JPS5930836B2 - Squeezing mechanism with enlarged nip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved mechanism for dewatering a running paper web and, more particularly, to dewatering a running paper web for a longer period of time than conventional devices in which the web passes between two opposing press rolls. The present invention relates to an expression apparatus known as an enlarged nip expression, in which the apparatus is subjected to an expression pressure.

More particularly, the present invention relates to a squeeze nip construction where the residence time of the web in the nip is longer than the residence time of the roll pair and the improved construction is used to dewater the web.

Other structures have been provided in the past to continuously move the web at the speeds required for high speed paper machines, while being intended to increase the amount of time the web is under pressure.

Such structures have met with some success, for example, in U.S. Pat. No. 3,748,225 (Busker et al.);
No. 783097 (Reissue No. 30268) (Justus), No. 3797
No. 384 (Hoff), No. 3798121 (B
usker et al.), No. 3804707 (Mohr
), No. 3808092 (Busker),
No. 3808096 (13usker and others), No. 3840429 (Busker and others), No. 385
No. 3698 (Mohr) and No. 4201624 (Mohr)
Mohr) et al.

The devices and methods described by these prior patents take advantage of the knowledge that applying static mechanical pressure to a wet paper mat can reduce the moisture content in the mat to below 40%. There is.

It is often difficult to maintain moisture content below 60% under the short term dynamic mechanical squeezing that occurs in conventional paper machines, where the web runs between a series of nips formed between a pair of squeezing rolls. .

Efforts to increase dryness in conventional roll pairs are usually made by increasing the crushing nip pressure, but eventually an upper limit is reached and increasing roll load results in relatively small moisture loss. Become.

As is known, it is much more efficient to dewater in the press section of a paper machine than in the heated drying section, resulting in a significant reduction in energy costs and a significant reduction in the required footprint for the drying drum section of the paper machine. This is achieved for each moisture content that can be further removed in the pressing section.

The difficulty of removing water in the press increases with the speed of the paper machine.

This is because the limiting factor that compressing and squeezing the web results in high nip pressures and resulting high liquid pressures in the paper mat spills over into the squeezing nip pressure.

The most suitable method discovered to enhance dewatering even at high speeds is to increase the retention time in order to allow a long time for the flow that occurs in the paper mat, the liquid pressure that disperses, and the water that is squeezed from the web into the felt. Another option is to lengthen the compression time.

It is an object of the present invention to develop an improved system which utilizes the principles of enlarged nip squeezing to increase the time the web is subjected to squeezing pressure and which utilizes opposing shoes in the construction to accommodate relatively high running speeds of the paper web. The objective is to provide a compressing force that is controlled to the optimum nip pressure for the mechanism and type of paper being produced.

It is another object of the present invention to provide an improved enlarged nip press of relatively uncomplicated construction that can be operated continuously for long periods of time without requiring repairs or adjustments or significant monitoring that would require stopping the paper machine. Our goal is to provide the following.

Another object of the present invention is to provide an improved enlarged nip press having the feature of permitting uniform press pressure to be applied across the width of the running web to provide more uniform dewatering.

Yet another object of the present invention is to provide an improved method and structure for enlarged nip pressing that improves sheet quality, improves dewatering, provides a better pressing operation, and eliminates rewetting.

Another object of the present invention is to provide an improved squeezing nip that uses the principle of an enlarged nip and has an improved structure for driving an impermeable belt that clamps the web and felt in the nip.

A feature of the invention is to provide opposing shoes defining a squeezing nip between the shoes with an impermeable belt sandwiching the web and felt through the nip, the shoes having a lubricating hydraulic membrane; It is supported by at least one of the pivotally mounted shoes so as to assume a hydraulically balanced position to accommodate the lubricating hydraulic membrane carried between the shoe and the belt.

Hydraulic fluids not only act to provide pressure;
Nip pressure is applied by a piston-cylinder arrangement supplied with hydraulic fluid to ensure that the pressure is completely uniform across the width of the pressure cannula.

The opposing shoe is sufficiently flexible to allow flexing along the length of the shoe without applying forces due to flexing of the shoe that would increase or decrease nip pressure along the length of the shoe;
Also, by simply applying nip pressure with hydraulic fluid, a completely uniform pressure can be achieved across the entire width of the nip.

Other objects, advantages and features, or equivalent structures and methods, which are intended to be included in the present invention will be described in conjunction with the disclosure of the preferred embodiments of the specification, claims and drawings. It will become clearer with the teachings.

The nips N for squeezing and dewatering the web are the first and second nips.
It is formed between the shoes 10 and 11.

Said shoe has a symbol 12°13 leading to the pressing surfaces 14, 15.
It has a dissociated leading end as shown.

The squeezing surfaces each face an enlarged nip and are smooth and substantially linear so as to apply squeezing pressure to the web as it passes through the nip.

As is well known by those skilled in the art, the shoe extends laterally across the web and is slightly wider than the web width (with respect to the run of the web as indicated by the arrow above the web). It can be referred to as extending laterally.

The web is sandwiched between fels N8, 19 which provide a means for containing the water expressed from the web.

And felt and web are annular impermeable endless hel) 16
, 17.

The web is guided into the nip and then guided out of the nip by suitable guide members, not shown.

The upper felt 18 is then guided into and out of the nip by rolls 18at18b and the lower felt 19 by rolls 19a, 19b.

The annular bells N6, 17 are made of very strong reinforcing rubber or equivalent material and are driven at the speed of web travel, so that the belts carry the web and felt through the nip.

And these belts are 16a, 16b, 16c, 16
d is tensioned on the guide rolls shown against the belt 16.

The roll 16c may be a tension roll movable in the arrow direction by an appropriate tension mechanism.

Similarly, the lower belt 17 also has a guide roll 17 a t 17.
b.

17c and 17d, and an appropriate mechanism is provided for roll 17c to move the roll in the direction of the arrow in order to maintain the desired tension on belt 17.

An important feature for proper processing of the web is the means for driving the belt, for each belt N6, 17 a grooved traction roll 20, 22 is provided.

The belt preferably has a circular arc of 90° or more and extends over the roll 2.
0,22, and it has been found that an improved trajectory and drive relationship can be achieved by providing each roll 20,22 with a groove shown schematically by dashed line 21,23. There is.

The grooves are annular cut grooves at uniform intervals along the roll surface leaving flat ridges between the grooves.

It is clear that these grooves can drain away any moisture that may be present between the belt and the roll, and that by tensioning the belt, the belt can be rolled down slightly into the grooves. , which increases the traction between the belt and the rolls and also increases the uniformity of the driving and guiding relationship.

Uniform treatment of the belt is necessary so that the web and felt can be drawn uniformly through the nip.

The grooved pull rolls 20, 22 engage the outer surface of the belt, which is the surface adjacent to the felt at the nip.

In this way, no driving or traction forces are applied to the inner surface of the belt whose surfaces slide over the shoes 10,11.

Any friction caused by the drive is not applied to the sliding surface of the belt.

Furthermore, it is noteworthy that it is the outer surface of the belt that is moistened in contact with the felt, and it is known that such wetting of the belt surface is accommodated by the unique grooved traction roll 20.22. It is.

The leading ends 12, 13 of the shoes are separated and the injection 24.
25, the flat surface 14. of the shoe is continuously supplied with lubricant at the location of said separated edges.
A lubricating fluid film appears continuously during the 15-hour period.

The lubricant is composed of various materials such as oils and fats, and is applied in such a way that each shoe essentially acts as a sliding bearing while being pressurized against each other, and the lubricating fluid film is continuous so that the lubricant The hydraulic pressure of the shoe is transmitted to the belt.

Of course, the above fact reduces the friction between the belt and the shoe, but there must be a liquid between the shoe and the surface of the belt so that the liquid exerts a uniform pressure along the elongated length of the shoe. This fact enhances the uniformity of pressure and provides a further improved squeezing action.

Hydraulic pressure reaction on the shoe due to the lubricating layer between the shoe and the belt causes the shoe to tilt to a neutral position.

That is, the shoes are shown mounted at central pivot points 27 and 29, respectively.

The pivot point is located approximately midway between the leading and trailing edges of the shoe such that the pressure of the lubricant in front of the pivot point is the same as the pressure behind the pivot point. Operates in equilibrium position.

A line seal may be provided at the edge of the belt to prevent lubricant from transferring to the edge of the belt, but experience shows that the amount of lubricant passing through the edge of the belt is minimal, so Sealing is not absolutely necessary.

When the belt emerges from the pressure line of the shoe, the pressure line of the shoe is
0a and 11a are slightly round.

Each shoe is pivoted by a pivot pin that extends laterally across the width of the paper machine, so that the shoe is supported pivotably about a transverse axis, but in some cases only one shoe is pivoted. It is desirable that you do so.

Since one pivot shoe is pivoted in a neutral position where the hydraulic pressure across the pivot point is uniform, hydraulic pressure balance is achieved in the nip in this case as well.

The shoes are supported by opposing weight beams 26 and 28 above and below the shoes 10 and 110.

As mentioned above, pivot pin 27 may be omitted in some cases.

The shoe is fixed to the beam 26 and is provided with a pivot pin 29.

This is a structure that selects one of the two, but it is preferable that the shoe is pivotally supported relative to each shoe.

It can be placed at a significant location relative to the leading edge and pressure line of the shoe so as to create a uniform pressure over the length of the enlarged nip.

Also, it may be set slightly downstream in the direction of web movement, but
At this time, a slightly lower two-tube pressure is generated in front of the pivot pin than behind the pivot pin.

The shoe will occupy an equilibrium position where the total hydraulic pressure of lubricant in the nip in front of the pivot pin is equal to the hydraulic pressure in front of the pivot pin.

The lower shoe is mounted on a piston 30 seated in a cylinder 31 to pressurize the shoe to apply squeezing force in the nip.

Hydraulic fluid is supplied to the piston from below the cylinder by suitable means, indicated by line 32.

Preferably, the cylinder or channel 31 below the piston is continuous; even if separated, the same pressure is applied to each chamber, so that the upward force at the shoe is equal to the length of the paper machine. uniform throughout.

If the cylinders or chambers 31 are continuous, the hydraulic fluid is at the same pressure throughout the successive cylinders 31, so a uniform upward force is applied over the length of the shoe, and the squeezing force at the nip is uniform across the paper machine. It is guaranteed that there is.

At high nip pressures, the upper beam 26 will flex slightly upwards in its center, but the shoes 10, 11 are sufficiently flexible to flex with the beam without adding too much force to the shoe's flex resistance.

This does not change the uniform pressure in the nip.

Similarly, although the piston flexes slightly as the upper beam 26 bends, the amount of curvature due to said flexing is minute and does not affect uniform nip pressure across the paper machine.

Even if the lower beam 28 bends downward, its shape is not transmitted to the shoe.

This is because the only upward force on the piston comes from the force of the hydraulic fluid in the cylinder 31 below the piston.

In some cases, it may be desirable to support the upper shoe on a piston and cylinder similar to piston and cylinder 30, 31 so that both the upper shoe and the lower shoe are pressurized.

Of course, it will also be understood that the lower shoe may be without a piston and cylinder and be supported directly on the pivot beam, and the piston and cylinder may be provided on the upper beam and the upper shoe.

If a single piston and cylinder is used, it is preferred to use the lower beam 28.

This is because the weight of the upper beam 26 will oppose the upward reaction force from the shoe pressing the nip.

During operation, the two bells N6, 17 are connected to the grooved traction roll 20
, 22 at the web travel speed.

The fels N8,19 carry the web between the felts in the nip, and from the time the web is introduced into the nip at the leading end of the shoe 10.11 until the web leaves the shoe, the web normally moves as water is removed from the web. It is supported by felt which is dried in the following manner.

The nip pressure is controlled by the pressure of hydraulic fluid supplied from the line 32 to the cylinder chamber 31.

At start-up, the shoe is held in loose engagement with the belt, and as the paper machine reaches operating speed, the pressure increases and is adjusted according to the desired operation and the amount of water removed from the web in the enlarged nip.

Although some moisture remains on the surface of the belt, the grooved pull roll drives the belt at a uniform speed while maintaining constant and uniform acquisition.

The advantage of the unique grooved traction roll is that by driving the grooved drive roll into contact with the other side of the belt, it can be expanded to other shapes, such as the structure described in U.S. Re-Patent No. 30,268. It should be understood that it can also be used for nip squeezing.

Other structural and method modifications within the spirit and scope of the invention are intended to be within the scope of the claims, and this application is not intended to be limited to the particular preferred embodiments disclosed.

[Brief explanation of drawings]

The figure is a schematic side view of the press section of a paper machine implementing the structure and principle of the present invention. N...Nip, W...Web, 10,
11... Shoe, 12, 13... Leading end, 14, 15... Compressing surface, 16, 17...
...belt, 16a, 16b. 16c, 16a, 17a, 17b, 17c, 17d...
...Guide roll, 18, 19...Felt, 18a. 18 b t 19 a, 19 b”...roll, 2
0, 22... Grooved traction roll, 21, 22.
...Dotted line, 24°25...Injection, 27,
29... Pivot pin, 26° 28... Beam, 30... Piston, 31... Cylinder, 32... Line.

Claims (1)

Claims: 1. A pressing mechanism for dewatering a running fibrous web, comprising: a first pressing shoe on one side of the nip having a disengaged leading end on one side of the nip and a subsequent elongated pressing surface; an elongated, enlarged squeeze nip formed between a separated leading end on the other side of the nip and a second squeeze shoe on the other side of the nip having a subsequent elongated squeeze surface; first and second running belts that pass through the nip between the shoes with a moisture storage means sandwiched between the web and the nip; and a driving relationship provided for each of these belts. a grooved traction roll around which the belt is wound; a lubricant at the leading end of each shoe to create a hydraulic wedge of lubricant between each shoe and the belt running through the nip; means for applying a squeeze force to at least one shoe that biases the shoe toward the nip to apply a dewatering squeeze force to the web at the nip. Squeezing mechanism.