MIL-F-80056C
3.4.3 Type I furnace cover. When specified (see 6.2), the Type I furnace shall
be equipped with an insulated swivel-mounted, split-type cover.
3.4.4 Type II and Type III furnace cover. When specified (see 6.2), the Type
II and Type 111 furnace shall be provided with a hand operated one or two piece
rolling cover. The cover shall be insulated or made of castable refractory. When
specified (see 6.2), the cover shall be electric motor powered.
3.4.5 Insulation. Each furnace shall be insulated with insulating fire brick,
block,
ceramic fiber, or pre-formed insulation selected to insure long life and
minimum heat loss. Powdered, shredded or granular insulation is not acceptable.
Quality and thickness of the insulation shall be such that the outside surface
temperature of the furnace will not exceed the maximum surface temperature
specified in 3.4.5.1,
3.4.5.2, and 3.4.5.3 for the respective type and class
furnace specified.
3.4.5.1 Type I. furnace in sulation. The insulation adjacent to the heating
elements shall have a temperature rating of not less than 2000 degrees F and the
temperature rating of the back-up insulation shall be not less than 1600 degrees
F. The maximum outside surface temperature of the furnace shall not exceed 80
degrees F above ambient air temperature with the bath temperature stabilized at
1600 degrees F.
Type II, Class A and Type III, furnace insulaltion. The insulation
3.4.5.2
adjacent to the steel pot shall have a temperature rating of not less than 400
degrees F above the maximum temperature of the furnace. The maximum outside surface
temperature of each furnace shall not exceed 60 degrees F above ambient air
temperature with the bath of the Type II furnace stabilized at 1100 degrees F and
the bath of the Type III furnace stabilized at 750 degrees F.
3.4.5.3 Type II. Class B and C furnace insulation. The Type II, Class B and C
furnaces,
when furnished with ceramic pots,
shall have back-up insulation
consisting
of refractory lumnite cement block or pre-formed insulation of
sufficient quality and thickness to insure not more than 8 percent by volume bath
or a secondary leak
material (salt) absorption during the life of the furnace,
proof steel pot separating the ceramic pot from the insulation. The secondary steel
pot ,
if used, shall be not less than 3/16 of an inch thick and welded inside and
out . Maximum outside surface temperature for the Type II, Class B furnace shall
not exceed 80 degrees F above ambient air temperature with the bath temperature
stabilized
at 1600 degrees F, and 140 degrees F above ambient air temperature
for the Type II, Class C furnace, with the bath temperature stabilized at 2200
degrees F.
3.4.6 Pot. Each furnace pot shall be capable of continuous operation at the
maximum operating temperature specified in 1.2 for each type and class furnace
without sagging or warping. Metal pots shall be not less than 3/8 inch thick and
shall be free from porosity. Additional characteristics shall be in accordance
with 3.4.6.1, 3.4.6.2, and 3.4.6.3 for the type and class of furnace specified.
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