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Making "Core" Sand

The lawyer's version of CYA!

WARNING!!!: You got a brain... USE IT! Building and working with a foundry furnace is "NOT" child's play. It can be very dangerous and if 'you' screw-up don't come crying back to me! If you don't know what you're doing and didn't take the time to read and study all the safety procedures that are available on the net, and you get hurt that's 'your' problem. You are responsible for yourself and your own actions and safety.
--- "NOT ME!" ---

Doing my research on the net, I've found 100's of furnace designs. Some were just fire brick stacked into a circle on a steel rack another was nothing more than refractory jammed into nothing more than a cut in half milk jug. :-(

The same thing applies to making core sand for your molds. Everyone has their own "PET" formula for making their sand.... AND many won't give out their 'secret' formula.

Many of my designs are not new... just modified the basic concepts to my own ideas and I think improvements.

I can say without a doubt I've LEARNED A LOT!!! Of what NOT to do and things I FORGOT to do, and some things I SHOULD HAVE DONE, so if you try to do this understand right off that this is a learning process and you WILL make mistakes.

I'm not sure just what I can show you in the way of pictures, after all it's just a box of sand/flour and other ingredients mixed together.

So here's my list of Core recipes; see which one works the best for you.

Core Sand Recipes

Core Mix with CO2

  • 100g Fine Sand (Sifted Sand)
    (that's about one cup)
  • 6.5 grams Sodium Silicate
    (Try a 2 or 3 oz. to start)
    (2.40 is the best grade to 3.22 wt. ratio)

Mix it well then dry/harden with CO2. (air drying will take over 24 hours. Bigger cores will take days.)

No CO2 available -- then get a big plastic tub with a 'tight' fitting snap-on lid.

Place part (still in the mold), in the bottom and a half a cup of vinegar, (For small cores), along side, then dump in a heaping teaspoon of 'bi-carb.' (Baking Soda) and snap on the lid -- check it in two hours. If not completely hardened gently remove from form and repeat. For larger cores use a full cup of the vinegar and a heaping tablespoon of the bi-carb for 3 or 4 hours.

Sodium silicate formula #2

  • clean dry silica sand.
  • 3%-5% sodium silicate (waterglass) by weight
  • Gas with C02 to set (about 10 sec. at about 3 psi)

Corn Flour Recipe

  • Fine (Sifted) Sand
  • Corn Flour 10/20%
  • Dark Molasses mixed at 25/75% molasses with water

Bake at 200/250 degrees till it stops smoking, (But smells good)
If it's not hard enough increase the molasses to 30%.

Wallpaper Paste Recipe

  • 525g Sharp Sand
  • 18g Flour
  • 10g Extra Strong Wallpaper Paste (mixed thick)
  • 12ml Linseed Oil

Let it harden several hours in the mold then gently remove and
place on a cookie sheet and bake at the max heat your oven
can go and the smoking stops.

Baked core formula 1(Mark Fowler's formula)

  • 10 parts molding sand.
  • 2 parts clean dry sand
  • 1 part molasses water
    (which is 1 part molasses to 8 parts water).
  • 1 part boiled linseed oil.
  • 1 part flour (may be left out)

Baked core formula 2 (tested successfully by Rupert Wenig)

  • 20 parts clean, dry silica sand.
  • 1 part wheat flour.
  • Molasses water to temper
    (1 part molasses to 10 parts water)

Mix dry ingredients, then temper with the molasses water.

There's also a recipe using OatMeal, but haven't found a good
recipe for it yet.

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