Types of Grease
 
  Types of Grease  
 

Lithium, Calcium, Soda, Aluminium,Complex and Mixed soap base Greases, Soap free Grease, PTFE, Silicone and Molybdenum modified Greases, Specialty and Synthetic Greases.

 
     

Basic Defination

 
  The original Definition of ASTM of Grease was "A” solid or semi solid combination of petroleum products and a soap or mixtures of soaps with or without fillers, suitable for certain types of lubrication.

Subsequent technological advances have led to the use of synthetic lubricating fluids on the one hand and non-soap thickener’s on the other hand.

Current - Modified Definition of Grease is "A solid or semi solid product of dispersion of thickening agent in liquid lubricant. Other ingredients imparting special properties may be included”.

Most greases are in fact is a combination of petroleum oils and metallic soaps.

 
 

Grease is a lubricant of higher initial viscosity than oil, consisting originally of a calcium, sodium or lithium soap jelly emulsified with mineral oil.

Greases are typically used in areas where a continuous supply of oil cannot be retained, such as open bearings or gears.

Grease is a fine dispersion of an oil-insoluble thickening agent - usually soap in a fluid lubricant which is generally mineral lubricating oil. The soap is made up of fatty acid, tallow or vegetable oil saponified with alkali which can be hydrated lime, caustic soda, lithium hydroxide or aluminum hydroxide. The lubricating oil component is refined base oil-naphthenic, of medium viscosity index, or cylinder oil stock. Structurally grease is a “water-in-oil” emulsion. Its appearance is smooth, mostly translucent, soft or hard.

Properties essential for performance of grease are structural stability, lubricating quality, low and high temperature performance (which are provided by the selected lube oil base stock), where as properties such as water resistance, high temperature quality, resistance to break down through continuous use and ability of grease to stay in place are provided by the soap.

Additives e.g. Graphite, modified clay, asphalt, oxidation and corrosion inhibitors, extreme pressure additives molybdenum disulphide etc. are used to impart specific properties as required by end application.

Factors to be considered when selecting greases are the type of grease, which in turn depends on operating temperatures, water resistance, oxidation stability etc. The second factor, no less important, are the grease's characteristics, including viscosity and consistency.

 
     
 
Basic Types Of Grease  
SOAP TYPES GREASES NON SOAP THICKNER GREASES
Metallic soaps + Lubricating Oils + Additives for imparting Special properties Thickening Agent + Lubricating Fluid (Synthetic oils) + Additives for imparting Special properties
 
     
 

The value of plastic lubricants has been recognized since very early times when animal fats were used for Axles and the like.

In general any lubricating fluid can be gelled by means of a suitable thickness to form a lubricating Grease. In practice mineral oils are almost exclusively used. For soap type Greases mineral oils of relatively low viscosity index 60 are preferred since the greater solvency of the more aromatic oils for soaps makes manufacture easier and gives greases with lower soap contents and with better properties.

Synthetic Fluids: Esters and silicones are used, only in greases for special applications, where cost is secondary to performance to meet low temperature and high temperature requirements; - 75ºC to + 320ºC.

The Soaps used are the metallic salts of long chain fatty acids derived from wide range of natural fatty materials. Soaps are mainly produced by specifying the fat or fatty acid with appropriate alkali in the presence of oil.

In some cases pre-formed soaps are used, such as aluminium stearate, lithium sterate etc.

Non Soap – Thickners may be inorganic e.g. silica or clay or organic with a very high melting point . e.g. terephthalamates, arylureas (these may be either pre-formed or formed in situ) and the dye stuffs, indanthrene and phthalscyanine. They need to be oleophilic and this characteristic may be imparted either in the thickner formulation (i.e. by including a long chain hydrocarbon chain or surface esterification ) or by coating the particle surfaces with organic cations. In the latter case about 75 percent of the particle surface is covered, which gives the desired effect without affecting inter –particle forces too much. Pre-treated clays (i.e. coated and dried) need aids to facilitate dispersion in oil. These dispersion aids are low molecular weight polar organic compounds such as methanol, acetone, diacetone Alcohol and propylene Carbonate.

A satisfactory Grease for a given application is expected to:

  1. Provide adequate lubrication to reduce friction and to prevent harmful wear of bearing components
  2. Protect against corrosion
  3. Act as a seal to prevent entry of dirt and water.
  4. Resist leakage dripping or undesirable throw off from the lubricated surfaces.
  5. Resit objectionable change in structure or consistency with mechanical working (in the bearing) during prolonged services.
  6. Not stiffen excessively to cause undue resistance to motion in cold weather.
  7. Have suitable physical characteristics for the method of application.
  8. Be compatible with elastomer seals and other materials of construction in the lubricated portion of the mechanism.
  9. Tolerate some deqree of contamination, such as moisture, without loss of significant characteristics.

Soap Greases consist of dispersions of soap fibres in oil in concentrations mostly in the range 5 to 22%. By weight sometimes solid block greases contain 50 to 40% of soap.

The thickeners in non-soap greases are usually particulate rather than fibrous in nature and in this case the structure is maintained by 3 dimensional linkages due to very short range inter –particle forces (Vander waal’s forces). These linkages are readily broken and re-formed.

 
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 Types Of Greases  
 

The metallic radical of the soap largely determines the characteristics of the greases the fatty radical having a secondary effect. Greases are therefore classified in terms of the metal they contain.

 
     
Calcium Soap Greases  
 

The conventional types ( excluding the complex soap greases have a smooth buttery texture and are water resistant, with dropping points around 90- 100 ºC. They are water stabilized, that is , the water is present in the soap crystals as water of crystallization. The optimum amount of water varies considerably with the type of formulation, fatty material and mineral oil used, but is usually within the range of 0.5 – 1.3% by wt. at high temperatures the water is gradually lost and the soap structure is weakened. Consequently, calcium soap Greases are restricted to use at fairly low maximum temperatures about 50 – 60ºC. They all turn fluid after exposure to high temperatures and may separate into the oil and soap phases. Only those which contain other stabilizers besides water ( e.g. wool grease) will regain their structure on cooling.

 
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Sodium Soap Grease  
 

These are usually more or less fibrous in structure/ texture depending mainly on the nature of the fatty material, high unsaturation yielding very fibrous greases. They have high dropping points usually not less than 150ºC and sometimes as high as 200ºC and are useful for relatively high temperature service. Owing to the solubility of the soap in water they are not water resistant.

 
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Lithium Soap Greases  
 

These greases first appeared during -the World War II and were made from Lithium Stearate preformed soap. Now a-days lithium hydroxy stearate greases made by saponification in situ from hydrogenated castor oil predominate. Depending on the composition Lithium greases are smooth or slightly grainy in appearance. They have the highest dropping point about 190ºC of the conventional greases and the highest service temperatures. They are water resistant, mechanically stable, and can be made with a greater variety of types of oil than other greases. Their versatility and wide operational scope especially in high-speed service has led to their use as Multipurpose greases to the displacement of earlier types of more specialized greases.

 
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Aluminium Soap Greases  
 

Aluminium Greases have an attractive translucent smooth and polished appearance. The dropping points are low about 90ºC and the greases tend to become rubbery at high temperatures. They are almost invariably made from high viscosity oils and often incorporate polymers. Such products are water Resistant; stringy, and adhesive, and find application as chassis and gear lubricants. They are not recommended for rolling bearings.

 
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Mixed Soap Greases  
 

A variety of mixture is used, the commonest being Sodium-Calcium and the greases are generally manufactured by saponifying the fatty materials with mixed alkalies derived from different metals. One of the soaps usually predominates and determines the general character of the grease, while the other modifies the structure in some way. This results for example, in changes in texture and improved mechanical stability.

 
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Complex Soap Greases  
 

The normal soaps can be complexed with various inorganic salts, usually short-chain aliphatic compounds. The commonest type is a calcium soap –calcium acetate complex although many other combinations have been patented. The greases are water resistant and have very high dropping points, in the range 200 -300ºC. With EP additives incorporated they are encountered as steel mill greases. New greases have recently been introduced for multi-purpose.

 
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Non Soap Greases  
 

There are two main types, these intended for general industrial use and those for specialized applications. The former include greases thickened with silica and clay ( Bentonite) and organic derivatives,such as terephthalamates, diamido dicarbonyl and aryl substituted ureas. High temperatures, mechanical stability, water resistant etc. suggest that they are multipurpose greases with a wider scope than soap greases. However, they have not made any great impact on the market. The type used for specialized applications includes greases made from the dye stuffs indanthrene and phthalocyanine which are generally combined with synthetic fluids, such as diesters and silicones and hence are very expensive. One such product is claimed to operate between - 75ºC and + 320ºC.

 
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Factors  
     Factors to be considered when selecting greases include  
 
  Lithium Calcium conv. Calcium anhyd. Aluminum Lithium Complex Calcium Complex Aluminum Complex Polurea Organo Clay
Dropping point 177-204 96-104 135-143 110 260 260 260 243 260
Max. Temp. 135 93 110 79 177 177 177 177 177
Water resistance 0/++ +/++ ++ ++ +/++ 0/++ +/++ +/++ 0/++
Oxidation stability 0/++ -/++ 0/++ ++ 0/++ -/+ 0/++ +/++ -/++
Rust protection -/++ -/++ -/++ +/++ 0/++ 0/++ +/++ 0/++ -/++
Pumpability 0/++ +/++ 0/++ - +/++ 0/+ -/0 +/++ +  
EP properties V V V V - V V V -
 
 

Reference: NGLI Lubricating grease guide, 4 th ed.

 
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BIS Standards  
     BIS STANDARD FOR GREASES - SUMMARY  
 
IS NUMBER TITLES NUMBER OF GRADES NUMBER OF TESTS
IS 506 : 1993 AUTOMOTIVE AND OTHER GENERAL PURPOSE GREASES 5 10
IS 507 : 1993 GENERAL PURPOSE GREASES FOR DEFENCE APPLICATIONS 3 11
IS 719 : 1990 ANTIFRICTION BEARING GREASES 3 11
IS 720 : 1986 LOCOMOTIVE GREASES 3 11
IS 7514 : 1994 GREASES LOW TEMPERATURE 1 11
IS 7623 : 1993 LITHIUM BASE GREASES FOR INDUSTRIAL PURPOSE Regular -3
EP-3
14
15
IS 9136 : 1993 CALCIUM COMPLEX GREASES 3 14
IS 9917 : 1993 CALCIUM BASE HEAT STABLE GREASES 1 11
IS 12203 : 1999 LITHIUM BASE GREASES FOR AUTOMOTIVE PURPOSE 3 17
IS 12790 : 1999 NON SOAP GREASES 3 15
IS 14383 : 1996 SILICON GREASES 3 11
 
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Test  
     TEST FOR VARIOUS GREASES  
 

Sr.no.

TEST

SPECIFIED FOR

1

Appearance

14383

2

Consistancy

  • Unworked
  • 60 strokes (P: 60)
  • 10,000 strokes
  • 100, 000 strokes

 

720,12203
All
All aspects 506, 507
12203, 1483 (Annex.E)

3

Drop Point, Min. (P: 52)

All

4

Organic acidity (P:53)

All

5

Free Alkalinity (P:53)

All

6

Evaporation loss (P: 61)

719, 720

7

Corrosion test at 24 hours (P:51)

At 100ºC
75ºC
25ºC

 

719,720,7623,9136,9917,12203,12790,148383
506,507
7514

8

Oil separation (P:85)

719, 7514

9

Thermal Stability (P:89)

719,720,7623,9136,12203

10

Leakage (Wheel bearing tests (ASTM D --- 1263)

719,7623,9136,12203,12790

11

Roll stability ( ASTMD - 1831)

719,7623,12203,12790

12

Sulphated Ash (P: 4)

506,507,720,7514

13

Water Content (P:40)

506,507,7514,9914

14

Apparent Viscosity at -40ºC (ASTM D- 1092)

7514

15

Rust preventive properties (ASTM D- 1743)

506,507,7514,7623,12203,12790

16

Low temperature Torque ( IP-186)

7514,7623,9136,14383

17

Heat Stability (Annx A)

506,507,9917

18

Extracted mineral oil (P:94)

 

19

Low temperature pumping (P:62)

506,507

20

Oxidation stability (100 hrs) (P:94)

719,7623,9136,12203,12790,14383

21

Resistance to water wash out (P:90)

7623,9136,12203,14383

22

Soap content (ASTM D-124)

720

23

Four ball test (ASTM)

  1. Wear scar dia (D-2266)
  2. Weld load (D-2596)

 

7623,12203,12790
7623,9136

24

Elastomer compatibility (ASTM D- 4286)

12203

25

MOS 2 content (P:58)

12203,12790

26

Lift performance (ASTM D- 3527)

12203

27

Low temperature Torque ( ASTM D- 4693)

12203

28

Freedom from deleterious particles (ASTM D-1404)

7623, 9136

29

Timken ok load (ASTM D 2509)

7623,9136

30

Emcor rust test (IP-220)

9136

31

Oxidation test (P:34)

14383

32

Glycerine content (ASTM D -128)

507

33

Resistance to water (Annx. C)

9917

34

Working stability in water (Annx. D)

9917

35

Leakage wheel bearing (ASTMD -4290)

 

36

Mobility test (ASTM D -4092)

12790

37

Water spray off test (ASTMD 4049)

12790

38

Evaporation loss (P:68)

14383

39

Bleed test (Annx F)

 

40

Heat stability 48 hrs (Annex B)

9917

41

Plastic Abrassion test (P:125)

12760

 
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