Читать книгу Henley's Formulas, Recipes and Processes (Applied Chemistry) - Various - Страница 686

—I.—It is often difficult to form flat back or half castings out of the softer metals so that they will run full, owing mostly to the thin edges and frail connections. Instead of using solid metal backs for the molds it is better to use cardboard, or heavy, smooth paper, fastened to a wooden board fitted to the back of the other half of the mold. By this means very thin castings may be produced that would be more difficult with a solid metal back.

II.—To obtain a full casting in brass molds for soft metal two important points should be observed. One is to have the deep recesses vented so the air will escape, and the other is to have the mold properly blued. The bluing is best done by dipping the mold in sulphuric acid, then placing it on a gas stove until the mold is a dark color. Unless this bluing is done it will be impossible to obtain a sharp casting.