How to Choose Flat Washers and Spring Washers?

We often see in mechanical equipment:some bolts are connected with flat washers, and some bolts are connected with spring washers.

Today, we will share some knowledge about bolt connection design.

Flat Washers

Flat washers are commonly used to reduce friction, prevent leakage, isolate or disperse surface pressure. They are divided into200HVand300HVhardness grades. Here are some precautions:

Washers with hardness grade200 HVare suitable for:

- Hexagonal head bolts and screws with performance grade up to8.8and product grade ofAandB;

- Hexagonal nuts with performance grade up to8and product grade ofAandB;

- Hexagonal head bolts, screws, and nuts made of stainless steel or similar chemical compositions;

- Surface hardened self-tapping screws.

Washers with hardness grade300 HVare suitable for:

- Hexagonal head bolts and screws with performance grade up to10.9and product grade ofAandB;

- Hexagonal nuts with performance grade up to10and product grade ofAandB.

Flat washers can protect the connecting parts from surface scratches. In some cases, in order to ensure that the bolt holes of two connecting parts can match one by one, the diameter of the holes needs to be increased to compensate for the positional deviation of the holes. When the bolt holes exceed standard requirements, flat washers need to be added; sometimes, in order to facilitate installation and adjustment, the bolt holes are made into elongated holes, which can adjust the installation position of the workpiece within a certain range. When using elongated holes, it is recommended to add flat washers.

Spring Washers

The anti-loosening principle of spring washers is that after flattening the spring washers, they will generate a continuous elastic force, which keeps a frictional force between the threads of the nut and the bolt, producing a resisting torque to prevent the nut from loosening.

At the same time, the sharp corners at the opening of the spring washers are embedded in the surface of the bolt and the connected part, preventing the bolt from rotating relative to the connected part.

Spring washers are mainly used for anti-loosening,usually used in occasions where the pre-tightening force of the bolts is not high,and the dynamic load is small.