How to make washers play a better value in bolt connection

- Aug 05, 2020-

As a common connection part, bolts are commonly used in machinery, automobiles, trains and building structures. Choose suitable bolt types according to different requirements. The bolt connection is also the most basic structural form of the fastener connection, and the anti-loosening effect is a part that cannot be ignored. The anti-loosening effect of many bolt connections is to use washers to improve the anti-loosing effect.


We all know that the bolts will loosen due to vibration, high and low load changes, and long-term working conditions during the use of the equipment. In many cases, in order to prevent the bolts from loosening, we will add washers to the bolts to make it more secure.


The anti-loosening device with additional friction has three main structures: double nut tightening structure, spring washer tightening structure and self-locking nut tightening structure. Among them, the spring washer tightening structure: the spring washer is widely used in the assembly site because of its simple structure, convenient use and low cost, and is generally used in conjunction with bolts or nuts. After the bolts or nuts are tightened, the elastic reaction force produced by the flattening of the washers makes the screw threads tight. At the same time, the tip of the oblique mouth of the washer resists the bearing surface of the bolt or nut and the connected part to prevent loosening.


But in the bolt connection, is it really effective to reduce the loosening of bolts when using washers?

First, let's look at the bolted connection-no washers:


Bolt connection-with flat washers:


Stud connection-spring washer anti-loosening:


During the operation, whether to use a washer or what washer should be used depends on the actual situation.

The role of flat washers

1. In order to protect the connecting piece from being scratched by the surface, a flat washer is placed on the nut and bolt head to prevent the surface of the connecting piece from being scratched.

2. When the bolt strength is relatively high, in order to reduce the compressive stress of the pressure-bearing surface of the connected parts, flat washers are generally needed.

3. In the bolt connection, the pressure transmission of the pressure bearing surface of the bolt head or nut is gradually enlarged in a trumpet shape. The larger the pressure bearing surface, the smaller the compressive stress. Therefore, the addition of a flat washer can reduce the pressure on the contact surface of the connected part. Stress to ensure the effectiveness of the bolt connection.

4. In some occasions, in order to ensure one-to-one correspondence between the bolt holes between the two connectors, the diameter of the hole needs to be increased to compensate for the deviation of the hole position. When the bolt hole exceeds the standard requirement, a flat washer needs to be added.

5. Sometimes for the convenience of installation and adjustment, bolt holes will be made into long holes, so that the installation position of the workpiece can be adjusted within a certain range. When long holes are used, thick flat washers must be used. According to the specific situation, special washers or more Washers.


The role of spring washers

1. When the clamping length of the bolt is relatively short, the bolt stress relaxation is more obvious, and the spring washer can compensate for the stress relaxation.

2. Under dynamic load conditions, high-strength bolt connection spring washers have almost no anti-loosening effect, and will cause rapid attenuation of bolt clamping force, so it is necessary to reduce the use of spring washers in high-strength bolt connections.

Spring washer

Of course, in some cases, the bolt connection does not need to use washers, the specific conditions are as follows:

1. Shear stress bolt connections generally do not require washers. First of all, the bolts do not need too much pre-tightening force, and do not bear axial force during work. In this case, the bolt holes are generally relatively small, and the bearing surface of the nut or bolt head Generally, they are relatively large, no need to reduce the compressive stress, and the connected parts can bear it.

2. When flange nuts or bolts are used, washers are not needed, and the pressure surface of flange nuts is large enough.


In different situations, the selection of washers according to the actual situation can greatly reduce the wear of bolts.