过程装备和控制工程专业英语翻译5.doc

Reading Material 5 Static and Dynamic Balance of Rotating Bodies The unbalance of a single disk can detected by allowing the disk to rotate on its axle between two parallel knife-edges, as shown in Fig.1.22. The disk will rotate and come to rest with the heavy side on the bottom. This type of unbalance is called static unbalance, since it can be detected by static means. In general, the mass of a rotor is distributed along the shaft such as in a motor armature or an automobile-engine crankshaft. A test similar to the one above many indicate that such parts are in static balance, but the system may show a considerable unbalance when rotated. As an illustration, consider a shaft with two disks, as shown in Fig. l. 23. If the two unbalance weights are equal and 180 deg. apart, the system will be statically balanced about the axis of the shaft. However, when the system is rotated, each unbalanced disk would set up a rotating centrifugal force tending to rock the shaft on its bearings. Since this type of unbalance results only from rotation we refer to it as dynamic unbalance. Fig. 1. 24 shows a general case where the system is both statically and dynamically unbalanced. It will now be shown that the unbalanced forces P and Q can always be eliminated by the addition of two correction weights in any two parallel planes of rotation. Consider first the unbalance force P, which can be replaced by two parallel forces and . In a similar manner Q can be replaced by two parallel forces and . The two forces in each plane can then be combined into a single resultant force that can be balanced by a single correction weight as shown. The two correction weights C1 and C2 introduced in the two parallel planes completely balanced P and Q, and the system is statically and dynamically balanced. It should be further emphasized that a dynamically balanced system is also statically balanced. The converse, however, is not always true; a statically balanced system m