Caster
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A caster (or castor) is an undriven, single, double, or compound wheel mounted on an object to make movement easier. Found on shopping cart, rolling chairs, and material handling equipment, casters may be fixed to roll in one direction, or mounted on a pivot, such that the wheel will automatically swivel, aligning itself to the direction in which it is moving. Swiveling casters are sometimes themselves attached to handles, so users can turn the caster into the desired direction. Casters are used in many industrial applications. Heavy duty and high capacity casters are used on platform trucks, carts, assemblies, and tow lines in plants.
[edit] Designs and Applications
There are two types of basic caster designs: swivel and rigid. The key to the function of a swivel caster is a bearing above the wheel assembly that allows the wheel assembly to turn 360 degrees. This allows the caster to turn easily so larger loads can be rotated with relative ease. A rigid caster is set between forks and does not swivel. Rigid casters are utilized to help move a load in a straight line. Material handling hand trucks and carts use two pairs of rigid and swivel casters, allowing maneuverability, as the truck can pivot about the tangent point of one of the fixed casters, but also allowing an operator to easily push or tow it a straight line. Carts with four swivel casters allow movers to push a load in any direction. Casters allow users to easily move heavy items, such as sports equipment, medical, industrial, and office equipment and furniture. Casters on the bottoms of office chairs and equipment stands permit quick and easy repositioning. Devices such as vacuum cleaners have casters allowing them to be moved to any area on a floor. Wheels may be disc shaped, wide cylinders, or even spheres, depending on the requirements of carrying capacity and maneuverability.
Skateboards utilize specialized casters positioned on metal "trucks" joined to the board with a semi-rigid flexible joint, rather than a swivel, that permits the board to be steered by tilting the board to the side in the desired steering direction. Casters attached to the soles of footwear allow people to move across smooth surfaces with less work, and for greater speeds with roller skates and blades. Most casters are designed for smooth floors, though some outdoor equipment uses casters with pneumatic or hard rubber tires. The wheelbarrow is essentially a box or platform, mounted on a fixed caster. A chair mat can provide a hard surface for a chair with casters over soft carpeting and protect the carpet from indenting under the casters. Wheels can be made of metal, plastic, rubber, or wood, depending on how and where they will be used.
Ball casters are a type of swivel caster where the spherical ball forming the wheel of the caster freely swivels in a socket, allowing free motion in any direction. Material distribution applications use ball casters, attached to a table in an inverted array, so that the exposed rotating surfaces of the balls are oriented upwards, allowing boxes and other flat-bottomed objects to be pushed atop the casters in any direction desired.
