Do you know the wrong cognition of grease use in bearing repair process?（Section two）

11. The higher the viscosity of the lubricant, the better 

In order to prevent wear on the contact surfaces between moving parts, the lubricant must have sufficient viscosity to form an oil film between the moving parts at various temperatures. However, the viscosity of the lubricating oil must not be higher than the degree of engine start-up and requires minimal friction under continuous operating conditions. The use of excessively viscous lubricants increases the wear of the part because: 

(1) The viscosity of the engine lubricating oil is too large, the flow is slow, the upstream is slow, and the oil pressure is high, but the amount of lubricating oil is not much, and it cannot be added to the friction surface in time. 

(2) Due to the high viscosity of the lubricating oil, the friction between the friction surfaces of the parts increases, and in order to overcome the increased friction, the fuel is consumed more, and the output power of the engine is also reduced. 

(3) The viscosity of the lubricating oil is large, the circulation speed of the oil is slow, and the cooling and heat dissipation effects are poor, which tends to overheat the engine. 

(4) Since the lubricating oil circulation speed is slow, the number of passes through the lubricating oil filter is small, and it is difficult to timely clean the worn metal chips, carbon particles, and dust from the friction surface. 

Therefore, do not use excessively viscous engine oils, and do not think that the viscosity is as high as possible. Under the condition of ensuring lubrication, depending on the temperature range during use, use a lubricant with a small viscosity as much as possible. However, for engines with relatively serious wear and large gaps, a slightly larger viscosity lubricant may be used. 

12. Universal joint cross shaft with butter 

It is clearly stated in the general vehicle maintenance manual that the key teeth and the intermediate bearing of the transmission shaft telescopic sleeve use calcium-based grease, the needle bearing of the cross shaft and the intermediate bearing of the three-bridge driving rear axle of the automobile use gear oil. However, in actual work, due to the lack of filling equipment, some repairmen erroneously lubricate the cross-shaft needle bearing with calcium-based grease for the convenience of the drawing, resulting in premature failure of a large number of cross bearings. Since the mouth of the universal joint cross shaft filled with gear oil is a very common grease mouth, it often causes a misunderstanding.

In fact, the butter is not added to the needle bearing. Because the viscosity of the butter is large, when the butter is used to add grease to the inner cavity of the cross shaft through the grease nipple, the resistance of the butter into the oil passage of the narrow inner oil groove is great, and the pressure of the butter will overflow against the pressure reducing valve opposite the oil nozzle. The repairman mistakenly believes that the bearing has been filled with oil. In fact, the butter is not only unable to enter between the needles, but it is also difficult to reach the end of the cross journal. Therefore, the wrong way of lubricating the universal joint cross shaft with butter instead of gear oil should be changed. Instead, the gear oil should be filled with a gear oil pressure gun. 

13. The more grease the hub bearing is, the better. 

Some car owners fill the hub bearings and cavities with grease when maintaining the hub bearings, and think that the more the better, it is not. Filling the hub cavity with grease will cause most of the grease to get into the hub cavity. Instead of being added to the bearing, it will flow to the brake shoe in the brake drum, causing the brake to fail. An increase in rolling resistance causes the hub to overheat and cause unnecessary waste. Therefore, it is only necessary to apply a thin layer of grease to the hub cavity. It not only ensures the lubrication of key parts, but also facilitates the cooling and cooling of the hub, and at the same time saves a lot of grease. 

14. Thinning the grease with the addition of lubricating oil 

Some repair workers prefer to add lubricating oil to the original grease when using grease in winter. This approach is wrong. Because the structure of the grease is a colloidal structure system composed of a thickener and a base oil, the thickener forms a structural network, and the base oil (generally a common lubricating oil) is adsorbed in the network to form a stable structural system, which will thicken. The agent and base oil will not separate. If the lubricating oil is added after the fat is formed, although it is stirred, it cannot be uniformly dispersed and contained in the network, and is easily separated and lost during use, which is disadvantageous for lubrication. If you need to use a small consistency grease in winter, you can use a small number 1 or 2 calcium-based grease. 

15. Mix old and new grease 

New greases and old greases cannot be mixed even if they are of the same type. Because the old grease contains a lot of organic acids and impurities, if mixed with new grease will accelerate its oxidative deterioration. Therefore, when changing grease, be sure to re-add new grease after cleaning the old grease on the parts. 

16. Add butter when servicing leaf springs 

Some repair personnel add grease to the assembly to prevent the steel sheets from being worn during maintenance and assembly of the leaf springs. In fact, this is a wrong way of not meeting the technical requirements. Since the butter is easily squeezed out from between the steel sheets and easily adheres to the dust, the leaf springs are quickly rusted and disassembled, reducing the life by more than 40%. 

When repairing or combining leaf springs, graphite calcium-based grease should be applied. Graphite calcium-based grease is made by adding 10% flake graphite to calcium-based grease. Graphite itself is a good lubricant, its pressure resistance is good, in the car driving, especially on the uneven road, the steel plate has strong vibration and friction, using graphite calcium-based grease, due to its resistance It has good pressure and is not easy to be squeezed out from between steel plates. It can lubricate and protect for a long time and prolong the life of leaf springs. 

17. Apply oil to the tire bolt nut 

In order to easily tighten the nut and prevent rust, many owners and repairers apply oil to the bolts and nuts of the tire. In fact, this is a wrong approach. Because, according to the mechanical principle knowledge, after the tire nut is tightened, the thread has a self-locking feature. This is due to the fact that the thread helix angle is less than the equivalent friction angle between the threads. In a given bolted joint, the helix angle is a certain value, and the equivalent friction angle varies with the friction state between the threads. Obviously, the equivalent friction angle between the threads after oiling is reduced, and the self-locking performance of the bolted joint is deteriorated. Therefore, never apply grease or oil to the bolts and nuts of the tire. In doing so, the nut will be loosened and the tire will run away, causing a serious accident. 

18. Starter bearing grease 

The starter bearing generally adopts a self-lubricating bearing or a porous oil-bearing bearing alloy, and is an oil-containing antifriction alloy prepared by mixing metal powder (iron or copper powder), mixing, pressing, sintering, and immersing in a lubricating oil having a certain temperature. material. It is mainly used for refueling difficulties, light load high speed or low speed load and frequent reversing. According to the composition of the material, it is divided into iron graphite and bronze-graphite. When starting the machine maintenance, do not use gasoline to clean the bearings, so as not to dilute the lubricating oil, you should use a clean cloth or cotton yarn, and should not add grease, because the bearing fit clearance is relatively small, the grease can not remain in the bearing, pull out Falling on the brush and the commutator will cause the starter to be weak, and in severe cases, the commutator will ablate. However, a few drops of GL-3 85/90 gear oil can be applied to the bearing. After driving for 50,000 km, the bearings are cleaned with gasoline and then immersed in GL-3 gear oil at about 120 °C for 1 h. 

19. Dip lubrication clutch release bearing 

Most of the domestic automobile clutches use closed side pressure ball separation bearings. Most of the selected greases are calcium based grease and calcium sodium based grease. Most maintenance personnel use a method of heating and melting the separation bearing by heating and melting the separation bearing into 50% of the oil and then diluting the separation bearing into the oil to fill it and then cooling it. Although this method completes the filling task, the effect is not good, because the heating will damage the structure of the calcium-based grease, and the lubrication performance of the grease will be degraded, resulting in premature wear of the separation bearing and shortening its service life. The correct way is to use the injector to raise. 

20. Premium cars must use imported lubricants 

Some car owners and vehicle management personnel believe that high-end cars are expensive, and imported lubricants are of good quality. Imported lubricants are safer and more secure. In fact, it is not the quality of the advertising, but the quality indicators and actual use. At present, most of the imported lubricants sold in the domestic market are jointly produced by foreign companies and China. Most of these lubricants are produced in China using domestic base oils and compound additives, while domestic Hengyun and Great Wall advanced lubricants use domestically produced high-quality foundations. Oil and compound imported additives are blended and produced in China, and the quality of their products has passed ISO9002 international quality certification. Therefore, high-end cars should choose the corresponding quality domestic or imported lubricants according to their working conditions, technical indicators and technical performance, and the price difference between domestic and imported lubricants is self-evident.