US 3729374 A
Description (OCR text may contain errors)
April 24, 1973 H. R. LISSALDE PRODUCTION OF A FIBROUS WEB BETWEEN AN ENDLESS BELT AND AN ENDLESS PERMEABLE BELT Original Filed Feb. 15, 1968 United States Patent O Int. (:1. 10213? 1/00, 11/04 US. Cl. 162203 5 Claims ABSTRACT OF THE DISCLOSURE Process for the production of a web or carrier of fibrous elements comprising placing a suspension of fibres in a liquid bath, causing a flow of the suspension through a part of the bath having a progressively decreasing width to concentrate the suspension and causing the concentrated suspension to be advanced between two travelling belts to form the web or carrier.
This application is a continuation of application Ser. No. 705,735, filed Feb. 15, 1968, now abandoned.
BACKGROUND OF THE INVENTION This invention relates to the production of fibrous and/ or like structures of different types, such as paper, Wadding, non-woven fabrics, for domestic, clothing, hygienic, medical, industrial and other purposes.
With the scope of this specification, these structures will be referred to by the term carrier, and this description will be applied to the webs or sheets produced in the form of unitary sections of optional size, as well as to sheets produced continuously to constant width and indefinite length and which may be wound on reels.
This invention relates to carriers produced from elements of a variety of origins, being natural, synthetic, metallic, artificial or the like, possessing optional features in respect of their nature and dimensions, and which may be employed in the crude state or after subsequent processing.
However, the invention is highly suitable for use in the production of long-fibre carriers which are diflicult or impossible to obtain by some existing production methods, and which are of pronounced interest in industries, such as, for example, the non-woven fabrics industry, as well as in the production of a variety of goods produced from crude fibrous carriers containing little or no bonding substance.
In some known production processes, the fibres or mixture of fibres are placed in suspension in water, and this suspension is guided to flow in sheet-form to form a fibrous sheet or web. If these processes are to be applied in the case of long fibres, the dilution of the suspension must be increased. This requires an increase in the rate of flow in sheet form, to obtain a sheet or web of definite unit weight, and the flow becomes turbulent so that production is impracticable.
The main object of the present invention is to provide for the uncomplicated production of carriers from suspensions of fibres of optional length, even of great length amounting to 30 mms. and more for example, and requiring very low concentrations, which may be equal to or lower than 0.07 g/litre for example, instead of concentrations of 2 to g./litre employed at present in existing processes.
The invention equally has as its object to assist in the forming of a carrier comprising randomly directed 3,729,374 Patented Apr. 24, 1973 or slightly directionalised fibres, and thus of more isotropic structure than the existing carriers.
SUMMARY According to the present invention, a process for the production of a web or carrier of fibrous elements comprises. placing the elements in suspension in a liquid bath, so as to be drawn along in suspension towards a constricted part of the bath having a progressively decreasing width to form an area of progressively increasing concentration in the suspension, and to issue from the area between two conveyor belts to form the carrier.
The restricted space preferably extends in depth.
The restricted space is preferably bounded by quickly converging surfaces, at least one being of curved shape, to cause sudden transfer of the fibres from a region of great dilution into a region of high concentration and to prevent formation of a directionalised structure by immobilisation of the fibres in the tangled condition.
Transverse orientation of some fibres relative to the faces of the conveyor belts may appropriately be established, for example by engendering a guiding flow within the bath, or by stirring the suspension in the high-concentration space, or immediately upstream of this space, to enhance the tangling of the fibres.
A device for carrying out the process of the invention comprises a tub or vat to contain a suspension of fibres, a space of progressively decreasing width forming a volume for agglomeration of the fibres being arranged in the tub and having an outlet between two entraining or conveying belts or sheets to form a web or sheet of fibrous materials between them, and means of setting the fibres of the suspension into motion towards the said space, and of feeding them in the agglomerated condition to the forming webs or belts.
At least one surface of the agglomerating volume may be formed by a portion of forming web or belt. This volume may extend in depth and hydraulic pressure may prevail therein.
In another construction a deflecting plate positively directs the fibres to the agglomerating volume in a transverse direction to the plane of formation of the sheet or web. Alternatively a sheet or layer of fluid such as air or water is injected into the agglomerating volume or immediately upstream of the same to cause tangling of the fibres.
The suspension may be fed to the bath in a continuous liquid flow with gradual loss of head or speed, so as to preserve the homogeneity of the suspension. A condition of constant flow without sudden speed changes is thus established between the inflow and the agglomerating space.
It has been found that feed by spill-over causes violent agitation in suspensions of long fibres in particular, causing formation of froth and agglomeration nodes, Which impairs the quality of the product.
In order that the invention may be more fully understood some embodiments in accordance therewith will now be described by way of example with reference to the accompanying drawings, in which:
DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows diagrammatically a device for production of the carrier; and
FIGS. 2 and 3 show modified forms of the device of FIG. 1.
The device of FIG. 1 comprises a chest or vat 1 to The vat 1 comprises stationary wall elements 4, 5 and 6, a moving wall element 7 forming part of the endless belt 2 and situated in the extension of the stationary element 5, as well as a moving wall element 8 situated in the extension of the stationary element 6 and forming part of the endless belt 3.
The vat or tub 1, which is joined in gradual manner to a feed duct S, comprises a reception space A for the suspension, an expansion space B and an outflow space C whose downflow extreme portion D has a progressively decreasing width with its outlet between two parallel sections 9 and 10 of the two endless belts 2 and 3.
The space D is bounded by the moving wall elements 7 and 8. The element 7 is in contact with a roller 11 of the endless belt 2 and thus has a curved shape coming close tangentially to the element 8, so that the reduction in width of the space D occurs suddenly and may be dimensioned by appropriate choice of the diameter of the roller 11.
Being closed off at the top, the vat or tubmay be pressurised or depressurised. An open tank may be employed.
The endless belt 3 may, for example, consist of a metal or plastic cloth whose weave is of texture and mesh size appropriate for the carriers which are to be produced; or else of a felt permeable in respect of the liquid of the suspension, or else of a liquid-proof material. In this last case, the endless belt 2 is made of a material permeable by the liquid phase of the suspension of fibres.
The endless belt 3 runs over rollers 12, 13, of Which one imparts drive, and over guiding and tensioning rollers 14. Its lower section between the rollers 12 and 13 may, if appropriate, be acted upon by cleansing rinsing elements 14A and of smoothing bars or the like 14B. The roller 13 may be solid or perforated, and in the latter case may be co-ordinated with an internal suction chest. If appropriate, it may be operated in conjunction with a thrust roller 13A.
The upper section of the endless belt 3 extending between the rollers 12 and 13, is stretched in horizontal or other position and, if appropriate, is equipped with a variety of removable accessories abreast of the wall element 8 of the vat or tub 1, which operate separately or simultaneously and may comprise the features to be described.
A solid, perforated or grooved displaceable face-plate 15 is in contact with the belt 3 to close off an area of the latter wholly or partly and to cause or prevent draining of the suspension through the side 8 in controllable manner; the displaceable plate 15 is preferably positioned so that it may be adjusted in position during operation of the device.
A box 16 is provided open at the top, with one or more compartments covering the whole or part of the draining area controlled by the plate and adapted for controlling this area instead of the latter; one or more of these compartments may receive the liquid drained through their open side aligned under the belt, and discharging the same by gravity or pumping in controlled manner; each compartment is separately adjustable and is organised so that it may be depressurised or fed with liquid in order to accelerate the settling of agglomerated fibres on the belt 3, or on the contrary to delay and transpose the same downstream.
A narrow sheet-like jet 17 of fluid such as air or water, may be applied as shown at an appropriate point of the space D, to change the orientation of the fibres before or during their agglomeration, or to create, abreast of the openings of the belt 3, areas of reduced density in a carrier in process of formation, for example being hinge areas to reduce the rigidity of the carrier.
One or more draft chests 18 may be provided to draw off the interstitial water through the part 10 of the belt 3. One or more steam distributors 19 may be provided, as may be one or more compressed air distributors 26 4 to separate the web or fibrous formed between the belts 3 and 2 from the belt 3.
The endless belt 2 consists of a metal or plastic cloth, or of a woven or knitted felt, or of a more or less liquidproof cloth, or of any other material corresponding to the nature of the carrier to be produced. The belt 2 runs over the rollers 11 and 21 and over the guiding and tensioning rollers 22. It is driven by a separate driving system, synchronously with the belt 3, or by the belt 3 by being gripped between the latter and the roller 11 or 21.
If appropriate, washing and smoothing devices (not shown) are disposed along the run of the belt 2.
The roller 11 is solid, or perforated like the draining cylinders in paper-making machines, and in the latter case is internally equipped for discharge of the draining liquid.
If appropriate, the belt 2 is constructed to lift the sheet formed between it and the belt 3 and to transfer the same to a subsequent processing device, for bonding, pressing, drying or the like.
In operation, a suspension of fibrous products fed at A to the inlet of the tub 1, expands in the space B and travels to the space C under the action of hydrostatic pressure assisted, if appropriate, by negative pressure in the box 16 and/or in the roller 11, or by means of any other device intended to cause liquid to be drawn to the space D.
The fibres accumulate between the sides 7 and 8 and, drawn into the space D of progressively decreasing width, suddenly change from the state of a suspension to that of an agglomeration, and are thus immobilised in the position they were occupying in the first of these two conditions, that is to say in random pattern, and without preferential orientation. They are then drawn along by the two belts 2 and 3 and issue from the bath to form, between the two sections 9 and 10 of these two belts, a web or carrier 23 of fibrous homogenous and isotropic structure, formed by fibres pointing in all directions.
If appropriate, the tangling of the fibers may be accentuated by the sheet of liquid or fluid 17.
In a modification, an internal partition 24 drawn dashdotted and positioned in the manner of a baflle-plate with respect to the flow of suspension fed into A, causes the suspension to drop downwards in the direction of the arrow G to force some fibres to assume a transverse position relative to the plane of formation of the carrier 23.
In another variant, a grid of wires extending in one or more directions, or an optional web which may be pliable and continuous, such as for example netting, screening or curves of textile or metallic material, or a meshwork fabric, may be appliedon one side or within the depth of the web or carrier in process of formation. This layer 25 may be introduced between the wall elements 6 and 8 or 5 and 7, or through the inside of the tub as shown dash-dotted in FIG. 1, in this latter case playing a part in drawing the fiibres towards the agglomerating space D.
The device in FIG. 1 thus renders it possible to place a fibrous suspension in motion by controlled draining towards a constricted space of the vessel, therein to cause a sudden agglomeration of fibres so as to immobilise these relative to each other in the non-directional tangled condition, and to entrain the fibres thus agglomerated between two belts or webs in order to form a carrier in intermittent or continuous manner, the unit weight of the carrier per square metre being liable to vary between very wide limits, for example from less than 5 gr./m. to more than 1000 gr./m.=
The controllable devices 15, 16 and 17 assist the evolution of the process by preventing premature settling of fibres on one of the belts and by limiting the region of contact and entrainment of fibres by the belts to the area in ch. th y were actually agglomerated in suspension,
The devices of FIGS. 2 and 3 are variants of FIG. 1, and comprise analogous or equivalent elements, having the same references. In FIG. 2, the forming element 3 consists of a metal cloth situated on a drum-shaped frame, instead of an endless belt. In the device of FIG. 3, the moving sides 7 and 8 are inclined to either side from the vertical, the fibre accumulation space D being situated in the foot of a V-shaped tub, accentuating the sudden transfer of the fibres from a region of great dilution into one of high concentration, and if appropriate, renders it possible to produce a carrier both faces of which are of identical structure.
The invention is applicable to the production of sheets of special non-fibrous elements, such as fine particles, rodlets, granules, or of elements which are not naturally fibrous but are produced in the form of fibres.
Having described my invention, I claim:
1. A method for the production of a fibrous web of nonwoven fabric comprising the steps of feeding a dilute suspension of fibers through a pipe duct having walls smoothly diverging towards an extremity thereof and a transverse closure wall at said extremity and defining an expansion chamber with a said duct portion adjacent thereto, thus offering to flow a passageway of progressively increasing cross section smoothly merging with said chamber, a said diverging duct wall having a portion thereof at said expansion chamber formed by an endless permeable belt, said transverse wall having a portion thereof formed by a second endless belt, said second belt and permeable belt forming therebetween an outlet in the shape of a slot for said expansion chamber, said suspension of fibres having a concentration not substantially higher than 0.07 gram/liter, and creating a higher pressure on the chamber side of the permeable belt than on the opposite side of the permeable belt thereby causing fibres from the expansion chamber to settle on the permeable belt as a layer and be carried out of the chamber through said slot outlet.
2. A method according to claim 1, wherein the fibres are at least about 30 millimeters in length.
3. A method according to claim 1, including blanking ofi against drainage an area of said permeable Wall section except for a controllably limited portion thereof to define said region and applying vacuum at said region on the face of the permeable belt remote from said suspension to create said higher pressure.
4. A method according to claim 1, and injecting fluid into the chamber and through said permeable belt after said higher pressure creating step.
5. A device for the production of a fibrous web of nonwoven fabric by means of a dilute suspension of fibres, comprising a pipe duct having walls smoothly diverging towards an extremity thereof, a transverse closure wall at said extremity and defining an expansion chamber with a said duct portion adjacent thereto, thus defining a flow passageway of progressively increasing cross-sectional area smoothly merging with said chamber, a permeable endless belt forming a portion of a said diverging wall at said chamber, an endless belt having a portion trained over a roller and forming therewith a portion of said closure wall, said trained belt portion and permeable belt defining therebetween an outlet in the shape of a slot for said chamber, means for creating a higher pressure on the chamber side of the permeable belt than on the opposite side of the permeable belt at said Wall portion and means for injecting fluid into said chamber through said permeable belt after said higher pressure creating means.
References Cited UNITED STATES PATENTS 1,927,360 9/1933 Edge 162336 X 2,356,285 8/1944 Street l62203 X 3,293,116 12/1966 Opderbeck et a1. 162320 X 2,983,627 5/1961 Williams 162130 X 3,125,485 3/ 1964 Constantine et al. 162-149 X 3,167,470 1/1965 Moore 162-342 X 3,547,775 12/1970 Bossen 162198 2,960,162 11/1960 Simpson 162301 3,350,260 10/1967 Johnson 162211 X FOREIGN PATENTS 384,308 1940 Italy 162-344 S. LEON BASHORE, Primary Examiner ALFRED DANDREA, JR., Assistant Examiner US. Cl. X.R.