MXPA01005050A

MXPA01005050A - Stopper rod

Info

Publication number: MXPA01005050A
Application number: MXPA/A/2001/005050A
Authority: MX
Inventors: Hanse Eric
Original assignee: Hanse Eric; Vesuvius Crucible Company
Priority date: 1998-11-20
Filing date: 2001-05-18
Publication date: 2001-12-04

Abstract

The present invention concerns a stopper rod whose gas tightness and rigidity are improved. In particular, the stopper rod of the present invention has means for maintaining the compression of the sealing gasket (11, 11') in contact with the annular sealing surface (10) of the body of refractory material when the stopper rod is brought to a high temperature. According to one embodiment of the invention, these means are furnished by a sleeve (12) comprised of a material with a high coefficient of thermal expansion, the dilatation of which maintains the sealing gasket under compression when the stopper rod is brought to a high temperature.

Description

COLADA PLUG DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new plug for regulating the flow of a molten metal from a casting group, for example, steel or cast iron, from a distributor or a ladle, and more especially, a plug in a piece that has a means to attach to a lifting mechanism. In a particular embodiment, the plug further possesses a means for introducing an inert gas, such as argon, into the bath of molten metal during continuous casting operations. The aforementioned stopper and its use are well known to the expert, in particular by US Patents 4,946,083 and 5,024,422, to which reference is made. Among others, these documents describe a casting plug in a single piece that can be attached to a lifting device, composed of: a) an elongated body of refractory material having an orifice located coaxially with respect to the body of the pouring plug and adapted to receive fixedly a metal bar for its attachment to a lifting mechanism. The axial bore of the body of the refractory material has an elongated portion with an annular sealing surface separated from the upper end of the body of refractory material. The means for joining the metal bar is generally located between the elongate portion and the lower end of the body of refractory material. At its lower end, the body of refractory material may have a means for introducing gas into the bath of molten metal; and b) an elongated metal rod joined to the body of refractory material and having an axial hole that communicates in its lower part with the orifice of the body of refractory material. The bar has a collar that has an annular sealing surface facing the annular sealing surface of the refractory material body orifice to create a gas tight seal. The upper end of the bar is adapted to be attached to a lifting mechanism that allows the pouring plug to be displaced in a vertical direction inside a casting system as a distributor. The plug is connected to a gas supply conduit, usually, but not necessarily, through the upper end of the bar. The means of attachment to the body of the refractory material is generally located between the collar and the lower end of the metal bar. During the use of the stopper, the gas introduced into the stopper is conveyed towards the axial hole of the body of refractory material in its lower part. Thanks to the means for introducing gas into the bath of molten metal that the body of refractory material has in its lower part, the plug allows the introduction of gas into the bath of molten metal. The opposing annular sealing surfaces of the bar and the body of refractory material avoid significant losses of inert gas, as well as air infiltration. To improve even more this sealing, it was proposed to place an annular seal gas tight between these sealing surfaces. U.S. Patent 4,946,083, for example, indicates that when a gasket with a thickness of about 0.4 mm and a material resistant to high temperatures, eg graphite, is located in its position, the interface between the annular closing surfaces of the bar and the body of refractory material provide a seal able to withstand a pressure of up to 3 bar. German patent DE-C14040189 discloses a plug comprising an elongated refractory body having a) an axial hole and a means (lock pin) for attaching a metal bar, b) a metal bar, and c) a body in the form of a sleeve comprises a closing seal under the action of a nut. With the device of this document, it is necessary to correct or fine tighten the tightening when the mounting bar is fixed to the body of the cap by screwing the nut against the upper end of the cap. The system is not self-tightening and requires human intervention (screw the nut) when the cap has reached the final temperature. Such intervention before the bath of molten metal is difficult and extremely dangerous. This hermetic seal is fundamental for the casting of high quality cast metal. First, it is necessary to ensure a good protection against the infiltration of air responsible for oxidation of the molten metal during casting. On the other hand, it is also essential to minimize the losses of inert gas (in the case that an inert gas is injected through the plug) that can cause production costs due to gas supply excesses that are far from insignificant. Apart from this aspect of sealing, it is also essential that the connection of the plug to the lifting mechanism remains as rigid as possible. The system used at present still does not provide a totally satisfactory solution for these two points of view. In carrying out their research in this technical field, the applicants discovered that these problems are due to the fact that the sealing gasket between the annular closing sces of the bar and the body of refractory material facing each other did not remain compressed throughout the pouring operation. It is believed that this loss of compression in the seal is due, at least in part, to the difference between the coefficients of thermal expansion of the different materials that constitute the plug. In particular, under the effect of the temperature at which the plug arrives during casting, the metal bar expands greatly with respect to the body of refractory material. This more substantial expansion of the metal bar has the effect of separating the annular closing sces of the bar and the body of refractory material and consequently reducing the compression of the gasket with all the adverse consequences involved. According to the present invention, this problem is solved by providing the pouring plug with a particular means for maintaining the compression of the sealing gasket in contact with the annular closing sce of the body of refractory material when the cap reaches a high temperature. The stopper involved in the present application is, regardless of the means to maintain the compression of the seal, similar to that described in US Patents 4,946,083 and 5,024,422 to which reference is made. According to one embodiment of the invention, the means for maintaining the compression of the sealing gasket when the cap is subjected to a high temperature is provided by a sleeve having the shape of a cylinder open at its ends, which is installed on the metal bar. The present invention relates to a one piece casting plug that can be attached to a lifting mechanism, composed of an elongate body of refractory material comprising: (i) an orifice located coaxially with respect to the body and adapted to receive from fixed form a metal bar for its attachment to a lifting mechanism, the axial hole having an elongated part having an annular closing sce separated from the upper end of the body; (ii) a means for joining said metal bar; an elongated metal rod fixed to the body adapted at its upper end to join a lifting mechanism to vertically move the plug inside a casting group; and a sleeve having a closing surface at its lower end facing the body closing surface, the cap having a locking means located on the rod, the cap characterized in that the sleeve is formed of a material that has a coefficient of thermal expansion greater than that of the metal bar and has a sufficient length so that, under the effect of the temperature at which the plug is subjected during the casting, it dilates sufficiently compensating at least the effect of the dilation of the metal bar. According to a particular embodiment of the invention, the plug can be connected to a gas supply conduit. Therefore, said elongate body of refractory material has, at its lower end, a means for introducing gas into the bath of molten metal and said metal bar has an orifice communicating in its lower part with the orifice of the body of refractory material . Figure 1 is a fragmentary cross-sectional view of the upper end of the plug according to a particular mode of carrying out the invention. In this figure, the plug 1 is composed of an elongated body of refractory material 2 with an axial hole 3 extending from its upper end 4 towards its lower end (not shown). At its lower end, the body of refractory material may or may not be provided with a means for introducing inert gas (not shown) into the metal bath. The body of refractory material also has a means 5 for joining the metal bar 6. The metal bar 6 can also have an axial hole 7 passing through it from its upper end 8 to its lower end 9. The upper end 8 it can be designed to house a connector (not shown) for supplying an inert gas. In addition, the upper end 8 of the bar is adapted to be fixed to a lifting mechanism (not shown). A pressurized gas (such as argon) can be introduced into the axial hole 3 of the body of refractory material by means of the bar 6 and said gas be transported to the metal bath through the lower end of the body of refractory material. The body of refractory material 2 has an elongated part 10 that forms a closing surface. Two graphite seals (11 and 11 ') rest on this closing surface and thus avoid air infiltration or inert gas losses. On the rod 6 a sleeve 12 is mounted which maintains the joints 11 and 11 'in compression. The upper part 13 of the sleeve is blocked by a washer 14, retained in turn by a nut 15. Preferably, the washer 14 is in contact with the upper end 4 of the body of refractory material 2 in order to impart to the assembly a greater rigidity. The sleeve 12 is constituted by a material that has a coefficient of thermal expansion greater than that of the metal bar 6 and has a sufficient length so that, under the effect of the temperature at which the cap is subjected during the casting, it is dilate sufficiently towards the lower end of the metal bar, compensating at least the effect of the expansion of the metal bar. Preferably, the dilation of the sleeve substantially and precisely compensates for the expansion of the metal bar. As can be seen in Figure 1, the sleeve 12 can be projected onto the upper part 4 of the body of refractory material 2 if this were necessary to allow a sufficient length of the sleeve. In this case, a washer 14 provided with a projection 16 that allows the locking of the sleeve 12 is preferred, while ensuring a contact between the washer 14 and the upper end 4 of the body of refractory material 2. The sleeve 12 is mounted on the metal bar 6 and form therewith a rotating and sliding or simply sliding assembly. The upper end 13 of the sleeve 12 rests on the locking means 14 and 15 fixedly disposed on the metal bar 6 so that, under the effect of dilation, the sleeve 12 is extended in the axial direction only in the direction opposite said blocking means. According to one embodiment of the invention, the locking means comprises a collar similar to that described in United States Patents 4,946,083 and 5,024,422, to which reference is made. The material that constitutes the sleeve, as well as its length, are chosen according to the dimensions and materials that make up the metal bar (usually machined from a steel bar with a coefficient of thermal expansion of the order of 12 , 5 μm ° C "1) and the body of refractory material (typically composed of a refractory material obtained by isostatic pressing with a coefficient of thermal expansion of 3 to 6 μm ° C" 1). The material that constitutes the sleeve, as well as its length, are easily determined from the basic principles of thermal physics. Starting from the values thus determined in a first approximation and which, in general, provide excellent results, it is then possible to optimize the system by trial and error without any difficulty. According to the invention, the sleeve is composed of a material with a high coefficient of thermal expansion, able to withstand the high temperatures at which the plug is subjected during casting. For example, refractory materials with a high coefficient of thermal expansion such as fritted magnesium oxide can be used. Preferred materials for this application are among metals or metal alloys with a high coefficient of thermal expansion and having a high melting point. In general, a material having a coefficient of thermal expansion varying from 1.1 to 3 times that of the material of the steel bar is chosen for the sleeve. Stainless steel (for example, with a coefficient of thermal expansion of the order of 17.5 μm ° C "1) is particularly appropriate when the metal bar is machined from a steel bar that has a coefficient of thermal expansion of the order of 12 μm ° C "1. The body of refractory material is typically composed of a conventional refractory material such as a refractory material based on alumina-silica-graphite, commonly used. A typical composition is, for example, in percentages by weight: AI2O3: 53%, SiO2: 13%, carbon: 31% and approximately 3% of other materials such as, for example, zirconia, Zr02. Preferably, an annular seal 11 is placed which is gas tight between the sealing surfaces. Typically, a graphite gasket with a thickness of 0.2 to 30 mm is used. In accordance with the present invention, one or more conventional gaskets are used. The annular sealing gasket (s) are placed between the lower surface of the sleeve and the closing surface of the body of refractory material. The best results were observed when two graphite joints of 9 mm each were placed between the lower surface of the sleeve and the closing surface of the body of refractory material. According to a preferred form of carrying out the invention, the closing surface formed by the elongate part 10 of the body of refractory material 2, as well as the sealing gasket (s) 11 (and 11 ') are flat. In fact, it was found that in this case, much better compression of the board (s) 11 (and 11 ') was obtained. In an exemplary embodiment, a body of refractory material obtained by isostatic pressing (coefficient of thermal expansion: 3.5 μm ° C "1), each having a thickness of 9 mm, The metal bar is machined from a steel bar with a coefficient of thermal expansion of 12.5 μm ° C "1. If a stainless steel sleeve with a coefficient of thermal expansion of 17.5 μm ° C "1 is used, it is estimated that the sleeve will have a length of about 61 mm According to another embodiment of the invention, the means for maintaining the compression of the sealing gasket when the plug is subjected to a high temperature is achieved by placing the fixing point of the metal bar to the body of refractory material at a point located between the closing surface and the upper part of the bar. case, the greater the expansion, the greater the compression of the sealing gasket, the metallic bar that expands under the effect of the temperature to which the plug is subjected during casting. According to a particular form of carrying out the invention, the plug has a means for preventing the metal rod from separating from the body of refractory material. Thus, if an inserted metal part having a threaded internal axial hole anchored in the body of the refractory material is used as a means of fixing the bar to the body of refractory material, it will be avoided that the bar is unscrewed from the insert by providing it with a pair of parallel flat surfaces at the point of exit from the body of refractory material and resting on these flat surfaces a solid fork flange fixedly attached to the body of refractory material. This fixed connection can be made by a bolt inserted in a rod through the fork flange and extending to the body of refractory material. In this case, the washer according to the present invention can also advantageously perform the function of the fork flange. According to another particular embodiment of the invention, the body of refractory material of the plug comprises at least partially a refractory material relatively impermeable to gases. More particularly, the body of refractory material is composed of at least two different refractory materials, a first part formed by a mixture relatively impermeable to gases, substantially surrounding the region in which the gasket is located and a second part formed by a refractory material resistant to corrosion by molten metals.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - Casting plug (1) comprising: (a) an elongated body (2) of refractory material comprising (i) an orifice (3) located coaxially with respect to the body (2) and adapted to receive fixedly a metal bar (6) for its attachment to a lifting mechanism, the axial hole (3) having an elongated portion (10) having an annular closing surface separated from the upper end (4) of the body (2); (ii) a means (5) for fixing said metal bar (6); (b) an elongated metal bar (6) fixed to the body (2) and adapted at its upper end (8) for its attachment to a lifting mechanism to vertically displace the cap (1); inside a casting group; and (c) a sleeve (12) having a closure surface at its lower end facing the closure surface (10) of the body (2), the cap having locking means (14,15) for the sleeve (12) located on the metal bar (6), characterized in that the sleeve (12) is formed of a material that has a coefficient of thermal expansion greater than that of the metal bar (6) and has a sufficient length so that , under the effect of the temperature at which the plug is subjected during the casting, this is sufficiently dilated, compensating at least the effect of the expansion of the metal bar (6).

2. The plug according to any one of claims 1, characterized in that it has one or more annular sealing gaskets (11, 11 ') in contact with the closing surface (10) of the body (2).

3. The plug according to claim 2, characterized in that the annular gasket (s) (es) (11, 11 '), as well as the closing surface (10) of the body (2) are flat.

4. The plug of a casting group according to claim 1 to 3, characterized in that said metal bar (6) has an axial hole (7) communicating in its lower part (9) with the hole (3) of the body (2).

5. The plug according to claim 1 to 4, characterized in that said body (2) has, at its lower end, a means for introducing gas into the bath of molten metal.

6. The plug according to one of claims 1 to 5, characterized in that the sleeve (12) is projected on the upper end (4) of the body (2).

The plug according to any one of claims 1 to 6, characterized in that the sleeve (12) is composed of a material having a coefficient of thermal expansion of 1, 1 to 3 times the coefficient of thermal expansion of the material that constitutes the metal bar (6).

8. The cap according to any one of claims 1 to 7, characterized in that the sleeve (12) is composed of stainless steel, the metal bar (6) is composed of steel and the body (2) is composed of refractory material obtained by isostatic pressing.

9. The cap according to any one of claims 1 to 8, characterized in that the means for locking the sleeve (12) on the metal bar (6) comprises a collar.

10. - The plug according to any one of claims 1 to 8, characterized in that the locking means of the sleeve (12) on the metal bar (6) is a nut (15) screwed in a fixed manner on the metal bar (6) and on which the sleeve (12) rests.

11. The cap according to claim 10, characterized in that the locking means of the sleeve (12) on the metal bar (6) further comprises one or more washers (14).

12. The cap according to claim 11, characterized in that said washer (14) has an internal projection so that the sleeve (12) can be projected on the end (4) of the body (2) while the washer ( 14) is in contact with the upper end (4) of the body (2).

13. The cap according to any one of claims 1 to 12, characterized in that it also comprises means for preventing the metal bar (6) from separating from the body (2).