In general, the principles of layout and fabrication
2. Insert the sheet all the way into the brake, with
that apply to making new objects also apply to making
the reverse side up and the layout lines down.
replacement parts. To replace a section of ventilation
3. Completely form the single hem.
system ductwork, for example, you would make up a
new section according to the layout and fabrication
4. Remove the sheet from the brake and turn it over
procedures described in the previous paragraphs.
so that the layout lines are up. Reinsert the sheet in the
brake and form the flange for the stop (C in fig. 12-103).
Sometimes you will be able to patch ductwork
rather than to manufacture a new section. Patches are
5. Remove the sheet again. This time, with the
installed by welding, brazing, or using sheet metal
layout lines down, insert the sheet in the brake and form
screws or pop rivets.
the depth of the jamb (B in fig. 12-103).
Many ducts throughout the ship are insulated to
6. Slide the sheet out to the next line and form A
reduce the amount of heat and noise transferred between
the duct and the surrounding spaces. When insulation
The next step is to form the sides, top, and bottom
and lagging are removed for the repair or replacement
of the locker. Start with the sheet all the way in the brake.
of a section, the area must be reinsulated and relagged.
Form the tab for riveting first, then slide the sheet out
Ducts are insulated by applying the specified
to the next brake line to form the bottom. Form one side,
insulating material, and tying the insulating material in
the top, and then the other side in the same way.
place with galvanized steel wire or fibrous glass thread.
Form the door by making the single hem C all the
The insulating material is then covered with lagging.
The lagging is fastened with an adhesive.
way around. Then form flanges B and A on each section
of the door.
Before applying insulation to bulkheads, inspect
the area carefully and be sure that the protective coating
Assemble the locker by riveting the side seam. Then
of the metal is intact and that the surface is free of any
install the back with the Pittsburgh lock seam. Solder or
oil, grease, or dirt. Insulation may be applied to
braze the jamb miters at the front of the locker and also
bulkheads by one of two approved methods. In the first
at the corners of the door. (These miters and corners
method, the studs are laid out and welded to the
should NOT be welded. The extreme heat of welding
bulkhead and the insulation is then pushed onto the
will cause severe distortion of the structure.) File off any
studs. In the second method, each piece of insulation is
excess metal, and clean the soldered or brazed areas
fitted into its proper place and the location of the studs
thoroughly to remove all traces of the flux.
is marked by punching through the insulation. The
Fit the door in the jamb. There should be enough
insulation is removed and the studs are welded to the
clearance all around so that the door fits loosely. Insert
marked spots. The insulation is then put on over the
thin strips of metal between the door and the jamb on
all four sides to equalize the clearances. Then using
Detailed information concerning approved
either rivets or screws, fasten the hinges to the locker
insulating materials and approved methods of using
and to the door. Install a knob or handle on the door so
them may be obtained from NAVSEA plans and from
that you can open and close it. The locker is completed.
NSTM, chapter 635.
MAINTENANCE AND REPAIR
OF SHEET METAL STRUCTURES
We have discussed the tools and procedures for
The ventilation ducts and other sheet metal
sheet metal layout and fabrication. Study your pattern
structures aboard ship are maintained and repaired by
development methods and refer back to them while you
HTs. Such structures may require the fabricating of
are laying out your patterns. As with anything you do,
replacement parts, the patching of existing parts, and
experience will help you become more efficient in your
the overhauling of closures and other fittings. You will
work. However, accuracy is one of your major concerns.
most likely repair or replace insulation and lagging,
Double check your layout before you start making your
periodically clean the ventilation ducts, and do various
cuts and bends. A little extra effort will save time and