Have you ever wondered how high-speed bearings enable machines to spin effortlessly at incredible speeds? Are you excited to discover the secrets hidden within their finely crafted designs? If you are, you’ve come to the right place.  

In this blog, we aim to satisfy your inquisitive nature by unraveling the questions and answers surrounding high-speed bearings. 

 

What is high speed from the perspective of a high-speed bearing? 

The rotational speed or RPM (revolutions per minute) that is considered “high-speed” for a bearing can vary depending on the specific application, bearing type, size, and design. However, generally speaking, high-speed bearings are designed to operate reliably at rotational speeds greater than 10,000 RPM. A bit more specific technical specification can be penciled in based on the surface velocity of the rotating object. This definition considers both diameter and rpm. With this definition, the high speed can be defined as more than 100 m/s surface velocity.  

In small machines, 10 000 RPM is low, with big diameter, it can be the ultimate maximum speed and knock the boundaries of physical material properties. Thus, RPM is not everything, but the size of the machine is equally important while drafting the definition of high-speed in applications that require high-speed bearings. 

SpinDrive active magnetic bearing for high-speed applications

Figure 1. SpinDrive active magnetic bearings for high-speed applications

In various industries, such as aerospace, automotive, and manufacturing, high-speed bearings can reach speeds ranging from 10,000 RPM to well over 100,000 RPM. For example, in turbochargers or gas turbines, high-speed bearings can exceed 200,000 RPM. 

High-speed bearings are engineered to withstand the challenges associated with these rapid rotations, such as increased centrifugal forces, higher temperatures, and potential vibration issues. Manufacturers provide specific speed ratings and guidelines for their bearings to ensure safe and reliable operation at high speeds. Therefore, it is important to consult the manufacturer’s specifications and recommendations when determining the appropriate RPM range for a particular high-speed bearing. 

 

What is a high-speed bearing? 

Bearings are, traditionally, mechanical components that support the rotational motion of a shaft or other moving parts while reducing friction and enabling smooth movement. A high-speed bearing is a type of bearing specifically designed to operate efficiently at high rotational speeds.  

In high-speed applications, such as turbines, high-speed electrical machines, machining spindles, turbo blowers and turbo compressors, the rotational speeds can be extremely high. These high speeds can generate significant heat and cause excessive wear if not properly managed. Therefore, high-speed bearings are engineered to address these challenges and maintain reliable performance under demanding conditions. 

 

Which high-speed bearing technology to choose? 

At SpinDrive, we are in the active magnetic bearing (AMB) business and obviously, we love AMBs and their special features that make them extraordinary from any other bearing types. Naturally, there are applications where other bearing types are suitable or even better than AMBs. Ball bearings are good for generalistic applications where the RPMs do not hit extreme boundaries. They require more maintenance than other high-speed bearing technologies. Air bearings are mostly good for lowerpower applications where high precision is needed. They are costefficient yet require a good understanding of the technology. Fluid film bearings have the greatest load capacity of contactless high-speed bearings making them suitable for big machines. However, there is always a concern that the oil gets into the process and contaminates the end-product. 

Magma AMB control units

Figure 2. Magma X800 magnetic bearing controller developed by SpinDrive

 

Which bearing is used in high RPM? 

There are different technologies that are suitable for high-speed applications, namely high-speed ball bearings, air bearings, fluid film bearings, and magnetic bearings. These bearing technologies are introduced briefly in our earlier blog post here https://spindrive.fi/why-magnetic-bearings/. 

High-speed ball bearings minimize internal friction through precision manufacturing, lightweight design, and features like low-friction cages and specialized lubrication. They are ideal for applications demanding dynamic load capacity.  

Angular contact ball bearing by GMN

Figure 3. Angular contact ball bearing by GMN. In order to cut the rotating inertia, the bores are thin, balls are small, and the cage is made out of polymer. 

Air bearings, relying on compressed air, offer precise motion control, non-contact design, low heat generation, ease of integration, and customization. They are suitable for low-power applications due to limited load capacity 

Air bearings by OAVAir thrust bearing by OVA

Figure 4. Air bearings by OAV. Journal bearing controlling radial direction in the above and thrust bearing in the bottom.

Fluid film bearings, utilizing a lubricating film, provide adjustable load capacity and high damping. They provide good load capacity, much higher than other contactless bearing technologies making them appealing options for large machinery. 

fluid film bearings from Waukesha

Figure 5. A fluid film bearing by Waukesha. There are four radial pads on the inner circle in the backside of the structure. Eight most visible pads control the thrust load. 

Active magnetic bearings excel in precise position control, offering features like fast response time, variable stiffness, and maintenance-free operation. They are suitable for high-speed applications in across different applications in both low- and high-power segments with adaptive control and monitoring capabilities for optimal performance. 

 

What material is used in a high-speed bearing?

High-speed ball bearings utilize steel, such as chrome or stainless steel, for high hardness, strength, and wear resistance, crucial in minimizing friction. Ceramics, like silicon nitride or zirconia, are preferred for their lightweight nature, high-temperature resistance, and excellent corrosion and wear resistance, making them ideal for applications where reducing weight and friction are essential. Combining ceramic balls with steel rings in hybrids enhances overall performance, offering improved efficiency and reduced wear in high-speed conditions. 

Air bearings use materials like ceramics and polymers for non-contact support, reducing weight, providing high-temperature resistance, and minimizing friction for smooth, high-speed operation without physical contact. Structural components like aluminum, stainless steel, or ceramics are chosen for their specific properties, balancing weight, durability, and performance in air bearing systems. 

Fluid film bearings utilize materials like bronze providing high-load capacity, and composites addressing specific needs like corrosion resistance, selected based on desired characteristics for load-carrying capacity and environmental conditions. Steel is chosen for standard applications, while ceramics are used for reduced weight, high-temperature resistance, and enhanced wear resistance. The fluid is another important element to select. Typically, the used fluid is oil of some sort, but also water with some additives and special polymer-based lubricants are used. 

Active magnetic bearings are primarily based on electromagnets that are made from laminated electrical steel sheets stacked together and copper coils. Lamination stacks are used in both rotors and stators. In some special designs, permanent magnets such as neodymium, samarium-cobalt, or ferrite magnets can be used to provide additional magnetic flux. Permanent magnets are also used in passive magnetic bearings. Power electronic controller is the brain of the system located outside of the high-speed machine. 

Interested in learning more about active magnetic bearings? Check other blogs about active magnetic bearing applications in various industries: 

Active magnetic bearings for turbo blowers 

Active magnetic bearings for turbo compressors 

Active magnetic bearings for high-speed spindles 

 

About the author

SpinDrive CEO, Janne Heikkinen holds a doctoral degree from mechanical engineering. In his doctoral studies, he explored the effect of geometric inaccuracies of bearings to the vibrations of rotors. 

 

Janne Heikkinen portrait

Author: Janne Heikkinen

 

Click the links to learn more about additional topics:

Magnetic bearings FAQ

Why Magnetic bearings for high-speed applications?

Applications of active magnetic bearings

Benefits of active magnetic bearings