What Is The Difference between Carbon Fiber PEEK And Bearing Grade PEEK?

Polyether ether ketone (PEEK) is a high-performance engineering thermoplastic renowned for its exceptional mechanical, thermal, and chemical properties. Within the family of PEEK materials, two specialized grades—Carbon Fiber PEEK and Bearing Grade PEEK—stand out for their unique enhancements and application profiles. This article provides a comprehensive comparison of these two advanced materials, exploring their composition, properties, performance, and typical uses.

Table of Contents

• Introduction to PEEK and Its Grades

• What is Carbon Fiber PEEK?

• Composition and Manufacturing

• Key Properties

• Typical Applications

• What is Bearing Grade PEEK?

• Composition and Manufacturing

• Key Properties

• Typical Applications

• Comparative Analysis: Carbon Fiber PEEK vs. Bearing Grade PEEK

• Mechanical Properties

• Tribological (Wear and Friction) Properties

• Thermal and Chemical Resistance

• Cost and Machinability

• How to Choose Between Carbon Fiber PEEK and Bearing Grade PEEK

• Frequently Asked Questions (with Answers)

• Article Summary

Introduction to PEEK and Its Grades

PEEK is a semi-crystalline thermoplastic with a unique combination of high temperature resistance, chemical stability, and mechanical strength. It is widely used in demanding industries such as aerospace, automotive, medical, and electronics. To meet specific application requirements, PEEK is available in several grades, each tailored with different fillers or additives to enhance certain properties.

Among these, Carbon Fiber PEEK and Bearing Grade PEEK are two of the most advanced and widely used variants, each engineered for high-performance applications but with distinct characteristics.

What is Carbon Fiber PEEK?

Composition and Manufacturing

Carbon Fiber PEEK is a composite material created by reinforcing the PEEK polymer matrix with carbon fibers, typically at concentrations of 10% to 30% by weight. The carbon fibers are uniformly dispersed throughout the PEEK, resulting in a material that combines the inherent advantages of both components.

• PEEK Matrix: Provides chemical resistance, thermal stability, and baseline mechanical strength.

• Carbon Fiber Reinforcement: Dramatically increases stiffness, tensile strength, and dimensional stability.

Key Properties

• Superior Strength and Stiffness: Carbon fiber reinforcement boosts tensile strength (up to 138 MPa) and modulus (up to 14 GPa), making it significantly stronger and stiffer than unfilled or glass-filled PEEK.

• High Thermal Resistance: Can operate continuously at temperatures up to 250–300°C, with short-term resistance up to 300°C.

• Excellent Wear Resistance: The addition of carbon fibers enhances abrasion resistance, making it suitable for moving parts.

• Low Density: Lighter than metals and even glass-filled PEEK, offering a high strength-to-weight ratio.

• Improved Thermal and Electrical Conductivity: Carbon fibers increase both thermal and electrical conductivity, which is beneficial for dissipating heat and static.

• Dimensional Stability: Low coefficient of thermal expansion ensures minimal deformation under heat.

• Chemical and Corrosion Resistance: Maintains PEEK’s resistance to acids, bases, and solvents.

Typical Applications

• Aerospace structural components

• Automotive under-hood parts

• High-performance gears and bushings

• Pump and valve components

• Medical implants and devices

• Electrical and electronic parts requiring conductivity and strength

What is Bearing Grade PEEK?

Composition and Manufacturing

Bearing Grade PEEK is a specialized formulation designed for applications where low friction, high wear resistance, and excellent machinability are critical. It is typically a composite containing:

• PEEK Matrix

• Carbon Fiber (usually 10–30%)

• Graphite (typically 10%)

• PTFE (Polytetrafluoroethylene, typically 10–20%)

This combination is engineered to optimize tribological properties—specifically, to reduce friction and wear in dynamic, load-bearing environments.

Key Properties

• Lowest Coefficient of Friction: The addition of PTFE and graphite provides self-lubricating properties, resulting in extremely low friction.

• Exceptional Wear Resistance: Designed to withstand continuous motion and high loads without significant wear.

• High PV (Pressure-Velocity) Limit: Can operate under high loads and speeds, making it ideal for bearings and bushings.

• Excellent Machinability: Easier to machine than many other high-performance plastics.

• Thermal Stability: Maintains performance at elevated temperatures, though typically slightly lower than pure carbon fiber PEEK.

• Chemical Resistance: Retains PEEK’s resistance to a wide range of chemicals.

• Color: Usually gray or black due to the fillers.

Typical Applications

• Bearings and bushings

• Thrust washers

• Pump wear rings and seals

• Valve seats

• Sliding and rotating components in automotive, aerospace, and industrial machinery

Comparative Analysis: Carbon Fiber PEEK vs. Bearing Grade PEEK

Mechanical Properties

• Carbon Fiber PEEK excels in strength and stiffness, making it ideal for structural and load-bearing applications.

• Bearing Grade PEEK sacrifices a small amount of strength for superior wear and friction performance.

Tribological (Wear and Friction) Properties

• Bearing Grade PEEK is specifically engineered for dynamic applications where low friction and minimal wear are essential.

• Carbon Fiber PEEK offers excellent wear resistance but is not as self-lubricating as bearing grade.

Thermal and Chemical Resistance

Both grades maintain PEEK’s outstanding resistance to chemicals and high temperatures, but:

• Carbon Fiber PEEK can typically withstand slightly higher continuous use temperatures.

• Bearing Grade PEEK is optimized for thermal stability under frictional heating, but its maximum temperature may be marginally lower due to the presence of PTFE.

Cost and Machinability

• Carbon Fiber PEEK is generally more expensive due to the cost of carbon fibers and the complexity of manufacturing.

• Bearing Grade PEEK is also costly, especially with high PTFE and graphite content, but is often easier to machine and finish.

How to Choose Between Carbon Fiber PEEK and Bearing Grade PEEK

Consider Carbon Fiber PEEK When:

• Maximum strength and stiffness are required.

• The application involves high static or dynamic loads.

• Dimensional stability and resistance to deformation are critical.

• Electrical or thermal conductivity is needed.

• The component will be exposed to high temperatures for extended periods.

Consider Bearing Grade PEEK When:

• The application involves continuous sliding, rotation, or oscillation.

• Low friction and minimal wear are essential.

• Self-lubricating properties are desired to reduce or eliminate external lubrication.

• The component will operate under high PV (pressure-velocity) conditions.

• Machinability and ease of fabrication are important.

Frequently Asked Questions

1. What is the main difference between carbon fiber PEEK and bearing grade PEEK?

Answer:
Carbon fiber PEEK is reinforced solely with carbon fibers to maximize strength, stiffness, and thermal conductivity, making it ideal for structural and load-bearing applications. Bearing grade PEEK, on the other hand, is a composite of PEEK, carbon fiber, graphite, and PTFE, specifically engineered for low friction, high wear resistance, and self-lubricating properties, making it the best choice for dynamic bearing and sliding applications.

2. Can carbon fiber PEEK be used for bearings?

Answer:
Yes, carbon fiber PEEK can be used for bearings, especially where high strength and stiffness are required. However, for applications where the lowest friction and wear are critical, bearing grade PEEK is generally preferred due to its optimized tribological properties.

3. Is bearing grade PEEK more expensive than carbon fiber PEEK?

Answer:
Both materials are premium and relatively expensive compared to standard PEEK, but the cost can vary depending on the specific formulation and filler content. Generally, carbon fiber PEEK may be slightly more expensive due to the high cost of carbon fibers, but bearing grade PEEK with high PTFE and graphite content can also be costly.

4. What are the color differences between the two grades?

Answer:
Carbon fiber PEEK is typically black due to the carbon fibers. Bearing grade PEEK is usually gray or black, depending on the proportions of carbon fiber, graphite, and PTFE.

5. Which grade is better for high-temperature applications?

Answer:
Both grades offer excellent high-temperature performance, but carbon fiber PEEK can generally withstand slightly higher continuous use temperatures. However, bearing grade PEEK is optimized to handle the heat generated by friction in dynamic applications.

6. Are both grades chemically resistant?

Answer:
Yes, both carbon fiber PEEK and bearing grade PEEK retain the excellent chemical resistance of the PEEK matrix, making them suitable for use in aggressive chemical environments.

7. How do I decide which grade to use for my application?

Answer:
Consider the primary demands of your application. If you need maximum strength, stiffness, and dimensional stability, choose carbon fiber PEEK. If your application involves continuous motion, sliding, or requires low friction and high wear resistance, bearing grade PEEK is the better choice.

Article Summary

Carbon fiber PEEK and bearing grade PEEK are two high-performance variants of PEEK, each tailored for specific engineering challenges. Carbon fiber PEEK excels in strength, stiffness, and thermal conductivity, making it ideal for structural and load-bearing applications. Bearing grade PEEK, with its unique blend of carbon fiber, graphite, and PTFE, offers unmatched wear resistance and low friction, making it the material of choice for dynamic bearing and sliding components. Understanding the differences between these grades ensures optimal material selection for demanding industrial applications.