Thermal Management of Permanent MoldsThermal Management of Permanent Moldsfor the Casting of Aluminum Alloysfor the Casting of Aluminum Alloys

Chunhui Zhang Frank Mucciardi

andJohn Gruzleski

Dept. of Mining, Metals and Materials EngineeringMcGill University

Frank.Mucciardi@mcgill.caWeb Site: www.mmpc.mcgill.ca/~frank

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Objectives:

• Control the cooling of a permanent mold toproduce aluminum castings of superior quality.

• Use heat pipes to control the heat transfer.

• Selectively cool: specific locations, atspecific times.

Methodology:

History of the Heat Pipe

• Dates back to the early 1960’s

• Used extensively in electronics

• NASA and Los Alamos Labs were prime developers

• 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 thermalconductivity (as much as 1,000 timesthat of Cu)

(Heat outHeat out)

(Heat inHeat in)Evaporator Section

Condenser Section

Liquid Pool

Condensate Film

Vapor

Heat Pipe Wall

Capillary Wick

Classical Heat Pipe

Major Problems with Classical Heat PipesMajor Problems with Classical Heat Pipes

While the potential of heat pipes is enormous,There are 2 major problems:

1.1. Film boilingFilm boiling2.2. Entrainment of returning liquidEntrainment of returning liquid

McGill Heat Pipe (patents pending)McGill 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 disclosed as soon as we are allowed to.

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What Was Done:

• Designed and built waterwater--basedbased McGill Heat Pipes.

• In casting systems - permanent molds- DC casters

• Incorporated such pipes in a permanent moldpermanent mold atMcGill.

Applicability of Results:

• Found an industrial partner, Grenville Grenville CastingsCastings, tosponsor and conduct plant trials (Oct. 2002).

Features of the McGill Heat PipeFeatures of the McGill Heat Pipe

Can handle heat flux loadings of Can handle heat flux loadings of 1 MW/m2 andmore with water as the working substance..

ON/OFF heat extraction capability.heat extraction capability.

External chill absorbs the heat duringExternal chill absorbs the heat duringON mode.mode.

Cooling air dissipates the heat stored in the chill Cooling air dissipates the heat stored in the chill duringduring OFF mode.mode.

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Permanent Mold Cooled by Heat Pipes

Unit: mm

è èè

è

Unit: mm

Cooling Air Lines

Permanent mold

Heat pipes

Data acquisition system

On/Off Valve Configuration

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Heat pipes

X

ZY

Simulation by SOLIDCast

Heat pipes

Heat pipe

Plan View of the Casting, Heat Pipes and Plan View of the Casting, Heat Pipes and the Thermocouplesthe Thermocouples

TC1

TC2

TC3

Heat Pipe 1 Heat Pipe 2 Heat Pipe 3

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100

Time (s)

Tem

per

atu

re (o C

)

Casting in the parting plane

Mold without HP

Mold with HP

Typical Casting Experiment

Using Heat Pipe 1 only

Al 356 alloy

Initial mold temperature of 200oC

0

100

200

300

400

500

600

700

0 50 100 150 200 250

Time (s)

Tem

pera

ture

( oC

) TC2 Casting on the parting plane

TC3 Mold without HP

TC1 Mold with HP

Air gap formation

HP ON

HP OFF

A: The side without heat pipe, DAS=40±6µm B: Center, DAS=41±10µm

C: The side with heat pipe cooling, DAS=27±3µm

Alloy A356Tmold= 200oC

Typical Casting Experiment

Using Heat Pipes 1, 2 and 3

Al 356 alloy

Initial mold temperature of 300oC

Heat Pipe 1 Heat Pipe 2 Heat Pipe 3

L M S

Thermocouple Locations

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350Time (s)

Tem

pera

ture

(oC

)

Casting-L

Casting-MCasting-s

Mold-L

Mold-M

Mold-S

Mold-HP1-L

Mold-HP2-M

Mold-HP3-S

Max. Heat Flux to the Heat Pipes: 500-600 kW/m2

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HP DAS=27±±2 µµm

Middle DAS=41±±5 µµm No HP DAS=39±±4 µµm

Alloy A356Tmold= 300oC

With HP Cooling

HP DAS=46±±7 µµm

Middle DAS=53±±6 µµm No HP DAS=42±±4 µµm

Alloy A356Tmold= 300oC

With no HP cooling

McGillMcGillEffect of Heat Pipe Cooling on DAS

46±±741±±331±±5 None (Ref)1

Decrease

L(Location C)

M(Location D)

S (Location E)

27±±2 27±±3 24±±4

41%33%21%

S M L2

DASSection withCooling

CASTING

(unit: µm)

McGillMcGill Summary

We have developed a controllable, water-based McGill Heat Pipe for high heat flux applications,such as permanent molds.

Heat dissipation rates equivalent to those associated with conventional water cooled passages are achieved with air cooling.

Cooling with heat pipes is very effective in controlling the microstructure of the casting and the mold temperature.

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Cont’dSummary

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?

McGillMcGillLet’s visit our lab at

Testing the Water-Based Heat Pipein the Gas Furnace

Condenser

Evaporator

Typical Heat Flux:~ 500 kW/m2

Air-cooled condenser

Heat Extraction:~ 6 kW for 10 cm

insertion

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Testing the Water-Based Heat Pipe Directly in Molten Aluminum

Typical Heat Flux:~ 1,500 kW/m2

The cooling of permanentmolds is simple in

comparison.

Other applications:- Superheat reduction in

DC casting molds- Cooling of the electrolytic

cells- Cooling the off gases

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Condenser

Insulation

Heat Pipe

Crucible

Aluminum Melt Temperature Data for 5.1 cm Immersion

Leading End of the Heat Pipe After the Test

Note the uniform but roughsolidification surface.

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So, where are we now?

Full scale oxygen lances for steel refining and lead refining

Cooling elements for aluminum and magnesium casting

Heat pipe units for cooling lead furnace taphole

In addition to our work in the lab, we have a number of industrial sponsors for the following:

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