EP0361903A1

EP0361903A1 - Monitoring of tobacco smoke filter rods

Info

Publication number: EP0361903A1
Application number: EP89309853A
Authority: EP
Inventors: John Andrew Banks; John Nigel Tredinnick White
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1988-09-30
Filing date: 1989-09-27
Publication date: 1990-04-04
Also published as: DE361903T1; GB8822972D0

Abstract

There is disclosed a method and apparatus for monitoring the quality of tobacco smoke filter rods (1) formed by passing filter tow (4) through a narrowing passage (42) to laterally compress the filter tow. The invention relates to the monitoring of the pressure of gaseous medium in a space (45) communicating with the narrowing passage (42) via an orifice (46), the gaseous medium being supplied to the space (45) via the orifice (46) as a result of being expressed from the filter tow as the latter is laterally compressed during movement through the narrowing passage (42).

Description

This invention relates to a method of monitoring the quality of tobacco smoke filter rod formed by passing filter tow through a narrowing passage to laterally compress the filter tow. The invention also relates to an apparatus for producing tobacco smoke filter rods.
Conventionally tobacco smoke filter rod sections are manufactured by drawing filamentary filter tow, e.g. of cellulose acetate fibers, from a bale, stretching the tow as it is sprayed with droplets of a plasticizer, e.g. triacetin, converting the tow into rod-like form wrapped with a web of wrapping material and severing the resulting rod at regular intervals to produce a succession of filter rod sections typically six times the length of a filter used in a filter cigarette. The filter tow is a bundle of crimped filaments which may have slight variations in density along its length usually as a result of variable tensioning of the filaments during processing which can cause slight differences in crimp character. These variations can translate into variations in pressure drop in filter rods made from different sections of the tow. Accordingly it has proved necessary to monitor the quality of the tobacco smoke filter rods, either after or during their production, and to control the supply of the filter tow in dependence on the amount the monitored quality deviates from a desired value.
One known method of monitoring the quality of tobacco smoke filter rod sections is described in U.S. Defensive Publication No. T 941,011. In this known specification the filter tow is converted into wrapped, rod-like form by being passed through a garniture defining a narrowing passage which serves to condense the filter tow to its rod-like form prior to the filter tow being wrapped with filter paper. An air sensor device is mounted on the garniture and enables air to be supplied under pressure from an external source to a plenum chamber which communicates with the narrowing passage by means of a series of apertures. Air supplied to the plenum chamber flows through these apertures and through the filter tow moving through the narrowing passage. The back pressure in the plenum chamber resulting from the resistance to the flow of air through the filter tow is transmitted to a differential pressure cell or transducer for generating an electrical signal representative of the eventual consolidation of the filter tow in the filter rod. In order to generate this electrical signal it is thus necessary to supply air at a controlled rate to the plenum chamber and to provide means to sense the back pressure in the plenum chamber.
Another known method of monitoring the quality of tobacco smoke filter sections is described in GB-A-1588506. In this known specification the filter tow is supplied to a garniture which defines a narrowing passage and in which the filter tow is laterally compressed and wrapped with a web of wrapping material. A pair of spaced apart chambers communicate with the narrowing passage at spaced apart locations along its length. Air under pressure is supplied to each chamber and, in normal operation, passes from the chamber into the filter tow moving through the narrowing passage. The back pressure in the two chambers is compared in a comparator for generating an electrical signal representative of the pressure drop occurring longitudinally through the filter tow in the narrowing passage between the spaced apart chambers. In order to generate this electrical signal it is necessary to mount two pressure tappings on the tongue of the garniture, to supply air at a controlled rate to each of the chambers and to provide a separate pressure monitoring connection between the comparator and each of the chambers.
The present invention seeks to provide a simplified method for monitoring the quality of tobacco smoke filter rods.
According to one aspect of the present invention a method of monitoring the quality of tobacco smoke filter rod formed by passing filter tow through a narrowing passage to laterally compress the filter tow, comprising supplying a gaseous medium to a space which communicates via orifice means with the narrowing passage and generating a control signal, dependent on the pressure in said space, which is representative of the eventual consolidation of the filter tow in the filter rod, is characterised in that the said supply of gaseous medium to the said space occurs as a result of gaseous medium, previously entrained in the filter tow, being expressed from the filter tow and passing through said orifice means during said lateral compression of the filter tow as the latter passes through the narrowing passage.
Preferably the orifice means is positioned between inlet and outlet ends of the narrowing passage.
Preferably means are provided for controlling the filter tow prior to its passage through the narrowing passage. In particular the amount of stretch of the filter tow and the speed of passage of the filter tow through the narrowing passage may be controlled.
Conveniently the control signal is supplied to display means to provide a visual indication of the quality or density of filter tow as it passes through the narrowing passage. On the basis of this visual indication, e.g. a display on a monitor attached to a computer, an operator is able to adjust parameters, e.g. the speed of delivery rolls, feed rolls and/or tension rolls, controlling the supply of the filter tow to the narrowing passage. Alternatively, or in addition, the control signal may be employed to automatically control filter tow supply parameters.
Suitably the control signal is generated at the output side of a pressure transducer which is connected to the said narrowing passage by a tubular passage defining, at least in part, the said space.
According to another aspect of the present invention apparatus for producing tobacco smoke filter rods from filter tow including means for transporting the filter tow from a source along a path, means for stretching the filter tow in a first portion of said path, compressing means including a narrowing passage having inlet and outlet ends for laterally compressing the filter tow and converting it into rod-like form in a second portion of said path, means for severing the rod-like form to produce discrete lengths of filter rod sections, means defining a space which communicates with said narrowing passage via orifice means and means for generating a control signal dependent on the pressure in said space and which, in use of the apparatus, is representative of the eventual consolidation of the filter tow in a filter rod section, is characterised in that the said space is closed apart from its communication with said narrowing passage via said orifice means so that, in use of the apparatus, the pressure within said space is determined by the amount of gaseous medium, previously entrained in the filter tow, which is expressed from the filter tow and passes through said orifice means during lateral compression of the filter tow as the filter tow passes through the narrowing passage.
Suitably the apparatus further includes means for wrapping a web of wrapping material, e.g. filter paper, around the rod-like form in a third portion of said path downstream of said compressing means.
Conveniently the compressing means comprises a conventional garniture in which the narrowing passage is defined in a generally frusto-conical form by a downwardly concave upper tongue which overlies a base having an upwardly-concave channel in which runs the endless tape used to support the wrapping material.
Preferably the means defining said space is a tube lying in an axial plane of said narrowing passage. Typically the tube is disposed at an angle of less than 90°, e.g. between 30 - 60°, to the axis of the narrowing passage.
Suitably the control signal generating means includes a pressure transducer for sensing the gas pressure in said space. The control signal generating means may also include an amplifier connected to an output of the pressure transducer. The control signal may be supplied to control means for automatically controlling the filter tow transporting means and/or the filter tow stretching means.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side elevation of apparatus for producing tobacco smoke filter rods,
Figure 2 is a longitudinal sectional view on an enlarged scale through part of the apparatus shown in Figure 1,
Figure 3 shows a number of different plots for different apparatus speeds showing how the control signal varies for different densities of filter rod, and
Figure 4 is a plot showing how the control signal varies as the speed of the apparatus is changed to produce filter rods at different rates.

Figure 1 shows apparatus for producing tobacco smoke filter rod sections 1 of desired length, typically six times unit length, comprising a filter rod making machine 2 and a filter tow processing unit 3. The filter rod making machine 2 is of the type known as "KDF-2" produced by Hauni-Werke körber Co., K.G. of Hamburg, Federal Republic of Germany.
The filter processing unit 3 draws filter tow 4, typically comprising crimped fibers or filaments of cellulose acetate, from a bale 5 and passes the filter tow along an elongate path defined by a guide roller 6 and first, second and third pairs of driven advancing or transporting rolls 7, 8 and 9, respectively. First and second banding devices 10 and 11 are positioned on either side of the guide roller 6 and serve to spread out the tow into a relatively flat and wide layer before it reaches the rolls 7. The banding devices 10 and 11 each comprise means for discharging at least one stream of a compressed gaseous fluid against one side of the filter tow 4 and a barrier opposite the discharging means on the opposite side of the filter tow. A plasticizer unit 12 is positioned between the pairs of rolls 8 and 9 for applying atomised liquid plasticizer, e.g. triacetin, to the filter tow 4.
The pairs of advancing or transporting rolls 7, 8 and 9 have driven lower rolls 7a, 8a and 9a, respectively. The lower rolls 8a and 9a are driven by belts or chains 13 and 14, respectively, which derive their motion from the output of a variable-speed transmission device 15. The lower roll 7a is driven from the output of a further variable-speed transmission device 16 which itself is driven by a belt or chain 17 from the lower roll 8a. The peripheral speeds of the pair of rolls 8 exceed the peripheral speeds or the pair of rolls 7 so that the filaments of the tow 4 are stretched or subjected to tensional stresses to deregister the crimp of filaments of the filter tow 4 prior to the filter tow reaching the plasticizer unit 12.
The third pair of advancing or transporting rolls g transport the filter tow to the filter rod making machine 2 and assist in transporting the filter tow along its elongate path to the outlet side of the machine 2. The filter rod making machine 2 comprises a garniture 20 of conventional form (shown schematically in Figure 2) for laterally compressing the spread out filter tow 4 and converting it into a rod-like filter, a wrapping mechanism 23 for wrapping a web 24 of wrapping material, e.g. cigarette filter paper, around the rod-like filter and a severing mechanism 25 for cutting the continuous wrapped filter rod into the discrete filter rod sections 1. The machine 2 also includes an endless tape 21 for drawing the web 24 from a supply bobbin 22, the web 24 being moved past a pasting device 26 prior to being supplied to the wrapping mechanism 23. Drive to the conveyor 21 and for operating the severing mechanism 25 is provided by endless belts or chains 27 and 28, respectively, driven from a prime mover 29, e.g. a variable-speed electric motor. The prime mover also drives the variable-speed transmission device 15 by means of a further endless belt or chain 30.
The wrapping mechanism 23 comprises three separate units; namely a folding unit 31, which folds the web 24 around the rod-like filter exiting from the garniture 20 so that overlapping edge portions of the web 24 adhere to each other and form a lengthwise extending seam, a seaming unit 32 for completing the formation of the seam and a sealing unit 33 for heating or cooling the seam in dependence on whether the adhesive in the pasting device 26 is a wet adhesive or a hot melt adhesive.
The severing mechanism 25 serves to cut the filter rod into the discrete sections 1 which are propelled into flutes on the circumference of a drum-like conveyor 47. The conveyor 47 delivers the filter rod sections 1 into the upper reach of a belt conveyor 48 for transport away from the apparatus.
The garniture 20 is shown schematically in Figure 2. It is of a usual general form in which a narrowing passage 42 with an inlet end 40 and an outlet end 41 is defined on its upper side by a tongue 20a and on its lower side by a channel member 20b in which the endless tape 21 runs. As the tongue 20a and channel member 20b are conventional items they are depicted in the simplified form shown for purposes of clarity.
The narrowing passage 42 has an upstream portion 43 and a downstream portion 44 of which the upstream portion 43 has a greater degree of convergence than the downstream portion 44. Each portion is approximately, but not truly, frusto-conical in form. Although the tongue 20a is similar to the "KDF-2" tongue of the "KDF-2" filter rod making machine, it is modified by the provision of a tube 45 which opens into the downstream portion 44 of the narrowing passage via an orifice 46. The tube 45 is inclined at an angle of from 30° - 60° , e.g. 45°, to the horizontal and lies in an axial plane of the narrowing passage. By way of example, the dimensions of the narrowing passage 42 of the garniture 20 are as follows: a = 109 mm, b = 145 mm, c = 55 mm, d = 2 mm, e = 12 mm and f = 21 mm. The internal diameter of the tube 45 is approximately 1 mm. The tube 45 is connected directly to a pressure transducer 50 having an output connected to the input of an amplifier 51 for delivering an electrical control signal thereto. The amplifier 51 is connected to a computer 53 via an A/D converter 52. A monitor 54 and disk drive 55 are connected to the computer for providing a visual indication and a stored record, respectively, of pressure in the tube 45 sensed by the pressure transducer 50. In addition to, or as alternative to, the output of the amplifier 51 being connected to the items 52 - 55, the amplifier may be connected via connection lead 56 and/or connection lead 57 to the variable-speed transmission device 15 and/or 16 to provide automatic control of the drive rolls 7, 8 and 9.
In use of the apparatus, the passage of the filter tow through the filter tow processing unit 3 causes air and/or other gaseous fluid to become entrained in the filter tow. The banding devices 11 and 12 assist in this entrainment but, even without these devices, air would naturally become entrained in the filter tow 4. During passage of the filter tow 4 longitudinally through the narrowing passage 42, the filter tow 4 is laterally compressed and entrained gaseous fluid, e.g. air, in the filter tow is expressed laterally outwardly through the orifice 46 and into the tube 45. As the filter tow passes through the narrowing passage 42, the pressure transducer 50 continuously monitors the gas pressure in the tube 45 and supplies an electrical control signal to the amplifier 51. As previously described, the signal at the output of the amplifier 51 may be passed to the computer 53 and/or to control the pairs of rolls 7, 8 and 9. Since the diameter of the narrowing passage 42 at the outlet end of the tongue 20 is only 2 mm, the filter tow is over compressed in the passage 42 and, on exiting the tongue 20, the rod-like filter expands radially outwardly into the web 24 of wrapping material. The filter rod exiting the wrapping mechanism 23 is cut into discrete sections by the severing mechanism 25 and the severed filter rod sections 1 are moved away from the apparatus by the conveyors 47 and 48.
The apparatus described is intended to enable monitoring of filter tow material during production of filter rod sections to give an indication of the variability in linear density of the filter tow material in the eventually produced filter rod sections. By continuously monitoring the filter tow material, the need for subsequent quality testing of the filter rod sections after they have been produced is eliminated. If there is any deviation in the control signal from an expected value, action can be taken immediately to alter parameters of the filter rod producing apparatus to improve the quality of the filter rod sections being produced. This action can be effected manually or automatically as previously described.
Figure 3 shows a series of plots illustrating how the expelled air control signal (i.e. the signal at the output of the amplifier 51) varies with the pressure drop measured axially through filter rod sections produced on the apparatus for five different rates of movement of filter tow through the narrowing passage 42 (measured in terms of filter rod sections produced by the apparatus per minute). The pressure drop along a filter rod section is measured using conventional filter rod testing equipment, e.g. a Filtrona testing unit, and the five plots A-E are for rates of 1000, 2000, 2500, 3000 and 3500 rods/minute, respectively. The plots A-E illustrate that, for any given rate of movement of filter tow through the narrowing passage 42, there is a linear relationship between the control signal and the measured filter rod section pressure drop. Thus the control signal provides a good indication of the eventual quality or "density" of the eventual filter rod sections produced in the apparatus.
Figure 4 illustrates the manner in which the expelled air control signal varies as the rate of movement of filter tow, measured in terms of filter rod sections produced per minute, varies. The graph illustrates a direct linear relationship between these measured quantities.
Although the invention has been described above with particular reference to the modification of the tongue of a "KDF-2" machine, the invention is applicable to other types of filter rod making machines employing a garniture or other unit having a narrowing passage in which filter tow material is laterally compressed as the filter tow is moved longitudinally through the narrowing passage. Although primarily concerned with the manufacture of filter rod sections formed from a filter of filter tow material and a wrapper of paper or other material, the invention may also be applied to the manufacture of filter rod sections having no wrapper.

Claims

1. A method of monitoring the quality of tobacco smoke filter rods formed by passing filter tow (4) through a narrowing passage (42) to laterally compress the filter tow, comprising supplying a gaseous medium to a space which communicates via orifice means (46) with the narrowing passage and generating a control signal, dependent on the pressure in said space, which is representative of the eventual consolidation of the filter tow in the filter rod, characterised in that the said supply of gaseous medium to the said space occurs as a result of gaseous medium, previously entrained in the filter tow, being expressed from the filter tow and passing through said orifice means (46) during said lateral compression of the filter tow as the latter passes through the narrowing passage (42).

2. A method according to claim 1, characterised in that the amount of stretch of the filter tow (4) prior to its passage through the narrowing passage (42) is controlled in dependence on said control signal.

3. A method according to claim 1 or 2, characterised in that the speed of passage of the filter tow (4) through the narrowing passage (42) is controlled in dependence on said control signal.

4. A method according to any one of the preceding claims, characterised in that said control signal is supplied to display means (54) to provide a visual indication of the quality of filter tow as it passes through the narrowing passage (42).

5. A method according to any one of the preceding claims, characterised in that the control signal is generated at the output side of a pressure transducer (50) which is connected to the said narrowing passage (42) by a tubular passage (45) defining, at least in part, the said space.

6. Apparatus for producing tobacco smoke filter rods from filter tow (4) including means (6-9) for transporting the filter tow from a source along a path, means for stretching the filter tow in a first portion of said path, compressing means (20) including means defining a narrowing passage (42) having inlet and outlet ends (40 and 42) for laterally compressing the filter tow and converting it into rod-like form in a second portion of said path, means (25) for severing the rod-like form to produce discrete lengths (1) of filter rod sections, means (45) defining a space which communicates with said narrowing passage (42) via orifice means (46) and means (50) for generating a control signal dependent on the pressure in said space and which, in use of the apparatus, is representative of the eventual consolidation of the filter tow in a filter rod section, characterised in that the said space (45) is closed apart from its communication with said narrowing passage (42) via said orifice means (46) so that, in use of the apparatus, the pressure within said space (45) is controlled by the amount of gaseous medium, previously entrained in the filter tow, which is expressed from the filter tow and passes through said orifice means (46) during lateral compression of the filter tow as the filter tow passes through the narrowing passage (42).

7. Apparatus according to claim 6, characterised by means (21, 23) for wrapping a web of wrapping material around the rod-like form in a third portion of said path downstream of said compressing means (20).

8. Apparatus according to claim 6 or 7, characterised in that the means defining said space comprises a tube (46) lying in an axial plane of said narrowing passage (42).

9. Apparatus according to claim 8, characterised in that said tube (45) is disposed at an angle of less than 90° to the axis of the narrowing passage (42).

10. Apparatus according to claim 9, characterised in that said angle is from 30° to 60°.

11. Apparatus according to any one of claims 6 to 10, characterised in that the control signal generating means includes a pressure transducer (50) for sensing the gas pressure in said space.

12. Apparatus according to claim 6, characterised in that the control signal is supplied to control means for automatically controlling the filter tow transporting means and/or the filter tow stretching means.

13. Apparatus according to any one of claims 6 to 12, characterised in that the said orifice means (46) is positioned between inlet and outlet ends (40 and 41) of the said narrowing passage (42).