Papers by Author: Se Doo Oh

Abstract: The carbon dioxide (R-744) as a natural refrigerant has been an attractive alternative refrigerant to replace HFC (hydrofluorocarbon) refrigerants currently used in air conditioning systems, due to the environmental concerns. Because new compressors with CO2 are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressor, especially scroll type, the friction and wear characteristics of sliding surfaces between a fixed scroll and an orbiting scroll in the scroll compressor were investigated in this paper. The sliding tests of pin-on-disk type were carried out between scroll surfaces under various sliding speeds, normal loads, surface roughness, and refrigerant pressures. Two types of lubricants were used, namely POE (polyol ester) oil and PAG (polyalkylene glycol) oil. The friction forces, wear amounts and surface temperatures were monitored during the tests. Test results showed that the wear amounts increased with increasing normal load and rotating speed, and also decreased with decreasing surface roughness. Also, the results of the sliding tests showed that using PAG oil has an advantage over POE oil in CO2 environment. As the pressure of CO2 refrigerant became higher, the amount of wear and coefficient of friction became larger in CO2/POE mixed environment, but wear and friction remained constant in CO2/PAG mixed environment. The wear coefficients in CO2/PAG and CO2/POE mixed environment were 8.60×10-9 ㎣/N·m and 2.35×10-8 ㎣/N·m, respectively.

Abstract: The CO2 was investigated as an alternative refrigerant to replace HFC (hydrofluorocarbons) refrigerant in air conditioning systems due to the environmental concerns. Because new compressors with CO2 are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. Two types of lubricants were used, namely POE (polyol ester) oil and PAG (polyalkylene glycol) oil. The vane-on-disk type sliding tests were performed with an exclusive high pressure wear tester. From the tests, wear volumes of vane surfaces applied various coatings were compared. Test results showed that WC/C and CrN coatings showed good tribological properties. Also, the results of the sliding tests showed that using PAG oil has an advantage over POE oil in CO2 environment.

Abstract: Oilless bearings, which are made with metal powders and then impregnated by oils, are widely used in rotating components. The friction coefficients and the oil loss rates of two types of oil-impregnated sintered-metal bearings (porous bearings, oilless bearings, or oilless metals) with varying loads were measured. One is the Cu-based bearing and the other is Fe-based bearing. The frictional forces of the bearings were measured using the journal bearing tester. By measuring the change of weight before and after sliding tests, the oil losses of oilless bearings were surveyed. Also, PV curves, which could be used to predict the life of the oilless bearing, were plotted. By observing the roundness, the cylindericity and the images of scanning electron microscopy of bearings before and after sliding tests, the tribological characteristics of the bearings were evaluated. It was found that Fe-based bearing show lower friction, more oil flow, less wear and longer life than Cu-based bearing.

Abstract: The tribological performances of two types of oilless sintered-metal bearings with varying loads were investigated. One is the Cu-based bearing and the other is Fe-based bearing. The frictional forces of the bearings were measured using the bearing tester. By measuring the change of weight before and after sliding tests, the oil losses of the bearings were surveyed. Also, PV curves, which could be used to predict the life of the oilless bearing, were plotted. By observing the roundness, the cylindericity and the images of scanning electron microscopy of bearings before and after sliding tests, the tribological characteristics of the bearings were evaluated. It was found that Fe-based bearing show lower friction, more oil loss, less wear and longer life than Cu-based bearing.

Abstract: The carbon dioxide (CO2) is investigated as an alternative refrigerant to replace HFC (hydro fluorocarbon) refrigerants in refrigerators and air conditioning systems due to the environmental concerns. Because new compressors with the carbon dioxide are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressors, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN, and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-disk type sliding tests were carried out under the various sliding speeds, normal loads, and carbon dioxide pressures with an exclusive high pressure wear tester. From the tests wear volume of vane surfaces applied various coatings were compared. During the tests coefficients of friction and surface temperatures were monitored. Test results showed that WC/C coatings showed good tribological properties. TiN and CrN coated vanes showed good wear resistance properties but produced high friction.

Abstract: The tribology of lubricated sliding vanes in the rotary compressor was investigated to replace the HFC refrigerants by the carbon dioxide. The carbon dioxide is a natural refrigerant and very favorable to environment. Because new compressors with the carbon dioxide are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressors, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN, WC/C and two types of nitridings, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-disk type sliding tests were carried out under the various sliding speeds, normal loads, and carbon dioxide pressures with an exclusive high pressure wear tester. From the tests wear volume of vane surfaces applied various coatings were compared. During the tests coefficients of friction and surface temperatures were monitored. Test results showed that WC/C coatings showed good tribological properties. TiN and CrN coated vanes showed good wear resistance properties but produced high friction.

Abstract: In this paper, the effects of the residual stresses on the life of structural engineering components were investigated to predict the wear-life. Residual stresses are usually created by the surface treatment, such as shot peening or deep rolling. The objective of the experimental investigation was focused on the influence of friction and wear characteristics due to the residual stress under dry sliding condition and the measurement of the interleaf friction. Test specimens were made of SUP9, the leaf spring material. The residual stresses were created on their surface by shot peening treatment. Residual stress profiles were measured on the surface and subsurface by means of X-ray diffraction method. Also, the sliding tests were carried out under the different contact pressure and the same sliding velocity of 0.035m/s in order to investigate the friction and wear characteristics of leaf surfaces. Leaf spring assembly tests were performed by the ultimate tensile machine with sticking strain gauges on the leaf surfaces in order to evaluate interleaf friction characteristics. We compared friction coefficients, wear volumes and wear rates of the shot-peened specimens with those of the unpeened specimens, and evaluated the effects of residual stress on the tribological characteristics. We obtained the load-displacement curves, and measured interleaf friction force and interleaf friction coefficient of leaf spring assembly from these curves.