Heating Conveyor Belt Designations Explained: Cover and Temp Codes

Look at the edge of almost any belt that runs through or carries heat and you will find a printed line that reads something like EP 400/3 · 4+2 · T2 · Y. To a buyer who has never decoded one, that string is decoration. To an engineer checking a specification, it is a complete sentence about what the belt will and will not survive, and it is usually the only sentence that separates a five-year belt from a five-week one.

The first problem is that the phrase "heating conveyor belt" is used for two different machines, and the codes on each answer two different questions. Before you read a single number you have to know which machine the belt is going into. This guide walks through that disambiguation first, then breaks the code line down item by item: the cover grade, the temperature class versus the instantaneous peak, the carcass code, the standard number, the thickness marking such as 4+2, and the edge form. It ends with a plain test you can apply to any quotation, so you can tell a verifiable rating from a sales phrase.

Send us your belt code or a photo of the belt edge and we will decode it line by line

01Two Machines, One Name: Dryer Belts and Hot-Material Belts

Half of the confusion around this product starts with the name itself. A heating conveyor belt can mean a belt that is heated, or a belt that carries something hot. The two applications use different rubber compounds, different carcass constructions, and, most important for this article, different code systems. A buyer who asks a conveyor belt manufacturer for "a heat belt, the 200-degree kind" without saying which machine it is for will get a quotation that may be right for one machine and useless for the other.

The first machine is the dryer or oven belt. Here the belt runs inside a heated chamber, a baking oven, a curing tunnel, a powder-coating line, or an infrared drying stage, and the heat is applied to the belt and to the product from the outside. The belt itself gets hot because the chamber is hot. This is common in food baking, textile printing and curing, glass lamination, and shrink-tunnel packaging, and it is covered more fully on our food and packaging page. The vocabulary that matters here is mostly about the material, PTFE-coated glass, silicone, food-grade polyester, and the failure modes are cover embrittlement, fabric shrinkage, and delamination from long heat soak.

The second machine is the hot-material belt, and this is where the standardized codes live. Here the belt carries a load that is already hot, clinker from a kiln, sinter, foundry sand, hot-mix asphalt, steel mill scale, or castings straight off a shakeout, and the heat conducts up from the material into the cover rubber. The belt itself is not inside an oven; the hot load is the heat source. This is the world of the heat-resistant conveyor belt, and its codes are pinned down by DIN 22102, ISO 4195, and GB/T 20021. As a general rule, when a catalog prints T2, 4+2, or EP 400/3, it is talking about this second machine.

The distinction matters because the numbers mean different things. A dryer belt sold as "200°C" is usually quoting the oven air temperature it can sit in continuously. A hot-material belt marked T2 is quoting the continuous temperature of the material resting on its top cover, which is a harder condition because the load conducts heat directly into one surface while the bottom surface is cooling on the return run. Confusing the two is how a textile-curing belt ends up on a sinter line and is scrap within days.

This article explains only how to read the codes on the hot-material, heat-resistant belt. If you need working-condition case studies, for example belts running through extreme summer operations or high-temperature cement plant lines, see our separate guides on heat-resistant conveyor belts for extreme summer operations and conveyor belts in cement plants at high temperature. The fire-retardant question, which is a different property from heat resistance, is handled in fire resistant vs flame resistant conveyor belts, and the test documents behind every claim are explained in heat-resistant conveyor belt factory test reports. Here we stay on the printed code.

Once you are sure you are dealing with a hot-material belt, the rest of the code line opens up cleanly. Every field below appears on a typical edge marking, and each one has a fixed place in the sequence. We will take them in the order they usually print, because that order also happens to be the order of importance when a belt fails in the field.

02The Cover Grade Letter: What Y, X, W and the RMA Marks Mean

Most edge markings put the cover grade as a single letter near the temperature class, and that letter is easy to misread. It is not the heat rating. The letter grades the cover rubber for abrasion and general mechanical quality, and it survives on the belt edge even when the cover itself is a heat-resistant compound. You can have a W-grade heat belt and a Z-grade heat belt, and both can carry the same T2 temperature class, the difference is how long the surface survives being scraped and worn by the load.

The cleanest system is DIN 22102, which splits cover rubber into W, X, Y, and Z, with W being the most abrasion-resistant. The numbers behind those letters come from a rotating-drum abrasion test in which a sample is worn against a reference sheet under a fixed load, and the volume of rubber lost is reported in cubic millimetres. A W cover must lose no more than 90 mm³, X no more than 120 mm³, Y no more than 150 mm³, and Z, the general-purpose grade, no more than 250 mm³. In practice, a cement plant running sharp clinker wants W or X, while a smooth, soft load such as dried grain might run perfectly well on Y for years.

ISO 14890 uses different letters for the same idea: H for high abrasion resistance, D for normal, and L for low, with limits around 100 mm³, 120 mm³, and 150 mm³ respectively. If you buy from an American or Australian catalogue you will instead see RMA grades. RMA Grade I calls for a minimum tensile strength of about 17.2 MPa (2,500 psi) and Grade II about 13.8 MPa (2,000 psi), with Grade I being the tougher cover. When two suppliers quote the same belt but one says "W" and the other says "H," they are usually quoting the same performance level through two different national filters, and a quick check of the abrasion figure in millimetres cubed settles which is which.

For a heat-resistant belt the cover letter sits on top of a compound choice, and that choice is what actually does the heat work. Standard heat-resistant covers up to about 150°C are typically built on SBR (styrene-butadiene rubber), while belts that must hold 150°C to 200°C switch to EPDM (ethylene-propylene-diene monomer), which survives higher temperatures and oxidises more slowly. The trade-off is real: EPDM heat covers are often slightly softer and can wear faster than a well-formulated SBR abrasion cover, which is why a heat belt still prints an abrasion letter. You are choosing between two properties that pull against each other, and the code line is the only place both are stated.

A common mix-up is to assume every "belt" in a plant follows this lettering. It does not. A rubber conveyor belt with an EP carcass and a cover letter is a flat material-handling belt, while a V-belt on a motor is a power transmission part with its own size system, handled by a transmission belt manufacturer. The cover letter Y or W appears only on the flat conveying belt, never on a wrapped V-belt, and if you see it quoted against a drive application, someone has copied the wrong specification line.

The practical point is simple. When you see Y or W printed beside a heat class, you now know it is the wear rating of the rubber surface, not the temperature it can stand. Keep the two columns separate in your head and half of the bad quotations you receive will start to explain themselves.

03Temperature Class Versus Instantaneous Peak: Two Numbers That Are Not the Same

The single most useful code on a heat-resistant belt is the temperature class, and the single most misused number in a quotation is the peak temperature. The class is the continuous rating, the temperature of the material that can rest on the cover day after day without the rubber degrading faster than it wears. The peak is a short, sharp allowance on top of that class. They are printed or quoted side by side so often that buyers start to think they are the same thing, and that mistake is expensive.

Under DIN 22102 and ISO 4195, heat-resistant belts are split into classes. Class 1, printed T1, is rated for material at 100°C continuous. Class 2, T2, is 125°C, and Class 3, T3, is 150°C. The Chinese standard GB/T 20021 pushes the same ladder one step further with a fourth type rated for 175°C continuous. The compound behind the rating changes with the class: T1 and T2 are usually SBR-based, T3 can be SBR or EPDM depending on the maker, and the 175°C belt is EPDM throughout because SBR simply oxidises too fast above about 150°C.

How a belt earns a class is worth knowing, because it is a test, not an opinion. The standard method ages the cover rubber in hot air, typically per ISO 188, for a fixed period at the class temperature, then measures how much of the original tensile strength and elongation the aged sample has kept. If the compound retains the required percentage, it passes the class. A belt that has not been through this aging test has no honest claim to a T number at all, and a supplier who cannot produce the aging report is selling you a guess.

The peak, by contrast, is a softer concept. Hot material is never perfectly uniform: a clinker lump straight out of the cooler, a run of foundry sand with a hot core, or a surge of asphalt at the loading point can push the instantaneous cover temperature well above the class for seconds or minutes at a time. Manufacturers therefore quote a short-term peak, often 50°C or so above the continuous class, on the understanding that the spike is brief and the cover has time to shed the heat on the return run. The problem is that this peak is not pinned down by one shared standard the way the class is, so the same "200°C" claim can mean a T3 belt with a 200°C peak, or a cheaper T2 belt being marketed at its absolute flash point.

I saw the cost of this confusion on a clinker line that was handling material at around 300°C. The top cover surface measured about 180°C at the loading point, and the belt, marked T3, held up. It held because 300°C was the lump temperature while the sustained contact temperature at the cover stayed near the 150°C class limit. The supplier had been selling it as "a 300°C belt," which was true only in the loosest peak sense. The maintenance team had, by luck, ordered the right class. Had they believed the marketing number and applied it to a genuinely 300°C continuous surface, the cover would have hardened and cracked within months.

So when you read a belt edge, the class is the number you bank on, and the peak is the number you ask to see justified. A clean marking looks like T2 or T3. A quotation that leads with "400°C" or "withstands 300°C" without naming a class is usually a peak figure dressed up as a rating, and that is the first marketing phrase this guide teaches you to catch.

Two more details stop a lot of arguments before they start. First, the class temperature is the temperature of the material on the cover, not the ambient air around the conveyor, so a belt quoted for a "200°C furnace area" has not been rated for anything unless the cover contact temperature is stated. Second, the class assumes a running belt that gets to cool on the return; park a fully loaded belt stationary over a hot surface and even a T3 cover can be cooked from the bottom. Both points live inside the code once you know what the number is actually counting.

04The Carcass Code: What EP 400/3 and NN 200/3 Actually Say

The carcass is the load-bearing skeleton under the rubber, and its code is the part of the belt that carries the tension. On a textile belt this code looks like EP 400/3 or NN 200/3. The two letters name the fibre, the first number is the tensile strength of each fabric ply in newtons per millimetre, and the number after the slash is how many plies are stacked. Multiply the two and you get the belt's total tensile rating, which is the figure the drive design is built around.

EP means the warp yarns are polyester and the weft yarns are polyamide, nylon to most buyers. Polyester in the running direction gives low stretch, which is what you want on a long conveyor, while nylon across the width gives impact absorption and troughing flexibility. NN means both directions are nylon, a construction that stretches more and is usually chosen for shorter, high-impact, or very troughed applications. For a heat-resistant belt, EP is the workhorse: the polyester warp holds its strength better as the belt warms, and the construction resists the growth in length that heat can drive into a nylon warp.

The number is easy to misread and worth taking slowly. EP 400/3 does not mean 400 N/mm total. It means 400 N/mm per ply, three plies deep, so the belt is actually rated for 1,200 N/mm of working tension. EP 100/3 is only 300 N/mm total, one quarter of the strength for the same three plies. Buyers who read the first number as the total have ordered belts a full strength class too light, and the result shows up as a carcass that tears at the splice or stretches beyond the take-up within weeks of commissioning.

Common EP grades run in a rough ladder: EP 100, EP 125, EP 160, EP 200, EP 250, EP 315, EP 400, and EP 500, always as newtons per millimetre per ply. A small cement elevator might run EP 200/3, a long overland conveyor EP 400/4, and a heavy clinker main line EP 500/5, with the exact selection set by tension, belt width, and the sag limit. The grade is not decorative, it is the answer to a calculation, and the standard that pins the test method for that number is ISO 283, the tensile strength and elongation test that every serious conveyor belt supplier runs on finished belt.

Steel-cord belts use a different, simpler code. ST 1000 means a steel cord belt rated for 1,000 N/mm, and the number is already the total, with no per-ply multiplication. If you are deciding between a textile carcass and a steel cord one, the trade-off is elongation and splice style rather than just strength, and the full comparison is laid out on our steel cord conveyor belt page. For most heat applications under a few hundred metres of centre distance, an EP carcass with a heat cover is the default, and the steel cord option only enters when tension or length pushes the textile construction out of its range.

Heat changes the carcass question in one specific way that buyers forget. The cover is not the only part that gets hot; conducted heat eventually reaches the top fabric ply, and the bond between rubber and fabric is usually the first thing to fail when a belt is pushed past its class. The adhesion strength, measured in newtons per millimetre under ISO 252, is part of the carcass specification too. An industrial conveyor belt that keeps its tensile strength at room temperature but loses ply adhesion at 140°C is still a heat failure, which is why a heat belt's carcass is specified for adhesion after aging, not just adhesion as built. A conveyor belt distributor quoting you a bare EP number without the aging figures is quoting half a specification.

Read the carcass code as two numbers and a fibre pair, multiply before you order, and check the ply adhesion after heat aging. That single habit catches more ordering errors than any other step in this guide.

05The Standard Number: Which Rulebook the Belt Was Built Against

Buried on the belt edge or in the datasheet is a standard reference, and it is the most underused code of all. The standard number tells you which rulebook the belt was built and, more important, tested against. Two belts can both say "heat resistant" and "T2," and still be different products, because the T2 in one rulebook may not require the same aging test as the T2 in another. The standard number is what makes the class enforceable.

The reference you will meet most often on textile heat belts is DIN 22102, the German standard that covers textile-carcass conveyor belts and sets both the cover grades W, X, Y, Z and the heat classes T1 to T3. Its international heat-resistance cousin is ISO 4195, which is split into a test-method part and a requirements part and is the document that says exactly how long and how hot the rubber must be aged before you measure strength retention. General requirements for rubber- and plastics-covered textile belts sit under ISO 14890, while steel cord belts live under ISO 15236 and, in Germany, DIN 22131. On the Chinese side, GB/T 20021 is the heat-resistant belt standard with its four temperature types, and GB/T 7984 covers general-purpose textile belts.

North American and Australian buyers will see RMA and AS 1332 instead. RMA is the American grade system behind Grade I and Grade II covers, while AS 1332 is the Australian standard that carries its own heat-resistance requirements. None of these are interchangeable at the level of fine print: each one fixes slightly different limits for the same letter, which is exactly why the number matters more than the letter it describes.

I have seen the difference land on a conveyor floor. Two batches of belt arrived in the same month, both stamped "heat resistant" on the invoice, both bought on price. One edge carried DIN 22102 and a T2 class with an aging report stapled to the delivery note. The other carried only the words "made to ISO standards" with no number at all and no report. The second batch hardened and cracked before the first was even due for a re-splice. The price gap was small; the documentation gap was the whole story.

When a conveyor belt factory quotes a standard, ask for the specific number and the clause, not the brand of the standard. "ISO" by itself means nothing, there are dozens of ISO documents touching conveyor belts, and a supplier who will not name ISO 4195 or ISO 14890 is usually unable to show the test behind the claim. The same discipline applies across the product range: a V-belt manufacturer works to a different set of drive-belt standards entirely, and you would not accept a V-belt quote that cited a conveying-belt number. Matching the standard to the product is part of reading the code correctly.

If you are buying wholesale conveyor belts across several sites or countries, the standard number is also the cheapest way to keep everything comparable. Ordering to DIN 22102 in one country and RMA Grade I in another without mapping the two means you are comparing covers by feel, not by test. Nailing the standard at the quotation stage, before any belt is cut, is how professional buyers keep a mixed fleet consistent.

The test methods behind these standards are worth naming, because they are the verifiable part. Tensile strength and elongation fall under ISO 283, ply adhesion under ISO 252, cover abrasion under ISO 4649, thickness under ISO 7590, and heat aging under ISO 188. A datasheet that lists these numbers next to the belt code is a document you can check; a datasheet that lists only adjectives is not.

06Thickness Marking 4+2 and Edge Forms: The Small Print Buyers Skip

After the carcass code, the belt edge usually carries a pair of numbers joined by a plus sign, written 4+2, 6+3, or 5+1.5. The first number is the top cover thickness in millimetres, the rubber on the carrying side that touches the material, and the second is the bottom cover on the pulley side that runs over the idlers. The two are deliberately different, and the difference is a piece of design logic, not a typo.

The top cover is thicker for two reasons. It is the sacrificial layer that takes the wear, the abrasion letter we covered earlier lives there, and on a hot-material belt it is also the thermal barrier that keeps heat away from the fabric carcass underneath. Every millimetre of top cover is time: it is how long the surface can wear and crack before the heat reaches the plies. The bottom cover can be thin because its only job is to protect the carcass from the pulleys and idlers, and it wears slowly. A clinker belt might be specified 6+3, a lighter hot-sand belt 4+2, and a clean hot-air application 3+1.5.

Thickness is a measured property with a standard behind it, ISO 7590, and it carries a tolerance. That tolerance is where a cheap belt hides. I once mic'd a belt delivered as 4+2 and found the top cover reading 3.4 mm, under the nominal 4 mm by 0.6 mm, with the bottom at 2.1 mm. It sat inside the maker's allowed tolerance, at the bottom of it, but the thermal barrier the design assumed was thinner than the drawing said. On a hot line that missing fraction of a millimetre is the difference between heat reaching the carcass in year one or year three, and it is invisible to anyone who never measures the delivered belt against the marking.

The edge form is the second half of the small print, and it comes in two flavours. A cut edge, also called an open edge, is simply the belt sliced to width with the fabric plies left exposed at the sides. A moulded edge, sometimes a closed or sealed edge, has the side finished with rubber so the carcass is not visible. Cut edge is cheaper and perfectly workable in dry, clean conditions, but the exposed plies wick moisture and let heat and dust into the carcass over time. For a belt that runs hot and possibly wet, most engineers specify a moulded or sealed edge to stop the fabric ends from acting like a wick and pulling damage inward from the sides.

The edge form matters more on a hot belt than on a general one because heat accelerates exactly the kind of oxidation and moisture attack that a cut edge invites. On a abrasion-resistant conveyor belt in a dry plant, a cut edge is a routine cost decision. On a heat belt carrying material that is both hot and damp, such as quenched foundry sand or washed sinter, an open edge can shorten belt life by a full season, and the saving disappears the first time a side delamination forces an unscheduled splice.

The thickness pair and the edge finish are the two fields buyers skip most often, because neither changes the headline heat class. Both change how long that heat class actually lasts in the field, and both are checkable with nothing more than a calliper and a look at the belt side.

07Verifiable Codes Versus Marketing Talk: A Filter That Works

Everything printed on a belt falls into one of two piles, and the cleanest skill a buyer can build is sorting the two instantly. A verifiable code is one that maps to a measurement and a test method, so a third party could confirm or falsify it on delivery. A marketing phrase is one that sounds technical but maps to nothing you can check. The two piles look similar on a quotation, which is the whole trick.

The verifiable pile is the list this guide has already built. Tensile strength is measured under ISO 283, ply adhesion under ISO 252, cover abrasion under ISO 4649, thickness under ISO 7590, and heat aging under ISO 188 or the requirements of ISO 4195. The cover letter, the temperature class, the carcass code, the thickness pair, and the standard number are all entries in this pile, because each one has a number and a method behind it and each one should appear on a quality assurance document you can actually read.

The marketing pile is everything that dresses up a claim without a measurement. "Premium grade," "European quality," "lifetime performance," "specially formulated compound," "high-tech rubber," and "withstands 400°C" with no class, no duration, and no standard number are all in this pile. None of them is false by definition, some premium compounds are genuinely good, but none of them is checkable, which means the day the belt fails there is nothing written down to hold against the promise. "Made to ISO standards" with no number is the most common one, and it means the least.

Heat resistance is where the marketing pile does the most damage, because temperature is a number people remember but rarely define. A claim of "200°C" is meaningless until you know whether it is the continuous material temperature, a short peak, the oven air around the conveyor, or the flash point of the compound in a one-off test. The class system exists precisely to kill this ambiguity, T1, T2, T3 pin the continuous rating, and everything else has to be labelled as a peak and justified with an aging curve. A supplier who will not put a class on the quote is telling you, politely, that the number is a peak or worse.

The same sorting works across the whole catalogue. An oil-resistant conveyor belt has a measurable swelling test behind its rating, a chemical-resistant conveyor belt has a stated resistance against named media, and a fire-resistant conveyor belt carries a flame test, usually ISO 340, that is entirely separate from its heat class. Heat resistance and fire resistance are different properties answering different questions, and a belt can pass one and fail the other. Confusing them is another way a marketing phrase slips in, because "fire resistant" sounds like a stronger version of "heat resistant" when it is actually a different requirement about how the belt behaves in a flame.

The filter to apply to every quotation is two questions. Is there a standard number attached to this claim, and is there a test report that shows the measured value? Two yeses and the claim is verifiable. One no and it is, at best, half a specification. Two noes and it is marketing, whatever font it is printed in.

08Turning the Codes Into an RFQ That Cannot Be Misread

Reading the codes is half the job; the other half is writing them down so the supplier cannot substitute around them. An RFQ that says "heat-resistant belt, 200 degrees, 800 mm wide" is an invitation to receive the cheapest thing that does not look obviously wrong. An RFQ that pins each field from this guide removes the gap the marketing pile lives in.

Start with the machine, because the disambiguation from the first section changes everything. State whether the belt runs inside a heated chamber or carries a hot load, and give the material temperature as two numbers, the continuous class you need and the peak you expect at the loading point. A clear line might read "T2 (125°C continuous), 175°C short peaks at the feed point." That single sentence stops a dryer-belt quote arriving for a sinter line.

Then fix the belt body in the order the edge prints it. Name the carcass as grade and plies, EP 400/3 rather than "strong belt," and the cover as its grade letter plus its heat class, W cover, T2. Add the thickness pair and the edge form, 4+2 top and bottom, moulded edge. Finish with the standard you want, DIN 22102 or ISO 4195, and the test reports you expect to see attached. Where the load is lumpy or sharp, the same discipline applies to the ancillary equipment: our impact and cut resistant belt page covers the carcass choices for that duty, and mining and quarrying or cement plant conditions add their own requirements on top.

For inclined or sticky hot loads, the body code is only part of the picture. A chevron conveyor belt or a sidewall conveyor belt changes the incline capability, and those surface profiles must be specified alongside the heat class, not as an afterthought. The point of the RFQ is to close every loop so the quotation comes back comparable, and comparison is impossible when two suppliers have each quietly assumed a different belt.

Finally, ask for the measured values, not just the nominal ones. A mill test certificate should list the actual tensile, adhesion, abrasion, thickness, and aging-retention numbers for the batch you are buying, because those are the verifiable codes from the last section made concrete. Our service page describes how we handle selection and documentation, and a belt that arrives with a certificate matching its edge marking is the clean end to a clean RFQ.

Send us your RFQ fields and we will quote each code back to you

09Frequently Asked Questions

What do the letters and numbers printed on the edge of my belt actually mean?

Each field in the printed line answers one question. The letters EP or NN name the carcass fibre, the number before the slash is the per-ply tensile strength in newtons per millimetre, and the number after it is the ply count. The cover letter such as Y or W is the abrasion grade, the T number is the heat class, the pair such as 4+2 is the top and bottom cover thickness in millimetres, and the standard number tells you which rulebook the whole thing was tested against. Read in order, the line is a full specification, not a serial number.

Is the temperature printed on the belt a continuous rating or a peak?

If it carries a class such as T1, T2, or T3, the class is a continuous rating for the material resting on the cover, 100°C, 125°C, and 150°C respectively. A larger number quoted without a class is usually a short-term peak or a flash figure, and it is not the same thing. The class is the number you bank on; the peak is the number you ask the supplier to justify with an aging curve.

What does EP 400/3 mean and how do I read the slash?

The slash separates strength from ply count. EP 400/3 means an EP carcass, polyester warp with nylon weft, rated at 400 N/mm per ply across three plies, so the total tensile strength is 1,200 N/mm. The number before the slash is never the total, and buyers who read it as such have ordered belts a full strength class too light.

What is the difference between heat resistance and fire resistance?

They answer different questions. Heat resistance is how well the rubber survives sustained contact with hot material, and it is graded by classes such as T1, T2, and T3. Fire resistance is how the belt behaves in a flame, tested separately under standards like ISO 340. A belt can pass one and fail the other, so a heat belt is not automatically a fire-rated belt, and the two terms must not be swapped on a quotation.

What does a 4+2 marking tell me about the belt?

It gives the two cover thicknesses: 4 mm of rubber on the top, carrying side that touches the material, and 2 mm on the bottom, pulley side. The top cover is thicker because it is both the wear surface and the thermal barrier that keeps heat away from the carcass. Thickness is a measured property with a tolerance, so it is worth checking the delivered belt with a calliper against the marking.

How do I tell a real temperature rating from a marketing claim?

Apply two questions to every claim. Is there a standard number attached, such as DIN 22102 or ISO 4195, and is there a test report showing the measured value? Two yeses means the claim is verifiable; a missing number or a missing report means the figure is, at best, half a specification. Phrases like "premium grade" or "withstands 400°C" with no class and no report fall on the marketing side of the line.