The brake is an important safety device for lifting machinery, and the service brake and electromagnetic brake are also, its setting, control and debugging is correct or not is crucial, if there is improper, it will cause equipment accidents and casualties. For example, in May 2008, a shipyard in Nantong City, Jiangsu Province newly installed a 32t gantry crane, soon after it was put into use, there was a hull segment fall accident, the reason is that the control disc brake contact due to the iron core pole surface attached oil delay release, resulting in the brake failed to close the brake in time and a major safety accident occurred, resulting in huge economic losses.