MME 345 Lecture 03 Introduction 3. Creating quality casting Ref: J. Campbell, Casting Practice: The 10 Rules of Castings , Elsevier, 2004 Topics to discuss today …. 1. Defects in casting 2. How to create quality casting 3. Ten casting rules by J. Campbell
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MME 345
Lecture 03
Introduction3. Creating quality casting
Ref: J. Campbell, Casting Practice: The 10 Rules of Castings, Elsevier, 2004
Topics to discuss today ….
1. Defects in casting
2. How to create quality casting
3. Ten casting rules by J. Campbell
Castings can be difficult to get right. Creating things never is easy.
The production of good castings can be highly economical and rewarding.
The production of bad castings is usually expensive and damaging.
The „good casting‟ can be defined as one that meets or exceeds the
customer‟s specification.
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Metal castings are fundamental building blocks, the three-dimensional
integral shapes indispensable to practically all other manufacturing industries.
Creating good casting every time, without any defect is a challenge to behold!
In this lecture, we shall first see the type of defects commonly found in
casting and then discuss, generally, the method of obtaining good castings.
1. Defects in Casting
Porosity (gas hole, pin hole, blow hole)
Slag, inclusion, oxide film
Metal penetration
Hot tear
Shrinkage cavity
Cold shut and miss run
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Porosity
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Hot tear
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Shrinkage Cavity
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Cold shut
Miss run
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2. How to Create Quality Casting
1. Making a perfect mould
2. Preparing a clean melt
3. Pouring efficiently of liquid metal into the mould cavity
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Cross-section of a typical mould
Cope
Drag
Sprue Gate
Core
Feeder/
Riser
Mould Cavity
Sand
Mould
Conical cup
2.1 Making a perfect mould
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An Open Mould
Top surface not required
Liquid metal poured directly into the
mould cavity
Skill of moulder important
cope
drag
A Closed Mould(Partially Sectioned)
Represents the greatest of challenge
Flow of liquid is controlled by the laws of fluid dynamics
Skill of moulder is not important
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High temperature of liquid metal
High pressure of liquid metal and dissolved gases
Expansion of sand due to high temperature
Reaction of liquid metal with the mould
Velocity of liquid metal inside the mould cavity
Turbulence of liquid metal inside the mould cavity
Why is a perfect mould necessary?
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Requirements of an ideal mould
Adequate strength and hardness
Adequate refractoriness
Adequate permeability
Appropriate design of the gating/running system
Adequate use of feeder, if necessary
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Method of making an ideal mould
1. Use of an appropriate moulding and casting process and use
of appropriate moulding raw materials
Greensand (sand-clay-water) system
Dry sand (sand-chemical binder) system
Gravity die / Pressure die (metal mould - high/low pressure) system
2. Use of appropriate gating and feeding design
Top pouring vs. bottom pouring system
Pressurised vs. unpressurised system
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(a) Top pouring system, (b) Bottom pouring system, (c) Side pouring system