Lock washers prevent threaded connections from loosening due to vibration, temperature cycling, and wear. They come in different types and sizes, such as split lock washers, star lock washers, and tabbed lock washers. They resist force through friction and can create a mechanical gripping force. They are extensively used in aircraft manufacturing and structural applications for safety reasons.
Threaded fasteners are commonly used to attach and secure two or more objects together. While very effective, a threaded connection can loosen over time due to reasons such as vibration, temperature cycling, and wear. A lock washer is a type of fastener used to prevent a joint secured by threaded fasteners from loosening and separating. Lock washers come in different types and sizes, such as split lock washers, star lock washers, and lock washers. These are used extensively in aircraft manufacturing and in numerous structural applications where loosening of connections could have significant safety implications.
Threaded connections between two or more objects typically involve the use of a screw or bolt and nut. Lock washers are used for threaded connections using a screw and nut combination. The screw has a large head on one end and an externally threaded shaft, which is a helical structure that allows the screw to advance when it is turned. The nut, usually hexagonal in shape, has a hole with an internal thread that corresponds to the thread of the screw.
When a screw is inserted and turned into a nut, the screw advances. A significant force can be generated when the screw and nut are tightened against two or more objects located between the screw head and nut surfaces. A lock washer is placed between the nut and the surface to be fastened or joined. Resists the force applied by the nut and prevents the nut from loosening.
A split lock washer is shaped like a donut — a circle with a hole in the center — and has a single cut that extends from the outside diameter to the inside hole. The shear is why this type of washer is called a split lock washer. The two sections adjacent to the cut are misaligned in the direction perpendicular to the washer surface. This misalignment allows the lockwasher to resist the force by creating friction through the resulting spring action which prevents the nut from loosening.
In addition to resisting force through friction, the shape of some types of lock washers can cause them to bite into the mating surface and create a mechanical gripping force. Star lock washers have inner and outer teeth and each adjacent tooth is bent in alternating directions perpendicular to the washer surface. The teeth bent on one side fit into the nut, while the teeth bent in the opposite direction fit into the work surface during the fixing phase. Similarly, tabbed lock washers have tabs bent at the edges that mate with the surface of the nut and lock the nut in place.
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