CA1242563A

CA1242563A - Sizing molds for continuous casting

Info

Publication number: CA1242563A
Application number: CA000478112A
Authority: CA
Inventors: Helmut Bestgen; Wolfgang Hoernschemeyer; Manfred Moik; Eckhard Tuschy
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1984-04-03
Filing date: 1985-04-02
Publication date: 1988-10-04
Also published as: DK173037B1; AU573806B2; AU4072085A; DD232211A5; MX167851B; DK150385A; FR2565513B1; NO165058C; BE902066A; IT8520191A0; ZA852492B; ES539558A0; FI851307L; IT1183553B; CH667021A5; JPS60221150A; NL8500973A; NO851354L; FI851307A0; PT80215A

Abstract

ABSTRACT OF THE DISCLOSURE
Molds for continuous casting are made or improved by using a blank or a mold of tubular configuration made of copper or a copper alloy and placing the same onto a mandrel having a cross section deviating from a rectangular, round or square shaped cross section, the tube or the mold is forced onto the mandrel under exertion of force, the mandrel being subsequently removed from the then completed mold. The tubular blank may be prepared to have comparable geometry.

Description

~2':~3 The present invention relates to making a mold for con~
tinuous casting using a tube made of copper or a copper alloy by shaping the tube upon a mandrel having dimensions corresponding to the dimensions of the mold to be macle, whereby the forming process usually involves exertion of force upon the tube being thus press worked onto the mandrel~ The mandrel of course has to be removed subsequently.
German printed patent 1,809,633 proposes the manufacture of a curved mold to be used in a machine for continuous casting wherein the casting strand is run along a circular withdrawl path.
The method as proposed in this patent begins with a straight tube into which a curved mandrel is forced having outer dimensions as well as a shape which corresponds to the shape and dimensions of the mold to be made. Subsequently the tube with the mandrel is forced through a die so as to force the interior surface of the tube into a tight contact, by press working onto the surface of the mandrel. Subsequently the mandrel is forced out of the tube.
German printed patent application, laid open to the public inspection on February 19, 1976 in the name of Concast Inc.,

2,533,528 proposes the utilization of a sizing mandrel wherein the force by means of which the tubular blank is forced upon the mandrel is produced by explosion of a particular charge. The so-called explosion shaping has also been applied for improving the quality of used molds; see for example German patent 2,425,573. In all these instances of explosion shaping the mold walls are shaped by discharge of an explosive forcing the wall of a blank or of a mold upon the shaping and sizing mandrel which has been placed into the interior of that tube. Independently from the manner of applying the shaping force, emp oyment of a sizing and/or shaping ~24%563 mandrel as a basic implement ensures that the interior walls and surfaces of the mold thus made assume a high degree of accuracy;
moreover the interior surface of the mold has a very high quality.
Molds made or improved for example as described above are used for example for continuous casting of steel. They have round, rectangular or square shaped cross section. These are the basic cross sections and further working has to use the thus shaped cast-ing as a blank. For example, certain sections such as T or double T, i.e. I sections, U or L sections may have to be made for example by way of rolling. Clearly, a large number of rolling steps is required in order to shape a simple cross sectional con-tour (rectangle, circle, square) of a casting into a complex con-tour for purposes of making the final product.
German printed patent application 1,282,861 which was published on November 14, 1968 in the name of The British Iron and Steel Research Association discloses molds for continuous casting in which the interior shape deviates from a rectangular or cir-cular configuration. Elowever, the mold here is a so-called parti-tioned mold with variable wall thickness and has, therefore, different cooling conditions for various portions of the casting.
Tubular molds for continuous casting with a cross section that deviates from a rectangular or circular one but also having uniform thickness of the wallS bounding the mold cavity are also known through Zak-Fab "Welded Molds", Mold Bulletin Nr. 410 of November 21, 1968. However, as far as tubular molds are concerned these welded mold configurations have not yet gained any significance because, possibly, the quality does not always meet standard requirements.

~2~25~i3 It is an object of the present invention to provide a new and improved method for making or restoring tubular molds for continuous casting having any kind of interior shape but including also conventional - 2a -~2~

rectangles, whereby, however high demands on the mold itself is made.
In accordance with the preferred embodiment of the present invention it is suggested to apply a method for making or improving molds for contimlous casting by forcing a tube or a mold made of copper or a copper alloy upon a mandrel, having a contour and dimensions corresponding to the mold to be made. The mandrel is of a shape other than a rectangular or square or round cross section and is removed subsequent to the process of shaping. The resulting product therefore is a mold for continuous casting which at least approximates the shape of the parts made by continuous casting and subsequent rolling and other finishing and shaping process. Therefore the mold is made so that casting is carried out by making a casting ingot having a cross section which matches in a favourable manner the subsequent occurring of a rolling process particularly towards minimizing material displacement and reshaping corresponding to the desired quality of the final e.g. steel product.
For example in the case of rail road track like rails to be made the mold for continuous casting will have a double T like cross section. A rail road track like rail can be made rather easily from such a double T casting by way of rolling with little material displacement.
This means that the rolling process does not have to include a large plurality of passes. Aside from these advantages the quality of the product is improved simply by the minimizing of the amount of deformation the casting is to experience by the subsequent rolling.
The invention therefore relates to molds of the so-called profiled section type, i.e. profiles or cross sections that deviate from rectangular, square shaped or circular round cross sections. A particular advantageous filed of employment are envisioned with sections of the double T, T, U, or L shape. It is essential for the invention to use a suitable mandrel which is forced into the tubular blank or a previously used mold to be refinished. This mandrel may for example have a conical contour or a doubl~ conical contour in order to make sure that the conicity that may be required for the mold is established in reality. The mandrel can be straight or curved in order to match the mold more favourable to the withdrawal path configuration for the ingot and casting beillg made.
In cases, undercut portions may be provided in the sizing mandrel.
After a tubular blank generally has been forced upon such a mandrel the particular sizing of the interior space and its boundary is directly established therewith. In order to make sure that the mandrel can subsequently be forced out of the finished mold, it may be of advantage to size the mold or the tube subsequently from the outside. The tube, i.e.
mold made by forcing the blank or the previously used tube onto the mandrel may to some extent be outwardly deformed during removal of the sizing mandrel. Subsequent reshaping of the mold from the outside can therefore be used to restore the internal contour of the mold. Another possibility for overcoming the problem of cross section modifications of undercut sections occurring during removal of the mandrel, can be seen in providing the mandrel in a bi - or multiple part manner, wherein the dividing line or planes of partition run longitudinally, transversely or both with regard to the axis of the product, i.e., of the mold to be made.
Decisive for the invention is the utilization of a sizing mandrel for making a non-round, non-square shaped, and non-rectangular mold for continuous casting under exertion of force from the outside. This force 7J~.a~

can be produced in -various ways. As it is known for example for making rectangular molds, the mandrel where carrying the mold may be forced through an appropriately shaped die. Alternatively explosion shaping can also be used. Still alternatively, the force for sizing may be exerted through drop forging; rolling; or hydrostatic pressure.
A completely new method of making a mold or improving the quality thereof is the so-called electro hydraulical shaping. Herein energy is provided by means of an electric arc acting in the pressure medium, such as water, and the resulting shock wave is transferred through the water upon the part to be made. The requisite electrical energy is provided by a pulse source.
A method for shaping work pieces through particular application of energy is the so-called electro magnetic shaping. This method uses the electrical energy stored in a capacitor and being discharged through a coil.
The coil is arranged around the mandrel and tube configuration. The current flowing through this coil produces a magnetic field which induces an opposing current in the mold wall. The magnetic field exerts a force upon the tube which forces that tube or blank onto the surface of the mandrel. By means of so-called field shapers one can control the spatial distribution of force and, therefore, the pressure distribution as it is effective on the mold wall being made. The last two particular tube methods just mentioned are suitable for making molds of any cross section, including complex cross sections, as we]l as rectangular or round sections.
For practicing the invention, one can begin with any kind of initial shape, because after insertion of the sizing mandrel and upon appropri~te distribution of the exerted forces the blank is forced to adapt to the dimensions of the mandrel whatever its shape. In cases however it may ~2~5fi~

be of advantage to use already near T shaped blanks or near double T blanks or U or L shaped blanks, as far as the respective cross section is concerned, and the appropriately contoured mandrel is then inserted into the interior of such a tube.
By way of example these initial blank sections may be made for example by means of extrusion of the copper or copper alloy in order to obtain a blank at a suitable contour into which the mandrel with the final shape is subsequently inserted. The shaping with the aid of additional mandrel could therefore be limited to about a 15 to 25~ cross sectional modification as compared with the initial cross section made through an extrusion process. This particular and relatively low degree of shaping improves the quality of the mold, for example, by increasing the so-called Brinell hardness.
A profiled blank within the meaning established here may alternatively be made from an initially extruded round or ovally shaped tube which is subjected subsequently to drawing or rolling to obtain the overall outline of the final shape, and the finislling work is then carried out in accordance with the invention through insertion of the appropriately contoured mandrel.
It was mentioned above with reference to the prior art that certain tubular molds are known to have been made of welded sheets. Beginning with this kind of state of the art one may use the welding technique for making T, double T, U, or L shaped molds in form of blanks, and subsequently these blanks are then reshaped in accordance with the method of the invention. Moreover, welded molds made and deemed completed as per the state of the art may be further improved by practicing the invention, namely through the insertion oE a mandrel and exerting force from the outside to thereby obtain a considerable improvement in quality and surface finish.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention, and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:
Figure 1 is a perspective view illustrating a copper blank from which a mold is to be made;

Figure Z is a perspective view of the blank of Figure 1 subsequent to a preliminary operation having been carried out;
Figures 3 through 3d are perspective views showing five different alternative mandrels;
Figure 4 is a perspective view showing a mandrel being inserted into the blank of Figure 2; and Figure 5 is a perspective view of the finished mold.
Proceeding now to the detailed description of the drawings, Figure 1 illustrates a blank in the form of a straight copper pipe or tube with a Brinell hardness of about l-IB50 to 60. This copper pipe 1 was made originally by extrusion, possibly followed by drawing. This more or less endless extruded tube is then cut into length to the desired mold length.
In accordance with the next process and working step, the tube or tubular blank 1 made and as shown in Figure 1 is subsequently drawn by means of an appropriately contoured die and appropriately contoured mandrel, or it may be rolled by means of appropriately contoured roll. The end result here is the particular produc-t 2 shown in Figure 2. This is a kind of distorted rectangle and cons-titutes the blank for subsequent working. In 5~i~

particular this blank shown in Figure 2 has to come extent a con-tour which approximates the final contour that is desired, namely a double T cross section. This blank 2 must now be brought into the final shape.
To obtain the final mold shape one needs a mandrel 3 as shown in Figure 3. This mandrel 3 is hard and chromium plated and it is provided with a double T shape cross section. Tlle cross section therefore will resemble the cross section of the product (e.g. a steel rail) that is later being made by continuous casting. As shown in Figure 4 this mandrel

3 is forced into the blank 2. There is of course a deviation of cross section between the internal outlining of blank 2 and the outer contour of mandrel 3. This may necessitate forcing the mandrel 3 into the blank 2.
Subsequently and through some exertion of force from the outside blank 2 is brought into intimate, surface to surface contact with the entire periphery of the mandrel 3 requiring of course a sufficient amount of force and sufficiently oriented and directed application of force. This forcing of the blank 2 into intimate contact with the mandrel 3 may for example be carried out by means of a pressure die-like element so as to force the blank 2 into intimate contact with the entire periphery of the mandrel 3. The presently considered final shaping process of the copper blank 2 is basically a cold working process and it was found that the si~e and dimensions thus obtained of the final product 4, are extremely accurate.
Following th;s working step the mandrel is removed from the blank 2 which in fact has now the shape and contour of the final product namely the mold 4 as depicted separately in Figure 5. The Brinell hardness is increased by this procedure to about 80 to 120 HB.
Instead of described above the shaping of the blank 2 onto the mandrel 3 may be carried out differently. For example one can use the earlier described method of discharging an e~plosive; alternatively the blank may assume final shape 5 by means of drop forging or rolling iTI
which case mandrel and blank are run through one or several working stages in step like fashion.
Another possibility of forcing the blank tightly onto the mandrel is to be seen in sizing througll electrical discharge or by means of a magnetic field or by means of hydrostatic pressure.
the particular blank 1 could also be made through welding from metal sheets or an earlier made mold such as 4 may have been made by welding together metal sheets. In any event the mold may be subjected subsequently to the steps as described with reference to Figure 4.
The mandrel 3 to be used may be curved as shown in Figure 3a so as to match the mold to be produced to a circularly shaped casting withdrawal path of the machine for continuous casting in whic}l the mold is going to be used. Also the mandrel 3 may fully or partially be provided with a conical or tapered contour from one end to the other. Upon forcing such a tapered mandrel into a straight blank a certain preshaping is obtained therewith. Of course the blank may be provided in curved configuration already prior to mandrel insertion.
The examples demonstrate and illustrate the manufacture of a mold or a quality improvement of the mold particularly with regard to cross sections in the double T contour. Other sections and type of cross sections can be made, for e~ample, T, L or U shaped cross sections. The respective mandrels are shown in Figures 3b, 3c and 3d and have to be appropriately contoured. The preshaped blanks may respectively match, in an overall geometric sense but with larger cross-section, the particular blank so as to 12~25~

limit the degree of plastic deformation which the blank must undergo when shaped on the mandrel into a mold.
lndependently from the section and cross section envisioned here, the invention guarantees high quality tubular molds with uniform wall thickness and therefore a better and more uniform cooling process during operation oE the mold than was heretofore possible with known molds.
Herein is decisive that the mandrels are in fact shaped corresponding to the desired mold and casting cross section. The par-ticular geometrically corresponding blank is then placed on the mandrel and shaped thereon whereby particularly the deforming forces act upon the blank from all sides, including particularly the edge portions. During shaping by means of a pressure ring or a die or by means of rolls one needs tooling whose operating surfaces match the contour to be made.
The figures (except Figure 3a) illustrate the blank, the mandrel and/or the completed mold in a straight configuration. The straight configuration was chosen for purposes of illustration and particularly for purposes of facili-tating description of the invention. Ilowever the invention is not to be limited to straight molds. Particularly one will use generally a curved sizing mandrel such as shown for a double T contour in Figure 3a because most continuous casting machines for steel are provided with a curved i.e. circularly curved withdrawal path so that the mold itself is matched to the curve. A curved mandrel with the cross section of a T, double T, U, or 1. will then analogously either be forced into a precurved blank or the blank remains straight until being forced to undergo curving as a mandrel is forced into it. The same is true of course with regard to operations involving the mandrel shown in Figure 3a.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making or improving the quality of a mold for continuous casting of tubular configuration starting from a tube or rough mold made of copper or a copper alloy, comprising placing the tube or rough mold onto a mandrel having a cross section deviating from a rectangular, round or square shaped cross section; and forcing the tube or the rough mold onto said mandrel under exertion of force, the mandrel being subsequently removed from the then completed mold.

2. A method as in claim 1, wherein said cross section is of the T double T, U or L shaped variety.

3. A method as in claim 1, wherein said force is provided by running said rough mold or tube with the mandrel inserted through a die.

4. A method as in claim 1, wherein said force is provided through an explosive charge.

5. A method as in claim 1, wherein said force is provided through electrical discharge.

6. A method as in claim 1, wherein said force is provided by a magnetic field.

7. A method as in claim 1, wherein said force is provided by drop forging.

8. A method as in claim 1, wherein said force is provided by rolling.

9. A method as in claim 1, wherein said force is provided by hydrostatic pressure.

10. A method as in claim 1, wherein said tube is provided with a preliminary cross section approximating the cross section of the mandrel and of the mold to be made finally.

11. A method as in claim 10, wherein said approximation is chosen such that the cross sectional change by said force application requires a deformation from 15 to 25% in relation to the cross section of the blank.

12. A method as in claim 10, including making a blank by extrusion at said preliminary cross section.

13. A method as in claim 10, including the step of making said blank by extrusion followed by drawing or rolling to obtain said preliminary cross-section.

14. A method as in claim 1, including the step of using a curved mandrel.

15. A method as in claim 1, including the step of using an at least partially conically tapered mandrel.

16. A method as in claim 1, including the step of using a two or multi parted mandrel.

17. A method as in claim 1, including the step of making the tube by means of welding sheet metal.

18. A method as in claim 1, including the additional step of sizing the mold from the outside following withdrawal of the mandrel.