IMPLICATIONS FOR THE DEVELOPMENT OF A UREA MOULDING COMPOUND

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INTRODUCTION

Metals are essential industrial materials due to their good mechanical properties. Metals combine properties of high strength with the ability to change shape without brittle fracture compared with wood, plastics and stone. This enables metals to be formed into a wide range of shapes. Metals are normally extracted from ores and are prepared using various metal-forming processes such as casting, forging and extrusion. Casting involves the pouring of molten metal into a mould or a die. After cooling, the metal takes the shape of the mould and can then be used to form metal components. Common examples of casting processes include sand, dies, centrifugal casting, full moulds, squeeze, investment casting, etc. Alternatively, forging can be used to form metal components. Forging involves forming a metal by heating it in a forge and beating or hammering it into the required shape.

History of investment casting

Investment casting originated several thousand years ago: Ancient Egyptian and Chinese museum pieces suggest that they were made by investment casting processes (Little, 1977). According to Black, et al. (1984), “Dentists have also used the process since the turn of the century”. It did not, however come into common industrial use until World War II ( 1939-1945) when high-quality jet turbine blades and supercharger buckets for aircraft engines were in great demand.

Investment casting process

Figure 1 illustrates the current industrial investment casting process. It starts with the manufacture of a pattern using an injection moulder or a wax injector. The patterns are attached to a common sprue and then invested, i.e. “dipped”, in slurry to create a thin coating on the surface. Dipping in a refractory slurry mixture is repeated until a coat of the correct dimension is achieved and finally a granulated refractory ‘stucco’ shell is applied (Repp, 1994). The pattern-sprue system is then conditioned and left to dry.

Wax based moulding compounds for investment casting

Fillers, additives, resin, paraffin and microcrystalline waxes are typical ingredients used to formulate wax-based moulding compounds for investment casting. There are basically five types of wax based moulding compounds for investment casting, as discussed below (Rajesh, 2004).

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ABSTRACT
ACKNOWLEDGMENTS
CHAPTER 1 INTRODUCTION
CHAPTER 2 INVESTMENT CASTING
2.1 HISTORY OF INVESTMENT CASTING
2.2 INVESTMENT CASTING PROCESS
CHAPTER 3 MOULDING COMPOUNDS FOR INVESTMENT CASTING
3.1 WAX BASED MOULDING COMPOUNDS FOR INVESTMENT CASTING
3.3 OTHER MOULDING COMPOUNDS FOR INVESTMENT CASTING
3.3 PRINCIPLES OF COMPOUND FORMULATION
3.4 FILLERS
3.4 UREA
3.4.1 Applications of urea
3.4.2 Physical and thermal properties of urea
3.5 POLYMERS
3.5.1 Ethylene vinyl acetate
3.5.2 Polyvinyl alcohol
3.6 PLASTICISERS
3.6.1 Glycerol
3.6.2 Mechanism of plasticisation
3.6.3 Factors influencing plasticisation
3.7 LUBRICANTS
3.8 FILLED POLYMERS
3.8.1 Filler-polymer interaction
3.8.2 Factors affecting polymer-filler interaction
CHAPTER 4 COMPOUNDING TECHNIQUES
4.1 BATCH MIXERS
4.2 CONTINUOUS COMPOUNDERS
CHAPTER 5 CHARACTERISATION TECHNIQUES
5.1 MECHANICAL PROPERTIES
5.1.1 Three-point bending test
5.1.2 Impact testing
5.2 DYNAMIC MECHANICAL ANALYSIS PROPERTIES
5.3 THERMOMECHANICAL ANALYSIS PROPERTIES
5.3.1 Thermodilatometry
5.3.2 Volumetric expansion
5.4 PHYSICAL PROPERTIES OF WAXES
5.4.1 Melting/softening point
5.4.2 Dimensional analysis
5.4.3 Density
5.5 THERMAL PROPERTIES
5.5.1 Differential scanning calorimeter (DSC)
5.5.2 Thermogravimetric analysis
5.6 RHEOMETRY AND MELT FLOW INDEX
5.7 IMPLICATIONS FOR THE DEVELOPMENT OF A UREA MOULDING COMPOUND
CHAPTER 6 MATERIALS AND SAMPLE PREPARATION
6.1 MATERIALS
6.2 PVOH UREA-BASED MOULDING COMPOUNDS
6.2.1 Experimental design.
6.2.2 Sample preparation
6.3 EVA UREA-BASED MOULDING COMPOUNDS
6.3.1 Experimental design.
6.3.2 Sample preparation
6.3.3 Determination of the urea-acetamide phase diagram
CHAPTER 7 CHARACTERISATION OF THE COMPOUNDS
7.1 MECHANICAL PROPERTIES
7.1.1 Three-point bending test
7.1.2 Impact strength
7.2 DYNAMIC MECHANICAL ANALYSIS
7.3 THERMOMECHANICAL ANALYSIS
7.4 THERMAL PROPERTIES
7.4.1 Differential thermal analysis and thermogravimetric analysis
7.4.2 Differential scanning calorimetry
7.5 MELT FLOW INDEX
7.6 SCANNING ELECTRON MICROSCOPY
7.7 DENSITY
CHAPTER 8 RESULTS AND DISCUSSION
8.1 PROCESS RESULTS
8.1.1 Oven
8.1.2 Single-screw extruder
8.1.3 Two-roll mill
8.1.5 Injection-moulding
8.2 THERMAL PROPERTIES
8.2.1 Differential scanning calorimetry
8.2.2 Vicat softening temperature
8.3 MECHANICAL PROPERTIES
8.3.1 Charpy impact test
8.3.2 Three-point bending test
8.4 DYNAMIC MECHANICAL ANALYSIS.
8.5 THERMAL EXPANSION PROPERTIES
8.6 MELT FLOW INDEX
8.7 SCANNING ELECTRON MICROSCOPY
8.8 DENSITY
CHAPTER 9 CONCLUSIONS AND RECOMMENDATIONS
REFERENCES