US3785384A

US3785384A - Method of treating tobacco

Info

Publication number: US3785384A
Application number: US00196652A
Authority: US
Inventors: H Sylvester; C Partridge; I Goss
Original assignee: Carreras Rothmans Ltd
Current assignee: Carreras Rothmans Ltd
Priority date: 1971-11-08
Filing date: 1971-11-08
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15

Abstract

A method of treating tobacco to cause its cellular structure to expand and/or to cause the fibres to move apart from one another which includes passing it through a high frequency field on a conveyor and beneath an overlying static sheet.

Description

Unite States atet n91 Sylvester et al.

[ Jan. 15, 1974 METHOD OF TREATlNG TOBACCO [75] Inventors: Herbert A. Sylvester, Basildon;

Christopher M. Partridge, Canvey Island; lra D. Goss, Rayleigh, all of England [73] Assignee: Carreras Rothmans Limited, Essex,

England [22] Filed: Nov. 8, 1971 [21] Appl. No.: 196,652

[52] US. Cl 131/121, 131/140 P [51] lint. Cl A24b 3/18 [58] Field of Search 131/121, 66 A, 69 A,

[56] References Cited UNITED STATES PATENTS Russell 131/121 X Kennedy et a1. 131/121 UX 3,665,932 5/1972 Goldbach 131/21 A X 2,739,599 3/1956 Abbott 131/121 3,057,361 10/1962 Respess l 131/121 X 3,535,629 10/1970 Gibson et a1 131/21 A FOREIGN PATENTS OR APPLlCATlONS 947,280 1964 Great Britain 131/121 132,374 1902 Germany 131/84 A 958,621 1964 Great Britain l 1. 131/121 407,757 1944 Italy 131/121 Primary Examiner-Robert W. Michell Assistant Examiner-Vincent A. Millin Attorney-Donald M. Wight et a1.

[57] ABSTRACT A method of treating tobacco to cause its cellular structure to expand and/or to cause the fibres to move apart from one another which includes passing it through a high frequency field on a conveyor and beneath an overlying static sheet.

19 Claims, 6 Drawing Figures PATENIEUJAN l 5l974 SHEET 1 0F 2 METHOD or TREATING TOBACCO This invention relates to a method and apparatus for treating tobacco which is to be used in smoking products such as cigarettes, cigars and the like and such products will be referred to herein as tobacco products.

According to the present invention a method of treating tobacco to cause its cellular structure to expand and/or to cause the fibres to move apart from one another includes passing it through a high frequency field on a conveyor and beneath an overlying static sheet.

In one method the static sheet is impervious and may be made from glass fibre coated with silicon-rubber, for example, that sold under the Trade Mark Symel."

The static top sheet appears to act as a high frequency damper by retaining the moisture vapour whilst the tobacco is in the high frequency field, thus maintaining a more even dielectric constanct or loss factor. It also greatly reduces arcing and/or burning which would otherwise be caused by a volatage breakdown at localised areas.

In another method the static sheet is pervious and may be made from a woven glass fibre material the sheet to allow the moisture vapour to escape.

Preferably the high frequency field is caused by displaced electrodes between which the tobacco is passed.

The invention also includes a method in which the tobacco is compressed on the conveyor to provide a layer of constant thickness prior to entry into the high frequency field and which assists in flattening any vertically oriented slivers on the top surface of the tobacco layer.

In any case, the tobacco is preferably carried on a conveyor belt made from a material having a low dielectric loss factor, for example, a material made by LG]. Fibres and Sold under the Trade Mark Terylene.

According to a further feature of the invention tobacco is cooled in a cooling unit after passing through the high frequency field.

According to another aspect of the invention a method of treating tobacco includes supplying it as a layer to a moving belt, passing the belt through a high frequency field, in a dielectric oven, caused by electrodes between which the belt passes, and beneath a static sheet arranged in the oven and subsequently cooling the tobacco in cooling means by passing air through it.

In any case, the high frequency electric field may be caused to pulse in the manner described and claimed in the Applicants co-pending British Pat. Application No. 32237/68, now British Pat. No. 1,276,496.

The invention also includes apparatus for treating tobacco to cause its cellular structure to expand and/or to cause the fibres to move apart from one another comprising means for producing a high frequency electric field, a conveyor to pass the tobacco through the field and a static sheet arranged to lie over the conveyor.

In this apparatus the static sheet can be impervious and is preferably made from glass fibre coated with silicon-rubber, or it can be pervious and may conveniently be made from woven glass fibre material.

Means may also be included for compressing the tobacco on the conveyor to provide a layer of constant thickness prior to entry into the high frequency field, and which assists in flattening any vertically oriented slivers in the top surface of the tobacco, and the compressing means may be provided by a roller extending transversely across the conveyor.

With this arrangement the roller is preferably driven at a speed in excess of the speed of the conveyor.

The conveyor may include a travelling belt made from a material having a low dielectric loss factor, for example, Terylene.

Preferably a cooling unit for cooling tobacco after passing through the high frequency field is included and this cooling unit may have means for passing air through the tobacco and may thus comprise an open mesh conveyor to receive the tobacco and a fan for blowing ambient air through the conveyor.

According to another feature of the invention means are included for delivering tobacco to be treated to the conveyor comprising a metering duct from one end of which tobacco is delivered in a uniform layer on to the conveyor and means for maintaining uniform head of tobacco in the duct.

The means for maintaining the uniform head of tobacco may comprise two spaced light sensitive cells which are spaced vertically apart in the wall of the duct and which are connected to operate a device for feeding tobacco to the duct.

With this construction the walls of the duct are preferably transparent and light means are provided which shine through the transparent walls on to the light sensitive cells.

According to another feature of the invention a number of electrodes are provided on each side of the conveyor and means are included to allow their relative positions to be adjusted to vary the power density of the field.

The invention may be performed in many ways. but one embodiment will now be described by way of example and with reference to the accompanying drawings in which:

FIG. l is a diagrammatic side elevation of apparatus for carrying out a method according to the invention,

FIG. 2 is an isometric view of a metering duct for delivering tobacco,

FIGS. 3 and 4 are diagrammatic side elevations of part of the apparatus shown in FIG. 1,

FIG. 5 also shows part of the construction of the apparatus shown in FIG. 1, and

FIG. 6 is a cross-sectional end elevation of the cooling unit.

As shown in FlGfl the apparatus for carrying out the dielectric treatment of the tobacco comprises a standard kind of tobacco feeding machine indicated at A which delivers cut tobacco having a moisture content of, say, 18.5 percent to a main conveyor band G through a delivery duct indicated at K.

The layer of tobacco J is delivered through oven units C on the conveyor G to a second conveyor S by means of which it is carried through a cooling unit H in which it is rapidly cooled immediately prior to its transfer for either storage or immediate use on a cigarette making machine.

As shown in FIG. 2 the cut tobacco J at 18.5 percent moisture content is metered on to the conveyor G in such a way as to maintain a uniform thickness of the tobacco layer and a uniform distribution across the width of the conveyor G. This uniformity of thickness is essential for good control of moisture removal in the type of radio frequency oven used in the invention.

To maintain the uniform head of tobacco in the metering tube K photo cells and light sources M are mounted behind the front and rear panels of the tube K which are made from transparent material such as Perspex. If the head of tobacco falls below the lower photo cell, the drive to the feeder A, as shown in FIG. 1, is automatically increased in speed and more tobacco is fed upwards and into the duct. Alternatively if the tobacco head rises above the upper photo cell, the drive to the feeder is automatically slowed down. It will be appreciated that the feeder A is of a variable speed type and is controlled by an electric circuit actuated by the photo cells M in a conventional manner.

Prior to its entry into the oven C, the tobacco on the belt G is compressed by a large diameter 8 inch roller X having drive means (not shown) for driving the same at a speed slightly in excess of the speed of the belt. The purpose of this roller X is to reduce the thickness of the tobacco layer J in its delivered form to a constant height acceptable to the radio frequency field and to flatten any vertically protruding slithers of tobacco which would otherwise cause arcing in the oven.

Best results have been obtained from tobacco which has been conveyed through the oven units C on belts woven from 100 percent Terylene. The advantage in using the woven Terylene is that it has a very low dielectric loss factor and is therefore not affected by the radio frequency field in the oven. Moreover, it does not burn easily. If and when burning does occur, due to voltage breakdown, the belt is merely carbonised at that point without catching fire. Belt cleaning brushes V are used to clean the belt automatically of loose tobacco and any carbon which may collect as a result of occasional burning.

The tobacco J is sandwiched between the conveyor belt G and an overlying static sheet T whilst the tobacco is being progressed through the oven units, as is most clearly shown in FIGS. 3 and 4. The static sheet is non porous and made of glass fibre which has been coated with silicon-rubber, for example, Symel. This sandwiching between the static sheet T and conveyor G prevents the removal of moisture until the heated tobacco has cleared the electrode area in the ovens. It is thought that the static top sheet acts as a radio frequency damper by retaining the moisture vapour under the electrodes E, thus maintaining a more even dielectric constant or loss factor across the area of the electrodes E, which include a base electrode underlying logitudinally spaced positively and negatively charged electrodes with current fiow between the electrodes being diagrammatically illustrated by arrows in FIG. 3 and 4. This greatly reduces arcing and/ or burning which would otherwise be caused by a voltage breakdown at localised areas. The siliconised glass fibre is resistant to any burning which does take place beneath it and it will be seen from the drawings that only one end of the sheet is anchored at T1, the sheet trailing over the tobacco beneath it.

FIGS. 3 and 4 also show two settings of the electrode system in the ovens which can be used for the treatment of tobacco in this form. Both settings provide a simulation of a pulsed electric field on the tobacco passing between the electrodes E, for example, as set forth in the aforementioned British Pat. No. 1,276,496.

In FIG. 3 the setting of the electrodes E is used to give a high power density, this setting also providing the maximum pulsing effect and it will be seen that the electrodes E are immediately opposite each other across the conveyor belt.

In FIG. 4 the same electrode system is used but is set to give a more continuous radio frequency field over the whole area. In this setting the power density is lower and the pulsed effect is less and it will be seen from the drawing that this is because the electrodes are not directly in line with each other.

Either setting can be set up on the apparatus because the electrodes are adjustable to give any condition required between the two settings referred to above.

It will be seen that two separate oven units C are shown in FIG. 1 but these are interconnected by a common attenuation duct F to prevent loss of heat and the static sheet T extends right through the duct F.

Apart from'increasing the filling power which takes place during drying by radio frequency means a more uniform level of moisture content is obtained in the tobacco when compared with tobacco which has been dried down to the same level by conventional means.

From FIG. 1 it will be seen how the tobacco is progressed through the oven unit C and finally through a cooling unit H immediately prior to the delivery to storage. The cooling unit H, as shown in FIG. 6 comprises a woven wire belt S on which the tobacco .I is conveyed and which is supported on bars W. The conveyor is housed in a casing Y and fan Z is provided in the upper part of the housing to draw ambient air upwards through the hot tobacco J and vented to atmosphere. Uniform transfer of the hot wet tobacco from the Terylene oven conveyor G to the woven wire conveyor S in the cooling unit is achieved by extending the oven conveyor G over the woven wire conveyor as shown in FIG. 5. Both conveyors are driven at the same linear speed as it has been found that if uniform transfers are not achieved, then the air flow through the tobacco becomes uneven and this in turn results in uneven or patchy drying.

Rotary cleaning brushes V are used to prevent a build up of tobacco dust in both the mesh ofthe wire conveyors and on the surface of the oven conveyor G. Experience has shown that after tobacco emerges from under the static top sheet T (under the electrodes), the bulk of the latent moisture vapour is extracted through the oven compartments extraction unit. The tobacco is still at a temperature considerably higher than ambient (1 12 F) and not at the required moisture level. Passing the tobacco through the cooling unit 4 now reduces this temperature. To do this, ambient air is passed through the tobacco at a rate of approximately 270 cubic ft/min., the residence time for any part of the tobacco being 23 seconds. This rapid cooling helps to stiffen the cell structure of the tobacco after the R/F treatment which helps to improve the filling power of the tobacco.

Experience has shown that in order to achieve the desired effect of increased filling power, the tobacco should be subjected to the maximum power density which is possible for the required amount of moisture removal. For this consideration instantaneous power density" is taken as being the total power applied in kilowatts per lb. of tobacco under the electrodes at any instant. The instantaneous power density per lb. of tobacco is proportional to both the belt speed and the electrode length. For example, for a given amount of tobacco processed, the power density can be doubled if the tobacco is progressed through the oven in half the original time taken. Alternatively the power density can also be increased if the electrode length is shortened because at any instant the amount of tobacco under the electrodes is proportionally reduced. The limiting factor of high instantaneous power density is frequent voltage breakdown.

When the belt becomes carbonised through frequent burning, then the affected portion of the belt can itself become a voltage break-down area for the next circuit of the belt through the electrodes and so on. The rotating brushes V as shown in FIGS. 1 and 5 help to prevent a build up on the belt of dry tobacco which can also become a possible source of belt buring. The brushes also help to remove any carbon deposits on the belt brought about by burning.

In an alternative arrangement when the apparatus is used for treating cut rolled stem tobacco the impervious static sheet is replaced by a pervious sheet made from woven glass fibre material. It has been found that this allows a proportion of the water vapour to pass through it but at the same time it acts as a radio frequency damper and greatly reduces arcing and/or buring. With this arrangement hot air is forced into the oven compartment in order to raise the dew point and expel the water vapour. Thus preventing condensation occuring on the electrode system which leads to arcing and unit shut down.

We claim:

1. Tobacco treatment apparatus for treating tobacco in a manner to cause its cellular structure to expand and/or to cause fibres thereof to move apart from one another, said apparatus comprising charged spaced apart electrode means for producing a high frequency electric field, a conveyor for passing the tobacco between said electrode means and through said field, means for delivering a layer of tobacco onto said conveyor, electrically static sheet means overlying said conveyor in spaced relation thereto and in said high frequency electric field, and mounting means mounting said static sheet for floatingly contacting a layer of tobacco disposed on said conveyor and passing through said field.

2. Apparatus as claimed in claim 1 in which said static sheet means is impervious.

3. Apparatus as claimed in claim 2 in which said static sheet means is made from glass fibre coated with silicon-rubber.

4. Apparatus as claimed in claim 1 in which said static sheet means is pervious.

5. Apparatus as claimed in claim 4 in which said static sheet means is made from a woven glass fibre material.

6. Apparatus as claimed in claim 1 together with means for compressing the tobacco on said conveyor to provide a tobacco layer of constant thickness prior to entry of said tobacco into said high frequency field.

7. Apparatus as claimed in claim 6 in which said compressing means is provided by a roller extending transversely across said conveyor.

8. Apparatus as claimed in claim 7 wherein said roller operates at a speed in excess of the speed of the conveyor.

9. Apparatus as claimed in claim 1 together with a cooling unit for cooling the tobacco after the tobacco passes through the high frequency field.

10. Apparatus as claimed in claim 9 in which said cooling unit includes means for passing air through the tobacco layer.

11. Apparatus as claimed in claim 10 in which said cooling unit includes said conveyor being of an open mesh construction and a fan for blowing ambient air through said conveyor.

12. Apparatus as claimed in claim 9 in which a rotary brush means are provided for cleaning that surface of said conveyor which passes through said cooling unit.

13. Apparatus as claimed in claim 1 wherein means for delivering a layer of tobacco onto said conveyor includes a metering duct from one end of which tobacco is delivered in a uniform layer onto said conveyor, and means for maintaining a uniform head of tobacco in said duct.

14. Apparatus as claimed in claim 13 in which said means for maintaining a uniform head of tobacco in said duct comprises said duct having walls, feed means for feeding tobacco to said duct, and light sensitive cell means carried by at least one of said duct walls in an arrangement spaced in the direction of tobacco travel through said duct for controlling the operation of said feed means.

15. Apparatus as claimed in claim 14 in which at least certain of said duct walls are transparent and light producing means are provided for directing light through said transparent duct walls onto said light sensitive cells.

16. Apparatus as claimed in claim 14 in which said device for feeding tobacco to the duct has a variable speed drive.

17. Apparatus as claimed in claim 1 in which said high frequency electric field is provided by a plurality of said electrodes disposed on each side of said conveyor.

18. Apparatus as claimed in claim 1 in which a rotary brush means are provided for cleaning that surface of said conveyor which passes through said high fre quency field.

19. Apparatus as claimed in claim I wherein said mounting means anchors said static sheet means at one

Claims

18. Apparatus as claimed in claim 1 in which a rotary brush means are provided for cleaning that surface of said conveyor which passes through said high frequency field.

19. Apparatus as claimed in claim 1 wherein said mounting means anchors said static sheet means at one end only.