A band brake is a primary or secondary

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

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

train wheel A train wheel or rail wheel is a type of wheel specially designed for use on railway tracks. The wheel acts as a rolling component, typically press fitted on to an axle and mounted directly on a railway carriage or locomotive, or indirectl ...

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

Uses

Band brakes were 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 (physics), tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a Bobb ...

drums and

chain saw A chainsaw (or chain saw) is a portable handheld power saw that cuts with a set of teeth attached to a rotating chain driven along a guide bar. Modern chainsaws are typically gasoline or electric and are used in activities such as tree fell ...

s and is also used for some

bicycle brake A bicycle brake reduces the speed of a bicycle or prevents the wheels from moving. The two main types are: #Rim brakes, rim brakes and #Disc brakes, disc brakes. Drum brakes are less common on bicycles. Most bicycle brake systems consist of thre ...

s. Band brakes were commonly used to control the winding drum on railway inclines that lowered loaded wagons while raising empty ones over a steep slope. A former application was the locking of gear rings in

epicyclic gearing An epicyclic gear train (also known as a planetary gearset) is a gear reduction assembly consisting of two gears mounted so that the center of one gear (the "planet") revolves around the center of the other (the "sun"). A carrier connects the ...

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

Features

A band brake is a flexible band which warps around part or all of the outside surface of a wheel or drum. One end of the band is anchored in place, while the other is attached to a lever. Pressing on the lever brings the band into contact with the surface of the wheel and the friction causes the wheel's rotation to slow. 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. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

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.

References

{{reflist Brakes

Uses

Features

Effectiveness

See also

References