GB2156719A - Continuous casting moulds - Google Patents

Abstract

For the production of tube moulds for continuous casting plants, or for the improvement of the quality of such moulds, use is made of a mandrel (3) which has a non-circular, non-rectangular cross- sectional shape, e.g. a T-shaped, double-T-shaped, U-shaped, or L-shaped cross-section, and the mould tube (2) is shaped on the mandrel by the application of force from outside. The force can be applied by one of a variety of known techniques. <IMAGE>

Description

SPECIFICATION Production of continuous casting moulds This invention relates to the production (or improvement of the quality of) copper or copper-alloy continuous casting moulds for continuous casting equipment.

For the production of curved continuous casting moulds for circular-arc continuous casting equipment, it is known to press a mandrel suited to the inner measurements and the shape of the required mould into a straight piece of tubing, the latter thus being preshaped in accordance with the dimensions of the mandrel (German Patent Specification 1,809,633). In this known process, the piece of tubing and the mandrel are then together pressed through a die, in order to press the inner surface of the piece of tubing tightly on to the mandrel. The mandrel and the piece of tubing are then separated from one another by pressing out the mandrel.

Another known method (German Published Specification (Auslegeschrift) 2,533,528) likewise uses a shaping mandrel, the shaping force being applied from the outside, to at least one wall of the mould, by the detonation of an explosive; indeed, explosive forming has already been applied not only in the production of "tube moulds" but also in the reconditioning of used continuous casting moulds (German Patent Specification 2,425,573). For the last-mentioned purpose, and also for the purpose of initial production, the walls of the mould are shaped on a shaping or sizing mandrel disposed inside the continuous casting mould and determining the internal contour of the mould.Irrespective of the manner in which the force required for forming on a shaping or sizing mandrel is applied to the outer wall of the piece of tube or mould, the shaping or sizing mandrel ensures great accuracy of dimensions of the mould interior, which gives the casting its shape, and also a good surface quality of the bounding wall surfaces.

Continuous castings of steel which are produced with known tube moulds have rectangular, square or round cross-sectional shapes.

Subsequent processors have to start from these basic cross-sections when, for example, special cross-sectional profiles, such as T or double T sections, are to be rolled. Numerous rolling steps are necessary to produce the final product from known casting cross-sections.

Although continuous casting moulds whose mould cavity has a cross-sectional shape differing from the rectangular or circular form are already known (German Published Specification (Auslegeschrift) 1 ,282,86 1), these moulds are "split" moulds having differing wall thicknesses and consequently differing cooling rates during the casting operation.

Tubular continuous casting moulds having a profiled cross-sectional shape, this being a cross-sectional shape different from the known rectangular or circular shape, and having uniform thickness of the walls bounding the mould cavity, are likewise known (Zak-Fab "Welded Molds", Mold Bulletin No.410, 21st November 1968). In the field of tube moulds, however, these products, which are of a welded type, have not hitherto proved successful, apart from the fact that their quality has not always met the relevant requirements.

It is an object of the present invention to provide a method of producing tubular continuous casting moulds which have mould cavities of any non-rectangular non-circular crosssectional shape and which also are of similar quality to (e.g.) known rectangular tube moulds.

According to the present invention, there is provided a method for producing (or improving the quality of) a continuous casting mould for continuous casting equipment, the mould being of a non-rectangular non-circular crosssection, wherein a piece of tubing or mould, of copper or a copper alloy, is shaped on a mandrel having a configuration corresponding with the internal final dimensions and/or shape of the mould of non-rectangular noncircular cross-section which is to be produced (or improved), the piece of tubing or mould being pressed by the action of external force on to the mandrel, and the latter subsequently being removed from the piece of tubing or mould.

The particularly high accuracy of dimensions and good quality of the continuous castings obtainable from moulds produced by the present method make it possible for subsequent processors to start from profiles having initial shapes which are particularly suitable for their purposes and which, for the achievement of the required quality, need only slight reshaping of the material. For a "rail section, for example, it will thus be expedient to start from a continuous steel casting produced in a tube mould whose mould cavity has a double-T-shaped cross-section, for the purpose of then rolling it to the final shape and quality. A large number of rolling passes for the forming of the final profile can thus be saved. However, it is not only in that respect that the invention provides substantial advantages.In the application of the invention it is in fact possible, having regard to the desired final profile and its predetermined desired dimensions and qualities, to select a rolled section most suitable for that desired final profile.

The invention is concerned, as already specified, with cross-sectional shapes which differ from the rectangular shape, which includes the square shape, and from the circular shape. Examples of cross-sections which are of particular interest in connection with the invention are T-shaped, double-T-shaped, U shaped and L-shaped cross-sections.

The use of a mandrel which is introduced (usually pushed or pressed) into a piece of tubing, or into a previously used mould, is essential, as already indicated, to the method of the present invention. In the application of the method of the present invention, this mandrel may be singly or doubly conical in shape, as required to ensure whatever conicity of the mould cavity may be required. The mandrel may also be curved, in order to enable tube moulds produced by the method of the invention to be used for circular-arc continuous casting machines.

The different profiling of the mould cavity may entail undercutting in the shaping of the sizing mandrel. After the shaping of the walls of the tube or mould on the surface of the mandrel in the course of the sizing of the mould cavity and the subsequent pressing-out of the mandrel from the interior of the mould, it may therefore be found expedient for the tube or mould to be finally sized once more from the outside. It is thus possible to compensate for a pressing-out effect which may have occurred during the expulsion of the sizing mandrel, i.e. the tube or mould can thus be restored to the configuration which it had after shaping on the mandrel.

Another possible technique which can be advantageous in connection with the problem of expelling the sizing mandrel without affecting the shape of the mould cavity, in cases where undercuts exist, consists in dividing the mandrel into two or more parts. The mandrel may thus be divided longitudinally and/or transversely with respect to the axial direction of the mould.

Of decisive importance to the invention is the use of a sizing mandrel on which the tube or mould is shaped by the action of external force. The action of the external shaping force can be obtained in various ways. As already known for tube moulds of rectangular crosssection, the mandrel and the piece of tubing or mould may together be passed, for this purpose, through a forming die. However, the alternative known method, in which the action of the external shaping force is obtained by detonation of an explosive, can also advantageously be used for the purposes of the present invention.

In addition to these techniques known for other purposes, it is also advantageous in certain cases to consider obtaining the action of the external shaping force for sizing the tube or mould by a forging operation, by rolling, or again by means of hydrostatic pressure.

A further technique for producing shaping forces, which hitherto has been completely unknown for producing and/or improving moulds, is what may be called the electrohydraulic forming technique. Here the energy is introduced by means of an electric spark gap into an active medium (e.g. water) and transmitted to the work-piece which is to be formed. The electric power required can be produced by surge current equipment.

A still further technique for the forming of workpieces by means of active energy is what may be called electromagnetic forming. In this case electric energy stored in capacitors is discharged across a coil, which may for example be disposed around the mould which is to be formed. This current produces a magnetic field, which in turn induces a countercurrent in the walls of the mould. The magnetic field thus exerts on the walls of the mould a force which presses it on to the surface of the mandrel. With the aid of "field formers" any desired distribution of pressure over the walls of the tube can be set.

The last two techniques mentioned are actually suitable for producing, in conjunction with a sizing mandrel, moulds of any desired crosssectional shape (rectangular or round, as well as the previously mentioned profiled shapes) and of high quality and with great accuracy of dimensions.

In the method of the present invention, it is possible to start from workpieces of any initial cross-sectional shape, which, after insertion of the sizing mandrel, are formed and reshaped, in accordance with the dimensions of the mandrel, by the external application of force.

For the production of profiled cross-sectional shapes, however, it has been found particularly rewarding to use pieces of tubing having generally T-shaped, double-T-shaped, Ushaped, or L-shaped initial cross-sections, when it is desired to obtain respectively corresponding profiles of the mould cavity which determines the shape of the casting. One may, for example, produce initial cross-sections of these kinds by extrusion, the subsequent shaping of the cross-section with an inserted mandrel then amounting to only 1 5 to 25% of the cross-sectional reshaping, referred to the initial cross-section. This relatively slight reshaping will substantially improve quality, for example by increasing the Brinell hardness.

Again, a preform which itself has a "profiled" cross-section can be produced by extruding a round or oval tube, followed by drawing or rolling to afford the preform.

As already mentioned in our acknowledgement of the prior art, tube moulds made from welded sheeting are known. In this connection reference may be made to another advantageous application of the invention. For example, in the production of T-shaped, double-T-shaped, U-shaped, or L-shaped moulds, correspondingly shaped welded-sheeting preforms can be used, which are shaped on a sizing mandrel through the application of an external force. In this procedure according to the present invention, moreover, the weldedsheeting tube moulds can also be sized after production, whereby a substantial improvement of quality and up-grading can be achieved.

The invention will be further explained with reference to the accompanying drawing, in which an example of the production of double-T sections is illustrated in Figures 1 to 5.

Figure 1 shows a bright drawn straight copper tube 1, produced for example from an extruded round tube by tube drawing and having a Brinell hardness of for example HB 50-60. This tube 1 has been cut to the desired mould length, with an allowance for machining.

In a further working stage, this initial mould tube 1 is converted into a preform 2 of the shape shown in Figure 2, for example by drawing with the aid of a profiled die and a corresponding mandrel, or by rolling with correspondingly profiled rolls. This preform 2, having a cross-section compatible with the attainment of the desired cross-sectional shape in the final mould, has next to be brought to the desired dimensions, its quality being concurrently improved. The hard chromium-plated mandrel 3 shown in Figure 3, which has a double-T-shaped cross-section, is used for this purpose. As can be seen in Figure 4, this mandrel 3 is pressed into the preform 2, whereupon the latter is shaped against the mandrel 3 through the external application of a force.This shaping can be effected by passing the preform 2 together with the mandrel 3 through a compression ring (not shown), whereby the preform 2 is applied tightly against the surface of the mandrel 3. This cold working of the copper preform 2 gives the desired accuracy of dimensions of the resulting mould 4, which is shown with a certain degree of exaggeration in Figure 5. The Brinell hardness is at the same time raised from the original value to about HB 80--100.

The shaping of the preform 2 on the mandrel 3 may, however, be effected in a different manner from that just described, for example with the aid of the previously described explosive detonation process, or by a forging or rolling operation in which the mandrel and the preform are together passed through one or more processing stages in succession.

Other possible techniques for pressing the preform 2 tightly against the mandrel 3 are sizing by electrical discharge or by the action of a magnetic field, or again by means of hydrostatic pressure.

The mould 4 shown in Figure 5 may also be one produced for example by welding together sheet metal parts, which thereafter or after use for a long period of time, is subjected, for quality improvement purposes, to a sizing operation with the aid of an inserted mandrel.

Also, the mandrel 3 shown in Figure 3 may be curved, or again may if desired have a conical or partly conical shape, for the purpose of adapting the mould which is to be produced or reconditioned to a circular arc shape of the continuous casting equipment.

When a mandrel of this kind is pressed into the straight preform 2, the appropriate shaping of the mould tube is effected. By means of an additional working stage, the preform 2 can if desired be given a curved shape before a curved mandrel is inserted.

The present example has shown the production of moulds, or the improvement of their quality, in the case of profiled crosssections of a double-T type. Various other profiles can be similarly produced, though it should be noted in this connection that, in the case of e.g. T-, U- or L-shaped profiles and correspondingly shaped mandrels, the preform would have to be of a configuration compatible with the degree of reshaping being kept within the appropriate limits.

Irrespective of the shape of the profile, the method of the present invention can readily ensure the production of tube moulds of high quality, with particularly uniform walls and thus with particularly uniform cooling rates, in comparison with known moulds. A decisive feature is the fact that the mandrels are shaped in accordance with the desired casting cross-sections of the moulds, that is to say that they themselves, in a method according to the invention, have, for example, a Tshaped, double-T-shaped, U-shaped, or Lshaped cross-section. On a mandrel of this kind, the preform can be shaped in accordance with any of the possible methods mentioned. Here the force must act on all sides, that is to say including the edge region, and thus in the case of shaping with the aid of a compression ring, a die, a system of rolls or the like, the tools used must be shaped accordingly.

In the drawings, Figures 1 to 5 show straight types of preform, mandrel and finished mould. This straight type was selected merely to simplify the drawings, and it is to be understood that the invention is not restricted thereto. In practice, use will usually be made of a curved sizing mandrel, since the majority of steel continuous casting plants in operation at the present time are circular-arc plants with moulds having a corresponding circular arc shape. The curved mandrel, having for example a T-shaped, double-T-shaped, U-shaped or L-shaped cross-section, can be pressed, therefore, either into a precurved preform or into a straight preform, for example one corresponding to Figure 2.

Claims (22)

1. A method for producing (or improving the quality of) a continuous casting mould for continuous casting equipment, the mould being of a non-rectangular non-circular cross section, wherein a piece of tubing or mould, of copper or a copper alloy, is shaped on a mandrel having a configuration corresponding with the internal final dimensions and/or shape of the mould of non-rectangular noncircular cross-section which is to be produced (or improved), the piece of tubing or mould being pressed by the action of external force on to the mandrel, and the latter subsequently being removed from the piece of tubing or mould.

2. Method according to claim 1, wherein the said non-rectangular non-circular crosssection is a T-shaped, double-T-shaped, Ushaped, or L-shaped cross-section.

3. Method according to claim 1 or 2, wherein the action of external force is obtained by passing the mandrel together with the piece of tubing or mould through a die.

4. Method according to claim 1 or 2, wherein the action of external force is obtained by detonation of an explosive.

5. Method according to claim 1 or 2, wherein the action of external force is obtained by electrical discharge.

6. Method according to claim 1 or 2, wherein the action of external force is obtained by the influence of a magnetic field.

7. Method according to claim 1 or 2, wherein the action of external force is obtained by a forging process.

8. Method according to claim 1 or 2, wherein the action of external force is obtained by a rolling process.

9. Method according to claim 1 or 2, wherein the action of external force is obtained by means of hydrostatic pressure.

10. Method according to any of the preceding claims, wherein a mould having a Tshaped, double-T-shaped, U-shaped, or Lshaped cross-section is produced, use being made of a piece of tubing having a generally T-shaped, double-T-shaped, U-shaped, or Lshaped initial cross-section, respectively.

11. Method according to claim 10, wherein the said initial cross-section is obtained by extrusion, this extrusion being followed by reshaping, in a subsequent sizing by means of a mandrel, to an extent of 1 5-25%, referred to the initial cross-section.

12. Method according to claim 10, wherein the said initial cross-section is obtained by extrusion of a round or oval tube, followed by drawing or rolling to afford a preform.

1 3. Method according to claim 10, 11 or 12, wherein the said piece of tubing is curved when in a preform phase.

14. Method according to any of the preceding claims, wherein a mould having a Tshaped, double-T-shaped, U-shaped, or Lshaped cross-section is produced (or improved in quality), the piece of tubing or mould used being a welded mould of sheet metal material.

1 5. Method according to any of claims 1 to 14, utilising an undivided sizing mandrel, wherein the mould shaped on the mandrel is sized from the outside after removal of the mandrel from the mould cavity determining the shape of the casting.

1 6. Method according to claim 1, substantially as described with reference to the accompanying drawing.

1 7. Mandrel suitable for use in a method according to any of claims 1 to 16, having a T-shaped, double-T-shaped, U-shaped, or Lshaped cross-section.

18. Mandrel according to claim 17, being a mandrel preformed with a conical or partly conical shape.

19. Mandrel according to claim 17 or 18, being a mandrel which is curved.

20. Mandrel according to claim 17, 1 8 or 19, being a mandrel which is divided into two or more parts.

21. Mandrel according to claim 20, which is divided longitudinally and/or transversely to the axial direction.

22. A continuous casting mould for continuous casting equipment, produced (or improved in quality) by a method according to any of claims 1 to 16.