Nitrile Rubber Hardness Specification Guide
Nitrile Rubber Hardness Specification Guide
Nitrile rubber (NBR) compounds are available from 40 to 95 Shore A. Picking the correct hardness is essential for balancing sealing force, extrusion resistance, and dynamic wear. Use this guide to align hardness with your operating conditions.
## Hardness vs. Application
| Hardness (Shore A) | Typical Uses | Notes |
| — | — | — |
| 40β50A | Hand pumps, low-pressure vacuum, delicate assemblies | Highest flexibility but limited extrusion resistance |
| 60β70A | General-purpose static seals, moderate pressure hydraulics | Most common range; good balance of compression and sealing force |
| 75β80A | Dynamic shafts, rotary seals, medium-high pressure | Reduces rolling, improves wear resistance |
| 85β90A | High-pressure hydraulics ( >20β―MPa ), blow-out resistant seats | Requires precise hardware; add backup rings |
| 95A | Extrusion-critical or high-gap applications | Consider HNBR or FKM for better mechanical strength |
## Selection Factors
1. **Pressure & hardware clearance** β higher pressure or larger extrusion gaps demand higher hardness and backup rings.
2. **Dynamic vs. static** β dynamic applications benefit from 70β80A to manage friction and wear.
3. **Temperature** β higher hardness compounds may stiffen at low temperatures; confirm TR-10 values.
4. **Media** β chemical exposure can soften or harden compounds; plan for post-immersion hardness testing.
5. **Installation** β very hard seals require careful chamfers and lubrication during assembly.
## Testing & Tolerances
– Measure hardness per ASTM D2240 on a flat specimen of sufficient thickness.
– Maintain Β±5 Shore A tolerance unless otherwise specified.
– After chemical immersion or heat aging, re-check hardness to monitor degradation.
– For dynamic shafts, pair hardness with surface finish (Ra β€ 0.4β―Β΅m) and ensure adequate lubrication.
## Related Resources
– [Nitrile Temperature Resistance Guide](/materials/nitrile-rubber-temperature-resistance-guide/)
– [Oil-Resistant NBR Guide](/materials/oil-resistant-nitrile-rubber-o-ring/)
– [Design Services](/services/design-services/) β verify groove dimensions and hardware tolerances for chosen hardness.
Unsure which hardness to specify? Submit operating pressure, gap, and temperature data via the [custom quote form](/quote/custom/) for tailored recommendations.
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