In high temperatures, rubber can degrade, losing elasticity and strength, which leads to cracking, hardening, and potential failure of rubber products.
Rubber is a versatile material used in countless applications, but its performance changes dramatically under high heat. Understanding how rubber reacts to temperature extremes helps you choose the right materials for heaters, seals, and other hot environments.
What Happens to Rubber at High Temperatures?
When exposed to excessive heat, rubber undergoes physical and chemical changes that degrade its properties. The exact effects depend on the rubber type and temperature range.
Melting and Softening
Most rubbers soften between 120-180°C (248-356°F) and melt at higher temperatures. For example:
- Natural rubber melts around 180°C (356°F)
- Synthetic rubbers typically withstand higher temperatures before melting
Chemical Degradation
Heat breaks down rubber’s molecular structure through:
- Oxidation (reaction with oxygen)
- Chain scission (breaking polymer chains)
- Cross-link breakdown (loss of elasticity)
Physical Changes
Visible signs of heat damage include:
- Cracking and brittleness
- Shrinkage or expansion
- Loss of tensile strength
- Discoloration
Temperature Limits for Common Rubber Types
| Rubber Type | Max Continuous Temp | Peak Temp |
|---|---|---|
| Natural Rubber | 85°C (185°F) | 120°C (248°F) |
| Silicone | 230°C (446°F) | 300°C (572°F) |
| Viton (FKM) | 205°C (401°F) | 316°C (601°F) |
| EPDM | 150°C (302°F) | 175°C (347°F) |
| HNBR | 150°C (302°F) | 180°C (356°F) |
High-Temperature Rubber Applications
Heater Components
Rubber seals and gaskets in water heater thermostats and built-in gas heaters must withstand continuous heat exposure. Silicone and Viton are common choices.
Automotive Uses
Engine bay components like hoses and gaskets require heat-resistant rubbers that can survive under-hood temperatures exceeding 150°C (302°F).
Industrial Seals
According to Martin’s Rubber, FKM (Viton) offers the best combination of heat and chemical resistance for industrial sealing applications.
Improving Rubber’s Heat Resistance
Material Selection
Choosing the right rubber type is crucial:
- Silicone for moderate heat (up to 230°C/446°F)
- FKM/Viton for extreme heat and chemicals
- HNBR for oil resistance at high temps
Additives and Fillers
Manufacturers enhance heat resistance with:
- Thermal stabilizers
- Antioxidants
- Reinforcing fillers like silica
Design Considerations
Proper design can minimize heat effects:
- Thinner cross-sections dissipate heat better
- Thermal barriers protect critical areas
- Avoid sharp edges that concentrate stress
Testing Rubber Heat Resistance
Standard tests evaluate rubber performance at high temperatures:
- Heat aging tests (ASTM D573)
- Compression set (ASTM D395)
- Tensile strength retention
- Hardness changes
As noted by SSP Seals, proper material testing ensures rubber components will perform as expected in high-temperature applications.
