MIL-F-80056C
3.4.6.1 Type I furnace pot. The Type I pot shall be cylindrical with a rounded
bottom and shall be cast from an alloy containing not less than 35 percent nickel
and 18 percent chromium. Means shall be provided for properly sealing the space
between the pot flange and top plate.
3.4.6.2 Type II and Type III. Class A furnace wt. Unless otherwise specified
the pot for the Type II and Type III, Class A furnace shall be
(see 6.2),
fabricated from an aluminized low-carbon steel plate. All seams shall be welded
inside and out.
3.4.6.3 Type II. Class B and C furnace pot. Unless otherwise specified (see
the pot for the Type II and Type 111,
6.2),
Class B and C furnace shall be
fabricated from pre-formed and pre-fired salt-resistant ceramic material.
3.4.7 The furnace heating elements. Heating elements shall be of the rod or
ribbon type, fabricated from an alloy of 80 percent nickel and 20 percent chromium.
The elements shall be mounted on the heating chamber wall in the space between the
pot wall and insulation, properly insulated from each other, and distributed in
such a way to produce uniform temperature specified in 3.4.5. Heating elements
shall not be located in the bottom of the heating chamber. Power density on the
heating elements shall not exceed 15 watts per square inch of radiation surface
area.
The Type II furnace shall be
3.4.7.1 Type II furnace heating elements.
heated either by suspended immersion type electrodes or shall be heated by built-in
submerged electrodes. The electrodes shall be spaced and located in the bath in
such a way that full transformer power may be obtained through the transformer
taps. The portion of the electrode which is subject to salt corrosion shall be
stainless steel.
3.4.7.2 Type III furnace heating elements. The Type III furnace shall be heated
by sheath immersion resistance type elements. The elements shall enter the bath
from the top and be provided with necessary protection to prevent being damaged by
the work load.
3.4.8 Transformer. Type II furnaces designed to operate on single phase power
shall be provided with a single phase, continuous duty, 6 tap (7 or 8 tap optional)
transformer. Furnaces designed to operate on three phase power shall be provided
continuous duty, 6 tap (7 or 8 tap optional)
with three phase Scott connected,
transformers (2 units). One designated as a "main" and the other a `teaser". Each
transformer shall be rated 1/2 the total KVA required, and in the event of a line
fault causing a failure of one unit, either the main or the teaser can be used
all transformers at any KVA
single phase. Unless otherwise specified (see 6.2),
rating shall be water cooled. If air cooled transformers are specified, the design
shall provide for convection cooling. The design for either water or air cooling
shall be adequate to prevent a temperature rise in excess of safe operating
temperature for the insulation system used. Each transformer shall have a
thermostat system for overload protection.
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