bushing material selection

* Flange Bushing Depending on operating conditions, Metal-Polymer Hydrodynamic Composite Bearings, Metal-Polymer Self-lubricating Bearing Solutions …RED and the expected life and performance. Dimensional Stability.

PTFE composite bushings conform to ISO 3547:2006 and are ready for installation.
Any re-sizing of the bore, i.e. the sliding surface, will reduce the service life of the bushings and should only be done in exceptional cases. If re-sizing is necessary, the bore should be calibrated, using a mandrel/resizing tool . Because various criteria, like material and wall thickness of the housing as well as the deviation of cylindrical form, have to be taken into consideration, Viiplus recommends using a calibrated mandrel to re-size the bore. After resizing, bushing bore expansion tests and application field tests should be undertaken prior to the release of a final product.
Guideline values for the requisite interference of the calibrating mandrel as a function of the desired widening of the bushing bore for various bushing bore diameters can be obtained from diagram 1. The diagram is based on tests with bushings of different sizes and valid for bushings mounted in a housing.
with an outside diameter DG = 2* bushing outside diameter D . If mandrel expansion tests show that the bore is too wide, the calibrating mandrel should be reground and the tests repeated on new bushings.

PTFE composite bushings’ Chemical properties

The steel backing and the sintered tin/bronze layer are the primary factors in determining
the chemical resistance of Viiplus composite plain bearings, as the sliding (covering) layers
are resistant to most chemicals. The covering layer is virtually inert because of its PTFE
content, although at elevated temperatures molten alkali metals and free fluorine will attack it. The acetal resin-covering layer of the POM composite bearing is largely resistant to organic substances. At room temperature the sintered tin/bronze structure has good resistance to sea water, steam, atmospheric influences, salt solutions and sulphuric acid, but not to oxidizing acids or media containing ammonia.
All exposed surfaces of the steel backing are electrolytically tin-plated but this provides only limited protection against corrosion in most applications. In cases where the bearings are to be exposed to corrosive media, or where there is a danger of corrosion in the contact between the steel backing and the housing material, the backing can be protected by a nickel, chromium or zinc coating applied electrolytically. Further details can be supplied on request.

Where to use PTFE composite bearing?

Machinability of composite materials

PTFE composite bushings lubrication

The PTFE-based sliding surface permits smooth, low-friction operation without lubrication. During a short running-in phase, there will be some transfer of PTFE material from the sliding contact surface to the counterface. After this transfer, the characteristic low friction and wear properties of these bearings will be achieved.

The presence, or continuous supply of oil or other non-corrosive fluids may be advantageous and improve the performance of these bearings.

Characteristics

• Maintenance free
• Low friction coefficient
• Multiple areas of use
• Long lifetime

Type of applications

• Person lifts
• Packaging machines
• Pneumatic cylinders
• Pumps

Design

• Cylindrical bearings
• Flanged bearings
• Thrust washers
• Slide plates
• Drawing details

Metal-Polymer Self-lubricating Bushing

For technical information and standard dimensions, contact with us today!

The Unsung Hero: A Deep Dive into Metal-Polymer PTFE Low Friction Bearings

In the intricate world of mechanical design, seemingly small components often play the most critical roles. Bushings, or plain bearings, are prime examples. They manage friction, support loads, and ensure smooth movement between parts. While various bushing types exist, Metal-Polymer Low Friction Plain Bearings, particularly those utilizing a Bronze Backed PTFE structure, stand out for their unique blend of strength, self-lubrication, and performance.

Simply choosing any bushing isn’t enough. Selecting the right material and type is crucial for achieving desired performance, longevity, and avoiding costly downtime. Misapplication can lead to premature wear, high friction, seizure, or even catastrophic failure.

This article goes beyond the surface, exploring the composition, advantages, selection criteria, and applications of Metal-Polymer PTFE bearings, helping you understand why they are often the superior choice for demanding situations.

Deconstructing the Metal-Polymer PTFE Bearing

These aren’t simple, homogenous components. Their strength lies in their layered composite structure, typically consisting of:

1. Steel Backing: This forms the structural backbone. Usually made of low-carbon steel, it provides high mechanical strength, rigidity, and excellent load-bearing capacity. It allows the bushing to handle significant forces and press-fit securely into housings. The exterior is often tin-plated for corrosion resistance.

2. Porous Bronze Sinter Layer: This intermediate layer is crucial. It’s metallurgically bonded to the steel backing. Its porous structure serves two primary functions:

   • Mechanical Lock: It creates a strong anchor for the PTFE sliding layer.

   • Thermal Conductivity: Bronze efficiently draws heat away from the sliding surface, preventing overheating, especially under high load/speed conditions.

3. PTFE-Based Sliding Layer (Often Red or Black): This is the functional surface. A paste of Polytetrafluoroethylene (PTFE) mixed with special fillers (like graphite, MoS₂, or other performance enhancers) is rolled into the bronze sinter layer and heat-treated.

   • PTFE: Provides the extremely low coefficient of friction

   • Fillers: Enhance wear resistance, load capacity, and thermal conductivity, overcoming the inherent softness and tendency of pure PTFE to cold-flow (deform under load).

Visualizing the Structure:

Imagine a sandwich:

• Bread (Bottom): Strong Steel Backing

• Rough Spread (Middle): Porous Bronze Sinter (creating nooks and crannies)

• Filling (Top): PTFE + Fillers, pressed firmly into the bronze layer.

This composite design delivers benefits that single-material bushings often can’t match.

Why Choose Metal-Polymer PTFE Bearings? Key Advantages

These bearings offer a compelling combination of properties:

• Maintenance-Free Operation: The self-lubricating nature of the PTFE layer means no external grease or oil is required for operation. This is ideal for applications where lubrication is difficult, undesirable (e.g., food processing), or likely to be neglected.

• Very Low Friction: PTFE provides one of the lowest coefficients of friction of any solid material, minimizing energy loss and stick-slip issues (jerky movement at low speeds).

• High Load Capacity: The steel backing provides rigidity, allowing these bearings to handle significant static and dynamic loads, far exceeding most solid polymer bushings.

• Wide Temperature Range: They can typically operate from cryogenic temperatures (around -200°C) up to +280°C.

• Excellent Wear Resistance: The fillers embedded in the PTFE significantly enhance wear life, especially under dry running conditions. During the initial run-in period, a thin transfer film of PTFE moves to the mating shaft, further reducing friction and wear.

• Compact Design & Dimensional Stability: The thin-walled nature saves space and weight. The rigid steel backing ensures excellent dimensional stability – they don’t swell significantly with moisture like Nylon (PA) or deform easily under load like pure PTFE. They often conform to ISO 3547, ensuring interchangeability.

• Good Chemical Resistance: The PTFE sliding layer is resistant to almost all chemicals. Overall resistance depends on protecting the bronze and steel layers (tin plating helps significantly). Custom coatings (Nickel, Chrome) are possible for highly corrosive environments.

Forms and Types: Beyond the Basic Sleeve

While the standard cylindrical Sleeve Bushing is common, Metal-Polymer PTFE material lends itself to various forms:

• Flange Bushings: These are essentially sleeve bushings with an integrated flange at one end.

  • Function: The flange provides axial location, preventing the bushing from shifting side-to-side within the housing. It can also act as a thrust-bearing surface for light axial loads.

  • Applications: Automotive suspensions, linkages, pivot points where axial positioning is critical.

• Thrust Washers: Flat, washer-shaped components designed purely to handle axial loads between rotating or stationary parts.

• Slide Plates: Custom shapes and larger flat pads for linear motion applications.

Selection Deep Dive: Matching the Bearing to the Task

Choosing the right Metal-Polymer PTFE bearing involves considering operating conditions against the material’s capabilities:

What about “Hydrodynamic”? While these bearings can operate with lubrication (which may create a partial hydrodynamic film at higher speeds, improving performance), their primary strength lies in boundary and mixed lubrication regimes, including completely dry running. They don’t rely on generating a full hydrodynamic fluid film like traditional oil-fed plain bearings designed for high-speed rotation.

Installation, Machinability, and Important Considerations

• Installation: Metal-Polymer PTFE bushings are designed for press-fitting into a rigid housing bore with specific tolerances (check manufacturer recommendations). This ensures proper interference fit and prevents rotation.

• Machinability:

  • Sliding Surface (Bore): DO NOT MACHINE. The PTFE layer is thin and precisely formed. Machining or reaming removes the functional layer, drastically reducing bearing life. These bushings are supplied ready-to-use according to ISO 3547 dimensions.

  • Re-Sizing (Calibration): In exceptional cases, minor bore calibration might be possible using a specialized mandrel. This is complex, requires careful control (see manufacturer guidelines like the diagram mentioned), and extensive testing is mandatory afterward. It’s generally best avoided.

  • Other Surfaces: The outside diameter (OD) or ends (length) can often be machined (e.g., shortening length, adding chamfers) before installation. Ensure no burrs enter the sliding surface and protect newly exposed steel from corrosion. Drilling lubrication grooves or holes is possible but rarely needed. Work from the PTFE side inwards to minimize burrs.

Common Applications: Where Do They Shine?

Thanks to their versatile properties, you’ll find Metal-Polymer PTFE bearings in countless applications:

• Automotive: Suspension joints, steering systems, hinges (door, hood, trunk), pedal systems, seat mechanisms.

• Industrial Equipment: Pivot points on construction and agricultural machinery, hydraulic cylinder eyes and rod guides, conveyor systems, packaging machinery, textile machines, robotics.

• Aerospace: Control linkages, landing gear components.

• Office Equipment: Photocopiers, printers.

• Consumer Goods: Exercise equipment, appliances.

• Anywhere requiring: Maintenance-free pivots, high loads with slow/oscillating motion, compact design, or where lubrication is forbidden/impractical.

Finding the Right Solution

Manufacturers like VIIPLUS.COM offer a wide range of these bearings, including standard sleeve and flange types conforming to ISO 3547, as well as thrust washers and custom solutions. They can provide detailed technical data, competitive pricing, and guidance on selecting the optimal bearing for your specific operating conditions. Exploring their offerings and requesting quotes is a practical next step when considering these components.

Conclusion

Metal-Polymer PTFE Low Friction Plain Bearings are sophisticated composite components offering a powerful combination of high load capacity, self-lubrication, low friction, wide temperature range, and excellent dimensional stability. Their layered structure, leveraging the strength of steel, the bonding/thermal properties of bronze, and the lubricity of filled PTFE, makes them ideal for demanding applications where traditional lubricated bearings or simple polymer bushings fall short. By understanding their composition, advantages, and proper selection criteria, engineers and designers can leverage these remarkable bearings to create more reliable, efficient, and maintenance-free mechanical systems.