A manufacturer of door closers had been using plain bearings with an
inner surface comprising a mixture of PTFE and lead. They performed well
for up to 250,000 cycles, after which the hydraulic mineral oil in which
they were submerged reacted with the lead, degrading the sliding surface.
After being approached by the company for help, Glacier Garlock Bearings
recommended the use of its DP4 lead-free bearings. These have a rigid
steel backing, bonded to which is a porous bronze sinter interlayer,
impregnated and overlaid with a fibre-filled PTFE bearing layer. The
configuration ensures extremely low friction.
Since their inclusion, DP4 bearings have exceeded the manufacturer's test
protocol of 500,000 cycles and routinely achieve well over a million
cycles in the field. Typically, the bearings are immersed in hydraulic
mineral oil, but in some cases the company uses water glycol, a non-oil
based hydraulic lubricant that is particularly corrosive. Neither of
these lubricants have had any adverse effect on DP4, says the company.