The rheostat is connected directly to the mouth and throat heater and is not controlled by the dynamic thermometer.
The crucible heaters are intended for heating the metal to the proper temperature, and the mouth and throat heaters are only intended to keep the metal at the proper temperature while being forced from the crucible to the mold.
If the voltage is irregular and remains too high for some time, or a speedy operator casts large slugs at a rapid rate continuously, the mouthpiece is apt to become heated and the slugs will have hollow backs. In this case it will be necessary to turn rheostat knob left-handed, but if the voltage remains low for some length of time, or a slow operator casts small slugs slowly, the mouthpiece may become cold and the slugs will have poor faces, in which case the rheostat knob should be turned right-handed.
When casting large slugs in rapid succession the mold is apt to become heated, but attempting to regulate the temperature of the metal in the crucible to overcome the heating of the mold will fail, because the electric pot is a heating unit only and will not cool the mold.
The control panel consists of a magnet switch mounted on a slate panel enclosed in a steel cabinet. The cabinet also has a suitable fuse cut-out and the switches which control both the pot and the electric motor (if used) and places all controls within easy reach of the operator. Connection is made between the pot proper, the dynamic thermometer, and the control panel by suitable wiring enclosed in a flexible conduit.
Care of Electric Metal Pot
The contact points on the thermometer and the magnetic switch should be kept clean and free from corrosion. Use No. 00 sand-paper. (Never use emery cloth or paper.) Dirt and corrosion are electrical insulators, and if these contacts become dirty, electrical contact may not be made when the temperature reaches 550 degrees F.; the magnetic switch will not open and the crucible heaters will continue to increase the temperature of the metal until the fuses are blown; the dynamic thermometer permanently injured, or the heating units burned out. When the temperature reaches above 550 degrees, the metal is too hot, causing back squirts. When the metal has cooled, the contacts, owing to the dirt, will not operate, and the metal will continue to cool until it can not be used. The contact points should be cleaned about once each two weeks.
The hole in the hollow tube connecting the bulb and the flattened coil spring of the dynamic thermometer is very small and care must be taken that the tube is not injured when feeding metal to the pot, or that no sharp bends are made in it, as it will close the hole and interfere with the proper working of the thermometer.
Occasionally some of the parts such as the heaters, thermometer, or the wiring inside the pot may become damaged and will have to be replaced. In ordering the new parts for replacements, be sure to specify the voltage being used and the serial number of the pot. This number plate can be found on top of the pot cover.
It is seldom that both crucible heaters will be burned out at the same time, so if your pot is a 100 to 125-volt equipment, and one of the crucible heaters tests open or grounded, and must be removed and replaced, the metal in the crucible may be heated by the crucible heater that is in good condition; but if your pot is 200 to 250-volt equipment, and one of the crucible heaters must be replaced, it will be necessary to melt the metal in the crucible with a blow torch before either crucible heater can be removed. It is not necessary to remove the metal from the pot. Merely keep the metal agitated while melting it with the blow torch.