Coupling.— Pipe couplings are made from bars of iron corresponding to the width and thickness of the desired coupling. The smaller sizes are made by a machine which cuts up the bar into the proper lengths and forms up the pieces on a mandrel with great rapidity. These pieces are then heated in a welding furnace and welded under the blows of a quick-acting steam hammer. The larger sizes are made from bar iron of the proper length, which is formed up by a machine consisting of a vertical cylin drical mandrel of a diameter equal to that of the desired coupling. A vertical roller attached to the end of a horizontal arm travels around the mandrel. One end of the heated bar is placed between the mandrel and the roller; the roller is then revolved around the mandrel and bends the bar into the required circular form. The piece is then reheated, slipped over a cylindrical mandrel and the joint welded under 'the blows of a quick-acting steam hammer.
Varieties.— Spiral-riveted and spiral-welded pipes are made by winding thin iron plates spirally around a mandrel into tubular forms, and the overlapping edges riveted or welded together. They are made in standard lengths of 20 feet and range from 3 to 24 inches in diameter. The metal plates used range from .035 to .109 inch in thickness. They are capa ble of withstanding bursting pressures up to 1,330 pounds to the square inch.
The locking-bar pipes are made of two semi circular plates of metal joined together longi tudinally by a channel bar of soft steel, the flanges of which are pressed into the edges of the plates until a tight joint is effected. The earliest forms of wood pipes were simply bored logs. Their first use as a continuous tube was the six-foot penstock built at Manchester, N. H. in 1874, •by J. T. Fanning. The use of metal bands around wood-stave pipes was first sug gested in 1880 and were first extensively used in Denver, Colo., in 1883. This particular kind of pipe is built in a trench. The staves are of different lengths, which allows continuous con struction. They are bound together by light metal rods or hands provided with screw ends and nuts for tightening. These rods are spaced on the pipe according to the amount of in ternal pressure they are expected to withstand. The staves used are thin enough to secure com plete saturation and to deflect readily to the curvature employed; yet, thick enough to pre vent an undesirable amount of percolation through them. The proportion between the thickness of the staves and the strength of the hands is such that the swelling of the wood does not produce injurious strains upon the bands. Such pipes or conduits range from 10
to 72 inches in diameter ; are capable of with standing pressures as high as 1,100 pounds to the square inch, and have done service, in the United States, for periods ranging from 20 to 50 years, without any material deterioration.
Fibre Pipe.— Fibre pipes are made by wind ing sheets of wood pulp around a core. The desired thickness being obtained, the tubes are saturated with a wood preserving solution and dried. The joints at the ends are turned in a lathe and they are provided with screw coup lings. They may be made in any size or thick ness, but usually range from one to eight inches in diameter, with a uniform length of five feet. Being made of a non-corrosive material, they are especially useful for conveying chemicals.
Clay Pipe.— Earthenware or terra-cotta pipes are represented by the various forms of drain tiles, designedly made porous or vitrified, and with or without joint sockets, according to the purposes for which they are used. They were first made in England about the close of the 18th century and were mere cylinders of porous baked clay. In recent years their manu facture has attained the proportions of a great industry. They are produced by forcing pre pared plastic clay through a die into the form of a continuous tube, which is subsequently cut up into shorter lengths and thejoint sockets molded by a special machine. They are then baked in kilns by a very high temperature. The vitrified variety are glazed by the introduction of salt into the fire holes of the kilns while the pipes are being baked, so that the salt is volatilized and combines with the silica in the clay. They range from 1% to 36 inches in diameter and from one to three feet in length. Pipes are also made of cement and concrete. They are usually molded in place by the use of a movable mold and core, which is shifted along the work or by stationary built up molds, which are torn out after the cement has set. Wire nettings and iron rods are often inserted in the cement to give additional strength.
Bibliography.— Special articles may be found in the files of following named publica tions: Engineering News, New York; Street Railway Review, Chicago; Journal Am. Soc. of Naval Engineers, Washington; Progressive Age, New York; Scientific American Engineer ing Record, New York; Engineer, London; Engineering, London. Consult also Rjorling. P. R., and Tubes' (New York 1908); Sharp, John, Some Considerations Regarding Cast-Iron and Steel Pipes> (1914).