Plate stack

Abstract

Joining a first metal plate and a second metal plate. A melting point depressant is applied at a first area of at least one of the plates. The first area is elongated in a planar direction. The plates are stacked along a stacking direction being transversal to the planar direction. The plates defining a plate interspace between themselves being less than the thickness of any of the plates. The plates are heated thereby melting a surface layer of at least one of the plates at the first area and forming a melted surface layer together with the melting point depressant. The melted surface layer contacting both plates. The melted surface layer is allowed to solidify at a second area being elongated in the planar direction, thereby forming an elongated joint between the plates at the second area and an elongated groove at the first area.

Description

[0001] PLATE STACK

[0002] Technical field

[0003] The present invention relates to a method of joining a first metal plate and a second metal plates and a stack of metal plates.

[0004] Introduction

[0005] Plate stacks can be permanently joined by different technologies. Joints may be formed by a joining method in which the plates are subjected to a heat lower than the melting point of the plates. Such joining methods may be brazing with an added brazing material in the form of a foil, a paste, or a powder comprising e.g., copper or nickel.

[0006] The above techniques are commonly used for permanently joining corrugated metal plates of permanently sealed heat exchangers. The corrugations of opposing plates contact each other at well defied contact points. The melted brazing material will accumulate at the contact points between the corrugated plates due to capillary forces and wet the contact point and this ensures a proper leak free joint between the plates.

[0007] Permanently joining of non-corrugated plates is however much more challenging than joining corrugated plates as with non-corrugated plates there are no well defied contact points between the plates. Non-corrugated plates are useful for manufacturing fuel cells, electrolysers or similar, but can also be used in some heat exchanger applications. Noncorrugated plates are understood to mean plates defining a plane surface which is intended to be joined to a corresponding plane surface of an opposing plate. However, the plates typically have throughgoing channels and port holes for accommodating fluids.

[0008] The non-corrugated plates are typically permanently joined along the edges of the plates or along the port holes by applying brazing material at the edges of the plates. However, it will typically not result in a leak free joint. As the opposing plates in practice cannot be positioned perfectly flat relative each other there will typically be a random contact point between the plates when stacked. During stacking of the plates, there will always be areas where there will be more of less play between the opposing plates. Since the capillary forces are stronger at areas with less distance between the opposing plates and weaker at areas with more distance between the opposing plates, the melted brazing material or plate material will flow from the areas with more play, i.e. greater distance, between the opposing plates to areas with less play, i.e. smaller distance, between the opposing plates. Thus, the areas with more play between the plates may not receive enough melted material and thus may not be sufficiently joined, and there may be leaks at those locations. This is considered a fault.

[0009] It is also difficult to ensure that the plates are joined at the correct location, i.e. adjacent the edge or adjacent port holes, using non-corrugated plates. In case the smallest distance between the plates is closer to the centre of the plate, there is a risk that all or most of the melted material accumulates at that location. This may also lead to a failure. Below follows a short description of some applications of non-corrugated plates:

[0010] Fuel cells make use of non-corrugated plates and generate electrical power from an electrochemical reaction between a hydrogen-based fuel and an oxidant. Fuel cells typically comprise a set of fuel cell substrates assembled in series. Each fuel cell substrate comprises a plate package of four (or more) metal plates. The fuel cell substate comprising a fuel plate, a separator plate, an oxidant plate and an electrolyte plate positioned between the fuel plate and the oxidant plate. The fuel plate and the oxidant plate each comprise channels for distributing the fuel and oxidant, respectively. The electrolyte plate comprising an electrolyte material. The separator plate separates the fuel plate and the oxidant plate. An electric current is generated by an electrochemical reaction between the fuel and the oxidant occurring at the electrolyte plate.

[0011] Electrolysers also make use of plates are used to generate hydrogen and oxygen from water using electrical energy. Electrolysers like fuel cells comprises a set of metal plates and may face similar challenges as the fuel cell plates.

[0012] The plates of fuel cell substrates or electrolysers are successively arranged face to face and joined along their outer edges to be leak tight. They are also joined along port holes. However, as described above, it is very challenging to join flat surfaces due to the lack of a well-defined contact area between the plates. The melted material may therefore, due to capillary forces, accumulate at a random location where there is a small distance or a contact between the plates and leave other areas will be left open. The likelihood of a fault in the joint is therefore very high. A faulty joint may lead to leaks between the plates. As an alternative to brazing, two metal components (parent materials) can be joined together using a melting point depressant (MPD) applied to the metal components. The metal components are heated to a temperature above which the melting depressant composition causes the surface layer to melt and form a melted metal layer, but at a temperature that is below a melting temperature of the material in the metal parts. In brief, when heating the metal parts, the melting depressant composition diffuses into the first metal parts and causes it to melt at a temperature that is lower than the melting temperature of the material in the metal parts. The melting depressant composition is applied on the surface at amounts that causes the surface layer to melt and form the melted metal layer. Thus, the amount of melting depressant composition is chosen so that the melting point depressant diffuses mainly into the surface layer. However, too much melting point depressant may melt the entire metal parts. Metal in the melted metal layer then flows, typically by capillary action, towards the contact point. In the context of the present patent application, the expression “contact point” should be construed as also including other geometric shapes than points, such as lines, curves and areas.

[0013] Melting point depressant diffuses into the metal parts when metal in the melted metal layer has flown towards the contact point where a joint now is formed. The joint now comprises metal that previously was part of the metal parts. The melting point depressant composition is no longer present on the surface of the metal parts since it has diffused into the metal parts. Since the joint is formed from metal from the metal parts, the metal parts are now thinner than before the heating. Further details of melting point depressants can be found in US10131011 which is hereby incorporated by reference.

[0014] When joining corrugated plates having ridges, the melting point depressant lowers the melting point at the location of the ridge and thus when the plates are heated above the lowered melting point of the plate material, it becomes liquid at the location of the melting point depressant and fills the gap between the plates by capillary action. When cooled down the plate material comprising the melting point depressant solidifies to form the joint.

[0015] Joining flat plates applying the above-mentioned melting point depressant would result in the formation of liquified grooves in the plate when heated above the lower melting point of the plate material where the melting point depressants have been applied. The liquid plate material in the groove will not be able to fill the gap between the plates by capillary action or even wet the surface of the opposing plate. Heat exchangers and similar products having extremely narrow internal channels can often be very costly and difficult to produce as special manufacturing methods are needed such as 3D printing etc. There is thus a need for technologies for both joining stacked plates and provide internal channels between the plates. Examples of such applications include electrolysers and printed circuit heat exchangers which are useful for renewable power applications such as thermal energy storage systems, supercritical CO2 power cycles, gas turbine fuel gas pre-heating and hydrogen refuelling stations, etc.

[0016] The prior art includes JP 2016176618 describes a plate heat exchanger having circumferential shaped projections having its apex parts brazed to the next plate. Brazing is performed by a brazing material flowing into a gap between opposing plates formed by the projections.

[0017] WO 2024 / 089125 describes a stack of plates, whereby one of the plates defining a first ridge protruding a first distance in a first plate interspace. The first distance is less than the thickness of the plates in the first plate interspace. The plates in the first plate interspace being permanently joined at the first ridge.

[0018] US 4653581 describes a plate heat exchanger having side wall members in the form of rods fixed to the heat transfer plates by brazing.

[0019] US 10458725 describes a plate heat exchanger with flat plates that may have circular rods to form frame members. The plates and the frame will be brazed together to form sealed passageways by capillary flow of molten brazing filler metal.

[0020] EP 3 301 747 describes an internally manifolded solid oxide fuel cell stack.

[0021] WO 2013 / 144211 A1 describes a method for joining metal parts using a melting depressant composition.

[0022] The object of the present invention is therefore to find technologies for permanently joining flat plates without the deficits mentioned above. of the invention

[0023] The above object can according to a first aspect of the present invention be realized by a method of joining a first metal plate and a second metal plate comprising the steps of: providing the first metal plate and the second metal plate, applying a melting point depressant at a first area of at least one of the first metal plate and the second metal plate, the first area being elongated in a planar direction, stacking the first metal plate on top of the second metal plate along a stacking direction being transversal to the planar direction, the first metal plate and the second metal plate defining a plate interspace between themselves being less than the thickness of any of the first metal plate and the second metal plate, heating the first metal plate and the second metal plate above a reduced melting temperature of the first area of the at least one of the first metal plate and the second metal plate where the melting point depressant has been applied, but below a melting temperature of a second area of the at least one of the first metal plate and the second metal plate where no melting point depressant has been applied, the second area being adjacent to the first area, the at least one of the first metal plate and the second metal plate together with the melting point depressant forms a melted surface layer at the first area, the melted surface layer at the first area wets both the first plate and the second plate and is drawn by capillary action in the plate interspace towards the second area where the melting point depressant has not been applied, thereby leaving an elongated groove at the first area from where the melted surface layer has been drawn, and cooling down the melted surface layer to ambient temperature causing it to solidify at the second area which is elongated in the planar direction and form an elongated joint between the first metal plate and the second metal plate at the second area.

[0024] The metal plates can be made of stainless steel, nickel and / or titanium. The plates do typically not have any corrugations or bends which exceed the thickness of the plate. The metal plates can define port holes for inlet and outlet of fluid, such as fuel or oxidizer. The thickness of the metal plates typically is less that 2mm, more typically less than 1mm, more typically less than 0.5 mm. The thickness of the metal plates typically is less that 2mm, more typically less than 1mm, more typically less than 0.5 mm. The planar direction can be defined as being parallel to the general extension of the plate. The planar direction is typically parallel to the of the flow, however, it can also be zigzag or round. The stack may comprise more than two plates, such as at least three plates defining a first and a second plate interspace between themselves or at least four plates defining a first, a second and a third plate interspace between themselves.

[0025] The plate interspace can be formed by natural irregularities in the plates. Port holes can be used to introduce fuel and oxidiser into the fuel cell and can be encircled at the plate interspaces in which the ports are not used.

[0026] The stack comprises at least two plates defining a plate interspace between themselves.

[0027] The plate interspace typically is very small. It essentially defines a contact plane between the plates. By forming an elongated groove at the first area and joining the metal plates at the second area an elongated channel between the first metal plate and the second metal plate can be formed. The channel can be used for conducting a fluid. Depending on the application, the channel can be made very thin. The plate interspace is increased at the first area due to the formation of the elongated groove. Using three or more plates, channels formed by elongated grooves may be formed on opposite sides of the middle plate. Such channels can be formed in a staggered relationship with each other on the opposite sides of the middle plate, or the channels may form a cross pattern with each other on the opposite sides of the middle plate. In this way a heat exchanger can be constructed.

[0028] Before the plates are stacked together a melting point depressant is applied at the first area of at least one of the metal plates. The melting point depressant can be a chemical composition capable of reducing the melting temperature of a base material onto which the melting point depressant is applied. Some examples of melting point depressants include Silicon, Boron, Phosphorus and Manganese. Some examples of plate materials include Iron and Nickel. Typically, the melting point depressant material comprises at least 25 wt% boron and / or silicon and / or carbon, preferably 45 wt% boron and / or silicon and / or carbon, more preferably 85 wt% boron and / or silicon and / or carbon. Printing techniques can be used for an accurate deposit of the melting point depressant. The plates are then stacked in a conventional fashion such that the surface areas of adjacent plates are overlapping.

[0029] When the metal plates heated, the surface layer at the first area of metal plate will melt before the rest of the metal plates. The plate interspace defines a distance between the metal plates which is sufficiently small to allow the melted surface layer to be drawn by capillary action towards the opposite metal plate and bridge the plate interspace at the second area. It should be ensured that the second area is sufficiently large to provide a sufficient volume to accommodate the melted surface layer of the first area. Typically, the second area will be larger than the first area.

[0030] When the first metal plate and the second metal plate are allowed to cool down, the melted surface layer will solidify, forming the joint between the first metal plate and the second metal plate.

[0031] According to a further embodiment of the first aspect, the first area and the second area of at least one of the first metal plate and the second metal plate are flat

[0032] A flat area will be useful for establishing the capillary action to be able to draw the melted surface layer from the first area to the second area.

[0033] According to a further embodiment of the first aspect, the plate interspace comprises a spacer element extending between the first metal plate and the second metal plate along the stacking direction, the first metal plate and the second metal plate contacting each other via the spacer element, the spacer element preferably defines a ridge protruding from the first metal plate and / or from the second metal plate into the plate interspace..

[0034] By placing a spacer element extending into the plate interspace and contacting the opposing plate, there will be a well-defined contact area between the metal plates and a well-defined distance between the metal plates. The space between the plates will also define the minimal play between the plates. The spacer element may be in the form of a ridge which may be coined or pressed, or the spacer element can alternatively be formed as a rod which is applied or printed onto the plate. Alternatively, the spacer element may be formed by natural irregularities in the plate or by manufacturing tolerances. Allowing the spacer element to encircle the plates will allow the plate interspace to form an inner region which is fluid tight. The height of the spacer element is typically less than 1mm, however, more typically less than 0,1 mm.

[0035] The height of the spacer element defines the plate interspace and is less than the thickness of the plate. As the plates are typically very thin, the spacer element will not influence the flow or establish a flow channel in the interspace but just establish the plate interspace and, optionally, a well-defined contact point for the joining of the plates. The spacer will bridge the plate interspace and thereby contacting both the first metal plate and the second metal plate.

[0036] When using pressing technique for providing the spacer, a ridge is formed and the ridge will cause a valley on the other side of the plate. This causes a problem when joining more than two plates along the same path as the ridge on one plate may then coincide with the valley of the opposite plate in the contact plane. This may cause a leakage as the ridge will fall into the valley, causing a larger distance between the plates and cancelling the effect of the ridge. The ridges in adjacent contact planes of adjacent plates should therefore be offset and should not coincide each other.

[0037] According to a further embodiment of the first aspect, the first metal plate and the second metal plate are joined at the spacer element.

[0038] Applying the melting point depressant at or adjacent the spacer element can ensure that the melted surface layer will contact both metal plates. Further, it can be prevented that the melted surface layer forms a “pool” of melted metal which possibly can remain without contact with the opposite metal plate and not be drawn towards the opposite metal plate, thereby failing to provide a joint between the metal plates. The spacer element may further providing sufficient plate material to be melted for forming the joint.

[0039] Applying the melting point depressant at the spacer element will therefore ensure that there is melted plate material at the spacer element. Therefore, the joining of the plates will be free of any faults. The spacer element can preferably define a curvature to increase the capillary force between the plates, applying melting point depressant at the spacer element, the spacer element itself will be partially melted and thereby no groove will form. This ensures a strong joint between the plates.

[0040] Applying the melting point depressant at least partially spaced apart from the spacer element will allow the melted surface layer to be drawn towards the spacer elements the capillary strength is higher close to the contact point between the metal plates. The first area can be at least partially adjacent the spacer element.

[0041] As the melted surface layer at the first area is drawn to the second area a groove will be established at the first area. This is a way to sculpture the metal plates and increase the plate interspace at the first area. By locating both the first area and the second area entirely spaced apart from the first spacer element, the spacer element can be used for establishing the plate interspace only. The melted surface layer can be drawn to the second area being adjacent to the first area. The second area is non melted and will define a smaller plate interspace than the first area as the melted surface layer at the first area is drawn to the second area and a groove will be established at the first area. This is a way to sculpture the metal plates and increase the plate interspace at the first area.

[0042] According to a further embodiment of the first aspect, the first area and the second area being formed in an alternating pattern.

[0043] The first area and the second area may be distributed over the surface of one or both the metal plates. One or more grooves can be established at the first area. Joints are established at the second area between the grooves. In this way, parallel grooves can be formed. In a special embodiment, the width of the grooves is approximately equal to the plate interspace at the channel.

[0044] According to a further embodiment of the first aspect, the melted surface layer substantially fills the plate interspace at the second area

[0045] By properly adjusting the plate interspace, the amount of melting point depressant, the position and the size of the first and second areas, the amount of melted surface layer can be made to match the volume defined by the plate interspace at the second area. In this way it can be ensured that sufficient material is provided to ensure that the complete second area is filled by the melted surface layer and provides a proper seal and that no melted surface layer remains in the groove. Also, when the second area is located on both sides of the first area, for example when, the first area and the second area being formed in an alternating pattern, it can be ensured that both sides are filled by the melted surface layer, avoiding leaving one of the sides of the groove open.

[0046] According to a further embodiment of the first aspect, the first metal plate and the second metal plate each comprise at least two port holes, the elongated groove extending between the portholes.

[0047] In this way one or more channels can be created between portholes in the plates. According to a further embodiment of the first aspect, the first metal plate and / or the second metal plate include stainless steel, nickel and / or titanium.

[0048] The above materials are suitable for the purpose of making heat exchangers, fuel cells or electrolysers.

[0049] The above object can according to a second aspect be realized by a stack of metal plates comprising a first metal plate stacked on top of a second metal plate along a stacking direction, at least one of the first metal plate and the second metal plate comprising an elongated groove at a first area, the first metal plate being joined to the second metal plate by an elongated joint at a second area, the second area being adjacent to the first area, the first area and the second area being elongated in a planar direction being transversal to the stacking direction, the joint comprising a solidified surface layer of at least one of the first metal plate and the second metal plate having been drawn from the first area for establishing the groove and being melted together with a melting point depressant having originally been applied at the first area.

[0050] The present stack according to the second aspect is preferably used with the method according to the first aspect. Further, any of the embodiments of the first aspect can be equally implemented with the second aspect.

[0051] The above object can according to a third aspect of the present invention be realized by a stack according to the second aspect used in a heat exchanger, fuel cell or electrolyser. Heat exchangers, fuel cells and electrolysers are examples of systems where plates are used, especially plates having channels. The channels can be used for conducting fluids. The fluids can be oxidizers and fuel such as in fuel cells or electrolysers. The channels can also be used for conducting heating fluids and / or cooling fluids for heat exchange with fluids in adjacent channels, such as heat exchange between fluids in channels being located on opposite sides of the plate. .

[0052] Brief description of the drawings

[0053] FIG. 1 A-C are a first embodiment of a stack with 2 plates having pressed ridges.

[0054] FIG. 1 D-F are a second embodiment of a stack with 2 plates having pressed ridges.

[0055] FIG. 1G-I are a third embodiment of a stack with 2 plates having pressed ridges. FIG. 1 J-L are a fourth embodiment of a stack with 2 plates having pressed ridges.

[0056] FIG. 1M-0 are a fifth embodiment of a stack with 2 plates having pressed ridges.

[0057] FIG. 1 P-R are a sixth embodiment of a stack with 2 plates having pressed ridges.

[0058] FIG. 2A-B are side cross-sectional views of a stack with 3 plates having pressed ridges. FIG. 3A-B are side cross-sectional views of a stack with 4 plates having pressed ridges. FIG. 4A-B are side cross-sectional views of a stack with 4 plates having rod ridges.

[0059] FIG. 5A-B are side cross-sectional views of a stack with 4 plates having coined ridges.

[0060] FIG. 6 is a perspective view and a closeup of a stack after permanent joining of the plates. FIG. 7 shows the results of a proof-of-concept test.

[0061] Detailed description of the drawings

[0062] FIG. 1A shows a side cross-sectional view of a first embodiment not forming part of the presently claimed invention of a stack of plates 101defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The second plate 12b defines a pressed ridge 14 having a height h being less than the thickness t of the plate. The height of the ridge 14 relative to the thickness t of the plate can be much less than illustrated, such as less than 1 / 10 of the thickness t of the plate. The heigh h can be less than 1 mm, preferably less than 0.1 mm. The ridge 14 has a melting point depressant 16 applied to it. The melting point depressant can be made of compositions comprising boron, silicon, phosphorus and manganese. The melting point depressant can be applied by e.g. screen printing. The ridge 14 is made by pressing, thus producing a valley 20 on the opposite side of the second plate 12b. The melting point depressant 16 is applied on the surface of the plate 12b at amounts that causes the surface layer of the plate 12b to melt at a lower temperature than the plate 12b. Thus, the amount of melting depressant composition 16 is chosen so that it only diffuses into the surface layer of the plate 12b but not melt the entire plate 12b. Suitable amounts of the melting point depressant 16 are known per se.

[0063] FIG. 1B shows a side cross sectional view of the first embodiment not forming part of the presently claimed invention of the stack of plates 101when the first plate 12a and the second plate 12b contact each other at the ridge 14. The first plate 12a and the second plate 12b define a plate interspace 22 between themselves. The plate interspace 22 is about equal to the height of the ridge 14. When heating the stack 10 the melting point depressant diffuses into the plate 12b (and optionally 12a) and causes it to melt at a temperature that is lower than the melting temperature of the material in the plate 12b (and optionally 12a) to form a melted surface layer 17. By heating the stack 101above the reduced melting temperature of the second plate 12b at the ridge 14 but below the melting temperature of the plate 12b outside the ridge 14, the surface layer of the ridge 14 is melted and wets the surface of the ridge 14 and the adjacent surface of the first plate 12a. Metal in the melted surface layer 17 of the ridge 14 and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards the contact point between the plate 12a at the ridge 14.

[0064] FIG. 10 shows a side cross sectional view of the first embodiment not forming part of the presently claimed invention of the stack of plates 101when the first plate 12a and the second plate 12b have been joined together at the ridge 14. When cooled down to ambient temperatures, the melted metal layer forms a joint 18 between the first plate 12a and the second plate 12b. The ridge 14 creates a well-defined contact area where the capillary forces can ensure that the melted layer is accommodated between the ridge 14 and the adjacent surface of the first plate 12a. The curved shape of the ridges allows the melted surface layer to accumulate even better due to the capillary effect and the ridge provides the metal material needed for the joint 18. In this way the melted surface layer is kept at a well-defined position until it solidifies.

[0065] FIG. 1D shows a second embodiment according to the present invention of a stack of plates 10" similar to FIG 1A defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The melting point depressant 16 is applied on the plate 12b at an area spaced apart from the ridge 14.

[0066] FIG. 1 E shows the second embodiment of a stack of plates 10" similar to FIG 1B. The melting point depressant causes the area of the plate 12b (and optionally 12a) where it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plate 12b (and optionally 12a) where melting point depressant has not been applied.

[0067] By heating the stack 10" above the reduced melting temperature of the second plate 12b at the area where the melting point depressant has been applied, but below the melting temperature of the plate area where the melting point depressant 16 has been applied, the surface layer of the area of the plate 12b (and optionally 12a) where the melting point depressant has been applied is melted and wets the surface of the plate 12b and the adjacent surface of the plate 12a forming a melted surface layer 17. Metal in the melted surface layer 17 and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards an adjacent area of the plate 12b and opposing plate 12a where the melting point depressant has not been applied.

[0068] FIG. 1 F shows the second embodiment of a stack of plates 10" similar to FIG 10. When cooled down to ambient temperatures, the melted metal layer forms a joint 18 between the first plate 12a and the second plate 12b. As the melted surface layer of the plate 12b (and optionally 12a) is drawn from the area of the plate 12b (and optionally 12a) where melting point depressant has been applied to the adjacent area of the plate 12b (and optionally 12a) where melting point depressant has not been applied, a groove 19 will be formed at the original location where melting point depressant was applied. In this way, the plate can be sculptured and elongated channels may be formed.

[0069] FIG. 1G shows a third embodiment according to the present invention of a stack of plates 10111similar to FIG 1A defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The melting point depressant 16 is applied on the plate 12b at an area adjacent the ridge 14.

[0070] FIG. 1 H shows the third embodiment of a stack of plates 10111similar to FIG 1 B. The melting point depressant causes the area of the plate 12b (and optionally 12a) where it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plate 12b (and optionally 12a) where melting point depressant has not been applied.

[0071] By heating the stack 10111above the reduced melting temperature of the second plate 12b at the area where the melting point depressant has been applied, but below the melting temperature of the plate area where the melting point depressant 16 has been applied, the melted surface layer 17 of the area of the plate 12b (and optionally 12a) where the melting point depressant 16 has been applied wets the surface of the plate 12b and the adjacent surface of the plate 12a. Metal in the melted surface layer 17 and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards an adjacent area of the plate 12b and opposing plate 12a where the melting point depressant has not been applied.

[0072] FIG. 11 shows the third embodiment of a stack of plates 10111similar to FIG 10. When cooled down to ambient temperatures, the melted metal layer forms a joint 18 between the first plate 12a and the second plate 12b. As the melted surface layer of the plate 12b (and optionally 12a) is drawn from the area of the plate 12b (and optionally 12a) where melting point depressant has been applied to the adjacent area of the plate 12b (and optionally 12a) where melting point depressant has not been applied, a groove 19 will be formed at the original location where melting point depressant was applied. In this way, the plate can be sculptured and elongated channels may be formed.

[0073] FIG. 1 J shows a fourth embodiment according to the present invention of a stack of plates 10lvsimilar to FIG 1A defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The melting point depressant 16 16’ 16” is applied on the plate 12b at an area distributed in an alternating pattern from a point adjacent the ridge 14 to a point spaced apart from the ridge 14.

[0074] FIG. 1K shows the fourth embodiment of a stack of plates 10lvsimilar to FIG 1B. The melting point depressant causes the area of the plate 12b (and optionally 12a) where it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plate 12b (and optionally 12a) where melting point depressant has not been applied.

[0075] By heating the stack 10lvabove the reduced melting temperature of the second plate 12b at the area where the melting point depressant has been applied, but below the melting temperature of the plate area where the melting point depressant has been applied, the melted surface layers 17 17’ 17” of the area of the plate 12b (and optionally 12a) where the melting point depressant has been applied wets the surface of the plate 12b and the adjacent surface of the plate 12a. Metal in the melted surface layers 17 17’ 17” and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards an adjacent area of the plate 12b and opposing plate 12a where the melting point depressant has not been applied.

[0076] FIG. 1 L shows the fourth embodiment of a stack of plates 10lvsimilar to FIG 10. When cooled down to ambient temperatures, the melted metal layer form joints 18 18’ 18” 18’” between the first plate 12a and the second plate 12b. As the melted surface layer of the plate 12b (and optionally 12a) is drawn from the area of the plate 12b (and optionally 12a) where melting point depressant has been applied to the adjacent area of the plate 12b (and optionally 12a) where melting point depressant has not been applied, grooves 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plates can be sculptured and elongated channels may be formed.

[0077] FIG. 1M shows a fifth embodiment according to the present invention of a stack of plates 10vsimilar to FIG 1A defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The second plate 12b comprises a plurality of ridges 14. The melting point depressant 16 16’ 16” is applied on the plate 12b at an area distributed in an alternating pattern between the ridges 14.

[0078] FIG. 1 N shows the fifth embodiment of a stack of plates 10vsimilar to FIG 1 B. The melting point depressant causes the area of the plate 12b (and optionally 12a) where it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plate 12b (and optionally 12a) where melting point depressant has not been applied.

[0079] By heating the stack 10vabove the reduced melting temperature of the second plate 12b at the area where the melting point depressant 16 has been applied, but below the melting temperature of the plate area where the melting point depressant 16 has been applied, the melted surface layers 17 17’ 17” of the area of the plate 12b (and optionally 12a) where the melting point depressant 16 has been applied wets the surface of the plate 12b and the adjacent surface of the plate 12a. Metal in the melted surface layers 17 17’ 17” and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards an adjacent area of the plate 12b and opposing plate 12a where the melting point depressant has not been applied.

[0080] FIG. 10 shows the fifth embodiment of a stack of plates 10vsimilar to FIG 1C. When cooled down to ambient temperatures, the melted metal layer form joints 18 18’ 18” between the first plate 12a and the second plate 12b. As the melted surface layer of the plate 12b (and optionally 12a) is drawn from the area of the plate 12b (and optionally 12a) where melting point depressant has been applied to the adjacent area of the plate 12b (and optionally 12a) where melting point depressant has not been applied, grooves 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plate can be sculptured and elongated channels may be formed.

[0081] FIG. 1P shows a sixth embodiment according to the present invention of a stack of plates 10vlsimilar to FIG 1A defining a first plate 12a and a second plate 12b both made of metal, typically stainless steel. The second plate 12b comprises a plurality of spacers 21 2T. The melting point depressant 16 16’ is applied on the plate 12b at an area distributed in an alternating pattern between the spacers 21. The spacers 21 2T may be printed onto the plate.

[0082] FIG. 1Q shows the sixth embodiment of a stack of plates 10vlsimilar to FIG 1 B. The melting point depressant causes the area of the plate 12b (and optionally 12a) where it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plate 12b (and optionally 12a) where melting point depressant has not been applied.

[0083] By heating the stack 10vlabove the reduced melting temperature of the second plate 12b at the area where the melting point depressant has been applied, but below the melting temperature of the plate area where the melting point depressant 16 has been applied, the melted surface layers 17 17’ of the area of the plate 12b (and optionally 12a) where the melting point depressant has been applied wets the surface of the plate 12b and the adjacent surface of the plate 12a. Metal in the melted metal layers 17 17’ and the opposing plate 12a, together with the melting point depressant, is drawn by capillary action towards the spacers 21 2T and opposing plate 12a where the melting point depressant has not been applied.

[0084] FIG. 1 R shows the sixth embodiment of a stack of plates 10vlsimilar to FIG 10. When cooled down to ambient temperatures, the melted metal layer form joints 18 18’ 18’ between the first plate 12a and the second plate 12b. As the melted surface layer of the plate 12b (and optionally 12a) is drawn from the area of the plate 12b (and optionally 12a) where melting point depressant has been applied to the spacers 21 2T area of the plate 12b (and optionally 12a) where melting point depressant has not been applied, grooves 19 19’ will be formed at the original location where melting point depressant was applied. In this way, the plate can be sculptured and elongated channels may be formed.

[0085] FIG. 2A shows a side cross sectional view of a stack of plates 10v" not forming part of the presently claimed invention defining a first plate 12a, second plate 12b and a third plate 12c. The first plate 12a and the third plate 12c each has a pressed ridge 14 14’ facing the second plate 12b. The second plate 12b is in between and does not have any ridge / valley. Each ridge 14 14’ has a melting point depressant 16 16’ applied to it. The first plate 12a and the second plate 12b defines a plate interspace 22 between themselves and the third plate 12c and the second plate 12b defines a plate interspace 22’ between themselves.

[0086] FIG. 2B shows a side cross sectional view of the stack of plates 10VHnot forming part of the presently claimed invention when the first plate 12a, the second plate 12b and the third plate 12c have been joined by joints 18 18’, similar to FIG 10.

[0087] FIG. 3A shows a side cross sectional view of a stack of plates 10VIHaccording to the present invention defining a first plate 12a, second plate 12b, a third plate 12c and a fourth plate 12d. The first plate 12a has two ridges 14 facing the second plate 12a, the second plate 12b has one ridge 14’ facing the third plate 12c, the third plate 12c has a ridge 14” facing the second plate 12b. The fourth plate 12d has two ridges 14’” which are facing the third plate 12c. The ridges 14 14’ of the first plate 12a and the second plate 12b are offset to prevent the ridge 14 to fall into the valley 20’. This would have cancelled the effect of the ridge 14. Similarly, the ridges 14” 14’” of the third plate 12c and the fourth plate 12d are offset to prevent the ridge 14’” to fall into the valley 20”. The first plate 12a and the second plate 12b defines a plate interspace 22 between themselves and the third plate 12c and the second plate 12b defines a plate interspace 22’ between themselves. In addition, the third plate 12c and the fourth plate 12d defines a plate interspace 22” between themselves.

[0088] Either each ridge 14 14’ 14” 14’” has melting point depressant 16 16’ 16” 16’” applied to it, or the melting point depressant 16’ 16” 16’” is applied to the opposite plate. In particular, the ridges 14” 14’” of the third plate 12c and the fourth substantially flat plate 12d have melting point depressant 16” 16’”, and the second substantially flat plate 12b and the third plate 12d have melting point depressant 16’ 16” opposite the ridges 14 14’. Further, melting point depressant 16’ 16” 16’” is applied on the plates 12b 12c 12d at an area distributed in an alternating pattern from a point adjacent the ridge 14 14’ 14” 14’” to a point spaced apart from the ridge 14 14’ 14” 14’” or between the ridges 14 14’ 14” 14’”.

[0089] FIG. 3B shows a side cross sectional view of the stack of plates 10VI" when the first plate 12a, the second plate 12b, the third plate 12c and the fourth plate 12d have been joined together by joints 18 18’ 18”, similar to FIG 10. As the melted surface layer of the plates 12b 12c 12d (and optionally 12a) is drawn from the area of the plates 12b 12c 12d (and optionally 12a) where melting point depressant has been applied to the adjacent area of the plates 12b 12c 12d (and optionally 12a) where melting point depressant has not been applied, grooves 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plates can be sculptured and elongated channels may be formed.

[0090] FIG. 4A shows a side cross sectional view of a stack of plates 10lxaccording to the present invention defining a first plate 12a, second plate 12b, a third plate 12c and a fourth plate 12d. The first plate 12a and the second plate 12b defines a plate interspace 22 between themselves, the third plate 12c and the second plate 12b defines a plate interspace 22’ between themselves, and the third plate 12c and the fourth plate 12d defines a plate interspace 22” between themselves. Each plate interspace 22 22’ 22” comprises a rod 24 24’ 24” having a diameter less than the thickness of the plates. (The rods have been exaggerated for better visibility.) The rods 24 24’ 24” can be made of the same material as the plate or a similar metal material. The rods 2424’ 24” can be covered by melting point depressant, alternatively the melting point depressant may be applied to the plates adjacent the rods 24 24’ 24”, yet alternatively the melting point depressant may be part of the rods 24 24’ 24”. Further, melting point depressant 16 16’ 16” is applied on the plates 12a 12c 12d at an area distributed in an alternating pattern from a point adjacent the rods 24 24’ 24” to a point spaced apart from the rods 2424’ 24”.

[0091] FIG. 4B shows a side cross sectional view of the stack of plates 10lxwhen the first plate 12a, the second plate 12b, the third plate 12c and the fourth plate 12d have been joined together at the rods 24 24’ 24”. The circular shape of the rods 24 24’ 24” allows the melted surface layer of the plate material to accumulate at the rods 24 24’ 24” similar to the curvature of the ridge. Using rods avoids valleys on the plate and thus the rods 24 24’ 24” can be located without any offset. As the melted surface layer of the plates 12a 12c 12d (and optionally 12b) is drawn from the area of the plates 12a 12c 12d (and optionally 12b) where melting point depressant has been applied to the adjacent area of the plates 12a 12c 12d (and optionally 12b) where melting point depressant has not been applied, grooves 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plates can be sculptured and elongated channels may be formed.

[0092] FIG. 5A shows a side cross sectional view of a stack of plates 10xaccording to the present invention defining a first plate 12a, second plate 12b, a third plate 12c and a fourth plate 12d. The first plate 12a and the second plate 12b defines a plate interspace 22 between themselves, the third plate 12c and the second plate 12b defines a plate interspace 22’ between themselves, and the third plate 12c and the fourth plate 12d defines a plate interspace 22” between themselves. Each plate interspace 22 22’ 22” comprises a coined ridge 26 26’ 26” having a height less than the thickness of the plates. Coining is a specific technique which differs from pressing in that is does not produce a valley on the opposite side of the plate. The coined ridges 26 26’ 26” provides similar functionality to a pressed ridge and can either be covered by melting point depressant or alternatively the melting point depressant can be located space apart from the coined ridges 26 26’ 26”. Further, melting point depressant 16 16’ 16” is applied on the plate 12a 12c 12d at an area distributed in an alternating pattern from a point adjacent the rods 24 24’ 24” to a point spaced apart from the rods 2424’ 24”.

[0093] FIG. 5B shows a side cross sectional view of the stack of plates 10xwhen the first plate 12a, the second plate 12b, the third plate 12c and the fourth plate 12d have been joined together by joints 18 18’ 18” at the coined ridges 26 26’ 26”. The curved shape of the coined ridges 26 26’ 26” 24 24’ 24” allow the melted surface layer to accumulate at the coined ridges 26 26’ 26”, similar to a pressed ridge. However, using coined ridges 26 26’ 26” avoids valleys on the plate and thus the coined ridges 26 26’ 26” 24 24’ 24” can be located without any offset. As the melted surface layer of the plates 12a 12c 12d (and optionally 12b) is drawn from the area of the plates 12a 12c 12d (and optionally 12b) where melting point depressant has been applied to the adjacent area of the plates 12a 12c 12d (and optionally 12b) where melting point depressant has not been applied, grooves 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plates can be sculptured and elongated channels may be formed.

[0094] FIG. 6 shows a perspective view of a fuel cell stack 28 according to the present invention comprising plates 10xlsimilar to FIG 1J defining a first plate 12a, a second plate 12b and a third plate 12c all made of metal, typically stainless steel. The plates comprise elongated channels 19 19’ 19” The first plate 12a and the third plate 12c each define a ridge / valley 20 which is protruding towards each other and contacting the second plate 12b which is located between the first plate 12a and the third plate 12c. The melting point depressant was applied on the plates at an area distributed in an alternating pattern from a point adjacent the ridges / valleys 20 to a point spaced apart from the ridges / valleys 20. As described in connection with the previous embodiments, the melting point depressant causes the area of the plates 10xlwhere it has been applied to melt at a temperature that is lower than the melting temperature of the material of the plates 10xlwhere melting point depressant has not been applied.

[0095] By heating the plates 10xlabove the reduced melting temperature at the area where the melting point depressant has been applied, but below the melting temperature of the plate area where the melting point depressant has been applied, the melted surface layers where the melting point depressant has been applied wets the surfaces of the plates 10xl. Metal in the melted surface layers in the plate interspaces, together with the melting point depressant, is drawn by capillary action towards an adjacent area of the plate interspace where the melting point depressant has not been applied.

[0096] When cooled down to ambient temperatures, the melted metal layer form joints 18 18’ 18” 18”’ between the first plate 12a and the second plate 12b, and, between the second plate 12b and the third plate 12c. As the melted surface layer of the plates 10xlis drawn from the area of the plates 10xlwhere melting point depressant has been applied to the adjacent area of the plates 10xlwhere melting point depressant has not been applied, the channels 19 19’ 19” will be formed at the original location where melting point depressant was applied. In this way, the plates can be sculptured and elongated channels may be formed. The channels 19 19’ 19” may be formed on opposite sides of the second plate 12b as in the present embodiment, or the channels 19 19’ 19” may formed a staggered relationship with each other on the opposite sides of the second plate 12b, or the channels or the channels 19 19’ 19” may form a cross pattern with the channels on the opposite sides of the second plate 12b. Further, four or more plates can optionally be used in a similar way.

[0097] FIG. 7 shows the results of a proof-of-concept test according to the present invention. Melting point depressant was applied between two plates 12a 12b defining a plate interspace between the plates 12a 12b which is smaller than the thickness of the plates 12a 12b. When heated, the surface layer of the plates 12a 12b where the melting point depressant has been applied melts and is drawn by capillary action into the adjacent plate interspace where no melting point depressant has been applied. When cooled down, a groove 19 is established where the melting point depressant was applied and two joints 18 joining the plates 12a 12b are established on opposite sides of the groove 19. The amount of metal removed from the plates 12a 1b to form the groove is the same as the amount of metal forming the joints 18 in the plate interspace resulting in wide joints 18 in the present case.

[0098] In relation to drawings accompanying the above detailed description of the present invention, the ridges, rods and plate interspaces described herein have been exaggerated for better visibility. It is further contemplated that the ridges may be formed by natural irregularities in the plate material or by manufacturing tolerances instead of being pressed using a pressing tool or the like. In the present

Claims

Claims1. A method of joining a first metal plate and a second metal plate comprising the steps of: providing the first metal plate and the second metal plate, applying a melting point depressant at a first area of at least one of the first metal plate and the second metal plate, the first area being elongated in a planar direction, stacking the first metal plate on top of the second metal plate along a stacking direction being transversal to the planar direction, the first metal plate and the second metal plate defining a plate interspace between themselves being less than the thickness of any of the first metal plate and the second metal plate, heating the first metal plate and the second metal plate above a reduced melting temperature of the first area of the at least one of the first metal plate and the second metal plate where the melting point depressant has been applied, but below a melting temperature of a second area of the at least one of the first metal plate and the second metal plate where no melting point depressant has been applied, the second area being adjacent to the first area, the at least one of the first metal plate and the second metal plate together with the melting point depressant forms a melted surface layer at the first area, the melted surface layer at the first area wets both the first plate and the second plate and is drawn by capillary action in the plate interspace towards the second area where the melting point depressant has not been applied, thereby leaving an elongated groove at the first area from where the melted surface layer has been drawn, and cooling down the melted surface layer to ambient temperature causing it to solidify at the second area which is elongated in the planar direction and form an elongated joint between the first metal plate and the second metal plate at the second area.

2. The method according to claim 1, wherein the first area and the second area of at least one of the first metal plate and the second metal plate are flat.

3. The method according to any of the preceding claims, wherein the plate interspace comprises a spacer element extending between the first metal plate and the second metal plate along the stacking direction, the first metal plate and the second metal plate contacting each other via the spacer element, the spacer element preferably defines a ridge protruding from the first substantially flat metal plate and / or from the second substantially flat metal plate into the plate interspace..

4. The method according to claim 3, wherein the first metal plate and the second metal plate are joined at the spacer element.

5. The method according to any of the preceding claims, wherein the melted surface layer substantially fills the plate interspace at the second area6. The method according to any of the preceding claims, wherein the first area and the second area being formed in an alternating pattern.

7. The method according to any of the preceding claims, wherein the first metal plate and the second metal plate each comprise at least two port holes, the elongated groove extending between the portholes.

8. The method according to any of the preceding claims, wherein the first metal plate and / or the second metal plate include stainless steel, nickel and / or titanium.

9. A stack of metal plates comprising a first metal plate stacked on top of a second metal plate along a stacking direction, at least one of the first metal plate and the second metal plate comprising an elongated groove at a first area, the first metal plate being joined to the second metal plate by an elongated joint at a second area, the second area being adjacent to the first area, the first area and the second area being elongated in a planar direction being transversal to the stacking direction, the joint comprising a solidified surface layer of at least one of the first metal plate and the second metal plate having been drawn from the first area for establishing the groove and being melted together with a melting point depressant having originally been applied at the first area.

10. The stack according to claim 9, wherein the first area and the second area of at least one of the first metal plate and the second metal plate are flat.

11. The stack according to any of the claims 9-10, wherein the plate interspace comprises a spacer element extending between the first metal plate and the second metal plate along the stacking direction, the first metal plate and the second metal plate contacting each other via the spacer element, the spacer element preferably defines a ridge protruding from the first metal plate and / or from the second metal plate into the plate interspace.

12. The stack according to claim 11, wherein the first metal plate and the second metal plate are joined at the spacer element.

13. The stack according to any of the preceding claims, wherein the solidified surface layer substantially fills the plate interspace at the second area.

14. The stack according to any of the claims 9-13, wherein the first area and the second area being formed in an alternating pattern.

15. The stack according to any of the claims 9-14, the first metal plate and the second metal plate each comprise at least two port holes, the elongated groove extending between the portholes.

16. The stack according to any of the preceding claims, wherein the first metal plate and / or the second metal plate include stainless steel, nickel and / or titanium.

17. Use of the stack according to any of the claims 9-16 in a heat exchanger, fuel cell or electrolyser.

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