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

Abstract

The present invention relates to a casting apparatus for the production of a cast web of homogenized tobacco material, said casting apparatus comprising • o a casting box (4) adapted to contain a slurry of said homogenized tobacco material; • o a movable support; • o a casting blade (6) adapted to cast the slurry contained in the casting box onto the movable support so as to form the cast web; • o wherein said casting blade has a transverse cross section defining a blade edge, said blade edge including a first point having a first radius of curvature and a second point having a second radius of curvature, said first and second radii of curvature being comprised between about 1 and about 500 and being different from each other.

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; a movable support; a casting blade adapted to cast the slurry contained in the casting box onto the movable support so as to form the cast web of said homogenized tobacco material; wherein said casting blade has a transverse cross section defining a blade edge, said blade edge comprising a first point having a first radius of curvature and a second point having a second radius of curvature, said first and second radii of curvature being comprised between about 1 mm and about 500 mm and being different from each other.

2. Casting apparatus according to claim 1, wherein said blade edge comprises a first arc of circumference having said first radius of curvature and a second arc of circumference having said second radius of curvature.

3. Casting apparatus according to claim 1, wherein said blade edge comprises a portion of an ellipse.

4. Casting apparatus according to claim 1, wherein the first radius of curvature is comprised between about 1 mm and about 50 mm.

5. Casting apparatus according to claim 1, wherein the second radius of curvature is comprised between about 10 mm and about 500 mm.

6. Casting apparatus according to claim 1, wherein said casting blade has a longitudinal width comprised between about 40 cm and about 300 cm.

7. Casting apparatus according to claim 6, wherein said longitudinal width is adjustable.

8. Casting apparatus according to claim 1, wherein said second point is located in a bottom part of said casting blade substantially facing said movable support.

9. Casting apparatus according to claim 1, comprising a controllable pump adapted to regulate an amount of slurry contained in said casting box.

10. Casting apparatus according to claim 9, comprising a level sensor adapted to send a feedback signal dependent on the height of said slurry contained in said casting box to said controllable pump.

11. Casting apparatus according to claim 1, wherein a mean distance between said casting blade and said support is comprised between about 0.1 mm and about 2 mm.

12. 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 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.

13. Casting apparatus according to claim 12, including an actuator or a motor, and wherein the control unit is adapted to command the actuator or the motor 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.

14. Casting apparatus according to claim 1, including at least a first and a second actuator coupled to a first and a second longitudinal end of said casting blade and a motor to command said first and second actuators so as to regulate a local distance of said casting blade from said movable support.

15. Casting apparatus according to claim 1, comprising a distributor positioned along a longitudinal width of said casting box adapted to distribute the slurry in the casting box in a plurality of locations along its width.

16. Casting apparatus according to claim 1, comprising a mixing device to mix the slurry inside the casting box.

17. Casting apparatus according to claim 1, wherein the casting box forms a pressurized enclosure.

Description

[0051] Further advantages of the invention will become apparent from the detailed description thereof with no-limiting reference to the appended drawings:

[0052] 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;

[0053] FIG. 2 is a schematic perspective view of a casting apparatus according to the invention;

[0054] FIG. 3 is an enlarged perspective view of a detail of the casting apparatus of FIG. 2;

[0055] FIG. 4 is a lateral view in section of the casting apparatus of FIG. 2;

[0056] FIG. 5 is an enlarged lateral in section of a portion of the casting apparatus of FIGS. 2 and 4;

[0057] FIG. 6 is a lateral view of an element of the casting apparatus of FIG. 2;

[0058] FIG. 7 is a perspective view of another element of the casting apparatus of FIG. 2;

[0059] FIG. 8 is an enlarged perspective view of a detail of the element of FIG. 7;

[0060] FIG. 9 is a lateral technical drawing of the element of the casting apparatus of FIG. 6; and

[0061] FIG. 10 is a flow diagram of a method of production of a homogenized tobacco web using the apparatus of the invention.

[0062] 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.

[0063] 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.

[0064] 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 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.

[0065] Pump 5 is advantageously designed to ensure that slurry transfer times are kept to the minimum necessary. The pump 5 is fluidly connected, for example by means of a tube 12 (visible in FIG. 2), to a distributor 11 to distribute the slurry within the casting box. 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 the appended drawing 2) 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. In this way, the amount of slurry dropping 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.

[0066] 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 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.

[0067] 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.

[0068] 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 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 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 20, commanded by motors 21 (see FIG. 2), is connected to the board 18. Preferably, the number of actuators 20 is equal to three and they can be independently commanded, that is, each of them for example is connected to a respective motor 21. The motors and actuators are connected to the board 18 for example by means of flaps 22 protruding outwardly from the board 18. Preferably, each actuator 20 is connected to its own flap 22. Motors 21 therefore may move actuators 20 in order to raise or lower the blade 6. Due to the fact that the actuators 20 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. In addition, the blade may be in operational engagement with an ultrasonic actuator that permits the blade to vibrate in a set frequency, within a range of frequencies or at a certain time dependent frequency, that is, a frequency that regularly or randomly alternates within a range of frequencies. This may clean the blade and remove the risk of fibers or other material adhering to the blade. Material adhering to the blade may cause so called “draggers” that in turn can create inconsistencies in the continuous homogeneous tobacco material.

[0069] 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 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.

[0070] The casting apparatus 2 also comprises the mobile support 7 on which the slurry is cast to form the web of homogenized tobacco material. The mobile 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.

[0071] Further, with again reference to FIG. 1, the casting apparatus 2 includes a plurality of sensors. A first sensor 30, a level sensor, 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. 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 further sensors 31, 32 are arranged above the movable support 7 to measure the weight per square centimeter and the thickness of the homogenized tobacco layer 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.

[0072] Preferably, all the sensors send signals relative to their respective parameters to be measured (temperature, moisture slurry level, defects, and so on) to a central control unit 40. Central control unit 40 is preferably electrically connected to one, to some or to all of pump 5, actuators 20, motors 21 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. For example, a feedback loop to the actuators 20 of the casting blade 6 is present to adjust the thickness of the cast web.

[0073] 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 minimize any changes to 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 middle of the surface of the drum 8 may be between about 0.5 degrees and about 10 degrees higher than 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 movable support 7, such as the stainless steel belt 7, has also a temperature on entering the casting box 4 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.

[0074] 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.

[0075] With now reference to FIG. 10, the functioning of the apparatus 1 including the casting apparatus 2 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.

[0076] The thickness of the web of homogenized tobacco material and grammage controlled by nucleonic gauge immediately after casting are continuously monitored and feedback-controlled using slurry measuring device. The casting is performed by means of casting blade 6 forming a gap with the movable support 7, gap that 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.

[0077] Further, the cast web undergoes a drying step by 101 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.

[0078] 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, 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).