Seals play a crucial role in machinery, and the choice of lubricant directly affects their lifespan and performance. Incompatibility between seal materials and lubricants can lead to swelling, hardening, cracking, or even seal failure. Therefore, during the selection and application of seals, it is essential to fully consider their chemical compatibility. This article will explore the compatibility of seal materials with different types of lubricants (such as mineral oil, synthetic oil, water-based liquids), and how to optimize seal selection to enhance equipment reliability and service life.

1. Interaction between seal and lubricant

The main function of lubricants is to reduce friction, minimize wear, and improve the operational efficiency of equipment. However, the components of lubricants (such as base oils, additives, antioxidants, etc.) may chemically react with sealing materials, leading to a decline in seal performance. Here are several typical ways these interactions occur:

Swelling: the volume of the sealing material expands after absorbing the lubricant, resulting in the failure of the seal.

Hardening: Certain components in the lubricant will extract the plasticizer from the seal, making it hard and brittle.

Degradation: Some lubricants contain strong oxidizing components that may decompose or corrode seal materials.

Penetration: Low viscosity lubricants may penetrate into the seal and affect its structural integrity.

2. The effect of different lubricants on seals

(1) Mineral oil

Mineral oil is the most common industrial lubricant, widely used in hydraulic systems, gearboxes, bearings and other equipment. Mineral oil is usually compatible with rubber and plastic seals, but different sealing materials have different performance:

Preferred sealing materials: NBR (nitrile rubber), FKM (fluororubber), HNBR (hydrogenated nitrile rubber)

Potential problems: Some mineral oils may cause EPDM (ethylene propylene diene monomer) swelling or degradation

(2) Synthetic oil (PAO, ester, silicone oil)

Synthetic oil is widely used in aviation, automobile, wind power and other fields because of its excellent high and low temperature performance and chemical stability. However, different types of synthetic oil have different effects on seals.

PAO (poly α -olefin): relatively stable and compatible with NBR and FKM, but may affect silicone rubber (VMQ)

Ester synthetic oil: it is easy to undergo plasticizer extraction with NBR, resulting in hardening of the seal

Silicone oil: good compatibility with most sealing materials, but may affect the mechanical strength of some polymer sealing materials

(3) Water-based liquids (emulsified oil, brake fluid, coolant)

Water-based lubricants are widely used in hydraulic systems, braking systems and cooling systems because of their environmental protection and low viscosity characteristics. However, the presence of water may lead to the hydrolysis, swelling or degradation of some sealing materials.

Emulsified oil: usually compatible with NBR, but may affect PU (polyurethane) seals

Brake fluid (DOT 3/4/5): Ethylene glycol based brake fluid (DOT 3/4) can severely damage NBR and EPDM seals should be used

Coolant: Long-term exposure may cause aging of silicone rubber. FKM seals resistant to chemical corrosion are recommended

3. How to optimize the selection of seals

(1) Select sealing materials according to lubricants

When selecting seals, it is necessary to select suitable sealing materials according to the specific type of lubricant. The following table summarizes the compatibility between different lubricants and sealing materials:

(2) Measures to prevent seal failure

laboratory test

Before actual use, the seal and lubricant were soaked to observe the volume change, hardness change and chemical degradation.

It is recommended to conduct ASTM D471 (liquid compatibility test of rubber) or ISO 1817 (tolerance test of rubber and liquid).

Optimize the sealing design

Choose materials with strong resistance to chemical corrosion, such as fluororubber (FKM), hydrogenated nitrile rubber (HNBR) and so on.

Special coating or surface treatment is used to enhance the oil resistance and aging resistance of the seal.

Regular inspection and replacement

Make a reasonable maintenance plan, check the aging of seals regularly, and avoid long-term lubricant effects leading to seal failure.