The iron frame, used in the piano as we know it today, was invented in 1825 by Alpheus Babcock (1785-1842). He was an employee of the Chickering Piano Co. U.S.A. who used an iron frame for the first time in their Grand Pianos in 1840.
Until iron reinforcement pieces were introduced to pianos in 1799, frames were generally made out of wood, which were liable to warp and twist under string tension, eventhough it was generally much lower than it is on a modern piano. An iron frame has the ability to withstand 19+ tons of string tension, along with increases in resonance, overall power and tuning stability.
There are 2 major types of casting for piano frames: sand cast & vacuum processed. With green sand casting (also known as wet sand casting), after the sand has been pressed into the desired shape, the pattern is removed from the sand, and a ‘negative’ imprint remains. Molten iron is poured into the mould, and when cool, the sand is broken away, leaving an exact shape behind, ready to be polished, primed & sprayed, to the manufacturers specifications.
The Vacuum mould casting process, also known as the V process, employs a sand mould that contains no moisture or binders. The internal cavity of the mould holds the shape of the casting due to forces exerted by the pressure of a vacuum. Vacuum moulding is a process that was developed in Japan around 1970.