Washers, an important part for weight distribution in many machines, are thin, disc-shaped plates with a hole in the center. Though they are commonly metal, washers come in a variety of materials and are used as spacers, springs, pre-loading screws, and vibration reducers. Washers come in three types: plain, spring, and lock. This blog will explore each type and provide insight to their characteristics and applications.
Plain washers are used to distribute loads to larger areas and prevent damage to assembled surfaces. Within the subset of plain washers, there are flat washers, fender washers, shoulder washers, and countersunk washers. Flat washers are the standard plain washer, a thing, flat, circular piece with a hole in the center. They are used to distribute loads and provide support to head fastener screws. Fender washers are similar to flat washers, but the central hole has a much smaller diameter than that of a flat washer. Shoulder washers have a shoulder-like structure and are used to insulate screws, wire or other assembly parts. They come in fiberglass, phenolic, nylon, as well as PCTFE and PTFE metals. A countersunk washer has a 90 or 120 degree countersink in its center. These washers work well for countersunk screws and provide a flush surface to countersunk screws.
Spring washers operate during vibration or shock to provide axial load relief to whatever they are affixed to. Like plain washers, they come in many subtypes such as conical, crescent, and dome spring washers. Conical washers are used to keep assemblies tight in instances of thermal expansion or contraction. Crescent spring washers provide a constant spring rate over the deflection range and have unique applications in flexible load-cycling products. Dome spring washers are curvaceous to create a spring load-bearing surface, providing them with a very high load capacity with a small deflection range.
The third type of washer, the lock nut bearing, is a variation of the spring washer. Their purpose is to prevent loosening by minimizing rotational unscrewing. Tooth and helical lock washers are the main types of lock washers, each with unique capabilities. Tooth lock washers, whether external or internal, use teeth to prevent nuts or bolt heads from loosening and absorb shock and vibration. Helical spring lock washers provide protection against loosening during vibration and corrosion by increasing the preload on a screw when it is tightened.