A recent project involving the upgrade of a 1970’s overhead crane highlighted the need to discuss various types of bridge brakes. There are at least three types of bridge brakes in mainstream use today: (1) the spring-applied flange-mounted brake most commonly used; (2) the foot-mounted “shoe brake” electrically operated; (3) the hydraulically-operated “shoe brake” that typically requires the operator to step on a brake pedal.
The spring-applied flange-mounted brake is the most common. One or more discs are keyed to the motor shaft extension and several brake liners are held rigidly in the brake case. When the electric hoist is running, the brake is released by electricity sent to the solenoid. When current is interrupted, the solenoid loses power and springs force the discs and friction material back together, slowing the motor shaft.
A shoe brake works much in the same way, but a cast metal wheel is keyed to the motor shaft and surrounded by a deck-mounted frame where the solenoid is mounted and “shoes”, much like those on a car or truck drum brake, are held off the wheel by the solenoid when activated. When the current is interrupted, the springs close the shoes and slow the wheel.
Bridge motions are unique in that occasionally an older crane has a foot-operated shoe brake where a brake pedal in the operater cab feeds hydraulic brake fluid through a system of master cylinders, tubing, and reserve cylinders to push the shoes together onto the wheel. These are exceedingly rare in the modern era and should be replaced by conventional electrically operated brakes when the overhead crane is modernized.