Spreader Shower For Fabric Belts Of Paper Making Apparatus

Abstract

In a shower for cleansing the fabric on a paper machine, the shower nozzles are angled outward towards the edges of the fabric so as to spread the fabric and prevent ridges and wrinkles from forming. Preferably the nozzles are angled between 20.degree. and 30.degree. from the shower pipe and the shower is located after a driven roll.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improvements in the operation of a paper making machine. More specifically, this invention relates to a shower for simultaneously spreading and cleansing the fabric endless belts of such a paper machine.

2. Description of the Prior Art

In the Fourdrinier section of a paper making machine for example, a suspension of fibres is discharged onto the upper surface of a moving endless fabric screen belt called a Fourdrinier or forming wire. The belt travels over dewatering devices and is subjected to considerable drag force as it is driven by its drive roll. The belt is therefore required to transmit considerable power to the dewatering components and this develops a high tension in the upper run immediately before the couch or drive roll. The high tension before the couch roll causes the belt to stretch slightly in the machine (lengthwise) direction, and, as is the case with most flexible materials, it will tend to contract in the cross-machine direction, i.e., it will be narrowed in the width thereof, just as it runs onto the drive roll. The belt remains under high tension for most of its passage over the drive roll but, just before it approaches the outgoing tangent of the roll, tension is gradually released and the belt will then tend to contract in the machine direction and to extend in the cross-machine direction. Some longitudinal contraction occurs while the belt is still in contact with the surface of the roll at the outgoing side and localized slippage of the belt on the surface takes place here causing relative motion between fabric and roll in the longitudinal direction. Possibly, just before the belt emerges at the outgoing tangent of the roll a small increase in width also occurs which produces relative motion between fabric and roll in the lateral direction. Then, as minimum tension is reached at the return section (lower run) of the belt, an increase in width occurs while the belt is still under lateral restraint from contact with the roll and this results in the formation of ridges and puckers.

Small temporary ridges or puckers are not harmful as long as they do not remain to spoil the flatness of the fabric as it passes over the dewatering section of the machine. As often happens, however, particularly in high speed machines where the power transmitted is high and the belt is wide, the ridges are especially pronounced and may become permanent so that they will adversely effect the smoothness of the belt in the dewatering section and so cause deformities in the paper that is being produced. In the extreme, one or more permanent ridges can become sufficiently large to form creases which may extend around the entire length of the belt so that further use is not possible and the belt must be removed from the paper machine.

In order to alleviate this ridging effect, a bowed spreader roll (not shown) may be installed near the point where the belt comes off the couch roll. The roll is bowed in the general direction away from the couch roll so that it provides a spreading out effect on the belt which induces lateral tension away from the center of the belt thereby minimizing or eliminating the ridges. However, these bowed rolls cause maintenance difficulties and are expensive to buy and install especially in the case of a wide paper making machine.

Although the problem of ridges is present to some extent where the belts are metallic, i.e., comprised of bronze or stainless steel materials, the ridges are most pronounced when the belt is comprised of a synthetic fabric in which the stability in the width direction is not as great as in the case of the metallic fabric, so that the tendency to form ridges is, therefore, greater when the belt is made of a synthetic fibre.

SUMMARY OF THE INVENTION

The invention comprises a spreader shower for use on a paper making machine wherein runs one or more endless fabric belts; said shower comprising a series of nozzles joined by a pipe means for providing fluid under pressure to said nozzles; the said pipe being disposed across the width of said fabric and in substantially parallel alignment with and in close proximity to the surface of said fabric. The invention is characterized in that the nozzles are angled from said pipe means so that fluid emerging under pressure from the nozzles is directed to impinge outwardly, substantially towards the edges in the lateral direction, on said fabric. As a preferred embodiment, the invention may comprise a spreader shower for use in the forming section of a Fourdrinier paper making machine wherein said forming section comprises a forming fabric in the shape of an endless belt having a high tension upper run and a low tension lower run, as described heretofore; said pipe being disposed between the upper and lower runs of the endless belt and extending along the width of the said belt and in substantially parallel alignment with the lower run; said nozzles being directed at the lower run; characterized in that they are tilted from said pipe means by an angle of less than 90.degree. whereby the nozzles are directed outward towards the edges in the lateral direction of said fabric.

The invention may also be applied to types of forming sections which employ endless fabrics other than the Four-drinier type, for example Vertiforma, Bel-Baie Former, Papri-former, etc.

The invention is not limited to the forming section of a paper machine but may also be adapted for use in the press section where oscillating showers having needle type jets are used to cleanse the conveying felts. In this adaptation a spreader shower may be used to replace one or more worm rolls.

The spreader shower may also be used in the dryer section of a paper machine in locations where the fabric has a tendency to ridge.

Preferably, the nozzles of the spreader shower are directed outward at an angle between 10.degree. and 60.degree. with angles of 20.degree. and 30.degree. being the most preferred; the nozzles predominantly on the left hand side of the pipe means being directed at the left hand edge of the Fourdrinier forming fabric, and the nozzles predominantly on the right hand side being directed at the right hand edge of the Fourdrinier forming fabric.

A high pressure oscillating shower on the low tension run of the fabric, normally used to unplug the mesh of the fabric of fibres, particles of pitch, filler material, etc., can be modified, as above-described to fulfill the spreading function as well as its normal function. This is a preferred arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by an examination of the following description together with the accompanying drawings in which:

FIG. 1 illustrates the Fourdrinier section of a paper making machine having a couch roll drive.

FIG. 2 illustrates the drive section of a Fourdrinier having a separate drive roll.

FIG. 3 is a perspective view of appropriate parts of a paper making machine to illustrate the problems the invention overcomes.

FIG. 4 illustrates one way of adapting the needle type shower in accordance with the invention.

FIG. 5 illustrates another way of adapting the needle type shower in accordance with the invention,

FIG. 6 illustrates the use of fan type shower nozzles and

FIG. 6a illustrates an end view of the fan type shower nozzles.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 3 in the Fourdrinier section of a paper making machine, a Fourdrinier fabric in the form of an endless belt 1, having an upper run 1a and a lower run 1b, is driven over dewatering devices comprising foils 4, table rolls 5 and suction boxes 7 by a couch drive roll 9 as is well known in the art. In order to overcome the problem of the belt becomming plugged by paper fibres, filler material, particles of pitch, etc., many mills install a high pressure, needle type oscillating shower pipe 11 on the bottom run 1b of the belt 1. As needle type nozzles are used, the head must oscillate back and forth across the fabric to insure cleansing of the entire fabric. These showers use high pressure jets of water to dislodge the foreign materials from the fabric without adding an uneconomical volume of water to the white water solution which is circulated to the incoming paper stock. The shower is generally installed just after the couch drive roll 9 in FIG. 1 embodiment. In an apparatus comprising separate couch and drive rolls, 9 and 13 respectively (see FIG. 2), the shower 11 is positioned after the drive roll 13. In each case the shower is positioned between the upper and lower run of the belt and the shower nozzles are placed a few inches from and are directed towards the bottom run. It has been found in practice that when the belt comprises a synthetic material instead of a metallic material, the mesh is more subject to plugging and the role of the high pressure shower is very important.

Ridges formed when the belt goes from the high tension area at the upper run to the low tension area at the beginning of the lower run and emerges off the roll 9, are shown at 15 in FIG. 3.

Shower pipes adapted in accordance with the invention are illustrated in FIGS. 4 and 5. Referring to FIG. 4, the shower pipe 11 comprises a plurality of nozzles 12 each ejecting a needle spray or jet of a fluid medium, usually water, 14. The nozzles are tilted by an angle from the pipe 11 in the lateral direction of the fabric so that the spray impinges on the bottom run of the belt 1b at an angle .phi. relative to the fabric. The nozzles to the left of the center nozzle 12c are directed at the left hand edge of the fabric while the nozzles to the right of 12c are directed at the right hand edge of the fabric. In this embodiment, the nozzles are equally spaced and each nozzle is angled at the same angle, so that the horizontal component of force exerted by each nozzle will be the same. If it is desirable to vary the force across the belt, the angle of tilt can be varied as shown in FIG. 5. Here, the angle of tilt .phi. gradually increases from each edge to the centre so that the angle of impingement varies from .phi. at the lateral edge in increasing angles .phi., .phi..sub.2, . . . to .phi..sub.c at the center nozzle. The nozzles are preferably angled identically on both sides of the centre nozzle.

The force across the belt may also be varied by providing a variation in nozzle size from the centre to each edge. Here again, nozzle size would vary identically on both sides of the center.

It is also within the scope of the invention to provide unequal spacing between nozzles if this is advantageous in specific cases.

Although needle type jets have generally been used for the cleansing shower, it has been discovered that other types of jets can be used to advantage in accordance with the invention. Thus, fish tail (fan type) jets have been found satisfactory and indeed, as will be discussed below, can even be preferable to the needle type jets. In addition, although cleansing showers use only water, it has been discovered that other fluids, such as air, and possibly steam, could be used in accordance with the invention.

In the above description, the angle .phi. refers to the angle of tilt between the jet and the average plane of the fabric, measured in the cross direction. Localized deviations from the plane due to ridging or deflection of the fabric resulting from the jet are not considered. For the purpose of this description the angle .phi., representing the angle of tilt from the shower pipe, is also the angle of impingement on the cloth. In considering the question of preferred parameters, it is known that the horizontal component of force exerted by each nozzle varies with the pressure of the fluid, the nozzle diameter and the angle of impingement of the fluid. Spreading can therefore be achieved with high pressure and small nozzle diameter (small volume of fluid) or low pressure and large nozzle diameter (large volume of fluid). In the case where the fluid is water the ratio of pressure and volume would normally be selected only after considering the extra volume of water that could efficiently be accommodated by the paper machine. It is usually preferred to minimize the quantity of water added to the system and this can be done by reducing nozzle size and using high pressure. In tests to determine the preferred parameters, it was discovered that satisfactory operation is obtained with an angle of tilt .phi., ranging from 10.degree. to 60.degree. . The most satisfactory results were obtained with angles of 20.degree. and 30.degree. and angles in between. The above results were obtained when the fluid used was either water or air.

In considering the question of preferred pressure, i.e., the pressure under which water is supplied, it was postulated that this would depend upon the amount of water that could be accommodated which in turn would depend upon the nozzle size. In any case for a given nozzle size, pressure should be high enough to provide adequate lateral force for spreading the fabric.

Although a complete operating range of pressures was not determined, satisfactory results were obtained with both air and water at pressures of 100, 200, 400 and 600 psi. Nozzle sizes tried ranged from 0.036 inch to 0.067 inch in diameter.

A further parameter is the height of the nozzle above the fabric. In tests conducted in this regard, the height was taken from the tip of the nozzle to the fabric at right angles to the fabric, i.e., the vertical height of the nozzle tips above the fabric.

It was found that, when water was the fluid, and at the testing heights of 2 to 6 inches, the results were virtually independent of height. With air as the fluid, on the other hand, it was found that if the nozzles were more than one-half inch above the fabric, the lateral component of force of the jet was seriously reduced so that an air shower should preferably be kept no more than one-half inch above the fabric.

As discussed above, it is possible to use fish tail (fan type) nozzles rather than the needle type nozzles in accordance with the invention. In this regard, the wide part of the fish tail jet could extend along the length of the fabric. However, it has been found that it would be advantageous to have the wide part of the jet extend along the width of the fabric as shown in FIG. 6. An end view of the fish tail (fan type) jet is shown in FIG. 6a. In this case, the spray from one nozzle should preferably overlap the spray from an adjacent nozzle. Thus, it is possible to cover the entire width of the fabric without oscillating the shower pipe 11 as is required when needle type nozzles are used.

It is also possible to rotate the nozzles of the fish tail arrangement so that cleansing takes place both along the width and the length of the fabric.

Although in the preferred embodiment, the cleansing shower is modified to fulfill both the functions of cleansing and spreading, it will be apparent that separate showers could be used for each of these purposes. Thus, as shown in FIG. 2, it would be possible to have a shower 11 for spreading the fabric, and a shower 25 for cleansing it. However, when the same shower is used for both purposes, the parameters must be adjusted to insure that both functions will be fulfilled. So, although a smaller angle of tilt from the shower head may give a better spreading action, it is possible that the cleansing action will be weakened. This must be taken into account when making and adjusting the apparatus in accordance with the invention.

In some cases where the deposition of pitch in the mesh of the fabric is a special problem and the pitch cannot be eliminated by any less than the full force of a needle shower placed at right angles to the surface of the fabric, it may be necessary to employ a separate cleansing shower in addition to a spreader shower. Or, if space is limited, to provide a single shower head incorporating vertically directed nozzles for cleansing as well as angularly directed nozzles for eliminating ridges.

Although only a spray at right angles to the lengthwise direction of the belt has been considered (14b in FIG. 1), it is also possible to angle the nozzle so that it is at some other angle to the lengthwise direction of the belt, e.g., 14a and 14c in FIG. 1. It is preferred that the spray will be directed against the direction of travel of the belt, i.e., the direction 14c. However, if the nozzles are so angled, then a guard 20 should be included to insure that water does not splash back onto the couch roll 9 from which it might undesirably be introduced into the formed paper through the underside of the belt as it travels onto the couch.

Although several embodiments have been described above, this was for the purpose of illustrating, but not limiting the invention. Various modifications, which will come readily to the mind of one skilled in the art, are within the scope of the invention.

Claims

We claim:

1. A paper making machine comprising at least one endless fabric belt,

said endless fabric belt being driven by a driving roll;

said endless fabric belt comprising a high tension portion and a low tension portion,

said high tension portion being disposed in that portion of the belt preceding said driving roll in the direction of travel of said belt,

said low tension portion being disposed in that portion of the belt following said driving roll in the direction of travel of said belt,

and comprising at least one spreader shower,

said spreader shower comprising a series of nozzles joined by a pipe means for providing fluid under pressure to said nozzles, said nozzles comprising outlet ends,

the outlet ends of said nozzles being directed at a surface of said endless fabric belt in said low tension portion thereof,

said pipe means being disposed across the width of said endless fabric belt and in substantially parallel alignment with and in close proximity to said surface of said endless fabric belt,

each of said nozzles forming an angle of less than 90.degree. with said pipe means, and directed at said surface of said endless fabric belt,

the outlet ends of substantially all of said nozzles, located in that portion of the shower extending substantially from the center of the pipe means to the left hand end thereof, being directed toward the left hand edge of said fabric,

the outlet ends of substantially all of said nozzles, located in that portion of the pipe extending substantially from the center of the pipe to the right hand end thereof, being directed toward the right hand edge of said fabric,

whereby fluid emerging under pressure from the outlet ends of said nozzles will impinge on said surface of said endless fabric belt and will be directed substantially toward the lateral edges of said endless fabric belt.

2. A paper making machine as defined in claim 1 wherein the angle between each said nozzle and said pipe means is between 10.degree. and 60.degree..

3. A paper making machine as defined in claim 2 wherein the angle between each said nozzle and said pipe means is between 20.degree. and 30.degree..

4. A paper making machine as defined in claim 1 where said fluid is water.

5. A paper making machine as defined in claim 1 where said fluid is air.

6. A paper making machine as defined in claim 1 wherein said nozzles provide a fish tail type spray having a wide bottom impinging on said fabric, the length of said wide bottom extending in the width of said fabric; and wherein the bottoms of said sprays of adjacent nozzles overlap one another to thereby provide cleansing action over substantially the entire surface of the endless fabric belt.

7. A paper making machine as defined in claim 1 wherein said nozzles provide needle-type jet sprays, said spreader shower oscillating in the cross-machine direction of said endless fabric belt to provide cleansing action over substantially the entire surface of the endless fabric belt.

8. A paper making machine as defined in claim 7 and further including intermediate cleansing nozzles extending at an angle of 90.degree. from said pipe means in the direction of the surface of said endless fabric belt.

9. A paper making machine as defined in claim 1 wherein said endless fabric belt comprises an upper run and a lower run and wherein said upper run comprises said high tension portion and said lower run comprises said low tension portion, and wherein said spreader shower is disposed between said upper run and said lower run and closely adjacent to said lower run, said nozzles of said spreader shower being directed toward the lateral edges of said lower run of said endless fabric belt.

10. A paper making machine as defined in claim 1 wherein said endless fabric belt comprises a synthetic material.