The Home Machinist!

I have watched some videos on green sand casting.
The put the pattern in the bottom half, sive sand over, "pound away" and make the sand solid around the pattern.
The top half it put on, sand sive'd over, and pound tight...then they remove the top half, take the pattern out, put the top have back.

My question, when you pound the sand in the top half, what keeps it from 'bonding' to the sand on the bottom half?

Perhaps it was the sand we were playing with..Kenetic sand..but once we pounded the tophalf down..it joined with the bottom half.

So suppose we used green sand, I understand you mix a bit of water with it...How long do you let it dry?
Do you let the green sand in the bottom half dry before you put the top half back on??

By the way, we had good luck with the kenetic sand..I used plastic wrap between top and bottom to keep them from joining...
The casting came out great, but watching the youtube videos, it seems so much "easier"!

Thanks for any advice!
-Mike

If you are using loose patterns in green sand, I used wheat flour, cornstarch, or baby powder, to make the )drag) lower half dry at the surface, so it doesnt stick. Mounted patterns do the same thing, as the sand does not ram together. The tightness you ram to is also an issue, and should only be tight enough to prevent fall out. Moisture levels have to be watched closely, so the sand is sticky enough but not damp. It makes a big difference in how much steam blows through the sand, that can have negative effects on the casting.

It is the reason that I changed to oil based sands for increased detail, and generally less headaches overall.

With a piece of 3/4 inch plywood for a pattern board, molding becomes much easier, and more consistant than loose patterns, so it is what I do.

Mike,

Welcome to the forum. There are many people here who have great knowledge.

I suggest you watch mrpete222 on you tube. He was a shop teacher and does an excellent job of covering the subject in detail. He casts his own live steam engine parts in aluminum and lead. I think you will find a lot of answers to your questions.

Good Luck,
Terry

1/2 the pattern goes in the bottom and 1/2 goes in the top. you fill (pound the sand into the mold) each separately and then join the two halves together to get the piece you want. Before you join them you cut the pour opening and any gates need to get the metal to flow to the part. You don't want sand falling into the hole left after taking the pattern out.

Tom C.

Bought some "petrobond" sand...going to give it a try this weekend.
Does anybody have experience with ZA-8?
I ordered a bar of that too...but it has a much lower melting point than aluminum. I am worried about burning it up
in the aluminum foundry.

I use talcum powder in an old tube sock. Once the bottom half of the mold is rammed, you install the top half of the pattern and coat the entire thing in talc. It separates super easy.

You sprinkle the talc on the pattern board as that is what u need to pull out of the sand without damage to the sand. That is where practice and proper sand moisture comes in handy.

Tom C.

Zinc based. or recycle die cast materials are ok to work with, but tend to be a little gassy and porous if mishandled or overheated. Still it is a quick answer for detail parts where high strength is not an issue. Zinc based materials are superior in permanent molds of simple design, for multiple detail parts. set up in gangs like fishing sinkers it is the way to go for great numbers of small parts.

in changing to oil based sands, you will find increased detail a double edged blessing, as I have recorded fingerprints in flat surfaces.

We tried some casting this weekend, but the weather was windy and cold so we had mixed results.
The one thing I have to agree with...the petrobond sand reproduced everything...Especially our our errors came out well!
Amazing the detail it could pick up.

The expense of the sand and the detail it captures nearly forces you to improve your process, and raise the quality of what you do. I find it a challenge to get it 'good enough' in the molding process, because perfection is often within reach with so little added effort.

If you get good at pouring metal you can do just what we did yesterday, pour Rail Joiners in C99700 brass, the sand is Petro Bond II. The second photo is from a pervious pour of the same thing; can never have enough Rail Joiners.