GB2527669A

GB2527669A - Method for producing at least one sealing element on a surface of a plate for a fuel cell system

Info

Publication number: GB2527669A
Application number: GB1508698.6A
Authority: GB
Inventors: Christian Martin Erdmann; Stephen Wade; Victor Keller; Marcel Maier; Jeremy Rodriguez; Annabelle Wong
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2015-05-21
Filing date: 2015-05-21
Publication date: 2015-12-30
Also published as: GB201508698D0

Abstract

A method for producing at least one sealing element on a surface 24 of a plate 10, 12 for a fuel cell system, such as a bipolar plate, by injection moulding, the plate having at least one protrusion (16, fig 1) bounding at least one guide channel (20, fig 1) on a side facing away from the surface. The method comprises: providing at least one mold 26 having: at least one cavity 28 by means of which the sealing element is produced by injecting a liquid plastic material into the cavity; and at least one element 38 configured to heat and/or cool the liquid plastic material, the element being arranged in the vicinity of the cavity; arranging the mould on the side of the surface such that the cavity runs angularly across the protrusion; and injecting the plastic material into the cavity. Preferably, the mould a gap is created between the mould and the surface, the mould having at least one recess 42 in the vicinity of the cavity; the recess being configured to receive a portion of the plastic material injected into the cavity flowing through the gap into the recess. The heating/cooling elements are used to cause fast curing of the plastic material to prevent or minimise flash.

Description

Method for Producing at least one Sealing Element on a Surface of a Plate for a Fuel Cell System The invention relates to a method for producing at least one sealing element on a surface of a plate for a fuel cell system, in particular a proton exchange membrane hydrogen fuel cell. Fuel cells such as proton exchange membrane (REM) hydrogen fuel cells are well-known from the general prior art. Usually, such a fuel cell system comprises at least one plate such as a bipolar plate arranged between individual fuel cells in a fuel cell stack so as to separate, for example, reaction gases from other fluids such as cooling fluids of the fuel cell system or the fuel cell stack. In particular, a bipolar plate is a conductive plate used in a fuel cell stack, wherein, for example, the bipolar plate acts as an anode for one fuel cell and a cathode for an adjacent fuel cell of the fuel cell stack. The bipolar plate may be made of metal or a conductive polymer which may be a carbon-filled composite.

The bipolar plate usually incorporates at least one flow channel for guiding at least one fluid such as a reaction gas or a cooling fluid. Usually, in a fuel cell stack, a bipolar plate needs to be sealed against at least one other component of the fuel cell stack.

WO 03/1 00894 A2 shows a method of masking a gas kitted fuel cell membrane electrode assembly.

It has been shown that the sealing of the plate plays an important role for the functioning of the fuel cell.

It is therefore an object of the present invention to provide a method by means of which a particularly advantageous sealing of a plate of a fuel cell system can be realized in a cost-efficient way.

This object is solved by a method having the features of patent claim 1. Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.

The invention relates to a method for producing at least one sealing element on a surface of a plate for a fuel cell system by injection molding. Preferably, the plate is a bipolar plate and/or the fuel cell system is configured as a proton exchange membrane (REM) hydrogen fuel cell. In the method, the sealing element is produced or manufactured by injection molding. The plate has at least one protrusion bounding at least one guide channel on a side facing away from the surface on which the sealing element is produced. In other words, the protrusion is a raised area or a raised wall area protruding from at least one other area or wall area of the plate. With respect to said side facing away from said surface, the protrusion is a recess or receptacle bounding at least one guide channel through which a fluid such as, for example, a gas, in particular a reaction gas, and/or a liquid such as, for example, a cooling liquid can flow. In other words, the guide channel is used to realize a flow management for guiding respective fluids of the fuel cell system or a fuel cell stack.

The method according to the present invention comprises the step of providing at least one mold. The mold has at least one cavity by means of which the sealing element is produced by injecting a liquid plastic material into the cavity. In other words, the sealing element is made of the plastic material which is injected into the cavity while the plastic material is in a liquid state. Then, the plastic material can cure thereby forming the sealing element. Moreover, the mold has at least one element configured to heat and/or cool the liquid plastic material, said element being arranged in the vicinity of the cavity.

The method according to the present invention further comprises the step of arranging the mold on the side of the surface such that the cavity runs angularly across the protrusion so that, in a completely manufactured state of the fuel cell system or fuel cell stack, the sealing element runs across the protrusion. Moreover, the method according to the present invention comprises the step of injecting the plastic material into the cavity.

The idea behind the method according to the present invention is that the correct functioning of a fuel cell or fuel cell system, in particular a REM hydrogen fuel cell, can be affected by loose particles of sealing material which the sealing element is made of. Said loose particles are also referred to as flash. The loose particles can build up in undesired areas within the system which can in turn affect the operating performance of the fuel cell.

Usually, during the injection molding process, high filling pressures and heat expansion induced pressure create a potential for molding defects near areas with reduced support for the sealing element. Such areas with reduced support for the sealing element are formed by the protrusion which is a raised geometry provided to form or bound the guide channel on the side facing away from the surface on which the sealing element is produced. Said molding defects can lead to excessive flashing of the injected plastic material into areas outside an intended design of the plate which is, for example, a bipolar plate or a bipolar plate assembly.

The guide channel is also referred to as a via or via area used to realize a gas and/or liquid flow management comprising the guide channel configured to guide, for example, a gas such as a reaction gas or a cooling medium. Said flash or flashing of material may also originate from seal off misalignment between the mold and the plate which is an over-molded substrate since the sealing element is produced on the surface by injection molding. Modification of flow length of the liquid plastic material can help reduce the fill pressure but will have a reduced impact on the pressures created from heat expansion after filling of the cavity is complete. The relationship between fill pressures and heat expansion pressures varies with the injection material chosen.

By using said at least on element for heating and/or cooling the injected liquid plastic material flash or flashing from the injected plastic material can be kept particularly low.

This can be achieved through realizing a rapid curing or vulcanization and/or cooling of the plastic material which is a sealing material since the sealing element is made of said plastic material. Said rapid curing or vulcanization and/or cooling of the plastic material can be realized by using the localized element placed in the vicinity of the cavity and, thus, the via, just outside the seal cavity area. Said element can be intended to cause a thin layer of sealing material directly under the element to harden in a sufficiently fast way to stop the plastic material from flowing any further into undesired areas and causing loose flash and potential processing defects such as, for example, voids, bubbles, flow lines, etc. The fill pressure can be further reduced by minimizing the flow length between respective gate locations at which the plastic material is injected into the cavity.

In a particularly advantageous embodiment of the invention the mold is arranged at a distance from the surface thereby creating a gap between the mold and the surface, the mold further having at least one recess arranged in the vicinity of the cavity, the recess being configured to receive a portion of the plastic material injected into the cavity and flowing through the gap into the recess. Said recess is used as a pressure relieving overflow pocket in the mold in the vicinity of the cavity and, thus, the via so that the fill pressure can be further reduced.

Preferably, said element comprises a heating element such as an electric heating element configured to heat the plastic material injected into the cavity. Moreover, said element can comprise at least one duct through which a cooling medium such as a cooling liquid for cooling the plastic material injected into the cavity can flow. By means of the method according to the present invention, a cost-efficient sealing of the plate, i.e. a higher yield/mold consistent process can be realized. Moreover, the impact of loose flash on fuel cell performance can be kept particularly low. Moreover, preferably, the mold is arranged in such a way that the cavity runs angularly across the protrusion from one side of the protrusion to the other.

Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respectively indicated combination but also in other combination or taken alone without leaving the scope of the invention.

The drawings show in: Fig. 1 a schematic perspective view of a plate in the form of a bipolar plate for a fuel cell system, wherein at least one sealing element is produced on a surface of the bipolar plate by means of injection molding; and Fig. 2 a schematic sectional view of the bipolar plate and a mold along a cutline A-A shown in Fig. 1, said mold being used to produce said sealing element.

In the figures the same elements or elements having the same function are indicated by the same reference signs.

Fig. 1 shows a plate element in the form of a bipolar plate 10 which is also referred to as BIP. The bipolar plate 10 is a plate element for a fuel cell or fuel cell system in the form of a fuel cell stack. For example, in the completely assembled state of the fuel cell stack the bipolar plate 10 is arranged between two individual fuel cells. The bipolar plate 10 comprises a first plate 12 being a cathode. Moreover, the bipolar plate 10 comprises a second plate 14 being an anode. This means the first plate 12 acts as a cathode for a first fuel cell of the fuel cell stack, wherein the second plate 14 acts as an anode for a second fuel cell of the fuel cell stack, the second fuel cell being adjacent to the first fuel cell. As can be seen from Fig. 1, the first and second plates 12 and 14 overlap each other.

The plate 12 and, thus, the bipolar plate 10 has at least one protrusion 16 protruding from other areas 18 of the plate 12, the other areas 18 being arranged beside the protrusion 16. The protrusion 16 bounds at least one guide channel 20 on a side 22 facing away from a surface 24 of the plate 12. As will be described in greater detail in the following, at least one sealing element is produced on the surface 24 facing away from the side 22, wherein said sealing element is produced by injection molding. Thus, in the following, a method for producing such a sealing element on the surface 24 is described. In order to produce the sealing element a first mold in the form of a top mold 26 is provided. The top mold 26 comprises at least one cavity 26 which can be seen in Fig. 2. The sealing element is produced by means of the cavity 28 by injecting a liquid plastic material in the cavity 28. For example, said plastic material injected into the cavity 28 in a liquid state is a liquid silicone. The top mold 26 is part of a tool by means of which the injection molding or injection molding process is carried out.

Said tool comprises two gates 30 by means of which the liquid plastic material is injected into the cavity 28 at respective injection points 32 and 34. Fig. 1 shows respective flow lengths fl and f2 for the liquid plastic material. The respective flow lengths fl and f2 are respective distances between the respective injection points 32 and 34 and the middle M of the cavity 28 having a longitudinal extension. As can be seen from Fig. 2, the tool further comprises a bottom mold 36 which is arranged on a side of the plate 14, wherein said side of the second plate 14 faces away from the top mold 26. As can be seen from Figs. 1 and 2, the top mold 26 comprises respective elements 38 arranged on both sides and in the vicinity of the cavity 28. The elements 38 are configured to heat and/or cool the liquid plastic material injected into the cavity 28.

For example, the respective element 38 comprises at least one heating element such as an electric heating element configured to heat the plastic material injected into the cavity 28. Alternatively or additionally, the respective element 38 comprises at least one cooling duct through which a cooling medium such as a cooling liquid configured to cool the plastic material injected into the cavity 28 can be cooled. In Fig. 2, a indicates a distance between the cavity 28 and the respective element 38. Moreover, in Fig. 2, b indicates an extension of the respective element 38.

In said method, the top mold 26 is arranged on the side of the surface 24 in such a way that the cavity 28 runs angularly across the protrusion 16. As can be seen from Fig. 1, the top mold 26 is arranged in such a way that the cavity 28 runs perpendicularly in relation to and across the protrusion 16 from one of the areas 18 to the other area 18 and, thus, from one side of the protrusion 16 to the other side.

As can be seen from Fig. 2, the top mold 26 is arranged at a distance y from the surface 24 thereby creating a gap 40 between the top mold 26 and the surface 24. Moreover, the top mold 26 has respective recesses 42 arranged in the vicinity of the cavity 28, the recesses 42 being configured to receive a portion of the plastic material injected into the cavity 28 and flowing through the gap 40 into the respective recesses 42. In Fig. 2, reference sign 44 indicates a thin layer of the plastic material, the thin layer 44 being a fast vulcanized and/or cooled portion of the plastic material. This means the elements 38 are used to realize a fast curing of the plastic material by cooling and/or heating the plastic material. In other words, with a strategic placement of the localized elements 38 and the recesses 42 acting as pressure relieve pockets for overflowing material, and with appropriately spaced locations of the gates 30 placed in the vicinity of the protrusion 16 being an area which is difficult to seal, flash from the injected material can be kept particularly low. In other words, the protrusion 16 and, thus, the guide channel 20 are areas which are also referred to as vias or via areas. Said via areas are difficult to seal since, usually, a sufficient bond between the surface 24 and the sealing element in said via areas is difficult to realize. However, by using the elements 38 and the recesses 42 an efficient bond between the sealing element or the plastic material and the surface 24 can be realized so that a particularly advantageous sealing of the plate 12 and, thus, the bipolar plate 10 can be realized in a particularly cost-efficient way.

List of reference signs bipolar plate 12 first plate 14 second plate 16 protrusion 18 area guide channel 22 side 24 surface 26 top mold 28 cavity gate 32 injection point 34 injection point 36 bottom mold 38 element gap 42 recess 44 layer a distance b distance Ii flow length 12 flow length y distance M middle

Claims

Claims A method for producing at least one sealing element on a surface (24) of a plate (10, 12) for a fuel cell system by injection molding, the plate (10, 12) having at least one protrusion (16) bounding at least one guide channel (20) on a side (22) facing away from the surface (24), wherein the method comprises: -providing at least one mold (26) having: o at least one cavity (28) by means of which the sealing element is produced by injecting a liquid plastic material into the cavity; and o at least one element (38) configured to heat and/or cool the liquid plastic material, the element being arranged in the vicinity of the cavity (28); -arranging the mold (26) on the side of the surface (24) such that the cavity (28) runs angularly across the protrusion (16); and -injecting the plastic material into the cavity (28).
2. The method according to claim 1, wherein the mold (26) is arranged at a distance (y) from the surface (24) thereby creating a gap (40) between the mold (26) and the surface (24), the mold (26) further having least one recess (42) arranged in the vicinity of the cavity (28), the recess (42) being configured to receive a portion of the plastic material injected into the cavity (28) and flowing through the gap (40) into the recess (42).
3. The method according to claim 1 or 2, wherein the element (38) comprises an electric heating element configured to heat the plastic material injected into the cavity (28).
4. The method according to any one of the preceding claims, wherein the element (38) comprises at least one duct through which a cooling medium for cooling the plastic material injected into the cavity (28) can flow.
5. The method according to any one of the preceding claims, wherein the mold (26) is arranged in such a way that cavity (28) runs angularly across the protrusion (16) from one side of the protrusion (16) to the other.