Turbine Engine Mid Frame

Discussion in 'Lost PLA casting' started by Monty, Dec 2, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's a pretty good reason to stick with the PVAcetate. One benefits of the PVAlcohol was it was so thin, there just wasn't much of it to get rid of.......but, it might not seal the PVA very well.
    I dip my foam patterns in soapy (Dawn=Propylene Glycol) then dip them in the refractory. Besides the surfactant, the sanded foam surface is a little fuzzy and retains some water which thins the refractory at the surface and helps buoyantly expel the air. On fine details like wax appliques and engraving, I'll work the area with a soft brush then dip. Even with all that, I can still get a few little boogers, but they are usually just an air pocket bead that has been fed by a tiny pin hole which is the only attachment point, and they can just be knocked off with a light tap with a punch or screw drive.

    You might just try dipping your pattern in a thinned version of your plaster investment (or maybe drywall joint compound) without the silica. Let it dry or at least set then invest it. When I was dipping in dry wall mud I put a little dawn in the mix an that helped it wet, level, and lay down.......it would benefit from being vacuum evacuated first......just thinking out loud.


  2. Monty

    Monty Copper


    I'm actually thinking of switching to ceramic shell for the engine parts. I originally came up with the process I'm using to cast pistons. Those investments were smaller and much more user friendly to work with!

    The large amount of investment required for these parts, and the size and weight of the finished block makes it a bit hard for one person to move around. This part was bad enough. Handling a delicate 30lb block of hot investment is a bit of a chore. The other problem is I have to get the burnout and casting done sequentially. I can't do burnout and then wait till later because the investment absorbs moisture from the air, and additional heating increases shrinkage. With shell, I can make all of them ahead of time, indoors without regard to the weather (soon to be a concern!). Because of the high temp; burnout will be complete. I can wash the shells out with water. I can choose my day weather wise for casting. I can just heat the shells up in the oven before casting. I can use filleting wax to fill the larger imperfections in the print. Plus, I can get all the castings done in a single day. Cleaning the shell off is a chore, but in this case, I think it's probably the best method. Other than lost foam. Unfortunately I don't have access to to a 5 axis router, and I want to move forward with this project, not learn a new process! I already know how to do shell.


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