Re: Inexpensive 2 Piece Die for Aluminium Casting

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Posted by bpfink on March 24, 19100 at 21:36:36:

In Reply to: Inexpensive 2 Piece Die for Aluminium Casting posted by Ben Mann on March 24, 19100 at 00:43:37:

Two possible systems jump to mind beyond the standard green sand casting system to handle such a challenge.

#1 If doing a plaster based investment that needs a dryout (would call it a burnout but without anything to burnout it goes much faster) try this approach:

Make a positive of the piece in a polyurethane rubber compound that is slightly flexible but rigid enough to hold it's own shape accurately. Then add a parting plane system (usually by cutting it in the proper parting line halves or thirds or whatever) and construct it into a mold for casting the investment sections that will fit together easily. This can even include a core section if necessary. Then burn out the investments to chemically dry them and reassemble for the metal pouring. To hold the sections together I have used just a wire and a pliers twist around each before packing in a slightly damp green sand frame.

I once did a run of 35 using a single urethane positive model mold and was casting the repeat negative investment sections this way. Mold was still like new when done, but my repeat patience was at its end.

In this case the mold needed 2 sections (sprues and airvents were included as part of the positive original) and once the first half was cast (but barely hardening), the plaster surface was parted with a color dyed soap seal and the 2nd plaster/sand based pour was put right over it. This made for an identical matched and keyed fit and the urethane model was easily taken out of each as soon as it seemed safe to do so. I was pouring about 12 to 15 complete investments each day but also was cutting the lawn and doing other mini jobs in between the plaster sets.

#2 There is also a sand commercially sold for core making that can also be used for the mold itself. It is a fine dry sand with a rosin powdered binder mixed in. Pours like dry sand and if you have a metal (aluminum is excellent here) positive that you can heat and then dip into a fluidized box of this stuff it immediately starts to build up a wall of the sand investment. Of course the new shell has to be slightly air cooled before taking off it and if the form pocks it on it may require a several piece system but it will make the equivalent of ceramic shell that needs NO burnout and can be assembled once again before pouring the metal. A green sand backing around it would also assure better success cause the investment sand bonded body itself will remelt and burn off after the metal pour. (Turns a dark brown and burns and stinks a bit first... just like rosin would so ventilation is needed.

Enough here. Have left off all kinds of details to follow through but that is what the creative mind doing it can fill in.

Don't have the brand names of this stuff, but have seen it work at an International Foundrymen's Convention in Canada I was also speaking at. bpfink


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