APPLICATIONS FOR INDUCTION FURNACES IN MANUFACTURING TECHNOLOGY COURSES. A Project. Presented. to the Faculty of. California State University, Chico

Transcription

1 APPLICATIONS FOR INDUCTION FURNACES IN MANUFACTURING TECHNOLOGY COURSES A Project Presented to the Faculty of California State University, Chico In Partial Fulfillment of the Requirements for the Degree Master of Science in Interdisciplinary Studies Instructional Curriculum Design for Manufacturing Management by Scott D. Brogden 2015 Summer 2015

2 APPLICATIONS FOR INDUCTION FURNACES IN MANUFACTURING TECHNOLOGY COURSES A Project by Scott D. Brogden Summer 2015 APPROVED BY THE INTERIM DEAN OF GRADUATE STUDIES: Sharon A. Barrios, Ph.D. APPROVED BY THE GRADUATE ADVISORY COMMITTEE: Sharon A. Barrios, Ph.D. Graduate Coordinator Joseph P. Greene, Ph.D., Chair Daren M. Otten, Ed.D.

3 PUBLICATION RIGHTS No portion of this project may be reprinted or reproduced in any manner unacceptable to the usual copyright restrictions without the written permission of the author. iii

4 DEDICATION This project is dedicated to my grandfather: James M. (Jerry) Burke ~~~~ As a youngster, I would watch my grandfather build the most amazing things from metal, never imagining that one day I might possess the knowledge and skills to follow in his steps. He demonstrated a sense of pride in workmanship, incredible time management, and creativity that are seldom seen in this world. iv

5 ACKNOWLEDGEMENTS The first person I would like to thank is Dr. W. Ray Rummell, who gave me countless hours of his time and teaching both when I was a student and a new lecturer. I want to express my gratitude to my parents, who did everything they could to give me an environment in which I could succeed. I am also very grateful to Victor Okhuysen (Cal- Poly, Pomona) and Martin Koch (Cal-Poly, San Luis Obispo) for the time they spent with me and the information they shared. Thank you to the other professionals I know and have known through my years, all of whom have helped to shape and nurture my love for manufacturing. A special thanks to the faculty and staff of California State University, Chico for their support, professionalism and passion for education. I thank my students, who make my teaching position rewarding and enjoyable. And lastly, I am grateful for the love, support, and gentle encouragement my wife has given me while I have trudged through this endeavor. v

6 TABLE OF CONTENTS PAGE Publication Rights... Dedication... Acknowledgements... List of Tables... List of Figures... Glossary of Terms... Abstract... iii iv v viii ix xi xiii CHAPTER I. Introduction... 1 Purpose of the Project... 2 Scope of the Project... 2 Significance of the Project... 3 Limitations of the Project... 4 II. Review of Related Literature... 5 The Induction Furnace... 5 Coreless Induction Furnaces Channel Induction Furnaces Comparison of Induction Furnaces to Direct Arc Furnaces Furnace Designs Furnace Refractories and Crucibles Gas Absorption, Slag Formation and Oxidation Induction Furnace Power Supplies Induction Furnace Inverters Induction Furnace Water Systems Purification and Maintenance of Cooling System Water vi

7 CHAPTER PAGE Water Requirements and Quality Other Supporting Systems Safety Purchasing and Operating Costs Furnace Efficiency III. Methodology Induction: Furnaces in Manufacturing Courses IV. Results and Conclusions Demands for Metal Casting Education Benefits of an Induction Furnace to Technology Programs Space and Utilities Required Conclusions V. Summary and Recommendations Summary Recommendations References Appendices A. Induction Furnace Brochures B. CSU, Chico Foundry Laboratory Floor Plans C. Personal Communication vii

8 LIST OF TABLES TABLE PAGE 1. Comparison of Volkswagen s New (1993) Gas-Fired Furnace to their Induction Furnace Occupational Outlook for Careers in which Metal Casting Knowledge is Important viii

9 LIST OF FIGURES FIGURE PAGE 1. Induction Furnace Current Flow View of Lamination Packs Between Furnace Case and Coil Pound Capacity Coreless Induction Furnace A Coreless Induction Furnace Coil Channel Induction Furnace Installing the Coil Refractory in a Coreless Induction furnace A 75 kw Induction Furnace Power Supply General Diagram of Evaporative Closed Loop Water System Typical Evaporative Type Cooling Tower An Evaporative Closed Loop Water System General Diagram of Dry Air Closed Loop Water System Typical Dry Air Fluid Cooler Induction Furnaces in the Cal-Poly, Pomona Foundry Styrofoam Sheets Waterjet Cut for the Lost Foam Process Styrofoam Patterns Ready to be Separated from the Sheet Casting Tree Ready to have Gating System Removed Pound Tilt Pour Induction Furnace at Cal-Poly, Pomona Induction Furnaces at Cal-Poly, San Luis Obispo CAM Software for Creating Pattern Machining Program CNC Machining Center Ready to Cut Wax Pattern ix

10 FIGURE PAGE 21. CNC Machining enter Cutting Wax Pattern Wax Pattern with Gating System Sand Mold Ready for Top Half and Sprue Complete Sand Mold Ready for Pouring Pouring Molten Aluminum into the Sand Mold Rough Casting Ready for Gating System Removal Energy Consumption vs Power Utilization Melting Rates at 40 kw Power Consumption x

11 GLOSSARY OF TERMS Alloying Castable Refractory Combining metals in the right proportions to form an alloy. A concrete or mortar that is reconstituted with water from a dryprepared mixture and is suitable for refractory use. Casting (noun) An object made by filling a mold with molten metal, then cooling the molten metal so it solidifies. Casting (verb) Charge Metal Crucible Dew Point Pouring liquid metal into a mold and allowing it to solidify. Metal that is placed into a furnace crucible for melting. A container in which metal is melted. The temperature at which water in air evaporates and condenses at the same rate. Dross Eddy Current Ferrous Metal Foundry Furnace Gate Gating System Hz Induction Foreign material on the surface of molten metal. Electric currents produced by a changing magnetic field. A metal that contains appreciable amounts of iron. A factory that produces metal castings. A device for heating or melting metal and other materials The part of the path of molten metal flow into the part cavity. The path for molten metal to flow into the part cavity. Hertz a measure of frequency. A heating process for electrically conductive objects. xi

12 kw kwh Ladle Lamination Pack Metal Bath Mold Non Ferrous Metal Oxidation Refractory Runnout Slag Soft Starting Transformer Kilowatt a unit of energy equal to 1,000 watts. Kilowatt-hour one kilowatt of power expended for one hour. A device for transporting molten metal from a furnace to a mold. Electrically conductive materials used to absorb Eddy currents. The pool of molten metal in a crucible. A structure into which molten metal is poured. A metal that does not contain appreciable amounts of iron. Reactions of metals with oxygen that result in corrosion. A material which will withstand high temperatures. Molten metal that escapes from a crucible or mold unintentionally. Waste matter separated from metals. Gradually increasing the current flow during furnace startup. A device that increases or reduces the voltage of an alternating current. Tree A metal casting that still has the gates and runners attached. Vibratable Refractory A refractory that is installed as a dry-prepared mixture using vibration and is suitable for refractory use. Wax Pattern A pattern made of wax which is used to produce a mold. xii

13 ABSTRACT APPLICATIONS FOR INDUCTION FURNACES IN MANUFACTURING TECHNOLOGY COURSES by Scott D. Brogden 2015 Master of Science in Interdisciplinary Studies Instructional Curriculum Design for Manufacturing Management California State University, Chico Summer 2015 The decline of metal casting education in our nation s schools is leaving many students with little or no knowledge of that important manufacturing method. Many manufacturing professionals see this as a serious problem and it is the primary motivator behind this project. CSU, Chico has a foundry in one of the manufacturing laboratories, but only non-ferrous metals can be cast. The best solution for increasing the casting capabilities of the CSU, Chico manufacturing foundry is the main goal of this research project. An electric induction furnace could be a good addition to the foundry and is used in a number of school foundries and many industrial foundries across the nation. The theory and operation of electric induction furnaces was then researched. They are quiet, efficient, versatile and safe melting furnaces in an educational xiii

14 environment. Induction furnaces are available in a wide variety of sizes to suit various melting needs. Prices for smaller units start at approximately $50,000 and space requirements are comparable to or slightly greater than a small electric resistance furnace. California Polytechnic (Cal-Poly) State University, San Luis Obispo and California Polytechnic State University, Pomona have strong metal casting curriculum, so those schools were visited to explore their metal casting capabilities and equipment. Both schools utilize electric induction furnaces, which allow a wide variety of ferrous and nonferrous metals to be melted. Induction Technologies Corporation (ITC), a manufacturer of electric induction furnaces in Adelanto, California was visited to learn more about the design, construction, and application of an induction furnace appropriate for a school foundry. The owner of the company graciously offered to donate a refurbished furnace to CSU, Chico if space and the required water and power could be supplied by the university. ITC was the supplier of the furnaces at both Cal-Poly universities. xiv

15 CHAPTER I INTRODUCTION Metal casting is one of the most important manufacturing practices in use today. Almost all transportation-related products, computing devices, pumps, machine tools, and many other manufactured items contain metal castings. It is therefore very important that an industrialized nation educate its workforce in the field of metal casting. In order to accomplish this, that nation s educational institutions must have metal casting equipment and faculty that are knowledgeable about the process (About AFS & Metalcasting). The United States metal casting industry, like most industries, was negatively affected by the 2008 to 2010 recession. However, the casting industry has seen favorable growth since the recession ended. From 2011 and projected through 2015, the industry will see casting sales grow over 45%. Ductile iron, aluminum, compacted graphite iron, and copper-based alloys are forecast to see the best growth in the long term. The automotive, oil and gas, construction, pump and compressor, turbine, and material handling industries will be most likely to take advantage of this growth (Modern Casting Staff, 2014). Students in technical programs should have at least a basic understanding of fluid metallurgy, casting processes, and the equipment used in these processes. Many schools have either opted not to teach these technologies or have discontinued teaching 1

16 them for a variety of reasons. These include a shortage of available space and funding for metal casting laboratories and a lack of teachers who are trained in these areas. 2 Purpose of the Project The main purpose of this project is to foster an understanding of the value of the metal casting induction furnace in the curriculum of a manufacturing technology program. Students who are not exposed to metal casting are at a distinct disadvantage compared to those who are when they design manufactured products or select production processes. When an item that could be efficiently produced using a casting process is made using other methods, it often increases the cost of the item. This rarely occurs intentionally, but is usually due to ignorance on the part of the design engineer or the manufacturing engineer. An induction furnace is a very useful tool in educating students about the metal casting process. Scope of the Project This project will provide the reader with an overview of what an induction furnace is and how it can be applied to a university s manufacturing curriculum. It explains how an induction furnace melts metal, what metals can be melted, how it is constructed, how it is safely operated, and how it can be used to teach students the metal casting process. The different types of induction furnaces are discussed, along with the advantages and disadvantages of each. Power and water requirements for operating the furnace are also covered. The intended audience for this project is college or university faculty and/or administration. Faculty could use this project to help convince the decision makers at

17 3 their school to acquire an induction furnace. Students might also use it to help them decide if the content of a school s manufacturing program fits their needs. Significance of the Project This project is significant because it gathers into one document all the information necessary to allow someone with limited knowledge of metal casting equipment to learn how an induction furnace works and how it could provide value in a school environment. It makes an attempt to help the reader understand not only why metal casting is an important part of manufacturing education, but how an induction furnace can be a useful tool as well. According to the American Foundry Society s website (2015), the following list is current information about the metal casting industry in the United States: There are 1,978 metal casting facilities in the United States. 80% of these facilities have less than 100 employees. There are over 200,000 people employed in these businesses. 90% of all manufactured items contain some metal castings. The United States is the global leader in casting applications and second in production. Persons in the United States are rarely more than 10 feet from a metal casting (About AFS & metalcasting, para. 2). Metal castings are found in 90 percent of nearly everything we touch and use. Examples of metal castings are the cast iron plate in a piano, faucets, automobile engine blocks, furnace fireboxes, stove grates, missile parts,

18 4 military tank parts, train parts, aircraft parts, and even tiny castings in cell phones and computers (Tower Productions, 2008). Limitations of the Project The furnace equipment varieties most closely studied in this project are those which were most accessible and demonstrable to the author, along with being deemed most appropriate for use in a college setting. The nearest locations of relevant equipment are a considerable traveling distance from California State University, Chico, making numerous research trips impractical. The few trips that were used for research had to be carefully planned so that all necessary information was obtained while at each site visited. Many commercial foundries use induction furnaces, but the demands on the furnaces and the environments in which they operate are significantly different than in an educational setting.

19 CHAPTER II REVIEW OF RELATED LITERATURE The Induction Furnace There are many different types of metalcasting furnaces, each with their own advantages and suitability to different metals and melting practices. No single furnace is best in every situation, so it is important to consider all aspects of any foundry s operation when choosing a furnace. Thorough communication between the foundry and furnace manufacturers helps to ensure that the right furnace is selected for the given application. If the wrong furnace is chosen, the foundry will not reap the desired benefits of reliability and performance that the correct furnace can provide. The main factors to weigh when considering a new furnace are the metal to be melted, the size of the melted metal batches (heats), the available funding for the purchase, the available space and utilities, emissions and environmental issues, and noise limits (Smith, 1992). Induction heating is simply a method of transferring heat energy from the primary coil surrounding the charge metal to that metal, which is to be melted. A high voltage alternating current is passed through the primary coil, which creates a magnetic field that induces Eddy currents to flow in the charge metal. This current causes the charge metal to become heated, and if enough current is generated, the metal will melt. 5

20 6 The heat is generated because the charge metal has resistance to the flow of the current being induced in it, and the greater the current or the resistance, the more heat is generated (Grant, 1991). Because of the way that the eddy currents flow in the charge metal, the surface of the metal heats more quickly than its core. This phenomenon is called the skin effect and along with the charge metal s amount of magnetic properties, determines the metal s current penetration depth. The speed at which the metal s core is heated depends on the current penetration depth. The deeper the current penetrates, the faster the core of the metal heats. The skin effect results in reduced eddy current flow in the charge metal toward its center, so the core of the metal is heated more by thermal conductivity than by eddy current flow (Rudnev, 2008). The induction furnace is essentially a refractory-lined hollow vessel surrounded by an electrically energized, current-carrying, water-cooled copper coil. The charge metal becomes the core of the induction path and electrical current in the coil forms an electromagnetic field, generating thermal energy that melts the charge. The magnetic currents in the molten metal cause an intense stirring action, ensuring a homogenous liquid mass. (Williams, 2010). As shown in Figure 1, the magnetic field produced by the primary coil (lines of induction field) flows perpendicular to the direction of the primary coil s current flow. Each piece of charge metal in the furnace will have Eddy currents flowing in its surface. If the charge metal is magnetic, the rapidly changing magnetic field in the metal will cause extra heat to be generated in the charge metal. It is important that this changing magnetic field is not allowed to flow in the iron-based parts of the furnace and its support

21 7 Figure 1. Induction furnace current flow. Source: Grant, A. (1991). Induction furnace melting. FWP Journal, American Foundry Society, document , Reprinted with permission. structure, otherwise these items will be heated as well. Unless non-electrically conductive and non-magnetic materials are used to build the furnace, lamination packs (Figure 2) must be used to absorb the extra magnetic field. Careful furnace design ensures that as much magnetic field as possible is used to melt the charge metal, yielding maximum furnace efficiency (Grant, 1991).

22 8 Figure 2. View of lamination packs between furnace case and coil. Photograph by the author. An induction furnace must have a chamber or melting cavity that will withstand the rigors of repeated cycling from room temperature to several thousand degrees Fahrenheit. It must also be durable enough to reliably contain the molten metal charge until it is dispensed into a mold, producing a metal casting. This chamber is called the crucible, and its lining is composed of a refractory material so that it can survive the high heat to which it is subjected. (Williams, 2010) When metal is melted in an induction furnace, its pure portion sinks to the bottom of the crucible, while most impurities rise to the surface. These impurities may be easily removed by scooping or skimming them from the surface with the proper tools (Meredith, n.d.). Advantages of induction furnaces are their rapid melting rate, their almost silent operation, their ability to precisely control the molten metal temperature, their very clean molten metal production, and the molten metal s homogeneity and accurate

23 9 composition. The homogeneity and accurate composition are due to the thorough stirring action inherent in an induction furnace. The fact that the electric induction furnace does not change the environment around the charge metal, along with its precision temperature control, allow fine composition control of any alloy produced (Lacoma, n.d.). Since the metal is heated from inside its surface, the metal is never exposed to temperatures higher than its own molten temperature. Since there is no flame heating the metal, there is no need for fume capture or recovery systems unless the metal being melted gives off fumes. This reduces oxidation of the molten metal and increases furnace yield (Smith, 1992). The design of induction furnaces and the fact that they use electric power makes them simple to operate and training of personnel is quick and easy. Since the early 1990 s, the induction furnace has gained industrial popularity because of its suitability to melting smaller batches of metal (heats) with special alloy compositions (Heine, 1990). The induction furnace was invented in the early 1900s, but the first single-coil units were not very efficient. When a second coil was added, the efficiency increased dramatically because the furnace was able to create eddy currents in the charge metal more easily (Lacoma, n.d). Initially, the furnaces had lids on their crucibles, but most were later eliminated to ease the slag removal process. Induction furnaces are ideal for melting and alloying a wide variety of metals with minimum melt losses, however, little refining of the metal is possible. Induction furnaces vary greatly in size, from those melting several pounds up to hundreds of tons of metal at a time (Lacoma, n.d.). The best induction melting system has the smallest possible furnace that will handle the largest required melt size while still adequately stirring the molten metal so a homogeneous mix

24 is achieved. (Heine, 1990) There are two main types of induction furnaces: coreless and channel (Meredith, n.d.). 10 Coreless Induction Furnaces The coreless induction furnace is the type most used today, with the main component being a coil constructed of a hollow section of heavy duty, electrically conductive copper tubing which is wound into a helical shape. Figure 3 shows a small induction furnace. The coil is placed inside a steel shell and magnetic shielding prevents the supporting steel shell from being heated. Because the coil must be kept relatively cool, water is circulated through it, then cooled in a cooling tower. The coil and shell assembly is supported on trunnions, which allow the furnace to be tilted to allow pouring the molten metal from the crucible (Meredith, n.d.). Some induction furnaces have crucibles with lids that seal tightly, keeping the surrounding atmosphere out of the melting chamber. This improves the purity of the molten metal inside the crucible, and any slag or impurities may be removed when the lid is opened just before pouring (Lacoma, n.d.). The refractory lining in the melting chamber is of a more critical nature in an induction furnace than in other furnace types because of the high speed at which induction furnaces heat. There is an inner lining (the crucible) that contains the molten metal and an outer lining that is imbedded into and around the heating coil (Williams, 2010). The thickness of the lining is critical, and carefully specified so that the furnace will melt the metal in the chamber as efficiently as possible. The calculation of the lining thickness takes into consideration a number of factors, including safety, the coil s

25 11 Figure pound capacity coreless induction furnace. Photograph by the author. electrical properties, the conductivity of the charge metal, the characteristics of the refractory material, production demands, and operational parameters (Duca, 2010). An induction furnace coil is shown in Figure 4. To help prevent molten metal runout from the furnace and to avoid damage to the copper heating coil, some high-powered induction furnaces incorporate a layer of conductive material (wire mesh) between the refractory layers. If any molten metal contacts this conductive material, it causes the furnace to shut down. (Svoboda & Griffith, 2002) The induction furnace power supply converts the incoming voltage and frequency of the main supply from AC to DC, then back to AC. Frequency of AC power is the number of times it changes polarity each second, and the units are Hertz (Hz). During the time the power is changed to DC, the frequency is altered (made higher), so

26 12 Figure 4. A coreless induction furnace coil. Photograph by the author. that it conforms to the required type of power for melting metal. Power frequencies used for heating in induction furnaces vary from the incoming 50 or 60 cycles per second to as high as 10,000 cycles per second (high frequency). According to Meredith (n.d.), The higher the operating power frequency, the greater the maximum amount of power that can be applied to a furnace of given capacity and the lower the amount of turbulence induced (p. 1). The amount of energy absorbed by the charge metal depends on the

27 13 magnetic field s density, the frequency of the power supply s output, and the electrical resistance of the charge metal (Smith, 1992). The higher the furnace s power frequency, the more shallow is the depth of penetration of the magnetic field into the charge metal. The opposite is true for low frequency power. If very thin metal pieces are used to charge a cold furnace, the magnetic field can penetrate deeply enough that it doesn t effectively heat the thin metal pieces. Using thicker pieces of charge metal when starting up a cold furnace will help the pieces to heat more quickly because the magnetic field will not over-penetrate them. If the magnetic field s penetration depth is equal to the thickness of the pieces of charge metal, a cancelling affect can occur, since the field penetrates from all sides of the pieces. When this happens, the only heating that occurs is due to the switching back and forth of the magnetic field s direction. As a result, the furnace power has to be increased to very high levels in order to get the charge metal above about 700º C (1,292º F) (Grant, 1991). Once the metal that has been charged into the crucible has melted, it begins to move inside the crucible. This stirring action is caused by the magnetic field and the electric currents in the induction coil interacting with the molten metal in the center of the coil (in the crucible). The molten metal pool tends to rise upward in the center, causing somewhat of a reverse meniscus on the surface of the pool. The amount the pool rises and the degree of stirring action is controlled by the power level and frequency of the current passing through the furnace coil, along with the shape and size of the coil. The most important influence of frequency is the degree of inherent stirring. This phenomenon results from the interaction between the primary field and the induced currents in the bath. The resulting forces, being strongest at the furnace center, propel the

28 14 metal inward where it divides to flow down as well as upwards, raising the center of the bath surface, then returning along the side walls. This quadrature stirring pattern or essentially the meniscus height is not only a function of the power density, but also proportional to the square root of the power supply frequency. Simply stated, the higher the frequency, the less the stirring (Smith, 1992, p. 13). There is a formula for calculating the height of the dome formed in the center of the molten pool by the stirring action. This formula can be used to find the maximum allowable power level for a given dome height. If the dome height will be too large, the required power level can be reduced by preheating the charge metal with a charge dryer. This speeds up the melting process and ensures there will be no moisture on the charge metal when it enters the furnace. From Calamari (1985), the formula (for dome height of molten pool) is: where h = height of dome in cm δ = specific power in kw/ton ps = specific weight of charge metal η = relative magnetic permeability e = electrical resistivity of charge metal f = frequency (1) The molten metal s density and viscosity also affect how much stirring occurs in the molten pool. This stirring action is desirable because it helps to mix the alloying ingredients in the pool, speeds the melting of metal chips (by-products of machining

29 15 operations), and produces a consistent temperature throughout the molten pool in the crucible. Caution should be used when adjusting the power and frequency, as too much stirring can increase gas absorption, crucible lining wear, and oxidation of melt alloys (Meredith, n.d.). Induction furnaces for foundry work come in a variety of styles and sizes. The smallest furnaces, with melting capacities of 50 lbs. of aluminum or less, are often the table type, and are tilted by hand from their small table-top supports. They have a small case which contains the primary coil and crucible, and a small high frequency (3,000 to 10,000 Hz and up to 100 kw) power supply. These furnaces are usually found where small numbers of small castings are made or in research laboratories (Smith, 1992). See Appendix A for brochures covering these various types of furnaces. Floor mounted furnaces range in capacity from about 50 lbs. to 250 lbs. of aluminum and have power supplies ranging from 50 to 350 kw and 1,000 to 3,000 Hz. The housing containing the furnace coil is sometimes separate from the crucible so that it can be hydraulically lifted away from the crucible containing the melt and swung over to another waiting crucible. Other floor mounted furnaces tilt hydraulically to pour the molten metal into molds or into ladles or trollies for transportation to the pouring area (Smith, 1992). High frequency furnaces commonly have aluminum plates on their four vertical side panels and refractory top and bottom sections. The top and bottom support the induction coil and the molten metal in the crucible. A hoist or hydraulic system tilts the furnace for pouring. High frequency furnaces have molten iron capacities of from 50 to 5,000 lbs. and 100 to 1,000 kw, 1,000 Hz power supplies (Smith, 1992).

30 16 The largest induction furnaces are called steel shell furnaces because of the circular steel shell that houses the induction coil and crucible. Around the outside of the coil are devices called flux diverters that keep the magnetic field from heating the steel shell of the furnace. These furnaces also tilt for pouring after the lids lift and swing out of the way. The higher strength of this type of furnace allows it to melt from 1 to 75 tons of metal. Power supplies normally operate at frequencies from 60 to 500 Hz and in the 350kW to 8,000 kw power range (Smith, 1992). Traditional gas-fired and electric resistance furnaces have mostly been replaced by the coreless induction furnace, especially for melting of high temperature alloys. A primary reason for this change is that all grades of steels, cast irons, and most non-ferrous alloys are efficiently melted in a coreless induction furnace (Meredith, n.d.). The Atlasfoundry.com website states about induction furnaces: The furnace is ideal for melting and alloying because of the high degree of control over temperature and chemistry while the induction current provides good circulation of the melt (Meredith, n.d., para 7). Atlas Foundry Company, established in 1893, is located in Indiana and produces small (.5 up to 50 pounds) gray iron castings using coreless induction furnaces. Channel Induction Furnaces The second and oldest type of induction furnace, the channel induction furnace (Figure 5), is constructed of a refractory lining inside a steel shell, in which the molten metal is contained. Usually underneath the steel shell and attached to it by a passageway called a throat, is an induction unit that melts the metal in the furnace. A ring-shaped iron core with a coil wrapped around it comprises the induction unit, and

31 17 Figure 5. Channel induction furnace. Source: Allied Mineral Products. (2015). Channel induction furnaces. Retrieved from Reprinted with permission. forms the primary side of the transformer. The molten metal that passes through the throat forms the secondary side of the transformer. As heat is generated in the throat, the charge metal is melted and caused to circulate upward into the furnace crucible, creating the same type of stirring action as in a coreless induction furnace (Meredith, n.d.). Once a channel induction furnace is started, it is not turned off nor fully emptied unless maintenance needs dictate that the upper or lower chambers must be relined (the refractory lining replaced). Their design requires that they are started with their chambers already full of molten metal. Since they operate continuously, only minor changes in the alloy melted can be made (AFS, 1989).

32 18 A channel induction furnace is often used to melt alloys in the lower melting point range, such as non-ferrous alloys like aluminum and brass. Another typical use is for holding metals already melted at a certain temperature or maintaining the proper level of superheat. Superheat is the amount of extra temperature added to a molten metal charge so that it does not solidify prematurely while filling a mold. These furnaces are also used to hold metal that has been melted during off-peak electricity billing hours, which lowers overall utility charges (Meredith, n.d.). Comparison of Induction Furnaces to Direct Arc Furnaces Prior to the late 1990s, direct arc furnaces were usually used for large volume production (melts of up to 65 tons) of carbon and low alloy steel castings, while induction furnaces handled most high alloy steel and low volume steel casting production. Since that time, several advances in coreless induction furnace technology have increased their suitability for somewhat larger scale steel casting operations (melts of 10 tons or less). The new types of power supplies that have increased the power density (power required per unit volume of metal melted), along with the operation of two furnaces per power supply, have raised induction furnace efficiencies to the 90 percent range (Svoboda & Griffith, 2002). When compared to direct arc furnaces, these newer induction furnaces cost about 30% less, have lower dust collection requirements, provide better chemistry and temperature control, stir the melt more for better homogeneity, emit far less noise, and yield a higher percentage of usable metal because of much lower oxidation rates. Conversely, the induction furnace uses slightly more electric power, makes refining the

33 19 melt more difficult, requires more precisely controlled and cleaner scrap for charging, and improper design can cause harmonic power line disturbances. It is more difficult to perform carbon boiling (an effective degassing procedure for steel) in an induction furnace. Since both types of furnaces have advantages and disadvantages, these must be considered when selecting either of these types for a metal casting process (Svoboda & Griffith, 2002). Furnace Designs Induction furnaces vary mainly in the way that the molten metal (melt) is extracted from the melting chamber. The two main types of coreless induction furnaces are stationary and transportable, with the stationary type being the least complex and expensive. Stationary furnaces are either tapped, bailed, or tilted to remove their molten metal. In some cases, compressed air or vacuum is used to remove the metal. A disadvantage of the tapping type is that they must be completely emptied every time they deliver any of the melt. Bailing furnaces require the melt to be extracted with casting ladles, which are metal buckets on the ends of pole-shaped handles. Ladles are dipped directly into the melt and then poured into transporting carts or directly into a casting mold. Since the ladles are small and handled manually by foundry workers, bailing furnaces are used when only a small amount of molten metal is required for each mold, as is the case with small castings. Bailing furnaces are also used for metals with melting temperatures below that of steel, or below about 1,370º C (2,500º F) ( A Guide to, 1968).

34 20 Tilting furnaces are the most common stationary induction furnace in use. The entire furnace box heating structure changes position (tilts) to deliver the molten metal through a pouring spout on one side of the furnace. Means of tilting the furnace include manual labor, motors, hydraulics, cranes, and geared handwheels. Melt capacities range from about one pound to hundreds of tons ( A Guide to, 1968). Transportable furnaces are used when smaller melt capacities are sufficient. The crucible is either lifted out of the furnace and the molten metal poured out of it into molds, or the induction coil is lifted by a crane or hoist from around the crucible, then the melt is poured from the crucible into molds ( A Guide to, 1968). Another induction furnace design that is becoming more popular is the vacuum induction furnace. Its popularity growth stems from its ability to lower the hydrogen content by degassing and, during the low pressure state of the process, deoxidizing steel melts with carbon. Vacuum degassing lowers a foundry s potential adverse environmental affects, reduces metal loss, and can speed up melting times. Vacuum induction furnaces have been widely used in the steel industry for many years. Though vacuum induction furnaces were previously considered uneconomical for use in small foundries, these units are becoming more cost effective. Development of small hand-held oxygen probe systems in the late 1980 s has made these processes less complicated and more reliable, resulting in fewer oxide pockets occurring in induction furnace castings (Heine, 1990). Modern induction furnaces are controlled by programmable logic controllers (PLC s) or industrial computers. These components enable many functions previously unavailable, such as automatic melting programs for a variety of alloys, automatic

35 21 sintering of furnace linings, automatic startup of a cold furnace, self-diagnostics of the furnace system, system data display, continuous temperature monitoring, and power demand limiting. The ability to continuously monitor furnace data and graphically display the data have made induction furnace operation more user-friendly and more error free. The furnace operator does not have to watch the system as closely, and is thus free to do other value-added tasks while the furnace is in operation. The system can alert operators to impending problems and notify them of upcoming scheduled maintenance required. Operators can also gather important operating data which can be used to calculate production efficiency (Heine, 1990). Furnace Refractories and Crucibles Refractories are the heat resistant materials that protect the furnace coil and form the metal melting cavity (crucible) in the furnace. They are not only selected based on the temperature they will withstand, but also how well they handle mechanical stress, thermal cycling, erosion, and corrosion by hot gases and molten materials. Refractories are grouped according to their ingredients and the forms in which they are available for use. Sometimes the function they are designed for will dictate how they are classified. There are many types of refractories made for industrial use, but the list of ingredients from which they are composed is fairly short. Silicon, aluminum, magnesium, calcium, chromium, and zirconium are the common elements used to produce refractories (AFS, 1989). Refractory materials are those that are able to maintain their physical and chemical properties at high temperatures. They are usually non-metallic, but there are

36 22 some metals that are considered refractory materials. The crucible s shape is formed by constructing a cylindrical steel form with a floor and placing this form inside the heating coil in the furnace. A refractory material is mixed with water (similar to the process of making concrete), then placed between the coil s refractory material and the hollow shell and allowed to dry (see Figure 6). The first time the furnace is heated, the metal form melts and is poured out and the refractory is cured, or sintered, leaving a durable lining and forming the crucible. (Meredith, n.d.) Figure 6. Installing the coil refractory in a coreless induction furnace. Photograph by the author. The refractory lining of an induction furnace is usually a monolithic type, meaning that the lining is one piece. Some other furnaces use pre-formed pieces that are

37 23 cemented in place. Monolithic linings have no joints that require filling with mortar, so the lining lasts longer and is less prone to cracking due to the absence of any interruptions in the lining. Heine (1990) states that the most common types of refractories are dry vibratables, damp ramming mixes, plastics, castables, and patches. When dry vibratables are used, a cylindrical, hollow metal form that is of a smaller diameter than the heating coil is placed in the furnace. The ground, dry refractory material is poured in around the outside of the form, filling the area between the form and the furnace shell, and thus encasing the heating coil. A vibrator is used to settle the material and get a uniform distribution and packed consistency. Dry bonding agents such as sodium silicate, boron oxide, clay, or phosphates are mixed in with the refractory so that when the furnace is heated the first time, sintering occurs and the refractory solidifies. Dry vibratables tend to be more porous and weaker than other types, so they don t last as long (Heine, 1990). Damp ramming mixes are ground refractories that are mixed with 3 to 5% water, similar to concrete, then rammed in place, filling the same area as dry vibratables. Silicon carbide is sometimes added to prevent slag and metal from penetrating the finished lining. This type of refractory has higher density and better strength, but takes longer to install and dry, and may erode if steam spalling (moisture turning to steam and causing flaking of the inside surface) occurs (Heine, 1990). Plastic refractories are used mostly for the repair of furnace linings, but also for induction furnace lids and pouring spouts. These materials are supplied ready to use, similar to modeling clay, and have more moisture (10-15%) than damp ramming mixes. They are either air curing or heat setting and are easy to install, but must be allowed to

38 24 cure slowly so that steam spalling does not occur when the furnace is heated the first time (Heine, 1990). Castable refractories are cast in place, similar to the metal casting process, but without heating. They are a mixture of heat resistant aggregate, cement (2 to 10%), and water (4 to 15%), and depending on the consistency of the mix, they can be poured, vibrated, or rammed into place. Two common additives are chromium oxide (prevents slag adhesion and corrosion) and silicon carbide (reduces penetration of metal and abrasion). Castables require the longest drying times and are only used to make the furnace s top ring, floor and for grouting the area around the heating coil (Heine, 1990). When furnace manufacturers determine the optimum lining thickness, a number of important factors must be considered. These include safety, the electrical characteristics of the heating coil, the type of metallic charge to be melted, the electrical conductivity of the charge metal, the structural limits of the furnace, the strength of the refractory material, operational parameters of the furnace, and the production needs of the foundry (Williams, 2010). Gas Absorption, Slag Formation and Oxidation As the furnace is used, the charge metal will leave behind residue and oxides (slag) that deposit on the lining of the cavity. Some slag will always form in a furnace when melting metal, but the cleaner the metal that is to be melted, the less slag will form. The nonmetallic particles that make up the slag formation stay suspended in the molten metal bath until they become large enough to float, at which time they may be skimmed from the surface. If they are not skimmed off, they will eventually contact the cooler

39 25 furnace lining and solidify on it. This slag adds to the thickness of the lining and changes the physics of the melting cycle. In attempting to restore full efficiency to the furnace, operators will scrape the deposits from the furnace lining, but this damages the lining s refractory face, causing accelerated erosion of the lining (Williams, 2010). Slag buildup can be reduced or eliminated by using fluxes during the melting process. Care must be used in selection of the proper flux, or erosion of the refractory lining will occur. Fluxes cause slag-forming particles to float to the surface more quickly and lower their melting point so they do not adhere to the cooler furnace walls. In some cases, the right flux and careful use of it can extend the life of the refractory lining. (Williams, 2010) The furnace s induction coil and melting chamber will degrade over time and must be replaced. They can be replaced independently of the rest of the parts of the furnace (Lacoma, n.d.). One challenge metal casters face is preventing the absorption of atmospheric gases by the molten metal in a furnace. The particular gas which the melt will absorb depends on the type of furnace being used, the metal being melted, the cleanliness of the metal being melted, and the type of atmosphere around the furnace during the melting process. When melting steel in an induction furnace, hydrogen and nitrogen will be absorbed to some degree by the molten steel. Introducing oxygen into the molten pool will reduce the hydrogen and nitrogen content. This can be accomplished by adding mill scale or taconite pellets to the initial furnace charge before starting to melt it. Melting low-nitrogen ferroalloys, using charge metal free of moisture and oil, and using not more than 50% foundry returns in the charge will also help keep gas absorption within

40 26 acceptable limits. Foundry returns are parts of the casting that are removed after the casting process and melted again (Svoboda & Griffith, 2002). Induction furnaces have excellent melting process and temperature control characteristics compared to most other types of furnaces due to the sophisticated electronic controls with which most are equipped. These computer-based systems not only monitor and control furnace operation, they provide a performance monitoring and diagnostic function for maintenance management. (Svoboda & Griffith, 2002, p. 14) When ferrous metals are melted, some amount of slag is generated, and must be removed from the molten pool. Since slag floats on the surface of the pool, it can be skimmed or poured off prior to filling any molds. Slag formation is much less significant in an induction furnace than in other types of furnaces, such as the direct arc type. Covering flux (such as calcium aluminate) can be sprinkled on top of the charge metal once it has become liquid, and this will reduce oxidation and slag formation (Svoboda & Griffith, 2002). An advantage offered by induction furnaces is the low level of molten metal oxidation losses. Compared to the 3-4% lost in a direct arc furnace, an induction furnace loses only about 1% to oxidation. This improves control of the chemistry of the melt and makes alloy recovery (getting the ingredients of an alloy back to specification) easier. Induction furnaces also produce only about 15% of the dust generated by arc furnaces. Small induction furnaces such as those used in schools and small foundries do not require dust collection equipment or the associated electrical power. Unlike arc furnaces, the noise levels around an induction furnace are very low, negating the need for ear protection and eliminating noise complaints from neighbors (Svoboda & Griffith, 2002).

41 27 Induction Furnace Power Supplies Whether large or small, electric furnaces that melt metals require sizable amounts of electric power. The amount of power needed is proportional to the melting capacity of the furnace. Many foundries schedule their melting activities only during offpeak power consumption periods in order to minimize utility costs. When investigating the possibility of installing an induction furnace, two areas that should be considered are adequacy of the electric service to the furnace and the possibility of voltage frequency distortion to the utility system. The local utility company should be consulted about service adequacy and distortion likelihood. An industrial furnace may require a new power meter or sub-meter, higher voltage supply lines, or even a new power substation and/or transformers. Small furnaces typically use 480 volt input power, which usually exists in most school laboratories that have manufacturing equipment and machinery installed (Svoboda & Griffith, 2002). Induction furnace power supplies (see Figure 7) allow soft starting, which lowers the current output to the furnace coil during initial heating, thereby increasing the life of the power supply and the furnace coil. Other benefits induction furnace power supplies offer are the ability to balance loads on each of the three electrical phases and provide high power outputs to the furnace for efficient melting. These benefits are attributed to the use of the silicon-controlled rectifier (SCR), or thyristor, whose introduction has allowed the accurate variation of the magnetic field in the furnace. The SCR allows frequencies of as low as 0.5 Hz all the way up to 250,000 Hz to be produced, and by electronically controlling the switching speed of the SCR, the power output of the furnace can be smoothly varied from its minimum to its maximum value (Heine, 1990).

42 28 Figure 7. A 75 kw induction furnace power supply. Photograph by the author. Modern solid-state power supplies with efficiencies well over 90% are replacing the older motor-generator power supplies, which were slightly less efficient. The overall efficiency of the furnace system (power supply, heating coil and all other components) is significantly lower, at a maximum of about 60%. The reduced maintenance requirements resulting from the elimination of moving parts, along with the faster melting times, makes the newer power supplies a good investment. Power supplies can be upgraded to the newer types without replacement of any of the other furnace system components. An added benefit to replacing older power supplies is the elimination of hazardous materials they contained, such as asbestos, PCB s, and leadbased paints (Smith, 1992).

43 29 The magnetic field generated in the cavity where the charge metal is melted causes the molten metal to circulate. The higher the frequency used to create the field, the lower the amount of this stirring action in the molten metal bath. The more electric power that is applied to the furnace coil, the higher power density, the greater the stirring action and the higher the dome formed in the center of the molten metal pool. The maximum power that can be applied is therefore limited by the amount of stirring that occurs. Too much power applied will cause molten metal to overflow the top of the crucible or be spit out of the furnace as flying droplets. Proper stirring levels will produce a good, homogeneous melt without oxides or unnecessary wear to the furnace lining (Grant, 1991; Smith, 1992). Prior to the availability of reliable sold state components, many larger furnaces operated on line frequency (60 Hz). With their advent, solid state devices have paved the way for power supplies that provide more flexible power ranges, cost less, have a smaller footprint, and require less maintenance since they have no moving parts. Medium frequency (180 to 350 Hz) and high frequency (1,000 Hz) power supplies are now the most popular because of the production flexibility they allow a foundry to utilize. They permit the melting of several alloys each day because of the ease with which these furnaces can be started, stopped, and emptied. Furthermore, as the operating frequency is increased, the power density of the furnace can be increased. What this means is that a higher frequency furnace can melt the same amount of metal as a low frequency furnace, but the furnace can be smaller. This equates to reduced induction furnace operating costs (Smith, 1992).

44 30 If two different sizes of induction furnaces are supplied the same amount of power, the smaller furnace will melt its charge metal at a faster rate. This equates to lower power costs per volume of metal melted in smaller furnaces, but the amount of metal that can be melted at one time is less. Other factors that influence power requirements are the amount of furnace insulation and how much heat loss occurs at the surface of the molten metal bath. An insulating cover on top of the furnace and adequate insulation around the furnace can yield significant savings in operating costs. Conversely, too much insulation can drive up the temperature of the furnace lining and reduce its life (Grant, 1991). Induction Furnace Inverters When compared to an arc furnace, the electric current that an induction furnace draws is very smooth and stable. However, induction furnaces incorporate large inverters in their power supplies. The inverter changes the incoming alternating current (AC) to direct current (DC), then back to AC at a higher frequency. The frequency of the AC voltage that is then sent to the induction heating coil can be varied while the metal charge is melted in order to achieve the fastest melting cycle. According to Heine (1990), modern inverters can deliver and maintain maximum solid state power throughout the entire melting cycle (p. 32). However, the inverter can cause frequency harmonics to be generated and fed back into the utility system. These harmonics can cause problems for nearby residents that have sensitive electronic equipment. Following the design rules set forth in The Institute of Electrical and Electronic Engineers standard IEEE-519 will help prevent this condition (Cignetti & Lazor, 2002).

45 31 Induction Furnace Water Systems Water is an important part of the induction furnace system, since it is used to keep the power supply and the furnace coils cool. The better the quality of the water, the more reliable will be the cooling system and the longer it will last. Water must be free of debris, supplied at the correct pressure and flow rate, at the correct temperature, and free of dissolved solids. Keeping the temperature of the furnace and the power supply s electrical components at proper levels is critical to proper furnace operation and maximum life of the power supply. Whether a closed or open water system is used, proper flow rate, pressure, and temperature is important. If the water in the system is too cold, it will cause condensation to form on the warm component surfaces in the power supply, which can increase the possibility of arcing between the components (Cignetti & Lazor, 2002). Poor cooling water quality will reduce the water s ability to transfer heat from the melting system components, cause corrosion of cooling system tubing, and because of the higher electrical conductivity of impure water, it will reduce the efficiency of the electrical components in the power supply. The impurities in poor quality water cause scale formation, fouling due to corrosion, and growth of biological elements in water passages. These conditions cause the cooling efficiency of the system to fall, resulting in a rise in cooling water temperature, which can eventually destroy electrical components (Cignetti & Lazor, 2002). There are two main types of water cooling systems in use with induction furnaces: Evaporative Closed Loop Water Systems and Dry Air Closed Loop Water Systems. Most modern coreless induction furnaces use the first of these two types of

46 32 cooling systems, as shown in Figures 8 and 10, which are composed of two separate water circulation loops. In this diagram, the left side (secondary side) cools the power supply, while the right side (primary) cools the furnace coils. The water is not mixed between the loops, nor is it open to the atmosphere. An advantage of having two separate loops is that only the secondary loop that cools the power supply requires high quality water (see the section Purification and Maintenance of Cooling System Water later in this chapter), so the rest of the system can use ordinary water, reducing operating costs (Cignetti & Lazor, 2002). Figure 8. General diagram of evaporative closed loop water system. Source: Cignetti, N.P. & Lazor, D.A. (2001). Coreless induction melting water systems. American Foundry Society Library, AFS Transactions , American Foundry Society, Schaumburg, Illinois. Reprinted with permission.

47 33 Most commercial induction furnaces utilize a closed loop evaporative cooling tower like the diagram shown in Figure 9. Using the cooling power of evaporation, the water circulated through the unit is cooled by spraying water from nozzles above the tubes through which the water is circulated. Some of the spray water evaporates, while the rest collects in a tray in the lower part of the tower. Additional water is continually added to the tray from the local water supply to replace the water that has evaporated. Depending on the quality of the spray water, treatment may be necessary to remove minerals or other contaminants (Cignetti & Lazor, 2002). Figure 9. Typical evaporative type cooling tower. Source: Cignetti, N.P. & Lazor, D.A. (2001). Coreless induction melting water systems. American Foundry Society Library, AFS Transactions , American Foundry Society, Schaumburg, Illinois. Reprinted with permission.

48 34 The other type of cooling system, the Dry Air Closed Loop Water System, is used when a foundry is located in a cooler climate (Figures 10 and 11). These systems have lower cooling capacities due to the absence of the evaporative water spray system in the cooling tower. An advantage of this system is that the maintenance a spray system requires is not needed. The cooling water in the system flows through tubes that are cooled by fans blowing ambient outside air over them, so the water can only be cooled as low as the outside air temperature. On unusually hot days, additional cooling, provided by a device called a trim cooler, may be required (see Figure 12). Consult the furnace manufacturer to determine which type of system fits the climate in which it will be used (Cignetti & Lazor, 2002). Figure 10. An evaporative closed loop water system. Photograph by the author.

49 35 Figure 11. General diagram of dry air closed loop water system. Source Cignetti, N.P. & Lazor, D.A. (2001). Coreless induction melting water systems. American Foundry Society Library, AFS Transactions , American Foundry Society, Schaumburg, Illinois. Reprinted with permission. Purification and Maintenance of Cooling System Water Since the quality of the water in the furnace cooling system is important to efficient operation of the system, the water must be adequately purified and maintained. One important property of the water is its electrical conductivity, which is controlled in newer cooling systems by a de-ionizer. The primary (furnace) side of the cooling system has less stringent water quality requirements, so the conductivity of the water may be kept at higher levels, generally around 100 to 300 micromhos/cm. The secondary side (power supply) system should have a water conductivity level of about 50 micromhos/cm (Cignetti & Lazor, 2002).

50 36 Figure 12, Typical dry air fluid cooler. Source: Cignetti, N.P. & Lazor, D.A. (2001). Coreless induction melting water systems. American Foundry Society Library, AFS Transactions , American Foundry Society, Schaumburg, Illinois. Reprinted with permission. The conductivity of a solution, such as water, is determined by the amount of ionic compounds present, and thus determines how well the solution will conduct electricity. The English unit of conductivity is mho/cm, while the Si unit is Siemens per centimeter (S/cm), and the two units are identical. Pure water has a conductivity of less than 1 x 10-7 S/cm, while distilled water is at about 1 µs/cm (Down & Lehr, 2005). The water conductivity in Chico is monitored by the California Water Service Company. Their 2014 Water Quality Report shows the average specific conductance of water in Chico to be 294 micromhos/cm (California Water Service Co., 2014). This is adequate for the primary side of the cooling system, but the secondary side would require a de-ionizer. Another option for the secondary side would be to fill it with food grade

51 37 glycol. California Polytechnic University, Pomona elected to go with this option in their closed-loop cooling system (M. Koch, personal communication, May 27, 2015). It is equally important that the conductivity of the water in the cooling system not be too low as well as not being too high, especially on the secondary side. If it is too low, the relatively pure water will become corrosive and can cause damage to power supply components. Furnace coils on the primary side of the system can also be damaged by corrosive water. Scaling and corrosion of components in the furnace system will change the resistance of electrical connections, which degrades the efficiency of the furnace system. Increasing temperature and air bubbles in it can increase water s conductivity. High conductivity water can be a result of direct current potentials in the furnace equipment, and will cause corrosion of pipe nipples. Annoying tripping of ground detectors and distortion of control signals can also occur when water conductivity is too high. If corrosive water is left in the cooling system too long, it can corrode iron piping and plates in the heat exchanger, raising the iron content of the water and thereby increasing its conductivity. The conductivity of the water can be effectively monitored by installing a conductivity meter in the system (Cignetti & Lazor, 2002). Periodic changing of the cooling water in closed systems is important to prevent microscopic organism growth in the system. If inspection (by disconnecting hoses or fittings) of the inside of the piping shows a black, slippery substance, the organisms are present, and will attack the piping, eventually causing water leaks to develop. If the organisms are present, the water should be drained and system first flushed with acid, then a basic rinse followed by a rinse and flush with water. When

52 38 refilling the system with water, all trapped air should be bled from the system components (Cignetti & Lazor, 2002). In localities where the amount of solids in the cooling water is higher, using a filtration system to remove the solids from the water may be advisable, but most water filtration systems require constant maintenance. Because of their many advantages, centrifugal separators for water filtering have become popular in recent years. According to Cignetti & Lazor, these advantages are: No moving parts to wear out (water path creates centrifugal force). No screens, cartridges, cones or filter elements to replace. No backwashing. No routine maintenance or downtime requirements. No standby equipment needs. Low and steady pressure loss. Easily automated. The centrifugal action of the separator removes solids from the water, which extends pump life, eliminates fouling of heat exchangers and small power supply component piping, and it helps the system operate at peak efficiency (Cignetti & Lazor, 2002). Water Requirements and Quality Before considering installation of a coreless induction melting system, it is very important to ensure that the proper quantity and quality of water will be available to the furnace system. Manufacturers of induction melting systems should include information regarding the specifics of these requirements in system quotations. Adequate

53 39 flow and quality of water must be supplied to the melting system at all times during its operation in order for the system to function reliably, efficiently, and safely. There should be sufficient flow available so that when the furnace is operating simultaneously with all other water-consuming systems in the building, there is still sufficient water pressure and volume to meet the cooling needs of the furnace. There must also be an emergency water supply available in case the furnace s closed water supply system ceases to function due to electrical power or pump failure. An emergency water system could be untreated city water (which is almost always available and reliable), a generator- or battery-powered pump, a turbine pump operated by the city water supply, or an elevated water storage tank (Cignetti & Lazor, 2002). An emergency water system is needed because if cooling water stops circulating while the furnace is in operation, the system will overheat, resulting in damage to the furnace and possibly other parts of the system. Even if the power supply is shut off, if there is molten metal in the furnace, it will radiate enough heat to turn the water in the furnace cooling coils to steam, increasing the pressure in the closed system. If the pressure rises to a high enough level, it can rupture water lines or blow hoses off of their connections, possibly injuring foundry personnel and damaging equipment. Once the system is open and the water escapes, there is nothing to cool the furnace, and the coils in the furnace lining may be seriously damaged due to the high temperature to which they are subjected. If the molten metal is quickly removed from the furnace after the loss of the cooling water, damage to the furnace may be avoided, along with the cost of repairs and lost production (Cignetti & Lazor, 2002).

54 40 Other Supporting Systems Every furnace must have a system for charging it with the metal that is to be melted. Most small furnaces lend themselves well to inserting the charge metal manually, using simple plier-like furnace tongs or even one s hands when the furnace is cool. Larger furnaces typically have mechanized charging systems which may include machinery such as conveyors, cranes, weighing equipment, dryers, and preheaters. Another support system the furnace needs is an array of hydraulic components for lifting the lid, swinging it aside, and tilting the furnace. Such a system will be made up of electric motors, hydraulic pumps, hoses, hydraulic cylinders, and a reservoir of hydraulic oil. Some type of exhaust system, which may include emission control devices, is usually required. The type of exhaust system depends on the fumes generated, which is determined by the metal being melted (Smith, 1992). In foundries where preheaters are used, there are two main reasons they are employed. One is to reduce the electrical energy required for melting the metal in the furnace by raising its temperature prior to charging it into the furnace. The more important reason is to increase production by speeding up the melting cycle. A preheater will also act as a charge dryer, removing any moisture on the charge metal, along with some oxides and oils. It is important that no moisture exists on the charge metal, especially if the furnace is already hot and contains a partial bath of molten metal when the charge metal is introduced into the crucible. Any moisture present on metal that is inserted into a hot furnace can cause a steam explosion, expelling molten metal from the furnace. This very hazardous condition can damage equipment and cause injuries or even death. Preheaters usually operate at about º C (1,290-1,380º F), use combustion

55 41 for production of heat, and operate either continuously or intermittently, depending on production demands (Calamari, 1985). Safety There are a number of areas related to induction furnaces, as well as metal casting in general, where safety is of the utmost importance. As is the case with most industrial environments, hazards exist in foundries, and injuries will occur. Most safety practices used in foundries are similar to those in other manufacturing plants, and include observing good housekeeping habits, the use of Personal Protective Equipment (PPE), and establishing and following an Injury and Illness Prevention Program (IIPP). PPE depends somewhat on the type of metal being melted and the size of the furnace. In small foundry settings such as those in school labs, students pouring molten metal should wear long pants, long sleeved shirts, closed toed shoes, and safety glasses. PPE should include leggings which completely cover the shoes, arm covers, heavy cotton gloves, and a full face shield. These items are adequate for most non-ferrous melting activities. For ferrous metal melting or larger volumes of non-ferrous metals, a full-body aluminized suit is recommended. Fume hoods over the melting and pouring areas are adequate for removing any smoke or fumes that are generated (CSUC, 2008). When melting metal, there exists the potential for molten metal explosions within the furnace if proper safety precautions are not observed. These explosions can occur when moisture becomes trapped beneath the surface of the molten metal pool. When this happens, the moisture is rapidly heated and immediately turns to steam, which is 1,600 times the volume of water. This rapid expansion causes molten metal to be

56 42 blown from the furnace in a violent explosion. The severity of the explosion is proportional to the amount of moisture beneath the surface of the molten pool, the volume of the pool, and the temperature of the pool Kohloff (2010). According to Kohloff (2010), the possible reasons for molten metal explosions are: Charge materials not properly inspected for liquids before charging. Furnace cooling lines accidentally ruptured. Furnace hydraulic lines accidentally ruptured. Objects (containers, pipes) containing liquids accidentally charged into furnace. Molten metal or slag spilled onto a floor where moisture or liquids exist. Furnace tools not properly preheated. Furnace bridging (metal charged on top of a molten pool is not in contact with the pool and an air gap forms between the charge metal and the pool). Incorrectly installed or improperly sintered new furnace lining. Proper furnace maintenance practices not followed. Freshly relined ladles not dried properly. By following rather simple rules and taking precautions, foundries can reduce or eliminate the risk of accidents related to molten metal explosions in the furnace area. According to Kohloff (2010), some of these rules and precautions are: Be sure that charge metals contain no trapped or surface liquids nor are they in sealed containers. Store all charge metals and scrap in a covered, dry area.

57 43 Carefully inspect all charge materials for moisture or oil. Never place any kind of sealed container in a furnace. Preheat all charge materials before placing them in the furnace. Using a remote-controlled automatic charging system places furnace personnel away from the danger zone in case a molten metal explosion does occur. Do not allow cold charge materials to bridge the top of the crucible, preventing them from contacting the molten metal in the bottom of the crucible and causing it to overheat. Keep the furnace pit or melting area clean and dry at all times. The induction furnace should be well maintained so that the cooling system never ruptures and causes an explosion. Allow molten slag or dross to cool before moving it to an area where it could be contacted my moisture. Do not install overhead sprinkler systems near melting furnaces. Keep the roof of the building containing the furnace well maintained to avoid water leaks that could introduce moisture to the furnace area. Make sure that butane lighters are never in the melting area. Purchasing and Operating Costs Initial purchase of an induction furnace is more costly than some of the other popular melting furnaces found in aluminum or steel foundries. When comparing furnaces of similar capacities and melting rates, the gas-fired melting and holding furnace has a lower initial cost and lower operating costs than an induction furnace. The lower

58 44 initial cost is mainly due to the more simple design and lower complexity system associated with the gas-fired furnace, while the lower operating cost is mostly attributed to the lower price of natural gas as a fuel (Miseresky, 1993). In 1993, the Volkswagen Canada wheel casting plant in Barrie, Ontario conducted a research project whose goal was to determine whether it would be more cost effective to expand the existing induction melting foundry capacity with more induction furnaces or by purchasing a high efficiency gas-fired melting furnace. A 550 kg per hour capacity induction furnace that was installed in the plant in 1984 was compared to a new gas-fired furnace with a capacity of 1,500 kg per hour. As shown in Table 1, disregarding the difference in purchase price, the operating cost of the gas-fired furnace is 38% less than the induction furnace. The quality of the molten metal produced by each furnace was determined to be equal (Miseresky, 1993). Using an inflation calculator provided by the U.S. Government, the purchase price of the induction furnace today would be $1,179,000, while the gas-fired furnace would cost $860,000 (U.S. Government, n.d.). Table 1 Comparison of Volkswagen s New (1993) Gas-Fired Furnace to their Induction Furnace Specification Induction furnace Gas-fired furnace Melting Capacity 550 kg/hour 1,500 kg/hour Dross Loss 0.43% 1.40% Operating Cost $ per kg melted $ per kg melted Purchase Price Estimated $720,000 $524, 980

59 45 Once an induction furnace has been acquired and is in operation, electricity is the main operating cost to be considered. According to Grant (1991), the two parts of the monthly power bill are the maximum demand charge and the consumption charge: Maximum Demand = Peak Power x Tariff Consumption = Power x Hours of Use x Tariff According to Tanneberger (2012), the consumption portion of a large company s (like a foundry) power bill makes up about 55% of the bill, while the demand charge makes up about the remaining 45% of the bill. Furnace Efficiency Induction furnace efficiency is defined as the ratio of the net power applied to the molten metal charge (P n ) to the amount of input power supplied to the furnace (P o ), or E = P n /P o. These two power values are different because of power losses that occur between the point where the power comes into the furnace power supply and the point where the molten metal bath is located. These losses (P e ) are mostly due to electrical resistance in the primary heating coil, and to a lesser extent, in the power supply. P e is usually a constant portion of P o. Another loss that reduces the efficiency of the furnace is thermal loss (P t ) from heat escaping through the walls and lid or top opening of the furnace. This loss is also mostly constant, and is independent of P o. The total net power available to melt metal is equal to the supplied input power minus the electrical loss minus the thermal loss, or P n = P o -P e -P t. The production rate the furnace can provide is directly proportional to the net power, P n. Various furnace types will yield different

60 46 values for P e and P t, but with all furnaces, the greater the utilization of the furnace, the greater the overall efficiency (Smith, 1992).

61 CHAPTER III METHODOLOGY Induction Furnaces in Manufacturing Courses The California State University, Chico (CSU, Chico) foundry currently has two casting furnaces: a 30-pound capacity gas-fired crucible furnace and a 200-pound electric resistance crucible furnace. These capacity values are the maximum amount of aluminum that the furnaces can melt at one time, and this type of capacity nomenclature is typical for small furnaces. Two universities in the CSU system have small induction furnaces which are used to teach metal casting technology. Both of these universities were visited by the author for the purpose of studying the induction furnace equipment they use and how they integrate these furnaces into their metal casting curriculum. California Polytechnic University, Pomona (Cal-Poly, Pomona), has three induction furnaces that are operated by one common power supply (see Figure 13). The 3,000 Hz, 75 kw, 440 volts AC maximum power supply is connected to the furnaces that may only be used one at a time. The capacities of aluminum that each furnace can melt are 7 pounds, 22 pounds, and 200 pounds. All three furnaces are used primarily for melting aluminum, but other metals are melted on a less frequent basis. Aluminum is most commonly melted because of the lower power needed and the lower temperature required compared to other metals like brass, cast iron and steel. Casting processes used 47

62 48 Figure 13. Induction furnaces in the Cal-Poly, Pomona foundry. Photograph by the author. are green sand, lost foam, and investment (V. Okhuysen, personal communication, March 16, 2011). One of the exercises used at Cal-Poly, Pomona to teach beginning-level students about metal casting is a simple lost foam process casting. Half-inch thick Styrofoam sheets (Figures 14) are cut into horse-shaped patterns (Figure 15) by a local shop with a waterjet cutting machine (V. Okhuysen, personal communication, March 16, 2011). The patterns are then separated from the sheet and glued onto a Styrofoam gating system in preparation for casting. Once the patterns are attached to the gating system, the completed tree of patterns and gating pieces is immersed in a bucket or tub of loose, dry foundry sand with the sprue of the gating system protruding slightly out of

63 49 Figure 14. Styrofoam sheets waterjet cut for the lost foam process. Photograph by the author. Figure 15. Styrofoam patterns ready to be separated from the sheet. Photograph by the author.

64 50 the top of the sand. The molten metal is then poured directly on the top of the sprue and immediately burns away and vaporizes the entire pathway of Styrofoam. As the molten metal solidifies, it forms the shape of the Styrofoam before it was vaporized (Figure 16). Once the metal has cooled sufficiently, it can be removed from the sand and the gating system cut from the castings. The gating system is then melted again to produce more castings (V. Okhuysen, personal communication, March 16, 2011). Figure 16. Casting tree ready to have gating system removed. Photograph by the author. California Polytechnic University, San Luis Obispo (Cal-Poly SLO), has an induction furnace system similar to the system in Pomona (Figure 17) that is employed in the teaching of metal casting technology. A 50-pound tilting box furnace and a 125- pound hydraulic lift furnace are utilized to teach casting to students (Figure 18).

65 51 Figure pound tilt pour induction furnace at Cal-Poly, Pomona. Photograph by the author. Figure 18. Induction furnaces at Cal-Poly, San Luis Obispo. Photograph by the author.

66 52 Beginning students in the Industrial Engineering and Manufacturing Engineering programs make a wax pattern and produce an aluminum casting from it. First, the students use Computer Aided Manufacturing (CAM) software to customize a 3D solid model of a medallion, adding their name to it (Figure 19) (M. Koch, personal communication, March 17, 2011). Figure 19. CAM software for creating pattern machining program. Photograph by the author. Next, the software is used to generate the G-code program for a Computer Numerical Control (CNC) machining center. The CNC machine cuts the design of the medallion into a piece of wax (Figures 20 and 21) (M. Koch, personal communication, March 17, 2011).

67 53 Figure 20. CNC Machining Center ready to cut wax pattern. Photograph by the author. Figure 21. CNC Machining Center cutting wax pattern. Photograph by the author.

68 54 After the wax pattern is machined, the gating system is added to it and it is placed on a block of ceramic material (Figure 22). Foundry sand mixed with sodium silicate is used to make the drag (bottom) half of the casting mold from the pattern (Figure 23). To the drag half of the hardened sand mold is then added the generic cope (top) half of the mold and a sprue for directing the molten metal into the mold (Figure 24) (M. Koch, personal communication, March 17, 2011). Figure 22. Wax pattern with gating system. Photograph by the author. 356 alloy casting aluminum is heated to the proper pouring temperature (about 730ºC (1,350ºF) and poured into the sand mold (Figure 25). After the molten aluminum solidifies and cools sufficiently (about 20 minutes), the mold is broken away to reveal the rough casting (Figure 26). The gating system is cut off with a band saw and the gates smoothed with a belt sander (M. Koch, personal communication, March 17, 2011).

69 55 Figure 23. Sand mold ready for top half and sprue. Photograph by the author. Figure 24. Complete sand mold ready for pouring. Photograph by the author.

70 56 Figure 25. Pouring molten aluminum into the sand mold. Photograph by the author. Figure 26. Rough casting ready for gating system removal. Photograph by the author.

71 CHAPTER IV RESULTS AND CONCLUSIONS Demands for Metal Casting Education According to the United States Department of Labor, Bureau of Labor Statistics, in the Occupational Outlook Handbook, the demand for careers in which knowledge of metal casting is important is shown in Table 2. Note that all four of the careers shown require a bachelor s degree, have significant growth projected, and pay $75,000 or more as of These careers all involve the design, specification, and manufacture of items that are often well suited to the casting process. Benefits of an Induction Furnace to Technology Programs Cal-Poly, Pomona utilizes their induction furnaces in a number of manufacturing and engineering courses. Those courses are Manufacturing Processes for Non-Manufacturing Engineers (MFE 201/201L), Manufacturing Processes for Manufacturing Engineers (MFE 230/230L), Design for Manufacturing (MFE 326/326L), and Foundry Process Engineering (MFE 334/334L) (V. Okhuysen, personal communication, May 20, 2015). The simple lost foam casting exercise that students perform at Cal-Poly, Pomona is an ideal casting exercise for a school setting because the pattern materials are very inexpensive, the castings produced are small, and only a small crucible is needed to 57

72 58 Table 2 Occupational Outlook for Careers in which Metal Casting Knowledge is Important Occupation Entry-Level Education On-the-Job Training Projected Number of New Jobs Projected Growth Rate 2012 Median Pay Aerospace Engineer Bachelor s Degree None 5,000 to 9,999 0 to 9% $75,000 or more Industrial Engineer Bachelor s Degree None 10,000 to 49,999 0 to 9% $75,000 or more Materials Engineers Bachelor s Degree None 0 to to 9% $75,000 or more Mechanical Engineer Bachelor s Degree None 10,000 to 49,999 0 to 9% $75,000 or more Source: Table adapted from U.S. Department of Labor, Bureau of Labor Statistics (2012). Occupational Outlook Handbook. Retrieved from melt the low volume of metal required. Simple lost foam casting processes are also perfect for school settings because they take very little time to complete. The whole process can be demonstrated in as little as one hour. Students can complete the same exercise in less than two hours. The school s small 22-pound furnace is used to pour the lost foam castings. Students are able to see and create a casting from start to finish in a very short time (V. Okhuysen, personal communication, March 16, 2011). Cal-Poly, San Luis Obispo utilizes their induction furnaces in the Industrial Engineering and Manufacturing Engineering majors. The main course that uses the furnace is Manufacturing Processes: Net Shape (IME 141), which focuses primarily on

73 59 the metal casting process and serves 150 to 175 students every quarter. The furnace also supports Manufacturing Process and Tool Engineering (IME 450), in which the students design and manufacture a permanent mold or die tooling. The furnace is also used for a variety of senior projects and club projects. (M. Koch, personal communication, May 23, 2015). The casting exercises students complete at Cal-Poly, San Luis Obispo offer the same benefits as at Cal-Poly, Pomona with a few additions. Students get to actually design part of their casting, they see it machined on a CNC machining center, and they produce a personalized keepsake at the end of the exercise. CSU, Chico could integrate an induction furnace into a number of courses in the department of Mechanical and Mechatronic Engineering and Sustainable Manufacturing. In the SMFG 160 (Manufacturing Processes) class, which had 120 students during the Fall 2014 semester, an induction furnace could be used to cast the cable drums for the hoist/winch project. Every 160 student builds a hoist/winch and needs a cable drum for it. The existing electric resistance furnace is used to cast student project castings and production parts for CSUC Manufacturing, a student-operated on-campus company that supplies manufactured parts to commercial customers. Most of the parts these customers require are made from 356 aluminum casting alloy, which is kept in the electric resistance furnace. An induction furnace would be ideal for casting 713 aluminum for the cable drums, as well as other aluminum alloys. It could also cast other non-ferrous and ferrous alloys. SMFG 260 (Material Removal) allows each student (about 30 per semester) to construct a small machininst s vise from cast aluminum and machined steel components.

74 60 The cast aluminum parts for the vise can be cast from either 356 or 713 aluminum alloy, so either the electric resistance furnace or an induction furnace could be used. SMFG 464 (Fluid Metallurgy) is now an elective, and an induction furnace would be highly beneficial to that course. Induction furnaces are studied in that course, and students could gain valuable hands-on experience with an actual induction furnace. There are additional opportunities to integrate an induction furnace into the engineering courses. Engineering students could design cast components for senior projects, create casting patterns with the rapid prototyping process, and do metallurgical research. An induction furnace would satisfy the following learning objectives: Students would learn how to operate an electric induction casting furnace. Students would learn the basics of melting metal and handling it properly. Students would melt aluminum or other metals in the furnace and pour it into a mold, creating a metal casting. Space and Utilities Required The space requirements for a small (50- to 100-pound) induction furnace are slightly larger than for a similar sized gas-fired or electric resistance crucible furnace because of the addition of the power supply. The CSU, Chico foundry s existing gas-fired crucible furnace, its piping and blower occupies an area of about 6 feet by 6 feet. The electric resistance crucible furnace consumes an area of about 8 feet by 6 feet, including its power supply. An electric induction furnace in the 50- to 100-pound range only requires an area as small as 2 feet by 3 feet, but there should be about 2 feet of clearance around the furnace. The power supply cabinet is about 4 feet wide by 2 feet deep by 6

75 61 feet tall, and should have about 2 feet of clearance around it. See Appendix B for existing and proposed CSU, Chico foundry laboratory floor plans. (M. T. Dicken, personal communication, March 14, 2011). For small induction furnaces in the 50- to 100-pound range, a water chiller system usually isn t required, because they will often make the water too cold, causing condensation to form on the system components. In hot climates, such as those where ambient outside air temperatures are above 90 degrees F., a small evaporative chilling system may be used and can be purchased for $2,000 to $3,000. When the evaporator is located on the roof of a building, it needs to be cleaned periodically of dirt, leaves or other buildup. The water temperature coming out of the evaporator should be 90 F or cooler, but above the dew point. If city water is used to cool the furnace, very hard water will cause buildup of minerals in the system. This can eventually lead to degradation in the system s efficiency. Simply circulating city water through the furnace cooling components is usually sufficient, and it can be discharged into the municipal drain system. This type of open system will consume a significant amount of water, so a closed system may be the best choice for that reason alone. A 50 kw induction furnace using city water for cooling will discharge 8 to 12 gallons per minute into the municipal drain system during the furnace s melting cycle. After the power to the furnace is shut off, the water flow rate can be reduced to about 1 to 2 gallons per minute. This flow rate should be maintained typically for about one-half to three hours, which will cool the furnace crucible down to room temperature (M. T. Dicken, personal communication, March 14, 2011).

76 62 Concerning electric power requirements, most small induction furnaces operate on 480 volt AC power. This is typically available in an industrial or laboratorytype of educational building. Induction furnaces are more efficient when operated at full power settings, as shown in Figure 27. If not operated at full power, the percent power utilization decreases, resulting in increased energy consumption. Furnaces in industrial environments always operate at full power unless the crucible needs to be scraped to remove metal and oxides buildup during production runs (Duca & Naro, 2010). Figure 27. Energy consumption vs power utilization. Source: Reprinted from Duca, W. & Naro, R. (2010, January). Saving electrical energy in coreless induction furnaces. Retrieved from feature/saving-electrical-energy-coreless-induction-furnaces Melting rates per hour for a 40kW, 3,000 Hz induction furnace are shown in Figure 28. This data was reproduced from empirical data supplied by Mike Dicken at

77 63 Melting Hz (lbs./hr) Steel Aluminum Copper Gold Silver Note. A 40 kw, 3,000 Hz induction furnace will achieve the above melt rates. Figure 28. Melting rates at 40 kw power consumption. Reproduced by the author (M. T. Dicken, personal communication, February 10, 2015) Induction Technologies Corporation (M. T. Dicken, personal communication, March 14, 2011). A furnace of this size and power would be suitable for a university setting because of its small size, yet adequate melting rate. The current Pacific Gas and Electric Company (PG&E) flat rate for electricity is $.164/kWh. This cost figure assumes typical demand charge rates and peak summer rates, which are highest (Pacific Gas and Electric Company, 2015). Consuming 40kWh, an induction furnace would cost approximately $6.56 per hour to operate if it were 100% efficient. Most induction furnaces are about 60% efficient, so dividing the previous $6.56 cost by.6 yields an actual cost of about $11.00 per hour. If the furnace was operating 8 hours per day, 5 days per week, and 50 weeks per year, the annual electricity cost would be $22,000. It is difficult to accurately

78 predict the electricity cost for an induction furnace in an educational laboratory because the use is so sporadic. In any case, the annual electricity cost would be much lower. 64 Conclusions The induction furnace is definitely a viable piece of equipment for use in a university environment where the subject of metal casting or fluid metallurgy is to be studied. California Polytechnic University, San Luis Obispo and California Polytechnic University, Pomona are both using inductions furnaces successfully in their Industrial Engineering and Manufacturing Engineering programs. Induction furnaces are available that are small enough and inexpensive enough to be installed in a university s manufacturing laboratory. Any of the induction furnace components in Appendix A could be assembled into a two-furnace system for under $50,000. See Appendix B for current and future floor plans for the Plumas 116 manufacturing laboratory. With enough power output, these furnaces will melt both ferrous and non-ferrous metals quickly and efficiently. They are safe to operate when proper procedures are followed and can lend themselves to a myriad of educational projects, such as pattern making, general casting production, tooling design and production, and research.

79 CHAPTER V SUMMARY AND RECOMMENDATIONS Summary Acquiring an induction furnace at CSU, Chico would be useful in teaching metal casting and its related technologies to manufacturing and engineering students. It would speed up the melting of small batches of metal, thereby reducing wasted metal due to oxidation losses. Foundry equipment suppliers are willing to donate furnaces and support equipment to schools that will teach the technology. The equipment is simple to operate, quiet, reliable, and safe. The demand for graduates with knowledge of metal casting is strong. Recommendations A number of small metal melting furnaces will work well in a school laboratory. The two furnaces currently in the CSU, Chico metal casting laboratory each have their own advantages and disadvantages. An electric induction furnace would allow metal casting work that is not currently feasible or possible. The author has already found a furnace equipment manufacturer willing to donate a 100-pound induction furnace for the CSU, Chico foundry. One of the primary reasons for seeking donation of an induction furnace is that it would allow the melting and casting of ferrous metals. This capability would greatly enhance the range of metal casting study areas and projects available to 65

80 66 manufacturing and engineering students, as well as students from other departments on campus. The existing furnaces can achieve a maximum temperature of approximately 1,150º C (2,100º F), which is only sufficient to melt non-ferrous metals and alloys, such as aluminum, brass, bronze, and zinc. It is difficult to melt copper-based alloys such as brass with the existing gas-fired crucible furnace because it takes a relatively long time for the brass to melt (about 1.5 hours). The lengthy melt time oxidizes the brass severely, resulting in high dross formation. This oxide layer must be removed from the surface of the molten metal, resulting in an undesirable loss of charge metal. Since induction furnaces can produce temperatures of over 1,650ºC (3,000ºF), a foundry equipped with one of these can melt cast iron, alloy steel, stainless steel, as well as non-ferrous metals (M. T. Dicken, personal communication, March 14, 2011). An induction furnace can melt the charge metal much more quickly, reducing energy costs and melt losses. Small induction furnaces (in the 20- to 100-pound melt range) are well suited to the production of small individual castings and small part production runs like are ideal for teaching metal casting in an educational setting. A manufacturer should be chosen and consulted so that the best furnace for the university s needs is selected. The exact requirements in terms of space and utilities also needs to be determined once a furnace is selected. Facilities and Management Services at CSU, Chico should provide a quotation for price and scheduling of the necessary tasks to be done prior and during installation of the furnace. As shown in Appendix A, there are quite a number of small furnaces to choose from, even when examining the available furnaces from just one manufacturer like Induction Technologies

81 67 Corporation. The owner has graciously offered to donate a refurbished induction furnace to CSU, Chico as long as the university will provide the necessary infrastructure to support it. An induction furnace would be a valuable tool to use to teach metal casting to the students in the department of Mechanical and Mechatronic Engineering and Sustainable Manufacturing.

82 REFERENCES

83 REFERENCES A Guide to basic furnace designs. (1968, October). Founding, Welding, Production Engineering Journal, 8 (10), 18. About AFS & metalcasting. (n.d). Retrieved from Allied Mineral Products. (2015). Channel induction furnaces. Retrieved from Calamari, E. (1985). Uses and prospects of the induction melting of steel. American Foundry Society, document California State University, Chico (CSUC) MMEM Dept. Faculty. (2008). Lab safety policies and procedures, edition 4. Unpublished manuscript. California Water Service Company. (2014) Water quality report. Retrieved from Cignetti, N.P. & Lazor, D.A. (2001). Coreless induction melting water systems. American Foundry Society Library, AFS Transactions , 1-8. Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp. Down, R. D. & Lehr, J. H. (2005). Environmental instrumentation and analysis handbook. New Jersey: John Wiley and Sons, Inc. 69

84 70 Duca, W. & Naro, R. (2010, January). Saving electrical energy in coreless induction furnaces. Retrieved from Grant, A. (1991). Induction furnace melting. FWP Journal, American Foundry Society, document , Heine, H. J. (1990, February). Update on induction furnace technology. Foundry Management and Technology, 119, Induction furnaces. Retrieved from Kohloff, F. (2010, July). 21 Ways to avoid molten metal explosions. Modern Casting, 100 (7), Lacoma, T. (n.d.). What is an electric induction furnace? Retrieved from Meredith, J. (n.d.). Induction furnaces. Retrieved from Miseresky, J. (1993). Comparative performance evaluation of aluminum melting technologies: Natural gas-fired Striko furnace and electric induction furnace. Proceedings of the 8 th International Sheet and Plate Conference. Lousville, KY. Modern Casting Staff. (2014, January). Steady rebound from recession. Modern Casting, 104(1), Pacific Gas and Electric Company. (2010, March). Electric schedule E-19 Medium general demand-metered TOU service. Retrieved from

85 71 Rudnev, V. Dr., Brown, D., Van Tyne, C. Dr., Clarke, K., Dr. (2008) Intricacies for the successful induction heating of steels in modern forge shops. 19 th International Forging Congress. Chicago, IL. Smith, M. A. (1992). The coreless induction furnace selection criteria. American Foundry Society Library, AFS Transactions, document A. Svoboda, J. M. & Griffith, L. E. (2002). Comparison of direct arc and induction melting for new foundry operations. American Foundry Society Library, AFS Transactions. Tower Productions (Producer). (2008). Spotlight on metalcasting [Video]. Retrieved from U.S. Department of Labor, Bureau of Labor Statistics. (2012). Occupational outlook handbook. Retrieved from U.S. Government (n.d.). CPI inflation calculator. Retrieved from Williams, D. C. (2010, January). Saving electrical energy in coreless induction furnaces. Foundry Management & Technology, 138,

86 APPENDIX A

87 INDUCTION FURNACE BROCHURES Figure A1. Induction: Melting and Heating Equipment, page 1 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp. 73

88 Figure A2. Induction Melting and Heating Equipment, page Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

89 Figure A3. Induction Melting and Heating Equipment, page Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

90 Figure A4. Induction Melting and Heating Equipment, page Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

91 Figure A5. Small EZ Lift Furnace brochure. 77 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

92 Figure A6. Large Lift and Swing Furnace brochure. 78 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

93 Figure A7. Compact Power Cube Furnace brochure. 79 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

94 Figure A8. Power Cube Furnace brochure. 80 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

95 Figure A9. MVP Solid State Power Supply brochure. 81 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.

96 Figure A10. Micro Melt Power Supply and Melt Station brochure. 82 Source: Dicken, M. T. (2011). [Induction Melting and Heating Equipment brochures] California: Induction Technology Corp.