Patent Application
20100139675
This invention relates to a high pressure forming process for tobacco material. Specifically, it relates to the production of cut tobacco material or fibre-shaped tobacco material, which can be used as a product for manufacturing smoking articles.
When preparing the tobacco, i.e. during those preparation processes which take place prior to actual cigarette production and packaging, the most important tobacco materials, namely tobacco leaves and tobacco ribs, are subjected to several process steps before they can be used to produce smoking articles. The rib material used, as well as coarse or incompletely cut raw ribs (winnowings) are very difficult to process using standard means (cutters, shredders) and obtain an optimum result, in other words produce a cut tobacco material which can be used as smoking article material. Too many small pieces or dusts are created and/or lengthy intermediate storage periods are necessary.
Rib preparation processes which enable the ribs to be processed into tobacco film are disclosed in patent specifications DE 40 05 656 C2 and DE 43 25 497 A1, for example. Such tobacco film processes produce product with moderate to poor filling capacity and sensory properties. Patent specification DE 100 65 132 A1 discloses a method of producing agglomerates, whereby larger particle complexes are produced from the smallest tobacco particles. Binding agents must be used for this purpose and such a process is not suitable for processing coarser tobacco material (such as ribs or winnowings for example).
Patent specification DE 10 2004 059 388 A1 describes a process of reducing tobacco material to fibres, in particular from ribs or winnowing material. To this end, the tobacco starting material is heated and brought to an increased pressure and is so by means of a screw conveyor, at the outlet of which a shearing gap is disposed. The processing of the material as it leaves the shearing gap accompanied by flash evaporation results in a tobacco material reduced to fibres.
One objective of the invention is to propose a method of producing cut tobacco material, which delivers a better product quality than can be achieved by the methods known from the prior art. In particular, a tobacco material quality should be obtained which is immediately suitable for producing cigarettes by machine and in particular even corresponds to the demands made on a tobacco material used for self-rolled cigarettes. Due to a special feature, wear should also be minimised compared with devices known from the prior art.
This objective is achieved by the invention on the basis of a method as defined in claim 1 and a device as defined in claim 11. Preferred embodiments of the invention are defined in the dependent claims.
The tobacco starting material may primarily be a coarse tobacco material, in particular with a particle size of more than 2 mm. It may be a tobacco rib material or a winnowing material, in particular with a rib size of more than 2 mm. In this respect, it should be pointed out that tobacco materials such as raw ribs, winnowings, short stems or stem fibres but also scraps (small leaf tobacco particles), other tobacco small pieces, tobacco dust or a mixture of the of components listed above may be used.
The method proposed by the invention for producing cut tobacco is based on the following steps. A tobacco starting material is heated and brought to a first increased pressure in one method stage. In a subsequent method stage, the tobacco material is then pumped to a second increased pressure which is higher than the first increased pressure, and finally the tobacco material, heated and placed under pressure, is expanded and fed through a forming tool.
The pumping process helps to increase the pressure significantly (figures given below are above atmospheric pressure) prior to being expanded and passing through the forming tool, thereby obtaining optimum process conditions for producing a product of even better quality. Very high pressures can be generated which can not be achieved with the apparatus known from the prior art and mentioned above (screw conveyors) and amongst other things, this affords a high degree of freedom as regards the choice of forming tool. Furthermore, an operating mode which creates little wear is possible. Details of the advantageous mechanisms proposed by the invention will be explained in detail below.
In one embodiment of the invention, the tobacco material is pumped to the second increased pressure without essentially increasing the temperature of the material. A pumping process permits such an approach.
In one embodiment of the invention, the tobacco starting material is heated to a temperature of 60 to 180° C., in particular 100 to 140° C., and brought to a pressure of 10 to 200 bar, in particular 1 to 100 bar, more especially 1 to 50 bar, during the first stage of the method. During the second stage of the method, a pressure of 100 to 700 bar is achieved as a result of this invention, in particular 200 to 700 bar and more especially more than 200 bar to 700 bar.
The tobacco material is expanded to atmospheric pressure as it passes through the forming tool and this takes place in particular by a controlled flash evaporation.
During the second stage, the tobacco material may be fed through a positive displacement pump, in particular a gear pump.
As it passes through the forming tool, the tobacco material is advantageously formed to a fibre shape, in particular reduced to fibres, and the forming tool may be an outlet gap, a shearing gap, a die or a nozzle, for example. Due to the conditions of the method which can be achieved by pumping to the second raised pressure, the risk of blockages can be avoided and a freer choice of tools is available, which is a major advantage because the shape to be imparted to the tobacco material can also be selected more freely.
During the first method stage, the tobacco starting material is placed under pressure by mechanical means in particular, especially by means of a conveyor screw or stuffing screw, which presses the material against the outlet of a screw conveyor, in particular one which can be heated.
After further processing, the tobacco material may be used directly for smoking article material, especially if the tobacco starting material is a winnowing material. However, it may also be subjected to a screening process, especially if the starting material is a coarse rib material. This being the case, the material separated out may be subjected to the method proposed by the invention again and the remainder which is not separated may be despatched directly for further processing as smoking material.
The device proposed by the invention for producing cut tobacco material has a pressure chamber, in particular one which can be heated, which has a tobacco material inlet, a tobacco material outlet and a conveyor mechanism for conveying the tobacco material from the inlet to the outlet and for raising the pressure of the material to a first increased pressure. It also has a forming tool, by means of which the tobacco material, heated and placed under pressure, is conveyed and expanded, and for the purpose of the invention, a mechanical pump is integrated between the pressure chamber and the forming tool which pumps the tobacco material to a second increased pressure which is higher than the first increased pressure.
The advantages which can be achieved by the device proposed by the invention are the same as those mentioned above in respect of the method proposed by the invention.
The mechanical pump may be a hydrostatic positive displacement pump, in particular a gear pump.
The forming tool is a tool which reduces the tobacco material to fibres, in particular cuts it to fibres, and it may specifically have an outlet gap, a shearing gap, a die or a nozzle.
In one embodiment of the invention, the pressure chamber forms or the pressure chamber comprises a heatable screw conveyor, in particular a stuffing screw, which serves as a conveyor mechanism for conveying the tobacco material from the inlet to the outlet.
The invention further relates to the use of a device of the type described above for producing fibre-shaped tobacco material, in particular for reducing tobacco material to fibres. Another embodiment relates to the use of such a device for producing fine-cut tobacco material, in particular for use in roll-your-own cigarettes. This invention further relates to one of the aforementioned uses, whereby a method of the type described above is implemented in various ways.
It should be pointed out that one or more of the following features may fall within the scope of the invention:
The invention will now be explained in more detail with reference to theoretical considerations and with the aid of an example of an embodiment. It may incorporate all of the feature described here, either individually or in any practical combination. The appended drawings illustrate the following:
The inventive device illustrated in
Adjoining the outlet 6 of the screw conveyor 1 is the gear pump 7, which in this example is a hydrostatic positive displacement pump. The rib material firstly passes through the inlet 8 provided in the housing 9 into the pump 7 and is then conveyed onward by the two pump-gears 11 and 13 and compressed. The compression, i.e. the increase in pressure, takes place due to the spaces between gears, which become smaller, thereby resulting in tobacco material that is highly compressed or at a very high pressure (second increased pressure) at the pump outlet 10. The pressures at the pump outlet 10 and at the pump inlet 8 are measured and are checked by pressure sensors 17 and 15 respectively. The operating mode of the pump can be set in order to influence these pressures and make a correction if necessary.
From the pump outlet 1, the tobacco material passes into a forming tool, which is denoted by reference number 23 in
The invention therefore relates to the cutting into fibres (reducing to fibres) and re-forming of tobacco material—as implemented on the device described above—in order to impart a fibre shape to tobacco particles. The process is distinctive due to a particularly low-wear operating mode and increased process flexibility. Tobacco coarse parts are cut, optionally together with small or very small particles already in or added to the starting material as required, formed in the tool and discharged as fibres. Of particular advantage is the robustness of such an apparatus in terms of the properties of the material to be processed which cause wear, especially because there are no restrictions as to the choice of formula. The tobacco material produced by a method and a device as proposed by the invention can be used directly for the production of smoking articles; in form and colour, it is no different from cut tobacco. The invention can therefore be used in conjunction with the production of smoking article products for self-prepared cigarettes (also referred to below as Roll-Your-Own products (RYO) or Make-Your-Own products (MYO)) with a short cut width, because the tool is flexible and in particular it is also possible to use tools with very small passages which can be used at particularly high pressures.
Amongst other things, the invention is based on the following considerations.
Known methods such as that disclosed in patent specification DE 10 2004 059 388 A1 mentioned above, for example, do not allow pressures to be generated, at least not directly, such as those that are actually desirable for producing an optimised tobacco material. This is attributable—as observed during the work done on this invention—firstly to the fact that an increase in pressure is accompanied by an increase in temperature due to the higher shearing energy generated, the degree of which is determined by the material and screw conveyor. Secondly, the design of the predefined tool is determined by the preliminary pressure because the drop in pressure—defined by the free tool cross-section—and the mass flow of the tobacco materials are proportionately correlated, as demonstrated in
In principle, such pressure can not be applied by a screw conveyor (extruder). One reason for this is that the so-called back-flow (sum of the pressure flow and leakage flow), dominates the drag flow, as illustrated in
Another problem resides in the energy generated by shearing which accompanies the conveying action and the associated increase in the temperature of the material being conveyed. If temperatures up to 200° C. and compaction up to 200 bar is reached with conventional devices, the product can already be damaged. The anticipated high product temperature at even higher pressures would cause structural damage after an isenthalpic pressure release based on the principle of capacitive drying) on leaving the tool due to the development of water vapour and would also lead to complete over-drying, which is not desired. This relationship is illustrated in
Due to the very low coefficient of heat throughput, cooling between a cooling medium and the product flow would barely be possible or would merely be of slight assistance so that it must be concluded, all in all, that the conventional system with the screw conveyor is not suitable for generating a chamber pressure of up to 700 bar. Although lower preliminary pressures can be generated with a screw conveyor (200 bar or less), the range of parameters as regards the formulas, filling capacity or very small fibre diameter to be obtained is limited. Using a pump (in particular a mechanical pump) to generate the second increased pressure overcomes the above problems and enables the production of optimised products at economically acceptable mass flows and in particular with a low-wear operating mode. In the embodiment illustrated, such a pump is the gear pump 7 and the screw conveyor 1 supplies this pump.
Gear pumps are hydrostatic positive displacement pumps and the conveying action is operated on the principle of a closed volume. As a result of this principle, very high pressures can be generated when conveying viscous masses with moderate rises in temperature. The material should be fed to the pump assisted by a (slight) pressure, thereby enabling a 100% filling level to be achieved, and a screw conveyor lends itself very well to generating this preliminary pressure.
Like liquids, fluid materials such as pastes, pulps, doughs, can be characterised on the basis of viscosity. Tobacco materials are solids but pseudo-plastic flow properties are imparted to them after adding water, an increase in temperature and shearing, and they can therefore be conveyed in a positive displacement pump. These basic flow properties are created in the screw conveyor. A typical flow curve of a plasticised tobacco material may be seen in
The tool 23 illustrated in
Due to the fact that compression takes place almost without any rise in temperature, the operating temperature and working pressure are effectively separate parameters. Accordingly, operating temperatures of 60 to 180° C., which have already been found to be of advantage, can be easily set in conjunction with final pressures of 200 to 700 bar, thereby avoiding any fear of the fibres being destroyed due to too intensive development of steam. It should also be pointed out that the specified rating of a pump or a positive displacement pump will also be lower due to the low increase in temperature.
Due to the high compaction of the tobacco material, the tobacco density is naturally increased. However, the controlled flash evaporation which occurs on expansion to atmospheric pressure reverses the compaction and leads to a loose cut tobacco. Surprisingly, this expansion and the restoration of the natural filling capacity is still possible even with the unusually high degree of compaction of the tobacco material which occurs due to the invention.
The combination of screw conveyor and pump, in particular a positive displacement pump, can also help to compensate for unavoidable wear. As already explained, the conveying behaviour of the screw conveyor is dependent on the state of wear, the final pressure and the properties of the material. Due to the proposed inventive design, it is possible to distribute the pressure needed to induce a flow through the tool differently between the screw conveyor and positive displacement pump. If the wear pattern becomes worse, the final pressure of the screw conveyor can be reduced, for example, in which case the positive displacement pump then automatically supplies the increase in pressure needed to induce a flow through the tool. Such behaviour is plotted in the operating curve shown in
Further evidence of the positive effects of this invention as regards operating the device and the mass flow will become apparent below from the explanation of the tests that were conducted:
Test 1:
In this test, the effect on wear of the different pressure distribution (screw conveyor/gear pump) and the same final end pressure were studied. A formula, based on 70% winnowings+30% tobacco dust is treated in the apparatus illustrated in
Results of Test 1:
Due to the low operating pressure and the lower operating temperature in the screw conveyor, the wear detected during the operating hours leading up to the point when conveying was halted was more or less halved. This resulted in a longer service life of the device. Naturally, the moisture content at the outlet due to the lower input of shearing energy was lower because the temperature load is lower.
Test 2:
During this test, increases in throughput and the associated pressure increase upstream of the forming tool were studied.
A formula based on 70% winnowings+30% tobacco dust is treated in the apparatus illustrated in
Results of Test 2:
Due to the additional pressure applied by the gear pump proposed by the invention, the mass flow was increased by approximately 60%, thereby increasing economic viability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 002 687.2 | Jan 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/010552 | 12/12/2007 | WO | 00 | 2/16/2010 |
