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Abrasion loss
Loss in volume of a sample of material treated with an abrasive liquid or subjected to abrasive action through rubbing. There are different methods to measure abrasion loss. Based on those methods, the material is subjected to different test conditions. Normally, abrasion loss is expressed in mm³ lost from the sample material during the test.
Reference standard: DIN 53516 - UNI 9185.
Aluminium
Ductile and malleable white-silver metal, present in a large number of silicates, industrially produced from bauxite and used to fabricate light and super light alloys.
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 standard: UNIEN 12526

Ball race ring
The part that encloses the castor swivel actions.
Bolt hole
Hole made in the top of the castor and used to attach the castor to the trolley.
Reference standard: UNIEN 12526
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 standard: UNIEN 12526
Brake
A device that blocks the rotation of the castor around its own axis, the wheel rotation or the rotation of the wheel and support assembly. Front, rear, central, total or directional brakes can be mounted on swivel castors.
Reference standard: UNIEN 12526.

Cast iron
Steel-making product consisting of an iron alloy containing high doses of carbon together with other elements added for particular purposes or that entered into the alloy as impurities.
Castor
Connection part between wheel and trolley. Normally, all wheels must use a castor to be applied to the trolley; an exception is made for wheels whose axle is built into the trolley.
Swivel castor: rotates around its vertical axis as the operating direction changes; it can be a swivel plate, swivel with through hole or swivel with stem. The swivel castor can be equipped with a brake.
Fixed castor: no rotation; it is designed to keep the wheel moving along a straight line.
Reference standard: UNIEN 12526.
Central pin
Swivel castor part that joins the plate, fork and ball race ring; the plate and fork form a single piece, while the ball race ring remains free to rotate around its own axis.
Centre
The centre is the wheel support that connects the covering to the bore. It comes in various shapes and is made with different materials; it can be a single piece or two or more parts joined together.
Reference standard: UNIEN 12526.

Compression set
Change in the geometric shape of a material sample caused by compression or traction; it depends on the geometry of the sample, on the degree of deformability of the material, on the duration of the deformation process, on the temperature and on the time elapsed after release.
Reference standard: DIN 53517.
Covering
This outer ring is made with a different material than the one used to make the centre. The covering is fixed when joined with the centre and is fitted when mechanically assembled on the centre.

Density
Ratio between the mass of a material sample and the mass of an equal volume of a reference substance. It is normally expressed in g/mm³.
Reference standard: ISO 2781 - ISO 1183
Die-casting
Production process in which molten metal is injected under pressure into a die.
Directionality
Possibility of an object to continue moving along a predetermined direction.
Dust seal
The part of the swivel castor that protects the swivel actions.
Dynamic load capacity
Value (expressed in daN) of a wheel's load capacity. The capacity of a wheel is measured experimentally under the test conditions indicated in standard UNIEN 12532.
Reference standard: UNIEN 12526-UNIEN 12527-UNIEN 12532.

Elastomer
Each natural or synthetic polymer that has the properties and the characteristics of rubber.

Fork
Fixed or swivel castor 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 standard: UNIEN 12526

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 standard: UNIEN ISO 868

Impact strength
Capacity of a material to resist sudden impacts without breaking.
Reference standard: ASTM D 945 - DIN 53512 - ISO 4662
Injection
Flow of a liquid substance, under pressure, into a cavity.

Manoeuvrability
Possibility of an object to easily change its operating direction.

Plate
Top part of the castor, with holes or slots used for the trolley connection. It can be made in different shapes: rectangular with four attachment holes, square with four attachment holes, triangular with three attachment holes, circular with a through hole, circular with a stem.
Reference standard: UNIEN 12526.
Pneumatic
This terms refers to an object that can be inflated by inserting air.
Pneumatic rubber: rubber with a wefted ply insert and inner tube.
Polyamide
Polymer characterised by the repetition, in the molecule, of the amide group.
Polypropylene
Propylene polymer; propylene: gaseous alkene produced in oil cracking, widely used for organic synthesis, to obtain high-octane petrol and to produce elastomers.
Polyurethane
Polyurethanes are chemical compounds obtained from a polymerisation reaction that is triggered by mixing two components belonging to two different families of compounds (Di-Isocyanates and Polyalcohols) previously heated to temperatures that keep them in the liquid state with relatively low viscosity. Owing to the wide range of available chemical compounds, various elastomer formulations can be created. Often, the compound's physical-chemical characteristics are similar in different stoichiometric formulations, but the performance of the material during use may also vary significantly depending on the product used.

Resin
Natural or synthetic product with enhanced plastic properties.
Thermosetting resin: a resin that, initially softened through heating, is later irreversibly hardened through polycondensation and reticulation reactions.
Rubber
Natural rubber: dense and viscous liquid resulting from the metamorphosis of the tissues of certain plants flowing out of incisions in that plant that harden in contact with the air.
Synthetic rubber: obtained through the polymerisation of monomers; compared to natural rubber, its chemical composition is different while the physical characteristics are similar.

Smoothness
Value (expressed in daN) 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 daN) of the maximum load that a stationary wheel can withstand without generating any permanent changes to that wheel.
Reference standard: UNIEN 12527
Steel
Alloy consisting of iron and a quantity of carbon varying from 0.3 to 1.7%, produced in the molten state from cast iron, with special mechanical strength, elasticity and hardness characteristics.
Stainless steel: special steel, containing high quantities of chrome and nickel, that does not oxidise.
Stem
Vertical end of the castor used to attach the castor into a hole in the trolley.
Reference standard: UNIEN 12526

Tearing resistance
Capacity of a material to resist the propagation of a cut. It is measured through a test under the conditions defined in standard ASTM D 624b. During that test, a cut perpendicular to the tractive force is made on a test piece placed under traction.
Thermoplastic material
Material that becomes plastic when it is heated and that hardens when it cools, but that can become plastic again when reheated.
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.

Ultimate elongation
Maximum extension that a material sample subjected to traction reaches before breaking. It is normally expressed as a percentage elongation with respect to the original length of the sample.
With Lr the length of the sample in at the breaking point and Li the initial length of the sample, the ultimate elongation (A) is calculated as follows:
A (%) = (Lr-Li) x 100 / Li
Reference standard: ISO 37 - ASTM D 412c - ISO R 527.
Ultimate tensile strength
Maximum load that a material sample withstands before breaking. It is normally expressed in MPa (1 MPa = 1 kg/mm2).
Reference standard: ISO 37 - ASTM D 412c - ISO R 527

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 centre, the bore and the rolling action. Depending on the different construction versions and materials used, wheels can be classified into four families: tyred, polyurethane, monolithic (hard tread) and pneumatic.
Reference standard: UNIEN 12526.