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Optimizing green sand properties of fluidized sand from aeration and developing new green sand testing technique

Dissertation
Author: Ananda Mani Paudel
Abstract:
Aeration sand filling is a new molding technique in foundry. Using this technique, sand with smooth flow can be filled in any orientation and shape using low-pressure air. This is not possible by conventional gravity and high-pressure blow filling techniques. Aeration was introduced as an energy-efficient and environmentally- friendly sand molding technique. In addition, aeration has its niche on quality of molds it could produce. Friability, one of the crucial green properties for the quality mold was significantly low in aeration in comparison to the gravity and high-pressure blow filling. The fluidization action in aeration acted upon the sand clay interfaces and created the interactions with them, and induced better surface abrasive property. In other words, aeration lowered the friability in the green sand allowing a lower compactibility levels in green sand molding, which was not possible with the conventional molding techniques. The range of 30-35% was suggested as the optimal working range of compactibility for aeration molding technique for selected sand and clay composition. Advance cone jolt and thermal erosion tester were developed and used to examine the green sand properties of the foundry sand. Advance cone jolt was sensitive to the clay composition and contamination in green sand, whereas thermal erosion tester demonstrated its relevance in evaluating mold surface behavior at an elevated temperature. Thermal erosion test displayed less sand erosion in the molds built in the aeration. Green sand in aeration was benefited by the favorable clay orientation. Homogeneous and isotropic distribution of clay platelets occurred during fluidization, which produced a better clay coating on the sand grains and increased the grain to grain bonding. Scanning electron microscope displayed a uniform clay coating and universal micro-tribometer showed greater bonding strength in the surface of the molds produced in aeration. Casting trial along with the relevant standard AFS tests for green sand properties were carried out, and analyzed using design of experiments and statistical tools.

TABLE OF CONTENTS ACKNOWLEDGEMENTS ii LIST OF TABLES ix LIST OF FIGURES xi CHAPTER I. INTRODUCTION 1 H. LITERATURE REVIEW 6 Sand Molding Techniques 6 Gravity Filling 7 High-pressure Blow 8 Aeration Filling 9 Fluidizing Bed 12 Fluidizing Mechanism 12 Viscosity of Fluidized Sand 14 Molding Materials 15 Sand 15 Silica Sand 16 Olivine 18 Chromite 18 Ceramic Media 19 in

Table of Contents-Continued CHAPTER Clay 19 Electrostatic Force 21 Surface Tension 22 Frictional Force 22 Water 23 Relationship between Clay and Moisture 24 Critical Bentonite Content 24 Water/ Effective Clay Ratio 25 Green Sand Properties and AFS Sand Test 26 Compactibility 26 Moisture Content 28 Bulk Density 28 Permeability 28 Green Compressive Strength 30 Splitting Strength 31 Mold Hardness 31 Percent Friability 31 Sand Toughness 33 Flowability 34 Volatility 34 iv

Table of Contents-Continued CHAPTER Sand Control Program 35 Sand/Metal Ratio 37 Chemical Properties 37 Alternative Sand System 38 Friability in Green Sand 39 Casting Defects Due to Moisture 42 Water Explosion 43 Scabbing 43 Friability Related Casting Defects 46 Comments on AFS Standard Tests 46 Cone Jolt Toughness Test 47 Erosion Test 48 AFS Standard Testing Procedure 49 Preparation of Green Sand 49 Design of Experiments 51 Sand-Clay Interactions 51 X-ray Diffraction 51 Scanning Electron Microscope (SEM) 53 Universal Micro-tribometer 54 m. OBJECTIVE 56 IV. METHODOLOGY 60 v

Table of Contents-Continued CHAPTER Design of Experiments 61 Decision Variables and Data Collection 64 Measure of Performance and Their Estimation 64 Determination of Minimum Number Replications 65 Analyzing Effects of Aeration and Comparison 66 Comparison of Multiple Alternative Sand Filling Techniques 66 Optimizing and Establishing Workable Range 68 Experimental Procedures and Setups 69 High-pressure Blow Setup 70 Experimental Setup for Aeration Sand Filling 70 Developing New Green Sand Testing Methods 74 Advance Cone Jolt Test 74 Thermal Erosion Tester 75 X-ray Diffraction Setup 77 Scanning Electron Microscope (SEM) Setup 78 Universal Micro-tribometer (UMT) Setup 78 V. RESULTS AND DISCUSSION 80 Results of Green Sand Test 82 Permeability 86 Green Compressive Strength 96 Mold Hardness 103 vi

Table of Contents-Continued CHAPTER Bulk Density 110 Friability 117 Relationships between Friability and Compactibility 125 Comparison of Aeration with High-pressure and Gravity Filling 127 Validation of Friability Test Results 131 Implication of Lower Friability and Other Observations 132 Optimizing Green Sand Properties of Fluidized Sand in Aeration 135 Friability versus Other Green S and Properties in Aeration 161 Advance Cone Jolt 167 Test Results of Thermal Erosion Tester 169 Sand Clay Interactions in Different Filling Mechanisms 171 Results from X-ray Diffraction 171 Results of Scanning Electron Microscope (SEM) 174 Results of Universal Micro-tribometer (UMT) 175 Validation of the Findings 178 Molding and Green Sand Properties 179 Preparation of Green Sand to Desired Compactibility 180 Green Sand Properties 182 Experimental Matchplate and Gating Design 183 Design of Experiments 187 Measuring Erosion Depth 190 vii

Table of Contents-Continued CHAPTER Conclusion and Recommendations 200 Benefits of Aeration Mixing 206 Limitations and Recommendations for Future Study 207 REFERENCES 212 APPENDICES A. Data Collection Tables 217 B. Material Data Sheet of Various Sands 220 C. Experimental Data 221 D. Post-hoc Duncan Test Results 227 E. Residual Plots 231 F. High-pressure Blow Systems Verification Data 232 G. X-ray Diffractometer Setting and Results 233 H. Scratching Force High-pressure Specimen 234 I. Scratching Force Aeration Specimen 241 J. Normality Test of UTM Data 249 K. SEM and UTM Data 250 L. X-ray Diffraction Data 251 M. Green Properties Test Results of Various Sands in Aeration 284 N. Green Properties of Lake Silica Sand for Validation 286 O. Results of the Test Casting: Erosion Depth 287 viii

LIST OF TABLES 1. Properties of Silica and Specialty Sands 17 2. Green Sand Testing Equipment 50 3. Factor and Level Codes for Design of Experiment 62 4. Environmental and Operating Conditions 63 5. Descriptive Statistics of Permeability 87 6. ANOVA: Permeability versus Sand, Technique, Compactibility 91 7. ANOVA of Individual Sand: Permeability versus Technique, Compactibility 92 8. Student-Newman-Keuls: Permeability 95 9. Descriptive Statistics of GCS Data 97 10. ANOVA: GCS versus Sand, Technique, Compactibility 99 11. ANOVA of Individual Sand: GCS versus Technique, Compactibility 100 12. Student-Newman-Keuls: GCS (lb/in2) 102 13. Descriptive Statistics of Mold Hardness 103 14. ANOVA: Mold Hardness versus Sand, Technique 106 15. ANOVA of Individual Sand: Mold Hardness versus Technique, Compactibility 106 16. Student-Newman-Keuls: Mold Hardness 108 17. Descriptive Statistics: Bulk Density (g/cm3) I l l 18. ANOVA: Bulk Density versus Sand, Technique 113 ix

List of Tables-Continued 19. ANOVA of Individual Sand: Bulk Density versus Technique, Compactibility 114 20. Student-Newman-Keuls: Bulk Density (g/cm3) 116 21. Descriptive Statistics of Friability Data 118 22. ANOVA: Friability versus Sand, Technique 121 23. ANOVA of Individual Sand: Friability versus Technique, Compactibility. 122 24. Student-Newman-Keuls: Friability (%) 124 25. Friability Data for High-pressure, Aeration and Gravity 128 26. Comparison of Friability in Aeration, Gravity and High-pressure Blow 130 27. Cone Jolt Results for Aeration and Gravity 168 28. T-test of Cone Jolt: Aeration versus Gravity 169 29. Thermal Erosion Test Results 170 30. One-way ANOVA: Sand Loss versus Technique in Thermal Erosion Test 170 31. Intensity Ratio of Two Highest Peaks in Diffraction Pattern 173 32. Comparison of Scratching Force in Aeration and High-pressure Samples.. 177 33. Typical Properties of the Lake Sand 181 34. Properties of the Green Sand at 35% Compactability Level 182 35. Depth of Erosion in Different Sand Molding Techniques 194 36. ANOVA: Erosion Depth versus Squeeze Pressure, Head Height, Techniques 195 37. Student-Newman-Keuls: Erosion Depth (mm) 197 38. Summary of the Research Findings 210 x

LIST OF FIGURES 1. Gravity Sand Filling 7 2. Aeration Filling Machine 10 3. Bed Expansion after Fluidization 13 4. Silica Sand Microscopic View 16 5. Various Types of Alternative Sands 19 6. Sand Particles Coated with Clay 20 7. Sand Testing Equipment 27 8. Green Sand Testing Equipment 29 9. Green Sand Test Equipment 32 10. Relationship between Friability and Clay 40 11. Relationship between Friability and Compactibility 41 12. Casting Defects 44 13. Casting Defects Due to Weak Mold 45 14. Sand Molding Process Flow 50 15. X-ray Diffractometer 52 16. Scanning Electron Microscope 54 17. Micro-tribometer Scratch Test 55 18. Schematic of High-pressure Blow System 70 19. Schematic of Aeration Sand Filling System 71 20. Experimental Matchplate with Half-section Sleeves and AFS Tubes 72 xi

List of Figures-Continued 21. Aeration Sand Filling Pressure Curve 73 22. Advance Cone Jolt 75 23. Thermal Erosion Tester 76 24. Specimen Holder for X-ray Diffraction and SEM 77 25. Close-up View of Specimen Setup in UTM 79 26. Relationship between Moisture and Compactibility 83 27. Relationship between Compactibility and Green Sand Properties 84 28. Dotplot of Permeability 90 29. Permeability of Different Sands, Techniques and Compactibility Level 93 30. Dotplot of GCS 98 31. GCS of Different Sands, Techniques and Compactibility Level 101 32. Dotplot of Mold Hardness 105 33. Mold Hardness of Different Sands, Techniques and Compactibility Level 108 34. Dotplot of Bulk Density 112 35. Bulk Density of Different Sands, Techniques and Compactibility Level.... 115 36. Dotplot of Friability 120 37. Friability in Different Sands, Techniques and Compactibility Level 123 38. Friability of Silica Sands 126 39. Friability of Specialty Sands 126 40. Friability of Green S and with Different Filling Techniques 129 41. Boxplot of Friability Comparing Different Filling Techniques 129 xii

List of Figures-Continued 42. Validation of Friability Results 132 43. Compactibility versus Green Sand Properties in Aeration 138 44. Relationship between Moisture and Compactibility 140 45. Bulk Density-Compactibility Relationship of Green Sand in Aeration 143 46. Moisture Content - Compactibility Relationship of Green Sand in Aeration 145 47. Permeability-Compactibility Relationship of Green Sand in Aeration 147 48. GCS-Compactibility Relationship of Green Sand in Aeration 149 49. Mold Hardness-Compactibility Relationship of Green Sand in Aeration ... 152 50. Friability-Compactibility Relationship of Green Sand in Aeration 153 51. Friability versus Green Properties of Lake S and in Aeration 162 52. Friability versus Green Properties of RG Sand in Aeration 164 5 3. Friability versus Green Properties of Olivine S and in Aeration 164 54. Friability versus Green Properties of Chromite Sand in Aeration 165 55. Friability versus Green Properties of Ceramic Media in Aeration 166 56. Advance Cone Jolt Test Results of Different Clays 168 57. Diffraction Pattern of Silica Sand and Clay Using Gravity Filling 172 58. Diffraction Pattern of Silica Sand and Clay Using Aeration Filling 172 59. Diffraction Pattern of Silica Sand and Clay Using High-pressure Blow 172 60. Intensity Ratio Interval Plot 173 61. SEM Picture High-pressure Blow Sand Specimen 174 xiii

List of Figures-Continued 62. SEM Picture Aeration Sand Specimen 175 63. Scratching Force Plot in High-pressure Blow Specimen with Vertical Load 176 64. Scratching Force Plot in Aeration Specimen with Vertical Load 177 65. Schematic of Aeration Sand Molding System 180 66. Gating Design and Simulation Results 184 67. Test Flask with Cope and Drag Mold 186 68. Test Casting Process Flow Diagram 189 69. Non-contact Coordinate Measurement Machine 190 70. Erosion on Wedge Surface of the Test Castings 193 71. Sand Erosion and Resulting Irregular Casting Section 194 72. Interaction Plot for Erosion Depth (mm) 196 73. Friability versus Green Sand Properties of Olivine Sand in Aeration 209 xiv

CHAPTER I INTRODUCTION Sand casting, the oldest manufacturing technique, is still popular among metal casters due to its low cost, high productivity and flexibility afforded by the molding process (Schleg, 2003). Among the wide variety of molding techniques in use today, green sand is by far the most diversified and widely used. Green sand in particular is of interest because it is available naturally and is environmentally friendly. The term "green" denotes the presence of moisture in the molding sand and indicates that the mold is not baked or dried. Molding techniques and sand control are the major contributors in quality and productivity of foundries. Development of newer molding techniques to get better castings from the green sand casting is continuing. Various methods have been employed to shape green sand into molds such as gravity filling and high pressure blowing. Gravity filling and ramming is the traditional method, which is followed by gravity filling and squeezing. The majority of today's modern foundries use a high pressure blowing and squeezing technique to produce either horizontally or vertically parted green sand molds (Ramrattan, 2008). Lately, flaskless molding techniques are introduced. To improve the flowability and bonding of the green sands, various additives are introduced in the sand system (Kuz'min, 1987), (Lafay, 2009). However, none of the existing sand molding technologies has the capability to evenly fill or produce uniformly dense sand molds. Insufficient filling of sand to a complicated shape or deep pockets of small diameter will ultimately lead to casting 1

defects (Dietert, 1974). Aeration technique is proposed as a new sand molding method, which can fill complex shapes and produce uniformly dense molds. Aeration fluidizes the green sand before filling into the mold. In aeration sand filling, green sand is mixed with air in a fluidizing chamber. The fluidized sand flows smoothly into the mold cavity with low pressure. This is a promising way to fill sand in any shape and orientation. Making molds with complex shapes and deep pockets is now possible (Hirata & Sugita, 2005). Further, the aeration technique is environmentally friendly because it produces molds with better green sand properties and eliminates the requirement of chemicals. Krysiak, et al, (2002) have shown that properly controlled green sand also can produce certain smaller near-net-shape castings comparable to chemically bonded sand. Casting quality is directly related to mold quality and mold quality largely depends on sand control. Comparison of aeration filling technique with gravity filling and high-pressure blow techniques in terms of green sand properties signifies its worthiness. Over the years several noted papers on green sand system control are published with different approaches and views; however, focusing on the basic variables of green sand system is agreed on as the common theme for a successful sand control and comparison (Ramrattan, Paudel, Makino, & Hirata, 2008). American Foundry Society (AFS) green sand control program identifies four basic variables as: addition of water, bond, new sand, and carbonaceous material (Krysiak & Pedicini, 1990), (Krysiak, 1990 & 1994). The basic sand tests identified to study green sand systems include compactibility, permeability, green strength, mold hardness, bulk density, and friability (AFS, 2000). The design of the experiment is devised and green properties tests are conducted in a controlled environment. Different types of sand compositions are studied. Out of these 2

batteries of sand test results, friability appears to behave differently in aeration with the interactions of other factors. Test results from this research can be useful for establishing reference green sand properties for the sand casting industry. Sand control is essential, to produce world-class castings and meet the ever-increasing demands competitively, along with better quality and dimensional reproducibility (Bailey, 1983). Today's sophisticated molding equipment and control systems with a high level of automation hinder the understanding of how the green sand process works. A good understanding of the process is necessary to deal with day-to-day problems, and various operating parameters should be evaluated on a regular basis. Each molding application has an established control range with respect to green sand properties (Knight, 1973). Logically, new molding technology, like aeration sand filling, requires processing parameters to achieve desirable green sand properties. These parameters need to be identified and measured using related AFS tests. In some cases more vigorous tests are required. Permeability, GCS, mold hardness, bulk density, and friability are selected as the major green property test to evaluate the mold quality produced in aeration. The relationship between these green properties with compactibility decides the optimal working range for aeration molding. Grain fineness number (GFN), sand distribution and clay content are maintained in the same level throughout the experiment while comparing the green sand properties, molds after filling is recycled for the next experiment without pouring the metal. This prevents the effects of the weight, heat and temperature of the metal on the green sand properties. Green sand properties will change if it comes in contact with the metal at elevated temperature. Clay particles will burn, and irreversibly converted into dead clay due to the enormous heat and temperature of the liquid metal. Dead clay loses its bonding characteristics; however, for the 3

validation of the green properties test results, a casting trial was conducted in the green sand molds produced with different molding techniques. Although a long list of AFS standard green sand tests are followed by foundries, true control of the sand system is still not achieved. Thus, foundries are largely dependent upon the personal experience and hit and miss approach. The fundamental problem of the existing tests is the inability to capture the actual scenario of mold metal interface and dynamic nature of the mold making process. Currently, all sand tests are done in room temperature and it is well perceived that these tests cannot relate the actual situation of elevated temperature in casting. There is a need to develop new sand test procedures, which can bring the high temperature conditions into the test realistically. In experimental observation, friability has appeared as an interesting property, which behaves differently in the fluidized sand. To further study and investigate elevated temperature effects on friability, the thermal erosion tester is used, which measures the sand loss due to erosion at elevated temperature. Major AFS test such as green compressive strength are static in nature. The only existing dynamic test by the nature of loading is the cone jolt test, which has poor repeatability and accuracy. There is ample room for improvement in terms of accuracy and sophistication as well as efficiency of this test. The impact of fluidization in aeration on sand-clay interactions and resulting transformation in green sand properties are superior with that of conventional filling methods. Material properties of sand clay mix under different filling techniques are studied in detail to understand the effect of filling techniques, and to explain the cause of the lower friability in aeration. Following approaches were used to analyze the impact of different filling mechanisms on sand-clay-water mix and green properties. 1. Chemical composition and microstructure analysis 4

2. Visual inspection of the clay plates in micro scale 3. Mechanical testing of sand clay bonding X-ray diffraction helps to characterize the chemical composition and provides the information about the microstructure of the material. In sand clay mix, X-ray diffraction data is used to analyze the clay plate's orientation. Scanning Electron Microscope (SEM), another tool to study the materials in micro level, produces the structure of the clay pictorially. Micro-tribometer is used to measure the mechanical strength of the sand clay bonding. 5

CHAPTER H LITERATURE REVIEW In order to determine and select proper experimental methods and test procedures, a thorough review of relevant research is essential. In the same vein, to investigate the effects of aeration in green sand properties, researchers must understand the concepts of sand systems, theories behind the sand molding and common practices. This chapter is devoted to covering these aspects as the literature review of molding techniques and sand control. The first section relates to sand molding technique, which is followed by molding materials, green sand properties and casting defects. Sand Molding Techniques Sand casting is a cheap and simple metal casting technique. Sand, which is abundantly available and easy to form, is used to build the mold. Sand molds are popular among metal casters due to low initial investment to buy equipment, molds of different shapes can be made easily, and allow for faster design change. In addition, molding process has afforded higher productivity and flexibility. There are some limitations of sand casting in terms of accuracy, surface finish and shapes to be produced (Schleg, 2003). To eliminate these discrepancies and produce better quality castings with low cost, considerable effort has continually been made. Introducing new sand compositions and developing new molding techniques are some of the meaningful efforts. 6

Foundries in search of significant improvements in quality and productivity need to consider the molding system first. Improving molding systems results in better mold quality, which is the starting point for the journey of defect free castings. Various techniques were developed in an attempt to enhance quality of castings using sand moldings. These molding techniques can be broadly grouped into gravity, high-pressure blow and aeration filling. Gravity Filling This is a very primitive method of mold building. In this method, sand is mulled, riddled and fed into the flask manually. As the name gravity says, gravitational force drives the sand into the mold. Gravity sand filling process is shown in Figure 1. Figure 1. Gravity Sand Filling This is a simple way of sand molding and used by a small in-house foundry as well as big commercial casting companies. Low cost and easy to maintain are the chief 7

advantages of this molding technique. Low productivity and poor reproducibility hinders its application in high quality large volume castings. High-pressure Blow In the high-pressure blow technique, green sand after mulling is transferred into the flask with the help of high-pressure air shot (0.6 MPa). First, sand is delivered to a single location, acting as a feeder for a common blow tank. Sand from the blow tank is filled into the top of the cope and bottom of the drag of the mold at the same time. This design assures 45 to 55 mold hardness prior to the squeeze. Filling density is higher than gravity. As sand is blown into the mold cavity, less sand movement occurs during the squeeze cycle, which helps in reducing pattern wear. In addition, the blow-fill system has less sand spill than gravity fill. High-pressure molding practice also reduces moisture contents in the molding sand to get higher mold densities. Lately, with the aid of flaskless molding, the inventory of mold flask is eliminating in high-pressure blow molding lines (Schleg, 2003). In conventional flaskless molding, sand filling methods such as gravity, "top and bottom blow" or "side blow" with the aid of high pressure compressed air are popularly used. The conventional top blow, particularly with vertically positioned matchplate shows stable sand filling in wide varieties of molding sands. In North America, almost 90% of the sand casting foundries use high-pressure blow molding technique (Ramrattan, 2008). The development of newer techniques have demonstrated considerably better improvements in dimensional accuracy along with improved surface finish, closer to pattern accuracy and increased productivity (Bex, 1992). At the same time, extensive 8

maintenance and high-energy consumption by the high-pressure machines has raised the cost of production. Further, these techniques have limitations in the shape they can produce. They result insufficient sand filling in complicated shape and deep pockets of small diameter, and lead to casting defects (Hirata & Sugita, 2005). Aeration Filling Aeration filling technique is based on fluidization process. Fluidization is used in various industries for different applications such as mixing and transferring powders in pharmaceuticals and material transfer in casting industry (Bakhtiyarov, 1996a; Rhodes, 2001). However, the application and mechanism of fluidization is different. In sand molding, fluidization has recently been studied. In sand molding applications, green sand is fluidized by air and coined the name aeration molding technique for the process. In the aeration technique, green sand is first fluidized, which greatly increases its flowability, and low-pressure air applied afterwards drive it into the mold with smooth feeding. Aeration filling uses green sand and offers a means that can fill a mold in any orientation. Hirata et al., (2005) showed that complete sand filling and uniformly dense molds are possible by aeration. Furthermore, since the area of the blow nozzle is large, the speed of sand projection through the nozzle is much lower than conventional high-pressure blow method. Consequently, in aeration sand filling, sand with low density falls on the pattern surface slowly and gently, as opposed to being blasted out at high speeds of high- pressure blow. Accordingly, bridge-forming phenomenon at the area with complicated shape patterns and at the mouth of small size pockets is minimized. The sand streams down smoothly toward the vent plugs furnished at the bottom of each pocket riding on the 9

aeration air, and sand bulk density is further increased by airflow effect. The composite action of these effects makes it possible to achieve high-density sand filling to the areas with complicated configuration and pockets having a small diameter. Even with the air pressure much lower than blowing, the bulk density obtained in aeration is generally higher. It is considered that a decrease in friction resistance at the aeration filter area has contributed to achieve a higher bulk density. The effect of airflow acting on each sand particle increases the kinetic energy of the sand particles, and results in the achievement of higher bulk density (Hirata, 2002). Hirata, (2002) has discussed the design and describes the technology for an aeration sand filling system, which is shown in Figure 2. Figure 2. Aeration Filling Machine 10

As shown in Figure 2, aeration system consists of aeration chamber, air handling or inlet manifold, air tank, and pressure and time control module. The aeration sand filling system makes it possible to fill sand into complex shapes, deep pockets, and thin sections on a matchplate that heretofore were not possible by conventional molding method such as high-pressure blowing. Hirata et al., (2005) has made significant findings with respect to aeration filling of sleeves. Generally, the larger the inside diameter of the sleeve the higher the filling density will be. However, the lower the aeration pressure, the higher the filling density becomes, especially in the small diameter sleeve. When aeration air pressure is low, sand flows slowly and smoothly, filling the sleeve cavity in an orderly manner. On the contrary, at higher-pressure blow, sand builds up a bridge at the inlet area, and later, as the bridge collapses, the sand tries to fill the cavity in a series of surges resulting in unequal density distribution. Further, when the vent area at the bottom part of the sleeve is increased, filling density becomes higher. This improvement of filling density is caused by an increase in volume of smooth airflow streaming through the sleeve. The increase of smooth airflow volume causes to increase the speed of sand stream, and results in the uniform filling from bottom to top giving improved density. In summary, followings are the features of aeration sand filling (Hirata & Sugita, 2005) • Complete mold filling and uniform density distribution • Can fill a mold in any orientation and position • Smooth sand feeding can produce smooth surface finish • Bridge-forming phenomenon due to the change in cross-section area is minimized 11

• Possible to achieve high density even with much lower air pressure (Hirata, 2002) • High productivity with 200 molds/hour • Lower noise level due to lower air pressure in use Fluidizing Bed Fluidization is a process by which materials with fine solid particles are transformed into a fluid-like state through the contact with a gas or liquid (Kunii & Levenspiel, 1991). Fluidized beds are known for their high heat and mass transfer coefficients due to the high surface area-to-volume ratio of fine particles. Fluidized beds are used in a wide variety of industrial processes such as reaction, drying, mixing and granulation, coating, heating, and cooling. Fluidizing Mechanism When trying to describe the operation of a fluidized bed, fluidization velocity is a crucial parameter to start with, which is defined as the superficial fluid velocity at which the upward drag force exerted by the fluid is equal to the apparent weight of the particles in the bed. Another common characteristic of fluidized beds is the bed expansion. When incipient fluidization is achieved, the fluid flowing upwards pushes the particles up and the separation distance between particles increases. This increases the void volume within the bed of particles and the bed is expanded (Bakhtiyarov, 1996b). Mathematical model that describes the flow of a fluid through a bed of particles is constructed under the assumption that the bed behaves as a group of tubes, which follows 12

Full document contains 306 pages
Abstract: Aeration sand filling is a new molding technique in foundry. Using this technique, sand with smooth flow can be filled in any orientation and shape using low-pressure air. This is not possible by conventional gravity and high-pressure blow filling techniques. Aeration was introduced as an energy-efficient and environmentally- friendly sand molding technique. In addition, aeration has its niche on quality of molds it could produce. Friability, one of the crucial green properties for the quality mold was significantly low in aeration in comparison to the gravity and high-pressure blow filling. The fluidization action in aeration acted upon the sand clay interfaces and created the interactions with them, and induced better surface abrasive property. In other words, aeration lowered the friability in the green sand allowing a lower compactibility levels in green sand molding, which was not possible with the conventional molding techniques. The range of 30-35% was suggested as the optimal working range of compactibility for aeration molding technique for selected sand and clay composition. Advance cone jolt and thermal erosion tester were developed and used to examine the green sand properties of the foundry sand. Advance cone jolt was sensitive to the clay composition and contamination in green sand, whereas thermal erosion tester demonstrated its relevance in evaluating mold surface behavior at an elevated temperature. Thermal erosion test displayed less sand erosion in the molds built in the aeration. Green sand in aeration was benefited by the favorable clay orientation. Homogeneous and isotropic distribution of clay platelets occurred during fluidization, which produced a better clay coating on the sand grains and increased the grain to grain bonding. Scanning electron microscope displayed a uniform clay coating and universal micro-tribometer showed greater bonding strength in the surface of the molds produced in aeration. Casting trial along with the relevant standard AFS tests for green sand properties were carried out, and analyzed using design of experiments and statistical tools.