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The support ring of the hydraulic cylinder (also called guide ring/belt, wear-resistant ring) is one of the core components of the hydraulic cylinder. The choice of its material is directly related to the performance, life and reliability of the hydraulic cylinder.
I. Core Functions of Support Rings
1. Guiding and Supporting: Guides the piston and piston rod in linear motion, prevents direct contact between metal parts (piston and cylinder, piston rod and guide sleeve), withstands radial forces, and prevents eccentric wear.
2. Friction Reduction: Forms a low-friction pair with the metal cylinder/rod, ensuring smooth movement.
3. Absorbs Radial Force: Withstands lateral forces caused by load and mounting configuration.
II. Common Material Properties and Applications
1. Polyoxymethylene (POM)
- Advantages: High mechanical strength and excellent rigidity, among the best among engineering plastics; excellent fatigue resistance; low coefficient of friction and good wear resistance; self-lubricating properties; and low cost.
- Disadvantages: Not resistant to strong acids and alkalis; average high-temperature performance (long-term operating temperature approximately -40°C to +100°C); and some hygroscopicity.
Applications:
- One of the most commonly used and versatile options. Widely used in low- to medium-pressure, standard-duty industrial and vehicle hydraulic cylinders.
- Suitable for systems using mineral oil-based hydraulic fluids, water-glycol, and other fluids.
- Examples include auxiliary cylinders in injection molding machines, machine tools, agricultural machinery (tractor lift cylinders), and construction machinery.
2. Phenolic Fabric Resin (PF)
- Advantages: Extremely high compressive strength and impact resistance, excellent wear resistance, high temperature resistance (up to 160°C or above), low deformation resistance, and the ability to withstand significant impact loads and edge pressure.
- Disadvantages: The material is relatively hard, with a low tolerance for embedded foreign matter. Care must be taken during installation to avoid scratching the sealing surface.
Applications:
- Exercises involving heavy loads, high pressures, high temperatures, and severe shock loads.
- Commonly used in core cylinders in construction machinery and heavy industry.
- For example: boom and arm cylinders in excavators, cylinders in large hydraulic presses, and cylinders in metallurgical equipment. In these applications, POM may not be strong enough, and phenolic cloth is an ideal choice.
3. Copper Support Rings/Copper-Based Powder Metallurgy (Oil-Containing Bearings)
- Advantages: Excellent thermal conductivity, quickly dissipates frictional heat; high hardness, high compressive strength, and exceptionally high-temperature resistance (up to 250°C).
- Disadvantages: Requires a lubricating film for optimal lubrication; highly sensitive to media contamination; hard particles can become embedded, causing severe wear of the cylinder barrel or piston rod (similar to “abrasives”). Cost is relatively high.
Applications:
- Suitable for high-speed, high-temperature, heavy-load applications requiring extremely high oil cleanliness control.
- Commonly used in aerospace, high-performance machine tool servo cylinders, and other applications requiring extremely stringent dynamic response and thermal management requirements.
- In general industrial applications, due to stringent oil cleanliness requirements, it has been gradually replaced by high-performance engineering plastics.
4. Polytetrafluoroethylene (PTFE) composites (e.g., DU and DX bearings)
- Advantages: Extremely low coefficient of friction (close to ice), excellent self-lubrication (able to operate for short periods even in dry or oil-starved conditions), and strong chemical resistance.
- Disadvantages: Low mechanical strength, poor creep resistance (cold flow), and poor thermal conductivity.
Note: Pure PTFE is generally not used directly. It is often combined with bronze powder, glass fiber, carbon fiber, and other materials to create composite materials (such as the well-known DU material) to improve its mechanical strength and wear resistance.
Application Scenarios:
- Suitable for low-speed swing, poor lubrication, or applications requiring extremely low starting force.
- Commonly used in swing cylinders or rotary joints in aerospace, precision equipment, and some special operating conditions.
5. Polyamide (Nylon, PA)
- Advantages: Good toughness, wear resistance, oil resistance, and low cost.
- Disadvantages: High water absorption, inferior dimensional stability, and slightly lower strength and hardness than POM. High coefficient of friction in the dry state.
Applications:
- Commonly used in low-pressure, low-load, economical hydraulic or pneumatic cylinders.
- In the hydraulic field, its performance is generally considered inferior to that of POM, and therefore its application is not as widespread as POM.
III. Selection Recommendations
1. Load and Pressure: Choose POM for light loads and medium pressures, and phenolic cloth for heavy loads, high pressures, and high impacts.
2. Speed and Temperature: Choose copper-based for high speeds, high temperatures, and clean fluids; choose POM or PF for normal temperatures.
3. Media and Environment: Consider the material’s oil and chemical resistance. POM and PF are well-suited to common hydraulic fluids.
4. Cost: POM and PA are relatively low-cost, while PF and specialized composite materials are more expensive.
5. Installation and Maintenance: Engineering plastics like POM are relatively soft, making them easy to install without damaging the mating surfaces. Copper-based materials require extremely clean installation.
Currently, in most industrial applications (especially construction machinery), POM and phenolic cloth are the undisputed mainstream choices because they offer the best balance between performance and cost, and they do not require the same stringent system fluid cleanliness requirements as copper-based materials.
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