Metal founding – Means to shape metallic material – Including ladle or crucible type melt receptacle
Reexamination Certificate
2001-12-03
2004-07-20
Zimmerman, John J. (Department: 1775)
Metal founding
Means to shape metallic material
Including ladle or crucible type melt receptacle
C164S447000, C266S196000, C266S275000
Reexamination Certificate
active
06763877
ABSTRACT:
FIELD OF THE INVENTION
A method and device for tempering a casting trough; specifically a method and device for tempering a trough without causing the release of potentially hazardous substances to the immediate environment.
BACKGROUND OF THE INVENTION
Occupational hazards exist with regard to exposure to gases and particulates in a continuous casting plant for molten metals such as copper or copper alloys. Some of these hazards are related to the tempering of the casting trough of the continuous casting plant. The casting trough is the part in which the molten metal flows from a supply vessel—such as a melting furnace, casting furnace, or a ladle—to a continuous casting mold where the molten metal then solidifies into a metal billet.
Before the start of the continuous casting process, and thus the filling with the molten metal, it is necessary to heat the casting trough intensively. Only then can it be ensured that the molten metal will properly reach the continuous casting mold without prematurely solidifying.
It is a known method to heat a casting trough with gas burners when casting molten metals of copper or copper alloys. This procedure is feasible at an acceptable industrial cost and at relatively high heating rates.
Nonetheless, heating with gas burners has a number of disadvantages. First, there is often a considerable generation of noise, the cause of which is the high velocity of the combustion gas emerging from the burner jets. In addition, due to the high flow speeds of the combustion gases in the burner area, and due to thermal convection, oxidized cast metal, volatile components of the smelting residues, dust particles in the form of slag particles, and pulverized fluxing agents can be swirled up and may reach the environment of the continuous casting plant, where they can result in a detriment to the health of the persons employed there. Moreover, the hot flames of the gas burners usually break out of the casting trough and thus contribute to an appreciable occupational exposure as the result of heat.
An additional problem in using gas burners is the precision of temperature regulation of the walls of the casting trough.
Before the process starts, the temperature of the walls of the casting trough to be heated is not always precisely uniform since the burner flames themselves do not have the same temperatures throughout. This situation results from the existence of locally varying combustion zones with temperatures that deviate from one another within the burner flame. This results in locally varying temperatures on the walls of the casting trough. The position of the varying temperature zones is a function of the flame control within the combustion chamber. To an essential degree, the flame control is the consequence of the geometry of the combustion chamber and of the gas burner. In the case of the casting trough, the combustion chamber is the casting trough, the profile of which can be subject to changes, specifically by wear of the lining or trough cover as a result of the effect of heat and molten metal as well as by caking of metal slags and metal crusts. The burner nozzles are also subject to wear by the effect of heat.
As a consequence of the above-described local non-uniformities, the temperature of the walls of the casting trough cannot reliably be set in a reproducible manner so that, on the whole, the mean wall temperature is precisely uniform in each casting process. The consequence of this is that during the casting operation, the molten metal flowing through the casting trough gives off heat to the walls and/or absorbs heat from them in a different manner in the different casting runs.
Also, the temperature of the molten metal within the casting trough cannot be regulated sufficiently fast enough by directly heating the molten metal with gas burners since, for example, the heat transmission at the boundary surface of the burner flames/molten metal is not sufficiently great.
In practice, it is therefore the case that the molten metal gives off heat while flowing through the casting trough. The extent of the cooling of the molten metal is usually greater at the start of the casting than later when the walls of the casting trough have been uniformly heated by absorption of heat from the molten metal. The consequence of this is that the solidification process originates in the casting mold from temperatures of the molten metal that change during the casting process and are not so readily susceptible to regulation.
This results in additional disadvantageous effects.
During cooling, the cast molten metal in the form of the metal billet naturally experiences a contraction of volume. Since cooling in the interior of the metal billet inevitably occurs differently in comparison with the areas near the surface, this results in internal mechanical stresses in the metal billet, which influence the machinability of the material provided from the molten metal to a varying degree.
Thus, if the material strength is exceeded, cracks may occur within the material to be machined, which in many cases, results in production problems or disadvantageous properties of the end products. The formability of the material is also not uniform since it is dependent on the stresses in the metal billet. The result of this is that for error-free production, the machining process must be designed in such a way that even material with unfavorable stress states or low formability can still be machined. This, however, imposes economic limitations on machining.
The methods known heretofore include additional heating methods that are applied in different cases of applications for metallurgical troughs. The use of such heating methods can avoid at least some of the problems that are characteristic of heating with gas burners.
Thus, for example, known methods include heating casting troughs of vacuum furnaces with radiant heaters arranged above them. This method is based on glowing metal wires and is customary in vacuum melting and casting plants. Radiant heaters nonetheless have only a relatively low power density so that the heating of a casting trough requires a substantially longer time than with gas burners. Therefore, they are basically suitable only for applications in which adequate time for heating is available. In addition, it must be stated that, due to the low power density, it is impossible to regulate the temperature of a flowing molten metal under the conditions of an industrially operated production process with throughputs of several tons per hour.
Other radiant heaters use glowing silicon carbide rods. In this case also, there is the basic disadvantage of a low current density with the negative effects described above. Since silicon carbide oxidizes and is destroyed relatively rapidly in air, the life of such heating elements is also relatively short. Moreover, they are very sensitive to mechanical stresses and can thus break relatively easily. They are therefore not suitable in connection with the heating of casting troughs as components of continuous casting plants.
Inductive heating of metals is also a widely used technology. It is frequently used in induction melting furnaces. The inductive heating of a molten metal immediately upstream of the continuous casting mold of a continuous casting plant is also known.
Thus, French Patent No. 1,465,577 describes a device in which the molten metal flows from a supply vessel during the continuous casting through a sealed, tubular, refractory supply line to a continuous casting mold and in so doing is inductively heated. The feed pipe is only open at the ends so as to protect the molten metal against a reaction with the ambient air.
However, such a device is only suitable for such special casting plants in which there is a sealed connection between the feed of the molten metal and the continuous casting mold. Its use is not covered in a casting process as is customary with the continuous casting of copper or copper alloys in which the continuous casting mold must be arranged separately and the fill level in the continuous cast
Brüning Hubertus
Frankenberg Ralph
Krause Andreas
Olemann Hartmut
Quadfasel Uwe
Kenyon & Kenyon
KM Europa Metal AG
Zimmerman John J.
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