Microwave furnace

A system for melting a substance may be provided. The system may comprise a microwave generator, at least one wave guide, a melter assembly, and at least one thermal insulator. The at least one wave guide may connect the microwave generator to at least one power transfer element. The at least one wave guide may be configured to transfer microwave energy from the microwave generator to a refractory assembly. The melter assembly may comprise the refractory assembly and the at least one power transfer element connected to the refractory assembly. The refractory assembly may comprise at least one absorption element configured to transfer microwave energy, received from the at least one power transition element, into heat energy. The at least one thermal insulator may be configured to allow the microwaves to penetrate to the at least one absorption element.

COPYRIGHTS

All rights, including copyrights, in the material included herein are vested in and the property of the Applicants. The Applicants retain and reserve all rights in the material included herein, and grant permission to reproduce the material only in connection with reproduction of the granted patent and for no other purpose.

BACKGROUND

Metal melting is performed in a furnace. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. External scrap is material from other forming processes such as punching, forging, or machining. Internal scrap consists of the gates, risers, or defective castings.

Furnaces are refractory lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces. Furnace choice is dependent on the alloy system and quantities produced. Furnace design is a complex process, and the design can be optimized based on multiple factors.

SUMMARY

A system for melting a substance may be provided. The system may comprise a microwave generator, at least one wave guide, a melter assembly, and at least one thermal insulator. The at least one wave guide may connect the microwave generator to at least one power transfer element. The at least one wave guide may be configured to transfer microwave energy from the microwave generator to a refractory assembly. The melter assembly may comprise the refractory assembly and the at least one power transfer element connected to the refractory assembly. The refractory assembly may comprise at least one absorption element configured to transfer microwave energy, received from the at least one power transition element, into heat energy. The at least one thermal insulator may be configured to allow the microwaves to penetrate to the at least one absorption element.

DETAILED DESCRIPTION

A microwave furnace may be provided. Consistent with embodiments of the present invention, a microwave furnace may melt metals more efficiently and generate lower emissions than conventional furnaces. Consistent with embodiments of the invention, microwave energy may be used to generate heat inside a refractory wall. This heat may be transferred to a substance (e.g. metal) to be melted. The aforementioned substance may comprise any substance and is not limited to metal. The process may be continuous and may not leak hazardous amounts of microwave energy.

Furthermore, embodiments of the invention may crosslink polymers in-line. The process of crosslinking polymers may include heating the polymer to initiate the crosslinking reaction. Microwave energy may be applied to the polymer causing it to heat and the reaction to take place. This heat input to the polymer may occur quickly.

By using materials and certain geometries, the furnace's refractory walls may absorb a near maximum energy amount. A thermal insulation material may be used as a one-way energy device. This insulation material may allow microwave energy to flow freely while at the same time not allowing thermal energy to escape, for example, in a direction opposite to the microwave energy flow.

Embodiments of the invention may provide a method for melting using electrical energy. This process may avoid some or all issues associated with conventional melting. Moreover, processes consistent with embodiments of the invention may be cleaner, less dross or slag may be created during the melting process, and the molten substance's temperature may be easy to control. Furthermore, embodiments of the invention may avoid problems with conventional induction furnaces in that embodiments of the invention may not need to start with molten substance. Conventional induction furnaces must start with molten metal before more metal can be melted. In contrast, embodiments of the invention may start to heat with solid substance or even no substance.

Furthermore, embodiments of the invention may be modular. While, embodiments of the invention may include a module in a larger furnace, to increase the size, these modules may be stacked, for example, on top of one another and also end-to-end. The design of refractory may be modified to allow for the substance to flow from module to module. In addition, embodiments of the invention may allow for ‘zone’ heating. For example, by keeping lower modules hotter than upper modules, stirring may be induced in the molten substance through convection.

Also, embodiments of the invention may avoid the need for liquid cooling on the furnace. For example, none of the components near the furnace may require liquid cooling. This may reduce the chances of an explosion when water comes into contact with molten substance. Moreover, embodiments of the invention may at least be as efficient at melting as a conventional induction furnace. In addition, embodiments of the invention may be more efficient at melting aluminum than a conventional induction furnace, for example, because of aluminum's reduced melting temperature.

Embodiments of the invention may achieve a higher difference in the melting temperature of metal and the furnace walls when aluminum is used. For example, this aspect may be important to the furnace's ability to transfer energy into a metal, consistent with embodiments of the invention, the furnace may be designed to direct microwaves into proper material (e.g. absorption element) for heating. An efficient shape for the absorption element for absorbing microwaves may comprise, for example, a wedge shape with the thin edge facing the incoming microwaves. This wedge may be made of a material that is a good absorber of microwave energy. A good absorber may comprise a material that converts microwave energy into heat energy with minimal energy losses.

The absorption element for absorbing microwaves may be made of an absorbing material such as silicon carbide, for example. This material may absorb energy from both the magnetic field and electric field components of the microwave. The wedge shape of the silicon carbide absorption element may focus the energy from the microwaves into a specific point inside the absorption element. The material's electric properties along with the geometry may provide efficient microwave energy absorption.

The absorption elements may be insulated by insulating elements. The insulating elements may be made of a thermal insulation material that may be transparent to microwaves. This insulation material may be a good thermal and electrical insulator and may be a homogeneous material. For example, fused silica may be used to make the insulating elements because fused silica: i) has good electrical properties; ii) has a loss factor similar to that of air, which makes it transparent to Microwaves; and iii) has good thermal insulation characteristics. Furthermore, fused Silica may also withstand the temperatures required to melt metals.

Embodiments of the invention may also use a microwave generator comprising, for example, a power supply and a high power magnetron that creates the microwaves. The microwaves may then be directed to the furnace using various elements including a waveguide. Embodiments of the invention may provide a transition from the waveguide to the furnace without reflecting the microwaves off the fused silica insulation and without causing the microwaves to travel back to the microwave generator. This transition may facilitate energy transfer from the waveguide to the furnace and to simultaneously focus the microwave energy to obtain the desired shape before absorption.

FIG. 1shows a microwave furnace100consistent with embodiments of the invention. Microwave furnace100may comprise a refractory assembly105, a microwave generator110, wave guides115, and power transfer elements120. Refractory assembly105and power transfer elements120may comprise a melter assembly consistent with embodiments of the invention.

FIG. 2shows refractory assembly105in more detail. The silicon carbide parts (e.g. absorption elements) may be cast into one complete piece to avoid potentials for leaks. The fused silica shapes (e.g. insulation elements) may remain as individual bricks as shown. Refractory assembly105may be placed into the melter assembly as shown inFIG. 3. As shown inFIG. 3, power transfer elements120may be placed on the sides. Power transfer elements120may provide transfer from wave guides115to refractory assembly105. Refractory assembly105may include cold metal addition window on the top and the hot metal pour spout on the front. Both may be designed to allow metal to enter and leave furnace100and at the same time prevent microwave energy from escaping.FIG. 4shows power transfer elements120in more detail.FIG. 5shows examples of the aforementioned absorption elements (e.g. wedge shaped silicon carbide).

FIG. 6shows energy absorption simulation of the aforementioned absorption elements.FIG. 6illustrates a focusing effect of the silicon carbide wedge bricks and the power transfer assembly. The wedge shape was simulated and the focusing effect was confirmed.FIG. 7shows the focal pattern of the microwaves as they enter the melter assembly.

FIG. 8. shows, for example, a graph of temperature results for curing microwave furnace100. The test data may include the following:

Time to heat furnace to melting temp

Overall Melting Efficiency

Defined as

ECu=Theoretical energy to melt set amount of copper

EGen=Amount of energy consumed by microwave generator

Microwave to melted Copper Efficiency

Defined as

EWg=Microwave energy delivered to furnace

In the test shown inFIG. 8, the furnace did reach the required temperature to cure the refractory mortar. The furnace, exceeded melt point for copper

Preliminary analysis revealed the following:

T1=Time copper was inserted into furnace.

T2=Time copper was melted

ΔT=Total time required to melt the copper in seconds.

Average watts*ΔT=J1=joules of energy used.

Jc=Amount of energy required to melt x lbs of copper.

In the test shown inFIG. 8, using this formula and 45 lbs of copper, the efficiency of the melting apparatus was approximately 60% from MW energy to melted copper and 48% from electrical energy to melted copper.

FIG. 9shows other embodiments of refractory assembly105. As shown inFIG. 9, refractory assembly105may comprise a crucible905, insulation elements910, a spout915, an absorption element920, boards925, and gaps930. Microwave energy may be received from power transfer elements120as shown inFIG. 9. Absorption element920may comprise silicon carbide, insulation elements910may comprise fused silica, and gaps930may comprise sealed air gaps. Insulation elements910may be configured to insulate heat into crucible905.

Boards925may comprise silica and alumina fiberboards that may be arranged in assembly105so as to present the least amount of material to the microwaves, but still provide adequate thermal insulation. Boards925may be placed outside a zone of the highest electromagnetic energy density in assembly105. Gaps930between some of boards925may facilitate energy removal from the boards925. While no material may be perfectly microwave transparent, any losses that may occur in the material must be dissipated somewhere. For example, boards925that are furthest away from absorption element920may radiate any losses into power transfer elements120and into a furnace shell containing refractory assembly105. Boards925that are attached to crucible905may conduct their energy into crucible905. Boards925may comprise just boards or a combination of fibrous blankets and boards. Also, boards925may be configured to create a freeze plane for molten metal.

Silicon carbide parts (e.g. absorption element920) may be cast into one complete piece to avoid potentials for leaks. Fused silica parts (e.g. insulation elements910) may remain as individual bricks. Refractory assembly105may be placed into the melter assembly as described above with respect toFIG. 3. As shown inFIG. 3, power transfer elements120may be placed on the sides of assembly105. Power transfer elements120may provide transfer from wave guides115to refractory assembly105. Refractory assembly105may include a cold metal addition window on the top and a hot metal pour spout (e.g. spout915) on the front. Both may be designed to allow metal to enter and leave furnace100and at the same time prevent microwave energy from escaping.

Consistent with embodiments of the invention, microwave furnace100may be used to perform a continuous melting process. For example, microwaves from microwave generator110may be transmitted through wave guides115to power transfer elements120. As described above, the microwaves may be converted to heat and metal in crucible905may be melted by the heat. Refractory assembly105may include a cold metal addition window on the top and a hot metal pour spout (e.g. spout915) on the front. Consequently, the continuous melting process may allow metal to enter (e.g. through cold metal addition window) and leave (e.g. through spout915) microwave furnace100and at the same time prevent microwave energy from escaping. Power transfer elements120may be configured to match impedance between wave guides115and refractory assembly105to maximize energy transfer from wave guides115to refractory assembly105. The continuous melting process may be controlled by a computer running a program module. Among other things, the program module may monitor and/or control the microwaves generated by microwave generator110and the amount of metal entering and leaving microwave furnace100.