around the plaster of paris and secure it with seizing
wire. The textile cloth may extend far enough to protect
the wire rope from the torch while the terminal is being
heated.
Heat the terminal carefully and uniformly with the
torch, making certain the flame is not directed on the
exposed wire rope at the bottom of the asbestos cloth.
(See fig. 3-57.) Continue heating the terminal until it
begins to radiate heat waves. Remove the torch from the
terminal and leave the terminal undisturbed for 30
seconds. Make a mark on the thickest portion of the
terminal with a 550 and 600°F Tempilstik. Repeat this
at four areas, 90 degrees apart, to ensure an average
temperature.
The zinc should be at the proper temperature at this
time so that the pouring can take place when the
terminal is heated to the correct temperature. Do NOT
attempt to measure terminal temperature with the
portable pyrometer.
If the 550°F Tempilstik leaves a wet mark and the
600°F Tempilstik leaves a chalk mark at the four areas,
pour the zinc immediately. If the four areas show a wet
mark for both the 550 and 600°F Tempilstik, continue
checking the four areas every 20 seconds until the
600°F Tempilstik leaves a chalk mark and the 550°F
Tempilstik leaves a wet mark; then pour the zinc
immediately.
If the temperature has fallen below 550°F (550°F
Tempilstik leaves a chalk mark), reheat the terminal and
proceed again as previously described.
Skim the dross (impurities) from the top of the
molten zinc before pouring. Use the portable pyrometer
to measure the temperature of the molten zinc and to
determine, thereby, if the zinc has reached its proper
temperature
for
pouring.
(See
fig.
3-58.)
The
temperature of the zinc must be accurately measured
with a portable pyrometer.
Do not handle the portable pyrometer carelessly,
because the millivoltmeter on it is a sensitive, precision
instrument. When the portable pyrometer is not in use,
keep it in the carrying case.
Measure the temperature of the molten zinc by
holding the portable pyrometer in one hand and dipping
the iron tube of the portable pyrometer in the molten
zinc, being sure to keep the thermocouple in the center
of the molten zinc and not touching the bottom of the
pot. The temperature of the molten zinc will then be
indicated on the portable pyrometer dial. Pour zinc at a
temperature of 950 to 1,000°F.
Pour the zinc into the terminal. Fill it to within 1/2
inch from the top of the textile cloth to provide a
sufficient "hot top."
Tap the sides of the terminal lightly with wooden
sticks during and after pouring of the zinc, until a
surface crust forms. See figure 3-59.
3-54
HEATING TORCH
HEAT TERMINAL
TO 500 F - 600 F
O
O
ABEf0357
Figure 3-57.—Heating the terminal.
ABEf0358
Figure 3-58.—Pyrometer.
ABEf0359
WOOD STICKS
TAP TERMINAL
UNTIL SURFACE
CRUST HARDENS
Figure 3-59.—Tapping the terminal during pouring.
