Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
1999-11-12
2001-08-21
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S670000, C219S676000, C399S330000, C492S046000
Reexamination Certificate
active
06278094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to induction heating for a thermal roller having a roller jacket made of a ferromagnetic material and an inductor spool inside the roller jacket for low-loss transmission and adjustment suitable for processing of the heat output through generation of eddy currents of uniform density in totality or in targeted zones of the outer surface of the roller jacket.
2. Description of the Prior Art
Thermal rollers of the this type consist of a steel cylinder swivel-mounted on front-facing axial flanges. With inductive heating of these rollers the heat is generated directly in the jacket of the hollow cylinder by means of a magnetic alternating field, for which purpose the jacket comprises a material which is sufficiently conductive both electrically and magnetically.
A plurality of inductive heating arrangements for thermos rollers of this kind is known, which utilize induction spools or induction loops of various designs for generating the magnetic alternating field in the roller jacket. They are distinguished essentially by the position and direction of the ampere-turn axis of the induction spools or induction loops relative to the roller jacket or by the direction of the magnetic flow and of the induced eddy current in the roller jacket.
Thus, according to DE 19 53 20 44, an induction roller is known which primarily comprises an induction spool on an iron core in the interior of the roller jacket, of which the ampere-turn axis coincides with the roller axis. The magnetic circuit, in which the magnetic flow develops, essentially comprises the iron core of the induction spool and the ferromagnetic roller jacket, as well as the non-ferromagnetic interstice between the said iron core and roller jacket, forming the so-called air gap of the magnetic circuit.
The magnetic flow generated by the induction spool leaves its iron core, fanning out in the air gap and from there radially entering the roller jacket, where it is bundled in the axial direction before fanning out again in the air gap on exceeding the axial center of the induction spool, and thence entering the iron core again from the other side.
The eddy currents caused by the alternating field in the roller jacket current in a peripheral direction on paths concentric to the roller axis. The eddy current density and the associated heat source density are therefore constant in a peripheral direction. Both dimensions are modified in an axial direction, however, according to the change in the alternating current in the roller jacket as a result of its bundling out of or fanning out into the air gap. For this reason, eddy current density and heat source density in the roller jacket decrease towards its ends from the point located radially over the axial center of the induction spool.
For the purpose of achieving the desired uniform distribution of temperature in an axial direction on the roller surface despite this, in accordance with the known arrangement sealed heat pipes are provided in axial bores of the roller jacket. The heat pipes contain a heat transfer medium simmering in the vicinity of the operating temperature, which brings about a heat and temperature equalization between the center and the ends of the roller jacket on the way to evaporation, convection and condensation.
The manufacture of such axial boreholes in the roller jacket is a very expensive manufacturing process. Moreover, temperature equalization cannot be achieved right into the region of the axis flange in this way.
For this very reason, supplementary auxiliary induction spools are provided in the case of the known induction heat roller in the region of the axis flange. The current generated by the auxiliary induction spools enters the axis flange, where it leads to the additional heating required for complete temperature equalization.
Feeding a correspondingly higher calorific output into the windings of the auxiliary induction spools should prevent any radiation of heat into the unheated regions of the axis flange and into the roller frame during the heating process, thus reducing the time period required for heating up the roller to the level of operating temperature.
An essential drawback to this known arrangement is that it does not permit the development of axial zones of controllable heat output on the thermal roller, in particular in the edge regions of the roller body. This effectively restricts the roller in its usefulness to a predetermined width of the goods webs to be processed and thus to a very narrow range of products. The result is that this may lead to a low level of use of the machine's capacity, which in turn means a low return on capital investment.
One known method for achieving uniform current, eddy current and heat source density in the axial direction and developing axial zones of controllable heat output consists of arranging several induction spools axially adjacent to one another.
According to DE 19538261, each of the induction spools arranged axially adjacent to one another is embedded in an iron core having a U-shaped longitudinal section and terminals of its own.
The U-shaped iron cores and the ends of their flange-shaped legs together form a defined air gap against the inner surface of the roller jacket.
Because of their arrangement with appropriate dimensioning, these magnetic circuits formed by the iron cores and the roller jacket do not permit the current to bundle out from or fan out into the air gap, such that, with the exception of the borderline zones between the individual magnetic circuits, an almost constant current, eddy current and heat source density can be achieved along the roller surface in the axial direction.
This type of generation of the magnetic flow consumes a great deal of energy. When n induction spools are arranged along the roller jacket, the consequence of the smaller air gap width is that the magnetic resistance of a magnetic circuit amounts to approximately the n
th
multiple and thus the required exciter output is at least the n
2
multiple, while the overall exciter output is accordingly more than the n
3
multiple of a comparable roller having only one field spool.
The exciter output is converted fully into heat in the induction spool.
To avoid excessive heating of the induction spools, a cooling pipe is provided for a comparable, inductively heated roller, which draws off the heat generated in the induction spools, as in EP 0511549, for instance. This heat is lost to the roller heating, the result of which is a considerable reduction in thermal efficiency.
Another disadvantage of this arrangement is the necessity to monitor and control each of the individual induction spools separately with respect to their heat output, which leads to a very expensive power supply consisting of several independent circuits.
Apart from the fact that additional power losses are caused thereby, such a power supply plant is more expensive and naturally more susceptible to breakdown and accordingly requires continual monitoring during operation.
Particularly low power losses and high thermal efficiency of the inductive heating can be achieved with a solution as disclosed in DE 3416353. This solution contains a ferromagnetic core that fully encases the roller jacket on a peripheral point both inside and outside, which is provided with an exciting coil on its outer limb.
Since the magnetic circuit thus formed has no air gap, the exciter output required for the generation of the magnetic flow is very low. The uniformity of the eddy current and heat source density in an axial direction is very good because of a barely present fanning out of the current in the space between the parallel ferromagnetic limbs of the core.
This solution does not permit the development of axial heat zones. Moreover, a customary coaxial drive is not possible, because the iron core partially covers the roller jacket at its front ends.
In addition, inductive thermal arrangements for rollers are known that have a stationary inductor within the roller. Thus for e
Hellenthal Ludwig
Patt Walter
Rindfleisch Hans-Jochen
Von Schweinichen Jaxa
Collard & Roe P.C.
Leung Philip H.
Walzen Irle GmbH
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