For naïve people, let use what a washer is. A washer is thin sheet like structure with a hole in the centre of it.
A flat washer serves many purposes. The most common purposes are:
- It distributes the pressure of nut or the bolt evenly at the part it is used. It reduces the chance of damage.
- It provides smooth surface to nut or the bolt to fasten. Uneven fastening surfaces may result in loosening of nut and bolt.If you try screwing into uneven surface, the head of the screw may feel tight or can get stuck. Smooth surface allows screw to slide as it is installedand makes installation easy and more secure.
Some other uses of washers are:
- It can be used as aspacer.
- It can help in reduction of vibration.
- It can be used as locking device.
- It prevents galvanic corrosion.
- It prevents damage caused to the material for installation. If the material is soft, while you try to tighten the screw, it can crack the material. This is how surface damage. A washer will dispense the force over a large area. Thus,, preventing damage.
- It prevents pull-through. This is often observed in cars when the hole inside it begins to rust
Washers are generally of three types:
- Plain Washers
- Spreads load evenly
- Prevents damage to the surface
- Provides insulation
- Spring washers
- Prevents unfastening due to vibrations
- Locking washers
- Also called spring washers
- Contact washers
- Shim Washers
- Twin lock washers
- Split lock washers
- Tab washers
- Tooth lock washers
Washers can be of metal or plastic. Some materials are:
- Metal – copper, aluminium, iron, zinc
- Steel – CS, spring steel, 304 SS, 316SS
- Alloy – Silicon bronze, Monel, Hastelloy
- Plastic – Thermoplastics, PTFE
- Nylon – Nylon 6, Nylatron
Parameters in washers that vary are
- Outer diameter given as OD
- Inner diameter given as ID
- Thickness given as t
It is very important to prevent corrosion in washer. Some techniques are:
- Metallic coatings of zinc, cadmium and nickel
- Electroplating of chromium or silver
- Phosphating by layer of zinc phosphate or corrosion protective oil
- Browning or bluing of steel washers by an alkali
- Chemical plating using nickel-phosphor alloy
With the variety of industries available, variety of washers are available.
Metric flat washers and standard din 125 washers are most widely used washers. These are the standard ones and most easily available.