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 abuted 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. A method of producing a plate heat exchanger, the method comprising: placing two metal plates in 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 channel structures, forming the channel structures by local internal pressure forming of at least one of the plates under pressurization by the mold, heating the plates to a second temperature, and solder bonding of the plates by the solder material in abutted areas where the plates abut one another.

2. The method according to claim 1, further comprising: preheating the mold, wherein the heating to the first temperature is in the preheated mold.

3. The method according to claim 2, wherein the mold is preheated to a temperature of 550° C. to 700° C.

4. The method according to claim 1, wherein the solder bonding of the plates is in the mold under pressurization by the mold.

5. The method according to claim 4, 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.

6. The method according to claim 1, wherein a connection opening is formed in at least one of the plates.

7. The method according to claim 6, wherein a connecting element is disposed on or in the connection opening.

8. The method according to claim 6, wherein a medium for the internal pressure forming is introduced through the connection opening.

9. The method according to claim 1, wherein the first temperature is 200° C. to 550° C.

10. The method according to claim 1, wherein the second temperature is 550° C. to 650° C.

11. The method according to claim 1, wherein, adjacent to the cavities of the mold surfaces or at a circumference of the mold, sealing beads are provided and seal the channel structures obtained in the internal pressure forming.

12. The method according to claim 1, wherein the first plate is a base plate, the second plate is a forming plate, and the channel structures are formed in the forming plate.

13. The method according to claim 1, wherein the plates comprise an aluminum alloy.

14. The method according to claim 1, wherein the solder material is a plated layer on one of the two plates.

15. The method according to claim 1, wherein the mold surfaces have a coating to prevent adhesion of the plates.

16. The method according to claim 1, wherein a separating agent is disposed between the plates and the mold surfaces to prevent adhesion of the plates.

17. The method according to claim 1, further comprising: cooling the plates for a cooling period shorter than 60 seconds between the solder bonding and solder solidification of the solder material.

18. The method according to claim 1, further comprising: cooling the plates down to a temperature of less than 200° C. within a period of less than 60 seconds after the solder bonding of the plates, and within less than 72 hours after the cooling, performing a heat treatment of the plates at a temperature of 140° C. to 250° C. over a period of 20 minutes to 24 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is described in more detail below with reference to drawings. The figures show:

(2) FIG. 1 a working example of a process in accordance with at least one embodiment

(3) FIG. 2 a time-temperature diagram of a process in accordance with at least one embodiment

(4) FIG. 3 a representation of the microstructure in the solder layer of a plate heat exchanger in accordance with at least one embodiment

(5) The figures use the same reference numerals for identical or similar components, even when there is no repeated description on grounds of simplification.

DETAILED DESCRIPTION

(6) FIGS. 1 and 2 show a process of the disclosure 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.

(7) 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.

(8) 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.

(9) 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.

(10) For the internal pressure forming, a medium 14, 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 abuted 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.

(11) 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., or 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 abuted 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.

(12) 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.

(13) 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.

(14) 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, the formation of an oxide layer is prevented. The cooling is effected somewhat more evenly and reduces deformation of the plates that can be caused by internal stresses.

(15) There may optionally be further heat treatment steps during this period or thereafter.

(16) At time t5, the solder material has solidified. The time span between t4 and t5 is 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.

(17) FIG. 3 compares two sections. The top image shows an accumulation of solder in the transition region between the channel structures and the abuted 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.

(18) By contrast, the bottom image shows a solder layer that has been produced by a process of the disclosure. The corresponding eutectic microstructures are formed in the dark regions. These have much finer grains than in the top 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.

(19) The foregoing description of some embodiments of the disclosure has been presented for purposes of illustration and description. The description is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings. The specifically described embodiments explain the principles and practical applications to enable one ordinarily skilled in the art to utilize various embodiments and with various modifications as are suited to the particular use contemplated. Various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the disclosure.