The On-Line Magazine of Rideable Model Railroading

  NUMBER 127

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© March 01, 2009   

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Foundry101

Casting Simple Objects In Aluminum

 

Written by Steve Hoerner

Foundry Sand/Greensand

In commercial foundries the sand is used over and over thousands of times. Between uses, the sand is rejuvenated by adding water and mulling (mixing and smashing). If you do not let the sand dry out all the way, you do not have to mull, just add water. Sand grit is determined just like sandpaper. 150 is very fine and 50 grit is coarse. Fine sand will give good detail, coarse sand will give a pebbly or rough texture. If you look at the sand through a microscope there are gaps and spaces like a sponge. Any moisture that turns to gas during pouring can escape out the pores (gaps). Other materials like plaster do not have gaps for the gas to escape. The sand used in greensand is silica, common/ordinary sand. You can use beach sand, desert sand......it's all good as long as it is clean and fine. The sand is held together with bentonite, a powdered clay. Bentonite is also used for wine-making, well drilling, patching dry lake beds, cosmetics, farm-feed additive and milkshake thickener. Bentonite is also sold in health food stores for colon problems. You can purchase bentonite locally at well-drillers or well-drilling suppliers.

 

Editor's Note (do not try this at home yet)  This article only serves to demonstrate the basic procedure for making a simple casting. It does not include dozens of details that you will need to learn to be able to do this safely.  Before you attempt this, you should take a class on foundry work at your local community college.  This web site and the author are not responsible for injury or loss of life or property that may arise while attempting a foundry project.

 

Helpful Hints
  • Safety First.  Do not try this until you know exactly what you are doing (see note above).  Wear the proper protective equipment and know what the dangers are BEFORE you start.
  • When you are ready (see note above), start casting with aluminum (low-melting), then try brass or bronze. Practice with easy metals.
  • Finish molding before you start your furnace. DO NOT light the furnace then start molding.
  • Greensand is about 6% moisture. DO NOT let your sand dry out! Keep it covered or in a sealed container when not in use.
  • DO NOT melt aluminum cans. Can metal is sealed with vinyl to protect the aluminum from the contents of the can. All other aluminum is good to melt.

 

Casting by the numbers

1. Place pattern in flask with enough room for gating (click images to enlarge).

2. Dust pattern with parting dust to keep it from sticking. Parting dust is a hydrophobic material, it repels moisture.
Most powders (baby, talcum) absorb moisture.

3. Use a fine riddle to cover just the pattern, then fill up the flask with sand, level (flush) with the top. There is no need to riddle all the sand, just make sure there are no lumps. The riddle fluffs the sand up so it can be packed properly, the same way a flour sifter works.

4. Use paddle side of rammer to tuck edges.
5. Use the butt side of rammer east to west (lightly to protect pattern), then north and south (harder to pack mold tight).
6. Fill it up with sand to about 2 inches above flask.
7. Use rammer again North to South, then East to West pattern. Press hard, to pack the sand very tight.
8. Strike off drag section with rammer, then spread small amount of sand (handful) out to cushion bottom board.
9. Place bottom board on top of your mold.
10. Holding bottom board and flask together and flip it over.
11.Remove the cope and pattern board.
 12. Use your spoon and smooth the edges of the pattern and any rough areas.
13. Use your hole cutter and mark your sprue hole, put an X for the pop-up hole. A pop-up tells you when mold is full.
Repeat steps 2-8
14. Use your trowel to smooth top (cope).
15. Take cope off and set it aside. Use your hole cutter and cut a sprue hole by placing your hand on the back of the cope and push hole cutter through the other side, twisting slightly.
16. Form a cup on top of cope. Using smaller hole cutter make a hole on the X. Smooth out the hole using your spoon and finger. Patting down with finger, never rub.
17. Cut runner bar with “j” shaped gate cutter.
Use your spoon to make a smooth gate (if left rough your project will be rough and pity). Erosion eats at rough areas. Areas you cant get with the spoon, use your finger. Your finger is the most useful molding tool.
18. Use other end of hole cutter and push down to make the sprue base a little deeper (smooth edges with finger).
19. Use your spoon to gate to pattern, then smooth gating system using your spoon.
20. Tap on pattern to loosen, use a screw to take pattern out.
21. Blow out all loose sand, make sure everything is smooth.
22. Is your sand too wet? Torch the casting area until it turns orange, this will dry out excess moisture. This small mold was torched less than a minute, sand will blacken.
23. After making the mold, release snap flask to make another mold using the same flask.
24. Place your flask back together and pour your metal! For more molding tips read through our other step-by-step instructions and project pages www.foundry101.com .
25. Melting
  • Do not use furnace indoors or near combustibles.
  • Remove lid (top section of furnace) and place crucible inside furnace. Fill the crucible loosely with metal.
  • Light furnace and replace lid without lid plug.
  • Run the furnace with the propane setting on full. DO NOT OVERHEAT the crucible/metal.
  • When the last piece of aluminum turns molten, let the furnace run for 3 more minutes to reach pouring temperature.
  • Turn furnace off, remove lid, remove crucible and pour.

During melting, add more metal through exhaust vent. Preheat before adding directly into molten metal, no need to preheat if metal inside crucible is not molten. Protect your self. Use tongs and gloves for feeding. Use full face protection and a heavy apron long pants and shirt with heavy boots.  See www.foundry101.com  for details.

26. Place a brick or two on each mold to prevent leaking! Pour the metal into the large hole until it appears in the small hole.
27. After it cools, remove the casting and file the sharp edges.
 
Editor's Note (do not try this at home yet)  This article only serves to demonstrate the basic procedure for making a simple casting. It does not include dozens of details that you will need to learn to be able to do this safely.  Before you attempt this, you should take a class on foundry work at your local community college.  This web site and the author are not responsible for injury or loss of life or property that may arise while attempting a foundry project.

Here's a book on the subject:
Metal Casting : Appropriate Technology in the Small Foundry --Steve Hurst 

 

Written by Steve Hoerner


Read about
Pattern Making

Be sure to visit Steve's website www.foundry101.com

Purchase foundry supplies and kits from Steve at
Lost & Foundry

Would you like to discuss
the ideas in this article? 
Post a comment or question here.

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