Apparatus For Making Nonwoven Fibrous Webs

Abstract

An apparatus wherein a plurality of fibers are transported to and deposited on a foraminous conveyor by a flow of gas to form a nonwoven fibrous web. The passage of the flow through the conveyor is regulated by two independently operable, superposed means for selectively restricting such passage to control the deposition of the fibers on the conveyor and thereby control the thickness of the web.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and apparatus for making nonwoven webs, and particularly to a method and apparatus for making a nonwoven fibrous web wherein the thickness of the web is accurately controlled, including desired transverse variations in thickness.

2. Description of the Prior Art

Various methods and apparatus are known for making nonwoven fibrous webs, including webs adapted to be used as absorbent pads. Exemplary of the prior art methods and apparatus of this general type are those disclosed in Bertolet U.S. Pat. No. 2,581,069, Anderberg et al., U.S. Pat. No. 3,032,836, Labino U.S. Pat. No. 3,114,939 and Nordstrand U.S. Pat. No. 3,423,796. The apparatus disclosed in these patents include means for pneumatically depositing a plurality of fibers on a foraminous conveyor and means for controlling the deposition of the fibers, such as a plurality of pivotally mounted vanes positioned adjacent the conveyor. While such vanes are useful for controlling the thickness of the webs, they do not provide sufficient control over the pneumatic deposition means to permit the formation of webs having desired transverse variations in thickness.

For some uses of nonwoven fibrous webs, it is desirable that the webs have transverse variations in thickness. For example, a web having a central portion of greater thickness than the marginal portions, is ideally suited for use as an absorbent pad in a disposable diaper.

SUMMARY OF THE INVENTION

The method and apparatus of the present invention provide an effective and efficient solution to the above-mentioned deficiency of the prior art methods and apparatus, and are ideally suited for making nonwoven fibrous webs adapted for use as absorbent pads. Basically described, the apparatus of the invention comprises; a chamber; a foraminous conveyor having a portion extending through the chamber; means for generating a flow of gas through the chamber, said chamber being operable to direct the flow through said conveyor portion; means for feeding a plurality of fibers into the flow so that the fibers are transported to and deposited on said conveyor portion by the flow to thereby form a web; and first and second independently operable, superposed means for adjustably restricting the passage of the flow through said conveyor portion to control the deposition of the fibers on said portion and thereby control the thickness of the web.

Generally described, the method of the invention comprises; directing a flow of gas through a foraminous conveyor; feeding a plurality of fibers into the flow so that the fibers are transported to and deposited on the conveyor by the flow to thereby form a web; and regulating the passage of the flow through the conveyor to control the deposition of the fibers thereon and thereby control the thickness of the web, said regulating including adjusting two independently operable, superposed means for restricting the passage of the flow through the conveyor.

One of the independently operable passage restricting means preferably comprises a plate positioned adjacent the conveyor and having an opening therein. The other independently operable passage restricting means preferably comprises a plurality of movably mounted vanes also positioned adjacent the conveyor. The size and shape of the opening in the plate and the attitude of the vanes may be adjusted independently to produce a web having accurately controlled thickness variations transversely of the web.

The conveyor preferably includes a wire mesh belt, and the gas flow generating means preferably comprises a conventional blower. The blower preferably is connected to a suction box and the conveyor and passage restricting means preferably extend across the upper end of such box.

The fiber feeding means preferably comprises a pin mill adapted to abrade a sheet of wood pulp. The pin mill preferably is mounted above the suction box so that the pin mill and suction box form a chamber through which an air flow generated by the blower passes. The chamber thus directs the flow through the conveyor and passage restricting means so that the wood fibers are transported to and deposited on the conveyor by the flow.

With the foregoing in mind, it is an object of the present invention to provide an improved method and apparatus for making nonwoven fibrous webs.

It is also an object of the invention to provide a method and apparatus for making nonwoven fibrous webs having controlled transverse variations in the thickness thereof.

It is an additional object of the invention to provide a method and apparatus for making nonwoven fibrous webs in which a plurality of fibers are deposited on a foraminous conveyor by a flow of gas and in which the thickness of the web formed by such deposition is controlled by two independently operable, superposed means for restricting the passage of the flow through the conveyor.

These and other objects of the invention will be apparent upon a consideration of the following detailed description of the preferred embodiments thereof given in connection with the following drawings, wherein like reference numerals identify like elements throughout.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevational view, partially in section, of the apparatus of the invention;

FIG. 2 is a sectional view taken on line 2--2 of FIG. 1; and

FIG. 3 is a sectional view taken on line 3--3 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the apparatus of the invention is shown in the drawing, as designated by reference numeral 10. Apparatus 10 includes a pin mill 12 comprising a housing 14, and disposed within the housing, a pair of rotatably mounted feed rolls 16, a rotatably mounted attrition roller 18 and a nose bar 20 positioned between the feed rolls and attrition roller. Feed rolls 16 and attrition roller 18 are rotatably driven by conventional drive mechanisms (not shown). A feed slot 22 is formed in the side of housing 14 adjacent feed rolls 16. Also, a pair of openings 24 are formed in the side of the housing to permit air to enter the housing for a purpose described below, and a pair of windows 26 are mounted on opposite sides of the lower portion of the housing through which the operation of mill 12 may be observed.

A conveyor 28 is mounted below mill 12 and includes a foraminous wire mesh belt 30 and a plurality of rotatably mounted guide rolls 32 about which belt 30 is trained. One of rolls 32 is rotatably driven by a conventional drive mechanism (not shown). The upper run of belt 30 extends across the open lower end of housing 14.

A suction box 34 also is mounted below mill 12. The upper run of belt 30 extends across the open upper end of suction box 34, and the lower end of housing 14 is connected to the upper end of box 34 along the sides of the upper run of belt 30 so that the housing and suction box form a chamber 35 through which the upper run of the belt extends. If desired, a pair of resilient surfaced rollers 36 may be rotatably mounted on the lower end of housing 14 directly above and contacting belt 30 adjacent the entrance and egress of the belt to and from chamber 35. Rollers 36 minimize the flow of air into chamber 35 through the openings provided therein at the juncture of the lower end of housing 14 and upper end of box 34 through which belt 30 extends, for reasons which will become apparent below.

A pair of conduits 38 are connected between the ends of suction box 34 and a conventional blower 40. Blower 40 generates a flow of air through chamber 35 with air being drawn into housing 14 through openings 24 and out of suction box 34 through conduits 38. As will be apparent, the flow moves downwardly from housing 14 and into suction box 34 through the upper run of belt 30.

A rolled sheet 42 of wood pulp is rotatably supported adjacent housing 14. Sheet 42 is fed into the housing through feed opening 22 and between feed rolls 16. Rolls 16 feed the sheet across nose bar 20 and against the surface of attrition roller 18. The attrition roller abrades sheet 42 into individual wood fibers 44 and urges the fibers downwardly into the flow of air through housing 14. Fibers 44 are transported to the upper run of belt 30 and deposited thereon by the air flow, incident to movement of the flow from housing 14 into suction box 34. The fibers thus form a nonwoven fibrous web 46 on the upper run of the belt. Web 46 is thereafter transported out of chamber 35 by belt 30 and deposited on the belt of a transfer conveyor 48.

Apparatus 10 includes means for controlling the thickness of web 46, and in particular for varying the thickness of the web transversely thereof. Such means comprise two independently operable, superposed means for adjustably restricting the passage of the air flow through the upper run of belt 30. One of the passage restricting means comprises a plate 50 positioned beneath the upper run of the belt and having an opening 52 therein. The passage of the air flow though the portion of belt 30 adjacent plate 50 is thus restricted to the area of opening 52.

The other passage restricting means comprises a plurality of movably mounted vanes 54 positioned below plate 50. Vanes 54 preferably are pivotally mounted in the upper end of suction box 34 and extend transversely of belt 30. Vanes 54 may be individually pivoted to differentially restrict the passage of the air flow through the adjacent portion of belt 30.

Plate 50 and vanes 54 permit the thickness of web 46 to be accurately controlled, including variations in the thickness of the web transversely thereof. As mentioned above, this latter feature is particularly advantageous for making webs which are adapted to be used as absorbent pads.

Opening 52 may be of any desired shape and size to provide the desired fiber deposition pattern. The deposition pattern may be further controlled by individually adjusting the attitude of vanes 54.

An example of the combined effects of plate 50 and vanes 54 is illustrated by the embodiment of the apparatus shown in the drawing. In this embodiment, opening 52 extends generally diagonally across plate 50 and is narrower at the ends thereof than at the central portion thereof. Thus, a greater volume of air is permitted to pass through the central portion of the opening than at the ends thereof. Consequently, a greater number of fibers 44 are deposited on the central portion of belt 30 as the belt passes over plate 50 than on the marginal portions of the belt, and the resulting web 46 will have a central portion of greater thickness than the marginal portions. This particular web configuration is well suited for use as an absorbent pad in a disposable diaper.

The deposition of fibers 44 may be further controlled by individually adjusting vanes 54. In the embodiment of the apparatus shown in the drawing, the vanes are all adjusted to the same attitude so that the vanes do not differentially restrict the passage of the air flow through belt 30. However, if a further reduction in the thickness of the marginal portions of web 46 is desired, the vanes which underlie the narrower portions of opening 52 may be partially closed to thereby further restrict the passage of the flow through the adjacent portions of belt 30. Thus, a still greater number of fibers 44 will be deposited on the central portion of the belt and a lesser number will be deposited on the marginal portions of the belt. Other variations in the size and shape of opening 52 and the attitude of vanes 54 may be employed to provide other transverse variations in the thickness of web 46.

The method of the invention will be apparent from the foregoing description of the apparatus thereof.

The method and apparatus of the invention are effective and economical for making nonwoven fibrous webs, and particularly webs having transverse thickness variations, and thus are ideally suited for making webs adapted to be used as absorbent pads.

While the foregoing constitutes a detailed description of the preferred embodiments of the method and apparatus of the invention it is recognized that various modifications thereof will occur to those skilled in the art. For example, while the preferred embodiment of the apparatus includes a pin mill specifically adapted for feeding a plurality of wood fibers onto belt 30, other fiber feeding means as appropriate for the particular type of fibers desired may be employed. Thus, the invention is to be limited solely by the scope of the appended claims.

Claims

I claim:

1. An apparatus for making non-woven fibrous webs having transverse variations in thickness comprising:

a chamber;

a foraminous conveyor having a portion extending through said chamber;

means for generating a flow of gas through said chamber, said chamber being operable to direct said flow through said conveyor portion;

means for feeding a plurality of fibers into said flow so that the fibers are transported to and deposited on said conveyor portion by said flow to thereby form a non-woven web;

first means for restricting the passage of said gas flow through said conveyor portion comprising a plate positioned adjacent said conveyor portion on the downflow side thereof and having a generally diagonally extending opening thereacross for the passage of the gas flow therethrough, said diagonal opening is narrower at the ends thereof than the central portion thereof, thereby permitting a greater volume of gas to pass through the central portion of the opening than the ends thereof and

second means for restricting the passage of said gas flow through said conveyor portion comprising a plurality of movably mounted vanes superposed with respect to said plate.

2. An apparatus as recited in claim 1, wherein each of said vanes is mounted for pivotal movement about an axis extending transversely of said conveyor portion, whereby the fiber deposition pattern may be further regulated by differentially adjusting the vanes.

3. An apparatus as recited in claim 1, wherein said conveyor comprises a wire mesh belt.