ISO 283

What the test does

A strip cut through the whole belt — covers and textile carcass together — is clamped at both ends in a tensile machine. The machine pulls the strip along its length at a constant 100 mm/min while force and the separation of two reference lines are recorded, without interruption, until the carcass ruptures. Nothing is stripped down to a single ply, so the number reflects the belt as it is supplied.

What it measures, and why it matters

Three figures come out: full thickness tensile strength in newtons per millimetre of belt width, elongation at break, and elongation at the reference load — the stretch at one tenth of the belt's nominal rating. Strength per millimetre is what a belt is sold and rated on, so it is the acceptance figure against the nominal tensile strength on the specification. Elongation at the reference load sizes the take-up travel a conveyor needs, rather than describing ultimate performance. Elongation at break separates carcass constructions and is routine evidence in splice and belt-failure investigations.

Specimen

Test pieces are die-cut or sawn full thickness, with the cut sides perpendicular to the belt surface so no edge is drawn in or bevelled. Four test piece types, A to D, are defined by belt strength; the type D piece is used for the heaviest belts. Placement is constrained: no test piece may contain a ply joint, be taken within 50 mm of the belt edge, or within 12 mm of a sample edge. Covers are reduced within the gripped length and one carcass layer is stripped from one end before clamping, so the jaws bite reinforcement rather than rubber. Conditioning follows ISO 18573 — at least 16 h in a controlled atmosphere, or 3 h where only temperature is controlled — with at least 24 h between belt manufacture and test, and testing in the conditioning atmosphere, between 20 °C and 27 °C.

What the machine must be capable of

This is the heaviest routine pull in the belting cluster. The standard's own worked example puts a 1 600 N/mm belt on a 25 mm test piece at a 4 kN reference load, which implies roughly 40 kN at break; belts above 2 000 N/mm move to the type D test piece and demand a frame in the 100–250 kN class. Machines built for belting, strap and rope work span roughly 5 kN to 250 kN, and the frame must be chosen for the strongest belt in the programme rather than the average one. Force indication must meet ISO 7500-1 Class 1.

Speed is fixed at 100 mm/min ±10 mm/min, constant and uninterrupted, on a constant-rate-of-extension or constant-rate-of-traverse machine; textile carcasses are rate-sensitive, so a paused or drifting crosshead changes the break figure. Elongation is measured on the test piece, not from crosshead travel: the method sets its own device requirement of a measuring length of at least 100 mm, accurate to 0,1 mm or better, preferably producing a continuous graphical trace. That trace has to resolve a sub-4 % reference-load point and full travel to a break near 25 %. Grips must be shaped so the belt cannot slip — jaw faces with transverse serrations are illustrated and recommended — and hydraulic side-acting or wedge grips with belt inserts are used because the clamping force needed on a rubber-covered carcass is high and must be applied without crushing the plies.

What goes wrong in practice

Grip slippage is the dominant error: a belt creeping through the jaws inflates elongation and reports a break the carcass never reached. Ply separation inside the clamped length lets the layers share load unevenly, so the strip fails progressively at a low peak. Off-axis loading from a test piece cut with non-perpendicular sides loads one edge first and biases strength low. Extensometer damage at break is a real cost — 40 kN releasing suddenly will destroy a contact device left in the break zone.

Related and equivalent standards

ASTM D378 is the nearest counterpart, covering full thickness tensile properties of conveyor and elevator belting within a broader multi-property method; specimen dimensions and rate differ, so results are not interchangeable and the governing standard must be stated with the figure. EN ISO 283:2023 is the identical European adoption. ISO 18573 supplies the conditioning atmosphere and ISO 7500-1 the force verification class; neither is a test method in its own right.