Ultra high speed bearings provide the key to machine tool performance
The economics of manufacturing and engineering continue to push machine tool manufacturers and re-engineering companies to increase the production speed, precision and reliability or their machines. Higher speed cutting and increased machine accuracy require higher spindle speeds, so right at the heart of a machine’s accuracy are the spindle bearings. These bearings, more than many other components, dictate the upper limit of spindle speed.
To ensure the demand for higher speeds can be met, NSK has invested in new materials and production techniques to deliver a wide range of super precision bearings that allow machine tools to operate at higher speeds and help deliver greater accuracy and performance.
To enable machine tool spindles to achieve higher cutting speeds while maintaining a high degree of running accuracy super precision bearings have to be used. These are most common of the angular contact ball bearing type. From its collaborations with machine tool companies and spindle manufacturers, NSK has developed a product portfolio of angular contact bearings that covers machine tool spindle applications across the widest range of operating speeds.
The whole range is regarded as the most comprehensive available from one manufacturer and is backed-up by the research and development facilities of NSK”s European Technology Centre (ETC), one of the most advanced units of its type in Europe. The ETC conducts in-depth testing of angular contact bearings with new types of grease and with AIR MIST lubrication. The purpose of these tests is to establish how the physical properties of the lubricants used relate to bearing performance.
The frequent requirement for tool changes on modern machine tools, such as machining centres, means that to optimise production time not only are higher maximum spindle speeds required but also, critically, faster acceleration and deceleration. However, during periods of rapid acceleration or deceleration, spindle bearings are subjected to severe thermal load conditions. These are caused by drastic changes in the ambient environment that result from heat generated by the motor, housing cooling and other factors. NSK”s solution to these problems is the ROBUST series of bearings, designed for ultra high-speed spindles.
The ROBUST series of ultra high speed bearings employs a larger number of smaller diameter balls as their rolling elements, enabling them to operate at rotational speeds some 20 percent higher than conventional designs. The ROBUST range retains the same external dimensions as conventional angular contact bearing designs and as a result is directly interchangeable. However, the lower mass of its smaller rolling elements results in lower ball centrifugal force, and hence lower friction and heat generation. Ball centrifugal force is reduced at high speeds and internal stresses are lower, enabling speeds of 3 x 106 dmN to be achieved with air/oil lubrication.
Such high levels of performance owe much to the substantially improved rolling contact conditions within the bearings. These ensure reduced heat generation and considerably lower bearing operating temperatures than can be achieved with the standard design of angular contact ball bearings. Of course, reduced friction and cooler running add up to increased bearing reliability, a benefit further enhanced by the provision of a single shoulder which allows better lubricant distribution within the bearing.
Within the ROBUST range there are a number of options available to customers who may need to improve further on the standard configuration. These bearings can have ceramic (silicon nitride) balls rather than the standard steel option with rings manufactured from SHX, a new steel developed by NSK. SHX is a result of special proprietary materials and heat treatment technology, which offers ultra high speed performance and extended fatigue life, making it highly suited for use in machine tool spindles, which must run at ultra high speeds with a minimum supply of lubricant. Its heat resistance is nearly equal to M50 steel, a material which is used widely in bearings for jet engines, while its wear resistance, resistance to seizure and durability are all setting new industry standards.
Development of materials for use in ultra high speed bearings has also included the use of alternatives for the cage construction. With the base specification using a Phenolic cage, those requiring a higher specification would be advised to choose the Polyamide design. For ultimate performance, requiring speeds in excess of 2.5 x106 dmN, the PEEK cage is available which has excellent temperature characteristics.
Bearing design for such high speed applications must also focus on proper lubrication in order to deliver high levels of performance and durability. Some applications require oil jet lubrication and this requires the machine tool design to accommodate such a system, as well as suitable quantities of high grade oil together with adequate filtration capability.
An alternative is oil-air lubrication, which is a method of spraying oil by turning it into a mist using compressed air. This method requires a less complicated machine tool design and also greatly reduces the quantity of oil required. In addition, the bearing design is also simplified as there is no need for oil ports to be incorporated into the bearing ring.
The ROBUST range is also available with conventional grease lubrication or as a sealed version, which makes for easy handling and also improves grease life time. For a higher specification, the Spinshot™II, an exclusive oil air lubrication system developed by NSK, can be requested.
While investment continues year on year in research and development, NSK has also invested in the state of the art production facility in Newark, UK, where the super precision bearings are manufactured as well as streamlining the warehouse and dispatch areas allowing more efficient service to customers. NSK has a stock holding of £17 million in the UK warehouse, guaranteeing the best possible delivery times for the majority of the vast product range.
For more details on the super precision bearings or to discuss the specification of bearings for ultra high speed applications, contact:
NSK UK Ltd : Mary Fletcher, Marketing Communications Specialist,
Tel: 0500 2327464 Fax: 01636 643075
Web: www.nskeurope.com
Email: info-uk@nsk.com
Address: NSK UK Ltd, Northern Road, Newark, Nottinghamshire, NG24 2JF, UK
NSK Europe Ltd
- 01636 605 123
- info-uk@nsk.com
- Belmont Place, Belmont Road, Maidenhead, Berkshire, SL6 6TB GB
About us
Established over 100 years ago, NSK (Nippon Seiko Kabushiki Kaisha) is a Japanese-listed company that has evolved from a regional ball bearing supplier to a roller bearing specialist and automotive supplier with a global market presence. Today, NSK employs more than 31,400 employees in 30 countries. As per March 2019, NSK achieved sales of 991,4 billion Yen. This result has been driven by ever-increasing investment in research & development, enabling the company to continuously improve the quality of its products and services. This investment supports NSK’s objective of “No. 1 in Total Quality”. In addition to a complete rolling bearing portfolio, NSK develops and manufactures precision components and mechatronic products, as well as systems and components for the automotive industry, including wheel bearing units and electric power-steering systems. In 1963, NSK’s first European subsidiary, Düsseldorf, Germany, was opened and in 1976, the first European production facility in Peterlee, England. Today, NSK Europe supports pan-European sales with production locations in England, Poland and Germany, logistics centres in the Netherlands, Germany and England and technology centres in Germany, England and Poland. In 1990, NSK purchased the UPI Group including the renowned European bearing manufacturer RHP, with its factory in Newark (UK). Additionally, NSK has developed a comprehensive network of authorised sales distributors. NSK Europe is divided into application-based business divisions: Industry rolling bearing technologies & linear and precision technology (EIBU) as well as bearing modules and steering systems for the automotive industry (EABU & ESBU). In this organisation, NSK Europe's 4,260 employees achieved a turnover of over 1,045 million Euros as per March 2019.
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