Fibrous material moulding apparatus

Abstract

Apparatus for making a fibrous element includes an elongate foraminous former provided by at least one foraminous belt, with a foraminous forming chamber through which said belt passes and which is formed to a hollow shape thereby. The belt is driven through the forming chamber, and fluid is extracted in a fluid extraction zone which surrounds at least part of the forming chamber and formed by a closed drainage casing. An injection nozzle injects a fibrous dispersion into the former within said forming chamber with the injection nozzle being dimensioned so as to substantially exclude the ingress of air around an interface with the walls of said belt so that the apparatus produces an elongate fibrous element having an outer core of greater density than the inner core which it surrounds.

Description

This invention relates to an improved apparatus for manufacturing elongated fibrous elements, and is concerned particularly but not exclusively with the manufacture of fibrous rods from which cigarette filter elements can be formed.

The cigarette industry predominately uses smoking product filters of two basic kinds, namely cellulose acetate and crimped paper, and also a third kind consisting of a composite of the first two. All three kinds of filter require paper wrapping to maintain their cylindrical form, or suffer from other disadvantages which are set out in greater detail in copending British patent application No. 32179/76, which is directed to an improved smoking product filter.

It is among the objects of the present invention to provide an apparatus for forming an elongate fibrous element, which in a cylindrical form is suitable for use as a cigarette filter, and which has substantial structural integrity, obviating the necessity for paper wrapping. It has now been found possible by using a modification of the conventional Fourdrinier papermaking procedures to form such a product, which, subsequent to the initial forming process, requires no processing beyond drying and cutting to length before incorporation in a filter cigarette.

In conventional papermaking procedures using the Fourdrinier process, a dispersion is first prepared of paper making fibres, for example wood pulp fibres. This dispersion, which has a relatively low consistency of in the region of 0.5%, constitutes the papermaking stock which is projected from the slice of the paper machine headbox and deposited across the width of a moving Fourdrinier wire. A substantial proportion of the water content of the dispersion is removed on the wire, in part by direct drainage assisted by foils, and in part by the application of vacuum. Hydrogen bonds are formed between the residual fibres to form a web, which is then lifted from the wire and passed to the press and dryer sections of the paper machine.

In the Fourdrinier process, the efflux ratio (that is the ratio of the rate of deposition of the stock from the slice to the rate of movement of the Fourdrinier wire) is carefully controlled. In most cases it is in the region of 1:1 and even in specialised systems is unlikely to exceed 2:1. Too great a departure from the 1:1 ratio leads to poor paper formation and to a tendency for the fibres to orient in a manner which leads to a loss of strength.

The use of a modified Fourdrinier type machine for the production of cigarette filters has already been proposed in United Kingdom Patent Specification No. 748 095. A cigarette filter which it is proposed can be made with such a machine is also disclosed in United Kingdom Patent Specification No. 753 203.

Specification No. 748 095 discloses a machine in which one or more foraminous belts or similar elements are guided in co-operation to define a tubular forming zone. Moisturised cellulose fibre pulp is fed into the forming zone while the belts are in movement and water is removed from the pulp through the belts partly by simple drainage and partly by the application of vacuum.

The resultant fibrous structure issuing from the forming zone is variable in density and not sufficiently compact to be self supporting, and further processing is required to improve its compaction, in particular consolidation by the application of pressure.

Specification No. 753 203 accordingly proposes the use of a number of surface treatments, including paper wrapping, to provide the filter formed by the process of Specification No. 748,095, with sufficient structural integrity for it to be usable in high speed cigarette manufacturing machinery.

The need for compaction and surface treatment of the prior art product is believed to stem from the lack of cohesion between the fibres of the fibrous mass constituting the product as it leaves from the forming zone. This lack of cohesion would appear to result primarily from an incorrect choice of stock consistency and the use of too low an efflux ratio. Failure to exclude free air from the stock and the apparatus with which the process is carried out can also lead to unacceptable variations in product density.

It is among the objects of the present invention to provide an improved apparatus whereby sufficient structural integrity can be conferred on the product to obviate the necessity for subsequent compaction or surface treatments such as wrapping.

A further manufacturing operation or treatment is preferably applied to the element subsequent to forming, such as drying, but without applying or causing to be applied any bending or compressing forces thereto which affect the structural integrity of the crust, thus the element may be arranged to travel in a linear direction without bending to a dryer which causes air to be drawn into and then sucked out of it and/or it can be cut into lengths prior to being moved laterally for delivery to a radio frequency dryer.

Density variations in the product can be minimized by excluding free air from the fluid extraction zone, and by ensuring that flocculation of the dispersion is prevented, first by promoting turbulence in the dispersion immediately prior to injection, and secondly by maintaining the consistency at an optimum level relative to the particular injection velocity used.

It has been found that the maximum consistency of the dispersion used will vary both with the injection velocity and with the fibre type, but that a satisfactory element cannot be formed with consistencies in excess of about 3%.

Similarly, it has been found that the ratio of the injection velocity to the speed of the forming means (the efflux ratio) has a minimum value dependent upon the type of fibre used, but that even with the shortest fibres a satisfactory product cannot be formed at an efflux ratio of less than about 5:1. For high alpha cellulose softwood fibres such as are proposed for use herein for the manufacture of cigarette filters, the minimum efflux ratio is in the region of 10:1.

Apparatus according to the invention for carrying out the process comprises an elongate foraminous former provided for foraminous belt means, a foraminous forming chamber through which said belt means pass and which are formed to a hollow shape thereby, means for driving said belt means through said forming chamber, and fluid extraction means within which is a fluid extraction zone which surrounds at least part of said forming chamber and formed by a closed drainage casing, and an injection nozzle for injecting a fibrous dispersion into said former within said forming chamber, the injection nozzle being dimensioned so as to substantially exclude the ingress of air around its interface with the walls of said belt means so that the apparatus produces an elongate fibrous element having an outer core of greater density than the inner core which it surrounds.

It has been found that use of the process of the invention results in an element having a surface layer substantially denser than its core and that this surface layer or casing confers a hardness on the product which, when in the form of a cigarette filter, is comparable with that of cellulose acetate filters. By selecting a mesh of appropriate size and weave for the material of the foraminous belts, which are preferably of a plastic material such as nylon, an acceptable surface smoothness is also achieved. As a result, the product leaving the forming zone can, after drying and cutting, be fed directly to cigarette manufacturing machinery for incorporation in cigarettes without any intermediate treatment or wrapping operation being required.

The invention will now be further described with reference to the accompanying drawings in which:

FIG. 1 is a semi-diagrammatic block diagram of a former according to the invention in association with a suitable stock preparation system,

FIG. 2 is a sectional elevation of a component of the system shown in FIG. 1,

FIG. 3 is a semi-diagrammatic lay-out showing a former according to the invention and other components for forming a dried rod product,

FIG. 4 is a side elevation, partly in section, showing in greater detail a former according to the invention,

FIG. 5 is an end section on the lines V--V of FIG. 4,

FIG. 6 is an end section on the lines VI--VI of FIG. 4,

FIG. 7 is an end section on the lines VII--VII of FIG. 4,

FIG. 8 is a diagrammatic longitudinal sectional elevation of a former according to the invention showing the process whereby the product is formed in the forming zone,

FIG. 9 is a side elevation of another component of the assembly shown in FIG. 3,

FIG. 10 is a sectional elevation on the lines X--X of FIG. 9,

FIG. 11 is a longitudinal sectional elevation of another component shown in FIG. 3,

FIG. 12 is an end elevation on the lines XII--XII of FIG. 11,

FIG. 13 is an elevation on the lines XIII--XIII of FIG. 3,

FIG. 14 is a semi-diagrammatic sectional side elevation of part of a machine for forming a flat board-like product according to the process of the invention; and

FIG. 15 is a sectional elevation on the lines XV--XV of FIG. 14.

Referring first to FIG. 1, this shows a fibrous element forming unit 1 fed with a fibrous dispersion through a turbulence generating unit 2. The element forming unit 1 and turbulence generating unit 2 are described in detail below.

Stock is prepared and fed to the turbulence generating unit 2 as follows. A suitable fibrous pulp is first slushed in a pulper 3 and fed by means of a pump 4 to a dilution tank 5 in which an agitator 6 is located. The pulp is diluted to a consistency of about 1% in the tank 5 and is recycled by means of a pump 7 through a classifier 8 into the pulper 3. Fines removed from the stock in the classifier 8 are discharged at 9.

Diluted and classified stock is then fed by means of the pump 4 to the thin stock tanks 10 and 11 in which agitators 12 and 13 are located. Thin stock from the tanks 10 and 11 is fed via a pump 14 to a constant head tank 15 supplying a pump 16. The outlet of the pump 16 supplies the turbulence generating unit 2 and a recycling line 17 returning stock to the constant head tank 15 and the recycling line 17 prevent pressure and therefore speed variations in the stock flowing to the turbulence generating unit 2. The constant head tank 15 can be replaced by a Deculator unit (not shown). This comprises a closed tank into which the stock is sprayed, the constant head tank being subjected to vacuum, so that the stock passing from the Deculator unit to the turbulence generating unit 2 and then to the element forming unit 1 is deaerated.

In the element forming unit 1, water is removed from the stock by means of vacuum pump 19, so that a rod-like element 53 is formed. The process of formation is described in greater detail below. The vacuum pump 19 has a ballast tank 21 fitted in a recycling circuit therewith and discharges, either to waste at 22, or to a return tank 23. A pump 24 returns the extracted water to the dilution tank 5.

The internal configuration of the turbulence generating unit 2 is best seen in FIG. 2. The unit 2 is formed with a number of internal corrugations 25 which generate eddies and produce turbulence in the stock, thus preventing flocculation before the stock is injected into the element forming unit 1.

Turning now to FIG. 3, the assembly of components thereshown consists of the element forming unit 1, a rotary cutter unit 30 for cutting the element into predetermined lengths, a dry box 31, and a radio frequency drier 32. The dry box 31 and drier 32 serve respectively to reduce the water content of the product and to dry it to a final moisture content of about 10%.

The element forming unit 1 and the dry box 31 are each formed internally with perforated tubes 44 (see FIGS. 4 and 7) which are described in greater detail below, which serve to conform Fourdrinier wires 33 and 34, respectively into a generally cylindrical form 33 (see FIGS. 5 to 7) when passing through element forming unit 1 and dry box 31, respectively. The Fourdrinier wires are preferably formed of plastics materials such as nylon, and passed around tensioning rolls 35 and 36 respectively.

The element forming unit 1 is shown in greater detail in FIGS. 4 and 7 and consists of fluid extraction means provided by drainage casings I, II, III and IV defined by walls 40, 41, 42 and, 43. A perforated tube 44 which acts as a foraminous forming chamber passes through all the casings and, terminating in walls 43. End plates 45 and 46 are secured to the walls 43 and carry inlet and outlet guide tubes 47 and 48 coaxial with the perforated tube 44. A stock injection nozzle 49 formed by the end of an inlet guide 50 projects through the inlet guide tube 47 into the perforated tube 44. The nylon Fourdrinier wire 33 acts as an elongate foraminous former after passing around roller 51 in a flat condition and being progressively formed into a cylindrical configuration while passing through the inlet guide tube 47 and perforated tube 44 as seen in FIGS. 5, 6 and 7. The perforated tube 44, the injection nozzle 49 and the Fourdrinier wire 33 are so dimensioned that a tight sliding fit is achieved between these components, whereby the ingress of air is effectively prevented around its interface with the walls of the Fourdrinier wire 33 and through the inlet guide tube 47. Having passed outwardly through Fourdrinier outlet guide tube 48, the Fourdrinier wire 33 relaxes into a flat condition as it is drawn around roller 52 while the rod-like element 53 which has been formed continues to move axially in alignment with perforated tube 44.

Each of the casings I, II, III and IV which it will be seen are in tandem configuration is provided with an extraction port 54 for the application of vacuum and the withdrawal of water drained from the stock through the Fourdrinier wire 33 and perforated tube 44, so that a fluid extraction zone is provided within the drainage casings.

Operation of element forming unit 1 in producing the rod-like element 53 is best understood with reference to FIG. 8 which is an enlarged view of the perforated tube 44, the inlet nozzle 49 and the Fourdrinier wire 33. Provided that the fibrous dispersion is injected through the injection nozzle 49 at a suitable consistency and at an appropriate speed relative to the speed of the Fourdrinier wire 33, the forming process shown in FIG. 8 occurs. The fibrous stock 60 entering the former provided by the Fourdrinier wire 33 has a boundary layer 61 which rapidly drains in the first part of the fluid extract zone provided by first drainage zone 62. In a second drainage zone 63, a fibre mat begins to form on the surface of the Fourdrinier wire 33, as at 64. However, because of the high velocity of the stock relative to the wire 33, the fibre mat is disrupted into small flocs which break loose and are driven forward into a thickening zone 65.

The stock velocity reduces progressively along the thickening zone as water drains from the chamber through the Fourdrinier wire 33 and perforated tube 44, until disruption of the fibrous mat no longer occurs. The flocs then build up very quickly and fill the core in a final formation zone 66. Because the mat forms initially on the Fourdrinier wire 33 and builds up progressively towards the centre, a generally conical layering effect occurs. As flocs are driven into the conically concave rear end face of the rod being formed, pressure re-generation occurs, which assists both in compacting the fibrous structure and also in driving out a proportion of the residual water. The final formation zone at the end of the fluid extraction zone is analogous to the dry line on a paper-forming machine Fourdrinier.

The tightly packed fibres of the fibrous crust forming the residue of the fibre mat reduces the rate of drainage through the Fourdrinier wire 33 and tube 44 as the wire passes through thickening zone 65 and final 66. As a result, the fibre crust 67 is of greater density than the core 68 of the rod-like element 53, ViZ., the product as it leaves the element forming unit 1.

It is convenient to cut the rod-like element 53 into convenient lengths for further processing immediately after it has left the element forming unit 1 and this is achieved by means of a rotary cutter unit 30 which is described in greater detail in FIGS. 9 and 10. The rotary cutter unit 30 consists of a rotor 70 having an annular U-section groove 71 in its periphery which supports rod-like element 53 tangentially at the "12 o'clock" position. Within a radial slot 72 in rotor knife bar 73, having a cutting edge 74, is pivoted at 75. The rotor 70 is mounted on a hollow shaft 76 which is journalled for rotation in bearings not shown in the drawings. A knife activating rod 77 extends through the hollow shaft 76 and is pivoted to the rotor knife bar 73 at 78. The activating rod 77 is controlled by a suitable comming mechanism, not shown so as to activate the rotor knife bar 73 when it is at the "12 o'clock" position shown in FIG. 9. This causes the knife to rock about the pivot 75 and cut the rod-like element 53 with the knife edge 74.

The moisture content of the rod-like element 53 as formed is normally between 75% and 85% by weight, but this can be further reduced by the use of a dry box 31 which is shown in greater detail in FIGS. 11 and 12. The rod-like element 53 is carried through a perforated tube 80 by means of the Fourdrinier wire 34 passing around rollers 81. The perforated tube 80 extends through a series of chambers 82 which are subjected to vacuum through a manifold 83. Alternating with the vacuum chambers 82 are chambers 84 which are open to atmosphere through a manifold 85. During movement of the rod-like element 53 through the perforated tube 80, air is drawn in through the manifold 85 and laterally into and along the rod-like element 53. Water is thus drawn outwardly from the rod-like element 53 through the chambers 82 and the manifold 83.

FIG. 13 shows a radio frequency drier 32 formed with a tunnel 90 through which the upper run of an endless conveyor belt 91 passes, the belt being supported at each end of its run on drums 92. The conveyor belt 91 is made of a material, for example a woven nylon mesh, which is not susceptible to heating in a radio frequency field. Cut lengths of the rod-like element 53 received from the dry box 31 are supported and guided onto the conveyor belt 91 by means of a support and guide unit 93 (see also FIG. 3). The cut lengths 94 (also in FIG. 3) then pass through the tunnel 90 of the radio-frequency drier and emerge at 95 with a moisture content of about 10%. In this condition, they are suitable for further reduction into lengths which can be conveniently handled by cigarette manufacturing machinery.

Referring again to FIG. 3, it will be appreciated that the Fourdrinier wire belt 34 is operated at a speed slightly greater than the Fourdrinier wire belt 33 so that, after the rod-like element 53 has been cut by the rotary cutter unit 30, the cut lengths are spaced apart a slight amount before entering the support and guide unit 93. In this way, each cut length can be deposited on the conveyor belt 91 in time for it to effect lateral movement before the leading end of the next length is delivered onto the conveyor. Moreover the uses of lateral movement within the dryer enables the length of the apparatus to be reduced and for elements to be made fast enough for delivery from the dryer direct to a cigarette making machine.

It will be seen that delivery to the dry box 31 is a linear movement from the end of element forming unit 1 so that no bending or compressing forces are applied to the freshly formed element which might affect the structural integrity of the crust prior to its being dried and ready for use. Similarly the element is only moved sideways into the radio frequency dryer 32 after it has been cut so that again no bending or compressive forces are applied to the newly formed crust.

The following table relates to 32 examples of the production of fibre rods suitable for use as cigarette filters:

TABLE__________________________________________________________________________PART 1EXAMPLE 1 2 3 4 5 6 7 8 9__________________________________________________________________________ 100% 100% BLEACHED BLEACHED SOFTWOOD SOFTWOODPULP SULPHATE SULPHITEFURNISH STORA 32) (WEYERHAUSER AA)__________________________________________________________________________STOCKCONSISTENCY % 3.48 2.95 2.21 1.89 1.67 1.67 1.17 0.65 0.42STOCK PRESSURE 71.1 69.0 48.3 48.3 20.7 48.9 1.72 10.5 41.4KilopascalsINJECTION NOZZLEINTERNAL DIAMETER 7.0 7.0 7.0 7.0 6.5 6.5 6.0 6.0 6.5(mm)STOCK VELOCITY 62.29 79.73 103.0 115.5 78.0 240.0 984.0 552.2 534.0meters/min (x)WIRE FORMERSPEED 10.6 10.5 10.8 10.8 5.0 15.0 40.0 15.6 10.0meters/min (y) ##STR1## 5.88 7.59 9.54 10.70 15.6 16.0 24.6 35.4 53.4APPROXIMATEDRAINAGE LENGTH 50 50 50 100 118 180 400 180 160(mm)FORMERVACUUM-CHAMBER I 76.2 76.2 88.9 88.9 229 241 432 203 102(mm-Hg)FORMERVACUUM-CHAMBER II 165.1 152.4 165.1 165.1 241 292 406 140 178(mm-Hg)FORMERVACUUM-CHAMBER III 101.6 101.6 101.6 101.6 229 267 406 102 178(mm-Hg)FORMERVACUUM-CHAMBER IV 139.7 152.4 139.7 139.7 267 318 381 76 203(mm-Hg)% OPEN AREA 38.6 38.6 38.6 38.6 38.6 38.6 38.6 38.6 38.6FORMING TUBEROD WEIGHT 7.87 8.62 8.11 7.78 8.72 8.94 8.74 6.61 7.44(grams/meter)ROD DIAMETER (mm) 7.52 7.57 7.50 7.40 7.78 7.80 7.75 7.21 7.49__________________________________________________________________________PART 2EXAMPLE 10 11 12 13 14__________________________________________________________________________ 70% BLEACHED 100% SOFTWOOD SUL- BLEACHED 100% BLEACHEDPULP PHATE 30% SOFTWOOD SOFTWOOD SULPHATEFURNISH SYNTHETIC WOOD SULPHITE (BUCKEYE PV5)__________________________________________________________________________STOCK 0.25 0.2 0.15 1.2 1.1CONSISTENCY %STOCK PRESSURE 34.5 27.9 27.9 79.3 55.2KilopascalsINJECTION NOZZLEINTERNAL DIAMETER 6.5 6.5 6.5 7.0 7.0(mm)STOCK VELOCITY 69.8 88.8 132.5 496.1 192.7meters/min (x)WIRE FORMERSPEED 6.1 5.2 2.4 30.0 10.0meters/min (y) ##STR2## 69.8 88.8 132.5 16.54 19.27APPROXIMATEDRAINAGE LENGTH 60 180 160 80 60(mm)FORMERVACUUM-CHAMBER I 127 127 51 88.9 190.5(mm-Hg)FORMERVACUUM-CHAMBER II 102 102 51 254.0 254.0(mm-Hg)FORMERVACUUM-CHAMBER III 76 127 76 190.5 190.5(mm-Hg)FORMERVACUUM-CHAMBER IV 76 152 76 241.3 254.0(mm-Hg)% OPEN AREA 38.6 38.6 38.6 38.6 38.6FORMING TUBEROD WEIGHT 5.76 5.88 6.6 7.64 8.16(grams/meter)ROD DIAMETER (mm) 7.45 7.66 7.76 7.76 8.07__________________________________________________________________________PART 3EXAMPLE 15 16 17 18 19 20 21 22__________________________________________________________________________PULP 100% BLEACHEDFURNISH SOFTWOOD SULPHATE (BUCKEYE PV5)__________________________________________________________________________STOCKCONSISTENCY % 1.2 1.2 0.9 0.8 0.8 0.8 0.6 0.6STOCK PRESSURE 62.1 79.3 50.0 58.6 117.2 48.3 103.4 189.6KilopascalsINJECTION NOZZLEINTERNAL DIAMETER 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0(mm)STOCK VELOCITY 340.7 511.7 225.1 471.4 711.0 257.5 619.9 976.6meters/min (x)WIRE FORMERSPEED 20.0 30.0 10.0 20.0 30.0 10.0 20.0 30.0metres/min (y) ##STR3## 17.0 17.1 22.5 23.6 23.7 25.8 31.0 29.3APPROXIMATEDRAINAGE LENTH 60 150 60 60 150 60 230 250(mm)FORMERVACUUM-CHAMBER I 127.0 101.6 165.1 152.4 254.0 152.4 228.6 279.4(mm-Hg)FORMERVACUUM-CHAMBER II 292.1 304.8 279.4 279.4 165.1 266.7 139.7 241.3(mm-Hg)FORMERVACUUM-CHAMBER III 241.3 254.0 228.6 241.3 177.8 228.6 215.9 0(mm-Hg)FORMERVACUUM-CHAMBER IV 279.4 279.4 254.0 254.0 292.1 254.0 266.7 355.6(mm-Hg)% OPEN AREA 38.6 38.6 38.6 38.6 38.6 38.6 38.6 38.6FORMING TUBEROD WEIGHT 7.87 7.88 7.80 7.26 7.30 7.93 7.16 7.52(grams/meter)ROD DIAMETER (mm) 7.36 7.88 7.96 7.86 7.86 8.05 7.93 8.03__________________________________________________________________________PART 4EXAMPLE 23 24 25 26 27 28 29__________________________________________________________________________ 55% SOFTWOOD 100% BLEACHED SULPHATEPULP SOFTWOOD SULPHATE (BUCKEYE PV5)FURNISH (BUCKEYE PV5) 45% ESPARTO__________________________________________________________________________STOCKCONSISTENCY % 0.6 0.6 0.3 0.3 0.3 0.46 0.46STOCK PRESSURE 48.3 82.7 75.3 137.9 117.2 69.0 17.2KilopascalsINJECTION NOZZLEINTERNAL DIAMETER 7.0 7.0 7.0 7.0 7.0 7.0 7.0(mm)STOCK VELOCITY 331.6 637.2 613.0 1423.4 573.2 411.9 334.9meters/min (x)WIRE FORMERSPEED 10.0 20.0 10.0 20.0 10.0 9.8 10.4meters/min (y) ##STR4## 33.2 31.9 61.3 71.2 57.3 42.03 32.2APPROXIMATEDRAINAGE LENGTH 60 230 230 480 230 130 160(mm)FORMERVACUUM-CHAMBER I 101.6 241.3 215.9 279.4 228.6 127.0 101.6(mm-Hg)FORMERVACUUM-CHAMBER II 215.9 165.1 165.1 215.9 152.4 76.2 76.2(mm-Hg)FORMERVACUUM-CHAMBER III 165.1 101.6 101.6 0 76.2 127.0 101.6(mm-Hg)FORMERVACUUM-CHAMBER IV 215.9 241.3 254.0 152.4 241.3 127.0 114.3(mm-Hg)% OPEN AREA 38.6 38.6 38.6 38.6 38.6 38.6 38.6FORMING TUBEROD WEIGHT 7.66 7.36 7.08 8.22 6.62 7.44 5.7(grams/meter)ROD DIAMETER (mm) 7.95 8.04 8.02 8.33 8.01 7.76 7.69PART 5EXAMPLE 30 31 32__________________________________________________________________________ 55% SOFTWOOD SULPHATE 90% BLEACHED SOFTWOODPULP (BUCKEYE PV5) SULPHATE (BUCKEYE PV5)FURNISH 45% EUCALYPTUS (CELBI) 10% KAOLIN__________________________________________________________________________STOCKCONSISTENCY % 0.52 0.52 0.43STOCK PRESSURE 82.7 27.6 48.7KilopascalsINJECTION NOZZLEINTERNAL DIAMETER 7.0 7.0 7.0(mm)STOCK VELOCITY 438.3 323.7 494.4meters/min (x)WIRE FORMERSPEED 9.8 9.8 10.0meters /min (y) ##STR5## 44.7 33.0 49.4APPROXIMATEDRAINAGE LENGTH 160 160 130(mm)FORMERVACUUM-CHAMBER I 13.8 24.1 13.8(mm-Hg)FORMERVACUUM-CHAMBER II 41.4 139.7 76.2(mm-Hg)FORMERVACUUM-CHAMBER III 127.0 31.0 76.2(mm-Hg)FORMERVACUUM-CHAMBER IV 139.7 139.7 127.0(mm-Hg)% OPEN AREA 38.6 38.6 38.6FORMING TUBEROD WEIGHT 8.95 6.61 8.18(grams/meter)ROD DIAMETER (mm) 8.02 7.68 7.93__________________________________________________________________________

FIGS. 14 and 15 show a machine for making a board-like product. Two Fourdrinier wires 100 and 101 extending around press rolls 102 and 103, respectively, have opposed runs 104 and 105, also respectively, which, at their edges, extend in sealing slots 106 and 107, respectively, of side member 108. An injection nozzle 109 extends between the opposed runs 104 and 105 so as to provide a sliding fit and prevent the ingress of air. At its sides, seals 110 are provided with the side members 108. Vacuum chambers 111 and 112 are positioned above and below the runs 104 and 105 respectively between the side members 108 and are sealed thereto as at 113. The vacuum chambers 111 and 112 have extract ducts 114 and 115, respectively.

In use, a well dispersed fibrous stock is injected into the space between the runs 104 and 105 of wire through the broad injection nozzle 109 at a velocity at least 5 times that of the Fourdrinier wires 100 and 101, with the stock being at a consistency of not more than 3%. Vacuum extraction through the ducts 111 and 112 results in a board-like product 116 having surface layers which are denser than the core and which can be used for example as a filter material or for other purposes where it has application. It will be appreciated that the product has a substantially rectangular cross-section and similar apparatus could be used to produce an element of square cross section.

Claims

1. Apparatus for forming an elongated fibrous element comprising:

foraminous belt means for providing an elongate foraminous former;

a foraminous forming chamber through which said belt means passes, said belt means being formed to a hollow shape thereby;

fluid extraction means for providing a fluid extraction zone surrounding at least part of said forming chamber, said fluid extraction zone being formed by a closed drainage casing;

means for driving said belt means through both said forming chamber and said fluid extraction means and

injection nozzle means for injecting a fibrous dispersion into said elongate foraminous former within said forming chamber, said injection nozzle means having an injection nozzle being dimensioned so as to substantially exclude an ingress of air around an interface of said injection nozzle with walls of said belt means so that the apparatus produces an elongate fibrous element having an outer core of greater density than the inner core which said outer core surrounds.

2. The apparatus of claim 1 wherein said fluid extraction zone is formed by two or more drainage casings provided in tandem orientation along the forming chamber.

3. The apparatus of claim 1 wherein said closed drainage casing is connected to means for forming a vacuum.

4. The apparatus of claim 1, wherein the injection nozzle is provided with means for generating turbulence in the fibrous dispersion immediately prior to injection so as to prevent flocculation.

5. The apparatus of any one of claims 1-4 further comprising: means for deaerating the fibrous dispersion prior to delivery to the injection nozzle.

6. The apparatus of claim 1 further comprising: means for delivering the fibrous element after forming to means for applying a further treatment without bending and without compressing the element.

7. The apparatus of claim 6 wherein the means for applying a further treatment includes means for applying a drying process which causes air to be drawn into and then sucked out of the element.

8. The apparatus of claim 7 wherein the means for applying a drying process comprises a perforated tube through which the element is passed and which perforated tube extends through a number of chambers, alternate ones of said chambers being open to atmosphere and intermediate ones of said chambers being provided with a vacuum.

9. The apparatus of claim 6 further comprising: means for selectively cutting the fibrous element into lengths prior to carrying out the further treatment.

10. The apparatus of claim 6 wherein the further treatment includes a drying process provided by a radio frequency dryer.

11. The apparatus of claim 9 wherein the further treatment includes a drying process provided by a radio frequency dryer and wherein the element is arranged to emerge from the elongate foraminous former travelling in a linear direction and, after said cutting, means are provided for moving the element through a direction lateral to the linear direction to deliver the element to the radio frequency dryer.

12. The apparatus of claim 1 wherein said belt means include at least one endless foraminous belt made from plastics material.

13. The apparatus of claim 12 wherein the plastics material is nylon.

14. Apparatus for forming a fibrous element in an elongate closed foraminous former during movement of said former through fluid extraction means, said fibrous element comprising a fibrous core enclosed and stiffened by a fibrous crust which is integral with the core and has a density greater than that of the core, which comprises:

(a) means for forming an aqueous fibrous dispersion,

(b) means for generating a pressure gradient across an extraction zone within said fluid extraction means,

(c) means for continuously injecting the aqueous fibrous dispersion into the former at a predetermined efflux ratio, i.e., the ratio of the aqueous fluid dispersion injection velocity relative to the speed of the moving former, to cause some of the fibres, upon extraction of fluid as the dispersion traverses said extraction zone, to build up as a continuous crust on the inner surface of the former and the remaining fibres to pack together within the area inside said crust to form the aforesaid core so as to produce a continuous fibrous element, in said elongate, moving foraminous former, having a fibrous core enclosed and stiffened by a fibrous crust which is integral with the core but of greater density, and

(d) means for removing said fibrous element thus formed from said former.

15. The apparatus of claim 14 further comprising means for applying a further manufacturing operation to the fibrous element subsequent to forming without applying or causing to be applied any bending or compressing forces thereto which affect the structural integrity of the crust, the further operation comprising:

(e) means for drying by causing air to be drawn into and then sucked out of the element.

16. The apparatus of claim 15 further comprising:

(d') means for cutting the element into predetermined lengths.

17. The apparatus of claim 16 wherein said means for applying a further manufacturing operation includes a radio frequency dryer.

18. The apparatus of claim 17 further comprising:

(f) means for causing the element to emerge from the forming process travelling in a linear direction and,

(g) means for moving said predetermined lengths in a direction lateral to the linear direction of the element for delivery to the radio frequency dryer.

19. The apparatus of claim 18 further comprising:

(h) means for excluding intake of free air into the fibrous dispersion during its injection into the former and its passage through the fluid extraction means.

20. The apparatus of claim 14 further comprising:

(i) means for preventing flocculation of the dispersion prior to injection into the foraminous former by promoting turbulence in the dispersion immediately prior to said injection into the former.

21. The apparatus of claim 20 further comprising:

(j) means for de-aerating the fibrous dispersion prior to injection into the former.

22. The apparatus of claim 21 wherein the means for de-aerating includes a deculator unit.

23. The apparatus of claim 14 wherein the formed element is substantially circular in cross-section.

24. The apparatus of claim 14 wherein the formed element is rectangular or square in cross-section.

25. The apparatus of claim 21 further comprising:

(k) means for controlling the fibrous dispersion consistency and efflux ratio to cause some of the fibres, upon extraction of fluid from the dispersion entering the extraction zone, to build up initially a fibrous mat on the initial inner surface of the former entering the extraction zone, which mat, due to the efflux ratio, is partially disrupted into small flocs which break loose and pack together in a thickening zone as part of the core, the balance of the fibrous mat remaining to form the continuous crust enclosure of greater density than the core.

26. The apparatus of claim 25 further comprising:

(l) means for controlling fibrous dispersion consistency and the efflux ratio such as to cause a generally conical layering effect in the core as fibres build up progressively toward the centre of the core.