It’s a balancing act

June 1, 2003
A new bearing eliminates fan vibration and noise problems.

When you enter a theater on a warm summer night to enjoy a concert, you expect the air circulating inside to be cool, and the sounds you hear to come from the musicians on stage. You don’t expect noises generated by the airconditioning units in the theater to disrupt the show.

The challenge for industrial fan manufacturers is to build dependable fans capable of powering units in theaters, hospitals, department stores, and other commercial buildings, but without the noise that plagues these high-speed applications. Excessive noise often results when the fans begin rotating at higher speeds — causing vibration of the fan, supporting structure, and bearings. Eliminating this noise requires proper balance of the fan, but creating the perfect balance is not as easy as it sounds.

Greenheck Fan, Schofield, Wis., a manufacturer of centrifugal industrialduty fans, recognized an opportunity to improve the often difficult balancing process. Through dedicated testing and research efforts, they determined that the bearings commonly used in the industry were part of the problem. Their search for a solution led them to Rockwell Automation and the new Dodge Grip Tight Adapter ball bearing, specifically designed to handle high-speed applications.

Problems with bearing vibration begin when highspeed fans, generally those running between 3,000 and 5,000 rpm, start to reach their peak operating speeds. Greenheck engineers tested bearings from several manufacturers. But according to Terry Hrdina, senior product development engineer at Greenheck, the test results were often the same. “All of the bearings we tried posed similar problems when we tried to balance the fans at high speeds. To be successful, we knew we had to find a bearing that could run smoother and cause less vibration.”

Greenheck’s long-standing relationship with Rockwell Automation led them to ask the company’s engineers for help. “We had been using Dodge bearings on other applications for years,” says Hrdina. “So we asked them to come up with a bearing system that could meet our needs.”

Engineers at Rockwell Automation began work on a new bearing suitable for the high-speed fan applications. The result was the new Grip Tight Adapter ball bearing. It features an adapter-mount design that allows for a press fit to the shaft for full concentric contact, 360º through the length of the bearing. This centers the shaft in the inner race and takes out all clearances between the inner ring bore, adapter sleeve, and shaft. The result is superior holding power and more importantly to Greenheck, reduced system vibration levels.

“On the very first run, we saw that it would work,” says Hrdina. “We were able to balance our highest speed fan the first time we tried.”

Keeping vibration levels low during operation was also important, so Greenheck engineers decided to put the Grip Tight bearing through a rigorous testing process. For 1,800 total hours, engineers ran the bearing at speeds in excess of 5,000 rpm in room temperatures varying from 50° to 140° F. Test results proved the bearing would run within acceptable vibration levels for extended periods, with no bearing failures.

Throughout the testing process, engineers found additional advantages in the new bearing. The new mounting system allows installation and removal from the same side of the bearing, a helpful feature when bearings are hard to reach. A built-in bearing puller means no external tools are needed. And after 1,800 hours of testing, engineers found no damage on the shaft due to fretting corrosion.

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