Electric heating – Inductive heating – Specific inductor configuration
Reexamination Certificate
1999-11-30
2002-04-02
Walberg, Teresa (Department: 3742)
Electric heating
Inductive heating
Specific inductor configuration
C219S676000
Reexamination Certificate
active
06365884
ABSTRACT:
BACKGROUND OF THE INVENTION
The subject invention pertains to the art of induction heating and more particularly, solenoidal coil assemblies cast in a refractory. The assembly is especially intended for heating unusually wide strips, sheets or slabs.
Inductive heating of slab or strip work pieces with solenoidal coils is well known. It is also well known to protect the coils from the work piece by encasing it in a cast refractory such as cement or the like. Such prior assemblies have suffered from the principal problem of being prone to crack and break. Voids within the refractory itself, as well as normally occurring tension risers, will expand the crack over time and ultimately require reconstruction or repair. The cracking can occur due to normally occurring vibration of the coil, as well as part collision or stress cracking occurring at tension points due to the weight of the refractory material itself When such cracks expose the turns to the work piece, the turns can be damaged to the extent that the system should no longer be operational.
Another problem with such systems is that the encasement of the entire coil within the refractory can inhibit repair because the inductive turns are no longer easily accessible due to the difficulty in separating them from the refractory or to the extent that the cracking of the refractory will impart some physical damage to the turn itself
Yet another problem with such systems is when the inductive turns are encased in the refractory during the casting process, they become bound to the refractory. The binding causes the refractory and turn to vibrate together and sound levels created during the operating process can be very loud. In addition, the vibration of the bound refractory and turns enhance the prospects for refractory cracking.
In particular cases where extremely wide work pieces (even up to about 3½ meters wide) are being heated, the refractory can have a weight and span which can cause a bow and significant tension risers at cracks which can expand more quickly over time. In order to inhibit crack formation, it has been known to pretension the turns before refractory casting thereabout so that as the refractory hardens, the turns themselves which become bound to the refractory during the hardening process, can impart compressive forces on the refractory to counteract whatever tensioning forces may occur. A refractory under reasonable compression is much less likely to crack than a refractory under tension. However, this design embodiment, wherein the turns and refractory are bound together, has problems with quicker deterioration due to the direct communication of vibration from the turns to the refractory and the varying rates of thermal expansion between them during the repetitive heating and cooling of the induction heating operation. In addition, such assemblies also retain the particular problems in repair and reconstruction due to the close and rigid contacting between the conductor turns and the refractory casing.
Design considerations for such inductive heating assemblies seek to minimize the opportunity and likelihood for crack formations and still provide an assembly which is easily constructed, serviced and operated.
The subject invention comprises a new inductive heating assembly which overcomes the above referenced problems and others and which provides a rigid construction despite an unusually large solenoidal opening, facilitates ease of repair, reduces sound pollution during the coil operating periods, is efficient in operation and provides enhanced cost effectiveness.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an induction heating coil assembly comprising a plurality of copper turns encased in a refractory casing wherein the turns are loosely disposed within refractory cavities and are tensioned for maintaining the refractory in compression. The overall assembly is comprised of four major parts which are segmented to form a modular assembly. The segmenting is intended to occur where cracks are most likely to appear in a corresponding non-segmented assembly. The turns are disposed in top and bottom blocks with end connectors and jumpers extending out from the ends of the blocks for selective connection with the turns on the opposed bottom block. The top and bottom blocks are spaced by the end blocks.
In accordance with another aspect of the present invention, a compression rod is also disposed within the casting generally parallel to the turns and is also tensioned for enhancing the compression forces on the top and bottom blocks.
In accordance with yet another aspect of the present invention, the refractory holes or cavities accommodating the copper turns and compression rod are sized to accommodate a spacing between the refractory and the turn or rod for a nonbinding loose disposition within the hole or cavity to better accommodate vibrations and thermal expansions.
In accordance with another aspect of the invention, a method is disclosed for assembling the modular coil assembly.
An important benefit of the subject invention is a modular induction heating coil assembly which especially inhibits crack formation in an unusually wide solenoid opening for the coil assembly.
Another benefit of the present invention is the modular assembly in a coil which provides a rigid construction for the top and bottom refractory blocks and which inhibits gravitational forces from placing the block in a tension stress and thereby minimizes the likelihood of stress cracks occurring.
A further benefit of the present invention is an assembly wherein turns or compression rods may be easily removed, repaired or adjusted from an encasing refractory material. In addition, the assembly provides improved reduction in sound from vibrations, improved efficiency of assembly and operation and consequential improvements in cost effectiveness.
Other benefits and advantages of the subject new induction coil assembly will become apparent to those skilled in the art upon a reading and understanding of this specification.
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Ajax Magnethermic Corporation
Fay Sharpe Fagan Minnich & McKee LLP
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