JPS6132426B1 - - Google Patents

Description

[Detailed description of the invention]

The present invention describes an air-laydown process for collecting textile fibers into a web.
process) and equipment for dispersing textile fibers in an air stream to collect them on a moving screen to form a web suitable for use in the production of high quality nonwoven fabrics; Particularly concerned with improvements in transportation. Nonwovens are made from fibrous webs by bonding or combining fibers for durability and strength. The fibers of the web are entangled by liquid pressure by treatment with a high energy liquid stream, as shown in Evans, US Pat. No. 3,485,706, issued Dec. 23, 1969. When producing relatively heavy textile fibers, Lauterbach's 1959
As shown in U.S. Pat. No. 2,910,763, dated Nov. 3, fiber combination begins with processing using a needle loom and is completed by crimping or wrinkling the fibers. The manufacture of bonded non-woven fabrics was developed by Graham in 1956.
This is done as shown in U.S. Pat. No. 2,765,247, dated Oct. The quality of fabrics produced by these methods depends on the quality and uniformity of the web being processed. Webs suitable for producing high quality nonwovens can be provided by air laydown of textile fibers by processes of the type described above. Conventional air laydown processes and equipment are described in U.S. Pat.
No. 2,676,363 to Plummer et al., April 27, 1954, and US Pat. No. 3,381,069 to Simimson, April 30, 1968. Stable fiber is shipped as a tightly bound mass. Conventional picking and combing operations are used to separate the fibers. The resulting separated fibers are passed onto toothed dispersion rolls and an air stream is sucked or blown over the rolls. The roll rotates at high speed to force the fiber into the air stream. The purpose is to deliver the fibers as individual fibers rather than in bulk or groups. The fibers are carried by the air current in a spreading cloud through the conduit to the screen surface of the condensing roll, where the fibers are deposited over a relatively large surface in a layer on the moving screen. I am made to do so. The Plummer et al. patent discusses the importance of air turbulence to distribute the fibers substantially uniformly over a relatively large area throughout the conduit. By changing the direction of the air flow near the dispersion rolls, by keeping the air passages through the rolls narrow and connected to widened ducts, and by leaving irregularities in the ducts leading to the condensing rolls. This causes turbulence in the supply air. Commercially available embodiments of such conventional layering equipment are shown in FIGS. 38 and 40 of Evans, US Pat. No. 3,485,706. As stated in column 20, line 65, "Layer forming equipment processes a given amount of material at a relatively slow rate, whereas jet processing equipment is capable of high speed operation." A flawless, uniform web weighing 34 g/m ² (1 oz/yd ² ) has a maximum speed of about 5.5 m/min (18 ft/min) when using such layering equipment.
min) or about 112 g/cm/hr (0.63 lbs/in.hr) per unit width of the dispersion roll per unit time. Producing high quality webs at sufficiently high speeds is only possible with fundamental modifications to this layering equipment. The present invention provides an air laydown process and apparatus suitable for producing high quality, uniform webs from staple fiber feed butts at high speeds. The new air laydown process produces lightweight webs of 17 to 68 g/m ² (0.5 to 2 oz/yd ² ) from thin, long staple fibers (e.g., 1.25 denier, 3.8 cm (11/2 in) long fibers). It is possible to produce such webs at rates of greater than 3 lbs/in per unit width of web in one hour of operation, even if the
A highly uniform web weighing 136-340 g/m ² (4-10 oz/yd ² ) or more weighs 1785 g/cm.
hr (10lbs/in.hr) or higher, in some cases approximately 2680-3570g/cm. hr (15-20 lbs/in.hr). The present invention provides for flaws (i.e.
When evaluated for small anomalies (e.g. caused by depositing clumps of fiber), streaks (i.e. lines of different fiber density, e.g. caused by local variations in airflow velocity) and other visible imperfections; Provide high quality web.
The present invention also provides an effective air laydown apparatus for producing high quality webs. Other advantages will become apparent from the description and implementation. In accordance with the present invention, staple fibers are introduced into an air stream moving at an acute angle with a uniform initial velocity of at least 915 m/min, the air stream carries the fibers to a moving screen, and the fibers are moved onto the screen. A method of producing a web of randomly arranged textile fibers by collecting a web of textile fibers comprising: (1) controlling the airflow to form a region of stable airflow; and then moving the staple fibers into the region of stable airflow; The stable airflow area is defined by an average through-thickness velocity variation of less than ±15% for every 0.254 cm of thickness except for the first 0.254 cm adjacent to the wall, and for any 30.5 cm of (2) The angle at which the staple fiber is introduced is relative to the direction of the air flow. (3) a portion of the air flow carrying the staple fibers to the screen collector has an average turbulence intensity of less than 15%. A method of manufacturing a web is provided. 3050 to form a fiber flow with an initial thickness of less than 0.64cm (1/4in)
Preferably, it is fed at a uniform initial speed of ~6100 m/min (10,000 to 20,000 ft/min). moreover,
fiber per unit width of flow during one hour of operation
Preferably, it is dosed at a rate of 535-3570 g/cm (3-20 lbs/in). Preferably, the fibers are introduced at an angle of less than 12° to the direction of the airflow. In the stable flow region immediately upstream of the fiber flow, the air flow is 0.3 to 3.5 times the fiber initial velocity, more preferably 0.5
to have an average velocity (V) of ~1.2 times and be controlled to have an average velocity of 0.25 to 3 times, more preferably 0.4 to 1.2 times the velocity (V) after the fiber flow is formed. is more preferable. Furthermore, (a) in the stable flow region immediately upstream of the fiber flow and after the fiber flow is formed, the average turbulence intensity is less than 7%; (b) in the stable flow region immediately upstream of the fiber flow; Preferably, the average velocity variation across the thickness of the stable flow region is less than ±10% of the velocity (V), and the velocity variation across the width of the region is less than ±5%. The weight flow rate of the air stream is at least 25 times the weight flow rate of the fibers introduced into the air stream, and the fiber stream is approximately 1/2 to 1 inch (1.27 to 2.54 cm) as it approaches the web forming screen. ) is most preferred. The invention also provides a duct having a rectangular cross section for conveying staple fibers into an air stream, an air supply means for passing an air stream through the duct;
a rotating toothed dispersion roll and a stationary dispersion plate cooperating therewith for introducing the fiber through an opening in the duct to form a stream of fibers in the air stream, and separating the fiber from the air; In an apparatus for producing a web of randomly arranged textile fibers, the air supply means is larger than the duct 20 in order to produce a uniform web at high speed. It has an air passage 14 of highly uniform cross-sectional area, which passage 14 is directly connected to the duct 20 by a smooth gently converging section 18, and the air supply means is also free from turbulence. Screens 38, 42 and honeycomb structure 40 installed in the air passageway 14 to provide uniform airflow substantially free of currents and vortices.
furthermore, the distribution roll 8 and the distribution plate 10 are designed and arranged such that the staple fibers are introduced into the air stream at an angle of less than 25 degrees with respect to the direction of the air stream. An apparatus for producing a textile fiber web is provided. The dispersion roll has a diameter of 12.7~127cm (5~50in) and 1.2~54 pieces/ ^cm2 (8~350 pieces/cm2) per unit surface area.
in ² ) teeth, the teeth are shorter than 0.64 cm (0.250 in), and the distance between the teeth and the dispersion plate is 0.025 to 0.076 cm.
(0.010-0.030 inch) gap is preferred.
Boundary layer control means are preferably provided in the duct upstream of the opening to improve the boundary layer of air passing through when the fiber is introduced into the controlled flow. Boundary layer control means may include thin boundary obstructions extending across the duct wall to remove streamwise swirl in the boundary airflow, or openings in the duct wall to remove turbulent boundary airflow. Close suction slots are preferred. Additionally, the air supply means is larger than the duct means to provide a controlled flow having a substantially uniform velocity, except for the outer boundary layer of the fiber flow, up to where the fiber flow is formed. Preferably, it consists of a highly uniform wind tunnel with a cross-sectional area and a flow nozzle ground. Preferably, the ducting means has a substantially uniform rectangular cross-section along the fiber flow path to the condensing means. Preferably, the ducting means has a substantially uniform cross-section up to the dispersing roll and then converging to accelerate the airflow conveying the fibers to the condensing means. In another preferred embodiment the duct means has a substantially uniform cross-section up to the dispersing roll and then widens as the duct approaches the condensing means. Preferably, the duct means is substantially straight. Preferably, the vortex generator extends across the duct means upstream of the distribution roll. The fiber should be at least 915m/min. (3000ft.
It rotates at a surface speed of /min.). Preferably it is centrifugally scraped from a toothed dispersion roll. A feeding means feeds a substantially uniform layer of fiber onto a rotating distribution roll and a curved distribution plate placed in close proximity to a fiber scraping position at the tip of the distribution plate. Hold the fiber in a roll. At this point the fiber stream is introduced from the dispersion roll by a welding direction discharge through an opening into duct means for supporting the fiber in air. The roll is mounted outside and close to the wall of the duct means such that a small surface arc of the roll is directed towards the inside of the duct means without reducing in any way the cross-sectional area formed by the duct wall. is exposed and allowed to fill the aperture. The air supply means directs a steady, low-turbulence, low-swirl air flow of uniform velocity into the duct in the direction of motion of the roll surface, with the fibers at an angle of less than about 25°, preferably less than 12°. so that it is thrown into the air stream at an angle. This input angle is measured between a tangent to the distribution roll at a point close to the tip of the distribution plate and a straight line that corresponds to the general direction of the airflow in the chamber. Boundary layer control means are provided in the duct upstream of the exposed roll surface to create a controlled low level of turbulence in the air layer such that the fibers provide low turbulence and low vorticity in the airflow. Enables uniform dosing to reach areas with uniform flow. The duct geometry downstream of the dispersion rolls is such that it prevents boundary layer separation and associated vortex formation. That is, the shape of the duct is generally such that the cross section or direction of the duct does not change suddenly. Condenser means separate the fibers from the air to approximately 3.4~
A web with a weight of 340 g/m ² (0.1-10 oz./yd ² .) is formed. A conventional type of toothed dispersion roll is suitable for introducing the fiber into a uniform air stream. The curved surface of the distribution plate is placed a small distance from the rotating surface of the roll and forms a narrow passage through which the fibers are conveyed to the point of entry into the duct. The gap between the fixed dispersion plate and the tip of the dispersion roll teeth is 0.32 cm (1/8 in) from the point where the fiber is picked up by the teeth to the point where it enters the air stream, i.e. the tip of the dispersion plate. Must be smaller. The teeth of the dispersion roll are typically shorter than 0.64 cm (1/4 in.), preferably about 0.32 cm (1/8 in.).
The fiber flow introduced into the air flow is thicker than the gap between the tip of the tooth and the dispersion plate by the amount that the fiber penetrates between the teeth. The gap is 0.025~0.076cm. (0.10～
0.030in.) is preferable. The distributed role is
915m. /min. (3000 ft./min.) to the highest limit without damaging the fiber or generating excessive vibration. Surface speed is approximately 3050
~6100m. /min. (10,000 to 20,000 ft./min.) is preferable. The diameter of the roll should not be too large, since the fiber loses momentum after traveling only a short distance after being tangentially introduced, but it should be at least
41cm. (16in.) diameter. Preferably, the portion of the distributor plate facing the rolls has a low friction surface to aid in fiber loading. Duct means for transporting the fibers provides a conduit for a uniform velocity, low turbulence air stream to pass near the exposed surface of the distribution roll and over the fiber condenser means. The shape of the duct is such that substantially all of the fibers input from the dispersion rolls have an initial thickness of less than a thin fiber stream (e.g., 0.64 cm. (1/4 in.) and preferably 0.32 cm. (1/8 in.) .)
The fiber flow is shaped such that it is supported in the air stream as a highly turbulent, non-uniform flow or essentially separated from the separate flow layers. For economical operation, the cross section of the duct must be kept to the minimum necessary to carry out the process. Preferably, the duct is of substantially rectangular cross section. The cross-sectional area may increase or decrease as the duct approaches the condenser means, so long as the change does not disturb the fiber flow. Avoid the negative effects of boundary layer separation in ducts that widen too rapidly (eg, diffusers whose walls widen at angles greater than 30°). The curvature of the passageway within the duct must be kept to a minimum, but a slight curvature helps to keep the fiber flow centered in the duct. The length of the ducting means must be sufficient to provide space for the various equipment elements. Upstream of the duct means, conventional air supply means, such as those used in wind tunnels, are connected to produce an air flow with low turbulence intensity and minimum vortex size. The air supply means directs the air into a highly uniform passage having flow dispersion devices that also act as vortex removal devices, such as vanes, perforated plates, honeycomb sections, and turbulence reduction screens. A blowing fan must be installed. Typically, air is forced into a multi-cell structure having uniform cells of constant cross-section. Each cell is approximately 1.27cm maximum. (1/2.in.) (preferably 0.32cm (1/8in.) diagonal, maximum 0.16cm
(1/16 in.) (preferably 0.025 cm. (0.010 in.)) wall thickness and a cell length at least 25 times the cell width. Other equivalent vortex removal devices are known in the art. The air passages are usually the same width as the duct in the section where the fibers are introduced, and several times larger in other sections, so that screens, honeycombs, and perforated plates are located. , the air velocity in the larger air passage is much smaller than the air velocity in the relatively small duct means.The transition between the large air passage and the small duct means provides a good flow nozzle to accelerate the low turbulence air flow. is curved in accordance with the design of the fiber, and a substantially uniform velocity is delivered from the nozzle to the ducting means. Key to the invention is the ducting means through which the fiber is introduced. The flow conditions immediately upstream of the aperture.The region of the airflow that advances into the fiber passage is carefully controlled.The air velocity in this region is uniform both through the thickness of the region and across the width of the region. The velocity variation in each layer 0.254 cm. (0.1 in.) thick in the thickness direction of that region (except for the 0.254 cm. (0.1 in.) layer near the wall) is equal to the uniform velocity in that region. Within ±1.5%, preferably within ±10%, hereinafter △V/V
Use the symbol . Values of ΔV/V greater than ±1.5% result in excessive mixing within the layer, causing vortices that disrupt and widen the fiber flow. This results in a loss of control over the thickness and trajectory of the fiber flow, causing flaws in the web product. 30.5 cm in the width direction of the area that advances into the fiber flow of the air flow. (1ft.)
Wherever the interval is taken, the speed fluctuation within it is smaller than ±10%, preferably smaller than ±5%, and hereinafter the symbol ΔV/W will be used. △/V/W
Values of greater than ±10% create vortices that adversely affect the thickness and trajectory of the fiber flow, thereby causing flaws in the web product. The average turbulence intensity (i.e. standard deviation of velocity fluctuations over time) in that region is less than 15%, preferably 7%
smaller. These numbers refer only to the portion of the airflow that travels into the fiber passage, 0.254 cm from the wall. (0.1in.) excluding the boundary layer portion. If the average turbulence strength in this region (and the subsequent fiber flow path) is greater than 15%, or if large vortices are generated due to large velocity fluctuations and unstable local turbulence strength, thin fiber flow Formation is hindered, the fibers are dispersed in a widening cloud, and excessive flaws occur in the web product. Air passing outside the region of the ducting means which passes into the path of the fiber flow is such that its effect on the air flow conveying the fibers to the condenser is such that the air passing outside the region passing into the path of the fiber flow in the duct means has no effect on any cross-section of the fiber path from the distributor to the condenser. There are no limitations on turbulence intensity or velocity distribution as long as the average turbulence intensity is less than 15% and preferably less than 7%. The turbulence strength in this part of the fiber passage is
If it exceeds 15%, it will still cause damage to the web product. It is recognized that turbulence is caused by fluid friction with the duct walls. This uses smooth streamlined duct walls and allows air flow to be confined to a boundary layer next to the wall by feeding it into the duct under suitable conditions as described above. The duct is designed to maintain the fiber flow substantially in the center of a region of low turbulence, uniform flow so that boundary layer turbulence does not disturb the fibers after the thin fiber flow has formed. There is. However, the fibers must be introduced through boundary layer turbulence on the distribution roll side of the duct. Therefore, large inhomogeneities in the boundary layer must be avoided. A significant non-uniformity problem is caused by the phenomenon of streamwise vortices (ie small corkscrew vortices with high energy). These vortices are detected by scanning the flow with a hot wire anemometer in a straight line perpendicular to the duct sidewall within the flow cross section. The vortex exhibits a partial increase in turbulence intensity and a corresponding partial decrease in air velocity. Fibers introduced through such a vortex are deflected from their intended path. This results in an uneven distribution of fibers in the air stream, thereby creating streaks in the web product.
A suction slot can be used to remove the turbulent boundary layer upstream of the distribution roll.
Slots are most effective when placed in a wall close to the scatter roll. In the boundary layer region where the transition from laminar to turbulent flow occurs in the duct means slightly downstream of the point where the air enters the duct from the curved flow nozzle, or in the new boundary layer created downstream of the suction slot. Vortices also occur in The stripes in the web caused by these vortices are created by a layer of very thin obstructions (often called boundary layer trips) such as sandpaper or a piece of smooth round wire approximately 18 gauge (approximately 0.1 cm (0.04 in.) in diameter). It has been found that it can be removed if it extends across the duct wall and into the boundary layer just upstream of the flow-turbulence transition region. As a result, the transition to turbulence is uniformly accelerated to form a uniform stable turbulent boundary layer into which the fibers can penetrate uniformly. The turbulence added by these obstructions is usually small and generally does not significantly increase flow mixing on the distribution roll or flaws in the final web.
Combining a suction slot to remove the boundary layer before the boundary layer trip with a very thin wire to prevent uneven regeneration of the boundary layer allows the slot to be positioned close enough to the dispersion roll due to spatial constraints. preferred if it cannot be placed in Large, irregular vortices, which occur when the airflow directed into the ducting means is insufficient, cause the fibers to disperse uncontrollably as a cloud rather than as a thin stream as soon as they leave the dispersion roll. In such a case the air turbulence at a given point within the duct means is unstable. The characteristics of this instability are irregular and large, and even if the average turbulence intensity is well below the desired 15%, the turbulence intensity increases rapidly to a value of 1.5 to 2 times the average turbulence intensity at that point. There are things to do. Such sudden, large changes in turbulence make control of fiber flow thickness and trajectory impossible. These unstable flows are usually accompanied by large-scale, relatively low-frequency air velocity fluctuations. In operation of the present invention, a stable, substantially uniform velocity across the width of the duct means is maintained in a straight line parallel to and directly above the groove in which the fibers are introduced into the air stream. Velocity fluctuations within a 30.5 cm (1 ft) section along these straight lines (excluding edge or wall effects) are expressed by the symbol △V/W, as described above. less than ±10% and preferably less than ±5% of the average within the same 1 ft. The fibers are conveyed to a condenser means of the type conventionally used to separate the fibers from the air stream in the form of an irregular fiber web. The fibers are deposited uniformly in a continuous manner with some overlap, similar to stacking shingles. The shingle length is directly proportional to the width of the fiber deposition region and the apparent thickness of the fiber stream. A thin, low turbulence flow with a fixed (non-oscillating) trajectory produces shingles approximately 1/2 inch long. fiber-laydown area
area) is increased by tilting the condenser screen relative to the fiber passage. Alternatively, a modified embodiment of the present invention involves an equivalent effect by means of controlling airflow to increase the effective fiber placement area. Mixed flow generating means for the controlled generation of gradually increasing vortices with low turbulence intensity are located in the duct means between the duct inlet and the distribution roll position. For example, have a 0.32 cm (1/3 in) hole to create a 42% open area, and a 1.90 cm (3 in) hole fixed to the end wall of the duct to extend across the center of the duct. /4in) metal strip increases the width of the effective fiber installation area from 1.27cm (1/2in) to approximately 3.2cm
(11/4 in.), thus creating a "spread stream effect." Alternatively, round or square bars of various diameters or dimensions (0.16 to 0.64 cm in diameter) may be used.
(1/16 to 1/4 inch) rods) can be used to create this effect depending on the desired flow mixing and shingle length. The installation area can be further increased by blocking the upper half of the flow at the nozzle outlet with a solid or perforated plate. These mixed flow generators generate large, stable vortices, but do not substantially affect the area of airflow entering the fiber flow passages. The mixed flow generator of the present invention produces a stable average turbulence intensity in the fiber flow path of less than 15%, preferably less than 7%. Mixed flow generators and long ducts (e.g. length approx. 1.8
m (6ft)), the effective fiber installation area extends to approximately 30.5cm (12in). All of these mixed flow generators produce some lateral mixing in the fiber stream, which is desirable to eliminate fine spots in the web caused by small non-uniformities at the fiber exit point. However, these beneficial effects must be balanced against increased flaws due to the increased turbulence concomitantly produced by the mixed flow generator. To explain FIG. 1, in this embodiment,
A fiber feeding means consisting of a conveyor belt 2, a feed roll 3, a compression roll 4 and a shoe 5 is shown for feeding the fibers 1 to a distribution roll 8. The fiber feeding means is g/m ² (oz/yd ² )
approximately 3 of the weight of the web produced, measured in units of
Designed to deliver staple fiber butts ~150 times the weight. The distribution roll separates the fibers, conveys the fibers mixed with air near the roll surface through the space between the roll and the distribution plate 10, and discharges this mixture centrifugally into the duct 20 at area A. . A shroud or casing 9 extends around the distribution roll from a doff-bar 12 to the feed roll 3. The fibers introduced from the dispersion roll form a thin fiber stream 22 in the air flowing through the duct.
is formed and then separated from the air as a web 24 on a condensing screen 26. Air is supplied from an air passage 14 having a larger cross-sectional area than the duct 20. Parallel wall of air passage 1
6 is connected to the duct wall 20 by a convergence part 18 in the form of a flow nozzle. Screens 38 and 4
2 and honeycomb structure 40 provide uniform flow substantially free of turbulence and eddies. Air is blown into the air passageway through the duct arrangement 33 by one or more fans 36 as shown schematically. The fiber is driven by rolls 28 and 30;
It is deposited to form a web on a supported, continuous, moving screen 26.
Air flows through the screen and vacuum duct 34
It is collected through. The air is swirled to remove any particles passing through screen 26 and then recycled to fan 36. Several fans in series or one open air device with one or more fans for supplying air and one or more fans for discharging air may also be used. Screen 26 is sealed to fiber duct 20 and vacuum duct 34 by sealing means 32, such as a polyethylene plate. Figure 2 shows a rounded edge 13 and a sloped top surface 1.
5 shows another embodiment of the scraping rod 12, having the following.
The tip 13 of the scraping rod is 0.32 cm from the teeth of the dispersion roll.
(0.125in) by a distance smaller than, preferably about
0.025~0.038cm (0.010~0.015in) apart. FIG. 2 also shows that the distribution plate 10 has a slot 44 connected by a conduit 46 to a vacuum manifold 48 and a vacuum pump (not shown).
2 shows another aspect of the invention. In the illustrated apparatus, the walls 50 of the vacuum manifold 48 serve to support the distribution plate 10. The slot is 0.05~0.30cm (0.02
~0.12in) width. The suction slot 44 serves to reduce or completely eliminate the turbulent boundary layer in the air flow occurring on the lower side of the air duct. A vacuum of 1 to 20 inches of water is suitable. In FIG. 3, the dotted line 58 is tangent to the outer periphery of the teeth 7 of the dispersion roll. Upper end 54 of distribution plate 10
can be placed on the tangent line 58 or slightly below the tangent line, for example 1/2 inch below the tangent line. The tip 51 of the dispersion plate is at least
It is preferred to have a roundness with a radius of 0.038 cm (0.015 in), but less than about 0.15 cm (0.06 in). The front face 56 of the distribution plate is substantially concentric with the distribution roll. The gap between the front surface 56 and the teeth 7 is 0.32 cm to avoid premature turbulent mixing of the air and fibers on the underside of the plate, which can lead to fiber clumping.
(0.125in) smaller. Approximately 0.025~0.076cm
(0.01-0.03 inch) gaps are preferably used. Yet another aspect of the invention is illustrated by boundary layer tripping means 62 in FIG. The tripping means consists of a very thin obstruction, such as approximately 18 gauge round wire or a 1.27 cm (0.50 in) wide strip of 60 grit sandpaper, depending on the process conditions at the time. is located on the distribution plate top surface 54 approximately 1 to 10 inches downstream from the starting point of the ducting means. The resulting turbulent boundary layer (approximately 1/4 inch thick) is relatively uniform along the width of the duct. The center line of the fiber duct 20 may extend in a straight line parallel to the upper end of the distribution plate as shown in FIG.
Or it is curved as shown in Figure 4. The angle that the top surface of the distribution plate and the centerline of the fiber duct make at the condensing section is called the bending angle.
The bending angle is less than 30° and preferably from 0 to
It is 10°. FIG. 4 also shows how the cross-sectional area of the duct is reduced above the scraper bar 12 in order to accelerate the air after the fiber flow is formed and create a flat velocity distribution. Figures 4 and 6 show an alternative embodiment having vortex generator means 66 located in the air stream upstream of the fiber scraping point. The generator 66 is connected to the air duct 20
It consists of a perforated board or screen that covers about the middle third of the wall. The plate shown in Figure 6 has staggered holes (e.g. 0.32 cm (0.125 in))
diameter) and approximately 42% open area to create a sparge flow effect as the fibers are deposited onto the rotating condensing screen 26. A solid plate in the upper part of the air duct and a solid rod of small diameter in the middle of the air stream upstream of the fiber scraping point also serve as vortex generators. FIG. 5 shows another embodiment of a suitable machine in which a dispersing roll 8 is located above the fiber duct. FIG. 5 also shows the use of a condensing screen 26 moving at a 45 DEG angle to the fiber flow. The dispersion roll 8 is of conventional design,
They usually have a diameter of 12.7 to 127 cm (5 to 50 inches). It is usually a hollow structure. The cylindrical outer surface of the roll is usually provided with a narrow, narrow wire sheath 7 (FIG. 3) fixed by one or several serrated strips wound helically around the roll. ing. The sharp tips of the teeth are positioned such that the tips lie on a substantially perfect cylindrical surface about the axis of rotation of the roll 8. A typical arrangement is as follows. That is, Tooth inclination: Rake angle is less than 8° from the radial direction. Teeth length: shorter than 0.64cm (1/4in), about 0.32cm
(1/8in) is preferred. Tooth end: tip smaller than 0.076cm (0.030in). Teeth density: about 1.2~ per unit area of roll surface
54 sheets/cm ² (8-350 sheets/in ² )

The dispersion plate 10 and scraping bar 12 may be made of any material, such as plastic or metal, that maintains a narrow gap with the dispersion roll 8 for the high speeds used. The distribution plate must have a length at least 1/2 the length of the staple fibers used, but for mechanical reasons it may have a length that corresponds to an arc of 45° to 90° or more of the distribution roll. I have it. Although Figures 1 and 2 show a single dispersion plate and scraping bar,
Both parts can also be made in multiple parts with suitable accessories. In both of the above-described embodiments of the invention, the distribution rolls 8 cast the fibers into the air stream at an initial angle of less than 12 DEG to the general direction of the air stream. Although a small fiber insertion angle is preferred, angles as high as about 25° may be suitable in some cases. At angles greater than about 25°, the roll penetrates too far into the duct means, thereby creating an unstable vortex immediately upstream of the dispersing roll. This creates unstable and non-uniform regions in the air flow entering into the fiber stream introduced by the dispersion rolls, so that the fibers being dispersed do not form a thin stream but a thick cloud. Become. This results in a web product with scratches and stripes.
Furthermore, at angles greater than 25 degrees, the fibers impinge on the opposite duct wall, causing the fiber dispersion to harden and create a flawed web. An air supply means that provides a uniform, stable, low turbulence, low swirl air flow is used and is shown in FIG. The inner surface of the duct is streamlined and smooth, especially in the area between the last screen 38 and the distribution roll 8. The convergence part 18 is smooth,
It is gently curved. "Fan Engineering", 6th edition, page 89 (Buffalo Forge Co.)
), 1961) is satisfactory, but the preferred design is the one described in Mechanical Engineering, Volume 71, No. 3,
This is the design of Mr. Rouse and Mr. Hassan published in March 1974, and is the first
Close to the one in the picture. This air supply device provides a uniform air flow at the outlet of the nozzle. With the exception of the boundary layer (i.e., the layer within about 1/2 inch of the duct wall), the flow has a total velocity variation across the cross-section of less than ±10% both vertically and horizontally, typically ± Preferably, it is less than 5%, and it is preferred that the stable turbulence intensity is less than about 15%, and usually less than 7%. The peripheral speed (Vo) of the dispersion roll is at least 915 m/min (3000 ft/min)
It is. The appropriate range of air velocity (V) at the edge of the dispersion plate in area A is about 0.5 to 3.5 times Vo.
Preferably it is about 0.5 to 1.2 times Vo. A suitable range for the maximum air velocity in region A (i.e. the velocity at the point where the dispersion roll penetrates the most into the duct) is about 0.5 to 3 times Vo, preferably 0.7 of Vo.
~1.7 times. A suitable weight flow ratio of airflow to fiber is at least 25:1. Method of Measuring Air Flow Velocity and Turbulence Intensity The air flow velocity at various points is determined using commonly used velocimeters. A suitable instrument for this purpose and used for the measurements reported herein is a model 1050B-4 hot wire anemometer manufactured by Thermal System Inc. of Saint Paul, Minnesota. . Others are well known in the art. When the output of the anemometer is passed through an AC-coupled root-mean-square (RMS) voltmeter, such as the Model 3400A manufactured by Hewlett Packard Inc. of Loveland, Colorado, the airflow The effective value of the velocity variation in direction versus time is measured. The values reported here are the RMS readings averaged over 5-10 seconds.
The value obtained by multiplying the effective value of velocity fluctuation by 100 and dividing by the average velocity at that point is called the point turbulence strength here. Further details on the use of hot-wire anemometers to measure velocity and turbulence intensity can be found in Bulletin No. 53 of Flow Corporation, Cambridge, Mass. ”, etc., has been explained in many places. Theoretical discussion of turbulence strength is based on H. Schlichting's ``Boundary layer theory''.
Layer Theory), 6th edition, McGraw-Hill Books Company, New York, 1968, pages 455-457, 538-539, 558, etc. The velocity and turbulence intensity that are key to the invention are those associated with the air layer that travels along the fiber path and carries the fiber to the condenser. Determining the path of the fiber in the process of the invention includes:
The process is relatively simple as it provides a well-defined fiber flow. One method is to optically determine the fiber path through a transparent portion of the ducting means. Conveniently, the fiber flow can be illuminated from above and the thickness can be clearly viewed and measured from the edge of the transparent portion of the ducting means. Permanent records of the fiber passages are standard speed “Polaroid” photographs or high speed (approximately 10 ^-5
second exposure) can be made using a "Polaroid" photograph. High-speed photography shows the instantaneous position of individual fibers within the duct. Once the fiber path is determined, the velocity and turbulence intensity settings are made even without fiber flow. Measurements made without fiber flow are representative of the presence of fiber flow (all other things being equal) because the air-to-fiber weight flow ratio is very small (i.e., at least 25:1). it is conceivable that. Velocity and turbulence intensity are measured at at least three key representative points. (1) in the flow layer advancing into the fiber passage above the dispersion plate tip, just upstream of the dispersion roll, and (2) in the fiber passage flow just downstream of the dispersion roll, above the scraping rod tip. in,
and (3) in the fiber passage flow at the end of the scraper bar, just upstream of the condenser. At each of these points, the velocity and turbulence strength are measured at each of these points, starting at a point 0.254 cm (0.1 in) away from the duct wall containing the dispersion roll opening and continuing through the thickness of the fiber passage. in) interval (i.e., away from the sidewall). The measurements at each point are averaged over the passage thickness to yield an average velocity and an average turbulence intensity. If the width of the fiber passage is very wide, scanning of the passage must be performed at three additional points across the width of the flow at the three mentioned points. In all embodiments of the invention, the average turbulence intensity at each of these points along the fiber path is about 15% or less. Average turbulence strengths greater than 15% result in flawed webs. Velocity measurements (in the absence of fiber flow) at the three points described above across the width of the fiber passage also indicate the extent of large-scale, low-frequency velocity fluctuations. Immediately upstream of the dispersion rolls, the velocity variation within a 1 ft. width of the flow into the fiber passage is less than ±10%, and preferably less than ±5%, in embodiments of the present invention. 0.254cm (excluding 0.254cm (0.1in) near the wall) of this advancing flow
(0.1 inch) thick layer is within 15% (preferably within 10%) of the average velocity in that area. If the fiber path from the dispersion roll to the condenser is long, more than the three turbulence intensity measurement points described above may be needed to characterize the turbulence that the fiber stream is exposed to as it travels to the condenser. , should be used. It is recommended that the measurement points be substantially equally spaced from each other. The following examples, illustrating representative embodiments of the invention, are not intended to limit the invention in any way. Example 1 In this example, a 36 inch wide high quality web is produced using equipment similar to that shown in Figure 1 at the following speeds:

[Table] In each of the above runs, the feed to the dispersion roll was 1.90 cm long, 1.25 denier per fiber, in the form of a loosely opened 3390 g/m ² (100 oz/yd ² ) butt.
(3/4in) polyethylene terephthalate stable fiber. This is 0.23cm high
(0.09in), 6.2 teeth/0.023cm (0.009in) thick
Diameter 61cm with a density of cm ² (40 sheets/in ² )
(24in) distributed rolls. The gap between the end of the teeth of the roll 8 and the curved plate 10 is 0.064 cm
(0.025in). The roll rotates at 3000rpm, producing a uniform thin fiber flow at 5750m/min.
(18850ft/min) into the duct at a uniform initial speed. The average air velocity at the outlet of the contour nozzle connected to the rectangular duct 20 is 2740 m/
min (9000ft/min), the turbulence strength is about 0.4%. The velocity gradient across the width of the duct at this point is less than 1% per foot. Width 91.5cm
The approximate heights and average air velocities at various points of a (36 inch) rectangular duct 20 are as follows.

[Table] The distance between point X is approximately 23cm (9in.), and the distance between points 1 and 3 is approximately 21.5cm. (81/2in.) The distance between points 3 and 4 is approximately 48cm. (19in.). The fiber is introduced into the duct at an initial angle of approximately 9° to the airflow;
It is then carried through the air stream in a thin, straight path to a collection screen. The turbulence intensity at any point in the fiber flow is not greater than about 2%. The air flow at point 1 has the following characteristics; △V/V is within ±10% of V ₁ ;
ΔV/W is within ±5%, and I ₁ is within 2%. The thickness of the fiber stream (initially less than 1/4 inch) is approximately 1/2 inch near the condenser. Example 2 This example shows the effect of turbulence intensity along a fiber path on the production rate of a high quality, defect-free web. Using a device similar to that shown in Fig. 134
g. / m ² (1 oz./yd ² .) weight, 178 cm. (70in.
) width web at 55 m/min. (60yd.). The feedbutt consists of a 1.90 cm (3/4 in.) rayon staple with 1.5 denier per fiber, which is combed into a loosely open fiber burlap. This is 3820m. /min. (12500ft./min)
Rotating at a surface speed of 40.6 cm in diameter. (16in.) dispersion roll, 1115g. /cm. hr. (6.25lbs./in.
Air delivered at a speed of 1520 m. /min. (5000ft./min.) into the duct. A high quality uniform web is produced. The turbulence intensity leaving the nozzle is
If it increases from 0.4% to 0.7%, it will be about 37m. /min.
(40 yd./min.) or less produces equivalent flaws in the web. The air at the plate immediately upstream of the dispersion roll has the following characteristics; the average velocity (V) is in the range of 0.5Vo to 1.0Vo, △V/V is within ±10% of V, △ V/W is ±
Within 5%, I within 3%. After the fiber flow is formed, the airflow in the region has an average velocity of approximately
In the range from 0.6V to 1.3V, I is within 3%. Example 3 This example shows the advantageous effects obtained when using suction as a means of controlling the boundary layer. Using an apparatus similar to that shown in FIG. 1, but with suction means for removing boundary layer turbulence, as shown in FIG. 2, a width of 91.5 cm. (36in.), weight 34g/ ^m2 . (1oz./yd ² ) web for 73m. /
Produced at a speed of min. (80yd./min.). 1.90cm with 1.5 denier per fiber. (3/4in) polyethylene terephthal staple air formed butt is 4570m. /min. (15000ft./min.) rotating surface speed, diameter 61cm. (24in.) dispersion roll with 1480g. /cm. hr. (8.3 lb./in. hr.). Under the condition that the maximum turbulence intensity in the fiber passage is approximately 0.5%, the air
m. /min. (8000ft/min.) through the duct. A high-quality, wrinkle-free, uniform web can be obtained. If the above conditions are repeated without suction to remove boundary layer turbulence, some spots will form due to the non-uniform boundary layer. The air flow at the plate immediately upstream of the dispersion roll has the following characteristics; the average velocity (V) is approximately 0.8 Vo, △V/V is within ±10% of V, △V/W is ±5 % or less, and I is within 0.5%. The airflow in the region after the fiber flow is formed has an average velocity ranging from about 0.7V to 1.3V.
The change in the thickness of the fiber flow is 0.6 cm (1/4
inch) from a thickness smaller than about 1.2cm near the condenser
(1/2 inch). Example 4 In this example, a series of webs are produced under conditions of varying turbulence intensity along the fiber path. 27.9 cm wide using an apparatus similar to that shown in Figure 1. (11in.), weight approximately 34g. / ^m2 ． (1oz./
yd ^2. ) of 890g. /cm. hr. (5lb.
/in.hr.). The batts sent to the dispersion roll 8 are transferred to a land webber (Rando-
Webber) multiplex 68g. / ^m2 ． (2oz.
/Yd ^2. ) layer, 1.90 cm long with 1.25 denier per fiber. (3/4in.) polyethylene elephthalate staple fiber, 2370g. / ^m2
( _70oz./yd2 ). The diameter of the dispersion roll is 40.6cm. (16in.) and height 0.23
cm. (0.090in.), tip thickness 0.023cm. (0.009in.) 12.4 teeth/cm ² . It has a density of (80 sheets/in ^2. ). The gap between the tip of the tooth and the plate 10 is 0.051 cm.
(0.02in.). The distribution roll directs the thin fiber stream into the duct means at an initial angle of 1P to the general direction of the airflow, 3540 m. /min (11600ft.
/min) at an initial speed of V ₀ . The dimensions of the rectangular duct means at a particular point downstream of the Cubic nozzle are as follows:

In this device, a moving screen 26 intercepts the air-fiber flow at a 45° angle, just upstream of the table. The distances between points X and 1, 1 and 3, and 3 and 4 are respectively 20,
28, 30cm. (8, 11, 12 inches). A series of mixing flow devices were placed at point "X" to control the intensity of turbulence within the fiber passages. Using these devices, webs produced under the conditions described above were placed to increase flaws.
The results are summarized in the table below. Symbols V ₁ , V ₂ ,
V ₃ and V ₄ indicate the average air velocity at the above points 1, 2, 3, and 4, respectively. Measurements of turbulence intensity () were carried out at points 1, 3, and 4 as described above. Velocity fluctuations in the region of the airflow advancing into the fiber passage were also measured at point 1 (△V/
V). Weight approximately 102 g/cm ² without making any changes to the operation of the device other than reducing the speed of the web collection screen. (3 oz./yd ² ) series of webs are also produced. 34g. / cm ² (1 oz./yd. ² ) web and 102 g. /
^cm2 ． ² (3oz./yd. ₂ ) web flaws can be detected using a paper formation
Tester) Pulp and Paper Industry Technology Association, (Techni-
cal Association of the Pulp and Paper
Industry.Technical Papers), Series 18, 386
-391 (1935)). As a standard for determining the formation value (FV), an appropriate number of 34g. / ^m2 ． (1 oz./yd ² ) thin translucent paper is used to give a unit weight corresponding to the web sample being examined. report in table

【table】

[Table] The data shown is for one sample of each web.
This is the average of tests performed twice. Note: A wire or rod mixed flow generator is placed in the center of the incoming air stream at point X. +The gate is on the side of the duct opposite the distribution roll at point X (i.e. the opening of the gate is on the distribution roll side of the duct). V ₀ = initial velocity of fiber injection, m. /min.(ft.
/min.) V ₁ = average velocity of the incoming air flow, m. /min.(ft./
min.) △V/W = Widthwise velocity variation of the region of air flow advancing into the fiber flow channel, ±%/30.5 cm. Width (1 ft. width) △V/V = Velocity variation in the region of airflow advancing into the fiber flow path, ±% I = Turbulence intensity, ±% Number suffix refers to points 1, 2, 3, and 4 do. The webs produced under the conditions for trials a, b, c, d and e described in the table above were of good quality with almost no defects. The web of trial f was satisfactory, but had some flaws. Although the web of Trial G was produced within the scope of the present invention, it had more flaws and was close to the limit in terms of quality. Trial h produced the most scratches and stains in this series of trials and is considered unsatisfactory for the purposes of the present invention. This series of trials and others have shown that a low and stable turbulence intensity of less than 15%, preferably less than 7%, along the fiber flow path is required to produce high quality webs at high speeds. It is concluded that it is necessary. It is further necessary that the feed rate variation in the region where the air flow advances into the fiber passage be less than ±15%, and velocity variations of less than ±10% are preferred. In the second series of trials without the mixed flow generator, the velocity ratios V ₁ /V ₀ and V ₂ /V ₀ varied from 0.4 to 2.0 and from 0.6 to 3.1, respectively.
This series of tests and others to produce highly uniform webs at very high speeds
A suitable range of V ₁ /V ₀ is 0.5 to 3.5, preferably 0.5
˜1.2, and a suitable range of V ₂ /V ₀ was shown to be 0.5 to 3.0, preferably 0.7 to 1.7. Furthermore, according to these test results, the appropriate range of the average air velocity at any cross section downstream of the point where the thin fiber flow is formed is 0.25 to 0.25 of the average air velocity V ₁ .
It was shown to be 3 times, preferably 0.4 to 1.2 times.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal vertical cross-sectional view of an apparatus illustrating one aspect of the invention. FIG. 2 is a partially enlarged schematic longitudinal cross-section of a fiber dispersion section of a machine illustrating another aspect of the invention. FIG. 3 is a partially enlarged schematic diagram of a longitudinal vertical cross-section of a top portion of a fiber dispersion section illustrating another aspect of the present invention. 4 and 5 are longitudinal cross-sectional views of a portion of an apparatus illustrating another aspect of the invention. FIG. 6 is a partial view taken from line 6--6 of FIG. 4 illustrating another aspect of the invention. In the figure, 8 is a dispersion roll, 10 is a dispersion plate,
12 is a scraping rod, 20 is a duct, 22 is a fiber flow, 36 is a fan, 38 and 42 are screens, 4
0 indicates a honeycomb structure.

Claims (1)

[Claims] 1. A staple fiber is introduced into an air stream moving at an acute angle with a uniform initial velocity of at least 915 m/min, the fiber is carried by the air stream to a moving screen, and the fiber is moved through the screen. In a method of producing a web of randomly arranged textile fibers by collecting on a fiber, the method comprises: (1) controlling the air flow to form a region of stable air flow; The stable airflow area has an average velocity variation across the thickness of less than ±15% for every 0.254 cm of thickness except for the first 0.254 cm adjacent to the wall, and In any section, the velocity fluctuation in the width direction is less than ±10% and the average turbulence strength is less than 15%, and (2) the angle at which the staple fiber is introduced is relative to the direction of the air flow. (3) a portion of the air flow carrying the staple fibers to the screen collector has an average turbulence intensity of less than 15%. A method for producing a web. 2. A duct with a rectangular cross section for conveying the staple fibers into the air stream, an air supply means for flowing the air stream through the duct, and a flow of the fibers into the air stream by introducing the fibers through openings in the duct. randomly arranged textile fibers comprising a rotating toothed dispersion roll and a stationary dispersion plate cooperating therewith to form a web, and condensation means to separate the fibers from the air and form a web. In order to produce a uniform web at a high speed, the air supply means has a highly uniform air passage 14 with a larger cross-sectional area than the duct 20, 14 is directly connected to the duct 20 by a smooth gently converging section 18, and the air supply means also connects the air passageway to provide a uniform air flow substantially free of turbulence and eddies. Screens 38, 42 and honeycomb structure 40 installed in 14
furthermore, the distribution roll 8 and the distribution plate 10 are designed and arranged such that the staple fibers are introduced into the air stream at an angle of less than 25 degrees with respect to the direction of the air stream. An apparatus for producing a textile fiber web.