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Off-the-shelf linear system will ‘revolutionise’ designs

26 March, 2014

HepcoMotion, the UK specialist in linear motion systems, has developed a family of off-the-shelf stainless-steel linear and rotary guide systems that, it predicts, will “revolutionise” the design of motion systems for vacuum and extreme-temperature environments.

Until now, says Hepco, engineers needing to move products in vacuum or extreme-temperature environments were faced with two “unpalatable” choices. Either they had to design their own bespoke linear motion system – which would be unproven and could create problems in terms of timescales and budgets – or they could adapt commercially-available systems, with no guarantee that the materials would meet their demands.

“Material selection is a key factor in this ready-made system,” says Hepco sales director, Chris Rees. “The reason our system works in a vacuum or high-temperature environment is down to two things – material selection and some bespoke design.

“Vacuum environments will cause any porous materials to outgas and therefore fail,” he explains. “This effectively rules out the use of any polymers, plastics and some sintered materials. Stainless steel is the default choice for a vacuum because it doesn’t outgas, is inherently clean and non-corrosive and therefore suitable for vacuum applications which require a high level of cleanliness. Also, stainless steel doesn't melt in high-temperature environments.”

All of the bearings’ moving contact surfaces are made from hardened stainless steel, eliminating the risk of wear-generated debris causing contamination. Outgassing is also eliminated because all free spaces in the bearings are connected to a vent hole in the bottom of the retaining screw.

Another claimed advantage of the Hepco system is that a six-bearing carriage (above) can cross a large gap in the rail – unlike a re-circulating ball rail system. This allows the carriage plate (and any components that it is carrying) to move from outside into a vacuum chamber and to act, in effect, as an automated feed-in system The gap in the rail allows the vacuum chamber airlock door to be opened and closed. 

HepcoMotion's stainless-steel vacuum bearings are designed to avoid outgassing and wear debris

If an application demands it, the Hepco system can work without lubrication. All other bearings can be lubricated internally with grease suitable for their temperature application, with temperatures from –50 to +210˚C being covered by two types of grease.

The bearings are said to be simple and cost-effective to integrate, and to deliver good results throughout long operating lives. They are available in concentric or eccentric versions. The latter can extend the life of the system because when wear/play starts to develop, it can be eliminated by adjusting the eccentric.

The bearings are available in diameters from 18–54mm, with various fixing styles, and with load capacities from 180N–4.2kN. They have the same dimensions as Hepco’s SL2 range and can be supplied ready-mounted onto an SL2 or PRT2 carriage-plate, or as components that users can mount onto their own carriage assemblies.

Although there is a price premium for the new system compared to Hepco’s standard stainless-steel range (SL2) the company argues that it is much more affordable than designing a bespoke system.




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