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High-Speed Videography of Submerged Arc Welding
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- Author / Creator
- Sengupta, Vivek
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In submerged arc welding (SAW), the welding takes place under a flux bed. The physical phenomena taking place under the flux bed is crucial in determining the quality of the final weld. The presence of the flux layer prevents the direct visibility of the weld zone during welding; this limitation has prevented a lot of research in SAW. The thesis presents a technique to visualize the weld zone of SAW. The technique involves penetrating the flux bed with a tunnel made up of thin sheet steel. The tunnel provides an opening of the arc cavity and allows to capture the physical phenomena taking place under the flux bed into videos at 10,000 frames per second. With the developed technique the present work explores for the first time the effect of current on metal transfer in SAW between 500 A and 1000 A both DCEP and AC polarities. Additionally, the work explores for the first time the effect of fluxes on metal transfer and arc length in SAW between 500 A and 1000 A in both DCEP and AC polarities. The existing research in SAW is scattered among researchers from different places, times, and languages. The thesis presents an exhaustive literature review of the research done in the metal transfer, arc length, arc cavity and slag shell and dynamics of the weld pool in SAW. The review summarizes all the work done related to the physical phenomena in the weld zone of SAW from 1892 to present day. For the effect of current on metal transfer in DCEP-SAW experiments, analysis of the videos at 500 A, shows an irregular shaped droplet with chaotic, non-axial metal transfer. Between 600 A and 1000 A, a new mode of metal transfer based on electromagnetic kink instability is observed. The detachment frequency between 500 A and 1000 A increased from approximately 9~Hz to 82~Hz. The metal transfer observed at 500 A is in good agreement with five different researchers. The metal transfer observed at 800 A is also in good agreement with one more researcher. The weld pool was significantly depressed under the arc pressure and at 800 A and above the meniscus was not visible any more consistent with a change in penetration mode from recirculating flow to the gouging region. For the effect of current on metal transfer in AC-SAW experiments, the metal transfer shows many similar features as observed for DCEP experiments. The key feature in AC is the electrode negative~(EN) cycle with mobile cathode area on the droplet surface. At 500 A, the detachment takes place without forming a molten metal tail. Between 600 A and 1000 A, the detachment morphology is often different in EP and EN cycle. The detachment in the EP cycle is based on electromagnetic kink instability. The detachment in the EN cycle takes place by explosions. Most of the detachments (approximately 72\%) are in the EP cycle. The detachment frequency increases with increasing current and is higher than DCEP experiments at lower currents. The weld pool flows are found to be consistent with previous experiments done with radioactive tracer techniques. For the effect fluxes on metal transfer and arc length in SAW experiments, five different fluxes (Lincolnweld 760M, Lincoln ES200, Lincolnweld 980, Lincolnweld 880M, and an experimental flux with 85\% CaF$_2$) are tested with a 3.2~mm wire. Analysis of the videos shows, at 500 A, an irregular shaped droplet under all the fluxes for both DCEP and AC polarities. Frequent explosions at the droplet surface are seen under the oxide fluxes compared to fluoride fluxes. Between 600 A and 1000 A, the metal transfer observed under all the fluxes is based on electromagnetic kink instability in DCEP and EP cycle of AC polarities. In EN cycle of the AC, the detachments take place by explosions. The detachment frequency increases with the increase in current for both DCEP and AC polarities. In DCEP, a higher detachment frequency is observed under the oxide fluxes compared to the fluoride fluxes. In AC, a noticeable trend in detachment frequency is not observed among the different fluxes. The arc length observed under the fluoride fluxes is shorter compared to the oxide fluxes.
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- Graduation date
- Spring 2017
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.