Dryer Fabric

Abstract

A dryer filtration fabric for use in a drying section of a machine for producing and/or processing a fibrous web, in particular paper, cardboard, tissue or non-woven, has machine direction threads interwoven with machine cross direction threads to form a single-ply woven fabric having an air permeability between 40 cfm and 330 cfm. The machine direction threads and the machine cross direction threads have a flattened cross-sectional shape with a width-to-height ratio of more than 1. Each of the machine direction threads runs over and/or under a maximum of three, preferably a maximum of two, machine cross direction threads that are disposed directly beside one another. The number of the machine direction threads per 10 cm, viewed in the machine cross direction, lies in the range from 170 to 200, and the filling level of the machine direction threads lies in the range from 90% to 110%.

Description

The invention relates to a dryer filtration fabric according to the preamble of claim 1.

Dryer filtration fabrics have to meet a multiplicity of requirements. Dryer filtration fabrics for the use at the beginning of a drying section must thus have a low air permeability in order for the evaporation to be kept low in a controlled manner and, on account thereof, for an excessively rapid vaporization associated with damage to the as yet moist and thus sensitive paper to be prevented. Furthermore, dryer filtration fabrics for the reduction of contaminations that are difficult to clean, such as, for example, sticky deposits, have to have a small internal volume, that is to say an internal volume that is not directly accessible, this often being achieved by weaving designs having only short thread floats. It has furthermore proven advantageous for dryer filtration fabrics to be woven from machine direction threads and machine cross direction threads that are configured so as to be flat, since the latter on the paper and/or running side have a smoother surface and therefore can have a lower contamination tendency than woven fabrics having round machine direction threads and machine cross direction threads.

In the case of the dryer filtration fabrics that are known from the prior art, having a low permeability in the range of up to 330 cfm, in which the machine direction threads that are configured so as to be flat are disposed beside one another in the machine cross direction and are interwoven with machine cross direction threads that are configured so as to be flat and are disposed beside one another in the machine direction to form a single-ply woven fabric, and in which the machine direction threads when interwoven with the machine cross direction threads configure only relatively short thread floats, that is to say the machine direction threads when interwoven with the machine cross direction threads run over and/or under a maximum of three, in particular maximum of two, machine cross direction threads which are disposed directly beside one another, the machine direction threads often only have little possibility for mutual yielding, in particular when compared to woven fabrics having relatively long thread floats of the machine direction threads and high air permeability values. This minor “yielding possibility”, in particular in the case of woven fabrics in which the machine direction threads have been woven at low thread tensions, can lead to the machine direction threads being twisted and/or pushed on top of one another. For this reason it is particularly difficult to provide dryer filtration fabrics having a low permeability and a low contamination tendency and a good cleaning capability.

It is thus the object of the invention to provide dryer filtration fabrics having a low permeability and a low contamination tendency and a good cleaning capability, in which the machine direction threads have a lower tendency toward twisting and/or being pushed on top of one another as is the case in the dryer filtration fabrics which are known from the prior art.

The object is achieved by a dryer filtration fabric having the features of patent claim 1.

By providing a dryer filtration fabric having a density of the machine direction threads in the range from 160 to 185 per 10 cm and a filling level of the machine direction threads in the range from 90% to 115%, a dryer filtration fabric in which the air permeability can be set in a wide lower range, on the one hand, and in which twisting and/or pushing on top of one another of the machine direction threads are/is effectively suppressed or greatly reduced, respectively, is provided.

When mention is made in the context of the present invention of a flattened cross-sectional shape of a thread, this herein means a cross-sectional shape of the corresponding thread or threads, respectively, that deviates from the circular shape. The respective thread should therefore not be circular in the cross-section, or not have any purely cylindrical shape, respectively. The cross-sectional shape can nevertheless include circular arcs or circular arc portions.

The terms flattened and deviating from the circular shape according to the present invention are in each case understood to be synonyms. A respective cross-section is performed perpendicularly to the longitudinal extent of the thread, said longitudinal extent in the case of a machine direction thread corresponding to the machine direction, and in the case of a machine direction thread corresponding to the machine direction. In other words, cross-sectional shape therefore corresponds to the external contour of the thread in the respective cross-sectional plane.

If mention is made according to the invention of width or height, this means the respectively largest measured extent of the external contour of the thread that is defined by the cross-sectional plane in the mentioned cross-section. It could also be said that the width corresponds to the X axis and the height corresponds to the Y axis of a Cartesian coordinate system in the cross-sectional plane mentioned. In this case, the longitudinal extent of the thread would coincide with the respective Z axis.

The filling level in the context of the present invention is computed according to the following formula:

Filling level in %=A×B/100 mm×100,

where

A=the number of the machine direction threads per 100 mm in the machine cross direction,

B=the width of a machine direction thread in mm.

Advantageous design embodiments and refinements of the invention are stated in the dependent claims.

According to one particularly preferred design embodiment of the invention it is provided that the filling level of the machine direction threads is in the range from 95% to 105%. On account of this further limitation, the twisting and/or pushing on top of one another of the machine direction threads can be even more heavily suppressed or reduced, respectively, while simultaneously maintaining a low air permeability.

A specific design embodiment of the invention provides that the machine cross direction threads have a bone-shaped or lenticular cross-sectional shape.

Tests conducted by the applicant have furthermore demonstrated that the twisting and/or pushing on top of one another of the machine direction threads can be further reduced or suppressed, respectively, when the width-to-height ratio of the machine direction threads is in the range from 1.7 to 1.9, wherein a specific design embodiment of the invention provides that the machine direction threads have a height of 0.4 mm and a width of 0.6 mm.

In order for the contamination tendency of the dryer filtration fabric according to the invention to be further reduced it is in particular provided that the majority (that is to say more than 50%), in particular the, that is to say all, machine direction threads form groups of machine direction threads which are disposed directly beside one another, and the machine direction threads of the respective group in a side-by side-manner, following the same weaving path, are interwoven with the machine cross direction threads. The groups herein can be formed in particular from in each case two or three directly neighboring machine direction threads.

The solution according to the invention is then in particular advantageous when each of the machine direction threads when interwoven with the machine cross direction threads runs over and/or under a single machine cross direction thread; in other words, when each of the machine direction threads when interwoven with the machine cross direction threads, running on the paper side, crosses only a single machine cross direction thread and crosses the machine cross direction threads that directly neighbor said single machine cross direction thread when the respective machine direction thread runs on the machine side and/or when each of the machine direction threads when interwoven with the machine cross direction threads, running on the machine side, crosses only a single machine cross direction thread and crosses the machine cross direction threads that directly neighbor said single machine cross direction thread when the respective machine direction thread runs on the paper side. A refinement of the invention based thereon provides that the machine direction threads and the machine cross direction threads are mutually interwoven in a plain weave.

The density of the machine cross direction threads is preferably in the range from 15 to 55 per 10 cm, on account of which in particular the air permeability can be set in the desired range.

According to a further design embodiment of the invention it is provided that the machine cross direction threads have a height in the range from 0.7 mm to 0.8 mm, and have a width of 1.6 mm.

In particular in order for the abrasion resistance of the dryer filtration fabric according to the invention to be increased, it is expedient for the machine direction threads and the machine cross direction threads to be substantially from PET.

In order for the temperature resistance and the chemical resistance to be increased while largely maintaining the abrasion resistance of the dryer filtration fabric according to the invention, it can be furthermore advantageous for between 40% and 60% of the machine direction threads to be substantially from PET, and between 60% and 40% of the machine direction threads to be substantially from PPS, and for the machine cross direction threads to be substantially from PET, or for between 40% and 60% of the machine cross direction threads to be substantially from PET, and between 60% and 40% of the machine cross direction threads to be substantially from PPS.

For use at very high temperatures (for example <150° C., for example in oil-fired drying sections), it is advantageous for between 40% and 60% of the machine direction threads to be substantially from PPS, and between 60% and 40% of the machine direction threads to be substantially from PCTA, and for the machine cross direction threads substantially from PCTA, or for between 40% and 60% of the machine cross direction threads to be substantially from PCTA, and between 60% and 40% of the machine cross direction threads to be substantially from PPS.

The highest temperature and hydrolysis resistance is achieved when the machine direction threads are substantially from PPS, and the machine cross direction threads are substantially from PPS or from PCTA.

The term “substantially” in the case of the preceding exemplary embodiments is to be understood such that the respective material is present in the respective threads in a proportion of more than 50% by weight, preferably of more than 80% by weight, particularly preferably of more than 95% by weight.

The invention will be explained further hereunder by means of schematic drawings in which

FIG. 1 shows a dryer filtration fabric according to the prior art, in the plan view;

FIG. 2 shows an embodiment of a dryer filtration fabric according to the invention, in the plan view; and

FIG. 3 shows the dryer filtration fabric of FIG. 2 in a side view.

FIG. 1 shows a dryer filtration fabric 1 according to the prior art in the plan view. The dryer filtration fabric 1 comprises machine direction threads 2 which in the machine cross direction CD are disposed beside one another and which are interwoven with machine cross direction threads 3 which are disposed beside one another in the machine direction MD to form a single-ply woven fabric having an air permeability in the range from 40 cfm to 330 cfm. The woven structure of the woven fabric is such that each of the machine direction threads 2 when interwoven with the machine cross direction threads 3 runs over and/or under a maximum of three machine cross direction threads 3 which are disposed so as to be directly beside one another. The woven structure specifically configures a plain weave. Furthermore, the machine direction threads 2 and the machine cross direction threads 3 have a flattened cross-sectional shape having a width-to-height ratio of more than 1. The machine direction threads 1 specifically have a height of 0.36 mm and a width of 0.67 mm. The machine cross direction threads 3 have a bone-shaped cross-sectional shape and a height of 0.8 mm and a width of 1.6 mm. As can be further seen, the machine direction threads 2 form groups of in each case two machine direction threads 102 which are disposed directly beside one another, wherein the machine direction threads 2 of the respective group in a side-by side manner, following the same weaving path, are interwoven with the machine cross direction threads 3.

The dryer filtration fabric 1 shown in FIG. 1 has a filling level of the machine direction threads of 116%. FIG. 1 furthermore shows a location indicated by the reference sign 4, on which a machine direction thread 2a is pushed over a machine direction thread 2b, that is to say the former running partially over the latter.

FIG. 2 shows an embodiment of a dryer filtration fabric 101 according to the invention in the plan view, and FIG. 3 shows the dryer filtration fabric 101 of FIG. 2 in a side view. Only the points of differentiation in relation to the dryer filtration fabric of FIG. 1 will be discussed hereunder. Furthermore, the reference signs of FIGS. 2 and 3 for the same components correspond to those of FIG. 1, the former only having a number that is increased by 100. In the case of the dryer filtration fabric 101 of FIGS. 2 and 3 the number of machine direction threads 102 per 10 cm, viewed in the machine cross direction CD, is in the range from 170 to 200, and the filling level of the machine direction threads 102 is 104%. Furthermore, the width-to-height ratio of the machine direction threads 102 is in the range from 1.7 to 1.9. Specifically, the machine direction threads 102 have a height of 0.4 mm and a width of 0.6 mm. Moreover, the number of machine cross direction threads 103 per 10 cm, viewed in the machine direction MD, is in the range from 15 to 55 per 10 cm.

Claims

1-14. (canceled)

15. A dryer fabric for use in a drying section of a machine for producing and/or processing a fibrous web, the fabric comprising: machine direction threads that are disposed beside one another in a machine cross direction and interwoven with machine cross direction threads that are disposed beside one another in the machine direction to form a single-ply woven fabric having an air permeability in the range from 40 cfm to 330 cfm;said machine direction threads and said machine cross direction threads having a flattened cross-sectional shape with a width-to-height ratio of greater than 1;each of said machine direction threads, when interwoven with said machine cross direction threads, running over and/or under a maximum of three directly adjacent machine cross direction threads;wherein a number of machine direction threads per 10 cm, viewed in the machine cross direction, lies in a range from 160 to 185, and a filling level of the machine direction threads lies in a range from 90% to 115%.

16. The dryer fabric according to claim 15, wherein each of said machine direction threads runs over and/or under a maximum of two said machine cross direction threads that lie directly next to one another.

17. The dryer fabric according to claim 15, wherein the filling level of said machine direction threads lies in a range from 95% to 111%.

18. The dryer fabric according to claim 15, wherein said machine cross direction threads have a cross-sectional shape selected from the group consisting of bone-shaped and lenticular.

19. The dryer fabric according to claim 15, wherein the width-to-height ratio of said machine direction threads is in a range from 1.7 to 1.9.

20. The dryer fabric according to claim 19, wherein said machine direction threads have a height of 0.4 mm and a width of 0.6 mm.

21. The dryer fabric according to claim 15, wherein said machine direction threads form groups of groups of machine direction threads that are disposed directly beside one another, and said machine direction threads of a respective group in a side-by-side manner, following the same weaving path, are interwoven with said machine cross direction threads.

22. The dryer fabric according to claim 15, wherein each of said machine direction threads, when interwoven with said machine cross direction threads, runs over and/or under a single machine cross direction thread.

23. The dryer fabric according to claim 21, wherein said machine direction threads and said machine cross direction threads are interwoven in a plain weave.

24. The dryer fabric according to claim 15, wherein the number of machine cross direction threads per 10 cm, viewed in the machine direction, lies in a range from 15 to 55.

25. The dryer fabric according to claim 15, wherein said machine cross direction threads have a height in a range from 0.7 mm to 0.8 mm, and a width of 1.6 mm.

26. The dryer fabric according to claim 15, wherein said machine direction threads and said machine cross direction threads consist essentially of polyethylene terephthalate (PET).

27. The dryer fabric according to claim 15, wherein: between 40% and 60% of said machine direction threads essentially consist of polyethylene terephthalate (PET), between 60% and 40% of said machine direction threads essentially consist of polyphenylene sulfide (PPS); andsaid machine cross direction threads essentially consist of PET; orbetween 40% and 60% of said machine cross direction threads essentially consist of PET and between 60% and 40% of said machine cross direction threads essentially consist of PPS.

28. The dryer fabric according to claim 15, wherein: between 40% and 60% of said machine direction threads essentially consist of polyphenylene sulfide (PPS) and between 60% and 40% of said machine direction threads essentially consist of PCTA; andsaid machine cross direction threads essentially consist of PCTA; orbetween 40% and 60% of said machine cross direction threads essentially consist of PCTA, and between 60% and 40% of said machine cross direction threads essentially consist of PPS.

29. The dryer fabric according to claim 15, wherein said machine direction threads are substantially from PPS, and said machine cross direction threads essentially consist of PPS or PCTA.