Analysis of Automotive Bearing Materials and Heat Treatment Technology2018-08-28 12:40:10

The automobile industry is an important pillar industry in China, and it has a place to be reckoned with in the entire processing and manufacturing industry. The components of the body can be seen in multiple parts of the body. It has a special mission to withstand loads, reduce friction and guide moving parts. With the continuous development of China's economic development and industrial technology, China has become a major bearing manufacturer including automotive bearing steel, but there are still large gaps with leading manufacturers such as Schaeffler, SKF, TIMKEN, and KOYO in Japan. As a source, the future direction is still to strictly control metallurgical quality, non-metallic inclusion grade, carbide size and distribution, and improve the level of heat treatment technology.

Heat treatment is the key process in the manufacturing process of automotive bearings. The quality of processing and raw materials are two important factors affecting bearing life [1]. Heat treatment has an important influence on the microstructure, mechanical properties, surface quality, dimensional shape accuracy and stability of bearings and other components under the conditions of use. Therefore, the heat treatment process is optimized, and the appropriate heat treatment parameters are selected to obtain the use condition of the workpiece. The best comprehensive performance for the failure mode is an important topic of heat treatment technology [2].

1. Application of bearing materials in automobiles
As we all know, the bearing consists of the outer ring, the inner ring, the rolling elements (balls, cylinders, cones or needles, etc.) and the cage. Most of them have sealing rings, except for the sealing ring and part of the cage. The material of manufacture is mainly bearing steel.

When selecting the type and model of the automobile bearing, it mainly depends on the nature, direction, size, working environment of the actual part, and the requirements on the stiffness, limit speed, life and accuracy of the bearing, which are generally completed by the designer. Bearings are widely used in the entire vehicle and vary with vehicle type, mounting location and manufacturer, as shown in Figure 1.

I have visited some important domestic automotive bearing suppliers, such as Shanghai Renben, Zhejiang Wanxiang Seiko, Hubei New Torch, Changzhou Guangyang, Luoyang Dongsheng, Chongqing Yangtze River, etc. The following only combines the automotive power system (alternator in the engine) , air-conditioning electromagnetic clutch, tensioner and idler bearings, bearings, drive systems (shaft gears, differentials, clutches and other bearings in the transmission), wheel bearings and other related products for a brief introduction.

(1) Powertrain Bearing The engine is the heart of the car and continuously powers other components. The internal bearings were previously dominated by plain bearings. At present, most of them use sealed ball bearings under the premise of improving bearing performance. Figure 2 shows several typical bearings in the engine.

The alternator bearing is a single-row sealed ball bearing. It is mainly subjected to centripetal force. It is required to operate reliably under the conditions of more than 2000r/min and temperature above 180°C. The ferrule and rolling element are made of high purity GC r15. Requires 58~64H RC, the cage is generally made of nylon PA46, the sealing ring is generally made of acrylate rubber ACM, the reference standard is JB/T8167-2006 [3].

The electromagnetic clutch bearing of the air conditioner compressor is a double row angular contact ball bearing, the outer ring rotates, and the speed of the air conditioner pulley can reach 7000-13 0 0 0 r/min, the maximum temperature is 160 °C, the material is the same as above, the cage is composed of A part of a common single spherical pocket becomes a cylindrical surface, and the reference standard is JB/T 10531-2005 [4].

Tensioning wheel and idler bearing are high-performance sealed ball bearings. The former acts on the loose side of the synchronous belt. The latter acts on the tight side of the synchronous belt. The material is basically the same as above. The cage can be made of engineering plastic. 08 steel or 10 steel can also be used. Manufactured, the seal is made of ACM or FPM (fluororubber), the reference standard is JB/T 10859-2008 [5].

Pump shaft bearings are generally double row ball bearings with a radial dimension smaller than that of a normal bearing. It is essentially a simplified double-bearing bearing system. The two supported bearings have no inner ferrules. The raceways of the rolling elements are made directly on the shaft. The two bearing bearing outer rings are made in one piece. The two sides are sealed with seals. The rollers are usually made of high-chromium bearing steel. The shaft and outer ring are made of carburized steel or high-carbon chromium bearing steel. The reference standard is JB/T 8563—2010 [6].

(2) Drive system The typical representative of the bearing transmission system is the transmission. It can be divided into manual (M T), automatic (AT), continuously variable (CVT), double clutch (D C T), etc., and is the most used part of the bearing. There are often several bearings in the transmission with different gear positions. The main types are ball bearings, cylindrical roller bearings, tapered roller bearings, needle bearings and so on. The transmission can be regarded as a gear box, which often contains impurities (iron filings, burrs, sand, etc.) in the grease and anti-rust oil. The bearing rotates at a high speed, resulting in a significant shortened service life [7].

Figure 3 is a schematic diagram of the bearing position of our company's MA manual transmission (see the blue marking part in the figure), in which the one-axis and one-position gears are deep groove ball bearings 25D52E15, one-axis five-position is deep groove ball bearings 25D62E17, two The first gear position of the shaft is cylindrical roller bearing 32D62E16, and the two-axis five-position is deep groove ball bearing 22D57E17.

There are also two tapered roller bearings 38D63E17 in the differential, which are respectively located on the left and right sides of the differential case, and are mounted on the bearing housing hole of the reducer, which receives and transmits the driving force of the differential and the reducer, minus Small drive frictional resistance improves drive efficiency and reliability.

The rolling elements and inner and outer ring materials of the above bearings are mainly GCr15, 100Cr6, SUJ 2, SKF 3, using integral quenching + low temperature tempering, heat treatment hardness 6 0~6 3 HRC (rolling body requirements 6 0~6 4 HRC ), the nylon cage material is PA46+30%GF, the contact seal is ACM+SPCC, and the grease is Chevron SR I-2 (moisture injection 2.0~2.8g).

The clutch release bearing, commonly known as the clutch pin plate, is in the position shown in Figure 4. When the clutch pedal is depressed, the pressure plate or drive plate that receives the spring thrust can be moved toward the clutch cover, that is, the lever is separated to overcome the thrust of the plate spring. The separation of the clutch is completed. At present, it mainly relies on import. The rolling element is 100Cr6, the inner and outer ring material is C67S (requires minimum surface hardness of 680H V), the cage is PA66+25% FV, and the seal is made of hydrogenated nitrile rubber HNBR. See standard [8].

(3) Automobile wheel bearing With the improvement of the overall performance of the car, the life, strength, rigidity and maintenance-free requirements of the wheel bearing are becoming more and more strict, and people are becoming more and more aware of the importance of lightweight, reliability, versatility and modularity. Sex, automotive wheel bearings are moving in a highly integrated direction [9]. The automotive wheel bearing unit has been developed from the original ferrule locking type and cage locking type unit (first generation) to the second generation of the outer ring with flange, and then to the large filling angle with the inner ring. The third generation of flanges integrates sensors with ABS and flanges, as shown in Figure 5. They are double-row ball bearings to withstand the greater load of the entire body. Most of the front wheel hub bearings in our existing models use the first generation, and the rear wheels use the third generation. For example, the inner and outer ring material of a certain type of wheel bearing is SKF3, the steel ball material is SUJ2, the flange material is S55C, the bolt material is SCM435, the cage is nylon PA66+25%GF, and the combined sealing ring is NB R+SPCC. /NBR+SUS430.

1. Separation bearing 2. Separation plate 3. Working cylinder 4. Low pressure oil pipe 5. Liquid storage tank 6. Power spring 7. Push rod 8. Main cylinder 9. High pressure oil pipe