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I Forge Iron

Casting Zinc/Lead/Aluminium


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Hello all, for the last few months I've been experimenting with home foundries! As a bit of a back story, i'm doing a class 12 project on metallurgy and have over the past year researched and created a forge, electrical arc furnace, and a functional gas-can foundry. in regards to the use of the foundry i have been experimenting with low temperature metals (lead/zinc) to creating fishing sinkers and little fish trophies (zinc). some of the problems I've been finding are that the plaster moulds i'm using are too fragile and crack after the first use i have tried adding sand however that made the models very un-detailed, any solutions/alternative mould recommendations?

 

also as a side note, i know the dangers of lead, i wear welding gloves, goggles and a respirator whenever i'm working with it!

Pictures included to show what i've done so far:

including lead fish casting x2

failed zinc casting, sprue was too narrow and plaster too cool?

melting lead in my crucible over the foundry

the foundry

side view of the forge

front view of the forge (no fan/ash trap)

the forge is also painted hammerite green at the sides and back

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I recommend  "The complete book of SAND CASTING"  BY C. W. Ammen.  Sand Casting is the normal way higher temperature metals are cast.  There  is an intermediate mixture of the Plaster of Paris used by potters to make molds with quartz sand mixed in.  The plaster used by potters a slightly different composition that sold in hardware stores.  It is tougher and more durable as it is used repeatedly for slip cast items.    My first contact with it was helping a friend in college cast a small sculpture  in bronze.  That was lost wax.  After casting you just bust the plaster away and start finishing.

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Charlotte, i've been looking at making my own green sand however finding some of the materials has been tough and i don't really want to grind down  kitty litter for the bentonite!  thanks for the book recommendation, i'll check it out!

 

ThomasPowers, I've tried lost wax casting using paraffin wax (crazy) i made a silicon mold then cast the wax into the silicon then the solid wax into a plaster mold, it lost much of the detail and the other investment I've looked at is similar to dentist alginate however that costs a little too much for my budget!

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Silicone rubber has a working temp that is in the low end range of molten lead from what I remember when I looked into this stuff years ago.. The commercial lead soldier molds I was given as a kid by my grand parents and family in Germany were made of some sort of high temp rubber/silicone.

 

When I was looking to do lead casting to reproduce some old lead diving weights, I called both SmoothOn and PolyTek and talked to the techreps as to which products might work best. I forget now what silicone rubber I bought, but it had the highest working temp they had. I never did get to do a casting with my mold as when I left the shop, the mold  I had cast off an original weight mysteriously "disappeared". My money is on the boss who probably kept it planing to do castings and make some money off the project, but I can't prove anything. I haven't had a need to do any other castings like that, so I never got a chance to try and see if it would work well.

I was also given some high temp plaster like material to do molds with at the time by one of the customers who knew of the project I was trying to do. I wasn't there when he dropped off the stuff, so I didn't get a chance to get any real info on what he gave me.

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Drago, try investing your silicone with either:

- A mixture of either paraffin with HPDE melted into it (I've read but not tried 4:1)

- A mixture of Paraffin and hot glue sticks (7:1.5)

You may get better definition as a result, YMMV but it could be worth playing around with.

Full disclosure, I haven't tried playing with the casting myself, but have come across these ideas more than once whilst reading on the subject.

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Look around the yellow pages for a drill supplier they usually carry bentonite drilling mud in 50lb. bags unless you want bulk they you can get it in supers or truck loads. Don't get the specialty stuff like Easy Mud or Sea Mud, they're for special situations and are WAY more fancy than you need for binding green sand.

You can use plain old ground clay for green sand just be careful to clean out the weird stuff. A little sand is nothing but worms, roots, old leaves and finger bones can do . . . interesting things. No need to do a hydrology separation, just screening it over a 80 screen should be more than enough. One of the guys in our group is a caster and uses river sand for his green and prtrobond sands.

It more takes a feel when you make it than s formula. You need to know how good sand feels, more than just in the temper.

Frosty The Lucky.

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If you are using a plaster mould for casting metal you need to either heat it up to wax burnout temperatures or bake it around 400 degrees for a couple of hours minimum.  A former supplier of mine who was 2 blocks away was an aluminum foundry that cast aluminum match plates in plaster.  He used to bake his moulds in an oven at about 400 degrees for 24-48 hours.  But that was for a mould about 24"x36"x6" or bigger for one half. 

His process pressure cast the aluminum into the mould.  The pressure casting is not suitable for home casting as it required heavy cast iron flasks and top and bottom plates,  a heavy steel pressure pot and only ounces of air pressure.  Even then he occasionally had molten aluminum shoot out of a mould across the shop 15-20 feet.   The process also required asbestos paper as a consumable. 

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