The Introduction of The Belleville Washer

A Belleville washer, also known as a cupped spring washer, is a type of non-flat washer. It has a slight conical shape which gives the washer a spring characteristic. Belleville washers are typically used as springs, or to apply a pre-load or flexible quality to a bolted joint. Belleville springs are also used in a number of landmines e. G. The American M14 mine. They may also be used as locking devices, but only in applications with low dynamic loads, such as down-tube shifters for bicycles. Belleville washers are seen on Formula One cars, as they provide extremely detailed tuning ability. Another example where they aid locking is a joint that experiences a large amount of thermal expansion and contraction. They will supply the required pre-load, but the bolt may have an additional locking mechanism (like Loctite) that would fail without the Belleville. Multiple Belleville washers may be stacked to modify the spring constant or amount of deflection. Stacking in the same direction will add the spring constant in parallel, creating a stiffer joint (with the same deflection). Stacking in an alternating direction is the same as adding springs in series, resulting in a lower spring constant and greater deflection. Mixing and matching directions allow a specific spring constant and deflection capacity to be designed. To keep bolted connections tight, we can choose from several methods. The most common is the insertion of a locking device between the rotating part (nut) and the parts being fastened (i. E., bus bars). That locking device often is a split-ring lockwasher. Such a device does not meet all locking device requirements, however. Enter, the Belleville washer. The Belleville is a disk spring that applies pressure to the connection once you clamp down on it with the proper amount of force. The advantage of this washer is that it applies clamping pressure along a continuous arc pattern, instead of concentrating it at one point the way a split-ring lockwasher does. While you should use a split-ring washer only at the nut end of the connection (normally), you can use Belleville washers in tandem. One at the nut end and one at the bolt head end. This is a common way to use these washers, especially when assembling bus bar. Most often, you'll find Belleville washers in applications where you have to connect bare, soft aluminum to aluminum or copper, or where you have conditions of high current loading or cycling. These washers do wonders for accommodating thermal cycling, but they can't eliminate all the problems resulting from poor workmanship. You must prepare the joint properly (as with any connection), but the key is selecting the proper design and size of Belleville washer for the fasteners and conditions of your application. Selecting the right Belleville washer You have to deal with three parameters here: Torque, diameter, and finish. Vendors publish the specification data you need in various media, such as booklets, CD-ROMs, and websites. These are high-end fasteners for electrical applications, so your source would most likely be your electrical supply house you normally deal with. Let's look at these three parameters. In a Belleville washer application, the manufacturer may say to flatten the washer and then back off slightly. Make sure you don't back off too far, because when you flatten the washer a second time, it will have less clamping force than it was designed to have. Before energizing the system, check each connection to see if the Belleville washers are flat and not cracked. After the system has had some load cycling, give the bolted connections another visual check. If you assembled them properly, they will be secure. Recommended guide clearances are provided in the tolerance tables which Belleville Springs provides, and it is also necessary to pay some attention to the nature of the guidance and seating surfaces. Much depends on the severity of duty in the application; If the disc is to be used as a means of providing a static clamping force on mild steel or cast/forged steel surfaces, this is probably satisfactory. However, if the seating faces are in aluminium, copper, brass etc; Then it is preferable to provide a hardened thrust washer to alleviate face damage/indentation. For more severe applications of a dynamic or highly corrosive nature, the disc springs will benefit from maintained lubrication, and are often housed in an oil or grease filled chamber. Source: Globalfastenermarket. Com