Tech Insights · 2026-10-03
Conveyor Belt Selection Guide: Fabric vs Steel Cord, Cover Grades and Tension Ratings
Conveyor belting is the most expensive wear part on a bulk handling line, and the one that decides how much of the rest of the plant you ever get to use. When people talk about belt conveyor parts they usually mean idlers, pulleys, cleaners and frames — but the rubber belting itself is the element that carries the load, must survive at the splice, and sets the tension every structure, pulley and take-up on the line has to resist. This guide covers what a belt is built from, the three carcass families we manufacture belts on at HBXM, how cover grades are classified, how tension ratings are actually read, and how to choose between a vulcanised and a mechanical joint. Read it end to end and you can take a material, a temperature and a tonnage and come out with a belt specification you can quote against.
1. What a conveyor belt is made of
A conveyor belt is a composite, not a single material. Four layers do four different jobs:
- Carcass (tension member). The load-bearing structure — woven fabric plies, steel cords or a solid-woven mono-ply. It takes the belt tension and resists elongation.
- Top cover. The rubber that faces the material. It protects the carcass from abrasion, impact, oils and heat, and its grade is usually the decisive cost/life trade-off.
- Bottom cover (pulley side). Thinner, formulated for friction and wear against idlers and pulleys. On heavy lines it is often a different grade from the top cover.
- Breaker fabric and edges. A breaker ply under the top cover spreads impact over the carcass; the edge treatment seals the carcass against water ingress — the failure mode that quietly destroys belts in wet plants.
Almost every belt complaint that reaches a supplier traces back to one of these four elements being specified for the wrong job rather than to a manufacturing defect.
2. The three carcass families
Fabric carcass (EP / NN multi-ply)
The workhorse of general bulk handling. Plies of polyester-nylon (EP) or nylon-nylon (NN) are bonded between rubber layers, two to five plies depending on required strength. EP is preferred for long centre distances because polyester warp elongates far less than nylon, which keeps take-up travel manageable. Fabric belts trough easily, tolerate rough loading, splice quickly, and cover the range from a few hundred to around 630 N/mm of belt width. Their weakness is elongation: expect 1–2 % elastic stretch under working load, so the take-up frame has to travel accordingly.
Steel cord carcass (ST)
For high tonnage, long overland lines and high lift, steel cord belts replace fabric plies with a single layer of brass-plated steel cords running longitudinally. They carry from roughly 500 up to 7000 N/mm, barely elongate under load (about 0.2–0.4 %), and hold their tension at very long centre distances where a fabric belt would need an impractical take-up. The trade-offs are real: steel cord belts need larger pulley diameters, tighter transition distances, careful troughability checks and high-quality vulcanised splices. They are also heavy — a 1200 mm ST1600 belt is a crane job, not a two-man job.
Solid-woven and coated belts
For lighter duty, food-grade, sorting or recycling lines, a solid-woven PVC or PU belt — a single heavy fabric impregnated with polymer, with no separate rubber covers — is often the right answer. It is thin, flexible, easy to track, can take cleats and sidewalls, and is cleanable to food standards. It is not a substitute for a heavy rubber belt on abrasive ore.
Specialty constructions sit on top of these three families: chevron (cleated) belts for inclines above the material's natural repose angle, and sidewall belts that replace a steep incline with a vertical section — both of which we supply. See the chevron belt and sidewall belt pages for the geometry limits of each.
| Property | Fabric (EP / NN) | Steel cord (ST) | Solid-woven / coated |
|---|---|---|---|
| Tension range | ~100–630 N/mm | ~500–7000 N/mm | Low, <100 N/mm |
| Elongation at working load | 1–2 % | 0.2–0.4 % | 1–3 % |
| Splice | Vulcanised or mechanical | Vulcanised only in practice | Mechanical / laced |
| Pulley diameter | Moderate | Large (belt thickness driven) | Small |
| Troughability | Excellent | Needs verification | Excellent (thin) |
| Impact resistance | Very good with breaker ply | Poor without protection | Limited |
| Typical use | General bulk, short–medium lines | Long overland, high tonnage, high lift | Food, sorting, light unit load |
3. Cover grades: the numbers that actually decide belt life
The cover is where abrasive damage happens, so the cover grade is often a bigger driver of service life than the carcass rating. Abrasion resistance is classified by DIN 22102 (and its ISO equivalent) using a rotating-drum abrasion test; the resulting volume loss in mm³ sorts covers into four classes.
Abrasion classes
- W — ≤ 90 mm³. Premium abrasion resistance. Iron ore, sinter, coke, granite, sharp crushed rock.
- X — ≤ 120 mm³. Heavy duty. Limestone, gravel, dry sand, cement clinker.
- Y — ≤ 150 mm³. Standard general duty. Coal, grain, light aggregates, packaged goods.
- Z — ≤ 250 mm³. Light duty. Fine, non-abrasive, low-tonnage service.
Oil, heat, fire and cold
Abrasion is only one axis. Where the material carries oil or fat — asphalt, oily scrap, some coking coal — a standard rubber cover swells and delaminates, so an oil-resistant compound is mandatory. Where surface temperature climbs — clinker, sinter, cement, foundry sand — the cover must be heat-rated; standard rubber hardens and cracks well before the carcass fails. Underground coal and any potentially explosive atmosphere requires a fire-resistant, antistatic belt that passes the drum-friction and electrical-resistance tests. Cold climates add a further requirement: covers that stay flexible at −30 °C or below instead of shattering on the first cold start.
| Duty | Cover specification | Key property | Typical service | Limit to respect |
|---|---|---|---|---|
| General abrasion | Y (≤150 mm³) | Balanced wear/cost | Coal, grain, bagged goods | Not for sharp or hot material |
| Heavy abrasion | X (≤120 mm³) | Thicker cover, tougher compound | Clinker, gravel, limestone | Cost per metre rises fast |
| Extreme abrasion | W (≤90 mm³) | Highest wear life | Iron ore, coke, granite | Justify only where wear is measured |
| Oily material | Oil-resistant compound | Resists swelling and delamination | Asphalt, oily scrap, coke | Still limits top temperature |
| Hot material | Heat-rated cover (up to ~120 °C / ~200 °C peaks) | Thermal stability | Cement, sinter, foundry sand | Needs heat-stable carcass bond too |
| Underground / ATEX | Fire-resistant, antistatic | Drum friction + electrical resistance | Coal mines, tunnels | Certification is per market |
| Cold climate | Low-temperature compound | Flexibility below −30 °C | Open-pit, northern ports | Cold storage / warm restart checks |
4. Reading the tension rating correctly
Belt strength is quoted as a rated tensile strength per unit of belt width — N/mm, often written kN/m. An "EP 500/3" belt is polyester-nylon with a 500 N/mm rating over three plies; an "ST 1600" is steel cord at 1600 N/mm. That number is the breaking strength, not the working strength. You divide it by a safety factor — commonly 8–10 for fabric belts and 6.7–8 for steel cord, depending on splice efficiency and the standard you are designing to — to get the allowable working tension.
Then check it against the duty. Effective tension is roughly drive power divided by belt speed, so a 250 kW drive on a 3.0 m/s belt works at about 83 kN, and a 1200 mm belt carrying that load needs at least 70 N/mm of allowable tension — a mid-range fabric belt, or a modest steel cord if the line is long enough for elongation to matter. Where engineers get into trouble is the moment of starting: a loaded belt at rest needs roughly 1.4–1.6 times the running tension to break away, and take-up travel must be sized for elastic stretch plus the permanent stretch the belt takes in its first weeks. Our take-up and tensioning guide covers the travel calculations.
5. Splices: where the belt is weakest
A belt is only as strong as its joint. A correctly vulcanised splice recovers 85–100 % of belt strength on fabric belts and up to 90 % on steel cord; a bolted or stapled mechanical joint typically delivers 50–75 %. That difference changes the whole calculation — a belt rated 500 N/mm with a mechanically fastened joint is realistically a 300 N/mm belt.
| Joint type | Efficiency | Install time | Best for | Watch-out |
|---|---|---|---|---|
| Hot vulcanised | 85–100 % | Hours, needs press | Permanent joints, steel cord, high tension | Needs clean site and skilled crew |
| Cold vulcanised | 70–90 % | Hours, no press | Field repairs, short belts, medium duty | Cure time and temperature sensitive |
| Bolt-plate mechanical | 60–75 % | Under an hour | Temporary joints, low tension | Catches on cleaners and scrapers |
| Hinge / staple laced | 50–70 % | Minutes | Light duty, frequent belt changes | Lowest efficiency, staff wear quickly |
Splice choice is also a spares question: a mechanical joint lets a maintenance team replace a belt section without a vulcanising press, which matters far from a workshop. The fastener geometry, plate width and hook spacing for each option are compared in our mechanical belt fasteners guide.
6. A four-step selection method
- Characterise the material. Bulk density, lump size and shape, moisture, oil or fat content, surface temperature, and abrasiveness. This fixes the cover grade and the impact protection level.
- Fix the duty class. Design tonnage, belt speed and centre distance give you the effective tension and therefore the minimum tension rating — with the starting condition applied, not the running one.
- Choose the carcass. Below roughly 500 N/mm and moderate centre distance, fabric. Long overland, high lift or high tonnage: steel cord. Light, clean, unit-load duty: solid-woven.
- Choose the joint and check compatibility. Splice method, pulley diameters, transition distances and troughability all have to be verified against the chosen belt thickness before you commit. Pulley geometry is covered in the pulley selection guide; idler spacing and load-zone protection in the idler selection guide.
7. The mistakes we see on real projects
- Specifying tension rating without the splice. A 630 N/mm fabric belt with a bolted joint is weaker than a 400 N/mm belt that is properly vulcanised.
- Choosing the cover by price. Moving one abrasion class down saves a small amount per metre and regularly costs a belt replacement inside a year on sharp material.
- Ignoring oil or fat in the material flow. A swollen cover delaminates from the carcass and no amount of retensioning helps.
- Steel cord over short transitions. The belt is too stiff for an aggressive trough transition and will crack along the cord line.
- Undersized pulleys. Bending stress on the carcass rises as pulley diameter falls — the belt fails at the pulley, not in the run.
- Forgetting edge damage in the loading zone. Spillage and off-centre loading destroy edges; see the transfer point guide and our belt maintenance checklist.
8. FAQ
What is conveyor belting made of?
A tension-bearing carcass (woven fabric plies, steel cords or a solid-woven fabric) bonded between rubber or polymer covers, with a breaker ply under the top cover and sealed edges. The carcass carries the load; the covers protect it.
What is the difference between fabric and steel cord conveyor belts?
Fabric belts are multi-ply textile carcasses rated roughly 100–630 N/mm, elastic and easy to trough and splice. Steel cord belts use a single layer of steel cables, rated 500–7000 N/mm, with almost no elongation — chosen for long, high-tonnage or high-lift lines.
What do W, X, Y and Z mean on a conveyor belt cover?
They are DIN 22102 abrasion classes. W is the most abrasion-resistant (≤90 mm³ volume loss in the drum test), then X (≤120 mm³), Y (≤150 mm³) and Z (≤250 mm³), the lightest duty.
Should I vulcanise or use a mechanical splice?
Vulcanise wherever the belt runs at more than about half its rated tension, runs steel cord, or must not catch on cleaners — a vulcanised joint keeps 85–100 % of belt strength. Use mechanical fasteners for temporary joints, light duty and emergency field repairs.
How do I know when a conveyor belt needs replacing?
By condition, not calendar: cover wear down to the breaker ply, edge damage longer than a few metres, cord or ply separation, or a splice that no longer holds. Track measured cover thickness rather than guessing — it turns belt replacement into a planned outage.
Can you supply belts and the belt conveyor parts together?
Yes. HBXM manufactures belting alongside idlers, pulleys, belt cleaners, impact beds, take-up stations and frames, so a line can be specified as one matched package. Send the material data, tonnage and layout through the quote form.
Bottom line
Belt selection is three decisions made in order: cover grade from the material, tension rating from the duty, carcass from the tension and centre distance — then a splice that does not throw the rating away. Get those four right and belting stops being a maintenance problem. HBXM supplies fabric and steel cord belting, chevron and sidewall belts, and every belt conveyor part around them as a one-stop factory. Send us your conveyor data and we will return a belt specification with the matching pulley, idler and take-up schedule.
References & Sources
- DIN 22102-1. Conveyor belts for bulk materials — Textile carcass conveyor belts — Part 1: Dimensions, requirements (abrasion classes W / X / Y / Z).
- ISO 15236-1. Steel cord conveyor belts — Part 1: Design, dimensions and mechanical requirements for conveyor belts for general use.
- ISO 340. Conveyor belts — Laboratory scale flammability characteristics — Requirements and test method.
- CEMA. Belt Conveyors for Bulk Materials, 7th ed. (2nd printing, 2020). Conveyor Equipment Manufacturers Association. ISBN 978-1891171-44-4.