Table of contents：
1. O-ring material selection
2. O-ring size calculation
3. Coating on O-ring
4. O-Ring weight calculator
1. O-Ring Material Selection
O-Ring material need to be selected mainly according to the working enviroment. It is included such as:
- O-ring working temperature range
- the medium contacting with o-rings (such as chemical, gas, oil,fuel)
- O-ring working pressure
1.1 Here is the chart listing the gerneral performance of different rubber material.
| Rubber Material | Temperature Range | Chemical Resistance | Abrasion Resistance | Compression Set | Flexibility | Cost |
| Nitrile (NBR) | -40°C to +120°C | Good | Good | Good | Good | Moderate |
| HNBR (Hydrogenated Nitrile) | -30°C to +150°C | Excellent | Excellent | Excellent | Good | High |
| Silicone (VMQ) | -60°C to +230°C | Fair | Fair | Fair | Excellent | Moderate |
| EPDM(Ethylene Propylene Diene Monomer) | -50°C to +150°C | Good | Good | Good | Good | Moderate |
| Fluorocarbon (FKM/Viton) | -20°C to +200°C | Excellent | Excellent | Excellent | Poor | High |
| FVMQ (Fluorosilicone) | -60°C to +225°C | Excellent | Fair | Good | Excellent | High |
| AEM (Ethylene Acrylic) | -40°C to +150°C | Excellent | Fair | Good | Good | High |
| ACM (Polyacrylate) | -25°C to +150°C | Good | Good | Good | Good | Moderate |
| Neoprene | -40°C to +120°C | Good | Excellent | Good | Good | Moderate |
| FFKM (Perfluoroelastomer) | -20°C to +325°C | Excellent | Excellent | Excellent | Poor | Very High |
Reference Reading:
- HNBR O-ring including lubricants
- Silicone/VMQ O-ring including Lubricants
- FKM O-Ring including Lubricants
- Abrasion Resistance/Wear Resistance Performance of Rubber
- How to choose between HNBR and AEM?
- Properties and Applications of HNBR rubber
- How to choose between HNBR and FKM(Viton) for O-Ring/gasket?
- Low Temperature FKM Rubber: Ideal for Automotive, Aerospace, and Chemical Processing
- FVMQ: Low-Temperature and Chemical Resistance Rubber Material
- Conductive rubber for an EMI shielding
- Certifications for Rubber Seals in Food and Hygiene industry:FDA,WRAS, NSF61, and KTW
1.2 Choose the right O Ring Hardness for Working Pressure Conditions
2. Calculate O-Ring Dimensions
2.1 Define the interference between the groove and the O-ring
1)Static Sealing Applications:
For static sealing applications, such as groove or flange sealing, the interference or compression set is typically in the range of 10% to 30% of the O-ring’s cross-sectional diameter.For example, if the O-ring’s cross-sectional diameter (CS) is 5 mm, the interference may range from 0.5 mm to 1.5 mm.
2)Dynamic Sealing Applications:
In dynamic sealing applications, such as reciprocating or rotary motion seals, the interference is usually lower to minimize friction and wear.
The interference for dynamic seals is typically in the range of 5% to 15% of the O-ring's cross-sectional diameter.
For example, if the O-ring's cross-sectional diameter (CS) is 5 mm, the interference fit may range from 0.25 mm to 0.75 mm.
3) Material Considerations:
Softer O-ring materials, such as silicone or EPDM, may require less interference to achieve proper sealing compared to harder materials like fluorocarbon (FKM) or nitrile (NBR).
The groove should be designed to provide sufficient compression on the O-ring without causing excessive deformation or stress.
Reference Reading:
2.2 Define the tolerance of O-ring
The tolerance standards for O-rings are primarily based on international standards such as ISO 3601-3, AS568 (U.S. standard), JIS B 2401 (Japanese standard), and GB 3452.1 (Chinese standard). These standards define tolerance ranges for different precision grades to meet various application requirements.
The ISO 3601-3 standard specifies tolerances for three grades:
P Grade: Designed for high-performance sealing needs, with a tolerance range of ±0.12 mm.
G Grade: Suitable for general sealing needs, with tolerances varying based on the inner diameter. For example:
Inner diameter of 1.80–6.29 mm: Tolerance ±0.13 mm
Inner diameter of 6.30–10.59 mm: Tolerance ±0.14 mm
S Grade: Intended for strict sealing requirements, with even smaller tolerance ranges.
Inner Diameter Tolerance Standards
| Inner Diameter (ID) Range (mm) | Tolerance (±mm) |
|---|---|
| 0.00 – 1.79 | ±0.10 |
| 1.80 – 6.29 | ±0.13 |
| 6.30 – 10.59 | ±0.14 |
| 10.60 – 18.99 | ±0.17 |
| 19.00 – 31.49 | ±0.22 |
| 31.50 – 41.19 | ±0.30 |
| 41.20 – 51.49 | ±0.36 |
Cross-Section Diameter Tolerance Standards
| Cross-Section (CS) Range (mm) | Tolerance (±mm) |
|---|---|
| 0.00 – 1.79 | ±0.07 |
| 1.80 – 2.64 | ±0.08 |
| 2.65 – 3.54 | ±0.09 |
| 3.55 – 5.29 | ±0.10 |
| 5.30 – 6.99 | ±0.13 |
| 7.00 – 8.00 | ±0.15 |
| 8.01 – 10.00 | ±0.20 |
3. Coating on O-ring
For some application, coating is required to be applied on the surface of the o ring for :
- less friction
- less assembly force
- better chemical resistance
From reducing friction and improving chemical resistance to extending durability and enabling use in extreme temperatures, the right coating can make a substantial difference. We could offer PTFE, PFPE, or other specialized coatings, based on the understanding of your application.
Reference Reading:
- How to choose correct coating for O-Rings?
- What factors are related to the coefficient of friction of rubber surface?
- How is the relationship between rubber hardness and friction?
4. O-Ring weight calculator
O-ring Weight Calculator
We OBT could offer O-Rings with different types rubber material, and different coatings including PTFE and PF coating.
