Industrial electric heating furnaces – Induction furnace device – Core-type
Reexamination Certificate
2000-06-22
2001-05-29
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Induction furnace device
Core-type
C373S161000, C373S164000, C373S146000
Reexamination Certificate
active
06240120
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and induction furnace for melting fine metallic and/or metal-containing particles, in particular chips of iron, copper, copper alloys, and/or aluminum and its alloys by means of inductive heating.
BACKGROUND OF THE INVENTION
In order to melt fine metallic and/or metal-containing particles, in particular chips produced by machining, according to the prior art two types of induction furnaces are known. Both types of furnaces are based on the use of magnetic induction.
It is standard to melt metal chips, in particular brass chips, in an induction crucible furnace comprised of a heat-resistant crucible surrounded by a water-cooled copper coil. This coil is energized with alternating current so as to produce an alternating magnetic field in the crucible charge which causes it to melt. The thus produced alternating field creates an intense mixing of the melt which pulls in metal particles added from above. In this manner, since the often oil-covered metal chips are rapidly pulled into the melt, metal losses of all types are minimized and there is minimal generation of toxic carbon compounds.
The currents in the magnetic coil and in the melt produce together with the magnetic field forces directed along the axis of the cylinder so that the upper surface of the melt is convex. Slag deposits itself annularly around the upper melt surface on the inner wall of the furnace, the thickness of the slag ring being smaller with greater movements of the melt.
As a result of the process the described crucible furnaces have the following disadvantages:
First the thermal efficiency of the crucible furnace is relatively low so that specific energy consumption is high. In addition the crucible furnace can only work in batches. Once the crucible furnace is full, the melt must be poured off before more metal can be melted. This produces down times that substantially reduce the capacity of the unit.
As a result of deposits on the walls of the crucible there is substantial cleaning work. Finally slag deposits on the crucible wall lead to intolerable losses in efficiency.
An alternative is the so-called channel furnace where the melt is held in a closed channel around the iron core of a low-frequency transformer. The melt forms the short-circuited secondary winding so that heat is produced by the high currents flowing in the melt. Such a channel-type furnace does mix the melt so that there is the danger of scorching of the metal when metal particles lying atop the melt are exposed to an oxidizing atmosphere. Plungers or mixers can be used to reduce scorching of the metal, but this entails a technical expense. Although the thermal efficiency of a channel furnace is considerable, only small melts can be processed since the mechanical mixing takes quite some time. As a rule only about 30% of the melt can be metallic scrap chips in order to achieve acceptable efficiency. Even so, like crucible furnaces, the channel furnaces work discontinuously. This also has the disadvantage of considerable down time.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to improve the above-described induction method and furnace while eliminating the above-mentioned disadvantages. In particular the aim is a continuous and efficient melting of metallic scrap particles and an induction furnace that takes little maintenance.
SUMMARY OF THE INVENTION
The solution according to the method is that the metallic particles are fed from above onto a melt in a furnace vessel and the melt is subjected in an upper region to mixing movements by an alternating field by means of a first magnet coil (crucible coil, mixing coil) surrounding the furnace vessel, the melt being simultaneously heated in a lower region in a melt channel around an iron core of a low-frequency transformer with a short-circuited secondary winding. The described method has the advantage that by means of an electrically energized crucible coil depending on the frequency of the supplied alternating voltage a strong mixing movement is produced to avoid burning of the metal and to minimize the amount of slag. The melting channel in which there is no mixing action can be thus optimally used with respect to its thermal efficiency. Overall the method according to the invention achieves a substantial energy saving of about 20%.
According to a further feature of the method of the invention the melt is continuously drawn off through a siphon with an inlet opening into the furnace vessel below the crucible coil at a rate preferably corresponding to an infeed rate of metal particles. This ensures a constant level of the upper surface of the melt so that the slag zone is always at the same region of the furnace wall and a thickening of the furnace wall as in crucible furnaces and the cleaning work related to it are avoided. The melting process can run continuously with a stabilized process.
Preferably there are no down times as with the prior-art methods for measuring and setting temperature, removing slag, emptying, and cleaning. As a result according to the invention one achieves an increase in productivity in the order of about 30% as well as an operating cost decrease of about 10%. The availability of the apparatus for production is substantially increased.
As already stated, the method of the invention makes it possible to use more than 50%, preferably 60% to 70%, of the overall electrical heating energy for producing the melt in the channel and the remainder in the crucible coil, so that the higher thermal efficiency is used by energy transfer in the channel.
According to construction of the siphon it can if necessary be heated.
Preferably the melt is drawn off from an outlet of the siphon at an acute angle to the vertical or vertically according to the principle of communicating tubes. Thus according to a further feature of the invention the siphon inlet is so positioned relative to the channel inductor that its heating and mixing action are effective in the siphon inlet. With this feature it is possible to convey heat from the furnace via the melt into the siphon so that heating of the siphon can be eliminated. In the employed furnace vessel the melt level is kept at the same height as the outlet of the siphon. To the extent that metallic particles are melted, melt flows out of the siphon outlet into a ladle. With such a continuous method no cleaning of the furnace wall is necessary, so that down times for the furnace are eliminated.
Preferably a melt diameter determined by the furnace vessel is so large that a slag-free convex upper melt surface produced by the mixing action is greater in diameter than twice the width of a ring of slag sitting at the edge of the vessel. The diameter of the so-called crown relative to the slag-ring width can be influenced by the frequency and power of the alternating field, which is set by the crucible coil. Lower frequencies in the region of line frequency are advantageous since they promote mixing. In order to avoid scorching the metal the added metallic particles are fed exclusively to the convex slag-free melt upper surface, preferably by a funnel.
According to a particular embodiment of the invention the crucible coil is supplied with alternating current at a frequency of 50 to 250 Hz, preferably 50 to 120 Hz, and the channel inductor with an alternating current at a frequency of 50 to 60 Hz.
The apparatus achieves the described object with the induction furnace of the invention that is characterized in that the furnace is formed in an upper region with a single chamber as a crucible-type induction furnace and in a lower region is formed as a channel-type induction furnace.
Thus the induction furnace has a siphon having an inlet below a crucible coil of the induction-type crucible region. The siphon extends vertically or at an acute angle to the vertical and has an outlet above the crucible coil. This avoids a long flow path which the fluent melt otherwise would have to go through from the furnace to the outlet. In addition this arrangement uses heat conv
Bebber Hans
Fähnrich Juan
Phillipps Gunter
Dubno Herbert
Hoang Tu Ba
Induga Industrieofen und Giesserei-Anlagen GmbH & Co. KG
Wilford Andrew
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