DE102017106393B4 - Plate heat exchanger manufacturing process - Google Patents

Abstract

Plate heat exchanger manufacturing method, in which first plates (1) and second plates (2) are alternately stacked on top of each other and soldered together in such a way that a stack of plates with channels (3) running between adjacent plates (1, 2) is formed, the method having the following process steps having:
- Providing at least a first plate (1) and a second plate (2), wherein the first plate (1) and the second plate (2) have indentations and elevations, which when the first plate (1) and the second plate ( 2) form the channels (3);
- Coating the first plate (1) by means of a brazing material layer (5);
- Stacking the first panel (1) and the second panel (2); and
- High-temperature treatment of the soldering material layer (5), so that the soldering material layer (5) produces soldering connections (59) between the first plate (1) and the second plate (2) at contact areas (15), characterized in that the first plate (1) during the high-temperature treatment is arranged so that the brazing material layer (5) arranged on it faces downward.

Description

The invention relates to a plate heat exchanger manufacturing method. In the plate heat exchanger manufacturing method, first heat exchanger plates, subsequently shortened first plates, and second heat exchanger plates, subsequently shortened second plates, are stacked on top of one another and soldered together in such a way that a stack of plates is formed with channels running between adjacent plates.

A plate heat exchanger manufacturing process is, for example, from WO 2002/090032 A1 is known which describes a method for joining thin plates of an iron-based material provided with through-holes and a printing pattern of ridges and depressions over a heat exchange area of the plates and, if present, over a distribution area. The plates are coated with a brazing material such that 5-40% of the heat exchange area and the distribution area are coated with the brazing material, and arranged before joining in such a way that contact between adjacent peaks and valleys is achieved. A coating of 13-15% of the boards with solder material immediately before the soldering process is described as ideal. The plates are then soldered to one another at the contact points formed by means of a heating process. At the in WO 2002/090032 A1 The method described above applies the soldering material to contact points or contact lines on the boards, i.e. at the points at which the contacts between the boards are created by the soldering process.

Another manufacturing process for plate heat exchangers, which are composed of plates stacked on top of each other, is described in WO 2015/062992 A1 described. In contrast to the case described above, the contact points are left out when the soldering material is applied, so that the soldering material is applied around the contact points in the shape of a crescent, ring or double bracket, but without touching the contact points before the soldering process itself. In WO 2015/062992 A1 a coverage of the plates before the soldering process of 5% and less is specified.

In the methods described above, it seems to be of great importance to keep the surface area of the plate covering by means of the brazing material within a certain, sometimes narrow, percentage range before the brazing process. On the other hand, the quality of a soldered connection is largely determined by the amount of solder and the distance between the plates at the contact points, the soldering gap. Adjusting these parameters precisely for good contact formation is often difficult and often contradictory. For example, plating with a lot of solder at the contact points will result in the boards not being pushed close enough together to get a good connection.

Furthermore, from the JP 2000-121286 A a plate heat exchanger manufacturing method is known in which a first plate, a second plate and a further first plate are stacked one on top of the other. The first two plates delimit the flow channel, while the second plate is soldered between the two plates in the form of a vortex cell insert plate.

the JP 2006-297450A describes a plate heat exchanger manufacturing process in which a plate is brazed using a sintering process and then reshaped. Before the soldering process, stacks of such plates each have the same spacing as the sintered layers between the plates. During the soldering process, usually under weight, they have to be brought to the solder gap thickness assigned to the respective solder, which is usually very small. Only a capillary effect acts as a gap-filling force.

U.S. 6,568,465 B1 describes a plate heat exchanger manufacturing process in which at least one plate is coated with a special brazing material and brazed to another plate.

It is thus an object of the invention to provide a plate heat exchanger manufacturing method for reliably and repeatably manufacturing plate heat exchangers with strong and durable brazed joints.

According to the invention, this object is achieved by a plate heat exchanger manufacturing method having the features of claim 1. Advantageous developments of the invention are listed in the dependent claims.

During the soldering process, the plates of the plate stack are stacked on top of one another in such a way that first plates and second plates lie alternately on top of one another. Between the plates is a braze layer of braze material. The solder material contains a metal which melts during the high temperature treatment and combines with the metal of the mating plates to form the solder joint at contact areas. If the solder metal and the plate metal are different, an alloy will form at the contact areas. Furthermore, the solder material contains a binder which serves to hold the solder metal at the location of the coating on the board th, and a solvent that determines the viscosity of the solder material, such as water. In addition, the soldering material can contain other elements which influence the soldering behavior, for example melting point depressants, which are admixed with the soldering metal.

Before stacking the boards on top of each other, for each pair of boards, at least one board surface is coated with the brazing material to form the brazing material layer. When the boards are then stacked one on top of the other, the layer of solder material contacts both adjacent boards, between which it effects the solder connection after the high temperature treatment. The invention is now based on the idea of arranging the plate coated with the layer of soldering material on top and the respective other plate below for each pair of plates to be connected, so that the surface of the plate coated with the layer of soldering material points downwards. "Below" and "above" in this context mean the orientation of the plates or the plate stack with respect to the earth's surface. Thus, the board coated with the solder layer is subjected to the high temperature treatment with the coated surface facing down. Preferably, only the first plate is coated in order to solder the first to the second plate, so that there is only one layer of solder material between two plates.

The areas of contact between the plates are at the lowest points or areas of the plate surface of the upper, first plate, as seen from the first plate, that is, looking at the ridges in the plate profile. Arranging the first board with the solder material layer down therefore has the advantage that the solder, which melts during the high-temperature treatment, does not spread to larger areas of the first board. Because the solder does not spread to board surface areas that do not participate in the board-to-board solder joint or that are far from the contact areas, better solder joints are obtained.

The high-temperature treatment is preferably carried out in such a way that solder flows towards the contact areas during the high-temperature treatment. In particular, this can occur due to gravity when the solder melting due to the high temperature treatment moves due to the earth's gravity along the board surface of the first board to the lowest areas of the board surface. If the contact areas of the opposing plates are close enough together so that there is a small spacing between the plates at the contact areas, then this effect can be amplified by the capillary force that pulls the liquid solder further into the contact areas. The solder therefore collects in the contact areas during the high-temperature treatment in which the solder connections are formed. The concentration of solder or solder metal in the contact areas leads to reliable soldered connections.

The high temperature treatment causes the first and second plates to be soldered together at the contact areas. For this purpose, the stacked plates are heated to a temperature that is above the melting temperature of the solder. Preferably heating is above 900°C or 1000°C, more preferably about 1100°C. This temperature is maintained long enough for the entire stack of plates to heat up accordingly. The high-temperature treatment is preferably carried out under vacuum or in the presence of an inert or protective gas such as nitrogen, hydrogen, helium, argon or a mixture of one or more of these gases. For example, the high-temperature treatment is carried out in a vacuum furnace, or in a continuous furnace.

As explained above, the brazing material layer contains a brazing material made of a brazing metal or a brazing alloy, a binder and a solvent in a mixture or dispersion. The binder is preferably present in the braze material or braze material layer in an amount between 5 wt% (wt%) to 20 wt%. Irrespective of this, the proportion of the solvent in the brazing material or in the brazing material layer is preferably between 0.1% by weight and 5% by weight, more preferably between 0.5% by weight and 1.5% by weight.

Examples of the binder are gelatin-based, preferably cellulose-based or ethylene glycol or pyrene-based binders. The content of the binder and the solvent depends on the viscosity of the binder, the desired consistency of the mixture and the size and capacity of an applicator used. The mixture and/or dispersion can be applied to the first board by means of spraying, application in dot or bead form, dripping, sprinkling, rolling up, dipping, spraying, also metal spraying, screen printing, stencil printing or the like. Alternatively, the binder and/or the solvent can also be applied before the solder alloy. The solder alloy is preferably in powder form. It preferably has a melting point lower than the melting point of the base material of the first and second plates.

The soldering material can have such a consistency or viscosity and can be applied so thinly that the due to the Auftra gens formed layer of soldering material no longer changes in its spread along the board surface. Thus, if an area of, for example, 10 mm ^{2 of} the board surface is covered with the solder material, then this area will not increase. Preferably, however, the solvent content of the brazing material layer is selected and the brazing material layer is applied to the first board in such a way that the brazing material layer flows immediately after being applied to the first board and as a result coats the first board. The surface area covered by the layer of solder material thus increases immediately after application of the solder material. For this purpose, the soldering material has in particular a higher proportion of solvent, so that it is thinner.

If the solder material or layer of solder material flows under the influence of gravity after being applied to the first board, then the same amount of solder material is distributed over a larger area, so that the resulting layer of solder material covering the first board is thinner. In this way, a thinner coating of the first plate with the layer of soldering material can be achieved, which corresponds to a correspondingly thin layer of soldering material after the binder and/or the solvent has been expelled, if necessary. A thinner layer of soldering material at the contact areas between the first and second plates also has the advantage that a smaller distance between the plates can be achieved when the plates are stacked on top of one another. The contact spacing can therefore be selected to be correspondingly small. A better soldered connection can be achieved simply because of the smaller contact spacing. On the other hand, the capillary forces in the contact area also increase, so that after melting during the high-temperature treatment, the solder flowing to the contact area by gravity is sucked into the contact area more intensively. This in turn can also lead to an improved solder joint. Finally, solvents and binders can be better evaporated from a thinner soldering material layer if this is provided during the high-temperature treatment and/or during treatment steps which may precede the high-temperature treatment.

Preferably, the thickness of the layer of solder material, whether applied directly to that thickness and statically applied or to a greater thickness and flowed to that layer thickness, is a few grain diameters of the solder at least at the highest elevation in the first board surface. As an ideal, lower limit, a layer thickness of just one grain size can be achieved. The layer thickness of the brazing material layer is preferably less than 2 mm, preferably less than 1.5 mm or less than 1 mm. If the solder material is initially applied thicker and then flows to a thinner layer of solder material, the solder material is preferably applied with a material thickness of at least 1 mm, 1.5 mm or 2 mm, measured at the thickest point.

A suitable brazing alloy for the brazing material and thus for the brazing material layer is, for example, a nickel-based alloy, optionally with chromium, or an iron-based alloy. Alternatively preferably, the soldering material layer can contain a soldering alloy based on copper, cobalt or silver. The solder alloy particularly preferably contains iron. The solder alloy preferably also contains one or more additives that lower the melting point, such as silicon and/or boron. The additive that lowers the melting point can diffuse into the base material of the first plate during the high-temperature treatment. Furthermore, particles with better thermal conductivity and a higher melting point than the solder, such as silicon carbide, can be added to the solder alloy. The heat transfer can thus be further increased.

The following melting point depressants can be contained in the solder individually or in a desired combination, with each combination having particular advantages with regard to the flow properties of the solder during the high-temperature treatment and/or with regard to the resulting soldered connection. Boron can be contained in the brazing material layer, for example, in a proportion of 0.2-9% by weight. Silicon can be contained in the layer of soldering material, for example, in a proportion of 0.2-20% by weight. Phosphorus can be contained in the brazing material layer, for example, in a proportion of 0.1-16% by weight. Carbon can be contained in the brazing material layer, for example, in a proportion of 0.01-5% by weight. Manganese can be contained in the brazing material layer, for example, in a proportion of 0.1-16% by weight. Palladium can be contained in the layer of soldering material, for example, in a proportion of 0.1-10% by weight. Cobalt can be contained in the brazing material layer, for example, in a proportion of 0.01-2% by weight. Hafnium can be contained in the brazing material layer, for example, in a proportion of 0.1-18% by weight.

As explained above, it is advantageous if, during the high-temperature treatment, solder flows towards the contact areas due to gravity and possibly capillary force. In this case it is preferred that the solder contains one or more melting point reducers and that during the flow of the solder to the contact areas the melting point reducer diffuses from the solder into the base material of the first plate. Due to the diff When the melting point depressant is extracted from the molten solder, the solder becomes more and more viscous until it finally solidifies. The proportion of melting point reducer in the solder or in the layer of soldering material, as well as the course, temperature and duration of the high-temperature treatment are preferably selected in such a way that the solder no longer flows down the second plate again. With the correct setting of these parameters it can be ensured that the solder finally solidifies in the contact area between the two boards and as little solder as possible remains along the board surface(s) which does not participate in the soldered connection. The correct parameters in this respect can also depend, among other things, on the size, the material and the shape of the panels.

According to a preferred embodiment, it is provided that when the first plate and the second plate are stacked on top of each other, the second plate is pressed into the layer of soldering material at the contact areas. In other words, at least part of the board surface of the second board is pressed into the solder layer such that a flattening or dent is formed in the solder layer. In this way, the distance between the two plates can be reduced, which leads to an improved soldered connection, since a smaller soldering gap is metallurgically advantageous. In addition, this can increase the capillary effect of the soldering gap compared to the solder melt, so that the solder flows better into the soldering gap during the high-temperature treatment.

In an advantageous development it is provided that the soldering material layer coats at least 20%, 30%, 40%, 45%, between 45% and 65%, or between 45% and 85% of the surface of the first plate before the high-temperature treatment. In this case, the layer of brazing material can already be applied to the first plate with such a covering, or, as explained above, it can have achieved such a covering as a result of a flow process. A high coverage of preferably more than 40%, 45% or even 50% has the advantage that a large amount of soldering material is available for the production of the soldered connection. In combination with the feature of a thin layer of soldering material, there is then a sufficient amount of solder in the contact area to form a good soldered connection, even with very small contact spacings and thus small soldering gaps.

In an expedient embodiment, it is provided that the soldering material layer is subjected to a drying step before the high-temperature treatment, in which solvent contained in the soldering material layer is expelled. The solvent is advantageously driven off at a temperature between 105° C. and 250° C., for example at a temperature of 200° C., for several hours. If the solvent level in the solder layer is increased to promote flow of the solder after application, then the solder layer will contain more solvent that must be driven off. At the same time, however, the surface area of the soldering material layer is increased due to the flow of the soldering material, so that the solvent can escape more quickly.

In addition or as an alternative to the drying step, it is advantageous if, before the high-temperature treatment, the layer of soldering material is subjected to a temperature treatment in which the binder contained in the layer of soldering material is expelled. The binder is also expelled faster when the surface area of the brazing material layer is increased. When the binder is expelled, it is in particular partially converted into carbon dioxide or into hydrocarbons which evaporate at lower temperatures and escapes from the layer of brazing material. The temperature treatment is preferably carried out at a temperature between 330° C. and 390° C., in particular at about 370° C., over a period of several to 20 hours. After both the solvent and binder are driven off, a layer of solder is left at the contact area, covering substantially the same area on the first board as the layer of solder material previously, and consisting primarily of the solder.

According to a preferred development, it is provided that the first plates and/or the second plates are each formed from a metal sheet shaped in the form of a wave, with the depressions and elevations being formed from wave troughs and wave crests. After the soldering process, the soldered connections are formed between the wave troughs of the first plate and the wave crests of the second plate at punctiform or linear contact areas. The wave troughs and wave crests preferably form a herringbone pattern when viewed from above on the plate.

The second plate preferably has the same structure as the first plate and is rotated in the plate stack by 180° relative to the first plate about an axis running perpendicularly to a plate plane. In other words, the stack of plates is made up of plates with the same structure, which are alternately rotated by 180°.

It is also possible to alternately arrange plates with two different corrugated structures in the plate stack. This means that the first plates have a different wave structure than the second plates. It is also possible that the second plates have no corrugated structure at all, but are flat or at least flat in the contact areas.

It is also possible to arrange plates with more than two different plate structures in the plate stack. In this case there are therefore third plates which have a further plate structure, in particular a further corrugated structure.

In a preferred embodiment it is provided that the plates are made of steel, in particular stainless steel or carbon steel.

Carbon steel, also known as carbon steel, mainly contains iron and carbon as alloying elements. Anti-corrosive elements such as chromium are not present in carbon steel in sufficient amounts to form an anti-corrosive.

The solder used for the connection is advantageously free of anti-corrosion elements such as chromium. This can be advantageous for certain applications of the plate heat exchanger.

• 1 eine schematische Querschnittsansicht zweier miteinander verbundener Platten eines Plattenwärmetauschers; und
• 2a-2g schematische Querschnittsansichten zur Veranschaulichung der Schritte eines Plattenwärmetauscher-Herstellungsverfahrens gemäß einer bevorzugten Ausführungsform.

The invention is explained below using exemplary embodiments with reference to the figures. Here show:

• 1 a schematic cross-sectional view of two interconnected plates of a plate heat exchanger; and
• 2a-2g 12 are schematic cross-sectional views illustrating the steps of a plate heat exchanger manufacturing method according to a preferred embodiment.

the 1 Fig. 12 shows a schematic cross-sectional view of a first plate 1 and a second plate 2 stacked on top of each other. Only these two plates 1, 2 of a larger plate stack (not shown) made up of several first and second plates are shown here, which are stacked alternately on top of one another and soldered to one another in such a way that a plate stack with channels 3 running between adjacent plates 1, 2 is formed. A brazed plate heat exchanger generally has a larger number of plates brazed to one another, for example a stack of plates can have up to 300 plates.

Each plate 1, 2 has a corrugated structure with wave crests and wave troughs. In addition, openings 131, 231 are provided, which form an inlet opening 131 and an outlet opening 231 for the fluid flowing in the channels 3 (not shown) in the assembled and soldered plate stack. The two plates 1, 2 are soldered to one another at contact areas 15.

The soldering process is explained below using the schematic cross-sectional views in FIGS 2a until 2g explained in more detail. Only one contact area 15 is shown in these figures. the 2a shows a wave crest on the profiled first plate 1. A part of the wave crest will later serve as a contact area 15 for contact with a corresponding contact area of the second plate 2 for the soldered connection. In a first step, a drop of soldering material 50 of a soldering material is applied to the contact area 15 . This can be done, for example, by means of a nozzle.

The applied brazing material has a sufficiently low viscosity that it begins to flow immediately after application and is distributed over a larger area of the first plate 1 . This flow behavior is favored by gravity due to the flanks of the wave crest. After the flow of the soldering material comes to a standstill, the situation arises which is shown in 2 B is shown. The resulting layer of soldering material 5 has a larger surface area than the original drop of soldering material 50. Since the amount of material remains essentially constant, the layer of soldering material 5 that is created is correspondingly thinner.

First board 1 is now turned over and stacked on top of second board 2 with solder layer 5 facing down toward earth. This is in the 2c shown. As in the 2d recognizable, the second plate 2 is pressed into the soldering material layer 5 on the first plate 1. This reduces the distance between the two plates 1, 2, so that the soldering gap 53 filled with the soldering material also becomes smaller.

Subsequently, a drying step and a temperature treatment are carried out in order to expel the solvent and the binder from the brazing material layer 5 . The result will be in the 2e shown. A layer of solder 55 remains from the solder material layer 5 after these steps. In a further step, the plates 1, 2 are finally subjected to a high-temperature treatment, during which the solder 55 melts. The molten solder 55 flows down from the shoulders of the bump on the first board 1 towards the second board 2 and the soldering gap 53 due to gravity. The flowing solder 57 is at an intermediate stage in the 2f is shown as a solid line, while the outline of the original plumb 55 is shown as a dotted line for clarity. The flow process towards the soldering gap 53 is supported by capillary forces emanating from the soldering gap 53.

During the flow, melting point depressants emerge from the solder 55, 57 and diffuse into the base material of the first plate 1. This increases the melting point of the solder and, at the same temperature, the viscosity of the solder increases, so that the flow process is slowed down. This effectively prevents the flowing solder 57 from flowing further down from the contact region 15 along the second plate 2 . Finally, the flowing solder 57 comes to rest and forms a solid solder joint 59 between the first board 1 and the second board 2.

Reference List

1

first plate

131

entrance opening

15

contact areas

2

second plate

231

exit port

3

channels

5

solder layer

50

solder droplet

53

soldering gap

55

Lot

57

flowing solder

59

solder connection

Claims (13)

Plate heat exchanger manufacturing method, in which first plates (1) and second plates (2) are alternately stacked on top of each other and soldered together in such a way that a stack of plates with channels (3) running between adjacent plates (1, 2) is formed, the method having the following process steps comprises: - providing at least a first plate (1) and a second plate (2), the first plate (1) and the second plate (2) having indentations and elevations which, when the first plate (1) and the second plate (2) forming the channels (3); - Coating the first plate (1) by means of a brazing material layer (5); - Stacking the first panel (1) and the second panel (2); and - high temperature treatment of the soldering material layer (5) so that the soldering material layer (5) produces soldering connections (59) between the first board (1) and the second board (2) at contact areas (15), characterized in that the first board (1) is arranged during the high-temperature treatment so that the brazing material layer (5) arranged on it faces downward. manufacturing process claim 1 , characterized in that the high-temperature treatment is carried out in such a way that solder flows towards the contact areas (15) during the high-temperature treatment due to gravity and, if appropriate, capillary force. manufacturing process claim 2 , characterized in that during the flow of the solder to the contact areas (15) melting point reducer diffuse from the solder into the base material of the first plate (1). Manufacturing method according to one of the preceding claims, characterized in that when the first plate (1) and the second plate (2) are stacked, the second plate (2) is pressed into the soldering material layer (5) at the contact areas (15). Manufacturing method according to one of the preceding claims, characterized in that the brazing material layer (5) before the high temperature treatment covers at least 20%, 30%, 40%, 45%, between 45% and 65%, or between 45% and 85% of the area of the first Plate (1) coated. Production method according to one of the preceding claims, characterized in that the soldering material layer (5) is subjected to a drying step prior to the high-temperature treatment, in which the solvent contained in the soldering material layer (5) is expelled, and/or is subjected to a temperature treatment in which the soldering material layer (5) contained binder is expelled. Production method according to one of the preceding claims, characterized in that the solvent content of the soldering material layer (5) is selected in such a way and the soldering material layer (5) is applied to the first plate (1) in such a way that the soldering material layer (5) immediately after application on the first plate (1) flows and due to which the first plate (1) is coated. Manufacturing method according to one of the preceding claims, characterized in that for coating the first plate (1) with the soldering material layer (5), a soldering material with a solvent content of between 0.1% by weight and 5% by weight, or between 0.5% by weight and 1.5% by weight is used. Production method according to one of the preceding claims, characterized in that that the first plates (1) and/or the second plates (2) are each formed from a corrugated sheet of metal, with the depressions and elevations being formed from wave troughs and wave crests. Manufacturing method according to one of the preceding claims, characterized in that the second plate (2) has the same structure as the first plate (1) and is rotated by 180° in the plate stack relative to the first plate (1) about an axis running perpendicular to a plate plane is. Manufacturing process according to one of Claims 1 until 9 , characterized in that the second plate (2) has a different structure than the first plate (1). manufacturing process claim 11 , characterized in that plates with further structures deviating from the first plate (1) and the second plate (2) are arranged in the plate stack. Manufacturing method according to one of the preceding claims, characterized in that the plates (1, 2) are formed from steel, in particular from stainless steel or from carbon steel.

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