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

Ceramic trays. The trays shall be fabricated from a castable ceramic material to prevent the absorption of wax. Each tray shall be 3/8 inch high and shall have dimensions of 5-1/8 by 4-1/2 inches. The tolerances on the dimensions shall be ± 1/8 inch. The two trays shall fit on the floor of the heating chamber side by side with the door closed.

Automatic temperature control. The furnace shall be equipped with a completely automatic, built-in temperature control, by which the desired temperatures, heat rates (2), and hold times may be preset upon starting the furnace. The preset temperature shall be reached with power input to the heating elements determined by  the microprocessor heat rate control. The desired temperature shall be maintained regardless of normal line voltage fluctuations and changes in the heating element resistance.

The automatic temperature control system shall be rated at least 125 percent of the maximum current drawn at 115 volts. Any temperature within the range of the furnace shall be accurately set and maintained within ± 10 degrees F (6 degrees C).

A heat soak timer shall be settable 0.4 hours; there shall be a tone to indicate to the operator when the preset temperature time has elapsed. A digital display shall be indicate the status of the soak timer, once the timer has been preset and is in operation. Operation of the tone shall be selected by a switch located on the front panel of the furnace. The position of the tone switch (on or off) shall not affect the operation of the soak timer or digital status display. Furnace shall be equipped with self diagnostic; indicator lights to identify cause for furnace malfunction.

Pyrometer. The furnace shall be equipped with a pyrometer for indicating the furnace temperature. The pyrometer shall be calibrated, as specified herein, over a minimum range of 0°F to 1999°F, in increments of 1°F. The pyrometer shall be of the digital readout type.

Thermocouple. The furnace shall be equipped with a 14 gauge (B&S) diameter, Chromel/Alumel (type K) thermocouple. The thermocouple shall extend 1-5/8 inches into the furnace heating chamber.