FIELD The invention relates to methods for manufacturing a double-walled tube, which may, for example, be used as a heating tube in a device for heating smokeable material.

BACKGROUND

The manufacture of multiple walled containers such as double-walled tubes usually requires a number of manufacturing steps. Conventionally, inner and outer tubes are moulded separately and then combined and sealed together, prior to filling of one or more of a plurality of the chambers, if applicable.

SUMMARY

In accordance with some embodiments described herein, there is provided a method for manufacturing a double-walled tube, wherein the method comprises: a) forming two extruded tubes, wherein one tube is arranged inside the other; b) providing a first mould around the outside of the outer tube and a support along the inside of the inner tube; and, c) injecting fluid into a first cavity between the inner and outer tubes to mould the outer tube against the first mould; and wherein at least some of the fluid is retained in the cavity between the inner and outer tubes and wherein the fluid is, or comprises a component of, a substance that can be activated to act as a heat source or a coolant.

The fluid may be a phase change material.

The phase change material may comprise sodium acetate trihydrate. The method may further comprise forming an aperture in the moulded double-walled tube and injecting the fluid into the first cavity through the aperture.

An actuating means for activating the substance to act as a heat source or a coolant may be attached to the heating tube in the region of the aperture.

The double-walled tube may be a heating tube or a cooling tube for use in a device for heating or cooling a material to be heated or cooled, and a second cavity may be defined by the inner tube for receiving the material to be heated or cooled.

The double-walled tube may be a heating tube and the substance can be activated to act as a heat source, and the method may further comprise providing a smokeable material in the second cavity. In accordance with some embodiments described herein, there is also provided a method for manufacturing a double-walled tube, the method comprising: forming two extruded tubes, wherein an inner extruded tube is arranged inside an outer extruded tube; and applying a vacuum to a cavity between the outer extruded tube and a mould so as to vacuum mould the outer extruded tube against the mould.

The method may further comprise: inserting a substance that can be activated to act as a heat source or as a coolant into a cavity between the inner extruded tube and the outer extruded tube. The substance may be a fluid.

The substance may be a phase change material.

The phase change material may comprise sodium acetate trihydrate. The method may further comprise sealing the inner extruded tube to the outer extruded tube to define a first end of the double-walled tube prior to inserting the substance into the cavity between the inner extruded tube and the outer extruded tube. The method may further comprise sealing the inner extruded tube to the outer extruded tube to define a second end of the double-walled tube after inserting the substance into the cavity between the inner extruded tube and the outer extruded tube.

The method may further comprise cutting through the first and second ends to release waste material from the double-walled tube.

The method may further comprise attaching to the double-walled tube an actuating means for actuating the substance. The method may further comprise: pressurising the longitudinal cavity of the inner extruded tube with fluid when the substance is being inserted into the cavity between the inner extruded tube and the outer extruded tube.

The method may further comprise: supporting the inner extruded tube on a support inserted through the longitudinal cavity of the inner extruded tube when the substance is being inserted into the cavity between the inner extruded tube and the outer extruded tube.

The method may further comprise inserting a smokeable material into the longitudinal cavity of the inner extruded tube.

In accordance with some embodiments described herein, there is also provided a heating tube for use in a device for heating smokeable material, wherein the heating tube is obtained or obtainable by any of the above defined methods.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a double-walled tube; and,

Figure 2 shows a device comprising a double-walled tube;

Figures 3a to 3f illustrate schematically steps in the manufacturing of a double walled tube;

Figures 4a to 4e illustrate schematically steps in the manufacturing of a device comprising a double walled tube.

DETAILED DESCRIPTION

The application relates to a method for manufacturing a double-walled tube which may, for example, be used as a heating tube for use in a device for heating smokeable material.

Figure 1 shows an example of a double-walled tube 1. The double-walled tube 1 comprises an inner cylindrical tube 2 and an outer cylindrical tube 3. The inner cylindrical tube 2 and the outer cylindrical tube 3 are arranged concentrically with the inner cylindrical tube 2 within the outer cylindrical tube 3. The outer cylindrical tube 3 comprises a pair of annular ends 3a and 3b and the inner cylindrical tube 2 is open at both ends 2a, 2b. An enclosed annular space 4 is thus defined between the inner and outer cylindrical tubes 2, 3. The inner cylindrical tube 2 defines a cylindrical cavity 5 that extends along the central longitudinal axis of the double- walled tube 1.

Figure 2 is a schematic illustration of a device 7 that comprises a double- walled tube similar to the one illustrated in Figure 1. The device 7 is a smoking article that is configured to heat smokeable material.

In use, smoking articles such as cigarettes and cigars burn smokeable material such as tobacco to create smoke. Attempts have been made to provide alternatives to these smoking articles by creating products which release compounds without creating smoke. Examples of such products are so-called 'Tobacco Heating Device' products which release compounds by heating, but not burning, smokeable material. The device 7 shown in Figure 2 is configured to heat smokeable material without burning it. As used herein, the term 'smokeable material' includes any material that provides volatilised components upon heating. In some embodiments, it includes any tobacco-containing material and may, for example, include one or more of tobacco, tobacco extracts, tobacco derivatives, treated or modified tobacco such as expanded tobacco and reconstituted tobacco, or tobacco substitutes. For the avoidance of doubt, when devices such as that shown in Figure 2 are in use, the smokeable material will not be combusted and will not generate smoke.

The device 7 shown in Figure 2 comprises a double-walled tube 8 similar to that shown in Figure 1 which is employed as a heating tube for heating smokeable material. In the double-walled heating tube 8 of the device 7, the annular space 4 defines a heat source chamber 9, and the central longitudinal cavity 5 defines a heating chamber 10. The heating chamber 10 is configured to receive smokeable material 1 1 so that the smokeable material 1 1 can be heated in the heating chamber 10.

The heat source chamber 9 is for containing a heat source 12. The heat source 12 is activatable on demand to provide heat.

For example, the heat source 12 may comprise a phase change material which provides heat when it is induced to change between physical states (for example, from liquid to solid). Suitable phase change materials include hydrated salt phase change materials, comprising hydrated salts such as sodium acetate trihydrate, sodium hydroxide monohydrate, barium hydroxide octahydrate, magnesium nitrate hexahydrate and magnesium chloride hexahydrate. Sodium acetate trihydrate is stable at room temperature and is non-hazardous. The phase change of sodium acetate trihydrate from liquid to solid can also be reliably and quickly initiated by a variety of activating agents at least some of which can be incorporated into a separate actuator chamber, and transferred into contact with the phase change material to activate the heat source as required.

The heat source 12 may also comprise a plurality of reagents which are capable of reacting exothermically. The heat source 12 may comprise an exothermic chemical reaction between two or more reagents. The exothermic reaction may be a water- activated reaction, wherein water, or an aqueous solution or suspension, is added to one or more reagents in order to initiate an exothermic chemical reaction.

Reagents which may be used in combination with water to cause a water-based exothermic chemical reaction include calcium oxide (CaO), sodium hydroxide (NaOH), calcium chloride (CaCb) and magnesium sulphate (MgSC ). In some embodiments, these reagents are provided in solid form, for example in the form of a powder, granules, pellets or chunks, although they may also be used in other forms. These materials may be provided in a dedicated actuator, or otherwise transferred into contact with the water or aqueous solution to activate the heat source as required.

In other embodiments, the exothermic reaction may be a reaction between two or more reagents, none of which is water. For example, the exothermic reaction may include an organic liquid such as acetic acid.

Any one or a combination of the heat sources discussed above may be employed as a heat source 12 in devices of the type shown in Figure 2.

The heating tube 8 is configured such that the heat source 12 is able to heat the heating chamber 10 sufficiently to volatilize constituents of the smokeable material 1 1 without burning the smokeable material 1 1. Generally, and in the example shown in Figure 2, the heating tube 8 is configured such that the heating chamber 10 is located adjacent to the heat source chamber 9. Thus, in use, thermal energy from the heat source 12 heats the heating chamber 10.

In the example shown in Figure 2, the heat source chamber 9 and heating chamber 10 comprise co-axial layers within the heating tube 8, wherein the heating chamber 10 is located within the central longitudinal cavity of the heat source chamber 9. By means of this arrangement, efficient transfer of heat is provided from the heat source chamber 9 to the heating chamber 10. The device 7 further comprises at one end of the heating tube 8 an end cap 13 comprising air conduits 14. A mouthpiece 15 is arranged at the other end of the heating tube 8. The annular mouthpiece 15 comprises an opening which provides a passageway 16 for fluid communication between the smokeable material 1 1 in the heating chamber 10 and the exterior of the device 7. An actuator 17 is provided on the outer circumferential surface of the heating tube 8.

The actuator 17, examples of which are discussed in more detail below, comprises means to trigger the heating of heat source 12 to increase the temperature of the heating chamber 10. Accordingly, to initiate use of the device 7, the user activates the actuator 17 to heat the smokeable material 1 1. The user is then able to use the device 7 by drawing on the mouthpiece 15. External air is thus drawn via the air conduits 14 through the smokeable material 1 1 in the heating chamber 10 and then into the user's mouth via the passageway 16 in the mouthpiece 15. In this way, substances produced upon heating the smokeable material 1 1 , such as nicotine and aroma vapours, may become entrained in the gaseous flow as it is drawn by the user.

The type of actuator 17 used with the heating tube 8 may be selected on the basis of the type of heat source used. The actuator 17 may, for example, comprise an injection moulded unit or a thermoformed unit or a vacuum- formed unit and may be attached to the heating tube 8 by any suitable means including an interference fit and/or a suitable adhesive, welding, heat-sealing and the like. The actuator 17 may comprise a button or other means to activate the heat source 12.

For example, when the heat source comprises a phase change material, the actuator 17 may be configured to provide a nucleation point to trigger crystallisation of the phase change material. This may involve contacting the phase change material with a seed crystal to trigger the phase change. Alternatively, the phase change may be triggered by a sharp point or clicker providing the nucleation. In some embodiments, activation of the actuator 17 may result in the mixing of reactants with an activating agent. For example, calcium oxide (CaO) in particulate solid form (e.g. in the form of powder and/or chunks), may be added to water or an aqueous solution in the heat source chamber 9 to provide an exothermic reaction. The actuator 17 may comprise a rupturable element which may be ruptured upon activation of the actuator 17 to thereby activate the heat source 12. Sealing the heat source chamber 9 by attaching an actuator comprising a rupturable barrier to the surface of the heating tube 8 has the advantage that the heating tube 8 including the heat source 12 and actuator 17 may be formed and supplied as a separate component and therefore easily assembled with the other components of the device 7.

Moreover, this separate component can be formed in just two operations, a first step in which the heat source 12 is used as a fluid pressure medium to blow mould the heating tube 8 as will be described in a first example below, and a second step in which the actuator 17 is connected.

The mouthpiece 15 may comprise a filter 18. The filter 18 may include filtration material, which may be any material capable of binding and/or removing one or more substances derived from the heating of the smokeable material 1 1. For example, the filter 18 may comprise cellulose acetate tow.

The heating tube 8 is thus conveniently arranged such that the heat source 12 or heat source chamber 9 is not in fluid communication with the passageway 16 in the mouthpiece 15. Thus, any gases evolved by the heat source 12 cannot be inhaled by the user.

Indeed, by means of the double-wall arrangement, the heating tube 8 is configured to prevent any contact between the heat source 12 and the smokeable material 1 1.

The double-wall arrangement of the heating tube 8 may also advantageously allow heat generated by the heat source 12 in the heat source chamber 9 to be efficiently transmitted to the heating chamber 10. For example, the heating tube 8, or a portion thereof, may be configured to be thermally conductive.

Moreover, the heating tube 8 may also conveniently be configured to be sufficiently thermally stable to withstand the temperature generated by the heat source 12. The heating tube 8 may also be configured to be insulated to prevent the user from being burned by the heat source 12.

The heating tube 8 may also be sufficiently structurally resilient to provide support for the other components of the device 7 and to be sufficiently robust to withstand handling and use by the user.

In some examples, in which the heat source 12 comprises a phase change material, the heating tube 8 may be composed of a transparent material to enable the user to view the contents of the heating tube 8. In general, the heating tube 8 may be composed of any gas impermeable, thermally stable, and thermally conductive material, such as those listed. The heating tube 2 preferably comprises a thermoplastic polymer resin, such as PET.

In a device of the type shown in Figure 2, the length of the heating tube 8 may be approximately 130mm, and the diameter may be, for example, approximately 7-

8mm, or approximately 15- 18mm. The diameter may be the same at each end of the heating tube 8, or may vary along its length. For example, the heating tube 8 may be shaped for decorative or ergonomic purposes, or to provide a suitable shape for interference fit of the mouthpiece 15, end cap 13, actuator 17, or other attachment.

The double-walled tube 1 shown in Figure 1 comprises transverse, planar end walls. However, the ends of the double-walled tube may have any suitable shape or configuration as appropriate. In some examples, one end of the double-walled heating tube 8 may be shaped to provide the mouthpiece 15 so that a separate mouthpiece, such as an injection moulded mouthpiece section, is not required. In the same or other examples, one end of the heating tube 8 may be shaped to provide an end cap 13 so that a separate end cap, such as an injection moulded end cap, is not required.

First example of a method of manufacturing a double-walled tube.

There will now be described a first example of a method of manufacturing a double- walled tube such as the one illustrated in Figure 1.

In a first step, two open tubes are extruded from an extruder head of an extruder. The extrusion is configured to generate two tubes wherein a first, larger, outer tube is located around and spaced from the outer circumferential surface of a second, smaller, inner tube. An annular space is defined between the two extruded tubes. The inner extruded tube will ultimately form the inner cylindrical tube 2 of the finished double-walled tube 1 and the outer extruded tube will ultimately form the outer cylindrical tube 3.

The extruder may, for example, comprise two annular extrusion ports for extruding concentric tubular mouldable extrusions, wherein one annular extrusion port is positioned within the other.

As an alternative to the use of annular extrusion ports, one or a plurality of sheets may be extruded, with the one or more sheet extrusions being subsequently sealed together to form one or both of the extruded tubes. For example, split mould segments may be used to seal the extrusions.

The inner and outer extruded tubes may be extruded simultaneously. Alternatively, one of the extruded tubes may be extruded prior to extrusion of the other. For example, the inner extruded tube may be extruded into the core of a pre-extruded outer tube, or alternatively, an outer tube or one or more mouldable sheet extrusions may be extruded around a pre-extruded inner tube. The extruded material, preferably a thermoplastic material, may be supplied by one or a plurality of extruders. The one or more extruders may have a screw feed or piston.

A continuous or intermittent extrusion process may be used. An intermittent process in which the plastics material is not constantly extruded may conveniently allow sufficient time to complete a cycle of positioning, mould closing, blow moulding, and ejection steps. By way of an example, an accumulating head extruder may be suitable for use in this method, in which the extrudable material accumulates in a piston arrangement when extrusion is interrupted.

Alternatively, a continuous extrusion process may be used to form the extruded tubes, together with a means for cutting and transporting the extruded tubes away from the extruder head to be moulded elsewhere. This arrangement may provide the advantage of extrusion and moulding processes being performed simultaneously.

Tube cutting means may be provided and arranged to cleave the extruded tubes close to the extrusion port.

Any suitable thermoplastics material may be used to form the double-walled tube 1. Suitable thermoplastic materials include polyethylene terephthalate (PET), polyethylene (PE), poly( vinyl chloride) (PVC), polyproylene and polycarbonate (PC). One or both of the extruded tubes may comprise one or more co-extrusion layers. Accordingly, one or both extruded tubes may comprise a single or multiple layers. Either tube may comprises a layer, for example, an outer layer that comprises a material that acts as a moisture barrier to prevent or resist moisture passing through that layer.

In addition, or alternatively, one or both of the tubes may be extruded with decorative strips or a plurality of differently colored segments.

These effects may be achieved by means of a plurality of extruders, each extruding a material with a different composition. According to this arrangement, the extruders may be connected to a common extruder head, configured such that a tube extruded in one or more layers or sections emerges from the exit nozzle (an exit nozzle is often referred to in the art as a 'die and pin'). The extruded tubes are subsequently transferred to a blow moulding tool arrangement which comprises a first, outer mould and a second, inner mould.

The first outer mould may be a split mould, comprising a plurality of blow mould sections, which are configured to close around the outer extruded tube. Generally, the first mould comprises two sections that are substantially similar in size and shape.

The first mould is an external mould and has an internal surface for defining an outer surface of the outer extruded tube which will ultimately form the outer cylindrical tube 3 of the double-walled tube 1. In the case of the double-walled tube 1 shown in Figure 1 , the double-walled tube 1, and thus the cavity within the first mould, is substantially cylindrical. The second mould has the form of a mandrel and is inserted into the mould cavity down the centre of the inner extruded tube. The second mould functions to support the innermost longitudinal surface of the inner extruded tube, which will ultimately form the inner cylindrical tube 2 of the double-walled tube 1. The mandrel also serves to support the inner extruded tube during the moulding process. In the embodiment shown in Figure 1 , the inner surface of inner cylindrical tube 2, and thus the outer surface of the second mould, is substantially cylindrical. The inner mould may extend along the entire length of the extruded tubes.

In addition to maintaining the shape of the inner surface of the inner extruded tube, the inner mould also supports the inner extruded tube during the blow moulding process.

The inner mould may comprise a plurality of sections. For example, the inner mould may be made up of two mandrels which extend into the mould cavity from either end and contact one another near the centre. The use of an inner mould comprising a plurality of separable sections may assist in the removal of the inner mould from the finished heating tube.

In use, the sections of the first mould are brought together around the extruded tubes and the second mould is inserted longitudinally along the central core of the inner extruded tube.

When positioned for moulding, a portion of the first mould may form a seal with a portion of the second mould. In this way, one or both of the first and second moulds may comprise the tube cutting means. In addition, the moulds may be used to join the inner and outer extruded tubes at one or both ends, and thereby used as blow moulds to define and shape one or both ends of the double-walled tube 1.

The inner and outer extruded tubes may be joined at one or both ends by any suitable means, for example, by using a friction welding technique such as spin welding, by laser welding, by ultrasonic welding or by gluing.

The moulds may be formed from any suitable material, such as for example, a metal. The moulds may comprise means for controlling the temperature of the

thermoplastic material.

The blow molding tool arrangement comprises means for injecting fluid into the annular cavity between the first and second extruded tubes to thereby inflate the cavity and shape the thermoplastic material against the inner and outer moulds to form the double-walled tube 1.

The fluid pressure medium may include a gas such as air.

Alternatively, the fluid pressure medium may be a liquid. Any suitable liquid may be used.

As explained above, in some embodiments, the double walled tube 1 may be configured for use as a heating tube wherein the annular space 4 defined between the inner and outer tubes 2, 3 may be configured to comprise a heat source 12, arranged to heat the central longitudinal cavity 5 of the double-walled tube 1. In this case, a component of the heat source 12, which may be a liquid component, may

advantageously be used as the fluid pressure medium. In this way, the blow moulding of the double-walled tube 1 and filling of the annular space 4 with the heat source 6 may be performed simultaneously.

In some examples, the heat source 12 may comprise a phase change material, which releases heat upon changing physical states, for example in the transition from the liquid to the solid state. In this case, the fluid pressure medium may comprise a component or all of the phase change material.

The exact formulation of the phase change material may affect the temperature generated and also the suitability of the material for use as the fluid pressure medium. For example, where the phase change material comprises sodium acetate trihydrate, it has been found that the higher the water content of the formulation, the lower the temperature that may be achieved by the phase change. In addition, the formulation may improve stability of the phase change material in the liquid state, and may also increase the shelf life of the phase change heat source 12, whether already associated with the device or as a separate product to be associated with the device prior to use.

Phase change materials may be particularly suitable for use as the fluid pressure medium because the conditions of elevated temperature and pressure under which the fluid pressure medium is used have been found to be particularly helpful in preventing seeding and premature activation of the phase change material. In contrast, if the phase change material is used under these same conditions of elevated temperature and pressure to fill a pre-moulded double-walled tube, then the plastic can be caused to soften and deform. However, these effects do not cause a problem during the moulding of the double-walled tube, and indeed, may assist in shaping the thermoplastic material into the moulds. On the other hand, if a phase change material at a sub-optimal temperature and pressure is used to fill a pre- moulded double-walled tube then the risk of premature activation of the phase change material may be increased.

In examples in which the heat source 12 comprises a water-activated reaction, the fluid pressure medium may comprise water or an aqueous solution.

In examples in which the heat source comprises a reaction between two or more reagents, none of which is water, one of the reagents may be used as the fluid pressure medium.

The fluid pressure medium is introduced into the annular cavity between the inner and outer extruded tubes to blow mould the outer extruded tube against the outer mould, and the inner extruded tube against the inner mould to thereby form the double-walled tube 1.

In examples in which the fluid pressure medium includes at least a component of the phase change material, the two extruded tubes may first be sealed together at one end, prior to the fluid pressure medium being blown into the annular cavity between the two extruded tubes from the other end of the extruded tubes. The extruded tubes may then be sealed at the other end to seal the phase change material in the annular cavity.

The fluid pressure medium may be injected into the annular cavity between the two extruded tubes by any suitable means and at any suitable position. For example, the fluid may be injected by means of one or a plurality of modified blow mandrels or blow pins.

Each of the blow moulds and blow mould segments may be configured to

accommodate the one or more blow pins when the moulds are in the closed configuration. One or more of the pins may be retractable to assist assembly or removal of one or more of the moulds or mould sections.

Conveniently, one or a plurality of blow pins for blow moulding the double-walled tube 1 may enter the annular cavity via the gap between the two extruded tubes at one or both of the ends of the heating tube. Alternatively, the blow pin or pins may enter the annular cavity between the two extruded tubes at a position along one or both of the longitudinal cylindrical surfaces of the inner and/or outer extruded tubes.

Injecting into the longitudinal surface of the extruded tubes may advantageously allow the ends of the double-walled tube 1 to be shaped during the blow moulding process.

Removal of the one or more blow pins may leave one or more apertures 6 (see Figure 1) in the surface of the double-walled tube 1. The one or more apertures 6 may be subsequently sealed in an appropriate manner. For example, the aperture or apertures may be sealed by means of a plug or cap, bonded by means of a suitable adhesive or heat welding process. Prior to sealing, however, the one or more apertures 6 may be used to fill the annular space 4 defined between the internal and external cylindrical walls 2, 3 if

appropriate. For example, in embodiments in which the double-walled tube 1 is configured for use as a heating tube, the heat source may be inserted into the annular space 4 by means of the one or more apertures 6. This may be particularly applicable if the fluid pressure medium does not constitute the heat source, or all of the components of the heat source. In addition, or alternatively, one or more of the apertures 6 may be used to locate an actuator. For example, in embodiments in which the double-walled tube 1 is configured for use as a heating tube, an actuator configured to activate the heat source may be connected to one or more of the apertures 6 to thereby contact the heat source within the annular space 4.

In embodiments of the device 7 of the type shown in Figure 2, in which the blow pins enter the annular space 4 close to one or both of the ends of the double-walled heating tube 8 the remaining apertures may be covered by means of the mouthpiece 15 or end cap 13.

After blow moulding has been completed, and the double-walled tube 1 has cooled sufficiently, the sections of the inner and outer moulds are removed.

The shape of the inner mould may be limited by the need to be able to readily extract the mould following formation of the double-walled tube 1. The use of an inner mould comprising a plurality of separate sections may assist in the removal of the mould from the finished double-walled tube 1.

To assist in removal of the moulds from the double-walled tube, the blow moulding tool arrangement may further comprise ejectors. The ejectors may comprise ejection pistons or air valves or "popper valves" in which air pressure is used as an ejection means. Each blow mould and blow mould section may comprise one or a plurality of ejectors. The ejectors may be located in the peripheral regions of the blow molding tool arrangement and thereby act on one end of the moulded double-walled tube. For example, the ejectors may act on a region of the double-walled tube that that is intended to subsequently be covered by further components, such as, for example, an end cap, actuator, or a mouthpiece, in case the ejectors leave

impressions in the wall of the not yet completely cured plastic. Impressions left by the ejectors may adversely influence the appearance of the double-walled tube 1 , and, depending on their severity, may lead to structural weakening of the double- walled tube.

Depending on the material used to form the heating tube, it may be necessary to include the additional step of curing the polymer.

Second example of a method of manufacturing a double-walled tube.

There will now be described a second example of a method of manufacturing a double walled tube 1 such as the one shown in Figure 1.

Referring now first to Figures 3 a to 3f there is illustrated schematically an apparatus for performing steps in a second example of a manufacturing process of a double-walled tube.

The apparatus comprises a mould 200 comprising a first mould section 200a and a second mould section 200b. The first mould section 200a and the second mould section 200b face each other and define a first mould opening 200c at a first end of the mould 200 and a second mould opening 200d at a second end of the mould 200. The apparatus further comprises an extruding device comprising an extruding head 202 which faces the first mould opening 200c. The extruding head 202 comprises concentric outer 202a and inner 202b annular extrusion ports.

In a first step, illustrated in Figure 3a, the first mould section 200a and the second mould section 200b are in an open configuration and the extruding head 202 is arranged to extrude an inner extruded tube 102 and an outer extruded tube 103 into a mould cavity 208 defined by the first mould section 200a and the second mould section 200b. The outer extruded tube 103 is extruded from the outer extrusion port 202a and the inner extruded tube 102 is extruded from the inner extrusion port 202b and both extend into the first mould opening 200c, through the mould cavity 208 and out of the second mould opening 200d. The inner extruded tube 102 is arranged co-axially in the outer extruded tube 103 so that an annular tube cavity 104 is defined between the two.

The inner extruded tube 102 and an outer extruded tube 103 may comprise, for example, any of the thermo -plastic materials described above with respect to the first example.

In a second step, illustrated in Figure 3b, the first mould section 200a and the second mould section 200b are moved towards one another (as indicated by the Arrows B) into a closed configuration in which the mould 200 is closed around the outer extruded tube 103 and the inner extruded tube 102 so that the mould cavity 208 is substantially sealed off at the first and second ends.

In a third step, illustrated in Figure 3c, vacuum generating apparatus (not shown), for example, a vacuum pump, applies a vacuum to the mould cavity 208 by drawing air out of the mould cavity 208 (as indicated by the Arrows C) via an arrangement of venting channels 210 which connect the mould cavity 208 to the exterior of the mould 200. The vacuum applied to the mould cavity 208 results in a pressure differential being generated across the outer extruded tube 103 between the annular tube cavity 107 and the mould cavity 208 (the pressure in the annular tube cavity 107 is higher than that in the mould cavity 208) which causes the outer extruded tube 103, within the mould cavity 208, to be moulded against an inner surface 211 of the mould 200.

In a fourth step, illustrated in Figure 3d, a first bonding tool 212 bonds together the outer extruded tube 103 and the inner extruded tube 102 in the vicinity of the second mould opening 200d so as to close off the annular tube cavity 104 at one end. This bonding may be achieved in any one of a number of ways, for example, by using a friction welding technique such as spin welding, by laser welding, by ultrasonic welding, by gluing or by using residual heat from the extrusion process itself.

In a fifth step, also illustrated in Figure 3d, a heat source, e.g. a material that can be activated to provide heat 12 is filled into the annular tube cavity 104 through an open end of the annular tube cavity 104 as indicated by the arrow E. In one example, filling the annular tube cavity 104 with the material for providing heat 12 causes air to be vented from the annular tube cavity 104 as indicated by the arrow F. In a further example, air may be vented from the annular tube cavity 104 prior to filing it with the material for providing heat 12.

When the annular tube cavity 104 is being filled with material for providing heat 12, the inner extruded tube 102 may be supported so as to prevent pressure changes causing unwanted deformation of the inner extruded tube 102. For example, the inner extruded tube 102 may be supported by being filled with pressurised fluid, for example air.

Alternatively, the inner extruded tube 102 may be supported by a support member, for example, a mandrel inserted into the longitudinal cavity of the inner extruded tube 102.

As described above with respect to the first example of manufacturing a double walled tool, the material for providing heat 12 may be a phase change material that releases heat upon changing physical states. Accordingly, the material for providing heat 12 that is filled into the annular tube cavity 104 may be a liquid that generates heat if a phase change to the solid state is induced. Examples of suitable materials, for example, hydrated salts, have been given previously.

In a sixth step, illustrated in Figure 3e, a second bonding tool 214 bonds together the outer extruded tube 103 and the inner extruded tube 102 in the vicinity of the first mould opening 200d so as to close off the annular tube cavity 104 at a second end so that the annular tube cavity 107 is closed at both the first end and the second end and the material for providing heat 112 is sealed in the annular tube cavity 107. This bonding may be achieved using any of the techniques described above with respect to the fourth step. In a seventh step, illustrated in Figure 3f, first 216 and second 218 cutters are used to cut through the outer extruded tube 103 and the inner extruded tube 103 at the first and second ends respectively in order to remove waste tubing from each end. The cuts are made through regions at which the outer extruded tube 103 and the inner extruded tube 102 are bonded together and leave the inner extruded tube 102 open at both ends.

This seventh step results in a double walled tube similar to that described with respect to Figure 1 (although prefilled with a material for providing heat 12) which is then ejected from the mould 200.

Each of one or more of the manufacturing steps described with respect to Figures 3 a to 3f may be implemented by a different stage of a Rotary Wheel production apparatus (not shown) with the Rotary Wheel rotating to move a double walled tube that is being manufactured from one stage to the next. In this way, the Rotary Wheel production apparatus may handle the manufacturing of multiple double walled tubes

simultaneously, with each of the double walled tubes in the machine at a given time being at a different stage of manufacture. This arrangement may facilitate providing a high output of double walled tubes.

Referring now to Figures 4a to 4e, there are schematically illustrated steps by which such a double walled tube 1 is used as the starting point to assemble or manufacture a device 7 similar to that described above with respect to Figure 2. In a first step, illustrated in Figure 4a, an actuator 17 for actuating the material for providing heat 12 is attached, as indicated by the arrow G, to an outer tube 3. As explained with reference to Figure 2 above, the exact nature of the actuator 17 will depend upon the nature of the material for providing heat 12.

In some examples, the region of the outer tube 103 to which the actuator 17 is attached is thinner than the remainder of the outer tube 103. This is advantageous if the actuator 17 comprises a component, for example, a sharp point, that must penetrate through the outer tube 103, when the actuator is actuated, in order to initiate a process for causing a phase change of the material 12. The thickness of this region may be controlled by suitably moving a die and pin in the extrusion head during the extrusion process (this is referred to in the art as 'wall thickness control') or by creating a secondary draw area in the mould cavity.

In a second step, illustrated in Figure 4b, a vent cap 13 is attached as indicated by the arrow H, for example by snap fitting, to a second end of the double walled tube 1.

In a third step, illustrated in Figure 4c, a smokeable material 11 is inserted, as indicated by the arrow I, for example, pushed into the longitudinal cavity of the inner tube 2 through its open end. The smoking material 11 may take any of the forms described above.

In a fourth step, illustrated in Figure 4d, a mouthpiece 15 is attached over the end of the double walled tube 1, as indicated by the arrow J, to provide a completed device 7, as shown in Figure 4e. In this example, the vent cap 13 and the mouthpiece 15 are separate components to the double walled tube 1 and are assembled onto the double walled tube 1 after the extrusion and moulding process described above. In other examples, either or both of the vent cap 13 and the mouthpiece 15 are formed integrally with the double walled tube 1 during the extrusion and moulding process described above, for example, by using a suitably shaped mould.

Although in the above described examples, the double walled tubes are configured for use as a heating tube with the annular space defined between the inner and outer tubes configured to contain a material that can be activated to act as a heat source, alternatively, the double walled tubes may be configured for use as a cooling tube with the annular space defined between the inner and outer tubes configured to comprise a material that can be activated to act as a coolant. The material may be activated to cool a further material contained in the central longitudinal cavity of the double walled tool. The material that can be activated to act as a coolant may again be a phase change material.

Embodiments of the invention are configured to comply with applicable laws and/or regulations, such as, by way of non-limiting example, regulations relating to flavours, additives, emissions, constituents, and/or the like. For example, the invention may be configured such that a device implementing the invention is compliant with applicable regulations before and after adjustment by a user. Such implementations may be configured to be compliant with applicable regulations in all user-selectable positions. In some embodiments, the configuration is such that a device implementing the invention meets or exceeds required regulatory test(s) in all user-selectable positions, such as, by way of non-limiting example, the testing threshold(s)/ceiling(s) for emissions and/or smoke constituents.

The various embodiments described herein are presented only to assist in

understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.