What is Function Of Washer – Types Of Washers

Introduction to Washers ( Hardware )

A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring (Belleville, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer). Washers usually have an outer diameter (OD) about twice the width of their inner diameter (ID).

Washers are usually metal or plastic. High quality bolted joints require hardened steel washers to prevent the loss of pre-load after the torque is applied.

Rubber or fiber gaskets used in taps (or faucets, or valves) to stop the flow of water are sometimes referred to colloquially as washers; but, while they may look similar, washers and gaskets are usually designed for different functions and made differently.

Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminum surfaces.

Washers can be categorized into three types;

• Plain washers, which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as electrical
• Spring washers, which have axial flexibility and are used to prevent fastening loosening due to vibrations
• Locking washers, which prevent fastening loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers.

Types Of Washers:

In order to define a washer with any degree or accuracy an adjective must be used to place its in proper categories. Some of the basic categories are;

1. Flat washers
2. Shoulder washer
3. Tab washer
4. Lock washers
5. Countersunk washer
6. Spring washers

Flat washers 

A plain washer (or ‘flat washer’) is a flat annulus or ring, often of metal, used to spread the load of a screwed fastening. Additionally, a plain washer may be used when the hole is a larger diameter than the fixing nut

Flat washers are round outer diameter thin plates with a center hole punched to the size of the bolt or screw. Flat washers are used to distribute loads of threaded bolts, screws and nuts evenly as the fastener is tightened.

Shoulder washer

Shoulder washers , sometimes called ” Step ” or  ” Flange” washers,have in profile the appearance of a low crowned top hat. the category is rather unique since shoulder washers are used primarily in the electronics equipment industry as insulators , and are therefore made of non-conductive materials.

Tap Washers :

Tab Washers are made in an almost infinite variety of configurations with internal and /or external notches and or tabs , singles or multiple, Formed and Flat .

Lock washers :

Lock washes are of course familiar to most of us in the conventional helical split and internal and external tooth types.

Countersunk Washers :

Countersunk washers come in a number of shapes : 90 degree countersunk, angle countersunk, flanged, unflanged, rolled flange, etc. Most people are familiar with the finishing types used for cosmetic purposes on many consumer products .

Spring Washers:

A split washer or a spring lock washer is a ring split at one point and bent into a helical shape. This causes the washer to exert a spring force between the fastener’s head and the substrate, which maintains the washer hard against the substrate and the bolt thread hard against the nut or substrate thread, creating more friction and resistance to rotation.

Spring Washers absorb any looseness resulting from vibration or thermal expansion . They also eliminate  side play in assemblies and are used with bearings to control end pressure and play. Vibration mountings also often use spring washers.

There are Three basic types of spring washers .

Belleville washers, also known as cupped spring washers or conical washers, have a slight conical shape, which provides an axial force when deformed.

A curved disc spring is similar to a Belleville, except the washer is curved in only one direction, therefore there are only four points of contact. Unlike Belleville washers, they exert only light pressures.

Wave washers have a “wave” in the axial direction, which provides spring pressure when compressed. Wave washers, of comparable size, do not produce as much force as Belleville washers. In Germany, they are sometimes used as lock washers, however they are less effective than other choices.

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