Cast Iron

Cast Iron has been used for many year's and has many uses from architectural to ship building, It is a self lubricating metal and as such lends itself to many uses in engineering. The amateur foundry man will find that it is a very practical metal to work with, and the engineer will be able to make those odd machine tool accessory’s that are always needed but are far too costly to buy, even if they are available. It is easy to machine provided that suitable annealing processes are used.

The basic structure of cast iron is that it is impure, and as such contains a lot of carbon; this is a very useful impurity, as the metal can be made from a soft machineable metal, to something as hard as a hard thing on a cold frosty morning, for finished items. And a wonderful range of colours can be achieved with simple heat treatment.

Having cast and tempered the casting, you must first remove the sand crust casting flash and oxide from the casting, ( this is called fettling ) before machining or the tool tips will be worn away quicker than spending the money in your wallet!!

But with a little care when preparing the mould and a deft swing with an angle grinder equipped with a stiff wire brush, a beautiful grey/blue dappled finish can be achieved!!

Melting:

In preparing for the melt I would suggest that the iron be broken into, as smaller pieces as possible and the best material to use are old machine castings, as this will prove to be the best quality metal. Always use small pieces, as Small bits heat quicker than big bits, and the cutting will reassure you that the quality is high, it should cut with a quiet abrasive noise and not vibrate or make any high-pitched sound as these indicate either unknown impurities or hard spots. Do not use swarf, as this will produce a lot of slag if not protected from the effects of oxidization whilst heating. When melting cast iron in a crucible, be sure that the expanding metal has room to move, which is general practice and not packed tightly, as this will crack the crucible.

As the metal approaches the melting point, slag will form as the oxide that forms on the surface melts, it looks as if it is sweating droplets of molten metal, along with slag (oxidised metal), and the surface may well look as if it is bubbling, this will all collect at the bottom of the crucible, if the items are a little on the big side, a gentile poke with a stainless steel rod will easily break up the metal, but be careful not to be too violent or you might damage the crucible, also choose the rod very carefully as it may well melt if exposed to the extreme heat for too long.

Slag:

The slag is the black crust that is formed by iron when heated to the point where the metal starts to oxidise, this is more familiar as the black shale as seen on the floor of any blacksmiths shop, this collects on top of the melt, and forms a gooey glassy substance. A lid is recommended to keep out excess air during the melt, but with a lid it is difficult see what is happening inside, you can of course work without one if you choose, but more slag will be produced as of the increased oxygen content that will be circulating with the melting metal. The slag should be cleaned out of the crucible as soon as possible after the pour has been completed, whilst the crucible is still very hot, or the crucible will rapidly become unusable. The best method is to get your helper scrape out the inside of the crucible using a tool that is similar in shape to an army trenching tool, but much smaller this tool must of course fit inside the crucible easily.

NEVER BUT NEVER CHIP OR PRISE OUT ANYTHING FROM THE INSIDE OF THE CRUCIBLE.

Pattern making and annealing:

Pattern making is the same as with other metals except a larger more sturdy box is required, the sand which is closest to the metal soon reaches red heat after the pour, it is quite conceivable that if too small wooden casting box is used then it may well catch fire.

Safety:

Cast Iron is a heavy metal and a surprising weight can amount in relatively small castings, therefore some form of lifting apparatus is recommended to assist in bringing out the crucible from the furnace as the radiated heat from the crucible is considerable. Close proximity to the crucible should be avoided at all costs. Protective gloves may well prolong your exposure, but these will eventually heat up and themselves cause burns.

My friend Eric, who comes to help when a particularly large pour is being preformed, suffered a bad burn on his hand from radiated heat whilst pouring cast iron, despite wearing protective clothing,

Asbestos gloves,

Leather arms,

Face visor,

Leather apron,

Good quality waterproof work boots, Not Wellington boots,

I have once observed a man dancing around a scrap yard with a small blob of molten Aluminium in his Wellington boot, heaven only knows what cast iron would do!!

These items are the bare minimum that should be considered, and pride must be shown when storing these items, they are expensive and easly damaged and

they just might save your life one day.

So be warned this is not for the faint hearted If you look at the photos on this page, you will notice the protective clothing being worn, and that I am hanging the lifting shank from the hook on the electric hoist whilst pouring, this enables the operator to remain at a greater distance from the melt and to control the pour with greater precision.

I would suggest that due to the increased danger working with these temperatures you should never work alone, always have a helper to hand and let other people know what you are doing.

All that is left to do now is to let your imagination run wild and produce some wonderful patterns,

after all anybody can make a hole in the sand, can’t they??