A band brake
is a primary or secondary brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
, consisting of a band of friction material that tightens concentrically around a cylindrical piece of equipment to either prevent it from rotating (a static or "holding" brake), or to slow it (a dynamic brake). This application is common on winch
A winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...
drums and chain saws and is also used for some bicycle brakes. Another application is the locking of gear rings in epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
Advantages and disadvantages
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.
One way to describe the effectiveness of the brake is as
is the coefficient of friction between band and drum, and
is the angle of wrap. With a large
, the brake is very effective and requires low input force to achieve high brake force, but is also very sensitive to changes in
. 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
increases the input force required to achieve a given brake force, but some low-
materials also have more consistent
across the range of working temperatures.