Joseph Kolly, Ph.D., Grease Group ChairmanJoseph Kolly, Ph.D., Grease Group Chairman

Investigation of Lubricating GreaseInvestigation of Lubricating Grease

Role of Lubrication in Accelerated Wear of the Acme NutRole of Lubrication in Accelerated Wear of the Acme Nut

• Leading up to the time of the accident, Alaska Airlines used two brands of lubricating grease on its jackscrew assemblies:

– Mobilgrease 28– Aeroshell 33

• Leading up to the time of the accident, Alaska Airlines used two brands of lubricating grease on its jackscrew assemblies:

– Mobilgrease 28– Aeroshell 33

Role of Lubrication in Accelerated Wear of the Acme NutRole of Lubrication in Accelerated Wear of the Acme Nut

• Leading up to the time of the accident,

• Alaska Airlines used two brands of lubricating

grease on its jackscrew assemblies:

– Mobilgrease 28

– Aeroshell 33

• Long history of satisfactory performance using

Mobilgrease 28.

• Leading up to the time of the accident,

• Alaska Airlines used two brands of lubricating

grease on its jackscrew assemblies:

– Mobilgrease 28

– Aeroshell 33

• Long history of satisfactory performance using

Mobilgrease 28.

Flight 261 Grease Sample AnalysisFlight 261 Grease Sample Analysis

Highly degraded grease sample from accident airplane’s jackscrew.

Highly degraded grease sample from accident airplane’s jackscrew.

1 mm1 mm

Fresh grease shown for comparison.

Fresh grease shown for comparison.

Wear particle laden grease.Wear particle laden grease. Magnified wear particles.Magnified wear particles.

• Particles consistent with sliding wear (normal wear mode).• No evidence of corrosive wear or abrasive wear.• Particles consistent with sliding wear (normal wear mode).• No evidence of corrosive wear or abrasive wear.

Flight 261 Grease Sample AnalysisFlight 261 Grease Sample Analysis

Side by side, comparative testing

of the two greases was performed under

all pertinent conditions related to jackscrew operations.

Could Switch to Aeroshell 33 Have Resulted in Accelerated Wear?

Could Switch to Aeroshell 33 Have Resulted in Accelerated Wear?

Grease Testing

Wear Testing

ExposureTesting

Test ProgramTest Program

Performed by:NAVAIR Aerospace Materials DivisionPerformed by:NAVAIR Aerospace Materials Division

Grease Testing

Wear Testing

ExposureTesting

Standardized Grease TestingStandardized Grease Testing

Findings:• Mixing of Aeroshell 33 and Mobilgrease 28 did

not significantly deteriorate their properties.

Mo

bil

gre

ase

28M

ob

ilg

reas

e 28

Aer

osh

ell

33A

ero

shel

l 33

MixturesMixtures

Performed by:

• NAVAIR Aerospace Materials Division• Science Applications International

Corporation (SAIC)

Performed by:

• NAVAIR Aerospace Materials Division• Science Applications International

Corporation (SAIC)

Grease Testing

Wear Testing

ExposureTesting

AluminumBronze

Mobilgrease 28Aeroshell 3350/50 blend

WaterDe-icing fluidAnti-icing fluid

75º F150º F212º F

24 hours2 weeks

Grease TypesGrease Types

TemperaturesTemperatures DurationsDurations

ContaminantsContaminants

Exposure TestingExposure Testing

Findings: • Aeroshell 33 does not corrode aluminum bronze.• Staining caused by anti-wear additives (not harmful).

Findings: • Aeroshell 33 does not corrode aluminum bronze.• Staining caused by anti-wear additives (not harmful).

Test SpecimenTest Specimen

Exposed to airExposed to air

Exposed to greaseExposed to grease

Exposure TestingExposure Testing

Performed by:

•Rensselaer Polytechnic Institute

•Battelle Memorial Institute

Performed by:

•Rensselaer Polytechnic Institute

•Battelle Memorial Institute

Grease Testing

Wear Testing

ExposureTesting

Block–on–Ring Block–on–Ring

StationaryBlock

StationaryBlock

RotatingRing

RotatingRing

GreaseGrease

ForceForce

1. Materials same (fabricated from actual

parts)

2. Pressure similar (wide range)

3. Speed similar

4. Motion similar (sliding, reciprocating)

5. Contact Geometry similar (finite area)

1. Materials same (fabricated from actual

parts)

2. Pressure similar (wide range)

3. Speed similar

4. Motion similar (sliding, reciprocating)

5. Contact Geometry similar (finite area)

Comparison of Block-on-Ring Characteristics to Actual J/S Operation

Comparison of Block-on-Ring Characteristics to Actual J/S Operation

Test Conditions of the Block-on-Ring Experiments

Test Conditions of the Block-on-Ring Experiments

• Low, Medium, High, and Very High Average Pressures

• Neat greases and mixtures

• Water, salt water, and de-icing fluid contamination

• Aged grease with wear debris

• Sub-freezing temperatures

• Low, Medium, High, and Very High Average Pressures

• Neat greases and mixtures

• Water, salt water, and de-icing fluid contamination

• Aged grease with wear debris

• Sub-freezing temperatures

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Wear Rate of Aluminum Bronze

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Severe wear(accident airplane)

Wear Rate of Aluminum Bronze

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Severe wear(accident airplane)

Contaminated Greases

Wear Rate of Aluminum Bronze

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Severe wear(accident airplane)

Contaminated GreasesUsedGrease

Wear Rate of Aluminum Bronze

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Severe wear(accident airplane)

Contaminated GreasesUsedGrease –20° F

Wear Rate of Aluminum Bronze

0

10

20

30

40

50

60

70Ae

rosh

ell 3

3

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Mob

ilgre

ase

28

50/5

0 M

ix

Aero

shell

33

Aero

shell

33

Used

Aer

oshe

ll33

Aero

shell

33

Mob

ilgre

ase

28

Dry

water added salt water

addedde-icingadded

Pure Greases

Wea

r ra

te F

acto

r (m

m3 /

N·m

) x

106

Severe wear(accident airplane)

Contaminated GreasesUsedGrease –20° F Dry

Wear Rate of Aluminum Bronze

• No evidence that the use of Aeroshell 33 would have caused accelerated wear.

• The only factor that could explain the severe and accelerated wear is a lack of lubrication.

Conclusions Regarding Severe Wear of Acme NutConclusions Regarding

Severe Wear of Acme Nut