Casting apparatus and method to check a thickness of a cast sheet

Abstract

The invention relates to a casting apparatus (1) for the production of a cast sheet (10) of homogenized tobacco material, said casting system comprising: ⋅a casting box (4) adapted to contain a slurry of the homogenized tobacco material; ⋅a movable support (7); ⋅a casting system adapted to deposit the slurry contained in the casting box (4) onto the movable support (7) so as to form the cast sheet (10); ⋅a sensor (30) to detect a thickness of the cast sheet (10); ⋅wherein the sensor (30) includes a slider (33) comprising a planar surface (36) adapted to be in contact to a top surface of the cast sheet and a height detector (38) adapted to measure the height of the planar surface (36) so as to derive the thickness of the cast sheet (10). The invention also relates to a method to measure the thickness of a homogenized tobacco sheet (10).

Claims

1. Casting apparatus for the production of a cast sheet of homogenized tobacco material, said casting apparatus comprising a casting box adapted to contain a slurry of the homogenized tobacco material; a movable support; a casting system adapted to deposit the slurry contained in the casting box onto the movable support so as to form the cast sheet; a sensor to detect a thickness of the cast sheet, wherein the sensor includes: a slider comprising a planar surface adapted to be in contact to a top surface of the cast sheet; and a height detector adapted to measure the height of the planar surface so as to derive the thickness of the cast sheet; and a drying unit, the slider being positioned downstream the drying unit, in the direction of motion of the movable support.

2. The casting apparatus according to claim 1, wherein the casting system includes a casting blade adapted to cast the slurry onto the movable support, a distance separating said casting blade from said support.

3. The casting apparatus according to claim 1, wherein the casting system includes two casting rollers forming a gap therebetween, said gap being positioned below said casting box.

4. The casting apparatus according to claim 1, including a pressing device adapted to press said planar surface towards the cast sheet.

5. The casting apparatus according to claim 4, wherein said pressing device includes an air pressure generator and a nozzle, said nozzle being adapted to eject compressed air towards the slider so as to press said planar surface towards the movable support.

6. The casting apparatus according to claim 5, including an air pressure regulator to vary a pressure value of the compressed air exiting the nozzle.

7. The casting apparatus according to claim 1, comprising a plurality of sliders positioned one parallel to the other.

8. The casting apparatus according to claim 7, wherein the plurality of sliders is positioned in a row formed perpendicularly to a direction of motion of the movable support.

9. The casting apparatus according to claim 7, wherein a distance between two adjacent sliders perpendicularly to the direction of motion of the movable support is comprised between about 0 centimeters and about 200 centimeters.

10. The casting apparatus according to claim 1, wherein the planar surface includes a rectangular surface.

11. The casting apparatus according to claim 10, wherein a side of the rectangular surface is positioned perpendicular to a direction of motion of the movable support.

12. The casting apparatus according to claim 1, wherein said height detector is adapted to measure the height of the planar surface with reference to the movable support.

13. The casting apparatus according to claim 1, including a control unit connected to the sensor, the control unit being adapted to determine variations in height of said slider on the basis of signals sent by the sensor.

Description

(1) Further advantages of the invention will become apparent from the detailed description thereof with no-limiting reference to the appended drawings:

(2) FIG. 1 is a schematic lateral view of a portion of a casting apparatus according to the prior art;

(3) FIG. 2 is a schematic lateral view of an apparatus for the production of a homogenized tobacco sheet including an apparatus for casting the homogenized tobacco sheet according to the invention;

(4) FIG. 3 is a schematic lateral view of a portion of the casting apparatus of FIG. 2;

(5) FIG. 4 is a schematic perspective view of a different embodiment of the portion the casting apparatus of FIG. 3;

(6) FIG. 5 is a flow diagram of a method of measuring the thickness a homogenized tobacco sheet using the method of the invention; and

(7) FIG. 6 is a schematic lateral different embodiment of a casting system to be used in the casting apparatus of FIG. 2.

(8) With initial reference to FIG. 2, an apparatus for the production of a sheet 10 of homogenized tobacco material according to the present invention is represented and indicated with reference number 1.

(9) The apparatus 1 for the production of the sheet 10 of homogenized tobacco material includes a casting apparatus 2 realized according to the present invention and further preferably also a drying apparatus or unit 3 positioned downstream the casting apparatus 2 in the direction of motion of the sheet of homogenized tobacco material.

(10) 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.

(11) Pump 5 is advantageously designed to ensure that slurry transfer times are kept to the minimum necessary.

(12) 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.

(13) The casting blade 6 is attached to the casting box preferably by means of an adjustable board (not shown in the appended drawings) which allows a precise control of the position of the casting blade 6. 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 sheet 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.

(14) 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 21 (only one shown in FIG. 2).

(15) In a different embodiment of the casting apparatus 2, depicted in FIG. 6, casting rollers are used instead of a casting blade. The slurry is collected in the casting box 4 which includes an opening 51 from which slurry by gravity may fall onto a first and a second casting roller 52, 53 substantially parallel to each other and having their axis substantially on the same plane, which is preferably horizontal. The two casting rollers 52, 53 form a gap therebetween, for example equal to about 0.4 millimeters. The two casting rollers 52, 53 are driven into rotation and their speed (they rotate in the same direction) is of about 3.25 meter/minute for the first casting roller and equal to about 1.62 meter/minute in the second casting roller.

(16) The first casting roller is substantially coated by the slurry and it transports the slurry onto a third casting roller 54 located below the first casting roller. The third casting roller also rotates and brings the slurry onto the movable support 7. The speed of rotation of the third casting roller is of about 2.31 meter/minute.

(17) In any of the above embodiments, the casting apparatus 2 also comprises the mobile support 7 on which the slurry is cast to form the sheet 10 of homogenized tobacco material. The mobile support 7 comprises for example a continuous stainless belt 7 comprising a drum assembly. The drum assembly includes the 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.

(18) The movable support shifts the cast sheet 10 along a direction depicted with an arrow 40 in FIG. 3.

(19) Further, with again reference to FIG. 2, the casting apparatus 2 includes a sensor 30 to measure the thickness of the cast sheet 10. The sensor 30 includes a slider 33 having a planar surface 34 (better visible in FIG. 3) and a height detector 38, which is adapted to measure the height of the planar surface 34. The sensor 30 can be raised or lowered towards the cast sheet 7, for example by means of actuators 35. The planar surface 34 has for example a size of about 1.2 square millimeters.

(20) Further, as visible in FIG. 3, slider 33 includes a further planar surface 36, inclined with respect to the planar surface 34, positioned upstream the planar surface 34 in the direction of motion of the movable support 7. The further planar surface 36 is inclined with respect to the planar surface 34 of an angle larger than about 90°. Preferably, this further planar surface 36 is not in contact with the cast sheet 10. In a different non depicted embodiment, the connection between the two planar surfaces is obtained by means of a curved surface.

(21) The apparatus 1 further comprises a compressed air generator 37 (visible in FIG. 3) adapted to eject a steam of compressed air towards the slider 33. The slider is pressed towards the movable support 7 by the compressed air. To achieve it, the generator 37 preferably comprises a nozzle 38 directed towards the slider 33 and properly oriented.

(22) The apparatus 1 may include a plurality of sensors 30. As depicted in FIG. 4, a plurality of sensors 30 are positioned along a row which is substantially perpendicular to the transport direction 40. The row of sensors is used to determine the thickness of the cast sheet 10 along its whole width. Preferably each sensor of the plurality can vary not only its height via actuator 35, but also its location within the width of the cast sheet, that is, its position in a direction perpendicular to the moving direction of the movable support 7, as depicted by the arrow 60.

(23) Each of the sensors of the plurality 30 is preferably realized as depicted in the enlarged view of FIG. 3. However, differences among the sensors of the plurality can be present as well.

(24) Preferably, the plurality of sensors or the single used sensor 30 is located downstream the drying apparatus 2 in the direction of motion 40 of the cast sheet 10.

(25) Preferably, the sensors of the plurality are placed equidistant from each other, so that they each monitor one portion of the width of the tobacco cast sheet 10.

(26) Further sensors can be provided in the casting apparatus 2, for example a level sensor (not depicted), is adapted to control the height of the slurry within the casting box 4. Further, preferably further sensor 31 is arranged above the movable support 7 to measure the weight per square 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.

(27) 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 50. Preferably, also sensor or sensors 30 are connected to central unit 50 to send signals relative to the height of the slider 33. Central control unit 50 is preferably electrically connected to one, to some or to all of pump 5, actuators 21 or to further circuits and actuators in the casting apparatus 2 or in a slurry preparation apparatus (not visible). In case the cast sheet reveals defects or inhomogeneity or the characteristics of the cast sheet are outside a preset range, the central control unit 50 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.

(28) The drying apparatus 3 preferably 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.

(29) With now reference to FIG. 5, 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 sheet of desirably 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.

(30) The casting is performed by means of casting blade 6 or the casting rollers 52-54 forming a gap with the movable support 7, gap that can also be feedback controlled.

(31) 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. Also the drying profile, that is all characteristics of the drying, can be feedback controlled depending on the measurements of the thickness of the cast sheet.

(32) 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 cast sheet 10.

(33) Before the doctoring step 103, and preferably after the drying step 101, preferably a step 104 of measurement of the thickness of the sheet 10 of homogenized tobacco material is performed. Preferably the thickness of the sheet is continuously monitored and feedback-controlled using sensor 30 or the plurality of sensors 30.

(34) Sensor 30 is moved into contact with a top surface of the cast sheet 10 in order to measure its thickness 80 (see FIG. 2). The planar surface 34 comes into contact with the top surface of the cast sheet due to movements of the actuator 35. Also the position of the planar surface 34 onto the top surface of the cast sheet 10 can be varied, that is, the position of the planar surface 34 along the width of the sheet can be varied as well, as depicted by arrow 60 of FIG. 4.

(35) A pressure is applied onto the cast sheet 10 by means of the planar surface 34 due to ejection of compressed air from the generator 37. The generator 37 ejects, through the nozzle 38, air having a given pressure which is set according to characteristics of the cast sheet. For example, control unit 50 may send a command to the generator 37 to set the proper pressure value depending on the inputted characteristics of the cast sheet.

(36) For example, the area of the planar surface could be of about 3 square centimeters applying a force between about 1 and 2 Newton to the cast sheet 10.

(37) The height of the planar surface 34 is then detected. From the detected height, an initial height is subtracted, the initial height being the height of the planar surface when in contact to the movable support 7. This subtraction is preferably performed in the control unit 50, to which height signals are preferably sent by sensor 30. The result of the subtraction gives the thickness 80 of the cast sheet 10.

(38) In the control unit 50 preferably a comparison is made between the detected thickness 80 of the cast sheet 10 and a preferred value, or range of values, of the thickness of the cast sheet 10.

(39) A feedback step 106 may then follow the measurement step 104. In the feedback step, the control unit 50 may send signals to motor or actuators to change parameters of the slurry formation or of the slurry casting step. The feedback step 106 is preferably performed in case the measured thickness of the cast sheet 10 is outside the desired range or it is not uniform. For example, if two different sensors 30 of the plurality depicted in FIG. 4 detect different thicknesses, then a non-uniform thickness is present. Further, the feedback step 60 may be performed also if monotonic variations in the cast sheet thickness are detected, even before the resulting thickness 80 is outside the desired range.

(40) Further, preferably the feedback step 106 is performed in-line, that is, the parameters to be changed in order to obtain either a thickness 80 within the desired range or a uniformly thick cast sheet 10 are varied during production.