Cannon casting consists of a long process of molding, casting, cooling, and finishing.  Molding consisted of placing a pattern of the gun to be cast in a box, termed a flask, which was arranged to allow the escape of air and steam.  Next, the flask was injected with sand, which after being removed, left a cavity into which the melted iron could be poured.  Upon assembly, the mold would be thoroughly dried.
    Next the mold was placed in a pit and readied for casting, where it would be filled with either bronze, a mixture of nine parts copper to one part tin, or iron.  Tennessee (as well as the rest of the South) had no facilities for casting steel guns.  Once the proper metal had melted, the workmen poured it into the mold, from the bottom up.  The workmen agitated the mold as it filled with a long rod to bring the impurities to the top.  This process took between five and ten minutes, and then the workmen removed the flask for the cooling process.
    Cooling created stress and strain on the gun.  In an effort to prevent this as much as possible, the flask was placed in a pit and surrounded by sand and charcoal.  Here it stayed for three to six days, depending on it size.  When it finished cooling, the flask was removed from the pit.
    Last came the finishing process.  The rough casting was placed in a lathe and the exterior turned and finished.  The cannon was bored, and then the trunnions were machined to size.  Before completing the process, the exterior was finished and the vent drilled.

    In the 1840s T. J. Rodman invented a new revolutionary method of casting. He created the method to overcome the cracks and weak spots that developed in larger tubes cast under the traditional method.  His new method allowed guns to be cast on a hollow core with water continuously flowing in and out.  Using the old method, weapons cooled from the outside.  Each successive ring to cool would thus tend to shrink away from that which had already cooled, producing voids and tension cracks.  The Rodman method of cooling occurred from the inside out, so that successive shrinkage of each layer produced compression instead of tension.  This method resulted in the ability to produce stronger and heavier guns.
    No Southern foundry adopted this method of casting until late in the war, but no guns were ever produced by the South using it.
 

  Return to Cannon Foundries page

Last update:  May 5, 2000