METHOD AND DEVICE FOR FORMING MICROSTRUCTURED FIBRE

Abstract

A die and method for extruding an extrudable material to form an extruded member is described. In one embodiment, the die comprises a barrier member comprising a plurality of feed channels that extend through the barrier member. Furthermore, the die incorporates a passage forming member extending from the barrier member substantially in the direction of extrusion. The feed channels are arranged with respect to the passage forming member to allow the extrudable material to substantially flow about the passage forming member to form a corresponding passage in the extruded member.

Claims

1. A method for extruding an extrudable material to form an extruded member, the method comprising: introducing a billet of material into an inlet chamber of a die, the billet of material comprising a solid polymer or glass material; heating the billet of material in the inlet chamber to a predetermined temperature to form extrudable material; initially forcing the extrudable material from the inlet chamber through a barrier member into an open ended extrudate forming chamber of the die, wherein the barrier member is located between the inlet chamber and the extrudate forming chamber in the direction of extrusion and comprises a feed hole plate having a plurality of spaced apart feed channels each extending independently without flow communication through the barrier member and at least one passage forming member extending from the feed hole plate in a direction of extrusion into the open ended extrudate forming chamber, and continuing to force the extrudable material at a ram speed from the inlet chamber into the open ended extrudate forming chamber to form the extruded member, wherein the extrudable material is caused to substantially flow about the passage forming member on exit from the spaced apart feed channels to form at least one corresponding passage in the extruded member.

2. The method for extruding an extrudable material as claimed in claim 1, wherein the barrier member comprises a plurality of passage forming members extending substantially in the direction of extrusion into the open ended extrudate forming chamber and wherein the extrudable material is forced through the spaced apart feed channels to flow on exit from the spaced apart feed channels about the plurality of passage forming members and form passages in the extruded member corresponding to the plurality of passage forming members.

3. The method for extruding an extrudable material as claimed in claim 2, wherein the passages in the extruded member are formed having different sizes by modifying corresponding passage forming members to have different size, shape or cross section.

4. The die method for extruding an extrudable material claimed in claim 2, wherein the feed channels and the passage forming members are arranged in a regular lattice.

5. The method for extruding an extrudable material as claimed in claim 1, wherein the extrudable material is forced through the plurality of spaced apart feed channels at different flow rates.

6. The method for extruding an extrudable material as claimed in claim 4, wherein the extrudable material is forced through the plurality of spaced apart feed channels at different flow rates by modifying the plurality of feed channels to have different size, shape or cross section.

7. The method of claim 1, wherein the billet of material is a solid polymer and the predetermined temperature is 165 C.

8. The method of claim 1, wherein the billet of material is a glass material and the predetermined temperature is 520 C.

9. The method of claim 1, wherein the ram speed is 0.1 mm/min.

10. The method of claim 1, wherein the extruded member is a microstructured fibre preform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiment of the present invention will be discussed with reference to the accompanying drawings wherein:

[0049] FIG. 1 is a side sectional view of a die for extruding an extrudable material according to a first embodiment of the present invention;

[0050] FIG. 2 shows perspective views depicting the rear or inlet end of the die collar component and a front view of the sieve or feed hole plate component which together form the die illustrated in FIG. 1.

[0051] FIG. 3 is a rear perspective view of the die components illustrated in FIG. 2 as assembled;

[0052] FIG. 4a is an end view of the feed hole plate illustrated in FIG. 3;

[0053] FIG. 4b is an end view of a fibre preform extruded from the feed hole plate illustrated in FIG. 4b;

[0054] FIG. 5a is an end view of a feed hole plate incorporating 7 rings of pins according to a second embodiment of the present invention;

[0055] FIG. 5b is an end view of a fibre preform extruded from the feed hole plate illustrated in FIG. 5a;

[0056] FIG. 6a is an end view of a feed hole plate incorporating 4 rings of pins and varying feed channel size according to a third embodiment of the present invention;

[0057] FIG. 6b is an end view of a fibre preform extruded from the feed hole plate illustrated in FIG. 6a;

[0058] FIG. 7a is an end view of a feed hole plate incorporating multiple cores according to a fourth embodiment of the present invention;

[0059] FIG. 7b is an end view of a fibre preform extruded from the feed hole plate illustrated in FIG. 7a;

[0060] FIG. 8 is an end view of a fibre preform having a central longitudinal portion supported by four equally space walls;

[0061] FIG. 9 is a rear end view of a die for extruding the fibre preform having the geometry illustrated in FIG. 8 according to a fifth embodiment of the present invention;

[0062] FIG. 10 is a side sectional view of the die illustrated in FIG. 9;

[0063] FIG. 11 is a rear end view of a die for extruding the fibre preform having the geometry illustrated in FIG. 8 according to a sixth embodiment of the present invention; and

[0064] FIG. 12 is a side sectional view of the die illustrated in FIG. 11.

[0065] In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings.

DESCRIPTION

[0066] Referring now to FIG. 1, there is shown a side sectional view of a die 100 for extruding an extrudable material in the direction indicated by arrow 200 to form an extruded member as indicated generally by arrow 300 according to a first embodiment of the present invention. In this first embodiment, die 100 is for the fabrication of an optical fibre preform from a billet of polymer such as polymethylmethacrylate or alternatively a soft glass material selected from one of the classes of fluoride, chalcogenide or heavy metal oxide glasses. Additionally, combination billets may also be formed by stacking two or more individual billets of the same or different composition. As would be apparent to those skilled in the art, the method and device described here may well be employed in a number of applications where an extruded member having a complex transverse structure is desired.

[0067] Die 100 is machined from chromium-nickel stainless steel grade 303 but equally other machineable materials with suitable corrosion and heat resistance properties may be used. In the case of extrusion of soft glass material, the inclusion of at least 8% nickel in the steel alloy used to form die 100 will function to prevent sticking of glass material to the die 100 in the extrusion process.

[0068] Die 100 includes a die nozzle or collar 120 and a feed hole or sieve plate 130 forming a barrier member between a die inlet chamber 110 and an extrudate forming chamber 150 having an internal wall 123 that terminates in end channel 155 whose diameter is defined by stepped ridge portion 125 thereby forming an end channel 155 whose internal wall 126 is of a greater diameter than extrudate forming chamber 150. End channel 155 allows for an extra degree of freedom in the vertical positioning of feed hold plate 130 within die 100 and therefore the length or height of the extrudate forming chamber 150 for a die collar 120 of fixed height. This is due to the fact that extruded member does not interact with the internal wall 126 of end channel 155 due to its larger diameter when compared to the extrudate forming chamber 150. In this manner, many different combinations of inlet chamber 110 and extrudate chamber 150 heights may be realised for a given die collar size 120 without having to change the extrusion chamber in which the billet and die 100 are mounted during the extrusion process.

[0069] The interface between end channel 155 and extrudate forming chamber 150 forms a plane defining the extrudate forming chamber outlet face 151. The terminating edge of end channel 150 also forms a plane defining the die outlet face 152. Die inlet chamber 110 includes circumferential tapered or fluted wall portions 121 which function to force the material to be extruded uniformly towards feed hole or sieve plate 130. Generally, the source material is in the form of a billet having a diameter similar to the diameter of the collar at the inlet plane 122 of the inlet chamber 110.

[0070] Feed hole plate 130 is supported by a circumferential stepped recess or shoulder 124 formed in the wall of die collar 120. In this first embodiment, feed hole or sieve plate 130 is forced against shoulder 124 during the extrusion process and may be simply removed from die 120 by pressing feed hole plate 130 in the opposite direction to shoulder 124. Feed hole plate 130 includes a number of regularly spaced feed channels 131 extending through plate 130.

[0071] Extending from feed hole plate 130 into extrudate forming chamber 150 and generally in the direction of extrusion are a number of passage forming members 160 which function to form longitudinal passages in the extrudate as material is forced through feed channels 131 and exits feed hole plate outlet face 133 in the extrusion process. In this embodiment, each passage forming member 160 is formed from the exposed shaft portion 142 of pin 140 which further includes a head portion 141 and is located in a corresponding location hole 134 which extends through feed hole plate 130. Exposed shaft portion 142 extends from feed hole plate 130 in the direction of extrusion up to the extrudate forming chamber outlet face 151 ensuring that in this embodiment the resultant passages formed in the extrudate have substantially the same transverse size and shape as the exposed shaft portions 142 of pins 140.

[0072] Whilst in this first embodiment, pins 140 are mounted or attached directly to the feed hole plate 130 by insertion into corresponding location holes 134, equally other embodiments whereby passage forming members form part of a separate overlay member having corresponding apertures aligned with feed channels 131 are contemplated to be within the scope of the invention.

[0073] Pins 140 are press-fitted into location holes 134 and locate with feed hole plate 130 in the direction of extrusion by virtue of head portion 141. Thus pins 140 may be removed from feed hole plate 130, but as would be appreciated by those skilled in the art, pins 140 may also be integrally formed with feed hole plate 130. By providing for the disassembly of the feed hole plate 130 and individual pins 140, as well as the removal of feed hole plate 130 from die collar 120, each of these components may be cleaned and polished more readily, further improving the preform quality by reducing the roughness of the inner surfaces of the die and thus reducing the surface roughness of the resultant preform.

[0074] In this feed embodiment, feed channels 131 are all of the same diameter thereby channelling similar amounts of material in the extrusion process. However, these channel diameters may be varied to deliver material at different rates at different locations through feed hole plate 130 as required to allow even and homogeneous flow around the exposed shaft portion 142 of each pin 140 thereby minimising the distortion of the holes or passages in the extruded member (see for example FIGS. 6a and 6b). Additionally, whilst in this first embodiment feed channels 131 are circularly shaped and regular in cross section, equally they may be hexagonal or any other shape and also vary in cross section as required.

[0075] Similarly, the exposed shaft portions 142 of pins 140 or more generally passage forming members 160 may be of varying shape and size depending on the desired resultant transverse structure in the extruded member. In addition, the length of passage forming members 160 may be of varying length extending into extrudate forming chamber 150 implying that the free end of individual pins 140 may terminate either above or below extrudate forming chamber outlet face 151 as desired. Furthermore, individual passage forming members 160 may be tapered or more generally change shape or cross section as they extend into the extrudate forming chamber 150 (see for example FIGS. 10 and 12).

[0076] In the circumstances, where the orientation of pin 140 with respect to the location on feed hole plate 130 is important, then location grooves and corresponding registration ridges may be incorporated into the side walls of location holes 134 and pins 140 respectively. In another embodiment, location holes 134 and feed channels 131 are of equal diameter and essentially equivalent, thereby providing maximum freedom for location of the pins 140 on the feed hole plate 130 as pins 140 may be located within the lattice of feed channels 131 as desired.

[0077] Referring now to FIGS. 2 and 3, there are shown a number of views of die 100 in the unassembled (see FIG. 2) and assembled (see FIG. 3) state. Whilst in this first embodiment, feed hole plate 130 is removable from collar 120, it would be apparent to those skilled in the art that these components may be formed integrally to provide a unitary die. The interspacing of feed channels 131 and pins 140 ensures that the extrudate flows uniformly about each pin 140 thereby forming the walls of the passages that make up the transverse structure of the preform.

[0078] In this embodiment, die 100 incorporates a feed hole plate 130 having a diameter of 18.0 mm, extrudate forming chamber 150 of diameter 15.5 mm, feed channels 131 of diameter 0.8 mm and pins 140 of diameter 1 mm. The distance between each pin 140 is 2 mm and die 100 includes three rings of pins 140 resulting in a total of 36 pins forming a hexagonal lattice structure. An advantage of the present invention is that the die design is easily scalable, for example a feed hole plate 130 having a diameter of 36 mm diameter will allow almost seven rings of pins (i.e. 162 pins), which results in the fabrication of a 30 mm preform having 162 holes each of 1 mm diameter and with an inter-hole or pin spacing of 2 mm (see for example FIGS. 5a and 5b).

[0079] Of course other regular or non-regular lattice structures may be formed by suitable arrangement of pins 140 and feed channels 131 with respect to feed hole plate 130. Additionally, where a longitudinal passage corresponding to a cut-out portion is required in the extruded member, say for example to expose an inner region of the extruded member, a passage forming member or combination of passage forming members of appropriate sectional profile corresponding to the shape of the cut-out section may be located towards the edge of the feed hole plate 130.

[0080] For fabricating a polymer preform by extrusion using die 100, a billet of cross sectional diameter of 30 mm is introduced at a chamber temperature of 165 C. and fixed ram speed of 0.1 mm/min. The force required to extrude the billet through die 100 at this chamber temperature and ram speed is approximately 4.5 kN corresponding to a resultant pressure on the billet in the region of 6 MPa. For fabricating a preform from lead silicate glass using die 100, the billet chamber temperature required is 520 C. with an associated fixed ram speed of 0.1 mm/min. As such, the force required is approximately 25 kN corresponding to a pressure on the billet of 35 MPa.

[0081] The method for forming a preform having a complex transverse structure as described herein may be readily adapted to an extrusion machine which will automate what has hereto been in the prior art a delicate process requiring significant manual input and highly specialised background knowledge. Broadly the extrusion machine incorporates a receptacle for receiving a billet of material and heating means to heat the billet of material to form the extrudable material. The extrudable material is then forced by forcing means as is known in the art through the die which is located in a die receiving chamber which allows the die to be rapidly changed out as required. Finally the extruded member is then received in an output chamber where it is allowed to cool before collection. Clearly, this represents a significant advance over the prior art with the most important advantages of such an extrusion machine being the precise speed and force control via computer control.

[0082] Referring now to FIGS. 4a and 4b there is shown an end view of the three ring pin feed hole plate 130 illustrated in FIGS. 2 and 3 and an end view of the corresponding fibre preform 230 extruded from feed hole plate 130. Fibre preform 230 includes an outer region 232 and an intermediate region consisting of a number of longitudinal channels or passages 231 which extend through the preform 230, these being formed by corresponding pins 140 located in feed hole plate 130 as has been described above thereby defining a core region 233.

[0083] Similarly in FIGS. 5a and 5b, corresponding views of a seven ring pin feed hole plate 170 and the corresponding fibre preform 270 are depicted in accordance with a third embodiment of the present invention. This clearly demonstrates the ability to scale the die design and hence the corresponding fibre preform as required. Once again longitudinal channels or passages 271 are formed within an outer region 272 and correspond to the location of pins 172 in feed hole plate 170 which again define a core region 273 in fibre preform 270. The distribution of feed channels 171 ensures that the extruded material flows uniformly about pins 172 to form the passages 271. In this case seven rings are employed as opposed to three as in the previous embodiment.

[0084] FIGS. 6a and 6b depict similar views of a four ring pin feed hole plate 180 and fibre preform 280 in accordance with a fourth embodiment of the present invention. In this embodiment, the feed channels are of two different sizes as compared to the feed channels 131, 171 of the three and seven ring designs respectively. In this manner, extruded material will flow more readily through the increased diameter feed channels 181b when compared to the smaller diameter feed channels 181a. In this application, this difference of flow rates has functioned to reduce the distortion and displacement of the longitudinal channels 281 in the fibre preform 280 as formed by pins 182 which may be an important consideration depending on the potential application for the resultant drawn fibre.

[0085] Referring now to FIGS. 7a and 7b, there is shown respective end views of a multi-core feed plate 190 and corresponding fibre preform 290 according to a fifth embodiment of the present invention. In this embodiment, five outer core regions 294, 295, 296, 297, 298 and in inner core region 293 are defined by the arrangement of longitudinal channels 291 which correspond directly to the arrangement of pins 192 which themselves defined corresponding core regions 193, 194, 195, 196, 197, 198 on feed hole plate 190. Once again varying size feed channels 191a, 191b have been employed to modify the flow of the extruded material to compensate for distortions introduced by the extrusion process. As would be appreciated by those skilled in the art, the range of preform designs depicted here clearly demonstrates the use with which the present invention may be adapted to provide extruded members having widely varying complex transverse geometries.

[0086] Referring now to FIG. 8, there is shown an end view of a fibre preform 800 having an outer wall 810 and a central longitudinal portion 830 supported by four equally space walls 820, 821, 822, 823. This geometry has applications for the forming of nanowires which are described in detail in co-pending application entitled Fabrication of Nanowires claiming priority from Australian Provisional Patent Application No. 2005905619 filed on 12 Oct. 2005, and assigned to the applicant of the present application, and whose contents are incorporated by reference in their entirety herein.

[0087] Referring now to FIGS. 9 and 10, there are shown rear and side section views of a die 400 for extruding the fibre preform 800 illustrated in FIG. 8 according to a sixth illustrative embodiment of the present invention. In this sixth illustrative embodiment, the required transverse structure involves forming a central longitudinal portion 830 corresponding to feed channel 431 supported by four equally spaced walls, struts or web members 820, 821, 822, 823 corresponding to the sparing 445 between each of the four pins 440 being fed by material extruding through feed channels 435, 436, 437, 438 located in feed plate 430. Similar to die 100, die 400 includes a collar 420 having fluted or tapered walls 421 and a sieve or feed hole plate 430 that abuts shoulder 424 formed in the wall of collar 420 thereby forming a barrier member between die inlet chamber 410 and extrudate forming chamber 450.

[0088] Each pin 440 includes an inner tapered portion 442d, opposed side tapered portions 442c, opposed intermediate tapered portions 442e extending between the inner tapered portion 442d and the opposed side tapered portions 442c and an outer tapered portion 442a. The tapered portions 442a, 442b, 442c, 442d, 442e extend approximately half way down pin 440 and terminate in a vertical walled portion 442b that extends in the direction of extrusion into the extrudate forming chamber 450. The tapered portions 442a, 442b, 442c, 442d, 442e and parallel walled portion 442b act in combination as a passage forming member 460.

[0089] Tapered portions 442a, 442b, 442c, 442d, 442e function to guide the extruding material from feed channels 435, 436, 437, 438 to form walls, struts or web portions 820, 821, 822, 823 that support the central longitudinal portion 830 formed from material extruding from feed channel 431. The extrudate chamber walls 423 of collar 420 are arranged in a box or square configuration thereby forming the square profile of outer wall 810 of preform 800. Each pin 440 is attached to the feed plate by a top screw 441 located in location hole 434 which screws into a corresponding threaded aperture 446 extending into pin 440 from a top flattened section 447.

[0090] In terms of the dimensions of die 400, feed plate 430 has a length and width of 30 mm with the extrudate forming chamber 450 having a length and width of 26 mm. The arrangement and size of pins 440 results in wall, strut or web portions in the preform of an approximate length of 16 mm and a thickness of 0.5 mm respectively with a core diameter of 2 mm and an outer wall thickness of 1.5 mm.

[0091] Referring now to FIGS. 11 and 12 there are shown once again rear and side section views of a die 500 for extruding the fibre preform illustrated in FIG. 8 according to a sixth illustrative embodiment of the present invention. In this sixth illustrative embodiment, the geometry of the pins 540 has been modified to further facilitate the flow of extruded material about the pins 540 by changing the degree and extent of tapered portions 542a, 542b, 542c, 542d, 542e with respect to vertical wall portions 542b for each pin 540. Additionally pins 540 are removably attached to feed hole plate 530 by screw 541 which is located in a lower recess 543 of pin 540 and screws upwardly into a threaded receiving aperture 534 located on feed hole plate 530. As would be appreciated by those skilled in the art, the present invention provides the capability to form new fibre preform designs which were not previously capable of being formed using prior art techniques.

[0092] Whilst the present invention is described in relation to fabricating a preform for an optical fibre it will be appreciated that the invention will have other applications consistent with the principles described in the specification.

[0093] A brief consideration of the above described embodiments will indicate that the invention provides an extremely simple, economical method and device for fabrication of optical fibre preforms that have a large number of transverse features in them, thereby satisfying the growing demand for optical fibres of this type motivated by the growing interest in soft glass photonic bandgap and large mode area fibres.

[0094] The nanowires and fibres produced from the preforms that are extruded according to various aspects of the present invention have many applications, including, but not limited to sensors for use in scientific, medical, military/defence and commercial application; displays for electronic products such as computers, Personal Digital Assistants (PDAs), mobile telephones; image displays and sensors for cameras and camera phones; optical data storage; optical communications; optical data processing; traffic lights; engraving; and laser applications.

[0095] It will be understood that the term comprise and any of its derivatives (e.g. comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0096] Although a number of embodiments of the device and method of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.