INVESTIGATION OF WEAR CHARACTERISTICS OF CONICAL DELRIN THRUST BEARINGS

This study focuses on the wear rate in conical thrust bearings, which is responsible for field failures of stepper motors in optical disk drives (ODD). These bearings support the stepper motor worm shaft and consist of a steel ball supported in a polymer conical bearing cup. The tribological behaviors of polymers used in bearing application has been addressed by using Archard's wear model, a well known classical model for fretting wear in the literature. However, these studies were for planar bearing surfaces and other geometries, not for the conical geometry addressed in this study. Tests were designed and implemented to study the wear rate of the conical bearing cups at with different load levels. The tribological behavior of Delrin in conical thrust bearing applications has been characterized, by quantifying the wear factors used in the modified Archard's model. Distinct reduction of wear rate is observed due to formation of a polymer transfer film on the steel ball. The variability of the wear properties is explored through replication of the test conditions. Destructive physical analysis is conducted to gain insight into the fundamental wear mechanisms as a part of this study. The results of the wear tests are used to develop a life model of the stepper motor as a case study, to demonstrate an application of this approach. The life model is used to study the effect of variability in the initial axial bearing preload (due to manufacturing tolerances), on the wear rate and life of the stepper motor

Hydraulic characterization and removal of metals and nutrients in an aerated horizontal subsurface flow “racetrack” wetland treating primary-treated oil industry effluent

Summarization: Constructed wetlands (CW) are an attractive technology due to their operational simplicity and low life-cycle cost. It has been applied for refinery effluent treatment but mostly single-stage designs (e.g., vertical or horizontal flow) have been tested. However, to achieve a good treatment efficiency for industrial effluents, different treatment conditions (both aerobic and anaerobic) are needed. This means that hybrid CW systems are typically required with a respectively increased area demand. In addition, a strong aerobic environment that facilitates the formation of iron, manganese, zinc and aluminum precipitates cannot be established with passive wetland systems, while the role of these oxyhydroxide compounds in the further co-precipitation and removal of heavy metals such as copper, nickel, lead, and chromium that can simplify the overall treatment of industrial wastewaters is poorly understood in CW. Therefore, this study tests for the first time an innovative CW design that combines an artificially aerated section with a non-aerated section in a single unit applied for oil refinery wastewater treatment. Four pilot units were tested with different design (i.e., planted/unplanted, aerated/non-aerated) and operational (two different hydraulic loading rates) characteristics to estimate the role of plants and artificial aeration and to identify the optimum design configuration. The pilot units received a primary refinery effluent, i.e., after passing through a dissolved air flotation unit. The first-order removal of heavy metals under aerobic conditions is evaluated, along with the removal of phenols and nutrients. High removal rates for Fe (96–98%), Mn (38–81%), Al (49–73%), and Zn (99–100%) generally as oxyhydroxide precipitates were found, while removal of Cu (61–80%), Ni (70–85%), Pb (96–99%) and Cr (60–92%) under aerobic conditions was also observed, likely through co-precipitation. Complete phenols and ammonia nitrogen removal was also found. The first-order rate coefficient (k) calculated from the collected data demonstrates that the tested CW represents an advanced wetland design reaching higher removal rates at a smaller area demand than the common CW systems.Presented on: Water Researc