An intro to mechanical brakesAmy J. Born | June 08, 2020
In industrial settings, mechanical brakes are necessary for power transmission applications such as material handling and manufacturing. Unlike hydraulic brakes that use fluid to create the pressure that triggers the braking mechanism, mechanical brakes work by generating force (typically friction) to stop the energy of a machine or object. Mechanical brakes absorb the energy and convert it into heat. In addition to creating enough force to stop a rotating shaft, for example, dissipating the generated heat is a concern.
Mechanical brakes function via force delivered to a body in rotary or linear motion, such as a shaft, axle or wheel, to slow or stop motion. They are often in an assembly with a mechanical clutch for engaging and disengaging shafts. Mechanical brake and clutch assemblies are well-suited to applications that require regular disengaging and engaging gears, such as conveyors, bottle capping machines, box makers, fill and sealers, and textile processing equipment.
Friction-based brakes use a brake liner consisting of a coarse and rugged material tightened or pressed against a body in motion to decelerate. They generate noise as well as heat. The engaged surfaces degrade and brake capacity decreases with every cycle, making regular inspection and replacement a necessity. Friction-type brakes are heavily used in automotive applications. Drum brakes, cone brakes and disc brakes are all friction brakes.
Mechanisms besides friction are used in other types of mechanical brakes.
Toothed brakes have tooth-shaped contact surfaces that transmit power without slippage or heat generation. Teeth are engaged only when stopped or running at slow speeds (<20 rpm). Because the torque comes from the teeth, there is no slipping when the brake is engaged. Toothed brakes are used in access control systems, indexing systems in machine tools and labeling machines.
Non-contact brakes use technology such as a magnetic field or eddy currents to provide the braking action. Braking force is generated proportionately to velocity. Because there is no friction with eddy current and magnetic brakes there are no parts that wear out. One disadvantage, however, is that they do not have any holding force for stationary objects. Trams and trains, aircraft, industry and robotics are common applications for non-contact brakes.
A wrap-spring clutch and brake work by connecting an input shaft and output shaft with an interference fit helical clutch spring. When the input shaft rotates in the direction of the wind of the clutch spring, torque is transmitted to the output shaft. A separate brake spring spins until the brake spring control tang is locked, which tightens the brake spring around the output shaft in position to a stationary brake hub that is bolted to a plate. Simultaneously the clutch spring releases. Wrap-spring brakes provide precise stopping (± 0.5°) in industrial machinery, but fully mechanical wrap-spring clutches and drives are limited to smaller sizes; larger sizes are electromagnetic. This type of brake is used in index systems, industrial and aeronautical applications, weaponry actuators, scanning equipment, and medical devices such as hospital beds and wheelchairs.