The Dropping Point Test - NLGI

The Lubrizol Corporation© 2019 The Lubrizol Corporation

The Dropping Point Test

Dr Gareth Fish, PhD CLS CLGS The Lubrizol Corporation,

86th NLGI Annual MeetingJune 2019


The Dropping Point Test – What is the point of it?




The Dropping Point Test – Time to Drop it?




Today’s Presentation• Introduction• Dropping point test methods• Upper operating temperature• Thermal stability of high temperature greases • Summary• Conclusions• Acknowledgments

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Introduction• In 1967, McCarthy proposed to delete the existing ASTM D566 test method on

the grounds that it took too long to run and was not safe‒ It is still here 52 years later‒ The equivalent British method, IP132 was deleted in 2004‒ An ASTM G 2015 proposal to delete the ASTM D566 method was defeated

• When the ASTM D2265 was standardized in 1964, a fudge was introduced to try to match the dropping points of the two methods

‒ In 1991, Labude identified that the factor did not work for then current greases

• In 2008 Coe re-iterated that the dropping point test was not a good way of defining the upper operating temperature of a lubricating grease

• This presentation will now explore these related issues

5


Introduction• There are at least five different definitions of what the dropping point of a

lubricating grease is:‒ They all approximate to a calculated temperature at which a drop of material

falls from the bottom orifice of a test cup that is heated

• Several of these definitions note the following:‒ The dropping point is not the melting point of lubricating grease ‒ Dropping point is used in many grease specifications‒ It is primarily a quality control tool ‒ This test has very limited or no relevance to service performance ‒ Dropping point should not be used to determine the upper operating

temperature of a grease

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Dropping Point Test Methods


19th Century Dropping Point Test• A form of the dropping point test was widely

used in the 1880s‒ A blob of grease was put or melted onto the bulb

of a thermometer‒ This was heated in a test tube with a Bunsen

burner or hot oil bath‒ The temperature at which the grease dropped of

the bulb was recorded as the melting temperature of the grease

‒ Described in the literature as Pohl’s test method

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Blob of testgrease

Test tube

Thermometer

Thermometer holder

Heat


Early 20th Century Dropping Point TestsIn the early 1900s there were several other non-standardized methods to determine the melting point of greases

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Ubbelohde method from 1905 High temperature greases melting test 1909Stocks method 1889


ASTM D566 Standardized Test Method• The current manual method ASTM D566

was first approved in 1940‒ It is not clear how we got from the Stocks

method to the current set up

‒ IP 31/46 was developed around the same time but used a different cup shape

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ASTM D566 Test Temperature Ramp Rates

Defined ramp rates

Low rate 3 °C per minute up to 17 °C below the expected dropping point and then 1 °C per minute until it drops

High rate 7 °C per minute up to 17 °C below the expected dropping point and then 1.5 °C per minute until it drops

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The Dropping Point of Lubricating GreaseASTM D566 DefinitionDropping point — a numerical value assigned to a grease composition representing the temperature at which the first drop of material falls from the test cup

The numerical value is the average of the values read from the two thermometers when the first drop of material falls• If the test is run properly there should be a maximum of 2 °C between the

sample cup and the bath thermometers• The reported dropping point should therefore be a maximum of 1 °C above

the value recorded on the sample cup thermometer

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D2265 Grease Dropping Point Test Apparatus

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Aluminum block is set to a fixed temperature based on the expected dropping point of the grease

Cup with grease

Cup support

Thermometer

Thermometer holder

Test tube

Thermometer Test Tube

Test Cup

Test Grease Applied to the Wall of Cup

Thermometer DoesNot Touch Grease

Aluminum Block Oven


ASTM D2265 Block TemperaturesOriginally approved Currently approved

Block temperature

(°C)

Block temperature

(°F)

Maximum observed dropping point (°C)

Maximum observed dropping point (°F)

121 ± 3 250 ± 5 116 241

232 ± 3 450 ± 5 221 430

343 ± 3 650 ± 5 329 625

Block temperature

(°C)

Block temperature

(°F)

Maximum observed dropping point (°C)

Maximum observed dropping point (°F)

121 ± 3 250 ± 5 116 241

232 ± 3 450 ± 5 221 430

288 ± 3 550 ± 5 277 531

316 ± 3 600 ± 5 304 579


ASTM D2265 Test Temperature Ramp Rates

15

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350 400

Tem

pera

ture

(°C

)

Time (s)

232°C 288°C 316°C


Comparison Study of Dropping Points (1967)

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Thickener GII # ASTM D566 Average (°C)

ASTM D2265 Reported (°C)

ASTM D2265 Observed (°C)

Reported difference (°C)

Observed difference (°C)

Sodium 113A 205 202 187 3 19

Lithium 115A 175 167 134 8 41

Aluminum 116 89 88 71 1 17

Calcium 117 94 97 85 -4 8

Calcium 118 103 102 93 1 10

Lithium 119 189 183 158 7 31

Sodium 120 216 221 216 -5 1

Sodium 121 168 193 173 -25 -5

Calcium complex 124 283 279 247 4 36


Energy Institute: IP 396• This uses a programmable furnace to heat the

cup and grease until a drop is detected• The dropping point cup used has the same

internal dimensions and grease fill as the D2265• This filled cup is fitted into a metal sample holder

which is inserted into the middle of the furnace• The sample is heated at 10 °C / minute until

close to the expected dropping point then switches to 1 °C / minute

• The dropping point is detected by an electronic eye in the furnace which records the value and switches of the heater

• The equipment for this test is no longer manufactured

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IP 396 Test Temperature Ramp Rates

Defined ramp rates

10 °C per minute up to 20 °C below the expected dropping point and then 1 °C per minute until it drops

If the dropping point is above 220 °C, it is heated at 10 °C / minute up to 200 °C

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IP 132 (ISO 2176) v IP 396 Study

IP 132

The spread of results was from 191 °C to 199 °C

The mean was 195 °C

The testing took 4 days

IP 396

Five results were obtained at 194 °C and five results at 195 °C

The mean was 195 °C

The testing took <1 day

10 repeat tests of a lithium grease were run in both IP 132 and IP 396

Similar testing on anhydrous calcium greases also showed that the IP 396 was a significant improvement over the traditional dropping point test methods for conventional soap thickened greases

Not using mercury in glass thermometers was also a significant advantage


New Dropping Point Tester• A new dropping point tester to replace the IP 396 apparatus has been proposed• Uses a furnace and controller as one unit

‒ Heating rate is programmable

• Further work is need to establish this test method as it is seemingly consistent with the previous apparatus for conventional soap thickened greases

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Sample ASTM D2265 Data (°C) Dropping Point (°C) with Different Ramp Rates

Block setting Observed Reported As per ASTM D566 As per IP 396 10 °C per minute

Lithium soap 232 195 207 204 206 206

Lithium complex 316* 259 278 233 230 228

Calcium sulfonate 316 None >304 None None None

* When tested at 288 °C block the sample did not drop


Caveat Exertor (Testing Issues)• The grease being filled into the dropping point cup needs to be free of air

bubbles and pockets• The removal of the excess needs to be done carefully so as to not gouge

material from the thin layer• A thermometer depth gage needs to be used when setting the installation gap of

the thermometer‒ The thermometer should not touch the grease in the cup

• Heating rate is defined for IP 396 and a range for ASTM D566 ‒ ASTM D566 operator needs to control the heating rate consistently‒ No Heating rate is defined for ASTM D2265

• ASTM D566 and ASTM D2265 need to be watched constantly until the drop falls21


Dropping Point of Lubricating GreaseTemperature Ramp Rates ASTM D566 v ASTM D2265 v IP396

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Dropping Point Tester Issues• ASTM D566 (ISO 2176) and ASTM D2265 use mercury in glass thermometers

‒ EU and US States are trying to remove them from Commerce‒ Galinstan thermometers are still unproven

• IP 396 equipment worked much better for conventional soap greases but has issues with high temperature (HT) greases

‒ A HT grease tested repeated‒ Equipment is no longer manufactured‒ Replacement equipment does not give valid results on HT greases

• For most HT greases, the thickener is too thermally stable to give a good, useful dropping points

‒ There is no correlation between high dropping points and performance‒ Only use is to tell if the complexing reaction has been carried out properly

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Upper Operating Temperature of Lubricating greases


Upper Operating Temperature of Lubricating Greases• In 1927, Klemgard stated that the melting temperature of grease was important for

grease selection to know at what temperature the grease melted‒ He reported that some cup greases softened significantly as they approached their

melting temperature‒ He looked at different factors affecting their melting behavior

• The type and viscosity of base oil used • The fat to lime ratio and • The amount of water present

• These factors still influence the upper temperature behavior of greases today

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Upper Operating Temperature• The NLGI Grease Guide (6th Edition, 2015) introduces the concept of the

maximum usable temperature of a grease in Chapter 3

• In ISO 12924:2010 the two lower classifications with upper operating temperatures use the dropping point as a guide

‒ For a grease for use up to 60 °C a dropping point ≥ 90 °C is required‒ For a grease for use up to 80 °C a dropping point ≥ 130 °C is required

• In ISO 12924:2010 the higher classifications with upper operating temperatures use the DIN 51821 as the arbiter

‒ Not applicable to many types of greases‒ For electric motor bearing greases the ASTM D3336 Pope test is better

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Upper Operating TemperatureThe Dropping Point of Lubricating Grease is the approximate temperature at which the grease changes to a liquid state from a semi-solid state or the approximate temperature at which grease rapidly separates oil under the conditions of test• The dropping point temperature does not relate to the upper service

temperature of the grease as other factors need to be considered when defining its upper operating temperature

‒ Base oil viscosity and volatility‒ Oxidation stability‒ Additives

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Conventional Soap Grease - Dropping Point – Rules of Thumb • At some point in time, two rules of thumb appeared

1. The maximum operating temperature of a grease is 100 °F (56 °C) lower than the dropping point

2. The maximum operating temperature of a grease is 2/3 of that of the dropping point

• For conventional sodium soap thickened greases, the dropping point ranges from 160 °C to 220 °C but the reported maximum usable temperature is 120 °C so neither rule works

• For conventional hydrated and anhydrous calcium greases, neither rule of thumb works

• For conventional lithium soap greases, the 2/3 rule of thumb seems to be most appropriate (dropping point = 180 °C, maximum usable temperature 120 °C)

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Conventional Soap-Thickened Lubricating Greases

Thickener TypeDropping Point

(°C) (°F)Maximum Usable

Temperature (°C) (°F)

Hydrated Calcium (cup grease)

90 – 110 (200 – 230) 80 (180)

Anhydrous calcium 135 – 150 (275 – 300) 100 (210)

Aluminum stearate 85 – 95 (185 – 200) 80 (180)

Sodium 160 – 220 (320 – 430) 120 (250 )

Lithium 175 – 205 (350 – 400) 130 (265)

It needs to be noted that components such as polymers can influence the dropping point of conventional soap thickened grease by slowing down the rate at which the fluid migrates from the grease on the walls to the orificeSome additives polymerize to reduce or inhibit oil bleed or soap melting

29 *Data taken from NLGI Grease Guide 6th edition 2015


Lubricating Greases with High Temperature Thickeners

Thickener Type Dropping Point (°C) (°F)

Maximum Usable Temperature* (°C) (°F)

Calcium complex > 260 (> 500) 150 (300)Calcium sulfonate (including complex) > 300 (> 570) 150 (300)

Also base oil dependent Aluminum complex > 260 (> 500) 150 (300)Polyurea(including complex) > 260 (> 500) 150 (300)

Also urea type dependentLithium complex > 260 (> 500) 175 (350)Silica Does not drop Base oil dependentBentonite Clay Does not drop Base oil dependent

30 *Data taken from NLGI Grease Guide 6th edition 2015


Upper Operating Temperature Summary• The test methods for the determination of the dropping point of lubricating grease

warn that they are not to be used to define the upper operating temperature

• Published data showed that the original ASTM D566 dropping point test:

‒ Gave an a rough indication of the upper operating temperature of convention

anhydrous calcium and lithium 12-hydroxystearate greases

‒ The method is unsafe to use on high temperature greases

• Data showed that the ASTM D2265 dropping point test does not relate to the upper

operating temperature of grease

‒ The only use for the test is as a QC test to tell if the complexing has been

carried out successfully

‒ The results from the proposed new method still need validating

• The ASTM D2265 needs to be dropped as a test method

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Thermal Stability of High Temperature Greases


Thermal Stability of High Temperature Greases • As discussed in previous NLGI papers, there are many ways to ensure good

thermal stability of high temperature greases

• As reported previously achieving a high dropping point is not an indication of

high temperature performance

• These techniques will be explored now

‒ Using anhydrous lithium hydroxide dispersions

‒ Using borate esters as complexing agents

‒ Using boric acid or acetic acid to increase the thermal stability of high soap calcium

sulfonate complex greases

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Anhydrous Lithium Hydroxide Dispersions

• It has been show that using anhydrous lithium hydroxide dispersions improved thermal stability can be achieved compared to using lithium hydroxide monohydrate powder and water

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Grease Recipe identity 75 58 66 65

Steps 2 1 2 1

Base oil blend (wt%) 90.00 87.90 90.00 88.20

12-Hydroxystearic acid (wt%) 7.38 7.38 8.63 8.63

Azelaic acid (wt%) 2.29 2.29 1.07 1.07

Acid molar ratio 2:1 2:1 5:1 5:1

Lithium hydroxide dispersion (wt%) 3.35 2.78

Lithium hydroxide monohydrate powder mixed with water (wt%)

2.14 1.77

ASTM D2265 Dropping point (°C) 275 >304 243 285

Unworked / worked penetration 241 /243 220 /220 231 /245 239 / 239


Borate esters as complexing agents

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Three greases were made up, one convention lithium grease (90), one using azelaic acid as a complexing agent (89) and the other grease used a low odor borate complexing (91)Grease identity 89 90 91Complexing agent Diacid None Borate esterProperty Method Unit - - -Unworked / Worked penetration ASTM D217 dmm 283/299 285/285 289/285Dropping point ASTM D2265 °C 308 193 279Water washout (at 79 °C) ASTM D1264 wt% 9.4 12.9 2.9

High Temperature Oil bleed at 100 °C ASTM D6184 wt% 2.6 3.7 3.3Oxidation induction time at 180 °C ASTM D5483 mins 73 71 106FE9 F50 grease life at 140 °C DIN 51821 hours 178 93 175

• Grease 89 with the highest dropping point did not give the best HT performance• FE9 Grease life at 140 °C were the same but the oxidation stability of Grease 91 was better


Borate Esters as Complexing AgentsRheology testing – temperature ramp

10

100

1000

10000

160 170 180 190 200 210 220 230 240 250 260

Sto

rage

Mod

ulus

G' (

Pa)

Temperature (°C)

GREASE 89 GREASE 90 GREASE 91

The G’ data shows that azelate lithium complex grease softened similarly to the conventional lithium 12-hydroxystearate grease grease up to 190 °C

Rheology measurements offer the potential to help in the determination of HT behavior of greases

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Borated Additive Thermal Stabilizer• Two samples of conventional lithium 12-hydroxystearate grease were made, one

was treated with a borated dispersant and tested for thermal stability

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Video goes in here


Calcium Sulfonate Complex Greases

• To adjust the behavior and performance of calcium sulfonate gels, fatty acids such 12-hydroxystearic are add and saponified

• Low levels of calcium soap have little effect on the thermal stability of the grease• High levels of added soap, reduce the thermal stability

‒ It can be easily seen with dropping point fall off‒ By adding boric or acetic acids as complexing agents thermal stability is restored

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Property Standard sulfonate

High sulfonate complex

Medium sulfonate complex

Low sulfonate complex

sulfonate (wt%) 65 50 40 30

Calcium soap (wt%) 0 1.5 4.0 6.0

Dropping Point (°C) >316 >316 290 - 300 260 - 280


Summary and Conclusions• Dropping point testing has been around for more than 130 years

‒ Today the old methods seem like alchemy

• With the current growth of HT greases demands a new test method

‒ 36% of greases globally have HT thickeners

‒ 40% of European greases globally have HT thickeners

‒ 70% of greases in North America have HT thickeners

• The current methods are nothing more than a QC to check the complexing reaction of HT greases

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Summary and Conclusions• The three main test methods in use today, ASTM D566, ASTM D2265 and IP

396 have all reached the end of their useful life for various reasons‒ Safety, mercury in glass thermometers and equipment availability

• As it will take 10+ years to get the dropping point test out of standards, it is time that the process was started

‒ Proposed replacement tests need working on more urgently

• A few methods for improving the thermal stability of HT greases were presented

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Acknowledgments• Lubrizol Industrial Additives Colleagues

• The author wishes to acknowledge many co-workers and departments within The Lubrizol Corporation for their contributions to this work

• The author would also like to acknowledge the members of ASTM D02 G0 Grease sub-committee for their participation in discussions on this topic

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Appendix - Dropping Point Definitions• ASTM D566 Test Method

‒ A numerical value assigned to a grease composition representing the temperature

at which the first drop of material falls from the test cup; that temperature being the

average of the thermometer readings of the sample and bath.

‒ Discussion—In the normal and proper operation of this test method the

temperature of the interior of the grease test cup and the temperature of the oil bath

are monitored simultaneously as the bath is heated. When the first drop of material

falls from the cup, the temperature of the grease test cup and the bath temperature

are averaged and recorded as the result of the test.

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Appendix - Dropping Point Definitions• ASTM D2265 Test Method

‒ A numerical value assigned to a grease composition representing the corrected

temperature at which the first drop of material falls from the test cup and reaches

the bottom of the test tube.

‒ Discussion—In the normal and proper operation of this test method, the observed

dropping point is corrected by adding to it a value representing one third of the

difference between the oven block temperature and the observed dropping point

temperature. This corrected value is recorded as the dropping point of the grease.

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Appendix - Dropping Point Definitions• IP 396 – Test Method

‒ The temperature at which

a) A conventional Soap-thickened grease passes from a semi-solid to a liquid state or

b) Certain other non-soap-thickened greases rapidly separate under the conditions of

the test

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Appendix - Dropping Point Definitions• NLGI Grease guide 6th Edition 2015

‒ A small quantity of grease is heated. The temperature at which a drop of material separates from the grease is noted. That temperature is adjusted according to ASTM D 2265. The dropping point is not the melting point of lubricating grease. Dropping point is used in many grease specifications. However, this test has very limited relevance to service performance. Dropping point should not be used to determine the upper operating temperature of a grease. To estimate how grease performs at high temperature certain bearing life tests may be helpful.

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Appendix - Dropping Point Definitions• NLGI Website definition of Dropping Point

‒ The temperature at which a drop of fluid falls from the orifice of the test apparatus

under the conditions of ASTM D 2265. The dropping point is not the melting point of

lubricating grease. Dropping point is used in many grease specifications. However,

this test has very limited relevance to service performance. Dropping point should

not be used to determine the upper operating temperature of a grease. However,

certain bearing life tests can show how well lubricating grease performs under

applied loads at high temperatures under actual operating conditions.

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