Über die Autorin bzw. den Autor

Dr Hasse Fredriksson is professor in Casting of Metals at the Royal Institute of Technology in Stockholm, Sweden. He is the leader of a very active research group since more than three decades. Dr Fredriksson is internationally known. He is author or co-author to more than 200 scientific papers. He has organized many Summer schools and international conferences in his field, the last one in June 2005.

Dr Ulla Åkerlind is a physicist (research field molecular physics) with long experience of undergraduate teaching at the Department of Physics at the University of Stockholm. She has co-operated in a set of text books in basic physics for the Swedish 'gymnasium' and produced learning aids for the undergraduate university level in physics.

Von der hinteren Coverseite

This text covers most aspects of casting. It deals with the principles behind modern casting with applications incorporated for both ferrous and non-ferrous metals. The text consists of 11 chapters:

• Chapters 1-2 presents a short introductory survey methods and equipment.
• Chapters 3-6 describe the theoretical basis behind modern casting processes in foundries and cost houses.
• Chapters 7-11 have a more practical approach to the casting of various metals. The principles derived in the earlier chapters are applied to teach the reader how various problems can be designed in an optimal way, according to the present knowledge of casting science. Due to the importance of steel and iron-based alloys a good deal of the content is devoted to these alloys but the principles and phenomena are general.

Most chapters contain several solved examples and at the end of chapters 3-11 aa selection of exercises is given. The answers to all of the exercises are listed at the end of the book.

An accompanying 'Guide to exercises' provides complete solutions to all of the exercises, step by step. The solutions in the Guide are designed to encourage the students to work on their own, i.e. the idea is help to self-help to achieve increased understanding of the topic. The Guide can be downloaded in PDF format from http://www.wiley.com/.

This extensive book offer materials for several courses on different aspects of the subject with the option of varying the level of the courses. It is appropriate for undergraduate as well as masters students in materials technology, as well as for students in mechanical engineering with some knowledge of materials processing. This text can be used by PhD students and researcher in material science who are working with problems connected to casting processing.

Aus dem Klappentext

This text covers most aspects of casting. It deals with the principles behind modern casting with applications incorporated for both ferrous and non-ferrous metals. The text consists of 11 chapters:

• Chapters 1-2 presents a short introductory survey methods and equipment.
• Chapters 3-6 describe the theoretical basis behind modern casting processes in foundries and cost houses.
• Chapters 7-11 have a more practical approach to the casting of various metals. The principles derived in the earlier chapters are applied to teach the reader how various problems can be designed in an optimal way, according to the present knowledge of casting science. Due to the importance of steel and iron-based alloys a good deal of the content is devoted to these alloys but the principles and phenomena are general.

Most chapters contain several solved examples and at the end of chapters 3-11 aa selection of exercises is given. The answers to all of the exercises are listed at the end of the book.

An accompanying 'Guide to exercises' provides complete solutions to all of the exercises, step by step. The solutions in the Guide are designed to encourage the students to work on their own, i.e. the idea is help to self-help to achieve increased understanding of the topic. The Guide can be downloaded in PDF format from www.wiley.com.

This extensive book offer materials for several courses on different aspects of the subject with the option of varying the level of the courses. It is appropriate for undergraduate as well as masters students in materials technology, as well as for students in mechanical engineering with some knowledge of materials processing. This text can be used by PhD students and researcher in material science who are working with problems connected to casting processing.  

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Materials Processing During Casting

John Wiley & Sons

Chapter One

1.1 Introduction 1 1.1.1 History of Casting 1 1.1.2 Industrial Component Casting Processes 1

1.2 Casting of Components 1 1.2.1 Production of Moulds 1 1.2.2 Metal Melt Pressure on Moulds and Cores 4 1.2.3 Casting in Nonrecurrent Moulds 5 1.2.4 Casting in Permanent Moulds 8 1.2.5 Thixomoulding 11

1.1 INTRODUCTION

1.1.1 History of Casting

As early as 4000 years BC the art of forming metals by casting was known. The process of casting has not really changed during the following millennia, for example during 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 the Renaissance up until the middle of the Nineteenth century. Complete castings were prepared and used directly without any further plastic forming.

Figures 1.1, 1.2 and 1.3 show some very old castings.

In addition to improving the known methods of production and refining of cast metals, new casting methods were invented during the Nineteenth century. Not only were components produced but also raw materials, such as billets, blooms and slabs. The material qualities were improved by plastic forming, forging and rolling. An inferior primary casting result cannot be compensated for or repaired later in the production process.

Steel billets, blooms and slabs were initially produced by the aid of ingot casting and, from the middle of the Twentieth century onwards, also by the aid of continuous casting. Development has now gone on for more than 150 years and this trend is likely to continue. New methods are currently being developed, which involve the production of cast components that are in size as close to the final dimensions as possible.

1.1.2 Industrial Component Casting Processes

As a preparation for a casting process the metal is initially rendered molten in an oven. The melt is transferred to a so-called ladle, which is a metal container lined on the inside with fireproof brick. The melt will then solidify for further refining in the production chain. This is performed by transferring the melt from the ladle into a mould of sand or a water-chilled, so-called chill-mould of metal. The metal 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 problems associated with the various methods are discussed briefly when the methods are described. These problems are general and will be extensively analysed in later chapters.

In Chapter 2 the methods used in cast houses will be described. The methods used in foundries to produce components will be discussed below.

1.2 CASTING OF COMPONENTS

1.2.1 Production of Moulds

A cast-metal component or a casting is an object that has been produced by solidification of a melt in a mould. The mould contains a hollow space, the mould cavity, which in every detail has a shape identical to that of the component.

In order to produce the planned component, a reproduction of it is made of wood, plastic, metal or other suitable material. This reproduction is called a pattern. During the production of the mould, the pattern is usually placed in a mould frame, which is called a flask or moulding box. The flask is then filled with a moulding mixture which is compacted (by machine) or rammed (with a hand tool). The moulding mixture normally consists of sand, a binder and water.

When the compaction of the flask is finished the pattern is stripped (removed) from it. The procedure is illustrated in Figures 1.4 (a-d). The component to be produced is, in this case, a tube.

Stage 1: Production of a Mould for the Manufacture of a Steel Tube

The cavity between the flask wall and the pattern is then filled with the mould paste and rammed by hand or 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 normally contain cavities, which must influence the design of the mould. The cavities in the component correspond to sand bodies, so-called cores, of the same shape as the cavities. The sand bodies are prepared in a special core box, the inside of which has the form of the core. The core box, 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 baking process in an oven or hardening of a plastic binder. Figures 1.4 (e) and 1.4 (f) illustrate the production process of a core, corresponding to the cavity of a tube.

Stage 2: Production of the Core in what will become the Steel Tube

When the mould is ready for casting the complete cores are placed in their proper positions. Since the fireproof sand of the cores has a somewhat different composition than that of the mould, one can usually distinguish between core sand and mould sand.

A necessary condition for a successful mould is that it must contain not only cavities, which exactly correspond to the shape of the desired cast-metal component, but also channels for supply of the metal melt. These are called casting gates or gating system [Figure 1.4 (c)]. Other cavities, so-called feeders, which serve as reservoirs for the melt during the casting process, are also required [Figures 1.4 (c) and 1.4 (g)]. Their purpose is to compensate for the solidification shrinkage in the metal. Without feeders the complete cast-metal component would contain undesired pores or cavities, so-called pipes. This phenomenon will be discussed in Chapter 10. When the casting gate and feeders have been added to the mould, it is ready for use.

Stage 3: Casting of a Steel Tube

The casting process is illustrated in Figures 1.4 (g), 1.4 (h), and 1.4 (i).

1.2.2 Metal Melt Pressure on Moulds and Cores

During casting, moulds and cores are exposed to vigorous strain due to the high temperature of the melt and the pressure that the melt exerts on the surfaces of the mould and cores.

To prevent a break-through, calculations of the expected pressure on the mould walls, the lifting capacity of the upper part of the mould and the buoyancy forces on cores, which are completely or partly surrounded by melt, must be performed. These calculations are the basis for different strengthening procedures such as varying compaction weighting in different parts of the mould, locking of the cores in the mould and compaction weighting on or cramping of the upper part of the mould.

The laws, which are the basis of the calculations, are given below. The wording of the laws has been adapted to the special casting applications.

The laws given on above are valid for static systems. During casting the melt is moving and dynamic forces have to be added. These forces are difficult to estimate. The solution of the problem is usually practical. The calculations are made as if the system were static and the resulting values are increased by 25-50 %.

An example will illustrate the procedure. The pressure forces are...