Thin wall castings

Abstract

The fundamental concepts of alloy fluidity and liquid flow are examined to highlight the main problems in the production of thin walled castings and to identify areas where research is required. Subjects covered include the problems of entrained oxides of varying degrees of severity, and the introduction of the concept of ‘old’ and ‘new’ oxide and other films. The limitations of direct gating (the usual method of gating in which the metal is plumbed directly into the mould) are examined, and the hairpin runner and slot gate is considered in some detail as a major potential solution to thin wall casting production. The limiting conditions of flowrate are examined with indications that speed is not necessarily required to cast thin sections. The instabilities assessed by Weber and Froude numbers are areas for future work, and unintentional variations in section thickness are shown to be extremely deleterious, underlining the importance of accurate tooling and accurate moulds. The confluence weld is introduced as a new concept in metal castings. This and other filling difficulties are examined for complex castings, as are the benefits of filters. Some current achievements in thin wall castings are given as examples.

MST/741