Heat resistance of rubber conveyor belts up to 500 °C. Reality or myth?
The work of conveyor belts with hot products is always a difficult challenge and a painful issue for many engineers and mechanics. When the passport says "heat resistance of the belt 200°C", and it starts to "crumble" already at 150°C, it seems that the manufacturer simply lied.
In fact, the problem is usually not in direct deception, but in the difference between laboratory tests and real life. Here are the main reasons why heat resistance on paper does not coincide with reality:
1. Material temperature vs. Ambient temperature
Technical charts usually indicate the temperature of the material being transported. But the surface temperature of the belt itself is of critical importance.
• In the passport: This means short-term contact with hot cargo.
• In reality: If the belt is long, it has time to cool down on the return branch. If it is short, heat accumulates, the rubber overheats "throughout", and destruction begins.
2. Effect of lump size
Fine fraction (sand or cement) is much more dangerous than large pieces of ore or sinter.
• Large fraction: There is air between the pieces, which removes heat.
• Fine fraction: Creates a “blanket” effect. Heat does not escape, and the belt cover simply “bakes”.
3. Rubber aging
Even if you don’t exceed the limit, constant high temperatures trigger irreversible chemical reactions. The rubber loses its elasticity and cracks when bent on the drums. This process is called rubber aging.
4. The problem of the carcass
Rubber can withstand 200°C, but the fabric carcass (ER) has a limit. With prolonged overheating above 150°C, the adhesion (bonding) between the rubber and the fabric is destroyed. The tape simply peels off.
What to do about it?
1. Increase the diameter of the drums: The "oak" belt from the heat cracks more easily at small radii.
2. Cooling: Install additional blowers or a water irrigation system on the return branch.
3. Check the speed: Sometimes a slight acceleration of the belt allows the load to have less time in contact with the same section of rubber.
EPDM (ethylene-propylene-diene rubber) based belts are considered the "heavy artillery" in the world of conveyors. They are significantly superior to conventional SBR belts, but even they have a limit that is often confused.
Here are the real numbers for high-quality EPDM:
1. Temperature modes
The maximum temperature resistance depends on how the temperature is measured:
• Constant operating temperature: up to +200°C. This is the mode in which the belt can operate stably for a long time.
• Short-term peaks (shocks): up to +250°C (sometimes up to +400°C is claimed for very short contacts with a large fraction). These are situations when hot material touches the tape, but quickly drops or cools down.
• The temperature of the frame base itself: should not exceed +150°C. If the fabric inside heats up, the tape will simply “float” (delaminate).
2. Why is EPDM better than others?
The main advantage of EPDM is not that it does not heat up, but how it ages:
• Conventional rubber (SBR): When overheated, it becomes hard, brittle and cracks
• EPDM: Even after prolonged exposure to high temperatures, it retains elasticity.
3. Critical limitations
Despite its excellent heat resistance, EPDM has an "Achilles heel":
1. Oils and fats: EPDM does not hold oil contact at all. If your hot load contains even a little oil or fat (for example, hot asphalt or certain types of agglomerate), the belt will swell and fail in a matter of weeks.
2. Abrasive: Pure EPDM is slightly less resistant to abrasion than standard rubber. Therefore, special mixtures of EPDM + Abrasive resistance are used for abrasive material.
Can the belt withstand a temperature of 500°C
This is a classic example of marketing balancing, where the physical capabilities of the material and real operating conditions are mixed. When you see the figure of 500°C for a rubber-fabric belt, it is important to understand the "asterisks" in the notes.
Here is how manufacturers justify such cosmic numbers:
1. Short-term peak contact (Spot heat)
The figure of 500°C usually does not apply to the entire mass of the load, but to individual red-hot particles (for example, pieces of agglomerate or foundry slag).
• EPDM rubber has a high activation energy of thermal destruction.
• If a red-hot scale falls on the belt and cools quickly (or the belt moves quickly), the surface layer of the rubber does not have time to warm up deep down.
2. Thermal inertia
Upon contact with a very hot object, the upper micron layer of rubber begins to decompose with the release of gases. These gases create a microscopic “layer” that insulates the rest of the belt from heat for a fraction of a second. Manufacturers conduct laboratory tests where a hot rod touches the belt for a few seconds, and if it does not ignite, they write “up to 500°C”.
3. Special protective layers
Belts marked “500°C” are not just a piece of rubber. They often have a combined structure:
• Sacrificial layer: The top layer of rubber, which is designed to gradually burn out (ablate).
• Thermal barrier: A special fabric between the cover and the carcass (for example, fiberglass or basalt fiber), which prevents the temperature from reaching the synthetic cord.
What is the danger of such numbers?
If you load such a belt with a layer of sand at a temperature of 500°C, it will burn through in minutes. Here's why:
Temperature What really happens to EPDM belt
up to 200°C Stable long-term operation.
200°C – 250°C Start of accelerated aging, rubber loses 50% of its resource.
300°C – 400°C The cover starts to smoke, microcracks appear
500°C Only possible for large fractions (pieces > 50 mm) with constant air blowing.
Summary: Marketing vs Reality
Manufacturers specify 500°C to win a tender or show an advantage over competitors. But in the technical passport (Data Sheet) in small print
it will always be stated: "Short term peaks for lump materials only".