Self Locking Threaded Fasteners Virtually Eliminate Warranty Issues for Skid Loader Manufacturer

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Unique internal thread locking form is helping construction equipment manufacturers improve safety and performance.

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We tried just about everything from locknuts and adhesives to inserts, washers, and double nuts. But they either came loose in the field, posed assembly problems, or both. Another complication was that operators had to adjust the drive chains every 100 hours in the field, so fastener reusability was a requirement as well.

Every type of construction vehicle imaginable depends on quality components that perform as expected time after time. Yet, for all their high tech componentry, vehicles today must still hold together reliably and functionally with simple fasteners and thread forms. When components loosen, rattle, or fail, the problem can often be traced back to the lowly threaded fastener, a technology as old as manufacturing, basically unchanged for centuries until the introduction of self locking threaded fasteners.

Vibration, shock, or temperature extremes can drive up warranty and service costs, impair quality or safety, and raise liability issues. Also important are fastener assembly costs, as well as service issues in the field where operators or mechanics may adjust vehicles and need access to reusable fasteners.

Fortunately, vehicle manufacturers such as Gehl Products - a Madison, South Dakota-based manufacturer of construction equipment, are taking advantage of a unique internal thread locking design that not only virtually eliminates warranty and service concerns related to the vibration and shock of travel but also enhances product quality, safety, ease of assembly, and facilitates necessary adjustments in the field. By solving vehicle design issues, some manufacturers are enjoying six figure total cost savings simply by changing to the self locking threaded fasteners.

Through the physics of the thread locking form itself, Madison Heights, Mich.-based Spiralock Corp's self locking fasteners address fastener loosening and stripping problems caused by vehicular vibration, shock, and temperature extremes. The secret to the self locking fasteners is a 30º "wedge" ramp cut at the root of the female thread. Under clamp load, the crests of the threads on any standard bolt are drawn tightly against the wedge ramp. This causes thread contact forces to be applied at approximately 60º from the bolt axis, rather than 30º away as in a standard thread form. The mechanical advantage -- the angular relationship between the unique wedge ramp and the male thread -- restricts bolt or screw movement.

A decade ago, Roger Albertson, a manufacturing engineer at Gehl Products sought a solution for the abuse Gehl Products skid loaders received in the field, as warranty service costs were too high.

"Under constant back and forth motion and jarring vibration, certain fasteners wouldn't hold tight on typical threading," said Albertson. "We tried just about everything from locknuts and adhesives to inserts, washers, and double nuts. But they either came loose in the field, posed assembly problems, or both. Another complication was that operators had to adjust the drive chains every 100 hours in the field, so fastener reusability was a requirement as well."

After testing and investigation, Gehl Products chose to use self locking threaded fasteners for added vibration resistance and holding power. Because the design change worked so well, Gehl Products later added fasteners to all hard joints on products - such as motor mounts, lift control levers and rods - for locking ability and ease of assembly.

"The change has virtually eliminated service and warranty concerns in these areas," says Albertson of the self locking threaded fasteners. "By minimizing the need for warranty service and simplifying assembly, I'd estimate we've saved over $100,000 in the last nine years."

Spiralock Corporation

Kate Turowska

Phone: (248) 543-7800

Fax: (248) 543-1403

http://www.spiralock.com

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Kate Turowska
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