A tubular object of polyethylene terephthalate

(54) Title: Tubular element and method and apparatus for producing such (56) Publications cited: - (57) Abstract:

From an tubular blank (10) of polyester or polyamide thermoplastic material in the amorphous state, preferably of polyethylene terephthalate, an element is produced. Hereby, one or more portions (11) of substantially monoaxially oriented material are formed in the element, in that a mechanically controlled transition zone (13,14) is moved to material with reduced wall thickness along the blank (10). Mechanical means (71.81) abut in the transition zone against the material and move the transition zone along the blank while simultaneously reducing the thickness of the material wall. This, after the last transformation, is at most equal to the thickness corresponding to the material obtained upon free drawing to flow at a temperature below the glass transition temperature (TG).

During the transformation, the temperature of the material in the transition zone (13,14) is adjusted to a value that immediately before the transformation is close to the glass transition temperature (TG). In one embodiment, material reduction begins on the wall in a groove (12) in the blank wall and continues symmetrically around the groove. Fixing means (41,51,61) ensure the axial position of the blank. The element is suitable to be transformed, for example, into a container in which the orifice part also consists of oriented material. The invention provides opportunities for material savings compared to previously used technology while improving the thermal and mechanical properties of the container.

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8103302-9

The present invention relates to an element formed of a tubular blank of amorphous polyethylene terephthalate (hereinafter often abbreviated to PET) or similar material and a method and apparatus for providing the element. The element has one or more cylindrical material portions of reduced material thickness and consisting of axially oriented material. The element is formed by the blank through one or more transformation processes, the material wall of said cylindrical material portion obtaining a thickness corresponding to a sheet of material having the material thickness of the blank and having the material in the amorphous state obtained at monoaxial distance to flow with the material immediately prior to flow at a temperature corresponding to the material of that substance has immediately before the last conversion process. The starting temperature of the material during the transformation preferably falls below the glass transition temperature (TG) of the material and the transformation takes place by one or more outer draw rings and / or a

8103302-9 internal forming means. The temperature of the material in the forming region is controlled by heat transfer in the contact surfaces of the forming region between the draw rings and / or the inner forming member.

It is previously known from patent application SE 7905043-1 an element where the wall thickness of a preferably central portion of the element is reduced to about 1/3 of the original thickness of the material. The reduction is obtained by fixing a tubular blank with the material at an outlet temperature below the glass transition temperature (TG) at each end between two jaws, which are then moved from each other. By allowing the material to have a higher temperature than the surrounding material in an annular region, a starting instruction is obtained in which the thickness reduction is started during the drawing process. In some applications, the inner diameter of the element is stabilized by means of an inner mandrel. The known method provides an element where the material is axially oriented and has a crystallization less than about 30%, usually of the order of 10-25%.

By the Swedish patent application 7905045-6 it is known to mechanically influence a tubular substance for reducing the material thickness by means of an outer member. The member consists of one or more pulleys which abut against the outer and / or inner surface of the blank with such force that the desired thickness reduction occurs when the starting temperature of the material falls below the glass transition temperature. The outer member moves in the circumferential direction of the blank and at the same time in the axial direction of the blank. Sven with this technique obtains an element where in the areas of reduced material thickness the crystallization is less than about 30% and is of the order of 10 - 25%. However, the material is not as markedly oriented in the axial direction of the blank as when the method of the preceding paragraph is applied.

According to the above inventions, in certain applications, elements which differ from each other in the transition zone between stretched and unstretched material are obtained. This relationship occurs when, for example, a central portion of a tubular blank is stretched with the material of the blank at an outlet temperature below the glass transition temperature (TG) and the

8103302-9 stretched blank is divided into two parts to form two separate elements. The difference is because one element contains the start zone for the flow produced by the stretch, while the other element contains the stop zone for the flow.

In the application of the invention according to SE 7905043-1, an annular transition zone is usually formed between stretched and thinner material and non-stretched and thicker material, where the material surface of the transition zone forms an angle of about 45 ° with the material surfaces of the stretched and non-stretched material. In drawing, axially offset tip-like regions of the substantially annular transition zone are sometimes obtained, which regions usually result in the discarded element being discarded.

The present invention relates to a tubular element and to a method and apparatus for making the element. This is based on a tubular substance of mainly amorphous material. The element has wall portions where the wall thickness of the blank is reduced to a thickness corresponding to that of a sheet of the blank's material and with the blank's material thickness obtained by monoaxial pulling to flow. In PET, for example, this is equivalent to a reduction in thickness to about 1/3 of the original. The material in the wall portions of the element with reduced material thickness is generally oriented only in the axis direction of the element. In PET, crystallization is less than about 30% and preferably has a value in the range of 10-25%, with the crystallization resulting from the material orientation being at most 17%.

According to the invention, higher velocity is achieved in the reduction of the material thickness than in the prior art. In addition, the transition zone between materials of original wall thickness and materials of reduced wall thickness always obtains a predetermined shape, while the length of the portions of reduced wall thickness is always well defined because the material's transformation is mechanically controlled in the transition zone itself. For example, in the manufacture of an element of two preforms facing each other and starting from a tubular blank, double as

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moreover, the production rate by the drawing begins in a central zone and from there at the same time proceeds towards both ends of the pipe. After the cutting of the formed element and the closing of the cut parts, two preforms are obtained, where the transition zone between materials of original thickness and materials of reduced thickness always has a predetermined shape and has material properties that correspond from preform to preform.

Further, according to the present invention, it is possible to provide an element where the material thickness is reduced along the entire length of the element or in one or more cylindrical portions of the element.

The element consists of an open pipe at both ends or in some applications of a pipe closed at one end. The element is preferably intended to be transformed into containers, with each element forming either a single container or a plurality of containers. In the latter case, the element is divided into a number of parts which are then transformed into containers.

In the manufacture of an element according to the invention, a tubular blank is made of polyethylene terephthalate or similar thermoplastic material and with the material in the amorphous state. In one or more successive processes, the material thickness of the blank is reduced, for example, in polyethylene terephthalate to about 1/3 of the original thickness. The reduction occurs either along the entire length of the substance or in one or more portions of the substance. In certain applications, a pull ring is used which has an inner circumference related to the outer circumference of the blank in such a way that the pull ring when moving in the direction of the blank axis causes a reduction in the thickness of the material. The material then has a temperature immediately in the region of or below the glass transition temperature of the material immediately before the reduction of the thickness, hereinafter abbreviated to TG, and preferably a temperature maximum deviating from TG by 15 ° C. Although the technical effect of the invention is obtained at substantially lower temperatures, it is advantageous to use an outlet temperature in the vicinity of the TG, for example, below the TG of 1-3 ° C, since this outlet temperature of the material enables a high velocity in the movement of the draw ring. In some application examples

8103302-9, the tow ring cooperates with an inner forming member located inside the blank, the inner forming member having an outer boundary adapted to the inner boundary surface of the blank. In other applications, only the inner molding means is used. Upon movement of the draw ring and / or the inner forming member in the axis direction of the blank, the material thickness of the blank is reduced during contact with the draw ring and / or the forming member. During the transformation process, a transition zone is formed between materials of original thickness and materials of reduced thickness, which transition zone is gradually moved in the axis direction of the blank. The material in the transition zone is maintained during the transformation process at a temperature adjacent to TG by heat dissipation to the draw ring and / or the member arranged inside the tubular blank. However, in some applications, the material in the transition zone is allowed to assume a temperature in excess of TG with a maximum of 30 ° C and preferably with a maximum of 15 ° C.

In some applications, the material in the region adjacent to the transition zone is cooled to a temperature below TG immediately after its thickness has been reduced.

According to the invention, it is possible to provide an element having material portions of substantially monoaxial orientation and with reduced wall thickness and whose outer circumference is decreased and / or whose inner circumference is increased compared to the circumference of corresponding material portions of the blank.

In the case that reduced wall thickness portions are to be produced in areas located between the ends of the blank, the thickness reduction is initiated by the pressing of one or more peripherally directed grooves in the blank wall while subjecting the blank by external members to tensile forces in its axis direction. In the grooves, when stretching, the wall thickness of PET is reduced to about 1/3 of the original thickness while the blank is extended in the axial direction. The continued reduction of the thickness of the blank wall occurs by inserting the draw ring into said groove or groove and moving in the axis direction of the blank. In some applications, two rings are used, starting from a certain groove, the reduction of wall thickness occurs simultaneously in the direction of both ends of the blank.

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In the event that the blank is closed at one end and reduction of the wall thickness should occur adjacent to the closure, the draw ring is preferably moved from the closure to the other end of the blank. In some applications, the thickness reduction is thus allowed to continue along the entire length of the blank.

In the applications where the blank consists of a pipe open at both ends, in some cases this is closed after the thickness reduction by heating the material at one end of the element, after which the material is compressed in a shape which is, for example, bowl-shaped. Patent DE PS 1,704,119 gives examples of techniques suitable for such closure.

Reduction of the material thickness in several stages is preferably used in the case that the material is so thick that difficulties exist in deriving the required heat effect from the transition zone. By reducing the material thickness a number of times before the last thickness reduction, a thinner material is obtained which facilitates the heat transfer from the transition zone to the abutting draw ring and / or internal forming means.

A device for providing an element according to the invention includes two pull rings. Axially with the two draw rings and inside them is arranged a mandrel around which, when drawing, a tubular blank is placed. Furthermore, a fixing and positioning means (hereinafter referred to as fixing means) is provided at least in connection with one end of the blank. Each drawing ring consists of two drawing halves which are moved by drive means between a working position where the drawing halves abut one another and an open position where the drawing halves are separated from each other. The open position is used when inserting or removing the tubular blank or the element produced from the device.

Drive means are further arranged for the movement of the pull rings and the fixing means in the axis direction of the blank. At least during the movement of the draw rings towards the ends of the tubular blank, the movement of the draw rings is coupled to the movement of the fixing member so that the drawing ring and fixing means placed adjacent to each other are moved in the same direction and so that the ratio

8103302-9 between the speed of the respective ring and the fixing member is determined by the thickness reduction the material in the tubular blank is to undergo. In this way, it is ensured that the fixing means is moved at least corresponding to the elongation of the material that occurs during the movement of the pull rings to reduce the material thickness.

The fixing means is provided with axially movable suspension elements against which the edge of the tubular blank abuts. Any longitudinal tolerances of the blank are thereby taken up by the suspension elements.

Each draw ring consists in one embodiment of the invention of three sub rings with a certain thermal insulation between themselves. Each part ring is provided with channels for liquid, where the liquid either heats or cools the part ring. Also, the aforementioned mandrel is provided with channels for liquid. The middle portion of the ring comprises the portion of the draw ring against which the transition zone between materials of original wall thickness and material of reduced wall thickness is formed during the drawing of the tubular blank. During the draw, of the surrounding sub-rings, the one having the largest inner diameter abuts with materials of original thickness, while the other part of the ring having the smallest inner diameter abuts with thickness-reduced material.

A central fixing means is further provided for holding the blank in an area of ​​the aforementioned starting groove. In its working position, the central fixing means then presses against the material wall of the groove in an area located between the two draw rings. The central fixing means preferably consists of two halves which, in the working position of the member, enclose the blank wall and form, in the circumferential direction of the blank, areaally distributed abutment surfaces. This is achieved, for example, in that the faces of the central fixing member facing the blank wall form cylinder surfaces with an elliptical or polygonal cross-section.

When converting a tubular blank into an element, the blank is placed around the mandrel, its axial position being set by the fixing means for one end of the blank. The central fixing member, along with the draw ring 8103302-9, is then moved to the working position. In the tubular blank there is arranged, in accordance with the above description, a central circumferential groove in which the bottom wall thickness is reduced to the value the thinner material portions of the future element will hold. The shape of and the total axial length of the parts of the central fixing member and of the pull rings inserted into the groove are consistent with the shape and the axial length of the groove. Preferably, the material of the blank in the future tensile region is already heated to a temperature in the vicinity of but less than TG prior to placement on the mandrel. Through the contact surfaces formed between the material of the blank and the draw rings as well as the mandrel and, where appropriate, the central fixing means, the material obtains the correct drawing temperature.

During the drawing process itself, the drawing rings and the fixing means are moved in connection with the end of the tube by drive means in the direction from the groove. Wherein the previously stated velocity relationship between draw rings and the fixing means is maintained. The material thickness of the blank is thereby reduced by the pull rings as long as the movement is in progress. At the same time, the substance is extended in its axis direction.

Essential to the device is the temperature control of the material in the transition zone between amorphous material of original wall thickness and thickness-reduced material. The coating has an internal profile adapted to the change in material thickness that occurs in the transition zone. The profile is so selected that in the transition zone, as well as preferably also before and after it, during the drawing process, contact surfaces are formed against the inner surface of the drawing ring 25. Thereby, the draw ring controls the shape of the transition surface in the transition zone. By means of heat conduction between the material in the blank and the draw rings or mandrel, the temperature of the material in the blank is controlled throughout the drawing process. Particularly important is that the sub-ring of the drawing ring which contacts the material in the transition zone holds the material of the blank at a temperature adjacent to TG.

In a simplified embodiment of the invention, a single pull ring is used. from a starting groove, it is preferably moved all the way out to the edge of one of the ends of the blank. Hereby, an element having reduced wall thickness is obtained only at one end thereof. In this embodiment, only one drag 8103302-9 ring is used. The movement of the pull ring is interrupted in some applications before passing over the edge of the tubular blank. After the drawing, the edge is thereby surrounded by a wreath in which the thickness of the wall is not reduced. The element thus produced is suitable to be used as preform, possibly after some reshaping of the wreath, ie the edge of the future orifice, for a container intended to be closed, for example with a so-called crown cork. Prior to the transformation of the element into containers, the future orifice is stabilized by heating and thermal crystallization. Usually, crystallization is allowed to continue for as long as the material of the above mentioned wreath becomes opaque.

The central fixing means holds portions of the material wall in the bottom of the groove pressed against the mandrel at least during the initial stage of the drawing ring and the moving rings respectively. This fixes the position of the blank relative to the mandrel. In the embodiment of the invention where two pull rings are moved from each other, as mentioned, the central fixing means is arranged for engagement against the blank wall in an area located between the pull rings. By holding the blank against the mandrel, the axial movement of the blank with respect to the mandrel is prevented, which could occur due to the axially directed forces which arise in the contact surfaces between the respective ring and the material in the transition zone between the reduced wall and the thick wall of the blank. For example, a displacement could result in the disadvantage that the area with reduced wall thickness is placed asymmetrically in relation to the starting groove.

By using a fixing member according to the preceding paragraph, it is possible to provide any axial length of the area in which material the wall thickness is reduced. In some applications, material is thereby allowed to achieve such reduction over the entire length of the blank, while in other applications the thickness reduction is stopped before the draw ring and the draw rings reach and pass beyond the end and ends of the blank, respectively. By leaving an area consisting of amorphous material at the outer end of the blank, respectively, a material portion is obtained, for example, well suited to be closed to form the bottom of a preform, for example, by applying the technique described in the patent DE PS 1 704 119 or, after thermal crystallization, to form an orifice edge for cooperation with a so-called crown cork.

In an alternative embodiment, the material ring is reduced by means of the pull ring of a tubular blank closed at the bottom, which is already provided with a closing member in its orifice, for example provided with threads. The material whose material is intended to undergo the reduction in thickness is thereby made according to some prior art, for example by injection molding or extrusion with subsequent closure and molding of the bottom and orifice portion. In some applications, the starting groove is thus trained in the manner described above, while in other applications a starting instruction or starting groove is partly or wholly obtained in connection with the injection molding of the preform.

When the material thickness of the blank wall is reduced by means of an outer draw ring, a certain reduction of the inner diameter of the blank is already indicated. The mandrel within the blank thereby constitutes a forming member which determines the size of this diameter reduction. Surprisingly, it has been found that in the above-mentioned temperature ranges of the material during the transformation process, the abutment of the wall caused by the contraction causes relatively small abutment pressures between the inner surface of the blank wall and the outer surface of the mandrel, so that no problems arise after completion of molding ( the substance separates the formed element from the mandrel.

In some applications, the material is cooled immediately after assuming its reduced wall thickness to a temperature below the glass transition temperature (TG) of the material to keep the material's thermal crystallization as low as possible.

In some applications of the device, no internal mandrel is required, but the element is allowed to adopt an inner circumference smaller than the original circumference. By choosing in other application examples an inner mandrel whose outer perimeter is smaller than the inner perimeter of the blank, it is possible to control the reduction of the inner perimeter of the blank to a value adapted for the particular application example.

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In addition to the crystal isation the material obtains through the axial orientation, the material in some applications receives a complementary thermal crystal isation.

The crystallization values ​​given in this patent application relate to the theory set forth in the publication Die Makromolekulare Chemie 176, 2459-2465 (1975).

The numerical values ​​of crystallizations, thickness reductions and temperatures set forth above refer to PET, but for each of the thermoplastic materials whose properties allow the invention to be applied, are obtained in the application of the invention, at temperatures adapted to respective materials, crystallization values ​​as well as thickness reductions which have a corresponding in the values ​​specified for PET.

In this application, the invention is stated as suitable for application to the material polyethylene terephthalate (PET) or similar material. It is known in the art for a large number of materials of type polyester or polyamide having similar properties, so the invention as such is wholly or partly applicable even to these materials with adaptation of the thickness reductions and temperatures to the specific conditions set by each material. Examples of materials to which the invention is applicable after the aforementioned adaptation are polyhexamethylene adipannate, polycaprolactam, polyhexamethylene sebacamide, polyethylene 2,6- and 1,5-naphthalate, polytetramethylene-1,2-dioxybenzoate and copolymers of ethylene terephthalate, copolymers of ethylene terephthalate, similar polymeric plastics.

The invention is described in more detail in connection with a number of figures, in which Fig. 1 shows a perspective view of a pulling device, Fig. 2 shows a longitudinal section through the pulling device according to Fig. 1 with the pulling device's pull rings in the starting positions before the drawing;

8103302-9 central fixing means and with the draw rings and fixing means in the initial positions before drawing, Fig. 4 Fig. 5 Fig. 6 Figs 7-9 show part of a longitudinal section corresponding to Fig. 3 with the draw rings moved apart.

shows the central region of Fig. 3 in detail, shows the central region of Fig. 4 in detail, shows alternative embodiments of the element.

In Fig. 1, which shows an overview perspective view of a pulling device according to the invention, there is found a bottom part 30 from which a number of vertically arranged guide pillars 31 are shown in the figure. tningen associated to this orientation of the device, but the scope is in no way dependent on such a special orientation. In the future, the designations upper and lower or similar designations are sometimes used in connection with different organs, these designations being used only for clarifying purposes.

In connection with the bottom part are provided drive devices with gears (not shown in the figure) for a number of drive screws arranged parallel to the guide pillars 32. Perpendicular to the guide pillars and the drive screws are arranged four support plates 50, 60, 70, 80. In each support plate, bearings corresponding to the guide pillars 31 are found. and threaded holes 52, 62, 72, 82 for cooperating with a number of drive screws 32. Furthermore, the plates are provided with passages 58, 68, 78, 88 for the drive screws which are not in threaded engagement with the current support plate. The. the top and bottom support plates 50 and 60, respectively, are arranged for cooperation with the two drive screws 32 a and c, while the two intermediate support plates 70 and 80 are arranged for cooperation with the two remaining drive screws 32 b and d. Furthermore, the upper parts of the drive screws which cooperate with the support plates 50 and 70 are threaded in opposite directions to the lower parts of the drive screws which cooperate with the support plates 60 and 80. This means that, during the rotation of the drive screws, the two upper support plates are moved in the same direction but in the opposite direction in which the two the lower support plates are moved.

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Since the top and bottom support plate is driven by screws 32 a and c and the two middle support plates by screws 32 b and d, the speed of movement of the respective support plate is determined by the speed of rotation and the pitch of the screws with which the respective support plate cooperates. The pitch of the drive screw threads is selected so that the top and bottom support plates are always moved at a lower speed than the two middle ones. In the initial position, the two middle plates are close to each other and the top and bottom plates are in positions which allow movement to the end areas of the guide pillars. Upon completion of the transfer, the middle support plates have approached the upper and lower support plates, respectively.

The lower support plate 60 and in some applications the upper support plate 50 are provided with fixing means 61 and 51 respectively for retaining each end of a tubular blank 10. The blank is provided with a preferably centrally circumferential starting groove 12 (Fig. 2) in which the thickness of the material is for PET, about 1/3 of the original thickness. The starting groove is preferably formed prior to the placement of the blank in the device by applying an external pressure to the material wall, for example by means of a number of cooperating pulleys, at the same time as the tubular blank is subjected to tensile forces in its axis direction.

In forming the starting groove, by means of the pulleys, and by stretching, a predetermined axial length of the groove is obtained, thereby obtaining a profile broadly in accordance with the profile of the parts of the tension rings which, when converting the blank to the element, are introduced into the groove (cf. description to Fig. 2 below ). As the starting groove is formed, the tubular blank extends in the axis direction. The two middle support plates 70 and 80 are provided with a draw ring 71 and 81, respectively, where the latter draw ring is obscured in the figure. The fixing means 51 of the uppermost support plate and the pull rings 71, 81 of the two middle support plates consist of two halves 51 a, b, 71 a, b and 81 a, b, respectively, which of drive means 53, 73, 83 are moved to and from the closed position shown in FIG. (the drive 83 is obscured in the figure).

In Fig. 2, which shows a longitudinal section through the pulling device according to Fig. 1 and which shows the principle of the operation of the device, the left part of the figure illustrates the device when the upper fixing means 51

8103302-9 and the two draw rings 71.81 are in the open position and the right part of the figure device when the upper fixing member 51 and the two draw rings 71.81 are in the closed position (the working position).

In the figure there is also the blank 10. In its central part is arranged a peripheral circumferential starting groove 12 formed as described above.

In addition to that shown in Fig. 1, Fig. 2 shows that the upper and lower fixing means 51, 61 are provided with resilient support washers 54 and 64, respectively, against which the end edges of the tubular blank 10 abut. Springs 55, 65 enclosing control members 56 and 66, respectively, for the support washers 54 and 64, respectively, with the control means screwed into the support washers provide the necessary resilient function.

The figure further shows that the two draw rings 71 and 81, respectively, consist of two draw ring halves 71 a, b and 81 a, b, respectively. Each draw ring is divided into three parts rings 74, 75, 76 and 84, 85, 86 respectively, which in turn each consists of two half ring rings. The sub-rings are separated by a certain thermal insulation. The dividing rings are fixed to each other by the ring housings 77 a, b and 87 a, b respectively to form the two draw ring halves together. In each sub-ring there are channels 174, 175, 176 and 184, 185, 186 for transport of liquid.

The sub-ring rings consist of a sub-ring 74 and 84, respectively, with an inner circumference adapted to the circumference of material of the material where the material thickness is not reduced, a sub-ring 76 and 86 with an internal circumference adapted to the circumference of material of the blank where the material thickness is reduced and a sub-ring 75 and 85, respectively, to form contact surfaces against the material in the transition zone between reduced and unreduced material of the substance.

Finally, Fig. 2 shows a mandrel 20 adapted to the inner surface of the blank 10 and provided with fluid channels 21.

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Figures 3 and 4 show how a central fixing member 41 a, b is arranged in the region between the pull rings 71 and 81. The fixing means is thereby arranged on a central support plate 40 with a fixed position in the device. This fixed position is achieved, for example, in that the support plate is fixed to the guide pillars-31. The central support plate is further provided with drive means 43 a, b for moving the two parts 41 a, b of the central fixing means to and from the working position of the respective parts. In some embodiments, the central fixing means is provided with fluid channels 141 a, b. the other means of Figures 3 and 4 are similar in Figures 1-2 and, where applicable, have the reference numerals in accordance with the reference numerals of these figures. The fixing member 51 is missing in the figure and in some applications no such fixing means is used.

Fig. 4 shows in particular how the pull rings are displaced or moved from one another in the axis direction of the blank. At the blank 10 'is found a central blank part 11 in which the wall thickness of the material is reduced. In transition zones 13,14 between materials with original wall thickness and material with reduced wall thickness, contact surfaces between the middle sub-rings 75,85 and the material in the respective transition zone are formed. As a result, the part rings control the shape of the transition surface between materials of original wall thickness and materials of reduced wall thickness.

Figures 5 and 6 show in detail the central areas 11 in Figures 3 and 4, ie the areas where the material wall of the blank is arranged with a starting groove or where the material wall has undergone thickness reduction in connection with the movement of the draw rings. Reference numeral 112 marks an abutment area between the inner surface of the blank 10, 10 'and the outer surface of the mandrel 20 provided by some deformation of the blank wall caused by the fixing member 41 a when in working position. Reference numerals 115,116 indicate areas for abutting against the mandrel of the inner surface of the thickness-reduced material portions of the blank 10 'during the drawing process. Further, thermally insulating material 79a, 89a is arranged between the ring rings 75a, 76a and 85a, 86a, respectively.

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The central fixing means 41 is arranged according to the invention according to a variety of alternative embodiments. These are characterized by the fixing means 41a, b in the working position enclosing the blank wall and thereby forming in the circumferential direction of the blank, areaally distributed abutment surfaces against the outer surface of the blank wall. This distribution of the abutment surfaces is achieved by the fixing means, for example, in that the surfaces of the fixing means facing the blank do not constitute circular cross-sectional cylindrical surfaces but cylindrical surfaces of, for example, elliptical or polygonal cross-section.

Figures 7-9 show examples of elements 210 ', 210, 210' of the invention. The element 210 'of Fig. 7 has at its lower part a cylindrical wall portion 213 of amorphous material adjoining an enclosed bottom portion 211' of the element also of amorphous material. Fig. 8 shows an element 210 where the outer cylindrical surface of the element has the same diameter along the entire length of the element. The bottom part 211 of the element 11 closed in this embodiment also consists of amorphous material. Fig. 9 finally shows an embodiment in which the orifice edge of the element 212 consists of material of original thickness, while the remaining part of the element has a configuration similar to that of Fig. 8.

In the practice of the invention, blank 10 is inserted over mandrel 20 adjacent to 20 against abutment of the lower fixing member 61. This is a means which determines the axial position of the blank and thereby ensures that the groove 12 of the blank assumes a position adapted to the location of the pull rings 71,81. as well as against the fixing member 41. This situation is corresponded to by the left part of Figures 2 and 3. Where appropriate, the upper fixing member is moved to the closed position (right portion of Figure 2) to further lock the position of the blank. The drive means 43,73,83 then move the central fixing means 41 and the pull rings 71.81 to abut the outer surface of the blank in and adjacent to the groove 12. The two tensile rings thereby provide contact surfaces with the outer wall of the blank where the wall thickness is unreduced, where the wall thickness is reduced to its minimum value and where the transition zone between the aforementioned two areas is formed.

Preferably, the material of the blank has an elevated temperature, though less than TG, when placed on the mandrel. Material temperature is finally set

8103302-9 by heat transfer between mandrel and blank and between draw rings and blank. Normally, no heat transfer between the central fixing member 41 and the blank is required, but the fixing member always maintains a temperature which ensures that the material at the bottom of the groove maintains the necessary mechanical stability to keep the blank fixed by the central fixing member. The temperature control is effected by the liquid flowing through the liquid channels 21 of the mandrel and the fluid channels 174,175,176 and 184,185,186 of the draw rings and, where applicable, through the liquid channel 141 of the central fixing member 41. different material areas of the subject. The sub-rings 74,84 with the largest inner diameter in the position shown in the right-hand part of Figures 2 and 3 heat the material to a temperature just below TG, preferably to a temperature corresponding to PET, a temperature lower than TG of not more than 15 ° C. 85 has a similar function while the part rings 76,86 maintain a temperature well below TG, preferably a temperature below TG of at least 15 ° C to cool the material after undergoing thickness reduction.

When the material has reached the set temperatures, the bottom drive devices start the rotation of the drive screws 32, with the support plate 70 with its draw ring 71 and, where applicable, the support plate 50 with its fixing member 51 moving upwards in the figures. The support plates 80,60 and thus the pull ring 81 and the fixing means 61 are simultaneously moved downwards in the figures. The material thickness of the blank is thereby reduced by the pull rings as long as the movement is in progress. At the same time, the blank is extended in its axis direction, the extension being proportional to the reduction of the material thickness and to the axial displacement of the pull rings. The movement rates of the support plates 50 and 60 are thereby selected such that the fixing means are moved faster from the central fixing means 41 than the end edges of the blank. At the same time as the axial movement of the draw rings is started, the retention of the upper fixing member 51 is loosened by the upper end of the blank.

The middle draw ring 75 and 85, respectively, abuts the transition zone between materials of reduced thickness and materials of original thickness. The profile of the middle part of the ring is chosen so that the material during the transformation process forms contact surfaces against the inner surface of the part. Thereby

8103302-9, the ring controls the shape of the transition surface between materials of reduced thickness and materials of original thickness. The sub-ring also has a temperature controlling function in that in the said contact surfaces a heat transfer takes place so that during the entire drawing process the material in the transition zone is kept at a temperature adjacent to TG. Especially when drawing is done at high speed or at high material thickness, it is necessary that the middle drawing ring has a good heat dissipating ability so that the material in the transition zone does not get too high temperature.

After the pull rings have been moved apart so that the central blank portion 11 has reached a predetermined length, the movement of the support plates is interrupted. The drive means 43,73,83 then move the central fixing member 41 and the pull rings 71 and 81 to the open position, and the element formed in the manner described is removed from the mandrel, whereupon a new tubular blank is placed on the mandrel and the process is repeated.

In its working position, the central fixing member 41 encloses blank 10 in the bottom of the groove 12. Hereby abutment surfaces are formed against the bottom of the groove which are distributed in a number of areas along the circumference of the blank. The contact pressure in these surfaces, in turn, causes contact surfaces to form between the inner surface of the blank and the surface of the mandrel. The contact surfaces receive positions corresponding to the distribution of the contact surfaces. The contact surfaces arise because the fixing means deforms the shape of the inner boundary surface of the blank. The abutment pressure of the fixing member is chosen so that, during the deformation of the mold, the material thickness in the bottom of the groove is substantially unchanged. A contact surface is shown in detail in Fig. 6 and has the reference numeral 112.

As the drive members in the bottom part 30 (Fig. 1) rotate the drive screws 32, thereby moving the pull rings 71.81 from one another in the axis direction of the blank and while simultaneously reshaping the material wall and extending the blank, axially directed forces arise in the contact surfaces between the pull rings and the material in transition zones. The friction between the blank and the mandrel in the aforementioned contact surfaces 112 between the material in the bottom of the groove and the mandrel thereby fixes the position of the blank on the mandrel and ensures that the blank's reshaping occurs symmetrically around the groove 12.

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Figure 6 further shows that in conjunction with the stretching of the material that occurs during the remodeling of the blank wall, a contraction of the blank takes place, whereby its inner surface is moved to abutment against the mandrel 2G. In the figure, such abutment surfaces are indicated by the reference numerals 115,116. The formation of these abutment surfaces complements the fixation of the blank relative to the mandrel obtained by the central fixing means 41. It has been found that in most application examples, the complementary fixation by abutment surfaces 115,116 is not required to achieve the desired symmetrical reshaping of the blank.

The above description shows that a device according to the invention allows any length of the blank to obtain reduced material thickness. Thus, it is possible to allow the material reduction to cover the entire length of the blank, to cancel it immediately before the ends of the blank or to allow it to occur in a number of areas located in the axle direction of the blank separated by material portions where no thickness reduction has occurred. For each area of ​​reduced material thickness, the reduction of thickness begins in a new starting groove.

In the manufacture of an element with several thickness-reduced material portions, the central fixing means and the drag rings, respectively, are moved to a first starting groove and assume the working position therein. From the starting groove, the pull rings move one piece in the axial direction of the blank during reduction of the material thickness until the first material portion with reduced wall thickness is produced. The fixing member's fixation of the substance ceases and. the draw halves are moved from one another and then to the next starting track, after which the organs re-enter the working position. The pull rings are now moved again in the axial direction of the blank to provide a new material area with reduced material thickness, etc. The process is repeated until the desired number of areas with reduced material thickness is achieved. By controlling the lower and, where applicable, the movement of the upper fixing means 61,51 in the axis direction of the blank to correspond to the axial extension of the blank, correct engagement in the respective starting grooves for the central fixing means 41 and the draw rings 71,81 is ensured at each drawing occasion.

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Surprisingly, it has been found that when the blank is reshaped at the above temperatures, relatively small abutment pressures are obtained between the material of the blank and the mandrel, so that after completion of molding, there is no problem separating the element formed by the mold from the mandrel.

The embodiments of elements shown in Figures 7-9 are examples of elements made according to the previous description. In the manufacture of an element according to Fig. 7, the thickness of a preferred application of a tubular blank open at both ends is reduced, leaving at the end of the blank to be closed a material area of ​​amorphous material which is closed after heating as described above. Figures 8 and 9 relate to embodiments in which an already closed tubular blank of amorphous material obtains cylindrical wall portions consisting of substantially monoaxially oriented material. In Fig. 8, the monoaxially oriented material comprises the element throughout its length, while in Fig. 9 the orifice edge 212 consists of material which has not undergone such orientation.

In the formed element, the reduced wall thickness portion 11 constitutes in some applications a central portion in which the portion of the element is cut to form two symmetrical portions. Each part is sealed at the end with the original wall thickness and a preform to be used eg for blowing a container is completed. Those parts of the preform that have reduced wall thickness form the starting material for, for example, the starting material for, for example, the orifice portion of the future container.

For example, according to the invention, it is also possible to arrange two adjacent grooves separated by an amorphous material portion. The center: the fixing means thereby fixes the substance in this amorphous material portion and the draw rings move during the drawing from the material portion. By cutting off the formed material with stretched material in the material portion of the amorphous material, two tubular elements (possibly after closing the bottom of the tube) are obtained with an orifice portion corresponding to that shown in Fig. 9.

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Z1

Within the concept of the invention, the possibility of, in addition to the crystallization of the material obtained in connection with the monoaxial orientation, is further enhanced by the heating of the material, the crystallization of the material. In this case, this must not be driven so far that in the event that the element constitutes a preform which in a subsequent step is transformed into an article, the material's potential for further transformation is compromised. Normally, the crystallization of an element of PET is allowed to reach a maximum of about 30% when the same is to be further reformed. Preferably, however, the crystallization is assumed to be between 10-25%, with the crystallization resulting from the monoaxial orientation being at most 17%.

In the above description, it has been assumed that the reduction of the material thickness to its final value occurs in a single reduction step. Within the scope of the invention there is also the possibility of reducing the material thickness by a number of successive reduction steps in order to reduce the material thickness to the final in a final step.

The drag ring and the drag rings respectively consist of a number of rings for the successive stepwise reduction of the material thickness. The embodiment described in this paragraph is preferably applied when the material of the blank has a great wall thickness and / or at high rates of movement of the draw rings.

In the above description, tubular blanks with a circular cross-section have been shown. It is a given that the idea of ​​the invention is also applicable to tubular blanks with other cross sections.

In addition to the above description, the invention is also apparent from the following claims.

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