The former has been described and the latter is rather
out of the range of this volume, although I may mention that in the
latter part of 1918 there was launched from a British shipyard the first
rivotless steel vessel. In this the steel plates forming the shell,
bulkheads and floors are welded instead of being fastened together by
rivets. There are three methods of doing this depending upon the
thickness of the plates and the sort of strain they are subject to. The
plates may be overlapped and tacked together at intervals by pressing
the two electrodes on opposite sides of the same point until the spot is
sufficiently heated to fuse together the plates here. Or roller
electrodes may be drawn slowly along the line of the desired weld,
fusing the plates together continuously as they go. Or, thirdly, the
plates may be butt-welded by being pushed together edge to edge without
overlapping and the electric current being passed from one plate to the
other heats up the joint where the conductivity is interrupted.
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