Bearing Design – 1 Ball Bearing, 7 Pieces 2 Billion Varieties
At first glance the construction of a ball bearing is clear: An inner ring is mounted with an outer ring, the appropriate balls and retainer. Then the ball bearing is combined with the lubricant adapted to the requirements of use and, if necessary, a shield to protect against contamination.
Due to the numerous norms and installation recommendations, the external dimensions of the various ball bearing manufacturers differ only in nuances. The big differences come in the form of the internal values of the ball bearing, the materials used for rings and retainers, number of balls and their diameter, surface structure and profile precision, and the lubricant.
GRW has according to our customers’ requirements, different materials to choose from for the ball bearing rings. You can choose between 100Cr6, X65Cr13 (SS) or X30CrMoN15-1 (SV). Whatever the primary focus, from hardness, operating temperature or corrosion resistance, to the hardening process developed by GRW, the desired properties can be specified and implemented in our factory hardening shop. Moreover, further functional properties from the bearing ring, can achieved with coatings.
For a long time GRW has invested significant research and development in the coating of ball bearings. The aim of this development is among many things, to improve the tribological behavior or increase the corrosion resistance. From the use of dry lubricants to increase the dry running properties or for use in high vacuum, GRW offers the best solution for every requirement, with now over 90 different coating varieties. The newest development in this area is a metal-plastic hybrid band (patent:EP000001832765B1). In this case, a metal band is coated with a thin, solid PTFE sheet and then formed into a steel ribbon retainer. Due to the low friction coefficients of PTFE, ball bearings with the lowest friction moments and an excellent life span in dry operation can be realized with this retainer coating. Furthermore the newest procedures via PVD
(Physical Vapor Deposition) or CVD (Chemical Vapor Deposition) are leveraged fulfilling the highest standards for the coating quality. An unwanted dissolution of the coating will result in a serious early failure of the bearing. Therefore all coating varieties are subject to the strict GRW quality norms and tests.
The retainer must hold the balls at an equal distance from each other and prevent them from touching each other. Furthermore the retainer must have an appropriate construction with defined material strengths and balanced elasticity, in order to endure the load in the ball bearing as best as possible.
Not only are GRW ball bearing rings engineered to precision specifications and tight tolerances in surface finish, form precision and steel purity, but these same precision requirements apply to the design and production of the retainer. There are 3 basic variants for the retainers: inner ring, outer ring or ball controlled retainer. These basic types can be combined with 21 different materials. GRW offers a broad range of materials, from metal ribbon for steel ribbon retainers to special materials for aviation and space flight, to chemically-coupled heavy-duty plastic, and lastly “PAI – PTFE-cg” for applications with the highest standards for wear behavior, temperature resistance and sterilization ability.
Lubricants serve to reduce friction and wear, and provide cooling, shock absorption, seal effect and corrosion protection. Lubrication can be carried out using greases or oils and/or in special cases, solids. All 3 types are available in GRW products. The installation situation of the ball bearing is crucial for the selection of a suitable lubricant. Grease lubrication is recommended for general use for low to medium speeds and is therefore the most frequently used lubrication type. The primary part of lubricating grease consists of base oil, the secondary part consists of the appropriate thickener. Bearing lubrication is mostly carried out using base oil, which releases the thickener in small quantities over time. At GRW, lime soaps, Natron soaps, lithium soaps and complex soap greases are used. Oil lubrication is used if grease lubrication cannot be used for technical or economic reasons. This may be the case with high operating temperatures, caused by ambient temperature or frictional heat in the ball bearing. Oils are divided into mineral and synthetic oils. (Animal or plant oils are not suitable or only suitable to a limited extent for use in ball bearings.) GRW offers more than 400 lubricants and therefore our products can be engineered for a broad range of applications and in a wide range of industries from food to aviation and aerospace.
Finally the shield is mounted on the ball bearing as the last component, keeping impurities away and the lubricant in the bearing from the high precision functional surfaces of the bearing and therefore producing the least possible friction. This step is very important as impurities that get between the ball and the raceway might roll over and thereby damage the processed raceways. In order to prevent this, non-contact shields and contact shields are offered, with various sealing qualities. With the non-contact shields no increase in torque occurs, as the shield produces a gap ring. The non-contact shield does not produce any friction and therefore can be used at the highest speeds. With the contact shield the ball bearing seal touches the shoulder of the inner ring with a defined contact pressure and therefore causes an increased friction moment. Compared to the non-contact shields, all contact shields will wear over time. Dust shields are primarily produced from stainless steel or steel sheet reinforced Perbunan rubber. Established seals are made of a glass fiber, reinforced Teflon disk or steel sheet reinforced synthetic fluorine rubber. In total there are 63 shield variants to choose from.
At GRW individual products are made from each of these critical components in direct response to our customer’s requirements. Extensive, competent advice and construction of a ball bearing are the prerequisites for developing the highest and best solutions. In all stages, but especially in the development phase of new applications, GRW engineers contribute valuable technical and economic information. GRW offers a unique combination of technical expertise and strategy in working with our customers’ standard or special components. At GRW our goal is to meet the most diverse application requirements with the highest quality, and in doing so build our customer’s competitive advantage.
Alexander Strobl – Updated 2013