A band brake is a primary or secondary

brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

, consisting of a band of friction material that tightens concentrically around a cylindrical piece of equipment or

EMUs Emus may refer to: * Emu The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the g ...

to either prevent it from rotating (a static or "holding" brake), or to slow it (a

dynamic brake Dynamic braking is the use of an electric traction motor as a generator when slowing a vehicle such as an electric or diesel-electric locomotive. It is termed " rheostatic" if the generated electrical power is dissipated as heat in brake grid ...

). This application is common on

winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a spool (or drum) attache ...

drums and

chain saw A chainsaw (or chain saw) is a portable gasoline-, electric-, or battery-powered saw that cuts with a set of teeth attached to a rotating chain driven along a guide bar. It is used in activities such as tree felling, limbing, bucking, pruning, ...

s and is also used for some

bicycle brake A bicycle brake reduces the speed of a bicycle or prevents it from moving. The three main types are: rim brakes, disc brakes, and drum brakes. Most bicycle brake systems consist of three main components: a mechanism for the rider to apply the b ...

s. A former application was the locking of gear rings in

epicyclic gearing An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates the planet and sun gea ...

. In modern automatic transmissions this task has been taken over entirely by multiple-plate clutches or multiple-plate brakes.

Features

Band brakes can be simple, compact, rugged, and can generate high force with a light input force. However, band brakes are prone to grabbing or chatter and loss of brake force when hot. These problems are inherent with the design and thus limit where band brakes are a good solution.

Effectiveness

One way to describe the effectiveness of the brake is as

e^

, where

\mu

is the

coefficient of friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

between band and drum, and

\theta

is the angle of wrap. With a large

\mu \theta

, the brake is very effective and requires low input force to achieve high brake force, but is also very sensitive to changes in

\mu

. For example, light rust on the drum may cause the brake to "grab" or chatter, water may cause the brake to slip, and rising temperatures in braking may cause the coefficient of friction to drop slightly but in turn cause brake force to drop greatly. Using a band material with low

\mu

increases the input force required to achieve a given brake force, but some low-

\mu

materials also have more consistent

\mu

across the range of working temperatures.

Features

Effectiveness

See also