Selection of Lubricating Grease for Machine Tool Spindle Bearings
Lubricant selection machine tool spindle bearings can use grease lubrication or oil lubrication. Machine tool applications require longer operating cycles and higher speeds. However, oil lubrication must be able to dissipate heat under any circumstances. Lubricants often use mineral base oils. Mineral oil must meet the requirements of DIN 51517, see table. Special lubricants, such as synthetic oils, can only be used under extreme conditions. Under special conditions, lubricating oil has special requirements. For example, temperature and radiation. The effectiveness of rolling bearing additives has been proven by the lubricant manufacturer, see table. For example, anti-wear additives are particularly important for rolling bearings in a state of mixed friction. Base oil and its typical characteristics 1) Most of the base oil types used are natural and pollution-free because the product is a natural product. 2) The types of synthetic oils that are widely used, including lubricants that are allowed to be used in the food industry. Lubricant additives and base oils, abbreviations for working temperature viscosity/temperature performance and compatibility with synthetic rubber Price max. min.C °CMineral oil1), Min +120 20 1001 Polyalphaolefin2), PAO, SHC+150 40 160 Good 6 additive types Functional extreme pressure additive EP ■ Improved pressure absorption performance ■ Formation of a wear-reducing reaction layer friction modifier FM ■ Improves friction conditions under mixed and boundary friction conditions Wear resistance protection AW ■ Reduces adhesive wear and abrasion wear corrosion under mixed friction Agent KI ■ Anti-aging agent OI to prevent rusting of metal surfaces ■ Additives to retard the oxidation and adhesion of lubricants ■ Detergents and dispersants to increase the viscosity of lubricants on the surface ■ Enhance the separation of pollutants and the transparency of lubricants viscosity-temperature characteristics improver ■ Increase (reduce) viscosity/temperature characteristics of foam inhibitor ■ Prevent stable foam from forming flow point reducer ■ Reduce flow point. Lubricant viscosity is recommended to increase the life and safety by increasing the thickness of the lubricating oil film that divides the contact surface. Since the thickness of the lubricating oil film increases with the increase in the viscosity of the lubricating oil, when possible, you should choose a lubricating oil with a high operating viscosity. . If the ratio of kinematic viscosity to reference viscosity satisfies u003d 12, the bearing can reach a very long life. However, the friction of the lubricant also increases after the viscosity is increased. At low temperatures and normal temperatures, there may be problems with oil supply and drain. On the one hand, the viscosity of the lubricating oil should be large enough, but on the other hand, the energy loss due to increased friction should be as small as possible. It must be ensured that the bearings are adequately lubricated under all conditions. Operating viscosity In individual cases, the preferred operating viscosity cannot be achieved due to the following reasons: ■ Limited by other parts on the machine tool, a thinner lubricating oil film is required. ■ Circulating oil lubrication should use lubricating oil with good fluidity, the purpose is to dissipate heat and remove pollutants. ■ Although most lubricating oils can achieve the required operating viscosity. However, in some cases, such as high temperature or very low peripheral viscosity, the running viscosity will be lower than the required value. At this time, lubricating oil with lower viscosity can be selected. Lubricants must contain effective additives, and their suitability must be verified by bearing tests. According to the deviation from the normal value, the fatigue life reduction and the wear of the functional surface can be predicted, and it can also be determined by calculating the achievable RHP bearing life. For lubricants of normal viscosity conforming to ISO and SAE, see page 20, figure 1, and page 20, table. The choice of lubricating oil is selected according to the specific application. In most cases, the lubricating oil used is gearbox or hydraulic oil CLP or HLP, viscosity grade ISO VG 46, ISO VG 68 or ISO VG 100. Determine lubricating oil viscosity based on speed and load factor C/P. High speed parameters At high speeds, it is preferred to use lubricants with antioxidants, low foaming tendency and appropriate viscosity-temperature characteristics. The maximum allowable speed parameter for cylindrical roller bearings is n · dM u003d 250 000 min1 · mm, and thrust deep groove ball bearings are n · dM u003d 440 000 min1 · mm. Suitable synthetic oils with good viscosity-temperature characteristics are esters and hydrogenated polydecene PAO, because the viscosity of these oils decreases very little with increasing temperature. During the start-up phase, the temperature is relatively low, which can avoid the temperature rise caused by high splash loss. Once the higher equilibrium temperature is reached, the viscosity of the lubricating oil can still meet the lubrication requirements. Heavy load If the FAFNIR bearing is under heavy load (C/P 7) or the kinematic viscosity is lower than the reference viscosity 1, lubricants containing anti-wear agents must be used (code P conforms to DIN 51502). Anti-wear agents reduce the adverse effects of metal contact damage. The applicability of these anti-wear additives varies and is greatly affected by temperature. Their effect can only be evaluated by rolling bearing tests (for example, on the test bench FE8).