ISO 8094 Steel Cord Conveyor Belts - Adhesion Strength Test of Cover to Core Layer

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ISO 8094 — Steel Cord Conveyor Belts: Adhesion Strength Test of the Cover to the Core Layer

ISO 8094 specifies a test method for determining the adhesion strength between the cover rubber and the core layer of a steel cord conveyor belt, it applies exclusively to steel cord conveyor belts (not fabric/textile ply belts). It measures how strongly the top and bottom rubber covers are bonded to the steel-cord-reinforced core.

Core Test Principle

The fundamental testing principle is peel separation method: apply constant-speed tensile pulling force to mechanically strip top or bottom rubber cover away from steel-cord core layer of prepared belt specimens.

The test measures the force required to separate (peel/strip) the cover rubber from the core layer by pulling them apart in tension.

Conceptually, it is a 90° peel-type adhesion test adapted for conveyor belts:

The cover rubber is gripped in one jaw of a tensile tester.

The core layer (including the steel cords, with the opposite cover removed) is gripped in the other jaw.

As the jaws separate at a controlled speed, the cover is stripped away from the core, and the resisting force is continuously recorded.

The median force from the resulting force-vs.-time trace is used to calculate adhesion strength in N/mm.

Test Specimen Specification & Preparation Rules

Total 6 identical specimens shall be prepared per batch test, split into two groups (3 for top cover peel test, another 3 for bottom cover peel test), cut parallel to belt longitudinal axis and minimum 50mm away from finished belt edge; two dimension classifications based on belt internal construction.

Belt Type	Minimum Length	Specimen Width	Thickness Rule	Additional Rule
Without metallic weft (with/without textile insert)	≥150mm	≥25mm (must contain ≥2 embedded steel cords)	Full original belt thickness	Cut partial rubber along cord edge to make peel tabs
With metallic weft inside core	≥150mm	25mm ±0.5mm	Full original belt thickness	Same pre-cut peeling preparation

Specimen Preparation: Using a knife:

Cut the cover rubber on either side of the specimen along the upper and lower edges of the cords, along a length sufficient to create a free tab that can be safely gripped in the tensile machine jaws.

This prepares one side where the cover is peeled free while the core (with cords) remains intact for the opposing jaw.

ISO 8094 Steel Cord Conveyor belts Adhesion Peeling Test Equipment

Tensile test machine	Must conform to the equipment described in ISO 36 — calibrated tensile tester capable of constant crosshead speed and force recording
Jaws / Grips	One jaw holds the cover rubber strip; the other holds the core layer (cords + remaining structure) securely without slippage
Recording system	Must produce a graphical plot (trace) of force vs. crosshead displacement or time so ISO 6133 analysis can be applied to the multi-peak curve
Cutting tool / knife	A sharp knife to score/cut the cover rubber along the upper and lower edges of the cords so the cover can be lifted and gripped for peeling
Conditioning chamber / room	Capable of maintaining 23°C ± 2°C and 50% ± 5% RH (ISO 18573 Atmosphere B)

Key Mandatory Test Parameters & Stipulation

Fixed jaw opening separation speed: 100 mm/min ±10 mm/min, kept constant during all peel test runs.

Test Timing: Test shall be carried out no earlier than 5 full days after conveyor belt finished production vulcanization;

Standard lab environment: Temperature = 23℃ ±2℃, Relative Humidity = 50% ±5%RH, unless alternative condition agreed and noted formally on final test report.

Number of valid tests: 3 tests for top cover + 3 tests for bottom cover (6 total).

Step by step test procedure of ISO 8094 Steel Cord Conveyor Belts - Adhesion Strength Peeling Test of Cover to Core Layer

Step 1 — Conditioning & Timing	Ensure the test is conducted at least 5 days after belt manufacture and under Atmosphere B (23°C ± 2°C / 50% ± 5% RH per ISO 18573) unless otherwise agreed.
Step 2 — Prepare Specimens	Cut 6 specimens from the belt as described above (≥50 mm from edge, parallel to belt axis). Using a knife, cut the cover along both sides of the cord edges to free a peelable section for gripping.
Step 3 — Test Top Cover	Take the first 3 specimens, Grip the top cover rubber in one jaw. Grip the core layer (steel cords + any textile reinforcement, without the bottom cover) in the other jaw. Start the tensile machine at 100 mm/min ± 10 mm/min. Record the force trace graphically as the cover is stripped from the core. Repeat for all 3 top-cover specimens.
Step 4 — Test Bottom Cover	Take Remaining 3 Specimens; Grip the bottom cover rubber in one jaw. Grip the core layer (cords + top cover removed side) in the other jaw. Repeat at the same crosshead speed; record the force trace.
Step 5 — Special Failure Mode Check	If the adhesion strength of the cover to the core is GREATER than the tear strength of the core layer itself, the cover won't peel cleanly — instead the core tears. In this case: Record the maximum force obtained. Note the mode of failure in the report (i.e., tearing of core rather than cover-core debonding).
Step 6 — Results	Median Force: From the recorded force-variation plot (which shows peaks and valleys as individual cords are sequentially stripped), determine the median force F̃ in accordance with ISO 6133. Adhesion Strength: T = adhesion strength, N/mm; F̃ = median force from ISO 6133, N; b = specimen width, mm Mean Adhesion Strength For each cover (top and bottom separately): Single values T and mean values T̄ are rounded to 0.1 N/mm.
Step 7 — Test Report Content	a) Standard reference number: ISO8094:2013; b) Full unique identification of tested conveyor belt (batch number, grade, production date, specification); c) Actual measured width of each test specimen; d) Separately listed average adhesion strength of top cover-core and bottom cover-core bonding; e) Any non-standard test setup, abnormal incidents or deviation from specified ISO conditions which may influence test outcomes

Target Application Industry Fields

Conveyor Belt Manufacturing Industry: Factory incoming raw material inspection, semi-finished vulcanization process QC, finished steel cord belt factory outgoing inspection for coal, mine, port bulk transport belts;

Mining & Bulk Material Transportation: Coal mine, iron ore mine, quarry, seaport bulk cargo terminal (in-service periodic quality inspection of running conveyor belts);

Third-Party Independent Testing & Certification Labs: International commodity inspection, product certification (CE, mine safety certification), cross-border import customs compliance test for conveyor belts;

Rubber R&D Institutes & Compound Factories: New rubber formulation, bonding agent and vulcanization process development verification for steel cord conveyor belt;

Cement, Power Plant, Chemical Processing Plant: In-plant equipment maintenance and spare belt incoming acceptance inspection.

Related Test Standard:

GB/T 17044	Steel cord conveyor belts—Adhesion strength test of the cover to the core layer
UNE-EN 28094	STEEL CORD CONVEYOR BELTS. ADHESION STRENGTH TEST OF THE COVER TO THE CORE LAYER.
ISO 7622-1	Steel cord conveyor belts - Longitudinal traction test - Part 1: Measurement of elongation
ISO 7622-2	Steel cord conveyor belts — Longitudinal traction test — Part 2: Measurement of tensile strength
ISO 7623	Steel cord conveyor belts - Cord-to-coating bond test - Initial test and after thermal treatment
ISO 283	Belt-specific adhesion or elongation tests
ISO 36	Vulcanized/thermoplastic rubber – Adhesion test between rubber and textile fabric
ISO 6133	Rubber & plastics – Multi-peak force curve analysis for tear/adhesion test

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.

T-Peel Resistance Test Fixture for Adhesives is based on ASTM D1876 standard, used to measure the adhesion strength of adhesive maeterial. ASTM D1876 peel strength test method is commonly used to measure the strength of adhesive bonds between two sealed materials.

Webbing test fixture used for tensile testing of the webbing, belt test sample, determine the webbing, belt tensile strength, elongation etc., Webbing is a strong fabric woven as a flat strip or tube of varying width and fibres often used in place of rope.

Q1: What is ISO 8094:2013?

A: ISO 8094:2013 is an international standard that specifies a test method for determining the adhesion strength between the rubber cover and the steel-cord core layer of a conveyor belt. It is the second edition (published May 2013), replacing the original 1984 version with only minor revisions.

Q2: What does this test actually measure?

A: It measures the force required to peel (strip) the rubber cover away from the steel-cord reinforced core layer of a conveyor belt. The result is expressed as adhesion strength in newtons per millimetre (N/mm) of specimen width.

Q3: Which conveyor belts does ISO 8094 apply to?

A: It applies exclusively to steel cord conveyor belts. It is not intended for fabric-ply belts, solid-woven belts, or other reinforcement types.

Q4: Why is cover-to-core adhesion so important?

A: The rubber covers protect the steel cords from moisture, corrosion, and mechanical damage. If the bond fails (delamination):

Moisture penetrates → steel cords rust → loss of tensile strength → risk of catastrophic belt breakage.

Loose cover flaps can jam in pulleys, causing fire hazards and massive downtime.

Good adhesion is therefore a critical safety and durability factor in mining, ports, and bulk handling.

Q5: Why test top cover and bottom cover separately?

A: Top cover endures material abrasion during conveying, bottom cover bears roller friction; their rubber formulation and bonding processes differ, requiring independent strength assessment.

Q6: What if the adhesion is stronger than the core tear strength?

A: This is addressed in Clause 6.7: If the cover cannot be peeled because the core tears first, record the maximum force obtained and clearly state the mode of failure (tearing of core) in the report. The value is not a true adhesion strength but indicates exceptional bonding.

Q7: Can ISO 8094 be used for fabric conveyor belts?

A: No. The standard explicitly applies only to steel cord conveyor belts. Fabric-ply belts use different adhesion tests (e.g., ISO 36 for rubber-to-textile adhesion).

Q8: How many specimens are needed?

A: Six specimens total: three for the top cover and three for the bottom cover. Each set yields one mean adhesion value.

Q9: Why use the median force (ISO 6133) instead of the average?

A: During peeling, the force fluctuates as each steel cord is individually stripped, creating a multi-peak trace. ISO 6133 provides a standardized way to determine the median force, which is less sensitive to extreme peaks or troughs and gives a more representative measure of steady-state adhesion.

Q10: What is the mandatory waiting period before starting testing after belt production?

A: Tests can only be implemented no less than five full days after belt manufacturing completion for full vulcanization stabilization.

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