PROCESS FOR PRODUCING A PLATE HEAT EXCHANGER AND PLATE HEAT EXCHANGER

Abstract

A plate heat exchanger has two metal plates brought into abutment, with a solder material between the plates. The plates are heated up to a first temperature. The plates are placed into a mold, the mold surfaces of which have cavities for envisaged channel structures. Channel structures are formed by local internal pressure forming of at least one plate under pressurization by the tool. The plates are heated up to a second temperature. The plates are solder bonded at the abutted surfaces. A plate heat exchanger has two metal plates, wherein channel structures have been formed in at least one plate and the plates are bonded to one another by soldering away from the channel structures. Eutectic microstructures having a longest extent of less than 50 micrometers are formed in the solder layer.

Claims

1. Process for producing a plate heat exchanger having the following steps: providing two plates of a metallic material, wherein the plates are brought into abutment with a solder material disposed between the plates, heating the plates to a first temperature, inserting the plates into a mold having mold surfaces that have cavities for envisaged channel structures, forming channel structures by local internal pressure forming of at least one plate under pressurization by the mold, heating the plates to a second temperature, solder bonding of the plates in the abutted areas.

2. Process according to claim 1, wherein the mold is heatable and the heating to the first temperature is effected in the mold.

3. Process according to claim 1, wherein the solder bonding of the plates is likewise effected in the mold under pressurization by the mold.

4. Process according to claim 2, wherein the mold is preheated, especially to a temperature of 550 C. to 700 C., preferably to a temperature of 600 C. to 650 C., more preferably to a temperature of 615 C. to 625 C.

5. Process according to claim 1, wherein the first temperature is 200 C. to 550 C., preferably 300 C. to 350 C.

6. Process according to claim 1, wherein the second temperature is 550 C. to 650 C., preferably 600 C. to 615 C.

7. Process according to claim 1, wherein, adjacent to the cavities of the mold surfaces and/or at the circumference of the mold, sealing beads are provided in order to seal the resultant channel structures in the internal pressure forming.

8. Process according to claim 1, wherein one plate is provided as the base plate, the other plate as the forming plate, and the channel structures are generated in the forming plate.

9. Process according to claim 1, wherein the plates consist of an aluminum alloy, preferably of a high-strength aluminum alloy.

10. Process according to claim 1, wherein one of the two plates has been provided with a plated solder layer.

11. Process according to claim 1, wherein a connection opening is generated in at least one of the plates.

12. Process according to claim 11, wherein a connecting element is disposed on or in this connection opening.

13. Process according to claim 11, wherein the medium for the internal pressure forming is introduced through the connection opening.

14. Process according to claim 1, wherein a mold is used, the mold surfaces of which have been provided with a coating in order to prevent adhesion of the plates.

15. Process according to claim 1, wherein a separating agent is disposed between the plates and the mold surfaces of the mold in order to prevent adhesion of the plates.

16. Process according to claim 1, wherein, in the internal pressure forming, a first pressure is applied by the mold and, in the solder bonding of the plates, a second pressure is applied by the mold, the first pressure being higher than the second pressure.

17. Process according to claim 1, wherein the cooling period between the solder bonding and the solder solidification is shorter than 60 seconds, preferably shorter than 20 seconds, more preferably shorter than 10 seconds.

18. Process according to claim 1, wherein, after the solder bonding of the plates, these are cooled down to a temperature of less than 200 C., preferably less than 60 C., within a period of less than 60 seconds, preferably less than 20 seconds, more preferably less than 10 seconds, and wherein the cooling is followed within less than 72 hours by a heat treatment at a temperature of 140 C. to 250 C. over a period of 20 minutes to 24 hours, preferably of 20 minutes to 8 hours, more preferably of 20 minutes to 2 hours.

19. Plate heat exchanger comprising two plates of a metallic material, wherein channel structures are formed in at least one plate and the plates are joined to one another by soldering away from the channel structures, characterized in that eutectic microstructures having a longest dimension of less than 50 micrometers are formed in the solder layer.

20. Plate heat exchanger according to claim 19, wherein the eutectic microstructures are formed in solder accumulations in the transition region from the abutted plates to the channel structures.

Description

[0054] The figures show:

[0055] FIG. 1 a working example of a process of the invention

[0056] FIG. 2 a time-temperature diagram of a process of the invention

[0057] FIG. 3 a representation of the microstructure in the solder layer of a plate heat exchanger of the invention

[0058] FIGS. 1 and 2 show a process of the invention for production of a plate heat exchanger and the associated temperature progression in schematic form. First of all, a base plate 1 and a forming plate 2 are provided. The plates here are of a 3000 series aluminum alloy, for example an alloy designated 3003, 3005, 3903 or 3905. The thickness of the base plate 1 here is 1.3 millimeters to 2 millimeters. The thickness of the forming plate 2 is 0.5 millimeter to 1.5 millimeters. The forming plate 2 has been plated with a solder material. A connection opening 3 is generated in the base plate 1. A connecting element 4 together with a solder ring 5 is disposed at the connection opening 3.

[0059] The base plate 1 and the forming plate 2 are brought into abutment and introduced into a preheated mold 6. The mold 6 has been preheated to a temperature of about 630 C. The mold 6 comprises an upper mold 7 and a lower mold 8. Cavities 10 have been introduced into the mold surface 9 of the upper mold 7, corresponding to the channel structures provided in the plate heat exchanger to be produced. The lower mold 8 has receiving openings 11 for the connecting element 4. Feed channels 12 for a medium 14 for internal pressure forming are connected to the receiving openings 11.

[0060] Then the mold 6 is closed. This corresponds to time t0 in the diagram in FIG. 2. The heat provided in the mold 6 is transferred to the plates 1, 2, which are thus heated.

[0061] At a time t1, an envisaged first temperature T.sub.1 at which the internal pressure forming is started is attained. The specific time depends on the temperature of the mold 6 and the material and thickness of the plates 1, 2. In the case of plates 1, 2 of aluminum, owing to its good thermal conduction properties, the time span between t0 and t1 is only a few seconds. The first temperature T.sub.1 in this working example is 300 C. to 350 C.

[0062] For the internal pressure forming, a medium 14, preferably an inert gas such as nitrogen, is guided under pressure between the plates 1, 2 through the feed channel 12, the connecting element 4 and the connection opening 3. This deforms the forming plate 2 until it becomes abutted with the mold surface 9 of the upper mold 7. The mold 6 also subjects the plates 1, 2 to a first pressure p.sub.1 in order to counteract the internal pressure of the medium 14 and in order to seal the resultant channel structures. Adjacent to the cavities 10 of the mold surfaces 9, sealing beads 13 are provided, which ensure that the forming operation takes place exclusively in the region of the cavities 10. Thus, high dimensional accuracy and forming precision are assured.

[0063] When the forming operation is complete (time t2), the plates 1, 2 are heated further. At about 560 C., in this illustrative process procedure, the solder material begins to melt. At a time t3, the second temperature T.sub.2 is attained. The time span required for heating depends again on the materials used. The second temperature T.sub.2 here is from 600 C. to 615 C., preferably about 610 C. The solder bonding of the plates 1, 2 commences with application of heat and a second pressure p.sub.2 through the mold 6. This cohesively bonds the fully abutted regions of the plates 1, 2. At the same time, the connecting element 4 is cohesively bonded to the base plate 1 by the solder ring 5.

[0064] The second pressure p.sub.2 is lower than the first pressure p.sub.1, in order to counteract any possible adhesion of the aluminum plates 1, 2 to the mold 6. For this purpose, the upper mold 7 and/or lower mold 8 have/has a spring mount.

[0065] At a time t4, the solder bonding is complete. Thereafter, the mutually bonded plates 1, 2 are cooled back down to room temperature (time t6). For this purpose, the plate heat exchanger 15 is removed from the mold 6 and either transferred to a cooling mold or placed in a cooling frame.

[0066] More particularly, the medium for the internal pressure forming may be used for cooling or for assistance of the cooling process. In the case of use of nitrogen as inert medium, there is the additional advantage that the formation of an oxide layer is prevented. Moreover, the cooling is effected somewhat more evenly and reduces deformation of the plates that can be caused by internal stresses.

[0067] There may optionally be further heat treatment steps during this period or thereafter.

[0068] At time t5, the solder material has solidified. The time span between t4 and t5 is preferably very short and is only a few minutes or even seconds. The effect of the short cooling time before solder solidification is that eutectic microstructures having a longest dimension of less than 50 micrometers are formed in the solder layer.

[0069] FIG. 3 compares two sections. The left-hand image shows an accumulation of solder in the transition region between the channel structures and the abutted plates 1, 2 that would have been in the plane of the drawing on the right of the figure. This solder bond was generated in a conventional oven soldering process with long cooling times. Eutectic microstructures have formed, which are elongate or acicular and have a longitudinal extent of 200 micrometers or more.

[0070] By contrast, the right-hand image shows a solder layer that has been produced by a process of the invention. The corresponding eutectic microstructures are formed in the dark regions. These have much finer grains than in the left-hand image with extents of less than 50 micrometers. The effect of the fine-grain microstructure is that the solder bond is much more stable and fatigue-resistant. This is important especially in the region of the transition between the channel structures and the soldered regions, since high stresses that can lead to cracks and splitting-apart of the two plates 1, 2 occur there in operation.