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Designer's Corner
By John Lewis, Regional Technical Editor -- Design News, May 3, 1999
Cool-running ball screws
Because steel expands approximately 6.5 × 10-6 inch/inch/°F, the length of a 40 inch ball screw operating under normal running conditions in a CNC lathe could vary as much as 0.0024 inch. Positioning inaccuracies and rejected components result.
Hollow ball screws help overcome this problem. A hole drilled along the shaft's longitudinal axis accepts fluid pumped via rotary unions. The fluid transfers heat from the screw shaft to an external medium before recirculating.
By controlling fluid temperature entering the ball screw, a constant temperature can be maintained along the ball screw's length; ball screw lead remains steady and positioning accuracy is maintained.
| When ball screw is timing belt-driven, fluid passes through screw shaft’s entire length. For direct-driven ball screws, a blind hole is machined in the shaft and a duoflo rotary union fitted. Cooling effect applies to ball screw support bearings as well as ball screw itself. |
John DeGenova, Thomson Saginaw Ball Screw Co., LLC, 628 N. Hamilton St., Saginaw, MI 48602; Tel: (517) 776-5111; FAX: (517) 776-3632.
Versatile submersible
Designed to drive submersible pumps in both vertical and horizontal installations as well as hot-water operation, the environmentally safe, water-filled, three-phase squirrel-cage motors use potable drinking water or non-toxic antifreeze to cool the windings and lubricate the bearings.
An internal-cooling circuit boosts output range and power reserve compared to equivalent motors without internal forced cooling. Impeller design combined with complimentary flow-conducting components ensure sufficient thermal reserve is available to temperatures of 131F (55C) or higher.
The water-lubricated, tilting pad thrust bearing uses six stainless-steel pads that run against a hard carbon surface. The design operates at internal temperatures up to 185F (85C), and under continuous axial loads up to 11,250 lb. The motor handles even hard pressure surges from water hammer etc. up to 340,000 lb.
| Enhanced internal cooling-system efficiency, and a wear-resistant thrust bearing improve reliability and help the next generation Pleuger MI10 submersible pump motor perform in a wider range of applications. |
Tom Sgritta, Ingersoll-Dresser Pumps, Pleuger Operations, 264 Wilson Industrial Park, Statesville, NC 28677; (704) 872-2468.
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