Difference between dynamic and static coefficient of friction



Dr. Eng. Römer


Drum brakes or disc brakes are well known worldwide. The simple and effective functionality of these brakes ensures a high level of safety at a favorable price-performance ratio if the brakes have been correctly dimensioned.

The actuation of such brakes is mainly done by an electro-hydraulic thruster according to the German industry standard DIN 15430. Unfortunately, this simple brake system has only one function-related defect, especially when used for hoists in cranes – the dead time.

The dead time

Due to the functioning of the electro-hydraulic lifting device (thruster), you have to calculate with a dead time (reaction time) for emergency braking. The dead time describes the period from the moment of actuating the mechanical friction brake until its effectiveness.

Effectiveness of the brake means that only at that precise moment when the brake torque is effective, the brake shoes rub on the brake drum or brake disc. The produced mechanical energy is converted by friction in the friction layer into heat. This created friction energy in the friction layer changes the physicochemical properties of the friction pairing, especially the brake lining itself.

As a consequence and provided that certain safety limits are observed (contact pressure, temperature of the friction layer, sliding velocity) a certain friction coefficient, generally known as


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