ELECTRIC POT

The electrical equipment consists of four heaters, a dynamic thermometer, and a unit control panel. The passage of electric current through the windings inside the heaters generates heat which melts the metal in the crucible and raises it to the proper operating temperature, while the dynamic thermometer and the magnetic switch on the control panel operate to keep the metal at this predetermined temperature. These equipments are either 110 to 120 volts or 210 to 220 volts, direct current or alternating current.

The crucible heaters are the same for all voltages; they are connected in “series” for 200-volt to 250-volt circuits and in “parallel” for 100-volt to 125-volt circuits. They are immersed directly in the metal and partially surround the pump-well, heating the metal by direct contact. The heating element or resistor of these heaters is composed of resistant ribbon wound on strips of clear mica. Strips of mica entirely surround the resistor, completely insulating it from the metal parts of the pot. The resistors are protected by strong metal casings which surround them. They are not subject to wear and tear in normal service.

Heating the metal by direct contact from within the metal itself by these heaters, makes a very efficient equipment, as all of the heat generated is immediately transmitted to the metal exactly where it is required, and there is no loss of heat due to faulty conduction. The dynamic thermometer bulb being immersed in the metal adjacent to the heaters and the pump-well, permits of a very close temperature regulation.

As these heaters extend nearly the full height of the metal in the crucible and pass down through the top of the metal, there is no possibility of cracking a crucible. When the metal begins to heat, it is that portion in direct contact with the heaters which first becomes molten. Internal pressure is relieved by this melted pathway and the molten metal will flow to the top of the pot.

It is important that the pot never be filled with metal above the under side of the ring which is cast on the inside of the crucible. If the crucible is filled above this ring, metal may splash over into the heating insulating material and touch the electric terminals, grounding them.

The crucible heater must be entirely covered with metal at all times. If they are not, that portion that is exposed to the air will get very hot and continued exposure will burn them out, destroying them. They are not designed for operation in the air.

Do not pry around the units with a screwdriver or pound on them, if the metal envelope is punctured, molten metal will immediately enter, grounding the element and destroying the unit.

The temperature in the crucible is controlled by an adjustable dynamic thermometer mounted on the side of the pot, and which operates a switch in the control panel, turning the current on and off as needed. The bulb and tube of this thermometer contain mercury and the bulb is immersed in the metal in front of the well of the crucible. The tube is connected to a flattened hollow coiled spring tube. The mercury also passes through this air tight spring tube. On the free end of this coiled spring tube is fastened an insulated pin which operates the contact lever. The contact lever is suspended downward between two metal contact disks. These contact disks and the contact lever are connected to the main line through a magnetic switch mounted in the control panel. The thermometer only carries current long enough for the magnetic switch to connect and then the current is carried directly through the switch.

As the temperature of the metal rises the mercury in the bulb expands causing the coiled spring to uncoil slightly, driving the contact lever against the disk that shuts off the current, allowing the switch to fall open and disconnecting the circuit through the crucible heaters.

As the temperature of the metal falls, the mercury in the bulb contracts allowing the coiled spring to force the contact lever against the disk that turns the current on by connecting the switch to the main line. The variation in the temperature is held within 15 degrees of the average working temperature.

The temperature control is normally set for a maximum of 550 degrees and a minimum of 535 degrees, that is, with normal operation the temperature of the metal will always be between these limits. This is found to give the best all around casting results for average metal. In case it is desired at any time to change the operating temperature, this can be done by turning adjusting screw right-handed for hotter metal, and left-handed for cooler metal. The head of this adjusting screw projects through the right-hand side of the dynamic thermometer cover.

Do not change the position of the control disks, unless badly pitted, as their relative distance is determined at the factory, and very seldom need to be changed.

A good thermometer should always be used when adjusting the screw for proper heat. Guessing will not get the proper results.

With ordinary work, and after the metal is at operating temperature, the current will be on and the crucible heaters generating heat about three minutes, then off and not generating heat about twelve minutes, and will repeat this cycle as long as snap switch is left in the “on” position.

Throat and Mouthpiece Heaters

The mouth and throat heaters are clamped in close contact with the outside of the crucible throat to keep the metal at the operating temperature while being pumped from the crucible to the mold. The throat heater extends the full length of the pot throat and is held in close contact with it. The mouth heater is clamped tightly to the pot mouth. Both heaters are surrounded with heat insulating material and are held in close contact with the pot throat and mouth by a U-shaped clamp under the throat unit and a plate over the mouth unit, drawn tight by two nuts.

The mouth and throat heaters are always connected in “series,” one set being used for 100-volt to 125-volt and another set for 200-volt to 250-volt.

The heat for the throat and mouth units are controlled by a manually controlled rheostat moving from the left to the right, and fastened to the front of the control panel under and at the rear of the keyboard.

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.

Frequently a heating unit is burned out by a little metal splashing on the terminals, causing a gradual short circuit. This trouble can be eliminated by wrapping the heater terminals with asbestos tape.

When cleaning the contact points on the dynamic thermometer, it is necessary to remove the cover by taking out the two long flat head screws. This cover should be examined for small particles of metal before replacing.

To remove and replace a damaged wire in the pot, fasten another wire securely to one end of it, grasp the other end with a pair of pliers and pull. The new wire will be pulled in as the old one is removed.

Rubber covered wire or slow burning wire is not satisfactory. A special wire with a special grade of insulation should be used.

If it becomes necessary to remove the dynamic thermometer, heat the metal in the crucible to operating temperature and then turn the main switch off. Disconnect the thermometer wiring and dip out the metal to below the level of the thermometer bulb. Take off the pot cover and remove the two screws fastening the thermometer case to the bracket. Grasp the case with the hand and the bulb with a pair of pliers and raise up and out. Be very careful at all times not to damage or break the bulb or hollow wire which contain the mercury; to do so will cause trouble in regulating the heat.

Replace the thermometer while the crucible is hot. See that the bulb does not project out from the casting so as to interfere with the insertion of ingots of cold metal. Press the tube firmly but carefully into place over the edge of the crucible, being careful not to injure it. Fasten the case to the bracket and reconnect the wiring and put on the cover.

All the pot adjustments on the electric pot are the same as on a gas pot.

Current Consumption

The maximum current consumption is 1,500 watts and the minimum 325 watts, the average consumption throughout a day’s work is approximately 600 watts or .6 kilo-watts. The cost of current varies widely in different localities, but you may find the cost of operating your pot by multiplying the number of hours by the cost of current per kilowatt hour and then by .6. The result will be the cost in cents. For instance, operating a pot nine hours with current costing six cents per kilowatt hour would cost thirty-two and four-tenths cents—9 x 6 x .6 equals 32.4 cents.

Fuses

The main line fuses, which protect the entire system from overloads, when blown, should be replaced by other fuses of the same rating.

The fuse for the mouth and throat heater circuit is for the purpose of protecting this circuit from accidents, and should always be replaced by another fuse of the same rating. This replacing of the fuses by others of the same rating is very important. On a 200 to 250-volt circuit, the main line fuses should be 10 amperes. The mouth and throat fuse, which is located in the control box above the magnetic switch, should be 3 amperes. On a 100 to 125-volt circuit the main line fuses should be 20 amperes. The throat and mouth fuse should be 5 amperes. Fuses of a greater amperage than those mentioned may cause the units to burn out or cause a fire hazard.