In the threaded connection of fasteners, we often use flat washers and spring washers together, but some connections do not use washers, either only flat pads or only spring pads. So, how should the flat elastic pad be selected and used in the bolted connection? Today, I will share it with you.
First of all, the flat washer, its role should be known to everyone, increase the contact area of the connected parts, reduce friction, protect the surface of the connection from damage, but also play a role in pressure reduction, sealing, shock absorption, fixation and so on. At present, the selection of flat gaskets is referred to "GB/T 97.1-2002 flat gasket grade A (ISO 7089:2000, EQV)", this standard is according to Vickers hardness grade gasket is divided into 200HV and 300HV, the related selection standards, as shown in the figure below:
The reason why the hardness is used to express the performance of the gasket is because the gasket cannot test its tensile strength or yield strength. According to the above standards, if the gasket is selected incorrectly, the 200HV gasket is applied to the 10.9 grade or higher threaded connection, the compressive stress generated by the bolt preload on the gasket has exceeded the yield limit of the 200HV gasket material, the gasket will produce plastic deformation, the gasket becomes thinner, resulting in reduced bolt preload and connection problems.
In the application, the flat washer is either added between the bolt head and the workpiece to distribute the pressure of the bolt head; Or in some working conditions, in order to ensure that the bolt hole between the two workpieces can be aligned, the diameter of the hole will be increased, and if the bolt hole exceeds the standard requirements, a flat washer should be added; In order to facilitate installation and adjustment, bolt holes will be made into long holes, and flat washers also need to be added at this time.
Let's talk about the spring washer, its main function is to increase the friction between the nut and the bolt, to prevent the bolt connection loose due to the vibration of the equipment during operation, so the fastener connection on the equipment with vibration will be equipped with a spring washer.
Although the main function of the spring washer is anti-loosening, but its anti-loosening ability is limited, the role is actually to "compensate for the existing looseness" and "provide a solid support surface", in the high-strength bolt connection, the axial force of the bolt far exceeds the force required by the spring washer, so the spring washer does not play an anti-loosening effect, but will cause the rapid attenuation of the bolt clamping force, affecting the connection effect. Therefore, in the case of high preload requirements, spring washers are not recommended.
However, in the working conditions where the bolt preload is not high and the dynamic load is relatively small, the spring washer can still play a certain anti-loosening effect. And when the clamping length of the bolt is relatively short, the stress relaxation of the bolt will be more obvious, and the use of spring washers can make up for the stress relaxation.
In general, the selection of flat washers and spring washers must be selected according to specific working conditions, otherwise it will be too late, and even cause connection accidents.
#Headline Creation Challenge##Mechanics##Bolts##螺纹连接#