METHOD AND CONVERSION APPARATUS FOR THE CONVERSION INTO A COLLAR OF AN EDGE PORTION AROUND A HOLE IN A BLANK USING A CONVERTER TOOL AND CONVERTER MANDREL SUITABLE FOR THE CONVERSION APPARATUS

Abstract: A method and conversion apparatus for the conversion into a collar of an edge portion around a hole in a blank is described. The method comprises the stepwise turning-up of adjacent parts of the edge portion untill the full edge portion has been converted into a desired collar. The conversion apparatus comprises means for rotating the blank and a converter-mandrel of which the surface of rotation increases non-linearly from one extremity to the other extremity. Moving the converter-mandrel through the hole perpendicular to the surface of the blank and in contact with the edge portion turns up adjacent parts of the edge portion.

Description: The invention relates to a method of using a converter tool to convert an edge portion around a hole in a blank, which revolves relative to the converter tool, into a collar projecting out of the face of the blank. The invention also relates to converter-mandrel for the conversion into a collar of an edge portion around a hole in a blank. A method of this kind is known from the practice of making a packing lid for packing a coil of rolled steel. This packing has two packing covers, which cover respectively the flat bottom and flat top edges of the coil of rolled steel and a sleeve which covers the cylindrical side wall of the coil of rolled steel. In order to seal the packing against dripping water and to prevent damage occurring to the rolled steel, the packing cover is provided with a turned-up edge at its outer circumference. A method and apparatus for manufacturing a lid with a turned-up edge at the outer circumference is known from Dutch laid-open patent application 8302807. The packing cover can be provided with a cover hole corresponding with the coiler hole in the coil of rolled steel. It should also be possible to provide this cover hole with a collar around its circumference which, like the turned-up edge of the outer circumference of the packing cover has the function of sealing the packing against dripping water and preventing damage to the coil of rolled steel. In the method known in practice, the collar is formed by clamping the cover provided with its hole so that it can rotate, with a cylindrical hollow pressure plate on one side, the cylindrical inner wall of the pressure plate having the shape of the collar required, and then, by means of spinning, gradually pushing the edge portion around the hole against the inner side of the cylindrical wall of the hollow pressure plate. An inconvenience of this method is that for each dimension of cover hole with collar another size of pressure plate is needed. Not only does this represent high investment in pressure plates, but also carrying out this method is costly in that the tool has to be changed for each new dimension. Another disadvantage is that the spinning means are costly. It is necessary to have complicated spinning means in order to prevent the consequences of elastic spring-back in the turned-back edge of the collar. Additional measures for the spinning means are required to prevent angular distortion on the transition of the face of the blank towards the collar, which make the spinning means more costly still and place high demands on its use. The object of the invention is to overcome the disadvantages associated with the method known. Accordingly the invention is characterised in that in a first stage a first discrete part bordering the hole of the edge portion is converted into the first turned-up rim, in that thereafter in a second stage a second discrete part bordering the first turned-up rim of the edge portion is converted into a second turned-up rim, and in that the successive conversion of a part of the edge portion bordering the turned-up rim last formed is continued in stages until the entire edge portion has been converted, wherein in at least one of the stages conversion is on free air, and wherein the conversion in all stages takes place in the same direction relative to the face of the blank. In the method according to the invention, a first turned-up rim is formed from a first part of the edge portion around the hole, which rim reinforces the edge portion around the hole. Then, using the reinforcement obtained, it is possible to convert a second part of the edge portion into a second turned-up rim with a larger diameter than the first turned-up rim. The step-wise conversion of the edge portion is continued until the entire edge portion has been converted and the converted edge portion forms a collar on the blank at the position of the coil hole. This conversion of the edge portion in stages is carried out preferably on free air. The term "on free air" comes from the technique of spinning. Article 2.8 on page 17 of the brochure "Forceren en Vloeidraaien van Staal", No. 301, Sixth Edition, published by "Stichting Staalcentrum Nederland", states: "One of these operations is 'taking in on free air'. This is the local reduction in centreline without the presence there of a pattern form". By analogy in this application "converting on free air" is taken to mean the conversion of material without the presence there of a pressure plate or another kind of pattern form against which the material to be formed is pressed. US-A-2,370,666 discloses an apparatus for forming a flange at the edge of a circular opening within a blank of sheet metal, according to the first parts of claims 1 and 9. The blank of sheet metal is clamped between a top roll and a bottom roll. Further the blank is held down by a "hold-down" roll. The apparatus has a rounded flanging tool which is gradually reduced in diameter at the upper end and free to rotate upon a shaft. Before starting the flanging operation, the rounded flanging tool is retracted under the blank. Then the rounded flanging tool is moved relative to the top and bottom rolls and until the distance between the portion of the tool having the largest diameter and the end face of the top roll is substantially equal to the thickness of the blank. The tool is then moved upwardly until the curved surface of the tool contacts the rotating blank causing the tool to also rotate. Further upward movement of the tool causes the desired flange to be formed between the end face of top roll and the surface of the tool. According to this operation the flange is formed in one single continuous flanging operation. A further feature of the method in accordance with the invention is characterised in that a part of the edge portion is converted at right angles into a turned-up rim. This effect of the method results in a very high stiffness of the edge portion making the forming of a subsequent turned-up rim easier to achieve and a larger part of the edge portion to be formed can be converted at each stage. A particular feature of the method in accordance with the invention is characterised in that, after a number of turned-up rims has been formed, a turned-up rim already formed is converted on free air into a larger diameter turned-up rim. When using this effect of the invention on all the turned-up rims formed, a collar is obtained in which the originally formed edges are eliminated and pass into each other forming a collar of the required shape. Using this feature in combination with the effect described earlier produces a collar of a circular cylindrical shape perpendicular to the plane of the bank. As a result of the elasticity of the material of the blank, the collar springs back elastically. The spring-back is particularly noticeable at that outer end of the collar remote from the plane of the blank. In a particular embodiment of the method in accordance with the invention which is characterised in that at least the end part, remote from the plane of the bank, of the first turned-up rim is pushed into the size required, so as to at least partly compensate for elastic spring back of the end part, the consequence of the elastic spring-back is reduced to a desirable degree. An especially simple embodiment here is characterised in that a part of the blank bordering on the turned-up rim last formed is pushed out of the plane of the blank within the elastic region of that part of the blank and in that the inwardly directed force generated by this on the end part turned away from the blank of the first turned-up rim is opposed at least partly by the converter tool. In practice, it appears that good results are achieved, especially with steel blanks, in an embodiment which is characterised in that the edge region is converted in stages of about 1 cm length. When the method is applied in the manufacture of steel covers, good results have been shown to be achieved when the increase in height of a turned-up rim during conversion lies between 0,5 and 4 mm per rotation of a steel blank and in particular when the increase in height of a turned-up rim during conversion lies between 1 and 2 mm per rotation of a steel blank. The invention is also embodied in converter-mandrel for converting an edge portion around a hole in a blank into a collar, having a foremost and a rearmost extremity and of which the surface of rotation increases in diameter from the foremost extremity towards the rearmost extremity, characterised in that the increase in diameter is only in steps and in that in a meridian plane two connecting lines joining the outwardly projecting salient angular points of the rotation surface closest to the foremost extremity intersect each other at a right angle. With such a converter-mandrel, with all increases being stepwise, a first part of the edge portion bordering on the hole may be converted while initially a second part of the edge portion bordering directly on it remains untouched. By moving the converter-mandrel further in the direction of the blank parallel to the axis of rotation of the clamping device, the second part of the edge portion is converted. Using a converter-mandrel in accordance with this embodiment, and with only a small axial movement of the converter-mandrel, a large part of the edge portion may be converted without any large forces acting on the edge portion. If so desired, the converter-mandrel can be built up from a number of separately manufactured elements, for example by taking one disc per stepwise increase of the desired diameter and stacking all the discs on top of one another. In this, the discs may be fixed relative to one another or they may be rotatable relate to one another. In the embodiment in which individual discs are fixed relative to each other, or in which the converter-mandrel is essentially a single solid body, the rotational speed at different positions from the foremost extremity to the rearmost extremity depends on the position. In order to reduce the speed difference between different positions on the converter-mandrel and the parts of the edge portion already converted, another embodiment of the converter-mandrel in accordance with the invention is characterised in that the magnitude of the stepwise diameter increase decreases from the foremost extremity towards the rearmost extremity. This also achieves the advantage that, the more the converter-mandrel forms more turned-up edges, and the more it comes into contact with more material of the blank, the less quickly will the distorting forces increase with each successive conversion step. In order to prevent heavy local distortion of the blank, a further embodiment of the invention is characterised in that the salient angles of the converter-mandrel projecting outwards are rounded off and in particular in that the projecting salient angles are rounded off a radius of between 5 to 10 times the thickness of the blank. Practical trials have shown that with this embodiment there is a good balance between on the one hand the metallurgical reinforcing of the material of the blank as a consequence of the distortion, and on the other hand the conditions of tension occurring in the material of the blank which induce distortion. Another embodiment of the invention is characterised in that the largest diameter of the converter-mandrel may be larger than or equal to the height of the collar to be formed. During conversion any stretching in the material occurs mainly in the circumferential direction of a turned-up rim; only a little residual distortion occurs in the height direction of a turned-up rim. That means that the radial length of the turned-up rim to be converted is approximately equal to the height of the collar formed. It is desirable that at the start of conversion, the converter-mandrel axis should not cut the blank, because otherwise the edge of the hole displays an unstable behaviour during conversion of the first turned-up rim. Therefore, the maximum diameter of the converter-mandrel should be preferably larger than or equal to the radial length of the edge portion. In regard to the foregoing, this also means that the maximum diameter of the converter-mandrel should be preferably larger than or equal to the height of the collar to be formed. The converter-mandrel in accordance with the invention is characterised preferably in that the increase of the diameter in the foot part of the converter-mandrel bordering on the rearmost extremity is nil and that the height of this foot part is at least as high as the height of the collar to be formed. By moving the converter-mandrel over the entire foot part past the face of the blank in parallel with the axis of rotation of the clamping device, an essentially cylindrical collar is formed in the blank. Furthermore the foot part sets the part of the collar which is already formed and is further from the face of the blank, whereby that part springs back less elastically and a faithfully shaped collar is formed. For certain uses of blanks with extended collars, it is desirable to have a collar with an even more diminished elastic spring-back, which can be achieved with the converter apparatus which is characterised in that the converter-mandrel is provided on the rearmost extremity with an impressing edge for pressing up, out of the plane of the blank, a part of the blank that borders on the last formed turned-up rim. By pressing the converter-mandrel impressing edge against the transition from the flat part of the blank and the edge portion which was formed last, the transition is pressed locally and elastically out of the plane of the blank. Through this the part of the collar formed first, the upper side, undergoes an inwards force which presses a part of the upper side of the collar against the cylindrical foot end of the converter-mandrel. This distorts the upper side plastically and it springs elastically less far back after the converter-mandrel has been drawn back. An especially simple embodiment of the converter apparatus is characterised in that the converter-mandrel is free to rotate. With this embodiment of the converter-mandrel, the converter mandrel is brought into rotation on its axis by the friction of the material of the blank and so a separate drive for the converter-mandrel is not needed. The invention is also embodied in a conversion apparatus for converting an edge portion around a hole in a blank into a collar provided with clamping means for the rotatable holding of the blank and provided with a converter-tool comprising the converter-mandrel according to the invention, which converter-tool can be moved axially parallel to the axis of rotation of the clamping device. In the following, the invention will be illustrated with reference to the drawing, in which in Fig. 1 the invention is illustrated with reference to a first embodiment, in Fig. 2 another embodiment of the method is given schematically, in Fig. 3 an embodiment of the method is given in which the edge of the collar is extended and in which moreover Fig. 4 shows an embodiment of a converter-mandrel in which the invention is embodied and Fig. 5 shows a converter apparatus in which the invention is embodied. In Fig. 1 a disc shaped blank is indicated by 1 and this is provided with a central hole, bordered by an inner edge 2. The blank rotates perpendicularly to the plane of the drawing around the axis 3. A converter device in the form of a mandrel which rotates on its longitudinal axis 4 but is not driven, is indicated by 18. The longitudinal axis 4 of the mandrel does not coincide with the axis 3. At the start, the mandrel is in the position marked 6 partly opposite a part 5 of an edge portion around the hole. The edge portion 5 is to be converted into a collar. By moving the mandrel in the direction of arrow 14, a part 10 of the edge portion bordering on the hole is converted into a first turned-up rim. After this edge has been formed, the mandrel is moved backwards in the direction of arrow 15 and then advanced one step in the direction of arrow 16 into the position marked 7. Next the mandrel is moved upwards once again in the direction of arrow 14 converting the part of the edge portion marked 11. By moving the mandrel far enough in the direction of arrow 14, the first turned-up rim in the extension of the second turned-up rim is converted on free air. In the same manner as described above, parts 12 and 13 of the edge portion 5 are also converted from mandrel 18 positions marked 8 and 9 respectively. By converting the entire edge portion 5 in the manner described, the desired collar 17 is produced. Fig. 2 shows another way of converting an edge portion around a hole to a collar. The corresponding numbers from Fig. 1 indicate the corresponding parts in Fig. 2. Fig. 2A shows the blank 1 and the freely rotating converter-mandrel 19, in their stationary positions relative to one another. In the situation shown, the edge 2 extends from the hole to the longitudinal axis 4 of the converter-mandrel. This is the most extreme position for practical use; in a situation in which the edge 2 extends beyond the longitudinal axis, the longitudinal axis cuts the blank, and so the behaviour of edge 2 is difficult to control during conversion. Moreover, the closer the longitudinal axis 4 comes to the edge 2 the greater are the forces acting for conversion on the edge portion, while initially the edge portion is not yet reinforced. In the situation shown in Fig. 2B the converter-mandrel is moved in the direction of arrow 20 until it just touches the blank which is now rotation on its axis 3. By moving the converter-mandrel further in the direction of arrow 20, the situation shown in Fig. 2C is reached. Here the first of the turned-up rims is formed by the disc-shaped element 21 of the converter-mandrel. The first turned-up rim gives a reinforcement to the portion of the blank surrounding the hole, which now makes it simpler to form a second turned-up rim, and means that more converting force may be exercised than would be possible without the presence of the first turned-up rim. By moving the converter-mandrel 19 further in the direction of arrow 20, the upper surface of disc shaped element 22 pushes upwards that part of the edge portion bordering on the first formed turned-up rim, and by moving still further, element 22 forms the second of the turned-up rims as may be seen in Fig. 2D. In this way the previously formed turned-up rim is pulled along element 21 and is thereby further stretched over at least a part of its height. In the next stage, as shown in Fig. 2E, element 23 of the converter-mandrel forms another turned-up rim. The first of the turned-up rims formed has now left element 21 and is already partially pulled across element 22 and thereby is stretched out still further. Fig. 2F shows the last turned-up rim formed by the converter-mandrel being moved further and the last part of the edge portion being converted into a turned-up rim by element 24. By the movement of the converter-mandrel, the earlier formed turned-up rims are drawn further across the previous elements 22 and 23 and thereby continue to be formed and stretched. Figures 2G, 2H, 2I and 2J show how the turned-up rims formed are drawn successively across elements 22 and 23, and finally brought to a final dimension by element 24. Fig. 2L shows in section a blank with its collar as is obtained after removal from the apparatus described. The figure shows, though not is scale, that, as a result of elastic spring-back the collar does not have a cylindrical shape. When using the blank, or the cover made from it in places where it is desirable for the collar to have a better approximation of a cylindrical shape, the collar may be converted yet further by making use of a further embodiment of the invention, as shown in Fig. 3. Once again 1 indicates the blank, 17 the collar and 3 the rotation axis of the blank. By means of converter-tool 28 which is moved in the direction of arrow 20, a part of the blank adjoining the collar 17 is pushed upwards over part of the circumference in the direction of arrow 20 within the elastic region of the blank. The collar 17 experiences a force on its upper edge 27 directed towards the axis 3 of the collar. A movement of the upper edge 27 towards the axis 3 is blocked by a tool 29. The force with which the upper edge 27 is pressed against the tool 29 stretches the collar further into the plastic region of the material of the collar. This gives the collar a shape which more approximates a cylinder than the shape of the collar before the operation here described. Fig. 4 shows a drawing of a converter-mandrel for carrying out the method described above. Parts of the converter-mandrel with corresponding functions in previous figures have been given the same numbers as marked in those previous figures. Only the exterior contour of the converter-mandrel has been drawn, any design features needed to allow the converter-mandrel to rotate freely or to be driven being known and being apparent to an expert. A converter-mandrel contains elements 21,22,23,25 and 24 for the stepwise conversion of an edge portion around a hole in a blank, the height of the elements 21,22,23 and 25 indicated respectively by 30,31,32 and 33 being the same for all elements in the version as drawn. The elements are rounded off on their salient angles projecting outwards with round-off radii 30 which are also shown here as equal for all elements, including 24. In practice a useful value for the round-off radius, applicable for steel blanks among others, is 5 to 10 times the thickness of the blank. The cylindrical height of the lowest element 24 is indicated by 39 and is at least equivalent to the height of the collar to be formed, in order that the collar may be formed in one single operation. The radius of the uppermost element 21 is indicated by 38,34,35,36 and 37 indicate the amount by which the radius of each subsequent element increases relative to the previous one. This amount decreases in proportion to the increase in diameter, in order that, in later operating phases in which several elements take part in the converting process at the same time, the total distortion force acting on the converter-mandrel is reduced. It has already been observed in the description of Fig. 2A that the longitudinal axis 4 of the converter-mandrel preferably should not intersect the blank. Furthermore the collar height is determined by the distance from the edge 2 of the hole of a blank to the cylindrical part of the last element 24, as is shown in Fig. 2A by 42. The effect of the above two advantages combined is that preferably the radius of the cylindrical part 40 of the converter-mandrel should be greater than or equal to the height of the collar to be formed. The height of the collar which can be obtained without the collar cracking, depends on the distortion ability of the material of the blank. The edge 2 of the hole in the blank is stretched to the diameter of the collar. For a material like steel, the plastic stretching preferably should be limited to less than 30%. This value determines the attainable height of the collar for a given hole diameter. The two connecting lines 44 and 45 join each of the two uppermost angular points of elements 21 and 22 and lie in a meridian plane of the converter-mandrel. The two lines intersect each other transversely. The underside of the converter-mandrel is provided with an edge 28 for pressing up elastically the part of the blank bordering on the collar. In the manner described before, this can extend the collar in order to obtain a better approximation of a circular cylindrical shape. Continued extension can then take place following on directly from the shaping of the collar and in the same operation. For steel blanks, the height 4 of the pressing edge 28 is of the order of 1 to 2 mm. Fig. 5 shows diagrammatically a converter apparatus which embodies the invention. Such an apparatus may be used on its own, or may form part of a larger apparatus such as a spinning machine as described in Dutch laid-open patent application 8302807. In Fig. 5 a frame is shown by 50. A lower ring 51 supported in a bearing is set on the frame and it is provided with a sprocket 52. A driven pinion, not shown in the drawing, can be linked to the sprocket for rotating the lower ring 51. Above the lower ring 51 and coaxially with it, a freely rotating pressure plate 53 is suspended. Using a pneumatic cylinder-piston combination 54, partly shown, the pressure plate can be kept a certain distance from the lower ring. The blank 1 to be converted is placed in the slot between lower ring and pressure plate, and centered using a centering means not shown in the drawing. Suitable means for centering are known from, for example, Dutch laid-open patent pending 80006521. After the blank has been centered, the pressure plate 53 is moved downwards by means of the cylinder-piston combination 54, so that the blank is clamped in the apparatus. Furthermore, the apparatus is provided with a freely rotating converter-mandrel 55. The converter-mandrel is fitted on the nut of a screw-spindle 57. The screw-spindle 57 is drivably coupled to a motor 58 and a gear mechanism 59. The assembly 55,57,58,59 is fitted on the nut 60 of a second screw-spindle 61 which is drivably coupled to the motor 62. By means of motor 62, screw-spindle 61 and nut 60, the converter-mandrel 55 is positioned in the desired radial position relative to edge 2 of the blank. Then the radial position of the converter-mandrel is fixed relative to the frame 50. When the blank 1 is rotating at the desired speed, the converter-mandrel is moved in an axial direction by means of components 58,59,57 in the direction of arrow 20. The axial movement of the converter-mandrel 55 is synchronised with the rotation speed of the blank 1. For steel blanks the converter-mandrel is moved axially approximately 1 to 2 mm per rotation of the blank. After the collar has been formed and extended as required, the converter-mandrel 55 is moved downwards again and after the pressure plate 53 is lifted up, the blank can be taken out of the machine. When the apparatus in accordance with the invention forms part of a spinning machine for making lids, it is possible at the same time to spin an edge on the outer circumference and convert a collar around the hole in the blank. Then the rotation speed of the blank is determined initially by the spinning action. If this is rounded off, then for further collar forming, the rotation speed may be increased. By way of illustration the following are a few details of a converter apparatus for making a steel lid for a packing for a coil of rolled steel: outer circumference of the blank between 800 and 2100 mm; during collar forming the axial extension of the converter-mandrel is 1.5 mm/rotation of the blank, the hole diameter of the blank lies between 400 and 650 mm, the height of the collar formed lies between 45 and 65 mm, the radius of the uppermost element of the converter-mandrel is at minimum the round-off radius which in practice comes out at 7 mm; a practical value is 25 mm, the radius of the cylindrical part of the lowest element is 70 mm, the difference in radius between the uppermost element and the one below it is 15 mm; the reduction of this difference in radius is about 2.5 mm for each subsequent element.

Claims: Method of using a converter tool to convert an edge portion around a hole in a blank, which revolves relative to the converter tool, into a collar projecting out of the face of the blank, characterised in that in a first stage a first discrete part bordering the hole of the edge portion is converted into the first turned-up rim, in that thereafter in a second stage a second discrete part bordering the first turned-up rim of the edge portion is converted into a second turned-up rim, and in that the successive conversion of a discrete part of the edge portion bordering the turned-up rim last formed is continued in stages until the entire edge portion has been converted, wherein in at least one of the stages conversion is on free air, and wherein the conversion in all stages takes place in the same direction relative to the face of the blank. Method in accordance with claim 1, characterised in that a part of the edge portion is converted at right angles into a turned-up rim. Method in accordance with claim 1 or 2, characterised in that after a number of turned-up rims has been formed, a turned-up rim already formed is converted on free air into a larger diameter turned-up rim. Method in accordance with claim 1, 2 or 3, characterised in that at least the end part, remote from the plane of the blank, of the first turned-up rim is pushed into the size required so as to at least partly compensate for elastic spring back of the end part. Method in accordance with claim 4, characterised in that a part of the blank bordering the turned-up rim last formed is pushed out of the plane of the blank within the elastic region of that part of the blank and in that the inwards force generated by this on the end part remote from the blank of the first turned-up rim is opposed at least partly by the converter tool. Method in accordance with one of the foregoing claims, characterised in that the edge portion is converted in stages of about 1 cm length. Method in accordance with one of the foregoing claims, characterised in that the increase in height of a turned-up rim during conversion is between 0.5 and 4 mm per rotation of a steel blank. Method in accordance with claim 7, characterised in that, the increase in height of a turned-up rim during conversion is between 1 and 2 mm per rotation of a steel blank. Converter-mandrel for converting an edge portion around a hole in a blank into a collar, having a foremost and a rearmost extremity and of which the surface of rotation increases in diameter from the foremost extremity towards the rearmost extremity, characterised in that the increase in diameter is only in steps and in that in a meridian plane two connecting lines joining the outwardly projecting salient angular points of the rotation surface closest to the foremost extremity intersect each other at a right angle. Converter-mandrel in accordance with claim 9, characterised in that the magnitude of the stepwise diameter increase, decreases from the foremost extremity towards the rearmost extremity. Converter-mandrel in accordance with claim 9 or 10 or 11 characterised in that the outwardly projecting salient angles of the converter-mandrel are rounded off. Converter-mandrel in accordance with claim 11 characterised in that the projecting salient angles are rounded off at a radius of between 5 and 10 times the thickness of the blank. Converter-mandrel in accordance with one of the claims 9 to 12, characterised in that the largest diameter of the converter-mandrel is larger than or equal to the height of the collar to be formed. Converter-mandrel in accordance with one of claims 9 to 13, characterised in that the increase of the diameter in the foot part of the converter-mandrel bordering on the rearmost extremity is nil and that the height of this foot part is at least as high as the height of the collar to be formed. Converter-mandrel in accordance with one of the claims 9 to 14, characterised in that the converter-mandrel is provided on the rearmost extremity with a pressing edge for pressing up out of the plane of the blank a part of the blank that borders the last formed turned-up rim. Converter-mandrel in accordance with one of the claims 9 to 15, characterised in that the converter-mandrel is free to rotate. Conversion-apparatus for converting an edge portion around a hole in a blank into a collar, provided with clamping means for the rotatable holding of the blank and provided with a converter-tool comprising the converter-mandrel according to any of the claims 9 to 16, which converter-tool can be moved axially parallel to the axis of rotation of the clamping device.

Inventors: THOOLEN, FRIEDRICH WILHELMUS, ZONNEVELD, LOUIS MARIA
Applicants: HOOGOVENS GROEP B.V.
Application year: 1988
Main classification: B21D19
IPC codes: B21D19