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All About Washers

The use of incorrect washers happens more than you might think – and it occurs all across the globe. What are the consequences of using the wrong washer? The strength of the join is reduced and the risk of loosening in a dynamic joint is increased.

So how do you know which washer to use?

Comparing and contrasting lock washers, split lock washers and ribbed lock washers can help create a better understanding of the advantages and disadvantages of both types.

Flat washers are up first. When used correctly, flat washers can help reduce surface pressure on softer materials, minimizing the loss of clamp load due to embedment. You’ll notice that the bearing area is often larger than a screw or a nut. In addition to producing more frictional resistance, flat washers also protect softer materials and reduce the risk of loosening due to embedment.

You’ll need to reference the fastener property class to determine the proper washer hardness. Choosing the wrong washer hardness can increase the risk of embedment.

Split lock washers are up next. There is a misconception that these are added to reduce the risk of rotational loosening, but the true objective with split lock washers is to reduce the loss of clamp load due to embedment. Correct use will reduce the risk of loosening due to dynamic forces.

But the strength of this type of washer is often overrated, leading to a much higher risk of loosening due to embedment. Split lock washers are only able to withstand clamp forces introduced by fasteners up to property class 5.8. It is also important to mention that their effectiveness is very low or even non-existent when used with heat treated fasteners of 8.8 (grade 5) and higher.

Ribbed lock washers stand apart. These washers feature ridges on at least one side designed to anchor themselves into the clamped parts, as well as into the bolt or nut’s bearing area. The friction in the bearing area prevents spontaneous rotational loosening of the screw or nut by increasing friction between bearing areas. This washer is also intended to reduce the risk of embedment.

For the reasons stated in the paragraph above, ribbed lock washers represent a viable and effective alternative to flat and split lock washers.

Not sold on the idea of ribbed lock washers for your application? We’re here to help! Contact us at ProvenProductivity@bossard.com to start the conversation.


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November 06, 2015

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