The present invention relates to electric induction heating of a strip material particularly in applications where the width of the strip material, or another parameter, changes to alter the electrical impedance of the load circuit.
A flexible solenoidal induction coil, when connected to an ac power supply, can be used to inductively heat a workpiece passing through the coil. The flexible coil is of particular use when the workpiece has a changing crosss sectional dimension. In this arrangement the coil can be flexed to maintain a constant distance between the coil and the cross section of the workpiece presently passing through the coil. For example if the workpiece is a camshaft, irregularly shaped cams (features of the workpiece) will be spaced apart from each other along the shaft (workpiece). As the cam shaft passes through the coil for induction heat treatment, the flexible coil can be dynamically changed in shape-by attachment to suitable linear motion actuators that alter the cross sectional shape of the coil, for example, from circular to oval, to conform to the cross sectional shape of the feature of the workpiece passing through the coil.
For electric induction heating of a continuous strip material, the strip can be passed through a solenoidal coil that is powered from ac power source 112 as shown in
One object of the present invention is to selectively achieve a constant rate of production of inductively heated strip materials having different widths when the width of the strip changes by changing the distance between the strip and a solenoidal coil used to inductively heat the strip while keeping the load circuit operating at substantially resonant frequency by modulating the output frequency of the power supply providing power to the load circuit.
Another object of the present invention is to selectively achieve a constant rate of production of inductively heated strip materials having one or more different parameters that affect the electrical impedance of the inductive heating circuit by changing the distance between the strip and a solenoidal coil used to inductively heat the strip while keeping the load circuit operating at substantially resonant frequency by modulating the output frequency of the power supply providing power to the inductive heating circuit.
In one aspect the present invention is an apparatus and method of inductively heat treating strips when at least one parameter of the strips changes to change the impedance of the inductive load heating circuit. The apparatus comprises an ac power supply providing power to the load circuit. The load circuit comprises a capacitive element, a solenoidal induction coil having at least one flexible section, and at least one means for moving the at least one flexible section of the coil. A strip moves through the coil so that the strip is magnetically coupled with the load circuit. As the strip moves through the coil, the at least one flexible section of the coil is moved to change the load impedance. The output of the power supply is frequency modulated to change the output frequency as the at least one flexible coil section is moved so that the load circuit continues to operate at substantially resonant frequency.
Other aspects of the invention are set forth in this specification and the appended claims.
The foregoing brief summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary forms of the invention that are presently preferred; however, the invention is not limited to the specific arrangements and instrumentalities disclosed in the following appended drawings:
Referring now to the drawings, wherein like numerals indicate like elements, there is shown in
Power supply 12 outputs variable frequency ac power and can be an ac inverter fed from a dc rectifier having an input from utility power. Tuning capacitor 18 forms a resonant load circuit with solenoidal coil 14 and the equivalent electrical impedance of strip 16a by magnetic coupling with the primary load circuit. The output frequency of the power supply is selected so that the load circuit comprising the tuning capacitor, the induction coil and impedance of the strip reflected into the load circuit by magnetic coupling, which, in combination, is referred to as combined load impedance Zload, operates substantially at resonant frequency.
In
In
With the induction heating apparatus of the present invention, as shown in
Suitable feedback means, such as but not limited to, sensing of the actual position of the coil, or electrical sensing of instantaneous load power, can be used to adjust the output frequency of the power supply so that the load circuit is powered at resonant frequency as the position of the coil changes. A processing system comprising a computer executing a program to control the applied power to the load circuit may be used with suitable input and output devices to control the movement of the coil and output frequency of the power supply as the width of the strip changes.
In the above examples of the invention, changing of the width of the strip represents one parameter that will change the electrical impedance of the load circuit when the parameter changes. Other such parameters are, for example, the composition of the strip material and the composition of any coating on the strip as it passes through the solenoidal coil. In other examples of the invention, the induction heating apparatus of the present invention may be used to increase and decrease the applied power and rate of production of inductively heated strip as one or more of such parameters changes over a range by changing the position of the coil and modulating the output frequency of the power supply as described above.
Solenoidal coil 14 may comprise a singular coil that is flexible for movement between positions. In other examples of the invention the coil may comprise a number of sections, one or more of which may be flexible with means for moving the flexible coil section from one position to another. Coil 14 may comprise other arrangements, such as but not limited to, multiple coils, so long as at least one section of a coil can be moved to change the load impedance. While the above non-limiting example of the invention illustrates moving opposing coil sections, other examples of the invention include arrangements with one or more moveable coil sections not necessarily symmetrically arranged about the strip.
The above examples of the invention have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to various embodiments, the words used herein are words of description and illustration, rather than words of limitations. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may effect numerous modifications thereto, and changes may be made without departing from the scope and spirit of the invention in its aspects.
This application claims the benefit of U.S. Provisional Application No. 60/757,353, filed Jan. 9, 2006, hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60757353 | Jan 2006 | US |