5 research outputs found
The Effect of Dissolved Water on the Tribological Properties of Polyalkylene Glycol and Polyolester Oils
The effect of water dissolved in polyalkylene glycol and polyolester oils on the
tribological behavior of two material contact pairs in three test environments is evaluated. The
material contact pairs are M2 tool steel against 390 aluminum and M2 tool steel against gray
cast iron. The three oils are a polyalkylene glycol (PAG) and two polyolester (PEl and PE2)
oils. The test environments are R134a, air and argon. The tests are conducted in a specially
designed high pressure tribometer which provides an accurate control of the test variables.
The results indicate that the P AG oil performed better than the esters for both material
contact pairs. The wear on the aluminum plates for the tests conducted with the P AG oil in all
three environments is greatest at the lowest moisture content levels. From the stand point of
friction and wear, it is beneficial to have a water content level of 5000 ppm or greater in the
PAG oil when the plate material is 390 aluminum. The wear on the cast iron plates, when using
a PAG oil as the lubricant showed a slight increase with water content in a R134a environment.
This trend is opposite when air is the test environment.
Both ester oils lubricated aluminum much better than the cast iron . The difference in
the amount of wear can be as high as two orders of magnitude. This is probably due to the
ability of the esters to form bidentate bonds with aluminum. Esters do not form such bonds
with iron. The plate wear is greater for the PEl tests than for the PE2 tests for both material
contact pairs. This is most likely due to the difference in the viscosity of the oils. In PE2 oil,
water does not seem to affect the friction and wear of both aluminum/steel and cast iron/steel
contacts when R134a is the test environment. On the contrary, for the aluminum/steel contacts,
the water content significantly influences wear when argon or air is the test environment. For
the cast iron/steel contacts, the wear is strongly influenced by the water content when the test is
conducted in argon, but it is not influenced by the water content when the test is conducted in
air.Air Conditioning and Refrigeration Center Project 0
Tribological Evaluation of Compressor Contacts - Retrofitting and Materials Studies
Air Conditioning and Refrigeration Center Project 0
Scuffing of Aluminum/Steel Contacts Under Dry Sliding Conditions
Some typical applications where scuffing may occur are gear teeth, piston rings and
cylinder pairs, cams and followers, splines, sleeve bearings, and parts of swash and wobble plate
compressors. Unlike other tribology-related failures, scuffing occurs very fast, without any
warning, and usually leads to the complete destruction of the sliding pair. Practical experience
with steel has helped to outline safe ranges of operation for some components. Very little,
however, is known about aluminum, which is the second most commonly used engineering metal.
The aim of this study is to obtain a better understanding scuffing and seizure of aluminum/steel
contacts.
The research includes an experimental study of scuffing of aluminum/steel contacts under
dry sliding conditions, a study of the physics of the scuffing process, evaluation of various
hypotheses for scuffmg, and modeling of scuffing.
The experiments are conducted in a custom-designed tribometer, which provides accurate
control of the environmental conditions. Special instrumentation, experimental procedures and
software are developed as a part of the experimental program. These provide a reliable
reproduction and identification of scuffing under laboratory conditions. The scuffing
characteristics of five materials are obtained in air and refrigerant (R134a) environments. The
effects of load, sliding velocity, mechanical strength, environmental temperature, specimen
geometry, time, loading history, and type of environment are evaluated.
The mechanisms leading to scuffing are studied by examination of surfaces, subsurfaces
and wear debris of specimens in the process of scuffing. Quantitative measurements of subsurface
plastic strain are also obtained.
The theoretical part of the study includes the development of a finite element model for the
contact of runned-in rough surfaces and several other models for subsurface stresses,
temperatures, and strains. These models provide information about the local conditions in the
subsurface
Based on the experimental observations and the scuffing models a new hypothesis for
scuffing is proposed. According to this hypothesis, scuffing involves initiation of cracks due to
subsurface plastic deformation, propagation of these cracks leading to the removal of the existing
protective surface layers, and finally cold welding due to adhesion between bare metal surfaces.Air Conditioning and Refrigeration Project 4
Tribological Evaluation of Various Aluminum Alloys in Lubricant/Refrigerant Mixtures
The tribological characteristics of various aluminum alloys, aluminum composites and some
surface treated aluminum are evaluated in lubricant/refrigerant mixtures. All of these evaluations are
based upon a specimen testing program using a high pressure tribometer (HPT). This research program
mainly consists of two parts.
The first part of this study is mainly focused on materials screening of various aluminum
alloys/steel contact pairs lubricated by polyolesterlR134a and PAGIR134a lubricant/refrigerant (LIR)
mixtures. In this study, various aluminum alloys are tested under the same environmental and operating
conditions in order to compare their wear resistance. The results show that the lowest wear is obtained
with the 390 Die Cast alloy. This alloy has the largest amount of silicon content and the highest bulk
hardness. The results also show that, in general, the amount of wear decreases as the amount of silicon
content in AI-Si alloys increases. Better wear resistance is also achieved if the amount of copper and
bismuth are increased. Conventional anodizing does not improve the wear resistance of the 356
aluminum alloy under concentrated contacts. Hard anodizing and a SiC-AI composite provide very good
wear resistance. However, they cause increased wear on the counterface by abrasion due to the rough,
hard, surfaces generated by hard anodizing processes and the hard SiC particles. From the wear results
obtained, the Ester/R134a mixtures consistently provide better protection of the aluminum alloys
compared to the PAG/R134a mixtures. If sufficient amounts of R134a exists in the LlR mixture,
extensive surface fatigue on 356 aluminum is observed.
In the second part, two AI-Si alloys (356-T61 and 390-T61), widely used in critical components
of refrigerant compressors, are examined fortheir friction and wear behavior in different LIR mixtures.
The LIR mixtures tested include ester and PAG lubricants with R134a, mineral and alkylbenzene
lubricants with R22, R407C and R410A, as well as an ester lubricant with both R407C and R41OA.
Based on the wear data obtained, the capped P AG seems to be a better lubricant for 356 alloy than the
uncapped PAG. However, the lubricity of the PAG's is about the same with the 390 alloy. When the
ester lubricant is used, the wear on each alloy is about the same in R134a, R407C, R410A and air
environments. There is no significant difference in lubricity of mineral and alkylbenzene lubricants when
used with R22 and its possible substitutes R407C and R410A.Air Conditioning and Refrigeration Center Project 4
Simulative Friction and Wear Study of Retrofitted Swash Plate and Rolling Piston Compressors
Air Conditioning and Refrigeration Center Project 0