A-A-53468 Furnace, Dental Laboratory, ElectricThis commercial item description covers an electrically operated, heating plate type, burn-out and heat treating furnace, with pyrometer, automatic temperature controls and replacement heating plates, as specified below: Type I.-complete Furnace Type II,- Replacement Heating Plates Style 1-Rear Plates Style 2- Side Plates.

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A-A-53468

Door counterbalance test. The counterbalance test shall be performed at the two extreme positions of the door (fully open and fully closed). With the door in the fully closed position, a spring balanced, of adequate capacity, graduated in two ounce longitudinal center of the counterweight. A force shall be applied perpendicular to the longitudinal axis in the direction to the open the furnace door. The force shall be slowly and continuously applied perpendicular to the longitudinal axis until the door is fully open. The maximum force required to completely open the door shall be recorded. The test as specified above shall be repeated in the opposite direction and the maximum force to fully close the door shall be  recorded.

Strain relief. The electrical cord strain test shall be conducted in accordance with Underwriters Laboratories, Inc. Standard UL 1262.

Continuity to ground. A continuity indicating device shall be used to check continuity between the ground pin of the input plug at the end of the electrical cord and all exposed metal parts of the furnace. Grounding procedures shall be in accordance with UL-1262.

Calibration. Each furnace shall be tested for calibration accuracy by the use of Tempil pellets. A Tempil pellet, compounded to melt at 1300F (704°C) shall be used in accordance to the following procedure:

(a) With the furnace at, or near ambient temperature, place  an empty, medium sized flask (inlay casting ring) approximately at the center of the heating chamber.

(b) Set a small, thin, metal plate or tray on top of the flask and place a 1300°F (704°C) Tempil pellet at the center of the tray.

(c) Close the furnace door and place the power switch in the “on” position.

(d) Set the heat rate control at position number 4, and set the desired temperature for 1000°F (538°).

(e) Once the pyrometer indicates a furnace temperature of 1000°F (538°C), allow the furnace to heat soak at this temperature for three minutes.