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Step by Step

Here is a very abbreviated look at casting metal. In this case yellow brass.

Some steps are not shown in the photos. I'll be making the seahorse on a shell

and a small Kloudbusters Rocketry Club desk plaque. This is loose pattern mold making -

see Rocketry Logos Trailer Hitch Covers for molding using a match plate.

First you have to have a pattern. I made these from natural clay. 



The pattern is placed in the bottom section of the flask (called the drag).

There is a fitted board, called a pattern board, that the patternis placed

on for molding. The pattern and board are lightly dusted with parting dust.



Sand is then sifted into the flask and rammed firmly against the pattern.

The flask is then rolled over revealing the pattern in the sand.

The white material you see is the parting dust. It keeps the sand from

sticking to the pattern and to the sand in the other half of the mold.




The sand is cleaned around the pattern to the mid-line. Then the top half of the flask (the cope) is placed on top.

Sand is riddled (sifted) into the cope, rammed firmly, and then scraped off smoothly on top. Next a hole is bored into the sand.

This is where the metal is to be poured into the mold. This hole is called the sprue. I use a bathroom plumbing fixture to cut the sprue.



Next the two halves are separated and the pattern removed. Here is the cope (top).



And the drag (bottom). Channels, called gates, are cut in the sand to feed metal from the sprue to the pattern.



At this point, flour is lightly dusted on both halves of the mold. This is used to make the liquid brass flow better.

It is not used on aluminum molds. After dusting, the mold halves are reassembled and are ready

for pouring. Here is the other mold cope with the shell and desk plaque molds. In this case I cut the gate to the

plaque in the cope rather than the drag.

I wanted a "boss" on the underside of the shell to help support the seahorse when I attach it later.

I used a pencil and pressed a shallow hole in the shell. The casting will now have a small peg on the underside.



Here is the matching drag. I used a metal strap (1" x 1/8") to poke a hole in the sand at an angle to form the stand for the desk plaque.


After the cope and drag are reassembled, the sand on top is "scratched" to create some loose sand on top.

This is done when casting heavy metals like brass. There will be a heavy weight placed on top of the mold

and the loose sand helps provide a level cushion to support the weight without crushing the mold. 

 

 

Time to melt some metal!

I used some yellow brass ingots and .22 caliber bullet casings for the metal

.It takes about an hour to melt 10 or 12 pounds of brass in my furnace.

You can see the furnace setup under equipment on this site.



Here the metal is nearly ready. I am skimming off the material that has floated

to the top of the liquid metal. This is metal oxide and other contaminants.

It is called "dross". Dross is not the same as slag which is a byproduct of iron smelting.

The white smoke contains zinc fumes...avoid breathing this as it can cause health problems.



The flask containing the mold has a 1/4" steel plate and a heavy weight on top.

This is to keep the hydrostatic pressure of the metal pouring into the mold from

forcing the two halves apart. I made a pair of tongs sized specifically to hold

the crucible. Here I am just about to pour the metal into the mold.



The metal is white hot! Remember, don't breath the smoke. 

(As a matter of fact...this metal is too hot. I should not have heated it so long.


Here are the castings. The sprues and gates need to be cut off (& remelted later).



With a little grinding, polishing and chemical magic.....the finished products.

The seahorse and shell were joined with a brass pin inserted in a hole drilled

through the shell and into the tail. Epoxy was used to glue it all together.

This desk plaque needs more finishing work....but you get the idea!



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