The relationship between rubber material hardness and friction is quite significant. Hardness generally refers to the material’s resistance to indentation, measured using the Shore A scale for softer rubbers. Here’s how they are related:
Lower Hardness:
- Higher Friction: Softer rubber tends to exhibit higher friction due to its increased ability to conform to surface irregularities, creating more contact area between the rubber and the mating surface. This can increase the resistance to sliding, making the assembly or movement of parts more challenging.
- Increased Grip: The softer material’s ability to deform also results in a stronger grip on surfaces, which can be beneficial in applications requiring sealing or adherence but problematic when minimizing assembly force is a priority.For example, tires with softer rubber compounds provide stronger grip.
Higher Hardness:
- Lower Friction: As hardness increases, rubber becomes stiffer, reducing its ability to deform and make as much surface contact. This results in a lower coefficient of friction, making it easier to slide or insert the rubber part into another component, such as during assembly into a PTFE tube.
- Reduced Grip: Harder rubbers provide less grip or adhesion to surfaces, which can reduce the sealing effectiveness but make handling and installation easier.
Thus, lower hardness rubbers have more friction and higher hardness rubbers have less. However, the exact nature of friction also depends on other factors like surface texture, lubrication, temperature, and rubber formulation (presence of additives).
In practical applications, balancing rubber hardness and the friction needed for a specific performance (e.g., sealing vs. ease of assembly) is key.
Here is a table presenting the surface friction coefficients of common rubber materials:
| Rubber Material | Static Friction Coefficient | Dynamic Friction Coefficient |
|---|---|---|
| Natural Rubber (NR) | 0.7 – 1.0 | 0.5 – 0.7 |
| Chloroprene Rubber (CR) | 0.6 – 0.8 | 0.5 – 0.6 |
| Nitrile Rubber (NBR) | 0.5 – 0.8 | 0.4 – 0.6 |
| EPDM Rubber (EPDM) | 0.6 – 0.9 | 0.5 – 0.7 |
| Fluorocarbon Rubber (FKM) | 0.6 – 0.8 | 0.4 – 0.6 |
| Silicone Rubber (VMQ) | 0.4 – 0.6 | 0.3 – 0.5 |
We can offer coating solutions on O-rings to reduce assembly force without compromising the performance of the rubber material. One of the coatings we provide is our PF coating. It can reduce friction, while maintaining the essential properties of the O-ring, such as elasticity and chemical resistance.
Please contact us, OBT Rubber Seal, for better understanding your technical requirement and our proposal.
