Lubricant viscosity and lubrication method of spindle bearings

Lubrication is required to achieve: Sufficient spindle bearing life, Wear-free operation Low vibration An important prerequisite is the formation of a lubricating oil film in the contact area that separates the rolling elements from each other. To achieve this, a certain amount of lubricant must be guaranteed at each point of contact. To achieve the speed requirements should select the appropriate lubrication method Select the correct lubricant. Lubricant Viscosity The condition of the lubricating oil film depends on the viscosity ratio κ, which is the ratio of the working viscosity ν to the reference viscosity ν1. The reference viscosity ν1 is a function of bearing size and speed and can be found in Figure 1. Operating viscosity is the actual viscosity of the lubricant during operation. It is a function of operating temperature and lubricant base oil viscosity and can be found in Figure 2. Grease lubrication requires consideration of base oil viscosity. The viscosity of the lubricant at operating temperature should be at least 2 times the reference viscosity, ie κ u003d ν/ν1 2. Too high a viscosity ratio will not improve the lubricating oil film much but will increase friction. Lubrication method The choice of lubricating method should be based on the maximum working speed to be achieved by the bearing. The data sheets in this catalogue give the limiting speeds for the two most important lubrication methods (grease and oil) for super precision bearings. The allowable speed of a bearing set in a rigid preload arrangement can be obtained by multiplying the limiting speed of the individual bearing by a reduction factor, see figure 14. Most super precision bearings are grease lubricated. The main advantages of grease lubrication include: Low friction Lifetime lubrication Simple design Low system cost. If the spindle speed exceeds the limit speed of bearing grease lubrication, minimum oil quantity lubrication can be used. When a high speed index persists for an extended period of time, it makes sense to lubricate with a minimum oil quantity, so that a guaranteed lubricant life can be obtained. In some cases, grease lubrication can also meet the rotational speed requirements, but since grease service life (Figure 5) decreases with increasing rotational speed, in this case, minimum oil lubrication is more appropriate. The research on grease and bearings has made great strides, and the performance in all aspects has been significantly improved, especially the increase in rotational speed. Today the speed index n dm can reach 2 000 000 mm.r/min. The use of primary life grease and seals for spindle bearings has additional advantages, such as effectively preventing contamination and keeping the inside of the bearing clean. In addition, installation is easier. The greases suitable for super precision bearings are shown in Table 3. FAG ARCANOL L075 is a high-performance grease, widely used in high-speed spindle bearings with a constant temperature of the outer ring and a maximum temperature of 80°C. Due to the effect of liquid cooling, it is difficult for the temperature of the electric spindle to rise to 80 ℃, and L075 has become the standard grease for spindle bearings. FAG ARCANOL L210 is another high speed grease. Because of its high base oil viscosity, it can be used in applications over 80°C up to 100°C. FAG ARCANOL L055 is a high-load grease that is most commonly used for ball screw drive shaft end bearings, rotary table bearings and lathe tailstock central bearings, and has proven to be very effective. The amount of grease to be added Different types of bearings require different amounts of grease. The recommended values u200bu200bgiven in Table 4 are not affected by the rotating elements, but mainly depend on the bearing volume. Information on grease lubrication can be found in the Installation Instructions section (see page 204).