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Metal Casting Technologies : March 2011
Caution: a) Use only dry charge material. b) Inspect bundled or baled scrap for trapped moisture before adding it to the melt. c) Avoid charging partially closed containers (soft drink bottles or cans) that can contain trapped liquids. Liquids or pieces of combustible material can vaporize with explosive violence in the melt and cause an eruption of the molten metal. d) Inspect spill pit and runout apron to ensure that they are clear of water and debris. Warning: The failure to properly comply with these procedures may result in an explosion, with possible serious injuries to personnel and equipment. 3. Set the furnace selector switches (if installed) for operation on the desired furnace. 4. Turn the control power key switch ON and close the main circuit breaker. 5. Push the RED STOP BUTTON to reset the AC Interrupter. (This step may be by-passed on systems without the ACI.) Reset the circuit monitor, then push the start button. Note: On units with remote controls, pushing the start button also resets the circuit monitor. 6. Turn the control knob potentiometer to the full clockwise position for full power operation. The system will automatically maintain the highest allowable power without adjustment of the controls. 7. If less than full power melting is needed, set the desired KW output by observing the KW meter as the control knob is turned. 8. Check the panel indicator lights as follows: a) Main Power -- RED light is ON. b) Furnace ON -- The AMBER LIGHT is ON when the inverter is running. c) Full Power -- The GREEN LIGHT is ON when the inverter is at full power. d) Normal Operation -- With the system operating in a normal melt cycle, all other panel lights are extinguished. 9. Proceed with daily melting. 10. Test the Ground Detector prior to every heat. Press, and hold in, the "TEST" pushbutton. The leakage meter reading should increase momentarily, the inverter will shut off, the red "CURRENT TRIP" light will turn on, and the green "GLD ON" light will turn off. A ground leakage reading of less than 2 ma. may indicate a problem with the detector. If the Ground Detector does not function properly, do not operate the power supply. Call the Vendor's Service Department. Shutting down When melting operations are finished: 1. Turn the control knob to zero. 2. Turn OFF the high-frequency control push button. 3. Turn the circuit breaker OFF and turn OFF the control power key switch. 4. Allow the cooling water to continue circulating through the furnace coils, to prevent thermal shock and coil damage, until the refractory has cooled down. Note: Observe all safety precautions. When melting operations are finished, be sure that the main power red light is OFF. Refer to the troubleshooting section of this manual is faults are experienced. Cabinet doors should be kept locked during normal operation. Abnormal operations 1. Power Outage: The U.V. Trip on the circuit breaker will automatically shut down the furnace. 2. Water Pressure Failure: The furnace will automatically shut down. If the furnace is hot, minmum water flow must be re-established within minutes in order to prevent damage to the equipment and possible personnel hazard from emitted steam. 3, High Cooling Water Temperature: Try to reduce the power before the unit trips and then continue operations at reduced power while troubleshooting. After a "trip," it may be necessary to allow a considerable period for the water to cool down. Troubleshooting and corrective procedures for other abnormal conditions are covered in the "Safety Precautions," "Troubleshooting," and "Maintenance" Sections. Generally, these procedures are to be undertaken only under the direction of qualified maintenance and supervisory personnel. KWH counter operation Many systems are equipped with the optional microprocessor KWH Counter which offers even greater automation by allowing automatic melt cycling. The system consists of an LED digital display and four digital thumb switches mounted on the operator's station. A blue warning beacon announces the end of each melt cycle and a single thumb switch controls the operation of the KWH Counter system. Before operation, the system must be set up by making the following internal adjustments: Set the full scale meter reading of the unit KW meter with the internal thumb switches on the back of the KWH counter. Set the observed holding power loss in the other set of thumb switches. This quantity will be continually deducted from the furnace power so that the counter counts only the "net" melting power. Set the desired holding power using the internal potentiometer. This is the power level at which the unit is to operate during "hold" periods. For normal operation, the operator sets the KWH desired for each charge on the front panel of the counter. Melting is begun by moving the thumb switch to RESET and releasing it. After counting down the melt power, the unit automatically goes to "hold" power and lights the blue beacon. To bypass KWH counting, the thumb switch is placed in the OFF position. This would typically be done during daily startup. ■ References 1. Modern Casting Shopbook. ANSI Z241.2 -- 1981 "Safety Requirements for Melting and Pouring Metals in the Metalcasting Industry". American Foundrymen's Society, Inc., Golf and Wolf Roads, Des Plaines, IL 60016. 2. National Electrical Code (Latest Edition). National Fire Protection Association (NFPA) or NFPA No. 70-1978, 470 Atlantic, Avenue, Boston, MA 02210. METAL Casting Technologies March 2011 47