How to Select the Best High Temperature Bearings?

Bearings are essential components in machines, allowing them to rotate smoothly and efficiently. In industries like steel production, kilns, and gas turbines, temperatures can reach intense levels. Choosing the right bearing is essential in these conditions.

In this blog, we'll discuss how to pick the right materials and what to think about when using bearings in high temperatures. We'll also share practical tips for selecting the best types of high-temperature bearings for your needs.

Key Factors to Consider When Selecting High Temperature Bearings

Operating Temperature

Understanding Temperature Limits of Bearing Materials

Effect of Extreme Heat on Bearing Components

• Impact on Rings, Balls, Cages, and Shields: Extreme heat can damage these parts, making them weaker and less effective over time.
• Thermal Expansion Risks: High temperatures can make the bearing parts expand, which reduces space and increases friction.
• Material Stability: Using materials that maintain their shape and size at high temperatures is crucial. This ensures proper functioning and helps prevent failures in extreme heat.

Load Capacity and Speed

Types of Loads and Their Impact on Bearing Selection

• Axial and Radial Loads: High temperatures can weaken bearing materials.
• This makes it harder for the bearings to handle mechanical stress from both axial loads (along the shaft) and radial loads (across the shaft).
• Combined Loads: High temperature bearings need to be chosen carefully to manage both axial and radial loads. This is particularly important in high-temperature situations.

Speed Considerations in High Temperature Bearings

High temperature bearings used in high-speed applications face the challenge of generating more friction and heat. This makes it essential to use materials that can withstand both high rotational speeds and the thermal stress that comes with it.

A balance often exists between load capacity and speed. High-speed tool steel bearings like M50 are designed to work in extreme conditions. They provide a balance between fast performance and durability under heavy loads.

Lubrication for High Temperature Bearings

Challenges of Lubricating Bearings at Elevated Temperatures

High temperatures can cause traditional lubricants, like mineral oils, to break down. When this occurs, friction and wear escalate. This leads to reduced performance and a shorter service life for high-temperature bearings.

When choosing a lubricant, you have two main options: grease and solid lubricants. High-temperature greases, like fluorinated grease (such as EXSEV-EX), are effective in certain situations. They work well where liquid lubricants can be used.

Solid lubricants like molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are better for high temperatures. They don’t break down easily and provide good lubrication.

Selecting the Right Lubrication for Different Temperature Ranges

Material Selection for High Temperature Bearings

Ceramic Bearings

Advantages:

• High heat resistance
• Low thermal expansion
• Corrosion resistance
• Non-magnetic
• Non-conductive

Disadvantages:

• High cost
• Brittle nature
• Reduced load capacity compared to steel

Applications:

• Ideal for use in furnaces
• Aerospace components
• Cleanroom equipment

Hybrid Bearings

Advantages:

Combines the strength and durability of steel rings with the low-friction and high-heat resistance of ceramic balls.

Applications:

• High-speed machinery
• electric motors
• high-temperature industrial environments

High-Speed Tool Steel Bearings

Materials:

M50, BG42, and XD16N steels.

Advantages:

• Can handle extreme speeds and temperatures.
• Offers high strength and durability.

Applications:

• Steel mills
• aerospace turbines
• high-performance machinery

Special Considerations for High Temperature Bearings

Thermal Expansion and Clearance Management

Coefficient of Thermal Expansion (CTE)

Different materials expand at different rates when heated. Ceramics have a small expansion rate, while steel has a larger expansion rate.

Maintain the proper clearance for high-temperature bearings. This helps prevent problems like increased internal pressure and bearing seizing.

Managing Clearance in High Temperature Conditions

Extra space should be allowed at normal temperatures. This helps to account for material expansion as temperatures rise.

Incorrect clearance can lead to high temperature bearings misalignment, increasing friction and wear. This ultimately reduces the lifespan of the high temperature bearings and increases the risk of failure.

Corrosion Resistance in High Temperature Environments

Ceramic Materials vs. Stainless Steel

Silicon Nitride (Si3N4) is resistant to most acids and alkaline solutions. However, it can be affected by hydrofluoric acid.

Zirconia (ZrO2) and Silicon Carbide (SiC) provide excellent corrosion resistance. They work well in both highly acidic and alkaline environments.

Selecting the Right Bearings for Corrosive High Temperature Conditions

Ceramic materials are great for environments with corrosive gases, chemicals, or saltwater. This makes them perfect for use in chemical plants and marine industries.

Environmental Factors: Clean and Vacuum Applications

Bearings for Clean Environments

Using martensitic stainless steel (SUS440C) and polymer solid lubricants helps reduce particle emissions.

High temperature bearings are ideal for use in semiconductor manufacturing, food processing, and cleanroom environments.

Bearings for Vacuum Environments

For vacuum conditions, stainless steel (JIS SUS630) or ceramic bearings are preferred options.

In vacuum environments, common lubrication choices include WS2 and MoS2.

When using high-temperature bearings in vacuum environments, remember to consider the vacuum pressure and temperature changes.

Common High Temperature Bearing Types and Their Applications

Full Ceramic Bearings

Key Characteristics

• Made entirely from ceramic materials such as silicon nitride or zirconia.
• Appropriate for extreme temperatures of up to 1600°C.
• Applications include aerospace turbines, semiconductor equipment, and high-temperature industrial furnaces.

Strengths and Weaknesses

• Strength: Outstanding heat resistance and corrosion resistance.
• Weakness: Lower load capacity and higher cost compared to hybrid or steel bearings.

Hybrid Ceramic Bearings

Material Composition

• Hybrid ceramic bearings consist of steel rings paired with ceramic balls.
• They typically operate at temperatures up to 500°C.
• Common applications include high-speed industrial machinery, high-performance motors, and aerospace engines.

Advantages

• Combines the load capacity of steel with the heat resistance and low friction of ceramics.
• Greater cost-effectiveness compared to full ceramic bearings.

High-Temperature Steel Bearings

Best Uses

• Suitable for applications up to 350°C.
• Common materials include martensitic stainless steel (SUS440C) and deposition hardening steel (SUS630).
• Typical applications include steel mills, automotive exhaust systems, food processing ovens, and kilns.

How to Ensure Longevity and Performance in High Temperature Bearings

Proper Installation and Fit

Impact of Temperature on Bearing Fit

Different coefficients of thermal expansion affect how high temperature bearings fit during operation. Materials that expand at different rates can lead to changes in clearance, which may impact performance.

Maintain the right clearance for high-temperature bearings during installation. This is especially crucial during operation at high temperatures. This helps maintain alignment and reduces the risk of overheating or seizure.

Hoop Stress and Bearing Rings

Ensuring that the hoop stress on high-temperature bearing rings doesn’t exceed the yield stress at high temperatures is crucial. Too much hoop stress can cause the rings to deform or fail, which compromises their integrity and performance. Proper design and material choice are essential to maintain safe operating conditions and extend the high temperature bearings' lifespan.

Maintenance and Monitoring

Preventive Maintenance for High-Temperature Bearings

Routine inspections are important for high temperature bearings. Regularly check for wear, lubricant levels, and bearing clearance. This helps catch potential problems before high temperature bearings get worse.

Lubricant Management: Reapply lubricants when needed and replace high temperature bearings at the first sign of wear or damage. Timely maintenance can prevent unexpected failures and prolong the high temperature bearings' lifespan.

Early Detection of Bearing Failure

Look out for excessive noise, increased friction, or temperature spikes, as these can indicate potential high temperature bearings failure.

Using monitoring systems is vital for high-temperature applications. They can spot early signs of failure, allowing for timely maintenance and helping to prevent costly breakdowns.

Conclusion

In summary, the performance of high temperature bearings depends on operating temperature, material choice, load capacity, and lubrication. Selecting the right high temperature bearings increase their lifespan and reliability while lowering maintenance and downtime costs.

Customizing high-temperature bearings for specific uses is crucial for optimal performance. Consulting with experts is a good idea. They can provide valuable guidance to ensure you choose the right bearings for your application.