US3768120A

US3768120A - Improved air-laydown apparatus for producing webs for nonwoven fabric

Info

Publication number: US3768120A
Application number: US00152725A
Authority: US
Inventors: D Miller
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1971-06-14
Filing date: 1971-06-14
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30

Abstract

Apparatus is disclosed which is suitable for high speed production of uniform, lightweight webs by air-laydown of textile fibers. A toothed disperser roll projects the fibers into an airstream of high uniform velocity and low turbulence to form a thin fiber stream from which the fibers are deposited in web form on a moving screen. Air-flow control means adjacent the screen causes the depositing fiber stream to shift back and forth rapidly to eliminate web streaks.

Description

I United States Patent 11 1 Miller 1 1 Oct.31l,l973

[ IMPROVED AIR-LAYDOWN APPARATUS FOR PRODUCING WEBS FOR NONWOVEN FABRIC [75] Inventor: Donald Miller, Newark, Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: June 14, I971 [21] Appl. No.: 152,725

52 us. c1. 19/1563 51 1m. (:1 ..D01g 25/00 [58] Field of Search 19/84, 89, 155, 156-1564,

[56] References Cited UNITED STATES PATENTS 2,103,769 12/1937 Drill 19/155 FOREIGN PATENTS OR APPLICATIONS 93,843 4/1960 Netherlands 19/155 709,612 5/1954 Great Britain.... 19/163 1,050,832 12/1966 Great Britain.... 19/1564 Primary Examiner-Dorsey Newton Attorney-Norris E. Ruckman 57 ABSTRACT Apparatus is disclosed which is suitable for high speed production of uniform, lightweight webs by airlaydown of textile fibers. A toothed disperser roll projects the fibers into an airstream of high uniform velocity and low turbulence to form a thin fiber stream from which the fibers are deposited in web form on a moving screen. Air-flow control means adjacent the screen causes the depositing fiber stream to shift back and forth rapidly to eliminate web streaks.

2 Claims, 6 Drawing Figures Pmmlinncrao ms Sm W 2 3.768.120

34 INVENTOR DONALD F. MILLER BY mzm ATTORNEY PAIENIEDnmso ms 3,768,120

INVENTOR DONALD F. MILLER ATTORNEY IMPROVED AIR-LAYDOWN APPARATUS FOR PRODUCING'WEBS FOR NONWOVEN FABRIC BACKGROUND OF THE INVENTION This invention relates to an air-laydown apparatus for assembling textile fibers into webs and is more particularly concerned with improvements in collecting textile fibers to form webs which are suitable for use in producing high quality nonwoven fabric.

Nonwoven fabrics are produced from fibrous webs by bonding or interlocking the fibers to provide durability and strength. The fibers of the web may be hydraulically entangled by treatment with high energy liquid streams as disclosed in Evans U.S. Pat. No. 3,485,706, issued Dec. 23, 1969. When producing relatively heavy weight textile fabric Lauterbach U.S. Pat. No. 2,910,763, issued Nov. 3, 1959, discloses that fiber interlocking may be initiated by treatment with a needle loom and completed by crimping or shrinkng the fibers. Production of bonded nonwoven fabrics may be accomplished as disclosed in Graham U.S. Pat. No. 2,765,247, issued Oct. 2, 1956. The quality of fabric produced by these methods depends upon the 'quality and uniformity of the web which is treated.

Webs suitable for producing high quality nonwoven fabrics, by treatments of the above type, can be prepared by air laydown of textilefibers. Priorart airlaydown processes and apparatusare illustrated by Buresh U.S. Pat. No. 2,451,915, issued Oct. 19, 1948, Plummer et a1. U.S. Pat. No. 2,676,363, issued Apr. 27, 1954, and Owens et a1. U.S. Pat. No. 3,481,005, issued Dec. 2, 1969. Staple fibers are shipped as a compacted mass. Conventional picking and carding operations are used to separate the fibers. The. resulting loosely opened fiber lap is fed to a toothed disperser roll and a stream of air is sucked or blown over the roll. The roll is rotated at high speed to feed the fibers into the air stream, the objective being to feed individual fibers rather'than clumps or-groups of fibers. The fibers are carried by the air stream through a duct to the screen surface of a condenser roll or conveyor, where the fibers are deposited over a-relatively large surface area to form a layer on the moving screen.

It has been found that it is necessary to control the turbulence in the air stream in order to produce uniform, non-blotchy, lightweight webs (e.g., of 3 ounces per square yard or less) at rates greater than about 2 pounds per inch of disperser-roll width per hour (lb./in.hr.). At low turbulence levels, variationsin the air stream to the disperser-roll and/or density variations in the fiber lap can cause streaks in the machinedirection of the web. At higher turbulence levels these variations are blended and do not appear in the web, but the blotch level (small-scale fiber clumping) increases with turbulence.

SUMMARY OF THE INVENTION The present invention is an improvement in airlaydown apparatus of the type having duct means for conveying fibers in a controlled flow of air, fiber disperser means for projecting fibers into the duct means to form a thin stream of fibers in air, air supply means for directing a low turbulence flow of air through the duct means, and condenser means for collecting the fibers on a moving screen to form a web. The improvement is in providing air-flow control means near opposite edges of the screen for shifting the fiber stream rapfor alternately interrupting air flow on opposite sides of the fiber streams at a frequency of at least 25 cycles per minute for each yard per minute of screen travel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinal vertical section of a form of air-laydown machineto illustrate use of one embodiment of this invention.

FIG. 2 is a fragmentary enlarged longitudinal vertical section of the fiber condensing section of the above machine showing an embodiment of this invention.

FIG. 3 is a fragmentary section taken along the line 33 of FIG. 2.

FIG. 4 is a fragmentary enlarged section of FIG. 3.

FIG. 5 is a diagrammatic fragmentary plan view of another embodiment of this invention.

- FIG. 6 is a diagrammatic fragmentary plan view of another embodiment of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now toFIGJl, there isshown a fiber feeding means consisting, in this embodiment, of a conveyor belt 2, feed roll 3, compressing roll 4 and shoe 5 for supplying fiber 1 to the disperser roll 8. The disperser roll separates the fibers and carries them mixed with the air adjacent to the roll surface through the space between the roll and disperser plate 10, and discharges this mixture centrifugally into duct 20. A shroud or casing 9 extendsaround the disperser roll from the lower edge of doff-bar 12 to feed-roll 3. The fibers projected from the disperser roll form a thin fiber stream 22 in air flowing through the duct and are then separated fromthe air as web 24 on condenser screen 26.

Air is supplied from air passage 14, which haslarger cross-sectional dimensions than the duct 20. The parallel walls 16 of air passage are connected to the duct walls 20 by converging section 18 of the flow nozzle configuration. Screens 38 and 42, and honeycomb structure 40, provide a uniform flow substantially free of turbulence and vorticity. Air is blown into the air passage by one or more fans 36, through a duct system 33, shown diagrammatically.

The fibers are deposited to form a web on continuous, moving screen 26 which is driven and supported by rolls 28 and 30. The air flows through the screen and is withdrawnthrough vacuum duct 34. Part of the air passes through air-flow valve 13'. The air may be filtered to remove any particles passing screen 26 and then be recirculated to fan 36. Several fans in series or an open air system with one or more fans supplying the K airand one or more fans exhausting the air can also be used. The screen 26 is sealed against the fiber duct 20 and the vacuum duct 34 by sealing means 32 such as a plate of polyethylene.

FIGS. 2, 3 and 4 show air-flow valves 13 and 13, as preferred embodiments of the air-flow control means, in greater detail.

The valves shown comprise drums 23 and 23, each with two opposed openings 15 and each of which approximates the area of the closed area 17. Drums with four or eight openings can be used. The valves are located just behind the condenser screen 26 with appropriate seals 19. The two valves are synchronized so that when valve IB kQAhe right-hand edge of the fiber condensing area is fully open the other valve 13 is fully closed. This results in the fiber stream being shifted to the right and then to the left as the valves are turned.

As shown the two valves are mounted on a common shaft 21 driven by motor 25. The two valves could be mounted on separate shafts and driven by synchronized motors.

FIG. 5 shows the use of two oscillating deflectors 50 and 50 that serve as air flow control means. The deflectors are movably connected to duct at connections 52 and 52' and are given a synchronized motion by moving means 54 and 54'.

FIG. 6 shows the use of a rotating deflector 55 located in a shroud 56 as the air flow control means for the right edge of the condenser 26.

The air flow control means should be able to operate at a frequency of at least cycles (fully open to fully closed to fully open) per yard of travel of the web, e.g., 250 cycles/minute for web speed of l0 yards/minute.

The total area of the two air flow control means through which air flows should be at least about 2 percent of the total condenser area exposed to the air stream. As the severity of the streaks and/or speed of web increases (e.g., from 10 to 50 yards per minute or more) the total area of controlled air flow should be increased to as much as percent or more.

In operation, the frequency of operation of the air flow control means is increased from zero until the streaks have been blended into the adjoining areas of the web and are not apparent. This minimum effective frequency can be somewhat further increased but streaks may reappear at higher frequencies.

Other embodiments of air-flow control means include a shutter-like device that rotates in a plane parallel to the condenser screen. These can be placed at the edges of the air duct just upstream of the condenser screen, immediately behind the screen or can be placed behind a conduit in the vacuum duct that has an air seal on its forward edge that contacts the condenser screen.

EXAMPLE Apparatus of the general type shown in FIG. 1 is used to form a web weighing about 0.9 oz./yd. at a rate of yards per minute. The feed batt of 1.25-denier per fiber, 0.75 inch polyester staple, is fed to a 16-inch diameter disperser roll rotating at a surface speed of 14,600 feet per minute. Air is supplied through the duct at 6,800 feet per minute. The fiber stream is about 63 inches wide and 0.6 inch thick at the point of contact with the condensing screen. The condensing screen has an area 1.9 X inches exposed to the air duct. A rotating valve (FIGS. 2 and 4), 4.5 inches long and 3.87 inches in diameter, is located behind both edges of the condenser screen with the inner edges of the valves being located about 29 inches from the center of the condensing zone as shown in FIG. 3. The total area of the screen opened and closed by the two valves is about 13 percent of the condenser area exposed to the air stream. Operation of the valves at 500 revolutions per minute (1,000 cycles per minute) effectively blends out streaks.

I claim:

1. In an air-laydown apparatus having duct means for conveying fibers in a controlled flow of air, fiber disperser means for projecting fibers into the duct means to form a thin stream of fibers in air, air supply means for directing a low turbulence flow of air through the duct means, and a moving condenser screen for collecting the fibers thereon to form a web; the improvement for avoiding the formation of web streaks wherein the improvement comprises air-flow control valves located near opposite edges of the condenser screen for alternately interrupting air flow through the screen on opposite sides of the fiber stream at a frequency of at least 25 cycles per minute for each yard per minute of screen travel.

2. In an air-laydown apparatus having duct means for conveying fibers in a controlled flow of air, fiber disperser means for projecting fibers into the duct means to form a thin stream of fibers in air, air supply means for directing a low turbulence flow of air through the duct means, and a moving condenser screen for collecting the fibers thereon to form a web; the improvement for avoiding the formation of web streaks, wherein the improvement comprises air-flow control means for alternately interrupting air flow on opposite sides of the fiber stream characterized by a pair of rotating drums located behind opposite edges of the condenser screen and having opposed openings with each opening approximating the area of intervening closed drum areas.