The wear performance of journal bearing used in high speed applications

Abstract

In modern motor manufacturing, it is often a necessary exercise to seek ways to reduce the production cost to stay being competitive. Ball bearings are one of the main components that are used in most high performance motors. The typical cost for a set of ball bearing, that used in vacuum cleaner motor is around US$0.40 each, while the cost of oil-sintered porous bearings (porous bearings), which is a type of journal bearings, of equivalent size cost 3 times less. It is therefore financially desirable to replace the aforementioned ball bearings with the lower cost journal bearings. However, the application is often not viable due to material limitations, but recent advances in materials and surface engineering may make this a possibility. In present work, experiments were designed to study the feasibility of using journal bearings in high speed motor applications. Different journal bearing materials such as sintered bronze, sintered ferrite, modified-silica composite with carbon fibers, and advanced diamond-like carbon (DLC) coating deposited on shafts, are used in this study. The work was carried out using a purposely-built test rig which could run up to 30,000 rpm. A typical embedded industrial journal bearing, which are bronze and ferrite journal sintered with oil, were used for comparison purposes. Two industrial journal bearings operated with low friction coefficient when heavy load was applied. However, low friction coefficient mostly occurs when light load was applied. Journal bearings were tested under both lubricated and dry conditions. It was observed that different journal materials being tested under lubricated condition, they could survive for 2 hours whatever shaft material was used. In these situations, it showed that DLC coating did not make any significant improvement on bearing performance. However, the application of DLC coating improved the journal life when they were tested under dry condition. Under such dry running conditions, shaft material and surface coatings affected journal wear rate. It was proposed that with selected DLC coated shaft, the operating life of a sintered journal bearing could be extended even if the sintered bearing has inadequate oil lubricant.