Abstract
The object of this study was to investigate the effect of coating thickness on the weldability of the steel coated with a shop primer, and finding a shop primer for giving the highest weldability of steel in the T-type fillet welding under the worst welding conditions.Experiments were conducted on 11 kinds of shop primers giving high weldability of steel in butt welding.The shop primers employed were as follows: 5 kinds of organic zinc primers, 4 kinds of non-zinc primers, and each one kind of inorganic zinc primer and wash primer.The coating thicknesses of primers were about 15, 30, and 60μ. Blank tests were conducted on uncoated steel plates for reference.Arc welding process was conducted with a gravity type arc welder by T-type fillet welding.Welding operation test, bead appearance test, and T-type fillet weld bending test were conducted on these test pieces.The results obtained were as follows:(1) The arc of welding was more difficult to be generated with the increase in coating thickness of primer. The generation became impossible at more than about 30μ in non-zinc primers and a wash primer. Therefore, it was reguired to remove the primers in the arc starting zones for the welding of these coated steels.(2) The removal of spatter was easier with the increase in coating thickness of primer, but the arc stability, slag detachability, bead appearance, etc. became worse. As the result, the crack sensitivity in bending test became higher. In particular, a kind of organic zinc primer prepared by the combination of an epoxy resin and minium, and a kind of non-zinc primer containing a large quantity of chrome yellow displayed such a tendency.(3) The welding speed and deposition rate were lower with the increase in coating thickness of primer. In particular, non-zinc primers displayed such a tendency.(4) In general, the weldability of these steels coated with primers seemed to turn lower at about 30μ of coating thickness in T-type fillet welding process. Therefore, sufficient control of coating thickness of primer was needed in shop coating.
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