Functions and types of RDK bearing lubricants

  1 function of lubrication

  When the bearing works, in order to ensure the effective and reliable operation of the bearing, there must be sufficient lubrication. Function of bearing lubrication:

  Prevent or reduce the direct contact of metal between rolling element, raceway and cage in bearing to reduce friction and wear

  Oil film is formed on the friction surface. When the pressure oil film is formed, the contact bearing area of the parts can be increased. Therefore, the contact stress can be reduced and the rolling contact fatigue life can be prolonged

  The lubricant can prevent rust and corrosion

  Oil lubrication also has the function of heat dissipation and taking away the wear particles or invasive pollutants produced in the operation of the bearing

  Grease lubrication can increase the sealing performance and prevent the invasion of external pollutants

  It has the function of vibration and noise reduction

  2 selection of lubricants

  In theory, choosing lubricating oil or grease as the lubricant of rolling bearing can meet the lubrication needs of bearing. In addition to a small amount of lubricant used for lubrication or heat dissipation in rolling bearings, due to the large amount of lubricant required. When lubrication, as long as there is a lubricant that can form oil film on the moving contact surface and reach the ideal working temperature.

  In the actual selection of lubricants, it can be considered according to the mechanical structure, the service conditions of the bearing, the structure of the parts adjacent to the bearing, the lubrication method, maintenance and other factors.

  The lubricants used in bearings are mainly divided into grease lubrication and oil lubrication. Solid lubricants can also be used under special working conditions.

  3 grease lubrication

  Considering from the structure of the lubrication system, grease lubrication is used in many occasions because it does not need special devices, the seal is relatively simple and easy to use.

  Grease is a semi-solid lubricant made of base oil, thickener and additive. Among them, base oil accounts for about 70-95%, thickener accounts for 5-30%, and additive accounts for a small amount.

  The commonly used greases for bearings include calcium grease, sodium grease, lithium grease, calcium sodium grease, aluminum grease and disulfide grease.

  Main properties of grease:

  · base oil viscosity

  The lubricity of grease depends on the viscosity of base oil, which is very important for the formation of lubricating oil film. Generally, the viscosity of base oil used for rolling bearings is generally in the range of 15 ~ 500mm2 / S (40 ℃). If the viscosity is higher than 500mm2 / S (40 ℃), the lubrication is not sufficient, and if the viscosity is higher than 1000mm2 / S (40 ℃), the base oil is difficult to separate from the grease. The bearings will not be lubricated. If it is lower than 15mm2 / s, it is not easy to form oil film.

  Consistency

  The ability of grease to resist deformation under external force is called consistency. The consistency is measured by penetration, and the grade of grease is also expressed by penetration grade. The greater the penetration, the greater the consistency, the higher the hardness and the worse the fluidity of the grease. Penetration (or brand) is divided into nine levels. Among them, the penetration suitable for bearings is generally level 1, 2 and 3, and level 2 is the most common.

  Generally, low consistency grease is used for low temperature working conditions, while high consistency grease is used for low temperature working conditions.

  When the grease is used in the specified temperature range, the consistency will not change too much. If the working temperature is higher than the specified service temperature, the grease will become soft and easy to lose. If the working temperature is lower than the specified service temperature, the grease will harden, which will increase the movement resistance or affect the lubrication effect due to insufficient oil precipitation.

  Thickening agent

  The function of thickener is to keep grease in semi-solid state, and some properties of grease are also determined by thickener, such as service temperature, mechanical stability, heat resistance, water resistance and so on. The properties of grease are different with different thickeners.

  Thickeners can be divided into metal soap base and non soap base. Metal soap base includes lithium, sodium, calcium, steel, aluminum, etc., while non soap base includes silica gel, expansive bentonite, urea, etc.

  Additives

  The general base oil is difficult to meet the comprehensive performance requirements of friction pair lubrication. Therefore, in order to improve the performance of the oil, a certain amount of additives, which play an important role in improving the performance of the lubricant, must be added to the base oil to meet the needs of various special working conditions. But the use of grease with additives will bring some negative effects to bearing parts, such as corrosion.

  The main additives are as follows:

  Additives for protecting metal surface, such as extreme pressure additives, etc

  Additives to improve the performance of lubricating oil, such as adhesive, etc

  As well as additives to protect the grease itself, such as antioxidants, etc