As a common connecting component, bolts are commonly used in mechanical equipment, automobiles, trains, and building structures. Choose the appropriate type of bolt according to different requirements. And bolt connection is also the most basic structural form in fastener connection, and its anti loosening effect cannot be ignored. Below, Xiaorui will analyze how to make the washer play a better role in fastener bolt connection. It can be seen that many anti loosening effects in bolt connection are improved by using washers.
We all know that during the use of equipment, bolts may loosen due to vibration, changes in high and low loads, and long-term working conditions. In many cases, to prevent bolt loosening, we add washers to the bolts for better fastening.
In daily use, to prevent bolt loosening, bolt anti loosening measures can be roughly divided into two aspects: physical device anti loosening and process method anti loosening.
Anti loosening measures for physical devices:
(1) Anti loosening device with additional friction force
(2) Mechanical anti loosening device
(3) Adhesive anti loosening device
Process method anti loosening measures:
(1) Fixed torque tool anti loosening
(2) Training and anti loosening training
(3) Component quality control anti loosening
This time, we will analyze the anti loosening device with additional friction force for physical device anti loosening measures:
There are three main structures for anti loosening devices with additional friction: double nut tightening structure, spring washer tightening structure, and self-locking nut tightening structure. Double nut tightening structure: First tighten the lower nut, then tighten the upper nut. After tightening the two nuts against each other, the contact surface between the upper and lower nuts and the bolt thread is opposite, so that the screw threads are always subjected to additional pressure and friction. When the working load changes, this friction still exists. Its structure is simple and suitable for connecting stable, low-speed, and heavy-duty fixed devices.
Double nut tightening structure anti loosening installation
Among them, the tightening structure of spring washers: Spring washers are widely used in assembly sites due to their simple structure, convenient use, and low cost, and are generally used in conjunction with bolts or nuts. After tightening the bolt or nut, the elastic reaction force generated by flattening the cushion ring compresses the screw threads. At the same time, the tip of the slanted washer also has a locking effect against the supporting surface of the bolt or nut and the connected component.
But in bolted connections, can using washers really effectively reduce bolt looseness?
Firstly, let's take a look at the bolted connection - without washers:
Bolt connection - using flat washers:
Screw connection - spring washer anti loosening:
Whether to use gaskets or what gaskets to use during the operation process depends on the actual situation.
The function of flat washers
1. To protect the connecting components from surface scratches, flat washers are placed at the nut and bolt head positions to prevent the surfaces of the connected components from being scratched;
2. When the bolt strength is relatively high and the allowable compressive stress of the connected part is relatively low, in order to reduce the compressive stress on the pressure bearing surface of the connected part, it is generally necessary to add flat washers;
3. In bolted connections, the pressure transmission on the pressure bearing surface of the bolt head or nut gradually expands in a trumpet shape. The larger the pressure bearing surface, the smaller the compressive stress. Therefore, adding a flat washer can reduce the compressive stress on the contact surface of the connected part and ensure the effectiveness of the bolted connection;
4. In some cases, in order to ensure that the bolt holes between two connecting components correspond one-to-one, it is necessary to increase the diameter of the holes and compensate for the positional deviation of the holes. When the bolt holes exceed the standard requirements, flat washers need to be added;
5. Sometimes, for the convenience of installation and adjustment, bolt holes are made into long holes, which can adjust the installation position of the workpiece within a certain range. When using long holes, thick flat washers must be used, and more specifically, special washers or multiple washers may even be used.
The function of spring washers
1. When the clamping length of the bolt is relatively short, the stress relaxation of the bolt is more obvious, and the spring washer can compensate for the stress relaxation.
2. Under dynamic load conditions, high-strength bolt connected spring washers have almost no anti loosening effect and can cause rapid attenuation of bolt clamping force. Therefore, it is necessary to reduce the use of spring washers in high-strength bolt connections.
Of course, in some cases, bolt connections do not require the use of washers, as follows:
1. Shear stress bolt connections generally do not require washers. Firstly, bolts do not require too much pre tightening force and do not bear axial force during operation. In this case, bolt holes are generally small, and the pressure bearing surface of nuts or bolt heads is generally large, so there is no need to reduce compressive stress. The connected parts can withstand it;
2. When using flange nuts or bolts, there is no need for washers, and the pressure bearing surface of the flange nut is large enough;
Choosing washers based on actual conditions can significantly reduce bolt wear in different situations.
