Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – By means introducing treating material
Reexamination Certificate
1999-07-06
2001-05-15
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
By means introducing treating material
C266S217000
Reexamination Certificate
active
06231806
ABSTRACT:
STATE OF THE ART
In steelmaking processes, the steel ladle which in the past was used solely for purposes of transportation became, with secondary metallurgy, a steel refining equipment. In this connection, there were noted among other factors an extended time of permanence of the metal within the container, a higher working temperature, and the need that a greater amount of stirring be provided.
The stirring of the metal or alloy is usually achieved with the use of plugs or metallic lances coated with a refractory material. The choice of the lances is due to the possibility of addition of powdered materials, and to the operational safety thereof. The plugs, on the other hand, besides involving a lower cost, are more effective in spite of being limited to the injection of gasses.
The plug is a refractory part through which the gasses are injected, those more commonly used being argon and nitrogen in the case of steel. These gasses promote the bubbling which stirs the metal, or fused alloys. The primary objectives of this bubbling are chemical and thermal homogenization of the steel, as well as the cleaning thereof, since it promotes the withdrawal of inclusions. The plug is usually installed at the bottom of the container. Until the present day, the containers have a maximum number of 3 plugs.
The positioning of the plug at the bottom of the container is calculated in order to achieve the most effective stirring. However, there exist hazardous situations, since there is a discontinuity of the metallic casing of the container, and in consequence the possibility exists of the plug being excessively eroded to the point of allowing leakage of the metal. The results of this leakage may include from the partial or total loss of the metal, to the loss of human lives, including the destruction of equipments.
Having in view the importance of the safety consideration when employing plugs, it is believed that the safety systems having been developed to date are still unreliable. Some of these devices are described below:
Devices intended for evaluating the wear of the plug:
The existing devices are based upon visual examination. They may be constituted by a refractory material with different thermal conductivity from that of the plug itself, and will exhibit a different color upon being reached, during the course of wear of the plug. There also exist references which have cross sections of different geometries, with a square section body, within a circular section plug.
These references are, however, evaluated by means of analysis of the working face of the plug, i.e., by the inner side of the container wherein the metal is processed, and therefore it is required that this container be empty, and this takes place upon the pouring or ingot forming having been performed. This makes it impossible to evaluate the plug during the processing of the metal, restricting the possibilities of evaluation, and consequently decreasing the safety of the plug.
The plugs may be graded in accordance with the refractory material used, and they may be alumina based or magnesia based for instance. They may also be graded as being porous or having directional passage, which are distinguishable primarily by the fashion in which the gas passes therethrough, which in turn is evaluated by flow rate. The flow rate measures the volume of gas which passes by the part, per unit of time, and varies according to the pressure of this gas. In the porous plug the flow rate is associated with its permeability. For directed porosity plugs, on the other hand, the flow rate will depend on the dimension and number of “slits” or openings present in the refractory material.
Mechanical devices intended for safety and support of the plug at the bottom of the ladle:
The mechanical support devices normally used are of the bayonet or spline types which do not ensure the degree of safety required for this application. The bayonet or spline devices are much dependent on the manner in which the operator makes the installation, and may become unstable systems and be subject to cause serious accidents when in operation.
New Injection System for Gasses
The new system for the injection of gasses comprises the new device for indicating the end of the useful life of plugs and a new mechanical device to provide safety and support for the plug at the bottom of the ladle. These two devices when installed together provide better safety to the operation, although they may be installed and used separately.
REFERENCES:
patent: 4971295 (1990-11-01), Rothfuss et al.
patent: 5007366 (1991-04-01), Handler
patent: 5202079 (1993-04-01), Winkelmann et al.
patent: 5249778 (1993-10-01), Steichert et al.
patent: 5421561 (1995-06-01), Eisermann et al.
patent: 5435528 (1995-07-01), Guttery et al.
patent: 5478053 (1995-12-01), Richter et al.
Nunes Jose Mendes
Rodrigues Angela
Birch & Stewart Kolasch & Birch, LLP
Kastler Scott
Magnesita S.A.
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