GB2046323A - Apparatus and method for forming multi-ply webs - Google Patents

Abstract

An apparatus for forming multiply web includes a headbox 16 having an upper chamber 19 and lower chamber 20 for fibrous stock to form the outer surface plies of a finished web, and an intermediate chamber 21 for receiving a high consistency stock with the headbox chambers delivering to portions of a slice chamber. The outer portions 33, 34 of the slice chamber discharge through a slice opening 30 onto a travelling forming surface and the slice chamber portions have flexible trailing elements 35, 36 unsupported at their downstream ends. The slice chamber has an intermediate portion 41 receiving stock from the intermediate chamber 21 of the headbox and being defined between solid walls 37, 38 which have inwardly facing surfaces 39, 40 forming a tortuous undulating path for the high consistency stock flowing therethrough. <IMAGE>

Description

SPECIFICATION Apparatus and method for forming multi-ply webs The invention relates to apparatus and methods for making multi-ply webs from plural supplies of stock each having fibres suspended in a liquid. More particularly, the invention relates to an improved high speed forming arrangement which is particularliy well adapted to making multi-ply paper web.

In the formation of multi-ply webs, machines to be competitive must cope with the problems of forming a stronger stiffer finished web having multi-plies and must operate at increasing rates of speed in a manner to either improve the characteristics of the finished web or at least not to detract from those characteristics. To achieve the characteristics of a good multi-ply web, an intermediate layer must be employed which lends increasing strength and stiffness and outer covering plies must be used which cover the intermediate ply and which present an improved smooth surfaced finish capable of having good appearance and having satisfactory and improved printing qualities.

Technology in paper making has led itself to the formation of multi-ply webs in a single operation wherein the plural plies are simultaneously delivered between opposed travelling forming wires rather than being formed in a layer at a time with the layers laid down on top of each other and bound to each other. A type of multi-ply web forming machine wherein the layers are simultaneously formed is illustrated in U.S. Patent Specification No. 3,923,593.

This patent specification illustrates the simultaneous forming of multiple plies with the centre ply having a high ash content for improved qualities of strength.

In the present invention, the problem of the high rates of water drainage which must be encountered is considered, and in a preferred embodiment of the present invention, a centre ply is formed of a high consistency stock, reducing the water drainage which must occur from the intermediate layer through the outer layers. It has been discovered that with the utilisation of a mechanism in accordance with the present invention, improved machine capacities and speeds may be achieved and a higher quality multilayer board may be obtained. In using a high consistency stock to form the middle ply, a finished board with greater bending stiffness has been achieved. Furthermore, a heavier higher basis weight board can be formed in a machine with no increase in the water removal capacity.Present commercial methods of forming three ply board on a twin wire former result in a limitation in basis weight of the order of 42 pounds per thousand square feet.

Using a high consistency stock of the order of 2% to 5%, an increase in basis weight up to 90 pounds per thousand square feet has been obtained. It is also anticipated that bleach board could be made in the range of 33 to 110 pounds per thousand square feet.

One of the difficulties in the formation of multi-ply board with a higher consistency centre layer has been the uneven formation and arrangement of fibres in the centre board resulting in a bumpy surface on the outer layers and resulting in a less strong and less stiff finished board. It is an object of the present invention to eliminate the problems of an uneven or bumpy surface board and to increase the overall stiffness of the board by treating the centre or intermediate layer of stock in a different manner from the outer finished layers so that an energetic fine scale turbulence is maintained in the outer layers while the thicker inner layer is treated to a controlled turbulence by passing the intermediate layer of stock through a buffeted tortuous path.

According to the invention there is provided a paper machine for making a multi-ply web from stocks having a slurry of fibres in a liquid carrier, and comprising: a headbox having a lower wall and an upper wall and including an upper chamber and a lower chamber for fibrous stocks to form outer surface plies for a finished web; said headbox including an intermediate chamber for fibrous stock to form an intermediate ply between said outer plies; first and second stock delivery means connected respectively to said upper and lower chambers for delivering fibrous stocks for the outer surface plies; intermediate stock delivery means connected to said intermediate chamber for delivering a high consistency stock thereto; a slice chamber extending from the headbox having upper and lower slice walls and having a slice opening to discharge onto a forming surface, said slice chamber having an upper and a lower slice portion connected to receive stock from said upper and lower headbox chambers respectively; and an intermediate portion of the slice chamber between said upper and lower portions defined by upper and lower intermediate slice walls having face undulating surfaces so that the high consistency stock will flow through a tortuous path before being discharged onto the forming surface between the layers issuing from said upper and lower portions.

The invention also provides a method of forming a multi-ply web from paper stocks having a slurry of fibres in a liquid carrier comprising the steps of: delivering stocks to form outer plies through outer headbox chambers and outer slice portions of a slice chamber onto a travelling forming surface; and delivering an intermediate layer between the outer plies of a relatively high consistency in the range of 2% to 5% with the high consistency stock being directed through an undulating tortuous path prior to being discharged onto the travelling forming surface.

The following is a detailed description of a preferred embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 is an enlarged section taken through a multi-ply board formed by methods heretofore available, Figure 2 is a similar vertical section taken through a portion of board formed in accordance with the present invention, and Figure 3 is a vertical section taken through a headbox structure constructed and operating in accordance with the invention.

Figure 1 illustrates an enlarged section of multi-ply web formed by processes heretofore available. The centre ply 10 was formed from high consistency stock using conventional multi-ply forming methods. As a result, the top and bottom surfaces of the centre ply 10 are bumpy, much like the surface of small curd cottage cheese. Consequently, when the top and bottom plies are formed on the centre ply 10, they will conform to the bumpy surfaces as illustrated in Figure 1. In accordance with the present invention, the depressions and interstices of the centre ply are filled so that a smooth outer surface is produced as shown in Figure 2, wherein the centre ply 13 is covered by the outer plies 14 and 15 which are smooth surfaced.

In the headbox of Figure 3, the structure includes upper and lower walls 17 and 18to form the headbox 16. The headbox is formed with an upper chamber 19 and a lower chamber 20 for handling the stock forming the outer plies. The stockforthe centre ply is delivered to an intermediate chamber 21 ofthe headbox.

Stock is delivered to the upper chamber 19 and lower chamber 20 of the headboxfrom headers 24 and 25 which extend across the width of the headbox. To these headers, preferably at one end, are connected supply lines 22 and 23 for delivering the stock which is to form the outer plies of the finished web.

Extending through the upper chamber 19 of the head box, in the direction of travel, are a plurality of tubes 26, and similar tubes 27 extend through the lower chamber 18 of the headbox. These tubes generate and maintain a fine scale turbulence in the outer layers of the web.

The headbox delivers to a slice chamber having an upper wall 28 and a lower wall 29. These walls may be pivotally hinged on the headbox so as to control the size of the slice opening 30.

The stock for the upper ply will travel in a downstream direction through the upper portion 33 of the slice chamber. The stock for the lower outer ply will travel through the lower portion 34 of the slice chamber.

Positioned in each of the upper and lower portions of the slice chamber, so as to extend downstream, are trailing flexible elements which are preferably sheet-like in form, but which may take different forms such as trailing individual finger-like elements which are divided across the width of the headbox.

The trailing elements are anchored at their upper ends with their lower downstream trailing ends freely floating or freely positionable. This aids in maintaining the fine scale turbulence which is induced in the stock and ensures even distribution of fibres and elimination of flocculation which is parti cularly necessary to permit the application of fine thin layers of paper to the outer surfaces of the centre ply and to form a multi-ply web.

The stock is delivered from the slice opening 30 between dewatering forming surfaces comprising travelling forming wires 31 and 32.

Centrally located in the slice chamber is a separate path for the stock for the centre ply of the web. The structure for controlling the centre ply has an upper wall 38 and a lower wall 37, the walls being rigid. The walls 37 and 38 define an undulating tortuous path 41 therebetween through which the high consistency stock flows on its way from its header 21, to which the stock is delivered through a delivery line 21a. The stock flows through the tortuous path formed between the upper surface 40 and lower surface 39 of the walls 38 and 37 respectively. At the downstream end of the rigid walls 38,37 are flexible projecting lips 42 and 43 which guide the high consistency stock to the slice opening 30. At the slice opening, the outer plies are laid smoothly on the centre ply, and the combined plies flow between the forming surfaces 31 and 32.

The tortuous path 41 forthe high consistency stock may take modified forms from that shown, but the path is arranged to begin with relatively vigorous path deviations and to continue on for the remainder of travel, although with less violence, to where the centre ply of stock is discharged to flow between the forming surfaces.

The stock which is delivered to the intermediate path is high consistency, being in the range of 1% to 5%. The stock for the centre ply is preferably different from that for the outer plies, and will include long fibre kraft, hardwood fibres and reclaimed mechanical fibres.

In summary, a high consistency stock is delivered through aforced undulating ortortuous path between the flow of the outer plies. The outer plies are simultaneously delivered through the delivery end of the nip between travelling forming surfaces. The high consistency of the centre ply reduces the amount of drainage which must occur through the outer plies and, of course, this results in much less disturbance of the fibre arrangement in the outer plies and results in improved outer ply formation.

The reduced moisture flow also helps improve the arrangement of fibres in the centre ply and thereby improves the stiffness and quality of the multi-ply web.

The turbulence induced in the central ply stock, and in the outer plies, results in the outer plies filling the depressions in the centre ply, while the outer surfaces of the outer plies are smooth.

Claims (10)

1. A paper machine for making a multi-ply web from stocks having a slurry of fibres in a liquid carrier, and comprising: a headbox having a lower wall and an upper wall and including an upper chamber and a lower chamber for fibrous stocks to form outer surface plies for a finished web; said headbox including an intermediate chamber for fibrous stock to form an intermediate ply between said outer plies; first and second stock delivery means connected respectively to said upper and lower chambers for delivering fibrous stocks for the outer surface plies; intermediate stock delivery means connected to said intermediate chamber for delivering a high consistency stock thereto; a slice chamber extending from the headbox having upper and lower slice walls and having a slice opening to discharge onto a forming surface, said slice chamber having an upper and a lower slice portion connected to receive stock from said upper and lower headbox chambers respectively; and an intermediate portion of the slice chamber between said upper and lower portions defined by upper and lower intermediate slice walls having facing undulating surfaces so that the high consistencystockwill flow through a tortuous path before being discharged onto the forming surface between the layers issuing from said upper and lower portions.

2. A paper machine according to claim 1, including flexible sheet members in at least one of said upper and lower slice portions, the sheet members being secured at their upstream ends with their downstream ends being unattached.

3. A paper machine according to claim 2, wherein flexible sheet members are provided in both said upper and lower slice chamber portions.

4. A paper machine according to any of claims 1 to 3, wherein the intermediate slice walls are constructed so that said tortuous path is of substantially uniform depth from the head box to the slice opening.

5. A paper machine according to any one of claims 1 to 4, including tubes extending from said first and second stock delivery means to said upper and lower chambers for generating fine scale turbulence in the stock.

6. A paper machine according to any of claims 1 to 5, wherein the ends of said intermediate walls terminate in thin flexible portions at the slice opening.

7. A paper machine according to any of claims 1 to 6, wherein the intermediate stock delivery means deliver stock having a consistency in the range of from 2% to 5%.

8. A method of forming a multi-ply web from paper stocks having a slurry of fibres in a liquid carrier comprising the steps of: delivering stocks to form outer plies through outer headbox chambers and outer slice portions of a slice chamber onto a travelling forming surface; and delivering an intermediate layer between the outer plies of a relatively high consistency in the range of 2% to 5% with the high consistency stock being directed through an undulating tortuous path prior to being discharged onto the travelling forming surface.

9. A method according to claim 8, wherein the outer layers of stock are directed through the slice chamber portions over flexible unsupported trailing members to maintain and generate a fine scale turbulence in the stock.

10. A paper machine for making a multi-ply web substantially as hereinbefore described with reference to the accompanying drawings.