How to choose the right bearing grease !-NEWS-www.fv-bearing.com
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How to choose the right bearing grease !

Apr 19, 2022

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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.

Characteristics of respective greases

(1)Lithium greaseCalcium grease
(cup grease)
Sodium grease
(fiber grease)
ThickenerLithium soapCalcium soapSodium soap
Base oilMineral oilSynthetic oil(diester oil)Synthetic oil(silicon oil)Mineral oilMineral oil
Dropping point(℃)170 to 190170 to 230220 to 26080 to 100160 to 180
Operating temperature range(℃)-30 to +120-50 to +130-50 to +180-10 to +700 to +110
Rotation speed rangeMedium to highHighLow to mediumLow to mediumLow to high
Mechanical stabilityExcellentGood to excellentGoodFair to goodGood to excellent
Water resistanceGoodGoodGoodGoodBad
Pressure resistanceGoodFairBad to fairFairGood to excellent
RemarksMost 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.


(2)Complex base greaseNon-soap base grease
ThickenerLithium complex soapCalcium complex soapBentoneUrea compoundsFluorine compounds
Base oilMineral oilMineral oilMineral oilMineral/synthetic oilSynthetic oil
Dropping point(℃)250 or higher200 to 280-240 or higher250 or higher
Operating temperature range(℃)-30 to +150-10 to +130-10 to +150-30 to +150-40 to +250
Rotation speed rangeLow to highLow to mediumMedium to highLow to highLow to medium
Mechanical stabilityGood to excellentGoodGoodGood to excellentGood
Water resistanceGood to excellentGoodGoodGood to excellentGood
Pressure resistanceGoodGoodGood to excellentGood to excellentGood
RemarksSuperior 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℃.

(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, 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 penetration indexes, service conditions of grease. (NLGI : National Lubricating Grease Institute)

Table 12-4 Grease consistency

NLGI scaleAASTM penetration index
(25℃, 60 mixing operations)
Service conditions/ applications
0355 - 385For centralized lubricating
1310 - 340For centralized lubricating, at low temperature
2265 - 295For general use
3220 - 250For general use, at high temperature
4175 - 205For 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 FV bearings

Grease 
type

ThickenerBase oilAppearanceConsistency
60W
UnworkedWorked
Alvania 2LithiumMineral oilGrayish brown276275
Raremax AF-IUreaMineral oilPale yellow, viscous-300
FS841FluororesinFluorosilicone oilWhite-290
Sunlight 2LithiumMineral oilYellowish brown-280
Unirex N3Lithium complexMineral oilGreen-235
W191UreaPAO1), mineral oilPale yellow247275
Darina 2MicrogelMineral oilAmber-280
Emalube LUreaMineral oilLight brown, viscous-350
Palmax RBGSpecial lithium complexMineral oilYellow, viscous-300
4B greaseCarbon blackEthyl oilBlack-260
KRYTOX GPL 226FluororesinFluorinated oil
-280
Multemp PSNo.2LithiumMineral oil, ester oilPinkish white, viscous-275
KVC greaseUreaPAO1)、ester oilMilkish pink-244
SR greaseLithiumEster oilLight brown, viscous-250
KDL greaseFluororesin (PTFE)Fluorinated oilWhite-260
KHDLithiumPAO1)White-199
Nerita 2858LithiumMineral oil (XHVI)Yellowish brown-279
Arapen RB320Lithium, calciumMineral oilYellowish brown-315
Isoflex NBU15Barium complexEster oilBeige270280
Shell Cassida grease RLS2Aluminum complexPAO1)Transparent-280
Alvania EP2LithiumMineral oilBrown282276
Alvania 3LithiumMineral oilBrown240225


Application examples 

Grease
Type

NLGI
scale
Operating temperature range
AutomobileSteering columnAlvania 22-10 - 100
Wheel (hub unit)Raremax AF-I1-22)0 - 150
Fan couplingFS8412-40 - 220
Universal joint (shell type), steering jointSunlight 22-10 - 100
Clutch releaseUnirex N33-10 - 130
Water pump bearingW1912-30 - 130

Steel production

ConveyorDarina 220 - 150
Continuous casting machineEmalube L0-1 2)-10 - 200

Rolling mill roll neck
Lubrication of Roll Neck Bearings.pdf

Palmax RBG1-2 2)-10 - 150
Extra-small/miniature ball bearingsPhotocopier (high temperature/conductive),printer (high temperature/conductive)4B grease2-32)-30 - 250
Photocopier (high temperature),printer (high temperature)KRYTOX GPL 22620 - 250
Motor (for low temperatures)Multemp PSNo.22-40 - 100
Motor (for high temperatures), rotary encoder,fan motor (for high temperatures)KVC grease3-30 - 150
Extra-small/miniature ball bearings,automobileMotor, stepping motor, fan motor Center bearing (for propeller shafts), steering columnSR grease3-40 - 130
Semiconductor manufacturing equipmentFor high temperatures, for clean environment,for vacuum environmentKDL grease2-32)-30 - 200
For room temperature, for atmosphereKHD4-30 - 120
Railway rolling stockAxle journal (ABU)Nerita 28582-30 - 100
Axle journal (general)Arapen RB3201-30 - 90
Machine tool spindle
Isoflex NBU152-40 - 100
For food machinery
Shell Cassida grease RLS22-20 - 100
Slewing rim, automobileUniversal joint, king pin thrust bearingAlvania EP22-10 - 80
Agricultural machinery
Alvania 33-10 - 100

[Notes]

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



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