The Shop > Metal Stuff
Lost Foam Casting: a Crankcase in Zinc Alloy
vtsteam:
It is Matt. Here it is off the sprues:
Manxmodder:
--- Quote from: mattinker on August 10, 2014, 02:22:10 AM ---Al would be great for casting Zn and Zn alloys.
Regards, Matthew
--- End quote ---
Matt,I can confirm that aluminium works well for zinc casting molds.
About 20 years back I made some latch components for a customers double glazed windows to replace the original plastic items which were prone to fatigue failure.
The mold I made was a several piece jigsaw affair milled from aluminium,screwed together and preheated before each pour.
The detail and tolerance of the latch components was really good with the milling marks from inside the mold being clearly reproduced on each of the components.
Steve, that last cast you've done looks really good,looks like you've mastered that technique. :clap: :clap:
I'm looking forward to seeing more of this project.....OZ.
vtsteam:
Thanks Oz! :beer:
In case it helps others, these are my notes re. zinc and lost foam on this scale casting:
Pour temp 450C
A sprue is needed every 35 mm or so on perimeter of a 6mm wall, 2 spue minmum before loss of detail.
Max depth of 6mm casting wall is about 25 -35 mm before too much heat is lost.
Horizontal 6mm plate doesn't work. Keep mold cavities vertical.
Deep pouring basin/riser needed -- there is a great deal of shrinkage and this kind of thin casting needs good head pressure to maintain detail.
Use plaster of Paris in preference to drywall (calcium carbonate). It speeds up the process (pattern can be cast in 3-4 hours including cure and open air drying instead of 24-36 hours open air drying. )
And, critical difference noted today -- young plaster of Paris absorbs molten polystyrene, which drywall does not, thus removing it from the casting. That enabled good fidelity in this margnal low temp lost foam process. While zinc pour temps can't flash the foam into gas as aluminum can, poP makes up for this by absorbing the liquid polystyrene away from the melt. Calcium carbonate traps the polystyrene inside the mold.
mattinker:
Are you using pure Zinc or a ZA12 alloy?
Regards, Matthew
vtsteam:
Zamak 2
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