Process for manufacturing interconnected stacks of thermoplastic frames

Abstract

The present invention is directed to a method for manufacturing an interconnected stack of thermoplastic frames having two sides by stacking the thermoplastic frames to obtain a stack of frames such that the opposing sides of two adjacent frames contact each other at the contact area. During stacking, a longitudinal conduit is formed that runs along the length of the stack and a branching conduit is formed at the contact area. The interconnected stack of thermoplastic frames is obtained by feeding a pressurized melt of plastic material into the elongated conduit and the branching conduit.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing an interconnected stack of two-sided thermoplastic frames, which may be used as part of a plate-type heat exchanger. [Background technology]

[0002] Such a process is described in EP 2068107. This patent publication describes a method for producing a first resin frame by injection molding. A heat exchange sheet is combined with a frame and the resulting frames are stacked. The frames are connected to each other by ultrasonically melting the corners of the frames. When the molten resin solidifies, a bond between the frames occurs.

[0003] US 2018 / 0266774 and WO 2018 / 132014 describe heat exchanger frames obtained as insert moulded parts, which are connected by snap-fit ​​connections to obtain a stack of interconnected frames.

[0004] A problem with the lamination process of thermoplastic frames is the strength of the resulting stack if snap-fit ​​connections are used. Ultrasonic fusing is a disadvantage when connecting several frames into one stack as it is a laborious process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent No. 2068107 [Patent Document 2] US Patent Application Publication No. 2018 / 0266774 [Patent Document 3] International Publication No. 2018 / 132014 Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a method for manufacturing an interconnected stack of thermoplastic frames that does not have the problems of the prior art methods. [Means for solving the problem]

[0007] This object is achieved by a process for manufacturing an interconnected stack of a thermoplastic frame having two sides, the process comprising: In a process of stacking thermoplastic frames to obtain a stack of frames, such that the opposing sides of two adjacent frames contact each other at the contact area, As a result of stacking the frames and as a result of at least one opening present in the frames, at least one longitudinal conduit is formed that extends along the length of the stack; As a result of stacking the frames and as a result of the elongated grooves present on or in at least one side of the frames in the contact area, a branch conduit is formed in the contact area, the branch conduit being fluidly connected to the longitudinal conduit; a pressurized melt of plastic material is fed into the elongated conduit and the branch conduit while the stack is held together by external means to obtain an interconnected stack of thermoplastic frames; It is a process.

[0008] The applicants have found that a stack of frames that is firmly connected is obtained by this process. In the contact areas, fusion between the materials of the adjacent frames occurs. The plastic melt thereby mixes with the fusion surfaces of the frames, resulting in a strong bond. This bond is stronger than the previously mentioned snap-fit ​​connections. A further advantage is that these bonds are watertight, which is not always the case when using snap-fit ​​connections. A large number of frames can be connected simultaneously by performing one operation, i.e. by feeding a pressurized melt of plastic material. This is in contrast to the ultrasonic welding methods of the prior art, where each individual frame must be connected to the growing stack.

[0009] An additional advantage is that the frames are connected watertight. This is particularly advantageous when the stack is used as part of an evaporator plate type heat exchanger. This process makes it possible to create a stack with water chambers where water can be added to the spaces where evaporation occurs, without water leaking into the spaces between the frames where evaporation would not occur. Such a design makes it possible to supply pressurized water to such compartments without the risk of the aforementioned leaks occurring.

[0010] The invention also relates to an interconnected stack of two-sided thermoplastic frames, the opposing sides of two adjacent frames being connected by fusion bonding in the contact area.

[0011] The thermoplastic frame may be a polypropylene frame, a polyethylene frame or a polyamide frame. Preferably, the frame is obtained by injection molding. If the stack is used as a plate-type heat exchanger in which water evaporates in one of the gas channels, the frame is advantageously a polypropylene frame.

[0012] The injection molded frame may be provided with a surface where heat exchange takes place, which is part of the injection molded article and is made of the same thermoplastic material. Preferably, the surface is a heat exchange sheet, which can be combined with the frame after injection molding, as described in the aforementioned EP 2068107. Preferably, the frame is an insert article, also called an overmold, which includes an insert consisting of a heat exchange sheet. The heat exchange sheet may be a paper sheet, a plastic sheet or preferably a metal sheet. The metal sheet is preferably an aluminum sheet. Examples of such insert or overmold molding are described in the aforementioned US 2018 / 0266774 and WO 2018 / 132014.

[0013] The frame may have a square, rectangular, diamond or hexagonal shape. Preferably, the stack has a six-sided hexagonal shape, and more preferably, the stack has a four-sided square or rectangular shape.

[0014] The frame is provided with one opening present in the frame that forms a longitudinal conduit. The longitudinal conduit extends along the length of the stack. To minimize the required length of the branch conduits, it is preferred to form multiple longitudinal conduits when stacking. Thus, the frame is preferably provided with multiple openings that form longitudinal conduits.

[0015] Preferably, the at least two longitudinal conduits are formed as a result of stacking the frames, and the at least two longitudinal conduits are not fluidly connected to each other, and the two elongated conduits are each fluidly connected to a separate branch conduit.

[0016] For example, for a frame having a square or rectangular shape, it may be preferable to have an opening in the frame at each of the four corners of the frame. Thus, such a square or rectangular frame preferably has at least four openings.

[0017] At both ends of the stack there is an inlet as an end of each longitudinal conduit. To avoid pressurized melt entering the stack at one end and leaving the stack at the opposite end, it is preferred that one opening of the longitudinal conduit is closed. This closure of this one opening may be achieved by an external means to hold the stack together. For example, the stack may be held between two plates, which exert a reaction force on the stack as the pressurized melt is fed, thereby avoiding the frames separating from each other. By providing one plate with an opening aligned with the inlet of the longitudinal conduit and an opposite plate without such an opening, a system is achieved in which the longitudinal conduit and its branch conduits form a dead-end system that only feeds the pressurized melt and cannot escape.

[0018] The shape and dimensions of the longitudinal conduits and branches are such that a melt of plastic material can fill the entire system. Such shape and design may be obtained using well-known design rules for designing injection moulds for such melts of plastic material.

[0019] Thus, the external means for holding the stack together may be the two aforementioned plates between which the stack is placed. Preferably, the external means is an open container in which the stack with the two aforementioned walls can be placed. In addition, the sides and bottom of the stack may be supported by the container. More preferably, a closed container is used that allows support of all sides of the stack. This is advantageous because the pressurized melt supply may result in the sides of the stack expanding, and such a support avoids the melt of plastic material leaking out of the stack. By having an external wall present to counter this expansion, the shape of the stack can be maintained.

[0020] More preferably, the container has an open and a closed position and has an internal shape that is a negative of the interconnected stack when in the closed position, the container allows for positioning of the stack of thermoplastic frames and removal of the interconnected stack of thermoplastic frames when in the open position, the container is provided with an inlet for a pressurized melt of plastic, the inlet being fluidly connected to the longitudinal conduit when the container is in the closed position. Such a container may be a plastic, preferably metal, container. The container may be made by well-known additive or subtractive manufacturing processes.

[0021] The shape of the stack may also include any additional chamber or chambers added to the sides of the stack. Suitably, the upper and lower sides may be provided with chambers for feeding or collecting water from a part of the space between the heat exchanger frames of the stack. These chambers may be formed by adding a single plastic part to the upper and lower sides of the stack. This part opens to the upper side and the other part opens to the lower side. The added chamber may be a gas header for the gas exchanging heat and / or a chamber for feeding or collecting water from a part of the space between the frames. This part may be an injection molded part. Preferably, the part is made from the same thermoplastic material as the frame. Preferably, the added part is connected to the stack by feeding a melt of plastic material into the container, preferably such that the bundled parts are connected to the stack. When manufacturing a stack with added external parts, the container with open and closed positions preferably has an internal shape that is the negative of the interconnected stack and the one or two added parts. The flow path of the melt is then such that it connects the side of the added part to the side of the stack. The plastic melt is preferably fed simultaneously to this contact area and to the longitudinal conduit(s). The frame may, for example, comprise two recesses which form two parallel longitudinal grooves on one side of the stack as a result of stacking the frames. These grooves are designed to allow the side of the part to enter the groove and to allow the flow of the melt of plastic material. In this way, the parts can be placed in a fixed position on one or both of the upper and lower sides of the stack and connected to the stack in the process according to the invention.

[0022] The container may be made from metal and may be manufactured by subtractive processing. Alternatively, the container may be manufactured by additive manufacturing techniques from a variety of materials including metal and plastic. The container, also called a mold, can be designed for a specific fixed number of frames in a stack. The mold thus allows for the manufacture of multiple stacks of uniform size in a simple and rapid process. Preferably, stacks with a number of frames between 15 and 50 are produced by this process.

[0023] The frames are further provided with elongated grooves present on or in at least one side of the frames at the contact area, which form branched conduits at the contact area when the frames are stacked. Preferably, the contact area of ​​the adjacent frames facing the groove is flat. In this way, conduits are formed when the open end of the groove is placed against this surface. The frames are designed such that these resulting branched conduits are fluidly connected to the elongated conduits. An interconnected stack of thermoplastic frames is obtained by supplying a pressurized melt of plastic material to the elongated conduits and the branched conduits while the stack is held together by external means.

[0024] The melt of the plastic material is preferably a material that is compatible with the thermoplastic material of the frame. In this way, the material of the two opposing contact surfaces of the adjacent frames will fuse with the melt of the plastic material, resulting in a strong connection between the frames. Furthermore, the melt of the plastic material should have flow properties that allow the melt to enter the longitudinal conduit and its branch conduits. Thus, a frame with large dimensions and longitudinal conduits and branch conduits of larger dimensions may use a more viscous melt of plastic compared to when a frame of smaller dimensions is used for the stack. The melt of the plastic material is preferably a melt of a thermoplastic elastomer. An example of a suitable combination for a polypropylene frame is a melt of a styrene ethylene butylene styrene block copolymer.

[0025] The present invention therefore also relates to an interconnected stack of thermoplastic frames having two sides, the opposing sides of two adjacent frames being connected by fusion in the contact area, the frames being polypropylene frames and the insert being an aluminum sheet, the fusion being obtainable by pressing the opposing sides of the adjacent frames in the presence of a pressurized melt of a thermoplastic elastomer, preferably a styrene ethylene butylene styrene block copolymer.

[0026] The stack of interconnected frames as described above obtained by the method as described above is preferably used as part of a plate heat exchanger, which may be used in the process described in WO 2018 / 132014.

[0027] The invention is illustrated by the following figures. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 shows a frame with an aluminum sheet as an insert molding. [Diagram 2] FIG. [Figure 3a] FIG. 2 illustrates a method according to the present invention. [Figure 3b] FIG. 2 illustrates a method according to the present invention. [Figure 3c] FIG. 2 illustrates a method according to the present invention. [Figure 3d] FIG. 2 illustrates a method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] FIG. 1 shows a frame 1 provided with an aluminum sheet 2 as an insert moulding. The design of the frame shows an inlet 3 for a first gas stream and an outlet 4 for a second gas stream. The frame 1 is further provided with four openings (5, 6, 7, 8) which form longitudinal conduits when the frames are stacked. The frame is further provided with a system of grooves (9) formed by ridges (10) which extend upwards, relative to the observer of this figure, from the plane of the sheet 2. For a frame with a height and width of 35×38 cm, the ridges (10) may extend 3 mm. The opposite side of the frame, which is not visible in FIG. 1, is flat. When the frame 1 is covered by the flat underside of the frame (1a), as shown in FIG. 2, the grooves form branching conduits. The dimensions of these grooves are between 5 and 20 mm. 2 The stack may have a cross-sectional area of ​​0.1 mm to 0.2 mm. There is a fluid connection between the system (9) of ridges (10) and the openings (5,6,7,8) as shown. This results in the longitudinal conduits being fluidly connected to the branch conduits when the stack is formed. The stack is preferably used in a horizontal position. The sides of the stack and the sides (1,1a) of the frame are therefore referred to as upper (11), lower (12) and side (13,14).

[0030] Figures 1 and 2 also show openings (18) that are not filled with the melt of plastic material. In the interconnected stack, there is a space for water, extending along the upper side (11). By providing an inlet (not shown) in this space for water and by providing openings (not shown) in certain spaces between the frames 1 and (1a), an evaporative plate type heat exchanger may be obtained. Water from this space is fed to these spaces where it can evaporate. On the lower side, there may be openings (19) that are not filled with the melt of plastic material. This space may be used to collect the water that has not evaporated from the above spaces. There are then openings (not shown) that allow water to enter these lower spaces, extending along the lower side (12). A drain (not shown) for the collected water is present to drain this water.

[0031] Figure 2 shows frame (1a), which is the same as frame 1, except that it shows an inlet (15) for the second gas stream and an outlet (16) for the second gas stream. When frames 1 and (1a) are stacked one on top of the other, the row of inlets (3) is on one side of the lower half and the row of outlets (15) is on the same side (13) of the upper half of this side (13). This allows a header to be attached to the bottom side of the stack to supply the first gas, and a header to collect the second gas stream to be attached to the top side of the stack, utilizing the ridges (17).

[0032] Figures 3a-3d show the process according to the invention. Figure 3a shows a mould (20) and a cover (21) surrounding the mould (20) as a container in the closed position. In the mould (20) a stack (22) of eight frames (1, 1a) is placed. The internal shape of the mould (20) is just such that the stack (22) can be positioned in the mould. The thickness of the frames is not to scale. For the sake of clarity, a thicker frame is depicted to better illustrate the invention. The stack (22) comprises four longitudinal conduits (23), of which two are shown. These conduits are formed by openings (5, 6, 7, 8) in the frames (1, 1a). The cover (21) is provided with four inlets (25) for the pressurised melt of plastic. These inlets (25) are fluidly connected to the longitudinal conduits (23) as shown. The longitudinal conduit (23) is connected to a branch conduit (24) as shown diagrammatically.

[0033] In FIG. 3b, the plastic melt is fed through the inlets (25) into the longitudinal conduits (23) of the stack (22) of FIG. 3a. At the interface between two adjacent frames (1, 1a), the melt flows from the individual longitudinal conduits (23) through the branch conduits (24), as indicated by the smaller arrows (26). The feeding of the plastic melt stops when all of the branch conduits are filled with the melt (27), as shown in FIG. 3c. After the melt has solidified, the connected stack (22) is removed from the mould (20) by lifting the cover (21). The connected stack (22) is connected to the cover (21) by the solidified plastic in the inlets (25) and forms one mass with the solidified plastic in the longitudinal conduits (23). By simply cutting this connection, the connected stack (22) is obtained, and the cover (21) can be reused in the mould (20) after cleaning to produce the next stack having the same shape.

Claims

1. A process for manufacturing an interconnected stack of thermoplastic frames having two sides, the process being carried out by stacking the thermoplastic frames to obtain a stack of frames such that the opposing sides of two adjacent frames are in contact with each other in a contact area, comprising: As a result of stacking the frames and as a result of at least one opening present in the frames, at least one longitudinal conduit is formed that extends along the length of the stack; As a result of stacking the frames and as a result of the elongated grooves present on or in at least one side of the frames in the contact area, a branch conduit is formed in the contact area, the branch conduit being fluidly connected to the longitudinal conduit; a pressurized melt of plastic material is fed into the elongated conduit and the branched conduit while the stack is held together by external means to obtain an interconnected stack of thermoplastic frames; process.

2. 2. The process of claim 1, wherein the melt of plastic material is a melt of a thermoplastic elastomer.

3. The process according to any of claims 1 to 2, wherein the thermoplastic frame is a polypropylene frame, a polyethylene frame or a polyamide frame.

4. A process according to any of claims 1 to 3, wherein the frame is obtained by injection moulding.

5. The process of claim 4 , wherein the frame is an insert molded part with an insert made of a heat transfer sheet.

6. 6. The process of claim 5, wherein the frame is a polypropylene frame, the insert is an aluminum sheet, and the pressurized melt of plastic is a pressurized melt of styrene ethylene butylene styrene block copolymer.

7. 7. The process according to any one of claims 1 to 6, wherein as a result of stacking the frames at least two longitudinal conduits are formed, the at least two longitudinal conduits being fluidly not connected to each other and the two elongated conduits being each fluidly connected to a separate branch conduit.

8. 8. The process according to any one of claims 1 to 7, wherein the external means is a container having an open and a closed position, the container having an internal shape which is the negative shape of the interconnected stack when in the closed position and the container allowing the positioning of the stack of thermoplastic frames and the removal of the interconnected stack of thermoplastic frames when in the open position, the container being provided with at least one inlet for a pressurized melt of plastic, the at least one inlet being fluidly connected to the at least one longitudinal conduit when the container is in the closed position.

9. 9. The process of claim 8, wherein an additional chamber is added to the stack to obtain a stack having an additional chamber, the container having an internal shape which is the negative of the interconnected stack having the added chamber, the added part being connected to the stack by a melt of plastic material fed into the container.

10. The process according to any of the preceding claims, wherein the stack of interconnected frames is adapted to be part of a plate type heat exchanger.

11. An interconnected stack of thermoplastic frames having two sides, the opposing sides of two adjacent frames being connected by fusion bonding at the contact areas.

12. The interconnect stack of claim 11 , wherein the thermoplastic frame is a polypropylene frame, a polyethylene frame, or a polyamide frame.

13. An interconnect stack according to any of claims 11 to 12, wherein the frame is obtained by injection molding.

14. 14. The interconnect stack of claim 13, wherein the frame is an insert molded part with an insert comprising a heat exchange sheet.

15. 15. The interconnect stack of claim 14, wherein the frame is a polypropylene frame and the insert is an aluminum sheet, and the fusion can be achieved by pressing opposing sides of adjacent frames in the presence of a pressurized melt of a thermoplastic elastomer.

16. The interconnect stack of any of claims 11 to 15, wherein the additional chamber is connected to a side of the stack.

17. 17. The interconnect stack of claim 16, wherein the additional chamber is an injection molded part made from the same thermoplastic material as the frame and connected to the side of the stack by fusion bonding.

18. An interconnect stack according to any one of claims 14 to 17 as part of a plate type heat exchanger.

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