Dynamic behavior and prevention of the damage of material of the massive hammer of the scrap shredding machine

Shredders are used for comminuting the metallic scrap fed to the electric arc furnace and consist of a set of hammers connected to a main rotor, whose rotation converts the kinetic energy into a strong impact. Design of the hammer is still based on some daily practice, but often it looks insufficient to predict the effects of wear and the cracks monitored in service. To reduce costs and improve the product quality manufacturers of shredders urgently need for a design tool suitable to predict the hammer dynamic behavior, the damage of material and to locate the stress concentration. Unfortunately no comprehensive design approach was yet proposed in the literature. This paper investigates the behavior of an industrial prototype of shredder to develop such as design tool. A first rotor-dynamic analysis was combined with a numerical investigation, performed through the Multi Body Dynamics and Finite Element Method, respectively. Results were then compared to some experimental evidences. Damage effects were tentatively related to some design parameters, the material properties and the loading conditions of the hammer. Results were used to increase the performance of a new shredder hammer being designed by refining the cutting edge profile and by selecting a different material.