MXPA94008273A - Molding roller for an installation paramolating continuously on one or between dosrodil - Google Patents

Abstract

A roller for molding, for an installation of continuous molding of metals, on one of those rollers or between two of them, this roller comprises a core or core and a sleeve or sleeve, arranged coaxially with respect to each other, coupling means for coupling the sleeve and the male, including means for axial coupling and means for rotating coupling, as well as means for supporting and centering the sleeve on the core, characterized in that the axial coupling means comprises means for butt, axial connection, of the sleeve against the core, which are located in a substantially central plane, axially, with respect to the roller, and in that the centering means comprise means for elastic conical centering only of the edges of the sleeve with respect to the mac

Description

"ROLLER OF MOLDING FOR AN INSTALLATION TO MOLD CONTINUOUSLY ON ONE OR BETWEEN TWO ROLLERS" Inventors: PIERRE DELASSUS, French, domiciled at 13, rue Cornet Malo, 62400 Locon, France; HUGUES LEGRAND, French, domiciled at 10, rue de la Providence, 92160 Antony, France; GERARD RAISSON, French, domiciled at 2, rue des Ratoires, 58000 Nevers, France; MARC DI FANT, French, domiciled at 6, Boulevard de la Paix, 78300 Poissy, France; JACQUES BARBE, French, domiciled at 9, rue des 3 Meules, 42100 Saint Etienne, France and FRANCOIS MAZODIER, French, domiciled at 1, rue Edmond Charpentier, 42100 Saint Etienne, France.

Causation: USINOR-SACILOR, French corporation, domiciled at 4 Place de la Pyramide - La Défense 9, F-92800 Puteaux, France and THYSSEN STAHL AKTIENGESELLSCHAFT, a German company, domiciled at Kaiser Wilhelm Strasse 100, D-4100 Duisburg 11, Germany .

SUMMARY OF THE INVENTION The present invention relates to a molding roller for a continuous metal molding installation, on one of said rollers or between two of them. This roller comprises a core or sleeve and sleeve, arranged coaxially with respect to each other, coupling means for coupling to the sleeve and the core, including axial coupling means and rotary coupling means, as well as means for supporting and centering the sleeve on the core, characterized in that the axial coupling means comprises means for the axial, butt, connection of the sleeve against the core, which are located in a substantially axially central plane, with respect to the roller, and because the centering means comprise means for conical elastic centering, only, of the edges of the sleeve with respect to the core. The invention particularly applies to molding rolls for continuous molding between two rolls, for molding thin metal strips, especially steel strips.

DESCRIPTION OF THE INVENTION The invention concerns the continuous molding of metals, especially steel, on a roller or between two rollers; more particularly concerns the configuration of a roller of an installation for continuous molding, in accordance with the aforementioned technique. It is known that in order to directly obtain metal products of a reduced thickness by molding a metal, such as a thin strip of a thickness of a few millimeters, more particularly of steel, a special molding technique has been developed, which is generally called continuous roll molding. This technique consists in pouring molten metal into a molding space defined between two cooled rolls, with parallel axes and two side sealing walls, generally arranged against the front surfaces at the ends of the rolls. The metal solidifies upon contact with the walls of the rollers, and, by rotating the latter in opposite directions, a metal strip is extracted in a condition at least partially solidified and the thickness thereof is substantially equal to the distance between the two rollers. This technique makes it possible to obtain a thin metal strip, particularly steel, directly from the molten metal. The reduced thickness of this strip allows it to be subsequently subjected directly to a rolling treatment by means of a cold rolling process. Another molding technique is also known, which is used to obtain even thinner products. According to this technique, the liquid metal, which is emptied onto the surface of a single roller subjected to rotation, solidifies completely while in contact with the roller to form a continuous metal strip. The rolls that are used for the implementation of these molding techniques are generally internally cooled and comprise a core or core and a sleeve or sleeve, arranged coaxially with respect to each other, means for axial and rotary coupling of the sleeve on the core, as well as means for supporting and centering the sleeve on the core. These rollers are described, for example, in document FR-A-2 654 372. This document describes a roller comprising a core bearing a jacket of a material having a good thermal conductivity, for example a copper alloy. The sleeve comprises flow channels for a cooling fluid and is held on the core, in an axially central area, by means of a mechanical joint in the shape of a dovetail or "T". This gasket provides the axial positioning of the sleeve on the male and the transmission of the rotary movement of the male to the sleeve. It is intended that this mounting method prevents the jacket from deviating radially from the core, as a result of thermal expansion. To avoid the effects of this expansion on the edges of the jacket, these liners are also maintained by annular endplates which are designed in such a way as to prevent radial displacement of the edges while allowing or permitting their displacement in the axial direction. However, an arrangement or arrangement of this type ends up releasing the sleeve in the form of a bulky piece so that it is capable of guaranteeing its assembly on the core. This makes this piece expensive, especially since the mechanical work required to assemble or assemble this system and maintain it on the male has to be carried out with high precision. In addition, the assembly system with the joints in the form of "T" or dovetail leads to the need efe that the canias is very thick in its central part and that is thinner towards its edges; these important variations of the cross section cause an irregular deformation of the jacket during its expansion.

Other methods to make the rollers have been suggested. For example, JP-A-04.224054 shows a roller constituted by a jacket and by two half-cores. The inner surface of the sleeve is biconical, and the half-males show a taper which is complementary to that of each of the inner surfaces of the sleeve, which is supported by the half-cores on substantially the entity of its width, The cores are coupled to one another by means of elastic connecting means, which act in the axial direction of the roll to maintain the contact of the sleeve with the core, even if the sleeve expands radially. The objective sought by this method of execution is to avoid losing the contact between the sleeve and the male under the influence of the cyclic thermal deformations of the sleeve. In an arrangement such as this, the operation of the sleeve by the males is carried out by friction at the level of the conical surfaces, and it is not excluded that, under the effect of the radial and axial expansions, which vary along the Circumference, contact interruptions and consequently risks of a bad operation may occur and this problem worsens considerably if the jacket undergoes a torsion or thermal warpage. Furthermore, in this achievement, maintaining the position of the sleeve in the axial direction of the roller is subject to a symmetrical displacement of the half-males. If these displacements are not perfectly symmetrical, this will result in an axial displacement of the sleeve with respect to the initial position. This displacement is detrimental to the required tightness between the edges of the jacket and the side sealing walls of the molding space, and these sealing walls have to ensure the narrowness of the molding space at the ends of the rolls as a result of contact with the mold. the front faces on the edges of the shirt. Indeed, it will be readily understood that in a plant for molding between two rollers, it is not possible to maintain the necessary contact between the sealing wall and the edges of the liners if the axial displacements of the liners of the two rollers are not identical. Generally speaking, it has been seen that mainly under the effect of thermal expansions, the roller sleeves have a tendency to twist or deform, and, if the adjustment of the sleeves to the rollers is not guaranteed in an optimal manner, disturbances occur in the rotation of the sleeves, mainly under the influence of the pressure forces exerted by the metallic product during molding; the turn does not take place any more in a perfectly regular and circular way and causes a phenomenon of "false circular motion". These disturbances can be strongly detrimental to the quality of the molding product, generating geometrical or metallic defects on its surface. On the other hand, if the support and the centering of the sleeve are not made by the same parts, whatever the degree of expansion of the sleeve may be, the mechanical work of the contour or profile of the sleeve, which is executed while it is cold, in a perfectly concentric way with respect to the axis of rotation, you can try to be excentric, when it is hot, due to the change of the supports. The purpose of the present invention is to solve the aforementioned problems, and more particularly to provide an economical method for producing the molding rolls, especially their sleeves, which are pieces exposed to wear and which must be easily exchangeable and obtainable at the lowest possible costs as a result of an economy of materials and mechanical work. One of the purposes of the invention is also to guarantee, either when the rollers are cold or when they are hot, a continuous and constant support of the sleeve in the course of molding, and more particularly to: - ensure a good axial centering and radial of the shirt on the male, - ensure the best possible symmetry with respect to the median plane of the roller, which extends orthogonally with respect to the axis of the latter, - ensure a constant drive of the sleeve by the male and a constant torque transmission despite the possible deformations of the shaft. the sleeve, - limit the forces on the sleeve and on the male, even during deformations due to expansion, - ensure the clamping of the edges of the sleeve when the latter suffers a thermal warping, - ensure the concentricity of the axis of rotation with the contour of the shirt, both when it is cold and when it is hot. Having these purposes in view, the invention concerns a molding roll for a continuous molding installation of metals in one of those rolls or between two of them, each roll comprises a core and a sleeve, arranged coaxially with respect to each other, coupling means for the sleeve and the core, including means for axial coupling and rotary coupling means, as well as means for supporting and centering the sleeve radially on the core. According to the invention, the roller is characterized in that the axial coupling means comprise means for the axial butt butting connection of the sleeve against the core, which are located in a substantially axially central plane, with respect to the roller, and because the conical elastic centering means, only, of the edges of the sleeve with respect to the male. Thanks to the invention, the axial and radial centering of the sleeve with respect to the core are guaranteed by the same parts, whatever the condition of the expansion may be. In effect, the means for the axial butt connection, which are located in the middle plane of the roller, the deformations due to the expansion of the jacket in the axial direction distribute them equally on both sides of this plane, which guarantees a accurate and fixed positioning of the sleeve and consequently an optimum symmetry of the molding surfaces with respect to the median plane. In addition, the conical centering means guarantees the radial centering of the edges of the sleeve and consequently of the entity of the latter, independently of its axial position. One will readily understand that the invention, by means of the disentangling of the means for the axial centering of those for radial centering, allows to provide the best possible positioning of the sleeve with respect to the entity of the molding installation, whatever the condition may be. of expansion or warping of the shirt. On the other hand, as the sleeve is not rigidly secured to the male in its central area, excessive thickness and mechanical work are not necessary for this assembly. In this way the section of the shirt is flatter over its full width and this reduces the risks of irregular deformation of its surface during its expansion. According to a special arrangement of the invention, the means for the conical centering comprise two ridges centered and sliding on the male with the lightest possible clearance and this sliding is provided thanks to measures such as a sliding resin or a Bearing of the type with an oil film. Each flange comprises a truncated part which cooperates with an internal surface of a generally truncated shape which is provided on the corresponding edge of the jacket and the elastic means for attracting the flanges towards each other. Preferably, these means for attracting the flanges, side by side, comprise means for elastic coupling for the two flanges, independently of the male and the sleeve. Thus, the forces exerted by these ridges on the edges of the sleeve are equal and this guarantees a perfect symmetry of the forces exerted on the sleeve. According to a particular arrangement of the invention, which is intended to ensure the rotating coupling of the sleeve on the male, the roller comprises pressure means for exerting an axial load on the means for the butt connection, in such a way that the friction of the sleeve on the male, at the level of the means for joining to the butt, is sufficient to guarantee the less in part the rotary drive of the sleeve by the male. According to another arrangement, which can be replaced by itself, or which can come in addition to the use of the pressure means, the flanges are swiveled into the male, and, thanks to this rotary coupling and this coupling of friction of the edges of the sleeve with the flanges, the latter transmit at least in part the rotating torque of the male to the sleeve. Preferably, at least one of the conical contact surfaces, whether of the jacket or of the flanges, shows, when cold, a recessed surface, at the level of the front ends of the jacket. This recessed surface is carried out in such a way that, at its level, the conical surfaces are separated one from the other, when they are cold, and approach one towards the other, when they are hot, while the shirt It is exposed to the effect of warping or thermal warping. This arrangement allows to maintain fixed, or even increase, the contact area of the conical surfaces at the time of deformation of the jacket by thermal buckling. Indeed, if the conical surfaces of the sleeve and flange have exactly the same taper and a perfectly straight generation line, when they are cold, then there appears, during the thermal buckling of the sleeve, a deformation that is located essentially at the edges of the sleeve and which tends to cause the edges to pivot around themselves, with the effect of reducing the taper of the conical surfaces of the sleeve. As a result of the same, the conical contact between the sleeve and the flange tends to be restricted to a circular linear contact, just at the level of the front ends of the sleeve. This reduced contact is not favorable to a good axial centering and a good rotational drive of the sleeve. The recessed surface foreseen by this invention makes it possible to avoid this reduction of the contact area by displacing this contact area, at the moment when buckling deformation occurs, towards the ends of the edges of the sleeve, without causing, however, a separation of the conical surfaces from their contact area that is closer to the median plane of the roller, or at least allows maintaining that separation to a minimum. This effect will be better understood, and other features and advantages of the invention will become apparent, starting from the specification that will be given later, only as an example, of a molding roll, for a continuous molding installation, to produce products steel, thin, between rollers. Reference is made to the accompanying drawings in which: - Figure 1 is a view showing a se-mi-section along a radial plane of the molding roll, - Figure 2 is a view, at a scale enlarged, of the detail A identified in figure 1, - figure 3, is a view of a partial section along the line III-III of figure 2, - figure 4, is a simplified view of the roller, which shows the relative position of the shirt, the flanges and the male, when they are cold, - figure 5, is a view which is similar to that of figure 4, but when they are hot, at the moment when thermal buckling occurs of the shirt. The molding roll, shown in Figure 1, comprises: - an axis or arrow 1, connected to a drive mechanism - not shown - for the rotary movement, - a male or center 2, rigidly attached to the axis 1 , for example by ring and / or by key, and, after assembly on the shaft, machined coaxially with respect to the last, - a jacket 3, which is made of a material having a good thermal conductivity, such as copper or a copper alloy, which is placed coaxially on the core 2 and which constitutes a removable and interchangeable element of the roller, - means for the axial coupling of the jacket 3 on the core 2, comprising means 4 for the butting, axial, support and centering means, for the jacket 3 on the core 2, which mainly comprise the flanges 5 and 6 placed between the male 2 and the edges of the sleeve, and - coupling means, in view of the rotating coupling of the sleeve on the male. As will be seen later in the present invention, these means are constituted on one side by the flanges 5 and 6 and their means of assembly or assembly, and, on the other hand, by the means 4 of butt connection and by the pressure means about this butt joint. The jacket 3 comprises, in the vicinity of its outer surface 31, the cooling channels 32 which are sealed at their ends to the supply channels 7 and 8 and back to a general circuit - not illustrated - for the circulation of a fluid Cooling. One of these circuits is described, for example, in document FR-A-2 654 372. The core 2 comprises a middle part 21 having a larger diameter than its axial end portions 22 and 23. The intermediate part 21 of the core 2 comprises a shoulder 24 located in a plane P which is substantially above the middle part of the roller and is perpendicular to its axis 11. The sleeve 3 comprises, in its interior, a corresponding projection 33 which is also located in the plane P. The centering of the sleeve 3 on the male 2, according to the direction of the shaft 11, is ensured by the projection 33 of the sleeve which is supported on the shoulder 24 of the male. This precisely defines the position of the sleeve with respect to the male and consequently with respect to the entity of the molding installation. The symmetry of the position of the sleeve with respect to the median plane P of the roller is thus guaranteed and maintained vertically, even when the sleeve expands axially during molding. The displacements of the edges of the jacket, caused by the expansion, occur symmetrically with respect to the median plane. The radial centering of the sleeve on the male is ensured by a conical elastic centering system 9 acting only on the edges of the sleeve. This centering system is constituted by two flanges 5 and 6, which are centered on the end portions 22 and 23 of the male and slide closely without free space on those parts. Each flange includes a truncated portion 51 and 61 which cooperates with the inner surfaces 34 and 35 which also have a truncated shape of the same taper and which are worked on the edges of the sleeve. The flanges 5 and 6 approach each other with the aid of elastic pulling means, which act in the axial direction of the roller in view of tilting the truncated parts 51 and 61 of the flanges against the internal surfaces 34 and 35 of the flanges. the shirt, to guarantee its centering and the support or support of its edges. It should be noted that the conical contact between the sleeve and the flanges is only guaranteed on the edges of the sleeve. The radial centering of the sleeve on the core is consequently ensured mainly by the edges of the sleeve. As will be explained later with more details, the last fact allows preserving is centered even when the middle part of the shirt moves away, when hot, from the male, under the effect of expansion with thermal buckling. The elastic, pulling means of the flanges may consist of pulling means which pulls the flanges towards the middle plane 21 of the core and which act independently of each flange. Preferably, as shown in Figure 1, these pull or pull means comprise elastic coupling means for coupling the flanges between themselves, constituted by a system of circumferentially arranged tension rods 71, which join together the flanges passing freely through holes 25 drilled in the middle part 21 of the male. When reference is made to Figure 2, it is seen that the tension rods 71 pass through the openings 72 in the flanges 5 and 6 and have at their ends the adjustment nuts 73. The elastic elements, such as for example the elastic washers 74, are placed between the nut 73 and the flange 5, in such a way as to exert a tension force acting from one of the flanges towards the other, while allowing its spacing at the same time. The tensile stress is regulated by the nuts 73, to apply to the flanges against the conical internal surfaces of the jacket with sufficient force to prevent a rotary sliding, while allowing a reduced sliding in the axial direction, when, while still hot. , the dimensions of the conical inner surface vary as a result of the expansion of the sleeve. The tensile force, which brings the edges towards one another, can also be provided by a screw jack system and can then be adjusted before or even during molding as a function of the molding conditions (heat flow that is will extract, deformations of the shirt, etc ....). The flanges 5 and 6 are made of a material having good frictional qualities, good corrosion resistance and high mechanical strength characteristics, for example aluminum to bronze or a similar alloy. The taper of the conical part is established in such a way that the reversibility of the displacements of the flange and the sleeve is guaranteed, this means that on the one hand, the flanges must be able to approach each other during the expansion radially of the jacket, and, on the other hand, a radial contraction of the edges of the jacket should cause a removal of the flanges by compression of the elastic washers 74. The taper will consequently be determined as a function of friction characteristics. at the interface between the jacket and the flanges and the stress exerted on the flanges, to minimize the hysteresis between expansion and contraction; this means that during the return of the roller in a given state of thermal conditions, the position of the ridges is as exactly, as possible, the same as that which they previously had in the same state, whatever the displacements that have occurred in the meantime. One therefore understands, easily, that the taper should be sufficient to prevent a blockage of the flanges in the sleeve, while at the same time being small enough to prevent the flanges from separating under the forces generated by the pressure exerted by the flanges. The product during molding. The centering of the flanges 5 and 6 on the axial end portions 22 and 23 of the core 2 is obtained with the help of the sliding resin 26 injected between the flanges and the core, or with the aid of other means, such as bearings. or an oil seal, which allows to reduce to a maximum the free space between the core and the flange, for example of the order of magnitude of 0.05 mm with respect to the diameter, while maintaining good conditions of axial sliding of the flanges on the male, to avoid blocking and the resulting disturbance in the movement of the flanges. To ensure the transmission of the rotary drive torque, between the tap and the flanges, it is possible to use a rotary coupling system, for example wedges. Preferably, however, the flanges are connected to the male by a coupling which establishes the continuity of the torque transmission, symbolized under 27, of the "Flexacier" type for example, while allowing a sliding freedom in the axial direction. In this way, the transmission of the driving torque of the male to the sleeve is ensured by this coupling system between the male and the flanges and by friction between the flanges and the sleeve. The transmission of the torque with the help of the means listed above is preferably completed by a friction drive at the level of the shoulder 24 of the male and of the projection 33 of the inner surface. To achieve this purpose the roller comprises pressure means for pushing the projection 33 of the sleeve against the shoulder 24 of the male. These means include an elastic rim 28 attached to the male 2 and resting on the sleeve through the intermediary of one of the different struts or clamps 81. This struts can be a continuous ring placed between the sleeve 3 and the central part 21 of the male 2. Preferably, as illustrated in FIG. 3, the struts 81 can be segmented and in this form form a plurality of independent, push pieces 82 which are in the form of tiles and which are placed in longitudinal notches provided in the interface between the shirt and the male. In this way a contact between the sleeve and the male can be maintained, at least when it is cold, and this results in an additional centering of the sleeve. These push pieces are pushed against a second projection 36 of the sleeve, provided in the vicinity of the projection 33 and opposite to the latter. These arrangements allow choosing a continuous form of a regular section all over its width for the shirt. This makes it possible to minimize the distortions, when hot, by returning them symmetrical with respect to the median plane P. As previously seen, the support and the radial centering of the jacket are obtained essentially by flanges 5 and 6. To provide constant support of the sleeve on the conical portions 51 and 61 of the flanges, even at the time of deformation of buckling of the sleeve, a recessed surface 37 is provided, on the outer edge of the ineternal, conical surfaces of the sleeve, in a form such that the sleeve remains in a support contact on the flanges in a zone 38 of the latter; This zone is located towards the center of the roller, in the place where the deformations that result from warping and circularity deformations are small (less than 0.1 mm). As well, the recessed surface is such that, when the edges of the sleeve undergo a constriction that leads them to be closer to the axis of the roller, either as a result of the effect of thermal warping or as a result of the pressure exerted by the molded product, the part of the recessed surface of the sleeve progressively extends its bearing on the flange, increasing the length of the conical support surface. With reference to figures 4 and 5, the behavior of the jacket during the operation of the roller will now be described.

Figure 4 shows schematically the shape and position of the shirt, when it is cold. The sleeve is then supported by the flanges 5 and 6 and centered with respect thereto. During molding, the jacket heats up and expands (in the direction of arrow Fl) and generates a buckling or warping (see Figure 5). The central part of the sleeve moves radially away from the male, but the contact of the axial butt joint of the projection 33 of the sleeve and of the shoulder 24 of the male remains vertical. The connection and centering of the sleeve are guaranteed by the flanges. When the temperature increases, the edges of the shirt have a tendency to pivot around them (see arrow F2) and, while behaving in this way, they tilt the recessed parts of the shirt against the conical portions of the flanges. This does not cause a loss of contact in the zone 38 of the conical part and the exact contour of the recess has been determined by a model for calculating the hot deformation of the jacket. At the time of the different deformations of the sleeve, the flanges support the displacements in the directions of the arrows F3, to permanently adapt them to the dimensional variations of the sleeve. This invention is not limited to that established in the previous description, as an example. More particularly, instead of locating the recess of the sleeve at the outer edge of the conical inner surface of the sleeve, the recess can extend itself by a greater length of the conical part, executing it for example in the form of a toric opening of a very long radius. Therefore, instead of being a straight line over its entire length, the generation line of the conical inner surface of the sleeve is a curve of a large radius. During deformations of the jacket, as a result of thermal buckling, the curve is expanded by twisting the conical portion of the flange and, by the tendency to become a straight line, increases the length of the conical contact. The invention can also be applied to the molding rolls, for the continuous molding of thin metal products, on a single roller.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, the contents of the following are claimed as co or property:

Claims (10)

1. CLAIMS (1) a roller for molding, for a continuous metal molding installation, on one of said rollers or between two of them, this roller comprises a male or center and a sleeve or sleeve, arranged coaxially with respect to each other, means of coupling for coupling the sleeve and the male, including means for axial coupling and means for rotating coupling, as well as means for supporting and centering the sleeve on the male, characterized in that the axial coupling means comprises means for attachment to stop, axial, of the jacket against the core, which are located in a substantially central plane, axially, with respect to the roller, and in that the centering means comprise means for elastic conical centering only of the edges of the sleeve with respect to male.")
2. 2. The roller according to claim 1, characterized in that the means for the conical centering comprise two ridges centered and sliding on the core, each flange comprises a truncated part cooperating with an internal surface of a generally truncated shape provided on the edge corresponding to the shirt and elastic means to attract and put together the two flanges, one against the other.
3. 3. The roller according to claim 2, characterized in that the means for attracting and placing the flanges together comprise elastic coupling means for the two flanges, independently of the male and the sleeve.
4. 4. The roller according to claim 1, characterized in that it comprises pressure means for exerting an axial load on the means for abutting.
5. 5. The roller according to claim 1, characterized in that the means for butting connection comprise a shoulder of the male which is inclined against a projection of the sleeve.
6. 6. The roller according to claim 4, characterized in that the pressure means comprise an elastic rim and a strut or platform that is placed between the sleeve and the male and that is applied by the rim against a projection that is in an opposite place to the projection.
7. 7. The roller according to claim 6, characterized in that the strut is segmented into several independent thrust pieces, placed in grooves or longitudinal notches provided in the interface between the sleeve and the male.
8. 8. The roller according to claim 1, characterized in that the ridges are joined or linked to the male at the moment of rotation.
9. 9. The roller according to claim 1, characterized in that at least one of the conical surfaces, which are in contact with the jacket and with the flanges, show, when they are cold, at the level of the front ends of the jacket, a surface recessed, carried out in such a way that the conical surfaces are spaced with respect to one another at the level of the recessed surface.
10. 10. The roller according to claim 3, characterized in that the elastic coupling means of the flanges comprise tension rods and elastic elements. In testimony of which I sign the present in this City of Mexico, D.F., on October 26, 199 -. By: USINDR- NGESELLSCHAFT