EP1055354B1 - Method and induction furnace for melting a metallic or metal-containing bulk material in the shape of small pieces - Google Patents

Abstract

The present invention relates to a method as well as to an induction furnace for continuously melting a metallic or metal-containing bulk material in the shape of small pieces. The metallic bulk material is supplied from the top onto the melt located in the vessel of the furnace. An stirring movement is applied to the melt located in the upper area using an alternating field produced by a first magnetic coil (induction coil 11) which is arranged around the furnace vessel. Heat is simultaneously supplied to the melt, used as a short-circuited secondary winding, in the lower region of the induction-furnace crucible (13) about the iron core (16) of a low-frequency transformer.

Description

The invention relates to a method and an induction furnace for melting small pieces of metal and metal containing Bulk material, in particular in the form of chips made of iron, copper, Copper alloys and / or aluminum and its alloys by means of inductive heating.

For melting small pieces of metal and / or metal containing Bulk goods, especially chips, such as those used in metal cutting incurred are two according to the prior art different types of induction furnaces are known. Both types of furnace are based on the use of magnetic induction.

The mainly for melting metal chips, in particular Brass chips, induction crucible furnace used consists of a refractory crucible, around which a water-cooled copper coil is arranged. This coil is powered by an alternating current flows through, so in the crucible insert an electromagnetic Alternating field induces the use for melting brings. The resulting alternating field causes an intense Melting movement, which is the stirring in of the given from above Promotes pieces of metal. Because the abandoned Often oil-containing metal chips are quickly stirred into the melt metal losses of all kinds can be minimized and the Prevent formation of toxic hydrocarbons.

The currents in the magnetic coil and in the melting material generate together forces with the magnetic field in the direction of the cylinder axis, which creates a convex weld pool surface. A ring around the surface of the molten bath settles on the inside of the furnace Scabies, the width of the scabies ring so much is less, the more violent the bath movement.

The crucible furnace described has the following due to the process Disadvantage:

First of all, the thermal efficiency of the crucible furnace is relative low, which is why there is a high specific energy consumption results. Furthermore, the crucible furnace can only be operated intermittently be worked. Is the maximum filling level of the Reached the crucible furnace, the melt must be poured before continue melting metal pieces can be. This creates non-productive times that affect system availability limit significantly.

Deposits on the crucible wall result in a high level of cleaning effort. Eventually, slag buildup on the Crucible wall to significant losses in performance.

An alternative is the so-called channel furnace, in which the melting material in a closed channel around the iron core a low-frequency transformer is located. The melt forms the short-circuited secondary winding, the heating effect is created by the high current flowing in the melting channel. However, the bath movement is missing in the channel furnace design, which increases the risk of metal burn-up, as far as the metal pieces lying on the liquid bath exposed to an oxidizing atmosphere. This can be conditional Metal erosion counteracted by using rammers or agitators that, however, increase the technical effort. Although the thermal efficiency of the channel furnace is great is only small melting capacities can be achieved, because that mechanical stirring is time-consuming. As a rule, only 30% metal chips to the lumpy scrap added to to achieve satisfactory melting performance. Just like that The crucible furnace only works discontinuously. He also has the disadvantage of high idle times afflicted.

DE-A-21 28 742 describes one device in one Melting or mixing furnace to make it easier to load it, the furnace being a main room for melting, alloying or Keeping warm a quantity of material introduced into the furnace. The lower part of the furnace is at least an upward loading channel in connection, which is located outside the furnace and which is on its upper section of a crucible coil for stirring the closed material is provided. At its bottom is the Oven with a heater in the form of an induction coil provided with a magnetic core, which is from a channel for the surrounded by molten metal. The stove also has one siphon-like outlet opening through which molten metal by dumping the furnace around a horizontal shaft can. The feed channel mentioned consists of a tubular assembly releasably attached to the furnace. The main room of the furnace is closed by a cover in which an opening is provided above this main room the melt with a pressure source with controlled Pressure to connect. By regulating the pressure above the melt in the main room of the furnace is supposed to be the mirror raised or lowered in the loading channel of the furnace become. By lifting the mirror in the feed channel allows that slag can be removed there, the has accumulated in the upper part of the feed channel. Elevated one becomes the pressure in the space above the melt equally the melt level in both the outlet opening as well as raised in the feed channel.

US 4,571,258 shows and describes an oven container, in whose melting chamber via a loading device on the Molten metal surface, namely aluminum, can be abandoned. The melting chamber is in the upper area surrounded with an induction coil and in the lower area as Channel induction furnace designed. Using one at the top the conveyor grate arranged there can be over a The melt flowing out into a separate melt from the furnace Be transferred to the heating vessel.

It is therefore an object of the present invention, the method and to improve the induction furnace of the type mentioned at the beginning, by eliminating the aforementioned drawbacks. In particular a continuous efficient melting of lumpy metal bulk goods and a suitable induction furnace be created that works with low maintenance.

This object is achieved by the method according to claim 1.

This is based on the melt generated in an oven container the metal bulk material fed from above and the melt in upper region of the melting chamber by means of a first Alternating field generated around the crucible coil exposed to a stirring movement, the melt simultaneously in the lower part of the furnace tank in a melting channel around the iron core of a low frequency transformer as short-circuited secondary winding heat is supplied. Further the melt is passed through a siphon with a below the Crucible coil lying opening in the furnace container continuously discharged, preferably to the extent that metal piece goods is fed to the melt. The procedure described has the advantage that by means of a current Crucible coil depending on the frequency of the applied AC voltage a strong stirring movement to avoid a Metal fire and to minimize the amount of dross is generated. The melting channel, in the area of which no stirring work was carried out must be, can be so in terms of their thermal Make optimal use of efficiency. Overall, the inventive method a significant energy savings of achieve approx. 20%. Furthermore, a constant melt pool surface level are generated, causing the Slag zone is always in the same furnace wall area, so that an overgrowth of the furnace inner wall as with the crucible furnace or so that necessary cleaning work can be avoided. The melting process can be carried out continuously at a stabilized Litigation will be carried out.

Advantageously, there are no idle times like after State-of-the-art methods for temperature measurements and settings, deslagging, emptying and cleaning are to be spent. According to the invention, this results in a Production increase in the order of approximately 30% as well an operating cost reduction of approx. 10%. The plant availability for production is significantly improved.

As already mentioned, the method according to the invention creates the Possibility of more than 50%, preferably 60 to 70%, of total electrical supplied to produce the melt Heating output of the melting channel and the rest via the crucible coil supply, with which the higher thermal efficiency Energy transfer into the gutter is used.

Depending on the design of the siphon, it can be heated if necessary.

The melt in the siphon is preferably at an acute angle to the vertical or vertically according to the principle of communicating Tubes discharged through an outlet of the siphon. Here will after a further development of the method, the siphon opening arranged with respect to the channel inductor so that Heating and stirring movement into the siphon opening flowing melt reaches into it. The above measures allow the heat generated in the furnace area over the Melt is transported into the siphon, so that in corresponding Dimensions a siphon heater can be omitted. In the used The furnace level will have the melt pool level in it Adjust the height level at which the siphon outlet opening located. To the extent that metallic piece goods melted down melt flows through the siphon outlet, for example in a casting plant. With such a continuous The procedure is also not to clean the inside of the furnace required so that related furnace downtimes omitted.

Preferably the one defined by the furnace container Melt pool diameter chosen so large that by the stirring movement generated convex dross-free melt surface in the Diameter is greater than twice the width of the edge of the furnace adjacent scraper ring. The diameter of the so-called "Bald" in relation to the width of the scraper ring can be determined by Frequency of the alternating field and the power influence which is fed to the crucible coil. Low frequencies in The range of the network frequency has an advantageous effect here. since they promote the stirring effect. To avoid metal erosion the abandoned metallic bulk material is exclusively on the convex dross-free melt pool surface, in particular fed via a funnel.

According to a special embodiment of the invention Crucible coil with an alternating current of a frequency of 50 to 250 Hz, preferably 50 to 120 Hz, and the channel inductor an alternating current of a frequency of 50 to 60 Hz.

The task described in the introduction is achieved by the Induction furnace solved according to claim 6. The oven is under training a single melting chamber in the upper area as Induction crucible furnace and in the lower area as an induction channel furnace educated. Furthermore, the induction furnace has one Siphon below the crucible coil of the induction crucible furnace part empties. The siphon outlet is vertical or acute to the vertical and has an outflow opening, which is preferably arranged above the crucible coil. By this measure avoids long flow paths, which the Otherwise, return the liquid melt from the furnace to the outflow would have. In addition, this arrangement allows heat convection and the heat transfer via the one in the furnace Take advantage of the melt.

Further preferred designs of the induction furnace are in claims 7 to 10.

Possibly. is the siphon thermally insulated and / or by means of an induction or resistance heating can be heated. The is preferably Siphon discharge diameter at least 150 mm.

In a further embodiment of the induction furnace, the Ratio of the induction coil height (stirring coil height) to the coil diameter chosen about 1: 2, positive and negative Deviations of 20% are permitted.

In a first embodiment of the induction furnace according to the invention the gutter of the gutter furnace part is perpendicular to Siphon and the channel inductor arranged horizontally. There are however also inclined arrangements of the channel inductor or Channel conceivable, for example around the flow movement of the melt in the direction to support the siphon outlet. Of course can also within the meaning of the present invention by 90 ° be arranged rotated relative to the siphon.

An embodiment of an induction furnace according to the invention is shown in the drawing, the cross-sectional view of this induction furnace shows.

The induction furnace according to the invention has only one Melting chamber 10, the upper area of which is water-cooled Crucible coil 11 is surrounded. The oven itself has one Fireproof lining known in principle according to the prior art 12. In the lower area of the furnace is a channel 13 formed, which is heated by means of the channel inductor 14. This channel inductor 14 consists of magnetic sinks 15 over a Iron core 16. This structure results in an upper one Area 17, which corresponds to an induction crucible furnace, and a lower region 18, which corresponds to an induction channel furnace. Below the crucible coil 11 but above the Channel 13 of the induction furnace has an outlet, namely the opening 19 of a siphon 20 opening into the furnace container Longitudinal axis is inclined at an acute angle to the vertical. The Siphon overflow opening 21 is located above the crucible coil 11. From there, the melt flowing away enters one Casting container 22 or the like. The power supply lines for the crucible coil 11 and the channel inductor 14 is 23 designated. The induction furnace according to the invention or the invention Procedures work as follows:

The via a funnel 24 or other pouring device abandoned metal chips reach the so-called bald head 25, this is the dross-free convex melt pool surface around which around is the so-called scraper ring 26. The metal chips task is directed in such a way that metal chips on the Bald 25 fall. Through the crucible coil, with a frequency is fed between 50 Hz to 120 Hz, the melt is in a stirring movement by which the on the bald 25th any chips or pieces of metal lying on top and carried into the Melt are drawn. The melting of the small pieces Metal particles essentially happen in the melt, which can prevent metal erosion. Preferably is only about a third of the the entire heating power supplied to the induction furnace, two thirds of this heating power is generated by the channel inductor 14 delivered. According to the principle of communicating tubes forms a melt column in the siphon 20 corresponding to the Melt bath surface 25. Is the induction furnace as shown "Filled", leads everyone else by adding metal chips generated melt inflow related to a drain Quantities over the overflow 21. The control of the process is designed so that the heating power is large enough to the imported Melt metal chips completely. processable Chips consist in particular of iron, copper, aluminum and their alloys. However, the method according to the invention is also applicable to metal-containing bulk goods that are used for recycling of residues such as ashes, filter dust etc. occur.

In one specific embodiment, the induction furnace had an output of 2 MW, with 1100 kW via the gutter and 900 kW have been delivered via the crucible coil 11. By appropriate The furnace dimensions could melt 8 t / h brass chips become. The energy savings achieved compared a crucible furnace was about 20%.

Claims (10)

1. A method for melting a metallic or metal-containing bulk material in the shape of small pieces, in particular chips of iron, copper and/or aluminum, and/or their alloys by inductive heating, whereby the metallic bulk material is supplied from above onto a melt produced in a furnace vessel with a single pot-like melt chamber (10) and the melt is subjected in an upper region of the melt chamber (10) to stirring movements using an alternating field generated by means of a first crucible coil (11) which is arranged around the furnace vessel, whereby heat is simultaneously supplied to the melt in a lower region of the furnace vessel in a melt channel (13) around an iron core (16) of a low-frequency transformer as a short-circuited secondary winding, and the melt is continuously drawn off at a rate corresponding to an infeed rate of metal bulk material through a siphon (20) with an inlet opening (19) leading into the melt chamber (10) below the crucible coil (11) and with a siphon overflow opening (21), in which siphon according to the principle of communicating tubes a melt column is formed corresponding to the melt bath surface (25).
2. Method according to claim 1, in which more than 50%, preferably 60% to 70%, of the overall electrical heating energy applied to the generating of the melt is applied to the melt channel (13) and the remainder to the crucible coil (11) and/or the siphon (20) is heated, preferably by means of an induction or a resistance heater.
3. Method according to one of claims 1 or 2, in which the melt in the siphon (20) is drawn off continuously from an outlet (21) of the siphon (20) at an acute angle to the vertical or vertically according to the principle of communicating tubes, whereby the siphon inlet opening (19) is positioned relative to the crucible coil (11) such that the stirring movements of the melt are effective that far in the siphon inlet (19).
4. Method according to one of claims 1 to 3, in which a melt bath diameter determined by the furnace vessel is so large that a scrapings-free convex upper melt surface (25) produced by the stirring movement is greater in diameter than twice the width of a ring of scrapings (26) arranged at the edge of the vessel, whereby preferably the metal bulk material is fed exclusively to the convex scrapings-free melt upper surface (25), furthermore preferably centrally by a feed funnel.
5. Method according to one of claims 1 to 4, in which the crucible coil (11) is supplied with alternating current of a frequency of 50 to 250 Hz, preferably 50 to 120 Hz, and a channel inductor (14) supplied with an alternating current of a frequency of 50 to 60 Hz.
6. Induction furnace for continuously melting a metal and/or metal-containing bulk material, in particular in the shape of chips of iron, copper, and/or aluminum and their alloys, the furnace being formed with a single pot-like chamber (10) above which a bulk material input is arranged and being formed by arrangement of a crucible coil (11) around its upper region (17) as a crucible-type induction furnace and in the lower region (18) of the melt chamber (10) being formed as a channel-type induction furnace, and in which a siphon inlet opening (19) leads into the melt chamber (10) below the crucible coil (11), the longitudinal axis of the siphon (20) extends vertically or at an acute angle to the vertical and the siphon has an overflow opening (21) and wherein according to the principle of communicating tubes a melt column corresponding to the melt bath surface can be formed so that the melt is continuously drawn off at a rate corresponding to the infeed rate of metal bulk material
7. Induction furnace according to claim 6, in which the siphon overflow opening (21) is arranged above the crucible coil (11) and/or that the siphon outlet is arranged vertically or at an acute angle to a vertical line.
8. Induction furnace according to claim 7, in which the siphon (20) is heat insulated and/or is heatable by means of an induction or resistance heater and/or that the siphon outlet has a diameter of at least 150 mm.
9. Induction furnace according to one of claims 7 or 8, in which the ratio of the mixing-coil height to the mixing-coil diameter is 1 : 2 and/or that a channel (13) of the lower region (18) is arranged perpendicular to the siphon (20).
10. Induction furnace according to one of claims 7 to 9, in which the channel inductor (14) is arranged horizontal or angled to the axis of the siphon or that the channel inductor (14) is set at 90° to the vertical.

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