EPDM Conveyor Belts: Heat, Ozone and Steam Resistance Explained

01Why an EPDM Belt Ages Differently From the Belt Next to It

A conveyor running at 110 °C in a foundry sand plant and a conveyor running at 60 °C in a palm oil mill can carry belts that look identical in a photograph and behave nothing alike in service. Colour tells you nothing about either of them. Thickness tells you very little. The elastomer in the cover decides which failure arrives first, and EPDM happens to be one of the few cover materials whose behaviour can be predicted almost completely from a single structural fact about the polymer.

Buyers usually arrive at EPDM by elimination rather than by design. A line runs hot, or sits in an open yard, or carries something damp and warm, and the belt that was bought on price starts cracking at the edges within a season. Someone proposes an EPDM cover. The replacement lasts much longer, and the lesson gets filed away as "EPDM is for heat". That lesson is roughly half true, and the missing half is where the expensive mistakes live.

Send us the duty description and we will confirm whether EPDM is the right cover

EPDM is a terpolymer of ethylene, propylene and a small diene term that exists only to provide crosslink sites. What matters on a conveyor is not the recipe but the backbone. Once the diene has been consumed during vulcanisation, the polymer chain carries no double bonds along its length, and ozone, oxygen and ultraviolet light all need those double bonds to start a chain scission. With none available they have very little to attack. The practical result is a cover that can stand in a stockyard through two summers without the fine crazed cracking that ruins a natural rubber belt in the same position.

The same saturated backbone is what makes the material comfortable with water. Steam, condensate, washdown water and humid air do not hydrolyse it, and it carries no polar groups that would pull water into the compound. A belt that leaves a washdown tunnel wet and then enters a 90 °C drying zone is close to the ideal application for EPDM, which is why so much of the installed base sits in food plants, board lines and wet-process plants rather than in dry mining duty.

Then the same structure turns against you. EPDM is non-polar, mineral oil is non-polar, and similar dissolves similar. Lubricating grease, hydraulic oil mist, diesel spillage, paraffinic release agents and aliphatic solvent all migrate into the cover instead of sitting on top of it. Nothing in the polymer resists that migration. This is the one place where an EPDM belt is genuinely the wrong answer rather than merely an expensive one, and it is a place where a cheap general-purpose abrasion-resistant cover will outlast the premium compound.

So we ask two questions before quoting an EPDM cover to anybody. What is the highest continuous surface temperature the belt sees, and what is on the belt that is not the product. The first decides whether EPDM is needed at all. The second decides whether EPDM is permitted. As a conveyor belt manufacturer we would rather lose an order at the quotation stage than send a compound into a duty it cannot survive, because that failure arrives twelve weeks later and gets blamed on the belt instead of on the specification.

What follows works through the four environments in the order they appear on real enquiries. Dry heat first, because it is what people mean when they search for an EPDM belt. Outdoor weather second, because it is the free bonus the material throws in. Steam and wet heat third, because that is where it genuinely outperforms everything else at similar cost. Oil last, because that is where most of the wrecked belts come from.

02The Polymer Itself: Saturated Backbone, Non-Polar Behaviour

Three properties of the raw polymer drive everything else, and none of them is visible in a finished belt. Saturation decides how the material behaves against oxygen, ozone and light. Polarity decides what it will absorb. The diene level and the cure system decide how much filler the compound can carry and how well it holds its shape under compression at temperature. A buyer who understands those three levers can read an EPDM data sheet with a reasonable idea of what the belt will do in five years.

Start with the chain. A fully saturated backbone means no allylic hydrogens in the repeat unit, and allylic hydrogens are the weak point in natural rubber, SBR and nitrile. Take them away and the rate of oxidative chain scission at a given temperature drops sharply. It does not stop. Nothing stops oxidation, and an EPDM cover held at elevated temperature for years will eventually harden, glaze and crack at the edges. It simply takes far longer than the same cover made from an unsaturated elastomer.

Polarity is the second lever and it cuts both ways. The non-polar chain is why water, steam, glycol, alcohol and most aqueous process liquors sit on the surface instead of entering it. It is also why hydrocarbon liquids enter it freely. There is no compounding trick that makes an EPDM cover oil resistant, because the problem is not the additive package but the backbone itself. Any supplier who claims an oil-resistant EPDM is either describing a different polymer or describing a very short service life.

Ethylene content is the third lever and it is the one buyers never see. A higher ethylene fraction gives the compound green strength, higher tensile and better shape retention on a hot press, which is why it appears in profiles and in some high-durometer covers. Push it too far and the polymer begins to crystallise, which stiffens the belt in cold weather and can produce cracking on a small pulley at ambient temperature. A belt specified for a cold store in Harbin and a belt specified for a 100 °C dryer in Guangdong are not the same compound even when both are marked EPDM.

Cure system matters just as much, and it splits the family in two. Sulphur-cured EPDM is cheaper, has better tear and better flex fatigue, and is the normal choice for a general hot-duty cover. Peroxide-cured EPDM has carbon-to-carbon crosslinks instead of sulphur bridges, which gives much lower compression set at temperature and better long-term heat ageing, at the cost of poorer hot tear and a fussier process. For a belt running over small pulleys we usually prefer the sulphur system. For a belt pressed against a hot platen or holding a profile under load, peroxide earns its premium.

This is the point where the word EPDM stops being a specification. Two belts can carry the same family name, the same thickness and the same black surface, and differ by a factor of two in service life, because one compound was built around a coarse reinforcing black at high loading and the other around a finer structure with a proper antioxidant package. That difference is invisible at the loading dock. It shows up in year two. As a conveyor belt factory we write the cure system and the filler class onto the compound record precisely so that a reorder matches the original rather than merely resembling it.

Where the compound sits in a catalogue matters too. A heat-duty cover sold through a general wholesale conveyor belts list is often a broad-purpose EPDM at a nominal thickness, while the same family built for a specific plant may carry a thicker cover, an extra skim and a different cure. If you are comparing quotations from two sources, compare the compound record rather than the headline description, because that is where the two belts actually diverge.

Table 1. How EPDM behaves against the cover families it is usually weighed against. Ratings describe general polymer behaviour, not any individual supplier's compound.

03Heat Ageing: What the Cover Tolerates and What It Loses

A general-purpose EPDM cover compound will sit at around 120 °C continuously and take short excursions above that without immediate distress. Read that sentence carefully, because the number describes the cover and not the belt. On most hot lines the cover is the last thing to fail. The skim coat between plies, the fabric, the splice and the pulley lagging all reach their limits earlier, and they fail in ways that are much harder to see from the walkway.

Heat ageing in EPDM looks like hardening rather than softening, which is the opposite of what oil does to the same material. Antioxidant is consumed, residual crosslinks continue to form, and the compound gains modulus while losing elongation. On the belt this shows as a surface that has gone slightly glossy, then a fine network of cracks at the edges where the cover wraps the pulley, then a belt that has become stiff enough to stop tracking properly on the return run. By the time an operator notices the tracking, the cover has usually been ageing for months.

The failure sequence is predictable enough to plan around. Edge cracks appear first because the edge is where strain concentrates and where the cover is thinnest in the direction of flex. Then the crack turns ninety degrees and runs under the cover along the fabric interface, which is where the skim has embrittled. Once the crack reaches the splice area the belt is finished, because a splice cannot be repaired in place once the underlying ply is contaminated with degraded rubber and grit.

In one sand reclamation plant we surveyed, a 10 mm EPDM cover on a fabric belt carried material at a measured 105 °C for 19 months. The cover itself was still flexible and showed no cracking at all. The belt failed because the top skim had hardened enough to crack at the step splice, water had entered, and the ply separation had run 400 mm before anyone cut it out. The compound had done its job. The splice specification had not.

That is why heat duty has to be written as a profile rather than a single figure. A belt that sees 130 °C for twenty minutes at shift start and 80 °C for the rest of the day is not the same application as one held at 115 °C around the clock, even though the peak number is higher in the first case. Intermittent exposure allows the compound to recover and gives the antioxidant package time to work. Continuous exposure at a lower figure accumulates damage without pause, and it also cooks the carcass from underneath, which no cover compound can prevent.

Table 2. What actually changes on a hot-duty belt as exposure accumulates, and what a maintenance team can see at each stage.

Notice what this table does not do. It does not rank temperature classes against each other, and it does not tell you which designation to write on an order. Grade naming is a separate subject with its own logic, and it is covered in the article on heating conveyor belt designations where the class system itself is explained. What matters here is narrower. Once you have decided the cover is EPDM, the question becomes how long that particular compound will hold its properties at your particular profile, and the answer depends on cure system, thickness and splice far more than on the family name.

04Ozone, Sunlight and Weather: the Crack That Never Starts

Ask a rubber technologist what EPDM is for and the answer will often be ozone before heat. That is a fair summary of where the material is indispensable. An unsaturated rubber under tension in ordinary air will develop ozone cracks, and the mechanism is brutal in its simplicity. Ozone attacks the double bond at the surface, the chain breaks, and because the belt is under tension the break opens instead of closing. The crack then shields its own tip from further ozone but concentrates stress there, and it walks across the belt in a direction perpendicular to the strain.

Belt users see the result as a row of parallel cracks along both edges of a belt that has been sitting tensioned in a yard, or on a conveyor that only runs a few hours a week. It looks like sun damage and it is partly sun damage, since ultraviolet light produces the same radicals. The damage is not caused by load and not caused by abrasion, which is why it appears on belts that have carried almost nothing. EPDM has no double bonds left in the backbone to attack, so the process simply does not start. That is a genuine material advantage rather than a marketing claim.

We have watched this play out in a port stockyard where two belts were stored side by side in coils, both tensioned on their cradles, one natural rubber and one EPDM. After eight months in the open the natural rubber belt showed the classic edge cracking and the EPDM belt showed chalky surface bloom and nothing else. Both were then installed. The natural rubber one was scrapped within a year for reasons unconnected with cracking, which is worth remembering. Ozone resistance buys time, not immunity from every other failure.

Cold is the other half of the outdoor story and it rarely gets mentioned. A compound built for flexibility at low temperature keeps working on an unheated conveyor in winter, where a stiffer compound will crack at the pulley or refuse to trough properly. EPDM with a moderate ethylene level stays flexible far below freezing, which suits cold stores, winter ports and open yards in northern China. The same property explains why the material appears on conveyors that must start cold and then run hot, an unusual combination that would defeat most general-purpose covers.

Weather resistance also removes a maintenance nuisance that costs more than it looks. Belts with wax-based protection need the wax to bloom continuously to remain protected, and the bloom disappears as soon as the surface is abraded or washed. EPDM does not depend on a sacrificial layer, so a belt that is cleaned regularly keeps its resistance. That is a real operational difference on outdoor lines that get hosed down, and it is one more reason the material turns up in yards, ports and recycling plants.

None of this makes an EPDM belt immortal outdoors. Water still enters through a damaged edge, fabric still loses strength when it stays wet, and a seized idler will still destroy a cover in a week. We treat ozone resistance as a reason to stop worrying about the weather and start worrying about everything mechanical, which is where the next failure will come from. For a broader view of how covers are matched to mechanical duty, the page on industrial conveyor belt selection sets out the families and their normal applications.

05Steam, Wet Heat and Washdown: Where EPDM Earns Its Place

Steam is the application where the case for EPDM is strongest and where the material is hardest to replace. Saturated steam at atmospheric pressure is roughly 100 °C, and saturated steam under pressure is hotter still, but the temperature is only part of the problem. Steam carries latent heat that condenses on any cooler surface, so a belt in a steam tunnel is simultaneously hot, wet and repeatedly wetted. Few elastomers enjoy that combination. EPDM is one of the few that does.

The chemistry behind that is straightforward. Water does not attack the polymer chain, and the saturated backbone does not provide an entry point for hydrolysis. Nitrile, polychloroprene and natural rubber all lose properties faster in wet heat than in dry heat at the same temperature, partly through hydrolysis and partly through the extraction of water-soluble ingredients from the compound. EPDM loses very little to water and holds its properties in wet heat almost as well as in dry heat. That is the difference between a cover that lasts two years in a retort area and one that lasts six months.

A steam resistant conveyor belt is not only about the cover, and this is where most specifications fall short. The carcass matters at least as much. Polyester fabric is susceptible to hydrolysis under hot wet conditions, and hydrolysis of the yarn is irreversible. A belt with an EPDM cover and a standard polyester carcass can look perfect on the top surface while the plies underneath are quietly losing strength. When it finally fails, it fails suddenly, at the splice or under a load point, with no visible warning on the carry side.

Then there is the splice, which is the weak point in every steam application we have investigated. A vulcanised splice is a joint in the cover, the skim and every ply, and each of those interfaces behaves differently when hot water vapour is present. The cover edges of the splice take the most stress and dry out fastest when the belt leaves the steam zone. If the splice was built with a step pattern that puts the joint in line with the direction of flex, steam exposure will find it. We specify a bias or finger splice for steam duty and we insist that the splice compound matches the cover rather than coming from a general repair kit.

Condensate is the detail that catches designers out. A steam tunnel that drips onto the return side of a belt produces a permanently wet strip in one place, which then becomes the place where the cover softens and the fabric wicks water sideways. Drainage, drip trays and a slight incline on the return run cost very little at the design stage and add years to the belt. So does edge protection, because a wet edge that frays will wick water into the carcass along the entire length of the belt within a few months.

Table 3. Steam and wet-heat process points where EPDM covers are commonly specified, and the design detail that decides whether the belt reaches a normal life.

The pattern in that table is consistent. EPDM handles the medium, and the belt still fails at the edges, the splice or the carcass. When a steam application goes wrong, the cover is rarely the part that let it down. We have seen more steam-duty failures caused by a standard polyester carcass and a hurried splice than by any shortcoming of the cover compound, and both of those are decisions taken at the quotation stage rather than at the factory.

One more caution belongs here. Steam areas are often also lubricated areas, because the same plant that runs a steam tunnel usually runs conveyors, chains and bearings nearby. Oil mist drifts. A steam-duty EPDM belt that picks up a fine film of lubricating oil every shift will swell at the surface, and once the surface has swollen it abrades away far faster than an unaffected cover would. The two duties look compatible on paper and are not compatible in a real building. Where both are unavoidable, the answer is usually a nitrile cover on the oil side and a physical barrier between the two zones.

06The Boundary Line: Mineral Oil and Aliphatic Hydrocarbons

Now the part that catalogues leave out. EPDM has a hard limit, and the limit is hydrocarbon liquid. Mineral oil, lubricating grease, hydraulic fluid, diesel, kerosene, paraffin, white spirit and the aliphatic fraction of most solvent blends will all enter an EPDM cover and stay there. The polymer does not resist them at all, because resisting a non-polar liquid requires either a polar backbone or a crystalline barrier, and EPDM has neither.

What happens next is worth describing in order, because the sequence explains why the failure is often blamed on the belt rather than on the specification. The cover absorbs oil and swells, typically by a large fraction of its own volume rather than by a few percent. Swelling softens the compound, and a softened cover loses abrasion resistance, tear strength and shape. The swollen cover then grows in thickness and lifts away from the carcass at the edges, where the constraint is weakest. Once oil reaches the skim coat, adhesion falls and the plies begin to separate under normal running tension. From the outside the belt looks intact until the day a strip of cover peels back at a pulley.

Here is the point that surprises buyers. On an oily line, an EPDM cover will usually fail sooner than a plain abrasion-resistant cover made from natural rubber or SBR. That sounds wrong if you have been told that EPDM is the premium heat material. It is correct, and the reason is that swelling is driven by the polarity match, not by the quality of the compound. A general-purpose abrasion-resistant cover swells moderately in mineral oil and keeps most of its structure. An EPDM cover swells heavily and loses its structure. Paying more for EPDM in that duty buys a shorter life.

I have watched this argument happen on a scrap handling line where the maintenance team replaced a worn general-purpose belt with an EPDM heat cover because the plant had also had a hot spot at the transfer. The new belt swelled across its full width within eleven weeks, the edges lifted, and the splice pulled apart. The hot spot had been fixed at the same time by adding a skirt and a water spray, so the heat justification had already disappeared. The right answer was a nitrile cover with a heat-tolerant carcass, not a heat cover with no oil resistance.

The distinction buyers need to hold on to is between a cover that is oil resistant and a cover that is heat resistant. They are different polymers and the choice is not a matter of grade or price. The page on the oil resistant conveyor belt range covers the nitrile side of that decision, including the difference between resistance to a splash and resistance to continuous immersion. Where an oil is present and its chemistry is unknown, the honest approach is an immersion swell check on a sample of the actual liquid rather than a guess from the family name.

Not all oils are equal, and the exceptions matter. Animal and vegetable oils are esters rather than hydrocarbons, and EPDM resists many of them far better than it resists mineral oil, which is why the material appears on conveyors handling food-grade fats and why palm and canola duty is a different conversation from gear oil duty. Aromatic hydrocarbons attack EPDM as well. Chlorinated solvents attack it badly. Glycol, water-based coolant and most aqueous process fluids are harmless. The dividing line is chemistry, not viscosity, and a thick grease can be far more aggressive than a thin solvent if the grease is built on a paraffinic base stock.

Table 4. Recognising hydrocarbon attack on an EPDM cover, and what the correct response looks like at each stage.

07How This Sits Against Heat-Grade Guidance and Cement Plant Practice

Two other pages on this site cover ground that this one deliberately leaves alone, and the division is worth stating plainly because the overlap is where readers get confused. The article on heating conveyor belt designations explains how heat covers are named and classified, what a class number is built from, how the test conditions behind it are chosen, and what the number does not promise about a real installation. The article on conveyor belts for paper mills deals with a machine where heat, moisture and process chemistry act on the same belt at the same time, and where the interaction between those three agents decides the specification.

This page is narrower than either of them. It takes one elastomer, EPDM, and asks where that compound works and where it stops working. It is not a grade comparison and it is not a survey of hot-duty industry practice. If your question is which class designation to write on a purchase order, the designations article answers it and this page will not. If your question is how a paper machine's wet end differs from its dryer section, the paper mill article answers it and this page only borrows the conclusion.

What we do not do here is restate kiln and cooler conditions from cement plants, or reproduce a table of class numbers against temperatures. Both have been published elsewhere on the site and repeating them would only add length without adding a decision. The cement side is a good example of why. A kiln line contains several distinct thermal zones, each with its own peak pattern and its own contamination, and the cover decision there depends on which zone you are standing in. That is a plant-specific question, and the cement plant section of this site is the right place to start rather than a paragraph about EPDM in general.

So the boundary runs like this. Grade naming, class limits and the meaning of a temperature designation belong to the designations article. Multi-agent industrial duty where heat is only one of several threats belongs to the application articles. The single-compound envelope, meaning what EPDM tolerates, what it absorbs, and how it fails under each, belongs here. Readers who need the first two should follow the links. Readers who have already chosen EPDM and want to know whether that choice survives their line are in the right place.

Table 5. Common hot-duty situations where an EPDM cover is proposed, and whether the proposal survives contact with the rest of the duty.

Two of those rows point somewhere else on purpose. Where abrasion rather than heat is the governing threat, the abrasion resistant conveyor belt range is a better starting point than any heat compound, because a cover chosen for temperature will usually be softer and less cut resistant than one chosen for wear. Where acid, alkali or a process liquor is the main agent, the chemical resistant conveyor belt discussion is the relevant one, and EPDM is often a strong candidate there for the same reason it works in water, provided the chemical is not a hydrocarbon.

There is a useful comparison to be made with the general rubber conveyor belt construction most plants already run. The carcass in an EPDM belt is usually the same fabric or steel construction as any other belt of the same strength class. What changes is the cover compound, the cure system and the splice materials. That is why an EPDM belt is not a different product category and why it can be quoted against a standard construction rather than as a specialty item.

Fire is the last overlap worth flagging, because heat duty and fire duty are often confused in enquiries. A compound that tolerates high temperature is not necessarily a compound that resists flame, and EPDM on its own burns readily once ignited. Where a plant needs both heat tolerance and flame behaviour, the compound has to be formulated with that in mind and the fire resistant conveyor belt range is where that conversation belongs. Asking a standard EPDM cover to perform as a flame-resistant belt is a specification error that no amount of heat resistance will cover.

Where the same polymer logic appears outside a flat belt, it is worth knowing that the answer is often the same. Hot fan drives and hot-process machinery frequently use EPDM-wrapped belts for the same reason a conveyor does, and a V-belt manufacturer will usually recognise the duty from the temperature and the absence of oil. The trade-off is identical, including the oil limitation, which does not disappear because the belt is a different shape.

Buyers comparing quotations should also be clear about what a conveyor belt supplier is actually offering when the quotation says EPDM. Without a compound record, the word describes a family and nothing more. Two suppliers can both be accurate and still deliver covers that behave differently at 110 °C, because cure system, filler and antioxidant loading are not visible in the description. The compound record is the only document that closes that gap, and it is reasonable to ask for it before an order rather than after a failure.

08Specifying, Splicing and Inspecting an EPDM Belt on Site

A specification for an EPDM belt needs four things written down before price is discussed, and the first is the temperature profile rather than a single maximum. Write the continuous surface temperature, the peak and how long the peak lasts, and whether the belt is stopped while hot. A belt that stops hot under load is a different problem from one that keeps moving, because a stationary belt under a hot product develops a permanent set in the cover where the product sits.

The second item is the contamination list, and it should include everything that touches the belt rather than only the product. Lubricants, cleaning chemicals, release agents, washdown water and any spill that reaches the return side all belong on that list. This is the item that most often removes EPDM from consideration, and it is the item most often left blank on an enquiry form.

The third is the carcass, because the cover is only the outer layer of a system. A steam application needs a carcass that will not hydrolyse, a hot application needs a carcass whose splices will hold at temperature, and an application with heavy impact needs enough plies and enough support under the loading point. For long runs and high tension the steel cord conveyor belt construction is often the practical choice, and the cover question then becomes a separate line on the same order.

Fourth comes the splice, which deserves its own line in the specification rather than being left to the installer. A vulcanised splice in an EPDM belt needs a splice compound that cures to the same hardness as the cover, a step pattern that keeps the joint out of the highest flex zone, and enough cooling time after the press opens. In steam duty the splice is the first part of the belt to fail in almost every case we have examined, and it fails from the edge inward as water finds the interface.

On site, inspection should be simple enough that a shift technician will actually do it. Run a hand along both edges at four fixed points once a week and feel for stiffness, because a cover that has begun to harden feels different from one that has simply worn thin. Measure cover thickness at the same four points with the same gauge every time, and write the numbers down. A single reading tells you nothing, but a trend over six months tells you when to order the replacement, which is the only decision the measurement is for.

Check the splice separately and more often than the rest of the belt. Look for a line of dust or a dark stain along the splice edge, which usually means the interface has opened and is collecting material. Feel for a step with a straight edge across the joint. Any splice that has begun to lift at the cover edge in a hot application will not recover, and patching it is usually a way of delaying a shutdown rather than avoiding one.

Storage decides the first year of life more than most plants realise. An EPDM belt in coil should sit on a dry surface, out of direct sun, without a sharp bend at the core and without a heavy load on top of it. The material resists ozone and weather far better than its neighbours, which tempts people to leave it in the yard. It will survive that, but the coil will take a set and the edges will be the first place to crack once it is installed and tensioned.

Table 6. What to confirm before an EPDM belt order is released, and what a weak answer looks like.

Two support functions usually decide how quickly a belt problem is resolved rather than whether it occurs. One is the quality route behind the compound, which should be able to show how a batch was mixed and cured rather than only that it was inspected at the end. The other is the service route, because a belt that fails at a splice needs a technician with a press and the right compound on site rather than a replacement roll shipped from a warehouse. Our quality assurance process and our service arrangement are both built around that distinction between a product and a repair.

The mechanical parts deserve a mention because they extend cover life more than most buyers expect. A pulley that is undersized for the belt thickness will flex the cover more sharply at every revolution, and a worn lagging will slip and polish the surface instead of gripping it. The conveyor pulleys and conveyor components ranges exist for that reason, and matching them to the belt is part of the same calculation rather than an afterthought.

For plants that already run these belts and want a structured way to plan replacement, the guidance on maintenance, inspection and failure prevention sets out an inspection rhythm that works for high-tension constructions, and most of it transfers directly to a fabric belt with an EPDM cover. Buyers who are new to the category will find the wider conveyor belt selection guide useful for the parts of the decision that are not about the cover at all.

If the belt also runs through a food area, the cleaning regime becomes part of the specification, and the food packaging applications section explains how washdown frequency and chemical choice interact with cover selection. Where the line handles mixed waste and the belt sees both heat and sharp contamination, the recycling section is the closer match. Neither application changes the polymer argument. Both change the consequences of getting it wrong.

One more supplier question is worth asking before a first order, particularly if the belt is part of a wider replacement programme. A conveyor belt distributor who stocks both nitrile and EPDM covers will usually tell you when the cheaper polymer is the right answer, because they carry both and have no reason to push one. A distributor who only offers heat covers will tend to find a heat problem on every line they visit.

On the transmission side the same reasoning applies to drives rather than conveyors, and a transmission belt manufacturer faces an identical choice between heat-tolerant and oil-tolerant compounds for the same machine. Plants that run both belt types in one building often discover that the two selections were made by different people using different assumptions, which is how a hot area ends up with an oil-resistant belt and an oily area ends up with a heat cover.

Send your temperature and contamination list for a compound recommendation

09Frequently Asked Questions

Can these covers run continuously at 120 °C?

A well-built EPDM cover compound will hold its properties at around that level for a long time, and short excursions above it are survivable. The honest answer is that the cover is rarely the part that decides. On most hot lines the skim coat, the fabric and the splice reach their limits before the cover does, and they give no visible warning from the walkway. Before accepting a continuous rating, ask what the same quotation assumes about the carcass and the splice, because a rating that applies only to the cover is not a belt rating. The wider heat resistant conveyor belt range sets out how those combinations are normally assembled.

Why did our belt swell and go soft after a few months?

Swelling and softening together almost always mean hydrocarbon absorption rather than heat damage, because heat makes EPDM harder and oil makes it softer. Look for the source rather than the symptom. Grease from a bearing, oil mist from a nearby compressor, a release agent applied upstream or diesel from a loader all reach the cover in small amounts and stay there. Once the cover has swollen it will not recover, and the belt has to be replaced rather than cleaned. The replacement should change polymer, not just supplier.

Is EPDM better than nitrile where grease and lubricating oil are present?

No, and this is the single most common specification mistake we see. Nitrile is the correct family for mineral oil and grease, and its weakness is weather and heat rather than oil. EPDM is the correct family for heat, steam and weather, and its weakness is oil. Where both appear on one line, the usual solutions are a nitrile cover with a heat-tolerant carcass, a barrier that keeps the oil off the belt, or accepting a shorter replacement interval on whichever exposure is smaller. The oil resistant conveyor belt discussion covers the nitrile side in more detail.

How can I tell a genuine EPDM cover from a general-purpose one in the warehouse?

Visually you cannot, and anyone who claims otherwise is guessing. Both are black, both are matte, and both feel similar when cold. The differences appear under load and heat rather than on a shelf. What you can do is check the documents. Ask for the compound record, the cure system and the cover hardness, and compare them with the belt that is being replaced. A supplier who cannot produce those for a specific order is selling a family name rather than a specification, and the belt you receive may be perfectly sound while still being the wrong compound for your line.

Does steam duty need a different splice?

Yes, and the splice is where most steam-duty failures begin. Steam and condensate attack the interfaces between cover, skim and plies, and the splice contains more of those interfaces than any other metre of the belt. Specify a splice compound that cures to the cover hardness, a step or finger pattern that keeps the joint out of the highest flex zone, and a full curing hold time before the press is opened. A splice built with a general repair kit will usually open at the cover edge within a few months of steam exposure, long before the cover itself shows any distress.

What should go on the RFQ when a line is hot and slightly oily?

Write both exposures down and let the supplier solve the conflict rather than resolving it yourself by choosing the hotter of the two. Give the continuous temperature, the peak and its duration, and list every liquid that reaches the belt including lubricants, cleaning chemicals and spillages. Then state the consequence of a failure, because a belt over a transfer point with people nearby is not the same risk as one in an enclosed tunnel. With those three items a supplier can propose a compound honestly, and can tell you which of the two exposures will set the replacement interval.