THE MANUFACTURE OF SEWER-PIPE.
THE clay from which sewer-pipe are made is a grade of fire clay. Much care is required to be exercised by those who select the clay from which sewer-pipe are manufactured. The coarse, open, non-plastic clay used for fire-brick will not answer the required purpose. Earthenware pipe of this char acter require that the clay shall be plastic, so as to form a close homogeneous body similar to that used for architectural terra cotta. It is also desirable that the should contain a large proportion of silica, which is of material assistance in applying the salt glaze, as will be hereafter explained.
There are two quite well marked ways of making sewer-pipe in the State of Ohio, which leads to their classification usually as the river process (that used in the Ohio Valley in Jefferson county), and the Akron process (used at Akron and Colum bus). The process is the same in all cases, and even extends into the manufacture of fire-brick as far as the grinding and tempering goes.
When the clay has been ground, sifted and tempered, it is usually elevated by a belt to the upper story of the works, and deposited in a bin beside the top of the sewer-pipe press. All sewer-pipe machines act on the same principle, but the mechanical details differ.
The pipe-press consists of a large steam cylinder, upon a high iron ; the piston runs into a second cylinder of less diameter situated beneath it ; this is called the mud-drum or mud-cylinder, and into it the clay to be pressed is introduced, and from its lower end it is forced out as pipe by the pressure from the upper or steam cylinder. The piston at the upper limit of the stroke leaves a passage into the inside of the mud drum near the top, which is closed as the piston moves down further. Into this opening is shoveled the tempered clay. It is tempered so dry that it may be shoveled with perfect ease, and it has no tendency to stick together by contact alone, though it does so readily by pressure. The cylinder being filled with clay, the piston is given steam and moves down slowly, consolidating the clay and expressing the inclosed air through small holes in the piston-head and the cylinder bot tom. When, through these holes, the clay begins to issue, the pressman knows that the clay has filled the shape of the cavity perfectly ; and as the bottom is a movable one, it is loosened and dropped upon a balanced platform close beneath it. This
platform under the weight of the cylinder head, which is so shaped as to form the pipe, is just counter-balanced, and by any pressure can be moved up or down, carrying the socket shaper on its top. The bottom being pushed out of the way, continued pressure from above causes the pipe to issue. When enough has come out, it is cut off by a rotary knife from the inside, and the separated length of pipe is carried away either on a cart or in the hands. It is next sponged and pared, to smooth it. The pipe is shaped by being forced out between the walls of the mud-drum and a conical core which is sus pended from higher up in the drum. This cone parts the clay evenly on all sides, and causes it to leave the press in an even, regular shape and thickness. The dimensions of the presses used are various ; the Pittsburgh press at Walker's has a steam cylinder 44 inches in diameter, and 23 inches of mud-drum. The ordinary diameter is from 35 to 36 inches, and about 18 inch mud-drum.
The river works make this pipe just as easily as they do the thinner kinds, and they claim an advantage here over their competitors who make no thick pipe.
The differences in the manufacture of pipe in the Akron and Columbus district from the river process begin in the material employed. The grinding machinery of the Akron district con sist of the machines called tracers. The tracer is an excellent machine for grinding a true clay of a sandy or plastic nature, and though its work in shale is successful, yet it seems as if the heavy wet mill of a fire-brick works could not fail to be better. It would at any rate grind much more in the same time than the tracer, if it did not grind it any better. The frac ture of an Akron made sewer-pipe shows frequently small pieces of shale which have escaped the wheels, and in burning, these pieces usually shrink away from the bond clay so as to make a loose spot in the pipe, and they are consequently weakening in their effect.