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Machine Design

Force tube provides fast and reliable linear motion

When it comes to linear motion, hydraulic cylinders provide top-notch protection against contamination. Acme and ball screws, on the other hand, are not usually a designer's first choice when large loads and fast speeds are involved.

The FT Series of force tubes from Exlar Corp., Chanhassen, Minn. (, can handle the speeds and loads, and has its important components sealed in a housing, so dirty working environments aren't a problem.

To provide the motion, they use a roller screw inside a telescoping tube. A follower attached to the movable tube extends and retracts as the screw rotates. The Series is compatible with a wide variety of standard motors, and mounting and gearing configurations are available to meet most application needs. The standard force tube, for example, includes three frame sizes with strokes from 12 in. to 8 ft. Continuous duty thrust-load rating is 2,000 to 20,000 lb-ft, with a peak load rating of 40,000 lb-ft.

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