Ellen Bergseth

Open System Tribology and Influence of Weather Condition

The tribology of an open system at temperatures ranging between 3 °C and −35 °C, with and without snow, was investigated using a pin-on-disc tribometer mounted in a temperature-controlled environmental chamber. The relationship between the microstructure and ductility of the materials and the tribology at the contacting surfaces was investigated. The study shows that during continuous sliding, pressure causes snow particles to melt into a liquid-like layer, encouraging the generation of oxide flakes on the contact path. The friction coefficient and wear rate are dramatically reduced through an oxidative friction and wear mechanism. In the absence of snow, the tribological process is controlled by the low temperature brittleness of steel in the temperature range from 3 °C to −15 °C. At these temperatures, cracks are prone to form and extend on the worn surfaces, resulting in the spalling of bulk scraps, which are crushed into debris that increases the friction coefficient and wear rate due to strong abrasion. When the temperature falls to −25 °C, an ice layer condenses on the metal surfaces and relaxes the tribological process in the same way as the added snow particles, which significantly decreases the friction and wear.

Effect of Gear Surface and Lubricant Interaction on Mild Wear

In this study, a twin-disc test machine was used to simulate a rolling/sliding gear contact for three surface finishes, each run with two types of lubricants, thus seeking to develop insight into the tooth flank/lubricant tribological system. The test disc surfaces were case-carburised before the surfaces were produced by: transverse grinding followed by a mechanical abrasive polishing process; transverse grinding only; and transverse grinding followed by preheating as a final finishing step (intended to enhance the build-up of an easily sheared surface boundary layer using a sulphur additive). The twin-disc contact was lubricated with an ester-based environmentally adapted lubricant or a polyalphaolefin-based commercial heavy truck gearbox lubricant. To obtain information about the composition of chemically reacted surface layers, the specimens used were analysed using glow discharge-optical emission spectroscopy. The results indicate that the interactions between different surface finishes and lubricants have different impacts on friction behaviour, wear and the reacted surface boundary layer formed by the lubricant. Running a smooth (polished) surface with the appropriate lubricant drastically reduces the friction. Surface analysis of the ground surfaces gives clear differences in lubricant characteristics. The commercial lubricant does not seem to react chemically with the surface to the same extent as the EAL does. Micropitting was found on all ground discs with both lubricants, though at different rates. The highest amount of wear but less surface damage (i.e. micropits) was found on the preheated surface run with the commercial lubricant.

Pin-on-Disc Study of Tribological Performance of Standard and Sintered Gear Materials Treated with Triboconditioning Process: Pretreatment by Pressure-Induced Tribofilm Formation

ABSTRACT Coating is one of the innovative approaches used to improve the wear resistance and load-carrying capacity of surfaces in rolling–sliding contact, such as gears and rolling element bearings. In this study, the tribological performance of standard gear material (EN 16MnCr5) and two kinds of powder metallurgy (PM) gear material (Distaloy AQ + 0.2% C and Astaloy 85Mo +0.2% C) with and without tribofilms formed by a pretreatment were evaluated. Specimens treated with the pretreatment and the substrate were subjected to pin-on-disc tests under boundary lubrication conditions. The friction and wear performance of the two different PM gear materials with the pretreatment-formed tribofilm were compared to RS-RS (EN 16MnCr5 material disc and pin combination) for reference. It was found that the pretreatment lowers the friction coefficient and enhances the wear resistance of pins because of the tribofilm formed. The tribofilm caused good running-in due to the existence of and Fe and W oxides. Mo-Mo (Astaloy 85Mo + 0.2% C material disc and pin combination) and Mo-RS (Astaloy 85Mo + 0.2% C disc and EN 16MnCr5 pin combination) showed statistically significant higher wear resistance.

Assembly feature data instance modeling: Prototype implementation and outputs

This paper introduces the assembly feature data schema instance modeling to pre-examine the schema functionality and output-as the preliminary step for data modeling. In order to link assembly with product design, it is essential to determine which entities of product design are involved at the automated assembly planning and operations. It is possible to assign meaningful attributes (assembly features) to the part model entities in a systematic and structured way. Using object-oriented design, the assembly feature data structure and its relationships are modeled. As a part of the research on product and assembly system data integration within the evolvable production system platform, the instance models for proposed assembly feature data structure provide a deeper understanding and error reduction that might possibly occur at the development of the database. Moreover through instance modeling, the assembly feature data query output format from the database prototype is simulated. An industrial assembly model example with its 3DPart models is chosen to demonstrate the realized assembly feature data set with string data type. The models support the desired simplicity at the database prototype implementation. The output format envisions the interoperability factor between product models and the assembly planning systems.