US3530035A - Suction box for draining pulp web on papermaking machine - Google Patents

Description

"231 22, J. WEY SUCTION BOX FOR DRAINING PULP WEB ON PAPERMAKTNG MACHINE Filed Sept. 6, 1966 2 shee'iswheei 1 Iwvemok 24cm; WEY

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J. W EY SUCTION BOX FOR DRAINING PULP WEB ON PAPERMAKING MACHINE Sept. 22, 1970 Filed Sept 6. 1966 IN V M/10k JBSEPH may United States Patent 3,530,035 SUCTION BOX FOR DRAINING PULP WEB ON PAPERMAKING MACHINE Joseph Wey, Lucerne, Switzerland, assignor to Nippon Denso Kabushiki Kaisha, Aichi-ken, Japan Filed Sept. 6, 1966, Ser. No. 577,508 Claims priority, application Switzerland, Sept. 6, 1965, 12,487/65 Int. Cl. D21f 1/50 US. Cl. 162-373 2 Claims ABSTRACT OF THE DISCLOSURE A support surface for the permeable belt carrying the pulp web across a suction box of papermaking machines, for draining the pulp web, includes cylinders mounted for rotation about axes extending transversely of the belt movement and spaced longitudinally of the belt, the cylinders being commonly tangent to the belt. The cylinders are supported on roller assemblies, the supporting rollers of each roller assembly being coaxial and axially spaced on a common shaft for rotation about an axis parallel to and spaced below the axes of the web supporting cylinders. The roller shafts are supported on spaced bearings, and the rollers are relatively narrow axially, the axial spacing of the rollers being substantially in excess of the axial width of the rollers.

This invention relates to suction boxes for draining the pu p -web on papermaking machines and, more particularly, to a novel, improved and more efficient suction box support surface for the permeable belt carrying the pulp web.

In the manufacture of paper, the pulp web is pulled, in sheet form, over a suction box by means of a conveyor belt which is pervious to water. These suction boxes form a substantial part of the suction zone in the wet unit of papermaking machines.

In known suction draining devices used on papermaking machines, the pulp web is transported, at the suction point, over at least one suction box connected with a vacuum pump. The pulp, which is mostly paper pulp in the form of a sheet, and having a high liquid content comprising paper pulp-water, is supported, during such movement, by a permeable conveyor belt. The conveyor belt is drawn, in sliding engagement, over the upper edges of the suction box, with the belt por tion ladden with pulp being pressed by atmospheric pressure, existing above the suction zone of the individual suction box, against the suction or support surface of the box. Thus, corresponding friction forces are produced, and these have a braking effect on the belt and a friction effect on the slidably engaged surfaces.

These friction forces, and thus the braking and the friction effect, are the greater the lower the vacuum in the suction box. In order to obtain a good draining effect, the vacuum should be as low as possible but, because of the above-mentioned friction effect, it must be set far above otherwise desirable values. For example, it must be set at only 2 m.w.c. (meters water column) instead of the desirable value of 5 m.w.c. For this reason, the suction box has been provided with devices ice which greatly reduce the friction between the conveyor belt and the upper surface of the box slidably engaged by the conveyor belt.

In a known and widely used arrangement, and endless perforated rubber belt, which is grooved on its exterior surface in a direction transverse to its direction of motion, is placed loosely around the suction box. On the surface of the suction zone of the suction box, this nubber belt is closely engaged, due to the suction effect, with a conveyor belt running over the rubber belt. The rubber belt moves with the conveyor belt in the range of the suction box. The rubber belt moves around the box over glide rolls operatively mounted on the box. At the suction surface of the box, the friction between the rubber belt and the conveyor belt is very low because both belts are running at practically the same speed. However, at the reversing points of the rubber belt, a higher friction cannot be avoided because the surface of the rubber belt, at these points, undergoes a slight variation in its speed.

The friction between the rubber belt and the suction box is greatly reduced by a special arrangement of the suction holes and by water lubrication. Overall, the friction is reduced to such an extent that it is only about /5 of the friction in conventional suction boxes in which the permeable belt has a sliding engagement with the suction box.

However, even with these improvements, the friction forces are still high enough to wear out the rubber belt relatively soon, both on its inner bearing surface and on its outer bearing surface. When the lubricant water, which would counteract the draining if provided in excessive doses, is added too sparingly or shut-01f completely, the inner surface of the rubber belt can be softened and spoiled in a short time by the resulting heat of friction. Wear on the outer surface is caused primarily by the unavoidable effect of the reversing points, as mentioned above.

Since the suction grooves are arranged transversely to the direction of motion of the rubber belt and move within the suction zone along with the pulp web, they can leave permanent marks on the pulp web because of the special suction effect at these points. This is highly undesirable. Frequently, damage is observed on the edges of these rubber belts, and these are caused by undesired forces acting on the belt transverse to its direction of motion and which push the belt to one side or the other against the lateral guiding ledges.

In high speed papermaking machines, the unavoidable centrifugal forces act to an increasing extent at the reversing points on the rubber belt, so that the use of suction boxes with revolving rubber belts is no longer of practical interest because of the difficulties encountered. These difficulties include detachment of the rubber belt at the first point of contact, resulting in suction difficulties and looseness, respectively, and in the requirement for guide cylinders or rollers having large diameters and expensive rubber belts With metal braid inserts. The difficulties also include increased danger of edge damage due to the high speed of operation, and the necessity of providing suction devices which are very expensive from the standpoint of initial cost and maintenance cost.

An object of the present invention is to provide a suction box belt support surface for papermaking machines and which is free of the disadvantages of the prior art as mentioned above.

Another object of the invention is to provide a suction box for papermaking machines in which the upper covering of the suction box, serving as a support surface for the permeable belt, is formed by at least two rotatable cylinders which are spaced apart in the direction of travel of the belt.

A further object of the invention is to provide a suction box for papermaking machines in which said cylinders are rotatable about horizontal axes extending transversely to the direction of motion of the belt.

Yet another object of the invention is to provide a suction box for papermaking machines, of the type mentioned in the two preceding paragraphs, in which each cylinder is supported on respective rotatable roller means rotatable about axes parallel to and below the axes of rotation of the cylinders.

A further object of the invention is to provide a suction box for papermaking machines, of the type just mentioned, in which substantially entire interior of the suction box is in direct communication with the part of the paper pulp web above the suction box through intervals between the cylinders so that a uniform distribution of the suction effect over the entire pulp web, in the area of the suction box, is attained.

An advantageous feature of the invention is that each cylinder is supported by a pair of rollers which are coaxially mounted for rotation beneath the associated cylinder, this pair of rollers avoiding any bending of the associated cylinder even if cylinders with a small diameter are used. Smaller diameter cylinders have the advantage that a relatively large number of cylinders can then be provided, which results in only a slight sagging of the web.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a partial vertical longitudinal sectional view through one form of suction box embodying the invention;

FIG. 2 is a partial horizontal sectional view of the suction box shown in FIG. 1; and

FIGS. 3, 4 and 5 are views, similar to FIG. 1, illustrating, respectively, a second, third and fourth embodiment of the suction box bel-t supporting surface in accordance with the invention.

Referring first to the embodiment of the invention shown in FIGS. 1 and 2, a suction box 1 is connected with a suction device (not shown) and has an inwardly directed upper rim flange 1a. A plurality of roller asemblies 2 are mounted in suction box 1, beneath the upper surface of the latter, for rotation about horizontal axes extending transversely of the path of movement of the pulp and spaced substantially longitudinally of such path.

In FIG. 1, the direction of movement of the pulp web P is indicated by arrow a. Each roller assembly 2 includes a common shaft 2a having a plurality of rollers 2b mounted thereon for rotation. Each shaft 2a is supported at relatively short axial spacings in bearing blocks 3, and the distance between the axes of adjacent shafts 2a is, as shown in FIGS. 1 and 2, somewhat greater than the diameter of rollers 2b. It will further be noted that rollers 2b are relatively thin, or relatively narrow in an axial direction, and are spaced at substantially uniform distances along the associated shaft 2a. The inner height of suction box is only slightly larger than the diameters of rollers 2b.

In the embodiment illustrated in FIGS. 1 and 2, each pair of adjacent roller assemblies 2 rotatably supports a cylinder 4 for rotation about a horizontal axis, the cylinders 4 extending over the full width of suction box 1.

Cylinders 4 are guided by the lateral walls of suction box 1, and their axes of rotation are substantially in the horizontal plane of the upper opening of the suction box. The diameter of supporting cylinders 4 is preferably substantially equal to the diameter of rollers 2b, as illustrated in FIGS. 1 and 2. In any case, however, the diameter of each cylinder must not be so great that the cylinders 4 will contact each other. On the other hand, the cylinder diameter should not be so small that the permeable belt Q passing over cylinders 4 can sag, together with pulp web P, between a pair of cylinders 4 and onto the rollers 2b.

Due to the arrangement and dimensioning of cylinders 4, the vacuum produced in suction box 1 can act effectively between cylinders 4 over practically the entire web portion then above the suction box. Naturally, measures have to be taken to be sure that the openings between the suction box and the pulp web, at the sides thereof, are sufficiently sealed. The sealing of the suction box at its front and rear edges, extending transversely to the direction of motion, and with respect to cylinders 4, is effected by means of sealing flaps 5 secured on upper flange 1a of suction box 1 and bearing against cylinders 4. While cylinders 4 can be driven in any manner, the driving can be effected, if necessary and by way of example, indirectly through one or more of roller assemblies 2.

Since the rollers 2b are relatively thin in an axial direction, they fill only a relatively small inner space of suction box 1, as compared to solid cylinders. Thus, cylinders 4 are completely exposed between the relatively thin rollers 2b and thus a satisfactory uniform distribution of the suction effect, over the permeable belt extending freely between the narrow supporting areas on cylinders 4, can be obtained.

Rollers 2b, in turn, provide a satisfactory support for the relatively long and heavily loaded cylinders 4, so that bending of these cylinders is substantially impossible and a completely planar belt support is provided. It will be undestood that rollers 2b need not necessarily be combined into roller assemblies 2, as rollers 2b could be supported individually for rotation. In order to keep the supporting circumferential surface of the rollers 2b small, they can have tapered or bevelled peripheries. Impurities adhering to the surfaces of cylinders 4 cannot cause any unsteadiness when engaged with a relatively sharp-edge bearing surface of rollers 2b. The surfaces of rollers 2b are subjected to minor wear only, and no special lubricant, such as water, is required. Since the conveyor belt bears on the cylinders only above the suction Zone, so that only a rolling friction is produced, the wear on the belt is also reduced. For this reason, it is possible to use relatively high belt velocities.

In the embodiment of the invention shown in FIGS. 1 and 2, as just described, each of the individual cylinders 4 has a bearing on two adjacent roller assemblies 2 including several rollers 2b, which roller assemblies are, in turn, supported in fixed bearings 3. However, the individual cylinders 4 can also be supported on only a single roller assembly, or on one or several coaxial rollers, provided care is taken that cylinders 4 are secured against displacement in the direction of motion of web P. An example of such an arrangement is shown in FIG. 3.

Referring to FIG. 3, a plurality of roller assemblies 12 are supported in suction box 11, these roller assemblies 12 each having a common axle 12a on which there are supported, in axially spaced relation, a plurality of rollers 12b. In the arrangement of FIG. 3, the rollers 12b of adjacent assemblies 12 are staggered axially with respect to each other. In other words, and considered in the direction of travel of web P, the rollers 12b of adjacent roller assemblies overlap each other. The rollers 12b of each roller assembly 12 support two relatively small diameter cylinders 14a extending over the entire width of suction box 11.

In order to prevent displacement of cylinders 14a rela--' tive to the supporting rollers 12b, cylinders 14a are retained by supporting plates 1601. These plates serve, at the same time, as splash guards, and thus prevent water picked up by the rotating cylinders 14a from being splashed onto the adjacent supporting cylinder 14a wherefrom it can again reach the screen or perforated belt Q. As can be seen from FIG. 3, the stagger or offset of the axes of the cylinders 14a with respect to the axle 12a of the associated roller assembly 12 is only very small. Thus, in practice, only relatively small retaining forces need be exerted by supporting plates 16a.

Referring again to FIG. 3, additional web and belt supporting cylinders 14b, of a larger diameter than cylinders 14a, are disposed between each pair of supporting cylinders 14a. The relatively larger diameter intermediate supporting cylinders 14b are supported on the rollers 12b of adjacent roller assemblies 12. Retaining plates are not necessary for cylinders 14b, but a plate 16b is associated with each cylinder 14b to serve as a splash guard. It will be noted that the support of cylinders 14b on rollers 12b is similar to the support of cylinders 4 on rollers 2 of the embodiment of the invention shown in FIGS. 1 and 2. In contrast to the embodiment of FIGS. 1 and 2, wherein all of the supporting cylinders have the same diameter, the cylinders 14b, which are borne in the depression between two adjacent roller assemblies 12, have a larger diameter than supporting cylinders 14a which are disposed symmetrically with respect to a vertical plane through the axis of the associated roller assembly 12. However, the relative diameters of the two cylinders 14a and the cylinder 14b are so selected that all the cylinders 14a and 14b are tangent to a common horizontal plane.

Another arrangement in which each web supporting cylinder is supported on only one roller assembly is illustrated in FIG. 4. Referring to FIG. 4, the web supporting cylinders 24 are offset rearwardly, by the distance e, with respect to the vertical plane through the axis 22a of the associated supporting roller assembly 22 in order to counteract, during operation of the suction device 21, the tendency of the supporting cylinders to move in the direction of motion of the permeable or perforated belt P. Supporting plates 26a are provided in association with each cylinder 24 and serve to restrain backward and downward movement of the associated cylinder, particularly when the plant is at a standstill. However, with a correct selection of the offset distance e, the necessary restraining force is very small.

n the other side of each supporting cylinder, there is arranged a similar plate 26b which, however, does not have to exert a restraining force on the associated cylinder 24. Each retaining plate 26b has mounted, adjacent its upper end, a splash guard element 26c. The two plates 26a and 26b, form a unit together with one or more bearing blocks 27 supporting the axle 22a of the associated roller assembly 22. The several units are secured in suction box 21 by screws or bolts 28, and can be inserted, removed, or interchanged as a unit. In contrast to the embodiment shown in FIGS. 1, 2 and 3, the cylinders 24 of the embodiment shown in FIG. 4 are hollow or tubular. However, it should be understood that either hollow or solid cylinders can be used in any one of the embodiments.

The magnitude of offset e is small, and is determined by the desired effect that cylinder 24, which is loosely supported by plates 26a and 26b and rollers 22b, is prevented from applying undesired forces against the forward one of the plates under the action of the moving belt. If the magnitude of offset e is too large, cylinder 24 would no longer be supported by rollers 22b. Furthermore, the cylinders and the rollers must be arranged between the plates, and thus the cylinder, if offset, may not extend beyond the plates. In the example shown in FIG. 4 the radius of cylinder 24 should not be substantially 6 smaller than the radius of roller 22b. Taking these factors into consideration, the magnitude of offset e should be of the order of the relatively small difference between the radius of rollers 22b and the radius of cylinder 24.

In the embodiment of the invention shown in FIG. 5, tubular web and belt supporting cylinders 34 are provided, and each cylinder 34 is rotatably supported on a pair of adjacent intermediate roller assemblies 32. In contrast to the embodiment of FIGS. 1 and 2, intermediate roller assemblies 32 are not supported di ectly in fixed bearings. Instead, the axle 32a of each intermediate roller assembly 32 is rotatably supported on a pair of adjacent support roller assemblies 39, each including an axle 39a and a plurality of axially spaced support rollers 39b. Axles 39a are arranged in fixed bearing supports 33, and it will be noted that the rollers 39b of adjacent roller assemblies 39 overlap each other in the same manner as described in connection with the embodiment of the invention shown in FIG. 3. Intermediate roller assemblies 32 act as reduction means between supporting roller assemblies proper 39 and web supporting cylinders 34, and by means of so acting, the friction forces counteracting the belt drive can be kept small. correspondingly, the bearing stresses on supports 33 can be kept small. In FIG. 5, supporting cylinders 34 are tubular or hollow. Not only can either solid or hollow web and belt supporting cylinders be used in each of the embodiments, as necessary or desirable, but also the supporting rollers such as 2b can be, in any one of the embodiments, either supported on a common continuous shaft or individually supported in side-by-side relation and in axial alignment.

What is claimed is:

1. In papermaking machines of the type including a suction box having an upper support surface over which a permeable belt, supporting the paper pulp web in sheet form, is drawn for draining the pulp web: an improved suction box support surface for the belt and web comprising, in combination, at least two cylinders mounted for rotation about parallel axes extending transversely of the path of movement of the belt and spaced longitudinally of the path, said cylinders being commonly tangent to the path of the permeable belt; a roller assembly of at least two coaxial and axially spaced support rollers rotatably supporting each cylinder, the support rollers being mounted on a common shaft for rotation about an axis parallel to and space below the axis of the supported cylinder; the axis of said common shaft being offset laterally relative to the axis of the supported cylinder by a distance of the order of the difference between the radius of the supported cylinder and the radius of said support rollers; plural bearing blocks rotatably supporting each common roller shaft; at least one retaining plate connected to said bearing blocks to restrain displacement of the associated cylinder along the path of travel of the belt; each cylinder, its supporting roller assembly, the associated bearing blocks and the associated retaining plate being combined to form a removable unit; each retaining plate serving also as a splash guard with respect to adjacent units along the path of travel of the belt; and flap means sealing the sides of the suction box with the adjacent cylinder.

2. In papermaking machine of the type including a suction box having an upper support surface over which a permeable belt, supporting the paper pulp web in sheet form, is drawn for draining the pulp web; an improved suction box support surface for the belt and web comprising, in combination, a plurality of cylinders mounted for rotation about axes extending transversely of the path of movement of the belt and spaced longitudinally of the path, said cylinders being commonly tangent to the path of the permeable belt; a plurality of adjacent roller assemblies, each said roller assembly including at least two coaxial and axially spaced support rollers mounted on a common shaft with a plurality of stationary bearings, in axially spaced relation to each. other, rotatably supporting each common shaft; the support rollers of adthe suction box sealing the sides with the adjacent jacent assemblies being staggered axially relative to each cylinder. other with the rollers of one assembly overlapping the rollers of the adjacent assembly; intermediate roller as- References Cited semblies including coaxial and axially spaced rollers, the 5 UNITED STATES PATENTS rollers of each intermediate roller assembly being dis- 1,955,399 4/1934 W ton 162- 373 XR posed on a common intermediate roller shaft, each inter- 2,990,015 6/1961 Carrel 162373 X mediate roller shaft being rotatably supported on the support rollers of two said roller assemblies; each said cylin- S. LEON BASHORE, Primary Examiner der being rotatably supported on the rollers of two said 10 R H TUSHIN Assistant Examiner intermediate roller assemblies; and flaps at each side of

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