Lost foam aluminium casting issues

[Gennady]

Hello team.
I wanted to give it a try to lost foam casting. I've watched several youtube videos and read quite a lot of articles - seems quite simple? Not really

First - faces of the part are extremely rough
Second - bigger problem - sand often is collapsing making cast completely ruined.

So here are few questions - sand is really dry, should I wet it a bit to prevent collapsing? Should I use a refractory coating - I've. seen many guys are using drywall compound to preserve sand from collapsing,

 

[bhowden]

I have done a couple. Some came out trash and others very good. I used drywall compound which is a bit messy and took longer to dry than I expected. I often wondered about a hybrid where I would pack the foam casting in green sand but I have not tried it.

Brian

 

[Gennady]

pack the foam casting in green sand

That I already tried - quite messy as well (for me) . You need to provide channels for gases to escape otherwise it is all with bubbles. For drywall compound I found that dunking model in the compound (liquified) several times and letting it dry in between is usually produces better results, still lot of mess, you are right.

 

[Dan Dubeau]

I have only done 2. Dry sand, and I used a thinned down drywall coating. While I got really good surface finishes, I've been plagued by venting and fill issues. I have one more pattern made ready to cast, and I think I have learned enough from the various mistakes so far and "expect" a good pour this last time around. If not, I'll make a weldment lol.

I learned a lot from watching Kelly Coffield's videos on youtube, and he helped me with issues when I posted over at https://forums.thehomefoundry.org/index.php

If we weren't in the middle of a heat wave, I would have had another shot at it the last two days. Maybe tomorrow morning, it's supposed to be a bit cooler. I'm hoping this last one is a success, as I'm hoping to employ this process for a few other various projects in the queue.

 

[Tom O]

Go for it you’ll be surprised just how much cooler it is once you back away from the furnace.

 

[djberta]

What I have done for success. Do not follow regular green sand or ptrobond practices. First foam prep, use the blue or pink foam from HD or Rona. Use low Melt hot glue to attach pieces together. Lightly fillet with the glue. You don’t need to glue the pieces directly together just fillet or cover the outside gap. Make sprues from the bottom and up, high points and anywhere with a decent under cut. Be sparing but cover all joints with the glue. If compound gets in then gasses can’t get out and AL cont get in. Dip in thinned drywall compound. Dry. Then dip in thick compound. Dry completely. Next you have to use loose sand it has to breath. Also you need some depth, I like 6 inches at least. Your sprues and gate should be large, I use 1.5 x 1.5 gates to a large soup can. With the soup can down about an inch or more over the gate. With the molten Al, fluxed with no dross. Pour steadily in to the gate until Al shows on the sprues. Leave for some time. You can lightly pack the sand but don’t ram it. But make sure it is all around your shape. I use a 7 gallon drum for casting, 5 gal works as well. Depends on the size.

If you watch Kellie’s videos he pours in to fairly tall flasks which is one of the reasons for success. He is also using a commercial compound and very precise tempature that he pours at.

Even with more failures then success, can be a steep learning curve. Once you hit your sweet spot it is incredibly satisfying. Next on my list is the parts for a float lock vise and a spindle mount.