Tempering Casting Sand with Water

Home enthusiasts discuss their Foundry & Casting work.

Moderator: Harold_V

Post Reply
sierevello
Posts: 92
Joined: Sat Feb 01, 2003 3:24 am

Tempering Casting Sand with Water

Post by sierevello »

I went to www.foundry101.com and was looking at their site. They have alot of good info and pics but they temper their sand with WATER ONLY. I am new to metal casting and though that water would cause problems because it boiled and then steamed ruining the part that was being cast. Any help greatly appreciated. Thanks, Steve
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Tempering Casting Sand with Water

Post by Harold_V »

Hi Steve,
I've not done any casting with water tempered sand, but it's the material of choice for those that really understand the trade. Petrobond (oil tempered sand) is very good, but I'm not convinced you can use it for casting iron.

Water tempered sand is what they mean when you read "Green sand". The amount of water and other ingredients is critical for good performance. Too much water and the problems you mentioned exist. Not enough and the mold will collapse.

Best thing you can do is get a few books and read about sand and how it's prepared and why. Lindsay offers some great casting and pattern books, web page

Also, if there's a green sand foundry in your area, why don't you drop by and ask if they will permit you to watch the guys ram up some molds? Tell them of your interest and your lack of knowledge. I can't tell you the number of hours I used to spend doing that when I was a teenager. I was always interested in the trade, but not enough to work there. I learned a great deal, now to eventually apply it in my retirement.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
jpfalt
Posts: 982
Joined: Sun Jan 05, 2003 12:55 pm

Re: Tempering Casting Sand with Water

Post by jpfalt »

The water tempered green sand they are talking about is usually about 5% bentonite clay, 1% charcoal and contains 3.5% water. The charcoal is not used in sand for aluminum, brass or bronze. You are right that Petrobond is not recommended for iron as petrobond is not as strong a sand and the heat of the iron burns out an excessive amount of oil and results in a long flame plume coming off the top of the mold.

The foundry supply places sell a device that looks like an aluminum jug with a clamp on cap and a pressure gage. You put a weighed sample of sand and a measured quantity of calcium carbide in the jug, seal it and shake. The water from the sand and the carbide make acetylene gas and the pressure in the jug tells you how much water was available from the sand.

Another way to do the measurement is to take a weighed sample of sand, spread it on a cookie sheet and dry it in the oven, weigh it again and calculate the water percent from the weight loss.

In the 3% range, water won't cause a problem unless the mold is rammed too hard and permeability of the sand drops, or if you don't vent the mold enough. There is a tool called a vent rod and it's just a steel rod, 1/8 inch diameter sharpened up like a pencil on one end. When you have each half of the mold rammed, you stab it all over with the vent wirebefore you remove the pattern to let the steam out, kinda like stabbing a potato with a fork to keep it from blowing up in the oven.

If it's really critical to keep water from the iron, you use a mold wash. This is silica or other dust mixed with denatured alcohol. This gets sprayed on the mold cavity surfaces before closing the mold and is then set on fire. The denatured alcohol burns out and leaves a dry surface for the metal to contact. You rarely need this with iron. One thing I do if my sand seems to be running a bit wet is to ram the mold and leave it sitting open for a couple of hours for the surface to dry some.

This does point out one important issue with water tempered sand. It drys out. You have to keep it covered with a water vapor barrier to keep it from getting too dry and it's a good idea to mix it regularly. I keep my molding sand in a 32 gallon plastic garbage can and periodically dump it on a concrete floor to mix and stir it before putting it back in the can. You test the sand by grabbing a fistfull and squeezing it. It shouldn't ooze out between your fingers, but should stay in a firm lump indicating it's not too wet. It shouldn't fall apart when you release the pressure, indicating it's not too dry. When you shake out the mold, the sand against the metal will be baked into hard, dry lumps. These need to be crushed and mixed back in with the rest of the sand.
AndrewMawson
Posts: 286
Joined: Sat Jan 04, 2003 5:46 pm
Location: Battle, East Sussex

Re: Tempering Casting Sand with Water

Post by AndrewMawson »

The testing apparatus that was mentioned in the former post for measuring water content is called a 'Speedy Moisture Meter' When I first started out casting I had no end of problems getting the water content right - and of course if you are only doing it infrequently your sand pile will change markedly over time. I bought a Speedy and was able to put some science into the task to make up for lack of experiance - it's very easy to use. I aim for 3.5 to 4%.
Andrew Mawson
Battle, East Sussex, UK
Post Reply