Tube (Lat. tuba), a pipe or hollow cylinder. Tubes play an important part in engineering and other works for the conveyance of liquids or gases, and are made of diverse materials and dimensions according to the purpose for which they are intended, metal pipes being of the greatest consequence. According to the process of manufacture metal tubes may be divided into seamed and seamless. One of the earliest uses of seamed wrought-iron tubes was for gun-barrels, and formerly these were made by taking a strip of wrought iron, bending it so that the edges overlapped and then welding by hammering, with or without the aid of grooved swages. The development of gas lighting increased the demand for tubes, and in 1824 James Russell introduced the butt-welded tube, in which the edges of the skelp are not made to overlap, but are brought into closest possible contact and the welding is effected in a double swage, having corresponding grooves of the diameter of the tube required; this method required no ma,ndrel as did those previously in use. The following year saw another improvement in making these pipes, when Cornelius Whitehouse effected a butt weld by drawing the bent skelp through a die. Stronger tubes are obtained by using grooved rollers instead of a die, the skelp being mounted on a mandrel. This is the method commonly adopted at the present day for making this class of tube. Seamed tubes, especially of copper and brass, are made by brazing or soldering the edges of the skelp. Another method is to bend the edges so that they interlock, the contact being perfected by rolling. Seamless tubes, which are stronger than those just described, are made by drawing a bloom of the metal perforated by an axial hole or provided with a core of some refractory material, or, in certain cases, by forcing the plastic metal by hydraulic pressure through an appropriate die. The seamless steel tube industry is now of great dimensions owing to the development of steam engineering. Another type of seamless tube is the cast-iron tube,. usually of large diameter and employed for gas and water mains; these pipes are made by casting.
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