A Search for Optimal Friction Resistant Material to Cover Contact Surfaces: A Case Study in the Senior Mechanical Engineering Design Student Project

Abstract

The University of Connecticut Department of Mechanical Engineering has developed an industry recognized Senior Design Capstone course that provides students the opportunity for a major design experience. This paper will discuss the issues and challenges associated with project demonstrated on the base of the Search for Optimal Friction Resistant Material to Cover Contact Surfaces in an Electric Manual Switch. In order to determine the viability of potential substitute materials, the team produced custom testing rigs to evaluate material wear and corrosion performance. The construction of these rigs, the fabrication of the testing coupons, testing results and the final choice of the covering material were the primary deliverables of this project. The wear rig allowed the team to determine mechanical performance on the basis of mass loss. In the evaluation of mechanical performance, the coated test coupons were revolved on a testing plate while a flat coated column contacted the surface to wear the plating. After a certain number of cycles, the coupons were subjected to environmental testing. The corrosion rig was designed to provide aggressive corrosion on the worn coupons, and was modeled after the industry standard salt fog test. The worn test coupons were immersed in a humid salt fog test chamber and held at temperature until corroded. A series of calibration checks were completed to evaluate the UConn test severity to ASTM (American Society of Testing Materials) standard testing. The surfaces before and after the corrosion process were analyzed in a number of ways. Optical microscopy, profilometry, and surface metrology techniques were employed to determine which platings were likely to meet the consumer standards necessary for replacement. The large set of data on volume loss, mass loss, and surface degradation provided good metrics for the evaluation of material suitability. The project described in this paper is based on the contribution of the students’ team as well as is the result of consulting effort of the faculty who were directly involved in the course and also the other department’s faculty who were consulting the detail processes. General Electric (GE) especially its Industrial Solution Division that sponsored the project, is a company that provides a wide variety of services in electrical appliances, power, and home and business solutions. It has tasked the team with identifying a suitable replacement for Hexavalent Chromium Chromate passivation. This material is plated on many components in GE electrical appliances due to its resistance to abrasion and corrosion. However, because of changing regulations and the health risks that come from dealing with HCC, the sponsor has determined that it is necessary to remove the plating from production by 2019. In order to determine the viability of potential substitute materials, the team produced custom testing rigs to evaluate material wear and corrosion performance. The construction of these rigs and the fabrication of the 400+ testing coupons, the environmental and mechanical tests results and the final conclusions were the primary deliverables of this project. The team examined three different plating materials (JS 600, trivalent chrome, and zinc phosphate) and compared their performance to that of the original HCC plating. The resulting comparative analysis drove the final recommendation of the best candidate material for the sponsor on the basis of mechanical and environmental performance.