JPS5934840B2 - Squeezing mechanism for paper-making machine web dewatering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a paper machine, and in particular to a squeezing mechanism for dewatering the web.

In high-speed paper machines, a dewatering device or vent reservoir is provided behind the wet press felt in the nip area of the wet press nip through which the web passes, thereby increasing the press performance by creating a lateral flow of water through the felt. It is generally believed that it is possible to measure

Various types of compression rolls have been used for this purpose, such as those with blind drilled holes on the outer surface of the roll, or perforated rolls such as suction rolls or grooved rolls.

Suction rolls were devised before grooved rolls or other dewatering methods, and it was believed that the vacuum in the roll holes aided in dewatering the paper; It was found that dehydration did not have much of an effect.

Looking at the history of suction roll design, the thickness of 50mm (
The smallest possible diameter hole was drilled through either 2 inches (2 inches) or 76 mm (3 inches) of metal.

The spacing of the holes was chosen to give acceptable stress values in the intervening metal parts, and the arrangement of the holes was chosen to minimize noise generation.

These variables, such as hole diameter, hole spacing, hole arrangement, etc., have made it difficult to take into account the feasibility of dewatering the felt.

However, as evidenced by the fact that the non-porous press rolls in ordinary smoothing machines do not work well, that is, there is no dehydration effect behind the felt, the reason for the performance deterioration is that the dehydration of felt is This is an important issue.

In a smooth press, the longest path length of the water removed is half the nip length, which is practically 19 mm (3/4 inch) to 25 mm (1 inch), which is essentially corresponds to the lateral flow of water on the felt surface.

The flow in the lateral direction creates a large flow resistance, and in the end, only a small amount of water can be removed from the paper with the given pressure and time, and high water pressure is generated within the felt, causing the paper to collapse. .

It was found that the dewatering performance of suction rolls was lower than that of non-perforated rolls, and that of grooved rolls covered with textile sleeves6.Moreover, the dewatering performance of suction rolls with the current standard perforation arrangement was insufficient. It was found that there is room for improvement.

Research has shown that a channel length of 1.9 (0,075 inches) is desirable and achieves the best squeezing performance with this channel length, but even shorter channel lengths will not improve performance even further. It turned out that no improvement was possible.

A typical wet pressed felt will have a thickness t ranging from 1.2 mm (0.05 in.) to 1.9++ m (0.075 in.) depending on the applied pressure and the weight of the felt. This is the basis for explaining the highest value.

Although the actual water path from the paper through the wet-pressed felt to the dewatering area may be tortuous, the dewatering path length is essentially the length of the felt thickness.

If the water channel is oriented radially, the channel length is equal to the thickness of the compressed felt, and if the water flows laterally at a 45 degree angle toward the aperture, the channel length is equal to the thickness of the compressed felt. The length is approximately 1.4 times the thickness of the felt.

The flow of water at an angle of 45 degrees can be considered by breaking it down into flows in the transverse direction and in the lateral direction of the felt.

These flows are shown in FIG.

This figure shows the paper web W, the felt f, the dewatering openings V and the non-dewatering areas U, and the radial flow path of the water is t.
, the diagonal flow path of water to the dewatering aperture is denoted by l, and the lateral flow distance is denoted by p.

Current trends in felt design have been directed toward lowering the transverse flow resistance without, or often even reducing, the transverse flow resistance.

This felt design exaggerated the problem of the length of the flow path within the felt, which has a large lateral component.

It has been found that a paper membrane water felt provides good dewatering performance when the ratio of compressed felt thickness t to channel length p is about 1 or less.

If this ratio in the suction roll is much larger than 1, for example 2, the best dehydration condition cannot be obtained.

An important factor in dehydration is the uniform application of pressure.

This means that the load is evenly transferred from the press rolls through the felt to the paper.

Squeezing the paper with a suction roll for felt hooks is
This creates an area of high moisture content and weak bonding of the paper fibers above the perforations.

This becomes visible as a “shadow mark” on the paper.

The factors contributing to uniformity include the open area of the roll surface and, more importantly, the bridge distance, ie, the dimension indicated by D in FIG. 1.

The maximum distance over which the felt is not supported is called the bridge distance.

In a suction press, the part of the felt directly above the aperture is unsupported and only applies a small amount of pressure to the paper in this area.
No.

The pressure versus dryness relationship is highly non-linear, and a small increase in dryness on the land does not equate to a loss in dryness over the aperture.

This results in a net loss in dryness.

An object of the present invention is to provide a press roll for a paper making machine that applies more uniform pressure to the paper surface and reduces resistance to the flow of water from the web through the felt to improve dewatering performance.

It is another object of the present invention to provide an improved suction roll that can reduce the distance of lateral flow of water through the felt and into the suction roll perforations while employing standard perforation dimensions and perforation arrangements. There is a particular thing.

A further feature of the present invention is that it can be used for both new rolls and existing rolls, and is preferably used for suction rolls in which a thin sleeve is fitted on the outer surface of the roll, and this sleeve is arranged in a circumferential direction. It has elongated slots spaced such that at least 80% of the slots are in communication with the drill holes, and the slots have a radial spacing that is less than the spacing between the drill holes.

Such a perforated metal sleeve can reduce the bridge distance of conventional suction rolls by 3.6 mm (0.14 inch).
0.13 mm (0,005 inch) to 1.
Give a short bridge distance of k (0.04 inches).

This roll structure combined with the perforated metal sleeve provides a more even pressure distribution and reduces paper shadow marks.

In addition to reducing the bridge distance, the flow path length for the standard drill hole arrangement in the suction roll is 2.4 mm (0,0
Shorter flow path lengths of 1.3 (0.05 inches) or less are obtained compared to 93 inches (0.05 inches) or more.

This arrangement also increases the aperture area from 14% to 18%, which is currently achievable.
%, the open pore area is 20% to 50% higher.

Other objects, advantages, and features will become apparent from the principles of the invention set forth in connection with the description of the preferred embodiments in the specification, claims, and drawings.

As mentioned above, FIG. 1 shows the maximum and minimum distances that water will flow through the felt f in a conventional press roll.

The paper or web W is squeezed so that the squeezed out water particles must travel within the felt at least a minimum distance indicated by t.

The water required to reach the dewatering aperture from the most remote point must also migrate laterally along flow path l.

A first object of the present invention is to reduce the lateral distance p and the maximum distance l.

D is the bridge distance of the roll.

A second object of the invention is to reduce the distance where the felt is not supported, ie the bridge distance, and to increase the uniform pressure action on the paper.

FIG. 2 shows a pair of press rolls, with an upper smooth roll 10
forms a nip n with the lower roll 11.

The lower roll is shown as a suction roll, which roll consists of a roll shell with a suction box 15 inside the shell in a position opposite the nip n.

Although not shown, a device for feeding the running web into the nip is provided.

The web W on the upper smooth roll 10 side passes through the nip together with the felt on the lower roll 11 side.

The lower roll shown in FIGS. 3 to 5 consists of a roll shell 13 with holes 14 drilled therein.

These holes are separated by a lateral distance d, and the duck of this distance is approximately the maximum distance p.

A water particle must travel this maximum distance laterally to reach one of the suction roll holes.

The holes 14 are drilled with conventional hole arrangements and diameters, but the holes are usually placed as close together as possible to maintain the integrity and strength of the roll shell.

Roll shell 13 includes an outer cover or sleeve 12 that is perforated to form a circumferentially extending slot.

The slots are spaced laterally by a distance d' which is considerably less than the distance d of the suction roll apertures, so that the water particles must reach the apertures at a distance d'. represents the maximum lateral distance.

The slots 16 are laterally or axially spaced apart such that at least 80 degrees or more of the slots contact portions of the suction bore.

If the slot borders the suction hole or a portion thereof, the slot provides a low pressure in the vicinity of the felt that is necessary for water to flow through the felt.

The water particles enter the slot and either settle therein, or some of them enter the drilled hole at the nip and are thrown off after the slot passes through the nip and through the suction box 15.

The perforated metal sleeve, which is attached to the outer surface of the suction roll, can be attached onto the suction roll by a shrink fit or by a shrink fit and weld.

In the conventional perforated suction roll shown in Figure 3, the distance d is approximately 4.6 mm (0.18 inch)
As shown in the figure, it is 2 X p).

The elongated slot in the sleeve is 0.13 mm (0.005
The spacing d' ranges from 0.51 mm (0.02 inch) to 0.51 mm (0.02 inch), and this spacing reduces the water migration distance.

The length of the slot ranges from 0.5 m71+ (0.02 inches) to 5.0 mm (0.2 inches).

Metal sleeves range from 0.25 mm (0.01 inch) to 3
．． Available in thicknesses ranging from 2 mm (0,125 inches)
In addition, all of the water expelled from the felt can be retained, and the suction holes can be easily bridged without being pushed into the suction holes by the pressure of the nip.

The opening area of the slot hole must be at least 20%C, preferably a large value of 40% to 50%.

The effect of aperture area is well illustrated in FIG.

As can be seen, since the width of each slot 16 is less than the width of the hole 14, the felt supported on the rolled surface has a larger support surface, i.e. a shorter bridge distance than simply sitting over the hole. have

This short bridge distance provides a more even pressure on the felt and provides a more even pressure within the web to more evenly squeeze the water out of the web.

FIG. 5 shows a lateral water migration distance p' which is considerably shorter than the lateral distance p in the conventional device of FIG.

4 and 5 show a small bridge distance and a short distance of lateral travel of the water, and FIG. 5, which is similar to FIG. 1, shows the felt f being supported and In the figure, the felt is supported on the surface of a thin sleeve 12, with the web W being pressed against the felt by a counterroll 10.

This water is squeezed into the slot opening 16 and either is retained within the slot or has a portion passing down the hole while a portion of the roll faces the suction box 15.

After a portion of the roll has passed through the suction box, the water is removed or splashed off in a conventional manner, and provision is made to reduce the risk of refilling the dampener or other device.

This device allows for a more uniform pressure distribution through the nip,
It also reduces paper shadow marks.

In addition, the flow path of the paper can be shortened and good dewatering can be achieved.

As the web passes through the nip, the water is squeezed into the felt, and the flow through the felt enters the slots radially and axially, and some even into the suction holes, forming roll holes and sleeves. After the holes pass through the suction box, they are discharged.

[Brief explanation of the drawing]

FIG. 1 is a schematic partially enlarged sectional view showing the migration distance and bridging distance of water through the felt; FIG. 2 is a schematic front view of a press nip including press rolls embodying the principles of the invention;
Fig. 3 is a somewhat schematic drawing of the press roll in Fig. 2, Fig. 4 is a front view substantially enlarging a part of the press roll surface, and Fig. 5 is a line drawn along the line ■-■ in Fig. 4. FIG. 10... Upper smooth roll, 11... Lower roll, 12... Sleeve, 13...
・Suction roll shell, 14...Suction roll hole, 15...Suction box, 1
6... Slot, D... Bridge distance of roll hole, D'... Bridge distance of slot, d... Distance between roll holes, d'. ...Distance between slots, f...Felt, l...
・Maximum water migration distance, n...Nip, pjl)'
...Water lateral migration distance, t...Felt thickness, U...Dewatering opening, ■...
Non-dewatering area, W...Paper web.

Claims (1)

[Claims] 1. In a squeezing mechanism for web dewatering of a paper making machine, an upper squeezing roll, a lower suction roll arranged to form a squeezing nip between the upper squeezing roll and having a large number of holes extending in the radial direction, and a dewatering a furtle which is adjacent to the lower suction roll and receives water squeezed out of the web through the nip while supporting the web to be processed; an annular thin sleeve of non-conforming material having a plurality of elongated slots extending therethrough, the slots of the sleeve being axially more closely spaced than the radial holes of the lower suction roll; A squeezing mechanism for web dewatering, characterized in that the lateral distance of migration of water squeezed out from the web is reduced and the uniformity of pressure application to the web is increased.