Method and apparatus for forming an extrusion

Abstract

A method of forming an extrusion, the method including steps of: receiving a flow of extrudable material; extruding a plurality of flow streams from the flow of extrudable material; inducing a change in volumetric flow rate of at least one of the flow streams relative to another one of the flow streams; and combining each of the flow streams to form an extrudate having a velocity gradient.

Description

METHOD AND APPARATUS FOR FORMING AN EXTRUSION Field

[0001] The present invention relates generally to a method and apparatus for forming an extrusion. More particularly, the invention relates to an extrusion method and apparatus for forming an article with a helical profile. However, while some embodiments will be described herein with particular reference to that application, it will be appreciated that the invention is not limited to such a field of use, and is applicable in broader contexts.Background

[0002] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] Extrusion systems typically include an extruder, an expanding section and a forming die. The extruder melts the feedstock (such as plastic) and forces the melt through the expanding section towards the forming die. The expanding section permits sufficient travel distance from the extruder to ensure the molten plastic engages the input face of the forming die with an equal pressure across the face. The flow rate / velocity of molten plastic moving through the forming die is a function of two competing forces: the driving force which equates to pressure created by the extruder multiplied by the cross-sectional area of the negative space in the forming die; and the drag force which equates to friction created between the molten plastic and the walls of the forming die.

[0004] At a local scale, under highly ideal conditions, the velocity of the molten plastic is typically a parabolic function of the distance from a wall, with the parabolic function being related to the viscosity of the molten plastic.

[0005] Disadvantageously, such extrusions systems are inadequate in forming accurate helical profiles.Summary of Invention

[0006] With the above issues in mind, an aspect of the present disclosure provides a method of forming an extrusion, the method including steps of:receiving a flow of extrudable material;extruding a plurality of flow streams from the flow of extrudable material;inducing a change in volumetric flow rate of at least one of the flow streams relative to another one of the flow streams; andcombining each of the flow streams to form an extrudate having a velocity gradient.

[0007] In one or more embodiments, the method further includes a step of providing an extrusion die having a plurality of cavities each providing a respective flow path through the extrusion die, wherein extruding the plurality of flow streams includes introducing the flow of extrudable material to the plurality of cavities of the extrusion die.

[0008] In one or more embodiments, each of the flow paths has a cross-sectional area transverse to a direction of flow of the respective flow stream, with each of the cross-sectional areas varying with respect to each other for inducing relative changes in the volumetric flow rates among the flow streams to achieve a linear velocity gradient of the extrudate.

[0009] In one or more embodiments, the extrudate has a geometric form approximating a helical ribbon.

[0010] Another aspect of the present disclosure provides an extruded helical channel formed by the above-described method.

[0011] Yet another aspect of the present disclosure provides an apparatus for extrusion forming, the apparatus including:a distribution region configured to receive a flow of extrudable material and divide the flow into a plurality of flow streams;a transition region configured to receive the plurality of flow streams from the distribution region and induce a change in volumetric flow rate of at least one of the flow streams relative to another one of the flow streams; andan output region to receive the plurality of flow streams from the transition region and combine each of the flow streams to form an extrudate having a velocity gradient at a downstream outlet of the output region.

[0012] In one or more embodiments, the transition region includes a plurality of channels each configured to convey a respective one of the flow streams from the distribution region towards the output region.

[0013] In one or more embodiments, each of the plurality of channels has a cross-sectional area transverse to a direction of flow of the respective flow stream, with each of the cross-sectional areas varying with respect to each other for inducing relative changes in the volumetric flow rates among the flow streams.

[0014] In one or more embodiments, each of the plurality of channels is separated from an adjacent channel by a partition to isolate adjacent flow streams from each other.

[0015] In one or more embodiments, the cross-sectional area of each of the channels of at least a majority of the plurality of channels tapers from an upstream inlet of the transition region to a downstream outlet of the transition region.

[0016] In one or more embodiments, each of the plurality of channels are generally aligned along a width of the apparatus, with the cross-sectional areas varying across the width to achieve a linear velocity gradient at the downstream outlet of the output region.

[0017] In one or more embodiments, the distribution region extends from the transition region to form a plurality of passageways to respectively divide the flow into the plurality of flow streams, with each of the plurality of passageways fluidly communicating with a respective one of the plurality of channels.

[0018] In one or more embodiments, each of the plurality of channels is sloped relative to a respective one of the plurality of passageways.Brief Description of Drawings

[0019] For a more complete understanding of the present invention, exemplary embodiments of the invention are explained in more detail in the following description with reference to the accompanying drawing figures, in which like reference signs designate like parts and in which:

[0020] FIG. l is a dimetric view of a forming die according to an embodiment of the present disclosure, showing throttling, feeder and face sections of the forming die with internal features in hidden lines;

[0021] FIG. 2 is a dimetric, transverse cross-sectional view of the throttling section of the forming die of FIG. 1;

[0022] FIG. 3 is a dimetric view of the feeder section of the forming die of FIG. 1;

[0023] FIG. 4 is a dimetric view of an alternative face section of the forming die of FIG. 1;

[0024] FIG. 5 is a dimetric view of a forming die according to another embodiment of the present disclosure;

[0025] FIG. 6 is a schematic representation of a merge zone of the forming die of FIG. 1, showing a plurality of flow streams merging to form an extrudate;

[0026] FIG. 7 is a flowchart illustrating steps of a method of forming an extrusion according to the present disclosure;

[0027] FIG. 8 is a perspective view illustrating an extrusion system employing the forming die of the present disclosure in an example application; and

[0028] FIG. 9 is an additional perspective view of the extrusion system of FIG. 8.

[0029] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate particular embodiments of the invention and together with the description serve to explain the principles of the invention. Other embodiments of the invention and many of the attendant advantages of the invention will be readily appreciated as they become better understood with reference to the following detailed description.

[0030] It will be appreciated that common and / or well understood elements that may be useful or necessary in a commercially feasible embodiment are not necessarily depicted in order to facilitate a more abstracted view of the embodiments. The elements of the drawings are not necessarily illustrated to scale relative to each other.Description of Embodiments

[0031] With particular reference to FIG. 1, an apparatus 100 for extrusion forming according to an embodiment is shown. In the illustrated embodiment, the apparatus 100 is configured as a forming die 100, 100' to be utilised as a component of an extrusion system 500 (see FIGs. 8 and 9). The forming die 100 is primarily configured to form an extruded article with a bending radius or profile exhibiting a degree of curvature. In particular, as will be discussed in greater detail below, the inventors have surprisingly found that the forming die 100 is able to effectively create an extrudate 101 (see FIG. 6) having a linear velocity gradient to form an extruded article (see, for example, helical channel 502 in FIGs. 8 and 9) exhibiting a helical profile. The helically extruded profile formed by the forming die 100 advantageously permits creation of a channel or other structure with a predetermined geometry such as, for example, a generally thinwalled, generally flat-bottomed helical channel, helical ribbon or planar helical plate, or other rectilinear helical structure having a radial cross-section which is relatively constant and uniform relative to the helical axis. Embodiments of the present disclosure may also provide for other velocity gradients such as parabolic or exponential to vary the shape of the extruded profile.

[0032] The forming die 100 includes a die body 102 which is constructed from a plurality of plate-shaped sections to simplify manufacture of the die body 102. In other embodiments, the die body 102 may be formed from two sections or be of a unitary construction.

[0033] The die body 102 of the illustrated embodiment includes a throttling section 104, a feeder section 106 and a face section 108 as will be discussed in greater detail below.Throttling Section

[0034] As shown in FIG. 2, the throttling section 104 includes planar first and second major faces 110, 112 separated by a thickness of the throttling section 104. The first major face 110 provides an upstream input side 114 of the forming die 100 to receive a melt or flow of materialto be shaped by the forming die 100. In some embodiments, the material may be supplied in a molten or extrudable state to the upstream input side 114 via one or more extruders (not shown), such as a screw-type extruder.

[0035] The throttling section 104 includes a plurality of inlets 116 formed through the first major face 110 of the throttling section 104. Each of the inlets 116 is generally aligned alongside one another to form a row along a width of the first major face 110. However, in other embodiments, the inlets 116 do not need to be aligned, and instead can be at various angles and geometries to achieve a desired output. A plurality of outlets 118 is formed through the second major face 112 of the throttling section 104 such that each of the outlets 118 generally opposes a respective one of the plurality of inlets 116.

[0036] Fluidly connecting each of the inlets 116 with a corresponding one of the outlets 118 is a throttling passageway 120. Each of the plurality of passageways 120 is separated from an adjacent passageway 120 by an internal partition or wall 122. In some embodiments, the partition or wall may not extend the entire height of the respective passageway but rather may terminate short thereof. In this way, each of the inlets 116 of the throttling section 104 is configured to divide the melt or flow received at the upstream input side 114 into a flow stream to be conveyed in an initial extrusion direction Di from the inlet 116 to the opposing outlet 118 via the respective passageway 120. In this way, each of the walls 122 serves to isolate adjacent flow streams, effectively de-coupling competing drag forces between adjacent flow streams, permitting tailored control over each of the flow rates or velocities among the flow streams.

[0037] In the illustrated embodiment, each of the passageways 120 has a generally tubular geometric form such that, in substantially any cross-sectional plane extending transversely to the initial extrusion direction Di, each of the passageways 120 surrounds a generally rectilinear (such as square or rectangular) cross-sectional area. In other embodiments, the cross-sectional area may be of another polygonal form.

[0038] The cross-sectional area surrounded by each of the passageways 120 varies incrementally or linearly along the width of the throttling section 104 between a minimum area and a maximum area. As will be discussed below, the variation in cross-sectional area among the passageways 120, in addition to varying the length of each of the passageways 120, confers control over the flow behaviour of each of the flow streams to suit the intended application.Feeder Section

[0039] As shown in FIG. 3, the feeder section 106 includes planar first and second major faces 124, 126 separated by a thickness of the feeder section 106. In the illustrated embodiment, the thickness of the feeder section 106 is greater than the thickness of the throttling section 104. In other embodiments, the relative thicknesses of each of the feeder and throttling sections 106, 104 may vary.

[0040] Formed through the first major face 124 of the feeder section 106 are a plurality of inlet openings 128. Each of the inlet openings 128 of the feeder section 106 has a profile corresponding with a profile of a respective one of the outlets 118 of the throttling section 104. In this way, as shown in FIG. 1, the feeder section 106 is assembled with the throttling section 104 such that the first major face 124 of the feeder section 106 generally opposes the second major face 126 of the throttling section 104 so that each of the inlet openings 128 of the feeder section 106 is aligned with a respective one of the plurality of outlets 118 of the throttling section 104 to receive a respective one of the plurality of flow streams from the throttling section 104.

[0041] A plurality of outlet openings 130 is formed through the second major face 126 of the feeder section 106. In the illustrated embodiment shown in FIG. 3, each of the outlet openings 130 of the feeder section 106 is offset from a respective one of the plurality of inlet openings 128 by an angle a away from the initial extrusion direction Di to define an offset direction Do. In other embodiments, each of the outlet openings 130 of the feeder section 106 generally opposes a respective one of the plurality of inlet openings 128 (see FIG. 5) such that each of the flow streams move along the initial extrusion direction Di through the feeder section 106.

[0042] Fluidly connecting each of the inlet openings 128 with a corresponding one of the outlet openings 130 is a channel 132. Each of the plurality of channels 132 is separated from an adjacent channel 132 by an internal partition or wall 134. In some embodiments, the partition or wall may not extend the entire height of the respective channel but rather may terminate short thereof. In this way, each of the channels 132 is configured to convey a respective one of the flow streams in the offset direction Dofrom the inlet opening 128 to the corresponding outlet opening 130 via the respective channel 132. Like the walls 122 of the throttling section 104, each of the walls 134 of the feeder section 106 serves to maintain the de-coupling of drag forcesbetween adjacent flow streams. Additionally, sloping each of the channels 132 away from the initial extrusion direction Di serves to control the pitch of the helical form extruded from the forming die 100.

[0043] In the illustrated embodiment, each of the channels 132 has a generally tubular geometric form such that, in substantially any cross-sectional plane extending transversely to the offset direction Do, each of the channels 132 surrounds a generally rectilinear (such as square or rectangular) cross-sectional area. In other embodiments, the cross-sectional area may be of another polygonal form. A cross-sectional area of each of the channels 132 at the respective inlet opening 128 defines a “capture area”, being a plane of maximal cross-sectional area through which a given flow stream passes along the forming die 100. Without being bound by theory, the inventors have surprisingly found that the velocity of the flow stream is a function of the respective capture area.

[0044] The cross-sectional area surrounded by each of the channels 132 of at least a majority of the plurality of channels 132 tapers in the offset direction Do, that is, from each of the inlet openings 128 to each of the corresponding outlet openings 130. In this way, each of the outlet openings 130 of the feeder section 106 is of a generally uniform size.Face Section

[0045] As shown in FIG. 4, the face section 108 includes planar first and second major faces 136, 138 separated by a thickness of the face section 108. The thickness of the face section 108 is greater than the thickness of the throttling section 104 but less than the thickness of the feeder section 106. In other embodiments, the relative thicknesses of each of the face, feeder and throttling sections 108, 106, 104 may vary.

[0046] Formed through the first major face 136 of the face section 108 are a plurality of inlet orifices 140. Each of the inlet orifices 140 of the face section 108 has a profile corresponding with a profile of a respective one of the outlet openings 130 of the feeder section 106. In this way, as shown in FIG. 1, the face section 108 is assembled with the feeder section 106 such that the first major face 136 of the face section 108 generally opposes the second major face 126 of the feeder section 106 so that each of the inlet orifices 140 of the face section 108 is aligned with a respective one of the plurality of outlet openings 130 of the feeder section 106 to receive a respective one of the plurality of flow streams from the feeder section 106.

[0047] The face section 108 includes a plurality of outlet orifices 142. In the embodiment shown in FIG. 1, each of the outlet orifices 142 is formed through the second major face 138 of the face section 108. In the other embodiments, such as in the embodiment shown in FIG. 4, each of the outlet orifices 142 terminates short of the second major face 138 of the face section 108. In the embodiment shown in FIG. 1, each of the outlet orifices 142 of the face section 108 is offset from a respective one of the plurality of inlet orifices 140 by the angle a away from the initial extrusion direction Di. In other embodiments, such as in the embodiment shown in FIG. 4, each of the outlet orifices 142 of the face section 108 generally opposes a respective one of the plurality of inlet orifices 140 such that each of the flow streams move along the initial extrusion direction Di through the face section 108.

[0048] Fluidly connecting each of the inlet orifices 140 with a corresponding one of the outlet orifices 142 is a passage 144. Each of the plurality of passages 144 is separated from an adjacent passage 144 by an internal partition or wall 146. In some embodiments, the partition or wall may not extend the entire height of the respective passage but rather may terminate short thereof. In this way, each of the passages 144 is configured to convey a respective one of the flow streams in the offset direction Door the initial extrusion direction Di from the inlet orifice 140 to the corresponding outlet orifice 142 via the respective passage 144. Like the walls 122 of the throttling section 104 and the walls 134 of the feeder section 106, each of the walls 146 of the face section 108 serves to maintain the de-coupling of drag forces between adjacent flow streams.

[0049] Each of the passages 144 has a generally tubular geometric form such that, in substantially any cross-sectional plane extending transversely to the the offset direction Door the initial extrusion direction Di, each of the passages 144 surrounds a generally rectilinear (such as square or rectangular) cross-sectional area. In other embodiments, the cross-sectional area may be of another polygonal form.

[0050] The cross-sectional area surrounded by each of the passages 144 remains substantially constant or uniform along the offset direction Door the initial extrusion direction Di from each of the inlet orifices 140 to each of the corresponding outlet orifices 142.

[0051] The second major face 138 of the face section 108 provides a downstream output side 148 of the forming die 100 including a lip 150 from which the extrudate 101 emerges or exits from the forming die 100.Merge Zone

[0052] With particular reference to FIGs. 4 and 6, the lip 150 surrounds a cavity 152 of the face section 108 which is formed through the second major face 138. The cavity 152 extends from the lip 150 partially through the thickness of the face section 108 to reach each of the outlet orifices 142, thereby communicating each of the outlet orifices 142 with the lip 150 of the face section 108. The cavity 152 defines opposing upper and lower lands 154, 156 of the forming die 100 which extend between the lip 150 and each of the outlet orifices 142. In the illustrated embodiment, each of the upper and lower lands 154, 156 provides a substantially planar surface which is devoid of walls. In other embodiments, one or both of the upper and lower lands 154, 156 may include partial extensions of each of the respective walls 146 and / or may include other surface features or finishes. Extending between each of the upper and lower lands 154, 156 is a merge zone 158.

[0053] As will be discussed in greater detail below, each of the flow streams exit a respective one of the outlet orifices 142 to sufficiently merge within the merge zone 158 to form a single extrusion or extrudate 101 with no or minimal visible boundary or discontinuity between each of the flow steams, whilst maintaining the linear velocity gradient caused by the varying flow stream velocities in proportion to a distance away from a helical axis of the formed helical channel profile.

[0054] A thickness (that is, a length or distance along the offset direction Dofrom each of the outlet orifices 142 towards the lip 150) of the merge zone 158 may be varied according to a width between corresponding walls 146 of each of the passages 144 and a speed of the extrusion flow. Simply put, the merge zone 158 requires a thickness above a lower limit to permit forming of an extrudate 101 with no or minimal visible boundary between each of the flow streams, but below an upper limit so that the linear velocity gradient is not substantially diminished which would otherwise reduce the accuracy of the helical form.

[0055] Without being bound by theory, the inventors have surprisingly found that the distance needed to merge is a function of size of the forming die 100, the width between correspondingwalls 146 of each of the passages 144 and the relative velocity difference between each of the flow streams exiting a respective one of the outlet orifices 142.

[0056] For a forming die 100 with a separation of 0.1-1 mm between adjacent walls 146 of each passage 144, a flow stream flow rate of 10-30,000 kg / hr (or speed of 5-50 mm / second), and a flow velocity difference of 1-20% between each corresponding flow stream, the inventors have surprisingly found that a thickness of about 5-100 mm for the merge zone 158 is optimal in forming a relatively precise helical channel profile with no or minimal visible discontinuity between each of the flow streams.

[0057] FIG. 5 shows a forming die 300 according to another embodiment. The forming die 300 is similar to that of the forming die 100 except that each of the channels of the 332 of the feeder section 306 and each of the passages 344 of the face section 308 is not sloped in an offset direction but rather extends along the initial extrusion direction Di, facilitating creation of an extrudate with a generally circular form. Accordingly, features of the forming die 300 which are equivalent to the features of the forming die 100 are provided with the same reference numeral to that of the forming die 100, increased by 200. For features that are equivalent between the forming die 100 and the forming die 300, it will be appreciated that the above description of those features in relation to the forming die 100 is also applicable to the corresponding equivalent features found in the forming die 300.Exemplary Extrusion Method and Use

[0058] As shown in FIG. 7, a method 400 of forming an extrusion utilising the forming die 100 will now be described. Initially, in step 402, a melt or flow of material to be shaped by the forming die 100 is supplied to the upstream input side 114 of the forming die 100. Optionally, one or more processes may be performed upstream to ensure the flow of extrudable material is supplied in a pressure equalised state across each of the inlets 116 of the throttling section 104. In other embodiments, the flow of extrudable material may be supplied with unequal or varying pressures across each of the inlets 116 of the throttling section 104 for distribution among the different passageways 120. For example, the forming die 100 does not need to be “centered” on the axis of the extruder, but rather may be laterally offset and placed in proximity thereto to ensure that the pressure does not equalize.

[0059] In step 404, continued pressure applied across each of the inlets 116 causes the flow of extrudable material to be divided among the passageways 120 into the respective flow streams. In step 406, as each of the flow streams is conveyed along the respective passageway 120, the varying cross-sectional areas serve to induce relative changes in volumetric flow rates among each of the flow streams. In other embodiments, each of the passageways 120 may have a variable cross-section or may be configured to impart varying frictional drag forces onto the respective flow stream to induce relative changes in flow behaviour. In yet other embodiments, each of the passageways 120 may be configured to heat the respective flow stream or otherwise alter its rheological properties (for example, viscosity, shear sensitivity, and flow resistance) thereby inducing relative changes in flow rate among the flow streams. In this way, the cross-sectional areas do not need to vary linearly or otherwise to achieve a linear velocity gradient. Rather, without being bound by theory, the velocity through a particular passageway or channel may be dependent on several variables including, but not limited to, perimeter, length, surface area, temperature, and viscosity with each having a non-linear effect. In some embodiments, one or more of the passageways or channels may be provided with an adjustment mechanism to interrupt or induce the flow for fine adjustments to the flow. For example, one or more of the passageways or channels may be provided with a flow disruptor to modify the effective area and thus resist or impede the flow for reducing the velocity thereof.

[0060] After passing through the throttling section 104, each of the flow streams, which now exhibits a distinct flow rate or flow velocity, enters the feeder section 106 under pressure via a respective one of the inlet openings 128 of the feeder section 106. The tapering cross-sectional area of each of the channels 132 serves to guide and control each of the flow streams into a near-net-shape or desired cross-sectional profile of the extrudate.

[0061] Upon entering the face section 108 via the inlet orifices 140, each of the passages 144 further guides the respective flow stream into the final form before entering the merge zone 158 via the respective outlet orifice 142 in step 408. Each of the upper and lower lands 154, 156 serves to guide each of the flow streams through the merge zone 158 towards the lip 150 but not before adjacent flow streams merge and combine with unequal velocities to form the extrudate 101 with a linear velocity gradient.

[0062] As shown in FIG. 6, the flow stream which is closest to the helical axis (that is, the center of curvature) of the extrudate 101 has a first velocity Vi. The velocity of each subsequentflow stream increases linearly the further from the helical axis up to a final velocity Vncorresponding to the total number of flow streams such that Vi< V2<V3<...<Vn-2<Vn-i<Vn. Although, in other embodiments, the desired output may be achieved in other ways; for example, the velocity relationship for five flow streams may be Vi>V2«V3>V4«V5. The combination of one flow stream with the corresponding successive (that is, adjacent) flow stream results in a series of output velocities Voi, V02, ... Von-i, Von which are each a function of the merging velocities of each of the flow streams. The resulting linear velocity gradient across the extrudate 101, caused by the combining of unequal velocities, curves the extrudate 101 to form a helical extruded profile with a substantially uniform rectilinear cross-section. Each of the throttling, feeder and face sections 104, 106, 108 of the forming die 100 may include additional cavities or through-holes 160a-f to extrude additional flow streams for creating sidewall features with helical curvature which ultimately merge with the flow streams emerging from the outlet orifices 142 to form a thin-walled, generally flat-bottomed helical channel.

[0063] The forming die 100 of the present disclosure enables the extrusion of a generally flat-bottomed channel, a flat plate or a substantially rectangular complex profile in the form of a helix in a relatively cost-effective manner. The helical form can be created with multiple layers without any substantive increase in tooling costs and enables creation of a substantial surface area with a potentially unlimited number of revolutions at minimal cost. The continuous manufacture of the helical structure reduces the dominant cost of the extrusion which at the limit will approximate to the cost of the plastic or other raw material. The helical structure can be formed with a uniform profile in cross-section and a circular form in plan view. Calendering equipment (such as rollers and the like) or other extrusion tooling or support equipment may be utilised in conjunction with the forming die 100 to ensure the pitch between each revolution of the helical form is constant, the helical structure is uniform and the profile remains constant. Depending on the intended application and material choice, gaps or separation between successive revolutions of the helical form may be closed by exerting a force along the helical axis and remain intact within the boundaries of the material property. This process of “closing” the helical form may create a closed cylindrical object comprising multiple coils. Compensation may be provided to the forming die 100 to minimise distortions and bulging. In some embodiments, the forming die 100 may be configured to form an extrudate with variations in thickness across the channel and / or variations in the profile of the floor or bottom of the channel, such as parabolic or wedge-like profiles.

[0064] The forming die 100 may be fed from a single extruder to minimise costs. However, it is also possible to utilise co-extrusion of different materials from different extruders, and these features can be incorporated into the forming die 100.

[0065] In addition, for relatively large helices, two extruders could be used to create inner and outer helices which merge in the final die section to form a helix of substantially larger cross-sectional dimension. This method may be utilised for larger profiles to achieve the velocity gradient across the entire cross-section of a relatively wide channel which may be too wide for a single extruder. The extrusion method and apparatus of the present disclosure may also be utilised in creating a double helix, one created clockwise and the other anti-clockwise. These helices can be combined or interwound to form two joined helical channels, with the flows of material in each channel being separated from each other. This may have potential utility in heat exchange applications where the fluids need to be kept separate from each other. By utilising two helices of similar dimensions, it may be possible to create a high surface area heat exchanger out of two relatively cheap extruded helices wound together. Other applications could include in refrigeration and air conditioning systems, algae production where the second helix is used as a way of controlling the temperature of the algae helical channel; chemical industry, where high temperatures may be required for plastics or extruding a ceramic or metal paste that is then sintered to form the final double helix.

[0066] The forming die 100, 300 of the present disclosure may also be utilised to create “circular sections” or a “partial annulus”, such as by cutting the extrudate before a single rotation has occurred. In this manner, embodiments of the present disclosure may provide for cheaper manufacturing for certain applications than creating a large injection mold.

[0067] Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternative and / or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from thescope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0068] It will also be appreciated that in this document the terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus, assembly or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, device, apparatus, assembly or system. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.Reference Numeral List100 Forming die according to an embodiment 101 Extrudate102 Die body104 Throttling section106 Feeder section108 Face section110, 112 First and second major faces of throttling section 114 Upstream input side of forming die116 Inlets of throttling section118 Outlets of throttling section120 Throttling passageway122 Wall separating adjacent passagewaysDi Initial extrusion directionDo Offset direction124, 126 First and second major faces of feeder section 128 Inlet openings of feeder section130 Outlet openings of feeder section132 Channel134 Wall separating adjacent channels136, 138 First and second major faces of face section 140 Inlet orifices of face section142 Outlet orifices of face section144 Passages146 Wall separating adjacent Passages148 Downstream output side of forming die150 Lip of die152 Cavity154, 156 Upper and lower lands of forming die158 Merge zonea-f Additional cavities or through-holesForming die according to another embodiment Die bodyThrottling sectionFeeder sectionFace sectionMethod of forming an extrusion according to the present disclosure , 404, 406, 408 Steps of the methodExtrusion systemHelical channel

Claims

CLAIMS1. A method of forming an extrusion, the method including steps of:receiving a flow of extrudable material;extruding a plurality of flow streams from the flow of extrudable material;inducing a change in volumetric flow rate of at least one of the flow streams relative to another one of the flow streams; andcombining each of the flow streams to form an extrudate having a velocity gradient.

2. The method of claim 1 further including a step of providing an extrusion die having a plurality of cavities each providing a respective flow path through the extrusion die, wherein extruding the plurality of flow streams includes introducing the flow of extrudable material to the plurality of cavities of the extrusion die.

3. The method of claim 2, wherein each of the flow paths has a cross-sectional area transverse to a direction of flow of the respective flow stream, with each of the cross-sectional areas varying with respect to each other for inducing relative changes in the volumetric flow rates among the flow streams to achieve a linear velocity gradient of the extrudate.

4. The method of claim 3, wherein the extrudate has a geometric form approximating a helical ribbon.

5. An extruded helical channel formed by the method of any one of claims 1 to 4.

6. An apparatus for extrusion forming, the apparatus including:a distribution region configured to receive a flow of extrudable material and divide the flow into a plurality of flow streams;a transition region configured to receive the plurality of flow streams from the distribution region and induce a change in volumetric flow rate of at least one of the flow streams relative to another one of the flow streams; andan output region to receive the plurality of flow streams from the transition region and combine each of the flow streams to form an extrudate having a velocity gradient at a downstream outlet of the output region.

7. The apparatus of claim 6, wherein the transition region includes a plurality of channels each configured to convey a respective one of the flow streams from the distribution region towards the output region.

8. The apparatus of claim 7, wherein each of the plurality of channels has a cross-sectional area transverse to a direction of flow of the respective flow stream, with each of the cross-sectional areas varying with respect to each other for inducing relative changes in the volumetric flow rates among the flow streams.

9. The apparatus of claim 8, wherein each of the plurality of channels is separated from an adjacent channel by a partition to isolate adjacent flow streams from each other.

10. The apparatus of claim 8 or 9, wherein the cross-sectional area of each of the channels of at least a majority of the plurality of channels tapers from an upstream inlet of the transition region to a downstream outlet of the transition region.

11. The apparatus of any one of claims 7 to 10, wherein each of the plurality of channels are generally aligned along a width of the apparatus, with the cross-sectional areas varying across the width to achieve a linear velocity gradient at the downstream outlet of the output region.

12. The apparatus of any one of claims 7 to 11, wherein the distribution region extends from the transition region to form a plurality of passageways to respectively divide the flow into the plurality of flow streams, with each of the plurality of passageways fluidly communicating with a respective one of the plurality of channels.

13. The apparatus of claim 12, wherein each of the plurality of channels is sloped relative to a respective one of the plurality of passageways.

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