Segmented plastic wipers have several edges oriented at approximate right angles with the direction of motion. They must fit closely because their effectiveness depends largely on the defined line contact with the screw surface.
Spring loading of wipers keeps segments stiff enough to remove tough dirt from the screw but flexible enough to stay in contact through the spring preload. A felt ring deposits a lubricating film.
The proper sealing and lubrication can greatly extend a machine's ballscrew life. That's the premise behind a new lubrication/sealing design that combines segmented plastic wipers with felt rings. This combination wiper, promoted by Steinmeyer Inc., Bedford, Mass., reportedly offers a significant increase in ballscrew reliability.
Generally, it's difficult to sufficiently cover ballscrews to completely prevent contamination from particulate contamination. According to Steinmeyer, regular noncontacting wipers (labyrinth seals) and brush wipers aren't effective for today's precision machine tools.
Lip seals made from elastic materials work better, providing a tight fit. However, they wear quickly because they typically offer just one lip that slides on the ballscrew surface with considerable pressure. In addition, these seals can flex significantly in the axial direction when teamed with ballscrews with a large pitch.
With conventional segmented plastic wipers, several edges are oriented at approximately right angles with the direction of motion. However, these wipers must fit tightly, because their effectiveness depends on the defined line contact with the ballscrew surface. Segments have to be stiff enough to remove dirt from the screw but flexible enough to stay in contact through the spring preload.
Combination wipers go a step further, using segmented plastic wipers with the proper mechanical properties to ensure the desired line contact and proper guidance of contaminants away from the ballscrew. The continuous felt ring stores the lubricant and distributes a thin, even film. This type of system enables up to a 90% reduction in lubricant consumption and can be used with any liquid lubricant oil, or liquid grease. The felt material stores lubricant at up to 75% of its volume, and the reservoir is easily refilled.
As an added advantage, the felt works as a second wiper, absorbing tiny particles that get past the plastic wiper. This feature is useful in applications with fine, abrasive dust or sludge, such as grinding machines.
This system is an alternative to polymer-ring products that also seal and lubricate ballscrews but require heat to perform properly. Also, polymer rings do not offer the flexibility of lubricant choice.