1 Component Casting

1 Component Casting 1.1 Introduction 1 1.1.2 Industrial Component Casting Processes 1.1.1 History of Casting 1 As a preparation for a casting process the metal is initially 1.1.2 Industrial Component Casting Processes 1 rendered molten in an oven. The melt is transferred to a so- 1.2 Casting of Components 1 called ladle, which is a metal container lined on the inside 1.2.1 Production of Moulds 1 with fireproof brick. The melt will then solidify for further 1.2.2 Metal Melt Pressure on Moulds and Cores 4 refining in the production chain. This is performed by trans- 1.2.3 Casting in Nonrecurrent Moulds 5 ferring the melt from the ladle into a mould of sand or a 1.2.4 Casting in Permanent Moulds 8 water-chilled, so-called chill-mould of metal. The metal 1.2.5 Thixomoulding 11 melt is then allowed to solidify in the mould or chill-mould. This chapter is a review of the most common and most important industrial processes of component casting. The 1.1 INTRODUCTION problems associated with the various methods are discussed briefly when the methods are described. These problems are 1.1.1 History of Casting general and will be extensively analysed in later chapters. As early as 4000 years BC the art of forming metals by In Chapter 2 the methods used in cast houses will be casting was known. The process of casting has not really described. The methods used in foundries to produce com- changed during the following millennia, for example during ponents will be discussed below. the Bronze Age (from about 2000 BC to 400–500 BC), during the Iron Age (from about 1100–400 BC to the Viking Age 800–1050 AD), during the entire Middle Ages and 1.2 CASTING OF COMPONENTS the Renaissance up until the middle of the Nineteenth century. Complete castings were prepared and used directly 1.2.1 Production of Moulds without any further plastic forming. Figures 1.1, 1.2 and 1.3 show some very old castings. A cast-metal component or a casting is an object that has In addition to improving the known methods of produc- been produced by solidification of a melt in a mould. The tion and refining of cast metals, new casting methods were mould contains a hollow space, the mould cavity, which invented during the Nineteenth century. Not only were in every detail has a shape identical to that of the component. components produced but also raw materials, such as bil- In order to produce the planned component, a reproduc- lets, blooms and slabs. The material qualities were tion of it is made of wood, plastic, metal or other suitable improved by plastic forming, forging and rolling. An infe- material. This reproduction is called a pattern. During the rior primary casting result cannot be compensated for or production of the mould, the pattern is usually placed in a repaired later in the production process. mould frame, which is called a flask or moulding box. The Steel billets, blooms and slabs were initially produced by flask is then filled with a moulding mixture which is com- the aid of ingot casting and, from the middle of the Twen- pacted (by machine) or rammed (with a hand tool). The tieth century onwards, also by the aid of continuous casting. moulding mixture normally consists of sand, a binder and Development has now gone on for more than 150 years and water. this trend is likely to continue. New methods are currently When the compaction of the flask is finished the pattern being developed, which involve the production of cast com- is stripped (removed) from it. The procedure is illustrated in ponents that are in size as close to the final dimensions as Figures 1.4 (a–d). The component to be produced is, in this possible. case, a tube. Stage 1: Production of a Mould for the Manufacture of a Steel Tube Materials Processing during Casting H. Fredriksson and U. A˚ kerlind The cavity between the flask wall and the pattern is then Copyright # 2006 John Wiley & Sons, Ltd. filled with the mould paste and rammed by hand or 2 Component Casting Figure 1.1 Stone mould for casting of axes, dating from 3000 BC. Figure 1.3 Picture of a cast bronze Buddha statue, which is more than 20 m high. The statue was cast in the Eighth century AD. Its weight is 780 Â 103 kg. A very special foundry technique was used in which the mould production and casting occurred simulta- neously. The mould was built and the statue was cast in eight stages, starting from the base. The mould was built around a frame- work of wood and bamboo canes. Each furnace could melt 1 Â 103 kg bronze per hour. Reproduced with permission from Giesserei- Verlag GmbH. Figure 1.4 (a) A pattern, normally made of wood, is prepared as two halves. It is equipped with a so-called core print at the ends as dowels. Reproduced with permission from Gjuterihistoriska Sallskapet. Figure 1.2 A knife and two axes of pure copper, cast in stone moulds of the type illustrated in Figure 1.1. compacted in a machine. The excess mould paste is removed from the upper surface, and the lower part of the future mould is ready. The upper one is made in the same way. Components due to be cast are seldom solid. They nor- Figure 1.4 (b) Half the pattern and the patterns of inlet and cast- mally contain cavities, which must influence the design of ing runner are placed on a wooden plate in half a flask. A fine- the mould. The cavities in the component correspond to grained powder, for example lycopodium powder or talc, is distrib- sand bodies, so-called cores, of the same shape as the cav- uted over the pattern to facilitate the future stripping of the pattern ities. The sand bodies are prepared in a special core box, the [see Figure 1.4 (d)]. Reproduced with permission from Gjuterihis- inside of which has the form of the core. The core box, toriska Sallskapet. which is filled and rammed with fireproof so-called core sand, is divided into two halves to facilitate the stripping. The cores normally obtain enough strength during the Stage 2: Production of the Core in what will become the baking process in an oven or hardening of a plastic binder. Steel Tube Figures 1.4 (e) and 1.4 (f) illustrate the production process When the mould is ready for casting the complete cores are of a core, corresponding to the cavity of a tube. placed in their proper positions. Since the fireproof sand of Casting of Components 3 Figure 1.4 (c) The upper pattern half and the upper part of the mould flask are placed on the corresponding lower parts. A thin layer of fine-grained dry sand, so-called parting sand, covers the contact surfaces. Special patterns of the future sprue and the fee- Figure 1.4 (e) The cavity in what will become the tube is formed ders are placed exactly over the inlets in the lower parts of the by a sand core, produced in a core box. The two halves of the core tube flanges. Reproduced with permission from Gjuterihistoriska box are kept together by screw clamps while the sand is rammed Sallskapet. into the mould. A cylindrical steel bar is placed as core grid in the lengthwise direction of the core to strengthen the future core. Reproduced with permission from Gjuterihistoriska Sallskapet. Figure 1.4 (f) The core is lifted out of the parted core halves. The core is often baked in an oven to achieve satisfactory strength. Figure 1.4 (d) The mould parts are separated and the pattern Reproduced with permission from Gjuterihistoriska Sallskapet. parts are stripped, i.e. lifted off the upper and lower parts of the mould. The patterns of the inlet, sprue and feeders are also removed. The figure shows the lower part of the mould after the A necessary condition for a successful mould is that it pattern stripping. Reproduced with permission from Gjuterihistor- must contain not only cavities, which exactly correspond iska Sallskapet. to the shape of the desired cast-metal component, but also channels for supply of the metal melt. These are called the cores has a somewhat different composition than that of casting gates or gating system [Figure 1.4 (c)]. Other cav- the mould, one can usually distinguish between core sand ities, so-called feeders, which serve as reservoirs for and mould sand. the melt during the casting process, are also required Figure 1.4 (g) The core is placed in the lower part of the mould. The parts of the mould are joined with the parting surfaces towards each other. The dowels through the holes in the outer walls of the flask parts guarantee the exact fit of the corresponding cavities in the upper and lower halves of the mould. A so-called casting box, which insulates the upper surface of the melt and prevents it from solidifying too early, is placed exactly above the sprue and the parts of the mould are kept together by screw clamps. The mould is ready for use. Reproduced with permission from Gjuterihistoriska Sallskapet. 4 Component Casting [Figures 1.4 (c) and 1.4 (g)]. Their purpose is to compensate The laws, which are the basis of the calculations, are for the solidification shrinkage in the metal. Without given below.

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