When I first started pouring, it was pre-internet and I didn't really have anybody to talk to, so there was a lot of reading and experimentation for me. Mixing up the green sand was one of the hardest things for me to figure out, so welcome to the party.
As for proportions, it might help to understand WHY the proportions are what they are. To start, you need sand that will retain an impression long enough to pour into it. Straight sand certainly won't do that.
Enter, stage right, clay (bentonite), with enough water to get it to do its thing. You want enough clay to 'stick' the individual grains of sand together. Because your green sand has some water in it, the water is going to turn to steam when you pour. That steam is going to find a way out, one way or another; the trick is to do it in a controlled manner. If your clay proportion is too low, your green sand won't hold a shape. If you keep your clay proportions down enough so there's still breathing room between the grains, the steam can meander its way out through the green sand mix. If your clay proportion is too high, those gas passages are going to get plugged up and your molds will be more prone to blowing apart.
If your water proportion is too dry, the clay can't work as well and your molds won't hold. If your water proportion is too wet, you'll generate excessive steam and risk another blow.
Water-based molds require venting to give all that steam some place to escape. I always vented generously when using my green sand mix. And as you use your sand you're going to have to mull it and add more water to replace what was steamed out of it. I got a little tired of all this and switched to petrobond, which is oil-based. Petrobond is stinkier than my green sand was, and the oil does burn, but there's no water involved, so you don't have to worry about venting so much.
Unless specifically stated otherwise, I've always figured proportions by weight, not by volume. I've got a basic digital bathroom scale and a small kitchen scale which will go up to about 4 lb and appears to be accurate to about a quarter-ounce or so. These two have gotten me by for a long time. Don't forget to subtract out the weight of your containers, if they're significant to your numbers.
Jim Ash
-----Original Message-----
From: Rod
Sent: Aug 4, 2011 5:45 PM
To: gingery_machines@yahoogroups.com
Subject: [gingery_machines] Re: green sand...
--- In gingery_machines@yahoogroups.com, "anthony" <ima_cute_dork@...> wrote:
>
> i need help on how to mix green sand!! i've googled how to mix green sand and i cant really find anything...i found some stuff where people say use 90 to 95% of sand and 10% of bentonite 7% water but i dont know how to do that...how do i figure out how much percent i need from what i have?
>
Anthony
Your proportions are about right. It's a lot easier to mix the bentonite and sand in a closed contained and then slowly add water. The sand and bentonite is very dusty. It's easy to add too much water, so add a little at a time. Also let it sit overnight before doing the squeeze test. Start with a small test batch of 10 pounds or less.
To keep your sand in a useable condition, try to keep it in a closed container, so it doesn't dry out. Cats love this stuff, which is another reason to keep it closed. You may find that you have to add a litle water if your sand hasn't been used for a time.
My personal preference is for petrobond. About the only disadvantage is cost. It doesn't need to be vented. It's always ready to use and the commercially blended sand is more likely to give you better results "out of the box".
<http://mifco.com/MS/catalog.php?op=inventory&cat=10> is once source.
Best of luck
Rod
http://groups.yahoo.com/group/gingery_machines/app/peoplemap/view/map
No comments:
Post a Comment