Posted to News on 8th Jul 2007, 14:18
High-tech polymer cages improve machine tool bearings
NSK has developed super-precision bearings equipped with next-generation polymer cages that help improve the quality of machine tools. These include the TYN cage, which offers silent operation and 20 per cent lower temperature generation in angular contact bearings used in machining centres and grinding spindle applications. In addition, NSK has created the TB cage for double-row cylindrical roller bearings. Designed using finite element analysis, the TB cage offers similar or superior high-speed performance to brass cages, together with up to 40 per cent lower heat generation, and as much as a ten-times improvement in durability when operating under severe conditions.
Development of the TYN cage came as a result of research that showed that silent operation is one of the key features for high-quality machine tools, helping to improve their performance. The TYN cage is made of a high-performance engineering polymer, and has a design (which is claimed to be unique) to overcome the problem of noise sometimes experienced with precision angular contact bearings using conventional phenolic cages and grease lubrication. The NSK TYN cage can eliminate this kind of noise; in particular, it gives greater benefits in machining centres or grinding spindle applications, which require 'silent' operation as specified by builders of high-quality machine tools.
The NSK TYN cage provides not only 'silent' operation, but also up to 20 per cent lower heat generation and improvements in the reliability of the lubrication performance. These improvements are achieved by shortening of the running-in procedure, and by ensuring that grease is retained effectively within the bearing.
Availability
TYN cages are available for use in both the Standard ACBB bearings and the Robust series of bearings, which are designed for use in high-speed spindles (eg up to 16,000rpm on 70mm spindle shaft diameters); this type is designed to contribute significantly to the higher accuracy of spindles. It will be stocked as a universal combination (SU) with P3 accuracy (running accuracy: ISO class 2 and dimensional accuracy ISO class 4).
Also new to NSK's next-generation high-performance polymer cages is the TB cage for double row cylindrical roller bearings (CRB's). In contrast to conventional CRBs, which generally have brass cages and can suffer grease degradation from wear particles, the TB cage is produced from PPS polymer (polyphenylene sulphide). NSK has developed and refined this material in order to satisfy technical requirements such as extended higher speed capability, and higher levels of durability.
NSK has also conducted extensive finite element analyses to determine the best shape and design of the TB cage under high-speed operation. As a result, the TB cage provides similar or superior high-speed performance, compared to brass cages, together with up to 40 per cent lower heat generation and as much as a ten-times improvement in durability when operating under severe conditions.
What all these performance improvements mean for machine tool builders is that a CRB equipped with a TB cage can operate in a similar speed range to angular contact ball bearings; this was not possible in the past. In addition, it is now possible to operate the spindle and achieve both high-speed performance and greater stiffness characteristics from the combination of a CRB with a TB cage.
The NSK CRB bearing specification contains high-accuracy 1:12 tapered bore, oil holes on outer ring, ISO class 4 accuracy and newly defined internal clearance, which has a narrower tolerance range to improve the spindle assembling process.
