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tions. Consider using modeling software to optimize vent placement and size. Inadequate venting pressure prevents effective distribu-


tion of the amine through the core. Install a pressure gage on the gas head; gages with a Polytetrafluoroethylene seal are ideal for this application. Target sand blow pressures


between 40 and 80 lbs./sq. in. gauge (psig), amine vapor gas pressures ramping up from 10-20 psig at the end of the cycle, and purge gas pressures ramping up from about 25-45 psig at the end of the cycle. Check venting exhaust pressures. Te corebox should be open to the atmosphere during the sand blow. Apply a 1-psi vacuum during gassing to help extract vapors from the core. Excessive negative pressure can cause poor amine distribution in the core, leading to excessive amine use. Increase the vacuum at the end of the purge cycle to improve vapor extraction. Use an ample, heated purge air cycle. Heated purge air helps ensure core curing and is the key to achieving low amine consumption. Purge air should be 180F (82C) at minimum but should never approach the auto-ignition temperature for the amine you are using. Te purge times will vary depend- ing on the blow weight and system design, i.e. generator, hose size, venting and heat. A 5-15-second purge time is typical for small blow-weight core boxes, and a 10-25-second purge cycle is typical for larger blow-weight boxes. Keep the tooling clean. Vent channels can become plugged


Some facilities use increased amounts of amine to improve minor perfor- mances problems rather than resolving the underlying issue. A sign your facility is using too much amine is a strong odor in the core room.


after long run times. A small amount of metal cleaner placed in the vent channel after each shift is one of the best ways (other than vent removal) to keep this area clean, as ice or media blasting normally will not clean these spots.


38 | MODERN CASTING November 2011


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