Plastic-Coated Bearing PP, POM, and PA Materials: Differences and Application Scenarios
May 20, 2026| 1. Overview of Plastic-Coated Bearing Outer Layer Materials
Plastic-coated bearings are composite bearings made by coating an engineering plastic onto the outer ring of a metal bearing. The choice of outer layer material directly affects wear resistance, corrosion resistance, friction coefficient, operating temperature range, and service life. Common coating materials include polypropylene (PP), polyoxymethylene (POM), and polyamide (PA). These three materials have significantly different properties and are suitable for different operating conditions.
PP offers low cost and excellent chemical resistance but has weaker mechanical properties. POM provides excellent self-lubrication and dimensional stability. PA offers high mechanical strength, good toughness, and excellent oil resistance. Understanding the differences between these three materials is key to scientific selection and extending bearing life.
2. PP-Coated Bearings
Material Overview: Polypropylene (PP) is a semi-crystalline thermoplastic with low density (0.90-0.91 g/cm³), excellent chemical resistance (especially to acids, bases, and organic solvents), and low price.
【Table 1: Core Properties of PP】
| Performance Indicator | Value |
|---|---|
| Continuous operating temperature | 0℃~80℃ (long-term) |
| Short-term peak temperature | 100℃ |
| Density | 0.90-0.91 g/cm³ |
| Tensile strength | 25-35 MPa |
| Friction coefficient | 0.3-0.4 (high) |
| Wear resistance | Moderate |
| Acid/alkali resistance | Excellent (resists most acids, bases, organic solvents) |
| Oil resistance | Good |
| Moisture absorption | Very low (<0.1%) |
| Cost | Lowest |
| Self-lubrication | Poor (requires external lubrication) |
Advantages:
Lowest price, suitable for mass production and low-cost applications
Excellent chemical resistance to acids, bases, and organic solvents
Low density, good lightweighting effect
Very low moisture absorption, good dimensional stability
Disadvantages:
High friction coefficient, poor self-lubrication, typically requires external lubrication
Moderate wear resistance, unsuitable for high-wear conditions
Low-temperature brittleness (becomes brittle below 0℃), not suitable for low-temperature environments
Relatively low mechanical strength and limited load capacity
Poor UV resistance, prone to aging outdoors
Suitable Scenarios:
Environments with strong chemical corrosion (e.g., electroplating lines, chemical plant conveyor rollers)
Cost-sensitive, light-load, low-speed applications
Food contact applications (PP is food-grade, common FDA certification)
Aqueous environments (PP does not absorb water, hydrolysis-resistant)
Packaging machinery guide wheels, low-load conveyor rollers
3. POM-Coated Bearings
Material Overview: Polyoxymethylene (POM, commonly known as acetal) is a high-crystallinity engineering plastic with excellent self-lubrication, high rigidity, and excellent dimensional stability.
【Table 2: Core Properties of POM】
| Performance Indicator | Value |
|---|---|
| Continuous operating temperature | -50℃~110℃ |
| Short-term peak temperature | 130℃ |
| Density | 1.41 g/cm³ |
| Tensile strength | 60-70 MPa |
| Friction coefficient | 0.1-0.2 (excellent self-lubrication) |
| Wear resistance | Excellent (better than PA and PP) |
| Acid/alkali resistance | Poor resistance to strong acids |
| Oil resistance | Good |
| Moisture absorption | Very low (0.2%-0.4%) |
| Cost | Medium |
| Self-lubrication | Excellent (dry running) |
Advantages:
Excellent self-lubrication, dry running without external lubrication
Low friction coefficient, low operating resistance
Good dimensional stability, low moisture absorption
Good rigidity, high creep resistance
Wide operating temperature range (-50℃~110℃)
Best wear resistance among the three materials
Disadvantages:
Poor resistance to strong acids, unsuitable for strong acid environments
Poor elasticity, weak vibration damping and shock absorption
Relatively brittle, lower impact resistance than PA
Suitable Scenarios:
High-precision transmission, sliding components (e.g., guide pulleys, precision conveyor rollers)
Dry-running conditions (environments where lubricants cannot be used)
Food packaging machinery (FDA-certified POM can be used for food contact)
Automation equipment guide wheels, AGV drive wheels
Room temperature to medium temperature environments (-50℃~110℃)
Applications requiring low friction resistance
4. PA-Coated Bearings
PA (polyamide) is a general term for polyamide plastics. PA66 (nylon 66) and PA6 are commonly used in plastic-coated bearings. PA materials offer high mechanical strength, good toughness, and excellent oil resistance.
【Table 3: Core Properties of PA66】
| Performance Indicator | Value |
|---|---|
| Continuous operating temperature | -40℃~120℃ |
| Short-term peak temperature | 150℃ |
| Density | 1.14 g/cm³ |
| Tensile strength | 80-90 MPa |
| Impact strength (unnotched) | 60-80 kJ/m² |
| Friction coefficient | 0.2-0.3 (moderate self-lubrication) |
| Wear resistance | Good |
| Acid/alkali resistance | Poor resistance to strong acids/bases |
| Oil resistance | Excellent |
| Moisture absorption | High (1.2%-2.5%) |
| Cost | Medium |
| Self-lubrication | Moderate |
Advantages:
High mechanical strength, tensile strength ≥80 MPa
Good toughness, excellent impact resistance
Excellent oil resistance, suitable for applications contacting oils
Wide operating temperature range (-40℃~120℃)
Can be reinforced with glass fiber to further improve strength
Disadvantages:
High moisture absorption, significant dimensional changes in humid environments
Moderate self-lubrication, higher friction coefficient than POM
Poor resistance to strong acids and bases
Suitable Scenarios:
High impact load applications (e.g., vibrating screens, crusher conveyor rollers)
Equipment contacting oils (e.g., machine tool transmission wheels, automotive parts)
Conveyor rollers in rough environments containing stones and grit
Applications requiring high toughness and impact resistance
Dry environments preferred; moisture absorption should be considered in humid environments
5. Comprehensive Comparison of PP, POM, and PA66
【Table 4: PP vs POM vs PA66 Comparison Summary】
| Dimension | PP | POM | PA66 |
|---|---|---|---|
| Continuous operating temp | 0~80℃ | -50~110℃ | -40~120℃ |
| Density | 0.90-0.91 | 1.41 | 1.14 |
| Tensile strength | 25-35 MPa | 60-70 MPa | 80-90 MPa |
| Impact strength | Medium | Medium | Excellent |
| Friction coefficient | 0.3-0.4 | 0.1-0.2 | 0.2-0.3 |
| Self-lubrication | Poor | Excellent | Moderate |
| Wear resistance | Moderate | Excellent | Good |
| Acid/alkali resistance | Excellent | Poor (strong acids) | Poor (strong acids/bases) |
| Oil resistance | Good | Good | Excellent |
| Moisture absorption | Very low | Very low | High |
| Dimensional stability | Good | Excellent | Moderate (worse when wet) |
| Impact resistance/toughness | Moderate | Moderate | Excellent |
| Cost | Lowest | Medium | Medium |
| Typical applications | Corrosion-resistant, low-cost light load | Precision transmission, dry running | High impact, oil contact |
【Figure 1: Performance Radar Chart of PP, POM, PA66】
(The radar chart concept with five dimensions: wear resistance, self-lubrication, toughness, chemical resistance, dimensional stability, temperature resistance – not shown in text, but a visual diagram would be provided.)
6. Selection Decision Guide
【Table 5: Plastic-Coated Bearing Material Selection Decision Table】
| Operating Condition | Recommended Material | Selection Rationale |
|---|---|---|
| Strong acid/alkali, chemical contact | PP | Best chemical resistance, lowest cost |
| Aqueous environment, frequent washing | PP or POM | PP non-absorbent, POM low-absorption; PA not recommended |
| Dry running, no lubrication | POM | Excellent self-lubrication, no external lubrication needed |
| High precision, low friction, low noise | POM | Dimensional stability, lowest friction coefficient |
| High impact, vibration loads | PA66 | Best toughness, strong impact resistance |
| Oil contact (engine oil, hydraulic oil) | PA66 | Best oil resistance |
| High temperature (100℃-120℃) | PA66 or POM | Both acceptable, PA66 slightly higher limit |
| Low temperature (below -30℃) | POM | Withstands -50℃; PP becomes brittle |
| Rough environments with stones, sand | PA66 | Good toughness, not easily broken |
| Food contact, FDA requirement | PP or POM (FDA grade) | Both have FDA-certified grades |
| Heavy load conveying, high wear requirement | POM | Best wear resistance |
| Cost-sensitive, light load | PP | Lowest price |
7. Application Examples
| Application Scenario | Recommended Material | Specific Reason |
|---|---|---|
| Electroplating line conveyor rollers | PP | Acid/alkali corrosion resistant, low cost |
| AGV drive wheels (indoor) | POM | Self-lubricating, low noise, wear-resistant |
| Food filling line conveyor wheels | POM or PP (FDA) | Food safety compliant, wash-resistant |
| Mining conveyor idlers | PA66 | High impact load, resists stone impacts |
| Textile machinery guide wheels | POM | Low friction, does not damage yarn |
| Automotive door limit rollers | PA66 | Oil resistant, impact resistant |
| Packaging machinery guide wheels | POM | High precision, dimensional stability |
| Chemical pump plain bearings | PP | High corrosion resistance required |
| Fitness equipment pulleys | POM or PA66 | Low noise or high toughness |
8. Summary
PP, POM, and PA have their own characteristics as outer layer materials for plastic-coated bearings. The core of material selection is matching the operating conditions:
PP: Best chemical resistance, lowest price, non-absorbent. Suitable for corrosive environments and aqueous applications. However, mechanical properties are weaker and self-lubrication is poor. Suitable for light-load, low-speed, low-cost scenarios.
POM: Best self-lubrication, best wear resistance, best dimensional stability. Suitable for precision transmission, dry-running, and low-friction applications. It is the most versatile high-performance material for plastic-coated bearings.
PA66: Highest mechanical strength, best toughness, best oil resistance. Suitable for high-impact, heavy-load, and oil-contact scenarios. However, high moisture absorption leads to dimensional changes in humid environments.
In actual selection, comprehensively consider operating temperature, chemical media, load type, lubrication availability, precision requirements, cost budget, and other factors to choose the most matching material. For combined conditions (e.g., high temperature + corrosion), modified materials or special additive formulations may be required.