Joseph Kolly, Ph.D., Grease Group Chairman

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Joseph Kolly, Ph.D., Grease Group Chairman

• Investigation of Lubricating Grease

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Role 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

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Role 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.

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Flight 261 Grease Sample Analysis
1 mm
Highly degraded grease sample from accident
airplanes jackscrew.
Fresh grease shown for comparison.
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Flight 261 Grease Sample Analysis
Wear particle laden grease.
Magnified wear particles.

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

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Could Switch to Aeroshell 33 Have Resulted in
Accelerated Wear?
Side by side, comparative testing of the two
greases was performed under all pertinent
conditions related to jackscrew operations.
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Test Program
Grease Testing
Wear Testing
Exposure Testing
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Grease Testing
Wear Testing
Exposure Testing
Performed by NAVAIR Aerospace Materials Division
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Standardized Grease Testing
Mixtures
Mobilgrease 28
Aeroshell 33

• Findings
• Mixing of Aeroshell 33 and Mobilgrease 28 did not
  significantly deteriorate their properties.

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Grease Testing
Wear Testing
Exposure Testing

• Performed by
• NAVAIR Aerospace Materials Division
• Science Applications International Corporation
  (SAIC)

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Exposure Testing
Grease Types
Contaminants
Water De-icing fluid Anti-icing fluid
Mobilgrease 28 Aeroshell 33 50/50 blend
Aluminum Bronze
75º F 150º F 212º F
24 hours 2 weeks
Temperatures
Durations
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Exposure Testing
Test Specimen
Exposed to grease
Exposed to air

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

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Grease Testing
Wear Testing
Exposure Testing

• Performed by
• Rensselaer Polytechnic Institute
• Battelle Memorial Institute

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

• Materials same (fabricated from actual parts)
• Pressure similar (wide range)
• Speed similar
• Motion similar (sliding, reciprocating)
• Contact Geometry similar (finite area)

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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

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Wear Rate of Aluminum Bronze
Pure Greases
Wear rate Factor (mm3/Nm) x 106
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Wear Rate of Aluminum Bronze
Pure Greases
Severe wear (accident airplane)
Wear rate Factor (mm3/Nm) x 106
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Wear Rate of Aluminum Bronze
Pure Greases
Contaminated Greases
Severe wear (accident airplane)
Wear rate Factor (mm3/Nm) x 106
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Wear Rate of Aluminum Bronze
Used Grease
Pure Greases
Contaminated Greases
Severe wear (accident airplane)
Wear rate Factor (mm3/Nm) x 106
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Wear Rate of Aluminum Bronze
Used Grease
Pure Greases
Contaminated Greases
20 F
Severe wear (accident airplane)
Wear rate Factor (mm3/Nm) x 106
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Wear Rate of Aluminum Bronze
Used Grease
Pure Greases
Contaminated Greases
20 F
Dry
Severe wear (accident airplane)
Wear rate Factor (mm3/Nm) x 106
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Conclusions Regarding Severe Wear of Acme Nut

• 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.

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