Practical Requisites In Hand Molding

Devising methods for increasing production and decreasing its cost is one of the important problems of modern engineering in the foundry as well as elsewhere. In the jobbing foundry where there is a great variety not only in the patterns themselves, but in the number of castings called for from each pattern, the molder makes up a sand match as already described. On this match he arranges such an assortment of patterns as will fill his flask, and beds them into place. From a well-made sand match two or three hundred molds may be made up. When the desired number of castings is made from one pattern on the match, that one is removed and another one which fits in its place is substituted.

Gated Pattern

For manufacturing purposes thousands of the same casting may be required, calling for more durable patterns and match. Metal patterns are made and as many as can be cast in a flask are soldered to a smoothly finished metal gate pattern. With a draw screw inserted in this gate, all of the patterns may be drawn at once. Two steady pins should be screwed and sweated into the drag side of the gate pattern. These should be of small round brass rod and should project below the deepest point of the patterns, for they guide the pattern as it is being drawn and prevent it from swaying and breaking the edges just as it leaves the sand. Patterns so arranged are termed gated patterns.

Permanent Match

When such patterns have a flat joint, a special mold board should be provided, and the patterns stored on the same board. When the joint is irregular, a permanent oil match should be made. Make a strong hardwood frame the size of the flask and about 1 inch deep, with the bottom board arranged to screw on to the back. Nails should be driven into the inner sides hanging parallel to the bottom board. Measure the quantity of sand needed to fill this match. Mix thoroughly and, while dry, put through a fine sieve one-half this quantity of burnt sand, one-half new molding sand, and about one-fortieth litharge. Temper the same as molding sand, using boiled linseed oil. Ram up the drag and joint the mold very carefully. Put on the match frame and ram up with the above mixture; strike off, and screw on the bottom board. Remove the drag and allow the match to dry for a day with the patterns left in it. A coat of shellac when dry improves the surface. Fig. 88 shows a set of gated patterns bedded in a hard match.