How to Select the Right Bearing for Extreme Special Environments (EXSEV Bearings) (Part 2): Bearings for clean, vacuum, high-temperature, or corrosive environments

In Part 1, we explained about the materials and lubricants used in bearings for extreme special environments.
How to Select the Right Bearing for Extreme Special Environments (EXSEV Bearings) (Part 1): Materials and lubricants

In this part, we will discuss important points for selecting bearings for extreme special environments used in clean, vacuum, high-temperature, or corrosive environments.
Note that because ball bearings are often used as rolling bearings for extreme special environments, this column uses ball bearings as an example.

1. Specifications of bearings for clean environments

Bearings made of high carbon chromium bearing steel cannot be used in most clean environments because they require anti-corrosion oil. For this reason, bearing rings (outer and inner rings) and balls are made of martensitic stainless steel (JIS SUS440C) used without applying anti-corrosion oil. Also, a lubricant with low particle emission is selected.
Figure 1 shows a list of bearings suitable for use in clean environments.

Figure 1: Bearings suitable for use in clean environments

Table 1 shows the specifications of each type of bearing.

Table 1: Specifications of bearings for clean environments

These bearings for clean environments generate less particles, making them suitable for clean environments.

Figure 2: New Clean Pro Bearing-PR (polymeric solid lubricant coating)

Figure 3: EXSEV-EX Bearing (fluorinated grease)

Figure 4: EXSEV-FA Bearing (fluorocarbon resin cage)

See the following for details on bearings for clean environments.
Clean environments

2. Specifications of bearings for vacuum environments

Martensitic stainless steel (JIS SUS440C) is used as the standard material for bearing rings and balls used in vacuums. Precipitation hardening stainless steel (JIS SUS630) is used when corrosion resistance is required, while high-speed tool steel (JIS SKH4, AISI M50, etc.) is used when high temperatures are involved. Ceramic materials with excellent heat and corrosion resistance are also used.
A bearing used in an ordinary vacuum chamber is repeatedly exposed to atmospheric air and vacuum. There is no rolling bearing lubricant that is effective for use under such a wide pressure range. Select a lubricant that is most suitable for the pressure and temperature that are normally used, and if necessary, based on the required cleanliness and corrosion resistance.

Figure 5 shows a list of bearings suitable for use in vacuum environments where cleanliness is not required.

Figure 5: Bearings suitable for use in vacuum environments where cleanliness is not required

Table 2 shows the specifications of each type of bearing.

Table 2: Specifications of bearings for vacuum environments (when cleanliness is not required)

(*) Separators are components that prevent direct contact between balls, as shown in Figure 7.

Figure 6: EXSEV-WS Bearing (separator including tungsten disulfide)

Figure 7: Separator

See the following for details on bearings for vacuum environments.
Vacuum environments

3. Specifications of bearings for high-temperature environments

Figure 8 shows bearing materials for high-temperature environments.

Figure 8: Bearing materials for high temperatures

Select a material suitable for the ambient temperature in which the bearing will be used.

Figure 9 shows bearing lubricants for high-temperature environments.

Figure 9: Lubricants for high temperatures

In ambient temperatures up to approx. 260°C, EXSEV-EX fluorinated grease can be used.
In ambient temperatures that exceed 260°C, EXSEV-XT fluorinated grease or layer lattice materials (molybdenum disulfide: MoS₂ or tungsten disulfide: WS₂) are to be used.
Because all layer lattice materials emit a large amount of particles, they are not suitable for applications where cleanliness is required.
Because there are no lubricants effective for use in ambient temperatures that exceed 500°C, unlubricated Full Complement Ceramic Ball Bearings are sometimes used.

Figure 10 shows the specifications of bearings for high-temperature environments.
Table 3 shows the specifications of Full Complement Ceramic Ball Bearings. For the specifications of bearings other than Full Ceramic Bearings, see Table 2.

Figure 10: Bearings suitable for high temperatures

Table 3: Specifications of Full Complement Ceramic Ball Bearings"

Figure 11: Full Complement Ceramic Ball Bearing (uses silicon nitride)

See the following for details on bearings for high-temperature environments.
High-temperature environments

4. Specifications of bearings for corrosive environments

1） Corrosion resistance of special steels
Table 4 shows the corrosion resistance of special steels when subjected to common corrosive solutions.
Among stainless steels, JIS SUS630 exhibits better corrosion resistance than JIS SUS440C. However, stainless steel cannot be used in highly corrosive solutions such as acids and alkalis, or when trying to avoid rust caused by corrosion mixing with the solution.

Table 4: Corrosion resistance of special steels

Temperature: 25°C
Corrosion rate (mm/year) ◎: 0.125 or less, 〇: over 0.125 to 0.5, △: over 0.5 to 1.25, ×: over 1.25

2）Corrosion resistance of ceramic materials
Table 5 shows the corrosion resistance of ceramic materials. Although silicon nitride has excellent corrosion resistance and is a standard material used for ceramic bearings, it may corrode under conditions involving highly corrosive solutions or temperatures, etc. Zirconia and silicon carbide are to be used for such environments.

Table 5: Corrosion resistance of ceramic materials

◎: Unaffected 〇: Mostly unaffected
△: May be slightly affected ×: May be affected

3） Specifications and applications of bearings for corrosive environments
Table 6 shows the specifications and main applications of common types of bearings used in corrosive environments.

Table 6: Specifications and main applications of common types of bearings used in corrosive environments

Using bearings for corrosive environments in a solution causes the solution itself to act as a lubricant for the bearing and significantly affects the service life of the bearing. Consult with JTEKT when selecting a bearing for such applications.

Figure 12: Corrosion Guard Pro Bearing-SC (uses silicon carbide)

Figure 13: Corrosion Guard Pro Bearing-ZO (uses zirconia)

See the following for details on bearings for corrosive environments.
Corrosive environments

5. Conclusion

In this part, we discussed important points for selecting bearings for extreme special environments used in clean, vacuum, high-temperature, or corrosive environments.

These bearings for extreme special environments are used in the clean, vacuum, high-temperature, and corrosive environments of manufacturing equipment for semiconductors.
Product Series for Use in Semiconductor Manufacturing Processes
JTEKT also offers a selecting tool for bearings for extreme special environments.
Selecting tool for bearings for extreme special environments

In the next column, we will discuss important points for selecting bearings that require special properties such as non-magnetism, insulation, and high-speed rotation.

If you have any technical questions regarding bearings for extreme special environments, or opinions/thoughts on these "Bearing Trivia" pages, please feel free to contact us using the following form.

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