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Metal Casting Technologies : Whos who September 2011
METAL Casting Technologies September 2011 67 ● It will take up to half-an-hour for the metal to become too cold to pour, depending on the temperature. ● If the furnace is to be dumped, the runout area or ladles must be able to handle the full volume of the metal. The runout pit MUST be clean and DRY. WARNING: Mettal poure edinttoap pit orr run nou ut arrea where the excess mois sture o or sta andin ngw watter a are present could c cause a violen nt exp plosiion whiich cou uld cause injury to p personn nel. ● Dumping of a load of metal may release a tremendous quantity of heat into the foundry, perhaps causing damage. ● It will take one to four hours for the metal in the furnace to solidify enough to potentially damage the lining, depending on the bath temperature and the furnace size. ● Water cooling MUST be maintained. This is even more important than handling the molten metal. Consider these factors, a decision can be made on dumping or partially dumping the metal in the furnace. If the furnace is dumped, normal shutdown procedures should be followed. To partially dump a furnace, enough metal should be removed to expose 50% of the furnace floor. The furnace must then be left in the tilted position and the charge remelted in the tilted position; this will minimize expansion-cracking of the lining. It is always more desirable to fully dump a furnace. Partial dumping should be attempted only when the runout pit and/or ladle capacity is insufficient. In many cases, it may be both more desirable and safer to simply allow the furnace to freeze and accept some probable loss of the lining. If furnace power is restored quickly, there is nothing lost. If the slag freezes solid, it may be possible to remelt it and then dump the load of the furnace. Remelting a frozen furnace The following general procedure applies to remelting a fully frozen furnace load or a partially dumped furnace. ● The furnace should be tilted. ● Furnace power must be applied very slowly. It should take at least as long to melt a slug as it took to freeze it. WARNING: Meltting a frrozen load d too rap pidlyy will cause the liining to crackk, lea adingg to run noutts which may pose eahaza ard to o the equiipm mentt and personnel. ● Monitor the ground leakage conditions. At any sign of metal leakage, shut down and pull the slug and the lining. ● Empty the furnace immediately after remelt, allow it to cool, and thoroughly inspect and repair the lining. If there is any doubt as to its condition, it should be replaced. WARNING: Therre is dan nger h here tthat the me etal in tthe bottom of the fu urnace w will su uperh heat w whille th hes surfface e in contact with a air rema ains frrozen n. Forr thiis re easo on, the furnace should be ttilted u up so o tha at an nym meta al that melts below wthesu urface eisin n intim matte co onta act with the undersiide of th he fro ozen s surfa ace. Pou urin ng tthe furnace dry as ffast as tthe me etal m melts s willl ea ase the e stress on the lin ning. In a any ca ase, tthe liining gsh hould b be inspected and p patchedd as ne ecess sary befo oreafu ull h heatt is attempted. If the solid slu ug coverrs the wholle fu urnac ceb botttom m, it is advisable to o pull ou ut and d repla ace tthe linin ng tto remove the slug g.Thed da angerr of a linin ng fa ailurre a and the e consequences o of a runo out m must b bew weigh hedd aga ains st the material, lab bor, andd lost p produ uctio on re equiired d to pulll out and replace the liniin ng. W With sm mall furn nac ces a and d furnaces with crrucibles s insta alled, the p possibiility of salvaging the e lining, even by a care eful m mellt-ou uto of a solidified slug that co overs tthe en ntire e furrnac ceb botto om,, is remote. Power unit troubleshooting If power to the furnace is lost due to power unit failure, the foregoing procedures should first be followed to protect the furnace and the lining. Power unit troubleshooting by a qualified technician can then proceed. Power unit failure is evidenced by trips of the AC interrupter (if installed) and/or the circuit breaker, or by "zero" KW output from the unit. If the power unit will run at partial power, proceed to a later section here. Occasional tripping An occasional circuit breaker or AC Interrupter trip may occur due to line transients. Under such circumstances, no harm would be done in resetting the circuit breaker and restarting the inverter immediately. However, the cause of such a shutdown is not immediately obvious. Therefore, it is a wise precaution to inspect the unit and make at least the power section continuity checks before restarting the unit. Repeated attempts to reset the unit and restart the inverter with certain serious malfunctions existing can result in damage to the very components that the circuit breaker and the ACI are designed to protect. Repeated tripping can also lead to premature circuit breaker failure. Water cooling problems The circuit monitor will indicate water cooling problems. Be sure that water circulation is maintained throughout the unit to preclude component failures. The unit runs but will not reach rated power Induction furnaces should run at rated power into a properly tuned load from cold charge to fully molten. Induction furnaces are designed as backcharge melter and reach full power on a backcharge with 50% or greater molten load.
Whos who September 2012