Patent Description:
Numerous products formed from fibrous material may be produced by gathering the fibers into an assembly, for example a thread, web, skein, roving, mat, or rod. Such assemblies may be treated to retain the fibres in a cohesive whole, for example by heating, or by applying an adhesive or plasticiser, to cause the fibres to adhere to each other at their points of contact. For example, cigarette filters may be formed from fibres of filter material, such as cellulose acetate fibres, by gathering the fibres to form a strand or skein of entangled fibres, often referred to as filter tow, and then compressing the strand by rolling and drawing to form rods of higher density, which can then be wrapped and cut into individual short lengths suitable of incorporation on cigarette.

In processes and equipment for gathering fibres, it is desirable to reduce variations in the density fibres in the assembly, since such variation may affect the quality of the end product.

It is known from <CIT> to provide apparatus according to the precharacterising portion of claim <NUM>.

Apparatus according to the present invention is characterised by the features recited in the characterising portion of claim <NUM>.

Preferred features of the apparatus of the invention are defined in the dependent claims numbered <NUM> to <NUM>.

According to another aspect of the invention, there is provided a method of forming an assembly of gathered fibres, as recited in claim <NUM>.

Preferred method steps according to the invention are defined in claims <NUM> and <NUM>.

In the drawings, for ease of reference, like parts or components in different embodiments have been given similar reference numerals.

Referring to <FIG> and <FIG>, the illustrated embodiment of the invention is equipment for forming rods of filter material suitable for use as cigarette filters. The equipment is of modular construction and comprises three modules: a melt blowing module <NUM>, for generating fibres of a plastics material entrained in a gas stream, a fibre gathering module <NUM>, for gathering the fibres from the melt blowing module <NUM> and forming a web <NUM> therefrom, and a rod forming module <NUM>, for forming the web into a continuous rod <NUM>.

The melt blowing module <NUM> may be of conventional construction, and is illustrated schematically in the upper part of <FIG>. The fundamental feature of the melt blowing module is a die head <NUM> into which molten polymer material indicated by the arrow P may be fed, and from which the molten polymer emerges as a liquid through an array of jets <NUM>. Gas passages are formed in the die head immediately adjacent the jets. Hot gas, such as air, indicated by the arrows A, A, is fed into the die head and emerges from the gas passages as two convergent high velocity gas streams. The streams of hot gas blow the polymer emerging from the array of jets <NUM> into thin streams of molten polymer <NUM>, which solidify within a few centimetres of the jets <NUM> to form a multiplicity of continuous small diameter fibres <NUM>. The fibres <NUM> become entrained in the gas stream to form a complex pattern of entangled fibres entrained within a fast-flowing stream of gas.

The fibre gathering module <NUM> is arranged vertically beneath the melt blowing module <NUM> to receive fibres entrained in the air stream therefrom. The vertical distance between the melt blowing module and the fibre gathering module is exaggerated in <FIG> for clarity.

The fibre gathering module <NUM> comprises a rigid frame <NUM> supporting a hollow casing <NUM> formed from metal plates welded or bolted together and secured to the supporting frame <NUM>. The casing <NUM> is generally rectangular in plan with its major axis extending horizontally in a longitudinal direction from an upstream end <NUM> to a downstream end <NUM> and comprises two similarly shaped box units <NUM>a and 24b (<FIG>) with a removable partition <NUM> which divides the interior of the casing into two chambers. The partition <NUM> may be removed to place the two chambers in communication with each other.

As best seen in <FIG>, a conveyor <NUM> is mounted on the casing <NUM>, providing a transport system for moving fibres from the melt blowing module <NUM> part of the way along a pathway <NUM> (the envelope of which is indicated by broken lines in <FIG>) through the fibre gathering module <NUM> to the rod forming module <NUM>. The conveyor <NUM> comprises a tensioning roller <NUM> of relatively large diameter mounted in bearings fixed to the upstream end of the casing <NUM> for rotation about a horizontal axis that extends transversely of the casing. At the downstream end <NUM> of the casing <NUM>, an idler roller <NUM> and a drive roller <NUM>, each of smaller diameter than the tensioning roller, are mounted in bearings fixed to the casing <NUM> for rotation about horizontal axes parallel to that of the tensioning roller <NUM>, the idler roller <NUM> being mounted above and upstream of the drive roller <NUM>. An electrical drive motor is mounted in the downstream end <NUM> of the casing <NUM> to rotate the drive roller <NUM> about its axis in an anticlockwise direction as seen in <FIG>.

The three rollers <NUM>, <NUM> and <NUM> support a conveyor belt <NUM> of endless construction having an upper run that extends in the longitudinal direction of the casing <NUM> from the tensioning roller <NUM> along the upper surface of the casing <NUM> to the idler roller <NUM>, downwardly and around the drive roller <NUM>, and then back to the tensioning roller <NUM> in a lower run parallel to the upper run. The idler roller <NUM> and the tensioning roller <NUM> may be adjusted in their bearings to align the upper run accurately with the upper surface of the casing <NUM> and to provide sufficient tension in the conveyor belt.

The conveyor belt <NUM> is constructed to allow the passage of gas through the belt whilst fibrous material entrained with the gas is deposited and retained on its surface as a web <NUM> of entangled fibres. For example, the conveyor belt <NUM>, or at least part thereof, particularly the central region extending the length of the belt, is provided with perforations, slots or apertures, or is otherwise porous, to allow the passage of gas therethrough whilst supporting fibrous material on its surface. For this purpose, the conveyor belt may for example be a fabric material woven to a density sufficient to permit a desired flow of gas therethrough under pressure.

The upper surfaces of the upstream and downstream box units 24b, <NUM>a of the casing <NUM> are each provided with apertures or slots that lie beneath the upper run of the conveyor belt <NUM>, allowing gas to pass through the conveyor belt into the interior of the box units. The portions of the upper surfaces immediately surrounding the apertures or slots provide support for the upper run of the belt <NUM>.

The box units <NUM>a and 24b provide an exhaust chamber <NUM> that communicates with an exhaust gas outlet <NUM>a (<FIG>) in one side of the casing <NUM> through which gas may pass out of the exhaust chamber. The exhaust outlet <NUM>a may be connected to a vacuum pump (not shown) to enable gas to be drawn from the exhaust chamber <NUM>. With the partition <NUM> removed, the interiors of both box units may be evacuated to the same pressure. With the partition in place, the interior of the upstream box unit 24b may be evacuated separately from the downstream box unit <NUM>a. A further exhaust outlet 41b (shown closed in <FIG>) is provided in one side of the downstream box unit <NUM>a to allow the part of the exhaust chamber within the downstream box unit 24a to be evacuated separately.

An enclosure <NUM>, illustrated in detail in <FIG>, fabricated from a sheet material such as steel, aluminium or a temperature resistant plastics material, is mounted on the casing <NUM> and overlies the conveyor <NUM> to define a chamber <NUM> in which the fibres from the melt blowing module <NUM> may be gathered together and separated from surplus gas.

The enclosure <NUM> together with the upper run of the conveyor belt <NUM> surrounds and partially encloses the path of the fibres between the die head <NUM> and the conveyor <NUM>. The enclosure is formed by an upright end wall <NUM>, which is generally rectangular with bevelled upper corners. The end wall <NUM> is connected to two upright side walls <NUM>, <NUM> aligned in the longitudinal direction of the casing <NUM>. Each side wall <NUM> comprising a generally rectangular downstream portion 52a and a generally rectangular upstream portion <NUM>b of smaller aspect ratio than the upstream portion, so that the upstream portion of each side wall <NUM> is higher than the downstream portion. The profiles of the upstream and downstream portions are blended smoothly into each other by an arcuate connecting portion <NUM>c.

The lower edges of the side walls <NUM> have inwardly-turned flanges <NUM>, <NUM> (<FIG>) which define between them a longitudinal gap in the base of the enclosure sufficiently wide to overlie the central region of the conveyor belt <NUM> that carries the web of fibres <NUM>. The flanges <NUM> are each provided with three longitudinally extending apertures <NUM>, <NUM> that overlie corresponding apertures in the upper surface of the casing <NUM>, allowing a flow of gas from within the enclosure <NUM> into the exhaust chamber <NUM>.

The horizontal upper edges of the downstream portions <NUM>a of the side walls are connected by an apron <NUM>, which has a curved upstream portion <NUM> that connects the arcuate connecting portions <NUM>c of the side walls to each other, thereby providing a downstream end wall for the enclosure <NUM>, opposite the end wall <NUM> at the upstream end of the enclosure.

A fibre outlet <NUM> at the downstream end of the enclosure <NUM> is formed by a central longitudinally projection extending from the downstream end of the apron <NUM>. The projection is in the form of an open-ended tunnel portion <NUM> of inverted U-shaped transverse cross-section overlying the central region of the conveyor belt <NUM> and having the same height above the conveyor as the downstream end of the apron <NUM>. The top of the tunnel portion is integral with the apron <NUM>, and the side walls of the tunnel are formed by extensions of baffle plates <NUM>, <NUM> described below.

Two vertical end plates <NUM>, <NUM> extend transversely away from the sides of the tunnel portion <NUM> and are connected to the downstream ends of the side walls <NUM>, <NUM> so that the fibre outlet <NUM> defines a relatively confined rectangular aperture around the conveyor.

As best seen in <FIG>, <FIG> and <FIG>, the upper edges of the end wall <NUM>, the upstream portions 52b of the side walls and the apron <NUM> form a rectangular inlet <NUM> to the enclosure <NUM> and the chamber <NUM> within the enclosure. The inlet is spaced from the die head <NUM> to allow excess gas from the die head to escape laterally with respect to the path of the fibres, outside the enclosure. The inlet <NUM> is aligned with the die head <NUM> to receive the gas stream carrying entrained fibres <NUM> from the die head and to direct the fibres downwardly along the pathway <NUM>, into the chamber <NUM> and on to the conveyor <NUM> in a direction normal to the direction of movement of the upper run of the conveyor. The conveyor <NUM> is correspondingly disposed to move the fibres in a direction generally orthogonally, or at right angles to the direction of the gas stream.

Within the enclosure <NUM>, the chamber <NUM> has a receiving zone R, upstream of the apron <NUM>, in which the upstream portion of the conveyor is housed in alignment with the inlet <NUM>, and a downstream stabilising zone S, housing the downstream portion of the conveyor, which moves fibres deposited thereon through the chamber <NUM> to the fibre outlet <NUM>, as indicated generally in <FIG>. The receiving zone R and the stabilising zone S communicate through a funnel <NUM> formed by the arcuate connecting portions 52c of the side walls, the curved upstream end portion <NUM> of the apron <NUM> and the upper run of the conveyor <NUM>. The funnel <NUM> forms a tapered or convergent guide, having a decreasing cross sectional area through which the fibres <NUM> pass into the stabilising zone S.

The receiving zone R is in communication with the exhaust chamber <NUM> through the apertures <NUM> in the flanges <NUM> of the side walls, the upper run of the conveyor <NUM>, which is porous, and the apertures in the upper surface of the upstream box unit 42b. Gas entering the chamber <NUM> may therefore pass into the exhaust chamber <NUM> and leave the equipment through the exhaust outlet <NUM>.

As seen in <FIG>, two baffles <NUM>, <NUM> are positioned in the receiving zone of the chamber <NUM> each opposing one of the sidewalls <NUM>. Each baffle comprises a flat plate with an elongated tongue <NUM> extending from its lower downstream end arranged in the longitudinal direction of the casing <NUM>. Each baffle has an upstream edge fixed to the flat end wall <NUM>, a lower edged <NUM> fixed to one of the flanges <NUM> on the lower edges of the side wall <NUM>, and a curved upper downstream edge that is fixed to and conforms to the curved the apron <NUM>. The upper edges of the elongated tongues <NUM> thereof lie in contact with the inner surface of the flat, downstream portion of the apron <NUM> and form the side walls of the tunnel portion <NUM>.

The baffles are positioned in the inlet <NUM> so as to direct the fibres in the gas stream on to the transport surface provided by the conveyor. In this regard, the baffles <NUM>, the apron <NUM> and the end wall <NUM> form the sides of a central or primary passage <NUM> in the inlet. The upper parts of the baffles are curved though about <NUM>-<NUM>° away from the vertical so that the primary passage converges in the downward direction towards the conveyor <NUM>. The lower edges <NUM> of the baffles provide an exit or outlet that is directed on to the transport surface of the conveyor <NUM>.

The baffles <NUM> and their tongues <NUM>, the conveyor <NUM>, the funnel <NUM>, the apron <NUM> and the downstream portions 52b of the side walls <NUM> provide a conduit <NUM> for the fibres through the enclosure along the pathway <NUM> that decreases in cross sectional area from the inlet <NUM> to the fibre outlet <NUM>.

Referring to <FIG>, the upstream portions 52b of each of the sidewalls <NUM>, the opposing baffle <NUM>, the end wall <NUM> and the apron <NUM>, form two peripheral or auxiliary vertical passages 49a, 49b, that lie alongside the central passage <NUM>, each with an exit or outlet that is directed to one side of the conveyor. As a result of the inclination or curvature of the baffles, the auxiliary passages diverge in the downward direction towards the conveyor <NUM>. Gas discharging from the auxiliary passages to the sides of the conveyor <NUM> passes through the conveyor belt and the apertures in the upper surface of the casing <NUM> into the exhaust chamber <NUM>. The baffles <NUM> are thus positioned in the pathway to direct surplus gas away from the transport surface of the conveyor and thereby to reduce turbulence among the fibres <NUM>, as described in more detail below.

The downstream portion of the stabilising zone S comprising the conduit <NUM> has an elongated section of substantially uniform, generally rectangular vertical cross section along it length and is arranged to receive fibres <NUM> which extend continuously from the die head 14through the receiving zone R and through the funnel <NUM>. The conduit <NUM> is defined by the low downstream portions 52a of the side walls <NUM> of the enclosure, the connecting portion of the apron <NUM> and the tunnel portion <NUM>, and terminates in the fibre outlet <NUM> which lies above the downstream end of the conveyor <NUM> and from which the fibres <NUM> may be withdrawn from the chamber as a gathered web <NUM> of generally rectangular cross-section.

The rod forming module <NUM> (<FIG>) comprises a rigid frame <NUM> supporting a number of components of rod forming equipment <NUM>-<NUM> and a control panel <NUM> therefor. The rod-forming components are adjustably mounted on a rail <NUM> secured to the frame <NUM> in alignment with the path of the fibres through the fibre gathering module <NUM>. The relative longitudinal positions of the components along the rail may be adjusted as required to match the prevailing operating conditions of the equipment.

The rod forming equipment comprises a forming cone <NUM>, which is mounted on the frame <NUM> in alignment with the rail <NUM> carrying the other rod-forming components. The forming cone <NUM> is composed of upper and lower half shells 74a, 74b (<FIG>) each generally triangular in plan, having an outer flat surface and an inner recessed surface, which together define a tapering central passage extending in the downstream direction from a generally rectangular upstream inlet <NUM> to a circular downstream outlet <NUM>. The inlet <NUM> is arranged to receive the gathered fibres <NUM> in the form of a flattened mat or web <NUM> directly from the fibre outlet <NUM> of the fibre gathering module. The tapered central passage of decreasing cross sectional area is arranged to guide and compress the fibres into a cylindrical shape as the fibres move towards the outlet <NUM>.

A transporter jet <NUM> (<FIG>) is mounted on the rail <NUM> to receive the cylindrically formed fibres directly from the forming cone <NUM>. The forming cone and the transporter jet may be spaced apart axially along the rail <NUM> by a short distance in order to allow gas from the transporter jet <NUM> to vent to the atmosphere.

The transporter jet <NUM> comprises an outer tube <NUM> and a tubular insert <NUM>. The outer tube defines a central cylindrical passage <NUM> which communicates with an outlet <NUM> at the downstream end thereof and a socket <NUM> at the upstream end of the tube <NUM>, which has an internal and external diameter larger than central passage <NUM>. The tubular insert <NUM> has a spigot <NUM> at its downstream end having an external diameter slightly less than that of the central cylindrical passage <NUM>, and a socket <NUM> at its upstream end, which defines a funnel shaped entrance to transporter jet. The insert <NUM> is mounted in the upstream end of the outer tube <NUM> so that the spigot <NUM> of the insert is received within the upstream end of the cylindrical passage of the outer tube <NUM> to define a narrow annular gas passage therebetween. The socket <NUM> of the insert is received within the socket <NUM> of the outer tube <NUM>. The inner and outer tubes are secured to each other by axially extending bolts <NUM> extending through a flange on the outer surface of the socket <NUM> of the insert into axial threaded bolt holes in the walls of the socket <NUM> of the outer tube. A gasket <NUM> received in a peripheral groove in the external surface of the socket on the insert provides an air-tight seal to the internal wall of the socket on the outer tube.

The insert 806and the outer tube <NUM> are axially spaced so that an annular chamber <NUM> is formed between the sockets of the insert and the tube. Pressurised air may be introduced into the chamber <NUM> through two gas inlet connections <NUM> mounted on the outer surface of the socket of the outer tube. In use, gas under pressure emerges from the chamber at high speed through the gas passage between the insert and the outer tube to generate a downstream flow of air through the transported jet <NUM>. A reduced pressure is thereby created sufficient to draw the cylindrically formed fibres into the transporter jet <NUM> and to transport them downstream. The mouth of the socket <NUM> of the insert <NUM> is equal in diameter to the outlet <NUM> of the forming cone, whereas the outlet <NUM> of the outer tube <NUM> is smaller in diameter, so that the fibres are further gathered into a rod of smaller diameter as they pass through the transporter jet.

Immediately downstream of the transporter jet <NUM>, and in axial alignment therewith, a further transporter jet, or stuffer jet, <NUM> (<FIG>) is mounted on the rail <NUM> in axial alignment with the transporter jet <NUM> to receive the cylindrically formed fibres emerging therefrom. The stuffer jet <NUM> is similar in construction to the transporter jet <NUM> and performs a similar function in drawing the fibres in the downstream direction using the Venturi effect, and further compressing the gathered fibres to form a rod of still smaller diameter. The transporter jet and the stuffer jet may be spaced apart axially by a short distance in order to allow excess air from the transporter jet <NUM> to vent to the atmosphere.

The stuffer jet <NUM> comprises a tube <NUM> having a central cylindrical passage <NUM> which communicates with an outlet <NUM> at the downstream end thereof and a socket <NUM> at the upstream end. The socket <NUM> has a cylindrical internal surface at its open end, which is larger in diameter that the central passage 182and a conical inner surface that tapers from the open end of the socket towards the central passage <NUM>.

A tubular insert <NUM> is mounted in the socket <NUM>. The insert <NUM> has a cylindrical collar at its upstream end, which defines a funnel shaped entrance to stuffer jet equal in diameter to that of the outlet <NUM> of the transporter je <NUM>. The collar is provided with a flange <NUM> that limits the movement of the insert186 into the socket <NUM> on the tube <NUM>. The insert is retained in the socket by means of a grub screw locate in a threaded radial bore in the wall of the socket <NUM>. A conical spigot <NUM> extending axially downstream from the collar is tapered towards the central passage <NUM> and has an external diameter less than that of the central cylindrical passage182.

The insert <NUM> is positioned axially in the socket <NUM> so that the conical spigot <NUM> and the upstream end of the cylindrical passage <NUM> define a narrow annular gas passage therebetween. A circular gasket may be provided between the collar and the internal surface of the socket <NUM> of the insert <NUM> to provide an air-tight seal.

The facing conical surfaces of the insert <NUM> and the spigot 187are radially spaced so as to define an annular chamber <NUM> between them. Pressurised air may be introduced into the chamber <NUM> through two gas inlet connections <NUM> mounted on the outer surface of the socket of the tube <NUM>. In use, gas under pressure emerges from the chamber at high speed through the passage between the tube <NUM> and the insert <NUM> to generate a downstream flow of air through the stuffer jet <NUM>. A reduced pressure is thereby created sufficient to draw the compressed fibres into the stuffer jet <NUM> and to transport the fibres downstream.

A thin-walled frusto-conical nozzle <NUM> is mounted on the extreme downstream end portion of the tube <NUM>. The nozzle is mounted in axial alignment with the central axis of the tube and has a diameter that tapers from its upstream end, which is larger in diameter than the downstream outlet of the tube, to its downstream end, which is of the same diameter as the central passage <NUM>. The nozzle directs fibres emerging from the tube in the downstream direction, whist permitting excess gas to escape to the atmosphere through the large upstream end of the nozzle. Perforations are provided in the wall of the nozzle for the same purpose.

A preforming block <NUM> is positioned on the rail <NUM> immediately downstream of the transport jet <NUM> to receive the compressed fibres. The preforming block <NUM> comprises a hollow cuboidal housing <NUM> (<FIG>) provided with a mounting bracket <NUM> by which the preforming block may be secured to the rail <NUM>. The upstream and downstream faces of the block are provided with apertures <NUM> for supporting a cylindrical die <NUM>. The die <NUM> is in the form of a hollow tubular structure, the walls of which are provided with perforations placing the interior of the die in communication with the exterior surroundings. The upstream end of the die carries a socket <NUM> with an interior surface in the form of a cone that is tapered in the downstream direction to a diameter equal to the desired diameter of the filter rods. The die can be installed in the housing so that its downstream end <NUM> projects out of the aperture in the downstream face of the housing, and the spigot is sealingly engaged in the aperture903 in the upstream face. A sealing plate <NUM> may be bolted to the housing and sealed thereto by O-rings.

The lateral faces of the housing <NUM> are provided with apertures <NUM> for receiving steam connectors (not shown) through which steam may be introduced into the housing. In use, the steam passes through the perforations in the die <NUM> and into contact with the fibres to increase the pliability of the rod and to facilitate formation of a rod of the desired size.

A steam block <NUM> is positioned on the rail <NUM> immediately downstream of the preforming block <NUM> to receive the preformed rod. The steam block is of similar construction to the preforming block, and permits superheated steam to be may be introduced into the steam block to penetrate and heat the rod to a temperature at which the fibres bond together.

An air block <NUM> of similar construction to the preforming block and steam block is positioned on the rail <NUM> immediately downstream of the steam block <NUM> to receive the rod from the steam block. Air is introduced into the air block to drive out any excess water from the rod.

Although occasionally some fibres may break as they pass through the equipment, most or substantially all the fibres in the rod emerging from the air block <NUM> extend as unbroken filaments from the air block all the way along the pathway <NUM> and up to the die head <NUM>. After treatment in the air block, the finished rod may be fed into a filter plug maker (not shown), where the continuous rod produced in the equipment described is cut into individual segments.

<FIG>, <FIG>, <FIG> and <FIG> illustrate alternative enclosures for use in the equipment of the kind described with reference to <FIG>. The enclosure of <FIG>, <FIG> and <FIG> is similar in construction to the enclosure of <FIG> and <FIG>, and is constructed in a similar manner to include a rear wall <NUM>, side walls and apron <NUM> that define and inlet and surround and partially enclose the path of the fibres between the die head and the conveyor <NUM>. The enclosure includes two modifications, namely modified baffles <NUM>a, <NUM>b, and a modified fibre outlet <NUM> in the downstream portion of the stabilising zone S. Either of these features may be incorporated in equipment together or independently of the other.

In the embodiment of <FIG>, <FIG> and <FIG>, the two baffles <NUM> of the embodiment of <FIG> are replaced by modified baffles 65a, 65b, both of which are provided with louvres <NUM>. Each of the louvres comprise a series of apertures in the baffle in form of parallel elongated rectilinear slots extending transversely to the direction of flow of gas over the surface of the baffle within the gathering chamber <NUM>, arranged to divert fibres or other material approaching from one side of the baffle away from the baffle, whilst allowing gas to flow through the slot in either direction, depending upon the prevailing pressure conditions on either side of the baffle. In the baffles illustrated in <FIG>, each of the slots is provided with a cowl <NUM> along its upper edge, which projects inwardly into the central passage <NUM> in order to deflect downwardly-moving fibres in the gas stream away from the slot and towards the middle of the central passage <NUM>.

<FIG> illustrates an alternative baffle <NUM>c that may be used in the enclosure of <FIG>. This baffle incorporates a rectangular array of louvres <NUM>a arranged together in alignment in regularly spaced columns and rows. Each louvre comprises a slot 68b shorter in length than those of <FIG>, and an associated cowl <NUM>a. The array of relatively short louvres provides an even distribution of gas flow over and through the baffle. The flow characteristics of the baffle may be modified by providing fewer or more louvres of different dimensions and or shape. Two such baffles are used in the modified enclosure, each a mirror image of the other, so that the cowls <NUM>a face inwardly on both sides of the primary passage when the baffles are installed in the enclosure.

Referring now to <FIG> and <FIG>, the conduit <NUM> in the downstream portion of the stabilising zone S of the enclosure is modified in the region of the fibre outlet <NUM>. In this embodiment, the fibre outlet <NUM> provides an outlet orifice <NUM> that discharges into a channel <NUM>, which forms a central recess in the downstream end of the conduit. The channel <NUM> is bounded on each side by walls formed by elongated tongues <NUM> extending downstream from the baffles and arranged beneath the apron <NUM> on each side of conveyor. The channel is open to the exterior of the enclosure and extends in the downstream direction of movement of the gathered fibres.

The channel <NUM> provides a controlled release of gas from the interior of the housing in comparison with a simple rectangular aperture, the side walls of the channel reducing turbulence in the atmosphere above the conveyor. The effect of the channel is influenced by it longitudinal length, and may be selected to suit the operating conditions of the equipment, such as gas flow rate, gas temperature, internal gas pressure, conveyor speed, the vertical distance between the die head <NUM> and the conveyor <NUM>, and the rate at which polymer is fed through the die head. Typically the channel may extend up to <NUM>%, <NUM>%, <NUM>%,<NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% of the length of the conduit, e.g. from <NUM> to <NUM> %,<NUM> to <NUM>% of the length L of the conduit (see <FIG>). In the embodiment illustrated the channel extends about <NUM>%of the length of the conduit.

<FIG> illustrates the web <NUM> of gathered fibres emerging from the outlet orifice as it is carried by the conveyor along through the channel <NUM>. The movement of the fibre bundle in the downstream direction out of the enclosure is accompanied by a flow of surplus gas. The emerging gas stream flows more quickly than the fibre bundle and is confined by the sides of the channel <NUM> and the conveyor <NUM>. The flow rate of gas downstream of the outlet orifice is also greater than the flow of gas within the enclosure. The resulting hydrodynamics of the gas as it passes out of the orifice and along the channel assist in keeping the fibre bundle clear of the sides of the channel and in releasing the fibres from the surface of the conveyor as the fibres approach the rod forming module <NUM>.

The equipment of <FIG> is operated as follows. In the melt blowing module <NUM>, the die head <NUM> is supplied with molten polymer and hot gas. The molten polymer emerges as a liquid through the array of jets <NUM> and is blown by the hot air into thin streams which solidify to form small diameter fibres <NUM> and become entrained in the gas stream.

The die head may be configured to produce mono-component fibres from a single polymer material or bi-component fibres having a core formed from a first polymer encased in a sheath formed from a different polymer. For the production of filter rods, mono-component fibres may for example be formed from polyester, polyamide, ethyl vinyl acetate, polyvinyl alcohol or cellulose acetate, optionally incorporating other materials for modifying the properties of the polymer, for example a plasticiser such as triacetin. Bi-component fibres may be formed from any combination of the aforementioned polymers, having for example, a core of polypropylene and a sheath of cellulose acetate, optionally incorporating a triacetin plasticiser.

Using air as the blowing gas, the die head is typically positioned <NUM>-<NUM> above the upper run of the conveyor belt <NUM> and is operated with an air temperature of <NUM>-<NUM>, e.g. <NUM>-<NUM>, an air flow rate of <NUM>-<NUM> cubic feet or <NUM>,<NUM>-<NUM>,<NUM> litres per minute, and a polymer throughput of <NUM>-<NUM> grams per jet hole per minute. The resulting fibres typically have a diameter of <NUM>-<NUM> microns, e.g. about <NUM> microns and can be gathered to form a filter rod having a circumference of about <NUM> and a weight of about <NUM> per <NUM> length of rod.

The stream of gas and entrained fibres <NUM> is directed through the inlet <NUM> of the enclosure <NUM> into the gathering chamber <NUM> and on to the upstream portion of the conveyor <NUM> in the receiving zone R of the enclosure <NUM>. The fibres <NUM> gather together in an entangled mat on the upper run of the conveyor belt <NUM>. The conveyor <NUM> is operated to move the belt <NUM> in the clockwise direction as seen in <FIG>, thereby moving fibres relative to the direction of the gas stream, as they gather on the belt, out of the gas stream and downstream towards the fibre outlet <NUM>.

The transporter jet <NUM> of the rod forming module <NUM> withdraws the web of gathered fibres from the chamber <NUM> and through the forming cone <NUM>, which guides and compresses the fibres <NUM> into a rod <NUM> of cylindrical shape. The rod then passes through the preforming block <NUM>, into which steam is introduced to render the rod pliable. The rod then passes from the preforming block <NUM> into the steam block, in which the rod is contacted under pressure, for example at a pressure of <NUM>-<NUM> bar, typically about <NUM> bar, with superheated steam produced for example by heating steam to a temperature in the range <NUM>-<NUM>. This treatment causes the fibres in the rod to bond together at their points of contact. The rod then passes to the air block <NUM> which removes excess water from the rod. The formed rod <NUM> may then be drawn through further processing equipment, for example a cutting machine which severs the rod into consecutive segments of a desired length.

The volumes and pressures of gas necessary to form fibres by melt-blowing are such that the gas stream emerging from the melt-blowing module <NUM> is turbulent and capable of disrupting or interfering with the fibres, and the process for forming them into a skein, web or mat or other gathered arrangement. In particular, turbulent surplus gas can lift the mat of gathered fibres along part of the pathway, creating chaotic movement of the mat as it breaks away from the conveyor surface, which creates a non-uniform distribution of fibres in the mat, and may interrupt the manufacturing process. The susceptibility of the process to such break-aways increases with the speed at which the fibres are fed through the equipment.

In order reduce interference by the gas stream with the manufacturing process, surplus gas is separated from the fibres <NUM> in the gas stream as the gas and entrained fibres pass along the pathway <NUM> through the enclosure <NUM>. By separating surplus gas from the gas stream and diverting it away from the gathered fibres, turbulence in the gathered fibres is reduced and the fibres <NUM> are stabilised. The production of a gathered product with a more uniform and consistent fibre density can therefore be achieved.

In the embodiments illustrated in the drawings, the separation of surplus gas is performed in a series of stages. As shown in <FIG>, the fibres <NUM> are drawn into the primary or central passage <NUM> of the enclosure <NUM>, and directed on to the upper run <NUM> of the conveyor by the baffles <NUM>, <NUM>, which converge in the direction of the conveyor. A primary separation of surplus gas from the gas stream and the fibres is made upstream of the conveyor <NUM> by the external walls of the enclosure, including the side walls <NUM> end wall <NUM> and apron <NUM>. These walls direct surplus gas from an outer zone on the periphery of the gas stream away from the fibres, causing the peripheral gas to pass outside the walls of the enclosure <NUM> and to discharge into the surrounding atmosphere, as indicated in <FIG> by the arrows D, D. This primary stage of separation of surplus gas from the stream has a stabilising effect on the fibres because turbulent, excess gas is well separated from the fibres in the housing.

A secondary separation of surplus gas is made upstream of the conveyor by the baffles <NUM>, <NUM>, which direct surplus gas within the enclosure from inner zones of the gas stream, inwardly of the peripheral zone, into the auxiliary passages 49a, 49b, between the baffles and the adjacent portions of the side walls <NUM> of the housing, as indicated in <FIG> by the arrows E, E. The diverted gas discharges from the enclosure <NUM> into the exhaust chamber <NUM> through apertures in the upper surface of the casing <NUM> adjacent the upper region of the conveyor <NUM>, as indicated by the arrows H, H in <FIG>. The gas separated in this secondary stage is directed away from the fibres into the exhaust chamber <NUM> and thence to the atmosphere through the outlet <NUM>. Turbulence in the fibres in the housing is therefore further reduced and the fibres are gathered into a web under stable conditions.

Gas and entrained fibres in a central zone of the gas stream, which lies generally inwardly of the inner zones, are directed into the central passage <NUM>, as indicated by the arrows F, F, and on to the conveyor <NUM> by the baffles <NUM>, <NUM>, which converge in the direction of the conveyor <NUM>. Due to the porous construction of the surface of the conveyor belt <NUM>, the fibres <NUM> in the gas stream collect on the upper run of the conveyor, while surplus gas is directed from the enclosure <NUM> through the conveyor and discharges into the exhaust chamber <NUM> beneath the enclosure, from which it is evacuated through the exhaust outlet <NUM>, as indicated by the arrows G, G in <FIG>. The relative movement between the conveyor and the gas stream forms the fibres into a continuous web which is moved downstream out of the gas stream, at right angles thereto. Surplus gas from the gas stream in the central passage passes through the conveyor into the exhaust chamber without disrupting the fibre, thereby reducing turbulence in the housing and stabilising the web of fibres on the conveyor.

In a tertiary separation phase, the web of fibres is carried out of the receiving zone R through the funnel <NUM> into the conduit <NUM> in the stabilizing zone S, which has a transverse cross-section that conforms along its length to the desired, generally rectangular, cross section of the web on the conveyor, with a relatively small air gap above the web. The conduit may for example be from <NUM>%, <NUM>% or <NUM>% or more wider than the desired width of the web, and may have an aspect ratio (width: height ratio) in the range from <NUM>: <NUM> to <NUM>:<NUM>, e.g. <NUM>: <NUM>, <NUM>:<NUM>, or <NUM>:<NUM>. Surplus gas entering the conduit is confined closely to the web in a substantially laminar flow, along a low turbulence or substantially non-turbulent flow path, and therefore stabilises the web as it is conveyed through the conduit.

In this embodiment, most of the surplus gas is directed to the exhaust chamber <NUM> and to the exhaust outlet, and a minor proportion of the surplus gas is directed to the fibre outlet <NUM> to leave the chamber <NUM> together with the fibres.

Where the equipment described with reference to <FIG> is used in conjunction with the modified enclosure described with reference to <FIG>, the pattern of flow of air and gas through the housing is as illustrated in <FIG>.

Referring to <FIG>, a primary separation of surplus gas from the gas stream and the fibres is made, as in the embodiment of <FIG>, by the side walls <NUM>, the end wall <NUM> and the apron <NUM>, which direct surplus gas from the outer zone on the periphery of the gas stream away from the fibres into the surrounding atmosphere outside the enclosure, as indicated by the arrows D, D. A secondary separation of surplus gas is effected within the enclosure by the baffles <NUM>, <NUM>, which direct surplus gas from inner zones of the gas stream, into the auxiliary passages 49a, 49b, as indicated by the arrows E, E and thence into the exhaust chamber, as indicated by the arrows H, H. Gas separated in this stage can no longer cause turbulence in the fibres <NUM>, which are gathered to form the web <NUM> under stabilised conditions. Again, as in the embodiment of Figure 3A, gas and entrained fibres in the central zone of the gas stream are directed into the central passage <NUM>, and on to the conveyor <NUM> by the baffles <NUM>, <NUM>. The fibres <NUM> in the gas stream collect on the upper run of the conveyor, while surplus gas is directed from the enclosure <NUM> through the conveyor and discharges into the exhaust chamber <NUM> beneath the enclosure as indicated by the arrows G, G in <FIG>.

The louvres <NUM> in the baffles <NUM>a, <NUM>b provide an alternative route for separation of the gas from the fibres. The gas stream entering the central passage <NUM> experiences resistance to its flow through the passage, caused by the conveyor belt <NUM>. The conveyor offers a higher resistance to the downward flow of gas in the central passage than that offered by the casing to the downward flow of gas through the auxiliary passages. As a result, a higher pressure of gas may develop in the central, primary passage <NUM> than in the auxiliary passages. In this embodiment, the louvres provide passages through which gas may flow from the central passage into the auxiliary passages, in the direction of the arrows J-J, hereby reliving the higher pressure in the central passage, improving the separation of the fibres from the gas, further reducing turbulence within the housing and improving the stability of the fibres on the conveyor.

The flow of gas and fibres through the housing described with reference to <FIG> is similar to that illustrated in <FIG>, though the characteristics of the flow of gas and fibres over and through the baffle will vary with to the pattern and configuration of the louvres.

The effect of using an enclosure according to the embodiments described above is demonstrable by comparing the performance of the equipment incorporating the enclosure with that of equipment similar to <FIG>, but without the enclosure <NUM>.

In the absence of an enclosure, it is found that surplus gas from the melt blowing module <NUM> tends to disrupt the formation of the web of fibres on the conveyor <NUM>. Random fluctuation in the flow of surplus gas over the equipment <NUM> causes variations in the thickness and density of the web as it advances in the downstream direction along the conveyor, and can also cause the web to break out, or separate from the surface of the conveyor. These effects increase as the rate of delivery of fibres from the melt blowing head or the speed of travel of the conveyor <NUM> are increased. Consequently, in the absence of the enclosure <NUM>, the equipment must be operated at a relatively low rate of production of the web to avoid disruptions in the distribution of fibres in the gathered fibres and variations in the density of the fibrous material formed and inconsistency in the quality of products formed therefrom.

Claim 1:
Apparatus comprising:
melt-blowing equipment (<NUM>) for generating fibres of plastics material entrained in a gas stream, the melt-blowing equipment (<NUM>) comprising a die head (<NUM>) having an outlet (<NUM>) from which fibres entrained in a gas stream emerge from the melt-blowing equipment (<NUM>), and
equipment (<NUM>) to receive the fibres entrained in a gas stream emerging from the die-head (<NUM>) of the melt-blowing equipment (<NUM>), and for gathering said fibres, wherein the equipment (<NUM>) for receiving and gathering said fibres entrained in a gas stream comprises an enclosure (<NUM>) having an inlet (<NUM>) through which the fibres entrained in a gas stream are directed into a primary passage within the enclosure (<NUM>), a fibre outlet (<NUM>) from which gathered fibres are withdrawn from the enclosure (<NUM>), and an exhaust outlet (41a) through which the entrained gas separated from the gathered fibres in the primary passage passes out of the enclosure (<NUM>), the enclosure being constructed to provide a pathway (<NUM>) for the fibres through the enclosure (<NUM>) from the inlet (<NUM>) to the fibre outlet (<NUM>),
wherein the melt-blowing equipment (<NUM>) and the equipment to receive the fibres entrained in a gas stream and to gather the fibres is spaced such that a first portion of surplus gas in which the fibres are entrained is separated from said entrained fibres as said entrained fibres are directed to the inlet (<NUM>) of the enclosure (<NUM>) and before the fibres entrained in said gas stream enter the enclosure (<NUM>), said first portion of surplus gas being exhausted to atmosphere outside of the enclosure (<NUM>),
characterised in that the enclosure (<NUM>) comprises a baffle (<NUM>) extending in the direction of the gas stream and the pathway (<NUM>) for the fibres and which defines an auxiliary passage (49a,49b) alongside the primary passage within the enclosure (<NUM>), the baffle (<NUM>) being arranged to direct fibres entrained in the gas stream into the inlet of the primary passage, and a second portion of surplus gas from a periphery of the gas stream into said auxiliary passage (49a,49b) as said entrained fibres are directed to the inlet (<NUM>), wherein said exhaust outlet (41a) includes an outlet from the auxiliary passage (49a, 49b) to exhaust said second portion of surplus gas to atmosphere outside of the enclosure (<NUM>).