Page:The American Cyclopædia (1879) Volume IV.djvu/85

 CASTING 77 FIG. 11. Section of Mould. surfaces of both parts of the mould, and the cope is gently replaced and secured with keys or clamps. The relation of the parts as they now exist is represented in section in fig. 11. All that now remains to be done is to melt the metal and pour it into the mould ; a criti- cal operation, requir- ing much care, and not safely performed ex- cept by experienced moulders. The pouring is done from iron pots lined with clay, called ladles. They are of various forms and sizes, to suit the work to be done. Some have one handle, and are intended to be carried by one man. Others have the form repre- sented in fig. 5, but with longer handles, capa- ble of holding from 200 to 300 Ibs., and are carried by two or more men. When the moulds are ready the furnace is charged in the manner already described, and one of the large carrying pots is placed under the spout. The melting point of cast iron varies somewhat, owing to its freedom from other metals and the quantity of carbon which it contains. Hard, gray cast iron melts at about 2,900 F. Scotch pig melts at a lower temperature than many other kinds, because of its large quantity of carbon. The best American iron is harder, contains less carbon, and requires more heat to melt it. It is a common practice among foun- ders to melt different brands oif iron together to give the mixture desired characteristics which they do not possess separately. The practice varies at different establishments, each founder having his own favorite formulas. When a sufficient quantity of metal in the cu- pola has attained the proper degree of fluidity, the clay stopper or plug is removed by the workman whose special duty it is to attend to the filling of the pots, and the molten iron is caught in the vessels which are held under the spout. Two or three men usually pour into one mould at the same time, through different gateways or holes, by which means the streams of metal, having a shorter distance to run than if poured through one gate, have less risk of losing the proper degree of fluidity by cooling. It is a common practice in founderies to pour the metal in the afternoon. The smaller arti- cles are taken from the flasks the same evening, and the larger ones on the following morning. After the sand is rubbed from them they are carried to an adjoining apartment, where any roughnesses are chipped away by the chisel, and they are otherwise suitably finished. Hol- low articles are often cast in moulds composed of parts, some of which are of greensand and some of dry sand or loam. The casting of a hollow column is an example. The outer part of the mould is made in a flask of two parts with greensand, from a solid pattern of the column. A core somewhat longer than the mould, made of a mixture of sand and paste, baked dry, is then placed in the axis of the hollow mould, its extremities resting upon the sand beyond. The thickness of the walls of the column will of course be in inverse propor- tion to the size of the core. Small columns may be cast lying horizontally, but larger ones d FIG. 12. Mould for a Column. should be cast vertically, and, if of much height, in sections. If cast lying down, they are liable to warp and to be of inferior strength in conse- quence of the opposite sides wanting uniformity of molecular structure and density. The cast- ing of long, slender articles, such as ornamen- tal railings, is simplified by a method patent- ed by Mr. Jobson in England. He secures a finished brass or iron pattern to a plaster of Paris back or ramming block, upon which the mould is formed. When the model is removed the mould remains in the drag. A cop'e with a plane surface, or having a device correspond- ing to the other side of the pattern, and which has been formed from a reverse block, is then placed over the mould, and the necessary holes having been prepared, the metal is poured. Mr. James L. Jackson, of New York, has ta- ken out a patent for making patterns entirely of plaster of Paris and other plastic materials, thereby greatly reducing their cost. They are swept with a templet which may be made to move in either straight or curved lines. The labor and time of making the large and accu- rate castings for the fronts of buildings are by this process very greatly reduced. A bed piece or rest, of plaster, is first swept with a templet, and after the surface of this is properly pre- pared, another layer of plaster mixture is spread on, and this swept with a templet of corresponding form but of larger size. In moulding, the pattern lies upon the rest when the first side is rammed in the drag. When the pattern is long it is sawed into transverse sections to facilitate the handling. These may be adjusted together and will serve the pur- pose of a whole piece. Greensand moulding is often practised with only part of a flask, the cope, the sand bed of the floor taking the place of the drag. A bed is carefully pre- pared and levelled, the pattern imbedded in its surface, and the sand well rammed about it. The pattern is then carefully cleaned and the surface of the bed levelled and dressed, leaving a certain portion of the pattern projecting above the surface. Parting sand is then sprinkled over both pattern and bed, and a cope is laid down and rammed, it being prop-