|
A jackhammer (pneumatic drill or demolition hammer in British English) is a pneumatic or electro-mechanical tool that combines a hammer directly with a chisel. It was invented by Charles Brady King.〔(STEAM OR PNEUMATIC ENGINE )〕 Hand-held jackhammers are generally powered by compressed air, but some are also powered by electric motors. Larger jackhammers, such as rig mounted hammers used on construction machinery, are usually hydraulically powered. They are usually used to break up rock, pavement, and concrete. A jackhammer operates by driving an ''internal'' hammer up and down. The hammer is first driven down to strike the back of the ''bit'' and then back up to return the hammer to the original position to repeat the cycle. The bit usually recovers from the stroke by means of a spring. The effectiveness of the jackhammer is dependent on how much force is applied to the tool. In British English electromechanical versions are colloquially known as "Kangos". == History == Pneumatic drills were developed in response to the needs of mining, quarrying, excavating, and tunneling. The first "percussion drill" was made in 1848 and patented in 1849 by Jonathan J. Couch of Philadelphia, Pennsylvania.〔Henry S. Drinker,''Tunneling, explosive compounds, and rock drills'' … (New York, New York: John Wiley & Sons, 1878), (pages 153-157 ).〕 In this drill, the drill bit passed through the piston of a steam engine. The piston snagged the drill bit and hurled it against the rock face. It was an experimental model. In 1849, Couch's assistant, Joseph W. Fowle, filed a patent caveat for a percussion drill of his own design. In Fowle’s drill, the drill bit was connected directly to the piston in the steam cylinder; specifically, the drill bit was connected to the piston’s crosshead. The drill also had a mechanism for turning the drill bit around its axis between strokes and for advancing the drill as the hole deepened.〔Drinker (1878), page 160.〕 By 1850 or 1851, Fowle was using compressed air to drive his drill, making it the first true pneumatic drill.〔Drinker (1878), page 164.〕 The demand for pneumatic drills was driven especially by miners and tunnelers, because steam engines needed fires to operate and the ventilation in mines and tunnels was inadequate to vent the fires' fumes; there was also no way to convey steam over long distances (e.g., from the surface to the bottom of a mine); and mines and tunnels occasionally contained flammable explosive gases such as methane. By contrast, compressed air could be conveyed over long distances without loss of its energy, and after the compressed air had been used to power equipment, it could ventilate a mine or tunnel. In Europe since the late 1840s, the king of Sardinia, Carlo Alberto, had been contemplating the excavation of a tunnel through Mount Fréjus to create a rail link between Italy and France, which would cross his realm.〔Drinker (1878), page 266.〕〔The project was called the "Mount Cenis tunnel" although the tunnel passed under Mount Fréjus.〕 The need for a mechanical rock drill was obvious and this sparked research on pneumatic rock drills in Europe. A Frenchman, Cavé, designed, and in 1851 patented, a rock drill that used compressed air; but the air had to be admitted manually to the cylinder during each stroke, so it was not successful.〔Drinker (1878), page 152.〕 In 1854, in England, Thomas Bartlett made and then patented (1855) a rock drill whose drill bit was connected directly to the piston of a steam engine. In 1855 Bartlett demonstrated his drill, powered by compressed air, to officials of the Mt. Fréjus tunnel project.〔Drinker (1878), pages 168 and 266.〕 (In 1855, a German, Schumann, invented a similar pneumatic rock drill in Freiburg, Germany.〔Drinker (1878), pages 151-152.〕) Bartlett’s drill was refined by the Savoy-born engineer Germain Sommeiller (1815-1871) and his colleagues, Grandis and Grattoni, by 1861.〔Drinker (1878), pages 169 and 266.〕 Thereafter, many inventors refined the pneumatic drill.〔See: Drinker (1878), page 168. See also: (page 2 ) of Eustace M. Weston, ''Rock drills: design, construction and use'' (New York, New York: McGraw-Hill, 1910).〕 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「jackhammer」の詳細全文を読む スポンサード リンク
|