GB2101642A - Tow cutter - Google Patents

Abstract

In-line apparatus for continuously cutting filamentary tow (2) into fibres and delivering the cut fibres in a continuous stream, the apparatus comprising a tow inlet feeder (50) and a cut fibre exit gas jet (64) arranged in-line, and a knife blade (60) rotatably mounted for periodic passage therebetween to intersect tow passing there-through and cut it into fibres. The cut fibres are carried directly to an air separator (21) from which they are deposited in a device for forming them into filter rods. <IMAGE>

Description

SPECIFICATION Tow cutter The present invention relates to the cutting of filamentary tow into short, e.g. staple fibres.

UK Specification No. 1,221,346 describes a process for the production of filter rods of staple fibre in which a band of tow incorporating a bonding agent is fed continuously by a stuffer jet to a rotary cutter, a fan downstream of the cutter drawing the fibres away from the cutter in an airstream perpendicular to the tow feed path and then impelling the fibres in the airstream parallel to the tow feed path to a unit where the fibres are separated from the airstream and condensed to rod form for filter production. This is a commercial process, but its rate of throughput is not as high as is desirable, and various attempts to increase the rate of operation have led to undesirable lack of uniformity in the cut fibre length and/or in the distribution of the fibres in the rod product.

The present invention provides in-line apparatus for continuously cutting filamentary tow into fibres and delivering the cut fibres in a continuous stream, the apparatus comprising a tow inlet feeder and a cut fibre exit gas jet arranged in-line and separated by ledgers, and a knife blade rotatably mounted for periodic passage between adjacent ledgers to intersect tow passing therepast and cut it into fibres.

Preferably at least the downstream ledger is annular with the material path extending therethrough. Any tow feed to the ledgers may be used, but a stuffer jet may be preferred. The invention also provides an in-line method of continuously cutting filamentary tow into fibres and delivering the cut fibres in a continuous stream, the method comprising feeding the tow continuously to a rotary knife blade whose rotary path periodically intercepts the path of the tow, and immediately carrying the resulting cut fibres away from the knife blade by means of an exit gas jet acting in-line with the tow feed. A wholly inline path is thus provided for the passage of the tow to the cutter and of the cut fibres therefrom.

Furthermore, a unit for separating air from the cut fibres and condensting the latter to rod form can be attached directly to the outlet of the fibre exit jet, thus permitting minimum travel of the cut fibres prior to rod formation.

The apparatus according to the invention can be operated .satisfactorily at higher throughput rates than the apparatus previously proposed and used.

When cutting apparatus according to the invention is employed as described above for the fully in-line production of cut fibre filter rods from filamentary tow (i.e. with the fibre exit jet connected directly and in-line with the air separator and rod formation unit), the resulting rods have a detectable distinct fibre structure different from that of rods produced by the mentioned prior process. In rods obtained by the prior process, the fibres are randomly oriented, but with non-uniformity of fibre length and packing along the rod length; in rod formation according to the invention, the fibres tend to remain in their initially cut clumps as they travel to and through the air separator and rod former.

Accordingly the invention also provides a filter rod of cut fibres maintained in coherent rod form, the fibres being packed in clumps with the fibres of a clump being of substantially the same length; the clumps are usually of substantially the same girth.

The two may be cut into fibre clumps of equal length, or into clumps of two or (less usually) more different lengths. The clumps in the finished rod may tend to be packed with the fibres oriented transversely to the rod axis. In rods according to the invention the fibre packing can be more uniform along the rod length than in the prior products.

In apparatus according to the invention, a single knife blade may be mounted, e.g. on a rotary disc, for co-operation with a single pair of ledgers, but other arrangements are possible. For example, two longitudinally spaced pairs of ledgers could be provided, with a corresponding pair of knife blades being mounted (usually in circumferential register) on the rotary disc. In other embodiments, a plurality of knife blades or blade pairs may be spaced circumferentially around the rotary disc to provide for a corresponding plurality of cutting actions per revolution of the disc.

The apparatus according to the invention is normally mounted with the tow and fibre paths horizontal and the knife paths vertical.

The invention is illustrated, by way of example only, by the accompanying drawings, in which like numerals represent like parts and in which: Figure 1 is a diagrammatic elevation view of a complete filter rod production apparatus according to the invention; Figure 2 is a similar enlarged view of the air separation and rod formation portion of the Fig. 1 apparatus; Figure 3 is a diagrammatic side elevation view, partly in section, of a tow cutting device according to the invention suitable for use in the Fig. 1 apparatus; Figure 4 is a similar view of a modified tow cutting device according to the invention; Figure 5 is a diagrammatic side elevation in section of a prior fibre filter rod; and Figure 6 is a similar view of a filter rod according to the invention made using the apparatus of Figs. 1 to 3.

In the illustrated filter rod production method and apparatus described below, the rod is made from cellulose acetate continuous filamentary tow plasticised with glyceryl triacetate; this is the preferred material for cigarette filter production, but a variety of other materials can be used.

Referring to the drawings, from a bale 1 of continuous filamentary cellulose acetate tow, the two 2 is drawn upwardly first through an air banding jet 4, thence over a cylindrical guide 5, traction being given by rollers 3. The two 2 then passes to rollers 6 which rotate faster than rollers 3 and thereby stretch the tow between them and rollers 3. A further air banding jet 7 forms the tow into a band which form it retains as it passes into box 10 where it is sprayed over the whole of its width with glyceryl triacetate in known manner.

The banding jets 4 and 7 are of known form and comprise a slot through which the tow passes, having on one side a wall, divided by narrow slits to the outer side of which compressed air is supplied. This air passes through the slits and impinges upon the tow. On the other side of the slot is an undivided wall which retains the tow while the air impinges upon it. Rollers 11 hold the tow in band form until it enters the cutting device 1 3 according to the invention. A rotary knife cutter within the cutting device is driven by a belt, not shown, which is driven, via an infinitely variable gear, from the main-shaft of a plugmaker 20, as are rollers 3, 6 and 11 via other such gears. By varying the relative rates of rotation of the cutter and the rollers 11 the length of the fibres may be varied.By varying the relative rates of rotation of the rollers 3, 6 and 11 the weight per unit length of the rod may be varied e.g. by varying the rate of rotation of rollers 3 relatively to rollers 6, the percentage crimp of the filaments entering the cutting device 13 is altered. The cutting device 1 3 is described hereinbelow with reference to Figs. 3 and 4.

The combined delivery stream of air and fibre from cutting device 1 3 passes through exit 18 into an air permeable, e.g. perforate, frustoconical screen 21, preferably formed of wire mesh, through the wall of which most of the air escapes. The frusto-conical form ensures that the velocity of the air inside the cone is not unduly reduced by passage of air through its walls. The wire mesh can for example have openings 0.12 mm square. The remainder of the air deposits the fibres on a previous tape 22 and then passes out of holes in a surrounding heating block 24. The latter has a bore 25 through which the tape passes.

The bore has a cross section corresponding to the cross section desired in the rod, e.g. it is circular.

It holds the tape 22 so as to envelop the staple fibres in the rod 31. The heating block 24 is of substantial metallic construction so that the tape is held around the fibres in a constant configuration. It is preferred that the fibres remain in suspension until they meet the tape 22.

However it is undesirable that an excessive air flow be used for this purpose as fibres may be blown into the atmosphere instead of being deposited. The rate of flow may be increased by blocking off a part of the screen 21 next to the exit 18.

The tape which is driven by drum 26 and is trained about tension rollers 27 and 28 and guide rollers 29 and 30, carries the fibres now held in the form of the rod 31 through the heating block 24, wherein they are heated by steam coming from a source not shown via pipe 33. A plenum chamber within the heating block 24 serves to distribute the steam evenly around the whole of the periphery of the tape enclosing the fibres.

Upon passing from the heating block the tape, containing the rod formed from the fibres, passes through cooling enclosure 36 where it is cooled by air supplied to pipe 37. The latter connects with channels inside the cooling enclosure which distribute the air about the tape enclosing the rod, thereby cooling and hardening it so that at the exit of the cooling enclosure a firm rod is delivered. The tape 22, folding from the circular to the flat form, is separated from the rod as it passes on to the drum 26. The continuous rod 31 may pass to a cut-off 42 in which it is cut into equal length rods which are deposited upon a delivery band 35, or first to a wrapping garniture where the fibrous rods is wrapped with a paper wrapper in known manner and thence to the cutoff.

If the edges of the tape 22 as they envelop the fibrous material do not meet perfectly, fibres press between them and form a ridge. To eliminate this a ridge remover 41 can be provided between the heating block and the cooling enclosure. This comprises a narrow blade arranged between the edges of the tape. It presses upon the fibres protruding between the edges of the tape to return them into the body of the rod.

In this embodiment the function of the steam is to heat the cellulose acetate and glyceryl triacetate so that the solvent action of the glyceryl triacetate upon the cellulose acetate is accelerated. Thus solvent welding of the cellulose acetate fibres occurs. In the case of other fibrous materials or other bonding constituents the heating effect of the steam may accelerate the bonding by causing fusion or polymerisation.

Figures 3 and 4 illustrate cutting devices according to the invention which could be used for the cutting device 13 of Figs. 1 and 2.

In the Figure 3 device tow inlet stuffer jet 50, supplied with pressurised air via conduit 52 and jacket 54, draws tow 2 from rollers 11 through the relatively restricted orifices 56 of ledgers 58.

A knife blade 60 is mounted on a rotary disc 62 so that its circular travel path passes between ledgers 58 once per rotation to cut the tow into substantially uniform fibre lengths, this fibre length of course being the longitudinal distance by which the tow is advanced per revolution of the disc. The downstream ledger 58 is disposed at the inlet end of fibre exit jet 64 which is supplied with pressurised air via conduit 66 and jacket 68 so that the cut fibres are immediately swept from the downstream annular ledger to the widened exit 1 8 of jet 64. As shown in Fig. 3, this exit may be connected directly to the inlet of mesh cone 21 of the apparatus of Figs. 1 and 2.

The Figure 4 cutting device is essentially the same, except that three ledgers 58 are provided between the two jets, a pair of knives 60 being mounted in circumferential register on disc 62 to pass simultaneously as shown between the corresponding two ledger gaps.

The cutting device 1 3 is preferably run at such a speed relative to the speed of the tow that the fibres cut from it are about the same length (e.g. 6 to 12 mm) as the diameter of the rod to be produced (e.g. about 8 mm). The length of the fibres can, however, be varied, e.g. from 3 mm to 50 mm. Preferably the apparatus is coated on surfaces which come into contact with the tow and with the plasticiser with a substance which prevents adhesion.

The rods made as described above are deformation-resistant in that they may be handled by known cigarette filter rod handling devices without an unacceptable distortion. A paper wrapping may however facilitate some steps in the subsequent utilisation of the rods. If such a rod is desired it may be made by providing the plug-maker 20 with an additional drum similar to the drum 26 and garniture and roller system. The garniture is located downstream of the cooling enclosure and before the cut off. It is used to wrap paper around the continuous rod 31 as it comes from the cooling enclosure and adhere it around the rod by means of a lapped and stuck seam.The two tapes, i.e. the tape 22 and the tape passing through the garniture, will have a substantially identical linear speed, though the tape 22 may be run slightly faster than the garniture tape so as to prevent any tensile breakage in the fibrous rod as it is transferred from the cooling enclosure to the garniture.

Using this apparatus filter rods for cigarettes may be m-ade which have a higher pressure drop or greater hardness than rods of an equal weight made by the conventional tow processes.

Alternatively rods of equivalent properties may be made using less tow than the conventional process. This advantage which is believed to result from a more favourable arrangement of the fibres in the rod, as a result of the method of deposition of the fibres, produces a saving of tow.

Other materials such as fibres of paper pulp may be incorporated with the fibres cut from the filaments of the tow by feeding them simultaneously with the latter into the cutter 13 so that together they are dispersed in air, become blended, enter the heating enclosure and are bonded into a homogeneous rod.

Various filamentary tows such as polypropylene, polyethylene, cellulose triacetate, nylon or viscose may be used where their particular physical or chemical properties are needed, but for cigarette filters secondary cellulose acetate is preferred. Other bonding constituents such as fusible resins and fibres may be used instead of solvent plasticisers. Other plasticisers such as triethylene glycol diacetate may be used in place of glyceryl triacetate.

- Whilst the method and apparatus illustrated in Figures 1 and 2 employ a heating block to activate a bonding constituent on the fibres to yield a bonded rod, this is not essential. For example, the fibre (with or without bonding constituent) from the outlet of cone 21 could be deposited -instead on a strip of conventional plugwrap and passed through a conventional wrapping garniture tQ yield a wrapped rod.

In all rod formation embodiments according to the invention, there is continuous in-line travel of the filter material through the tow preparation, tow cutting, and fibre rod formation stages.

Figures 5 and 6 illustrate diagrammatically respectively a filter rod produced by the prior method and apparatus employing an impeller fan with initial travel of the cut fibres perpendicular to the tow feed, and a rod according to the invention produced by the method and apparatus of Figs. 1 to 3. In Figure 5 the fibres 80 within plugwrap 82 vary appreciably in length and are randomly oriented, and in practice there are variations in fibre length and distribution along the length of the rod. In the Figure 6 rod according to the invention, the fibres 80 are of substantially uniform length and are packed in distinguishable clumps 84 which are of substantiallly the same girth, the fibres of a clump being diposed generally parallel to one another and generally transverse to the rod axis; the rod diameter is for example about 8 mm, with the fibre length being about 12 mm. The improved uniformity of the rods according to the invention results in improved uniformity in pressure drop amongst the individual filter plugs cut from the initially produced continuous rod. It will be appreciated that, instead of cutting the tow into clumps of equal length, fibre clumps of two or more different predetermined lengths are obtainable by appropriate arrangement of a plurality of knife blades.

To take account of the longitudinal movement of the tow being.cut, and hence facilitate a cleaner cut and more uniform cut fibre length, the ledgers may be oscillated along the tow path.

Claims (14)

Claims

1. In-line apparatus for continuously cutting filamentary tow into fibres and delivering the cut fibres in a continuous stream, the apparatus comprising a tow inlet feeder and a cut fibre exit gas jet arranged in-line and separated by ledgers, and a knife blade rotatably mounted for periodic passage between adjacent ledgers to intersect tow passing therepast and cut into fibres.

2. Apparatus according to claim 1 wherein having a single knife blade or a plurality of circumferentially spaced knife blades rotatably mounted for co-operation with adjacent ledgers.

3. Apparatus according to claim 1 or 2 having at least three ledgers longitudinally spaced between said feeder and jet to provide a corresponding plurality of inter-ledger spacings each co-operating with one or more said rotatably mounted knife blades.

4. Apparatus according to any of claims 1 to 3 wherein at least the downstream ledger is annular with the material path extending therethrough.

5. Apparatus according to any of claims 1 to 4 wherein the tow inlet feeder comprises a stuffer jet.

6. Apparatus for the production of filter rods, the apparatus comprising tow cutting apparatus according to any preceding claim, means for supplying a continuous filamentary tow to the tow inlet feeder, and means attached directly to the outlet of the cut fibre exit jet for separating air from the cut fibres and condensing the cut fibres to permanent rod form.

7. An in-line method of continuously cutting filamentary tow into fibres and delivering the cut fibres in a continuous stream, the method comprising feeding the tow continuously to a rotary knife blade whose rotary path periodically intercepts the path of the tow, and immediately carrying the resulting cut fibres away from the knife blade by means of an exit gas jet acting inline with the tow feed.

8. A method according to claim 6 or 7 wherein the cut fibres are conveyed directly to a unit wherein conveying air is separated from the fibres which are then condensed to permanent rod form.

9. A filter rod of cut fibres maintained in coherent rod form, the fibres being packed in clumps of substantially the same girth with the fibres of a clump being of substantially the same length.

1 0. A filter rod according to claim 9 wherein the fibre length is substantially the same from clump to clump.

11. Tow cutting apparatus substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

1 2. Tow cutting apparatus substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

1 3. Filter rod production apparatus substantially as hereinbefore described with reference to the accompanying drawings.

14. A method for the production of filter rod, the method being substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A filter rod of cut fibres and substantially as hereinbefore described with reference to Fig. 6 of the accompanying drawings.