Washer Selection Guide
Standard Washers
A regular washer is a round or square thin metal plate with a hole in the middle and serve two key purposes.
- To minimise damaging the surfaces as the two metal surfaces come together during tightening.
- To increase the effective surface area of the nut and bolt assembling. Increasing the surface area distributes the load of the fastener over a larger area and prevent warping and bending of the load bearing surfaces.
Direct tension indicating (DTI) Washers
Direct tension indicating (DTI) washers or squirter washers are used to ensure the necessary tension in a
joint is achieved. They have raised bumps on the load bearing face. When the bolt is tightened, these bumps are deformed to a predetermined level and
therefore indicate the required tension in the assembly has been reached. During the process, silicone is extruded out, indicating to the eye that the correct tensions have been achieved.
Load Indicating Washers (LIWs)
These work in a very similar way to squirter washers except they dont extrude any silicon gel.
Split type or split lock washers
The loosening of bolt assemblies after tightening has long been an issue which the split type washer aimed to solve.
The washer ring surface is split and warped to become out of plane with the ability to become compressed back into a planar surface.
Ideally they are placed under the bolt head with tensions being achieved by rotating the nut. If they are to be placed on the nut side, another hardened flat washer should be placed between the split washer and the rotating nut.
When split washers are flattened, tension is created in the assembly. Split washers alone
do not highlight any over-tightening of the bolt assembly. The split lock washers
are made from hardened spring steel that opposes compression. When the threaded
bolt and nut units are tightened, the corner edges that stick out of the split lock washer bite into both
the compressing surfaces thus resisting counter-clockwise rotation brought on by vibration in a
manner similar to a ratchet.
Spring Washers • Shop Spring Washers
Threaded structures (bolts and nuts) inevitably involve the joining together of inclined planes under load. These
inclined planes consist of the angle of the screw or bolt thread and the angle of
the thread in the nut plate. Under vibration and disturbance to the assembly these threads can be inclined to undo themselves without outside force due to the planar surfaces naturally sliding (rotating) in a direction that opposes the tightening force. If assembled materials are soft or give way under
load, or if heating and cooling causes expansion and contraction of the metals, tension
is lost quite quickly.
Belleville Washer
A Belleville washer, is a type of spring shaped like a washer. It is also known as a conical spring washer or cupped spring washer. It is a type of frustum shape (the planar top bottom slice through a 3 dimensional object - such as a cone). It is this frustum conical shape which gives the washer its spring. In the first phase of tightening its action is similar to that of a split type washer.
However, as tightening increases and the conical washer shape is flattened towards a disk, it reduces the
applied resisting force in the assembly. As such if the bolt and nut assembly is loosened, the opposing washer force will increase and
thus counteract the loosening of the assembly.
Multiple Belleville washers may be applied one on top of the other to change the spring effect.
Spherical Washers
Spherical washers are designed to allow the mating together of non-parallel planar surfaces in the bolt assembly.
Convex and concave washers fit inside each other respectively allowing free planar sliding movement to occur as the assembly comes together. This reduces bending and twisting forces on bolts as two misaligned mating surfaces come under load.
Lock Washers
A toothed lock washer has teeth which extend either inwards or outwards.
This causes reduced likelihood of the bolt and nut assembly coming undone once under load.
Unlike other washers, lock washers maintain the assembly through mechanical action and friction as opposed to primarily spring tension.
Lock Washers – 2 piece type (Nord-Lock)
Coming soon.