US3606785A

US3606785A - Apparatus and method for eliminating or reducing the internal flaws of semifinished products,especially at cast ingots,blocks,blooms,slabs,billets or the like

Info

Publication number: US3606785A
Application number: US751484A
Authority: US
Inventors: Erik A Olsson
Original assignee: ERIK OLSSON AG
Current assignee: ERIK OLSSON AG
Priority date: 1967-08-12
Filing date: 1968-08-09
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21
Also published as: DE1602127A1; FR1603608A; CH490912A; JPS4841132B1; GB1242446A

Abstract

THE INVENTION DISCLOSES AN APPARATUS AND METHOD FOR ELIMINATING OR AT LEAST REDUCING THE INTERNAL FLAWS OF SEMIFINISHED PRODUCTS, ESPECIALLY AT CAST INGOTS, BLOCKS, BLOOMS, SLABS, BILLETS OR THE LIKE. THE INVENTIVE METHOD COMPRISES THE STEPS OF EXERTING A PRESSING FORCE AT ONLY PORTION OF AT LEAST ONE SIDE SURFACE OF THE SEMIFINISHED PRODUCT, AND COMPRESSING THE INNER PORTIONS OF THE SEMIFINISHED PRODUCT BY MEANS OF SAID PRESSING FORCE, SO THAT THE PORTIONS OF THE SEMIFINISHED PRODUCT WHICH HAVE NOT BEEN SUBJECTED TO THE PRESSING FORCE PROVIDE RESISTANCE AGAINST A CHANGE IN SHAPE OF THE SEMIFINISHED PRODUCT, AND THEREFORE, AT LEAST PARTIALLY PREVENT AN ELONGATION OF SUCH SEMIFINISHED PRODUCT. THE INVENTIVE APPARATUS FOR THE PERFORMANCE OF THE AFORESAID METHOD COMPRISES MEANS PROVIDING A PRESSING FORCE-EXERTING EDGE WHICH IS SMALLER THAN THE WIDTH OF THE SURFACE OF THE SEMIFINISHED PRODUCT.

Description

Sept. 21, 1971 OLSSQN 3,606,785

APPARATUS AND METHOD FOR ELIMINATING OR REDUCING THE INTERNAL FLAWS 0F SEMIFINISHED PRODUCTS, ESPECIALLY AT CAST INGOTS, BLOCKS, BLOOMS, SLABS, BILLETS OR THE LIKE Filed Aug. 9, 1968 2 Sheets-Sheet 1 Fig. 7

PRIOR AR T PRO DUCT Fig. 3

PRIOR ART Fig. 2

PRIOR ART m 9 10a 10a 7 7 7 F' .4 Fi .5

lg 9 Fig.6

INVENTOR ERIK H. 0055011) BY WQ ATTORNEY P 1, 1971 E. A. OLS N 06,785

APPARATUS AND METHOD FOR ELIMINAT OR REDUCING THE INTERNAL FLAWS OF SEMIFINISHED PRODUCTS, ESPECIALLY AT CAST ING BLOCKS, BLOOMS, SLABS BIL LETS OR THE LIKE 1 2 Sheets-Sheet 2 Filed Aug. 9, 19

v 100R ART PRODUCT Fig.9 C Fig. Fig. 17a //40 K} Fig. a

INVENT OR 81K 19- 01.55am

BY MMQ ATTORNEY United States Patent US. Cl. 72-199 5 Claims ABSTRACT OF THE DISCLOSURE The invention discloses an apparatus and method for eliminating or at least reducing the internal flaws of semifinished products, especially at cast ingots, blocks, blooms, slabs, billets or the like. The inventive method comprises the steps of exerting a pressing force at only portion of at least one side surface of the semifinished product, and compressing the inner portions of the semifinished product by means of said pressing force, so that the portions of the semifinished product which have not been subjected to the pressing force provide resistance against a change in shape of the semifinished product, and therefore, at least partially prevent an elongation of such semifinished product. The inventive apparatus for the performance of the aforesaid method comprises means providing a pressing force-exerting edge which is smaller than the Width of the surface of the semifinished product.

BACKGROUND OF THE INVENTION The present invention relates to an improved apparatus for, and method of, eliminating or at least reducing the internal flaws or defects of semifinished products, especially at cast ingots, blocks, blooms, slabs, billets or the like.

During the casting of semifinished products, especially ingots, blocks, blooms, slabs, billets or the like, whether such be by conventional ingot casting techniques or by a continuous casting process, different types of internal defects or flaws oftentimes occur, primarily due to the shrinkage occurring during solidification. Typical examples of such are axial porosity, primaryand secondarypipe, which occur during the casting of ingots formed of killed and semikilled steel, owing to an incomplete flow of the metallic melt into the shrinkage cavities or holes occurring during shrinkage. The rate of growth of the solidified layer mainly reduces with increasing thickness or time-the thickness of the solidified layer S is approximately a function of the square root of the solidification time t, that is to say, S =f t-whereby, the vertical heat flow assumes practically no importance, and the solidification faces or fronts tend to approach one another with tapered or conical molds having a downwardly reducing acute angle. On the other hand, with approximately parallel sides of the mold, the solidification faces or fronts can be approximately parallel at the top of the basin, and asymptotically approach the solidification center. In so doing, the still liquid melt in the sump or basin transforms rapidly into a mushy-like condition, and it can be readily understood that bridges can form which prevent ice the further flow of salt into the lower situated hollow spaces formed by virtue of the contraction or shrinkage of the material.

During the casting of ingots it is attempted, on the one hand, to considerably suppress this phenomenon by using a conicity or tapering of the molds which is as large as possible but still economical and compatible for the subsequent rolling operation; and on the other hand, to generally provide the molds with insulating and/or exothermic pouring heads. Even if these measures are carried out quite carefully, a portion of the weight of the ingot amounting to 8% to 18% still contains pipe to such an extent that it must be scrapped. In order to improve output, there is used, if the demands placed upon the final product permit, such steel production or casting techniques wherein there are cast ingots of unkilled or semikilled steel, whereby instead of forming pipe at the central region of the ingot spaces or voids are formed inside thereof which, during subsequent rolling, must be welded together. However, the danger always exists that, for instance owing to an oxidation of the bubbles prior to rolling or because of the collection of slag in such bubbles, several of these bubbles will not be fused or Welded together. This again results in scrapping of the product. Other reasons for an insufficient weld during the sub sequent rolling operation are too low a temperature or incomplete pressing.

Similar problems occur during continuous casting. With this technique there does not exist, as in the case of stationary or stand casting, the possibility of improving the filling operation by providing a conicity or tapering of the strand. The formation of blowholes at the center of the strand is therefore extremely difficult to prevent.

There are, however, still other reasons why internal flaws or defects occur. The gases dissolved in the melt, but which tend to evolve or escape during solidification as the temperature drops, can result in the formation of bubbles. Furthermore, the contraction or shrinkage process leads to internal stresses, which can result in the formation of cracks or fissures.

Even if the above-mentioned hollow spaces, porosity or flaws, are generally welded shut by the subsequent rolling operation, provided that their surfaces are not oxidized, still it must be observed that a considerable reduction of the cross-section is necessary in order to obtain the cast material completely without defect or flaws. ln such instance, there must be performed a working or shaping operation which, depending upon the quality of the steel and the roller temperature, results in a reduction in the cross-section of 1:4 or even 1:10 of the original cross-section. Under certain circumstances, for certain special steels, a still greater reduction may be necessary.

The reason why the cast ingots or blocks must be pressed together so strongly until the porosity at the center is welded shut, can best be explained in that with the conventional rolling techniques, the pressure exerted in radial direction upon the ingots or blocks is not completely effective to the desired extent at the central region. Thus, the applied rolling or deformation work, for the most part, appears in the form of an elongation or stretching, and possibly, also in a spreading or widening of the material. While it is indeed possible, in order to prevent or limit the spreading of the material, to use a closed rolling pass, to thereby obtain an improved kneading at the center, such technique has thus far provided only limited success.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to effectively overcome the aforementioned drawbacks associated with the prior art techniques.

Another, more specific object of the present inveniion relates to an improved apparatus for, and method of, eliminating or at least reducing the internal flaws of semifinished products, especially at cast ingots, blocks, slabs, billets or the like.

Still a further significant object of the present invention is to carry out a pressing of the center of the ingot or strand which contains the flaws in such a way that the work employed for shaping or deforming does not primarily result in a stretching or widening of the material, rather causes a flow of material which is directed more toward the inside.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the inventive method is generally characterized by the features that the inner portions of the semifinished product are compressed by applying a pressure to only a portion of at least one side surface of the semifinished product, so that the portions of the semifinished product which are not subjected to such pressure provide a resistance against any change in shape and, therefore, at least partially prevent an elongation.

The inventive apparatus for carrying out the inventive method aforedescribed utilizes means providing a pressing or pressure edge, the width of which is smaller than the width of the surface of the semifinished product. According to one embodiment of the invention, the pressing or pressure edge is provided by means of a roller having a bead defining such pressure edge, and the width of which head is smaller than the width of the surface of the semifinished product. Furthermore, a number of rollers can be provided which at least partially enclose in form-locking fashion, the semifinished product.

BRIEF DESCRIPTION OF DRAWINGS The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a cross-sectional view of a cast ingot;

FIG. 2 is a schematic representation of the rolling operation for an ingot of the type shown in FIG. 1;

FIG. 3 schematically illustrates the rolling operation of FIG. 2, as viewed from the infeed side of the rolling mill;

FIG. 4 schematically illustrates the inventive method;

FIG. 5 is a sectional view taken perpendicular to the illustration of FIG. 4;

FIG. 6 schematically illustrates a second variant of of the invention;

FIG. 7 schematically depicts a first embodiment of apparatus for carrying out the inventive method;

FIG. 8 schematically depicts a second embodiment of apparatus for carrying out the inventive method;

FIG. 9 illustrates in sectional view an ingot or block serving as the starting material and is helpful in explaining the difference between the previously conventional technique and the inventive method;

FIG. 10 shows the final condition of an ingot processed according to the prior art or conventional technique;

FIG. 10a is a sectional view taken perpendicular to the showing of FIG. 10;

FIG. 11 shows the final condition of an ingot or block processed according to the teachings of the invention; and

FIG. 11a is a sectional view taken substantially perpendicular to FIG. 11.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, in FIG. 1 there is depicted an ingot or block 1 having the blowholes 2 at its center. According to FIGS. 2 and 3, this ingot 1 is guided between the schematically illustrated rollers 3 and 4 of a rolling mill, thus subjected to a lengthening or stretching, indicated by reference numeral 5, as Well as a widening or spreading, as indicated by reference numeral 6 (FIG. 3).

The fiow of material has been schematically represented by two auxiliary lines a and b. Prior to engagement of the rollers 3 and 4, the auxiliary line a extends perpendicular to the cross-section of the ingot 1. Owing to the internal friction of the material, during passage of the ingot 1 through the rollers 3 and 4, the portions of the ingot at the region of these rollers 3 and 4 and in contact with such rollers tends to rust or move ahead with respect to the central portionthis phenomenon has been conveniently designated as a leadingor moving-ahead motion. The applied deforming work primarily results in a stretching or elongation of the material which, in the first instance, occurs at that portion of the cross-section which is in contact with the rollers 3 and 4, and at the region thereof. The internal material layers are entrained by the leading portions, but because of the resistance against deformation, the elongation at the center of the strand is smaller than in the outer layers. Consequently, the original fiat cross-section as defined by the line a is deformed by the rolling operation and assumes the curved form of the line b and, specifically, in such a way that the edges lead the inner portion of the material, as shown.

Now, with the inventive method according to FIGS. 4 and 5, on the other hand, only one portion of a side of a billet 1 of the like is pressed by means of a relatively narrow and rounded edge 10a of a tool 10. In so doing, the non-pressed corner portions 7 and the portions 8 of the remaining sides of this billet 1 provide resistance against stretching or elongation of the material as well as i also partially against a spreading or widening of such material.

According to a further improvement of the inventive method, as shown in FIG. 6, the non-pressed portions of the material of the billet 1 or the like are enclosed in form-locking fashion in a form or mold 9 and pressed by means of a tool 10, so that a more pronounced compaction or compression of the inner portions of the crosssection of the material is achieved.

According to- FIGS. 7 and 8, the inventive method can be carried out by means of a rolling operation. In FIG. 7, 'both of the rollers 13 and 14 are provided with narrow beads .15 for pressing-in two oppositely situated portions of the sides of a billet 1 or the like. The flanges or collars 16 of the rollers 13 and 14 limit the width, that is the material flow in the direction of the roller axes. Also, in this case, the two sides of the billet 1 which have not been pressed in and the corners of such billet prevent any appreciable lengthwise elongation, so that the flow of material is primarily directed inwardly or forced inwardly.

In the arrangement of FIG. 8 there are shown four rollers 20, each having a press edge or bead 21, whereby the partial pressing of each of four sides of an ingot or block 1 or the like is possible. Whether it is desirable to press in one, two or a number of sides, depends primarily upon the configuration of the cross-section of the final product. The rollers 20 can be either driven or the ingot or the like can be pushed through between nondriven rollers or pulled through. If desired, the tools can synchronously move along with or follow a continuously moving cast strand.

According to the invention, the ingot or the like can also be cast to possess partial bulges or protruding portions at one or a number of sides, which during pressing or rolling, while compacting the inner portions, can be pressed in. These bulges should only be so large that the portions which are not deformed by the tools or by the rollers provide sufficient resistance against any elongation or against any rushing ahead of the material as previously explained.

Also, within the framework of the invention, it is possible to superimpose upon the inventive method of a rolling operation. Accordingly, there is achieved just as good a welding of the inner pipes as with successive operations, as long as the partial pressing in of the material does not have any appreciable influence upon the elongation or stretching of the material, in other words, if the relationship between the total cross-section and the pressed-in cross-section portion remains as large as possible.

Furthermore, even if a rolling operation is superimposed upon the inventive method, then this presupposes that the temperature at the inside of the material during pressing is maintained as high as possible in order to achieve a positive fusing or welding together of the bubbles or the fissures, with a relatively small degree of deformation. This means, however, that the material located at the inside and which is almost liquid, possesses rather poor plastic properties and can be only subjected to small tensile loads. Therefore, too large an elongation at the region of the solidification point, and up to approximately 150 C. therebelow, for certain qualities of material even lower than this, results in the formation of cracks or fissures at the inside of the material.

FIGS. 9 to 11 illustrate the mode of operation of the inventive method in contrast to the previous prior art methods. After a conventional rolling operation, the billet 11 according to FIG. 9', after one pass, has become approximately one-third longer and possesses only approximately two-thirds of its original height mass (FIG. The internal defects or flaws, such as the blowholes 2 of the thus processed billet 16 are indeed somewhat pressed together, but on the other hand, elongated in the lengthwise direction. Because of too high temperatures at the inside of the material or because of poor plasticity, transverse fissures or cracks 12 can appear in the billet 16 as shown in the illustration of FIG. 10.

Now, FIG. 11 shows an ingot or block 17 after it has been treated or processed according to the inventive method. In contrast to the billet v16, as such has been illustrated after the rolling operation of the prior art technique in FIGS. 10 and 10a, this FIG. 11 shows a practically unchanged length for the in-got or block 17, because only a portion of its periphery has been pressed in. The previously present internal defects or flaws have not been elongated in the lengthwise direction, rather the material flow which has been forced toward the inside has resulted in a pressing together of the material associated with a welding together of such material, and therefore, in a removal of the internal flaws. Since during the pressing operation, undertaken with the inventive method, practically no elongation or stretching of the material occurs, also no transverse fissures or cracks appear. When the temperature at the inside of such an ingot =17 has dropped to a value which is acceptable for a normal rolling operation, then the rolling operation can, of course, take place with a standard succession of passes or rolling program.

The inventive method can, as already mentioned, be carried out with a number of different types of tools, or apparatuses, for instance, with press dies or tools, or profiled rollers, which stepwise or in one working operation carry out the pressing operation, and for which purpose so-called oscillating presses or hydraulic presses or roller mills of different constructions can be effectively employed.

During stationary casting the method can be considerably automated. The ingots or the like, in order to maintain the temperature suitable for the pressing and-welding together of the material, are removed at the proper time from the molds or forms, and placed beneath the press tool or between the rollers, whereby there can be used a table roller or roller bed. The sequence of operation of the press tool or roller mill can, of course, occur completely automatically with the aid of conventional control devices, terminal switches, photoelectric cells or the like.

If the pressing-in devices of the invention are used in conjunction with a continuous casting installation, then they are preferably mounted after the sprayingor cooling station. They can be of completely simple construction since no particular infeed and withdrawal devices are required. It is sufficient to use profiled rollers, press tools, hammers and so forth which, if desired, can be synchronously moved during the pressing-in operation together with the strand. The deformation of the strand necessary for the further processing can occur subsequently, before or after the cutting of the strand into the desired lengths. In so doing, however, the internal temperature of the strand should have dropped to a value suitable for a normal rolling operation.

In the figures and in the description of the invention, the inventive method has been generally described in conjunction with a cast ingot or block. Naturally, other types of cast pieces, for instance cast billets, slabs, blooms, blanks, and so forth can be deformed or worked by means of the inventive technique or method. The cast piece can be, in this case, an endless strand or a piece which has been 'cut from the strand with the help of suitable gas burners or cutters.

It should be apparent from the foregoing detailed description that the objects set forth at the outset to the specification have been successfully achieved.

Accordingly, what is claimed is:

1. Method for eliminating or at least reducing the internal flaws of semifinished products, especially in cast ingots, blooms, blocks, slabs, billets, or the like, comprising the step of exerting a pressing force at only a portion of at least one side surface of the semifinished product, and compressing by means of said pressing force the inner portions of the semifinished product at such time as such inner portions are at a temperature below the solidification temperature therefor, and said inner portions having substantially solidfied with the trapped gases already having escaped to form cavities and shrinkage having occured, and the walls of any existing cavities having not yet oxidized, so that the cavities are welded shut and the portions of the semifinished product which have not been subjectedto the pressing force provide resistance against a change in shape of the semifinished product, and therefore, at least partially prevent an elongation of such semifinished product.

2. Method as defined in claim 1, including the steps of retaining in substantially form-locking manner the partial surfaces of the semifinished product which have not been subjected to the pressing force.

3. A method as defined in claim 1, including the step of combining the pressing operation with a rolling operation.

4. Method for eliminating or at least reducing the internal flaws of semifinished products, especially for closing the cavities of continuously cast semifinished products, comprising the steps of exerting a pressing force at only a portion of at least one side surface of the semifinished productin a direction towards said cavities at least at such time as the core portion of the continuously cast semifinished product is at a temperature below the solidification temperature therefor, and said core portions having substantially solidified with the trapped gases already having escaped to form cavities and shrinkage having occurred and such core portion is no longer molten, said pressing force being exerted during continuous casting of the semifinished product and at a location thereof where such semifinished product during the casting operation has just solidified.

5. The method as defined in claim 4, wherein said 7 8 pressing force is exerted by subjecting the semifinished FOREIGN PATENTS product to a rolling operatlon 1n its lengthwise direction. Ad. 58,498 7/1953 France References Cited 625,127 3/1927 Australia 29-5263 UNITED STATES PATENTS 5 MILTON S. MEHR, Primary Examiner 3,307,230 3/1967 Goss 164-282X 1 3,483,915 12/ 1969 Schneckenburger et a1. CL

16482X 609,693 8/1898 McDonald 29-5263 10 16 82; 29- 2 1,349,733 8/1920 Read 29526.3