5. Record the temperature at the freeze point
(solidification) of the zinc. Solidification has
occurred when the temperature-sensitive element of
the pyrometer cannot be removed from the zinc.
6. For the pyrometer to be accurate, the
temperature recorded at the zinc freeze point must
not be greater than 798°F or less than 778°F.
7. Reheat the pouring ladle to remove the
temperature-sensitive element of the pyrometer
from the zinc.
PYROMETERS THAT DO NOT MEET
T H E S E R E Q U I R E M E N T S M U S T B E
REPLACED.
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 3-58.
Using a short piece of seizing wire thoroughly
degreased, pierce the bubbles that rise to the
surface of the hot top. Do not poke the wire into
the zinc more than 1/2 inch. Skim the surface of
the hot top with the end of the seizing wire to allow
the gas bubbles to rise and be accessible for
piercing.
After the zinc has solidified, allow the poured
terminal to air-cool at room temperature for 30
minutes.
During this time the zinc will harden.
After the cooling period, proceed as follows:
1. Remove the textile cloth and plaster from
the terminal.
2. Pour 4 gallons of preservative oil into a
clean 5-gallon metal container.
3.
With
the
preservative
oil
at
room
temperature, immerse the entire poured terminal for
30 minutes. This will rapidly cool the terminal.
4. Immediately after the 30-minute oil quench
period, remove the terminal and allow the excess oil
to drain into the container.
5. Using the hot-top cutter assembly, cut off
the hot top flush with the top of the terminal after
the terminal has cooled (fig. 3-59).
Figure 3-58.—Tapping the terminal during pouring.
Figure 3-59.—Cutting the hot top.
3-59
