NSK’s (www.nsk-corp.com) Moulded Oil, a solid composite comprised of plastic impregnated with large quantities of oil, may benefit linear guide action. Moulded oil is formed by melting polyolefin resin and oil mixture, then cooling the material into a solid causing the polyolefin molecules to freeze in an elongated state.
Oil is supplied inside the structure ensuring a stable lubrication supply for extended periods. Properties include a tensile yield strength of 4.2 to 4.7 MPa and tensile yield elongation of 13 to 14%. It has a hardness of 91 HDA (somewhere between rubber and plastics) and liquefies when sufficiently heated allowing it to become malleable. Oil content is 70% by weight and in this respect differs from typical oil impregnated plastics, whose oil content is usually only a few percent by weight.
In one of a number of tests the Moulded oil seal, called K1, was used with linear bearings to discover its performance capabilities. After degreasing the end cap, bearing and rail, frictional forces rapidly increased on the linear guide with a corresponding decrease in operating performance. But, after a number of cycles oil supplied by the K1 seal reduced friction and restored operating levels to pre-degreasing levels.
Bearings manufacturer, SKF (www.skf.com), also use a 70% oil composite Solid Oil to fill the internal space in a bearing and encapsulate the cage and rolling elements. By releasing oil from the polymer during operation, both rolling elements and raceway are sufficiently lubricated.
Slide systems specialist Hepco (www.hepco.co.uk), however, has a different attitude to this technology, aiming for a design principle that leaves built-in lubrication unnecessary.
‘Hepco have never needed to flood large quantities of lubricant into linear motion systems. A unique Vee-guide principle is incredibly tolerant of dirt and contamination, even at high speeds, allowing the product to run dry in some highly demanding applications. The advantage of the Hepco system is that it can be used with a vast range of oils/greases, for any application, with a greater capacity and longer periods between refills, giving the option to refill whenever there is a necessary pause in use,’ says Scott Bullock.
‘All makes of re-circulating ball systems require copious supplies of lubricant to function correctly. An oil impregnated composite lubricator seems to offer the advantage of extended lubrication schedules, however, even in dirty environments the entire runner block must be purged with grease on a regular basis in order to continue functioning correctly.’ Cincinnati Machine 00 1 513 841 8559 enter 43