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A steam hammer is a power hammer driven by steam. It is used for tasks such as shaping forgings and driving piles. Typically the hammer is attached to a piston that slides within a fixed cylinder, but in some designs the hammer is attached to a cylinder that slides along a fixed piston. The concept of the steam hammer was described by James Watt in 1784, but it was not until 1840 that the first working steam hammer was built to meet the needs of forging increasingly large iron or steel components. In 1843 there was an acrimonious dispute between François Bourdon of France and James Nasmyth of Britain over who had invented the machine. Bourdon had built the first working machine, but Nasmyth claimed it was built from a copy of his design. Steam hammers proved to be invaluable in many industrial processes. Technical improvements gave greater control over the force delivered, greater longevity, greater efficiency and greater power. A steam hammer built in 1891 by the Bethlehem Iron Company delivered a 125-ton blow. In the 20th century steam hammers were gradually displaced in forging by mechanical and hydraulic presses, but some are still in use. Compressed air power hammers, descendants of the early steam hammers, are still manufactured. ==Mechanism== A single-acting steam hammer is raised by the pressure of steam injected into the lower part of a cylinder and drops under gravity when the pressure is released. With the more common double-acting steam hammer, steam is also used to push the ram down, giving a more powerful blow at the die. The weight of the ram may range from . The piece being worked is placed between a bottom die resting on an anvil block and a top die attached to the ram (hammer). Hammers are subject to repeated concussion, which could cause fracturing of cast iron components. The early hammers were therefore made from a number of parts bolted together. This made it cheaper to replace broken parts, and also gave a degree of elasticity that made fracture less likely. A steam hammer may have one or two supporting frames. The single frame design lets the operator move around the dies more easily, while the double frame can support a more powerful hammer. The frame(s) and the anvil block are mounted on wooden beams that protect the concrete foundations by absorbing the shock. Deep foundations are needed, but a large steam drop hammer will still shake the building that holds it. This may be solved with a counterblow steam hammer, in which two converging rams drive the top and bottom dies together. The upper ram is driven down and the lower ram is pulled or driven up. These hammers produce a large impact and can make large forgings. They can be installed with smaller foundations than anvil hammers of similar force. Counterblow hammers are not often used in the United States, but are common in Europe. With some early steam hammers an operator moved the valves by hand, controlling each blow. With others the valve action was automatic, allowing for rapid repetitive hammering. Automatic hammers could give an elastic blow, where steam cushioned the piston towards the end of the down stroke, or a dead blow with no cushioning. The elastic blow gave a quicker rate of hammering, but less force than the dead blow. Machines were built that could run in either mode according to the job requirement. The force of the blow could be controlled by varying the amount of steam introduced to cushion the blow. A modern air/steam hammer can deliver up to 300 blows per minute. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「steam hammer」の詳細全文を読む スポンサード リンク
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