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© 2018 Eaton. All rights reserved..
A/C Compressor Oils And Their Effect On Elastomers
Aaron D. Clark M.S
Eaton Corporation
© 2018 Eaton. All rights reserved.. 2
Overview
This presentation covers a detailed study examining the compatibility between common elastomeric materials and relevant compressor lubricants using quantitative processes. The objective is to characterize suitable materials for mobile A/C applications and aid the designer with selection and troubleshooting.
3© 2018 Eaton. All rights reserved..
Agenda
• Purpose Statement
• Causes of A/C Failure
• Mechanism of Chemical Compatibility
• Test Fluids and Materials
• Data
• Conclusions
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Common Causes of AC Failure• Dirty Coils or Corrosion
• Blocked/damaged Suction Lines
• Low or Overcharge of Refrigerant
• (Electrical Problems)
• Hose and Seal/O-Ring Related
• Inadequate Oil Lubrication – Loss of refrigerant resulting in poor oil circulation and reduced lubrication for the compressor
• Moisture - Degradation of a hose or seal allowing moisture to enter the system, mix with the refrigerant and form an acid.
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The Dangers of Low Refrigerant• Reduced System Performance
• Icing - If there is insufficient refrigerant inside the evaporator coil, the coil will lose its heat absorption ability and condensation in the system will freeze causing heat exchange to cease.
• Compressor Failure -The loss of refrigerant will cause a compressor to potentially overheat and eventually burn-out.
Compressor motor extreme failure
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Fluid Compatibility - Hose
• Incompatible fluids can make the hose assembly swell, shrink, blister, deteriorate and delaminate
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Causes of O-Ring Failures:• Design Related• Material Related
• Abrasion• Chemical Compatibility• Compression Set• Extrusion• Spiral failure• Thermal capability• Weathering
• Installation Related• Production Quality Related
Fluid Compatibility - O-Rings & Seals
• Material swell and loss of properties may lead to o-rings & seals becoming susceptible to mechanical degradation and failure during use, especially in dynamic applications.
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O-Ring/Seal Failure Modeso Extrusion Failure :
• Seal material migrates between the mating surfaces.
o Compression Set :• Rubber compounds can permanently deform under strain which decreases sealing force
resulting in leakage• Compression set is the percentage of deflection that the elastomer fails to recover after a
fixed period of time under a specific squeeze and temperature.
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Factors Influencing Chemical Compatibility
• Polymer Related:
• Plasticizer and filler type and content:
• Crystallinity and Cross link Density
• System Related:
• Temperature & Pressure: Diffusive rates increased by a factor of about 1.6 for every 5 degree increment.
• Fluid Related:
• Molecular Weight : Inverse relationship to diffusive uptake. Relates to Viscosity
• Solubility : Hansen Solubility Parameters characterize the interactions between an elastomer and a fluid by estimating the relative miscibility of polar and hydrogen bonding systems.
10© 2018 Eaton. All rights reserved..
Mechanism of Fluid Compatibility
Solution-Diffusion Model (Thomas Graham, 1866) –Permeants dissolve in a material and then diffuse through the membrane acrossa concentration gradient
Two steps:1. Adsorption or adherence of the fluid
onto the surface of the solid based on solubility.
2. Diffusion through the channels in the polymer interstitial space along a concentration gradient (Fick’s Law) from highto low concentration
R’ I
RO-(CH2-CH-O)n-R”
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Mechanism of Fluid Incompatibility
Once inside the interstitial space
• Swelling/shrinking of the elastomer
• Plasticization of the polymer strands
• Loss of physical properties
• Chemical attack on the polymer
Exposure to Fluids
Time/Temperature
Diffusive Uptake
Higher Conc. Lower Conc.
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Chemical Degradation
• Abstraction of a tertiary hydrogen atom from the polymer chain as a result of oxidation.
• The hydroperoxide that forms can cycle and abstract another hydrogen until bond scission occurs.
+ RHeat/O2
+ ROOH
ROOH RO + OHHeat
+ RO
Type 1: Hydrogen Abstraction from an Alkane Bond
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Chemical Degradation
• Rupture of pi bond leads to formation of a carbonyl (aldehydes and ketones)
Type 2: Oxidation of an Alkene Bond
Type 3: Deterioration of Cross Links:
O2/Heat
O2
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Chemical Compatibility Testing
Chemical Compatibility Rating
Testing:• Oil Exposure - ASTM D471• Physical Properties - ASTM D412• C Set – ASTM D395
Worst Case Scenario Testing
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o Polyalkylene Glycol (PAG): Pro: Good hydrolytic stability Pro: Burns cleanly without generating residue Pro: Acceptable with R-134a and R-1234yf Con: Absorbs water Con: Not compatible with PAO and Mineral Oil
o Polyolester (POE):• Pro: Compatible with Mineral Oils and PAO Pro: Acceptable with R-134a Mandatory for hybrid electric systems Con: Absorbs moisture Con: Can generate sludge Con: Hydrolytically unstable at high temperatures Con: Acceptability in R-1234yf TBD
Refrigerant Oils
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o Polyvinyl ether (PVE) –• Pro: Good hydrolytic stability• Pro: Good compatibility with other oils• Pro: Better than POE for R-410a• Pro: Compatible with R-134a• Con: Acceptability in R-1234yf TBD
o Polyalphaolefin (PAO) -• Pro: Good hydrolytic stability • Pro: Compatible with Mineral Oils and POE• Pro: Low moisture absorption• Con: Can form deposits when used at high temperatures• Con: Acceptability in R-1234yf TBD
Refrigerant Oils
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Refrigerant Oils - Composition
Refrigerant Oil Requirements:• Good anti-wear / lubricity• Low foam and rapid air release• Low pour point• Low floc point• Good chemical / thermal stability• Compatibility with rubber & plastic
components• Compatibility with refrigerants• Prevention of acid, sludge, rust and
deposit formation.
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Materials Studied
EPDM Polyamide (PA)
Acrylonitrile (NBR) Butyl (IIR)
Chloroprene (CR)
Polymer Temperature Capability Application
Acrylonitrile (NBR) -40°C to 125°C Hoses/Seals
Chloroprene (CR) -30°C to 100°C Hoses/Seals
Butyl (IIR) -50°C to 125°C Hoses/Seals
EPDM -50°C to 150°C Hoses/Seals
Polyamide -40°C to 140°C Hoses
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Study 1: Fluid Type vs. Polymer Tensile Strength
• Total test time is 168 hours @ 100°C
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Study 1: Fluid Type vs. Polymer Elongation
• Total test time is 168 hours @ 100°C
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Study 1: Fluid Type vs. Polymer Volume Swell
• Total test time is 168 hours @ 100°C
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Study 2: Effects of Time on POE Volume Swell
40%
• Test temperature is 100°C
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Study 3: PAG Oil Comparison
• Materials studied include CR and Polyamide• Various PAG 46 type oils tested from different manufacturers• Total test time is 168 hours @ 100°C
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Study 4: Oil Viscosity Study
• PAG oils with 46, 100 and 150 viscosities examined.• Total test time is 168 hours @ 100°C
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Rubber Formulations Vary!
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Study 5: Formula Variance vs. Compatibility • 2 Chloroprene recipes were examined that varied 25% in total filler content.• The exposure was 168 hour immersion in PAG oil @ 100°C
Low Cost Standard
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Standard Practice -ASTM D2000 “Call Out”
© 2018 Eaton. All rights reserved.. 28
Conclusions
• Quantifiable variation exists in material response to refrigerant oils
• Oil Viscosity does have a minor effect on material properties
• Significant differences in oil formulations exist between products and can generate mixed results
• Use caution when selecting hose and seal materials to avoid incompatibilities
29© 2018 Eaton. All rights reserved..
• “The most common cause of a Refrigerant Leak is due to an O-Ring”• http://xpectmoreautomotive.com/ac-system-and-coolant/• https://aristair.com/blog/8-preventable-causes-of-ac-compressor-failure/• https://www.quora.com/What-causes-a-car%E2%80%99s-air-conditioner-hose-to-start-leaking-from-the-
crimped-fitting• http://blog.parker.com/top-8-reasons-hydraulic-hoses-fail• Patech; http://slideplayer.com/slide/1425457/• https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2250&context=icec• http://www.hydraulicspneumatics.com/hose-tubing/guide-recognizing-causes-hose-failure• http://flodynamix.com/o-ring-failure-chart.html• https://www.bimmerforums.com/forum/showthread.php?1226116-catch-can-install-gt-oil-leak-around-
dipstick• http://www.brianb.org/images/Scuba/Homemade/Gas%20Booster/gas_booster.htm
References
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Acknowledgements
• Chris Seeton• Derrick Craddock• Doris Showalter• Gina Clark• Karl Myers• Keith Swearingen• Matt Sexauer
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