Practical approach to continuous casting of copper alloys and precious metals A PDF

Introduction Continuous casting of non-ferrous metals applying the closed head immersed die system with intermittent pulse withdrawal has been practised for well over 100 years. The first patents covering vertical casting of non-ferrous metals was in 1840-43 by Sellers" and Laign ' with horizontal casting some considerable time later by Peherson" in 1914. The equipment described in the early vertical casting patents very closely resembles the equipment used in modern casting processes, indicating, even today, the use of a relatively simple system of 'continuous solidification and withdrawal from a shaping mould'. The process has many advantages over static ingot and book mould casting, the most important being improved yield, reduced energy consumption and reduction in manpower, thus reducing production costs significantly. This book is intended to provide an account of how continuous casting technology has developed and how the process can be used within an engineering environment, casting a range of copper based alloys, precious metals including gold and silver and selected nickel alloys. The text is confined to the closed-head immersed die process applying intermittent withdrawal and is approached from a practical aspect. Wheel casting, although accounting for very large tonnage copper production, is a highly specialised technology, and apart from a brief description of the process, is not within the scope of this book.

Chapter 1 gives a brief historical background to continuous casting of non-ferrous metals with some insight into the evolution of the casting plant. Furnace design is discussed covering resistance-heated all-graphite system and induction-heated furnaces. Vertical, horizontal and upcasting systems are reviewed.

Die and cooler design are discussed in detail. Withdrawal systems are examined together with process control and monitoring. The final part of the section gives an in-depth study of casting practice.

Chapter 2 is concerned with heat transfer within the mould or casting die from a practical aspect only. The influence of die cooler design and withdrawal characteristics on the coefficient of heat transfer and solidification morphology are examined. Boundary heat transfer and heat tranfer along the mould are discussed. The heat balance equation applied to practical casting programmes illustrate its application in determining thermal efficiency of the system.

Chapter 3 describes the range of continuous casting equipment available from suppliers. Special systems such as wheel casting are discussed although not in detail.

Chapter 4 outlines graphite technology as applied to continuous casting giving a brief account of manufacture and data on all relevant properties. Suppliers of die quality graphites are listed and recommended grades cross referenced for all casting applications.

Chapter 5 deals with copper and copper based alloys. Casting of strip, rod and hollow section in horizontal and vertical mode is described and account of the upcasting method used primarily on high conductivity copper. Examples are given of casting runs on selected alloy systems giving guidance on process control. Deoxidation of copper is discussed fairly extensively.

Improved alloy systems, such as Cu-Mg replacing Cu-Cd, and the introduction of Cu-Bi alloys as an alternative to Cu-Pb free machining alloys used in potable water plumbing systems are outlined.

Chapter 6 deals with precious metal casting in a similar way to the previous chapter on copper. Fine gold and the carat alloys are considered fairly extensively and examples of casting runs are discussed. Most of the carat alloys are confined to ternary systems with additional trace metal additions. These are discussed in relation to published data on phase diagrams on gold alloys. This information is useful in understanding the freezing characteristics and ascertaining the solidification range which is not always available. A wide range of industrial golds are now continuous cast. Fine silver and sterling silver are examined together with industrial alloys such as Ag-Mg-Ni. Dental and brazing alloys are also considered in the precious metal section.

The final Chapter covers alloys which dissolve or are aggressive to graphite. Ceramic crucible containment is considered and die material, generally a modified boron nitride, is discussed The metal systems such as high nickel and nickel chrome alloys and precious metal engineering alloys such as Au-Ag-Pd and Au-Ag-Pd-Pt are considered. Methods for casting Tin-lead alloys which are not suitable for processing through graphite dies are discussed. The principle of 'break ring' casting is briefly mentioned and the features of the OHNO Continuous Casting Process with a unidirectionally solidified structure with no equiaxed crystals is also included.

Edited by: Robert Wilson