PIPE, Manufacture of. Pipes are hollow cylinders made of various materials and used as conduits for liquids, air or gas. The ma terial of construction varies according to the character of. the substance to be conveyed, its availability in any particular locality and its relative cheapness. They may be divided into five general classes characterized by the ma terials of which they are made — metal, wood, earthenware, cement and rubber. Metal pipes are made of lead, block-tin, zinc, brass, copper, cast iron, wrought iron and steel. Lead pipes have been used from the earliest times. Up to the close of the 15th century, they were made of sheet lead bent around a metal core and welded or soldered along the horizontal joint. About the beginning of the 16th century, a casting method was invented by Robert Brooke, which was extensively employed in England up to the close of the 18th century, when it was superseded by the pressing and drawing methods in use at the present time. They are made in continuous length, by squeezing the molten metal through a die (a steel plate perforated with a hole containing a central core) by hydraulic pressure. Different sizes of pipes are produced by changing the dies, the cores of the dies determining the diameter of the bores. Sizes of pipes are designated according to the measurement of their internal diameters. Lead water-pipes range from three-eighths to five inches, while the waste pipes range from one and one-half to five inches. Lead pipes as small as one-sixteenth of an inch and as large as eight inches are made for various purposes. The high cost of lead and the great thickness of metal required to withstand high press pres practically prohibit the production of the larger sizes. Pipes of ductile metal, such as block-tin, brass and copper, are made by draw ing methods. An ingot of metal is cast in cylindrical shape with a conical end and with a hole through its axis corresponding in size to the bore of the desired pipe. A mandrel (long iron rod) is thrust into the hole so that it projects slightly beyond the conical end.
This end is then placed in a funnel-shaped hole drilled through a steel post fixed to the draw ing table and gripped at the outer end by a pair of pincers at the end of a chain attached to the power machinery. The ingot together with the mandrel is then drawn through the hole, the former being thus extended uniformly over the latter in the form of a complete pipe. Unlike the pressure method, the metal is drawn cold and often requires annealing, as it hardens under the repeated drawings. Block-tin pipes are used in soda fountains and as conveyors of Leer and chemicals. Copper pipes are used in distilleries, and when employed in chemical works are tin-plated within to protect them from corrosion. Brass is generally used for pipes exposed to great heat, such as the tubes of steam boilers, etc. Block-tin pipes range from three-eighths to two and one-half inches in diameter.
In making cast-iron pipes, the mold used consists of two parts — the core which shapes the interior and the flask which bolds the pattern for the exterior form. The core is made by winding a hay-rope around a spindle and coating it with several layers of clay. It is then shaped in a lathe to the desired size and dried in an oven. Tempered clay and sand are rammed around the pattern in the flask and then dried in an oven to form a mold. The pattern is then removed the flask is placed in a vertical position and the core exactly central within it. The molten metal is run into the space between the mold and the core and, when partly cooled, the core is drawn out and the interior of the pipe is coated with asphaltum to prevent corrosion. In size they range front two to 60 inches and are made in standard lengths of 12 feet. The larger pipes are generally cast in shorter. lengths in order to keep down the weight of the individual pipes so as to permit convenient handling. They are used for water mains, pneumatic tubes, exterior casings for other tubes and pipes, etc.