EP1196655A1

EP1196655A1 - A method for forming a web from aerosuspension of fibrous material

Info

Publication number: EP1196655A1
Application number: EP99972278A
Authority: EP
Inventors: Viktor Mikhailovich Drobosyuk
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1998-11-16
Filing date: 1999-10-25
Publication date: 2002-04-17
Also published as: CA2350508A1; WO2000029668A8; RU2157867C2; WO2000029668A1; AU1220600A

Abstract

A process and an apparatus for making paper by an aerodynamic method. An aerosuspension is fed onto a moving forming wire positioned at an angle relative to the aerosuspension flow. Then, an air component is removed by means of a suction device located on the opposite side of the wire. The aerosuspension feed and air removal are performed in a direct-flow channel in which the value of a suction force is set to increase in the direction of the forming wire motion so that the suction force applied to the fibrous material in the surface layer of the web being formed is approximately the same along the forming wire in the web formation zone. As a result, a low fiber concentration in the aerosuspension is maintained up to the moment the suspension reaches the forming wire followed by an effective air removal featuring no vortexes in the vicinity of wire, the fibers are reliably held on the wire, and the possibility of shear of the fibers falling onto the wire is excluded. The above factors, combined, enable production of paper with a high degree of uniformity at a high production rate.

Description

A METHOD FOR FORMING A WEB FROM AEROSUSPENSION OF

FIBROUS MATERIAL

FIELD OF THE INVENTION

The present invention relates to making paper by an aerodynamic

method, and more particularly, to a method of forming a web from

aerosuspension of fibrous material on a forming wire.

BACKGROUND OF THE INVENTION

A method for forming a web from aerosuspension of fibrous material

is known, in which the aerosuspension is fed onto a moving wire positioned

perpendicular to the direction of the aerosuspension flow and an air

component of the aerosuspension is removed by means of a suction

device, the so-called suction box, installed on the opposite side of the wire.

This method also provides for redistribution of the sucked airflow across the

formed web width, which permits production of a web profile of various

configurations. USSR Author's Certificate No. 1172975, 4 D 21 H 5/26,

published 08/15/85, Information Bulletin No. 30. This method, however, is

unable to produce a web of high uniformity at high production rates, since

the aerosuspension flow shears the web being formed due to the

interaction of the flow pressure and high velocity of moving wire.

Generating a high vacuum in the suction box to enhance pulling of the web to the wire could prevent the web shear. However, this is difficult and

costly.

According to another conventional method for forming a web from

aerosuspension of fibrous material, the aerosuspension is fed onto a wire

positioned at an angle relative to the aerosuspension flow and an air

component of the aerosuspension is removed by means of a suction

device located on the opposite side of the wire, with the airflow sucked off

from the opposite side of the wire being normal to its surface. USSR

Author's Certificate No. 746015, 2 D 21 H 5/26, published 07/07/80,

Information Bulletin No. 25 - prototype. This method represents the closest

one to the invention claimed. In this method, the wire positioned at an

angle relative to the direction of the aerosuspension flew decreases the

web velocity component that is normal to the aerosuspension flow

direction. This allows achievement of an increase in the web velocity

without causing web shear.

In addition, a removal of a certain part of the air component of the

aerosuspension is also provided as the aerosuspension passes through a

feeding channel before reaching the forming wire. Thus, one of the main

problems of such methods, namely removal of a large volume of air from

aerosuspension in order to provide a high production rate, is solved. This

solution, however, results in a portion of fibers (1 - 5%) being carried away

by the sucked air when the aerosuspension passes through the feeding channel. Besides, the concentration of fibers in the aerosuspension grows

as the latter moves through the channel, which leads to fiber

conglomeration and, consequently, to non-uniformity of the formed web.

SUMMARY OF THE INVENTION

The present invention provides an effective method for forming a

substantially uniform web from an aerosuspension of a fibrous material.

According to the present invention, a method of forming a web from

an aerosuspension of fibrous material comprises feeding the

aerosuspension to a moving wire positioned at an angle relative to the

aerosuspension flow, and removing the air component of the

aerosuspension by means of a suction device located on the opposite side

of a wire, wherein the aerosuspension is fed and its air component is

removed in a direct-flow channel.

The claimed method provides for removal of air from the

aerosuspension only after the aerosuspension reaches the wire, thus

maintaining a low concentration of fibers prior to the specified moment,

which makes the formed web highly uniform. The most favorable regime

for an effective air removal that excludes occurrence of turbulent airflow in

the vicinity of the wire, the so-called sub-wire vortexes, is created by

feeding the aerosuspension and removing its air component in a direct-flow

channel. However, the implementation of the claimed method can give rise to

the following problem. The suction force F (Fig. 1) applied to layer-forming

fibers (point "A" in Fig. 1) starts featuring two components F_n, which is

normal to the wire surface, and F_t, which extends along the wire surface,

The F_n component presses the fibers falling onto the wire against the wire,

thus holding the formed layer on the wire. The F, component produces a

shearing effect upon the fibers that may shear them along the wire surface

and produce a "dune" at this spot, when this component reaches the value

exceeding the force of fibers friction against the wire. These

considerations are true in relation to the entire surface layer of the formed

web.

So, concurrent problems arise from holding fibers on the forming wire

by a vacuum generated by a suction device from its opposite side, and

preventing the shearing of fibers along the wire surface under the action of

the F_t component.

Solving this problem gives rise to a new problem: if the suction force

is uniformly distributed across the suction channel, this being the simplest

option from the standpoint of its technical realization, a non-uniform

aerodynamic resistance to the sucked air occurs due to the growth in the

formed web thickness. The above phenomenon leads to the following: if

the suction force is set at a value adequate for holding the fibers on the

wire surface at the beginning of the formation zone without their shear along the wire surface, the above value may turn out to be inadequate for

holding the surface layer of the fibers at the end of the formation zone,

since the suction force at the formed layer surface will decrease because of

the aerodynamic resistance of the latter. And vice versa, if the suction

force is set at a value adequate for holding the fibers on the wire surface at

the end of the formation zone (with the above aerodynamic resistance of

the formed layer taken into account), this value may turn out to be sufficient

for generating a value of the F_t component that will start shearing of fibers

along the wire surface, thus creating the above-mentioned non-uniformity

("dunes") in the formed layer.

To solve this problem, the claimed method additionally provides for

setting a value of the suction force that increases in the direction of the

forming wire motion so that the suction force applied to the fibrous material

on the surface layer of the formed web is approximately the same along the

forming wire in the web formation zone.

So, maintaining a low fiber concentration in the aerosuspension until it

reaches for the forming wire followed by an effective air removal is the

technical result achieved through the application of the above newly

introduced features, which ensures reliable holding of the fibers on the

forming wire in the process of web formation and excludes a possibility of

shearing of the formed web, thus, producing paper with a high degree of

uniformity at a thigh produce rate. BRIEF DESCRIPTION OF DRAWINGS

The Figure illustrates an arrangement for forming a web according to

an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figure, the aerosuspension is fed and its air

component is removed in a direct-flow channel comprising a feeding

section 1 , through which the prepared aerosuspension is fed, and a suction

section, represented by a suction box 2 which contains a suction device,

for example, an exhaust fan of an adequate capacity (not shown). The

aerosuspension is fed onto an endless moving belt, or wire, 3 set at an

angle to the aerosuspension flow direction. As wire 3 moves, layer 4 of a

formed web 5 becomes gradually thicker, being held on the surface of wire

3 by a vacuum generated by the suction box 2. At the outlet of channel 1 ,

an endless wire 6 moving at the same speed as the wire 3 picks up formed

web 5 and transports it to pressing and drying equipment (not shown) by

holding the web between both wires (i.e., wire 3 and wire 6).

Means for modifying the value of suction force along the direction of

moving wire 3 are also shown in Fig. 1. A section of suction box 2 adjacent

to the wire 3 is divided by partitions 7 erected consecutively one after

another along a direction of the movement of the wire 3 and across its

entire width. The partitions 7 form, together with the walls of the suction box 2, separate air ducts 8, the aerodynamic resistance of which is

determined, to a large extent, by their length. Partitions 7 are equipped

with turning plates 9 that can also modify the aerodynamic resistance of

ducts 8. This provides the ability to set and maintain a maximum value of

the aerodynamic resistance in a portion of that duct 8 which is adjacent to

the point where the wire 3 enters the feeding section 1 , and a minimal

value of the aerodynamic resistance in that duct 8 which is adjacent to the

point where the wire 3 exits the feeding section 1.

The specific value of suction force, as well as the number of ducts 8

and the ratio of their aerodynamic resistance, all being dependent on a

number of technological parameters, such as width and length of the layer

being formed, velocity of the forming wire, type of fibrous material, moisture

content of fibers, etc., are selected individually for each specific case.

While this invention has been described in connection with what is

presently considered to be the most practical and preferred embodiments,

it is to be understood that the invention is not limited to the disclosed

embodiments, but, on the contrary, is intended to cover various

modifications and equivalent arrangements included within the spirit and

scope of the appended claims.

Claims

WHAT IS CLAIMED:

1. A method for forming a web from an aerosuspension of fibrous

material comprising the steps:

(a) feeding the aerosuspension of fibrous material onto a moving

forming wire placed at an angle relative to a direction of the

aerosuspension flow; and

(b) applying a fluid pressure differential to the forming wire in a

forming zone, thereby removing an air component of the

aerosuspension, wherein the aerosuspension is fed and its air

component is removed in a direct-flow channel.

2. The method of claim 1 , wherein the step applying a fluid pressure

differential further includes a step of applying the fluid pressure

differential at an increasing level along the direction of the forming

wire motion so that the fluid pressure differential applied to the fibrous

material is approximately the same along the forming wire within the

forming zone.

3. An apparatus for forming a web from an aerosuspension of fibrous

material, the apparatus comprising:

a forming belt continuously moving in a machine direction;

a direct-flow channel comprising a feeding section and a removing

section, said feeding and removing sections being separated from

one another by said forming belt, and said feeding section being

configured for directing a flow of aerosuspension to said forming

belt; and

a vacuum apparatus configured to apply a fluid pressure

differential to said forming belt, thereby removing an air

component of the aerosuspension into the removing section of

said direct-flow channel.

4. The apparatus of Claim 3, further comprising a plurality of partitions

disposed in the removing section of said direct-flow channel, said

partitions being consecutively spaced from a first partition to a last

partition relative to said machine direction, to form a plurality of air

ducts between mutually adjacent partitions and between the partitions

and walls of the removing section adjacent thereto, said plurality of air

ducts being consecutively spaced in said machine direction from a first air duct to a last air duct, each of the air ducts being structured to

maintain an air resistance.

5. The apparatus of Claim 4, wherein the air resistance of the said air

ducts consecutively decreases from the first air duct to the last air

duct.

6. The apparatus of Claim 4, wherein each partition from said plurality of

partitions has a first end adjacent to said forming belt and a second

end opposite to said first end, and a length between said first and

second ends, said length decreasing consecutively from said first

partition to said last partition.

7. The apparatus of Claim 4, wherein at ieast some of said partitions

have turning plates articulably connected to the second ends of said

partitions.

8. An apparatus for forming a web from an aerosuspension of fibrous

material comprising:

a forming belt continuously moving in a machine direction;

a direct-flow channel comprising a feeding section and a removing

section, said feeding and removing sections being separated from

one another by said forming belt; said feeding section being configured for directing a flow of

aerosuspension to said forming belt;

said removing section comprising a plurality of air ducts

consecutively spaced therein in said machine direction from a first

air duct to a last air duct, each of said plurality of air ducts having

an air resistance that increases from said first air duct to said last

air duct; and

a vacuum apparatus structured to apply a fluid pressure

differential to said forming belt, thereby removing an air

component of the aerosuspension into the removing section of

said direct-flow channel.

9. The apparatus of Claim 8, further comprising means for controlling the

air resistance of each individual air duct.

0. A method for forming a web from aerosuspension of fibrous material

comprising the steps:

feeding the aerosuspension of fibrous material onto a moving

forming wire placed at an angle relative to the aerosuspension

flow, and

removing an air component of the aerosuspension by means of a

suction device located on the opposite side of the wire,

wherein the aerosuspension is fed and its air component is

removed in a direct-flow channel.