Method and roller arrangement for producing a single bipolar plate
Patent Information
- Application Number
- EP2024704707
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-10
- Filing Date
- 2024-02-07
- Publication Date
- 2025-12-17
AI Technical Summary
The production of metallic and graphite-based bipolar plates requires high flatness and uniformity, and existing methods struggle to efficiently increase the density of flow field channels while maintaining crease- and fold-free production in roll forming processes, especially at high feed rates.
A method and roller arrangement that guides the material web tangentially through a pair of rollers with controlled web tension, using a braking device on the unwinder to maintain optimal web tension and employing auxiliary embossing structures on the rollers to prevent slipping and ensure precise embossing of flow field geometries.
This approach enables efficient production of bipolar plates with increased flow field channel density and mechanical strength, ensuring crease-free and fold-free geometry, even at high feed rates, while maintaining belt tension and preventing web deflection.
Smart Images
Figure EP2024053006_15082024_PF_FP
Abstract
Description
[0001] Method and roller arrangement for the production of a single bipolar plate
[0002] The invention relates to a method and a roller arrangement for producing a single bipolar plate. A method according to the preamble of claim 1 is known from US 2017 / 0348811 A1.
[0003] The production of metallic, but also graphite-based, single bipolar plates places high demands on the flatness and uniformity of the web guide. To ensure this, appropriate web guidance is necessary. For this purpose, it is known from US 2017 / 0348811 A1 that the material web is guided through the nip tangentially to the two rollers forming the embossing nip.
[0004] To increase the efficiency of fuel cells, the density of the flow field channels in the bipolar plate needs to be further increased, which, among other things, will further reduce the distance between adjacent, parallel flow field channels. This places high demands on the crease- and wrinkle-free production of the flow field geometry in a roll forming process at the highest possible feed rate.
[0005] To achieve this object, a method according to claim 1 and a roller arrangement according to claim 13 are proposed. Advantageous embodiments are the subject of the dependent claims.
[0006] A single bipolar plate is one half of a bipolar plate, whereby two joined bipolar plates can form a bipolar plate. The material web can be and / or comprise, in particular, a metal sheet, such as stainless steel, or a graphite sheet, such as expanded graphite. The expanded graphite sheet can be compacted during the described roll forming process, so that in addition to imprinting the flow field geometry, its mechanical strength is also increased. This is described in US 2017 / 0348811 A1. The unwinder can be braked to maintain the strip tension. For this purpose, the unwinder can be braked by a braking device on the unwinder.
[0007] By braking, the material web can be fed to the embossing nip with a preferred web tension, since the rotationally driven roller pair pulls the material film into the embossing nip and the braked unwinder generates a counteracting holding force.
[0008] The unwinder can be decelerated depending on the rotational speed of the roller pair or depending on the detected tension of the material web, so that a desired tension value is achieved.
[0009] It can be provided that the material web is rolled up onto another roll after the pair of rollers or is separated into individual bipolar plates by a separation step.
[0010] It can further be provided that the material web is fed to a cutting process after the roller nip in the feed direction, during which perforations are optionally introduced in the area of a respective individual bipolar plate and / or an outer contour of the respective individual bipolar plate is formed, in particular cut. For this purpose, the material web can be discharged from the roller nip after leaving the roller nip essentially tension-free or with a web tension that is much lower than the web tension with which the material web is fed to the roller nip after unwinding.
[0011] According to a second aspect, the invention relates to a single bipolar plate which has been produced using an embodiment of the described production method.
[0012] Further details of the invention are explained with reference to the following figures.
[0013] Figure 1 shows a first embodiment of a roller arrangement;
[0014] Figure 2 shows a second embodiment of a roller arrangement;
[0015] Figure 3 shows an exemplary embodiment of an embossing roller for use in a pair of rollers according to Figure 1 or Figure 2;
[0016] Figure 4 shows exemplary embodiments of an adhesive structure; and
[0017] Figure 5 shows further exemplary embodiments of adhesive structures. Metallic, but also graphite-based bipolar plates, have high demands on flatness and uniformity. To ensure this, appropriate web guidance is necessary. Figure 1 shows a roller arrangement with an unwinder a and a pair of rollers b with two embossing rollers, which can be designed as a male and female die. The best results can be achieved with tangential web guidance. Braking is applied with a force F1 upstream of the embossing gap (e.g., at unwinder a), while the embossing unit pulls against the braking force with a force F2.
[0018] The web speed of the metal web is optionally 0m / min< v1< 300m / min. The web tension ensures crease-free embossing of the bipolar plates. At the exit nip, the web is preferably transported without web tension. However, it is also possible to transport the web with a light web tension F3. In this case, F3«F1 applies in order not to change the embossing (e.g., length of the embossing) and to ensure further processing of the web. For example, punching the web is not possible or only very difficult if the web tension F3 is too high. Deflection rollers or dancer units would also press the embossing out of the web.
[0019] As an alternative to the embodiment shown in Figure 1, in the embodiment shown in Figure 2, the tensile force is generated via a traction mechanism. Here, the material web is guided from the unwinder a over a braked friction roller c. In this variant, the braking force F1 can be precisely controlled and is therefore particularly suitable for flow field geometries with flow field lines in the circumferential direction. However, flow field geometries in any other direction can also be embossed without creases or wrinkles.
[0020] The tensile stress is calculated as follows: Tensile stress = force F1 / area of the material web cross-section.
[0021] For a stainless steel material sheet, the tensile stress is preferably 100 N / mm 2 and for a titanium material sheet considerable tensile stress preferably more than 50 N / mm 2 .
[0022] If the material sheet is a graphite sheet, it can preferably comprise and / or consist of expandable graphite. Alternatively, the graphite sheet can comprise and / or consist of impregnated expandable graphite. The graphite sheet can comprise a polymer highly filled with graphite.
[0023] Figure 3 shows a schematic representation perpendicular to the axial direction, in particular the axial direction of an embossing roller, of the outer surface or barrel surface of an embossing roller with an engraved flow field geometry. The roller 1 has an embossed structure for bipolar plates. The structured outer surface also has structural elements 2 for media openings. The material web has a width 3. An engraved auxiliary embossing is formed in an area 4 on the structured outer surface. The engraved flow field geometry has an embossed structure 5 for the formation of flow field channels.
[0024] To prevent the material web from slipping under particularly high tensile stresses, auxiliary embossing 4 is formed on roller 1. The auxiliary embossing 4 can be arranged outside the embossing structure for bipolar plates. Furthermore, the auxiliary embossing 4 can be formed in the area of the media openings 2 to prevent the embossing from wrinkling in this area. The auxiliary embossing 4 can be at least as wide, wider, or even narrower than the material web.
[0025] It can happen that the two embossing rollers are pushed out of position by the embossing structure of the bipolar plate. This can lead to an uneven embossed image and even cutting into the embossed area. Auxiliary embossing 4 can counteract this effect with a suitable geometry.
[0026] All geometries that return the rollers to a defined position during the embossing process are suitable for auxiliary embossing. Pyramids, for example, can be used as a geometry (Figure 4; l, ll). However, other elements such as a truncated cone or simple lines are also possible (Figure 4: III). The lines can have a triangular shape in cross-section, for example, in a plane perpendicular to the longitudinal direction, with the longitudinal direction optionally running perpendicular to the axial direction and / or parallel to the circumference of the embossing roller, or at a different angle to the longitudinal direction.
[0027] Pyramids with raised tips can be provided on one of the two rollers. The other roller can have recessed counterparts, so that in the event of a slight misregistration, the embossing force automatically returns it to register. The same applies to the line arrangement. The flank angle beta can be 0° < beta <= 90°.
[0028] It is also possible to structure the auxiliary embossing on separate rings. These rings can be attached to the outside of the rollers, especially the embossing rollers.
[0029] It is also possible for the auxiliary embossing to feature flattened pyramids and / or to rotate the pyramid by 45°. The length x of the base (Figure 5) can range from 1 mm to 10 mm. The element height can be from 0.05 mm to 3 mm. Furthermore, calendering of the material web can be avoided.
[0030] Figure 4 shows possible forms of auxiliary embossing: 1, 11 show top views of pyramid-shaped guide elements, with raised areas marked in white and depressions in black. III shows an example line arrangement for left / right guide elements. IV shows an example line pattern (white: raised; black: depressed). The cross-section of the line embossing can be triangular.
[0031] The features of the invention disclosed in the above description, in the drawings and in the claims may be essential both individually and in any combination for the realization of the invention in its various embodiments.
Claims
Claims 1. A method for producing a single bipolar plate, the method comprising the steps of: - unwinding a material web from an unwinder and feeding the unwound material web in a feed direction of the material web to a nip between two rollers, of which at least one roller is a three-dimensionally structured roller; Passing the unwound material web while maintaining the feed direction through a nip between two rollers, at least one of which is a three-dimensionally structured roller, wherein a flow field geometry is embossed into the material web; characterized in that, during the embossing of the flow field geometry into the material web, a channel arrangement of parallel flow field channels is generated in the material web, in which the parallel flow field channels run parallel to the feed direction.
2. Method according to claim 1, wherein the material web is guided tangentially to the two rollers during feeding.
3. Method according to claim 1 or 2, wherein the material web is removed from the roll gap after passing tangentially to the two rolls.
4. Method according to claim 3, wherein the material web, after leaving the roll gap, is led away from the roll gap substantially tension-free or with a web tension which is much smaller than a web tension with which the material web is fed to the roll gap after unwinding.
5. Method according to one of the preceding claims, in which a metal foil or a graphite sheet, preferably an expandable graphite sheet or a sheet of polymer-filled graphite, is unwound from the unwinder.
6. Method according to one of the preceding claims, in which the material web is unwound from the unwinder during unwinding while maintaining a web tension oriented in the feed direction.
7. Method according to claim 6, wherein the unwinder is braked to maintain the tape tension.
8. Method according to claim 6, wherein the unwinder is substantially free-running and the material web unwound from the unwinder is fed in the feed direction to the roll nip via a pulling device which provides and maintains the web tension in the feed direction.
9. Method according to claim 8, wherein the material web is deflected in the traction mechanism on a braked friction roller, wherein the material web wraps around the braked friction roller preferably along at least 30% of its circumference, particularly preferably by at least 40% and very particularly preferably by at least 50%.
10. Method according to claim 9, wherein the material web is deflected in the feed direction of the material web from the unwinder to the braked friction roller on a support roller, wherein the support roller preferably has an adjustable distance with respect to the braked friction roller, so that a degree of wrap of the friction roller with the material web can be adjusted.
11. Method according to one of the preceding claims, in which at least one of the two rollers between which the roller gap is formed is driven in its direction of rotation.
12. Method according to one of the preceding claims, wherein the material web is transported at a web speed between 0 and 300 m / min in the feed direction.
13. A roller arrangement for the production of a bipolar single plate, wherein the roller arrangement has an unwinder, from which a material web is fed in a feed direction to a nip between two rollers and is guided through the nip while maintaining the feed direction, wherein at least one of the two rollers is a three-dimensionally structured roller and the two rollers are designed for embossing a flow field geometry with a Channel arrangement of parallel flow field channels are set up in the material path.
14. A roller arrangement according to claim 13, wherein the embossed structure comprises a plurality of parallel and elongated structural elements for embossing the flow field channels, which extend in the circumferential direction of the at least one structured roller.
15. Roller arrangement according to claim 13 or 14, wherein the material web is fed tangentially to the two rollers, and wherein the material web is preferably led away from the roller gap in the feed direction behind the roller gap while maintaining the feed direction tangential to the two rollers.
16. Roller arrangement according to one of claims 13 to 15, in which the material web is led away from the roller gap in the feed direction behind the roller gap substantially tension-free in the feed direction or with a web tension in the feed direction which is much smaller than a web tension with which the material web is fed from the unwinder to the roller gap.
17. Roller arrangement according to one of claims 13 to 16, wherein the material web is and / or comprises a metal foil or a graphite web, preferably an expandable graphite web or a web of polymer-filled graphite.
18. Roller arrangement according to one of claims 13 to 17, in which the material web has a web tension oriented in the feed direction upstream of the roller gap.
19. A roller arrangement according to claim 18, wherein the unwinder is either a. braked or b. substantially free-running and the material web unwound from the unwinder is fed to the roller nip via a pulling mechanism in the feed direction, wherein the pulling mechanism is configured to provide and maintain the web tension in the feed direction.
20. Roller arrangement according to claim 19, in which the material web is deflected in the traction mechanism on a braked friction roller, wherein the material web preferably surrounds the braked friction roller along at least 30% of its circumference, particularly preferably by at least 40% and most preferably by at least 50%.
21. Roller arrangement according to claim 20, wherein the material web is deflected in the feed direction of the material web from the unwinder to the braked friction roller on a support roller, wherein the support roller preferably has an adjustable distance with respect to the braked friction roller, so that a degree of wrap of the friction roller with the material web can be adjusted.
22. Roller arrangement according to one of claims 13 to 21, in which at least one of the two rollers between which the roller gap is formed is driven in its direction of rotation.
23. Roller arrangement according to one of claims 13 to 22, in which at least one of the two rollers forming the roller gap has an adhesive structure on its roller shell, wherein the adhesive structure is designed to increase the coefficient of friction between the roller having the adhesive structure and the material web compared to a smooth roller shell.
24. Roller arrangement according to claim 23, wherein the roller shell has, at least in some regions outside a structured region of the roller shell for embossing a flow field geometry, a coefficient of friction which is increased compared to the structured region.
25. Roller arrangement according to claim 24, wherein the regions with the increased coefficient of friction surround, preferably completely enclose, the structured regions on at least two opposite sides.
26. Roller arrangement according to one of claims 23 to 25, wherein the adhesive structure has an embossed structure with a plurality of regularly or randomly arranged embossed projections, wherein the embossed projections preferably have a linear shape with a preferably triangular cross-section, a pyramid or cone geometry or a truncated pyramid or truncated cone geometry.
27. A roller arrangement according to one of claims 13 to 26, wherein the rollers forming the roller gap between them are designed as a male-female pairing at least with respect to a structured region of their roller shells for embossing a flow field geometry.
8. Roller arrangement according to one of claims 23 to 27, in which the rollers are designed as a male-female pairing in the region of an adhesive structure, in particular when the adhesive structure is designed as an embossed structure with a plurality of regularly or randomly arranged embossed projections.