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Home >> Application >> By Standard >> ISO >> ISO 5000~9999 >> ISO 7802: Metal Wire Wrapping test

ISO 7802: Metal Wire Wrapping test

Standard: ISO 7802: Metallic materials -- Wire -- Wrapping test.

ISO 7802 specifies the method for determining the ability of wire of diameter or thickness 0,1 to 10 mm inclusive to undergo plastic deformation during wrapping. The test consists of winding a wire to a specified number of turns around a mandrel of the diameter specified in the relevant standard to form a closely wrapped helix. It may also include a specified sequence of windings and unwindings, or even rewindings.

Test principle

The wrapping test involves tightly winding a test wire into a close‑pitched helix around a mandrel of a specified diameter for a defined number of turns. The procedure may also include controlled unwinding and/or rewinding sequences to assess ductility, surface integrity, and coating adhesion under repeated bending deformation.

Test Specimen Information

Size range: Diameter/thickness 0.1 mm – 10 mm (inclusive).

Type: All metallic wires, including coated wires (e.g., galvanized steel, copper alloy, aluminum wire).

ISO 7802 Test Equipment Required:

Wrapping Test machine

UnitedTest NCR series, Designed to wind wire helically so adjacent turns are in tight contact, with controllable speed and tension.

Wind the wire around the mandrel so the helix is formed with adjacent wraps in contact.

Control the process so the wire is not twisted (avoid induced torsion during wrapping).

ISO 7802: Metal Wire Wrapping test

Mandrel

The mandrel is a cylindrical tool of the diameter specified by the relevant standard.

A piece of the wire itself may be used as the mandrel — provided it matches the specified mandrel diameter and has sufficient hardness.

Key Test Parameters:

Winding speed: ≤1 turn per second; slower if heating affects results.

Tension: ≤5 % of the wire’s nominal tensile strength to ensure tight winding.

Unwinding/rewinding: Slow rate to prevent temperature rise; at least one turn remains wound at the end of unwinding.

Inspection: No visible cracks without magnification; wires <0.5 mm inspected at ~10× magnification.

Detail step by step ISO 7802 Wrapping Test procedure:

1, Prepare & measure the wire specimen; record diameter/thickness and identification data.

2, Select/install the mandrel of the diameter specified by the referencing product spec (mandrel may be a hardened pin—or, allowed by the standard, a suitable piece of wire itself).

3, Perform the wrapping at ≤1 turn/s, without introducing torsion, keeping wraps in contact, optionally with ≤5% Rm-equivalent tension to maintain tightness.

4, If the specification calls for it: execute the defined unwind and/or unwind + rewind sequence, keeping speeds low and leaving ≥1 turn still wound at the end of the unwind stage.

5, Inspect: normally visual (naked eye acceptable unless d < 0.5 mm → ~10× magnification), looking for cracks, splits, flaking/delamination of coating, or fracture, judged against the criteria defined by the relevant standard.

6, Report: reference to ISO 7802, specimen ID/material/coating, diameter/thickness, mandrel diameter, test conditions (turns or wound length), and result.

Industry / application fields

Because the test simulates tight-radius bending and coiling, it shows up wherever wire is drawn, coiled, payed off, bent over pins/sheaves, or formed:

Steel wire & wire products: spring wire, binding wire, general-purpose carbon/alloy wire, galvanized wire.

Cable & strand sector: ropes, ACSR messenger/conductors, overhead-line wires (aluminum & aluminum-alloy wires, coated/clad wires for concentric-lay stranded conductors).

Prestressed / concrete-reinforcement steel (where referenced by test-method standards for prestressing steel).

Automotive & harnesses / electrical conductor wire & process coils, where forming, routing, and reeling stresses are routine.

Aerospace titanium/titanium-alloy wire specifications (process/quality ductility checks).

Relatd Standard:

GB/T 2976	Metallic materials—Wire—Wrapping test
IS 1755	Metallic Materials - Wire - Wrapping test
AS 2505.6	Metallic materials, Method 6: Wire - Wrapping test
GOST 10447	Wire. Method of testing for winding
EN 10218‑1	Steel wire and wire products – General – Part 1: Test methods (often cited alongside wrapping tests).
ISO 15630‑3	Steel for reinforcement & prestressing – test methods for prestressing steel

Related products and device

ISO 7802 Metal wire wrapping testing machine

Wire wrapping testing machine used for determining the ability of wire of diameter or thickness 0,1 to 10 mm inclusive to undergo plastic deformation during wrapping.

Metal wire tensile testing machine

WDW Series Computer Control Electronic Universal Testing Machine made by UNITEDTEST range from 100N to 600KN load capacity with various models like single columns, table type, door frame type etc., is used to perform tension, compression, flexure/bending, shearing, peeling etc., test for metal and nonmetal specimens.

Related Standard

ISO 15630-3 Testing of Prestressing Steel Strands Relaxation, Fatigue, Tensile testing –

ISO 15630-3 specifies uniform, repeatable test methods for prestressing steel products: bars, wires, and strands used in prestressed concrete structures. Mainly include tensile test, bend test, reverse bending test, wrapping test, Axial force fatigue test etc.,

ISO 7800 Metal Wire Torsion twisting testing – Wire Simple torsion test –

ISO 7800 specify a unidirectional simple torsion test to evaluate the plastic deformation ability of metallic wire under torsional loading in one direction. It applies to round and shaped wire with diameter or characteristic dimension from 0.1 mm up to and including 14 mm.

ISO 7801 Metallic Wire Reverse bend testing –

ISO 7801: Metallic materials -- Wire -- Reverse bend test

Specifies the method for determining the ability of wire of diameter or thickness 0,3 to 10 mm inclusive to undergo plastic deformation during reverse bending. The range of diameters of thicknesses for which ISO 7801 is applicable may be more exactly specified in the relevant product standard. The test consists of repeated bending, through 90 in opposite directions, of a test piece held at one end, each bend being over a cylindrical support of a specified radius.

(FAQs) about the ISO 7802 Metallic Materials – Wire – Wrapping Test

Q1: What exactly does the ISO 7802 wrapping test evaluate?

A: It evaluates a metallic wire’s ability to undergo plastic deformation when tightly wound around a mandrel of a specified diameter. The test checks for cracks, fractures, or coating delamination that may appear only under such bending strain, revealing issues like poor ductility, surface defects, or inadequate coating adhesion.

Q2: Why is this test important for wire manufacturers and users?

A: Even if a wire passes tensile strength tests, it may still fail in real-world applications involving coiling, pay-off, or bending over sheaves. The wrapping test simulates these conditions and acts as a fitness-for-purpose check, catching hidden problems such as:

Surface cracks from improper drawing or heat treatment

Hydrogen embrittlement in high-strength steel wire

Coating flaws (e.g., zinc layer peeling on galvanized wire)

Insufficient ductility for forming operations

Q3: What size and type of wire can be tested using ISO 7802?

A: The standard applies to metallic wire with a diameter or thickness from 0.1 mm to 10 mm inclusive. It covers bare, plated, or coated wires (e.g., galvanized, copper-clad) used in various industries.

Q4: Can I use the wire itself as the mandrel?

A: Yes, if the wire piece meets two conditions: it has the exact diameter specified by the relevant product standard and sufficient hardness so it does not deform during the test. Otherwise, a separate hardened mandrel must be used.

Q5: How fast should I wrap the wire, and why is speed controlled?

A: The wrapping rate must not exceed 1 turn per second. This limit prevents heat buildup from friction or plastic deformation, which could artificially improve the wire’s apparent ductility and invalidate the test results.

Q6: Is tension allowed during wrapping? If so, how much?

A: Yes, a tensile stress up to 5% of the wire’s nominal tensile strength may be applied to ensure tight, contact-wrapped coils. Exceeding this could alter the stress state and compromise repeatability.

Q7: How do I judge if the wire passed or failed the test?

A: The acceptance criteria are defined by the relevant product or industry standard that references ISO 7802. If no criteria are given:

For wire ≥0.5 mm: absence of visible cracks without magnification is sufficient.

For wire <0.5 mm: inspect with approximately 10× magnification.

Coating damage (e.g., flaking) is also typically considered a failure.

Q8: What’s the difference between ISO 7802 and a simple bend test?

A: A bend test (e.g., ISO 7801) usually involves bending a wire back and forth over a pin. ISO 7802 focuses on continuous helical wrapping around a mandrel, which better simulates coiling, unreeling, and contact with sheaves in cables, springs, and conductors. It often includes unwinding/rewinding sequences to mimic service fatigue.

Q9: Why must at least one turn remain unwound after an unwinding step?

A: This ensures the wire is not fully relaxed back to its original straight state, preserving the residual stress/strain history that might influence crack propagation. It also prevents accidental damage during removal.

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