GB605405A - Improvements in and relating to method of making patterns - Google Patents

Abstract

605,405. Moulding processes; patterns. BRIGGS MANUFACTURING CO. Dec. 21, 1945, No. 34749. Convention date, Dec. 26, 1944. [Class 83 (i)] A method of making a metal pattern comprises making a mould impression of an article to be reproduced, casting a pattern in the said impression with a metal or alloy having the property of growing uniformly in size when allowed to stand, allowing this intermediate pattern to grow to a predetermined oversize, making a mould impression of said oversize pattern casting and casting in metal a final pattern from the last-mentioned mould impression. The article or pattern 10 to be reproduced is placed in a flask 11 and a flowable mixture of plaster or calcined gypsum and water is poured in and allowed to set. The mould 12 thus produced is removed from the flask and inverted within a box 13, 14 having a cover-plate 16 formed with a pouring aperture 19 and with depending cooling ribs 18. A low melting-point metal or alloy having low shrinkage properties and which will grow when allowed to stand is melted and poured through the opening 19 to form a pattern 20. A suitable alloy is one known under the Registered Trade Mark " Cerrobase " and comprising 58 per cent bismuth and 42 per cent lead. This pattern is allowed to stand until it has grown to a predetermined extent, for example .005 inch per inch and is then used in the manner already described to form a plaster mould in which the final pattern is cast in a mould similar to that shown in Fig. 2. The amount of growth of the intermediate pattern may be such as to compensate for the shrinking of the final pattern and also for the shrinking of the casting formed therefrom.