ABSTRACT
In Chapter 7, we found that inertia forces are created in machines due to the masses and the acceleration of the members. These inertia forces in turn cause shaking forces in the machines. The shaking forces, in most machines, cause vibrations, which have harmful effects. In a close look at any mechanism, for instance, the engine mechanism, we see that it consists of a rotating member (the crank), floating member (the connecting rod), and a reciprocating member (the piston). Generally speaking, the inertia forces due to the rotating members can be completely eliminated by adding countermasses. Complete elimination of the inertia forces due to the floating and reciprocating parts requires expensive solutions. However, it is possible to reduce their effects by partial balancing, which is acceptable in most applications.
In many applications, the machines consist only from rotating parts, for example, turbine rotors, centrifugal pumps, transmission shafts with gears, and pulleys. These parts are manufactured by different processes, which apparently guarantee balancing. However, under the most optimized circumstances, there is no guarantee that these parts are completely balanced due to the following reasons:
