CA1204908A

CA1204908A - Method and device for producing a tubular object

Info

Publication number: CA1204908A
Application number: CA000378503A
Authority: CA
Inventors: Kjell M. Jakobsen; Claes T. Nilsson
Original assignee: PLM AB
Current assignee: Rexam AB
Priority date: 1980-05-29
Filing date: 1981-05-28
Publication date: 1986-05-27
Also published as: SE8008652L; SE8008650L; DE3121524C2; ZA813572B; US4462950A; JPS5720331A; US4416927A; FR2483315B1; GB2076734A; SE8008651L; IE811193L; US4569866A; IN155280B; DE3121524A1; JPH0240486B2; BE888995A; MX159145A; SE446386B; CH668742A5; HK45688A

Abstract

ABSTRACT OF THE DISCLOSURE

An object is produced from a tubular blank of thermo-plastic material of the type polyester or polyamide, preferably of polyethylene terephthalate by reducing the thickness of amorphous material in one or several areas of the blank by means of one single or several consecutive re-shaping operations. A mechanical shaping device moves a transitional zone situated between thicker and thinner material along the blank and elongates simul-taneously the blank in the moving direction of the tran-sitional zone. After the last re-shaping operation the thinner material has preferably an oriented state. During the re-shaping operation the temperature of the material in the transitional zone is controlled at a level which, immediately before the re-shaping operation, is within or close to the range of the glass transition temperature.
In one embodiment the reduction of the wall thickness of the material is begun in a track in the wall of the blank and continues symmetrically around the track.
Clamping devices are used to maintain the axial position of the blank. The blank is suitable for re-shaping for instance into a container in which the mouth too consists of oriented material. The invention offers possibilities for materials savings by comparison with previously used methods, at the same time as the thermal and mechanical characteristics of the container are improved.

Description

PP 5~9 uans PLM AB, Malmo A method and device for producing a tubular object The present invention relates to a method and a device for producing a tubular object of polyethylene terephthalate or a similar thermoplas-tic material from a tubular blank of amorphous material. The object has one or more cylindrical areas of material in which the thickness of the material in the blank has, in the case of polyethylene terephthalate, been reduced by one or more shaping operations until it is approximately 1/3 of the original thlckness of the material~ In certain applications the thickness of the material is reduced along the entire length of the object. In the areas with reduced wall thickness the material is axially oriented and has, in the case of polyethylene terephthalate, a crystallinity of less than approximately 30 %, usually being of the order of 10 - 25 %. The initial temperature of the ma-terial during shaping is preferably below the glass transition temperature (TG) and the shaping operation takes 3~

4~

place with the temperature of the material controlled in the area of shaping', where the material is in surface contact with an external draw ring and/or an internal shaping device~

Previously disclosed in Canadian patent application 352,909 filed May 28, 1980 by K. M. Jakobsen et al', is an object in which the wall thickness preferably at a central point of said object has been reduced to approxima-tely 1/3 of the original thickness of the material. The reduction in thickness is produced by clamping each end of a tubular blank in which the material is at an initial temperature below the glass transition temperature (TG) in two jaws which are then moved apart. By causing an annular area of the material to have a higher temperature than the surrounding material', the obtained material properties of the area will cause the reduction in thickness to commence in the area during the stretching operation. In certain applications the internal diameter of the blan]c is stabilized by the use of an internal mandrel. The process as disclosed will produce an object in which the material is axially oriented and has a crystallinity of less than approximately 30%, usually being of the order of 10-25%.

Already disclosed in Swedish Patent Application SE 7905045-6', laid open for public inspection on December 11, 1980 naming K. M. Jakobsen as inventor, is a method for causing the thickness of the material in a tubular blank to be reduced mechanically by the use of an external device. The device consists of one or more rollers which make contact with the external and/or internal surface of the blank with such force that the desired reduction in thickness will occur as the initial temperature of the material approaches the glass transition temperature. The external device is moved around the periphery of the blank and along the axis of the blank simultaneously. This method will also produce an object in which the crystallinity in the areas of reduced material thickness will be less than approximately 30% and will be of the order of 10-25%.

However, the material will not have been oriented axially to such a high degree as when the process described in the previous paragraph is used.
In accordance with the inventions described above, certain applications will produce objects which differ in respect of the transitional zone between stretched and non-stretched material. This condition will arise, for instance, if a central section of a tubular blank is stretched whilst the material in the blank is at an initial temperature below the glass transition temperature (TG) and if the blank i5 then separated into two parts so as to form two separate objects. The difference is due to the fact that one of the objects contains the start zone for the yielding of material produced by the stretching operation, whilst the other object contains the stop zone for the yielding of material.
When practisin~ the invention in accordance with Canadian Patent application 352,309 an annular transi tional zone between the thinner material which has been stretched and the thicker material which has not been stretched will normally be produced. In the zone the surface of the material will form an angle of approxi-mately 45~ with the surfaces of the stretched and non-stretched material respectively. Axially displaced tapering areas will occasionally be produced in the essentially annular transitional zone during the drawing operation, the presence of said areas usually requiring the object to be scrapped.
A method is provided in accordance with the present invention for producing an object of thermoplastic material from a tubular blank with a wall of essentially amorphous material, wherein the object is adapted to be reshaped into a container, the method comprising forming the wall of the tubular blank with a region of thinner '` `

- 3a ~
material and a transitional zone between the thinner material and a remaining thicker portion of the wall.
The transitional zone is engaged by a mechanical shaping device, and axial force is applied to the transitional zone by moving the shaping device and blank axlally to move the transitional zone axially relative to the blank while simultaneously elongating the blank by increasing the length of the region of thinner material of the blank and reducing the length of the thicker portion of the blank and effecting an orientation of the thus elongated and reduced thickness of the blank in the region of thinner material corres-ponding to the orientation which would be obtained by monoaxially stretching to yielding a sheet of amor-phous material of the same thickness of the wall of the tubular blank.
The present invention also contemplates a process for the manufacture of a tubular pre-moulding object from a thermoplastic material, which comprises providing a tube of thermoplastic material with a substantially reduced material thickness in at least one zone by stretching the tube in the axial direction, to obtain, when stretching the materi.al, an orientation mainly in the axial direction, and heating the material in at least the oriented zone or zones to a temperature above glass transition temperature (TG).
An apparatus is provided in accordance with the present invention for forming a container body of thermoplastic material from a tubular amorphous blank having a wall of given thickness, the apparatus comprising a draw ring for engaging the wall of an amorphous tubular blank over a portion of the thickness thereof and means for applying axial force to the portion by the draw ring. Means are also provided for relatively displacing the draw ring and the tubular blank axially of the blank to reduce the thickness thereof substan-tially by the amount of the portion engaged by the draw ring while elongating the blank to produce crys-talliza-tion of the material of reduced thickness of -the elongated blank substantially with monoaxial orientation. The draw ring includes a plurality of ring sections each including transversely movable segments having open, inoperative positions and closed, operative positions and drive means for moving the segments between the open and closed positions.
An apparatus is also provided for producing an object from a tubular blank of amorphous, orientable, ther~.oplastic material, wherein the apparatus comprises draw ring means for producing in a wall of the blank a transitional zone between a region of thinner material and a remaining thicker portion of the wall or for engaging such a transitional zone already provided in the wall of the blank. Driving means are provided for producing relative displacement of the draw ring means .0 and the blank axially of the blank to move the transi-tional zone axially along the blank while concurrently axially elongating the blank by increasing the leng-th of the region of thinner material and reducing the length of the thicker portion of the wall to effect an orientation of the thus elongated and reduced thickness of the blank in the region of thinner material.
More specifically, the present invention relates to a method and a device for producing tubular objects with areas of the wall in which, in the case of polyethylene terephthalate, the original thickness has been reduced to approximately 1/3 of its ini.tial value, in which areas the material is oriented mainly along the axis of the object only, '1 ln which areas crys-tallinity is less -than approximately 30 % and is preferably within the range of 10-25 ~6, and in which areas -the crystallinity produced in the material by the aforementioned orientation will achieve a maximum value of 17 %. The material in these areas will also have been oriented mainly along the axis of the object.

The speed at which the thickness of the material is reduced is greater in accordance with the present invention than by previously disclosed methods.
Furthermore, the transitional zone between material with the original wall thickness and material with reduced wall thickness will always have a predetermined shape, at the same time as the length of the sections with reduced wall thickness will always be precisely defined due to the fact that the re-shaping of the blank in the transitional zone itself is mechanically controlled. For example, when star~ing from a tubular blank in order to rnake an object to be used for two preforms which face each other, the rate of production wi]l additionally be doubled by starting the drawing operation at a central point and by then continuing it simultaneously towards the two ends of the tube. The object which has thus been produced may be cut and the cut sections sealed to form two preEorms for future processing, in which the transitional zone between material with the original wall thickness and material with reduced wall thickness will always have a pre-determined shape and will always contain material with characteristics which are idential from one preform to another.

In accordance with the present invention it is also possible to produce an object in which the thickness of -the ma~erial is reduced along the entire leng-th of the object or in one or more cylindrica~ sections of the object. The object is in the form of a tube which is open at bo-th ends or, in cer-tain applications, in the form of a tube which has been sealed at one end. 'rhe objec-t is mainly intended to be moulded into containers, whereby each single objec-t is formed into ei-ther a single container or a number of containers. In the latter case, the object is divided into a number of parts which are then moulded into containers.

The production of an object of polyethylene -tereph-thalate in accordance with the present invention starts with a tubular blank or a similar thermoplastic material.
The material ln this blank will be in an amorphous state.
In one single operation or a number of consecutive operations the thickness of the material in the blank is reduced to approximately 1/3 of its or.iginal thick-ness. This reduction in thickness takes place ei-ther along the entire length of the blank or in one or more sections of the blank. Use is made of a draw ring in certain applications, in which the relationship between the internal circumference of the draw ring and the external circumference of the blank is such that the thickness of the material will be reduced as the draw ring is moved axially along the blank. The temperature .. ~ of the material immediately before the reduction in thickness -takes place must be in the range oE or lower than the glass transition temperature tTG) of the material, which temperature will be abbrev:iated to TG
in the following, and should deviate from TG preferably by no mor~e than 15 C. Although the technical effect of the present invention may be achieved at a much lower temperature, it is advantageous to use an initial temperature cl.ose to TG, for instance a temperature .which is between 1 to 3 C below TG, since material at this initial temperature will permit the draw ring to be moved at high speed. In certain typical.
applications, the draw ring operates in conjunction with an internal shaping device located inside the ~zo~o~

bl~, whereby -~he extern~l dimension o~ thc shaping device fits -the in~ernal surface o~ the blank~ In other applica-tions only -the in-ternal shaping de~ice is used~ ~he t~ickness o~ the material in the blank is reduced by contact with -the draw ring and/or the internal shaping device as sai.d draw ring and/or shaping device is moved axially along the blank~ Durin~ the re~shaping operation a -transi-tional zone is formed between material with the original thic~ness and material with reduced thic}~ess 9 said transitional ~one gradually moving axially along the blankO ~he material in the transitional zone is kept at a temperature close to ~G during the re-shaping operation by the -trans~er of heat to the draw ring and/or the shaping device located inside the tubular blank. In certain applications the material in the -transitional zone is, however9 allowed to assume a temperature which exceeds ~G by no more than 30C 9 and preferably by no more than 15~o In cer-tain applications the material in the area adjacent to the transitional zone is cooled to a temperature below ~G immediately after it has been reduced in -thicl~essa `:~
In accordance with the present lnvention the possibility is offered of producing an object with areas with mainly a monoaxial orientation and in which the material has been reduced in thickness and of which the external circumference has been reduced and/or the internal circumference has been increased compared to the circum-ference of the corresponding sections of material in the blank.

In the case of sec-tions with reduced wall thickness requiring to be produced in areas situated between the ends of the blank, the reduction in thickness is begun by forming one or more peripheral grooves in 3~2~
- 7a -the wall of the blank at the same time as external devices are used to subject the blank to tensile stress along its axis. This stretching operation reduces the walL
thickness in the grooves to about 1/3 of its original thickness at the same time as the blank is elongated axially. Further reduction of the thickness of the wall of the blank is produced by positioning the draw ring in the aforemencioned groove or grooves and moving it axially along the blank. Certain applications use two rings, whereby the reduction in wall thickness takes place simultaneously from a specific groove outwards towards the two ends of the blank.

In the case of a blank which is sealed at one end and in which the wall thickness is to be reduced adjacent to the seal, the draw ring should preferably be moved from the seal towards the other end of the blank. In certain appli-cations the reduction in thickness is allowed to continue along the entire length of the blank.

In those applications in which the blank is in the form of a tube open at both ends, this may be sealed in certain cases after the reduction in thickness by heating the material at one end of the object and then by press mouldin~
the material in a mould which may be cup-shaped, for instance.
Patent Specification DE PS 1 704 119 published January 17, 1974 in the name of Otto Rosenkranz et al contains examples of methods suitable for achieving sealing of this ~ind.

7 b The reduc-ti.on oE the -thickness of the material in several stages is used mainly in the event of the material being so -thick that problems arise i.n transferri.ng sufficient hea-t away from the -transi-tional zone. By reduciny the thickness of the ma-terial a number of times before the final reduction in -thi.ckness is made, a thinner material will be produced which will facilitate the transfer of heat away from the transitional zone to the adjacent draw ring and/or internal shaping device.

Two draw rings are included in one de~iee for producing an objee-t in accordanee with the invention.
A mandrel around which a tubular b].ank is placed during the drawing operation is positioned axially to and inside the two draw rings. Separate clamping devices are also positioned near the end seetions of the blank.
Eaeh draw ring consists of two draw ring halves which ~0~8 are moved by the driving device between an operati.ng position in which the halves of the draw ring are in contact wi-th each other and an open position in which the halves of -the draw ring are separated from each other~ ~he open position is used when inserting the -tubular blank or removiny the made ob~ect from the device.

--~ Driving devices are also positioned in such a way as to mo~e the draw rings and clamping devices ~ lly along lo -the blankt At least whilst the draw rings are moving towards the ends of the -tubular blank, the movement of the draw rings is connected -to the movement of the clamping devices in such a way that the draw ring and clamping device which are adjacent to each other a.re moved in the same direc;tion and in such a way that the correlation between the speed of the respective draw ring and clamping device is determined by the reduction in thickness which it is wished to produce in the material in the tubular blank. ~or example 9 when reducing the wall thickness of the blank -to 1/3 o.~ its original thickness, the ratio ~etween the speeds o.t` the clamping device and the draw rin~ shall be 2/3 , with a ratio of 1/2 when reducin~ the -thickness of the material to 1/2 of its original thickness~ etcO
~he clamping de~ices are fitted wi-th axially mo~able ~prung components agains-t which the edges of the tubular bla~X make contact~ Any longtit~;n~l tolerances which are present in the blanX both before and during the drawing operation are absorbed by the sprlmg components.

In one embodiment of the inventi.on each draw ring usually consists of three ring sections with a certain degree of thermal insulation between the sections.
Each ring section is provided with channels for a fluid, saicl fluid either hea-ting or cooling the ring section.
The aforemen-tioned mandrel is also provided with liquid channels. The central ring section includes that part of the draw ring against which the transitional zone be-tween material with its original thickness and material with reduced wall thickness is formed during the drawlng of the tubular blank. of the neighbouring ring sections, the one with the ]argest in-ternal diameter is in contact with the material with its original thick-"` 10 ness during the drawing operation, whilst the other ring section with the smallest internal diameter is in contact with the material with reduced thickness.

When drawing a tubular blank, said blank is positioned on the mandrel i~ such a wa~ that it is held securely by the clamping devices. A central peripheral groove in the base of which the wall thickness has been reduced to appro~imately 1/3 of its original -thickness is formed in the tubular blank in the manner described above~ ~he draw ring halves are -then moved to their operating position. The shape and the axial length of those parts o~ the draw rings which are introduced into the groove match the shape and the `" a~ial length of the grooveO ~he material of the blank in the area which is to be drawn should preferably be heated to a temperature close to bu-t below ~G before the bla~ is positioned on the mandrel~ ~he material will be raised to the correct drawing tempexature through the contact surfaces formed between the material cf -the blank and the draw rings and mandrel.

During the actual drawing operation the draw rings and `the clamping devices are moved away from the track by the driving devices, when the aforementioned relative speed between the draw rings and the clamping devices is`maintained. Thus the thickness of the material in the blank will continue to be reduced by the draw rings for as long as movement continues. ~t -the same time the blank is leng-thened along its axis.

An essential fac-tor rela-ting to the device is -the control of the temperature of the material in -the transitional zone between amorphous material with the original wall -thickness and material which has been reduced in thickness~ The draw ring has an internal profile which ma~tches the change in the thickness of ~the material which occurs in the transi-tional zone.
~he pro~ile has been selected in such a way that it will form contact surfaces with the internal surface of the draw ring not only in the transitional zone 9 but also ahead of and after i-t during the drawing operationO
The draw ring is able in this way to control the shape o~ the transitional surface in the transitional zone~
The temperature of the material in the blank is - regulated during the entire drawing operation by the -trans~er of heat between the ma-terial in the blank and the draw rings and/or the mandrel. It is particul~rly impor-tant tha-t the section of the draw ring which is in con-tac-t with the material in the transitional zone should maintain -the material in the blank at a temperature close to ~.
A simplified embodiment of the present invention makes use of a single draw ring which is moved from a start track preferably all the way to the edge at one of the ends of the blank. In this way an object is produced in which the wall -thickness is reduced at one end only~
~his embodimen-t preferably makes use of an in-ternal mandrei as a dolly which will take up the axial forces ~hich arise as the wall thickness is reduced. ~he movemen-t of the draw ring is interrupted in cer-tain applications before it passes over the edge of the tubular blank. ~he edge will thus be bordered by a rim in which the wall thickness has not been reduced after ll the drawing opera-tion is complete. The object which is produced in this way is suitable Eor use as a preform, possibly af-ter a certain amount of re-shaping of -the rim, i.e. what will become the edge of the mouth, for a container intended to be closed by means of a "crown cork", for instance. Before the object is moulded into a container, the area which will become the mouth is stabilized by heating and by thermal crystallization, with crystallization usually being allowed to continue until the material in the afore-mentioned rim becomes opa~ue.

In a preferred embodimént of the present invention the blank is provided with a start track of such a~ial length that space is provided in the track for a clamping device together with the draw ring or draw rings. At least during the initial stage of the movement of the draw ring or draw rings, the clamping device holds sections of the wall of the ma-terial in the base of the track pressed against the mandrel. In -this way the position of the blank relative to the mandrel is fixed. In the embodiment of the present invention in which two draw rings are moved away from each other, the clamping device is designed to hold the wall of the blank in an area situated between the draw rings. By holding the blank securely against the mandrel, this will ~5 prevent any axial movement of the blank in relation to the mandrel which might arise depending on the axial forces which occur at the contact surfaces between the respective draw ring and the material in the transitional zone between the wall of the blank with reduced thickness and the wall of the blank with non-reduced thickness. Any ; movement could, for instance, lead to the disadvantage that in the variant of the invention in which an area surrounding the track has the thickness of its wall reduced, the area with reduced wall thickness may be positioned unsymmetrically in relation to the start track.

The use of a clamping device in accordance with the previous paragraph offers the possibili-ty of producing any desired axial leng~h in the area in which the wall thickness of the material has been reduced. In certain applica-tions this involves producing such a reduction in the thickness of the wall of -the material along the entire length of the blank, whereas in other app:Lications the reduction in thickness is interrupted before the draw ring or draw rings reach and pass beyond the end or ends of the blank. By leaving an area of amorphous ma-terial at the very end or ends of the blank, a section of material will be produced which is highly suitable, for example, for sealing to produce the base of a pre form by the use of a method which is described in Patent Specification DE PS 1 70~ 119 or, after having been subjected to thermal crystallization, for forming a rim for use with the "crown cor~" type of closure.

In an alternative embodiment the draw ring is used to reduce the wall thickness of the material in a tubular blank with a sealed bottom, the mouth of which is already provided with a means of closure, for example screw threads. The blank in which the material is intended to be subjected to a reduction in thickness is produced by some previously disclosed method, for example by injection moulding or by extrusion followed by sealing and moulding the bottom and mouth. In certain applications the start track is formed in the manner described above, whilst in other applications a starting poin-t or the start track in whole or partly is produced during the injection moulding of the preform.

~hen using an external draw ring to reduce the thickness of the material in the wall of the blank, a certain reduction in the internal diameter of the blank will also be produced, as has already been mentioned. ~he mandrel inside -the blank thus acts as a shaping device which will d~termine -the ex-tent o~ the reduction i.n diarneter.
Surprisin~ly, i-t has been found that, for material wi~h-in the ran~e of temperatures indicated above during the re-shaping operation, the con-tact between the wall of -the m~terial and the mandrel and produced by the contraction, ~enerates relatively little con-tact pressure between the i.nternal surface of the wall of the blank and the external surface of the mandrel, fo~
which reason no problems are encountered in removing lo the ~inished blank from the mandrel after the shaping (drawin~) of the blank is complete.

No internal mandrel is called ~or in certain types of application for the device, in which the object is allowed to assume an internal circumference ~Jhich is smaller than its ori~inal circumference. By selectin~
an internal mandrel with an external circumference which is smaller than the internal circumference of the blank, it is possible in other typical applications to control the reduction in the interna~ circumference of the blank during the drawing operation -to a value which is suitable for the envisaged speci~ic application.

~he present invention is described in grea-ter detail with reference to a number of Figures, in whieh Fig. 1 shows a perspective view of a drawing deviee;
Figo 2 shows a long~itudinal section through the - drawing deviee in accordance with Fig. 1 in which the draw rings of the drawing device are in the initia~ position before drawing;
~ig. ~ shows part of a long~itudinal section eorrespon~ing to Fig. 2? in which the draw rings have been separated from each other;
Fig. 4 shows a support plate fitted with a draw ring in its operating position;

1'1 Fig. 5 shows a longitudinal section through a tubular blank wi-th a draw ring in its ini-tial position;
F`ig. 6 shows a longitudinal section through a tubular blank during drawing in -the clirection away from its sealed part;
Fig. 7 shows a section through a tubular blank with a draw ring in the initial position prior to drawing -the blank in a short section at one end;
Fig. 8 shows a section of the tubular blank in aceordance with Fig. 7 with the draw ring in its final position;
Fig. 9 shows a longitudinal seetion through a drawing device with a eentral clamping device and with the draw rings or the clamping device in the initial position before drawing;
Fig. 10 shows part of a longitudinal section corre~
sponding to Fig. 9 wi-th the draw rings moved apart, Fig. 11 shows the central area in accordance with Fig. 9 in de-tail;
Fig. 12 shows the eentral area in aecorclance with Fig. 10 in detail;

Fig- 13 show objec-ts of alternative embodiments.

Fig. 1, whieh shows an overall perspective view of a drawing device in accordanee with the present invention, portrays a base 30 from whieh a number of guide pins 31 project vertieally, as shown in the Figure. The rest oE -the description which follows will rela-te to the clevice in this position, although the idea of invention is in no way restricted to a special positi~n of this kind. The designations "upper" or "lowex" or other similar designations are occasionally used below in connection with a variety of components, said designa-tions being used only for the purpose of clarification.

~he base is fitted with driving devices with gearing (not sho~n in the Figure) ~or a number of drive screws 32 which lie parallel with the guide pins. Four support plates 50~60,70,80 are positioned at right angles to the guide pins and the drive screws. Each support plate is ~itted with bearings which ~it the guide pins 31 and threaded holes 52,62972782 which operate in conjunction with a number o~ the drive screws 32 O ~he plates are also provided with openings 58~68,78,88 for -those drive screws which are not in threaded contact with the actual suppor-t plate. The top and bottom support plates 50 and 60 are arranged to operate in conjunction with the two drive screws 32 a and c 9 whereas the two interjacent support plates 70 and 80 are arranged to operate in conjunction with the -two rem~.;n;ng drive screws 32 b and d O ~urthermore~ the upper parts of the drive screws which operate in conj~nction with the support plates 50 and 70 are threaded in opposîte directions to the lower parts of the drive screws which operate in conjunction with the support plates 60 and 80 O ~his means that as the drive screws are rotated the two .upper support pla-tes will move in the same direction, although this will be opposite to the direction in which the two lower supp~rt plates will move.

Since the -top and bo-t-tom support plates are driven by the screws 32 a and c and the two middle support plates are driven by the screws 32 b and d , the speed at which the respective support plates move will be de-termined by the robational speed and the pitch of the screws in conjunction with which the respective support plates operate~ ~he pi-tch of the thread on the drive screws is selected in such a way that the top and bo-ttom support plates ~ill always move at a lower speed than the two in the middle~ In the initial position, the two middle plates will be in close contact with each other and the top and bottom plates will be in positions ~hich will allow movement to take place towards the ends of the guide pins~ A~ter movement has taken place~ the middle support plates will have moved closer to the upper and lower support plate respectively, ~he -top support plate 50 and the bottom support plate 60 are provided with clamping devices 51 and 61 , each of which holds one end o~ a tubular blank 10 The blank is provided with a preferably central peripheral starting track 12 (Fig. 2) in which the thick-ness of the material is approximately 1/3 of its original thickness. ~he starting track is formed preferably be~ore ` ~ the blank is posi-tioned in the d.evice by the application of external pressure to the wall of the material, for instance by means of a number o~ interacting rollers 9 at the same time as the tubular blank is subjected to tensile stresses along its axisO When forming the start track~ the use~of rollers in conjunction with the stretching operation produces a track with a pre-determined axial length which is thus given a profile ` which is largely identical with the profile in those parts of the draw rings which are introduced into the track (see description of Fig. 2 below) when re-shaping the blank into the objec-t. The tubular blank is caused to lengthen a~ially when the start track is formed.

The two middle support plates 70 and 80 are each fi-t-ted with a draw ring 71 and 81l with the latter draw ring being obscured in the Figure. The clamping device 51 of the top support plate and the draw rings 71,81 of the two middle support plates consis-t of two halves 51 a,b , 71 a,b and 81 a,b which are moved by the driving devices 53,73,83 to and ~rom the closed position shown in the Figure (the clamping device 81 is obscured in the ~igure).
In ~igure 2, which shows a longtitudinal section through the drawing device in accordance with Figure 19 the le~t hand part of the Figure portrays the device with the upper clamping device 51 and -the two draw rings 71981 in their open position, and the right-hand part lS of the Figure portrays the device wi-th the upper clamping device 51 and the two draw rings 71,81 in their closed position (operating position).
~he ~igure also shows the blank 10 . At its centre is a peripheral start track 12 which is formed ln accordance with the above description, In addition to the details shown in Figure 1, Figure 2 shows that the upper and lower clamping devices 51961 are fitted with sprung support plates 54 and 64 against which the end edges of the tubular blank 10 make contact~ ~he required spring unction is provided by springs 55,65 around the guiding devices 56 and 66 for the support plates 54 and 64 , with the guiding devices screwed firmly to the support plates~
The Figure also shows that the two draw rings 71 and 81 consist of two draw ring halves 71 a~b and 81 a,b.
Each draw ring is divided into three sections 74,75,76 and 84,85,86 ~ each of which consists in turn o~ two ring section halve5- The ring sections are separated from .,~, each o-ther by a certain degree of -therm~l insulation The ring sections are he~d toge~her by means of the ring casings 77 a,b ana 87 a,b in such a way that they will combine to form -the two halves of -the draw rings. Each xing section is provided wi-th channels 174,175,176 and 184,185,186 to permit the ~low e~ liquid.
~he draw ring sections are in the form of a section 74 and 84 with an internal circumference which matches the circumference of the material in the blank in the areas in which the thickness of the material has not been reducedl another section 76 and 86 with an internal circumference which matches the circumference of the material in the blank in the areas in which the thickness of the material has been reduced~ and a further sec-tion 75 and 85 which forms contact surfaces with the material in the transitional ~zone ~etween ma-terial in the blank which has and which has not been reduced in thickness.
Finally~ Figure 2 shows a mandrel 20 which fits the internal surface o~ the blank 10 and which is provided with liquid channels 21 .
Figure 3 shows part of a longtitudinal section which corresponds to central sections of Figure 2 in which 2s the draw rings have mo~ed or are in the course of moving apart along the axis of the blank~ and portrays a central section 11 of a blank in which the thickness of the material in the blank 10~ has been reduced. At the transitional zone 1~,14 be-tween material with its original wall thickness and material with reduced wall thickness, contact surfaces are formed between the middle draw rings 75,85 and the material in the transitional zonec In this way the dràw rings are able to control the shape of the ~transitional surfaGe between material with its original wall thickness and material with reduced wall thickness.

~æ~o~

Figure 4 shows -the support plate 70 viewed from above ~nd wi-th the draw ring 71 in its closed position~ The Figure also illustrates the loca-tions of the bearings for the guide pins 31 and the openings 78 and for the threaded holes 72 fGr the drive screws 32 . ~he o-ther support plates which are fi-tted with the draw ring 81 or with the clamping devices 51 or 61 are similarly equipped. As has already been mentioned, the clamping de~ice 61 is not dividedy and has therefore no~hing corresponding to the drivin~ device 73.
Figures 5 and 6 show a typical ~pplication of the present invention in which the wall thickness of a tubular blank 15,l~' which is sealed at one end is reduced 9 starting at the sealed end o~ the blank. lhis requires -a draw ring 23 to ~e dimensioned preferably in such a way that both before and at the start of the drawing operation contact will be made between the middle ring section and the upper ring section and the outer surface o~ the -tubular blank. Here -too the draw ring is made up of three ring sections 24925,26 with liquid channels 124~125,126 . The ring sections are dimensioned in a similar fashion to the ring sections which have already been described and are held together by a ring casing 27 . A mandrel 28 operates in conjunction wi-th the draw ring 23 in the re-shaping of the blank. The mandrel is normally provided with liquid channels, which is not clear from the Figureg however.
Figure 6 shows the manner in which re-shaping is begun and in which a section 16 of the blank with reduced wall thickness is formed in the lower section of the blank~ Re-shaping normally continues until all the material in the cylindrical part of the blank has had ~.. ... , . ~ . .....

its wall thickness reduced. In ~he event of -the mouth already having been formed, which may be the case with an injection-moulded blank, the re-shaping of the blank is, of course, interrupted as the draw ring reaches the mouth. The transitional zone between ma-terial with its original wall thickness and ma-terial with reduced wall thickness is indicated in the Figure by the designation 113.

Figures 7 and 8 show an alternative embodiment of the present invention in which a draw ring 29 is composed of only two ring sections 96,97 with separate liquid channels 94 9 95 0 In this application too there should preferably be a certain degree of thermal insulation between the ring sections~ If necessary~ the draw ring may be extended by -the addition of a third ring section with a separate liquid channel and which is dimensioned in the manner already described. Here too the draw ring opera-tes in conjunction with an internal mandrel 28 , which is normally provided with liquid channels but which is not clear from the Figures. ~he draw ring re-shapes the mouth of a tubular blank 17 which is sealed at one end, In an area which is usually ~uite close -to the opening in the blank9 there will be a peripheral start track l9 in which the thickness of the ma-terial has been reduced to approximately 1/3 of its original thickness. ~he s-tart track is produced in the manner which has already been described.

In Figure 8 the draw ring 29 has been moved relative to the blank with the help of the mandrel 28 in such a way that a sec-tion 18 of -the blank with reduced wall thickness is produced adjacent to the opening in the blank 17'.

Figures 9 and 10 show a fùrther alternative embodimen-t of the present invention in which a central clamping device 41 a,b is located in -the area between the draw rings 71 and 81. The clamping device is positioned on a central support plate 40 with a fixed position in the device.
This fixed position is obtained, for example by attaching ~he support plate to -the guide pins 31. The central suppor-t plate is also fi-tted with driving devices 43 a,b for moving the two par-ts 41 a,b of the central clamping device to and from the operating position of the respective parts. In certain embodiments, the central clamping device is provided with liquid channels 141 a,b.
Other devices shown in Figures 9 and 10 correspond to devices shown in Figures 1-4, in which case their reference numbers agree with the reference numbers in those Figures.
An equivalent device to the clampin~ device 51 is not present in this embodiment.

Figures 11 and 12 show details of the central areas in Figures 9 and 10, i.e. those areas in which the wall of the material in the blank is provided with a start track or in which the wall of the material has undergone a reduction in thickness in conjunction with the movement of the draw rings. The reference designation 112 is used to indicate an area of contact between the internal surface of the blank lo, lo ~ and the external surface of ;~ the mandrel 20 caused by a certain amount of deformation in the wall of the blank produced by the clamping device 41 a when this is in the operating position. The reference designations 115,116 indicate areas of contact with the mandrel by the internal surface of sections of the material in the blank 10' of which the thickness has been reduced by the drawing operation.

In accordance with the present invention the central clamping device 41 may be designed in accordance with several alternative embodiments. These are characterized by the fac-t that the clamping device 41 a,b in its operating position surrounds the wall of the blank r thus forming contact surfaces with the external surface of the wall of the blank which are distributed at various points around the periphery of the blank. This distribution of the contact surfaces is produced by the clamping device for example by the surfaces of the clamping device which face the blank not being in the form of cylindrical surfaces of circular cross-section, but rather in the form of cylindrical surfaces of, for instance, elliptical or polygonal cross-section.

Figures 13-15 show examples of objects 210', 210", 210"' in accordance with the invention. The object 210' in Figure 13 has at its lower part a cylindrical wall section 213 of amorphous material adjacent to a sealed bottom 211' in the bottom also being of amorphous material. Figure 14 shows an object 210" in which the external cylindrical surface has the same diameter along the entire length of the object. The sealed bottom 211"
of the object is also of amorphous material in this embodiment. Finally, Figure 15 shows an embodiment in which the edge of the mouth 212 of the object consis-ts of ma-terial with its original thickness, whereas the remaining parts of the object are similar in design to those in Figure 14.

The blank 10 is positioned over the mandrel 20 in the embodiment of the present invention in accordance with the typical example shown in Figures 1-4. The clamping device 51 and the draw rings 71 and 81 will then be in their open position, corresponding to the posi-tion shown in the left-hand part of Figure 2. The blank which is placed around the mandrel forms the contact surfaces with the mandrel. Once the blank is in place and is in contact with the sprung support plate 64 of the lower clamping device 61 the upper clamping device 51 and the draw ring halves are then moved to their closed position.
The two draw rings 71 and 81 enter the start track 12 and in so doing forrn contact surfaces with the outer wall of the blank where the wall thickness has not been reduced, where -the wall thickness has been reduced -to its minimum val.ue, and at the transitional zone between the two aforementioned areas.

The material of the blank will preferably be at a high temperature, although preferably below TG, when it is placed on the mandrel. The final temperature of the material is set by the transfer of heat between the " mandrel and the blank and/or between the draw rings and lo the blank. The temperature is controlled by means of the liquid which 10ws through the liquid channels 21 in the mandrel and/or through the liquid channels 174,175, 176 and 184,185,186 in the draw rings. The thermal insulation which is present between the ring sections of the draw rings generally maintains a certain difference in temperature between different areas of material in the blank. The ring sections 74,84 with the largest internal diameter will, when in the position shown in the right-hand part oE Figure 2, set the mater.ial to a temperature in the range o~ or just below TG, and preferably to a tempera-ture which is no more than 15 C below TG. The ring sections 75,85 have a similar function, whereas the ., ring sections 76,86 preferably will maintain a temperature well below TG, and preferably at a temperature which is at least 15 C below TG, in order to cool the material once it has undergone the reduction in thickness.

Once the material has reached the specified temperatures the driving devices at the base will begin to rotate the driving screws 32, causing the support plates 50,70 . and the associated clamping device 51 and draw ring 71 to move upwards in the Figures, and the support pla-tes 60,80 ancl the associated clamping device 61 and draw ring 81 to move downwar.ds in the Figures. The thickness of the material in the blank is thus reduced by the draw rings as long as movement con-tinues. At the same

2~

time, -the blank will be lengthened axially an~l this ~lonyation will be proportional to the reduction in the thickness of the material and to the axial movement o~ -the d~aw rin~s. The speeds at which the support plates 50 and 60 move are therefore selected in such a way that the positions o~ the clamping devices 51,61 will match the elongation of the blank. Any irre~ularities which may occur will be absorbed by the sprung support plates 54 and 6~.

lo ~he middle draw rings 75 and 85 are in contact with the transitional zone between material with reduced thickness and material with its original thickness. ~he profile of the middle ring section is selected in such -~ a way that the material during the re-shaping operation will form contact sur~aces with the internal sur~aces of the ring section~ In this way the ring section will control the shape of the transitional surface between material with reduced thickness and material with its original thickness. ~he ring section also has a temperature regulating function in that the transfer of hea-t takes place at the aforementioned contact surfaces in such a way tha-t the material in the -transitional zone is maintained at a temperature close to ~'G
throughout ~the entire drawing operation. It is essential, particularly when drawing takes place a-t high speed or when the material used is very thick, tha-t the middle draw ring should have excellent heat conducting properties so that the material in the transitional zone will not reach too high a temperature.
Once the draw rings have been moved apart so that the cen-tral section 11 o~ the blank will be given a predetermined length, the movement of the support plates is stopped. ~he driving devices 53,73,83 then move the clamping device 51 and -the draw rings 71 and 81 to their open position, and the object ~hich has been formed in -the manner described is then removed from the mandrel whereupon a new tubular blank is placed on the mandrel and the operation is repeated The sec-tion 11 with reduced wall thickness in the finished object forms the central section at which the object is cut in o~dèr to produce two symm~iGal parts.
Each part is then sealed a-t the end with i-ts original wall thickness, thus producing a preform which may be used, for example~ to produce a blow moulded container.
lo ~hose sections of the preform which have reduced wall thickness are subsequently re-shaped to form the basis for the mouth of the future container~
In the application of the embodiment of the present in~ention shown in ~igures 5 and 6, the function is in principle identical with that described abo~e. ~he internal mandrel 28 acts as a dolly which takes up those ~orces which arise as the draw ring 23 is moved axially along the blankO Regula-tion of the temperature in the different areas of the material is also important in this typical application. ~he mandrel 28 is normally provided with liquid channels corresponding to the liquid channels 21 in the mandrel 20 shown in ' ' ~igures 2 and 3a In certain typical applications the thickness of all the material in the cylindrical section of the blank is reduced, whllst the re-shaping stops sooner in other typical applications.
~he embodiment shown in Figures 7 and 8 is applicable in those cases in which it is required to produce a number of areas of material in wnich the thickness of the material has been reduced. Each such area of material requires a start track in which the reduction in the thickness of the material may begin. When producing the object the draw ring 29 is moved to an initial start track and the halves of the draw ring 35 ~ take up theix operating position. ~he draw ring is ~æ~

moved from the star~ track over a short distance along the axis o~ -the blank, reduci~g -the thickness o~ the ma-terial until the first section o~ material with reduced wall thickness has been producedO ~he draw ring halves are the~ moved apart and the draw ring is moved to ~he next start track~ when the draw ring halves take up their new operating position~ ~he draw ring is now moved once more along the axis of -the blank in order to produce a new area o~ material with reduced wall thickness, and so on. ~he operation is repeated lmtil -the desired number of areas with reduced material thickness have been producedD
The blank used in conjunction with the unidirectional drawing described in connection with ~igures 5- 8 is sho~n as being sealed at one end. In this way -the seal will have operated in conjunc~ion with an inte~nal mandrel to absorb the axial forces required during the drawing operation. It is, o~ course, possible to use external clamping devices which replace the ~unction of the mandrel in this respec-tO ~his alter.native is used ~en drawing tubular blanks which are open at both ends.

In the application of the present invention which utilizes the embodiment shown in Figures 9-12, the blank 10 is slid over the mandrel 20 until it makes contact with the lower clamping device 61. In this case thc latter serves as a device for determining the axial position of the blank thereby ensuring that the track 12 on the blank adopts a position which is suitable for the positioning of the draw rings 71 81 .and Eor the clamping device 41. This situation corresponds to the left-hand half of Figure 9. The driving devices 43 73 83 then move the clamping device 41 and the draw rings 71 81 into contact with the external surface of the blank in and ad~acent to ~4~

the track 12. The temperature conditioning of the ma-terial in the blank then takes place in -the manner which has already been described, in addition to which in certain typical applications liquid is also caused to flow through the channels 141 in the clamping device ~1. This situation corresponds to wha-t is shown in the right-hand part of Figure 9 and in detail in Figure 11.

In its operating position the central clamping device 41 surrounds the blank 10 in the bottom of the track 12.
This forms con-tact surfaces with the bottom of the track which are divided into a number of areas around the circumference of the blank. The contact pressure present at these surfaces in turn causes the internal surface of the blank and the surface of the mandrel to bear against each other. The bearing surfaces adopt posi-tions which correspond to the distribution of the contact surfaces. The bearing surfaces are produced because the clamping device deforms -the shape of the surface defining the internal limits Qf the blank. The co~tact pressure of the clamping device is selected in such a way that in the even-t of the shape being deformed, the thickness of the material in the bottom of the track will remain largely unchanged. A bearing surface is shown in detail in Figure 12 and is given the reference designation 1120 The driving devices in the base 30 (Figure 1) then rotate the driving screws 32 causing the draw rings 71,~1 to move apart along the axis of the blank, simultaneously re-shaping the wall of the material and elongating -the blank. The friction between the blank and the mandrel at the aforementioned bearing surfaces 112 fixes the position of the blank on the mandrel and ensures that the re-shaping of the blank will take place symmetrically around the track 12. The driving of the support plate 60 is `35 selected in such a way that the clamping device 61 will be away reliably :Erom the end of the tube so as not to have any effect on the elongation of the tube which occurs in conjunction with the reduction in the thickness of the wall of the blank. This operating situation corresponds to Figures 10 and 12. Figure 12 also shows tha-t, .in addi-tion to the stretching of the material which occurs during the re~shaping of the wall of the blank, contraction of the blank also takes place, causing its internal surface to be moved lnto contact with the mandrel 20~ These contact surfaces are indicated in the Figure by the reference designations 115,116. The formation of these contact surfaces contributes to the fixing of the position of the blank relative to the mandrel which is achieved with the help of the central clamping device 41. It has been found in the majority of typical applications that additional fixing by means of the contact surfaces 115,116 is not essential to achieving the desired symmetrical re-shapiny of the blank The description in the previous paragraph indicates that the alternative embodiment of the invention in accordance with E'i.gures 9~12 will permit any ~esired length of the blank to have the thickness of i-ts materi.al reduced. It ;, is thus possible to reduce the thickness of the material along the entire length of the blank, to interrupt the reduction in thickness immediately before the ends of the blank, or else to reduce the thickness in a number of areas distributed axially alon~ the blank and separated by sections of material in which there has been no reduction in thickness.-In each area with reduced material .thickness, the reduction of the thickness is begun in a . new s-tart track.

Surprisingly, it has been found that when the blank is re-shaped at the temper.atures indicated above, relatively low contact pressure is produced between the material of the blank and the mandrel, for which reason no problems are encountered in removing the moulded object from the mandrel after the moulding operation is complete.

The embodiments of objects shown in Figures 13-15 are examples of objec-ts produced in accordance with the above description. When producing an object in accordance wi-th Figure 13 the thickness is reduced in one preferred embodiment in a tubular blank which is open at both ends, whereby at the end of the blank which will subsequently be sealed an area of amorphous material is left which is then heated and sealed in accordance with the method described above. Figures 14 and 15 rela-te to embodiments in which an already sealed tubular blank of amorphous material is given cylindrical areas of the walls consisting of essentially monoaxially oriented material. In Figure 14 the rnono-axially oriented material is present around the object over its entire length, whereas in Figure 15 the edge of the mouth 212 consists of material which has not undergone such orientation.

The idea of invention also contains the possibility of further increasing the crystallinity by heating the material, over and above the crystallinity which is produced in the material in conjunction with the mono-axial orientation. This crystallinity should not be allowed to continue to such a point that the ability of the material to undergo further re-shaping is impaired in the case of an object which is a preform which will be re-shaped in a subsequent operation to produce a finished article. The crystallinity of an object is normally allowed to reach a maximum level of approximately 30 % when the objec-t is to undergo further re-shaping.
Crystallinity is preferably allowed to lie between 10-25 %, whereas the crystallinity produced by monoaxial orientation will achieve a maximum value of approx. 17 %.

~9~

It has been assumed in the above description that the reduc-tion in the thickness of the material until it reaches its final value -takes place in a single reduction stage. The idea of inven-tion also con-tains S the possibility of reducing the thickness of the material in a number of consecutive reduction s-tages, before finally reducing the thickness of the material to approvimately 1/3 of its original thickness in a final sta~e. In this case the draw ring or draw rings will consist of a number of ring sections for the consecutive gradual reduction of the thickness of the material. The embodiment described in this paragraph is used mainly when the material in the blank has a large wall thickness and/or when the draw rings are moved at high speed.

Tubular blanks of circular cross-section have been shown in the above description. The idea of invention may, of course, also be applied to -tubular blanks of other cross-sections.

The above description relates to the plastic material polyethylene terephthalate. The values indicated in the description for the reductions in thickness and tempera-ture are therefore also related to this material.
A large number of materials of the type polyester or polyamide are known to exist, however, and to have similar charac-teristics, for which reason the invention as such is also applicable either in whole or in part to these materials, provided that the reductions in thickness and the temperatures are adjusted to suit the specific re~uirements of the respec-tive material.
The following are typical materials for which the present invention is suitable, after the indicated adjustments have been made: polyethylene terephthalate~
polyhexame-thylene adipamide, polycaprolactam, poly-hexamethylene sebacamide, polyethylene-2,6- and 1,5-~ 31 naphthalate, poly-tetrame-thylene-1,2-dioxybenzoate, and copolymers of ethylene teraphthalate, ethylene isophthalate, and other similar plastics polymers.

The crystallini-ty values stated in the present application relate to the theories disclosed in the publication "Die Makromolekulare Chemie" 176, 2459-2465 (1975).

-~ In addition to the above speci~ication, the invention is also described in the following Pat~nt Claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for producing an object of thermo-plastic material from a tubular blank with a wall of essentially amorphous material, said object being adapted to be reshaped into a container, said method comprising forming the wall of the tubular blank with a region of thinner material and a transitional zone between the thinner material and a remaining thicker portion of said wall, engaging a mechanical shaping device with said transitional zone, applying axial force to said transitional zone by relatively moving said shaping device and blank axially to move said transitional zone axially relative to said blank while simultaneously elongating the blank by increasing the length of the region of thinner material of the blank and reducing the length of said thicker portion of the blank and effecting an orientation of the thus elongated and reduced thickness of the blank in said region of thinner material corresponding to the orientation which would be obtained by monoaxially stretching to yielding a sheet of amorphous material of the same thickness of said wall of the tubular blank.

2. A method as defined in claim 1, wherein the thermoplastic material is a polyethylene terephthalate.

3. A method as claimed in claims 1 or 2, wherein a plurality of regions of thinner material are provided and the blank is elongated and reduced in thickness and the material oriented in a plurality of locations.

4. A method as claimed in claims 1 or 2, wherein the reduction of thickness of the blank is effected in a plurality of consecutive elongations of the wall of the blank.

5. A method as claimed in claims 1 or 2, wherein immediately before reduction in thickness of the wall of the blank, the material which will undergo said reduction in thickness is maintained at a temperature not greater than the glass transition temperature (TG) of the material.

6. A method as claimed in claims 1 or 2, wherein said shaping device is in contact with and forms a bearing surface against the material in the transitional zone, said material in the transitional zone being main-tained at a temperature in the vicinity of but not greater than the glass transition temperature (TG) by effecting transfer of heat to the material from the mechanical shaping device.

7. A method as claimed in claims 1 or 2, compris-ing cooling the material of the blank after it has assumed its reduced wall thickness immediately to a temperature below its glass transition temperature (TG).

8. A method as claimed in claims 1 or 2, wherein during the forming of the object, the external circum-ference of the cross-section of those sections of the material in which the thickness of the material is reduced will become smaller.

9. A method as claimed in claims 1 or 2, wherein during the forming of the object the internal circum-ference of the cross-section of those sections of the material in which the thickness of the material is reduced will become larger.

10. A method as claimed in claims 1 or 2, compris-ing separating the blank in the region in which the thickness has been reduced to obtain a plurality of objects each having an area of reduced wall thickness.

11. A method as claimed in claim 1, wherein said region of thinner material in the wall of the blank is an annular groove in the periphery of the blank, the reduction in thickness being effected in opposite directions from said groove.

12. A method as claimed in claim 11, comprising inserting as mandrel in said tubular blank prior to its reduction in thickness and holding the material of the blank against the mandrel as the wall of the blank is being elongated and reduced in thickness to secure the position of the blank relative to the mandrel, at least during an initial stage of reduction of thickness of said wall by said mechanical shaping device.

13. A method as claimed in claims 1 or 2, compris-ing sealing one end of the tubular blank by heating the material and press-moulding the end in a cup shaped mould.

14. A method as claimed in claim 2, wherein said material is polyethylene terephthalate and the thick-ness of the reduced thickness is approximately one third of the original thickness of the material, the tempera-ture of said material, at Least immediately before the final reduction in thickness takes place, being not greater than the glass transition temperature (TG).

15. A method as claimed in claim 14, wherein said temperature is between 3° and 15°C. less than said glass transition temperature.

16. A method as claimed in claim 1, wherein said forming of the wall of the tubular blank with the region of thinner material is effected by said mechanical shaping device.

17. A method as claimed in claims 1 or 2, wherein said region of thinner material in the wall of the blank is monoaxially oriented as it is formed.

18. A method as claimed in claims 1 or 2, wherein said temperature of the material deviates from TG by no more than 15°C.

19. A method as claimed in claims 1 or 2, wherein said temperature of the material deviates from TG by no more than 3°C.

20. A method as claimed in claims 1 or 2, wherein the temperature of the material in the transitional zone exceeds the glass transition temperature (TG) of the material.

21. A method as claimed in claim 16, wherein the formation of the transitional zone and the elongation and orientation of the region of thinner material is effected by fixing the position of the blank and axially moving the shaping device.

22. A process for the manufacture of a tubular pre-moulding object from a thermoplastic material, which comprises providing a tube of thermoplastic material with a substantially reduced material thickness in at least one zone by stretching the tube in the axial direction, to obtain, when stretching the material, an orientation mainly in the axial direction, and heating the material in at least the oriented zone or zones to a temperature above glass transition temperature (TG).

23. A process as defined in claim 22, wherein the thermoplastic material is a polyethylene terephthalate.

24. A process as defined in claim 1, wherein the temperature of the material at the commencement of reduction of thickness is not higher than the glass transaction temperature (TG) of the material.

25. Apparatus for producing an object from a tubular blank of amorphous, orientable, thermoplastic material, said apparatus comprising a draw ring for producing, in a wall of the blank, a transitional zone between a region of thinner material and a remaining thicker portion of the wall or for engaging such a transitional zone already provided in the wall of the blank, and driving means for producing relative displace-ment of said draw ring and said blank axially of said blank to move said transitional zone axially along the blank while concurrently axially elongating the blank by increasing the length of the region of thinner material and reducing the length of the thicker portion of the wall to effect an orientation of the thus elongated and reduced thickness of the blank in said region of thinner material, said draw ring including a plurality of ring sections each including transversely movable segments having open, inoperative positions and closed, operative positions and drive means for moving the segments between the open and closed positions.

26. Apparatus as claimed in claim 25 comprising means supporting said blank and draw ring for preventing relative rotation thereof during axial elongation of the blank, said draw ring having a substantially continuous annular inner surface bearing against said blank at said transitional zone and facing said region of thinner material and said region of thicker material.

27. Apparatus for forming a container body of polyethylene terephthalate or similar plastic material from a tubular, amorphous blank having a wall of given thickness, said apparatus comprising a draw ring for engaging the wall of an amorphous tubular blank over a portion of the thickness thereof, means for applying axial force to said portion by said draw ring and means for relatively displacing said draw ring and said tubular blank axially of said blank to reduce the thickness thereof substantially by the amount of said portion engaged by the draw ring while elongating said blank to produce crystallization of the material of reduced thickness of the elongated blank substantially with monoaxial orientation, said draw ring including a plurality of ring sections each including transversely movable segments having open, inoperative positions and closed, operative positions and drive means for moving the segments between the open and closed positions.

28. Apparatus for forming a container body of polyethylene terephthalate or similar plastic material from a tubular, amorphous blank having a wall of given thickness, said apparatus comprising means including a shaping element for engaging the wall of the amorphous blank over a portion of the thickness thereof, means for applying axial force to said portion by said shaping element, means for relatively displacing said shaping element and said tubular blank only axially of said blank to reduce the thickness thereof substantially by the magnitude of said portion of the thickness of the blank which is engaged by the shaping element while elongating said blank to produce crystallization of the material of reduced thickness of the elongated blank substantially with monoaxial orientation and means for providing a flow of a heat transfer fluid during elongation of said blank for controlling the temperature of said blank at said transitional zone during elongation of said blank to achieve said crystallization with substantially monoaxial orientation.

29. Apparatus as claimed in claim 28, comprising means supporting said blank and shaping element for preventing relative rotation thereof during axial elongation of the blank, said shaping element having a substantially continuous annular inner surface bearing against said blank at said transitional zone, and facing said region of thinner material and said region of thicker material.

30. Apparatus for producing an object from a tubular blank of amorphous, orientable, thermoplastic material, said apparatus comprising draw ring means for producing in a wall of the blank a transitional zone between a region of thinner material and a remaining thicker portion of the wall or for engaging such a tran-sitional zone already provided in the wall of the blank and driving means for producing relative displacement of said draw ring means and said blank axially of said blank to move said transitional zone axially along the blank while concurrently axially elongating the blank by increasing the length of the region of thinner material and reducing the length of the thicker portion of the wall to effect an orientation of the thus elongated and reduced thickness of the blank in said region of thinner material.

31. Apparatus as claimed in claim 30, comprising means for maintaining the temperature of the wall of the blank at a value in the vicinity of the glass transition temperature (TG) of the material.

32. Apparatus as claimed in claim 31, wherein said means for maintaining the temperature of the wall of the blank comprises channel means in said draw ring means adapted for flow of fluid therein.

33. Apparatus as claimed in claim 30, comprising a shape retaining means insertable in said blank and providing a bearing surface for said blank during elongation thereof.

34. Apparatus as claimed in claim 33, wherein said shape retaining means is provided with channels for flow of fluid therein to control the temperature of the wall of the blank.

35. Apparatus as claimed in claim 30, wherein said draw ring means comprises a draw ring encircling the blank for being driven in axial displacement by said driving means, said draw ring including a plurality of ring sections each including transversely movable segments having open, inoperative positions and closed, operative positions and drive means for moving the segments between the open and closed positions.

36. Apparatus as claimed in claim 35, wherein one of said ring sections is shaped to engage the wall of said blank in said region of thinner material and another of said sections is shaped to engage the trans-itional zone of said blank.

37. Apparatus as claimed in claim 36, wherein each ring section is provided with channel means for flow of fluid therein to effect heat transfer with said blank.

38. Apparatus as claimed in claim 35, wherein said draw ring externally encircles the blank.

39. Apparatus as claimed in claim 30, comprising a mandrel insertable in said blank and clamping means for holding said blank against said mandrel.

40. Apparatus as claimed in claim 30, comprising shaping means insertable in said blank for cooperating therewith to act in conjunction with said draw ring means to elongate the blank and reduce the thickness of the wall thereof.

41. Apparatus as claimed in claim 30, wherein said draw ring means includes means for engaging the blank to form said transitional zone.