Does anyone know the actual method used to compress fluid steel within the ingot mold? Since fluids are relatively incompressible, and I think it would be problematic to compress molten steel anyway, I wonder just how Sir Joseph Whitworth and others accomplished this.
I am familiar with "Capped Heats" where molten steel is poured into the ingot mold. Then bags of additives called rare earth were tossed into the molds on top of the molten steel. Then, a heavy cap was placed by the overhead ladle crane, on top of the mold opening to seal it. I was told that the rare earth degassed the steel and caused gas pockets and impurities within the steel to rise to the top. I was also told this was a somewhat dangerous process because pressure would build up within the capped ingot mold, and sometimes they would blow up. I saw this process when I worked in the Electric Furnace Dept. of a steel mill for a short time after college. It sticks in my mind because I was assigned by the boss to put on a set of woolies and stand by on the pouring platform to substitute for anyone who got "f***ed-up if a cap blows." Thankfully, there were no explosions that night.
