The mode
of working is as follows: For shell plates, from five-eighths inch
to seven-eighths inch thick, to warm each to a dark red heat before
rolling, having previously drilled a few holes to template for bolting
the strakes together; the longitudinal seams are usually lap joints
treble riveted, requiring the corners to be thinned, which is done after
rolling. The furnace plates are generally welded two plates in length,
and flanged to form Adamson rings, and at the back end to meet the tube
plate; the back flame-box plates are flanged, also the tube plates and
front and back plates; and wherever work is put on to the plate it
is annealed before going into the place. The rivet holes are drilled
throughout. In the putting together the longitudinal seams of the
thicker plates of the shells, great care is always taken to set the
upper and under plates for the lap to their proper angle before they
are bolted together, a point generally overlooked by the practical
boilersmith.
CORROSION OF BOILERS.
The question of corrosion is one which is gradually being answered as
time goes on; and so far very satisfactorily for steel. Some steel
boilers were examined a few weeks ago which were among the first made;
and the superintending engineer reports: "There is no sign of pitting
or corrosion in any part of the boiler; the boilers are washed out very
carefully every voyage, and very carefully examined, and I cannot trace
anything either leaking or eating away.
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