Apparatus For The Continuous Pressure Treatment Of A Web

Abstract

The apparatus includes a drum and a pressure belt surrounding the drum almost completely with both drum and pressure belt being movable with the web disposed inbetween. A sleeve is disposed about the pressure belt as a supporting surface with a friction-reducing means, such as interconnected rollers, between the sleeve and pressure belt to transfer force. The sleeve ends are spaced apart to permit passage of the web and pressure belt while at the same time being urged together to impart a tensile force in the sleeve. This tensile force serves to exert a uniform pressure on the moving web substantially over the entire surface of the drum, which may be heated.

Description

FIELD OF THE INVENTION

This invention relates to an apparatus for the continuous pressure treatment of a web, and particularly to the continuous pressure treatment of webs of paper, textiles and the like.

DESCRIPTION OF THE PRIOR ART

Heretofore, in the continuous pressure treatment of moving webs it has been known to use pairs of rollers to compress the web as the web passes through the nip formed by each roller pair. Thus, the zone of action of the pressure is only the narrow roller nip, which in theory is merely a line but in practice, due to the thickness and compressibility of the material and the deformation of the roller surface, is a narrow zone. To enable treatment to be performed adequately, therefore, the treatment must often be repeated. Thus, the web has been guided through a number of successive roller nips, one after the other. This is done in known manner, for instance, in a paper calendar which normally comprises stacks of up to 12 superimposed rollers over which the paper web is guided, being looped alternately over the successive rollers. The required pressure treatment is performed between each pair of rollers, and the total operative surface is the sum of the narrow pressure zones of the individual roller nips. However, this involves a considerable expense due to the large number of rollers needed to obtain the operative surface, a large roller stand and many drives.

In order to overcome the disadvantages of these systems, it has been known to use an apparatus for the continuous pressure treatment of webs in which the pressure is operative over a larger area than with rollers, without the expense of providing a large number of rollers connected one after the other. The basic concept of this apparatus is to extend the working nip, in which pressure is exerted between two rollers, over the surface of one roller or drum thus increasing the operative surface. To this end, the operative surface is increased by substituting a concurrently movable forming belt for the matching roller and by partly looping the forming belt around the drum. The web is guided between the co-rotating forming belt and drum and is pressure-treated therebetween.

In this latter apparatus, the pressure which can be exerted on a web corresponds to the pressure under which the forming belt bears against the drum, and is determined by the tensioning of the forming belt. Such tensioning is usually subjected to fairly precisely defined limits. The forming belt is, of course, endless and must be deflected several times over rollers or drums in its path. The resulting bending causes tensile and compressive stresses in the material of the forming belt which must remain in the resilient zone, i.e., below the flow limit of the material of the belt. Since the drum radii cannot be increased as required to improve the bending geometry, with any particular construction there is a maximum permissible belt thickness, from which the limit of the permissible tensile loading of the belt is determined. The resulting radial pressures are, however, inadequate to produce on a web, for instance, an effect comparable with the work of a calender.

German Pat. Specification No. 923,172 discloses an apparatus for continuous pressing which includes a rotating drum having a steel forming belt looped around the surface by about 120.degree., the material to be pressed being disposed between the forming belt and the drum. In addition, a segment which has a supporting surface adapted to the outer shape of the forming belt is disposed outside of the forming belt and is pressed radially against the drum. Also, rolling members which transmit pressure from the supporting surface to the forming belt are rollably disposed between the steel belt and the supporting surface. When pressure is exerted in this way, there is no need for special belt tensioning, which is difficult to control.

However, the radial application of pressure by the supporting surface causes radial forces on the drum which must be absorbed by the drum bearing. Consequently, in the case of an apparatus for processing fairly wide webs such as, for instance, webs of paper, and also, if the zone of application of pressure is to be widened in the peripheral direction, bearing loadings can cause considerable technical problems. The expense of the apparatus would also be increased if attempts are made to attain pressures comparable with arrangements of rollers.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an apparatus for the continuous pressure treatment of webs in which the pressure is operative over a large area without the expense of providing a large number of rollers connected one after the other.

It is another object of the invention to provide an apparatus for the continuous pressure treatment of webs using a drum in which a substantial circumferential portion of the drum is used for the treatment.

It is another object of the invention to decrease the bearing load on a drum bearing wherein a web is continuously pressed against the drum surface by a concurrently moving pressure belt.

Briefly, the invention provides an apparatus for the continuous pressure treatment of a web comprising a rotatable drum, a movable pressure belt looped about the drum and a sleeve forming a supporting surface about the belt. The sleeve is disposed about the drum surface for substantially more than 180.degree. with a pair of opposed ends in spaced apart relation to form an axial nip for passage of the belt. In addition, friction-reducing means are provided between the sleeve and belt and means are interconnected to the ends of the sleeve to impart a tensile stress in the sleeve.

The sleeve is looped around the drum by more than 180.degree. to terminate in a zone in which the ends of the sleeve approach one another after being looped around the drum. As a result of this and the tensile force existing between the ends of the sleeve, the sleeve can act like a tensioning belt whose tensioning in the peripheral direction exerts a radial force on the pressure belt and the drum. The force corresponds to the pressure exerted on the web. Whereas, in the prior art arrangement, the force was directed from the supporting surface one sidedly against the drum, now, at least, a proportion of the force is left inside the sleeve and kept away from the drum bearing.

If the sleeve were only looped about the drum for 180.degree., the forces exerted on the drum in the supposed 180.degree. portion of the sleeve would produce a resultant force representing a very considerable force on the drum bearing. However, by looping the sleeve around the drum by more than 180.degree., the zones of the sleeve acting on the drum outside the 180.degree. portion create forces which reduce the aforementioned resultant, since they partly cancel out the first-mentioned forces. However, the distribution of force is not completely uniform, since a gap for the entry and exit of the web and the concurrently moving pressure belt has to be left at one place in the sleeve.

Although the resulting bearing forces are reduced by the supporting surface being constructed in the form of a sleeve, the working surface is extended over almost the whole drum periphery.

The sleeve can take the form of a steel plate bent around the drum. For instance, the sleeve can be a plate about 6 to 12 millimeters (mm) in thickness which is pre-shaped to match the drum shape. In contrast with the pressure belt, which is constantly deflected and bent backwards and forwards, during operation, the sleeve is only slightly deformed. There is therefore the required freedom in the dimensions of the sleeve whereas the pressure belt which is relieved from the job of applying force, can have the thin wall necessary to reduce the bending stresses.

Conveniently, to make full use of the tensioning-bolt-like effect of the sleeve, the pressure belt is guided around the drum, in known manner, in the shape of a meander having a narrow neck, and the ends of the sleeve extend as far as the vicinity of the neck. In this way, the sleeve engages around almost the whole drum and the gap for the entry and exit of the web and pressure belt is as narrow as possible.

Conveniently, controllable force elements are provided which exert the tensile stress on the ends of the sleeve. This feature enables the required working pressure to be adjusted in the same way as the setting of a pair of rollers is altered.

In a preferred embodiment of the invention, the tensile stress operative on the ends of the sleeve is transmitted via tensioning elements disposed outside the web width. The web and pressure belt can thus enter between the sleeve and the drum in the space between the tensioning elements.

In another embodiment, the tensioning elements engage directly with the ends of the sleeve. This feature is, of course, on condition that the sleeve ends are suitably reinforced so as not to be deformed by the forces operative only on both sides.

Alternatively, the tensioning elements can engage with transverse yokes which are disposed in the vicinity of the meander neck, outside the neck and inside the pressure belt, and which extend transversely over the web width. In this case, force-transmitting members are distributed over the web width and engage with the ends of the sleeve and the yokes. In this way, the tensioning force can operate at a number of places on the sleeve edge distributed over the width of the web, and the uniformity of the force exerted no longer depends on the transverse-breaking strength of such edge. The transverse yokes can readily be made very rigid, so as to absorb the high bending forces.

In another embodiment of the invention, a support bearing against the rotary bearing of the drum is disposed in the zone of the meander neck, and tensioning members engaging with the support are disposed at both ends of the sleeve. The sleeve ends are not directly interconnected, but are connected via the support. In operation, the support deflects the forces resulting from the fact that the sleeve is not completely looped around the drum to the drum bearing.

In another embodiment of the invention, the tensioning members associated with the two ends of the sleeve can exert a tensioning force independently of one another between that particular end of the sleeve and the fixed support. The independent exertion of force is advantageous since it allows, by suitable adjustment, compensation for the forces transmitted peripherally by the rotating drum to the sleeve. Thus, some of the tensioning members can be adjusted for stronger tensioning oppositely to the peripheral force than others of the members.

In another embodiment, a force member is provided which can move the place of engagement of the tensioning elements with the support away from the drum bearing. In this case, the tensioning elements can take the form of rigid anchors, only one force-exerting device being needed on each side.

The pressure belt can be basically made of any suitable material, for instance, even plastics or the like. In one embodiment of the invention the pressure belt takes the form of a steel belt while a second movable belt is provided between the steel belt and the drum. This enables the web to be pressed between belts of different kinds, depending on the treatment required. The web can extend between the second belt and the drum, or between the second belt and the pressure belt. When the treatment calls for this, the second belt is made of a material having a different surface texture from steel. In that case, the steel surface acts on the web on one side, and the special surface on the other. For treating paper, for instance, polyamide has proved very advantageous and can therefore be the material of which the second belt is made.

According to the invention, the forces between the sleeve and the pressure belt are transmitted by friction reducing means in the form of rolling members rolling therebetween which reduce friction when the pressure belt leads on the sleeve. Conveniently, the pressure belt and the rolling members run on endless tracks which extend around the outside of the drum.

In a preferred embodiment of the invention, the rolling members take the form of a large number of endless roller chains which are constructed to advance closely adjacent to one another. These roller chains are so constructed as to leave behind no zones of the belt over which they have not rolled, but to roll over the whole belt surface. The roller diameter is selected according to circumstances.

It is not absolutely necessary for the rollers to follow closely one behind the other in order to prevent the forming belt from sagging noticeably between the rollers. The pressure belt can become slightly corrugated. In that case, a roller-nip-like situation occurs at each roller for the web trapped between the pressure belt and the drum and the result as a whole is a treatment effect corresponding to the web passing through a succession of the same number of pairs of rollers. For the rest, however, the roller diameter is determined in accordance with the required working speed. For a higher working speed, larger roller diameters are convenient to keep the speed of rotation down.

Use must be made of pressure and temperatures simultaneously in many treatments of paper, textile and similar webs. For this purpose, the drum can be heated either electrically or by steam.

Moreover, in the pressure treatment of a web of material, the two pressure surfaces working against one another must often perform a relative movement in relation to one another to produce a so-called frictional effect. This is usually done, for instance, in friction calenders to make paper glossy or produce a chintz effect in textiles.

Conveniently, in order to produce a friction effect of this kind in the apparatus according to the invention, the drum and the pressure belt or the drum and the second belt or the second belt and the pressure belt can each be driven at different peripheral speeds. Which of these possibilities is adopted in each individual case depends on the guiding of the web. That is, those surfaces which enclose the web of materials between them must be given different peripheral speeds.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates a side view of an apparatus according to the invention utilizing one tension element at each side of the drum for tensioning a sleeve;

FIG. 2 diagrammatically illustrates a side view of a modified apparatus according to the invention utilizing a pair of tension elements at each side of the drum for tensioning a sleeve;

FIG. 3 diagrammatically illustrates a view of a tensioning element according to the invention which cooperates with a support to relieve a drum bearing of load;

FIG. 4 diagrammatically illustrates a view of a tensioning element interconnected with longitudinally disposed yokes on opposite sides of the sleeve in accordance with the invention;

FIGS. 5, 6 and 7 each illustrate a plan view of a different roller chain for use with an apparatus according to the invention;

FIG. 8 illustrates a side view of an apparatus in which the web runs between the drum and a plastic belt; and

FIG. 9 illustrates a side view of an apparatus in which the web runs between a plastic belt and a pressure belt.

DETAILED DESCRIPTION

Referring to FIG. 1, a web 1 runs in meander shape around a drum 2 which rotates around a shaft 3 in the directon indicated by arrow 4. A pressure belt 5 co-rotates, i.e., moves concurrently with the drum 2, on the outside of the web 1. The belt 5 is looped over a large portion of the periphery of the drum 2 so that the web 1 is trapped between the pressure belt 1 and the drum surface. A sleeve 6 is disposed outside of the pressure belt 5 to also enclose the drum 2 over a large part of the drum periphery, for example, over 180.degree.. To this end, the sleeve 6 is sized to extend to the vicinity of the neck 7 of the meander-shaped course of the pressure belt 5 to leave a gap 8 through which the web 1 and the pressure belt 5 can enter and exit between the sleeve 6 and the drum surface.

The sleeve 6 is stationary in relation to the rotating drum 4 and corotating pressure belt 5. In order to reduce the friction occurring between the pressure belt 5 and the sleeve 6, friction-reducing means such as roller chains 9 are provided which roll between the outside of the pressure belt 5 and the inside of the sleeve 6. These roller chains 9 form a supporting surface when the pressure belt 5 rotates or moves about the drum axis. The roller chains 9 are disposed close, one beside the other, over a width of the web and allow a rolling transmission of pressure over the whole supporting surface of the sleeve 6.

The ends 6', 6" of the sleeve 6 are interconnected via a means for imparting tensile stress in the sleeve 6. As shown, these means are tensioning elements 10 provided outside the web 1 on both sides of the web. The tensioning elements 10 each pull the ends 6', 6" of the sleeve 6 towards one another so that the sleeve 6 acts as a tensioning belt and exerts a radial pressure on the roller chains 9 which, in turn, transmit the pressure to the pressure belt 5 and the web 1. Although the sleeve 6 is stable, but not completely rigid, the radial pressure produced by the peripheral pulling of the sleeve is distributed substantially uniformly over the periphery of the drum 2. The sleeve 6 can be made, for instance, from steel plate about 6 to 12 millimeters (mm) thickness.

Referring to FIG. 2, wherein like reference characters indicate like parts as above, the ends 6', 6" of the sleeve 6 are not interconnected directly, but via tensioning members 11, 12 which are associated with each end 6', 6". These tensioning members 11, 12 are disposed on both sides of the web width and engage with a support 13 bearing against the drum bearing (not shown). The support 13 serves to absorb the forces produced by the angular position of the vectors of force of the tensioning members 11, 12. The vectors of force of the tensioning members 11, 12 correspond to the plane of the tangent to the drum 2 at the level of the ends 6', 6" of the sleeve 6. The higher the ends 6', 6" are pulled up onto the drum, i.e., the nearer the approach to one another, the flatter will be the tangents and, therefore, the lower the resulting force to be absorbed by the support 13 and, more particularly, by its bearing on the drumshaft 3.

Referring to FIG. 3, wherein like reference characters indicate like parts as above, instead of associating a tensioning member with each end 6', 6" of the sleeve 6 on each side, the support 13 is provided with a force member 14 while the sleeve ends 6', 6" are connected together via anchors 16, 17 which extend from a common point 15. The anchors 16, 17 are also connected to the support 13 at this point 15. The force member 14 is constructed to urge the point 15 upwardly, i.e., away from the shaft 3 of the drum 2. This also produces a tensile force between the ends 6', 6" to create the required tensioning. The force or power member 14 can be a pressure generator. Alternatively, in order to produce the same effect, a tension generator might also be provided on the support 13 above the point 15.

Referring to FIG. 4, wherein like reference characters indicate like parts as above, the means for imparting the tensile stress in the sleeve 6 includes two tensioning members 10 and two transverse yokes 18 in the form of I-beams which extend over the width of the web. Each tensioning member 10 is located to one side of the web 1 and is connected at opposite ends to a respective yoke 18. In addition, a plurality of force transmitting members 19 are distributed over the width of the web and are connected to the ends 6', 6" of the sleeve 6 and to the respective yokes 18. The members 19 serve to transfer the force of the tensioning member 10 from the yokes 18 to the sleeve 6. The transverse yokes 18 absorb the bending stresses produced by the fact that the tensioning members 10 are only laterally anchored. To compensate for the different forces produced by bending, the force transmitting members 19 take the form of hydraulic force members which are hydraulically interconnected.

The force members 10, 11, 12, 14 described above can be of any nature. Spindles, hydraulic cylinders or the like can be used. Since the working parts of the force members are small, it is more particularly recommended to use hydraulic units of large surfaces operating with diaphragm-like pressure cushions.

Referring to FIG. 5, the roller chain 9 comprises two rollers 20, 21 per link of different lengths disposed one beside the other. These rollers 20, 21 are also disposed alternately in successive links and are interconnected by bent straps 22. The rollers 20, 21 are mounted overhung and form aligned end faces, so that adjacent roller chains can be disposed directly one beside the other without leaving a gap. The rollers 20, 21 cover all places in the chain width, due to the offset arrangement of the gap between the rollers 20, 21 of each link.

Referring to FIG. 6, the roller chain 9 can alternatively be constructed with three rollers 23-25 per link disposed one beside the other and having different lengths in successive links. The successive links are connected by straight straps, but for a number of successive links, the straps are disposed offset towards the same side. As a result, the straps extend as a whole in zig-zag shape inside a chain, and therefore a roller constantly rolls over each place in the chain width.

Referring to FIG. 7, the roller chain 9 can also be constructed substantially as shown in FIG. 6 but with straps that do not extend in zig-zag fashion. In this case, the straps always extend in the direction of the same side, the straps being discontinued when they approach a certain distance from the chain edge and being restarted on the opposite side of the chain.

A plurality of the chains illustrated in FIGS. 5 to 7 run directly one beside the other, but independently of one another, so that there are no difficulties with regards to tilting of the roller axes.

Referring to FIG. 8, an embodiment the general construction of which corresponds to FIG. 2 is shown in greater detail. In this apparatus, a pair of drums or rollers 30 are provided to form the neck 7 of the meander-shaped course of the web 1 and pressure belt 5 around the drum 2. In this embodiment, the roller chains 9 rolling between the pressure belt 5 and the sleeve 6 are guided in a closed path around the outside of the drum 2 over rollers 31 disposed substantially in a square pattern. Similarly, the pressure belt 5 is guided around the drum 2 over rollers 32 outside the roller chain 9. A second belt 34 is also disposed between the pressure belt 5 and the web 1 and is guided around the drum 2 over rollers 33 outside the pressure belt 5. The roller chains 9, the pressure belt 5 and the second belt 34 can be tensioned independently of one another by tensioning devices whose function is indicated by the arrows 35, 36 and 37. All the drums 30 to 33 have shafts extending parallel with shaft 3 of drum 2.

The second belt 34 is made of polyamide which has special advantages, for instance, for the surface treatment of paper. Where the web 1 is a paper web which is located between the polyamide belt 34 and the surface of the drum 2, the pressure treatment of the web can be boosted by heating the drum 2. The drive of the polyamide belt 34 and pressure belt 5 can also be controlled to produce a different speed in the polyamide belt 34 relative to the surface of the drum 2 and, therefore, a frictional effect on the web.

Referring to FIG. 9, wherein like reference characters indicate like parts as above, instead of running the web 1 between the second belt and the drum 2, the second belt 38 can be arranged in such a way that the web 1 runs between the second belt 38 and the pressure belt 5. In this case, the second belt 38, which may be of a plastic material, runs over a single supporting roller 39 disposed above the nip of the meander. In this embodiment, a suitable drive produces a difference in speed between the second belt 38 and the pressure belt 5, which receive the web 1 therebetween to produce friction.

Claims

What is claimed is:

1. An apparatus for the continuous pressure treatment of a web comprising

a rotatable drum having a surface for engaging the web;

a movable pressure belt looped about said drum for concurrent movement therewith with the web disposed between said drum and said belt;

a sleeve forming a supporting surface about said belt, said sleeve being disposed around said drum surface for substantially more than 180.degree. with a pair of opposed ends in spaced apart relation for passage of said belt therebetween;

friction-reducing means between said sleeve and said belt; and

means interconnecting said ends of said sleeve to impart a tensile stress in said sleeve.

2. An apparatus as set forth in claim 1 wherein said friction-reducing means includes a plurality of rolling members rollably disposed between said sleeve and said belt.

3. An apparatus as set forth in claim 1 wherein said sleeve is a bent steel plate.

4. An apparatus as set forth in claim 1 which further comprises means for guiding said belt around said drum in the shape of a meander having a narrow neck and wherein said ends of said sleeve extend into the vicinity of said neck.

5. An apparatus as set forth in claim 1 wherein said means interconnecting said sleeve ends includes controllable force elements for exerting a tensile stress on said sleeve ends.

6. An apparatus as set forth in claim 5 wherein said elements are disposed outside of the width of the web.

7. An apparatus as set forth in claim 6 wherein said elements are directly connected with said sleeve ends.

8. An apparatus as set forth in claim 6 wherein said means interconnecting said sleeve ends further includes a pair of transverse yokes, each yoke being disposed along said neck across the width of the web and connected to said controllable force elements, and a plurality of force transmitting members connecting each yoke to said sleeve over the width of said sleeve.

9. An apparatus as set forth in claim 5 further comprising a bearing journalling said drum therein, and a support mounted on said bearing in the plane of said neck with a pair of said controllable force elements connected to opposite ends of said sleeve bearing on said support.

10. An apparatus as set forth in claim 9 wherein each controllable force element is independently connected to said support relative to an opposed controllable force element.

11. An apparatus as set forth in claim 5 further comprising a bearing journalling said drum therein and a support mounted on said bearing in the plane of said neck, wherein said means interconnecting said sleeve ends includes a pair of tensioning elements on each side of the web connected to said ends and to a common point with said force controllable element connected between said point and said support to displace said point away from said bearing.

12. An apparatus as set forth in claim 1 wherein said pressure belt is a steel belt and which further comprises an additional belt movably mounted between said steel belt and said drum.

13. An apparatus as set forth in claim 12 wherein the web is disposed to run between said additional belt and said drum.

14. An apparatus as set forth in claim 12 wherein the web is disposed to run between said additional belt and said pressure belt.

15. An apparatus as set forth in claim 12 wherein said additional belt is made of polyamide.

16. An apparatus as set forth in claim 12 including means for driving said drum and means for driving said belts at different peripheral speeds.

17. An apparatus as set forth in claim 1 wherein said pressure belt and said friction-reducing means run on endless paths extending around the outside of said drum.

18. An apparatus as set forth in claim 17 wherein said friction-reducing means includes rolling members in the form of a large number of endless roller chains advancing closely adjacent to one another.

19. An apparatus as set forth in claim 1 further including means for heating at least one of said drum and said sleeve.

20. An apparatus as set forth in claim 1 including means for driving said drum and means for driving said pressure belt at different peripheral speeds.