Rubber seals are indispensable critical components in industrial equipment, automobiles, aerospace, and everyday products. Their performance directly affects the system’s sealing performance, safety, and service life. Different rubber materials, due to differences in their chemical structure and physical properties, are suitable for vastly different working conditions. Incorrect selection or improper use can lead to leakage and failure, and in severe cases, cause equipment failure or even safety incidents. Therefore, understanding the precautions for using sealants made from various materials is crucial.
This article systematically summarizes the characteristics of common rubber sealing materials and the key precautions during their use, providing a practical reference guide.
I. General Precautions (Applicable to All Materials)
Before discussing specific materials, the following points are general guidelines that should be followed for all rubber seals:
- Correct Installation: Before installation, ensure the sealing groove is clean, free of burrs and damage. Never use sharp tools for forced installation. It is recommended to use dedicated installation tools and apply appropriate lubricant (grease or silicone grease compatible with the medium) to prevent lip flipping, scratching, or twisting.
- Avoid Overstretching: During installation, avoid exceeding the ultimate elongation rate of the seal material to prevent permanent deformation or internal damage.
- Storage Conditions: Seals should be stored in a cool, dry, and dark environment, away from ozone sources (e.g., motors, high-voltage electrical equipment). The ideal storage temperature is 5-25°C. The “first in, first out” principle should be followed to avoid aging due to long-term storage.
II. Precautions for Specific Seal Materials
The following details the characteristics and special precautions for several mainstream rubber materials.
1. Nitrile Rubber (NBR) – The Universal Oil Seal King
- Characteristics: Excellent resistance to petroleum-based hydraulic oils, lubricants, fuels, and other mineral oils and hydrocarbon solvents; good abrasion resistance and gas tightness; but poor resistance to ozone, ketones, esters, and chlorinated hydrocarbons.
- Precautions:
- Media Compatibility: Strictly avoid use in phosphate ester-based hydraulic fluids (e.g., Skydrol), brake fluids (DOT3/DOT4), ketones (e.g., acetone), and ester solvents.
- Temperature Range: Standard NBR is typically suitable for conditions ranging from -40°C to +120°C. High temperatures accelerate its aging—pay attention to the continuous operating temperature limit.
- Ozone Protection: Avoid prolonged exposure outdoors or in environments with ozone, as it is highly prone to cracking.
2. Fluoroelastomer (FKM/Viton®) – The High-Temperature and Chemical Resistance King
- Characteristics: Exceptional high-temperature resistance, resistance to many chemicals (oils, acids, hydrocarbon solvents), ozone, and weathering. Represents high-performance sealing.
- Precautions:
- Low-Temperature Performance: Poor low-temperature performance; the low-temperature retraction temperature (TR10) for standard FKM is around -20°C, making it unsuitable for deep cryogenic environments. Special low-temperature grades (e.g., GLT type) are available.
- Media Compatibility: Not resistant to hot steam, amine compounds (e.g., some engine oil additives), ketones, low molecular weight esters (e.g., ethyl acetate), and Skydrol hydraulic fluid. Always check a chemical compatibility chart before selection.
- High-Temperature Application: Although resistant to high temperatures (can exceed 200°C), note that heat can cause hardening and reduce elasticity.
3. Silicone Rubber (VMQ) – The Broad Temperature Range Food-Grade Choice
- Characteristics: Extremely wide working temperature range (-60°C to +200°C and above), excellent ozone and weather resistance, inert and non-toxic. Often used for food, medical, and high-temperature static sealing applications.
- Precautions:
- Mechanical Strength: Its abrasion resistance and tear strength are among the poorest of common rubbers. Not suitable for dynamic sealing or applications with severe friction or shear forces.
- Media Compatibility: Not resistant to petroleum-based oils (which cause swelling), concentrated acids, alkalis, and high-pressure steam.
- Gas Permeability: High permeability to gases (especially carbon dioxide), making it unsuitable for high vacuum or applications requiring extremely high gas tightness.
4. Ethylene Propylene Diene Monomer (EPDM) – The Water and Steam Expert
- Characteristics: Outstanding resistance to hot water, steam, aging, ozone, and weather. Widely used in hot water systems, automotive cooling systems, and outdoor seals.
- Precautions:
- Media Compatibility: Its biggest weakness is resistance to virtually all mineral oils, lubricants, and fuels. Contact causes severe swelling and rapid failure. Only suitable for polar solvents and some brake fluids (DOT-based).
- Temperature: Excellent resistance to high-temperature steam, but note the compression set performance at high temperatures.
5. Hydrogenated Nitrile Rubber (HNBR) – The High-Performance NBR Upgrade
- Characteristics: Retains the oil resistance of NBR while significantly improving heat resistance, ozone resistance, and abrasion resistance. Overall performance is superior to NBR.
- Precautions:
- Its precautions are similar to NBR but with higher tolerance limits. Similarly, not resistant to phosphate ester hydraulic fluids and brake fluids. Although ozone resistant, extreme environments should still be avoided.
6. Polytetrafluoroethylene Coated Rubber (PTFE Encapsulated Rubber) – The Ultra-Low Friction Solution
- Characteristics: Combines the excellent chemical resistance and low friction coefficient of PTFE with the high elasticity of a rubber O-ring. Used for dynamic sealing without lubrication or with special media.
- Precautions:
- Avoid damaging the coating: The PTFE layer is very thin. Exercise extreme care during installation; any scratch can compromise its sealing ability.
- Pressure Resistance: Its pressure-bearing capacity is provided by the internal rubber core; pay attention to the working pressure range.
III. Summary of Selection and Use Decision Process
To ensure reliable seal operation, it is recommended to follow these steps:
- Identify the Medium: Determine what fluid or gas the seal will contact (e.g., ISO 46 hydraulic oil, tap water, acetone, ozone).
- Determine Operating Conditions: Precisely identify the working temperature range (max/min temperature), pressure (peak pressure, pulsation frequency), and motion type (static, dynamic reciprocating, rotary).
- Consult Compatibility Charts: Based on the medium and conditions, refer to a rubber material chemical compatibility chart to shortlist several candidate materials.
- Consider Special Requirements: Are there any special needs like food grade, flame retardancy, conductivity/insulation?
- Final Verification: Whenever possible, test samples under simulated actual conditions before final selection.
Conclusion
Although small, rubber seals are critical for system reliability. There is no “universal” rubber material that can handle all conditions. The key to success lies in a deep understanding of the performance boundaries of each material and strictly following the precautions for selection, installation, and maintenance. Through scientific selection and correct use, the effectiveness of seals can be maximized, ensuring long-term, stable, and safe operation of equipment.
Post time: Sep-01-2025