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 thermoplastic frames having two sides. The stack may be used as part of a plate-type heat exchanger.

Background Art

[0002] Such a process is described in European Patent No. 2068107. This patent publication describes a method of producing a first resin frame by injection molding. A heat exchange sheet is combined with the frame, and the resulting frames are stacked. The frames are connected to each other by ultrasonic melting of the corners of the frames. When the molten resin solidifies, a bond between the frames occurs.

[0003] U.S. Patent Application Publication No. 2018 / 0266774 and International Publication No. 2018 / 132014 describe a heat exchange frame obtained as an insert molded product. The heat exchange frames 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 when snap-fit connections are used. Ultrasonic melting is disadvantageous because it is a cumbersome process when connecting multiple frames into one stack.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

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

[0007] This objective is achieved by the following method: a process for manufacturing an interconnected stack of thermoplastic frames having two sides, In the process of stacking thermoplastic frames to obtain a frame stack, such that the opposing sides of two adjacent frames are in contact with each other in the contact area, As a result of stacking the frames and as a result of at least one opening present within 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 elongated grooves present on or within at least one side of the frames in the contact area, branch conduits are formed in the contact area, and the branch conduits are fluidly connected to the longitudinal conduits. To obtain an interconnected stack of thermoplastic frames, a pressurized molten plastic material is supplied to elongated conduits and branched conduits while the stacks are held together by external means. It is a process.

[0008] The applicants have found that a tightly connected stack of frames can be obtained by this process. Fusion occurs between the materials of adjacent frames in the contact area. Thereafter, the molten plastic mixes with the fusion surface of the frames, resulting in a strong bond. This bond is stronger than the aforementioned 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 a single operation, namely supplying a pressurized molten plastic material. This is in contrast to the conventional ultrasonic welding method, which requires connecting each individual frame to the growing stack.

[0009] A further advantage is that the frames are connected in a watertight manner. This is particularly beneficial when the stack is used as part of an evaporator plate heat exchanger. This process allows for the creation of a stack with a water chamber into which water can be added to the space where evaporation occurs, without water leaking into the space between frames where evaporation is not expected to occur. Such a design makes it possible to supply pressurized water to such compartments without the risk of the aforementioned leakage occurring.

[0010] The present invention also relates to an interconnected stack of thermoplastic frames having two sides, wherein the opposing sides of two adjacent frames are connected by fusion in a 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. When the stack is used as a plate-type heat exchanger in which water evaporates in one of the gas flow paths, it is advantageous for the frame to be a polypropylene frame.

[0012] The injection-molded frame may have a heat exchange surface, which is part of the injection-molded product and made of the same thermoplastic material. Preferably, the surface is a heat exchange sheet and can be combined with the frame after injection molding, as described in the aforementioned European Patent No. 2068107. Preferably, the frame is an insert product, also called an overmolded product, which includes an insert made 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 molding or overmolding are described in the aforementioned U.S. Patent Application Publication No. 2018 / 0266774 and International Publication No. 2018 / 132014.

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

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

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

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

[0017] At both ends of the stack, there are inlets, which serve as the ends of each longitudinal conduit. To prevent pressurized molten material from entering the stack at one end and exiting it at the opposite end, it is preferable that one opening of the longitudinal conduit be closed. This closure of the one opening may be achieved by external means for holding the stack together. For example, the stack may be held between two plates that exert a reaction force on the stack when pressurized molten material is supplied, thereby preventing the frames from separating from each other. By providing one plate having an opening aligned with the inlet of the longitudinal conduit and the 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 supplies pressurized molten material and cannot escape.

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

[0019] Therefore, the external means for holding the stack together may be the two plates described above, between which the stack is placed. Preferably, the external means is an open container in which the stack having the two walls described above 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 supply of pressurized molten material may cause the sides of the stack to expand, and such support is advantageous in preventing the molten plastic material from leaking out of the stack. The shape of the stack can be maintained by having an outer wall that is present to counteract this expansion.

[0020] More preferably, the container has an open position and a closed position, and has an internal shape that is a negative shape 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 pressurized molten plastic, the inlet is fluidly connected to a longitudinal conduit when the container is in the closed position. Such a container may be made of plastic, preferably metal. The container can be manufactured by a well-known additive manufacturing or removal method.

[0021] The shape of the stack may also include any additional one or more chambers added to the side of the stack. Appropriately, upper and lower chambers for supplying or collecting water from a part of the space between the heat exchanger frames of the stack may be provided. These chambers may be formed by adding a single plastic part to the upper and lower sides of the stack. This part is open to the upper side and the other part is open to the lower side. The added chamber may be a gas header for the gas exchanging heat and / or a chamber for supplying 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 of the same thermoplastic material as the frame. Preferably, the added part is connected to the stack by supplying the melt of the plastic material into a container, preferably such that the bundled parts are connected to the stack. When manufacturing a stack with added external parts, the container having an open position and a closed position preferably has an internal shape that is a negative mold of the interconnected stack and one or two added parts. In that case, the flow path of the melt is such that the side of the added part is connected to the side of the stack. The melt of the plastic is preferably supplied simultaneously to this contact area and the longitudinal conduit(s). The frame may, for example, have two depressions that result in forming 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 grooves and to allow the flow of the melt of the plastic material. In this way, the part can be arranged at a fixed position on one or both of the upper and lower sides of the stack and can be connected to the stack in the process according to the invention.

[0022] This container may be made of metal or manufactured by a machining process. Alternatively, the container may be manufactured by an additive manufacturing technique from a variety of materials including metal and plastic. This container, also called a mold, can be designed for a specific fixed number of frames within a stack. Thus, this mold enables the production of multiple stacks of uniform size in a simple and rapid process. Preferably, stacks having a number of frames between 15 and 50 are produced by this process.

[0023] The frame is further provided with an elongated groove present on or within at least one side of the frame in the contact area. This elongated groove forms a branched conduit in the contact area when the frames are stacked. Preferably, the contact area of the adjacent frame facing the groove is flat. In this way, when the open end of the groove is disposed relative to this surface, a conduit is formed. The frame is designed such that the resulting branched conduits are fluidly connected to an elongated conduit. While the stacks are held together by external means, an interconnected stack of thermoplastic frames is obtained by supplying a pressurized melt of a plastic material to the elongated conduit and the branched conduits.

[0024] The melt of the plastic material is preferably a material compatible with the thermoplastic material of the frame. In this way, the materials of the two opposing contact surfaces of adjacent frames fuse with the melt of the plastic material, resulting in a strong connection between the frames. Further, the melt of the plastic material should have flow characteristics that allow the melt to enter the longitudinal conduit and its branched conduits. Thus, frames having larger dimensions and larger longitudinal and branched conduits may use a more viscous melt of plastic compared to when smaller dimension frames are 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] Accordingly, the present invention also relates to an interconnected stack of thermoplastic frames having two sides, wherein the opposing sides of two adjacent frames are connected by fusion in a contact area, the frames being polypropylene frames and the inserts being aluminum sheets, and the fusion can be achieved by pressurizing the opposing sides of adjacent frames in the presence of a pressurized molten thermoplastic elastomer, preferably styrene-ethylene-butylene-styrene block copolymer.

[0026] The stack of interconnected frames obtained by the method described above is suitably used as part of a plate heat exchanger. The plate heat exchanger may be used in the process described in International Publication No. 2018 / 132014.

[0027] The present invention is illustrated by the following figures. [Brief explanation of the drawing]

[0028] [Figure 1] This figure shows a frame with an aluminum sheet as an insert molded part. [Figure 2] This is a diagram showing the frame. [Figure 3a] This figure shows the method according to the present invention. [Figure 3b] This figure shows the method according to the present invention. [Figure 3c] This figure shows the method according to the present invention. [Figure 3d] This figure shows the method according to the present invention. [Modes for carrying out the invention]

[0029] Figure 1 shows a frame 1 with an aluminum sheet 2 as an insert molded part. The frame design includes an inlet 3 for a first gas flow and an outlet 4 for a first gas flow. Frame 1 is further provided with four openings (5, 6, 7, 8) that form longitudinal conduits when the frames are stacked. The frame is further provided with a system of grooves (9) formed by a raised portion (10) extending upward from the plane of the sheet 2 to the observer in this figure. For a frame with a height and width of 35 × 38 cm, the raised portion (10) may extend by 3 mm. The opposite side of the frame, not visible in Figure 1, is flat. As shown in Figure 2, when frame 1 is covered by the flat underside of frame (1a), the grooves form branched conduits. The dimensions of these grooves are 5–20 mm. 2 It may have the following cross-sectional area. A fluid connection exists between the system (9) of the raised portion (10) and the openings (5,6,7,8) as shown in the figure. As a result, when the stack is formed, the longitudinal conduit is fluidly connected to the branch conduit. The stack is preferably used in a horizontal position. Thus, the sides of the stack and the sides (1,1a) of the frame are referred to as the upper side (11), lower side (12), and lateral side (13,14).

[0030] Figures 1 and 2 also show openings (18) that are not filled with molten plastic material. Within the interconnected stack, there is a space for water, extending along the upper side (11). An evaporative plate heat exchanger may be obtained by providing an inlet (not shown) in this space for water and by providing openings (not shown) in certain spaces between frame 1 and frame (1a). Water from this space is supplied to these spaces from which the water can evaporate. On the lower side, there may be openings (19) that are not filled with molten plastic material. This space may be used to collect water that has not evaporated from the above spaces. Then, there are openings (not shown) that allow water to enter these lower spaces extending along the lower side (12). A discharge section (not shown) for the collected water is provided for discharging this water.

[0031] Figure 2 shows frame (1a). This frame is the same as frame 1, except that it shows an inlet (15) for a second gas flow and an outlet (16) for a second gas flow. When frames 1 and frame (1a) are stacked alternately, the row of inlets (3) is located on one side of the lower half, and the row of outlets (15) is located on the same side (13) of the upper half of this side (13). This allows a header for supplying the first gas to be attached to the lower side of the stack, and a header for collecting the second gas flow to be attached to the upper side of the stack using a raised section (17).

[0032] Figures 3a-3d illustrate the process according to the present invention. Figure 3a shows a mold (20) and a cover (21) surrounding the mold (20) as a container in a closed position. Inside the mold (20) is a stack (22) of eight frames (1,1a). The internal shape of the mold (20) is such that it is possible to position the stack (22) within the mold. The frame thickness is not to scale. For clarity and to better illustrate the present invention, thicker frames are depicted. The stack (22) has four longitudinal conduits (23), two of which 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 pressurized molten plastic. These inlets (25) are fluidly connected to the longitudinal conduits (23) as shown. The longitudinal conduit (23) is connected to the branch conduit (24) as schematically shown.

[0033] In Figure 3b, molten plastic is supplied through the inlet (25) to the longitudinal conduit (23) of the stack (22) in Figure 3a. At the contact surface between two adjacent frames (1,1a), the molten plastic flows from the individual longitudinal conduits (23) through the branch conduits (24), as indicated by the smaller arrows (26). The supply of molten plastic stops when all the branch conduits are filled with molten plastic (27), as shown in Figure 3c. After the molten plastic has solidified, the connected stack (22) is removed from the mold (20) by lifting the cover (21). The connected stack (22) is connected to the cover (21) by the solidified plastic in the inlet (25) and forms a single mass with the solidified plastic in the longitudinal conduits (23). By simply cutting this connection, the connected stack (22) is obtained, and after cleaning, the mold (20) can be reused to produce the next stack of the same shape.

Claims

1. A process for manufacturing an interconnected stack of thermoplastic frames having two sides, wherein thermoplastic frames are stacked to obtain a frame stack, and the opposing sides of two adjacent frames are in contact with each other in the contact area, As a result of stacking the frames and as a result of at least one opening present within 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 elongated grooves present on or within at least one side of the frames in the contact area, branch conduits are formed in the contact area, and the branch conduits are fluidly connected to the longitudinal conduits. To obtain an interconnected stack of thermoplastic frames, a pressurized molten plastic material is supplied to elongated conduits and branched conduits while the stacks are held together by external means. process.

2. The process according to claim 1, wherein the molten plastic material is a molten thermoplastic elastomer.

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

4. The process according to any one of claims 1 to 3, wherein the frame is obtained by injection molding.

5. The process according to claim 4, wherein the frame is an insert molded product comprising an insert made of a heat transfer sheet.

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

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

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

9. The process according to claim 8, wherein an additional chamber is added to a stack in order to obtain a stack having an additional chamber, the container having an internal shape that is a negative of an interconnected stack having the added chamber, and the added part is connected to the stack by molten plastic material supplied to the container.

10. The process according to any one of claims 1 to 9, wherein the stack of interconnected frames is adapted to become part of a plate heat exchanger.

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