US3501813A - Method of forming a continuous fibrous web - Google Patents

Description

March 24, 1970' c. A. LEE ET AL METHOD OF FORMING A CONTINUOUS FIBROUS WEB Filed NOV. 10, 1965 9 Sheets-Sheet 1 A .W\\ L U I o kw. 5 |AO||\\ Q N m o WQ .6

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METHOD OF FORMING A CONTINUOUS FIBROUS WEB Filed Nov. 10, 1965 9 Sheets-Sheet 2 March 24, 1970 c. A. LEE' ET AL METHOD OF FORMING A CONTINUOUS FIBROUS WEB Filed Nov. 10. 1965 WIII4EZZEZI4IIII 774 75 9 Sheets-Sheet 5 March 24, 1970 c. A. LEE ET AL METHOD OF FORMING A CONTINUOUS FIBROUS WEB 9 Sheets-Sheet 4 Filed Nov. 10. 1965 I March 24, 1970 QAQLgE ETAL 3,501,813

METHOD OF FORMING A commuous FliBROUS WEB Filed Nov. 10, 1965 9 Sheets-Sheet 5 March 24, 1970 C. A. LEE ET AL METHOD OF FORMING A CONTINUOUS FIBROUS WEB Filed Nov. 10, 1965 9 Sheets-Sheet 6 March 24, 1970 c. A. LEE ETAL METHOD OF FORMING A CONTINUOUS FIBROUS WEB "9 Sheets-Shet 7 Filed Nov. 10. 1965- March 24, 1970 c. A. LEE ET AL METHOD OF FORMING A CONTINUOUS FIBROUS WEB Filed Nov. 10, 1965 9 Sheets-Sheet 8 March 24, 1970' c. A. LEE ET AL.

METHOD OF FORMING A CONTINUOUS FIBROUS WEB 9 Sheets-Sheet 9 Filed NOV. l0l 1965 United States Patent 3,501,813 METHOD OF FORMING A CONTINUOUS FIBROUS WEB Charles Allen Lee and Warren R. Furbeck, Knoxville, Tenn, and Thomas S. Bartley and Jeremy G. Beaty, Toronto, Ontario, Canada, assignors, by direct and mesne assignments, to Canadian International Paper Company, Montreal, Quebec, Canada, a body corporate and politic Filed Nov. 10, 1965, Ser. No. 507,089 Int. Cl. D01g 25/00 U.S. Cl. 19-1563 7 Claims ABSTRACT OF THE DISCLOSURE A single integral Web of loose fibrous material having a non-uniform cross sectional thickness is formed on a carrier moving at a uniform rate by causing first and second quantities per unit time of loose fibrous material to be conveyed by air and deposited on first and second different portions of the carrier.

The present invention relates to the forming of a web from a quantity of loose fibrous material and, more particularly, is directed to a method and apparatus for airlaying such material into a Web having a predetermined cross sectional configuration.

Webs formed of loose fibrous material have numerous applications. For example, in the furniture and bedding industries, such webs, commonly referred to as batts, are produced in relatively thick sheets and are utilized as padding. In the paper industry, such webs are generally thinner and are utilized principally for their padding, their insulating, or their absorptive characteristics.

Regardless of their ultimate use, such webs are frequently formed by a process known as air laying, in which a quantity of loose fibrous material is continuously deposited or laid on a moving screen supported intermediate a vacuum box and a feeding unit spaced from the vacuum box inlet. The vacuum box draws air through the screen and causes a flow of air past the feeding unit to the screen. The loose fibrous material is delivered into the air stream by the feeding unit and is carried by the air stream to the screen Where it is deposited in a layer having uniform thickness which is dependent upon the speed of movement of the screen, the speed of movement of the air stream, and upon the density of the loose fibrous material in the air stream. The web is removed from the screen at a later station and coiled, cut, or delivered directly to an assembly station.

One particular application of such a web is its incorporation into a disposable diaper in which, for example, the web may be in the form of a pad enclosed in an envelope of wet strength highly absorptive crepe tissue. The function of the web is to provide a soft but highly absorbent layer to receive body fluids. While the web is generally effective in this regard, it has been found that its effectiveness is increased substantially if a greater thickness of pad is provided in its longitudinally extending central portion than adjacent its edge portions since it is the central portion which receives directly the greatest quantity of body fluids. This increased thickness has in the past been provided by forming two separate webs, the first of which is substantially wider than the second, and laying the second onto the first. This method is expensive, however, since it requires a separate apparatus for the formation of each 'web and requires, in addition, equipment to effect the laying of the second Web upon the first. Moreover, the provision of a web having two layers is not as effective as a web of a single 3,501,813 Patented Mar. 24, 1970 layer because of the tendency of the layers to separate and allow fluid flow along the interfaces.

The present invention is directed to a method and apparatus for producing a single integral web of loose fibrous material having a non-uniform thickness for use in various applications including, but not limited to, a disposable diaper. It is therefore the principal object of the present invention to provide an improved method and apparatus for producing a web from a quantity of loose fibrous material.

Another object of the invention is to provide an improved method and apparatus for producing a web of non-uniform thickness from a quantity of loose fibrous material.

An additional object of the invention is to provide an improved method and apparatus for producing such a web of non-uniform thickness having a predetermined cross sectional profile for use in various applications including, but not limited to, a disposable diaper.

A further object of the invention is to provide an improved method and apparatus for producing a web from loose fibrous material, by which method and apparatus the thickness of the web in predetermined longitudinally extending areas thereof may be selectively controlled.

A still further object of the invention is to provide an improved method and apparatus for forming a web from loose fibrous material directly upon a moving sheet of air pervious material.

It is also an object of the invention to provide an improved web formed of loose fibrous material having a predetermined non-uniform thickness as measured at various points across its width.

Other objects and advantages of the invention will become apparent with reference to the following description and the accompanying drawings.

In the drawings:

FIGURE 1 is a side elevational view of an apparatus showing various of the features of the invention;

FIGURE 2 is a plan view of the apparatus of FIG- URE 1 with the charging unit removed;

FIGURE 3 is an enlarged fragmentary sectional elevational view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a fragmentary elevational end view;

FIGURE 5 is an enlarged fragmentary sectional plan view taken along line 5-5 of FIGURE 1;

FIGURE 6 is an enlarged plan view showing a porton of the apparatus of FIGURE 5 in greater detail and more fully in section;

FIGURE 7 is an enlarged fragmentary view of a portion of the apparatus of FIGURE 5;

FIGURE 8 is a fragmentary sectional element view taken along line 88 of FIGURE 7;

FIGURE 9 is an enlarged fragmentary sectional elevational view;

FIGURE 10 is an enlarged fragmentary partially broken-away view taken along line 1010 of FIGURE 9;

FIGURE 11 is an enlarged fragmentary sectional view taken along line 1111 of FIGURE 10;

FIGURE 12 is an enlarged fragmentary view of a portion of the apparatus shown in FIGURE 10;

FIGURE 13 is an enlarged fragmentary sectional view taken along line 1313 of FIGURE 12;

FIGURE 14 is a sectional end view of a web such as may be formed in accordance with the method and apparatus of the present invention;

FIGURE 15 is an enlarged fragmentary plan view taken in the direction of the arrows 15-15 of FIG- URE 1;

FIGURE 16 is a fragmentary elevational view;

FIGURE 17 is an enlarged partially broken-away sectional plan view;

FIGURE 18 is a fragmentary elevational view similar to that of FIGURE 9 but showing an alternate embodiment of the invention;

FIGURE 19 is an enlarged fragmentary partially broken-away sectional plan view taken along line 19-49 of FIGURE 18;

FIGURE 20 is an enlarged fragmentary sectional plan view taken along line 20-20 of FIGURE 18;

FIGURE 21 is an enlarged fragmentary sectional plan view taken along line 2121 of FIGURE 18; and

FIGURE 22 is an enlarged fragmentary sectional elevational view taken along line 2222 of FIGURE 18.

Very generally, in the practice of the method of the present invention, as shown in the illustrated embodiment thereof, a web of non-uniform thickness is formed from a quantity of loose fibrous material by conveying the material by means of an air stream to an elongated airpervious carrier and depositing it on the carrier in such a manner that a greater quantity is deposited on certain longitudinally extending areas of the carrier than on adjacent areas. In the method practiced through the use of the embodiment of the apparatus shown in FIGURES 1-17, this uneven distribution of the material on the carrier is achieved by providing the air stream with a velocity profile in which certain portions of the air stream have a higher velocity than the adjoining portions and thus convey a greater amount of material to associated portions of the carrier. The uneven distribution is also achieved by such embodiment by creating a greater vacuum or suction behind the associated portions of the carrier than behind adjacent portions so as to draw the air through the screen at the same rate as it arrives at the screen.

In the method employed in the use of the embodiment of the apparatus shown in FIGURES 18-22, the uneven distribution is achieved by shielding a portion of the carrier from the air stream while deflecting the air stream toward the unshielded portion.

The method of the invention will become clear by virtue of the following description of an apparatus 30 of the embodiment illustrated in FIGURES 1-17. Very generally, this apparatus comprises (FIG. 1) an endless conduit 32 having a material charging port 34 into which a quantity of loose fibrous material is delivered by a charging unit 36. The loose fibrous material is conveyed through the conduit by an air stream which, in the illustrated embodiment, is established by a blower 38 (FIG. 2) which draws air through a vacuum box 40 located in spaced relation to the charging port 34 and downstream thereof, the blower thereby creating a lower absolute pressure at the vacuum box than at the charging port and thus causing an air flow toward the vacuum box. However, it might also be possible to operate above rather than below atmospheric pressure, in which case the vacuum box 40 would not be maintained at a negative pressure. Operation below atmospheric pressure is preferred, however, since there is then no tendency for the fluff to leave the system and enter the surrounding atmosphere.

The fibrous material conveyed by the air stream is deposited in the form of a web 42 (FIG. 9) on a carrier 44 which is disposed intermediate the charging port 34 and the vacuum box 40 and which is continuously moved in a direction transverse to the longitudinal axis of the conduit. Bafiles 46 (FIG. are provided to constrict the conduit and create a desired velocity profile intermediate the charging port and carrier, and valves 48 are provided for permitting the establishment of a lower pressure behind certain portions of the carrier than behind adjacent portions. Both the bafiies 46 and the valves 48 are selectively operable to provide the web with a predetermined profile or cross sectional configuration.

The illustrated embodiment of the apparatus 30 which is hereinafter described is particularly adapted to provide the web 42 with the cross sectional configuration or profile shown in FIGURE 14. Such a web has a raised or thick center portion 50 flanked by substantially thinner edge portions 52, the portions 50 and 52 gradually merging with each other in fillets 54. The web shown in FIG- URE 14 also includes a carrier sheet 56, referred to in greater detail shortly, upon which the loose fibrous material might be deposited directly, thereby rendering it easier to handle and, among other things, making it unnecessary to subsequently lay the web onto such a sheet. However, it is to be understood that the web can also be deposited directly onto a mechanical carrier and transferred therefrom to any appropriate vehicle including a tissue sheet.

Referring now more specifically to the illustrated apparatus, the conduit 32, in the form of an endless loop (FIGS. 1 and 2), is defined by a primary duct 58 connected by a delivery duct 60 to the vacuum box 40 which, in turn, is connected by means of a return duct 62 through an air processing unit (Rotoclone) 64 back to the primary duct 58. The primary duct 58 is generally U-shaped and includes a lower section 66 which is of a generally uniform rectangular cross sectional configuration throughout its length and extends generally horizontally from the air processing unit 64 forwardly, i.e., toward the right as viewed in FIGURES l and 2. The lower section 66 contains an air stream moving forwardly and is connected at its forward end to an elbow 68 which is of generally semi-annular configuration and has a uniform rectangular cross sectional configuration similar to that of the lower section 66. The elbow 68 receives the forwardly moving air stream of the lower section 66 and directs it upwardly and rearwardly for entry into a horizontally disposed upper section 70 of the primary duct 58 to which it is connected.

The upper section 70 is approximately the length of the lower section 66 but is of non-uniform cross sectional configuration throughout its length, narrowing down to a segment of reduced cross sectional area to define a throat or venturi 72 located in spaced relation to its forward end, and flaring outwardly again toward its rearward end. The venturi is defined, in the illustrated embodiment, by an upward inclination of the top wall of the upper section but could also be accomplished by diverging side walls. The throat or venturi 72 creates a region of reduced pressure within the duct 70 which serves to draw an air-fiber mixture from the charging unit 36 through the charging port 34 located at the forward end of the top wall defining the throat. The rearward end of this top wall is connected to the delivery duct 60, as previously described. Air flows forwardly through the lower section 66 of the duct, is reversed in direction as it flows through the elbow 68, and flows rearwardly through the throat 72 and up per section 70 in the direction of the delivery duct 60 and vacuum box 40. As it flows through the throat 72, it receives an air-fiber mixture from the charging unit 36.

To insure that the flow pattern of the loose fibrous material fed through the charging port 34 and carried by the air stream will be generally uniform in the upper section 70 of the duct, and to provide for uniform distribution of the loose fibrous material throughout the air stream, a perforated plate 74 (FIG. 3) is provided within the upper section adjacent the forward end thereof and forwardly of the charging port 34. The plate 74 is generally vertically disposed so as to be normal to the longitudinal axis of the section 70 and includes a plurality of holes 76 which, in the illustrated embodiment, are arranged in four generally horizontal rows with the holes of each row being staggered relative to the holes of the adjacent row or rows. The holes of the upper row are downwardly and rearwardly inclined slightly so as to direct jets or streams of air flowing through these holes downwardly for passage through the narrowed throat 72 of the duct.

The perforated plate 74 serves to equalize the flow of air throughout the upper section of the duct, thereby assuring a uniform flow pa tern into the chute 60 and past the bafiles 46. The plate also serves to transform the flow of air passing beneath the charging port 34 into a plurality of individual jets or air streams which, because of their staggered relation to each other, cause the loose fibrous material to be distributed more uniformly through the conduit.

The charging unit 36 which deposits loose fibrous material through the charging port 34 and into the conduit 32 is shown most clearly in FIGURES 1 and 4. Very generally, this unit comprises a pulp moistener 80 which receives the raw pulp in sheet form and dampens it, a shredder 82 which reduces the pulp to small pieces, and a mill 84 which grinds the pieces produced by the shredder into fine particles. Preferably, raw pulp is supplied to the charging unit 36 either in the form of a single sheet or, as in the illustrated embodiment, in the form of a pair of superimposed sheets 86, withdrawn simultaneously from a pair of coils 88 suitably supported adjacent the forward end of the apparatus (FIGURE 4), on ground level, in horizontally spaced relation to each other.

The sheets are pulled upwardly over a single idler roll 90, through the pulp moistener 80', and into the shredder 82 by power-driven cooperating rollers 92 provided on the shredder, as hereinafter described.

The pulp moistener 80 is supported on an elevated platform 94 above the coils 88 and includes a tank 96 containing Water maintained at a given level and drums 98 disposed partially beneath the water level. The pulp sheet passes around the drums and, in so doing, becomes dampened. The moisture added to the stock decreases the possibility of the stock acquiring an electrostatic charge, and also lessens the temperature rise within the apparatus. The drums 98 assist in pulling the pulp sheet through the moistener.

After leaving the pulp moistener 80, the stock passes over a second idler roller 100 supported on a housing 102 into the nip of the power driven rollers 92, one of which has affixed to it a sprocket 104 connected by means of a link chain 106 to a sprocket 108 driven through vertically and horizontally disposed shafts 110 and 112 by a remotely located motor (not shown). As previously mentioned, the rolls cause the advance of the stock into the shredder 82 which contains appropriate cutters (not shown) driven by a motor 114 (FIG. 1) supported on the platform 94. The cutters reduce the stock to small pieces of approximately postage stamp size which are deposited through a chute 116 into the inlet of the mill 84. The shredder 82 is provided with an air intake 118 which permits a thorough mixing of air with the stock.

The mill 84 is supported on a platform 120 located below the shredder platform 94 and receives the pieces of stock from the chute 116 of the shredder and reduces them to fine particles. The mill may be of conventional construction and may include a pair of very closely spaced discs (not shown) which are rotated in opposite directions by a motor 121. The particles received from the shredder are delivered to the space between the discs where they are broken down into individual fibers or small bundles of fibers. The loose fibrous material thus produced is deposited, together with some air drawn in through the air intake 118, through a tube 122 of square cross section (FIGS. 1, 3 and 4) and through the charging port into the return duct 70.

The air stream carrying the loose fibrous material is directed through the venturi or narrowed throat 72 of the upper section 70 of the primary duct, through the flared remaining portion of the upper section, to the delivery duct 60 (FIG. 5). The delivery duct 60 is generally inclined relative to the upper section to permit the carrier to be inclined relative to the vertical in the area in which the loose fibrous material is deposited upon it, while yet remaining generally normal to the direction of flow of the air stream. Such a relationship between the carrier and air stream has been found to be preferable for reasons hereinafter set forth. The delivery duct is somewhat wider than the adjacent end of the duct 70 and is defined by top and bottom walls and 142 respectively, by side walls 144, and by an end wall 146 at its forward end, and by the carrier 44 and a carrier grid plate 148 at its rearward end. The grid plate 148 is defined by the outer ends of tubes located within the vacuum box 40, as hereinafter described. The delivery duct encloses the rearward end portion of the upper section 70 of the primary duct 58 and the forward end wall of the delivery duct is rigidly secured to the carrier grid plate 148 and to structural support members of the vacuum box 40.

The delivery duct further includes a pair of generally parallel inner wall members 150 which are aligned with the side walls of the upper section 70 of the primary duct 58 and, together with the top and bottom walls 140 and 142, define that portion of the conduit 32 which extends through the delivery duct. The inner wall members 150 together with the side walls 144 and top and bottom walls define a balancing chamber 152 on each side of the conduit, the function of which will become apparent shortly.

The inner wall members 150 each comprises three sections, namely, a forward section 154, an intermediate section 156 and a rearward section 158 (FIGS. 5 and 7). The forward sections are joined to the side walls of the upper section 70 of the primary duct 58 and are provided with a flange 160 at their rearward ends which is inclined forwardly at an acute angle to the forward wall section. The section 154 is pref rably provided with a transparent window 162 to permit the air stream to be viewed as it passes through the chute. The rearward end of the forward section is secured to the top and bottom walls 140 and 142 by brackets 164.

The intermediate sections 156 are relatively short and include a flange 166 at their forward end, which is at an obtuse angle to the remainder of the section, this angle being supplementary to the acute angle of the flange 160 so that when the sections 154 and 156 are placed in parallel planes, the flanges are parallel also and define a slot which receives a bafile 46, referred to in greater detail shortly. The slot is therefore inclined relative to the direction of flow through the conduit. Each intermediate section 156 is arranged in a plane parallel to but inset inwardly of the plane of the forward section 154 so that a portion of the flange 166 projects into the conduit and serves to provide a back-up support to a portion of the bafiie which is located within the conduit 32 and which is therefore subject to the pressure of the air stream. Each intermediate section is supported at its forward end by brackets 170 secured to the top and bottom walls 140 and 142, and includes a transparent window 172.

The rearward section 158 is in the form of a flat plate which is hingedly connected, as at 174, to the rearward edge of the intermediate section 156 and extends rearwardly therefrom but terminates short of the carrier grid plate 148 so as to provide a clearance space through which the carrier 44 may be moved. The distance between the wall members 158 defines the width of the web being formed on the carrier; thus, hinged movement of the sections toward and away from each other makes variation in the width of the web possible. Slotted bracket and bolt arrangements 176 enable the sections to be secured in any desired position. Thus, when the apparatus is used to manufacture pads for diapers, the wall members may be adjusted to provide for various diaper widths, each of which is particularly suited to children in a given size range.

As previously mentioned, baffles 46 are provided in the delivery duct 60 to form a velocity pattern in the air stream as it passes through the delivery duct, this velocity profile being such as to contribute to the desired profile or cross sectional configuration of the web being formed. In the illustrated embodiment, in which the web being formed is intended to include a central portion of greater thickness (FIG. 14), the air stream is desirably 1nfiuenced so that the central portion thereof, Le, a centrally disposed region extending from the top to the bottom of the conduit, is of greater velocity than the adjacent side portions. In this way, a greater quantity of air is caused to pass through the central portion of the delivery duct and, assuming a uniform distribution or density of the loose fiberous material in the air stream, a greater quantity of material will arrive at and be deposited on the central portion of the carrier than on adjacent portions.

In the illustrated embodiment, the baffles create the above-referred to velocity pattern. Each bafile is in the form of a fiat plate beveled at its innermost end and positioned in the slot defined by the flanges 160 and 166 of the inner wall sections 154 and 156. Because of the inclination of the flanges and, hence, the slots, the bafiles extend inwardly from opposite sides of the conduit and are inclined in the direction of flow of the air stream.

Thus, the baffles 46, extending into the conduit from opposite sides, constrict the conduit within the delivery duct 60, narrowing the airstream to a centrally disposed vertically oriented flow and, in so doing, increasing its velocity in the central area of the conduit. After the constricted airstream has passed the bafiles, it expands to the width of the conduit, but its central portion remains of increased velocity, as is desired.

To permit the width of the central vertically oriented flow of the air stream to be varied as, for example, to enable the raised central portion of the diaper to be provided with various widths depending upon the size of the child sought to be accommodated, the baffles 46 are rendered movable into and out of the conduit 32. In this regard, the flange 166 of each of the intermediate sections 156 of the inner wall members 150 is provided with a pair of vertically spaced blocks 178 having a threaded hole adapted to receive a threaded shaft 180. Each threaded shaft 180 also rotatably supports a plate 182 which is restrained from axial movement along the shaft and is connected to the outer edge of the associated baffle. Thus, rotation of the shaft moves it axially and, hence, moves the plate 182 and, consequently, the baffie 46, toward and away from the conduit. In addition, each shaft has secured thereto a sprocket 184, the sprockets of each vertically spaced pair of shafts being interconnected by means of a link chain 186. The uppermost shaft is rendered manually rotatable by a handle 188 which, when rotated and because of the aforementioned connection, rotates the lower shaft as well and effects entry or withdrawal of both the upper and lower portions of the bafiie simultaneously. Access to the handle is provided by means of a door located in each of the outer side walls 144 of the chute.

The carrier 44 and vacuum box 40 are supported at the rearward end of the chute, the vacuum box 40 serving to support the carrier as well as to control the passage of air through it. Very generally, the vacuum box 40 (FIGS. 1, 5 and 9) defines a vacuum chamber 190 in communication with the blower 38 via a pipe 192 constituting a portion of the return duct 62. The vacuum box includes the grid plate 148 disposed transversely of the conduit 32 and provided with a plurality of openings 196 which afford communication between the chamber 190 and the surface of the grid plate, thus creating a suction which removes air arriving at the surface of the plate. Each opening 196 has associated therewith a valve 48, thereby permitting selective control of the air pressure at each opening and, consequently, permitting variations in the degree of suction across the grid. Supporting members 198 (FIG. 1), disposed on opposite sides of the vacuum box, mount rolls carrying an endless screen 200 which may either itself function as the carrier 44 and directly receive the web 42 or may support a separate sheet or strip 56 of air-pervious material which serves as a carrier in receiving the web and, in addition, forms a backing therefor.

More specifically, the chamber defined by the vacuum box 40 has a height approximating the height of that portion of the conduit 32 defined by the delivery duct 60 (FIG. 9). It is somewhat trapezoidal in horizontal cross section (FIG. 5) being narrower adjacent one of its ends than adjacent the opposite end, which opposite end is connected to the pipe 192 leading to the blower 38 (FIG. 2). Projecting forwardly from the forward face of the box is a suction port arrangement 204 comprising a plurality of tubes 206, each of which defines at its forward end one of the openings 196 of the grid plate 148, and each of which receives at its rearward end a plug 208 of one of the valves 48, described in greater detail shortly. Each tube includes a generally cylindrical throat 210 at its rearward end to receive the plug 208, and flares outwardly from the throat toward its forwardmost end. In the illustrated embodiment, three vertically arranged rows of tubes 206 are provided, each row having twelve tubes. The tubes of the centermost row terminate in an opening 196 which is of lesser diameter than the opening defined by the tubes of the two outermost rows, with the diameter of the opening of the central tubes roughly approximating the desired width of the increased thickness central portion of the web 42. The diameter of the remaining tubes roughly approximates the 'width of the remaining or flanking portions of the web.

As has been previously set forth, the bafiles 46 disposed within the air stream cause the velocity of the central portion of the air stream approaching the carrier 44 to be greater than that of the remaining or side portions. This causes a greater amount of air carrying fibrous material to be delivered to the central portion of the carrier. In order to prevent a movement of air and material transversely of the carrier immediately adjacent its surface, a condition which might arise from a pressure differential across the surface, it is desirable that air approaching any given portion of the carrier be withdrawn therethrough at essentially the same rate per unit area and at essentially the same rate at which it arrives or impinges on the carrier. Thus, air is preferably drawn through the central portion of the carrier at a greater rate than through the side portions and hence, the flow of air through the central row of tubes 206 is preferably greater than the flow through the outer row of tubes. Preferably, the amount of per unit area drawn through the central portion of the carrier is significantly greater even after there has been a substantially greater build-up of loose fibrous material on this portion of the carrier than on adjacent portions. Accordingly, although the air is being delivered to the carrier at a non-uniform rate, this is compensated for by the non-uniform rate of removal of air through the carrier, thereby creating an essentially uniform pressure differential along the surface of the carrier and eliminating the tendency of the material to migrate along the surface.

Accordingly, a valve 48 is provided for each tube 206 to regulate the flow of air through the tube and each includes the plug 208 (FIGS. 5 and 6') having a cruciform guide 212 which is received within the throat 210 of a tube 206, the throat being provided with a liner 213 at the contacting surfaces. Secured to the rearward or inner end of each cruciform guide is a disk 214 having a conical peripheral surface 216 adapted to seat on a chamfered surface 218 provided at the rim defining the rearward end of the throat.

When the disk 214 is seated at the mouth of the throat, no air passes through the associated tube 206 and no suction effect is provided at the associated portion of the grid plate 148. However, selective withdrawal of the plug 208 rearwardly permits air to pass around the cruciform guide 212 and thus withdraw air arriving at the surface of the carrier to the extent desired. Preferably, the valves maintain the tubes 206 of the central row more fully open than the outer rows so that the rate of flow through the tubes approximates the rate at which the air is delivered to the carrier across its surface. The provision of a number of tubes in each row makes it possible to increase the suction in each row from one end to the other in the direction of movement of the carrier so as to compensate for the buildup of material on the carrier as it moves through the conduit.

Insertion and withdrawal of each plug 208 is accomplished by means of a shaft 220, secured to the plug at its forward or inner end and threaded at its rearward or outer end, which passes through a suitably threaded opening in a support 222 mounted on the rearward wall of the vacuum box. A handle 224 is secured to the rearward or outer end of the shaft 220 and, when rotated, effects axial movement of the shaft and, hence, insertion or withdrawal of the plug. Withdrawing movement is preferably limited, as by a stop nut 226 carried by the shaft intermediate its ends.

The grid plate 148, disposed along the forward wall of the suction box 40, defines the openings 196 and also provides support for the carrier 44 as it receives the Web. The plate includes (FIGS. 6, 10-13) horizontally disposed outwardly projecting slide or bearing strips 228 positioned in grooves provided in the outer face of the suction port arrangement 204 intermediate the tubes 206. The strips 228 provide support for the continuous or endless moving screen 200 forming at least a portion of the carrier 44. They extend across the three vertical rows of tubes and are preferably somewhat wider than the car rier screen (FIG. 10). Extending between the strips 228 on opposite sides of the centermost row of tubes 206 are vertically disposed bars 232 (FIG. 6) which also serve a supporting function. The outer or forwardmost edges of these bars are sculptured (FIGS. 12 and 13) to permit a small amount of air to pass intermediate the grid and screen from the openings 196 of the outermost row to the openings of the centermost row, thereby permitting a gradual pressure change between the adjacent rows, despite the fact that the pressure in the vicinity of the central row of openings is less. An abrupt change in pressure might cause fibrous material deposited on the carrier adjacent the inner edge of the outer rows of tubes 206 to migrate to areas of the carrier adjacent the center row of tubes. The sculpturing of the bars 232 also permits a suction force to be created at the surface of the bars and thereby effects a deposit of material on areas of the screen adjacent thereto which might otherwise be deprived of material. The material deposited at the bars 232 assumes the form of the fillet 54 at the merger of the central portion 50 and the edge portion 52 of the web 42 of the illustrated embodiment.

As previously mentioned, the clearance between the rearward end portions 158 of the inner wall members 150 and the carrier 44 is suflicient to permit movement of the carrier transversely of the conduit 32 without engagement between the carrier and the edges of the wall members. This clearance, of course, also creates a leakage gap 233 capable of allowing air to bypass the edge of the wall members. For example, it should be appreciated that the flow of air through the conduit adjacent the gap 233 creates a suction efi'ect which tends to draw air through the gap and into the conduit. If this inwardly directed air flow is of sufficiently high velocity, it tends to roll the edges of the web and, thus, is undesirable. On the other hand, it should be noted that the edge portions of the carrier 44 lie beyond the side walls 150' of the conduit and are exposed to the suction created by the edge portions of the vacuum box. This arrangement is particularly desirable when the web is being laid directly on a tissue sheet which is wider than the web, in which case the suction through this portion of the carrier tends to hold the edges of the tissue fiat against the carrier. However, this suction also tends to draw air through the gap 233 and outwardly of the conduit. If this air flow is of sufficiently high velocity, it causes loose fibrous mate- 10 rial to be diverted from the conduit and is likewise undesirable.

Ideally, the pressures on opposite sides of the gap 233 should be balanced so that there will be no air flow through the gap. This condition is approached Within the balancing chambers 152 through the use of elongated horizontally oriented plates 234 which are adjustably mounted in vertical rows on support columns 236 positioned on opposite sides of the vacuum box. The plates 234 are disposed in partially obstructing relationship to the outer row of openings 196 and, more specifically, to those portions of the outer rows of openings which are located behind the edge portions of the carrier 44. Hence, by varying the position of the plates, the degree of suction through the edge portions of the carrier adjacent the gap 233 can be controlled. While an ideal arrangement is achieved when the pressures on opposite sides of the gap are equal, such precise equilibrium is diflicult if not impossible to achieve. Accordingly, the plates are preferably positioned so that there is a slight fiow of air inwardly of the conduit. This slight inward flow eliminates the possibility of outward flow and, hence, insures that no fibers will pass outwardly of the conduit. The flow is not great enough to cause rolling of the web, however.

The carrier screen is preferably of a fine mesh to prevent fibrous particles from passing through it, although a coarser screen may be used when the web is laid directly onto a carrier sheet 56 supported by the screen. The carrier screen is in the form of a continuous or endless traveling loop which encircles the vacuum box 40 and is supported at various points thereabout by rolls located within the loop. The loop is arranged so that a generally flat upright portion thereof is located within the conduit 32 in the path of the air stream, is oriented generally transverse to the longitudinal axis of the delivery duct 60 and is continuously .moved upward. The angle between the plane of this portion of the carrier and the longitudinal axis of the delivery duct should be close to so as not to provide the fibers with a migration-inducing velocity component parallel to the surface of the screen. However, in a preferred embodiment, the flat upright portion of the screen is disposed at an angle of to the longitudinal axis of the duct 60 to compensate for the relative motion of the screen and air stream as the screen moves upwardly within the duct. That is, the angle between the carrier screen and the vertical is 5 greater than the angle between the longitudinal axis of the duct 60 and the horizontal.

The carrier is supported (FIG. 9) by a pair of relatively large diameter rolls 238 and 240 supported with their axes horizontal. The lowermost roll 238 is located forwardly of the vacuum box and forwardly of the uppermost roll 240, which is located above and rearwardly of the vacuum box. These rolls support the carrier in the area in which it receives the web and, because of their relative locations, provide this portion of the carrier with an upwardly and rearwardly inclined disposition conductive to retention of the formed and forming web.

The screen 200 is also supported by a pair of vertically spaced horizontally disposed rolls 242 and 244 of lesser diameter than the rolls 238 and 240. The rolls 242 and 244 are arranged with the lowermost roll 242 disposed behind and below the vacuum box, and with the uppermost roll 244 behind and above the vacuum box and also behind and above the roll 242. Also, the vertical spacing between the rolls 242 and 244 is less than the spacing between the larger rolls 238 and 240. One or all of the rolls 238, 240, 242 and 244 may be driven by suitable power means (not shown).

The outer rearward surface of the loop of the screen is engaged intermediate the smaller rolls 242 and 244 by a roll 246 which bears against the screen and is adjustable in the direction of the screen so as to enable it to take up slack in the screen. When it is desired to deposit the web 1 1 onto a base or carrier sheet 56 rather than directly onto the screen 230, the roll 246 also serves to guide the sheet 56 into engagement with the screen. In such an instance, the roll 246 places suflicient tension on the sheet to insure that it will remain in close contact with the screen until it is removed therefrom.

It will thus be seen that a carrier section is always disposed within the conduit 32 to receive the loose fibrous material and that this carrier is always moving transverse to the longitudinal axis of the conduit. In the illustrated embodiments, this carrier is defined by a section of the screen 200 which may or may not support a section of a base sheet 56.

Also disposed adjacent the outer surface of the carrier loop is a compressing and sealing roll arrangement 248 (FIGS. through 17) which effects engagement of the web 42 immediately after it is formed to provide it with a uniform configuration and a more compact consistency, and also serves to provide a seal between the carrier 44 and the top wall 140 of the delivery duct. A roll (not shown) is preferably also provided to afford a seal between the carrier and the bottom wall 142 of the delivery duct. This roll, of course, serves no compressing function. The roll arrangement 248 comprises generally a center section 250 and a pair of flanking outer sections 252 and 254. The center section is adapted to engage the central portion 50 of the Web and the flanking sections are each adapted to engage the side or edge portions 52 of the web. All of the roll sections rotate at the same speed incident to a driving connection with the uppermost large diameter support roll 240 of the. carrier screen. Since all portions of the web move at the same linear speed, all of the rolls are equal in diameter so as to have the same tangential velocity for a given speed of rotation. However, since the center portion 50 of the web is of greater thickness, the axis of rotation of the center roll section 250 is offset relative to the axes of the flanking rolls 252 and 254, as can be seen in FIGURE 17.

More specifically, the flanking outer section 252, located to the left as viewed in FIGURES 15 and 17, is of generally hollow cylindrical construction provided with solid end walls 255 to which are secured a horizontally disposed shaft 256 rotatably supported in bearings 258 provided at one end of a stationary strut 260. A pulley 262 is secured to one end of the shaft 256 and is connected by means of a belt 264 to a pulley 266 supported on a drive shaft 268 driven through a sprocket and chain connection 270, through a gear reduction 272 to the shaft 274 about which the upper large diameter roll 240 rotates. Hence, driving movement of the shaft 274 indirectly imparts rotation to the shaft 256 of the flanking roll section 252.

The central roll section 250 is of generally solid cylindrical construction and is secured at its end face farthest from the section 252 to a shaft 276 which extends away from the roll section 252 and is supported adjacent its outer end in bearings 278 provided at one end of a second stationary strut 280. A pulley 282 is secured to the shaft 276 and is interconnected by means of a belt 284 to a pulley 286 aflixed to the end of the drive shaft 268. Hence, rotation of the drive shaft 268 also imparts rotation to the center roll section 250.

The second flanking roll section 254 is of generally hollow cylindrical construction, having cut-away end walls 288 permitting passage therethrough of the shaft 276 of of the center roll section 250, previously referred to. The flanking roll section 254 has secured to its outer end wall a hollow sleeve or extension 290 which is mounted for rotation in bearings 292 provided at one end of a third stationary strut 294. The sleeve 290 also has rigidly secured to it a pulley 296 connected by means of a belt 298 to a pulley 300 mounted on the drive shft 268. Thus, all three roll sections 250, 252 and 254 are individually rotatably mounted and are driven at a uniform speed by rotation of the drive shaft 268 which is, in turn, driven by rotation of the upper large diameter roll 240.

It will be noted that the top wall of the delivery duct 60 is cut away at its forward end to accommodate the roll arrangement 248. It will also be noted that an extension of the top wall of the delivery duct at the vacuum box would lie below the upper edge of the uppermost openings 196 into the vacuum box. In other words, the vacuum box has a larger effective area than the delivery duct and the difference between them, e.g. 12% of the area of the face of the vacuum chamber, occurs at their upper ends at the location of the roll arrangement 248. The vacuum box thus exerts a suction eflect at the roll arrangement 248 to enhance the scalability thereof.

In order to prevent the loose fibrous material from clinging to the roll sections and eventually causing a buildup of the material such as might interfere with the operation of the roll arrangement, cleaning blades 301 are provided which engage the roll sections as they rotate. In the illustrated embodiment (FIGS. 15 and 16), three separate blades are provided, each of which is rotatably supported on a common rod 302. Each blade is biased for rotation about the rod 302 in a direction which urges its edge into engagement with the surface of an associated roll by a tension spring 303 extending from a lever arm 304 to a suitable bracket 306.

The web, with or wihout a base sheet 56, as the case may be, is removed from the carrier screen 200 into a take-off roll 308 (FIG. 9), supported rearwardly of the screen loop and the vacuum box 40. When it is desired to provide the web with an upper wrap, such may be applied in the same area guided by other suitable means, such as the rolls 310. Air nozzles 312 are positioned within the loop in the vicinity of the take-oh roll 308 to direct jets of air outwardly through the carrier screen, thereby assisting in the separation of the web from the screen and cleaning the screen of adhering fibrous particles.

Referring again to the conduit 32 of the apparatus 30 (FIG. 2) the blower 38 is connected by means of a pipe 314 to the air processing unit 64 which removes a portion of the air from the system, preferably so as to maintain a vacuum pressure throughout the entire system, and which also cleans the air and removes moisture from it. The treated air remaining in the system is delivered past the charging port 34, as previously described.

To summarize briefly the operation of the apparatus in providing the web shown in FIGURE 14, a continuous stream of air flows through the conduit 32 due to the operation of the blower 38. As the air stream passes the material charging port 34, a quantity of loose fibrous material is deposited into it and is conveyed by the air stream toward the carrier 44 which is disposed immediately forwardly of the vacuum box 40. Adjacent this carrier, however, are disposed the baflles 46 which influence the air stream so as to cause the central portion thereof to have a greater velocity than the adjacent portions. In addition, the valves 48 of the suction port arrangement of the vacuum box cause a greater suction force to exist on the central portion of the carrier than on the flanking portions. The effect of the baffles and the valves causes a greater amount of the fibrous material to be deposited on the central portion of the carrier than on the remaining portions, forming a Web 42 having a raised central portion 50 flanked by side portions 52, asis desired. The web is subjected to the action of the compressing roll arrangement 248 and then removed from the carrier screen 200. The particular web shown is, of course, highly suitable for incorporation into a diaper.

FIGURES 18-22 illustrate a portion of an air laying unit 30a which constitutes an alternate embodiment of the apparatus of the invention. Very generally, this unit comprises a conduit 32a adapted to contain an air stream conveying fibrous material and a carrier 44a upon which the fibrous material is deposited. In the alternate method employed through the use of the unit 30a, a web of nonuniform cross sectional configuration is obtained by shielding predetermined areas of the carrier 44a from the air stream and by diverting the air stream so as to concen- 13 trate the flow of fibers to unshielded portions of the carrier.

For purposes of discussion, that area of the carrier 44a of the illustrated embodiment which is located within the conduit 32a and exposed to the air stream will be considered as comprising three segments, namely, an elongated narrow center segment 316 which extends in the direction of movement of the carrier, and a pair of flanking or side sections 317. In the preferred alternate method of obtaining a web 42a, a portion but not all of each flanking segment 317 is shielded while the center segment 316 remains unshielded. Thus, the amount of fibrous material which arrives at and is deposited on each flanking segment is reduced or, to put another way, the amount of time during which the flanking segments are exposed to the air stream relative to the center segment is controlled. As a consequence, a lesser amount of fibrous material is deposited on the flanking segments than on the center segment. In addition, portions of the airstream originally destined for the flanking segments 317 are deflected onto the center segment 316, thus providing for an even greater buildup of material on such segment.

Referring now to the unit 30a employed in carrying out the alternate method, the conduit 32a includes a delivery duct 60a which is identical in construction to the duct 60 of the principal embodiment except that it contains no bafi'les 46 as such. Positioned at the one end of the conduit 32a is a vacuum box 400 which is essentially open along its rearward wall and which includes three valves 46a arranged in a single centrally disposed generally vertical row adjacent the upper edge of the front of the box. In this respect, the vacuum box 40a differs from the vacuum box 40 of the principal embodiment in which three vertically oriented rows of valves 46 are arranged side by side, each row containing twelve valves to provide a total of thirty-six. T he traveling carrier screen 44a is supported in loop form by rolls 238a, 240a, 242a, 244a and 246a and is identical to the carrier 44 of the principal embodiment, sealing and pressing roll arrangement 248a is also identical to the roll arrangement 24% of the principal embodiment.

A portion of each flanking segment 317 of the exposed area of the traveling carrier is shielded from the fibercarrying air stream by a shield 318. Each shield of the illustrated embodiment comprises a solid block of generally prismatic configuration which includes a pair of generally parallel triangularly shaped surfaces 319 and 320 and rectangular side walls 322, 324 and 326. The side walls 322 and 324 are mutually perpendicular while the surface 326 is opposite their included angle. The shields are arranged within the conduit 32a with the triangularly shaped surfaces 319 and 320 being uppermost and lowermost respectively and positioned generally parallel to top and bottom walls 328 and 330 of the delivery duct 60a. The uppermost surface 319 is positioned immediately adjacent the lower surface of the top wall 328. The rectangular-Side wall 322 of each shield is disposed flush with a side wall 332 of the delivery duct 60a, while the side wall 324 extends from the rearward edge of the wall 322 and is disposed at right angles to the side wall 332 of the delivery duct, normal to the air-stream, in adjacent and generally parallel relation to the carrier 44a.

The wall 326 of each shield extends from the forward edge of the wall 322 to the inner edge of the wall 324 and is thus inclined inwardly and rearwardly relative to the side walls 332 of the delivery duct 60a. Thus, the wall 326 extends into what would otherwise constitute the path of the air-stream and is engaged by the air-stream. It therefore shields from the air-stream that portion of the carrier 44a which lies behind it, i.e., a portion of a flanking segment 3.17, so as to allow fewer particles of fibrous material to reach such segment. In addition, because of its inclination, the wall 326 deflects portions of the air-stream toward the unshielded central segment 316 of the carrier.

It has been found desirable to position the shields 318 with the walls 324 thereof located sufliciently close to the carrier so that fibrous material will not have an opportunity to invade the area between the wall and carrier after passing the rearward edge of the inclined wall 326. On the other hand, it should be realized that the portion of the air-stream which is deflected by the inclined wall 326 will have a lateral velocity component immediately after passing the rearward edge of this wall and that such a component could cause an undesirable rolling of the fiber on the carrier, as previously set forth. Thus, it is preferable that each shield be spaced from the carrier at sufiicient distance to allow the deflected portion of the air-stream to resume a direction of travel generally parallel to its direction of travel before deflection, i.e., to allow it to resume a direction of travel normal to the face of the carrier. In a preferred embodiment, a distance of three inches between the wall 324 of the shield 318 and the forward face of the carrier 44a has been found to be satisfactory in both regards.

While the shields 318 could conceivably be located adjacent any section of the longitudinally extending flanking segments 317 of the carrier to provide the desired web configuration, it is preferable that they be located adjacent the top wall 328 of the delivery duct 60a since there is a tendency for the fibers to gravitate toward the bottom wall 330 and, if the shields were located adjacent this bottom wall, the fiber might accumulate behind the shields and be delivered in clumps to the carrier from time to time.

The width of the area of the carrier which is shielded is determined by the size of the inclined surface 326 and its angle of inclination. In the illustrated embodiment, in which the surface 324 is normal to the air-stream, the effective width of the surface 326 is equal to the width of the surface 324. Thus, the width of the area shielded, i.e., the width of the flanking segments 317, corresponds generally to the distance which the surface 324 extends inwardly of the center of the delivery duct 6041. In the use of the apparatus to produce a web having the configuration shown in FIGURE 14, the width of the surface 324 approximates the desired width of the thinner flanking sections 52 of the pad. In like manner, the distance between the innermost edges of the walls 324 or 326 approximate the width of the thicker central portion 50.

Each shield 318 shields only a portion of a segment 317 of the carrier 44a. The height of the surface 324, as measured along the inner edge thereof, relative to the total height of the delivery duct, determines the percentage of the segment 317 which is shielded and, thus, determines the ultimate thickness of those areas of the pad partially shielded relative to what the thickness of the pad would have been had it not been shielded. Thus, if the height of the shields 318 was equal to two-thirds of the height of the duct, the amount of material deposited on the segments 317 would equal approximately onethird of what the flow would be were the shields not provided. Since the portions of the air-stream which do not engage the shielded portions of the segments 317 are deflected onto the central segment 316, however, the thick ness of the material deposited on that segment will be significantly greater than three times that deposited on each of the segments 317, absent other adjustments.

The use of a solid shield causes the area behind the inclined surface 328 to be enclosed and prevents portions of the air-stream from swirling into such areas. Such a condition might give rise to an accumulation of fiber in this area which would periodically return to the airstream in clumps and cause an uneven buildup on the carrier. Of course, a shield defined by a hollow enclosure would function equally well in this regard.

While the invention has been shown and described with respect to two specific structural embodiments of an apparatus constructed in accordance therewith, it should be apparent various structural modifications may be made in the apparatus shown without departing from the scope of the invention. Also, it should be clear that the method of the invention might also be performed by other apparatus, and that webs of various profiles might be produced, all within the scope of the present invention.

Various of the features of the invention believed to be novel are set forth in the following claims.

What is claimed is:

1. A method of forming on a carrier a continuous, integral, fibrous web having a centrally disposed, longitudinally extending strip which has a uniform and predetermined width less than the width of the Web and a thickness greater than flanking portions of the web, said method comprising continuously moving an air pervious carrier along a given path, mixing fibrous material into an air stream and providing a substantially uniform distribution of fibrous material in said air stream, narrowing said fiber bearing'air stream to increase the velocity of the air and to increase the quantity per unit time of the air-borne fibrous material in the central portion of the air stream, expanding said air stream while said central portion thereof retains a velocity and a quantity per unit time of loose fibrous material greater than the velocities and quantities per unit time of loose fibrous material in the flanking portions of the air stream, establishing behind said carrier a first region at a first reduced pressure to draw said central portion of said air stream conveying said first quantity of fibrous material directly through the central portion of said carrier at the same rate as air approaches said central portion of said carrier thereby depositing said first quantity of loose material on said central portion of said carrier, and establishing behind said carrier at portions flanking said central portion another region at a second reduced pressure to draw the air carrying said second quantity of fibrous material directly through said flanking portions at the same rate the air approaches said second flanking portions thereby depositing said second quantity of loose material on said flanking portions of said carrier, the pressure in said second region being greater than the pressure in said first region.

2. A method in accordance with claim 1 including the step of mixing said loose fibrous material and the air bearing the same with jets of air arranged in a staggered relationship.

3. A method in accordance with claim 1 in which said fibrous material is formed from a sheet of wood pulp, and including steps of moistening and defibrating said sheet into said loose fibrous material.

4. A method in accordance with claim 1 including the step of depositing said loose fibrous material on an air pervious, creped tissue web.

5. A method of forming a continuous, fibrous web having a longitudinally extending strip which has a uniform and predetermined width less than the width of the web and a thickness greater than that of the remainder of the web, said method comprising continuously moving an air pervious carrier at a uniform rate successively through a first region and a second region downstream thereof along a given path, conveying loose fibrous material suspended in air to said first region along said path, in said first region passing the air through said carrier over a first predetermined transverse portion thereof while at the same time depositing said loose fibrous material on said carrier over said first portion, conveying loose fibrous material suspended in air to said second region along said path downstream from said first region, and in said second region passing the air through said carrier over a second predetermined transverse portion thereof which is different from said first portion but includes at least part of said first portion while at the same time depositing said loose fibrous material on said carrier over all of said second portion including that part common to said first portion and overlapping loose fibrous material on said material previously deposited on said common part, thereby providing said greater thickness at said common part of said first and second portions of said carrier and producing said longitudinally extending strip for said web.

6. A method in accordance with claim 5 including the step of conveying said loose fibrous material for deposition at said first and second portions in a single air stream and deflecting said air stream adjacent one of said portions to deposit said loose fibrous material in said first and second portions in respective widths different in the direction transversely of the carrier path.

7. A method in accordance with claim 5 including the step of directing said fibrous material in said second region to a position centered with respect to said fibrous material previously deposited at said first portion to form said strip centrally of said web.

References Cited UNITED STATES PATENTS 735,217 8/1903 De Long 19-148 1,510,252 9/ 1924 Wilhelm. 2,648,876 8/1953 Phillips et al. 19156.3 2,890,497 6/1959 Langdon et al. 3,114,939 12/1963 Labino 19156.3 3,187,387 6/1965 Schuller 19156.3 3,235,913 2/1966 Schuller 19156.3 3,396,433 8/1968 Roylo 19--156.3

DORSEY NEWTON, Primary Examiner

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