A Complete Guide to Stainless Steel Casing Oil Seals & Their Industrial Applications

Construction & Material Options

1. Stainless Steel Outer Housing
   • SUS304: General corrosion resistance for humid, freshwater and mild corrosive conditions.
   • SUS316L: Contains molybdenum, excellent resistance to chloride, salt spray, seawater and weak acids, widely adopted in marine, pharmaceutical and chemical industries.
     The stainless shell provides rigid interference fit after press installation. It avoids rust expansion and seizure inside the housing bore, which is a common failure of carbon steel skeleton seals.
2. Sealing Lip Types
   • Filled PTFE Lip (mainstream premium type): Carbon or graphite filled PTFE. No garter spring required. It relies on material memory to hold the shaft tightly. Single lip, double lip and helical oil return thread designs are available. Low friction, wide temperature range and dry-running tolerance.
   • Elastomer Lip (NBR / FKM): Equipped with stainless steel garter spring. NBR works well with mineral oils; FKM fluororubber delivers outstanding high temperature and chemical resistance.
3. Lip Configurations
   • Single lip: Retains lubricant, for clean, low-dust working conditions.
   • Double lip: Primary sealing lip plus auxiliary dust lip, blocking dust, moisture and contaminants for outdoor or dusty applications.
   • Oil return thread lip: Unidirectional pumping effect, suitable for pumps prone to leakage.

Key Performance Parameters

• Temperature range: -55℃ ~ +260℃
• Maximum surface speed: ≤30 m/s
• Working pressure: Up to 1.0–1.5 MPa for single lip; reinforced double lip version up to 3.0–3.5 MPa
• Compatible media: Lubricating oil, hydraulic oil, heat transfer oil, clean water, weak acid & alkali, compressed air and inert gas. FDA food-grade PTFE is available for hygienic applications.

Main Advantages

1. Superior anti-corrosion performance: Stainless steel housing will not rust under moisture and salt spray. No rust debris contaminates the process medium, easy disassembly for maintenance.
2. Wide temperature and high-speed capability: PTFE lip features low friction coefficient, reduces heat generation during high-speed rotation and supports intermittent dry running.
3. No spring failure risk for PTFE version: Eliminates spring corrosion and breakage failure points in aggressive environments.
4. Stable dimensional performance: Stainless steel casing maintains stable interference fit under temperature fluctuation, preventing outer ring creep.

Limitations

Typical Applications

Selection Guide

1. Dimensions: Shaft ID × Housing OD × Width
2. Lip structure: Single / double lip, oil return thread (left-hand or right-hand)
3. Housing material: SUS304 or SUS316L
4. Lip material: Filled PTFE, NBR or FKM
5. Working conditions: Medium, temperature, pressure, shaft surface speed, rotation direction, dust and chloride exposure
6. Certification requirements: FDA, 3.1 material certificate, etc.

Common Failure Modes & Tips

• Shaft grooving: Hard particles scratch the lip and abrade shaft surface. Solution: adopt double lip with dust exclusion. Recommended shaft roughness Ra 0.2~0.8.
• PTFE lip deformation: Caused by excessive shaft runout or eccentricity.
• Housing pitting: Wrong grade selection (SUS304 used in high chloride environment), replace with SUS316L.
• Installation damage: Lip scratching or shell deformation. Always use installation sleeve; never strike the seal directly.
• Chemical incompatibility: Lip swelling or hardening from incompatible fluid, re-select lip material.