Prevent Bolted Joint Failures with Solon Belleville Springs
Belleville springs prevent the failure of bolted fasteners in many applications where maintaining adequate load on the bolted connection is essential. Failure of a bolted connection is often due to a loss in load of the bolt or bolts holding the connection together. Loss of load is attributable in many cases to plastic movement in the joint or joints that make up the connection. Plastic movement in the joints of bolted connections results from several natural occurring events that cause loss of load: embedment of the high spots in the joint, changes in temperature, vibration, gasket set, yielding of the material making up the joint, relaxation of the bolts, over tightening or under tightening the bolts.
How do Belleville springs prevent bolting failures?
Belleville springs can be designed to produce high loads when deflected to their flat position. By selecting the proper spring, flat loads of between 50% and 80% of the yield stress of the bolt can be achieved. The deflection of the Belleville spring added to the stretch of the bolt significantly reduces the spring rate of the bolted system. The deflection of a Belleville spring adds between 3 to 10 times the bolt-stretch of the bolt, depending on the length of the bolt, for the same load applied to the bolt without the spring. Reducing the spring rate, by introducing added deflection for a given load on the connection, significantly reduces the change in load on the connection as movement in the connection occurs. This is a simple way to maintain adequate load on a bolted connection, particularly if the bolt is short. In addition, Belleville springs can be stacked in series to increase deflection for the same load, or stacked in parallel (nested) to increase load for the same deflection. By installing Belleville springs as part of bolted connections, a loss of preload is much less likely. Belleville springs can also aid in obtaining the proper preload. Since the deflection of the spring is added to the stretch in the bolt, any change in load due to a given rotation of the nut will result in less change in preload. This is beneficial when torque is used to control load. In addition, the sudden increase in rate that occurs when the spring flattens out can give the installer a “feel” for the flat load of the spring. There are other devices on the market that help the installer determine the specified load produced by torque on the bolt. However, all of these devices rely on stretching the bolt to obtain the proper load on the bolted joint. The advantage of using a Belleville spring is the added deflection for the same bolt load produced by the same torque. Added deflection significantly reduces the change in bolt load due to changes in the bolted system. For example, a one half inch steel bolt six inches long is loaded to 3400 pounds by torque. The bolt stretches 0.004 inch. If plastic movement in the joint over time results in a decrease in dimension of the joint of 0.003 inch, this represents a 75% decrease in the stretch of the bolt and the load of the bolt has dropped to 850 pounds on the joint. By applying a Belleville spring to the bolted joint that produces a load of 3400 pounds at the flat position and with a deflection of 0.022 inch, then the combined bolt stretch and spring deflection is 0.026 inch. Now the 0.003 inch movement in the joint represents only 11% decrease in the total deflection of the bolt and spring, and the bolt and spring maintain a load of 3026 pounds on the joint. This represents a significant improvement over using only bolt stretch to produce the proper load on a bolted connection.
Solon Belleville Springs are commonly called belleville washers, flange washers disc springs and compression washers. Solon Belleville Springs are available in English and Metric dimensions using a wide variety of materials. In many critical bolting applications where the safety of personnel and equipment are paramount, Solon's engineers can determine the proper use of Solon Belleville Springs that ensure bolting integrity.
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440-286-7149
800-323-9717
Email:
tdingers@solonmfg.com
