Firstly, we need to understand what a washer is and why it is used. A washer is a typically a disc-shaped thin plate with a central hole (almost always). Mostly it is used for distribution if load of threaded fasteners. Some washers are very specialized, like those sold by Belleville Disc Springs, which play an important function on the quick-action stop valves.
The washer has other names including conical spring washer, disc spring or cupped spring washer. As a result of the conical shape (frustum), the washer gets spring-like characteristics. When used, it possesses some distinct advantages when compared to other types of springs:
- The transmission of force is purely concentric due to the ring shape of the washer.
- It is possible to stack the washers in different configuration thus having the ability to attain extremely high damping effects in dynamic loading applications.
- The spring does not suffer impermissible relaxation as opposed to the ordinary helical springs. This advantage however remains only when the ultimate stress of the spring is not exceeded.
- When it is made to the correct dimensions, it will offer a longer service life compared to other springs when applied in dynamic applications.
- It can support very large loads in tight applications where space is very limited.
The washer applies pressure to a connection when it is clamped down with the right amount of force. To make full advantage of the washer, it is important to consider the locking torque, diameter of the washer and finish.
Torque has a profound effect on the clamping capabilities of the connection. This will be a measure of the amount of force required to flatten deform the washer elastically to a flatter optimum shape for clamping. To find the correct amount of torque, it is important to consider the bolt hardness, diameter and material. Dealers of the conical spring washer will normally have data where you can easily look up the torque required for various sizes and types of bolts.
Diameter if the washer is a big determinant of the clamping force. Overhanging due to a larger diameter compared to the fasteners will greatly reduce the clamping force. Too small a diameter on the washer may lead to destruction of the washer due to permanent plastic deformation as the locking torque of the fastener will most likely exceed that of the washer.
The material used and the finish will determine the soundness of a joint. We know that for example that electroplated washers are not suitable for hydrogen environments as they become brittle. You will also need a tougher material for an environment with vibrations.
It is important to note that the washer can be used in upright of upside-down position (reversed). The reversed position adds a little more clamping force to the joint. It is important to know for sure the washer you are applying is appropriate as poor choice will cause unsound connections both electrically and mechanically. Good luck choosing the right spring washer for your joint.