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

Simulative Friction and Wear Study of Retrofitted Swash Plate and Rolling Piston Compressors

Air Conditioning and Refrigeration Center Project 0

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

Tribological Evaluation of Contacts Lubricated by Oil-Refrigerant Mixtures

The tribological characteristics of the most common contact geometries found in compressors of air conditioning and refrigeration systems have been experimentally investigated by means of a unique high pressure tribometer (HPT). The HPT has been used to experimentally simulate the friction and wear behavior of various metal contact pairs lubricated by oil-refrigerant mixtures in environments found in compressors. The refrigerants used in this program are CFC-12 to obtain baseline data and its prime replacement candidate, HFC-134a. The CFC-12 has been tested with mineral oils and synthetic alkylbenzenes while the HFC-134a has been tested with monoether polyalkylene glycol (PAG's) and pentaerythritol polyolester oils. Since the amount of refrigerant dissolved in the oil is a function of both pressure and temperature, and the friction and wear of a given contact can be significantly affected by the concentration of refrigerant in the oil, the friction and wear data obtained from this test program should be a good indicator of what can be expected in compressors.Air Conditioning and Refrigeration Center Project 0