Abstract:
A lance adapted for metallurgical treatment comprising an elongated tube-shaped member having a refractory coating thereon and a sleeve of carbon bonded refractory fitted about the tube-shaped member at the slagline to protect the slagline region thereof.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to steel and iron-making injection lances, and more particularly to such lances which are protected by refractory concrete Steel and iron-making injection lances protected by refractory concrete have heretofore been known, illustrative of which are those which are generally offered for sale by Inland Enterprises, Inc. of Cleveland, Ohio. Typically, such lances comprise an inner steel pipe through which injected gasses pass for injection into molten steel or iron and a refractory concrete coating which is provided to protect the steel piping from the intense heat associated with molten steel. 
     In certain commercial applications, injection lances are inserted into the molten steel or iron bath through the slag cover that usually floats on top of the liquid bath and which serves to partially protect the molten metal from the environment. In other applications, care is taken to prevent contact between the environment and the molten metal which could cause undesirable gas incorporation or reoxidation of the metal. 
     It has been found that refractory coatings as typically employed on steel-making lances undergo preferential erosion at the slagline due to a reaction between the basic slag on the surface of the molten steel and the acidic alumina material within the concrete coating of the lance. Such reaction dissolves the concrete, thus creating a slagline cut which renders the lance unusable after a short period of time even though other areas of the lance (i.e., tip and top) have sufficient remaining concrete thickness to provide additional service. As an example, treatment lances with conventional exterior refractory concrete coatings typically are usable under service conditions for only about 160 minutes, at which time the lance is removed from service due to slagline cut and then discarded. Obviously, it would be highly desirable to extend the life of such lances since typical steel mills may employ 1,000 or more each year at a cost of $1,000 or more per lance. 
     SUMMARY OF THE INVENTION 
     It has been discovered that certain materials act cooperatively to interface with refractory concrete of the type employed for lance coatings while at the same time providing a high degree of resistance to slagline erosion. Accordingly, in accordance with the principles of the invention, a sleeve of such material is affixed to the exterior of the lance at a location where the slagline level occurs when the lance is in place in the molten steel or iron, and such sleeve advantageously reduces slagline wear by a substantial degree, thereby adding extensively to the life of the lance. In addition, such sleeves can be made readily replaceable so that in the event a particularly erosive condition is encountered, after a period of use, the lance may be withdrawn and the sleeve replaced so as to provide extended useful life equal to or greater than that of the refractory concrete in areas other than the slagline. 
     OBJECTS AND FEATURES 
     It is one general object of this invention to improve steel and iron-making lances. 
     It is another object of the invention to extend useful life of such lances. 
     It is yet one further object of the invention to provide for ready replaceability of an important component of a steel or iron-making lance. 
     Accordingly, in accordance with one feature of the invention, the slagline region on a lance is identified and a protective sleeve having compatible characteristics to steel or iron-making slag is installed at the lance slagline region, thereby providing a high degree of resistance to slagline erosion. 
     In accordance with another feature of the invention, such sleeve is made removable and replaceable so as to facilitate extended utilization of the lance to achieve markedly increased life expectancy. 
     In accordance with still another feature of the invention, the sleeve is made in sections so as to facilitate installation and removal. 
     In accordance with yet another feature of the invention, the preferred sleeve is made of carbon bonded magnesite or carbon bonded alumina, thereby achieving the aforementioned material compatibility and facilitating fabrication installation and use. 
     These and other objects and features of the invention will be apparent from the following detailed description by way of a preferred embodiment with reference to the drawings. 
    
    
     BRIEF SUMMARY OF THE DRAWINGS 
     FIG. 1 is an elevation view depicting a typical steel or iron-making lance in accordance with the principles of the invention; and 
     FIG. 2 is an enlarged view depicting that portion of the lance wherein the aforementioned sleeve is installed. 
    
    
     DETAILED DESCRIPTION 
     Now turning to the drawing, and more particularly to FIG. 1 thereof, it will be observed that there is therein depicted a steel or iron-making lance 10 constructed in accordance with the principles of the invention. Such lance comprises a tubular steel interior 11 onto which there has been applied a conventional refractory concrete coating 16. As is known to those skilled in the art, conventional refractory concrete coatings typically utilized on lances are substantially acidic and have an alumina content typically ranging from about 70 to about 90 weight percent. Such refractory concrete is applied to steel pipe 11 by conventional techniques well known in the refractory shape making arts. 
     At the upper end of the lance 10, there conventionally is provided a short length of chain 13 which serves to provide a means for hoisting and positioning the lance. Also, at the upper end of the lance there typically is a collar 14 which is affixed to the upper end 15 of pipe 12 by any suitable means such as clamping or shrink fitting. As will be observed from the figure, collar 14 provides a convenient interface between chain 13 and the upper end 15 of pipe 11. Collar 14 may also provide a useful means for affixing a plug to seal the exposed upper end 15 of pipe 11 and/or to protect any threads or other vulnerable surfaces that may exist, depending upon the particular construction of the lance. 
     At the lower end of the lance 10, there is a substantially thicker section of refractory concrete 16 which surrounds tubular steel interior 11. This section 16 may vary in length and in thickness, depending upon the specific application in which the lance is to be employed. As will be evident from the drawing, this thicker section extends from the lower end of square steel tube exterior 12 vertically to a point substantially below the intended location of the slagline when the lance is in use. Typically, the length of this thicker section 16 is approximately 14 feet, while the length of the upper portion of the lance is approximately 12 feet. 
     As previously mentioned, in accordance with the principles of the invention, a refractory collar 17 is installed around pipe 11 at the region of the expected slagline. This collar which typically is about 2 feet in length and about 12 inches in diameter, is installed and affixed to the lance pipe 11 as is shown in more detail in FIG. 2. There, it will be observed that collar 17 is comprised of four sections, 17a-17d, which are snugly fit together so as to occupy the recessed region 18 of refractory concrete layer 16. 
     Although collar 17 is shown as comprising four sections, 17a-17d, it will be evident to one skilled in the art that the collar could be formed in one unitary section. However, for ease in installation and maintenance, it has been found preferable to use a plurality of sections as shown in FIG. 2. To facilitate installation, each of sections 17a-17d is made in at least two parts as if the members were slit vertically, thus permitting ready removal and replacement. 
     As hereinabove described, the collar is comprised of carbon-bonded or carbon-bonded pitch impregnated refractory, preferably carbon-bonded magnesite or carbon-bonded alumina. The preferred magnesia content of the sleeve is above 80 weight percent with a residual being of up to 20 weight percent carbon with a preferential composition being near five weight percent. However, it should be understood that a wide range of carbon-bonded magnesite refractories ranging from 50 to 99 weight percent magnesia and trace to 50 weight percent carbon would offer service performance advantage over cement-bonded high alumina concrete composition. 
     For the magnesite sleeve, the magnesia may be in the form of sintered grain, fused grain or a combination of these two grains or in the form of sintered or fused spinel grain. The residual carbon bond may be derived from resin, tar or pitch, or a combination of these carbon sources. For the alumina sleeve, the preferred alumina content of the sleeve is above 70 percent with a residual carbon greater than 10 percent. However, it is understood that a wide range of carbon-bonded alumina refractories (50 to 90 weight percent alumina and trace to 50 weight percent carbon) offers service performance advantage over cement-bonded high alumina concrete compositions. The alumina of the alumina sleeve may be in the form of sintered grain, fused grain, or a combination of these two. The residual carbon may be derived from resin, tar, pitch, or a combination thereof. These materials are mixed together by conventional mixing and then are preferably formed by power pressing. However, the sleeve members may also be rammed, cast, injection molded, or isopressed. 
     The invention will be further described in connection with the following examples which are set forth for purposes of illustration only. 
     EXAMPLE 1 
     A carbon bonded high alumina sleeve was formed from the mix set forth below. The ingredients were admixed, pressed into the desired sleeve shape, and cured at a temperature of 250° -300° C. The shape was tested and the results are set forth below. 
     
         ______________________________________Tabular Alumina-6 mesh  61%Tabular Alumina-325 mesh                   10Reactive Alumina-325 mesh                   10Silicon Carbide-200 mesh                   5Flake Graphite          8Powdered Silicon        3Powdered Aluminum       3Plus AdditionPhenolic Resin          4.5Bulk Density, pcf       188Coked PropertiesBulk Density, pcf       183% Apparent Porosity     14.3Apparent Specific Gravity                   3.42Modules of Rupture, psiAt Room Temperature     4910At 2000° F. (Reducing)                   4180Crushing Strength at    6050+2800° F., psi______________________________________ 
    
     EXAMPLE 2 
     A sleeve was formed and tested as in Example 1, but the mix used to form the sleeve was a carbon bonded magnesite. The mix and test results are set forth below. 
     
         ______________________________________Mix:Deadburned Magnesite 4 + 10 mesh            29%10 + 35 mesh            34Ball Mill Fines         18Flake Graphite          17Powdered Aluminum        2Plus Additions:Phenolic Resin Bond     3.5Bulk Density, pcf:      183Coked PropertiesBulk Density, pcf:      174Apparent Porosity, %    9.45Apparent Specific Gravity:                   3.08Modules of Rupture, psiAt Room Temperature:    2270At 2000° F.:     1770Crushing Strength at    31402800° F., psi______________________________________ 
    
     It will now be evident that there has been described herein an improved lance construction which exhibits significant advantages over the corresponding prior art. Although the inventive concepts hereof have been illustrated by way of a preferred embodiment, it will be evident to those skilled in the art that adaptations and modifications may be employed without departing from the spirit or scope of the invention. Thus, for example, the carbon-bonded refractory sleeve could be extended the full length of the lance lower portion, although such would incur significant additional expense since carbon bonded refractories generally are more expensive than conventional refractory concrete. Likewise, it is understood that both carbon bonded compositions illustrated above may contain other powdered metals (for example, magnesium) which impart to the composition improved oxidation resistance. 
     The terms and expressions employed herein have been used as terms of description and not of limitation; and there is no intent in the use thereof to exclude equivalents, but on the contrary, it is intended to include any and all equivalents, adaptations and modifications that can be employed without departing from the spirit and scope of the invention as described in the specification and claims herein.