Turbomolecular Pump Bearings

In this article, I will discuss different bearing designs used in Turbomolecular pumps. The working principle of a Turbomolecular pump and the leading Bearing brands. I will add a list of turbomolecular bearing part numbers and where you can buy them. Pacific International Bearing (PIB) represents the highest quality turbomolecular pump bearings from manufacturers who have extensive knowledge and years of experience.

Bearings specified for use in Turbomolecular Pumps must survive in a very difficult environment. Turbomolecular pumps are commonly found in semiconductor, chemical analysis and SEM (Scanning Electron Microscope) equipment. Bearings in these environments must work in the 10-6 to 10-9mm Bar region.

Turbomolecular Bearings in vacuum conditions must be reliable, offer high-speed capabilities and last. Minimum life requirements exceed 30,000 hours of life, having only a small application of lubricant. To achieve the required high-speed rotation, somewhere in the range of 30,000 to 90,000 RPM, the bearings must have low friction, exceptional stability, and resistance to wear.

In operation, bearings must have low vibration and noise characteristics. Those manufacturers capable of designing and manufacturing turbomolecular bearings use special surface finish and harmonic standards during manufacturing. In many cases, bearings can be designed to have an infinite fatigue life.

Turbo Molecular Pumps operate where gas molecules move in very specific biased directions when hit by a solid surface. The moving pump blade due to its interaction with the gas molecules can be guided in a predictable direction. Ultra high operating pressures are present and range between 103 and 10-11 mbar, with pumping speeds of between 10 and 4,000 l/s. Bearings must operate with no downstream contamination and no lubrication loss.

In this difficult environment, the bearing rings must be of the highest precision and have controlled harmonic amplitudes for the raceways. The bearings must have a very high if not exceptional surface finish. In addition to supporting the rotor, TMP bearings need to maintain precise alignment between the rotor and the stator. If this precision is not maintained then catastrophic failure is likely. Bearings applied in TMP applications must maintain precision performance while subjected to high temperatures and corrosive environments many times without the benefit of conventional lubrication.  

Manufacturers such as Barden Bearing manufacture bearings specifically designed for use in Turbomolecular pumps and will manufacture special custom designed bearings for customers. Requirements for turbomolecular bearings include special low outgassing lubrication and are available from Pacific International Bearing in the normal bore size range from 4mm-12mm. 

Turbomolecular bearings can be manufactured from Cronidur 30 stainless steel material which has greater corrosion resistance and is longer wearing than 440C stainless steel. 

Leading Manufacturers like Barden Bearing commonly use AMS5898 high-nitrogen steel for optimum performance and reliability.

The use of AMS5898 material ensures excellent performance when paired with a ceramic ball rolling element. This design is employed to provide high performance and meet the demands for exceptional corrosion resistance and high-speed requirements. To meet the requirement for higher pumping speeds Barden turbomolecular bearings use high-speed ceramic small ball technology.

Barden offers shielded angular contact bearings to guard against contamination. Barden also offers these bearings in open and sealed versions as required by each application. The Barden part numbering system includes a “TMP Standard” having a special internal finish which provides for even more quieter running and therefore higher reliability and extended life.

Schaeffler Bearing has an outstanding reputation as a quality manufacturer of turbomolecular bearings

As Compressors and vacuum pumps function in many areas of commerce and industry Schaefller offer FAG, INA, and Barden product lines for almost every need. ln Schaeffler’s large portfolio of bearings they can conquer almost every application requirement. Schaeffler offers bearings for every purpose and has the largest range of bearings in X-life quality. The Barden product line is particularly suited for turbomolecular bearing applications.  

Schaeffler products used in applications for compressors 

1. Compression of compressed air, both mobile and stationary, for example in factory automation, materials handling, construction machinery, etc;

2. Refrigeration compression for industrial and commercial cooling and central air-conditioning systems;

3. Process gas compression in process engineering, the chemical industry or biotechnology;

4. Compression in the oil and gas industry, whether upstream, midstream or downstream.

Schaeffler products used in Application for Vacuum Pumps

1. Generation of negative pressure in packaging technology, as in the food and pharmaceutical industries; 

2. High-purity vacuum, dry-running vacuum pumps applied in the  manufacturing of silicon wafers;

3. Vacuum as an important component in the chemical industry;  

4. Simulation and component testing in the aerospace industry.

The challenge for turbo molecular pump bearings includes:

• Long life expectancy;
• Absolute reliability;
• High speeds;
• Low noise level;
• Low vibration;
• Cleanliness.

Significant performance can be achieved through bearing design optimization. In some cases, the use of enclosed bearings with seals and or shields are needed to protect against contamination and to increase life. Choosing ceramic balls (Si3N4) for higher speeds and negligible friction is essential for optimizing bearing dynamics. Using an Integrated tribological concept for lubricant, preservation, surface quality, and materials yields satisfactory results according to Barden Bearing. Some companies like GMN use their own GMN TXM cage resulting in lower vibrations and quiet operation.

GMN Bearing Company offers Spindle ball bearings for Turbomolecular Pump applications and are available in Open or shielded with  Silicon nitride balls with a Vacuum of up to 10-3 mbar and with Speed characteristics up to 1,1 x 106 mm/min.

• Service life > 30.000 h
• Cages: oil impregnated hard tissue cage or TXM cage
• Special design (dimensions, design, cage)
• Optimized grease reservoir

• Open or covered
• Silicon nitride spheres (Si3N4)
• Vacuum to 10-3 mbar
• Characteristic RPM up to 0,8 x 106 mm/min
• Oil lubrication
• Service life > 30.000 h

Vacuum Technology

GMN develops complete designs in collaboration with the industry for special bearings, in particular for turbomolecular pumps (TMP).

Emergency Touchdown Bearings

Barden Bearing has also developed Emergency Touchdown support bearings for when a magnetic bearing system fails. Many industrial applications such as turbo blowers, turbo compressors, and turbomolecular pumps may employ a magnetic bearing system and so it is possible to back it up with mechanical Barden emergency touchdown support bearings.

If a complete electronics failure occurs, Barden mechanical Touchdown bearings protect the system from a total crash. In this application, the bearing needs to accelerate from zero to 2.7 or higher ndm instantly, even if the TD bearing sat idle for years. In this case, the bearing system must instantly and accurately control the rotor and the extremely high radial, axial and shock loads. The initial shock load is high due to the gyroscopic forces generated.

Barden bearings have been developed for this application using ceramic balls and a full ball complement design. Barden uses AMS5898 material to create a reliable exceptional performance and corrosion resistant TD bearing. The  Barden bearing design is optimized for the maximum number of touchdowns.

Of course, you can specify and use Barden’s full complement hybrid ceramic bearings in numerous other applications.

Magnetic Bearings

As I mentioned earlier, Magnetic bearings are also used in Turbomolecular pump applications. Magnetic bearings have represented a significant technological advancement in TMP bearing design. These bearings operate without any physical contact by suspending the rotor using magnetic fields generated by electromagnets. This lack of contact means that there is no wear and tear, enabling the pump to operate more cleanly and with less maintenance. Magnetic bearings can be controlled actively by adjusting the electromagnetic fields to maintain the rotor position, a feature provided by brands such as Calnetix Technologies. This level of control can compensate for imbalances and external vibrations, contributing to the pump’s overall efficiency and stability.

Radial Ball Bearings

Ball bearings are the most conventional type of bearings used in TMPs. They typically consist of steel or ceramic balls contained within inner and outer raceways. In TMP applications, angular contact ball bearings are also widely used due to their ability to handle both radial and axial loads simultaneously, a crucial factor for the stability of the rotor at high speeds.

This listing is for bearings already designed into popular turbomolecular pumps.

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