Abstract
Dynamic loading of machine drives produces oscillations which may cause a failure. Dangerous oscillations can occur both in unsteady and steady motion states. In the case of steady motion, dangerous oscillations mainly arise when either the driving mass or the driven mass are subject to regular loads within non-equilibrium systems. A jaw crusher would be an example of a non-equilibrium system. In cyclic loading machines, especially when crushing hard metal ingots, the loads can often be close to impact loads, which creates high dynamic loads in the machines. The level of oscillating loads in these machines is extremely high, which leads to various failures and breakdowns. The causes include overloads and fatigue failures caused by dynamic loads, which can be 2.5 to 3 times higher than the operating loads. To study the oscillations of a drive system one should determine the natural frequency and compare it with the exciting force frequency. To not let the deformation f reach the critical point, the resonance transition should go fast. The actual angular velocity should be at least 30% higher or lower than the speed that corresponds to the resonance (critical) state. For example, traditional jaw crushers run in the pre-resonance zone of up to n ≈ 300 RPM, whereas the Krupp impact jaw crushers operate in the post-resonance zone of up to n ≥ 500 RPM and are equipped with powerful vibration absorbers. In terms of dynamics, the jaw crusher with a simple swing jaw is a better machine than a crusher with a complex swing jaw. Greater rigidity of the crusher toggle and a heavier movable jaw can help reduce the oscillations. This practically means that, if necessary, the front toggle can be reinforced and the movable jaw can be made heavier. The movable jaw in a simple swing crusher acts as a dynamic vibration absorber.
Keywords
Dynamic loading, oscillations, actuator, steady motion, resonance zone, crushing, non-equilibrium system, dynamic absorber.
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