sealing rings

PTFE (Polytetrafluoroethylene) sealing rings and reinforced oil seals are a category of dynamic sealing components that use PTFE as the core material, often combined with a metal reinforcement (skeleton). They integrate PTFE's extreme chemical stability with the structural strength of metal, specifically designed to conquer challenging rotary or reciprocating sealing applications.

Core Characteristics Overview

1. Physical and Chemical Properties

   · Chemical Properties: Excellent. Resistant to strong acids, strong alkalis, and most organic solvents.

   · Physical/Mechanical Properties: Superior but not uniform. Wide temperature range (approx. -200 to 260°C), extremely low coefficient of friction (approx. 0.05-0.1), self-lubricating. Disadvantages include relatively poor elasticity and weak resistance to creep (for pure PTFE). Filling/modification (e.g., with glass fiber, copper powder) or the addition of a metal skeleton is required to significantly improve compression resistance, wear resistance, and dimensional stability.

   · Tolerance Range: Operating temperature approx. -200°C to 260°C, with short-term tolerance for higher temperatures. Operating pressure varies greatly with structure; pure PTFE is suitable only for medium-low pressure; designs with a skeleton or composite structures (e.g., Step-Seals, Glyd-Rings) can withstand high pressure, with some capable of handling 35-40 MPa.

Application Areas

· Highly Corrosive Conditions: Sealing for rotating shafts or reciprocating rods of pumps, reactors, and valves in industries like petrochemicals, pharmaceuticals, and electroplating.

· High-Purity and Sanitary Fields: Equipment in food, semiconductor, and biopharmaceutical industries requiring non-contaminating, easy-to-clean seals.

· Extreme Temperature Environments: Seals for cryogenic equipment (e.g., liquid nitrogen) or high-temperature steam systems.

· High-Pressure and Long-Life Requirements: Critical locations in hydraulic cylinders, construction machinery, aerospace, etc., requiring highly reliable, maintenance-free seals.

Core Advantages Compared to Others

· vs. Rubber Oil Seals (e.g., NBR, FKM): Superior in chemical inertness, temperature range, self-lubrication, and anti-aging lifespan, especially suitable for corrosive media and dry-running/lubrication-free applications where rubber fails. Disadvantages include higher initial cost and poorer elasticity.

· vs. Pure PTFE Soft Seals (e.g., Packing/Gland Packing): Mechanical strength, dimensional stability, sealing reliability, and service life are significantly improved due to the skeleton or composite structure, making them suitable for higher pressure and more precise dynamic sealing applications.

Usage Precautions

· Do Not Exceed Limits: Must not be operated beyond their rated temperature and pressure.

· Prevent Mechanical Damage: Special installation tools must be used. Ensure the surface finish and chamfer of the shaft and housing meet requirements to prevent scratching the sealing lip.

· Consider "Cold Flow" and Elasticity: Under long-term high-pressure static conditions, be aware of potential slow deformation (cold flow) and periodically check preload. Due to limited elasticity, their ability to compensate for shaft runout and eccentricity is limited.

· Ensure Correct Installation: Apply appropriate lubricant to the lip before installation. Confirm the sealing lip faces the media side; installation in reverse is strictly prohibited.

Key Points for Selection

· Step 1: Define Operating Conditions: Primarily identify the corrosiveness of the medium, operating temperature and pressure, motion type (rotary/reciprocating), and speed.

· Step 2: Choose Structural Type:

  · Standard PTFE Reinforced Oil Seal: Suitable for rotary shaft sealing with generally corrosive media.

  · High-Pressure Combination Seals (e.g., Step-Seals, Glyd-Rings): These are high-performance forms of PTFE seals, using a combination of a PTFE sealing ring + elastomer (e.g., rubber) + sometimes a metal anti-extrusion ring. Designed specifically for high-pressure, high-speed, long-life hydraulic/pneumatic systems.

  · Filled/Modified PTFE Sealing Rings: Select specific formulations based on needs like wear resistance (add glass/carbon fiber), thermal conductivity (add copper powder), or self-lubrication (add molybdenum disulfide).

· Step 3: Verify Dimensions and Materials: Precisely measure shaft diameter and housing dimensions to select the correct specification. Confirm PTFE material purity or modification type, and whether the skeleton, spring, and other metal components (e.g., 304/316 stainless steel) are resistant to environmental corrosion.

· Step 4: Supplier Confirmation: Provide complete operating conditions to a professional supplier and request written confirmation of the selection and recommendation of a specific product series (e.g., Step-Seals, Glyd-Rings). For critical applications, request material compatibility reports and life test data.

Summary

In summary, PTFE sealing rings/reinforced oil seals are among the ultimate solutions for dynamic sealing challenges involving strong corrosion, wide temperature ranges, high purity, and high pressure. Their core value lies in successfully compensating for the mechanical shortcomings of pure PTFE material through "metal skeleton reinforcement" or "combination with elastomers." This establishes a robust, durable, and nearly maintenance-free sealing barrier beyond the failure limits of rubber seals. The key to selection is first identifying the core contradiction of corrosiveness, temperature, and pressure. Then, based on the motion type and pressure level, make a precise choice between standard reinforced oil seals and high-pressure combination seals (Step-Seals, Glyd-Rings, etc.). When traditional seals are plagued by corrosion, wear, or frequent leakage, correctly selected PTFE reinforced oil seals or combination seals often provide a reliable guarantee for long-term, stable equipment operation.