What is washer? Washer is a disk shaped thin plate with a center hole. Washers are used to distribute the load of a threaded fastener. Other application of washers are Spacers, Springs, preloading screws and vibration reduction. In this article we will discuss various type of washers and their applications.
According to application, washers are classified three categories:
- Plain Washer
- Spring Washer
- Lock Washer
Plain Washer are used to distribute load relatively in larger area. Therefore they prevent damage to the assembled surfaces.
Flat washer / Type-A plain washer
Flat Washer / Plain Washer are thin, flat and circular washers.
Plain washer application is to distribute load to relatively larger area and provide support to smaller head screw.
Fender Washers are washers with larger outside diameter as compared to the inside diameter. These washers distributes loads to relatively larger area compared to flat washers.
They have application in automobile, plumbing, sheet metal and electrical applications, attaching sign boards, panel and drywall.
Shoulder washer is a washer with shoulder type structure.
Their applications are insulating screw, wire or any other part from assembly.
Shoulder washers are available in fiber-glass, phenolic, nylon, PCTFE, PTFE and Metals
C- Washer are designed to slide in and out of position on a bolt or shaft.
They are the washers with 90 or 120 degree countersunk on top.
Countersunk washer works as a flat washer for flat head_ countersunk screws.
These washers provide a flush surface to countersunk screw.
Application of spring washers is to provide axial load to fasteners during vibration or shock.
Belleville / Conical Spring Washer
Belleville or Conical spring washers maintains the tension in assemblies during thermal expansion and contraction conditions.
They supports even more load with small deflection. Conical washer load-deflection characteristics depends on height and thickness ratio.
Crescent / Curved Spring Washer
Curved spring washer supports relatively small loads and wide deflection range.
They provide uniform spring rate over the deflection range and have linear load-deflection characteristics. These washers have application in flexible and load-cycling products.
Dome Spring Washer
Dome Spring Washers have a high load capacity with a relatively small deflection range.
They have ground curves to create a flatter load-bearing surface.
Finger Spring Washer
Finger Spring Washers are used to counteract noise, excess wear, vibrations and reducing skidding wear on rotating elements.
These washers are manufactured from carbon steel. Finger spring washers combine the flexibility of a crescent washer with the distributed load points of a wave washer.
Wave Spring Washer
Wave Spring Washer have good load capacity and deflection. They works as cushion springs or spacers on a shaft.
They have a moderate load capacity and deflection range.
Locking Washers is a type of spring washer. It prevent fasteners loosening by preventing unscrewing rotation. Lock washers secure fasteners that has a tendency to rotate or loose friction.
External tooth Lock Washer
External tooth lock washer prevents a nut or bolt head from loosening with its teeth strut action. These washers work best with larger head screws.
They also provide maximum torsional resistance, when the teeth bite into a mating surface and resisting compression force.
Internal Tooth Lock Washer
Internal teeth lock washer prevents a nut or bolt head from loosening with the strut action set up by the teeth. Washer teeth also absorb shock and vibration.
Helical / Split Lock Washer
Helical spring lock washers prevent assembly components from loosening by increasing preload on screws during tightening. Increased preload provides protection against loosening during vibration and corrosion.
To sum up, various types of washers are available according to their application and material. As per design requirements and application, washers are selected.
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