Greases Technical guide Characteristics and Tests
CONTENTS
page
1
INTRODUCTION Greases, our trade for almost a century
2
DESCRIPTION OF GREASES
6
TYPICAL GREASE PROPERTIES SOAP THICKENED GREASES
9
GREASES IN THE LABORATORY • • • • • • • • • • • • • • • • • • •
17
Grease testing (page 9) Consistency (page 9) Cone penetration (page 10) Drop Point Procedure (page 10) Oxidation stability (page 11) Roll stability (page 11) Oil separation (during storage) (page 11) Water washout test (page 12) Water spray off test (page 12) Behaviour in the presence of water (page 12) Grease life in ball bearings at elevated temperature high speed and load: FAG FE 9 (page 13) Grease life in ball bearings at elevated temperature (page 13) Copper corrosion (page 13) Dynamic rust test (EMCOR test) (page 14) Extreme Pressure (page 14) 4 ball weld test (page 15) Wear prevention (page 15) Other grease physical and performance tests (page 16) Approvals recommandations from OEM's (page 16)
CLASSIFICATION OF LUBRICATING GREASES
GREASES, OUR TRADE FOR ALMOST A CENTURY At TOTAL more than 2 000 people world-wide are working to develop, manufacture and sell Lubricants. In our head office, located in Paris we coordinate all efforts from our sales affiliates around the world, our Research and We commit Development team, and our grease plants located ourselves all over the world. Short communication channels is a key word in our organisation. When reacting to customers requirements, our R&D team, production team, product managers and sales force literally speak the same language.
Did you know that the vast majority of companies that market greases don’t actually manufacture them themselves? The financial, technological and human investment represented by our plants demonstrates our determination to remain among the market leaders. After having specialised for almost a century in We make production, our the greases grease current plants now rank we sell amongst the top and are considered to be amongst the most modern. Their sophisticated and flexible production installations allow them to produce almost any type of grease corresponding to the demands of the market. We control the manufacturing process so as to meet the quality and performance standards that you have a right to expect. Our process and production technology improvements have resulted in our ability to produce constant quality, furthermore it has enabled us to produce "emission" free and abandon the use of lead and other heavy metals in our products. With such high quality and organisational standards, it is only natural that our plants already received their ISO certificates several years ago.
Modern technologies, environmental legislation, the application of advanced materials and systems are continuously demanding systematic specialisation and considerable research and development. We have centralised the development of our We know greases in our worldwide the greases fully equipped research we sell and development laboratory located in France. Our plants R&D facilities act as satellites for our main R&D centre. In our centralised R&D centre we benefit from expertise and experiences available to us from all divisions of the TOTAL group, based on these we can create products for specific requirements, your requirements. Our Research and Development team has gained the respect from our peers in the grease business. The outstanding quality of our greases have earned us the “preferred supplier” status from many clients in numerous countries around the world.
Our expertise is therefore at your service. Thanks to our extensive prior to market launch testing, we are intimately familiar with the strong points of our greases, as well as their limits. Furthermore we remain in constant contact with the constructors of your equipment, and as a result we are able to We sell continuously improve our greases and anticithe greases pate future demands. you need Our team of specialised application engineers are continuously travelling the world to aid customers and sales people. This to make sure you have the right product in the right place. This may go without saying, but it still isn’t obvious where greases are involved, given their many possible applications, the wrong recommendation can have major consequences. TOTAL is a specialist in lubricants, our efforts are directed towards answering to all your lubrication questions, and to solve any particular lubrication problem you may have. We at are professionals who know exactly which greases meet your needs. To be sure.
1
DESCRIPTION OF GREASES Both grease and oil lubrication serve the same purpose, that of minimising friction and wear between moving surfaces. Because of their essentially solid nature, greases do not perform the cooling and cleaning functions associated with the use of a fluid lubricant. However, greases are able to provide many functions that cannot be provided by oils, and under many situations encountered in service the properties of grease can be superior thus making grease the lubricant to choose. Most grease is used in rolling element bearings with lesser quantities used in plain bearings, gearboxes and on open gears.
Having considered the reasons for using a grease, the task of actually selecting the correct type of grease for a particular lubrication requirement must now be considered. Unfortunately there is no totally all purpose grease. Whilst a modern premium quality multipurpose grease may be able to meet some 75% of all applications where grease lubrication is required, for the remaining 25% many different and special greases are necessary.
Total Greases Applications Required Number of Greases
80%
15 - 20
A satisfactory grease for a given application is expected to:
90%
50 - 100
● Provide adequate lubrication to reduce friction
99%
500
100%
1,000+
and to prevent harmful wear of bearing components. ● Protect against corrosion. ● Act as a seal to prevent entry of dirt and water. ● Resist leakage, dripping or undesirable throw off
from the lubricated surfaces. ● Resist objectionable change in structure or
consistency with mechanical working (in the bearing) during prolonged service. ● Not stiffen excessively to cause undue resistance to motion in cold weather. ● Have suitable physical characteristics for the
Even if a supplier has a very wide range of greases, selection is rarely a straight forward matter of choosing a grease with the right physical and chemical properties for the application. The customer wishes to have optimum (low) priced products (often not cost effective), readily available, and may if having a wide range of machinery seek the smallest possible range of products.
method of application. ● Be compatible with seals and other materials of
construction in the lubricated portion of the mechanism. ● Tolerate some degree of contamination, such as
moisture, without loss of significant characteristics.
These are all ways in which the properties of greases can be said to be superior to those of lubricating oils.
2
The machine designer / builder will require suitable lubricants regardless of whether such products are feasible, costly, widely available or require special development and manufacture. Selecting the right grease for the right application can obviously be a challenge.
A grease is defined by the ASTM (American Society of Testing Materials) as: a solid to semi-fluid product of a dispersion of a thickening agent in a liquid lubricant.
●
What is a grease?
A grease typically consists of the following three main components, base oil, thickener and performance enhancing additives Available greases range from simple metallic soap thickened mineral oils to complex soaps containing two or more thickeners as well as organic and mineral thickeners in combination with mineral and/or synthetic base oils.
The liquid lubricant portion of a grease usually represents about 90% of the total weight. This is commonly a mineral oil, but can be a vegetable oil or one of the very many synthetic lubricating fluids now available. In most grease sold today, refined petroleum oils (paraffinic and/or naphthenic) are used. They offer a good combination of performance characteristics and price.
Liquid phase/ Base oil
Synthetic oils are also used. Usually being chosen because of the need for some specific property which they contribute to the grease, e.g. lower or higher operating temperature ranges. The chemical nature of the oil is also important as this has considerable influence on thickening power (soap yield) of the grease thickener. The physical properties important for base oil selection include: - lubricating properties, - viscosity (strength of the lubricating film), - resistance to oxidation (high temperature and life time), - pour point (low temperature behaviour), - response to additives, - volatility (resistance to evaporation and higher operating temperature ability). A grease for a lightly loaded high speed bearing should typically use an oil with a low base oil viscosity between 40 - 110 cSt at 40°C. For general ball and roller bearing applications, an oil with viscosity ranging from 80 - 200 cSt at 40°C is normally required, and for heavily loaded, slowly rotating bearings, an oil with viscosity around 150 - 500 cSt and sometimes higher up to 1,500 cSt at 40°C is required.
●
▲ compatible
■ incompatible
Mineral
Synthetic hydrocarbon
Polyglycol
Ester
Silicon
Mineral
▲
▲
■
▲
■
Synthetic hydrocarbon
▲
▲
■
▲
■
Polyglycol
■
■
▲/■
■
■
Ester
▲
▲
■
▲
■
Silicon
■
■
■
■
▲
Base oil compatibility
3
Additives
Thickener
The additive concentrations used in greases are generally higher than for lubricating oils and additive choice is subject to in depth studies in view of their possible de-stabilising effect on thickener structures, and rheological properties.
Most lubricating greases use a metal soap as the thickener. The thickener forms a structure in which the lubricating oil is held in a similar way like water which is held in a sponge. This comparison of comparing a grease to a sponge holding water is not strictly a valid scientific description but is a useful and reasonable analogy for a basic understanding of grease composition and structure. Other non-soap thickeners may also be used.
Certain properties of the grease can be improved by adding additives. Many of the grease additives are oil soluble and are usually dissolved in the oil phase, but in addition a wide range of solid lubricants such as graphite, molybdenum disulphide, carbonates and various other powders are often used in lubricating grease.
The additives used in greases can be put in four categories: ● Anti-wear and extreme pressure additives, to improve resistance to impacts and heavy loads. ● Anti-oxidant additives, to improve resistance to degradation caused by high temperatures and oxygen in the air. ● Anti-corrosion and anti rust additives, to prevent corrosion to both ferrous and non-ferrous metals caused by the effects of humidity and aggressive chemical agents. ● Lubricity and adherence agents, to improve adhesion to lubricated surfaces.
Greases are usually classified by the type of thickener used, as the thickener is considered to have the biggest influence on grease properties.
It should always be remembered that a grease is not a thick oil but a thickened oil. Because the thickener used has such a specific influence on grease properties it is normal to identify grease types by reference to their specific thickener. Metallic soap thickeners can be sub-divided in Conventional Soaps (Lithium, Calcium, Aluminium, mixed soaps), and Complex Soaps (typical Lithium Complex, Aluminium complex and Calcium complex). The most recently developed thickener is the overbased Calcium Sulphonate complex which is a "super" complex soap. Similarly for non-soap grease thickeners, greases are identified by the thickener base, Clay, Silica, and Polyurea.
Greases are particularly well suited to be combined with solid lubricants, which have excellent friction properties as well as high resistance to load and seizure. In addition, solid lubricants provide greases with a higher level of safety due to their insensitivity to chemical agents.
Solid lubricants
In practice, the most widespread are: graphite and molybdenum disulfide, which tend to plate out and form a shield on the metal surfaces to reduce friction and prevent surface contact.
Since about 90% of grease currently marketed is of the soap thickened variety we will describe what a soap actually is, its basic chemistry and the influence the thickener chemistry has on properties of the grease. Many thickeners are based on organic soaps of alkali metals. Most of these are produced by saponifying fats, fatty oils or fatty acids with a metal alkali in a portion of the base oil during the manufacturing cycle. In simple chemistry terms the formation of a soap is analogue to the basic chemistry reaction: ACID + BASE
S A LT + W AT E R
4
+
++ +
++ ++
+
++
+
Corrosion Pumpability Adhesiveness Gen. purpose
+
++ ++ +
+
Calcium
Calcium sulphonate complex
Calcium complex
Aluminium complex
Polyurea
Bentonite
++
Lithium Calcium
+
++ +
Lithium complex
++ +
++ ++ ++
Lithium
Speed
++ ++ ++ ++ + ++
Bentonite
+ +
Polyurea
++ +
Aluminium complex
Calcium sulphonate complex
++
Resistance to water
Calcium complex
Calcium
Temperature
Lithium Calcium
●
Soap properties
The largest source of grease saponifiable material in use today is 12-Hydroxystearic acid, derived from Castor oil, available in the form of the methyl ester, acid or tri-glyceride, produced by hydrogenation of the oil.
Lithium complex
Most of the soaps produced for the manufacture of (continued) lubricating greases are produced by saponifying fats, fatty oils, or fatty acids with a metal alkali. The Saponification Process (soap thickener preparation) is usually carried out in a portion of the lubricating oil, during the processing cycle. The most common alkaline materials include hydroxides of lithium, calcium, and aluminium.
Lithium
●
Thickener
Lithium
▲
▲
▲
▲
▲
◆
■
■
■
Lithium complex
▲
▲
▲
▲
▲
▲
■
◆
■
Lithium/Calcium
▲
▲
▲
▲
▲
◆
■
◆
■
●
Thickener compatibility
Calcium
▲
▲
▲
▲
▲
◆
■
■
■
Calcium sulphonate complex
▲
▲
▲
▲
▲
◆
■
■
■
Calcium complex
◆
▲
◆
◆
◆
▲
■
◆
■
Aluminium complex
■
■
■
■
■
■
▲
■
■
Polyurea
■
◆
◆
■
◆
◆
■
▲
■
Bentonite
■
■
■
■
■
■
■
■
▲
Two greases are likely to be compatible, if when mixed together, the consistency and drop point of the mixture after working are within the specification limits. ▲ compatible
■ incompatible
◆ incompatible in certain proportions
5
TYPICAL GREASE PROPERTIES SOAP THICKENED GREASES In the following, we describe properties of typical greases which are made from soaps, soap complexes, and nonsoap thickeners. The objective here is to describe the thickener-oil system without additives (unless the additive is part of the thickener system). Different manufacturers report varying values and properties for these systems. The values reported here are believed to be representative. Important remark: TOTAL product family names are mentioned just as an information. TOTAL specifications are generally more severe.
The majority Lithium 12-Hydroxystearate of lithium greases Greases produced TOTAL MARSON today are ®
derived from 12-Hydroxystearate soap. These products are smooth textured and stable to heating. Dropping points are reported in a range from about 175°C to 200°C. For long-term use, the upper temperature limit is around 120°C. At low temperatures, these greases are easily handled. Under shear in laboratory equipment, these greases are excellent. It is again worth noting that shear rates in service are many times higher than obtained in laboratory test equipment. In practice shear stability of these greases is average.
There are two types of calcium greases, anhydrous ® and hydrated. These greases are smooth and buttery. Conventional (hydrated) calcium greases normally depend on water for structure stabilisation, the amount of water being critical and loss of this water is the reason for their limited high temperature properties. At high temperature some of this water is lost and the grease structure is destroyed resulting in the separation of the oil and the soap thickener. In service, they are thus limited to about 60°C, although dropping point is around 100°C. Anhydrous calcium greases are more performant, their dropping point is higher (130-140°C) and they may be used up to 80-90°C. These greases are easy to pump even at low temperatures. Mechanical and shear stability are fair (hydrated) to good (anhydrous). Oxidation stability is poor but can be improved with inhibitors. Water resistance is very good. Protection against rust is poor but can be enhanced with additives. Low temperature properties are satisfactory. Shear stability is good.
Calcium Soap Greases TOTAL MERKAN
Oxidation resistance is acceptable and easily improved with anti-oxidants. Water resistance is good, although not as good as with calcium or aluminium greases. Corrosion resistance is achieved by additives.
Aluminium complex Greases TOTAL COPAL
®
Low-temperature behaviour of these products is rated as fair to good.
Shear stability is good to excellent. Like many other greases, if thickener content is low, stability to working falls off significantly. Pumpability is considered as good. Water spray resistance is excellent. In the presence of only a little water they form emulsions which protect metal surfaces from rusting by drawing the water away from the metal. Adhesion to metal is excellent. These greases can be used up to 150-160°C. In high-temperature, high-speed ball bearing life tests, such as ASTM D 3336, these products give shorter live time results than most lithium complex or polyurea greases.
6
Calcium Complex Greases TOTAL AXA
Lithium Calcium These type of greases combine Greases the properties of TOTAL MULTIS Lithium and Calcium greases. and LICAL The manufacturing
This type of grease is found in many varia® tions. Some types have high thickener contents. One ingredient of these products is calcium acetate, which provides EP properties. In high-thickener-content grades: calcium complex greases have high drop points (above 280°C) and good water resistance.
®
®
process of these greases is very specialised and requires high tech computerised process control equipment. The advantages of these types of greases is that their water resistance is excellent as is the rust prevention.
Many calcium complex greases have inherent EP properties which are usually enhanced with additives.
The EP properties are “build in” in the soap skeleton. The results are excellent EP properties, compared to lithium and calcium greases.
The greases can be difficult to make and tend to harden on storage or under high pressure in lubricating equipment.
These greases can by used at constant operating temperatures up to 135°C without loosing their excellent properties.
These greases can operate at higher temperatures than conventional soap greases, and will lubricate bearings quite satisfactorily up to 150°C.
Test in practice have shown that LICAL® tend to be able to absorb water up to 10% without loosing any of the lubricating properties. Pumpability can be slightly lower than lithium greases.
●
The properties of basic calcium ® sulphonates have been known for a long time. But until recently it has been difficult to manufacture satisfactory lubricating greases based on this chemistry, due to unacceptable performance properties, such as poor pumpability and inadequate low temperature behaviour.
Calcium Sulfonate Complex Greases TOTAL CERAN
®
TOTAL CERAN
Worldwide you will find only a few manufacturers able to produce these high tech state of the art greases (TOTAL is one of the most important of them). The production is done via a new super complexing process, modifying the properties of the calcium sulphonate to eliminate the above mentioned drawbacks and allow the production of a grease with exceptional properties such as:
● These type of greases are the closest to an “ALL” purpose grease you will find on the market today, they are less suitable for high velocity/heavy vibrations.
1
Outstanding high load-carrying and antiwear properties
2
Outstanding water resistance (even with 40% of water!!!)
3
Excellent mechanical stability and high shear resistance
4
Excellent thermal stability (does not liquify until >300°C)
5
Low temperature performance is good
6
Very good oxidation resistance (under pressure and high temperature)
7
Very good corrosion resistance
7
Lithium (Lithium/Calcium) complex Greases TOTAL MULTIPLEX
Compared to lithium greases, lithium ® complex greases show several advantages especially when used at high temperature. Dropping point of the complex grease is generally more than 50°C higher than that of the conventional soap grease. These greases can be used up to 160°C. They handle well at low temperatures. Work stability, and oil separation are good to excellent. Bearing performance at high temperatures is very good to excellent. Pumpability can be somewhat lower than lithium greases.
These smooth products are used at high temperatures and high ® speeds. They are comparable to some of the complexes in this capability but with enhanced high temperature behaviour and long life time. Although used with all kinds of bearings, they have been particularly effective in lubricating ball bearings, such as are found in electric motors. This is indicated, too, in high temperature bearing tests. Dropping point is generally around 260°C, but the products are usable up to 180°C. Their structure and organic composition gives them "low noise" properties demanded for the lubrication of certain bearings.
Polyurea Greases TOTAL ALTIS
These greases have outstanding resistance to oxidation. Their thickeners contain no soaps or other metal-containing constituents, which are, to varying degrees, pro-oxidants. Handling at low temperatures is satisfactory. Water resistance is satisfactory - in some grades, excellent. Rust resistance requires the use of special and effective rust inhibitors. Polyurea greases have an excellent life time expectancy, making them very suitable for filled for life applications.
8
Bentone-clay Greases TOTAL CALORIS
These smoothtextured greases have outstanding ® heat resistance, since the thickener will not melt, at least up to the temperature at which its constituent oil evaporates, flashes off, or burns. However, since the baseoil is the limitation, maximum use temperature is usually given at around 180°C. These are about the same as was reported for the other high-temperature greases of the complex and nonsoap series. Although these high-temperature greases can be used for occasional use at peak temperatures, the need for frequent re-lubrication remains. For example, since this thickener has no melting point, bentone-clay greases have been used in applications in which short-term temperatures could hit 260°C, re-lubrication is then required after only a few hours of this high-temperature service. Low-temperature properties are satisfactory. However, many bentone-clay greases are formulated for high-temperature applications. Work stability must be rated as fair to good. Oxidation stability and rust resistance are satisfactory when enhanced with additives. Water resistance is good.
GREASES IN THE LABORATORY Most of the grease tests that have been standardised define or describe properties that are related to the performance type tests in actual or simulated operating mechanisms. They provide considerable useful information about a grease. However, it must be recognised that they are laboratory tests and have their greatest value as screening tests which give directional indications of what can be expected when a grease is placed in service in a specific application, and as physical standards for manufacturing control. Direct correlation between laboratory tests and field performance is rarely possible since the tests never exactly duplicate service conditions, and service conditions are never identical even in two outwardly similar applications. For these reasons, an understanding of the intent and significance of the tests is essential for those involved with the use of lubricating grease.
●
Over the years, several institutes like: ISO - ASTM IP - DIN - AFNOR, etc. have standardised tests that describe properties or performance attributes of lubricating greases. The National Lubricating Grease Institute (NLGI) has standardised a numerical system for classifying the consistency of greases. From all tests available TOTAL has chosen a number of tests, which are being performed on their greases at regular intervals.
●
Grease testing
Consistency is defined as the degree to which a material, such as lubricating grease, resists deformation under the application force. It is, therefore a characteristic of plasticity, as viscosity is a characteristic of fluidity. The consistency of a lubricating grease is not constant but varies with temperature. It may also vary as a result of the handling or mechanical working that the grease has been subjected to, before measurement of its consistency. Consistency is reported in terms of ASTM cone penetration, NLGI number, or apparent viscosity, each of which is determined at a specific temperature after described preparation of the sample.
Consistency
On the basis of ASTM Worked Penetrations, NLGI has standardised a numerical scale for classifying the consistency of greases. In order of increasing hardness, the consistency numbers are: NLGI Grease
ASTM Worked Penetration at 25°C
000
445 - 475
00
400 - 430
0
355 - 385
1
310 – 340
2
265 - 295
3
220 - 250
4
175 - 205
5
130 - 160
6
85 - 115
9
Cone penetration
Method/Standard: ASTM D 217 DIN 51804-T1 / ISO 2137 NF T 60-132 / IP50
Consistency is commonly measured by the Cone Penetration. In this test a normalised cone is allowed to sink for 5 sec., under its own weight into a sample of grease held at 25°C. The depth that the cone penetrates into the grease is expressed in tenths of a millimeter and reported as the penetration of the grease. Since the cone will sink further into soft greases, higher penetrations indicate softer greases. Currently you will find on the market as the softest grease a 000 grade (all "0" grades are normally referred to as central lubrication greases) and as the stiffest a 3 or 4 grade (grades 5 and 6 are no longer widely used). Penetrations are reported as follows: Prolonged Worked Penetrating (W ....)
Remark: Special procedures using one-quarter and one-half scale cones, method ASTM D 1403, are used for determining the penetration of small samples.
Method/Standard: ASTM D 217 / DIN 51804-T1 / ISO 2137 NF T 60-132 / IP50 Sample is worked for 60 strokes or more in a standard grease worker. Often the grease is worked 100,000 strokes, but also 5,000 and 10,000 strokes are used. It is accepted that these W ...... results give a basic impression on the grease stability. In some cases some water is added to the grease to measure the stability when the grease contains water (e.g. TOTAL CERAN®). This is normally done for grease used in wet environments.
Mechanical stability
10
Drop Point Procedure Method/Standard: IP 396 /NF T 60102C The dropping point of a grease is the temperature at which a drop of oil released by the grease falls from the orifice of a test cup under prescribed test conditions. Materials such as conventional soap thickened greases do not have a true melting point but have a melting range during which the material becomes progressively softer. In a standard cup containing grease, the grease is heated in a special computer controlled heating furnace (usually Mettler), within which the temperature at which a drop of material falls from the cup is detected and reported by electronic means The dropping point of a grease is commonly, but mistakenly, taken as measure of the service capabilities of a grease at elevated temperatures. The dropping point of a grease is not considered to have any bearing on service performance other than that normally a grease cannot be expected to resist leakage at temperatures above its dropping point, it does not establish the maximum usable temperature for the grease since performance at high temperatures depends on such other factors as: ●
whether the exposure to high temperature is continuous or intermittent,
●
whether cycling from high to low temperatures is involved,
●
evaporation resistance of the grease,
●
design of the lubricated mechanism,
●
frequency of relubrication,
●
a rule of thumb is however that dropping point minus 30% is operating temperature.
Oxidation stability
Method/Standard: ASTM D 942 DIN 51808 / IP 142
The reaction with oxygen may lead to deterioration of lubricating grease. This test conducted in the Norma-Hoffman oxidation bomb evaluates resistance of lubricating greases in a closed container to oxidation under specific conditions of static exposure. In this test, each of the five dishes in the bomb is filled with 4 g of the grease to be tested. The bomb is then sealed and pressurised to 110 psi (7.7 kg/cm2) with oxygen and placed in a bath held at 99°C. The pressure in the bomb is recorded at prescribed intervals throughout the test. At the end of the specified test time, usually 100, 250 or 500 hr, the pressure drop is calculated and reported. The drop in pressure is the net change resulting from absorption of oxygen by the grease and the release of CO2 from the grease. Frequently, the results of this test are reported as indicative of the oxidation stability of a grease; however, it is a static test. It is not intended for the prediction of the stability of grease under dynamic conditions.
Roll stability
Method/Standard: ASTM D 1831 (modified)
The ability of a grease to resist changes in consistency during mechanical working is named its roll stability or shear stability. A variety of laboratory tests are used to evaluate the roll stability of greases, but the two that have been standardised are the change in penetration after prolonged working in the ASTM D 217 grease worker, and the change in penetration after severe rolling in the ASTM D 1831 roll stability worker. In the Roll Stability Test a small sample (50 g) of grease is rolled at 165 rpm for a certain time at a certain temperature. Using a steel cylinder which contains a 5 kg heavy round steel block. Worked penetration at 25°C is determined on the grease before and after rolling. Due to the small size of the sample, working and penetrations are performed on ASTM D 1403 one-quarter or one-half scale equipment. TOTAL uses a temperature of up to 100°C to achieve a closer to practice test. Furthermore TOTAL has prolonged the duration of the test from 2 to 4 or even 100 hrs to determine the mechanical stability of their greases under very severe conditions. In both of these tests, the change in consistency
with mechanical working is reported as either the absolute change in penetration or the percent change in penetration. While both tests are used widely to indicate mechanical stability requirements, the significance has never been accurately determined. It is believed that the changes in worked penetration in these tests are an indication of mechanical stability, and are directionally indicative of the changes in consistency that a grease can undergo in service.
Oil separation (during storage)
Method/Standard: ASTM D 1742 ASTM D 6184 IP 121 / DIN 51817 NF T 60-191
Grease must release oil slowly in service to provide effective lubrication. Some oil release resulting in free oil on the grease surface is normal in storage. However, excessive separation of oil while the grease is in storage may result in loss of the user’s confidence in the product. The tendency of a grease to separate oil during storage in predicted by ASTM D 1742 / IP 121 / DIN 51817 / NF T 60-191 and ASTM D 6184. In ASTM D 1742 a sample of grease supported on a 200 mesh screen is subjected to air pressure and placed in an oven at 25°C for 24 hrs. Any oil that seeps from the grease is collected, weighed and reported as the percent by weight of oil separated. IP 121 / DIN 51017 / NF T 60-191 are more or less the same procedure, but grease is subjected to metal weight pressure and placed in an oven at 40°C for 42 or 168 hours. ASTM D 6184 is more or less the same procedure, but grease is subjected to metal weight pressure and placed in an oven at 100°C for 30 or 50 hours. These tests are correlated directly with oil separation which occurs in grease pails in storage, and are directionally indicative of the separation that may be expected in other sizes of containers. It is not suitable for greases softer than NLGI. n° 1, and is not intended to predict the bleeding tendencies of grease under dynamic service conditions. A maximum of 1 - 5% bleeding is considered to be normal under storage conditions (also depending on thickener).
11
Water washout test
Water spray off test
Method/Standard: ASTM D 1264 DIN 51807-T2 / IP 125
The objective of this test is to measure the resistance to spray off of a grease. A predefined grease film is put on a test plate. The test plate is exposed to a water spray (22 or 40 PSI). The result after a set time is expressed in weight loss of the plate with grease. This comparison test, can give an indication of the adhesive character of a grease on metal exposed to water sprayed under pressure on the grease.
The environment in which a grease must perform is important but is often neglected in grease selection. A wet environment, whether it be just moist air conditions or heavy direct water washing action, can affect many greases and is an important factor to consider when selecting grease for any service. When water intrudes into grease lubricated equipment the grease may become softer (may even become semi-fluid) or stiffen, it may emulsify or reject water, its adhesive properties may change, and metal surface protection may become inadequate from corrosive water action (rust).
●
The ability of a grease to resist washout under conditions where water may splash or impinge directly on a bearing is an important property in the maintenance of a satisfactory lubricating film. Comparative results between different greases under the prescribed test conditions can be obtained with this test, but the results may not necessarily predict field performance.
Method/Standard: ASTM D 4049
Behaviour in the presence of water Method/Standard: DIN 51807-T1 This test is developed to test the behaviour of grease against water under predefined static circumstances.
The test uses a specific ball bearing, equipped with front and rear shields having a specified clearance. It is packed with 4 g of the test grease and then rotated at 600 rpm for 1 hr while a jet of water at 80°C impinges on the bearing housing. At the end of this time the bearing will be removed, dried, and the percent weight of the grease lost determined.
A grease sample is put on a glass strip with the help of a template. The sample thickness is about 1 mm. The glass strip is then submerged into distilled water and put in an oven. The duration of the test is 3 hours at 40°C or 90°C. TOTAL has modified this test for CERAN® greases to make it much more severe, the duration is set at 8 hours at a constant temperature of 90°C.
The test is generally considered to be an useful screening test for greases, that are being used where water washing may occur, such as wheel bearings wet end-bearings on paper machines, and in the steel industry.
After the test the sample on the glass strip is immediately valued with the naked eye. Following scale is used for rating:
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0
No change.
1
Slight change, change of colour, slight water adhession on the grease.
2
Medium change, grease starts to dilute visible through white/yellow slime building on the grease, troubling of the water.
3
Big change, part or complete dilution of the grease into the water, building of milky white oil in water emulsion.
●
Grease life in ball bearings at elevated temperature high speed and load: FAG FE 9
Grease life in ball bearings at elevated temperature
Method/Standard: DIN 51821 Purpose: to determine the life of lubricating greases in rollingelement bearings under realistic testconditions.
Method/Standard: ASTM D 3336 The test method covers the evaluation of the performance of lubricating greases in ball bearings operating under light loads at high speeds and elevated temperatures. The ASTM D 3336 test evaluates the performance of lubricating grease in a (20 mm) ball bearing operating under light loads at temperatures up to 177°C (usual intervals 120, 150, 177°C) and shaft speeds of 10,000 rpm. Tests are run to failure or until the required number of test hours without failure has been completed.
The rolling-element bearing fitted in the apparatus as the test piece is filled with a specified quantity of the grease under examination. The test is conducted at a selected temperature, rotating speed and axial load. The lubrication conditions in the bearing change over a long period. Bearing failure is regarded as having occurred when the motor fails to drive the bearing under test.
2 mg
Test temperature
Adjustable up to +250°C
Rotational speed
3,000 or 6,000 rpm
Thrust force
1,500, 3,000 or 4,500 N
●
●
Quantity of grease
Copper corrosion
Method/Standard: ASTM D 4048 IP 112 / DIN 51811
These methods are used to detect substances in lubricating grease which could corrode copper. Since copper and copper alloys are used in bearings it is essential that greases not corrode such materials. The tests are similar, (commonly referred to as “Copper Strip Tests”) and involve a cleaned and smoothly polished copper strip immersed vertically in the grease sample. In the ASTM method the strip is totally immersed, in the IP method the strip is 2/3 immersed. The assembly is placed in an oven for a given time and temperature, then removed and cooled. The strip is cleaned and observed for staining or corrosion, and rated either in words and/or by a numerical rating system. With the ASTM/DIN method a comparison of the copper strip condition after test is made against a reproduction ASTM Copper Strip Standard.
Bearing failure with 520 Watt at 6,000 rpm power consumption of 320 Watt at 3,000 rpm driving motor
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The length of test and test temperature is not specific, but should be stated when reporting results. The test procedure for TOTAL is commonly carried out at 100°C, but other mutually agreed-upon test temperatures are permitted. The time may be specified as 3 hours, 24 hours or 7 days or may be established by mutual agreement.
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Dynamic rust test (EMCOR test)
Method/Standard: IP 220 / DIN 51802 ISO CD 11007
In this test up to eight 30 mm, double row self-aligning ball bearings are mounted in pillow blocks on a common bed plate and driven at 80 rpm by a common shaft.
4 ball weld test
Method/Standard: ASTM D 2596
This test derives its name from the 12.7 mm (0.5 in) diameter through hardened chrome alloy steel balls of 64066 Rockwell C hardness, that are used as test specimens. It provides a method for determining the load carrying properties of lubricating grease in terms of the Load-Wear index and the Weld Point. The three lower ball are locked firmly in a cup filled with test grease. The upper ball, which is held in a chuck, is in point contact with each of the lower balls and may be rotated against them under load at a speed of approximately 1770 rpm.
At least two bearings are required for a test. The standard pillow blocks are plastic. Each bearing is packed with 10 g of the test grease with no grease in the housings. After assembly, the bearings are run for 30 min to distribute the grease. The housings are then opened and 10 ml of distilled water (or IP135 synthetic sea water) is added to each side of each lower housing. After assembling the bearings are run for two 8 hrs periods followed by two 16 hrs shutdowns, and one 8 hrs period followed by one 108 hrs shutdown. At the end of this time (164 hrs) the bearings are disassembled and the outer races examined for rust and corrosion. The races are rated on a numerical scale from 0 to 5 with 0 being completely free of rust.
While little correlation has ever been obtained between the results of laboratory Extreme Pressure (EP) and service performance tests represent the only language that describes these properties at reasonable cost. Here after two methods are described.
Extreme Pressure
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The grease sample, which is brought to a temperature of about 27°C, is subjected to a series of 10 sec tests at increasing loads until welding occurs. After each 10 sec test the scar diameters on the three stationary balls are measured and recorded and all four balls discarded. The Load-Wear Index, in kilograms, is calculated from the scar diameters corresponding to the various loads. The weld point is reported in kilograms, definition of weld load: “weld point under the conditions of this test the lowest applied load in kilograms force (or Newtons) at which the rotating ball seizes and then welds to the three stationary balls, indicating the extreme pressure level of the lubricating grease has been exceeded”. Suggested form for Recording Test Results (Kgf) 80, 100, 126, 160, 200, 250, 315, 400, 500, 620, 800. ASTM states: “This test method, used for specification purposes, differentiates between lubricating greases having low, medium and high levels of Extreme Pressure properties. The results do not necessarily correlate with results from service”.
4 ball weld test
Method/Standard: DIN 51350-T4
This test uses the same test rig as described under the ASTM D 2596 test. The grease is tested in a four-ball system consisting of a rotating ball (running ball), sliding with an adjustable test force on three balls identical to it (standing balls). The test load is raised in stages until welding of the four ball system occures. The test is run for 60 seconds at 1420 rpm, the load is increased with steps. Between 2000 N and 4000 N with stages of 200 N, with loads above 5000 N each stage increases with 500 N. The results are reported with the Last Non Welding Load (LNWL) and weld load (WL) e.g. (320 daN 340 daN).
Two methods, ASTM D 2266 and DIN 51350-T5, are available for determining wear preventing qualities of lubricating greases. These methods, use four test balls in which the test parts are half-inch steel balls, in point contact, and one ball rotates. The two methods are described here after.
Wear prevention
4 ball wear test
4 ball wear test
Method/Standard: DIN 51350-T5
This test uses the same test rig as mentioned under test DIN 51350-T4.
The test can be performed according to following procedures: Procedure
Load
Running time
C
150 N
60 ± 0,5 minute
D
300 N
60 ± 0,5 minute
E
1,000 N
60 ± 0,2 second
TOTAL has chosen to run only procedure E. The grease is tested in a four ball system consisting of a rotating ball (running ball) sliding with the appropriate test force (C, D or E) on three balls identical to it (standing balls) (tests are done twice). After the test duration the scar diameter of 2 sets of standing balls is measured. This than leads to the reported mm’s wear.
Method/Standard: ASTM D 2266 / IP 239
This test is similar in principle to ASTM D 2596, the four ball Extreme Pressure test, but the machine is much more sensitive and the applied load is limited to 40 kg (392 N) rather than the 800 kg of the Extreme Pressure machine. The same composition and hardness steel balls as ASTM D 2596 are used. At the lighter loading, seizure or welding does not occur and the material removed from the balls is the result of wear. The test is run for 60 min at 1,200 rpm with a load of 40 kg. The grease sample is held at 75°C. At the end of the test sizes of the wear scars on the three stationary balls are measured and reported. The test is intended to determine the relative wear preventive characteristics of greases in sliding steelon-steel applications. It is not intended to predict wear characteristics with other metal combinations, and cannot be used to differentiate between Extreme Pressure and non Extreme Pressure greases.
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OTHER GREASE PHYSICAL AND PERFORMANCE TESTS Having looked at some of the most widely quoted grease tests, we will now briefly consider some of the other grease test methods which are used. Most of these tests are used to access a particular performance characteristic or grease property and thus it is convenient to group the various tests under the following general headings:
Low temperature flow pressure Method/standard: DIN 51805 To determine the lowest usable temperature of a grease. A sample of grease at a temperature of, for example, -35°C is placed in a sample holder. Afterwards the grease is put under pressure. The pressure is increased by step until the grease is released from the sample holder. The pressure needed to release the grease is expressed in mbar. If a grease is known to be less pumpable the results can be expressed in °C at a maximum pressure of 1,400 mbar. Penetration at low temperature method/standard: NF T 60-171 This method is the same as described under cone penetration. The results are given in 1/10 mm at a temperature between 0 to -40°C. Apparent viscosity (SOD) Method/standard: ASTM D 1092 By carrying out apparent viscosity determinations at low temperatures (method ASTM D 1092) the pumpability and flow properties of a grease at low temperatures can be determined. Greases designed for extremely low (sub-zero) temperature service should not stiffen and offer excessive resistance to rotation of bearings after soaking at low temperatures. The following methods (IP 186 and ASTM D 1478) measures starting and running torque’s of small lightly loaded ball bearings at temperatures down to -54°C. Low temperature Torque Method/standard: ASTM D 1478 The test bearing is fully packed with the test grease, installed on a spindle that can be rotated at 1 rpm, and inserted in a cold box, which can be maintained at any temperature down to -54°C. The outside of the bearing housing is connected through a string assembly to a scale so that the
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retraining force can be measured. After 2 hours, the motor is started, and the initial restraining force recorded. As rotation continues, torque drops, the restraining force is again recorded after running for 60 minutes. The two values are multiplied by the length of the lever arm and the products reported as the starting and running torque’s, in N-m units for the grease. Low temperature Method/standard: torque IP 186 This method of test determines the resistance caused by the grease at sub-zero temperatures down to -73°C in an axially loaded ball-bearing rotating at 1 rpm. Although the apparatus is of a different design the method of test is basically very similar to that of ASTM D 1478. A test bearing is packed with test grease, installed on a loaded spindle, that can be rotated at 1 rpm, and installed in a sealed unit which is immersed in a fluid cooling bath. The temperature of the cooling bath is steadily reduced to the test temperature, which may be down to -73°C over 1-1 1/2 hours. After 2 hours the motor is started and the initial restraining force recorded, after running for a period of time the restraining force is again measured. The starting and running torque’s are then determined and reported in mNm units.
APPROVALS RECOMMANDATIONS FROM OEM’s Many OEM’s (Original Equipment Manufacturers) give approvals to greases for use in their equipment. Most OEM’s use (a selection) of the previous described tests, sometimes they modify the tests to make them more suitable to reflect in practice use of the equipment. It is very important when recommending a grease that one observes the requirements of the OEM. In practice it is often the case that a suitable contra-type of an existing grease is asked for.
CLASSIFICATION OF LUBRICATING GREASES ISO 6743-9 For example: MULTIS EP 2: ISO-L-
X B C E B 2
Symbol 1 2 3 4 NLGI grade ISO
L
ISO
Lubricants class
X
Symbol 1
Symbol 2
Symbol 3
Symbol 4
Greases
Minimum operating temperature
Maximum operating temperature
Behavior in the presence of water
Extreme pressure properties
Temperature
Family
Temperature
Behavior in presence of water
Symbol 1 Mini T°C Symbol 2 Maxi T°C Symbol 3 A B C D E
X
0 -20 -30 -40 >-40
A B C D E F G
60 90 120 140 160 180 >180
A B C D E F G H I
L: Zero performance M: Protection with distilled water H: Protection with salt water
Anti-rust performance :
NLGI grade
Penetration after 60 strokes
000 00 0 1 2 3 4 5 6
445 - 475 400 - 430 355 - 385 310 - 340 265 - 295 220 - 250 175 - 205 130 - 160 85 - 115
Anti-rust Environment Symbol 4 L L L M M M H H H
L M H L M H L M H
Environment :
Character DIN 51 502
K P 2 K -25
Table 1 2
Consistency
A NON EP GREASE B EP GREASE
L: Dry atmosphere M: Humid atmosphere H: Water spray-off
Table 3
DIN 51502 For example: MULTIS EP 2:
EP Performance
NLGI grade
3
Highest application temperature °C
4
NLGI grade Table 1 Kind of grease - Application area
Character
Greases for bearings according to DIN 51 825
K
Greases for closed gears according to DIN 51 826
G
Greases for open gears
OG
Greases for friction bearings / sealing
M
Table 2 Additional information regarding additives
Character
C D E F G H K M N P R S T U
+ 60 + 80 + 100 + 120 + 140 + 160 + 180 + 200 + 220 Above 220
Behavior in presence of water according to DIN 51 807 Part 1 rating DIN 51 807 0 - 40 or 1 - 40 2 - 40 or 3 - 40 0 - 40 or 1 - 40 2 - 40 or 3 - 40 0 - 90 or 1 - 90 2 - 90 or 3 - 90 0 - 90 or 1 - 90 2 - 90 or 3 - 90 to be reported to be reported to be reported to be reported to be reported to be reported
Table 4
Solid lubricants added (e.g. MoS2, Graphite)
F
Ester
E
Lowest application temperature DIN 51 805 at 1400 mbar
Fluor hydrocarbons
FK
- 10°C
Polyglycol
PG
- 20°C
Siliconoil
SI
- 30°C
EP additive
P
- 40°C
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WD COMMUNICATION - 08/03 - Photos credit : TOTAL LUBRIFIANTS - Printed in France
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