Plastic-Coated Polyurethane Bearings vs. High-Temperature Polyurethane Bearings: Material Differences and Selection Guide

1. Overview

A plastic-coated bearing (also known as a polyurethane-coated bearing) is a composite bearing made by covering the outer ring of a metal bearing with an elastic material such as polyurethane, rubber, or POM. This "invisible protective coating" gives the bearing both the strength and rigidity of a metal core and the cushioning and protective functions of the outer elastic layer.

Polyurethane (PU) is one of the most commonly used coating materials for plastic-coated bearings. It combines the high elasticity of rubber with the high strength of plastic, while also offering excellent wear resistance, oil resistance, water resistance, mold resistance, and insulation/vibration damping properties.

In practical applications, polyurethane-coated bearings are mainly divided into two categories: standard polyurethane-coated bearings and high-temperature polyurethane-coated bearings. These two types differ significantly in material formulation, operating temperature, suitable environment, and application fields. Mastering these differences is key to scientific selection and extending bearing service life.

【Table 1: Common Coating Materials for Plastic-Coated Bearings】

Material	Typical Operating Temperature	Key Advantages	Main Limitations
Standard Polyurethane (PU)	-30~80°C	High wear resistance, high elasticity, oil resistance, insulation/vibration damping	Poor high-temp resistance, susceptible to hydrolysis in humid environments
High-Temp Polyurethane (HT-PU)	-30~120°C (short-term up to 150°C)	High-temp stability, good wear resistance, good chemical resistance	Higher cost
POM (Acetal)	-50~110°C	Excellent self-lubrication, dimensional stability, high cost-performance	Poor resistance to strong acids
PA66 (Nylon)	-40~120°C	High mechanical strength, good toughness, excellent oil resistance	High moisture absorption

 

2. Standard Polyurethane-Coated Bearings

2.1 Material Basic Properties

Standard polyurethane is a high-molecular elastomer formed by the reaction of isocyanate and polyol. It can be divided into two types based on processing technology: cast polyurethane (CPU) and thermoplastic polyurethane (TPU). TPU can be formed via injection molding, making it suitable for mass production.

【Table 2: Core Properties of Standard Polyurethane】

Parameter	Value	Notes
Recommended operating temperature	-30°C~80°C	Performance significantly decreases beyond this range
Maximum temperature	Short-term up to 100°C	Not recommended for long-term use above 80°C
Hardness range	Shore A 60~95	Can be customized based on operating conditions
Wear resistance	Excellent	DIN abrasion ≤80mm³
Friction coefficient	Low (self-lubricating)	Excellent dry-running performance
Water resistance	Moderate	Hydrolysis may occur in humid environments
Oil resistance	Excellent	Resists mineral oils and greases
Tear strength	Good	Shore D70 can achieve ≥50kN/m

Polyurethane offers better wear resistance than ordinary nylon and performs excellently in dry-running environments. Standard polyurethane-coated bearings are moderately priced and the conventional choice for most industrial conditions.

 

2.2 Key Features of Standard Polyurethane-Coated Bearings

High wear resistance: Polyurethane's wear resistance is far superior to ordinary rubber, several times that of traditional rubber materials;

High elasticity and cushioning: Absorbs impact and vibration, effectively protecting equipment;

Low-noise operation: The elastic coating can reduce operating noise by 40%~50%;

Shock absorption protection: Under high-speed operation or repeated impact, the coating reduces impact on components;

Workpiece surface protection: Avoids direct metal-to-workpiece contact, preventing scratching;

Oil resistance: Excellent resistance to mineral oils and greases.

 

2.3 Main Limitations of Standard Polyurethane

Standard polyurethane is susceptible to hydrolysis in humid environments. Long-term contact with water or high humidity air can lead to degraded performance, reduced elasticity, and even cracking. Additionally, its temperature resistance is moderate – mechanical properties degrade significantly above 80°C. Polyurethane also has certain limitations in strong acid and alkali environments.

 

3. High-Temperature Polyurethane (HT-PU) Coated Bearings

 

3.1 Material Basic Properties

High-temperature polyurethane is a specialty material produced by modifying standard polyurethane through optimized formulations. It primarily enhances heat resistance through aromatic isocyanates, heat stabilizers, antioxidants, and modified polyether polyols.

【Table 3: Core Properties of High-Temperature Polyurethane】

Parameter	Value	Notes
Recommended operating temperature	-30°C~120°C	Far exceeding the upper limit of standard polyurethane
Maximum temperature	150°C (short-term)	For transient high-temperature conditions
Thermal stability	Excellent	Heat stabilizers delay thermo-oxidative aging
Wear resistance	Excellent (comparable to standard PU)	Maintains good wear resistance at high temperatures
Chemical resistance	Good	Better suited to complex chemical environments
Cost	High	30%~50% more expensive than standard polyurethane

Covestro's Desmopan DP.460 series TPU features excellent temperature resistance, combining good low-temperature toughness with short-term resistance to 150°C.

Murtfeldt's Murylon® HT, a highly heat-resistant polyamide, can operate reliably at a constant service temperature of up to 155°C, offering high wear resistance, electrical insulation, and good sliding properties.

 

3.2 Core Advantages of High-Temperature Polyurethane

Extended operating temperature range: Stable long-term operation at 120°C, short-term tolerance up to 150°C;

Maintains good mechanical properties at high temperatures: Heat stabilizers delay thermal oxidative degradation, preserving material strength;

Excellent thermal aging resistance: Heat stabilizers and antioxidants effectively extend service life under high temperatures;

Special formulations for hydrolysis resistance: Some high-temperature polyurethanes (e.g., polyether-based formulations) perform better under combined high-temperature and high-humidity conditions;

Wider chemical compatibility: Suitable for equipment contacting high-temperature media or chemicals.

 

3.3 Limitations of High-Temperature Polyurethane

High-temperature polyurethane is more expensive, and formulation must be confirmed based on specific operating conditions. Not all high-temperature formulations offer equal hydrolysis stability and chemical resistance; different manufacturers have different modification approaches.

 

4. Standard Polyurethane vs. High-Temperature Polyurethane Comparison

【Table 4: Standard PU vs. High-Temperature PU Comparison】

Dimension	Standard Polyurethane (PU)	High-Temperature Polyurethane (HT-PU)
Recommended operating temperature	-30°C~80°C	-30°C~120°C
Maximum temperature	Short-term 100°C	Short-term 150°C
Thermal stability	Moderate	Excellent (with heat stabilizers)
Wear resistance (room temperature)	Excellent	Excellent
Wear resistance (high temperature 100°C+)	Significantly decreased	Maintains good performance
Hydrolysis resistance	Moderate	Excellent (polyether formulations)
Price	Baseline	1.3~1.5x baseline
Material modification	Basic formulation	Aromatic isocyanate + heat stabilizer + antioxidant
Suitable for high-temperature environments	Not suitable	Suitable

【Figure 1: Comparison of Operating Temperature Ranges for Standard vs. High-Temperature Polyurethane】 (Schematic bar chart)

*Standard PU: -30°C ────────── 80°C*
*High-Temperature PU: -30°C ────────────────── 120°C (short-term 150°C)*

 

5. Dual-Layer Structure of Plastic-Coated Bearings and Comparison with Other Materials

Plastic-coated bearings are composite structures: a metal bearing core provides load capacity and rigidity, while an outer elastic material (polyurethane, rubber, POM, nylon, etc.) provides cushioning, shock absorption, and protection.

【Table 5: Performance Comparison of Common Outer Layer Materials for Plastic-Coated Bearings】

Material	Operating Temp	Wear Resistance	Elasticity	Chemical Resistance	Cost	Typical Applications
Standard PU	-30~80°C	★★★★★	★★★★★	★★★☆☆	Medium	General industry, automation conveying
High-Temp PU	-30~120°C	★★★★★	★★★★☆	★★★★☆	Higher	High-temp ovens, thermal processing equipment
Rubber	-30~80°C	★★★☆☆	★★★★★	★★☆☆☆	Low	Medical devices, vibration-damping wheels
POM	-50~110°C	★★★★☆	★★☆☆☆	★★★☆☆	Low	Precision transmission, low-friction conditions
PA66	-40~120°C	★★★☆☆	★★★☆☆	★★★★☆	Medium	High-impact loads, rough environments

POM-coated bearings: Often used in precision transmission applications with high dimensional accuracy requirements. They have excellent self-lubrication but poor elasticity, not suitable for heavy-impact buffering.

Nylon-coated bearings: High mechanical strength and good impact resistance, suitable for complex environments with particles or debris. Harder than polyurethane, with slightly less vibration damping.

Rubber-coated bearings: Provide the best elasticity of all materials at the lowest cost, but have poor tear strength and poor resistance to oils and organic solvents. Suitable for pure vibration-damping applications.

 

6. Selection Guide

【Table 6: Plastic-Coated Polyurethane Bearing Selection Decision Table】

Operating Condition	Recommended Type	Rationale
General industrial conveying, room temperature dry environment	Standard PU	High cost-performance, good wear resistance
Automated production lines, AGV/AMR drive wheels	Standard PU	Vibration damping/low noise, stable load capacity
High-temperature ovens, hot presses, thermal processing equipment	High-temp PU	Long-term high-temp resistance up to 120°C
Food processing, beverage filling lines	Standard PU or FDA-certified material	Meets hygiene requirements, resistant to water washing
Frequent water washing, steam sterilization	High-temp PU (polyether type)	Strong hydrolysis resistance
Combined high-temperature + chemical conditions	High-temp PU	Wide temperature range + excellent chemical compatibility
High-speed operation, low-noise requirements	Standard PU	Elastic layer significantly reduces noise
Heavy-load impact, frequent start/stop	PU (AGV reference)	Good cushioning protects equipment

 

7. Detailed Application Scenarios

 

1. Industrial Automation and Smart Equipment

AGV drive wheels use 90A Shore hardness polyurethane coating combined with double-row angular contact ball bearings, achieving low-noise operation (≤65dB) under heavy loads (capacity ≥2 tons).

 

2. Conveying Machinery and Logistics Equipment

Conveyor rollers use a coating thickness of 8~15mm to increase the friction coefficient to above 0.8, preventing material slippage. If the material contains stones or sharp debris, nylon-coated bearings are recommended instead.

 

3. High-Temperature Industrial Environments (High-Temperature Polyurethane Scenarios)

High-temperature polyurethane-coated bearings are especially suitable for:

High-temperature ovens and drying equipment: Require long-term high-temperature resistance (>100°C), where standard polyurethane would rapidly soften and degrade;

Hot presses and thermoforming equipment: High-temperature, high-load conditions, with short-term tolerance up to 150°C for high-temperature polyurethane;

High-temperature conveyor lines: Direct contact with high-temperature materials (>80°C);

High-temperature steam environments: Some polyether-based high-temperature polyurethane formulations offer enhanced hydrolysis resistance.

【Table 7: Temperature-Based Selection Guide for Polyurethane-Coated Bearings】

Operating Temperature	Recommended Material	Notes
Below -30°C	Low-temp optimized PU	Special low-temperature formulation to prevent brittleness
-30°C~80°C	Standard PU (standard formulation)	Most economical conventional choice
80°C~100°C	Standard PU (short-term)/High-temp PU	High-temp recommended for long-term use
100°C~120°C	High-temperature PU	Modified high-temperature formulation required
120°C~150°C	High-temperature PU (short-term tolerance)	Only transient or intermittent high temperature allowed

 

4. Medical Devices (Quiet and Cleanliness Requirements)

Medical devices have strict low-noise operating requirements. The low-noise and vibration-damping properties of standard polyurethane-coated bearings make them an excellent fit for applications such as hospital cart wheels and rehabilitation equipment pulleys.

 

8. Key Parameters for Plastic-Coated Bearing Processing

The core of plastic-coated bearings is the injection molding process that coats the polyurethane material onto the outer ring surface of the bearing, forming a high-strength wear-resistant layer. Process parameter control directly affects bearing performance:

【Table 8: Key Injection Molding Process Parameters for Polyurethane-Coated Bearings】

Parameter	Recommended Range	Notes
Barrel temperature	177~232°C	Adjusted according to material hardness
Mold temperature	10~60°C	Higher hardness requires higher temperature
Injection pressure	20~110MPa	Adjusted according to product size
Holding pressure	50% of injection pressure	Ensures full filling and compaction
Cooling method	Constant temperature water circulation	Avoids internal stress from rapid cooling
Peel strength	≥8MPa	Verifies coating-to-metal bond quality

Metal substrate pretreatment: Sandblasting of the bearing outer ring increases surface roughness, improving the bond strength between polyurethane and metal. Some processes require chemical etching or adhesive application to enhance bonding.

 

9. Summary

Core selection principles:

Room temperature dry environments: Choose standard polyurethane-coated bearings – the most cost-effective option;

High-temperature environments (>80°C): Must select high-temperature polyurethane-coated bearings – standard polyurethane performance significantly degrades under these conditions;

Humid or high-humidity environments: Select polyether-type polyurethane formulations for stronger hydrolysis resistance;

Food processing environments: Verify that the coating material meets FDA or relevant food safety certification;

High-impact, heavy-load, debris-containing conditions: Choose standard polyurethane solutions first – AGV drive wheels are a typical application;

Continuous high-temperature (100°C~120°C) conditions: Such as high-temperature oven conveyors and hot presses – selecting high-temperature polyurethane-coated bearings is the only reasonable choice.