| Lubrication All ‘O’ rings, nitrile rubber extruded cord and sheet used in low vacuum applications should be lubricated with either vapor pump fluid, Fomblin® vacuum grease or Apiezon® grease M lubrication will prolong the life of the material and facilitate sealing. Apply the oil or grease very sparingly and evenly, coating the seal to give it no more than a shining surface with no visible smears. Excessive lubrication may cause leaks. In general, but with certain exceptions dictated by common sense, seals used in high vacuum applications should belubricated, but even more sparingly, using vapor pump fluid.Cleaning The only necessary and recommended method of cleaning ‘O’ rings and nitrile rubber extruded cord or sheet is by wiping with a dry, lint free, soft cloth. Most solvent fluids are liable to be absorbed by fluoroelastomer and nitrile rubber, swelling these materials and subsequently outgassing into the system. |
NITRILE RUBBER CORD
Nitrile cord should be cut perfectly square and to a length which is 5% above the mean circumference of the groove in which it is laid. Compression and sealing of the butt joint is thereby assured.
‘O’ RINGS
Nitrile ‘O’ rings Our nitrile (VOR) ‘O’ rings are manufactured from butadiene/acrylonitrile. Commonly referred to as nitrile rubber, its most useful characteristics for vacuum use are:
• Low outgassing rate
• Good deformation resistance (very resistant to set after compression)
• High resistance to most oils |
Fluoroelastomer ‘O’ rings Our fluoroelastomer (VIT) ‘O’ rings are manufactured from a copolymer of vinylidene fluoride and hexafluoro-propylene.
Fluoroelastomer ‘O’ rings should be used in systems operated below 10-6 mbar. Fluoroelastomer offers:
• Very low outgassing rate (especially after baking)
• Chemical stability at high temperatures up to 200 °C
• High resistance to oils and many chemicals
Fluoroelastomer ‘O’ rings take up a set as their operating temperature
increases, but this does not affect their sealing properties in vacuum applications.
A fluoroelastomer ‘O’ ring will restore to its normal shape after uncompressed exposure to atmosphere: accelerate this process by heating to 150 °C in air. The baking temperature of fluoroelastomer need not
exceed 150 °C, since a higher temperature will not, after cooling, further reduce the outgassing rate of the fluoroelastomer. For convenience, we give fluoroelastomer ‘O’ rings the same size reference figure group as corresponding nitrile ‘O’ rings, but although the two materials are molded to the same nominal sizes, fluoroelastomer ‘O’ rings have wider tolerances than those specified in BS1806. Safety note: fluoroelastomer can decompose to hydrofluoric acid if heated above the decomposition threshold of 315 °C. Request a copy of the Material Safety Data Sheet for more information. |
