CASTING APPARATUS FOR THE PRODUCTION OF A CAST WEB OF HOMOGENIZED TOBACCO MATERIAL

Abstract

The present invention is relative to a casting apparatus for the production of a cast web of homogenized tobacco material, said casting apparatus comprising •a casting box adapted to contain a slurry of said homogenized tobacco material; •a movable support; •a casting blade adapted to cast said slurry contained in said casting box onto said movable support in order to form the cast web; •wherein said casting apparatus further comprises a first, a second and a third actuator coupled to said casting blade in a first, a second and third position, respectively, said first, second and third actuator being suitable to change a distance between said casting blade and said movable support in said first, second and third position, respectively.

Claims

1. Casting apparatus for the production of a cast web of homogenized tobacco material, said casting apparatus comprising a casting box adapted to contain a slurry of said homogenized tobacco material; a movable support; a casting blade adapted to cast said slurry contained in said casting box onto said movable support in order to form the cast web; wherein said casting apparatus further comprises a first, a second and a third actuator coupled to said casting blade in a first, a second and third position, respectively, said first, second and third actuator being suitable to change a distance between said casting blade and said movable support in said first, second and third position, respectively.

2. Casting apparatus according to claim 1, wherein said first, second and third actuator are so configured that they can be actuated to change said distance between said casting blade and said movable support in said first, second and third position, respectively, independently one from the others.

3. Casting apparatus according to claim 1, wherein said first and second position are located at a first and at a second longitudinal end of said casting blade, respectively, and said third position is located in between said first and second longitudinal end of said casting blade.

4. Casting apparatus according to claim 1, further comprising a transverse displacement element that allow the transverse displacement of at least one of the first, second, or third position of said first, second or third actuator along said casting blade.

5. Casting apparatus according to claim 1, comprising a plurality of fine adjustment elements coupled to said casting blade, each fine adjustment element being adapted to locally vary the distance between said casting blade and said movable support, said fine adjustment element being located along a longitudinal width of said casting blade, a fine adjustment element every about 5 cm to about 12 cm.

6. Casting apparatus according to claim 5, wherein at least one of said fine adjustment element is adapted to locally vary the distance between said casting blade and said movable support of a value comprised between about 1 μm and about 200 μm.

7. Casting apparatus according to claim 5, wherein said fine adjusting elements comprise screws which are adapted to, when screwed or unscrewed, lower or rise said casting blade with respect to said movable support, respectively.

8. Casting apparatus according to claim 1, comprising: a sensor, and a control unit adapted to send signals to or receive signals from said sensor and to send signals to or receive signals from said first, second and third actuators, said sensor being adapted to detect a parameter of said cast web or of said slurry and send a corresponding signal to said control unit which in turn is adapted to send a command signal to said first, second or third actuator to operate said first, second, or third actuator, respectively.

9. Casting apparatus according to claim 1, comprising a control unit and one or more sensors adapted to send signals to said control unit, said one or more sensors comprising: a sensor to identify draggers on the cast web cast on the movable support; a sensor to determine the moisture of said cast web cast on the movable support; a sensor to measure the thickness or variations in thickness of said cast web cast on the movable support; a sensor to measure the viscosity of the slurry in said casting box; a sensor to measure the temperature of said slurry in said casting box; a sensor to detect the position of defects on said cast web cast on the movable support; a sensor to detect the density of the slurry in said casting box; and combinations of two or more of the above sensors.

10. Casting apparatus according to claim 9, wherein the control unit is adapted to command the first, second or third actuator in response to a signal received from one or more of said sensors in order to perform a feedback loop to vary one or more of the parameters detected by said one or more sensors in response to said signal.

11. Casting apparatus according to claim 1, wherein said casting blade has a transverse cross section defining a blade edge, said blade edge comprising a first arc of circumference having a first radius of curvature and a second arc of circumference having a second radius of curvature or said blade edge comprising a portion of an ellipse.

12. A method for forming a cast web of homogenized tobacco material, comprising Introducing a slurry of said homogenized tobacco material in a casting box; Casting said slurry onto a movable support with a casting blade so as to form a cast web; Determining a parameter of said cast web or of said slurry; and Changing the distance between said casting blade and said movable support as a function of said parameter; wherein changing the distance between said casting blade and said movable support as a function of said parameter comprises operating a first, a second and a third actuator coupled to said casting blade in a first, a second and third position, respectively, each of said first, second and third actuator being suitable to change a distance of said casting blade from said movable support in said first, second and third position.

13. (canceled)

14. Method according to claim 12, comprising, before casting said cast web, Fine tuning the distance between said casting blade and said movable support in a plurality of locations, said locations being spaced apart one from the other of a distance comprised between about 5 cm to 12 cm along a longitudinal width of said casting blade.

15. Method according to claim 12, wherein determining a parameter of said casting web or of said slurry comprises one or more of: detecting the presence of draggers on said cast web; determining the moisture of said cast web cast on the movable support; measuring the thickness or variations in thickness of said cast web cast on the movable support; measuring the viscosity of the slurry in said casting box; measuring the temperature of said slurry in said casting box; detecting the presence of defects on said cast web cast on the movable support; detecting the position of defects on said cast web cast on the movable support; detecting the density of the slurry in said casting box; and combinations of two or more of the above.

16. Method according to claim 12, wherein changing the distance between said casting blade and said movable support as a function of said parameter comprises Bending said casting blade into a nonlinear shape.

17. Method according to claim 12, wherein changing the distance between said casting blade and said movable support comprises obtaining an average distance between said casting blade and said movable support comprised between about 0.1 mm and about 2 mm.

Description

[0062] Further advantages of the invention will become apparent from the detailed description thereof with no-limiting reference to the appended drawings:

[0063] FIG. 1 is a schematic lateral view of an apparatus for the production of a homogenized tobacco web including an apparatus for casting the homogenized tobacco web according to the invention;

[0064] FIG. 2 is a schematic perspective view of a casting apparatus according to the invention;

[0065] FIG. 3 is an enlarged perspective view of a detail of the casting apparatus of FIG. 2;

[0066] FIG. 4 is a lateral view in section of the casting apparatus of FIG. 2;

[0067] FIG. 5 is an enlarged lateral in section of a portion of the casting apparatus of FIGS. 2 and 4;

[0068] FIG. 6 is a lateral view of an element of the casting apparatus of FIG. 2;

[0069] FIG. 7 is a perspective view of another element of the casting apparatus of FIG. 2;

[0070] FIG. 8 is an enlarged perspective view of a detail of the element of FIG. 7;

[0071] FIG. 9 is a lateral technical drawing of the element of the casting apparatus of FIG. 6;

[0072] FIGS. 10a-10c are four front schematic views of a different embodiments of a phase of the method of production of a cast web according to then invention; and

[0073] FIG. 11 is a flow diagram of a method of production of a homogenized tobacco web using the apparatus of the invention.

[0074] With initial reference to FIG. 1, an apparatus for the production of a web of homogenized tobacco material according to the present invention is represented and indicated with reference number 1.

[0075] The apparatus 1 for the production of a web of homogenized tobacco material includes a casting apparatus 2 realized according to the present invention and further preferably also a drying apparatus 3 positioned downstream the casting apparatus 2 in the direction of motion of the web of homogenized tobacco material.

[0076] The casting apparatus 2 comprises a casting box 4 where slurry to form the web of homogenized tobacco material is introduced, a pump 5, a casting blade 6 and a movable support 7. Casting box 4 may have any geometrical shape, and in the depicted embodiment it is substantially in a form of a prism. The casting box has an opening 43 in correspondence of its bottom and the opening extends along a width of the casting box. Slurry from buffer tanks (not shown in the drawings) is transferred by means of the pump 5 into the casting box. Preferably pump 5 comprises a control (not visible in the drawing) of flow rate to control the amount of slurry introduced in the casting box 4.

[0077] Pump 5 is advantageously designed to ensure that slurry transfer times are kept to the minimum necessary. The pump 5 is in fluid communication, for example by means of a tube 12 (visible in FIG. 2), to a distributor 11 of the casting box 4 to distribute the slurry within the casting box 4. Preferably distributor 11 extends along the width of the casting box 4 and it is located above the casting box 4. Distributor 11 includes either a plurality of openings or a single elongated slit (slit 13 visible in FIG. 3) in order to distribute the slurry uniformly along the width of the casting box, so that a filling level 41 of the slurry inside casting box 4 is substantially uniform along the width of the casting box 4. Distributor 11 with elongated slit 13 is better visible in the enlarged view of FIG. 3 where a portion of the distributor can be seen. Preferably, the breadth of the elongated slit 13, that is its dimension perpendicular to its width dimension, is tunable, for example by means of regulating means 14 such as one or more screws, as show in FIG. 3. In this way, the amount of slurry flowing into the casting box 4 from the distributor 11 per unit time can be controlled and adjusted. Therefore, two controls are present of the amount of slurry introduced into the casting box 4, a control on the pump 5 and a control on the distributor 11.

[0078] Casting box 4, in addition to one or more external walls 15, also further includes an internal wall 16 which delimits a feeding chamber 17 within the casting box 4. The feeding chamber 17 is in fluid communication with the rest of the casting box inner volume. Feeding chamber 17 is located below distributor 11. Due to the high viscosity of the slurry, the height of the slurry in the feeding chamber 17 can be higher than the height of the slurry in the remaining part of the casting box 4. The feeding chamber 17 is better visible in the cross sections of FIGS. 4 and 5.

[0079] Further, the casting apparatus 2 includes the casting blade 6 fixed to the casting box 4 in order to cast the slurry. The casting blade 6 has a main dimension which is its width and it is fixed to the casting box 4 at or in proximity of its aperture 43 at the bottom. Preferably, the longitudinal width of the casting blade 6 is between about 40 cm and about 300 cm depending on the desired width of the cast web of slurry. Preferably, such width is adjustable, for example by means of suitable width adjusting means (not visible in the drawings), so that the width of the blade or the active volume of the casting box can be adjusted to the width of the web to be cast. The active volume of the casting box is the volume of the casting box that is actually filled with slurry.

[0080] The casting blade 6 is attached to the casting box preferably by means of an adjustable board 18 which allows a precise control of the position of the casting blade 6. Adjustable board 18 is depicted as a whole and in an enlarged view of a detail in FIGS. 7 and 8, respectively. The adjustable board 18 includes a plurality of adjustment elements, all indicated with 19, to adjust a gap between the blade 6 and the support 7. The casting box 4 and the casting blade 6 are mounted above a drum 8 which rotates the movable support 7. Between the casting blade 6 and the movable support 7 a gap is present, the dimensions of which determine—among others—the thickness of the cast web of homogenized tobacco material. Thus, the dimension of the gap is controlled by controlling the position of the casting blade 6 by means of the adjustable board 18 which includes the adjusting elements 19 distributed along its width. Adjusting elements 19 for example include a plurality of screws 19, such as micrometer screws. The width of the adjustable board 18 substantially coincides with the width of the casting blade 6. The adjustable screws 19 are disposed along the width of the adjustable board 18 and can vary the distance locally between the casting blade 6 and the support 7. The distance between any two adjacent screws of the plurality of screws can be pre-set and fixed. Screws 19 are used for the fine adjustment of the casting blade 6 with respects to the movable support 7. Screws 19 can be used to compensate for inhomogeneity of the support surface or of the blade surface. In use, screws 19 are preferably adjusted in a first machine setup. However, the screws 19 may also be actuatable to allow online fine adjustments of the casting blade 6 shape. To further vary the dimension of the gap in the direction perpendicular to its width, that is to vary the breadth of the gap, a plurality of actuators 200, 201, 202 controlled by displacement means, such as motors 210, 211, 212, is connected to the board 18. According to the invention, the number of actuators 200, 201, 202 is equal to or above three. The actuators 200, 201, 202 can be independently controlled, that is, each of the actuators 200, 201, 202 is connected to a respective motor 210, 211, 212. The motors and actuators are connected to the board 18 for example by means of mounts 22 (all mounts indicated with the same reference numeral) protruding outwardly from the board 18. Preferably, each actuator 200, 201, 202 is connected to its own mount 22. Motors 210, 211, 212 therefore may move actuators 200, 201, 202 in order to raise or lower the blade 6. Due to the fact that the actuators 200, 201, 202 can be independently moved, the blade 6 can be locally lowered and raised, to take into account again inhomogeneity of the blade, of the support, and of the slurry. Preferably, the breadth of the gap is comprised between about 0.1 mm and about 2 mm. The connection between the adjustable board 18 and the casting blade 6 is shown in the lateral view of FIG. 6.

[0081] The distance among actuators 200, 201, 202, that is the position of each actuator along the width of the blade 6, can also be varied by means of further displacement means, not shown in the drawings.

[0082] Further, with now reference to FIG. 9, a section of the casting blade 6 is shown, taken along a plane (X, Z) perpendicular to the width of the casting blade 6. The section of the blade 6 taken along this plane defines an edge 23, which extends along a given curve. This curve includes at least a point 24 having a first radius of curvature and a second point 25 having a second radius of curvature, said first and second radii being between about 1 mm and about 500 mm and being different from each other. In the depicted embodiment, the edge 23 includes a plurality of points 24 all having the first radius of curvature and a second plurality of points all having the second radius of curvature. For example, the edge 23 includes two arcs of circumferences which are continuously connected among them, that is, the two arcs defines a single curve which is continuous and has a continuous first derivative. Alternatively, in an embodiment not depicted, the edge 23 may include a portion of an ellipse. Preferably, the second radius of curvature is wider than the first radius of curvature and the point 25 having the second radius of curvature substantially faces the support 7. In one embodiment, the first radius is between about 5 mm and about 25 mm and the second radius is between about 20 mm and about 50 mm. In the depicted embodiment, the casting blade 6 further includes a third point 26 having a third radius of curvature.

[0083] The casting apparatus 2 also comprises the movable support 7 on which the slurry is cast to form the web of homogenized tobacco material. The movable support 7 comprises for example a continuous stainless belt 7 comprising a drum assembly. The drum assembly includes a main drum 8 located below the casting box 4 which moves the movable support 7. Preferably, the casting box 4 is mounted on top of the main drum 8. Preferably, the tolerances of the above mounting are very strict, for example within about 0.01 mm. For example, the movable support drum 8 has a tolerance of below about 0.01 mm in concentricity and below about 0.10 mm across its diameter. The movable support 7 has a tolerance preferably below about 0.01 mm.

[0084] The displacement of the blade 6 with respect to the support 7 in order to change the dimension or the shape of the gap are schematically described with reference to FIGS. 10a-10d. In these drawings, the adjustable board 18 and the adjustment screws 19 are not visible, for clarity reasons. In FIG. 10a, the blade 6 and the support 7 are separated by a gap indicated with 300 having uniform dimension, such that the dimension of the gap is substantially uniform along the whole width of the blade 6. The dimension of gap 300 is selected in order to obtain the desired thickness of the cast web for a set of parameters of the casting process. In case the resulting thickness of the cast web is not the desired one, not even within the tolerances range, or it is not uniform, the gap 300 is preferably modified, by means of the actuators 200, 201, 202 coupled to blade 6. Preferably, a first and second actuators 200, 201 are located in a first and second position at or in proximity of opposite distal ends 60, 61 of blade 6, respectively. The third actuator 202 is preferably disposed in a third position there between, that is in a substantially intermediate portion 62 of the blade between the two distal ends 60, 61. The distance between the first and third actuators 200, 202 and the second and third actuators 201, 202 may be the same or different. Further, this distance between the first and third actuators 200, 202 or the distance between the third and the second actuators 201, 202 can be changed. The three actuators 200, 201, 202 are operated by three separate motors 210, 211, 212 not visible in drawings 10a-10d (motors 210, 211, 212 are visible in FIG. 2).

[0085] In order to change the gap dimension or shape, in a first embodiment of the invention, the gap 300 is modified as shown in FIG. 10b. In order to obtain a new gap 301 having a different dimension as shown in FIG. 10b, all actuators 200, 201, 202 are operated and the blade 6 is substantially displaced in a substantially vertical direction. For example, where the gap dimension needs to be increased, the gap may be enlarged by displacing the blade 6 from the support 7, as indicated in FIG. 10b by arrows 203 pointing away from the support 7. Each arrow 203 indicates the movement of the corresponding actuator 200, 201 or 202. The resulting new gap 301 has a dimension which is bigger than the dimension of the original gap 300 and it is preferably uniform, that is the dimension of the gap between the blade 6 and the support 7 is the same for the whole longitudinal width of the blade 6. In this case, the relevant dimension of the gap is the vertical dimension along the Z axis.

[0086] Alternatively, in case of a non-uniform casting thickness of the cast web, or irregularities in the blade, in the support, or in the distribution of the slurry in the casting box, the gap 300 of FIG. 10a is preferably modified in a non-uniform or asymmetric manner. Different modifications are possible. For example, as depicted in FIG. 10c, the dimension of the gap is maintained in proximity of one distal end 60 of the blade 6, and the gap is increased in proximity of the opposite distal end 61. The second and third actuators 201, 202 are then controlled for example by their respective motors 211, 212 (not visible in the drawings 10a-10d), so that one end 61 of the casting blade 6 is moved upwards according to arrows 203, forming a substantially “wedge-like” gap 302, having a non-uniform dimension along the Z axis. This way, a gap having a smaller dimension on one end 60 of the blade 6 and a wider dimension on the opposite end 61 of the blade 6 is created. A similar result, in particular if a small difference in the gap dimensions at the two opposite ends of the blade is to be obtained, can be achieved by actuating only the second actuator 202. Alternatively, all three actuators are operated, and the blade is displaced in all first, second and third positions, however the displacement in each position is not the same, but the displacement in the first position is different than the displacement in the second position and than the displacement in the third position.

[0087] In an additional embodiment depicted in FIG. 10d, the gap 300 of FIG. 10a is substantially modified bending the blade 6 so that the so formed new gap 303 in the intermediate portion 62 of the blade has a wider dimension than the gap at the distal ends 60, 61 of the blade 6. In this case, only the third actuator 202 located at the intermediate portion 62 is operated and displaced. In this way, the blade 6 can have an arc-like configuration, as depicted in FIG. 10d. This configuration can be obtained also operating all three actuators 200, 201 and 202, but wherein the displacement of the third actuator 202 in the middle position is greater than the displacements performed by the first and second actuators 200, 201 in the first and second positions. This configuration has been found to be especially advantageous where a non-uniform temperature distribution of the movable support is observed, in particular, where the temperature along the center of the movable support is higher than towards the transverse sides of the movable support.

[0088] Further, with reference to FIG. 1, the casting apparatus 2 includes a plurality of sensors. A first slurry level sensor 30 is adapted to control the height 41 of the slurry within the casting box 4. This sensor 30 preferably measures a distance 42 between the sensor itself and the surface of the slurry in the casting box 4 (see FIG. 5). The height 41 of the slurry is then derived from the known distance between the sensor 30 and the bottom of the casting box 4. Further, preferably additional sensors 31, 32 are arranged above the movable support 7 to measure the weight per square centimeter and the thickness of the homogenized tobacco web on the movable support 7. The sensor 31 may be for example a nucleonic measuring head. Additional sensors, not shown in the drawings, are preferably present as well, such as a sensor to locate and determine the positions of defects in the cast web of homogenized tobacco, a sensor to determine the moisture of the slurry and of the cast leaf at casting, and a temperature sensor for determining the temperature of the slurry in the casting box 4.

[0089] Preferably, all the sensors send signals relative to their respective parameters to be measured (for example temperature, moisture slurry level or position of defects) to a central control unit 40. Central control unit 40 is preferably electrically connected to one, to some or to all of pump 5, motors 210, 211, 212 or to further circuits and actuators in the casting apparatus 2 or in a slurry preparation apparatus (not visible). In case the cast web reveals defects or inhomogeneity or the characteristics of the cast web are outside a preset range, the central control unit 40 can instruct changes in the process parameters and thus influence characteristics of the slurry or the parameters of the casting. These process parameters may be for example the dimension of the gap between the casting blade 6 and the support 7 or the amount of slurry in the casting box 4. For example, a feedback loop to the actuators 200, 201, 202 of the casting blade 6 is present to adjust the thickness of the cast web.

[0090] The control unit 40 therefore sends signals to the motors 210, 211, 212 or to the actuators 200, 201, 202 directly to control the actuators to change the position of the blade and thus the dimension of the gap between the casting blade 6 and the movable support 7. Depending on the requirements, the signal sent by the control unit 40 may instruct the actuators 200, 201, 202 to move according to any of the configurations of FIGS. 10b-10d or any different configuration depending on the detected parameters.

[0091] Preferably, a continuous feedback from the sensors to the control unit 40 is sent, so that the actuators or motors are operated till the casting blade 6 is positioned in such a way that the desired thickness and characteristics of the cast web are obtained, as sensed by sensors 30, 31, 32 or others.

[0092] Preferably, the drum or roller 8 includes a temperature control device (not shown). The main drum 8 of the support 7 where the casting box 4 is located is preferably maintained at a constant temperature to allow precise predictions about the aging of the slurry. However, it may be desired that the drum 8 has a varying temperature profile across the drum 8 that is constant in time. For example, the temperature in the middle of the surface of the drum 8 may be between about 0.5 degrees and about 10 degrees higher than the temperature at the ends of the drum. This temperature is substantially similar to the temperature of the slurry present in the casting box 4 that is a temperature between about 5 degrees Celsius and about 26 degrees Celsius. Preferably, the temperature of the movable support 7, such as the stainless steel belt 7, on entering the casting box 4 remains substantially constant across the width of the belt. To ensure the belt and drum temperatures are optimal for the slurry, the temperature control device recirculate process water which is put in contact with the movable support 7 and the drum 8 on the return side.

[0093] The drying apparatus 3 includes a plurality of individual drying zones. Each drying zone preferably includes steam heating on the bottom side of the support and heated air above the movable support 7 and preferably also adjustable exhaust air control. Within the drying apparatus 3, the homogenized tobacco web is dried to desired final moisture on the support 7.

[0094] With now reference to FIG. 11, the functioning of the apparatus 1 including the casting apparatus 2 of the invention is as follows. A slurry, formed preferably mixing and combining tobacco powder and other ingredients, is transferred from a holding tank (not shown) using for example in line mixers (also not shown) to the casting apparatus 2 inside the casting box 4. The step 100 of casting of the slurry into a web of homogenous and uniform film thickness is performed on the movable support 7, for example the stainless steel belt 7. The casting step 100 includes transferring the slurry from the mixing tank to the casting box 4. Further, it preferably includes monitoring the level of slurry in the casting box 4, the moisture of the slurry inside the casting box 4, and the density of the slurry, by means of suitable sensors, such as sensor 30.

[0095] The thickness of the web of homogenized tobacco material and grammage controlled by nucleonic gauge immediately after casting are continuously monitored and feedback-controlled. The casting is performed by means of casting blade 6 forming a gap with the movable support 7, wherein the dimensions of the gap can also be feedback controlled. The shape of the casting blade 6 including two different radii of curvature in its edge 23 allows the reproducible formation of a substantially uniform web homogenized tobacco.

[0096] Further, the cast web undergoes a drying step 101 by means of the drying apparatus 3. The drying step includes preferably a uniform and gentle drying of the cast web in an endless, stainless steel belt dryer with individually controllable zones. During the drying, a monitoring step 102 of the cast web temperature at each drying zone to ensure a gentle drying profile at each drying zone is preferably performed. The cast web is dried to desired final moisture on the steel belt 7 with steam pan heating from bottom and top air drying. Every drying zone is equipped with steam flow and pressure control and air temperature and air flow are fully adjustable to provide the desired drying profile and ensuring product residence time is respected. Preferably, a TLC drying profile is employed.

[0097] Preferably, at the end of the casting step 100 and of the drying step 101, the homogenized tobacco web is removed from the support 7. Doctoring 103 of the cast web after the drying station at the right moisture content is preferably performed. The cast web goes preferably through a secondary drying process 104 to remove further moisture content of the web to reach moisture target or specification. Preferably, in this second drying step, the cast web is laid onto a wire, such that moisture can be easily removed from both surfaces of the web. After the drying step 101, 104, the cast web is preferably wound in one or more bobbins in a winding step 105, for example to form a single master bobbin. This master bobbin may be then used to perform the production of smaller bobbins by slitting and small bobbin forming process. The smaller bobbin may then be used for the production of an aerosol-generating article (not shown).