EP0023034B1 - Method of recalibrating a worn conical tube, especially a curved tubular mould for continuous casting - Google Patents

Abstract

A worn conical tubular mold, exhibiting irreparable surface flaws or defects at the inner tubular wall of the mold at the location of the former region of the molten bath level existing in the tubular mold when the same was previously used during continuous casting, is formed or reformed through the use of an explosive forming technique with the aid of a calibration arbor or mandril so as to possess a new reversed taper. As a result, the surface flaw or defect now is located at the region of what becomes the new strand outlet of the reformed tubular mold and unimpaired, fissure-free mold wall material comes to lie at the region of the tubular mold where there will appear the new molten bath level when the reformed tubular mold then is again used for casting purposes.

Description

The invention relates to a method for recalibrating a worn, conical, in particular bent, mold tube for continuous casting, a caliber mandrel being introduced into the mold cavity, explosive attached to the outside of the tube and the mold cavity being deformed by its detonation to the dimensions of the caliber mandrel (DE-B- 2 533 528).

In the continuous casting of metal, in particular steel, continuous molds with a straight or curved shape are used. In general, the walls of these molds forming the mold cavity are made of copper or copper alloys. For smaller strand cross-sections, e.g. B. billets and smaller bloom formats, they are usually made of pipes. In order to compensate for the pronounced shrinkage of the strand which solidifies on the surface in the mold with regard to sufficient cooling, the majority of the tubular molds is provided with a taper towards the withdrawal side of the strand. Especially in the area of the bathroom mirror and here especially in systems with bathroom mirror regulation, the molds are exposed to particular wear and tear, causing damage to the mold surface, e.g. B. large-scale measurements and often deep cracks, especially in pipes with high numbers of castings.

Unavoidable thermal stresses also lead to the mold tube being drawn into the bath level area and widening, reinforced by abrasion, at the strand withdrawal end of the mold, which leads to an undesirable “wrong conicity”.

The production of a drawn, conical mold tube with the smallest possible tolerances required requires a large outlay on equipment and is therefore associated with considerable costs, especially in the case of mold tubes with a curved shaped hollow space. In order to increase the lifespan of such expensive mold tubes through reprocessing, special recalibration techniques have been developed. Chill pipes with different cones were excluded from recalibration.

Currently used molds with practically unchanged taper and more or less only insignificant damage, such as. B. superficial cracks in the inner tube wall, after a mold trip for further operation to repair a mechanical post-processing, such as. B. grinding, planing, etc. of the inner surfaces. However, such a procedure is automatically associated with a format enlargement, often amounting to a few millimeters, which is due to the subsequent further processing of the continuous casting material, e.g. B. in the rolling mill, is not tolerable in most cases because of the pass caliber specified there.

These disadvantages have been partially improved with a further method known from DE-B-2 533 528, which has hitherto been rarely used, with the aid of which it is possible, on the one hand, to produce conical, but also differently conical, curved molds by deforming a blank via a To produce the die using explosives and, on the other hand, to reduce the size of used mold tubes, which have expanded due to wear, to the original mold mass in the same way. As a rule, the walls of the mold cavity should in turn be given the properties of a new mold.

In practice, however, it has been shown that the deeper cracks due to the bath level regulation mentioned above can no longer be removed by the recalibration described. An overlap of the crack walls during the explosive deformation is the result, which leads to unreasonable surface defects, even after any chromium plating, which also preclude reuse of the mold tubes due to poor strand surface quality. Because when the mold tubes are used again in their original position, the only partially closed cracks would again be in the area of the greatest thermal stress, would open again and liquid steel could penetrate them, which would lead to breakthroughs on the one hand and holes in the mold wall on the other with a dangerous cooling water leak. However, if the cracks were to be deeply ground before the explosive deformation to avoid such overlaps, this would lead to an inadmissible weakening of the mold wall in the corresponding tube area. Such molds can no longer be used in the casting operation and therefore only have scrap value according to the current state of the art. As bath level regulating devices are in ever increasing use, the number of mold tubes damaged in this way is increasing more and more, which severely diminishes the advantage of precise regulation of the bath level on the one hand by increased mold scrap on the other hand.

This is where the invention comes in, the aim of which is to make it possible to recalibrate a heavily worn, conventionally scrap-ready mold tube and in this way to significantly extend the life of the mold tube at a lower cost compared to new mold tubes.

This is achieved in that the conical mandrel with its smaller end face of the conical mold tubes original strand exit side of the mold tube introduced, and this strand exit side is deformed to the pouring side by means of the explosive force.

With the method according to the invention it is possible to provide a conical mold with a reverse conicity, i. H. the original strand exit side of the used mold becomes the pouring side of the recalibrated mold, whereby the aforementioned remaining defects in the former bath level area reach the area of the new strand exit end. In contrast to the bath level area, these faults have no negative influence on the solidification behavior of the strand, since a strand skin has already formed in this area of the mold, liquid steel no longer has access to the mold wall and can therefore no longer penetrate into the cracks. Surface defects on the solidified strand or strand breakthroughs in the mold can thus be avoided. A mold tube, which previously had to be scrapped, can be used for at least one further mold trip due to the recalibration according to the invention.

For many applications, it can be advantageous if the cross section of the original strand exit side of the mold is widened to make it easier to insert the mandrel. This is conveniently done by explosive deformation, advantageously explosive charges being detonated in the four corner areas of the mold cavity and at the same time essentially in the central areas of the outside of the mold tube.

By widening the tube end with a smaller cross section before recalibration, the caliber mandrel can be inserted easily even in the case of mold tubes that are very strongly drawn in the bath level area. By attaching the explosive charges, a uniform cross-sectional enlargement is achieved on all sides. As a result, mold tubes, which due to the described indentations and the associated intolerable changes in conicity could no longer be used or renewed, are also recalibrated and thus used again.

• Die Figur zeigt ein verschlissenes, quadratisches Kokillenrohr 1 aus einer Kupferlegierung für eine Stahlstranggießanlage zu einem Zeitpunkt nach Einbringung eines Kaliberdornes 2 in den Formhohlraum des Kokillenrohres 1. Sowohl Kokillenrohr 1 als auch Dorn 2 haben eine konische Form, wobei die Konizitäten, wie dargestellt, teilweise gegeneinander verlaufen. Mit 3 und 4 sind die Kantenlängen der gedachten Kokillenstirnfläche eines Bereiches 8 des ursprünglichen Strangaustrittes bzw. des Kaliberdornfußes bezeichnet, mit 6 und 5 diejenigen eines Bereiches 9 der ursprünglichen Eingießseite bzw. der Kaliberdornspitze. Im Badspiegelbereich der ehemaligen Eingießseite 9 sind irreparable Oberflächenfehler der inneren Rohrwand mit Bezugszeichen 13 versehen. Wenn der Dorn 2 mit seiner Spitze nicht vom ursprünglichen Strangaustrittsende 8 des Kokillenrohres 1 her eingeführt werden kann, muß deren Querschnitt aufgeweitet werden. Diese Querschnittserweiterung kann mittels hydraulischer oder anderer Kraftgeräte durchgeführt werden. In vielen Fällen bietet sich die Sprengverformung als vorteilhaftes Verfahren an. Hierbei werden in den Eckbereichen des Formhohlraumes entlang weniger Zentimeter und zur Erhaltung der quadratischen Form auch an den Mitten der Außenseiten des Kokillenrohres 1 gleichzeitig Sprengladungen gezündet.

The invention is explained in more detail below on the basis of a schematically illustrated drawing:

• The figure shows a worn, square mold tube 1 made of a copper alloy for a continuous steel casting system at a time after the insertion of a caliber mandrel 2 into the mold cavity of the mold tube 1. Both the mold tube 1 and the mandrel 2 have a conical shape, the conicity, as shown, partially run against each other. 3 and 4 denote the edge lengths of the imaginary mold end face of an area 8 of the original strand exit or the caliber mandrel foot, 6 and 5 those of an area 9 of the original pouring side or the caliber mandrel tip. In the bath level area of the former pouring side 9, irreparable surface defects of the inner tube wall are provided with reference number 13. If the tip of the mandrel 2 cannot be inserted from the original strand exit end 8 of the mold tube 1, its cross section must be widened. This cross-sectional expansion can be carried out by means of hydraulic or other power devices. In many cases, explosive deformation is an advantageous method. At the same time, explosive charges are detonated in the corner areas of the mold cavity along a few centimeters and, to maintain the square shape, also on the middle of the outer sides of the mold tube 1.

The caliber mandrel 2 is introduced in the direction of the arrow 7, the tube part 10 shown in broken lines being expanded further in accordance with the shape of the caliber mandrel 2. The deformation imposed on the tubular part 10 in this way is partly plastic, partly elastic. Between the mandrel tip 6 and the mold walls of the original pouring side 9, an air gap 11 is created due to the conicity oriented towards each other, which can be up to a few millimeters depending on the shape of the caliber mandrel 2.

According to the method described in DE-B-2 533 528, the ends of the mold tube are then closed by means of base plates (not shown), 12 explosive charges are attached to the outside of the tube, the mold tube 1 and mandrel 2 are placed as a unit in a container filled with water and the charges are ignited electrically. As a result, the mold tube 1 is plastically deformed with its internal dimensions to the external dimensions of the mandrel 2, the nominal size. This reverses the original taper of the mold tube. In this way, healthy, crack-free pipe material gets into the new bath level area, while the existing surface defects 13 are shifted into the area of the new strand exit, in which they cannot have a negative influence on the strand quality.

Of course, the above-described methods can also be used to recalibrate mold tubes with all other cross-sectional and conical shapes, and also mold tubes.

Claims (4)

1. A method of recalibrating a worn tapered and, in particular, curved mould tube (1) for continuous casting, wherein a calibrating mandrel (2) is introduced into the cavity of the mould, explosive material is applied to the exterior of the tube, and the shaping cavity is deformed to the dimensions of the calibrating mandrel (2) by detonating the explosive material, characterized in that, in the case of tapered mould tubes (1), the tapered calibrating mandrel (2) is introduced by its smaller end-face from the original strand-outlet end (8) of the mould tube (1), and this strand-outlet end (8) is deformed by means of the explosive force to create the ingate end.

2. A method according to claim 1, characterized in that the cross-section of the original strand-outlet end (8) of the mould tube (1) is expanded to facilitate introduction of the mandrel (2).

3. A method according to claim 2, characterized in that the cross-section is expanded by explosive deformation.

4. A method according to claim 1, characterized in that explosive charges are detonated in the four corner zones of the shaping cavity and, at the same time, mainly in the median zones of the exterior (12) of the mould tube (1).

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