Progressive modulated channel die casting box

Abstract

A slurry casting box for casting a layer of slurry onto a moving surface, the slurry casting box comprising: a main body portion extending along a longitudinal axis, the main body portion comprising: a rear wall extending along the longitudinal axis, and a top wall extending along the longitudinal axis; first and second side walls substantially transverse to the longitudinal axis; and a cover portion extending along the longitudinal axis, the cover portion defining a front wall of the slurry casting box; wherein the cover portion is movable relative to the main body portion so as to permit access to an interior of the slurry casting box; wherein the top wall of the main body portion comprises at least one inlet for slurry; wherein the slurry casting box is provided with an elongate slot on a bottom of the slurry casting box, the elongate slot extending along the longitudinal axis, and the elongate slot defining an outlet for slurry; wherein the cover portion is configured to be mountable on the main body portion so as to define, together with the rear wall, the top wall and the first and second side walls, an internal volume that is hermetically sealed except for the at least one inlet and the outlet; and wherein the cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, is positionally adjustable closer to or further from the rear wall of the main body portion while maintaining a hermetic seal with the main body portion so as to allow an internal shape of the internal volume to be adjusted.

Description

[0001] PROGRESSIVE MODULATED CHANNEL DIE CASTING BOX

[0002] The present disclosure relates to a slurry casting box for casting a layer of slurry onto a moving surface, and also to a method of casting a layer of slurry onto a moving surface.

[0003] In the manufacture of aerosol-generating articles, such as rod-shaped heat-not-burn tobacco sticks, it is known to use sheets of aerosol-generating substrate. Such aerosolgenerating substate sheets may be made from a slurry comprising homogenised tobacco or other botanicals, along with various additives to form the slurry. The slurry is then cast onto a moving surface and dried so as to form a sheet. The dried sheet may be much longer than it is wide, and is often rolled onto a bobbin. In subsequent manufacturing steps, the sheet may be unwound from the bobbin before being crimped, gathered and wrapped so as to define a rod-shaped element that will release an aerosol upon heating.

[0004] It is known to form sheets by conveying and homogeneously distributing a slurry through a casting box having an elongate slot at a bottom of the casting box, the elongate slot being disposed generally transverse to a moving belt (usually a metallic belt, for example made of Food and Drug Administration (FDA) Food & Beverage grade stainless steel alloy). The slurry may be cast to a relatively even thickness by way of a casting blade or doctor blade, as shown in schematic form in Figure 1 .

[0005] Figure 1 shows a casting box 5 with a rear wall 6 and a front wall 7, and a doctor blade 8 formed at a bottom edge of the front wall. The bottom of the casting box 5 has an opening 9 transverse to a direction of travel of a moving belt 10. A slurry 4 is fed into an open top of the casting box 5 by way of a slurry feed 11 , and the slurry 4 passes out of the opening 9 under gravity so as to be spread relatively evenly onto the moving belt 10 to a thickness T by the doctor blade 8.

[0006] Although this method of casting slurry is relatively simple, there are several drawbacks.

[0007] Firstly, there is significant exposure of the slurry 4 to ambient air at the open top of the casting box 5, which means that the temperature of the slurry 4 can be difficult to control. Moreover, there is a risk of the slurry forming dried residue on portions of the inside of the casting box 5, including the opening 9 and the doctor blade 8, which can lead to quality control problems such as streaking or uneven application of slurry to the moving belt 10. In addition, the formation of dried slurry residue can lead to the release of “noodles” of slurry, potentially causing unwanted lifting of the doctor blade 8 relative to the moving belt 10 and a consequent variation in the thickness of the layer of slurry cast onto the moving belt 10, leading to a sheet of uneven thickness.

[0008] Secondly, the geometrical and dimensional configuration of the casting box 5 is designed for a gravity-driven flow of slurry. Gravity-driven flows tend to have slow fluid mechanics, with an attendant risk of non-uniform fluidity and accumulation of material over time. The slow fluid mechanics may also promote the formation over time of dried residue on portions of the casting box where the slurry is exposed to air. It will be noted that the opening 9 has a has a large area (in particular, the width from front to back is large) so as to allow the slow gravity-driven slurry feed to pass through the opening 9.

[0009] Thirdly, exposure to air also has the potential risk of contamination of the slurry, for example by microorganisms in the surrounding air or present in cellulosic components of the slurry derived from natural sources. This microbial contamination can lead to fermentation of the slurry or other unwanted biological processes.

[0010] In order to address these drawbacks, it is necessary to perform thorough and regular cleaning of all slurry pipelines, casting box components and other components of the slurry casting system.

[0011] Another known method of casting slurry is shown in schematic form in Figure 2. In this method, a closed casting box 12 is used. The closed casting box 12 is not open to ambient air, other than at a casting die 13 formed by an elongate slot at the bottom of the casting box 12 from which slurry 4 is cast onto a moving belt 10. Slurry 4 is pumped into a top of the closed casting box 12 by way of an extruder 14, for example a dual screw extruder. The width (from front to back) of the elongate slot of the casting die 13 is significantly less than that of the opening 9 in the Figure 1 system. This is because the Figure 2 system uses the extruder 14 to pump the slurry 4 under pressure into the closed casting box 12 and through the casting die 13. It will be noted that the casting die 13 removes the need for a doctor blade.

[0012] While the system of Figure 2 reduces contact of the slurry 4 with ambient air prior to casting, and avoids problems arising from dried residue on the doctor blade, there remain a number of drawbacks.

[0013] For example, the arrangement of Figure 2 requires a high-pressure slurry supply upstream in the form an extruder 14, in order to ensure that a sufficient volume of slurry 4 is supplied to the closed casting box 12 at a defined pressure. Extruders 14 can be difficult to manage, and there is no managed distribution of the output of the extruder 14 in the closed casting box 12. This can result in non-uniform fluidity and flow of the slurry 4, including substantially stagnant volumes of slurry 4 in corner portions of the interior of the closed casting box 12. Such substantially stagnant volumes of slurry 4 may form volumes where microbial contamination can lead to fermentation of the slurry. Moreover, even where the microbial load is low and does not lead to fermentation, the presence of enzymes intrinsic to the tobacco in the slurry 4 can lead to degradation of the slurry 4. Such degradation may be particularly noted at temperatures of around 50 degrees Celsius, since these are optimum temperatures for mannanase enzyme activity.

[0014] Extruder pump systems such as that shown in Figure 2 tend to be expensive and complex systems requiring a horizontal gravity-driven feeding box 15 and horizontal installation, which can take up valuable real estate in a factory. Extruders require regular and expensive maintenance due to the wear of the screws that function based on tight tolerances, especially when operating with abrasive slurries with a high silica content, such as slurries containing tobacco leaves and particles. Extruder pump systems as shown in Figure 2 contain a large volume of slurry when operating, and if the extruder pump system needs to be stopped for maintenance, this large volume of slurry will be wasted. Extruder pump systems as shown in Figure 2 only allow pumping in a forward direction, and do not permit reverse pumping in order to discharge the extruder pump. Another disadvantage with extruder pump systems is that accurate slurry metering is difficult, since there is often not a direct and accurate relationship between a number of revolutions of the extruder screws with the volume being pumped.

[0015] According to a first aspect of the present invention, there is provided a slurry casting box for casting a layer of slurry onto a moving surface, the slurry casting box comprising: a main body portion extending along a longitudinal axis, the main body portion comprising: a rear wall extending along the longitudinal axis, and a top wall extending along the longitudinal axis; first and second side walls substantially transverse to the longitudinal axis; and a cover portion extending along the longitudinal axis, the cover portion defining a front wall of the slurry casting box; wherein the cover portion is movable relative to the main body portion so as to permit access to an interior of the slurry casting box; wherein the top wall of the main body portion comprises at least one inlet for slurry; wherein the slurry casting box is provided with an elongate slot on a bottom of the slurry casting box, the elongate slot extending along the longitudinal axis, and the elongate slot defining an outlet for slurry; and wherein the cover portion is configured to be mountable on the main body portion so as to define, together with the rear wall, the top wall and the first and second side walls, an internal volume that is hermetically sealed except for the at least one inlet and the outlet.

[0016] By providing a moveable cover portion that permits access to the interior of the slurry casting box, cleaning of the interior of the slurry casting box is facilitated, while still maintaining a hermetically sealed interior volume during casting of the slurry.

[0017] Configuring the slurry casting box so that the internal volume is hermetically sealed except for the at least one inlet and the outlet helps to reduce exposure of the slurry to air until after the slurry has been cast. This can help to reduce unwanted drying of the slurry inside the slurry casting box. This can also help to lessen the risk of unwanted microbial contamination.

[0018] The cover portion may be hingedly mounted on the main body portion. The cover portion may be hingedly mounted on the main body portion along a hinge line that is substantially parallel to the longitudinal axis. The cover portion may be hingedly connected to the top wall of the main body portion. This may allow a spacing of a lower edge of the cover portion relative to a lower edge of the rear wall of the main body portion easily to be adjusted so as to allow a front-to-back width of the elongate slot to be adjusted. Alternatively, the cover portion may be hingedly connected to a lower part of the main body portion. This may facilitate access to an interior of the slurry casting box for cleaning.

[0019] The first and second side walls may form parts of the main body portion.

[0020] Alternatively, the first and second side walls may form parts of the cover portion.

[0021] Alternatively, the first side wall may form part of the main body portion and the second side wall may form part of the cover portion.

[0022] The cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, may be positionally adjustable so as to allow an internal shape of the internal volume to be adjusted. By changing the internal shape of the internal volume, it may be possible to adjust flow characteristics of slurry flowing through the internal volume of the slurry casting box. This may give a degree of control over speed or thickness when casting the layer of slurry onto the moving surface.

[0023] The cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, may be positionally adjustable closer to or further from the rear wall of the main body portion while maintaining a hermetic seal with the main body portion. This may allow the internal shape of the internal volume to be adjusted. This may allow the front-to-back width of the elongate slot to be adjusted. Such adjustments may enable flow characteristics of slurry flowing through the internal volume of the slurry casting box to be adjusted, and may give a degree of control over speed or thickness when casting the layer of slurry onto the moving surface.

[0024] The cover portion may be positionally adjustable by way of at least one screw mechanism. A plurality of screw mechanisms may be provided along the longitudinal axis. The screw mechanisms may be adjustable independently of each other.

[0025] A surface of the rear wall of the main body portion that faces the internal volume may be a contoured surface with protruded and intruded regions.

[0026] A surface of the front wall of the cover portion that faces the internal volume may be a contoured surface with protruded and intruded regions.

[0027] Advantageously, a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions; a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions; and the contoured surfaces cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box. The fluid pathways defined between the cooperating contoured surfaces may have curved shapes, for example in cross-section and along their lengths, which may help to improve flow characteristics of slurry flowing through the internal volume of the slurry casting box. In particular, it may be possible to avoid stagnant regions or regions of poor flow, and this in turn can reduce the risk of the slurry drying out in regions of the internal volume of the slurry casting box and causing blockages. Moreover, it may be possible to avoid stagnant regions of slurry inside the slurry casting box where fermentation or other unwanted microbial activity might otherwise take place.

[0028] The top wall may comprise a plurality of inlets, and the contoured surface of the rear wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0029] The top wall may comprise a plurality of inlets, and the contoured surface of the front wall may comprises a plurality of hills, each hill being disposed under a respective one of the inlets.

[0030] The top wall may comprise a plurality of inlets, and the contoured surface of the rear wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets.

[0031] The top wall may comprise a plurality of inlets, and the contoured surface of the front wall may comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0032] Advantageously, the top wall may comprise a plurality of inlets; the contoured surface of the rear wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; the contoured surface of the front wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets; and the fluid pathways may be defined between the spurs and the hills.

[0033] Alternatively advantageously, the top wall may comprise a plurality of inlets; the contoured surface of the rear wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets; the contoured surface of the front wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; and the fluid pathways may be defined between the spurs and the hills.

[0034] The fluid pathways thus defined may help to avoid stagnant regions or regions of poor flow, and this in turn can reduce the risk of the slurry drying out in regions of the internal volume of the slurry casting box and causing blockages, or stagnant regions where the slurry might ferment or undergo other unwanted microbial activity.

[0035] By providing a plurality of inlets in the top wall, it may be possible to provide a more evenly- distributed flow of slurry through the slurry casting box. The plurality of inlets are preferably distributed along the top wall. The plurality of inlets may be substantially evenly distributed along the top wall.

[0036] The main body portion may comprise a temperature adjustment mechanism. The cover portion may comprise a temperature adjustment mechanism. The temperature adjustment mechanism may comprise internal channels in the rear wall or the front wall or both the rear wall and the front wall for passage of a thermal transfer fluid. The temperature adjustment mechanism may comprise electric heating elements in the rear wall or the front wall or both the rear wall and the front wall. By heating or cooling the slurry, it may be possible to adjust flow characteristics of the slurry flowing through the internal volume of the slurry casting box, and this may give a degree of control over speed or thickness when casting the layer of slurry onto the moving surface. For example, heating the slurry may make the slurry less viscous. For example, cooling the slurry may make the slurry more viscous.

[0037] The slurry casting box may further comprise at least one temperature sensor for determining a slurry temperature. The slurry casting box may further comprise a temperature controller connected to the at least one temperature sensor and the temperature adjustment mechanism and configured to maintain or adjust a temperature profile in the slurry. This may provide good control of slurry viscosity and flow characteristics.

[0038] The slurry casting box may further comprise at least one pressure sensor for determining a slurry pressure in the internal volume. Slurry pressure can also influence flow characteristics, including for example viscosity.

[0039] A width of the elongate slot transverse to the longitudinal axis may be adjustable. The width of the elongate slot may be adjustable by moving the cover portion relative to the main body portion. Adjusting the width of the elongate slot may give a degree of control over speed or thickness when casting the layer of slurry onto the moving surface.

[0040] The main body portion and the cover portion may be made of metal. Metal is a good thermal conductor, and this can allow control of the temperature of the slurry. The main body portion and the cover portion may be made of stainless steel. This can help to reduce corrosion and may also reduce the risk of slurry sticking to corroded parts during passage through the slurry casting box.

[0041] The slurry casting box may further comprise at least one clamp mechanism to secure the cover portion in position on the main body portion to define the internal volume. The clamp mechanism may assist in maintaining a hermetic seal between the front cover portion and the main body portion, even when slurry is pumped through the slurry casting box at high pressure.

[0042] An outer surface of the rear surface of the main body and an outer surface of the cover portion may be closer to each other at the bottom of the slurry casting box than at the top wall of the slurry casting box. The slurry casting box as a whole may have a wedge-shaped crosssection across the longitudinal axis, being wider at the top than at the bottom. The internal volume may have a cross-section orthogonal to the longitudinal axis that becomes progressively narrower from top to bottom. This can help to promote slurry flow through the internal volume of the slurry casting box, with pressure being applied at the at least one inlet by the supply of slurry, which may be pumped. The pressure at the at least one inlet forces the slurry to flow through the internal volume and out through the elongate slot. The progressive narrowing of the cross-section of the internal volume from the top wall towards the elongate slot helps to maintain the pressure profile by progressively compressing the slurry.

[0043] The at least one inlet may be connected to a progressive cavity slurry pump. In embodiments comprising a plurality of inlets, each inlet may be connected to an individual progressive cavity slurry pump. In one example, the slurry casting box may comprise at least four inlets, wherein each inlet is connected to an individual progressive cavity slurry pump. Providing a plurality of inlets may allow for a more even flow of slurry over the length of the slurry casting box along the longitudinal axis. The inlets may be substantially evenly spaced from each other along the top wall of the main body along the longitudinal axis. This can help to promote even slurry flow.

[0044] It has been found that progressive cavity pumps provide several surprising technical advantages over extruder pumps that are more usually employed with slurry casting boxes. Extruder pumps tend to be mechanically complex, which can result in unreliability and high maintenance costs and times. Mechanical complexity is also associated with greater equipment cost. Extruder pumps with many moving mechanical parts can be subject to wear, especially when operating on slurries at high pressure. Extruder pumps tend to have high energy consumption, especially when operating at high pressure. All of these disadvantages can lead to greater expense, more stoppages, costly maintenance and higher wastage of valuable slurry.

[0045] A progressive cavity pump is a type of positive displacement pump in which an elongate helical rotor, driven by an eccentrically-mounted driveshaft, is rotated within a stator formed as an elastomeric sleeve that fits around the elongate helical rotor. The inside of the elastomeric sleeve may present an inner surface with a helix pattern complementary to the elongate helical rotor. When the helical rotor is rotated, it rolls around the inner surface of the elastomeric sleeve stator. The motion of the helical rotor may be considered to be similar to that of planet gears in a planetary gears system. As the helical rotor simultaneously rotates and moves around, the combined motion of the eccentrically-mounted drive shaft is in the form of a hypocycloid. The helical rotor must be driven through universal joints or other mechanisms to allow for the eccentricity. The eccentricity and the universal joints allow some lateral movement of the helical rotor relative to a longitudinal axis of the elastomeric sleeve stator. When the helical rotor is rotated within the elastomeric sleeve, a sequence of partially helical cavities defined between an outer surface of the rotating stator and the inner surface of the elastomeric sleeve move from a first end of the progressive cavity pump to a second end of the progressive cavity pump. The partially helical cavities are effectively sealed within the progressive cavity pump due to engagement between points on the outer surface of the rotating stator and points on the inner surface of the elastomeric sleeve. Each partially helical cavity thus defines a discrete volume, and the discrete volume can be used to contain and move a fluid from the first end of the progressive cavity pump to the second end of the progressive cavity pump. In this sense, movement of the fluid is effectively by positive displacement, rather like a piston pump. Indeed, similarly to a piston pump, a progressive cavity pump can pump at very low rates, even to high pressure.

[0046] In contrast to extruder pumps, which are generally horizontally-mounted and require a gravity feed box at one end to supply slurry for pumping, progressive cavity pumps can be mounted vertically (with the longitudinal axis of the helical rotor and the elastomeric sleeve stator vertical). This provides an advantage of a smaller footprint on a factory floor. Moreover, progressive cavity pumps can be fed at the first end using a direct piping inlet, and do not require a gravity feed box. This can reduce exposure of the slurry to ambient air, and thus reduce contamination or unwanted drying. Another advantage of progressive cavity pumps over extruder pumps is that there is less wear, especially with abrasive high-silica slurries, such as tobacco slurries, and this leads to a reduction in required maintenance. The high wear in a dual-screw extruder pump arises from the squeezing abrasive slurry between the moving screw shafts at tight tolerances. In addition, an extruder pump will contain a large volume of slurry as a continuous mass at any given time. As a result, if the extruder pump has to be stopped for a long period of time, a large volume of valuable slurry may have to be discarded as waste. A progressive cavity pump, on the other hand, only contains small volumes of slurry at any one time within the cavities. A progressive cavity pump can be operated in both forward and reverse directions, whereas an extruder pump will normally only be operable in a forward direction. Finally, it is difficult to meter throughput of an extruder pump because there is often not an accurate relationship between the rotational speed of the extruder screws and the volume of slurry being pumped. In contrast, a progressive cavity pump allows accurate metering, since the volume of each cavity is known and the positive displacement of the cavities and the slurry contained in the cavities is directly proportional to the rotational speed of the helical rotor.

[0047] Accordingly, a combination of at least one progressive cavity pump and a hermetically sealed slurry casting box may provide significant advantages in terms of protecting the slurry from contamination from ambient air and avoiding non-optimal fluid mechanics due to sharp edges, corners and stagnation zones.

[0048] The slurry casting box may further comprise at least one pressure sensor for determining a slurry pressure in the internal volume, and a pressure controller connected to the at least one pressure sensor and to the progressive cavity slurry pumps and configured to maintain or adjust a pressure profile in the slurry. As noted above, flow characteristics of the slurry flowing through the internal volume of the slurry casting box may vary with pressure. For instance, rheological properties such as viscosity can change with pressure. For example, viscosity may depend on shear rate, which can be affected by the pressure drop across the slurry casting box from the at least one inlet to the elongate slit. Additionally, detection of an unexpectedly high pressure might indicate a blockage, and can generate a warning signal or initiate a shut-down procedure so that the slurry casting box can be opened and inspected for cleaning or maintenance.

[0049] According to a second aspect of the present invention, there is provided a method of casting a layer of slurry onto a moving surface, comprising the steps of: i) providing a slurry casting box of the first aspect; ii) pumping slurry into the at least one inlet; and iii) casting slurry onto the moving surface through the elongate slit.

[0050] The slurry may be pumped into the at least one inlet by at least one progressive cavity pump. Using at least one progressive cavity pump may provide advantages as described above in relation to the first aspect of the invention.

[0051] The slurry may comprise ingredients selected from the list comprising: water, ground botanical materials or other nicotine containing materials, fibres, for instance cellulose fibres, an aerosol former, for instance glycerine, and a binder, for instance guar. The ground botanical materials may consist of or comprise ground tobacco.

[0052] A surface of the rear wall of the main body portion that faces the internal volume may be a contoured surface with protruded and intruded regions.

[0053] A surface of the front wall of the cover portion that faces the internal volume may be a contoured surface with protruded and intruded regions.

[0054] Advantageously, a surface of the rear wall of the main body portion that faces the internal volume may be a contoured surface with protruded and intruded regions; a surface of the front wall of the cover portion that faces the internal volume may be a contoured surface with protruded and intruded regions; the contoured surfaces may cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box; and the slurry may pass along the fluid pathways from the at least one inlet to the elongate slit. The fluid pathways defined between the cooperating contoured surfaces may have curved shapes, for example in cross-section and along their lengths, which may help to improve flow characteristics of slurry flowing through the internal volume of the slurry casting box. In particular, it may be possible to avoid stagnant regions or regions of poor flow, and this in turn can reduce the risk of the slurry drying out in regions of the internal volume of the slurry casting box and causing blockages. Moreover, it may be possible to avoid stagnant regions of slurry inside the slurry casting box where fermentation or other unwanted microbial activity might otherwise take place.

[0055] The top wall may comprises a plurality of inlets. By providing a plurality of inlets in the top wall, it may be possible to provide a more evenly-distributed flow of slurry through the slurry casting box. The plurality of inlets are preferably distributed along the top wall. The plurality of inlets may be substantially evenly distributed along the top wall. The contoured surface of the rear wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets. The contoured surface of the rear wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets.

[0056] Alternatively, the contoured surface of the front wall may comprise a plurality of downwardly- extending spurs, each spur being disposed between an adjacent pair of inlets. The contoured surface of the front wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets.

[0057] The contoured surface of the rear wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; the contoured surface of the front wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets; the plurality of downwardly-extending spurs of the contoured surface of the rear wall may cooperate with the plurality of hills of the contoured surface of the front wall when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the plurality of inlets and the outlet of the slurry casting box; and the slurry may pass along the fluid pathways from the plurality of inlets to the elongate slit.

[0058] Alternatively, the contoured surface of the rear wall may comprise a plurality of hills, each hill being disposed under a respective one of the inlets; the contoured surface of the front wall may comprise a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; the plurality of hills of the contoured surface of the rear wall may cooperate with the plurality of downwardly-extending spurs of the contoured surface of the front wall when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the plurality of inlets and the outlet of the slurry casting box; and the slurry may pass along the fluid pathways from the plurality of inlets to the elongate slit.

[0059] Passing the slurry along the fluid pathways thus defined may help to avoid stagnant regions or regions of poor flow, and this in turn can reduce the risk of the slurry drying out in regions of the internal volume of the slurry casting box and causing blockages, or stagnant regions where the slurry might ferment or undergo other unwanted microbial activity.

[0060] A temperature profile of the slurry in the slurry casting box may be controlled by a temperature adjustment mechanism. The temperature adjustment mechanism may comprise internal channels in the rear wall or the front wall or both the rear wall and the front wall, and a thermal transfer fluid may be passed through the internal channels. The thermal transfer fluid may be water or another liquid that is heated or cooled to a required temperate by a heater or cooler. The temperature adjustment mechanism may comprise electric heating elements in the rear wall or the front wall or both the rear wall and the front wall, and the electric heating elements may be selectively activated or deactivated to control the temperature profile of the slurry.

[0061] The temperature adjustment mechanism may be configured to heat the rear wall or the front wall or both the rear wall and the front wall of the slurry casting box to a desired temperature. The desired temperature may be a temperature of 20 to 60 degrees Celsius. In some embodiments, the desired temperature may be a temperature of 40 to 60 degrees Celsius, for example 50 to 55 degrees Celsius.

[0062] A slurry temperature may be determined by at least one temperature sensor. The temperature profile of the slurry may be controlled or adjusted by a temperature controller connected to the at least one temperature sensor and the temperature adjustment mechanism.

[0063] The slurry may have a temperature of 20 to 60 degrees Celsius, preferably 21 to 42 degrees Celsius.

[0064] The slurry may have a d90 granulometry of 40 to 90 micrometres, preferably 44 to 70 micrometres.

[0065] A pressure profile of the slurry in the slurry casting box may be controlled by a pressure adjustment mechanism. A slurry pressure may be determined by at least one pressure sensor. The pressure profile of the slurry may be controlled or adjusted by a pressure controller connected to the at least one pressure sensor and to at least one pump that pumps slurry into the at least one inlet.

[0066] By adjusting a temperature profile of the slurry in the slurry casting box, or a pressure profile of the slurry in the slurry casting box, or both a temperature profile and a pressure profile of the slurry in the slurry casting box, it may be possible to adjust rheological properties of the slurry in a desired manner so as to obtain a desired thickness or quality of casting onto the moving surface.

[0067] The slurry may have a density of 880 to 1310 grammes per cubic centimetre, preferably 910 to 1270 kilogrammes per cubic metre.

[0068] The slurry may have a viscosity of 1500 to 5000 centipoises at a shear rate of 100 hertz, preferably 2000 to 4000 centipoises.

[0069] The exemplary density and viscosity values may be for a slurry temperature of 35 degrees Celsius.

[0070] The slurry casting box and the progressive cavity pumps may enable slurry to be passed through the slurry casting box at a very controlled pressure and temperature. The flow of slurry through the slurry casting box may be homogeneously modulated from a predominantly cylindrical flow coming out of the progressive cavity pump through an inlets, to an even ribbon-like linear flow emerging from the elongate slot. The slurry passes along flow paths that progressively change shape and orientation, avoiding sharp corners and stagnation zones, so as to avoid unwanted drying of the slurry within the slurry casting box, and to avoid stagnant areas where microbial contamination may lead to unwanted fermentation. The temperature of the slurry can be carefully controlled. The pressure of the slurry can also be carefully controlled. This assures that all the slurry is always flowing from the originally cylindrical upstream flow from the progressive cavity pump, through the flow paths that progressively modulate and convey the slurry to a thin linear consistent and uniform flow downstream.

[0071] The provision of a slurry casting box having a main body portion and a cover portion that can be opened relative to the main body portion provides the advantage of a hermetically sealed system during operation, while facilitating cleaning by allowing access to an interior volume of the slurry casting box when required.

[0072] Slurries used in the tobacco industry are predominantly non-Newtonian, and as such, the viscosities of such slurries can vary with shear stress. Accordingly, the flow properties of such slurries can be strongly affected by geometrical and dimensional aspects of a volumetric space through which the slurries are caused to flow. In order to obtain adequate controlled flow of rheological or non-Newtonian slurries, it is best to avoid sharp corners, right-angled bends and large volumetric spaces where stagnation can occur. Accordingly, the slurry casting box of embodiments of the present invention provides a hermetically sealed (except for the inlets and outlet) volume with flow paths defined by shaping or contouring of facing inner surfaces of the slurry casting box so as to provide a smooth transition from cylindrical flow coming out of the pumps to linear flow emerging from the elongate slot. The flow paths through the internal volume are configured to promote a consistent and homogeneous mass flow of slurry through a controlled cross-section so as to provide an even and controlled casting of slurry through the elongate slot without the formation of noodles or other unwanted irregularities.

[0073] In the context of the present disclosure, the term “hermetically sealed” is intended to describe two portions that are joined together such that slurry cannot escape through the join, even under elevated pressure.

[0074] In the context of the present disclosure, the term “hill” is intended to mean a protruding portion of a contoured surface that is higher than surrounding portions of the contoured surface.

[0075] In the context of the present disclosure, the term “spur” is intended to mean a protruding portion of a contoured surface that slopes from a higher region to a lower region, becoming narrower in width as the spur descends from the higher region.

[0076] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0077] Example Ex1 : A slurry casting box for casting a layer of slurry onto a moving surface, the slurry casting box comprising: a main body portion extending along a longitudinal axis, the main body portion comprising: a rear wall extending along the longitudinal axis, and a top wall extending along the longitudinal axis; first and second side walls substantially transverse to the longitudinal axis; and a cover portion extending along the longitudinal axis, the cover portion defining a front wall of the slurry casting box; wherein the cover portion is movable relative to the main body portion so as to permit access to an interior of the slurry casting box; wherein the top wall of the main body portion comprises at least one inlet for slurry; wherein the slurry casting box is provided with an elongate slot on a bottom of the slurry casting box, the elongate slot extending along the longitudinal axis, and the elongate slot defining an outlet for slurry; and wherein the cover portion is configured to be mountable on the main body portion so as to define, together with the rear wall, the top wall and the first and second side walls, an internal volume that is hermetically sealed except for the at least one inlet and the outlet.

[0078] Example Ex2: The slurry casting box of Example Ex1 , wherein the cover portion is hingedly mounted on the main body portion.

[0079] Example Ex3: The slurry casting box of Example Ex2, wherein the cover portion is hingedly mounted on the main body portion along a hinge line that is substantially parallel to the longitudinal axis.

[0080] Example Ex4: The slurry casting box of Example Ex3, wherein the cover portion is hingedly connected to the top wall of the main body portion.

[0081] Example Ex5: The slurry casting box of Example Ex3, wherein the cover portion is hingedly connected to a lower part of the main body portion.

[0082] Example Ex6: The slurry casting box of any preceding Example, wherein the first and second side walls form parts of the main body portion.

[0083] Example Ex7: The slurry casting box of any one of Examples Ex1 to Ex5, wherein the first and second side walls form parts of the cover portion.

[0084] Example Ex8: The slurry casting box of any one of Examples Ex1 to Ex5, wherein the first side wall forms part of the main body portion and the second side wall forms part of the cover portion.

[0085] Example Ex9: The slurry casting box of any preceding Example, wherein the cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, is positionally adjustable so as to allow an internal shape of the internal volume to be adjusted.

[0086] Example Ex10: The slurry casting box of Example Ex9, wherein the cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, is positionally adjustable closer to or further from the rear wall of the main body portion while maintaining a hermetic seal with the main body portion.

[0087] Example Ex11 : The slurry casting box of Example Ex8 or Ex9, wherein the cover portion is positionally adjustable by way of at least one screw mechanism. Example Ex12: The slurry casting box of any preceding Example, wherein a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions.

[0088] Example Ex13: The slurry casting box of any preceding Example, wherein a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions.

[0089] Example Ex14: The slurry casting box of any one of Examples Ex1 to Ex11 , wherein: a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions; wherein a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions; and wherein the contoured surfaces cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box.

[0090] Example Ex15: The slurry casting box of Example Ex12 or Ex14, wherein the top wall comprises a plurality of inlets, and wherein the contoured surface of the rear wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0091] Example Ex16: The slurry casting box of any one of Examples Ex13 to Ex15, wherein the top wall comprises a plurality of inlets, and wherein the contoured surface of the front wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets.

[0092] Example Ex17: The slurry casting box of Example Ex12 or Ex14, wherein the top wall comprises a plurality of inlets, and wherein the contoured surface of the rear wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets.

[0093] Example Ex18: The slurry casting box of any one of Examples Ex13 to Ex15, wherein the top wall comprises a plurality of inlets, and wherein the contoured surface of the front wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0094] Example Ex19: The slurry casting box of Example Ex14, wherein the top wall comprises a plurality of inlets; wherein the contoured surface of the rear wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; wherein the contoured surface of the front wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; and wherein the fluid pathways are defined between the spurs and the hills.

[0095] Example Ex20: The slurry casting box of Example Ex14, wherein the top wall comprises a plurality of inlets; wherein the contoured surface of the rear wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; wherein the contoured surface of the front wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; and wherein the fluid pathways are defined between the spurs and the hills.

[0096] Example Ex21 : The slurry casting box of any preceding Example, wherein the main body portion comprises a temperature adjustment mechanism.

[0097] Example Ex22: The slurry casting box of any preceding Example, wherein the cover portion comprises a temperature adjustment mechanism.

[0098] Example Ex23: The slurry casting box of Example Ex21 or Ex22, wherein the temperature adjustment mechanism comprises internal channels in the rear wall or the front wall or both the rear wall and the front wall for passage of a thermal transfer fluid.

[0099] Example Ex24: The slurry casting box of Example Ex21 or Ex22, wherein the temperature adjustment mechanism comprises electric heating elements in the rear wall or the front wall or both the rear wall and the front wall.

[0100] Example Ex25: The slurry casting box of any one of Examples Ex21 to Ex24, further comprising at least one temperature sensor for determining a slurry temperature.

[0101] Example Ex26: The slurry casting box of Example Ex25, further comprising a temperature controller connected to the at least one temperature sensor and the temperature adjustment mechanism and configured to maintain or adjust a temperature profile in the slurry.

[0102] Example Ex27: The slurry casting box of any preceding Example, further comprising at least one pressure sensor for determining a slurry pressure in the internal volume.

[0103] Example Ex28: The slurry casting box of any preceding Example, wherein a width of the elongate slot transverse to the longitudinal axis is adjustable.

[0104] Example Ex29: The slurry casting box of Example Ex28, wherein the width of the elongate slot is adjustable by moving the cover portion relative to the main body portion.

[0105] Example Ex30: The slurry casting box of any preceding Example, wherein the main body portion and the cover portion are made of metal.

[0106] Example Ex31 : The slurry casting box of Example Ex30, wherein the main body portion and the cover portion are made of stainless steel.

[0107] Example Ex32: The slurry casting box of any preceding Example, further comprising at least one clamp mechanism to secure the cover portion in position on the main body portion to define the internal volume.

[0108] Example Ex33: The slurry casting box of any preceding Example, wherein an outer surface of the rear surface of the main body and an outer surface of the cover portion are closer to each other at the bottom of the slurry casting box than at the top wall of the slurry casting box.

[0109] Example Ex34: The slurry casting box of any preceding Example, wherein the at least one inlet is connected to a progressive cavity slurry pump. Example Ex35: The slurry casting box of any one of Examples Ex1 to Ex33, comprising a plurality of inlets, and wherein each inlet is connected to an individual progressive cavity slurry pump.

[0110] Example Ex36: The slurry casting box of Example Ex35, comprising at least four inlets, wherein each inlet is connected to an individual progressive cavity slurry pump.

[0111] Example Ex37: The slurry casting box of Example Ex35 or Ex36, wherein the inlets are substantially evenly spaced from each other along the top wall of the main body along the longitudinal axis.

[0112] Example Ex38: The slurry casting box of any one of Examples Ex34 to Ex37, further comprising at least one pressure sensor for determining a slurry pressure in the internal volume, and a pressure controller connected to the at least one pressure sensor and to the progressive cavity slurry pumps and configured to maintain or adjust a pressure profile in the slurry.

[0113] Example Ex39: A method of casting a layer of slurry onto a moving surface, comprising the steps of: i) providing a slurry casting box of any one of Examples Ex1 to Ex38; ii) pumping slurry into the at least one inlet; and iii) casting slurry onto the moving surface through the elongate slit.

[0114] Example Ex40: The method of Example Ex39, wherein the slurry is pumped into the at least one inlet by at least one progressive cavity pump.

[0115] Example Ex41 : The method of Example Ex39 or Ex40, wherein the slurry comprises water, ground botanical materials, fibres, an aerosol former and a binder.

[0116] Example Ex42: The method of Example Ex 41 , wherein the fibres comprise cellulose fibres.

[0117] Example Ex43: The method of Example Ex41 or Ex42, wherein the aerosol former comprises glycerine.

[0118] Example Ex44: The method of any one of Examples Ex41 to Ex43, wherein the binder comprises guar gum.

[0119] Example Ex45: The method of any one of Examples Ex41 to Ex44, wherein the ground botanical materials consist of or comprise ground tobacco.

[0120] Example Ex46: The method of any one of Examples Ex39 to Ex45, wherein a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions.

[0121] Example Ex47: The method of any one of Examples Ex39 to Ex46, wherein a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions.

[0122] Example Ex48: The method of any one of Examples Ex39 to Ex45, wherein: a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions; a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions; and the contoured surfaces cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box; further wherein the slurry passes along the fluid pathways from the at least one inlet to the elongate slit.

[0123] Example Ex49: The method of any one of Examples Ex39 to Ex48, wherein the top wall comprises a plurality of inlets.

[0124] Example Ex50: The method of Example Ex49, wherein the contoured surface of the rear wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0125] Example Ex51 : The method of Example Ex49, wherein the contoured surface of the rear wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets.

[0126] Example Ex52: The method of Example Ex49 or Ex51 , wherein the contoured surface of the front wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets.

[0127] Example Ex53: The method of Example Ex49 or Ex50, wherein the contoured surface of the front wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets.

[0128] Example Ex54: The method of Example Ex49, wherein: the contoured surface of the rear wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; the contoured surface of the front wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; the plurality of downwardly-extending spurs of the contoured surface of the rear wall cooperate with the plurality of hills of the contoured surface of the front wall when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the plurality of inlets and the outlet of the slurry casting box; further wherein the slurry passes along the fluid pathways from the plurality of inlets to the elongate slit.

[0129] Example Ex55: The method of Example Ex49, wherein: the contoured surface of the rear wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; the contoured surface of the front wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; the plurality of hills of the contoured surface of the rear wall cooperate with the plurality of downwardly-extending spurs of the contoured surface of the front wall when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the plurality of inlets and the outlet of the slurry casting box; further wherein the slurry passes along the fluid pathways from the plurality of inlets to the elongate slit.

[0130] Example Ex56: The method of any one of Examples Ex39 to Ex55, wherein a temperature profile of the slurry in the slurry casting box is controlled by a temperature adjustment mechanism.

[0131] Example Ex57: The method of Example Ex56, wherein the temperature adjustment mechanism comprises internal channels in the rear wall or the front wall or both the rear wall and the front wall, and wherein a thermal transfer fluid is passed through the internal channels.

[0132] Example Ex58: The method of Example Ex56, wherein the temperature adjustment mechanism comprises electric heating elements in the rear wall or the front wall or both the rear wall and the front wall, and wherein the electric heating elements are selectively activated or deactivated to control the temperature profile of the slurry.

[0133] Example Ex59: The method of any one of Examples Ex56 to Ex58, wherein a slurry temperature is determined by at least one temperature sensor.

[0134] Example Ex60: The method of Example Ex59, wherein the temperature profile of the slurry is controlled or adjusted by a temperature controller connected to the at least one temperature sensor and the temperature adjustment mechanism.

[0135] Example Ex61 : The method of any one of Examples Ex39 to Ex60, wherein a pressure profile of the slurry in the slurry casting box is controlled by a pressure adjustment mechanism.

[0136] Example Ex62: The method of Example Ex61 , wherein a slurry pressure is determined by at least one pressure sensor.

[0137] Example Ex63: The method of Example Ex62, wherein the pressure profile of the slurry is controlled or adjusted by a pressure controller connected to the at least one pressure sensor and to at least one pump that pumps slurry into the at least one inlet.

[0138] Example Ex64: The method of any one of Examples Ex39 to Ex63, wherein the slurry has a density of 880 to 1310 kilogrammes per cubic metre, preferably 910 to 1270 kilogrammes per cubic metre.

[0139] Example Ex65: The method of any one of Examples Ex39 to Ex64, wherein the slurry has a viscosity of 1500 to 5000 centipoises at a shear rate of 100 hertz, preferably 2000 to 4000 centipoises.

[0140] Examples will now be further described with reference to the figures in which:

[0141] Figure 1 shows a prior art gravity-fed slurry casting box with a doctor blade;

[0142] Figure 2 shows a prior art closed slurry casting box with a dual screw extruder slurry pump; Figure 3 shows a slurry casting box of the present invention with progressive cavity slurry pumps fitted to the slurry casting box;

[0143] Figure 4 shows the slurry casting box of Figure 3 without the progressive cavity slurry pumps;

[0144] Figure 5 shows a side plan view of the slurry casting box of Figure 3;

[0145] Figure 6 shows a side plan view of the slurry casting box of Figure 3 with the progressive cavity pumps detached;

[0146] Figure 7 shows a vertical cross-section through a progressive cavity pump;

[0147] Figures 8 to 10 show the operation of the progressive cavity pump of Figure 7;

[0148] Figure 11 shows a side plan view of the slurry casting box of Figure 4 in a closed configuration;

[0149] Figure 12 shows a side plan view of the slurry casting box of Figure 4 in an open configuration;

[0150] Figure 13 shows a cross-section along plane A-A’ through the slurry casting box of Figure 3 during operation;

[0151] Figure 14 shows a cross-section along plane B-B’ through the slurry casting box of Figure 3 during operation;

[0152] Figure 15 shows a cross-section along plane C-C’ through the slurry casting box of Figure 3 during operation;

[0153] Figure 16 shows a cross-section along plane D-D’ through the slurry casting box of Figure 3 during operation;

[0154] Figure 17 shows a cross-section along plane E-E’ through the slurry casting box of Figure 3 during operation;

[0155] Figure 18 shows a cross-section along plane F-F’ through the slurry casting box of Figure 3 during operation;

[0156] Figure 19 shows cross-sections along planes G-G’, H-H’, l-l’ and J-J’ through a main body portion of the slurry casting box of Figure 4;

[0157] Figure 20 shows cross-sections along planes K-K’, L-L’, M-M’, N-N’ and O-O’ through a cover portion of the slurry casting box of Figure 4; and

[0158] Figure 21 shows a main body of the slurry casting box of Figure 4 and a cover portion of the slurry casting box of Figure 4, with exemplary dimensions indicated by the letters A to L.

[0159] Figure 3 shows, in isometric view, a slurry casting box 3 of an embodiment of the present invention comprising the slurry casting box 3 and a plurality of progressive cavity pumps 21 vertically mounted to a top wall 33 of a main body portion 31 of the slurry casting box 1.

[0160] Figure 4 shows, in isometric view, the slurry casting box 3 of Figure 3, but with the progressive cavity pumps 21 removed. The slurry casting box 3 has a generally wedge-shaped exterior housing, and comprises the main body portion 31 extending along a longitudinal axis, and a cover portion 32 also extending along the longitudinal axis. The cover portion 32 is mounted to the main body portion 31 by way of hinges 323 which may be located on the top wall 33 of the main body portion 31. The hinges 323 allow the cover portion 32 to be moved relative to the main body portion 31 so as to permit access to an interior of the slurry casting box 3, as shown in more detail in Figures 11 and 12. The main body portion 31 comprises a rear wall 34 extending along the longitudinal axis, the top wall 33 extending along the longitudinal axis, and first and second side walls 35 substantially transverse to the longitudinal axis.

[0161] The top wall 33 of the main body portion 31 comprises a plurality of inlets 3112 for slurry, as shown in Figure 4. The inlets 3112 can be connected to vertically-mounted progressive cavity pumps 21 as shown in Figure 3.

[0162] The slurry casting box 3 further comprises an elongate slot 3110, as shown in more detail in Figures 14 and 15, located at the bottom of the slurry casting box 3 and extending along the longitudinal axis. The elongate slot 3110 defines an outlet for slurry.

[0163] The cover portion 32 is mounted on the main body portion 31 so as to define, together with the rear wall 34, the top wall 33 and the first and second side walls 35, an internal volume that is hermetically sealed except for the inlets 3112 and the elongate slot 3110.

[0164] Referring now to Figure 4, the side walls 35 of the slurry casting box 3 are provided with mechanical assembly elements 312 that enable the slurry casting box 3 to be mounted in an external structure (not shown) that holds the elongate slot 3110 transversely over a moving surface (not shown) onto which slurry is deposited. The moving surface may be, for example a conveying belt, similar to the arrangement shown in Figures 1 and 2. The slurry casting box 3 is also provided with mechanical assembly elements 313 that engage with mechanical elements of the cover portion 32 so as to allow the cover portion 32 to be moved between closed and open positions relative to the main body portion 31 , as shown in Figures 11 and 12. Reinforcing ribs and buttresses 322 are provided on the cover portion 32 in order to help maintain structural rigidity of the cover portion 32 and to help avoid unwanted bulging or deformation of the cover portion 32 when slurry is being pumped through the slurry casting box 3 at high pressure. The ribs and buttresses 322 may extend in horizontal and vertical directions, and may be welded or otherwise formed on the cover portion 32.

[0165] Adjustment mechanisms 314, 324, for example in the form of screw mechanisms, are provided to allow coarse adjustment of a position of the cover portion 32 relative to the main body portion 31. By adjusting the adjustment mechanisms 314, 324, it is possible to move the cover portion 32 by a small amount relative to the main body portion 31 , about a fulcrum defined by the hinges 323, so as to allow a width of the elongate slot 3110 transverse to the longitudinal axis to be adjusted as required, while maintaining a hermetic seal between the cover portion 32 and the main body portion 31 (other than at the inlets 3112 and the elongate slot 3110). This can allow a slurry cast thickness to be adjusted.

[0166] Moreover, in addition to the adjustment mechanisms 314, 324, there may be provided micro-adjustment mechanisms 3211. The micro-adjustment mechanisms 3211 may also be in the form of screw mechanisms, but allow a finer degree of adjustment, for example by having a smaller screw pitch. The micro-adjustment mechanisms 3211 allow a fine adjustment of the width of the elongate slot 3110 transverse to the longitudinal axis.

[0167] Heat transfer fluid inlets and outlets 315 may be provided, for example in the side walls 35, to allow a heat transfer fluid to flow through walls of the main body portion 31 or the cover portion 32 or both the main body portion 31 and the cover portion 32. The heat transfer fluid may be water heated or cooled to a predetermined temperature. The heat transfer fluid can transfer heat to or from the walls of the slurry casting box 3 so as to heat or cool slurry within the slurry casting box 3. In this way, it is possible to apply a desired temperature profile to the slurry within the slurry casting box 3, and thereby to adjust rheological properties of the slurry. For example, at higher temperatures, the slurry may be less viscous and may flow more readily through the slurry casting box 3. Channels 319, shown in Figures 14 and 15, may be provided in the walls of the slurry casting box 3, connected to the heat transfer fluid inlets and outlets 315, for passage of the heat transfer fluid without contacting the slurry. It is not generally desirable for the heat transfer fluid to make direct contact with the slurry. The channels preferably extend along substantially the entire length of the slurry casting box 3, and may be configured to compensate for temperature gradients, for example by taking a serpentine route.

[0168] Temperature sensors 326 may be provided in the slurry casting box 3 so as to monitor a temperature of the slurry, and may be operatively connected to a source of heat transfer fluid so as to allow the temperature of the slurry to be dynamically monitored and controlled.

[0169] Pressure sensors 316 may be provided in the slurry casting box 3 so as to monitor a pressure of the slurry. The pressure sensors 316 may be operatively connected to the progressive cavity pumps 21 so as to allow the pressure of the slurry to be dynamically monitored and controlled.

[0170] Figure 5 shows a side plan view of the slurry casting box 3 of Figure 3, and Figure 6 shows a side plan view of the slurry casting box 3 of Figure 3 with the progressive cavity pumps 21 detached, with parts labelled as in Figures 3 and 4. Figures 5 and 6 show more clearly how the adjustment mechanisms 314, 324 and the micro- adjustment mechanisms 3211 enable very precise adjustment of the cover portion 32 relative to the main body portion 31 , and in particular the width of the elongate slot 3110. Depending on the nature of the slurry and the process conditions, it may not be appropriate for the width of the elongate slot 3110 to be precisely constant along the longitudinal axis. By providing adjustment mechanisms 314, 324 and micro- adjustment mechanisms 3211 at spaced intervals along the longitudinal axis, it is possible to set the width of the elongate slot 3110 very precisely at different locations along the longitudinal axis.

[0171] It will be noted that the vertical positioning of the progressive cavity pumps 21 , in contrast to the horizontal positioning required for the extruder pump 14 of Figure 2, means that a smaller factory floor footprint is required for the slurry casting box 3 and ancillary machinery.

[0172] Figure 7 shows a vertical cross-section through a progressive cavity pump 21. The progressive cavity pump 21 has a helical rotor 211 flexibly mounted on a drive shaft 212 by way of a universal joint 213. The helical rotor 211 rotates within an elastomeric sleeve 214 having an inner helical surface complementary to the helical rotor 211. The elastomeric sleeve 214 is contained within an outer metal casing 215, and defines the stator of the progressive cavity pump 21. It can be seen that closed cavities 216 are defined between the helical rotor 211 and the inner helical surface of the elastomeric sleeve 214. As the helical rotor 211 rotates within the elastomeric sleeve 214, it can be seen, as shown in Figures 8 to 10, that the helical rotor 211 is also able to move slightly from side to side due to being mounted on the drive shaft 212 by way of the universal joint 213. Rotation of the helical rotor 211 within the elastomeric sleeve 214 causes the cavities 216 to translate along a length of the progressive stator pump 21. Because the cavities 216 are closed at each end by contact between the helical rotor 211 and the inner helical surface of the elastomeric sleeve 214, slurry contained in the cavities will also be translated along the progressive cavity pump 21 by positive displacement. The direction of positive displacement can be reversed by rotating the helical rotor 211 in the opposite direction. Accordingly, in contrast to an extruder pump, the progressive cavity pump 21 can pump slurry both in a forward direction and a reverse direction. Moreover, in contrast to an extruder pump, there is a direct linear relationship between the number of rotations of the helical rotor 211 and the volume of slurry pumped by the progressive cavity pump 21 due to progression of the cavities 216 filled with slurry. This enables accurate metering of slurry volume as a function of helical rotor 211 rotation.

[0173] Figures 11 and 12 show a side plan view of the slurry casting box 3 of Figure 4 in respective closed and open configurations. As best seen in Figure 12, the cover portion 32 can be moved to an open position relative to the main body portion 31 by lifting the cover portion 32 around the hinge 323. In this way, access is provided to an internal volume 36 of the slurry casting box 3, for example to facilitate cleaning and maintenance. The cover portion 32 has a front wall 37 having an inner surface 38 that faces the internal volume 36 when the cover portion 32 is in the closed position. The inner surface 38 may be specially contoured as will be described in more detail below.

[0174] Figure 13 shows a cross-section along plane A- A’ through the slurry casting box 3 of Figure 3 during operation. Slurry 40 is pumped by the progressive cavity pumps 21 into the slurry casting box 3 by way of the inlets 3112. An inner surface 39 of the rear wall 34 of the main body portion 31 is contoured so as to define downwardly-directed spurs 41 between the inlets 3112. An inner surface 38 of the front wall 37 of the cover portion 32 is contoured in a complementary manner to define hills 42 located under the inlets 3112 and between the spurs 41. The spurs 41 are positioned between the hills 42 when the cover portion 32 is closed so as to define flow channels 45 for the slurry 40 to flow from the inlets 3112 to the elongate slot 3110. Alternatively stated, the inner surface 39 of the rear wall 34 of the main body portion 31 and the inner surface 38 of the front wall 37 of the cover portion 32 are provided with complementary protruded and intruded regions that together define the flow channels 45. The flow channels 45 are configured to avoid sharp edges or corners where slurry 40 might otherwise adhere and become dry. Moreover, the flow channels 45 are designed to avoid “dead” zones where slurry 45 might stagnate and not pass out of the elongate slot 3110. By avoiding stagnation zones, it may be possible to reduce the risk of slurry fermentation due to microbial contamination, since the slurry 40 will be continuously forced through the slurry casting box 3 without any regions having a significantly longer residence time than other regions. The flow paths 45 may be configured so as to promote an even pressure gradient along the length of the elongate slot 3110, thus helping to promote even casting of the slurry 45 onto a moving surface. Also shown in Figure 13 are the channels 319 for passage of heat transfer fluid, which can help to maintain a desired slurry temperature profile. The channels 319 may be formed in the main body portion 31 or the cover portion 32 or both the main body portion 31 and the cover portion 32.

[0175] Figure 14 shows a cross-section along plane B-B’ through the slurry casting box 3 of Figure 3 during operation. Slurry 40 is fed to inlets 22 of the progressive cavity pumps 21 , and is pumped into the internal volume 36 of the slurry casting box 3. Figure 14 shows how the internal volume 36 is narrowed in the cross-section by the hill 42 on the inner surface 38 of the front wall 37 of the cover portion 32 projecting towards the inner surface 39 of the rear wall 34 of the main body portion 31 to form the flow path 45. The slurry 40 passes along the flow path 45 and out of the slurry casting box 3 through the elongate slot 3110. The elongate slot 3110 may be bounded by a pair of opposed die elements 3210. The micro-adjustment mechanism 3211 can be operated to finely adjust a spacing between the die elements 3210. The ribs and buttresses 322 help to provide rigidity to the front wall 37 of the cover portion 32, even when the slurry 40 in the internal volume 36 is at high pressure. The heat transfer fluid channels 319 enable passage of heat transfer fluid to control a temperature of the slurry 40.

[0176] Figure 15 shows a cross-section along plane C-C’ through the slurry casting box 3 of Figure 3 during operation. Figure 15 shows how the internal volume 36 is narrowed in the cross-section by the spur 41 on the inner surface 39 of the rear wall 34 of the main body portion 31 projecting towards the inner surface 38 of the front wall 37 of the cover portion 32 to form the flow path 45. The slurry 40 passes along the flow path 45 and out of the slurry casting box 3 through the elongate slot 3110. As in Figure 14, the elongate slot 3110 may be bounded by a pair of opposed die elements 3210, and the spacing between the die elements 3210 can be adjusted by the microadjustment mechanism 3211. The ribs and buttresses 322 help to provide rigidity to the front wall 37 of the cover portion 32, even when the slurry 40 in the internal volume 36 is at high pressure. The heat transfer fluid channels 319 enable passage of heat transfer fluid to control a temperature of the slurry 40.

[0177] Figure 16 shows a cross-section along plane D-D’ through the slurry casting box 3 of Figure 3 during operation. Plane D-D’ is close to the inlets 3112 in the top wall 33 of the main body portion 31. The cross-section shows the rear wall 34 of the main body portion 31 , the rear wall 34 having an inner surface 39. The cross-section shows the front wall 37 of the cover portion 32 having an inner surface 38. The cross-section shows the spurs 41 between the inlets 3112. The width of the internal volume 36, between the inner surfaces 38 and 39, is widest directly under the inlets 3112 so as to facilitate entry of slurry 40 from the progressive cavity pumps 21 into the internal volume 36 of the slurry casting box 3. Coarse adjustment mechanisms 314, 324 are provided at distal ends of the slurry casting box 3, while micro-adjustment mechanisms 3211 are provided along the longitudinal axis of the slurry casting box 3. Heat transfer fluid channels 319 enable passage of heat transfer fluid to control a temperature of the slurry 40.

[0178] Figure 17 shows a cross-section along plane E-E’ through the slurry casting box 3 of Figure 3 during operation. Plane E-E’ is further down from the inlets 3112 in the top wall 33 of the main body portion 31 than plane D-D’ in Figure 16. The cross-section shows the rear wall 34 of the main body portion 31 , the rear wall 34 having an inner surface 39. The cross-section shows the front wall 37 of the cover portion 32 having an inner surface 38. The cross-section shows the spurs 41 between the inlets 3112 and the hills 42 between the spurs 41. The width of the internal volume 36, between the inner surfaces 38 and 39 at plane E-E’, is more constant that the width at plane D-D’, but has an undulating shape along the longitudinal axis where the hills 42 protrude between the spurs 41 . This can help to balance a pressure and flow rate of the slurry 40 along the longitudinal axis of the internal volume 36 of the slurry casting box 3. Coarse adjustment mechanisms 314, 324 are provided at distal ends of the slurry casting box 3, while microadjustment mechanisms 3211 are provided along the longitudinal axis of the slurry casting box 3. Heat transfer fluid channels 319 enable passage of heat transfer fluid to control a temperature of the slurry 40.

[0179] Figure 18 shows a cross-section along plane F-F’ through the slurry casting box 3 of Figure 3 during operation. Plane F-F’ is at the bottom of the slurry casting box 3, and shows the elongate slot 3110 defined between the opposed die elements 3210. A spacing between the opposed die elements 3210 can be finely adjusted by way of the micro-adjustment mechanisms 3211 to give fine control over slurry 40 being output through the elongate slot 3110.

[0180] Figure 19 shows vertical cross-sections along planes G-G’, H-H’, l-l’ and J-J’ at various points along the longitudinal axis of the main body portion 31. It can be seen how the thickness of the rear wall 34 of the main body portion 31 , and hence a protrusion of the inner surface 39 of the rear wall 34 of the main body portion 31 , varies along the longitudinal axis so as to define spurs 41.

[0181] Figure 20 shows vertical cross-sections along planes K-K’, L-L’, M-M’, N-N’ and O-O’ at various points along the longitudinal axis of the cover portion 32. It can be seen how the thickness of the front wall 37 of the cover portion 32, and hence a protrusion of the inner surface 38 of the front wall 37 of the cover portion 32, varies along the longitudinal axis so as to define hills 42.

[0182] Figure 21 shows the main body portion 31 of Figure 19 together with the cover portion 32 of Figure 20, with some exemplary dimensions indicated by the letters A to L. Although not intended to be limiting, the exemplary dimensions may be as set out in Table 1 below:

[0183] Table 1

[0184] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5% of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

CLAIMS:

1. A slurry casting box for casting a layer of slurry onto a moving surface, the slurry casting box comprising: a main body portion extending along a longitudinal axis, the main body portion comprising: a rear wall extending along the longitudinal axis, and a top wall extending along the longitudinal axis; first and second side walls substantially transverse to the longitudinal axis; and a cover portion extending along the longitudinal axis, the cover portion defining a front wall of the slurry casting box; wherein the cover portion is movable relative to the main body portion so as to permit access to an interior of the slurry casting box; wherein the top wall of the main body portion comprises at least one inlet for slurry; wherein the slurry casting box is provided with an elongate slot on a bottom of the slurry casting box, the elongate slot extending along the longitudinal axis, and the elongate slot defining an outlet for slurry; wherein the cover portion is configured to be mountable on the main body portion so as to define, together with the rear wall, the top wall and the first and second side walls, an internal volume that is hermetically sealed except for the at least one inlet and the outlet; and wherein the cover portion, when mounted on the main body portion so as to define the hermetically sealed internal volume, is positionally adjustable closer to or further from the rear wall of the main body portion while maintaining a hermetic seal with the main body portion so as to allow an internal shape of the internal volume to be adjusted.

2. The slurry casting box of claim 1 , wherein: a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions; wherein a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions; and wherein the contoured surfaces cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box.

3. The slurry casting box of claim 2, wherein the top wall comprises a plurality of inlets; wherein the contoured surface of the rear wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; wherein the contoured surface of the frontwall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; and wherein the fluid pathways are defined between the spurs and the hills.

4. The slurry casting box of claim 2, wherein the top wall comprises a plurality of inlets; wherein the contoured surface of the rear wall comprises a plurality of hills, each hill being disposed under a respective one of the inlets; wherein the contoured surface of the front wall comprises a plurality of downwardly-extending spurs, each spur being disposed between an adjacent pair of inlets; and wherein the fluid pathways are defined between the spurs and the hills.

5. The slurry casting box of any preceding claim, wherein at least one of the main body portion and the cover portion comprises a temperature adjustment mechanism.

6. The slurry casting box of claim 5, wherein the temperature adjustment mechanism comprises internal channels in the rear wall or the front wall or both the rear wall and the front wall for passage of a thermal transfer fluid.

7. The slurry casting box of any preceding claim, wherein a width of the elongate slot transverse to the longitudinal axis is adjustable.

8. The slurry casting box of any preceding claim, wherein the at least one inlet is connected to a progressive cavity slurry pump.

9. The slurry casting box of any one of claims 1 to 7, comprising a plurality of inlets, and wherein each inlet is connected to an individual progressive cavity slurry pump.

10. The slurry casting box of claims 8 or 9, further comprising at least one pressure sensor for determining a slurry pressure in the internal volume, and a pressure controller connected to the at least one pressure sensor and to the progressive cavity slurry pumps and configured to maintain or adjust a pressure profile in the slurry.

11. The slurry casting box of any preceding claim, wherein the cover portion is positionally adjustable by way of at least one screw mechanism.

12. The slurry casting box of any preceding claim, wherein an outer surface of the rear surface of the main body and an outer surface of the cover portion are closer to each other at the bottom of the slurry casting box than at the top wall of the slurry casting box.

13. A method of casting a layer of slurry onto a moving surface, comprising the steps of: i) providing a slurry casting box as claimed in any one of claims 1 to 10; ii) pumping slurry into the at least one inlet; and iii) casting slurry onto the moving surface through the elongate slit.

14. The method of claim 13, wherein the slurry is pumped into the at least one inlet by at least one progressive cavity pump.

15. The method of claim 13 or 14, wherein: a surface of the rear wall of the main body portion that faces the internal volume is a contoured surface with protruded and intruded regions; a surface of the front wall of the cover portion that faces the internal volume is a contoured surface with protruded and intruded regions; and the contoured surfaces cooperate with each other when the cover portion is mounted on the main body portion so as to define the hermetically sealed internal volume, thereby to define fluid pathways for slurry between the at least one inlet and the outlet of the slurry casting box; further wherein the slurry passes along the fluid pathways from the at least one inlet to the elongate slit.

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