The Rise of Flange Bolts: Why Are Washer Designs Fading Out?

Washers have long been an indispensable auxiliary tool for engineers in tightening operations. Their main responsibility is to protect the joint surface during tightening, prevent crushing and damage caused by direct contact, and reasonably distribute the load under the bolt head and nut to ensure uniformity and stability of tightening. However, with the advancement of technology and the development of engineering practice, washers have gradually been replaced by flange bolts in some applications. Today, let's take a deep look at the reasons behind this change.

First of all, we need to make it clear that using torque to indirectly control the clamping force of the bolt is the most commonly used method in engineering practice. This method is simple and easy to implement, and is well known to engineers. However, in actual operation, it is not difficult to find that the friction acting on the bolt thread and the bolt head will consume most of the tightening torque. This means that although we apply a lot of torque, the part that is actually converted into effective clamping force is actually quite limited.

In this context, the problems caused by washers are particularly prominent. Since the hardness of standard washers is usually lower than that of bolts and nuts, they are prone to plastic deformation under high stress. This deformation not only causes the washer itself to collapse, but may also affect the clamping force of the bolt, resulting in a loss of clamping force. In contrast, flange bolts do not have this problem. Their support surface maintains the same overall hardness as the fastener, and can maintain a stable shape and performance under high stress.

In addition, the clearance hole in the design of the washer may also cause a series of problems. In order to avoid interference with the transition arc under the bolt head, the washer needs to have a relatively large clearance hole. However, this clearance hole may cause the center of the washer to deviate from the bolt axis during tightening, resulting in eccentric loading and local stress concentration. This not only increases the risk of indentation and joint damage, but may also affect the stability and safety of the entire fastening system.

Another issue worth noting is the phenomenon of washer rotation. During the tightening process, the washer sometimes rotates on the joint surface with the nut. This rotation changes the relationship between the applied torque and the bolt clamping force, resulting in a significant loss of clamping force. Unless careful observation and monitoring are carried out during the tightening process, it is difficult to detect and correct this problem in time.

Finally, the use of washers also increases the number of contact surfaces in the joint. At the microscopic level, the embedding between these contact surfaces can lead to a loss of clamping force. This is especially true when the parts in the joint are first pressed into contact. For metal-to-metal contact surfaces, this loss is usually between 0.002 and 0.006 mm. For painted surfaces, the embedding effect is even more pronounced. Therefore, the use of washers exacerbates this effect and further reduces the clamping force of the bolts.

In summary, we can see that although washers play an important role in traditional fastening operations, their problems cannot be ignored. In contrast, flange bolts have higher stability, better reliability and lower maintenance costs. Therefore, more and more engineers are beginning to choose flange bolts to replace traditional fasteners with washers. Of course, during the replacement process, we also need to pay attention to adjusting the original installation torque to ensure the optimization of the fastening effect.

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• Michelle

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