Doctor of Philosophy
School of Mechanical, Materials and Mechatronic Engineering
Bothma, Nicolaas Christian, The influence of copper coating on the fume formation rate of carbon steel welding wire during the gas metal arc welding process, Doctor of Philosophy thesis, School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3761
Welding processes have been optimised to ensure that the best productivity and quality can be achieved.
However to ensure that this level of optimisation and quality can be maintained the focus of research has moved towards the occupational health and safety of the welder. Fume formation rates of welding consumables is one of the areas of interest. Copper has long been used in the production of welding wires firstly as a drawing aid but of late as a protective coating on carbon steel wires to improve the shelf life of the product and secondly to decrease the electrical contact resistance.Previous studies of the fume formation rate (FFR) have indicated that copper coated welding wires produce more fume than un-coppered wires. The copper content of welding wires is defined as a total value that will include the base metal copper content and the added copper in the coating.
The initial investigation focussed on the determination of the FFR of a group of welding wires of known chemical composition welded using a fixed set of welding parameters. The wires were further characterised by determining the quality and appearance of their surface condition and the possible influence that this may have had on the FFR results. The tests confirmed that there was an increase in the FFR with the copper coated wires, however a large variation in results was observed. It was further noted that the un-coppered wires were very unstable during the welding process, indicating that the welding parameters may not have been optimised for these wires.To eliminate fluctuations caused by variations in the chemical composition and manufacturing process that may have influenced the FFR a group of wires were specifically manufactured for this investigation. These wires originated from the same base material and were manufactured following the same manufacturing route. The major difference was that the amount of copper deposited on two of the wires was accurately controlled to deliver two levels of total copper content.
In addition to the control of the basic chemical composition of the wires, FFR testing was performed using an “auto-control” unit developed by the University of Wollongong to maintain optimum welding parameters.
The results of this testing indicated that the increase in FFR for coppered wires varied from 18% to 32%. The second part of the investigation concentrated on finding an explanation for the increased FFR as a result of increased copper content in the welding wire. Several hypothesis were developed and tested and the most likely explanation for the increase in the FFR seemed to be related to the increase in the droplet temperature between a copper coated and uncoated welding wire. This increase in temperature would lead to a higher evaporation rate with a resultant increase in the FFR. The thesis explores possible reasons for an increase in temperature.