(2000), "'Molded Oil' seal revolutionizes machine performance with simultaneous sealing and lubrication of linear guides and ball screws", Industrial Lubrication and Tribology, Vol. 52 No. 2. https://doi.org/10.1108/ilt.2000.01852bad.001
Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
'Molded Oil' seal revolutionizes machine performance with simultaneous sealing and lubrication of linear guides and ball screws
"Molded Oil" seal revolutionizes machine performance with simultaneous sealing and lubrication of linear guides and ball screws
Keywords: Oils, Seals, Lubrication
NSK's development of "Molded Oil" and the company's subsequent introduction of the K1 SealTM, which enables ball screws and linear guides to benefit from the technology, is revolutionizing the performance of machines, in terms of reliability, maintenance free intervals and operation in environments exposed to contamination such as dust and or water. The effectiveness of the K1 technology should also enable machine builders to make real cost savings by replacing existing, and often costly, methods of lubricating precision machine parts.
Improved machine performance from ball screws and linear guides
Ball screws and linear guides are essential components in any precision machine. Both have undergone remarkable developments over the last decade and these have contributed to the astounding speed and accuracy improvements which have been achieved in production machines.
The effective and reliable operation of ball screws and linear guides depends upon a number of factors, not least effective lubrication and sealing against the ingress of contaminants. These factors are particularly critical on machine tools, woodworking machines and in materials handling applications.
Depending upon the application, either grease or oil lubrication is used with ball screws and guides. In the case of grease, this entails a planned lubrication regime for the components, or, with oil, the integration into the machine design of a costly forced lubrication system.
Recently, increasing attention has been paid to plastic composite materials containing abundant lubricating oil (or grease) as a replacement for conventional lubricants.
Through its own material formulation and production techniques, NSK has developed a new material called "Molded Oil" which is a plastic containing lubricating oil. Differing from other marketed oil impregnated plastics, where the oil content is a mere few percent by weight, Molded Oil permits a lubricating oil content of more than 50 percent by weight.
The oil discharge rate from the new material depends on the operating temperature. Molded Oil has lubricating oil enclosed among polyolefin molecules. When the temperature rises the polyolefin molecules tend to shrink, resulting in discharge of the lubricating oil. This means that more lubricating oil is supplied through slide heat generation when needed.
Molded Oil benefits consolidated in K1 seal ...
NSK's new K1 Seal was developed so that linear guides and ball screws could take advantage of Molded Oil. The new seals play a double role in that they achieve the functions of sealing and lubrication simultaneously.
The major features of K1 Seals are: extended lubricant life, outperforming forced oil lubrication; consistent lubrication is maintained and this extends the maintenance free period, even under heavy loads and in the presence of contaminants; and environmental and maintenance costs related to the supply and disposal of forced oil lubricants are eliminated.
In tests, linear guides equipped with K1 seals achieved lubrication-free running to distances in excess of 25,000km. The K1 seals also performed well in durability load tests, achieving twice the service life of the standard double seal at an operating speed of 24m/min.
No oil pollution
The K1 seals are particularly effective in environments where oil related pollution must be prevented.
The food industry with its strict hygiene regulations is a good example, as are semi-conductor and medical equipment manufacture. In all these cases pollution can be avoided, and sufficient lubrication provided, using the K1 seal in conjunction with minimal grease.
Effective against washdowns
Another problem which the K1 Seal effectively addresses is loss of lubricant due to washdowns. Machines used in food production, pharmaceuticals and construction which would normally suffer in this respect can be assured of longer service life simply by specifying NSK K1 seals in combination with a suitable pre-packed grease.
Enhanced performance in dirty and inaccessible environments
Other areas where the K1 seals make a real difference include environments where lubrication is difficult to apply, and those - woodworking for example - where oil and grease absorbing dust is produced. In both cases long term linear guide and ball screw performance is greatly increased by the efficient oil lubrication the seal provides.
Machine tool industry enthusiasm
Since its launch, the K1's lubrication technology has enjoyed an enthusiastic response from the machine tool industry. NSK has supplied machine tool makers in the Japanese and other important markets with the K1 fitted linear guides and ball screws.
Two examples are the new Hitachi Seiki HS 630 and HS 500 High Performance Horizontal Machining Centres. Both operate at higher speeds and under more severe conditions, taking higher loads than standard machining centres. The HS 630 and HS 500 machines must maintain micron levels of accuracy and high rigidity. As such, the K1 went through numerous design phases and exhaustive trials where it was proven to outperform traditional intermittent forced oil lubrication.
On the Hitachi Seiki machines, the K1 Seals on the ball screw nut and linear guide slider are packed with grease. The lubricant in the K1 gradually seeps out onto the rolling surface to counteract grease loss and deterioration. Re-greasing is not required as the grease itself is a long-life type making the unit maintenance-free. These properties have been tested under severe environmental conditions and in the presence of contaminants.
For example, tests were conducted with cast iron powder mixed into the cutting fluid. With only grease lubrication, friction caused significant damage. But when fitted with a K1 Seal, pre-load was maintained for six times longer with no deterioration, representing a ten-fold increase in service life. Compared with tests conducted using intermittent forced oil lubrication, only half the friction occurred. The tests demonstrated that grease with the K1 Seal is clearly superior to the existing technology.
The example of the new Hitachi Seiki HS 630 and HS 500 machines shows that new technology, in the shape of the K1 Seal, can make a real difference not only in improving machine operation, but also in the continuing search for competitiveness in a global market and in meeting tougher environmental constraints.
At the recent EMO Machine Tool Fair at Hanover, Germany, Hitachi Seiki used the K1 Seal as the backbone of its "ECO - ECO" theme - taking Ecology and Economy into the machine tool design concept in readiness for the twenty-first Century. Users welcomed the dramatically reduced maintenance requirements, the improved performance and the elimination of oil contamination of cooling fluids.
The success in the machine tool industry is being followed in other market sectors where precision ball screws and linear guides are used widely. The benefits to the machine builder are obvious: replacements of the existing, often messy grease method of lubrication, leading to improved reliability, and the savings accrued by not having to design-in intermittent forced methods of lubrication.
For more information contact Michelle Whitfield, Marketing Communications Dept, NSK-RHP UK Ltd, Mere Way, Ruddington, Notts, NG11 6JZ. Tel: +44 (0) 115 936 6600.