US 3051998 A
Description (OCR text may contain errors)
Sept. 4, 1962 E. c. RUST, JR., ETAL 3,051,998
MACHINE FOR FORMING WEBS FROM FIBERS Filed June 27, 1960 corporation of Massachusetts Filed June 27, 1960, Ser. No. 39,136 9 Claims. (CL 19-156) This invention relates to machines for forming fibers into webs or non-woven fabrics. More particularly, the invention relates to an improved web-forming machine which is operable continuously at high speeds to produce continuously a web of randomly disposed fibers, which is of uniform thickness and consistency.
In prior web-forming machines, the fibers are delivered to a rotating toothed cylinder, as from a lap roll from which the fibers pass between a pair of feed rolls located adjacent the peripheral portion of the toothed cylinder. The teeth on the rotating cylinder pick up the fibers and carry them partly around the cylinder axis to a duct into which the fibers are discharged from the teeth. This duct leads to the perforated cylindrical surface of a rotating drum in which a partial vacuum is maintained, so that the fibers entering the duct from the cylinder teeth are drawn along the duct and deposited in the form of a Web on the perforated surface of the drum. As the drum rotates, the web is removed from the perforated surface at a region where the suction created by the partial vacuum in the drum is ineffective to prevent such removal.
To obtain a high rate of production, it is desirable to drive the toothed cylinder at high speed and to arrange the duct so that it extends generally tangentially from the peripheral portion of the cylinder in the direction of its rotation. This means that the duct should form an edge disposed in closely spaced relation to the peripheral portion of the cylinder and toward which the teeth carry the fibers when they enter the duct, the purpose of this edge being to cause fibers discharged from the teeth to be diverted into the duct and prevent them from being carried around the cylinder under the usual stationary cover and back to the feed point by the air stream induced by the rotation of the cylinder. In other Words, this edge serves as a cutoff to prevent recycling of the fibers around the toothed cylinder.
However, I have found that fibers discharged from the cylinder teeth will occasionally drape themselves over the cutoff edge, each fiber thus draped having one of its ends pulled toward the perforated drum by the air flow in the duct and having its other end pulled by the air stream induced by the toothed cylinder rotation and which flows back under the cylinder cover toward the feed rolls. The center portion of such a draped fiber is in the region of the stagnation point in the split air flow, that is, on the surface of the cutoff edge formed by the duct. The occasional draped fiber assists in draping additional fibers due to added friction, air turbulence, entanglement with the first fiber, etc. Very quickly, a build-up of fibers occurs on top of the first fiber on the cutoff edge, until the accumulated clump of fibers is displaced from this edge in one direction or the other. That is, the accumulated clump is deposited on the perforated surface of the rotating drum, either directly from the cutoff edge or by being cycled back to the feed point of the toothed cylinder and then back to the duct. In either case, the result is a mottled or splotchy web formed on the perforated drum.
In an attempt to avoid this difiiculty, highly polished edges have been used at the cutoff and various radii of the cutoff edge have been tried, but these measures give no significant improvement.
The principal object of the present invention is to proice vide a. web-forming machine operable at high speed and which overcomes the above-noted difiiculty.
According to the invention, I provide at the cutoff edge (that is, the aforementioned edge formed by the duct adjacent the periphery of the toothed cylinder) a nozzle arranged to direct a flow of air counter to the air stream induced by rotation of the toothed cylinder. More particularly, I provide a source of air at superatmospheric pressure, and means forming at the cutoff edge a nozzle communicating with this source for directing against the cylinder-induced air stream an air flow of sufiicient force to prevent the cylinder-induced air stream from impinging upon the cutoff edge. The air source associated with the nozzle may comprise means forming a plenum chamber from which the nozzle leads, and an air blower connected to the plenum chamber.
Thus, in the new web-forming machine, the nozzle introduces a counterflow of air which mushrooms against the air stream induced by rotation of the toothed cylinder and against the flow of fibers from the cylinder teeth, whereby the aforementioned stagnation point normally located at the cutofr edge is displaced to a point remote from this edge. In this way, the fibers discharging into the duct from the toothed cylinder are prevented from contacting the cutoff edge.
For a better understanding of the invention, reference may be had to the accompanying drawing in which the single illustration is a schematic view of a preferred form of the new web-forming machine.
Referring to the drawing, the reference numeral 10 designates a cylinder mounted for rotation about its axis and carrying at its peripheral portion a series of closely spaced, external teeth 10a. The toothed cylinder 10 is mounted for rotation on a suitable frame (not shown) and has a drive shaft 11 connected to a motor (not shown). Thus, the drive shaft 11 serves as a means for rotating the cylinder at high speed in the direction indicated by the arrow, that is, counterclockwise as viewed in the drawing. The teeth 10a, as shown, have leading edges which are not precisely radial but are inclined in the direction of rotation of the cylinder. The teeth 10a may be provided by a toothed Wire or wires wound around and secured to the cylindrical surface of the cylinder, as in a conventional garnett cylinder, it being understood that substantially the entire cylindrical surface of the cylinder 10 is clothed with teeth 10a.
The fibers for making the web are delivered to the peripheral portion of cylinder 10 from one side thereof by a feeding device which, as shown, comprises a lap roll 12, a pair of feed rolls 13-14, and a stationary inclined plate 15 on which the fibers pass from the lap roll to the nip between the feed rolls. The fibers F in mat form may be supplied to the lap roll 12 from a suitable lap (not shown), as will be readily understood by those skilled in the art. The upper feed roll 13 is provided with teeth, while the lower feed roll 14 has a substantially smooth cylindrical surface; and both of these rolls are rotatably mounted close to the periphery of toothed cylinder 10 and are positively driven in opposite directions, as indicated by the respective arrows. Thus, the feed rolls 13--14 continuously draw the mat of fibers F from the lap roll 12 and present these fibers to the teeth of the rapidly rotating cylinder 10 where they are picked up by the teeth and carried partly around the cylinder axis, as will be described in greater detail presently.
If desired, stripper and worker rolls 16 and 17, respectively, may be mounted adjacent the periphery of the toothed cylinder 10, as illustrated, and positively driven in the direction indicated by the respective arrows. However, these additional rolls 16-17 are not needed for normal operation of the web-forming machine.
A stationary duct 19 is provided at the side of the toothed cylinder opposite the feeding device 1215. The peripheral portion of cylinder 10 is disposed partly in the entrance end of duct 19 so that the duct is adapted to receive fibers discharged from the teeth 10a of the cylinder. The outer wall of the duct, opposite the periphery of cylinder 10, is provided with perforations 20 for admission of air, as will be described in further detail presently. The duct 19 extends generally tangentially from the peripheral portion of cylinder 10 in the direction of its rotation and leads to the perforated cylindrical surface 21 of a drum, the perforations of the drum being shown at 21a. The drum 21 is mounted for rotation about its axis on the machine frame and is provided with a drive shaft 22 connected to. a motor (not shown) and serving as a means for rotating the drum in the direction indicated by the corresponding arrow. At the end of the duct 19 adjacent the drum 21, sealing means are provided between the duct and the drum periphery to prevent any substantial flow of air from the duct except through the perforations 21a in the part of the drum periphery which is at the discharge end of the duct. Such sealing means may include a stationary seal 23 connected to and extending along the edge of one wall of the duct close to the periphery of drum 21, and a web roll 24 substantially filling the space between the drum periphery and the near edge of the opposite wall of the duct, the roll 24 being rotatably mounted on the frame and having its periphery substantially in engagement with the drum periphery.
The. lower portion of the foraminous drum 21 is located in a closed chamber formed by a housing 25. The space between the top of housing 25 and the periphery of drum 21 is closed at one side by the seal 23 and at the opposite side by a flexible sealing flange 26 connected to the housing and engaging the drum periphery. A suction fan 27 is connected to the interior of the housing 25 and serves to evacuate air from the interior of drum 21. Thus, a partial vacuum is maintained in the drum 21, causing a flow of air through the holes 2% into the entrance end portion of the duct and thence through the duct and through the perforations 21a in that part of the cylindrical surface of the drum which is at the discharge end of the duct. This air flow induced by the suction fan 27 acts to pick up the fibers discharged into the duct from the teeth of cylinder 10 and deposit these fibers in the form of a web on the perforated cylindrical surface of the rotating drum 21.
As the drum 21 rotates, the fibrous web W thus formed on the drum periphery'is carried under the web roll 24 and is continuously removed from the drum surface by suitable means. As illustrated, the means for removing the web from the drum surface comprises an endless belt or apron 28 mounted on rolls 29 and 30, one of these rolls being positively driven to move the apron in the direction indicated by the arrow. After passing under the web roll 24, the web W passes from the drum 21 over a roll 31 and onto the upper part of apron 28, which carries the web away from the machine. Within the drum 21 is a stationary baffle 32 of arcuate form which is located close to the inner cylindrical surface of the drum, this bafile extending in an are approximately from the web roll 24 to the flexible seal 26. By means of the baffle 32, the suction created by the fan 27 is inetfective at the region where the web W is withdrawn from the rotating drum 21.
The upper portion of toothed cylinder 10 is enclosed partly by a stationary cover 34- and partly by the duct 19, the outer wall of which terminates at the cover 34. At its lower portion, the toothed cylinder 10 is enclosed by a stationary cover 35, one edge portion of which is provided with a flexible sealing flange 36 engaging the cylindrical surface of the lower feed roll 14. The opposite edge portion of the lower cover is located adjacent an edge 19a formed by the duct 19 and which corresponds to. the cutoff edge previously described. The edge 19a partly defines the entrance end of the duct and extends lengthwise along the toothed cylinder 10a in closely spaced relation to the peripheral portion of this cylinder. As will be observed from the drawing, the direction of rotation of cylinder 10 is such that its teeth 19a, upon entering the entrance end of the duct, move toward the duct edge 19a. The lower cover 35 serves as a means forming at the edge 19a a nozzle 37 for directing a flow of air close to the cylinder teeth and counter to the direction of rotation of the cylinder. By means of partitioning 38 coactin-g with the lower cover 35 and the inner wall of duct 19, a plenum chamber 39 is formed from which the nozzle 37 leads. The plenum chamber 39 is adapted to contain air at superatmospheric pressure supplied through a duct 40 from a blower 41.
It will be understood that the toothed cylinder 10 is substantially enclosed by means including the stationary parts 19, 34 and 35 and the feed rolls 1314. The edge 19a and the adjacent nozzle 37, of course, extend lengthwise of the toothed cylinder along all of its toothed portion, as do the feed rolls 13-14. The various parts are dimensioned to handle any desired width of fiber stock delivered to the feeding device 12-15 and to discharge a web W of desired width.
The toothed cylinder 10 is driven at high speed to enable a high production rate, the foraminous drum 21 being driven at a relatively low speed which is such as to provide the desired thickness of the web W of randomly disposed fibers formed on the drum surface. As an example, the toothed cylinder 1% may be driven so that its toothed peripheral portion travels at a speed of about 7500 feet per minute.
In the operation of the machine as illustrated, the teeth 1G6: of the rotating cylinder pick up the fibers F as they are fed to the cylinder and carry them partly around the cylinder axis. As the fibers enter the entrance end of duct 19, they are subjected to a combination of forces including the centrifugal force tending to throw them radially outward from the cylinder, the air flow toward the drum surface 21 at the discharge end of the duct which is created by suction fan 27, and the air flow induced by the high speed rotation of the toothed cylinder and which is directed toward the duct edge 19a. As a result, the fibers are discharged from the cylinder teeth 10a into the duct 19 at high speed, this discharge being generally tangentially of the cylinder and in the direction of its rotation, that is, generally in the direction in which the duct 19 extends from the cylinder to the drum 21. Those discharged fibers which are directed toward the duct edge 19a are met by the opposing air flow from nozzle 37 and deflected away from the edge 19a and into the duct 19 before they can contact this edge. Thus, the air flow from nozzle 37 prevents draping of a fiber over the edge 19a and thereby avoids the previously mentioned build-up of a clump of fibers on this edge. The web W is continuously formed on the perforated drum surface 21, as the drum rotates, and is continuously removed from the drum by the discharge means 28-31, as previously described.
In the example given above, where the toothed cylinder 10 is driven at a peripheral speed of about 7500 feet per minute, measurements show that the velocity pressure in the air stream induced by the cylinder rotation at the duct edge 1921, when no air is blown through nozzle 37, is aproximately 3 /2" H O, which corresponds with the velocity pressure produced by an air velocity of 7500 feet per minute. The total pressure (static plus velocity pressure) provided in the nozzle 37 by the blower 41 should be in excess of the total pressure in the opposing air stream which would strike the edge 19a except for the air flow from the nozzle. In the above-noted example, nozzle plenum pressures of 5 to 7" H O give good results.
As will be observed from the drawing, the perforations 20 in duct 19 are distributed over the portion of the duct wall which is opposite the toothed cylinder 10.
This arrangement has a distinct advantage in the new machine because it acts to reduce the over-all air turbulence adjacent the perforated surface or screen of drum 21, where the fibers from the toothed cylinder are deposited. In other words, this arrangement serves to avoid an uneven deposit of fibers on the drum screen 21, which would result in a web W of irregular thickness.
1. A web-forming machine comprising an externally toothed cylinder mounted for rotation about the cylinder axis, a device for feeding fibers to the peripheral portion of the cylinder for engagement by the cylinder teeth, a rotating drum having a perforated cylindrical surface, a duct leading in a generally tangential direction from the peripheral portion of said cylinder to the perforated surface of the drum, said duct forming an edge disposed in closely spaced relation to the peripheral portion of the cylinder at a region remote from said feeding device, suction means for maintaining a partial vacuum in the drum to create air flow in one direction through the duct and thereby draw fibers along the duct from the cylinder to said perforated surface to form a web thereon, means for rotating the cylinder at high speed in a direction to cause said teeth to pick up and carry fibers from the feeding device partly around the cylinder axis into the duct and then toward said edge, whereby said cylinder rotation induces in the duct an air stream tending to flow toward said edge and the fibres are discharged in said generally tangential direction from the teeth into the duct under the actions of centrifugal force, said induced air stream and the air flow created by the suction means, a source of air at superatmospheric pressure, and means forming at said edge a nozzle communicating with said source for directing an air flow counter to said induced air stream and counter to said direction of the air flow created by the suction means, thereby preventing entrapment on said edge of fibers discharged from the teeth.
2. A web-forming machine according to claim 1, in which said air source comprises means forming a plenum 6 chamber from which said nozzle leads and adapted to contain air at superatmospheric pressure.
3. A web-forming machine according to claim 1, in which said air source comprises means forming a plenum chamber from which the nozzle leads, and an air blower connected to the plenum chamber.
4. A web-forming machine according to claim 1, comprising also means for continuously removing the web from said perforated surface of the rotating drum.
5. A web-forming machine according to claim 1, in which said teeth are inclined in the direction of rotation of the cylinder.
6. A web-forming machine according to claim 1, in which said air source is operable to create in the nozzle a pressure substantially in excess of the opposing pressure of said induced air stream.
7. A web-forming machine according to claim 1, in which said feeding device includes a pair of coacting feed rolls adjacent the peripheral portion of the cylinder.
8. A web-forming machine according to claim 1, in which said feeding device includes a pair of coacting feed rolls adjacent the peripheral portion of the cylinder, and a lap roll for delivering fibers to the nip of said feed rolls.
9. A web-forming machine according to claim 1, in which the duct has a first wall forming said edge and a wall located opposite said first wall and partly defining a duct space into which fibers are discharged directly from the cylinder teeth, said opposite wall having perforations distributed over that portion thereof which lies opposite the periphery of the toothed cylinder.
References Cited in the file of this patent UNITED STATES PATENTS 188,164 Miles et al Mar. 6, 1877 2,451,915 Buresh Oct. 19, 1948 2,676,363 Plummer et al Apr. 27, 1954 2,676,364 Plummer et a1 Apr. 27, 1954 2,726,423 Harwood et a1 Dec. 13, 1955 2,876,500 Buresh et al Mar. 10, 1959