Dry Sand Moulding is frequently done in connection with green sand. It is employed where a easting is of a complicated design. The method pursued is to make a partial pattern with it core print; then make a flask to lit this print and in it mould the balance of the pattern, using dry instead of green sand. This mould is then baked in the same manner as an ordinary core which is set in the print formed by the main pattern.
Sometimes the whole mould is made of dry sand. This is frequently done in the case of cylinders for steam engines. Let us consider such an example. The cylinder to be moulded is shown in side and end elevation in Fig. 57. The method of moulding is shown in Fig. 58. The actual moulding is very similar to that of green sand work. The pattern is made in two parts. The part including the steam chest is moulded in the drug. It has core. prints to correspond to the cores a a. These cores are made in a special box which forms at the same time the flange of the Steam chest. This half of the cylinder pattern also has core prints b, b, c for the port cores. The pattern is moulded in the ordinary way: first the drag and then the cope. The cores a a and those for the steam and exhaust ports arc made and dried as explained in "Pattern Making," page 56, As the core a a has an overhang which forms the flange of the steam chest and as that overhang is subjected to the upward pressure of metal, it is tied to the main body of the core by double headed chaplets f f. The cores d d and g, forming the ports are also subjected to an upward pressure. They arc, therefore, held down by bolts passing through the drag and plates on the bottom. As the cores d d are light and easily displaced by the flow of metal, they are held firmly against the center core by the chaplets e e. In this case the center core A is carried out through the side of the flask. This assists in carrying off the gases that are formed as it is not a solid core but is built upon a pipe as will be described later. This pipe has numerous holes so that it forms a Hue in the center of the mass for the escape of gas. In making large dry sand moulds of this sort, the sand is well vented before being dried. Sometimes short lengths of perforated pipe are built into the sand to facilitate this escape. The cope is rammed and set on the drag as in green sand, except that it is dried before being used.