GB748792A - Improvements in or relating to use of plaster of paris forms in making metal castings - Google Patents

Abstract

748,792. Moulds. HEINTZ CO., J. C. Oct. 14, 1953, No. 28310/53. Class 83 (1). In a method of casting the tread-forming part of a tyre-matrix, the bottom part of the mould is formed of plaster of Paris and the top is formed by a metal cover, preferably of cast iron, which serves as a chill. The plaster of Paris mould sections 50 are formed with runners 36, 52, and two of them with sprue openings 53 connecting with the runners 52. The sections are assembled on a baseplate 75, grooves 28 coacting with an annular bar 76, and are accurately centred with the aid of a gauge 88 on arm 85 rotatable about a central column 80. As a final step in the setting-up, the gauge may be replaced by a sanding block. The chill-ring or cover 90, its inner surface coated with china clay, is then positioned on the segments, guides 91 locating it, and is clamped by C-clamps 93, the plaster of Paris sections being also thereby held in place. Plaster of Paris risers are inserted in openings 96 in the cover, openings 97 in the risers co-operating with the runners 36 so that molten metal may flow to the mould cavity 98. Plaster of Paris pouring-sprues 100 are inserted in openings 101 and co-operate with the sprue-openings 53. Metal clips are pressed into cavities 39 between adjacent mould-sections and prevent leakage of molten metal from the runners 36 to the centre of the mould. Thickened areas 102, 103, with grooves 104 around the sprues and risers, prevent cracking of the chill-ring during expansion and contraction. Aluminium alloy is poured simultaneously, at 1250‹ F., into each of the two pouring-sprues 100. The mould cavity is vented through grooves 55 in the mould sections and opening 107 in the cover. After casting, the chill-ring is removed, the plaster of Paris mould sections broken away, and the cast tyre-matrix cleaned by air blast. During its cooling, a cast iron ring is inserted in the matrix to prevent distortion while shrinking. Specification 748,818 is referred to.