St. Louis--Consider the wear and tear on a door installed at a large school, shopping mall, government building, or airport. Typically, such doors must survive millions of operating cycles a year.
When Hager Companies wanted to re-engineer the bearings for its Roton continuous geared aluminum hinge that runs the full length of a heavy-duty, high-impact door, it needed a material that could take abusive use over many years. It found that material in Lubriloy(reg) RL, a lubricated nylon 6/6 composite supplied by LNP Engineering Plastics (Exton, PA). The composite features a proprietary, patented lubricant alloy instead of more traditional lubricants like PTFE or silicone.
Before making the final material selection, however, Hager engineers put Lubriloy through a series of tests. "While the acetal bearings used previously performed satisfactorily in several areas, it failed to do the job when it came to wear characteristics," reports Joanne Svejda, Roton's vice president of sales. "The acetal bearings wore out and caused the door to droop far more rapidly than the Lubriloy bearings."
In the Roton design, the bearings fit into multiple milled cutouts along the door's length. "When the hinge is mounted to the frame of a door, the bearings distribute the load, helping to carry the weight of the door," Svejda explains. "Our continuous geared hinge lessens the stress on the frame and the door lasts longer."
Conventional hinges, Svedja says, concentrate all the weight at three points. "A heavy-duty door can weigh anywhere from 250 to 500 or more lbs. With a conventional butt hinge, you have all of the weight hanging on three 2- to 4-inch hinges. This causes extreme stress on the frame and the door's edge. Frequently the frames become distorted and the hinges pull out. All this stress can cause the hinge bearings to crack."
The re-engineered bearings have another benefit. "We needed a material that would take abuse without squeaking, Svejda reports. "One of the materials we tested was great as far as wear was concerned, but caused a squeaking problem every time the hinge opened and closed. In contrast, the internally lubricated Lubriloy bearing gives us squeak-free performance."