JP2015108505A - Hybrid metal melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hybrid metal melting furnace high in metal melting efficiency, low in NOx emission, capable of removing impurity elements even without special auxiliary installation, and ensuring excellent durability.SOLUTION: A metal melting furnace includes: a crucible 11; a furnace main body 10 supporting the crucible 11; a furnace cover 20; a burner 23 that can inject a flame into the crucible 11; and induction heating means. The burner 23 is an oxygen burner using fuel gas and supporting gas having an oxygen concentration of not less than 21 mass% and not more than 100 mass%. An induction coil 14 serving as the induction heating means is provided at a position corresponding to a lower half region 11A of the crucible 11 so as to surround the crucible 11. A cooling pipe 15 is provided at a position corresponding to at least an upper half region 11B of the crucible 11 so as to surround the crucible 11. Furthermore, a cooling pipe 25 is provided in the furnace cover 20.

Description

  The present invention relates to a metal melting furnace, and more particularly to a hybrid type metal melting furnace in which a burner and an electric or electromagnetic heating means are used in combination.

  Recently, in the field of metal dissolution, it is required to reduce carbon dioxide emissions from the viewpoint of protecting the global environment. Moreover, development of the new construction method which suppresses or reduces electric power consumption in the melting process of cast iron by electric power is calculated | required. Against this background, a continuous melting system that directly injects a burner flame onto a metal material has also been proposed. However, this system is assumed to be installed in a large-scale factory that uses a large amount of the same molten metal, and it is difficult to introduce it into a small-scale casting factory that operates with a small amount of many materials. On the other hand, there is a movement to introduce a batch-type metal melting furnace using induction current of high frequency / medium frequency / low frequency in order to cope with the operation mode of “small amount of many materials”, but the world situation and other instability As a result, there are observations that electricity prices will rise or remain high in the future, and high-efficiency melting technology that does not depend on 100% electricity is also required.

  In recent years, steel materials used in automobiles and others have become increasingly high-tensile (high-tensile steel, that is, a high manganese content trend), and scrap materials that are reused as cast iron materials are contaminated with manganese and other impurity elements. (In the cast iron industry, this situation is called “contamination due to scrap / high tensile”). Due to this scrap high-contamination contamination, in many foundries, it is becoming difficult to produce a general cast iron material (for example, FCD450) according to the standard when scrap material is used in a conventional manner. .

  A hybrid metal melting furnace that has the potential to flexibly meet these demands, with the current trend toward carbon dioxide emission suppression, low power, support for small quantities of many materials, high efficiency, and the ability to remove impurities. Is getting attention. An example of such a hybrid metal melting furnace is the metal melting furnace disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-117640).

  Patent document 1 discloses the metal melting furnace which used the burner and the electric heater together. More specifically, the metal melting furnace includes a crucible 110 housed in a casing 130, an electric heater 180 for keeping the molten metal (aluminum molten metal) inside the crucible, and a metal to be melted charged in the crucible. A burner 220 for melting (aluminum) by direct fire and a rotary degassing apparatus 300 for removing impurities from the molten metal (aluminum molten metal) are provided.

  However, the metal melting furnace of Document 1 also has various difficulties. For example, the burner 220 employed therein uses liquefied propane gas (LPG) as the fuel gas and air as the supporting gas (supporting gas). Since air is used, the flame temperature is not so high, and since the exhaust gas volume is increased by nitrogen in the air, the melting efficiency is not good. There is also a problem that a large amount of nitrogen oxide is discharged. In addition, a) a mechanism that is unnecessary for melting cast iron, such as the rotary degassing apparatus 300 for removing impurities, b) indirect heating with an electric heater, so heat insulation efficiency is not good, and c) the heat insulation furnace itself. There is also a drawback that there is no cooling mechanism and durability is difficult, and d) the material to be dissolved is limited to ingots.

JP 2011-117640 A

  An object of the present invention is to provide a hybrid type metal melting furnace that has high metal melting efficiency, low nitrogen oxide emission, can remove impurity elements as much as possible without special incidental equipment, and has excellent durability. There is.

The present invention includes a crucible containing a metal to be melted and opened upward, a furnace body constituting a support housing for supporting the crucible, a furnace lid provided on the furnace body, and an upper part of the crucible In a hybrid type metal melting furnace provided with a burner that is located at a position that can inject a flame into a crucible, and induction heating means for induction heating by generating an induction current in the metal in the crucible,
The burner is an oxygen burner that uses a fuel gas and a combustion-supporting gas having an oxygen concentration of 21 mass% to 100 mass%,
The crucible has a lower half region and an upper half region arranged vertically along the depth direction thereof,
In the position corresponding to the lower half region of the crucible, an induction coil as the induction heating means is provided so as to surround the crucible,
In a position corresponding to at least the upper half region of the crucible, a coiled cooling pipe is provided so as to surround the entire circumference of the crucible outside,
The hybrid metal melting furnace is characterized in that a cooling pipe is provided inside the furnace lid.
Preferably, the cooling pipe provided in the inside of the furnace lid is provided so as to surround a flame injection port of a burner which is erected vertically at the center of the furnace lid.

  According to the hybrid-type metal melting furnace of the present invention, a high-temperature flame of an oxygen burner is used for melting the metal to be melted that is charged into the melting furnace as a material, and the obtained molten metal is kept warm and heated. It is possible to selectively use a heating source that uses induction heating by an induction coil. Therefore, a series of operations from the production of the molten metal to the hot water can be made more efficient than before, while flexibly handling a small amount of many materials.

In particular, according to the present invention, the effects listed below can be obtained.
・ Improvement of dissolution efficiency by using oxygen burner,
・ Reduce or reduce nitrogen oxide emissions by using oxygen burners,
・ The use of an oxygen burner enables the removal of impurity elements as slag as much as possible without special incidental equipment.
・ Improved efficiency of heat retention and temperature rise of molten metal by induction heating with induction coil,
-Durability can be improved despite the adoption of an oxygen burner by providing a cooling pipe that surrounds the crucible at a position corresponding to at least the upper half region of the crucible.

The outline | summary of a hybrid metal melting furnace is shown, (a) is a top view, (b) is a longitudinal cross-sectional view in the AA line of (a). The top view which shows the state which the furnace cover opened in the metal melting furnace of FIG. The time of use (at the time of a melting process) of the metal melting furnace of FIG. 1 is shown, (a) is a top view, (b) is a longitudinal cross-sectional view in the BB line of (a). The top view which shows another example of a hybrid metal melting furnace.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIGS. 1 and 2, a hybrid metal melting furnace according to an embodiment includes a furnace body 10 having a substantially rectangular parallelepiped shape and a furnace lid 20 provided on the furnace body 10.

  In the furnace body 10, a crucible 11 for housing the metal to be melted and the molten metal is provided, and the furnace body 10 constitutes a support housing that supports the crucible 11. The crucible 11 is made of a refractory material such as alumina, silica, or magnesia. As shown in FIGS. 1A and 1B, a pair of left and right horizontal support shafts 12 are provided at the upper front position of the furnace body 10, and these horizontal support shafts 12 are operatively connected to the driving means M. ing. The driving means M may be any of a hydraulic driving type, a pneumatic driving type, and an electric type (for example, an electric motor). Based on the power supply from the driving means M, the furnace body 10 rotates the horizontal support shaft 12 around the rotation center axis. Can be tilted back and forth. Thus, the pair of horizontal support shafts 12 and the driving means M constitute a tilting mechanism that tilts the furnace body 10 including the crucible 11.

  The crucible 11 supported in the furnace body 10 has a cup shape opened upward, and has a pouring spout (tapping port 13) extending from the upper end of the cup shape toward the front wall of the furnace body 10. Yes. In addition, the crucible 11 can be divided into two parts, a lower half region 11A and an upper half region 11B, which are arranged vertically along the depth direction. In this example, as the boundary between the lower half region 11A and the upper half region 11B, the position of the liquid level L of the molten metal formed when the metal to be melted is melted in the crucible (see FIG. 3B) is assumed. doing. Specifically, as shown in FIG. 1B, the position of the liquid level of the molten metal (height h from the bottom of the crucible) is 50% to 70% of the crucible depth d. Assumed. That is, the lower half region 11A of the crucible occupies a range of 50% to 70% of the crucible depth d, and the upper half region 11B of the crucible is the remaining range (that is, 50% to 30% of the crucible depth d). ). The lower half region 11A overlaps with the “melting region” or the “molten holding region”.

  In addition to the crucible 11, an induction coil 14 and a coiled cooling pipe 15 are provided in the furnace body 10. More specifically, the induction coil 14 is provided so as to surround the crucible 11 at a height position corresponding to the lower half region 11A of the crucible. The induction coil 14 is connected to an AC power source (not shown), and an AC current supplied from the AC power source flows through the induction coil 14, so that the induction coil 14 continuously has a high frequency, a medium frequency, or a low frequency in the internal region. A changing magnetic field is generated. As a result, an induced current (for example, eddy current) is generated in the metal placed in the continuously changing magnetic field, and Joule heat based on electric resistance is generated. That is, the induction coil 14 constitutes induction heating means for generating an induction current in the metal in the crucible and induction heating the metal.

  A cooling pipe 15 is provided so as to surround the crucible 11 at a height position corresponding to the upper half region 11B of the crucible. A cooling medium (for example, cooling water or refrigerant gas) is circulated or circulated through the cooling pipe 15 by a pressure pump (not shown), whereby the wall of at least the upper half region 11B of the crucible is forcibly cooled. In the metal melting furnace of FIG. 1, the coiled cooling pipe 15 is provided only at the height position corresponding to the upper half region 11B of the crucible, but at the height position corresponding to the lower half region 11A of the crucible. Similarly, a coiled cooling pipe may be provided. In that case, an induction coil and a cooling pipe are provided side by side at a height position corresponding to the lower half region 11A of the crucible.

  As shown in FIGS. 1 (a) and 1 (b), a vertical support shaft 16 is provided at a position to the left of the rear end of the furnace body 10, and a furnace lid 20 is provided via an arm 17 attached to the vertical support shaft 16. Is connected to the vertical spindle 16. As a result, the furnace lid 20 is rotatable in a horizontal plane with respect to the furnace body 10 about the vertical support shaft 16. FIG. 1A shows a case where the furnace lid 20 is disposed at a closed position where the upper opening of the crucible 11 is closed, and FIG. 2 shows an open state where the upper opening of the crucible 11 is opened by the horizontal rotation of the furnace lid 20. Indicates when placed in position.

  As shown in FIGS. 1 and 2, the furnace lid 20 includes a lid main body 21 having a circular shape in plan view, and a tap cover portion that covers the top of the crucible tap 13 when the furnace lid is disposed at the closed position. 22. When the furnace lid 20 is disposed at the closed position, the furnace lid 20 is preferably in close contact with the upper edge of the crucible 11 in order to suppress heat release from the inside of the furnace to the outside.

  An oxygen burner 23 is erected vertically at the center of the lid body 21 of the furnace lid. The oxygen burner 23 receives a supply of fuel gas from a first gas cylinder (not shown) and generates a flame by receiving supply of combustion-supporting gas from a second gas cylinder (not shown). Examples of the fuel gas include LPG and LNG. As the combustion support gas, for example, an oxygen-nitrogen mixed gas having a high oxygen concentration with an oxygen concentration of 21 mass% or more and 100 mass% or less (more preferably an oxygen concentration of 80 mass% or more and 100 mass% or less) can be mentioned. When the furnace lid 20 is placed at the closed position, the oxygen burner 23 injects the flame vertically into the crucible and melts the metal in the crucible. At that time, the flame length of the burner is preferably long enough to reach the bottom of the crucible.

  As shown in FIGS. 1A and 1B, a cooling pipe 25 is provided in the lid body 21 of the furnace lid so as to surround the flame injection port of the oxygen burner 23. As with the cooling pipe 15, a cooling medium is circulated or circulated through the cooling pipe 25. For this reason, even when the flame injected from the oxygen burner 23 rebounds and hits the lower surface of the furnace lid 20, it is possible to avoid melting of the furnace lid 20 as much as possible.

  Further, as shown in FIG. 1B, the furnace lid 20 is provided with an exhaust passage 26 that vertically penetrates the lid main body 21. The exhaust passage 26 is a passage for discharging exhaust gas, fumes (smoke) and / or dust inside the furnace to the outside of the furnace. However, an automatic opening / closing valve 27 is provided outside the furnace body in the middle of the exhaust passage 26, and the automatic opening / closing valve 27 automatically opens and closes the exhaust passage 26 in accordance with the change in internal pressure in the furnace (inside the crucible). To do.

Next, the use or operation method of the hybrid type metal melting furnace of this embodiment will be described.
When melting metal, first, steel scrap, pig iron (for example, cast iron, cast steel, stainless steel, alloy steel, etc.), alloy (Fe—Si, Fe—Mn, Fe—S) as main materials are placed in the crucible 11 of the melting furnace. Etc.), as well as a carburized material (see FIG. 3A). After the material is charged, the furnace lid 20 is placed at a closed position on the furnace body 10, and the oxygen burner 23 is ignited, and the main material is directly melted by the burner flame (see FIG. 3B). When the melting of the main material charged into the furnace is almost completed, the furnace lid 20 is opened, additional material is charged, the furnace lid 20 is closed, and the main material is directly melted again with a burner flame. The operation of charging the material and melting with the burner flame is repeated until the amount of the molten metal in the crucible 11 reaches a target level (for example, the level of the molten metal level L in FIG. 3B). During melting in the burner flame, the current supplied to the induction coil 14 is kept at a minimum or no state. Further, the slag S generated during the melting of the burner and floating near the surface of the molten metal (so-called “mineral”, generally including an impurity element) is removed by using a tool when the furnace lid 20 is opened, or the furnace body 10 is appropriately removed. It is desirable to incline and to flow out of the furnace from the tap 13.

  When the target amount of molten metal is obtained, flame injection from the oxygen burner 23 is stopped, and energization of the induction coil 14 is started, and final adjustment of the molten metal components and temperature rise to the hot water temperature are performed. When the temperature rise to the tapping temperature is completed, the furnace lid is opened and the furnace body 10 is tilted, and the molten metal in the crucible 11 is tapped out of the furnace through the tapping port 13.

  When the metal melting furnace is not used (when the melting process is not performed), the crucible 11 is emptied, or the steel crucible 11 is filled with an iron pipe or a metal to be melted. Cool the melting furnace naturally. Note that rapid cooling should be avoided because it causes cracks in the refractory material forming the crucible 11.

[Effect of the embodiment]
(A) Since the burner used in the metal melting furnace of the present embodiment is the oxygen burner 23 that uses a combustion gas having a high oxygen concentration, the flame temperature is high. Further, the volume of the exhaust gas is greatly reduced as compared with the case where air is used as the combustion supporting gas (for example, when the combustion supporting gas is pure oxygen, it can be reduced to about 1/5). Furthermore, compared with the case where air is used as the combustion supporting gas, the emission of nitrogen oxides can be greatly reduced.
(B) According to the present embodiment, it is not necessary to provide a special incidental equipment (for example, a degassing device) for removing the impurity element, and the impurity element can be efficiently removed only by using the oxygen burner 23. it can. This is because a relatively high-temperature portion and a relatively low-temperature portion coexist in the molten metal due to the instantaneous instantaneous melting of the metal material by the flame of the oxygen burner 23, and oxides of impurity elements such as Mn, Ti, and Cr are present. It is because it becomes the slag S and floats near the liquid surface of the molten metal. The floating slag S can be easily removed by the simple method as described above. It is also possible to appropriately change the removal efficiency of the impurity elements by adjusting the intensity of the burner flame and the atmospheric temperature in the furnace.
(C) Since induction heating by the induction coil 14 is employed as a means for keeping the molten metal melted by the burner flame, the efficiency of the molten metal can be increased and the heating temperature can be increased.
(D) Since the metal melting furnace of the present embodiment includes the cooling pipe 15, the durability or life of the refractory material and the furnace body forming the crucible 11 can be further improved. In particular, in the metal melting furnace of the present embodiment, since the coiled cooling pipe 15 is disposed in the upper half region 11B of the crucible, the crucible 11 and thus the furnace are heated despite the increase in the flame temperature due to the use of the oxygen burner 23. The body can be effectively protected from high temperature flames.

[Example of change]
As shown in FIG. 4, a material charging port 28 may be provided in the lid body 21 of the furnace lid. By providing such a material input port 28, additional materials can be supplied to the furnace through the material input port 28 while keeping the furnace cover 20 in the closed position without opening the furnace cover 20 once when the metal material is melted. Can be loaded inside.
In the example of FIGS. 1 to 4, only one oxygen burner is used, but the number of burners installed may be two or more. 1 to 4, the furnace cover 20 is movable in the horizontal direction, but a detachable furnace cover may be employed instead.
It is preferable that the oxygen burner 23 has a structure that can sufficiently withstand a flame and a high temperature atmosphere. For example, a cooling mechanism for circulating or circulating cooling water or a cooling gas may be provided around or inside the injection nozzle of the oxygen burner 23.
In the example of FIGS. 1 to 4, the horizontal support shaft 12 is a pair of left and right, but a single horizontal support shaft in which both are connected (integrated) may be employed.

  DESCRIPTION OF SYMBOLS 10 ... Furnace main body, 11 ... Crucible, 11A ... Lower half area, 11B ... Upper half area, 14 ... Induction coil, 15 ... Coiled cooling pipe, 20 ... Furnace lid, 21 ... Lid main body part, 23 ... Oxygen Burner, 25 ... cooling pipe in the furnace lid, L ... level of molten metal, S ... slag.

Claims (2)

A crucible containing the metal to be melted and opening upward;
A furnace body constituting a support housing for supporting the crucible;
A furnace lid provided on the furnace body;
A burner located above the crucible and capable of injecting flame into the crucible;
Induction heating means for generating induction current in the metal in the crucible and induction heating;
In a hybrid type metal melting furnace equipped with
The burner is an oxygen burner that uses a fuel gas and a combustion-supporting gas having an oxygen concentration of 21 mass% to 100 mass%,
The crucible has a lower half region and an upper half region arranged vertically along the depth direction thereof,
In the position corresponding to the lower half region of the crucible, an induction coil as the induction heating means is provided so as to surround the crucible,
In a position corresponding to at least the upper half region of the crucible, a coiled cooling pipe is provided so as to surround the entire circumference of the crucible outside,
A hybrid type metal melting furnace characterized in that a cooling pipe is provided inside the furnace lid.   The cooling pipe provided in the inside of the furnace lid is provided so as to surround a flame injection port of a burner that is erected vertically in the center of the furnace lid. Hybrid type metal melting furnace.

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