An installation for compacting paper and method of using the same

Abstract

 An installation for compacting paper comprises a processing device (13) shiftable along a rail (14) transversally to the direction of motion of a rubber blanket (4) running over blanket carrier rolls (1, 2, 3) which impresses a microcrepe-like structure on a paper web (9). The processing device (13) which is used to grind or roughen the outer surface of the rubber blanket (4), e.g., once a day, has a drivable processing wheel (15) rotatable about an axis parallel to those of the blanket carrier rolls (1, 2, 3) and exhibiting a structured surface covering at least part of its circumference which can be pressed against the rubber blanket (4). The structured surface can be formed by grinding teeth covering a base or, if the paper web (9) is to be provided with a high friction surface, with blade-like extensions arranged in parallel rows on a base. For siphoning off the cuttings a pipe (18) which is part of a suction apparatus is arranged at the processing wheel (15). The processing device (13) is shifted along the rail (14) at intervals, with the processing wheel (13) rotating and pressing against the outer surface of the rubber blanket (4) for processing, e.g., grinding, the same.

Description

Field of the invention

[0001] The invention concerns an installation for compacting paper and a method of using the same. Such installation is usually part of a paper machine where it provides a web of smooth paper with a microcrepe-like structure as is desirable or required in certain types of paper, in particular, kraft paper for large paper bags as used for transport and storage of powdery and granular materials.

Prior art

[0002] An installation generally conforming to the generic type, but not provided with a grinding device, and its function are described in EP 0 749 828 A2.

[0003] As the surfaces of the rubber blanket used for compacting paper tend to oxidise and become slippery such that the installation cannot satisfactorily fulfil its function of impressing a microcrepe-like structure on the paper web any more it is well known to provide the installation with a grinding device which can be used from time to time, e.g., once a day, for removing the oxide layer from the outer surface of the rubber band and grinding it by moving it over the rubber band in a transversal direction without interfering with the operation of the installation and the paper machine. The known grinding device comprises two rolls, one drivable by an electric motor and one a pulley, and an abrasive belt guided by the rolls whose abrasive outer surface can be pressed against the outer surface of the rubber belt while the grinding device moves along a rail which transversally extends along the rubber blanket.

[0004] A grinding device of this type is rather bulky and heavy. The possibilities of varying the properties of the abrasive belt are limited. Furthermore, there is always a risk of the belt breaking during operation and consequent damage of the rubber blanket which is relatively expensive and whose exchange is time-consuming and not possible without an interruption of the paper making process.

Summary of the invention

[0005] The above-mentioned problems are solved by the features in the characterising portion of claim 1. According to the invention, instead of an abrasive belt a processing wheel with a structured surface which is usually abrasive is used. The processing wheel has a much longer service life and a sudden break-up resulting in damage to the rubber blanket is unlikely. Towards the end of its service life it will merely become less effective in that its abrasive properties decline. In that case it can be rather easily exchanged and in most cases recoated and put to use again. Moreover, position and motion of the processing wheel can be controlled with much higher precision.

[0006] The properties of the processing wheel can be chosen within a wide range. The structured surface can be covered with an abrasive layer similar to those used on an abrasive belt or it can exhibit a rasp-like structure with larger radial extensions but it can also have a metallic surface of almost any structure, coated or not with some extremely hard and wear-resistant material like tungsten carbide. This opens, beside the grinding proper, also indirect ways of influencing the character of the compaction, i.e., of the resulting paper surface which may be optimised for tensile strength, tensile energy absorption, porosity, frictional coefficient and other parameters. Different processing wheels can be used in succession as the exchange of wheels is easy.

Brief description of the drawings

[0007] The invention is explained more fully in the following with reference to figures which represent merely exemplary embodiments, and wherein:

Fig. 1a

schematically shows a side view of an installation according to the invention,

Fig. 1b

schematically shows a top view of the installation of Fig. 1a,

Fig. 2a

shows a side view of a processing wheel used in the installation of Fig. 1a and Fig. 1b, according to a first embodiment of the installation,

Fig. 2b

shows a top view of the processing wheel of Fig. 2a,

Fig. 3a

shows a side view of a processing wheel used in the installation of Fig. 1a and Fig. 1b, according to a second embodiment of the installation, and

Fig. 3b

shows a top view of the processing wheel of Fig. 3a.

Description of the preferred embodiments

[0008] An installation for compacting paper comprises (Fig. 1a,b) blanket carrier rolls 1, 2, 3 of which at least one is drivable and one serves as a tensioning roll and a rubber blanket 4 which forms a closed loop running over the blanket carrier rolls 1, 2, 3 moving in the direction of the arrow 5 at a speed of up to 1200 m/min. An outer guide roll 6 contacts an outside of the rubber blanket 4. A nip bar 7 exerts a force on an inner surface of the rubber blanket 4 directed towards a heated cylinder 8 with a polished surface which is part of a paper machine, such that a paper web 9 consisting of paper with a water content of between 30% and 40% and which moves in the direction of arrow 10 is pinched between an outer surface of the rubber blanket 4 and the circumference of cylinder 8. Two spray tubes 11 and 12 spray the inner surface of the rubber blanket 5 with a fluid, usually water.

[0009] Having passed the gap between the cylinder 8 and the nip bar 7 where it is compressed and its velocity conforms to that of the cylinder surface the rubber blanket 4 moves slightly slower than the cylinder surface and the incoming paper web 9. The latter is therefore somewhat compressed in the direction of its movement and thereby a microcrepe-like structure impressed on it which improves its properties with respect to tensile energy absorption and frictional coefficient.

[0010] A processing device 13 can be shifted along a rail 14 which runs in a direction transversal to the direction of motion of the rubber blanket 4, preferably parallel to the blanket carrier rolls 1, 2, 3, e.g., by a chain driven by an electric motor. The processing device 13 comprises a processing wheel 15 which in the standard embodiment shown is a grinding wheel. The processing wheel 15 is partially covered by a housing 16 and drivable by an electric motor 17 to rotate about an axis parallel to the rail 14. A pipe 18 arranged just under the processing wheel 15 is part of a suction apparatus.

[0011] The processing device 13 can be switched in and out of an active state where the processing wheel 15 rotates, driven by electric motor 17, and is in contact with the rubber blanket 4. When it is not in its active state, the electric motor 17 is switched off and the processing wheel 15 is at a distance from the rubber blanket 4. The processing wheel 15 can be moved in and out of contact with the rubber blanket 4 by small clockwise and, respectively, counter-clockwise rotations of the rail 14. The position of the processing wheel 15 can in this way be controlled with great precision.

[0012] The processing wheel 15 (Fig. 2a,b) can have a generally cylindrical shape with a barrel-shaped circumferential abrasive structured surface 19. The latter can have a smooth base densely covered by small grinding teeth as indicated in Figs. 2a,b. The teeth consist of a very hard and wear-resistant material, e.g., tungsten carbide or steel. Processing wheels of this type are available and have been used for the purpose of roughening rubber conveyor belts and generally processing the surfaces of objects made of rubber and other elastomers.

[0013] The grinding of the rubber blanket 4 is carried out without interruption of the compacting process in that the processing device 13 is switched to the active state, i.e., the electric motor 17 is switched on and the processing wheel 15 which now rotates in a clockwise direction (Fig. 1a) pressed against the outer surface of the rubber blanket 4 at a first edge of the latter. Then the processing device 13 is shifted slowly along the rail 14 to the opposite edge of the rubber blanket 4. The cuttings which are removed from the same during this process are siphoned off into the pipe 18 of the suction apparatus which may be part of the grinding device 13 or a stationary component of the installation connected to the pipe 18 by a flexible hose.

[0014] For the processing wheel there are many possibilities. E.g., instead of using a one-piece processing wheel as explained above it is also possible to use a processing wheel consisting of several narrow discs which are aligned along the axis of rotation, one following immediately upon the other. The discs can be equal or different. This allows an even wider range of choices for the properties of the processing wheel 15 which in turn influence, via the rubber blanket 5, the properties of the finished paper.

[0015] The processing wheel 15 of Fig. 3a,b is a roughening wheel consisting of six equal discs 20. On the circumferential surface of each of the discs 20 an uninterrupted row of larger radially projecting blade-like extensions 21 is arranged. They can consist of a very hard and wear-resistant material line tungsten carbide or of steel in which case they are preferably coated with such material. The circumferential surfaces of the discs 20 form a base partially covered by the blade-like extensions 21 which together provide a very rough rasp-like structured surface 19. The processing wheel 15 can be used to imprint a correspondingly rough surface structure on the rubber blanket 4 which is in turn imparted to the surface of the paper web 9. In this way paper with a high frictional coefficient can be produced. Such paper is particularly suitable for the production of larger bags to be filled with heavy granular material as it reduces the risk of dangerous slides where the filled bags are stored in stacks.

[0016] The processing wheel may, of course, consist of more or less discs than shown in the example. The discs need not be equal either but may be different, in particular, with respect to the properties of the structured surface.

[0017] The processing device 15 is used at intervals, that is, whenever it is deemed necessary to adapt the properties of the outer surface of the rubber blanket 4, in particular, to remove an oxide layer which has formed on it by grinding. In many cases it is sufficient that this operation be carried out once a day.

List of reference symbols

[0018] 

1, 2, 3

blanket carrier rolls

4

rubber blanket

5

arrow

6

guide roll

7

nip bar

8

cylinder

9

paper web

10

arrow

11, 12

spray tubes

13

processing device

14

rail

15

processing wheel

16

housing

17

electric motor

18

pipe

19

structured surface

20

disc

21

blade-like extension

Claims

1. An installation for compacting paper, comprising a plurality of blanket carrier rolls (1, 2, 3) rotatable about parallel axes, at least one of them drivable, a nip bar (7) parallel to the said axes, a rubber blanket (4) forming a closed loop running over the blanket carrier rolls (1, 2, 3) and the nip bar (7), with the latter in contact with an inside surface of the rubber blanket (4), at least one spraying device for spraying the inside surface of the rubber blanket (4) with a fluid, and a processing device (13) switchable in and out of an active state and movable back and forth in a direction transverse to the direction of motion of the rubber blanket (4), characterised in that the processing device (13) comprises at least one drivable processing wheel (15) with a structured surface (19) which in the active state is in contact with the outside surface of the rubber blanket (4) for processing the same.

2. The installation of claim 1, characterised in that the structured surface (19) covers at least part of the circumference of the processing wheel (15) and that the same is rotatable about an axis which is parallel to the axes of the blanket carrier rolls (1, 2, 3).

3. The installation of claim 1 or 2, characterised in that the structured surface (19) is at least in part formed by grinding teeth covering at least part of a base.

4. The installation of claim 1 or 2, characterised in that the structured surface (19) is at least in part formed by blade-like extensions (21) covering at least part of a base.

5. The installation of claim 4, characterised in that the blade-like extensions (21) are arranged in rows extending along the structured surface (19) in a direction perpendicular to the direction of the axis.

6. The installation of one of claims 1 to 5, characterised in that the processing wheel (15) consists of a plurality of discs (20) aligned along the axis.

7. The installation of one of claims 1 to 6, characterised in that the processing device (13) comprises a suction apparatus with a pipe (18) arranged at the circumference of the processing wheel (15) for removing cuttings abraded from the rubber blanket (4).

8. The installation of one of claims 1 to 7, characterised in that it comprises a rail (14) extending in the transversal direction, the grinding device (13) being shiftable along the rail (14).

9. A method of using the installation according to one of claims 1 to 8, characterised in that the processing device (13) is, at intervals, moved along the rubber blanket (4) in a direction transversal to the direction of motion of the latter, with the processing wheel (15) rotating and its structured surface (19) pressing against the outside surface of the rubber blanket (4) for processing the same.

10. The method of claim 9, characterised in that the processing of the outside surface consists in a grinding of the same.

Drawing