Friction bearings replace motorized unit in vacuum system cover mechanism

A German company that supplies equipment to the high-energy physics community also specializes in the design and manufacture of vacuum systems for surface analysis and deposition techniques in semiconductor research and development.

Loading its vacuum systems requires raising a 200-kg special steel cover and 50-kg lifting frame and swinging them aside. A shaft guided by two EXALIGN™ pedestal bearings is installed next to the system so the cover can be raised and lowered in the axial direction by a jack. One end of a U-shaped crossbeam is attached to the shaft, and the other end to the cover. When the shaft is raised, the crossbeam lifts the cover. The cover and lifting frame are then manually swung aside. The cover is replaced by reversing this procedure.

The company had been using a motorized bearing mounted vertically on the shaft connected to the lifting frame. The covers are opened and closed twice a day, during which the bearing was subjected to both axial and radial loads, a stroke of 100mm/min. and pivoting movement of 90 degrees in three to four seconds.

“The motorized bearing unit presented many problems,” said the company’s director of design engineering. “It was impossible to operate the system reliably on a continual basis.”

The company turned to GGB, formerly Glacier Garlock Bearings, Heilbronn, Germany, for a solution, in which the motorized bearing was replaced by two DU® self-lubricating, metal-polymer plain bearings in EXALIGN™ friction bearing housings. In addition, GGB recommended the shaft be precision H6 steel.

“The friction bearings make it possible to lift and pivot the cover smoothly,” explained the head design engineer. “The self-adjusting bearing housings are able to compensate quite effectively for any alignment errors which may occur during installation.”

The DU® bearings provide excellent friction performance in rotating, sliding or oscillating motion applications. Unlubricated they can withstand loads of up to 3.5 Mpa x m/s, speeds up to 2.5 m/s and temperatures ranging from -200°C to +280°C. The structure of the bearings consists of a rigid steel backing, which provides exceptionally high load-carrying capacity, and a porous bronze inner layer impregnated with a homogeneous mixture of PTFE and lead.

“The application functions very well and we are very satisfied with GGB,” he concluded. “The good technical documentation they provided has made it possible for us to handle the bearing design issues ourselves. We’ve been using the DU® bearings since 2001, and our customers have reported no problems. We’re very confident in the durability of the GGB bearings in this application.”

In addition to durability, the company’s director of design engineering noted the bearings are maintenance-free, smooth-running, flexible in application, easy to adapt and more cost-effective than the motorized bearings they replaced.

The vacuum system is loaded by lifting the cover and swinging it aside. A shaft guided by two GGB DU® bearings allows the cover to be smoothly raised and lowered in the axial direction and pivoted aside in a radial direction.

The DU® bearings are contained in self-adjusting EXALIGN™ housings which compensate for any misalignment during installation.