Bearing slides from shaft without damage -- every time

DN Staff

March 6, 2000

4 Min Read
Bearing slides from shaft without damage -- every time

Downers Grove, IL--Removal of a standard adapter bearing from a shaft is not a pretty sight. Usually, maintenance workers use the time-honored technique of whacking the bearing's sleeve and nut with a big hammer, hoping they don't permanently damage the entire unit.

Problem is, that strategy doesn't always work. Too often the bond between two of the bearing's key elements--its sleeve and inner race--doesn't loosen. When that happens, the bearing doesn't come free from the machine's shaft. And with each additional whack of the hammer, maintenance workers drive the entire assembly--housing and all--down the shaft.

That, of course, isn't the desired result. Bearings removed in this way must be replaced at costs ranging from $200 for a small unit up to $3,000 or $4,000 for a big one. And those costs don't include the money lost due to downtime and additional maintenance.

Using a device known as the Tapered Adapter Sidekick, however, workers can now remove standard adapter bearings without incurring damage. The device, developed by an engineer at the Rex Bearing Div. of Rexnord Corp., is an integral part of a standard adapter bearing. Like all bearings of its type, it includes a tapered sleeve that fits around a machine's shaft, a roller set with an inner race, and an adapter nut.

The Tapered Adapter Sidekick breaks from the conventional, however, in its use of a two-piece adapter nut. The nut includes threads and a special mating groove on its inner diameter.

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During bearing removal, the threads and the mating groove play key roles. The threads engage similar threads on the unit's adapter sleeve. And the mating groove makes contact with a lip on the bearing's inner race. Together, those two engagements enable the bearing to be removed without damage.

To accomplish that, the Sidekick creates a shear force between the sleeve and inner race. Removal begins with a counterclockwise turn of the adapter nut. As the nut turns, the threads push against the threads of the sleeve. At the same time, the mating groove pulls on the lip of the inner race. Because it pushes on one element while pulling on the other, the Tapered Adapter Sidekick pre-loads the interface between the inner race and sleeve.

Why is that important? Because on virtually every spherical bearing, that interface has already been attacked by fretting corrosion. And the rust between the two elements effectively welds them together. So even when a maintenance worker hammers away, the two often refuse to separate. In many cases, the hammering force instead breaks another bond--the one between the sleeve and shaft. So the sleeve, inner race, and the bearing housing move together along the shaft, damaging the bearing and shaft.

But by pre-loading the interface--pushing on one while pulling on the other--the Tapered Adapter Sidekick creates a shear force that separates them. Once separated, workers can apply axial force with a hammer and slide the sleeve back through the bore of the inner race. Ultimately, they can then pull the bearing off the shaft.

The key to the design is the two-piece nut, say engineers. The two-piece design allows the mating groove to lock, or clamp, around the lip on the inner race. And the locking action enables it to pull the inner race while the threads push on the sleeve.

Rick Wucherer, the Rexnord engineer who developed the Sidekick, did so based on six years of working in a repair shop. "In the past, the load you put on the adapter nut depended on how big a hammer you used," Wucherer says. "But here you have a mechanical thread pitch advantage. It allows you to put a nice, concentric push on that sleeve."

Wucherer says the unit is ideal for applications that require frequent roll changes, such as roll coaters for the steel industry and food processing applications. Those applications, he says, often require changes every few months, and users can't always afford to replace the bearings at every interval. "When you have to cut off a five-inch bearing every time and throw it away, you're losing big money," Wucherer says. "This system not only helps free the bearing, it does so without damage."

Additional details...Contact Rick Wucherer, Rexnord Corp., Rex Bearing Div., 2400 Curtiss St., Downers Grove, IL; Tel: (630)719-2336; Fax: (630)969-8227; E-mail: [email protected].

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