Multi-ply Two Wire Former Wherein Multiple Headboxes Are Used And Inflatable Air Bellows Provide Adjustments Therebetween

Abstract

A method and mechanism for forming multi-ply continuous fibrous web by providing a twin wire former including first and second looped forming wires positioned to provide a dewatering run therebetween with a tapered throat at the upstream end of the run and supporting rolls within each of the wires including suction breast rolls having a plurality of suction glands within the rolls for the graduated application of suction to the wires and an intermediate headbox delivering a jet of stock slurry into the throat with outer headbox delivery outer jets for the outer layers of the web and the intermediate jet being delivered after the dry line of the outer layers. Air inflatable bellows are connected between the inner slice lips of the outer headboxes and the slice walls of the intermediate headbox to control the thicknesses of the outer plys.

Description

BACKGROUND OF THE INVENTION

The invention relates to improvements in methods and structures for making multi-ply web and particularly to a paper making machine wherein the web is formed of layers of stock with the layers having different characteristics.

While the principles of the invention can be employed in making webs of various types, such as nonwoven fabrics, they are particularly well adapted to use for making multi-ply paperboard and will be described principally in that environment. In the manufacture of multi-ply board, layers having different characteristics are used. The center or intermediate layer is frequently employed as a filler to give body and stiffness to the board while the outer layers, at least on one side is usually of a finer grade which has ink receptivity for receiving printing. To improve the quality of this board and to maintain the manufacturing cost at a minimum, each ply should be well formed and perform its function to contribute to the characteristic of the board as a whole. For this purpose it is desirable to avoid mixing of the plys and yet it is essential that the plys bond to each other with optimum strength.

To provide strength and body to the intermediate layer, it is essential that optimum strength formation with the type of stock provided be obtained. A minimum of flocculation will, of course, add to the strength and uniformity of thickness of the intermediate layer and provide the best strength intermediate layer for functioning to support the outer layers. Multi-ply board has been conventionally made by various processes and primarily by being made on cylinder machines where successive plys are formed on cylinders immersed in slurries of stock and with the stock layer being formed on the uprunning side of the cylinder as it emerges from the vat of the slurry. As each successive layer is formed, it is fed onto the top of a layer formed in another cylinder until the requisite number of layers are completed. This requires forming the intermediate layer by a conventional cylinder forming method which does not obtain absence of flocculation. Also, in this method of manufacture, good bonding between layers is not always attained since each of the layers are substantially dewatered when laid on the top of another layer and, therefore, interlacing or bonding between the fibers of the different layers is not achieved.

An object of the present invention is to provide an improved method of making multi-ply web wherein a better intermediate layer is formed with better fiber distribution for improved qualities of strength and uniformity.

A further object of the invention is to provide a multi-ply web making machine wherein the intermediate layer and the outer layers are formed substantially simultaneously with the intermediate layer being dewatered through the outer layers for improved bonding between layers, and with the intermediate layer formed of a higher consistency stock to reduce the amount of water which must flow through the outer layers. This includes the objective of an improved mechanism and method of forming the intermediate layer by preventing flocculation of the higher consistency stock.

A further object of the invention is to provide a mechanism for making multi-ply web wherein the plys are formed of different stock slurries which are dewatered substantially at the same time and wherein intermixing between the slurries is maintained at a minimum.

A feature of the present invention is the provision of a twin wire forming machine wherein outer layers are fed into a forming throat slightly in advance of the intermediate layer to prevent intermixing and the intermediate layer is fed into the throat after the dry line of the outer layers and is provided with a high consistency stock with means preventing flocculation of the high consistency stock.

Other objects, advantages and features, as well as equivalent structures and methods which are intended to be covered herein, will become apparent to those versed in the art in connection with the teaching of the principles of the invention in the disclosure of the specification, claims, and drawings, in which:

DESCRIPTION OF THE DRAWINGS

The FIGURE of the drawing is a somewhat schematic elevational view showing a multi-ply web making machine constructed and operating in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The mechanism includes first and second looped continuous forming wires 10 and 11. The wires are strung over supports so that they come together to form a dewatering run 12. Upstream of the dewatering run is a converging throat 13. In the dewatering run the wires travel through an arcuate path over a box 15 having a plurality of cross-machine extending foils 15a which are spaced in the machine direction so that the wires actually extend in sequential chordal spans between the foils. The wires gradually converge applying normal pressure to the layers of stock therebetween and water passes out through both sides of the wires 10 and 11 along the dewartering run 12. Following the box 15 is a suction box 25 within the wires 11 for additional dewatering, and the web will follow the wire 11 around a couch roll 16 which has a suction gland 16a. The web will be picked off of the wire 11 by a pick-up roll 17 having a suction gland 17a therein and carrying a pick-up felt 18. The wire 11 is additionally trained over return and tension rolls 19 and 20.

The wire 10 wraps up over the couch roll 16 being trained thereover by its couch roll 21, and it returns over a roll such as 22.

The wires 10 and 11 are carried into the forming throat 13 over breast rolls 23 and 24.

Within the breast rolls are a series of sequential suction glands such as shown at 23a, 23b and 23c for the suction roll 23 and at 24a, 24b and 24c for the suction roll 24. The suction rolls 23 and 24 have the usual perforate rotary shell structure, and the sequential glands are each connected to their own source of suction for drawing water through the shell and applying suction to the layer of slurry deposited on the wires to form the outer layers of the multi-ply web. Preferably, suction is applied so that it increases from 24a through 24c, and similarly so that it increases from 23a to 23c.

The first outer layer of the multi-ply web is formed by stock delivered through a slice opening 29 and the opposite outer layer of the web is formed by stock delivered through a slice opening 31. The slice opening 29 is formed between slice lips 39 and 40. The slice opening 31 is formed between slice lips 41 and 42. The inner slice lips 40 and 42 extend for some distance into the forming throat to guide the stock and aid in its initial formation on the wires 10 and 11.

The intermediate layer of stock is delivered through a slice opening 30 between the outer openings 29 and 31.

Stock for the intermediate layer is provided from a headbox 26. Stock for the outer layers is provided from headboxes 27 and 28. Separate flows of stock are delivered to the separate headboxes 27 and 28 through separate supply lines 27b and 28b as shown schematically in the drawing. The headboxes 27 and 28 have flow tubes 27a and 28a respectively extending in the direction of stock flow for orienting the flow of the slurry and helping maintain uniform fiber distribution in the stock. The intermediate headbox similarly has a plurality of flow tubes 32 extending in the direction of stock flow and maintaining turbulence and energy in the stock.

The stock supplied to the intermediate headbox is preferably a high consistency stock inasmuch as it is dewatered through the outer plys which are placed onto the forming wires in advance of the discharge of the intermediate jet of stock through the slice opening 30. With this arrangement, the slice openings 29 and 31 are positioned to first deliver onto the wires and the dewatering effect through the wires is such that the intermediate layer is delivered into the throat to engage the outer layers after their dry line has been formed. This insures adequate formation of the outer layers so that there is not a mixing of the stock forming the plys. Yet, additional dewatering will occur through each of the three plys, and a sufficient bonding will occur between the fibers of the plys to provide a strong monolithic multi-ply board web. As the outer layers are first formed, and the intermediate layers subsequently fed between the outer layers in the throat 13, additional vacuum is applied through the suction regions 24b and 24c, and 23b and 23c to dewater through the outer layers. Subsequent dewatering occurs throughout the dewatering run 12 as the multi-ply web is pressed between the wires in its travel over the dewatering box 15 and the suction box 25 and over the couch roll 16.

In order to help maintain the fine scale turbulence and distribution of fibers in the relatively high consistency stock of the intermediate layer, a tapered slice chamber leading to the slice opening 30 is provided by the tapering slice walls 33 and 34 for the intermediate headbox 26. Immediately upstream of the tapering slice chamber is a plate 35 with a plurality of flow distribution openings therethrough. This plate provides a support for a plurality of cross-machine extending flexible trailing elements 36. These trailing elements are of plastic or similar flexible material and are anchored at their upstream ends only with their downstream ends self-positioned by the pressures of the flowing stock within the slice. The trailing elements 36 may be continuous sheets extending in a cross-machine direction, or may be divided into separate strands. They are preferably uniform in cross section, but may be tapered in a downstream direction. Suitable means are provided for attaching the trailing elements to the upstream plate 35 in such a manner that pockets are not formed where concentrations of fibers can collect.

Suitable stock delivery means are provided for each of the headboxes, and these will be fully understood by those versed in the art and are omitted from the drawings for the sake of clarity.

The intermediate headbox 26 is rigidly supported and has rigid outer walls 37 and 38. These walls support operating mechanisms for positioning the inner slice lips 40 and 42 of the slices for the outer headboxes. These operating mechanisms are shown preferably in the form of air inflatable bellows or diaphragms 43 and 44 which extend continuously in a cross-machine direction to provide uniform support to the movable walls which position the slice lips 40 and 42. Air at a controlled pressure is directed into these bellows 43 and 44 to adjust the position of the slice lips 40 and 42 and thereby control the thickness of the outer layers. The slice walls 33 and 34 or the distal end which controls the size of the slice opening 30 is movable by a mechanism not shown to control the thickness of the intermediate ply for the web.

Thus, it will be seen that I have provided an improved multi-ply web forming mechanism which meets the objectives and advantages above set forth. The multi-ply web formed is of improved strength in that it obtains optimum preformance from the intermediate ply which usually is formed of an inexpensive low quality stock, and with the present arrangement, a high consistency stock is employed for improved dewatering efficiency and yet flocculation is avoided and good fiber distribution is attained.

Claims

1. A forming mechanism for forming a multi-ply continuous fibrous web comprising in combination,

first and second looped forming wires positioned to provide a dewatering run therebetween with the wires converging to form a throat at the upstream end of said run,

a supporting open breast roll within each of the wires positioned for converging them to form said throat,

an intermediate headbox having a slice opening for delivering a jet of stock slurry to the throat for forming an intermediate ply of said web,

a first outer headbox having a slice opening for delivering a jet of stock slurry to the throat outwardly of the intermediate slice opening for forming an outer layer,

a second outer headbox having a slice opening for delivering a jet of stock slurry to the throat on the opposite side of the intermediate slice opening for forming an outer layer, and first and second separate stock supply means connected respectively for delivering separate supplies of stock to said first and second headboxes,

the stock from each of said outer headboxes having initial dewatering in said throat into said breast rolls,

said slice openings of said first and second outer headboxes positioned for delivery of the stock to the throat at a position upstream relative to the intermediate headbox slice opening so that a dry line appears before the intermediate jet of stock engages the outer layers of the stock on the

2. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 1 wherein said breast rolls are provided with suction glands therein and having an outer perforate

3. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 2 wherein each of said breast rolls has a series of separate suction glands to provide successive different negative pressures within the suction rolls for dewatering the outer

4. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 1 wherein said outer headboxes each have a movable slice lip adjacent the intermediate headbox with means for

5. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 4 wherein said means for moving said movable slice lips of the outer headboxes is a control mechanism mounted

6. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 5 wherein said slice lip moving mechanism consists of air bags mounted on the outer walls of said

7. A forming mechanism for forming a multi-ply continuous fibrous web constructed in accordance with claim 1 wherein said intermediate headbox has an elongate tapered slice chamber leading to its slice opening with a plurality of flexible trailing elements in said tapered slice chamber supported only at their upstream ends and positioned downstream of their

8. A forming mechanism for forming a multi-ply continuous web constructed in accordance with claim 7 wherein each of said headboxes has a plurality of separate flow passages extending in the direction of stock flow toward

9. The method of forming a multi-ply continuous fibrous web which comprises the steps,

training first and second looped forming wires to provide a dewatering run therebetween with a tapered forming throat at the upstream end of said run,

directing an intermediate jet of stock slurry into the throat for forming an intermediate ply of said web,

and directing separate outer jets of stock slurry each outwardly of the intermediate jet into the throat to engage the wires in advance of the intermediate jet for forming the outer layers of the multi-ply web,

said intermediate jet of stock being delivered into the throat at a location after the appearance of a dry line through the outer layers on the forming wires.