PTFE (Polytetrafluoroethylene) plays a crucial role in structural sliding bearings due to its unique properties, primarily its low coefficient of friction and chemical resistance. These bearings are designed to accommodate vertical loads and movement in infrastructure applications, such as bridges and buildings. PTFE sheets are bonded to metal plates, with stainless steel plates on top to facilitate smooth sliding. The design considers compressive strength, lateral movement restrictions, and minor rotations, ensuring stability and longevity. Despite its advantages, PTFE has limitations like wear sensitivity and creep, which are mitigated by using filled PTFE or complementary materials like elastomers.
Key Points Explained:
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Function of PTFE in Sliding Bearings
- PTFE sheets are bonded to metal plates, acting as a sliding surface against stainless steel plates. This setup leverages PTFE's low friction (coefficient ~0.05–0.10) to enable smooth movement under vertical loads.
- The stainless steel plate is welded to another structural element, transferring loads while allowing displacement.
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Load Capacity and Design Considerations
- PTFE can withstand compressive stresses up to 40 MPa, but a safety factor of 50–60% is applied, limiting operational loads to 15–20 MPa.
- The required PTFE area is calculated based on load distribution and adjusted to fit the bearing assembly. For example, a 1000 kN load at 15 MPa requires ~667 cm² of PTFE.
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Movement Control Mechanisms
- Lateral movement is restricted using guide plates or dowel pins to ensure unidirectional sliding. Dowel pins must resist lateral forces without bending.
- Minor rotations (fractions of a degree) are accommodated by elastomers (e.g., neoprene), while spherical bearings address larger misalignments.
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Advantages of PTFE
- Chemical Resistance: Ideal for harsh environments, such as coastal or industrial settings.
- Temperature Stability: Performs reliably from -200°C to +260°C.
- Applications extend beyond bearings to custom ptfe parts like gaskets and valves.
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Limitations and Mitigations
- Wear and Creep: Unfilled PTFE wears quickly; fillers (e.g., glass fiber, bronze) improve durability.
- Non-Weldable: Requires mechanical fastening or adhesive bonding.
- Low Radiation Resistance: Unsuitable for nuclear applications.
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Industry Applications
- Common in bridges, seismic isolators, and heavy machinery.
- Also used in chemical processing (linings), medical devices (implants), and food processing (non-stick surfaces).
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Complementary Materials
- Elastomers (neoprene/silicone) compensate for PTFE's rigidity in rotational scenarios.
- Stainless steel (grade 304/316) ensures corrosion resistance in sliding interfaces.
By addressing these factors, PTFE sliding bearings achieve a balance of performance and reliability, making them indispensable in modern infrastructure. Their design exemplifies how material science meets engineering precision to solve real-world challenges.
Summary Table:
| Aspect | Details |
|---|---|
| Function | PTFE sheets bonded to metal plates enable smooth sliding under high loads. |
| Load Capacity | Operates at 15–20 MPa (40 MPa max with safety factor). |
| Movement Control | Guide plates/dowel pins restrict lateral movement; elastomers handle rotation. |
| Advantages | Chemical resistance, temperature stability (-200°C to +260°C), low friction. |
| Limitations | Wear/creep mitigated by fillers (glass fiber, bronze); non-weldable. |
| Applications | Bridges, seismic isolators, chemical processing, medical devices. |
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