Model Engine Maker

Supporting => Casting => Topic started by: A7er on August 16, 2021, 02:03:17 PM

Title: A long winded casting method
Post by: A7er on August 16, 2021, 02:03:17 PM
I am wondering if I could get a better finish to my castings using the following process.
1) Produce a 3D print. Make the surface good.
2) Take a silicon rubber mould of the print using high temp silicon. Remove the silicon mould from 3D print.
3) Pour wax or pewter into the silicon mould to produce a pattern of the part.
4) Use investment plaster or some other high temp coating to encase the pattern.
5) Melt the pattern out of the mould. Wax and pewter both have a low melting point.
6) Pour aluminium into the mould to, hopefully, get a better quality finish.
7) Is that just too much messing around!?
Title: Re: A long winded casting method
Post by: Dan Rowe on August 16, 2021, 02:40:03 PM
Just pouring metal into investment is not going to work well in my opinion. The two methods of lost wax casting are spin casting or vacuum casting. Gravity is not enough to completely fill a mold through a sprue. I use vacuum casting with similar steps but I use a rubber vulcanizer to make the mold for wax and a wax injector to fill the rubber mold. The investment is taken up to 13500 F for burnout and the flask needs to be around 8000F for pouring bronze. I am not sure about aluminum flask temp. So the oven in the kitchen is not going to work. I have a kiln for burnout.

It has gone out of print but I recommend the book "Centrifugal or Lost Wax Jewelry Casting for Schools. Trademen" by Murry Bovin. It has detailed step by step instructions for the process.
Here is a link to my setup:
https://www.modelenginemaker.com/index.php/topic,5452.msg153736.html#msg153736

Cheers Dan
Title: Re: A long winded casting method
Post by: A7er on August 16, 2021, 10:33:48 PM
Thanks for that info Dan, I will search for the book.
In my ignorance I thought the wax or pewter would just need "melting" out! For the finished casting I would be using an aluminium/zinc alloy that normally pours at 460C.
Lee
Title: Re: A long winded casting method
Post by: Elam Works on August 17, 2021, 03:29:11 AM
Tried plaster cores for homemade piston production an found two shortcomings. One, even when baked in the domestic oven, the plaster never shed enough moisture. First attempts had the cores venting enough residual steam the sprue erupted like Mount Vesuvius! Further baking still tended to have the cores crack when the aluminum was poured. Second, the plaster was not very permeable so there was nowhere for the gases near the surface of the casting, or that generated from the plaster, to go but into the solidifying aluminum making the surface porous. Mind you, these were larger piston cores for a vintage engine that were about four inches thick. At model engine scale the plaster will be a thinner section and easier to dry clear through.

I do not know if the composition of the investment slurry differs enough from plaster that it is more permeable to foundry gases, but certainly the high burn out temperature seems to solve the residual moisture problem.

-Doug
Title: Re: A long winded casting method
Post by: ddmckee54 on August 17, 2021, 06:52:22 PM
Not trying to chase you away from this fine forum...

But just in case you don't know about it, thehomefoundry.org has forums that are dedicated to just lost wax casting, lost foam casting, and lost PLA casting. http://forums.thehomefoundry.org/index.php (http://forums.thehomefoundry.org/index.php)

You can learn a lot, even if you just lurk in the shadows.

Don
Title: Re: A long winded casting method
Post by: A7er on August 20, 2021, 07:13:50 PM
Many thanks for the replies. I will try to explore all avenues suggested. The book suggested by Dan is available second hand on amazon at 30 or more. I am off to the local flea market tommorow to see if there is a copy there.
Lee
Title: Re: A long winded casting method
Post by: lohring on August 21, 2021, 04:10:55 PM
A really easy lost PLA casting method is shown in the video below.

Lohring Miller

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Title: Re: A long winded casting method
Post by: Jo on August 21, 2021, 05:40:01 PM
 :thinking:

That is very interesting, thank you Lohring for posting that for us  :) .

Jo
Title: Re: A long winded casting method
Post by: A7er on August 22, 2021, 08:41:19 PM
I agree Jo, a very interesting video indeed! I happen to have tub of jointing compound in my garage, unless it has gone off after 5 years. Thanks Lohring
Title: Re: A long winded casting method
Post by: Bearcar1 on October 26, 2021, 04:08:18 PM
I can see some flywheel castings in the future. This was a cool video demonstrating some relatively simple procedures. I would have liked to have seen a bit more PPE put to use.


BC1
Jim