Industrial electric heating furnaces – Induction furnace device – Core-type
Reexamination Certificate
1999-12-16
2001-03-27
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Induction furnace device
Core-type
C373S162000
Reexamination Certificate
active
06208682
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a channel inductor and to a furnace for melting, holding or refining of metal comprising such channel inductor.
BACKGROUND ART
A channel inductor is an electric device for melting and holding of metal. The inductor comprises a first primary winding, e.g. a multi-turn coil wound around a magnetic core. Around this core and the coil is a channel, normally called inductor channel, arranged. The channel opens at both its ends into a furnace vat. The inductor and the channel is normally contained in a removable inductor housing such that the inductor can be replaced without the need to reline the complete furnace vat.
The inductor channel, which during operation is filled with molten metal, constitutes a closed circuit. As the primary winding during operation is fed with an alternating current the melt in the inductor channel acts as a short-circuited secondary winding of a transformer. Power is thus induced in the melt which is heated and a flow pattern is developed in the channel. Due to the good stirring effect provided by the inductor a good homogenization as to temperature and composition will be achieved in the melt rendering this type of furnace suitable for many type of refining and alloying treatments. However the flow pattern generated in the channel, which normally is a two-loop flow over the channel cross-section, might also create erosion of the lining in the inductor or in some cases deposition of refining agents, solid particulate matter formed in the melt or other particles on the walls in the inductor channel resulting in a clogging of the channel. Such clogging will disturb the flow in the channel and thus the efficiency of the inductor.
A channel inductor is normally equipped with a cooling jacket for cooling of both the housing and the coil. The cooling jacket is arranged within the refractory lining provided around the coil, i.e. between the coil and the inductor channel and will shield the coil from any moisture given off by the lining material during sintering of the lining but will also constitute a protective barrier or shield around the coil which any melt which happens to penetrate the lining have to pass. The cooling jacket will, however, cause substantial thermal and electric losses. These losses will show as the heating of the water passing through the cooling jacket. Today refractory lining is normally applied as dried masses which are formed around templates without any water-additions. As the masses contain essentially no added water and there is no longer a need to protect the coil from moisture in the refractory lining and the primary object of the cooling jacket is in installations using this type of linings to protect the coil from any metal penetrating through the lining. Thereby has it become advantageous to design a channel inductor without the cooling jacket, giving the following advantages;
the inductive losses to the cooling jacket are eliminated;
possibility to reduce the thermal losses by an increasing the distance from the hot melt to the cooling system comprised in the coil;
possibility to increase the overall efficiency of the inductor;
possibility to increase melt and/or superheat capacity; and
reduced maintenance as the corrosion situation in the cooling jacket is eliminated as will all water couplings etc. and supply hoses or tubes for the cooling jacket.
The inductor and especially the coil must however be safe-guarded against melt penetrating through the lining and damaging the coil and also against excessive wear especially in cases with increased superheat or melt capacity which are likely to increase the temperature in the interface melt/refractory lining and possible also the flow rate in the inductor channel. It is also an object to reduce the thermal and mechanical stresses, which the lining around the coil is subjected to.
It is therefore the object of the present invention to provide a channel inductor with an improved thermal efficiency and reduced need for maintenance while maintaining or improving the operational safety. It is one object that the cooling jacket shall be removed but that the inductor still shall be safe guarded from damage to the coil due to metal penetration. That is any metal penetration shall be prevented to reach the inductor coil. Further it is also an object to improve the flow characteristics of the inductor channel to reduce wear and to improve the control of supplied electrical power to reduce depositions and clogging and also measures will taken reduce losses to the mechanical structure and cooling system.
SUMMARY OF THE INVENTION
The present invention provides a channel inductor which comprises a winding wound around a core, and a refractory lining, in which at least a part of the core and the coil are arranged enclosed and embedded and an inductor channel formed around and encircling the core in the refractory lining such that it when filled with melt constitutes a secondary winding. The channel inductor further includes detection means for detecting any melt penetration through the refractory lining arranged in the refractory lining between the coil and the inductor channel.
Preferably the winding is a multi-turn coil with conductors in the form of copper tubes in which water or other suitable coolant is flowing during operation. The core is preferably a laminated iron core which for installation purposes is divided. When assembled the core normally forms a four-legged square or rectangular core. A refractory lining mass are rammed or in other way formed around part of the core and coil after the core have been assembled and placed within a channel template. The used ramming mix preferably essentially free from water additions but can also be a cast lining with high water-additions provided the lining is dried before the coil is mounted. The coil, the core and the template are mounted in an inductor housing and positioned relative each other in a desired manner within the inductor housing. The housing is thereafter filled with the refractory mix. The refractory mix is rammed around the coil and the template in such a way that an inductor channel with openings at two ends is formed around the coil and the core.
According to an embodiment of the invention the inductor comprises detection means in the form of a detection wall or fire wall, such as a cylindrical tube-like wall made from a mesh or net of an electrically conductive material, such as a metal, arranged around the coil in the lining between the coil and the channel. The detection wall is connected to indication means for indicating any melt penetration into the lining as it reaches the detection wall. With the detection means will it also be possible to indicate other disturbances in the lining which are likely to affect the performance of the inductor, such as moisture in the refractory lining.
According to one preferred embodiment of the invention the inductor comprises detection means in which two walls are arranged in the refractory lining between the inductor channel and the coil. A first essentially cylindrical detection wall or fire wall is arranged at a suitable distance from the inductor channel. The fire wall is exhibits an open structure and comprises an electrically conductive material. Preferably the fire wall is backed on either side or both sides with a backing wall made from an electrically insulating material such as a material based on mica. The first or fire detection wall indicates any metal penetration reaching this far in the insulation. The first detection wall is placed at such a distance from the coil that metal penetration reaching the first wall do not constitute an immediate danger but the inductor can be taken out for relining and other suitable repair at a planned coming stop in the production. This first wall is also arranged to interact with a second wall to measure the resistance in the refractory lining between these two walls. By measuring the resistance in the refractory lining between these two walls it is possible to monitor the metal penetration
Archenholtz Åke
Bostedt Jan
Ebrahim Saeid
Löfgren Arne
Lundström Alf
ABB AB
Hoang Tu Ba
Jenkens & Gilchrist a Professional Corporation
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