FI93321B - Process for production of tubular chills - Google Patents

Description

93321

This invention relates to a process for the manufacture of tubular molds (also called ingot molds) from copper or copper alloys and which is shaped so as to have a substantially curved longitudinal axis and which is intended for installations in continuous steel casting. More specifically, the invention relates to a process according to the preamble of the appended claim.

In installations for continuous steel casting, as is known, a stream of molten metal passes through said molds, the metal starting to solidify as it passes through the molds under the effect of strong cooling, which is achieved by circulating coolant on the outer surface of the molds.

In order for the required tasks to be performed effectively, these types of cocktails must have a number of favorable characteristics. In particular, they must be provided with inner surfaces having a very high surface hardness 20 and finish so that the coating with a layer of coating material (e.g. chromium) is possible to effectively resist the wear effect of molten steel sliding, as well as low friction; on the other hand, the cross-section of the mold 25 decreases slightly in the direction of its axis (conical profile) in order to ensure a complete transfer of heat towards the coolant flowing on the outer surface of the mold: in fact it has been found that in the absence of axial cross-section reduction, due to the shrinkage of the solidifying material, it is possible for the metal to separate from the inner surface of the mold, which considerably reduces the heat transfer coefficient between the metal and the mold.

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For the production of molds of the above type, it is normal to start with a blank which is tubular in shape and has a rectilinear axis and which is obtained simply by drawing or other operation.

5 Next, it is given a curved shape normally by applying radial pressure to its outer surface by means of a punch of suitable shape; next, to create the desired surface finish and obtain the necessary axial cross-sectional variation for proper flow of steel in the die, the inner surface of the curved blank is machined by material removal processes such as grinding or grinding or other alternative process by chemical corrosion.

15 The molds obtained as described have a number of disadvantages, mainly consisting of the poor surface resistance of the inner surface of the mold and the poor finish of their surface; in addition, the mechanical machining and corneal corrosion process required to obtain the conical inner surface of the ingot mold are quite lengthy and complex operations.

To overcome these disadvantages, Italian Patent No. 1,160,132, in the name of the same applicant, describes a process in which an ingot mold or mold. 25 is formed to its desired size using only plastic deformation operations, thanks to the introduction of a curved mandrel inside a previously bent blank, and externally has the desired final shape of the ingot mold, and a subsequent drawing operation affecting the assembly of elements 30 consisting of a blank inside said curved mandrel.

However, even this process is not entirely without drawbacks; in particular, when it is necessary to make rather long ingot molds, in this known process the dimensional accuracy and the required shape are not achievable due to the difficulty of centering the mandrel inside the curved blank and due to the elastic discomfort problems of the blank during the pre-drawing step and is provided with an axial shoulder which also acts as a support for the mandrel during the drawing phase.

It is an object of the invention to provide a process for the production of molds or ingots of the type described which eliminates all the disadvantages associated with known processes.

Said object is achieved by the invention, which relates to a process for producing tubular molds or ingots from copper or a copper alloy and which is shaped so as to have a substantially curved longitudinal axis and which is intended for installations for continuous steel casting, the process comprising: a first step comprising a rectilinear turning the other end of the axial tubular blank by cold plastic deformation to form an axial shoulder at this end; A second step comprising shaping said blank so as to give it a curved shape so that its longitudinal axis takes on a substantially curved shape, said second step being performed by applying pressure in the mold to the outer surface of the blank approximately perpendicular to said axis of the blank; a third step comprising introducing the mandrel into said blank with a predetermined and relatively large radial clearance, the external shape and dimensioning of the mandrel corresponding to the desired internal dimensioning of the mold, and the first end of the mandrel being put together endwise against said shoulder; a fourth step of passing said blank through a tensile plate mold sized to deform the material of said blank, causing the inner surface of the blank to adhere tightly to the outer surface of said mandrel 93321 4, said fourth step being performed by applying an axial force to said mandrel so that said force is transmitted said mandrel in contact with said shoulder; and 5 a fifth step comprising applying, after said blank passes through said traction plate, an axial force applied to said mandrel, the direction of application of the force being opposite to the force applied in the previous step while the other end of said blank opposite said shoulder is brought into contact with said shoulder. corresponding support sectors located below the traction plate, the process according to the invention being characterized in that the first step is performed by forming said shoulder into an oblique annular shoulder coaxial with the longitudinal axis of symmetry of said blank.

In order that the basic steps of the process of the present invention may be better understood, they will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

Figures 1, 4 and 10 show blanks utilized or obtained during the process of the invention;

Figures 2, 3, 5, 6, 7, 8 and 9 show schematically the successive steps of a process according to the invention; and

Figures 11, 12, 13 and 14 show a longitudinal section and cross-sectional parts of a mold or ingot mold obtained by the process according to the invention.

A mold or ingot mold useful in continuous steel casting installations 30 obtained by the process of this invention is shown in Figures 11-14, where it is generally designated 100. The mold 100 is a substantially tubular element having a longitudinal axis of symmetry 101 of Arc-35 va, for example the arc of a circle (Fig. 11) and

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5,9321 having an inner cross-section decreasing parallel to said axis so as to form a cone on the inside in the axial direction 101 starting from the end 102 having a larger cross-sectional area and extending towards the opposite end 103 having an inner cross-sectional area smaller than the end 102; the cross-sectional shape of the mold or ingot mold 100 may be any suitable shape, and is preferably square, as shown in the drawings.

The process according to the invention starts from a billet 1 having a tubular shape, the axis of which is rectilinear and of the type shown in Figure 1; this preform 1 is made of copper or its alloys, for example simply by extrusion or other suitable method, and has a rectilinear longitudinal axis of symmetry, again denoted by reference numeral 101, which becomes, as will be explained below, an axis of ingot or die 100.

The process comprises a first step of turning the second end 2 of the blank 1 by cold plastic deformation 20 so that an oblique annular Ola-ke 3 is formed at this end, which is completely coaxial with the shaft 101, as shown in Fig. 4, which illustrates the blank at the end of the first step.

According to the main features of the process according to the invention, this first cold plastic deformation step

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performed by the functions schematically shown in Figures 2 and 3. Referring to these figures, the formation of the oblique shoulder 3 takes place by a tip forming device 4 comprising a plurality of sectors or "openings" 5 shaped into circular sectors and mounted radially movable, e.g. known and not described for simplicity) guided on an annular support structure (also not described) in which they are placed side by side at constant distances 35 as a circular ring, thus defining a corresponding 93321 6 oblique, radially inner surfaces 6 with a conical cavity 7 with walls obliquely towards the bottom is of variable width; the rectilinear blank 1 is placed coaxially with the conical cavity 7 and when it has been applied to its maximum dimensions the end 2 of the blank is inserted into the device 4 and just into the cavity 7; then the blank 1 the head 2 is applied at the same time radially compressing direction and the axial compression stress in the head between the two sectors 5 and moving them progressively to 10 per axis direction 101 of the arrow (figure 3) simultaneously at all points, so that the cavity 7 of the dimensions of the prog-ressiisvisesti reduced, and at the same time the blank 1 are forced axially towards the sectors 5, in particular towards the inclined drive surfaces in the direction 6 of the arrow, and as those in 15 public axial force which is just sufficient to maintain the element 2 permanently in contact with the surfaces 6 with so as to balance the axial jännityskomponent-thia which they transfer to the blank 5 centripetal säteissiirtymän one sector as a result towards the axis 101; in this way, the head 2 is plastically deformed, tapering in cross-section and thickness and lengthening it. In order for the grip of the sectors 5 from the end 2 of the blank 1 to keep the oblique working surfaces 6 of the device 4 provided with several steps 106, shown in Figures 2 and 3 on a very enlarged scale, the friction between the sector 5 and the blank 1 increases. At the end of this first process step, the produced blank 8 shown in Fig. 4, which in the specific example described here is the initial blank 1, which is square in cross section and has an annular oblique shoulder 3 which is approximately truncated pyramid-shaped.

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The process according to the invention then comprises a second step of shaping the blank 8 so as to have a curved shape, the longitudinal axis of which has a shape 35, for example the shape of an arc of a circle; this step, as clearly seen in Fig. 5 of 93321 7, is performed by applying a substantially radial pressure to the outer surface of the blank 8; these pressures can be effectively applied by means of a mold comprising a concavely curved connecting surface 9 5 and a movable part 10 which moves towards the surface 9 and which is also curved but convexly curved.

In the third step of the process according to the invention, a mandrel 12 is introduced into the blank 11 thus obtained, the external shape and dimensioning of which correspond to the internal dimensions of the desired mold; At this point, the lower end 120 of the mandrel 12 is engaged to engage an oblique annular shoulder, as clearly seen in Figure 6. The internal dimensions of the blank 1 shown in Fig. 1, which initially has a straight axis, are selected so that in this third step the internal dimensions of the partially finished product 15 11 are larger than the maximum dimensions of the mandrel 12 so that a predetermined radial clearance G is left between the mandrel 12 and the partially finished product 11, which is approximately constant at all points; according to the invention, this clearance G must be quite large, for example several millimeters or more, and must be approximately constant for the distance between the inner surface of the partially finished product 11 and the outer surface of the mandrel 12; the constant G of the clearance and the coaxial complete orientation 25 between the mandrel 12 and the partially finished product 11 are achieved by the oblique shape of the annular shoulder-shaped annular shoulder 3 in the form of a truncated cone, in this particular example, produced for the mandrel 12; be self-centering relative to the partially finished blank 30 11; according to the invention, the mandrel 12 also has the same curvature as its longitudinal axis, this curvature * ♦ is also desired to be given to the shaft 101 of the ingot mold to be produced and the mandrel is chamfered towards its end 120.

An assembly consisting in part of a finished mandrel 12 with a clearance and a self-centering effect of the oblique shoulder 3 centered therein and centered on the permanent mandrel 12 is passed through this draw plate mold 15 (Fig. 7), which is otherwise known, and whose dimensioning is such that it partially deforms the material of the finished blank and presses its inner surface tightly against the outer surface of the mandrel. In particular, the inner dimensions of the mold 15 are equal to the outer dimensions of the ingot mold to be produced and are close to the inner dimensions of the partially finished blank 11, thus eliminating the clearance G during this step, resulting in compression and elongation of the blank 11 against the mandrel 12.

Said step is performed by applying a considerable axial force to the mandrel 12 so that the force 15 itself is transferred to the blank 11 as the mandrel 12 engages the annular shoulder 3. As seen in Figure 7, during said fourth step the upper end 16 of the mandrel 12, opposite the lower end 120, is vibrated. the curved longitudinal axis of the mandrel 12 and which substantially coincides with the axis 101 of the blank 11, while the mold 15 also oscillates in the same plane about its axis, the line of which is denoted by reference numeral 17. This is achieved, for example, by known types of articulated joints.

During said step, due to the reduction in the cross-sectional dimensions of the partially finished blank 11 as it passes through the mold 15 as well as due to the fact that the inner surface of the blank assumes the shape of a mandrel, the surface material itself is subjected to considerable cold hardening. It has been shown that when the drawing operation to be performed in this fourth step is performed when the clearances between the mandrel 12 and the partially finished blank 11 are quite large, as previously shown, the inner surface of the blank 35 strongly assumes the shape of the outer surface of the mandrel 12, n 933219 together with the longitudinal axis of the mandrel 12 and at the same time the inner surface of the blank acquires a very high hardness. In fact, only in the presence of these very large clearances, as the material of the blank 11 transitions from its original shape to its final shape, are subjected to considerable radial and axial displacements produced by the radial and axial pressures applied by the mold opening to the outer surface of the workpiece. Figure 8 shows the assembly of the blank and the mandrel at the end of said fourth stage.

It has also been found that in order to achieve these results, it is essential that the clearance G is evenly distributed between the blank 11 and the mandrel 12, i.e. the blank is completely coaxial with the mandrel 12 and this is achieved in the process according to the invention by the oblique shoulder 3 self-centering function.

The process further comprises a fifth step performed after the blank 11 has passed through the mold 15 to apply a major axial force to the mandrel 12 in a direction opposite to the force applied in the previous step; during this step, the end 20 of the blank is made to engage with support sectors 21 located below the mold 15 and movable. . 25 towards the mandrel 12. It is therefore obvious that under the effect of the applied force · · • e · the mandrel 12 can be pulled out of the blank 19 quickly and simply when the blank remains in place under the influence of the sectors 21. Most conveniently, the sectors can be adjusted by actuators that operate fully automatically, for example by means of springs 22 (Fig. 9).

In order to obtain ready-made molds, it is necessary at this point to cut the end part of the blank 19, thus eliminating the shoulder 3, as shown in Fig. 10, and subjecting the blank to other known treatments, in particular coating the inner surface with a layer of coating material (grooming or corresponding).

The mold or ingot mold thus obtained has numerous favorable properties. Above all, the shape of its inner surface is strictly defined; this is due to the complete copying of the mandrel 12 and the blank 11, which is carried out in the fourth step of the process (Fig. 7); this favorable property is due to both the evenly distributed clearance G between the mandrel 12 and the blank 11, which induces the movement of the material of the blank 10, and the complete coaxiality of the mandrel 12 and the blank 11 as well as the real tensile effect that can be exerted by the mandrel 12; all these properties are achieved by the invention due to the oblique annular shoulder 3 and 15 also due to the forced conditions of the mandrel 12 and the mold 15, which were able to vibrate around the shafts 18 and 17 (Fig. 7).

In addition, due to said tensile effect, the inner surface of the mold acquires a surface hardness and comes into a condition suitable for receiving a layer of coating material which produces a high abrasion resistance. Finally, due to the conicity of the mandrel, the variation in the direction of its longitudinal axis according to the desired law of the interior of the mold can be obtained directly in the drawing phase, this part gradually decreasing, as can be seen from the cross-sections of Figures 12, 13 and 14. In particular, the radii of the angles denoted by R1, R2 and R3 between the sides of the parts can also be gradually reduced in order to achieve optimum conditions for the molten steel running in the mold 100.

Finally, it will be apparent that modifications and variations of the described steps of this process may be made without departing from the scope of the invention.

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Claims (6)

A process for producing tubular molds or molds (100) of copper or copper alloys, which molds or molds are so shaped that their longitudinal shaft (101) is significantly curved and which are intended for continuous casting installations; which process comprises: a first step comprising twisting one end 10 (2) of a tubular blank (1) with a rectilinear axis by means of cold plastic deformation, such that an axial shoulder (3) is formed at this end; a second step comprising forming said blank (1) such that it has a curved shape, its longitudinal axis (101) being considerably curved, which second step is performed by exerting a pressure in the mold on the blank (1) outer surface substantially perpendicular to the shaft (101) of the blank; a third step comprising introducing a mandrel into said blank (1) with a predetermined and relatively large radial clearance (G), wherein the outer shape and dimension of the mandrel (12) correspond to the desired internal shape and dimension of the mold (101), and the first end of the mandrel is positioned opposite the abutment (3); a fourth step, wherein said blank (1) is passed through a tensile disk mold (15) having dimensions which cause the material of the blank to deform, causing the inner surface of the blank (1) to adhere tightly to the outer surface of the mandrel (12), steps are performed by subjecting said mandrel (12) to an axial force such that the force is transmitted to the blank (1) where mandrel 30 (12) touches shoulder (3); and: a fifth step comprising exerting a considerable axial force against the mandrel (12) where the blank (1) is passed through the pull plate (15), the direction of directing of the force being opposite to the direction of the force exerted in a previous step, the one of the blank end (1) opposite said shoulder is brought into contact with support sectors (21) arranged under said drawbar (15), characterized in that the first step is performed so that said shoulder (3) is formed into an oblique annular shoulder coaxial with the elongate axis of symmetry (101) of the blank (1). Process according to claim 1, characterized in that the internal dimensions of the blank (1) are selected to be larger than the maximum dimensions of the mandrel and a predetermined radial clearance (G) is left between the mandrel (12) and the blank, which is approximately equal in all points. Process according to claim 1 or 2, characterized in that while said force is exerted during the fourth stage, the second end of the mandrel (12) is poured opposite said first end so that it vibrates in a pane 15 comprising the curved axis of the mandrel (12) ( 101) at the same time as said tension disk (15) also vibrates in the same piano. Process according to any of the preceding claims, characterized in that the first step is carried out by inserting the end of said rectilinear blank (1) into a tip forming device (4) comprising several radially moving sectors (5) arranged adjacent to each other at a constant mutual distance so as to form a circular ring which, with corresponding radially inclined inner work surfaces (6), defines a tapered heel (7) which slopes towards the bottom and has varying widths, the rectangular blank (1) is coaxially arranged in the conical heel (7) and simultaneously exerts a radial and axial compression tension on the said end of the rectangular blank (1) by pressing said first end of the rectangular blank (1) In said sectors (5), and simultaneously and to the same extent, displace them progressively towards the axis (101) of the rectilinear blank (1), so that the dimensions of the heel (7) are progressively reduced, and axially by sliding it directing the blank (1) towards said sectors (5) with an axial force just enough to pour said first end of the blank into continuous contact with the inclined working surfaces (6) of the sectors (5) to 5) offset balancing the axial tension component transmitted to the rectilinear blank (1). Process according to claim 4, characterized in that the oblique working surfaces (6) in said sectors (5) of the tip forming device are provided with a plurality of steps (106) which improve the engagement of said first end (1) of the rectilinear subject. Process according to claim 4, characterized in that said support sectors (21) arranged under said tension disk (15) at the end of the fourth stage are displaced in the direction of the mandrel (12) by means of actuating means (22). in such a way that an abutment for said end 15 (20) is formed in the blank (1), where the force mentioned in the fifth step is exerted on the mandrel (12). <- · n