Tomonaga Oyamada

Evaluation of the Wear Process of Cast Iron Coated with Manganese Phosphate

The authors investigated the wear property and wear process of a JIS-FC250 cast-iron surface coated with manganese phosphate, sliding against JIS-SKH51 steel by using an oscillating-rotation wear test rig and SEM-EDX surface analysis. The materials that appeared on the friction surface indicate that the wear process can be divided into three phases, the wear of the coating, the wear of the mixed layer (consisting of cast-iron and the coating) and the wear of the cast iron. The authors found that the value of parameter M, which is the exposure ratio of iron to the coating on the friction surface measured by SEM-EDX analysis, was found to characterize each phase quantitatively. The authors also found that changes in the wear rate are related to parameter M. The best wear resistance of the coated iron was found in the second phase of the wear process, where the exposure ratio on the friction surface ranged from 40 to 80%. The authors obtained the lowest wear rate when the exposure ratio M was 45% and it was less than 11300 that of the original coated surface. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

Effect of Gas Environment on Friction Behavior and Tribofilm Formation of PEEK/Carbon Fiber Composite

This study investigated the friction and wear behaviors of polyetheretherketone composites containing carbon fibers (PEEK-CF) sliding against stainless steel in terms of their dependencies on gas environments. Sliding tests with a block-on-ring apparatus were conducted in humid/dry air and dry nitrogen at normal temperature and nitrogen at cryogenic temperature of 113 K. Friction and wear significantly decreased when sliding occurred in low-humidity, low-oxygen, and low-temperature environments. The friction coefficient, initially 0.25 in ambient humid air, decreased to below 0.10 in the dry nitrogen environment and 0.03 in nitrogen at 113 K. Microscopic observations, surface roughness measurements, and surface composition analysis of worn surfaces were conducted after the sliding tests. After sliding in humid air, the surface roughness of the PEEK-CF block was increased from its initial value by adhesions of large wear particles. However, the surface roughness of the block decreased due to the formations of tribofilms that were micrometers thick and composed of fine wear particles of polymer and carbon fibers after sliding in dry nitrogen. X-ray photoelectron spectroscopy analysis and the Raman spectroscopy analysis indicated increased carbon content with graphite structures on the worn surface after sliding in dry nitrogen. Consequently, it was considered that PEEK-CF changed its wear process in the dry nitrogen environment and formed a smooth surface with carbon particles containing graphite, which is thought to be advantageous in reducing friction.

Application of Ultrasonic Sensing to Monitoring Lubrication Conditions in a Refrigeration Compressor

ABSTRACT Understanding lubrication conditions in a refrigeration compressor is valuable for machine design and ensures the reliability of air conditioners. In this work, the lubrication conditions of a journal bearing in a scroll compressor were evaluated by applying ultrasonic sensing. An ultrasonic probe was attached to a journal bearing supporting a crank shaft in the compressor. The probe transmitted ultrasonic pulses toward the lubricant film between the shaft and the bearing and then received reflections. The lubricant film can be monitored by measuring the reflection amplitude of the ultrasound, which increases with the thickness of the thin lubricant film. With the whirling shaft in the bearing, the minimum reflection amplitude was measured as an index of the minimum lubricant film thickness in the bearing during stable and transient operations of the compressor. Then the measured reflection amplitude was compared with the Sommerfeld number, which is also known to increase with lubricant film thickness. The measured minimum reflection amplitude mostly changed in trend similar to that of the Sommerfeld number. However, the measured minimum reflection amplitude behaved differently during the first 400 s in the startup process. An observation of the lubricant reservoir showed generation of small bubbles in the lubricant in the period. Overall, test results support the usability of the ultrasonic measurement to trend monitoring of the lubricant film thickness in the journal bearing in the compressor. The existence of bubbles in the journal bearing was indicated by the results of the ultrasonic measurement and observation.