6. GLOSSARY

Axle set

Connection through which the wheel is assembled to the castor. Normally, it consists of a threaded pin with nut, washers, tube and, where necessary, spacers.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Ball race ring

The part that encloses the castor rolling actions.

Bolt hole

Hole made in the top of the bracket and used to attach the castor to the equipment.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Bore

Central part of the wheel designed to house the axle set or the rolling actions that facilitate rotation (ball bearings, roller bearings, plain bearings...).

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Bracket

Connection part between wheel and equipment. Normally, all wheels must use a bracket to be applied to the equipment; an exception is made for wheels whose axle is built into the equipment. Swivel bracket: rotates around its vertical axis as the operating direction changes; it can be a swivel plate bracket, swivel bracket with through hole or swivel bracket with stem. The swivel bracket can be equipped with a brake. Fixed bracket: no rotation; it is designed to keep the wheel moving along a straight line.

Reference standards: UNI EN 12526:2001- ISO 22877:2004

Brake

A device that blocks the rotation of the bracket around its own axis, the wheel rotation or the rotation of the castor (wheel and bracket assembly). Front, rear brakes can be mounted on swivel castors.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Central pin

Swivel bracket part that joins the plate, fork and ball race ring; thanks to the central pin, the plate and fork form a single piece, while the ball race ring remains free to rotate around its own axis.

Wheel centre body

The wheel centre body is the wheel part that connects the covering to the bore. It comes in various shapes and is made of different materials; it can be a single piece or two or more parts joined together.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Covering

Outer ring of the wheel; it can be made of various materials and characterises the wheel. The covering is fixed when joined with the wheel centre body and is fitted when mechanically assembled on the wheel centre body.

Dynamic carrying capacity

Carrying capacity of a wheel is defined as the value (expressed in N) of the maximum load that can be supported by that wheel in conformity with European UNI EN 12532:2001 and International ISO 22883:2004 standards. Dynamic testing under constant speed (4 km/h, 1.1 m/s) requires overcoming 500 100mm-wide obstacles, with height equal to 5% of diameter for wheels with an elastic rolling strip (hardness up to 90 Shore A) and to 2.5% of the diameter for wheels with a rigid rolling strip (hardness greater than 90 Shore A), without permanent deformation of the wheel affecting its operating efficiency.

Directionality

Possibility of an object to continue moving along a predetermined direction.

Dust seal

The part of the swivel bracket that protects the rolling actions.

Fork

Fixed or swivel bracket part that supports the wheel; normally, it has an upside-down “U” shape. The holes to house the wheel axle set are made at the bottom ends of the fork; the swivel actions are installed in the top.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Hardness

Propensity of a material to be penetrated by another material. It is measured with empirical tests that are used to evaluate the magnitude of the penetration of a specific force in the material under specific conditions. The penetration hardness is inversely proportional to the penetration. Different tests can be performed to measure the hardness of a material. Shore A and Shore D durometers are used in some of the most widely used tests: durometer type A is used for the softer materials (elastomers), while type D is used for harder materials (thermoplastic material, polypropylene).

Reference standards: UNI EN ISO 868:1999 - ASTM D 2240-2004

Manoeuvrability

Possibility of an object to easily change its operating direction.

Plate

Top part of the bracket, with holes or slots used for the equipment connection. It can be made in different shapes: rectangular with four fitting holes, square with four fitting holes, triangular with three fitting holes, circular with a bolt hole, circular with a stem.

Reference standard: UNI EN 12526:2001 - ISO 22877:2004

Rolling resistance

Value (expressed in N) of maximum load, applicable for each single wheel that an operator can move, over level paths, even for long periods without fatigue.

Static load

Value (expressed in N) of the maximum load that a stationary wheel can withstand without generating any permanent changes to that wheel.

Reference standards: UNI EN 12527:2001 - ISO 22878:2004

Stem

Vertical end of the castor used to attach the castor into a hole in the equipment.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004

Tearing resistance

Capacity of a material to resist the propagation of a cut. It is measured through a test under the conditions defined in standards ASTM D 624b-2000 - UNI 4914:1987. During that test, a cut perpendicular to the tractive force is made on a test piece placed under traction.

Tread

Wheel external surface; the part of the wheel in contact with the ground. It can be smooth or sculpted with raised patterns to increase its grip on the ground.

Vulcanisation

Treatment with sulphur or sulphurous compounds applied to some substances, including rubber, to eliminate their plastic characteristics and to make them perfectly elastic.

Wheel

A circular mechanical assembly in which sliding motion is replaced by rolling motion through rotation around its own axis. The wheel consists of the following components: the tread, the covering, the wheel centre body, the bore and the rolling action. Depending on the different construction versions and materials used, wheels can be classified into four families: rubber, polyurethane, monolithic (hard tread) and pneumatic.

Reference standards: UNI EN 12526:2001 - ISO 22877:2004