A polyurethane (PU) oil seal is a sealing component made with polyurethane (PU) elastomer as the core sealing material, supplemented by a metal skeleton (or skeleton-free design). It is mainly used in dynamic sealing scenarios for rotating shafts or reciprocating shafts. Its core function is to prevent the leakage of internal fluids such as lubricating oil and hydraulic oil in equipment, while also keeping out external dust, impurities, moisture, and other contaminants, thus ensuring the normal operation of mechanical equipment.
The physical and chemical properties of polyurethane (PU) give it more prominent comprehensive advantages compared to traditional rubber oil seals (e.g., nitrile rubber (NBR), fluororubber (FKM)), which is the core reason for its wide application:
- Superior Wear Resistance: The molecular structure of polyurethane endows it with excellent friction resistance. Its wear rate is only 1/5 to 1/10 that of nitrile rubber, making it particularly suitable for shaft sealing in high-speed, long-cycle operations, and significantly extending the service life.
- Excellent Oil Resistance and Media Resistance: It has good resistance to common industrial oils such as mineral oil, hydraulic oil, and gear oil, and is less prone to swelling, hardening, or cracking. It only has weak resistance to strongly polar solvents (e.g., ketones, esters).
- Outstanding Elasticity and Sealing Performance: Within the temperature range of -30°C to 80°C (extendable to -50°C to 120°C with special formulations), it can maintain stable elasticity. Even if the shaft has slight eccentricity or vibration, it can tightly fit the shaft surface through the pre-compression of the lip to prevent leakage.
- High Strength and Tear Resistance: Its tensile strength and tear strength are much higher than those of ordinary rubber. During installation or use, it is less likely to suffer lip damage caused by external forces (e.g., shaft impact, contact with installation tools), reducing maintenance costs.
The structural design of polyurethane oil seals needs to adapt to different movement modes (rotation/reciprocation) and working conditions. Common types are as follows:
-
| Structural Type |
Core Features |
Application Scenarios |
| Single-lip Skeleton Oil Seal |
Only 1 sealing lip, with a metal skeleton (enhancing rigidity) |
Low-speed, low-pressure rotating shafts (e.g., motor shafts) |
| Double-lip Skeleton Oil Seal |
2 sealing lips (the main lip prevents oil leakage; the secondary lip keeps out impurities) |
High-speed, dusty scenarios (e.g., automotive crankshafts) |
| Skeleton-free Polyurethane Oil Seal |
No metal skeleton, soft overall and deformable |
Reciprocating shafts (e.g., hydraulic cylinder piston rods) |
| Combined Oil Seal |
PU lip + other materials (e.g., polytetrafluoroethylene (PTFE)) |
High-temperature, high-pressure, or strongly corrosive working conditions (e.g., hydraulic pumps) |
With the above characteristics, polyurethane oil seals are widely used in industries such as industry, automotive, and construction machinery. Specific application scenarios include:
- Automotive Industry: Sealing for engine crankshafts, camshafts, transmission input/output shafts, and shock absorber piston rods.
- Hydraulic and Pneumatic Equipment: Dynamic sealing for hydraulic cylinder piston rods, hydraulic pump main shafts, and air cylinder pistons.
- Construction Machinery: Sealing for excavator hydraulic motors, loader transmissions, and crane winch shafts (withstanding harsh environments such as dust and vibration).
- General Machinery: Sealing for motor shafts, main shafts of pumps (e.g., centrifugal pumps, gear pumps), and printing machine roller shafts.
Household Appliances and Medical Equipment: Sealing for washing machine motor shafts and transmission shafts of medical equipment (e.g., blood analyzers) (meeting requirements for low noise and high cleanliness)。
To ensure the optimal sealing effect of polyurethane oil seals, the following key points should be noted:
- Installation Specifications: During installation, ensure there are no burrs or scratches on the shaft surface (surface roughness is recommended to be Ra ≤ 0.8μm) to avoid damaging the sealing lip. Meanwhile, use specialized installation tools; hard knocking or hitting is prohibited to prevent lip deformation.
- Media Compatibility: Confirm the working medium (e.g., hydraulic oil type, temperature range) that the oil seal is compatible with to avoid swelling or aging of the oil seal due to inappropriate media.
- Maintenance Cycle: Although it has a long service life, regularly check the oil seal for signs of lip wear, cracks, or oil leakage. Especially under high-temperature and high-load working conditions, it is recommended to shorten the inspection interval.
- Storage Conditions: Unused oil seals should be stored in a cool, dry, and light-shielded environment, avoiding direct contact with grease and solvents to prevent premature aging of the material.
With the core advantages of high wear resistance, long service life, and strong sealing performance, polyurethane oil seals are the preferred alternative to traditional rubber oil seals in dynamic sealing scenarios, especially for equipment with high requirements for reliability and maintenance costs. When selecting, it is necessary to match the appropriate structural type and formula based on specific working conditions (speed, pressure, medium, temperature) to maximize its application value.
