ISO 4344

What the test does

ISO 4344 is a specification rather than a test method, and knowing that changes how it is used. It sets minimum requirements for the manufacture and testing of stranded carbon steel wire ropes for lifts, and publishes tables of minimum breaking forces by size, rope grade, class and construction.

The rope is verified against those tables. Breaking force is determined by ISO 3108, which the specification invokes rather than restates: force applied quickly to 80 % of the minimum breaking force, then at not more than 0,5 % of it per second — 1 kN/s on a 200 kN rope, 2,5 kN/s at 500 kN — at 10 °C to 35 °C.

Scope is specific about duty. It covers ropes for suspension duty on traction drive and roped hydraulic lifts, and for compensation and governor duties on passenger and freight lifts, dumbwaiters, personnel hoists and man lifts moving between guides. Diameters run from 6 mm to 38 mm, in bright or galvanized wire finish, supplied as bulk manufacture.

What it measures, and why it matters

A lift rope is a life-safety component, and the specification exists because the consequence of getting it wrong is not a warranty claim. The minimum breaking force tables are the floor beneath every lift installation using that rope, and the number a manufacturer quotes has to be demonstrated rather than calculated.

The distinction between duties matters more than it first appears. A suspension rope carries car and counterweight over the traction sheave thousands of times a day, so it is fatigued as much as loaded. A governor rope does almost nothing until the day it trips the safety gear. A compensation rope hangs beneath the car balancing the changing weight above. Three service lives, one standard.

Construction sets a rope's character. Strand count, wires per strand and lay decide the balance between breaking force, flexibility and fatigue resistance over a sheave. Fewer, thicker wires give strength for diameter and less tolerance of bending; many fine wires bend happily and wear faster. The tables cover the common constructions because those trade-offs are settled for lift duty.

Diameter verification sits alongside breaking force for a practical reason: a rope worn or stretched below nominal no longer sits correctly in the sheave groove, and traction depends on that fit.

Specimen

A length of rope tested whole. The breaking force of a rope is not the sum of its wires.

Form

A length of rope from bulk manufactureThe helix means no wire is loaded exactly along the rope axis, and load sharing between strands is imperfect — which is why individual wire tests do not add up to a rope figure.

Diameter range

6 mm to 38 mmBright or galvanized wire finish, in the constructions the tables cover.

Terminations

Resin or metal socketsDakThe rope must fail in the free length. A rope that fails at or inside the termination has measured the termination, and it always reads low.

Free length

Long enough for the helix to behave normallyDakToo short and the strands cannot settle into normal load sharing; the result is neither the rope's nor repeatable.

Test speed

ISO 4344 does not set a rate of its own — it invokes ISO 3108 for the breaking-force determination, and these are that method's figures.

Approach

Quickly to 80 % of the minimum breaking forceThe first four fifths can be covered fast, because nothing being measured happens there.

Controlled rate

Not more than 0,5 % of the minimum breaking force per second1 kN/s on a rope of 200 kN minimum breaking force; 2,5 kN/s at 500 kN. The machine has to change from the fast approach to this without overshooting.

Temperature

10 °C to 35 °COr 23 °C ± 5 °C where a strictly controlled test is required.

How the test runs

1. 01Take a length from bulk manufacture, long enough for a proper free length.
2. 02Socket both ends so failure will occur clear of the terminations.
3. 03Identify the size, grade, class and construction, and read the minimum breaking force from the tables.
4. 04Load quickly to 80 % of that minimum.
5. 05Continue at not more than 0,5 % of it per second to failure.
6. 06Confirm the rope broke in the free length before accepting the result.
7. 07Verify diameter alongside breaking force.

What travels with an ISO 4344 result

The tables are indexed by four things at once, so a force figure alone cannot be checked against anything.

• Size, rope grade, rope class and construction — all four.
• The measured breaking force against the tabulated minimum.
• Where the rope broke, and confirmation it was in the free length.
• Measured diameter against nominal.
• The duty the rope is intended for: suspension, compensation or governor.

What the machine must be capable of

Force well beyond the minimum breaking force of the largest rope in scope — a 38 mm lift rope runs to hundreds of kilonewtons — and daylight enough for a free length in which the helix behaves normally.

Rate control matters in the second half: ISO 3108 permits rapid loading to 80 % then requires a controlled rate to failure, so the machine must change from fast approach to slow regulated climb without overshooting.

Socketing equipment is as much a part of the capability as the frame. A rope test that fails at the socket has measured the socket.

What goes wrong in practice

Failure at or inside the termination is the classic invalid result, and it always reads low.

Loading the whole way at the fast approach rate is the second, and it reads high.

Testing a free length too short for the rope diameter is the third — the strands cannot settle into normal load sharing and the result is neither the rope's nor repeatable.

Finally, quoting a breaking force without the construction and grade beside it. The tables are indexed by size, grade, class and construction together, and a force figure without them cannot be checked against anything.

Three duties, one standard

The same specification covers ropes whose service lives have almost nothing in common.

A rope selected on breaking force alone ignores the duty. Suspension ropes are consumed by bending, not by load.

Questions we are asked about this test

Related and equivalent standards

ISO 3108 is the test method this specification invokes for measured breaking force. EN 12385-5 is the European specification for stranded ropes for lifts and covers similar ground. For the lift installation itself rather than the rope, the EN 81 series sets the safety requirements that make these minimum forces mandatory.