Eight selection principles for special lubricants for motor bearings
It can be seen from the failure examples of rolling bearings for oil-lubricated motors that most of the failures are caused by insufficient lubricating oil viscosity. The lower the viscosity of the lubricating oil, the worse the bearing capacity of the oil film, and the oil film is easy to rupture. The metal materials on the relative moving surface of the rolling bearing will have direct contact, resulting in increased friction and increased wear, and the service life of the rolling bearing will be significantly shortened or the bearing will be damaged. Accidents of burns and fractures. However, if the viscosity of the lubricating oil is too high, the frictional resistance will increase, the heat generated by stirring the lubricant will increase, and the energy consumption of the system will increase. On the other hand, for rolling bearings that operate under special conditions such as high speed, high load and high temperature, there may be special requirements for rust prevention, oxidation resistance, anti-wear and improving the absorption capacity of lubricating oil. Therefore, the choice of lubricating oil is mainly the determination of the viscosity grade of the lubricating oil and the determination of the types of additives used or the selection of different lubricating oils with certain additives. The general selection principle of lubricating oil is as follows. One: Working temperature Working temperature affects the viscosity change and lubrication effect of lubricating oil. Therefore, when the working temperature is low, lubricating oil with lower viscosity should be selected; when the working temperature is high, lubricating oil with high viscosity or with appropriate additives should be selected. Depending on the ambient temperature, the viscosity of the selected lubricating oil should also change. For example, lubricating the same bearing in winter should use lubricating oil with a lower viscosity than in the south or summer. When the working temperature changes frequently, lubricating oil with excellent viscosity-temperature characteristics should also be selected, that is, the viscosity of the lubricating oil used does not change much with the increase or decrease of the working temperature, so as to ensure that the oil film thickness is stable within a certain range. Two: The higher the speed of movement, the more lubricating oil with low viscosity should be used to avoid increased movement resistance and excessive heat generation; on the contrary, at low speeds, lubricating oil with higher viscosity should be used to increase the load bearing capacity. ability. Three: the nature of sports There are shocks, vibrations, frequent load changes, variable speeds, and starting in sports. When stopping, reversing frequently, and doing reciprocating or intermittent motion, it is not conducive to the formation of oil film, so higher viscosity lubricating oil should be used. Sometimes it is better to use grease or even solid lubricant to ensure reliable lubrication. 4: Working load The greater the load that the rolling bearing bears, the higher the viscosity of the lubricating oil should be, and it should have better oil and extreme pressure to prevent the lubricating oil from being squeezed out of the friction pair or direct contact between metals . Five: Structural features The smaller the radial clearance of the rolling bearing, the higher the machining accuracy of the friction surface, and the lower the viscosity of the lubricating oil. Six: Environmental conditions When the bearing is working under humid, corrosive gas, low temperature, dust, and strong radiation conditions, the lubricating oil is easy to be polluted and deteriorated. At this time, water resistance, wear resistance, corrosion resistance, cold resistance, and radiation resistance should be selected Strong lubricating oil. Generally speaking, lubricating oil should not be used in places where there is serious water splashing, emulsion spraying, humid air or dust and dust. Grease should be used. Seven: Bearing accuracy When the friction surface of the bearing movement is rough, oil with high viscosity is generally used to withstand large local pressure due to poor contact. When the precision of the movement friction surface is high, low-viscosity lubricating oil should be used to reduce Small unnecessary energy loss and temperature rise. Eight: bearing hardness When the bearing movement friction surface hardness is low, the lubricating oil with high viscosity should be selected, and the amount of oil should be sufficient; on the contrary, the viscosity of the lubricating oil can be reduced. In order to give full play to the role of the lubricant, it is necessary to choose a lubrication method and high-quality lubricant suitable for the conditions of use. When assembling the motor, the grease injected into the bearing chamber must be clean. Lubricating grease is not clean and mixed with impurities, especially hard impurities, which may easily cause abnormal bearing wear and cause bearing failure. The amount of grease filled should be appropriate. If the amount added is too small, the bearing will generate heat due to intermittent lack of oil and dry grinding and cause bearing failure; if the amount added is too large, the grease will stir and heat up and cause bearing failure, and it will become thinner and throw out to contaminate the inside of the motor. . The filling of the motor grease should be injected according to the design amount, and should be reasonably distributed in the bearing room space. The bearing chamber space is composed of three parts: the bearing chamber and the inner and outer bearing caps. Grease should be distributed as far as possible on the bearing chamber and the surface enveloping the bearing. The filling of the space is determined according to the speed. During the operation of the motor, it is necessary to prevent the lubricating grease from deteriorating and losing, causing bearing failure, and the special lubricating grease for the bearing should be replenished regularly, and the oil return pan should be used in the design. It is strictly forbidden to mix different grades of grease to prevent deterioration of the grease, loss of lubrication performance, and bearing failure.