McGillThermal Management of Permanent Molds for the Casting of Aluminum Alloys Chunhui Zhang Frank Mucciardi and John Gruzleski Dept. of Mining, Metals and Materials Engineering McGill University Frank.Mucciardi@mcgill.ca Web Site: www.mmpc.mcgill.ca/~frank
Objectives:• Control the cooling of a permanent mold to produce aluminum castings of superior quality.• Selectively cool: specific locations, at specific times. Methodology:• Use heat pipes to control the heat transfer.
History of the Heat Pipe• Dates back to the early 1960’s• NASA and Los Alamos Labs were prime developers• Used extensively in electronics• Used extensively in satellites, Space Shuttle and Space Station
• sealed chamber wherein a working substance evaporates and condenses• passive device (no moving parts)• extremely high, effective thermal conductivity (as much as 1,000 times that of Cu)
Classical Heat PipeCondenser Section Vapor (Heat out) outHeat Pipe Wall Condensate FilmCapillary WickEvaporator Section Liquid Pool (Heat in) in
Major Problems with Classical Heat PipesWhile the potential of heat pipes is enormous,There are 2 major problems: 1. Film boiling 2. Entrainment of returning liquidMcGill Heat Pipe (patents pending) overcomes theseproblems and thus makes heat pipe technology viablefor high heat flux systems.Details of the McGill Heat Pipe will be disclosedas soon as we are allowed to. McGill
What Was Done:• Designed and built water-based McGill Heat Pipes.• Incorporated such pipes in a permanent mold at McGill.• Found an industrial partner, Grenville Castings, to Castings sponsor and conduct plant trials (Oct. 2002). Applicability of Results:• In casting systems - permanent molds - DC casters
Features of the McGill Heat PipeCan handle heat flux loadings of 1 MW/m2 andmore with water as the working substance.ON/OFF heat extraction capability.External chill absorbs the heat duringON mode.Cooling air dissipates the heat stored in the chillduring OFF mode. McGill
Permanent Mold Cooled by Heat Pipes è è è è Unit: mmUnit: mm
Cooling Air Lines Data acquisition Heat pipes systemPermanent mold On/Off Valve Configuration McGill
No HP DAS=39± 4 µ m ± Middle DAS=41± 5 µ m ± Alloy A356 Tmold= 300oC With HP Cooling HP DAS=27± 2 µ m ±
No HP DAS=42± 4 µ m ± Middle DAS=53± 6 µ m ± Alloy A356 Tmold= 300oC With no HP cooling HP DAS=46± 7 µ m ±
McGillEffect of Heat Pipe Cooling on DAS (unit: µm)C DASAS Section withT Cooling S M LI (Location E) (Location D) (Location C)NG1 None (Ref) ± 31±5 ± 41±3 ± 46±7 ± 24±4 ± 27±3 ± 27±22 SML Decrease 21% 33% 41%
McGill SummaryWe have developed a controllable, water-basedMcGill Heat Pipe for high heat flux applications,such as permanent molds.Heat dissipation rates equivalent to thoseassociated with conventional water cooledpassages are achieved with air cooling.Cooling with heat pipes is very effective incontrolling the microstructure of the castingand the mold temperature.
McGill Summary Cont’d The DAS of A356 alloy is refined considerably with heat pipe cooling of the mold. Heat pipe cooling of the mold can alter the direction of solidification as well as the location of the shrinkage.
So, where are we now?Let’s visit our lab at McGill
Testing the Water-Based Heat Pipe in the Gas FurnaceCondenser Air-cooled condenser Typical Heat Flux: ~ 500 kW/m2Evaporator Heat Extraction: ~ 6 kW for 10 cm insertion McGill
Testing the Water-Based Heat Pipe Directly in Molten Aluminum Typical Heat Flux: ~ 1,500 kW/m2Condenser The cooling of permanent Insulation molds is simple in comparison.Heat Pipe Other applications: - Superheat reduction in DC casting molds Crucible - Cooling of the electrolytic cells - Cooling the off gases McGill
Aluminum Melt Temperature Data for 5.1 cm Immersion
Leading End of the Heat Pipe After the Test Note the uniform but rough solidification surface.McGill
So, where are we now?In addition to our work in the lab, we have a number ofindustrial sponsors for the following:Full scale oxygen lances for steel refining andlead refiningCooling elements for aluminum and magnesium castingHeat pipe units for cooling lead furnace taphole McGill