The logic of selection: environment first, hardness second
Three things decide the life of a rubber part: operating temperature, the fluids it touches (oil, fuel, water, chemicals) and the outdoor environment (ozone, UV, weather). The polymer type is chosen for these three; Shore A hardness, strength and the cure system are then tuned within that polymer by the recipe. The table gives general directions; exact limits depend on the recipe.
| Compound | Continuous service temperature (approx.) | Oil / fuel | Ozone / weather | Strength |
|---|---|---|---|---|
| NR (natural rubber) | −50 … +70 °C | Poor | Poor (needs protection) | Highest elasticity, tensile and tear, dynamic fatigue life |
| SBR | −40 … +80 °C | Poor | Poor–fair | Abrasion resistance, economical, common in NR blends |
| EPDM | −45 … +130 °C | Poor | Excellent | Outdoor, hot water/steam, polar fluids; long life |
| NBR (nitrile) | −30 … +100 °C | Good–excellent (by ACN content) | Poor | Mineral oil, fuel and hydraulic fluid resistance |
| CR (chloroprene) | −35 … +100 °C | Moderate | Good | Balanced profile, flame retardance, adhesion |
Recommendations by application
- Air-spring bellows and reinforced parts: NR and NR/SBR based coating compounds with a fabric adhesion package. See cord fabric coating.
- Vibration mounts, engine mounts: NR (high dynamic life, low heat build-up); CR or NR/CR where oil contact exists.
- Outdoor seals and profiles, automotive weatherstrips: EPDM.
- Oil seals, O-rings, fuel hose, hydraulic diaphragms: NBR; consider HNBR above 100 °C.
- Belts, hose covers, general technical parts: CR or SBR.
- Conveyor belting and abrasion applications: NR/SBR with highly reinforcing carbon black.
What to put in a specification
- Polymer type (or the environmental conditions that determine it).
- Shore A hardness and tolerance (e.g. 60 ±5).
- Minimum tensile strength and elongation at break.
- Ageing requirement (e.g. change in hardness and tensile after 70 h at 100 °C).
- Fluid immersion requirement (which fluid, hours, °C, volume-change limit).
- Cure system preference (sulphur / peroxide) and moulding method (compression, injection, transfer, calender).
- Delivery form: slab, calendered sheet/strip, thickness and width.
If you have no specification, we can start from an existing part, a drawing or a competitor compound's test report; our formulation team derives the target values. The technical compounds page gives detail by polymer.
Frequently asked questions
EPDM or NBR?
NBR if the part touches oil or fuel; EPDM if it works outdoors, in hot water or steam. They are not interchangeable: EPDM swells in mineral oil, NBR cracks in ozone.
Natural rubber or SBR?
NR for parts needing dynamic load capacity and maximum elasticity (mounts, bellows); SBR or an NR/SBR blend where abrasion and cost come first.
Is hardness set by the polymer?
No. Hardness is adjusted within the same polymer through filler and oil loading; most polymers can be compounded between 30 and 90 Shore A.
Do you make silicone or FKM compounds?
Our production focuses on black technical compounds based on NR, SBR, EPDM, NBR and CR; for silicone or fluoroelastomers we review your specification and advise.