Foundry 101 – Iron Ore to Iron Castings

Faircast Inc. is a rising force in the foundry industry. We’ve been a growing supplier of grey iron and ductile iron castings in the Midwest and are poised to grow more still. How though, does an iron foundry work? What is the process of taking raw iron from the ground and turning it into high-quality iron castings?

Naturally, one cannot simply find iron, melt it down and call it a day. Unless you get lucky and stumble across an iron meteorite you are going to have some work ahead of you. Once you get the ore out of the ground, then you have to separate it out from the dirt and other materials that it is mixed with. For that, a blast furnace works wonders.

The furnace needs to be charged with a flux such as a limestone to draw the slag out of the ore. The iron then is fed into the furnace and heated, allowing many of the impurities to separate and rise, joining the slag layer on top. Periodically, the molten iron is then allowed to flow out of channels and cool. The resulting pig iron is still virtually useless being that it is so brittle. In order to turn it into a useful product, the pig iron is then melted and mixed with scrap leftover from previous iron castings and mixed with other materials to create cast iron. This process also results in other impurities being removed, improving the quality of the iron. The slag, of course, must be removed and the material degassed. Gases can become entrained in the molten metal due to various chemical reactions as well as a byproduct of mixing.   Removing the gas is important as if it remains in the final iron casting it can create pockets of gas that are weak points in the casting. One of the best ways to remove gases such as hydrogen from the molten metal is to force an insoluble purge gas through it. As the insoluble gas rises to the surface it will also force out the entrapped gases.

If one desires a ductile iron casting instead, the iron foundry will add magnesium into the mix. This changes the way the graphite in the iron organizes itself from flakes (as in grey iron castings) to nodules. This results in a ductile iron casting that is stronger and much less brittle than its grey iron casting cousin.

Molten iron is poured into a variety of different kinds of molds. Commonly, a sand mold is used because of its ability to withstand the high temperatures. However, a mold made of a harder metal with a higher melting point can also be used depending on the need. If all that is needed is a simple beam or block of iron, this is a very simple process. For anything more complicated, such as an engine block, the iron foundry will need to make use of cores. These cores are often made of sand and constructed using a variety of processes. One of the older methods is the shell core method that involves using resin-coated sand that is poured into a pre-heated core box (essentially a mold for cores). The heat hardens only the outside of the core. This allows the sand inside the shell to be reused after the iron casting is made.

There is also the new Isocure method that mixes the sand and resin together and makes use of amine gas as the catalyst to harden the core. Both methods have their uses.

These days, there are many variations on the basic process described above. These might include not even allowing the original pig iron mix to cool, as one can just keep refining it into a higher quality iron casting. Blast furnaces themselves have increased dramatically in efficiency over the years. Once, the best furnaces could only produce a few hundred pounds of pig iron each day. Now, capacities are projected to reach over 4000lbs a day in the near future.

The refining process at our iron foundry has also continued to improve. New ways to melt the pig iron include induction furnaces which use electricity to melt iron by inducing an electric current in it. This process is more energy-efficient, faster, and safer than traditional methods.

The cupola type furnace is also a welcome addition to the iron foundry toolbox. A shaft furnace, it allows for the melting down of highly contaminated scrap that would not be able to be safely used in other furnaces. Because of the nature of this particular process, we are able to recycle a great deal of material that would otherwise go to waste.

Faircast has grown greatly in a short period of time and will continue to grow by making use of the latest technologies and developing the best people in the business.

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