Aluminum Sand Casting a Motorcycle Engine

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GreenTwin

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"Petrobond" is a tradename for an oil-based foundry sand.

It gives an excellent surface finish to castings.



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GreenTwin

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Some folks make their own mix of oil-based foundry sand.

One type is called "K-Bond".

I found this on the net.

K-bond
K-Bond, named for Kent State where it was developed by one of Tom Cobett's Students, is an almost smokeless oil bonded foundry sand.
It is used for casting zinc, aluminum, brass, bronze and iron.

The recipe is:
*100 lbs. sand - 100 mesh or finer
*6 lbs. bentone clay (such as Bentone 34 or VG-69)
*3 lbs. synthetic 2 cycle motor oil
*0.2 lbs. (3.2 fluid oz) Methanol (dry gas)

Mixing:
Mix the sand and bentone clay first (wear a dust mask!), then blend in the oil thoroughly.
Small batches (less than 10 lb.) can be done by hand with good results, but a muller is preferred.
The small batches can be done with a cheap kitchen electric mixer.
Add the alcohol and mix thoroughly.

"The sand won't seem like much until the alcohol takes effect and then it will become like stiff cookie dough.
How stiff? It bogs down my muller!

It will be much easier to handle when it is a day old and will get easier to use with time and use.

The sand gets powdery after it sits and it is best to mull it or warm it before use.

When green strength starts to fade, add in some alcohol."

... Ray Brandes, quoted from his old web site. Also the source of this recipe.
The definitive source:

Subject: The History of K-BOND
Date: Wed, 13 Feb 2002 13:05:03 EST

K-BOND was developed in about 1995 at Kent State University.

We set about to find a suitable alternative
(to Petrobond).
After about 3 months of testing, we had evaluated many sources of bentone and many sources of "smokeless" oils.
(By the way, Petrobond is also made with Bentone.)
We found that virtually all organo-bentones will work well. With this in mind, we bought the cheapest one we could find.

For the oil, we settled on AMOCO Indopol L-100. This was listed as being a "food grade" material that burned cleanly.
Later, we found out that Indopol is the main ingredient of most smokeless 2-stroke oils.

The basic recipe for K-BOND is: 100 lb. of very fine silica sand (100 to 150 GFN)
6 - 7 lb. of Bentone (cheapest you can find)
3 lb. of Indopol L-100 oil
0.10 to 0.20 lb. of Propylene Carbonate (or Methanol or Isopropanol)

If the sand become too dry to mold, we add more Indopol.
If it lacks any strength, first we add more Propylene Carbonate.
If that does not bring up the strength, we add more Bentone.

We have used this stuff several times a week for aluminum, bronze and iron castings.
We have never thrown out the pile, we just add too it.
We don't get a room full of blue haze when we pour our molds.
We make castings that are incredibly smooth with extremely fine detail.

Dedicated to Metal Casting Education...
Tom Cobett

Cleveland, Ohio

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GreenTwin

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I have used Petrobond a few times, and it does give a very good surface finish.

The local Metal Museum foundry uses it extensively, and they also get superb surface finishes on their castings, especially if the pour temperature is just right.

Petrobond will copy a fingerprint on a pattern.

Petrobond does tend to dry out, and it has to be mulled routinely, with a little alchohol added every so often.
You generally mull it before every use.

I started to build a muller, and then converted to resin-bound sand, so I did not finish the muller.

I mix my resin with sand (for my bound sand mold making), and I use a commercial Hobart kitchen mixer for that.
Mixing resin with sand is easier than mulling sand that has clay in it, and resin-bound sand is more fluid than clay-based foundry sand.

With clay-based sand, you see folks pounding away with all sorts of things, to compact the mold.

When using resin-bound sand, there is very little compaction of the sand, since it does not contain clay, and so you press the sand into the mold using the fingers and palms of the hand.
If you pound on resin-bound sand, it just shifts and tears away from the pattern, so you have to use a pressing techinique with the fingers/hands.

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