Good news for bad vibes

May 23, 2002
Washers that add tension rather than friction keep bolted joints tight.

Nord-Lock washers keep bolted joints tight in hydraulic hammers from Atlas-Copley.

Nord-Lock washers are available in yellow zinc chromate carbon steel (RC 48) in sizes from #5 to 5 in. and M3 to M130, or in stainless steel (RC 53) in sizes from #5 to 2.5 in. and M3 to M80. Washers come preassembled or as separate halves (shown). Nuts with integral washers are also available.

Bolted joints with nylon-insert nuts and conventional lockwashers can lose significant preload when subjected to vibration. Those fitted with Nord-Lock washers exhibit a relatively small preload loss, attributed mostly to thread settling.

Nord-Lock washers work in several different joint configurations.

Loss of preload in bolted joints can lead to fastener failure, especially in joints subjected to vibration. Conventional lockwashers and locking nuts use friction force to help maintain preload. They work in many cases though severe vibration can overcome friction and loosen fasteners. Tension is another way to maintain preload. Here, nuts and bolts attempting to loosen boost joint preload. This is the principle behind Nord-Lock washers from Nord-Lock Inc., Muskegon, Mich. (

Each Nord-Lock washer is comprised of two stacked halves. On both outside mating surfaces are small radial teeth. The teeth prevent relative movement between the washer assembly and fastener and joint surfaces. Washers are hardened up to Rockwell C 53 (RC 53)so fastener and mating surfaces coin (even at moderate torque levels) rather than the washers themselves.

Inside are two opposing ramped cams. The cam vertical surfaces engage one another as the fastener is turned clockwise (tightened). Counterclockwise movement forces the cams to ride up each other, raising the stack height and increasing joint tension. In other words, more torque is required to loosen the fastener than that associated with the prevailing preload. The washers self-lock because the cam-lead angle, , is greater than the thread-pitch angle, . And unlike conventional lock washers that need replacing each time a joint is disassembled, the NordLock washers are reusable.

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