Do you want to add washers to the bolt connection?

Do you want to add washers to the bolt connection?

We often see that some bolt connections use washers, some bolt connections do not use washers, some bolt connections use flat washers, some use spring washers, and some use spring washers and flat washers.

Flat Washer

When the bolts need to be removed frequently, in order to protect the surface of the connected parts from being scratched, it is generally necessary to place a flat washer at the nut or bolt head, so as to prevent the surface of the connected parts from being scratched, especially for the surface processed by precision machining.

At some joints where the friction coefficient is required to be accurate, there is no separate test requirement for the friction coefficient. For example, in the bolted connection of wind power, bolts, nuts and washers are generally purchased.

In this case, the bolts, nuts and washers are provided by the same manufacturer. The bolt manufacturer needs to treat the nuts and washers accordingly to ensure that the friction coefficient between the nuts and washers is consistent. At the same time, the supplier is required to test the torque coefficient to meet the technical requirements.

When the bolt strength is relatively high and the allowable compressive stress of the connected part is relatively low. For example, the lightweight requirements of automobiles are becoming higher and higher. Lightweight connection technologies and structures are widely used in the body and even chassis structural parts. In order to reduce the compressive stress of the pressure bearing surface of the connected parts in the bolted joints and prevent crushing and permanent plastic deformation, flat washers are generally required.

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

In some cases, for example, most automobiles use stamping parts and welding parts, and the positions of the holes between the two parts can not be accurately matched. In order to ensure one-to-one correspondence between the bolt holes of the two connectors, we need to increase the diameter of the hole to compensate for the positional deviation of the hole. When the bolt hole exceeds the standard requirements, the compressive stress exceeds the strength of the material. In this case, we need to add a flat washer.

Sometimes, in order to facilitate installation and adjustment, for example, when the control arm bracket is connected with the control meter, one of the two bolt holes will be made into a long hole, so that the installation position of the workpiece can be adjusted within a certain range. When a long hole is used, a thickened flat washer must be used, and even a special washer or multiple washers may be used according to specific conditions.

Spring Washer

The main purpose of the spring washer is to relax. It is generally used in situations where the bolt preload is not high and the dynamic load is small. At present, a large number of tests have confirmed that the spring washer has little anti loosening effect. Therefore, it is not recommended to use the spring washer for tightening occasions with high preload and important connections.

However, for the electrical connection joint, the spring washer still has a certain effect when it is finally completely loosened, especially when it is loosened to a certain extent, a certain preload can still exist when the preload is small. At this time, the spring washer can still play a certain role than the effect without the spring washer.

When the clamping length of the bolt is short, the stress relaxation of the bolt is obvious, and the spring washer can compensate for the stress relaxation. Of course, at this time, it can be considered to use the disc spring instead of the spring washer, and the disc spring can be more evenly distributed in the axial pressure.

Some experiments show that, under dynamic load conditions, the spring washer of high-strength bolt connection has almost no anti loosening effect, and it will also cause the rapid attenuation of bolt clamping force. Therefore, the spring washer is rarely used in high-strength bolt connection abroad.

We have already made it clear under what circumstances washers are required for bolt connection, and under what circumstances washers can not be used?

Generally, washers are not required for connection of shear stress bearing bolts (reamed hole bolts). First, shear stress bolts do not need too much pre tightening force and do not bear axial force during work. In this case, bolt holes are generally small, and the bearing surface of nut or bolt head is generally large. It is not necessary to reduce the compressive stress, and the connected parts can bear it.

When using the Flange Nut or bolt, because the contact area of the flange bolt or nut is large, the washer is usually no longer required to increase the contact area and reduce the compressive stress.