubricating material modification technology. At present, sliding bearings have been successfully applied in civil machinery, military machinery, aerospace machinery and other fields. As the continuous expansion of application fields and the continuous improvement of work requirements of sliding bearings, it requires us to continue exploring and studying the modification technology of bearing materials, manufacturing technology and application technology of sliding bearings and meaning while making progress.