ROLL COVER AND ROLL

Abstract

A roll cover and a roll in particular for use in a machine line for the production or processing of a fibrous web is provided, wherein the roll cover includes a radial outer functional layer which provides the surface of the roll cover in contact with the web, and wherein the functional layer has structural elements, in particular in the form of grooves and/or bores, wherein the functional layer is constructed of an elastomer material with a Poisson number greater than 0.4, between 0.45 and 0.5.

Claims

1. A roll cover for a roll, the roll cover comprising: a surface configured for being in contact with a web of fibrous material, the surface being formed by a radial outer functional layer, the radial outer functional layer including a plurality of structural elements and being composed of an elastomer material that has a Poisson's ratio greater than 0.4, a rubber material being used as the elastomer material.

2. A roll cover according to claim 1, wherein the roll cover is for the roll which is configured for being used in a machine for producing or processing the web of fibrous material, wherein the plurality of structural elements are at least one of a plurality of grooves and a plurality of bores.

3. A roll cover according to claim 2, wherein the rubber material has a rubber formulation based on hydrogenated acrylonitrile butadiene rubber (HNBR) or ethylene propylene diene rubber (EPDM).

4. A roll cover according to claim 1, wherein the plurality of structural elements includes a plurality of grooves each of which includes a groove width and a groove depth, and wherein a ratio of the groove width to the groove depth is less than or equal to 0.7.

5. A roll cover according to claim 4, wherein the ratio of the groove width to the groove depth is less than or equal to 0.5.

6. A roll cover according to claim 1, wherein the plurality of structural elements includes a plurality of bores each of which includes a bore diameter and a bore depth, and wherein a ratio of the bore diameter to the bore depth is less than or equal to 0.7.

7. A roll cover according to claim 6, wherein the ratio of the bore diameter to the bore depth is less than or equal to 0.5.

8. A roll cover according to claim 1, wherein a hardness of the radial outer functional layer is greater than 10 P&J.

9. A roll cover according to claim 8, wherein the hardness of the radial outer functional layer is between 15 P&J and 50 P&J.

10. A roll cover according to claim 1, wherein the elastomer material is water-resistant, such that during 672 hours of storage at 70? C. in water with pH=7 a hardness of the elastomer material changes by a maximum of 5 P&J.

11. A roll cover according to claim 10, wherein the hardness of the elastomer material changes by 3 P&J or less.

12. A roll cover according to claim 1, wherein the elastomer material is acid-resistant, such that during 672 hours of storage at 70? C. in sulfuric acid (H.sub.2SO.sub.4) with pH=1.5 a hardness of the elastomer material changes by a maximum of 5 P&J.

13. A roll cover according to claim 12, wherein the hardness of the elastomer material changes by 3 P&J or less.

14. A roll cover according to claim 1, wherein the elastomer material is alkali-resistant, such that during 672 hours of storage at 70? C. in caustic soda (NaOH) with pH=14 a hardness of the elastomer material changes by a maximum of 10 P&J.

15. A roll cover according to claim 14, wherein the hardness of the elastomer material changes by 5 P&J or less.

16. A roll cover according to claim 1, wherein a tensile stress value of the elastomer material changes by less than 10%, at 10% elongation (module 10, measured in a tensile test on an S1 or S2 strip according to DIN 53504) during 672 hours of storage at 70? C. in water at least one of pH=7, 5 weight-% sulfuric acid, and 5 weight-% caustic soda.

17. A roll cover according to claim 16, wherein the tensile value of the elastomer material changes by less than 8%.

18. A roll for a machine line for producing or processing a web of fibrous material, the roll comprising: a roll core which is substantially cylindrical; and a roll cover applied to the roll core, wherein the roll cover includes a surface configured for being in contact with the web of fibrous material, the surface being formed by a radial outer functional layer, the radial outer functional layer including a plurality of structural elements and being composed of an elastomer material that has a Poisson's ratio greater than 0.4, a rubber material being used as the elastomer material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing, wherein:

[0046] FIG. 1 shows the relative changes in the module 10 value for the materials from examples 1 and 2 as well as the reference material when stored in different media over 7 or respectively 28 days (672 hours).

[0047] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates at least one embodiment of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention is further explained below, with reference to examples.

[0049] The examples specify some examples of elastomers suitable for use in a roll cover according to one aspect of the present invention. These are different rubber materials. However, the present invention is not limited to these exemplary formulations.

[0050] The information on hardness or change in hardness is, unless explicitly described otherwise, to be found in P&J (Pusey & Jones).

Example Formulation 1: EPDM 25

[0051]

TABLE-US-00001 Category Designation Amount (wt-%) Polymer EPDM 40-60 Filler 1 Soot 25-35 Filler 2 Mineral 5-10 Crosslinking agent Peroxide 2-3 Other additives Remainder to 100%

[0052] Prior to storage, this rubber material has a hardness of between 25 and 30 P&J.

Example Formulation 2: HNBR 20

[0053]

TABLE-US-00002 Category Designation Amount (wt-%) Polymer HNBR 40-50 Filler Soot 20-30 Softener Ester 2-4 Crosslinking agent Peroxide 2-4 Other additives Remainder to 100%

[0054] Prior to storage, this rubber material has a hardness of between 20 and 25 P&J.

[0055] Consideration of storage in various media (pH values & chemicals) has proven to be effective in assessing the material behavior in the roll nip.

[0056] Table 1 shows the change in hardness in materials stored for 7, as well as for 28 days (=672 hours) in water, NaOH and H.sub.2SO.sub.4. Storage occurs at a temperature of 70? C.

[0057] Hardness changes which are shown in the following table were measured for example formulations 1 and 2, as well as for the reference formulation NBR 20 based on acrylonitrile butadiene rubber. The reference formulation also had a hardness of between 20 and 25 P&J before storage, which was however slightly below the hardness of HNBR 20.

[0058] In all three formulations, the elastomer material has a Poisson's ratio above 0.4, especially between 0.45 and 0.5. Thus, the materials are generally all suitable for use in a roll cover according to one aspect of the current invention.

TABLE-US-00003 TABLE 1 Change in hardness after 672 h storage in [P&J] Water (pH = 7) H2SO4 (pH = 1.5) NaOH (pH = 14) EPDM 25 +1 P&J +1 P&J +2 P&J HNBR 20 +3 P&J +2 P&J +4 P&J NBR 20 +4 P&J +5 P&J +10 P&J

[0059] One recognizes that in all cases the materials have a higher P&J value after storage, and thus become softer. However, the extent of this softening is highly dependent on the polymer material.

[0060] One recognizes that sample formulation 1 (EPDM 25) undergoes only a very small change in hardness in all storage situations. Even under the generally harshest conditions in caustic soda, an increase of only 2 P&J is measured. The material is therefore superbly water-resistant, acid-resistant, and alkali-resistant.

[0061] Sample formulation 2 (HNBR 20) also shows only a relatively small change in hardness in all storage situations. The material is therefore proficiently water-resistant, acid-resistant and alkali-resistant. Regardless, the measured change in hardness is already approximately twice as large as with formulation 1.

[0062] The reference formulation (NBR 20) shows by far the greatest changes in hardness. When stored in caustic soda, the hardness change is 10 P&J.

[0063] The changes in hardness of this reference formulation in water, acid and especially in lye are at the limit of what can still be considered stable. In applications where these resistance properties are important, it is advantageous not to use a formulation with such hardness changes and instead to rely on clearly more durable alternatives such as formulations 1 or 2.

[0064] The products that can provide a constant dewatering performance proved consistent over a wide range of media. An excellent indicator of this is the measurement variable module 10. It is generally advantageous if the tensile value of the elastomer material changes only slightly at 10% elongation (module 10, measured in the tensile test on the S1 or S2 strip according to DIN 53504) during storage in water, lye or acid.

[0065] Utilization of a material in which the tensile value module 10 changes less than 10%, optionally less than 8%, during 672 hours of storage in water at 70? C. ensures constant drainage conditions over the life of the cover.

[0066] FIG. 1 shows the relative changes in the module 10 value for the materials from examples 1 and 2 as well as the reference material when stored in different media over 7 or respectively 28 days (672 hours).

[0067] As in the investigation of the change in hardness, a considerable difference of the elastomer materials is noticeable.

[0068] Here, too, EPDM 25 proves to be highly advantageous, as the module 10 value changes by less than 10% even after 28 days, in most cases even by less than 8% when stored in water pH=7.5 weight-% sulfuric acid and also in 5 weight-% caustic soda.

[0069] HNBR also displays beneficial properties. When stored in water as well as in sulfuric acid, the change in module 10 value remains below 10% or even below 8%. Only when stored in caustic soda, the module 10 value is only around 80% of the initial value after 28 days.

[0070] Here, too, NBR 20 presents the worst performance. When stored in water, there is a pronounced change in elongation already after 7 days, and after 28 days in the range of approximately 10%. When stored in sulfuric acid or caustic soda, the module 10 value drops severely with NBR 20. After 28 days of storage in sulfuric acid, the value is only between 50% and 60% of the initial value.

[0071] Also, with regard to the module 10 value, the use of NBR 20 will not be optimal for many applications, so that here too, alternatives as described in examples 1 and 2 are preferred.

[0072] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.