Forging of Large Pieces by Hydraulic Press
Of late years much forging has been done, not by the hammer which gives such a sudden, superficial blow with shallow working of the piece, but by hydraulic or other press, which very slowly squeezes the hot piece to smaller and longer shape. Sir Henry Bessemer was one of the first to realize the advantages of and make use of the press for steel working.
Unlike the hammer the press exerts a deep working of the piece which can be seen to flow throughout under the stress rather than in surface only as occurs under the hammer. This is very desirable as the interior, which is known to have much coarser grain than outer parts, particularly needs to be “worked.” In plainer terms the press seems to knead the mass much as the bread-maker kneads dough, while the hammering method simply batters down the outside. At a glance an experienced eye can tell from the appearance of the end of a forging whether it has been pressed or hammered.
A Modern Hydraulic Forging Press
Pressures as high as 8,000 pounds per square inch are used in hydraulic presses, though much lower pressures are more common.