Re: Mullers: fact or fiction


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Posted by Lyle Landstrom on July 19, 19100 at 09:34:20:

In Reply to: Mullers: fact or fiction posted by Dave on July 18, 19100 at 13:06:20:

You need a muller to blend petrobond from scratch. A concrete mixer with the paddles taken off and some cannon balls or metal ingot chunks thrown in will be good enough to reconstitute the sand after casting but to make it from scratch you'll need the muller.

Petrobond and other oil bonded sands have about 1/2 the binder as regular green sand (5-6%). this is why they are so forgiving. You can ram them hard and still have porosity to let the gas escape. Also they have less oil% than green sand has a water% so there's less gas. Because of this, the sand particulates need to have a very even coating of the binder. Because there is not as much binder, it needs to be mulled (squished) onto the sand. A concrete mixer is designed to mix a slurry, that is, mixture with about a 3" slump which is way more liquid than a foundry sand. Because green sand has more water in it which acts as a lubricant between the sand particles, you can use a concrete mixer for green sand although some people mix green sand dry then add water and let it percolate overnight.

Before I got my muller, I tried mixing by hand, with a mixer, preheating to make the oil less viscous, etc. all to no avail. the muller is the way to go.

I built mine out of a 30" steel barrel that I had rolled with a 1/2" steel plate on the bottom, a truck rear end for the bevel gears, John deere chisel plows for the plows, and trailor hubs for the mull wheel hubs. My other muller is one that I bought at an auction. It is only 12" dia. so I could only mull about 5-7 lbs of sand at a time which lead to an inconsistant blend.

Alot of State Highway departments used mullers for trial asphalt mixes before they developed new "Superpave" Specifications. Because of this, some can be found at State surplus auctions as they are no longer needed for this purpose. Most States have a website with surplus listings.

Hope this helps.

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