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Linear guide developments deliver performance advantages

07 June 2015

The new precision UK manufactured NH and NS series linear guides from NSK satisfy needs for agility, long life and an ability to cope with ever higher loads.

Many engineers regard the introduction of new mechanical systems that replace tried and tested technology with mixed feelings; however, in this case there is nothing to fear as the new guides are dimensionally directly interchangeable with the outgoing LH and LS series models. Machines therefore only need to redesigned if the downsizing option is taken.

According to Kevin Delehanty, principal application engineer at NSK UK, the new NH and NS series have a 30 percent higher dynamic load rating. “We have achieved this by further optimising the geometry of the ball grooves,” he explains. This new design ensures a more uniform distribution of forces between the ball and the groove, so the contact surface pressures for the same loading are significantly lower, allowing the dynamic load ratings to be revised according to ISO guidelines.

The result is not only a 30 percent or more increase in dynamic load rating, but also a fatigue life that is effectively doubled. In real numbers this means that the calculated service life of the NH25AN linear guide, for example, is 2.24 times that of the LH25AN. At the same time the noise level drops by an average of 3dB(A). This is great for new designs, but what has changed for the engineer who is already using the old NSK linear guides?

“The dimensions have not been changed at all,” Delehanty emphasises. “Also unchanged is the high degree of self-alignment of the slide on the rail due to the face-to-face arrangement of the bearings, resulting in lower internal loads compared with a back-to-back arrangement. This allows the linear guide to compensate for greater installation errors without significantly reducing the service life.” The new versions can also be used in conjunction with NSK’s K1 lubrication units.

While the changeover to the new series poses little in the way of problems, it is also possible to mix old and new components in the same machine or system – though designers should note, the load rating of the old series will apply, and as the ‘weakest link’ in the chain this will determine the service life of the system.

Thanks to new end caps, the maximum allowable speed has been increased by a factor of three compared with previous models. Instead of 100m/min, the new NH/NS series can work at speeds of up to 300m/min. At the same time the smooth-running properties and the noise levels have been improved due to a completely redesigned ball circulation system. This allows the balls to be guided much more smoothly out of the load zone into the return cap.

The new series can be employed in a wide range of possible applications, particularly where precision, speed, service life and process reliability are important factors. Examples include metal-cutting machines, medical equipment, semiconductor manufacturing, packaging machinery, robots and material handling machinery in general.

In addition, NSK believes the option of downsizing to be of great importance. Due to the higher load ratings it is possible to replace the linear guides previously used with significantly more compact versions with the same service life. Instead of an LH30AN guide, for example, the system designer can now select the more compact NH25AN that is 20 percent narrower and slightly less deep. Moreover, the NH25AN weighs about 30 percent less than the LH30AN.

Easy UK availability for this new range is assured as it is manufactured at NSK's facility in Newark, Nottinghamshire. There is also a flexible precision engineering facility based at Newark that can design and assemble bespoke assemblies; for example, rails cut to custom lengths, changes to carriage preload or lubrication method. The workshop has significant capacity and is able to meet short lead times.

Rotary bearings
NSK’s Sealed-Clean roller bearings are helping a major steel producer to reduce maintenance costs on a plate rolling mill. Existing open roll bearings required a daily maintenance routine to ensure sufficient lubrication in one of the harshest environments in which power transmission equipment is expected to perform.

The four-row, sealed tapered roller bearings used on the roll necks of rolling mills are subject to extreme shock loads and the presence of high pressure water and scale debris.  New seal technology from NSK is now enabling a longer service life and improved reliability in addition to higher load capacity over conventional sealed roll neck bearings in this application.

The bearings are manufactured from NSK's Super-TF bearing steel. Research by the company has revealed that bearing life in conditions of contaminated or boundary lubrication can be improved by changing the microstructure of the bearing steel in order to enhance its ability to relax stress concentrations on the edges of indentations.  This microstructure, with a high volume of retained austenite and a high hardness, leads to longer life even under conditions where there is insufficient oil film leading to surface damage, such as peeling.

In tests, bearings manufactured from Super-TF steel have been shown to offer up to ten times the life of conventional carburized steel bearings operating with contaminated lubrication, and up to twice the life where the lubricant is clean.  Where the problem is related to insufficient lubrication, the average life of bearings made from Super-TF is still impressive, at around 5.5 times that of ordinary carburized steel.

Not only did NSK’s steel-making customer save over €46,000 annually on maintenance costs, but also significantly reduced the environmental cost of its operation.

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