When a belt is under‑rated, systems slip, splices fail, and take‑ups bottom out. When it’s over‑rated, you pay for stiffness, larger pulleys, and energy losses you don’t need. Here’s a practical, standards-aligned way to assess conveyor belt tensile strength—what the numbers mean, how to test, and how to judge results against real design tensions.
Units and what they mean
Engineers express belt rating as allowable longitudinal tension per unit width. In SI, you’ll see N/mm and kN/m; in North America, PIW (pounds per inch width) still shows up. These are just unit systems for the same concept.
- N/mm to PIW: 1 lbf = 4.44822 N and 1 in = 25.4 mm, so 1 PIW ≈ 4.44822/25.4 ≈ 0.174 N/mm. Rounded, use 0.175 N/mm per PIW; conversely, 1 N/mm ≈ 5.7 PIW.
- kN/m is simply 1000× N/mm.
A quick way to think about it: the belt class is the ultimate strength per width. But selection is based on the maximum working tension per width times a safety factor. Breaking strength vs working tension are different ideas; don’t mix them.
Elongation terms you’ll meet:
- Elongation at break: total stretch at rupture in a full-thickness test.
- Elongation at reference load: stretch measured at a defined sub‑breaking load used for design (modulus/settling behavior). For textile belts, ISO methods define this precisely.
- Elastic vs permanent elongation: elastic is recoverable; permanent is residual after cycling/settling.
Conversion table
| Rating format | Relation | Handy equivalence |
|---|---|---|
| PIW ↔ N/mm | 1 PIW ≈ 0.175 N/mm | 220 PIW ≈ 38.5 N/mm; 330 PIW ≈ 57.8 N/mm; 440 PIW ≈ 77.0 N/mm |
| N/mm ↔ kN/m | 1 N/mm = 1 kN/m | 800 N/mm = 800 kN/m |
For standards context and authoritative test method scopes, see the ISO conveyor belt standards index under ICS 53.040.20. The official index enumerates titles such as ISO 283, ISO 9856, EN ISO 14890, and the ISO 15236 series that underpin textile and steel‑cord belt testing; consult the index on the ISO site via the ICS category here: the ISO ICS 53.040.20 catalog page.
The standards you’ll reference
Your assessments should trace to established methods. The table below maps the main documents to what you’ll ask for on certificates.
| Standard | What it covers | What to request on certificates |
|---|---|---|
| ISO 283 (Textile belts) | Full-thickness tensile strength, elongation at break, elongation at reference load | Breaking strength per width (N/mm), elongation at break (%), elongation at defined reference load (%), specimen width/gauge, conditioning, test speed |
| ISO 9856 (Textile belts) | Elastic and permanent elongation via cyclic loading; modulus | Reference load and max load values, number of cycles, elastic vs permanent elongation at reference load, temperature/humidity |
| EN ISO 14890 | Textile belt product specification framework | Belt construction, cover grade per ISO/DIN class, stated rating and tolerances |
| DIN 22102 | Textile belts—cover grades and typical elongation limits | Declared elongation at reference load vs class limit, cover grade mapping |
| EN ISO 15236-4 (Steel cord) | Vulcanized belt joints—test methods and requirements | Joint tensile test results vs belt rating, splice geometry, conditioning |
| EN ISO 7623 | Cord-to-coating bond strength tests | Cord bond values (N per cord or N/mm), initial and after thermal treatment |
| DIN 22101 / ISO 5048 / CEMA | Conveyor resistance and tension calculation frameworks | Basis for design tensions (Te, T1/T2), safety factor selection rationale |
Authoritative references include the ISO catalog’s ICS 53.040.20 standards index, Rulmeca’s tutorial on calculating belt tensions, the Fenner Dunlop technical article on elongation limits and ISO 9856 context, and Nuera’s overview mapping EN ISO 14890 cover grades to DIN 22102 designations. For direct access to representative documents, use inline references:
- The authoritative standards list is maintained on the ISO website; see the ISO ICS 53.040.20 catalog which lists the official titles and scopes of ISO 283, ISO 9856, EN ISO 14890, and EN ISO 15236 series: consult the ISO catalog index under ICS 53.040.20 at the official portal: ISO ICS 53.040.20 — Conveyor belts standards index.
- Elongation limits and ISO 9856 cycling context are explained in Fenner Dunlop’s engineering note; the paper “Stretching the Limits” (2024) discusses practical elongation ranges and testing considerations: see the analysis in the Fenner Dunlop elongation article (PDF).
- For how EN ISO 14890 cover grades correspond to DIN 22102 designations (H/D/L ↔ X/W/Y), a helpful overview is provided by Nuera in their standards explainer: review the mapping in Nuera’s “Who sets the standards?” (2025) PDF.
- Translating power and resistance into belt tensions Te, T1, and T2 is outlined with examples in Rulmeca’s guide to calculating conveyor belt tensions.
Tools, specimens, and set‑up
You’ll need a calibrated tensile machine with grips designed for full‑thickness belt specimens, accurate width and thickness measurement, and a controlled environment to condition samples. For steel‑cord belts, fixtures for splice tensile and cord bond tests are required. Specimen preparation follows the standard: cut longitudinal strips to the prescribed width and gauge length, mark the gauge for elongation readings, and condition at the specified temperature and humidity. Expect 60–90 minutes for cutting and conditioning and 5–10 minutes per tensile pull; ISO 9856 cycling adds time because of repeated loading. Small choices matter here: wrong grip liners or a slippery jaw face can cause jaw breaks or slippage, corrupting results.
Step‑by‑step assessment of conveyor belt tensile strength
- Define scope and collect data. Gather belt ID, construction (EP/NN ply count and rating or ST rating), width B, cover grades, drive layout, and recent operating issues. Pull design or measured tensions from your calculation model or drive controller logs.
- Plan sampling. Cut full‑thickness strips along the belt length away from splice zones, following the prescribed strip width and gauge length. Record sample origin and lot for traceability.
- Run ISO 283 full‑thickness tensile tests on textile belts. Use the specified grip type and test speed; pull each specimen to rupture. Report breaking load per width (N/mm), elongation at break, elongation at the defined reference load, and failure mode.
- Determine elongation behavior via ISO 9856 on textile belts. Cycle between the defined reference load and maximum load; after cycling, measure elastic vs permanent elongation at the reference load. This informs take‑up travel and retensioning intervals.
- For steel‑cord belts, qualify the splice and bond. Test vulcanized joints to EN ISO 15236‑4 and perform cord‑to‑coating bond checks per EN ISO 7623 (initial and after thermal treatment as required). Note joint strength vs belt rating and any bond anomalies.
- Convert and compare units if needed. Translate PIW-based specs to N/mm using 1 PIW ≈ 0.175 N/mm, or express results as kN/m for system-level comparison.
- Link results to system design. From your maximum belt tension T1, compute required strength per width σreq = T1/B (N/mm). Apply a suitable safety factor S; select a belt class where the ultimate rating σult ≥ σreq × S.
- Document and verify. Ensure certificates cite the test standard, specimen dimensions, conditioning, test speed, reference and maximum loads, and results with clear units. Keep batch traceability and dates.
According to the engineering note from Fenner Dunlop that aligns elongation limits with DIN 22102, textile belts are commonly constrained to around 1.5% elongation at the reference condition up to 500 N/mm, 2.5% for 630–1250 N/mm, and about 3% at ≥1600 N/mm; see the ranges and discussion in the Fenner Dunlop “Stretching the Limits” PDF. For system tensions, the approach to calculating Te, T2, and T1 is outlined stepwise in Rulmeca’s tensions guide; use T1 to size the belt and to verify that measured elongation at the reference load won’t exhaust take‑up travel during normal duty.
Worked examples you can copy
Example 1 — Convert PIW to N/mm and kN/m. A 330 PIW belt: N/mm ≈ 330 × 0.175 = 57.75 N/mm; kN/m = 57.75 kN/m. If you’re starting from 600 N/mm, PIW ≈ 600 × 5.7 ≈ 3,420 PIW. These equivalences align with common manufacturer tables and the physics of the units.
Example 2 — From tension to required class. Suppose your tension analysis shows T1 = 320 kN on a 1,200‑mm‑wide textile belt. Required strength per width σreq = 320,000 N / 1,200 mm ≈ 267 N/mm. With a conservative fabric safety factor S = 8, you’d select σult ≥ 2,136 N/mm. In practice, you’d choose the nearest higher standardized class across available constructions (for example, multiple‑ply EP classes summed to the target or moving to a steel‑cord class if dynamics are severe). If your plant uses PIW, σreq ≈ 267 N/mm × 5.7 ≈ 1,522 PIW; the safety‑factored target is ≈ 8,673 PIW per inch width equivalence.
Example 3 — Elongation at reference load and take‑up travel. A textile belt shows 1.8% elongation at the ISO 9856 reference load after cycling, on a center distance of 200 m between take‑up and drive. Expected elastic stretch in steady operation is 0.018 × 200 m = 3.6 m of belt length; your take‑up needs more than this travel margin to maintain tension through loading cycles. If that exceeds available take‑up stroke, consider a higher‑modulus belt or adjust safety factor/drive layout.
For standard scopes and typical elongation ranges at reference load, consult the authoritative listing on the ISO ICS 53.040.20 page for titles like ISO 283 and ISO 9856, review the class‑based ranges in the Fenner Dunlop elongation note (PDF), and use Rulmeca’s tension framework to connect test results with design.
Reading a real datasheet (neutral example)
Disclosure: BisonConvey is our product. On a representative datasheet for an EP 630/3 belt from BisonConvey, you’d look for the stated rating in N/mm (EP 630), ply count and fabric type, and a note that tensile testing follows ISO 283 and elongation at reference load follows ISO 9856. Check that elongation at the reference load falls within the indicative DIN 22102 bands for that class and that the certificate lists specimen width, gauge length, conditioning, and test speed. If your site works in PIW, convert EP 630 to ≈ 3,591 PIW using 5.7 PIW per N/mm and record both units on the inspection sheet for clarity.
Troubleshooting test results
Excessive elongation at reference load on a textile belt usually points to either an under‑classed construction for the duty or a test setup issue. Re‑check specimen conditioning and the exact reference load definition and cycling per ISO 9856; compare your measured percentage with the DIN 22102 guide values summarized in the Fenner Dunlop article. If steel‑cord joint results lag rating, review splice geometry against EN ISO 15236‑4 and verify vulcanization parameters and cord bond using EN ISO 7623, including post‑thermal treatment where required. One more common pitfall: reading a cover rubber dumbbell tensile data point and assuming it represents carcass tensile strength—only full‑thickness ISO 283 results (and cord/joint tests for steel cord) define conveyor belt tensile strength.
A steel‑cord note on pulleys: higher classes require larger minimum pulley diameters to limit bending strain. Representative ranges and tables are provided in manufacturer documentation such as Fenner Dunlop’s Steelcord brochure and Continental’s steel cord belts overview; consult those tables for your specific ST rating and geometry.
Further reading and references
For the definitive list of test standards that govern conveyor belt tensile strength and related properties, start with the authoritative index on the ISO ICS 53.040.20 catalog page. For interpreting elongation at reference load and typical DIN‑aligned ranges, see Fenner Dunlop’s “Stretching the Limits” (2024). If you need to connect power, resistance, and sag criteria to select a belt class, work through the examples in Rulmeca’s guide to conveyor belt tensions. For steel‑cord specifics like minimum pulley diameters and joint behavior, manufacturer references such as Fenner Dunlop’s Steelcord brochure and Continental’s steel cord product pages are useful context. And for cover grade language between EN ISO 14890 and DIN 22102, Nuera’s explainer provides a quick map: see Nuera — Who sets the standards? (2025).
With standards in hand and a clear workflow, you can select and verify conveyor belt tensile strength without guesswork—and keep take‑ups, splices, and drives operating inside their comfort zones.
