12-2-1 Grease

Grease is made by mixing and dispersing a solid of high oil-affinity (called a thickener) with lubricant oil (as a base), and transforming it into a semi-solid state.
As well, a variety of additives can be added to improve specific performance.

(1) Base oil

Mineral oil is usually used as the base oil for grease. When low temperature fluidity, high temperature stability, or other special performance is required, diester oil, silicon oil, polyglycolic oil, fluorinated oil, or other synthetic oil is often used.
Generally, grease with a low viscosity base oil is suitable for applications at low temperature or high rotation speed; grease with high viscosity base oils are suitable for applications at high temperature or under heavy load.

(2) Thickener

Most greases use a metallic soap base such as lithium, sodium, or calcium as thickeners. For some applications, however, non-soap base thickeners (inorganic substances such as bentone, silica gel, and organic substances such as urea compounds, fluorine compounds) are also used.
In general, the mechanical stability, bearing operating temperature range, water resistance, and other characteristics of grease are determined by the thickener.

(Lithium soap base grease)
Superior in heat resistance, water resistance and mechanical stability.
(Calcium soap base grease)
Superior in water resistance; inferior in heat resistance.
(Sodium soap base grease)
Superior in heat resistance; inferior in water resistance.
(Non-soap base grease)
Superior in heat resistance.

Table 12-3 Characteristics of respective greases

Lithium greaseCalcium grease
(cup grease)
Sodium grease
(fiber grease)
Complex base greaseNon-soap base grease
Thickener Lithium soap Calcium soap Sodium soap Lithium complex soap Calcium complex soap Bentone Urea compounds Fluorine compounds
Base oil Mineral oil Synthetic oil(diester oil) Synthetic oil(silicon oil) Mineral oil Mineral oil Mineral oil Mineral oil Mineral oil Mineral/synthetic oil Synthetic oil
Dropping point(℃) 170 to 190 170 to 230 220 to 260 80 to 100 160 to 180 250 or higher 200 to 280 - 240 or higher 250 or higher
Operating temperature range(℃) -30 to +120 -50 to +130 -50 to +180 -10 to +70 0 to +110 -30 to +150 -10 to +130 -10 to +150 -30 to +150 -40 to +250
Rotation speed range Medium to high High Low to medium Low to medium Low to high Low to high Low to medium Medium to high Low to high Low to medium
Mechanical stability Excellent Good to excellent Good Fair to good Good to excellent Good to excellent Good Good Good to excellent Good
Water resistance Good Good Good Good Bad Good to excellent Good Good Good to excellent Good
Pressure resistance Good Fair Bad to fair Fair Good to excellent Good Good Good to excellent Good to excellent Good
Remarks Most widely usable for various rolling bearings. Superior low temperature and friction characteristics. Suitable for bearings for measuring instruments and extra-small ball bearings for small electric motors. Superior high and low temperature characteristics. Suitable for applications at low rotation speed and under light load.
Not applicable at high temperature.
Liable to emulsify in the presence of water.
Used at relatively high temperature.
Superior mechanical stability and heat resistance.
Used at relatively high temperature.
Superior pressure resistance when extreme pressure agent is added.
Used in bearings for rolling mills.
Suitable for applications at high temperature and under relatively heavy load. Superior water resistance, oxidation stability, and heat stability.
Suitable for applications at high temperature and high speed.
Superior chemical resistance and solvent resistance. Usable at up to 250℃.

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(3) Additives

Various additives are selectively used to serve the respective purposes of grease applications.

  • Extreme pressure agents
    When bearings must tolerate heavy or impact loads.
  • Oxidation inhibitors
    When grease is not refilled for a long period. Structure stabilizers, rust preventives, and corrosion inhibitors are also used.

(4) Consistency

Consistency, which indicates grease hardness, is expressed as a figure obtained, in accordance with ASTM (JIS), by multiplication by 10 the depth (in mm) to which the coneshaped metallic plunger penetrates into the grease at 25℃ by deadweight in 5 seconds. The softer the grease, the higher the figure. Table 12-4 shows the relationships between the NLGI scales and ASTM (JIS) penetration indexes, service conditions of grease. (NLGI : National Lubricating Grease Institute)

Table 12-4 Grease consistency

NLGI scaleAASTM (JIS) penetration index
(25℃, 60 mixing operations)
Service conditions/ applications
0 355 - 385 For centralized lubricating
1 310 - 340 For centralized lubricating, at low temperature
2 265 - 295 For general use
3 220 - 250 For general use, at high temperature
4 175 - 205 For special applications

(5) Mixing of different greases

Since mixing of different greases changes their properties, greases of different brands should not be mixed.
If mixing cannot be avoided, greases containing the same thickener should be used. Even if the mixed greases contain the same thickener, however, mixing may still produce adverse effects, due to difference in additives or other factors.
Thus it is necessary to check the effects of a mixture in advance, through testing or other methods.

Table 12-5 Typical examples of standard grease for JTEKT bearings

Grease nameThickenerBase oilAppearanceConsistency
Operating temperature range
Application examples
Unworked Worked
Alvania 2 Lithium Mineral oil Grayish brown 276 275 2 -10 - 100 Automobile Steering column
Raremax AF-I Urea Mineral oil Pale yellow, viscous - 300 1-22) 0 - 150 Wheel (hub unit)
FS841 Fluororesin Fluorosilicone oil White - 290 2 -40 - 220 Fan coupling
Sunlight 2 Lithium Mineral oil Yellowish brown - 280 2 -10 - 100 Universal joint (shell type), steering joint
Unirex N3 Lithium complex Mineral oil Green - 235 3 -10 - 130 Clutch release
W191 Urea PAO1), mineral oil Pale yellow 247 275 2 -30 - 130 Water pump bearing
Darina 2 Microgel Mineral oil Amber - 280 2 0 - 150 Steel production Conveyor
Emalube L Urea Mineral oil Light brown, viscous - 350 0-1 2) -10 - 200 Continuous casting machine
Palmax RBG Special lithium complex Mineral oil Yellow, viscous - 300 1-2 2) -10 - 150 Rolling mill roll neck
4B grease Carbon black Ethyl oil Black - 260 2-32) -30 - 250 Extra-small/miniature ball bearings Photocopier (high temperature/conductive),printer (high temperature/conductive)
KRYTOX GPL 226 Fluororesin Fluorinated oil - 280 2 0 - 250 Photocopier (high temperature),printer (high temperature)
Multemp PSNo.2 Lithium Mineral oil, ester oil Pinkish white, viscous - 275 2 -40 - 100 Motor (for low temperatures)
KVC grease Urea PAO1)、ester oil Milkish pink - 244 3 -30 - 150 Motor (for high temperatures), rotary encoder,fan motor (for high temperatures)
SR grease Lithium Ester oil Light brown, viscous - 250 3 -40 - 130 Extra-small/miniature ball bearings,automobile Motor, stepping motor, fan motor Center bearing (for propeller shafts), steering column
KDL grease Fluororesin (PTFE) Fluorinated oil White - 260 2-32) -30 - 200 Semiconductor manufacturing equipment For high temperatures, for clean environment,for vacuum environment
KHD Lithium PAO1) White - 199 4 -30 - 120 For room temperature, for atmosphere
Nerita 2858 Lithium Mineral oil (XHVI) Yellowish brown - 279 2 -30 - 100 Railway rolling stock Axle journal (ABU)
Arapen RB320 Lithium, calcium Mineral oil Yellowish brown - 315 1 -30 - 90 Axle journal (general)
Isoflex NBU15 Barium complex Ester oil Beige 270 280 2 -40 - 100 Machine tool spindle
Shell Cassida grease RLS2 Aluminum complex PAO1) Transparent - 280 2 -20 - 100 For food machinery
Alvania EP2 Lithium Mineral oil Brown 282 276 2 -10 - 80 Slewing rim, automobile Universal joint, king pin thrust bearing
Alvania 3 Lithium Mineral oil Brown 240 225 3 -10 - 100 Agricultural machinery

1)PAO:Polyalphaolefin oil
2)The value is within the range specified by the consistency numbers.

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12-2-2 Lubricating oil

For lubrication, bearings usually employ highly refined mineral oils, which have superior oxidation stability, rust-preventive effect, and high film strength. With bearing diversification, however, various synthetic oils have been put into use. These synthetic oils contain various additives (oxidation inhibitors, rust preventives, antifoaming agents, etc.) to improve specific properties. Table 12-6 shows the characteristics of lubricating oils.
Mineral lubricating oils are classified by applications in JIS and MIL.

Table 12-6 Characteristics of lubricating oils

Type of lubricating oilHighly refined mineral oilMajor synthetic oils
Diester oilSilicon oilPolyglycolic oilPolyphenyl ether oilFluorinated oil
Operating temperature range(℃) -40 to +220 -55 to +150 -70 to +350 -30 to +150 0 to +330 -20 to +300
Lubricity Excellent Excellent Fair Good Good Excellent
Oxidation stability Good Good Fair Fair Excellent Excellent
Radioactivity resistance Bad Bad Bad to fair Bad Excellent -

[Selection of lubricating oil]

The most important criterion in selecting a lubricating oil is whether the oil provides proper viscosity at the bearing operating temperature. Standard values of proper kinematic viscosity can be obtained through selection by bearing type according to Table 12-7 first, then through selection by bearing operating conditions according to Table 12-8.

When lubricating oil viscosity is too low, the oil film will be insufficient. On the other hand, when the viscosity is too high, heat will be generated due to viscous resistance. In general, the heavier the load and the higher the operating temperature, the higher the lubricating oil viscosity should be ; whereas, the higher the rotation speed, the lower the viscosity should be. Fig. 12-3 illustrates the relationship between lubricating oil viscosity and temperature.

Table 12-7 Proper kinematic viscosity by bearing type

Bearing typeProper kinematic viscosity at operating temperature
Ball bearing Cylindrical roller bearing 13mm2/s or higher
Tapered roller bearing Spherical roller bearing 20mm2/s or higher
Spherical thrust roller bearing 32mm2/s or higher

Table 12-8 Proper kinematic viscosities by bearing operating conditions

Operating temperature dmnvalue Proper kinematic viscosity (expressed in the ISO viscosity grade or the SAE No.)
Light/normal load Heavy/impact load
-30 to 0℃ All rotation speeds ISO VG 15、22、46 (Refrigerating machine oil) -
0 to 60℃ 300000 or lower ISO VG 46 (Bearing oil Turbine oil) ISO VG 68 (Bearing oil Turbine oil)
SAE 30
300000 to 600000 ISO VG 32 (Bearing oil Turbine oil) ISO VG 68 (Bearing oil Turbine oil)
600000 or higher ISO VG 7、10、22 (Bearing oil) -
60 to 100℃ 300000 or lower ISO VG 68 (Bearing oil) ISO VG 68、100 (Bearing oil)
SAE 30
300000 to 600000 ISO VG 32、46 (Bearing oil Turbine oil) ISO VG 68 (Bearing oil Turbine oil)
600000 or higher ISO VG 22、32、46 (Bearing oil Turbine oil Machine oil) -
100 to 150℃ 300000 or lower ISO VG 68、100 (Bearing oil) ISO VG 100 to 460 (Bearing oil Gear oil)
SAE 30、40
300000 to 600000 ISO VG 68 (Bearing oil Turbine oi) ISO VG 68、100 (Bearing oil)
SAE 30 SAE 30、40


  1. a_129_001.pngD:nominal outside diameter(mm)、d:nominal bore diameter(mm)、n:rotational speed(min-1)}
  2. Refer to refrigerating machine oil (JIS K 2211), turbine oil (JIS K 2213), gear oil (JIS K 2219), machine oil (JIS K 2238) and bearing oil (JIS K 2239).
  3. Please contact with JTEKT if the bearing operating temperature is under −30℃ or over 150℃ .

Fig. 12-3 Relationship between lubricating oil viscosity and temperature (viscosity index :100)

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