Machine Design

Making the case for lead screws

Case-packing machines must work fast and efficiently, and withstand the hustle and bustle of high-speed production.

Using Kerk's VHD lead screws on the case packing machine let RPT increase speeds, reduce bottlenecks, and eliminate grease and oil which trapped dust during tissue-box packaging.


The packer at a tissue manufacturer, for instance, was fed by a dual-conveyor setup designed by RPT Motion, Quebec. A two-position lane changer let product from one conveyor and then the other feed the case packer. But actuation was slow and the lane changer became a bottleneck.

The manufacturer wanted to install a second case packer to alleviate the problem, but the lane changer could not accommodate four lanes. It required a 40-in. stroke with indexing about every 10 sec or less for smooth product flow without enlarging the machine.

To find a solution, RPT teamed up with Kerk Motion Products, Hollis, N.H. to replace a ballscrew-and-nut lane changer with a lead screw. The existing design did not have a high enough pitch for fast operation, so the two companies collaborated to fit Kerk's VHD lead screws and nuts into the RPT Modular Slide System. This created a smooth running, high-speed, servo-powered system, with an anti-backlash lead screw assembly.

To meet the high speeds required, RPT chose a 0.75-in. diameter screw with a 2.4 in. travel/rev, with the same efficiency as a ball-nut configuration.

The servo-powered system hit the speeds necessary to accommodate the second case sorter and subsequently eliminated the manufacturer's bottleneck. It also combated environmental challenges, wear, and damage, and lessened the noise around the machine.

TAGS: Technologies
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