As appeared in DPA-Design Products & Applications, October 2003

Lead-free bearings stand up to lubricants in door closers

A major U.K. manufacturer of door closers had been using plain bearings with an inner surface consisting of a mixture of PTFE and lead. The bearings were installed at the top and the bottom of each closer, where they housed a pinion and provided low-friction operation. The bearings 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.

To solve this problem, the company turned to GGB, formerly Glacier Garlock Bearings, which recommended using its DP4 lead-free bearings, which provide superior friction and wear performance in lubricated applications. And because they are lead-free, they are not susceptible to lubricant-induced corrosion. The structure of the bearings consists of a rigid steel backing, to which is bonded a porous bronze sinter interlayer impregnated and overlaid with a PTFE bearing layer filled with rare-earth fibers.

“The new bearings are very low friction, making our closers easy to operate and highly durable,” said a spokesman for the firm. “DP4 is an absolutely marvelous material for our bearings.”

While the loads are not particularly high, the bearings are subjected to repetitive wear. “A busy door may be opened and closed several hundred times a day” explained the company's spokesman. “If you open a door 90 degrees, the pinion goes through 140 degrees of rotation, and another 140 degrees when you close it again.”

The DP4 bearings withstand the company's testing protocol of 500,000 cycles with no problems, and routinely achieve well over a million cycles in use. 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 especially corrosive. Neither of these lubricants has had any adverse effect on DP4, according to the company.

The DP4 bearings in its standard line of door closers “give similar or better performance than the needle roller bearings in our premium products at a fraction of the cost,” said its spokesman.

The company has been using the DP4 bearings in these closers, of which it produces about 100,000 a year, for seven years. “That's almost a million closers, and we've never had a failure using these bearings.”

Bearings at the top and the bottom of each door closer provide low-friction operation.

Low-friction, lead-free DP4 bearings make closers easier to operate, while withstanding repetitive wear.