WO2018033341A1 - Method for producing a heat exchange tube - Google Patents

Abstract

The invention relates to a method for producing a heat exchange tube (1) having an inner turbulence insert (2) for a heat exchanger (3). The method is characterized by the method steps of providing an austenitic heat exchange tube (1) and a preferably ferritic turbulence insert (2), inserting the turbulence insert (2) into the heat exchange tube (1), soldering the turbulence insert (2) and the heat exchange tube (1) by means of induction brazing, pressing the heat exchange tube (1) onto the turbulence insert (2) before, during and/or after the induction brazing. Due to the omission of previously used brazing ovens, in particular soft annealing and a decrease in strength associated therewith can be avoided.

Description

 Production method of a heat exchanger tube

The present invention relates to a manufacturing method of a

Heat exchanger tube with a turbulence insert for a heat exchanger according to the preamble of claim 1. The invention also relates to a heat exchanger with at least one such heat exchanger tube.

From DE 102 33 407 B4, for example, a heat exchanger tube with a turbulence insert soldered therein is known. Such a heat exchanger tube is also known from DE 10 2006 013 868 A1.

In general, heat exchangers and in particular exhaust heat exchangers, a high degree of robustness against pressure and temperature changes, a high

Power density, low pollution and low weight and low production costs in production while providing a high flexibility in terms of application. There are different solutions to these competing goals, but they always do one of these better than others. None of the known solutions is leading in all respects.

In heat exchangers and in particular exhaust gas heat exchangers, designs with and without gas-side ribs are usually differentiated. The designs without gas-side ribs (for example, winglet tube bundle) usually consist of a bundle of empty tubes, are embossed into the structures that generate the turbulence on the inside and thus the

Heat transfer and at the same time the tendency to fouling

to reduce. These tube bundles are combined via so-called tube plates, wherein the tubesheets together with a housing form a coolant flow space. At the tubesheets themselves are depending on Embodiment mounted directly or indirectly over the housing diffusers that form the gas side flow space. Usually, such heat exchangers are soldered as a whole or manufactured in a laser welding process.

Heat exchanger with gas-side rib achieve an increase in performance from an increase in a secondary surface of the heat exchanger, in which case a heat exchanger block of ribs (turbulence inserts), pipes and tube sheets is soldered as a whole. If a housing is required, this is also soldered or later in two-shell design with the

Tube sheets and welded between the shells.

A disadvantage of the known from the prior art heat exchangers, however, are in particular the comparatively complicated production of heat exchangers with gas-side rib and a not to be underestimated strength loss by a so-called soft annealing, which occurs during a long heating in a brazing furnace for the preparation of solder joints.

The present invention therefore deals with the problem of a

Specify a manufacturing process, by means of which a powerful

Heat exchanger tube manufacturing technology can be easily manufactured, but without experiencing a loss of strength during manufacture as before.

This problem is inventively achieved by the subject matter of

independent claim 1 solved. Advantageous embodiments are

Subject of the dependent claims.

The present invention is based on the general idea, for the first time in the production of a heat exchanger tube of a heat exchanger, For example, a Abgaswärmeübertragers to use an induction brazing, which in particular the soldering in a brazing furnace and associated soft annealing and the associated loss of strength of the heat exchanger tube and the other components can be avoided. The production method according to the invention is characterized by the following method steps: First, an austenitic

Heat exchanger tube and a preferably ferritic turbulence insert provided. In a second method step, the turbulence insert is inserted into the heat exchanger tube and then the turbulence insert is soldered to the heat exchanger tube by means of induction soldering and thus fixed. Before, during and / or after induction soldering, the heat exchanger tube can be pressed from the outside against the turbulence insert and thereby fixed. The soldering can be done for example by the fact that the

Heat exchanger tube with the turbulence insert disposed therein passed through an inductor while the heat exchanger tube, the solder and the

Heat turbulence insert so far that the solder melts. By pressing the heat exchanger tube to the turbulence insert, a reliable connection between these two components during cooling after leaving the inductor can be achieved. By the

Only local heat input cools the heat exchanger tube in comparison to a previously known soldering process in a brazing furnace significantly faster, which in particular also taking place in the brazing furnace by the long-lasting heating loss of strength can be reliably avoided.

An austenitic stainless steel may also be used for the turbulence insert, for example when corrosion requirements require certain alloys such as 1 .4404. When inductive heating of the heat exchanger tube is the

alternating electromagnetic field, which is registered by means of the inductor, partially or completely absorbed in the tube interior by the inventive and preferably ferritic material, so that the heating of the solder takes place only via the contact with the heated heat exchanger tube. A tube material with low magnetic permeability and high electrical resistance can penetrate the electromagnetic alternating field into the interior of the heat exchanger tube up to a certain depth. In this case is of the

Standard penetration depth δ spoken. In this case, the field strength has fallen to about 37% of the value outside the heat exchanger tube. In the case of an austenitic stainless steel which is not ferromagnetic and has a relatively poor electrical conductivity, this penetration depth is approximately 1 mm or more for the frequencies customary for inductive soldering from 50 to approximately 200 kHz. With a wall thickness of the heat exchanger tube of a maximum of 0.5 mm, thus a direct heating of the solder or the turbulence insert is possible.

The inventive design of the turbulence insert of a preferably ferritic material (steel) shifts the

Power input of the alternating field further in the direction of

Turbulence insert what the temperature differences between

Heat exchanger tube and turbulence insert and thus further reduced internal stresses. Particularly noteworthy here is that a standard penetration depth δ of eddy currents in an austenitic material at the same frequency is significantly greater than in a ferritic material, so that through the

Forming the heat exchanger tube made of an austenitic material, a good penetration of the same by means of the eddy currents can be ensured, while the trained from a preferably ferritic material turbulence insert has a worse or lower standard penetration depth δ and thus causes a certain shielding. This can In particular, an exact local heating of the solder can be achieved without the entire heat exchanger tube and the turbulence insert disposed therein, such as in a brazing furnace, must be heated long term.

It also heats the solder from two sides. With the

The production method according to the invention can thus be used

Heat exchanger tube of a heat exchanger, such as a

Abgaswärmeübertragers produce high quality, without sacrificing the occurring during a soldering in a brazing furnace by strength

To accept soft annealing.

In an advantageous development of the solution according to the invention, a solder is applied as solder foil or as solder paste on an inner side of the heat transfer tube and / or on the turbulence insert, in particular on contact points thereof with the inside of the heat transfer tube. Both that

Applying the solder as a solder foil as well as the application as a paste solder is doing a high-quality on the one hand and on the other hand cost-effective

Possibility dar. In particular, both of these methods can be integrated into a so-called "inline process".

According to an advantageous development of the solution according to the invention, the heat transfer tube is pressed against the turbulence insert before, during and / or after induction soldering with at least one pair of rollers or a rigid pressure device. Over the at least one pair of rollers is thus at least after induction soldering a contact pressure on the

Induction solder applied, which fixes them until the solder is solidified. In addition, to speed up this process, it may be considered to cool the pair of rolls, thereby speeding up the manufacturing process and reducing cycle time. In an advantageous development of the solution according to the invention, an austenitic stainless steel is used for the heat exchanger tube. Such an austenitic stainless steel offers the great advantage that it is both rust-proof and chemically resistant to exhaust gas and, moreover, can withstand sustained temperatures of up to 600 ° without subsequent heat treatment.

In a further advantageous embodiment of the method according to the invention, the induction brazing is carried out under a protective gas atmosphere. By means of such a protective gas atmosphere in particular oxygen from the

Soldering be kept away, which can be prevented that the oxygen reacts with the solder or the materials of the turbulence insert and the heat exchanger tube and here, for example, pores and thus weak points.

The present invention is further based on the general idea, a heat exchanger with at least one of the previously described

Equip the heat exchanger tube produced by a laser welding connection in an associated tube sheet of the

Heat exchanger is fixed. The heat exchanger tube produced by means of the method according to the invention can thus be used in known manufacturing processes for tube bundle coolers and compensates in particular the disadvantages arising from the prior art during soldering in brazing furnaces. The heat exchanger according to the invention thus makes it possible in particular to manufacture without the disadvantages known from the prior art

in terms of strength by soft annealing in the brazing furnace. The laser welding of the individual heat exchanger tubes with the tubesheet also causes only localized heat input and thus low thermal

Charges. In an advantageous development of the solution according to the invention, the heat exchanger tube of the heat exchanger has at least one longitudinal bead and / or one transverse bead. In particular, a stiffening of the heat exchanger tube can be achieved via such a longitudinal or transverse bead, whereby a stiffening of the heat exchanger block produced therewith can be achieved. Such longitudinal corrugations or transverse corrugations can be manufactured comparatively easily, even in an inline process.

In an advantageous development of the solution according to the invention, a longitudinal end region of the heat exchanger tube welded to the tubesheet is free of solder. This can be avoided that the solder during laser welding of the longitudinal ends of the heat exchanger tubes with the associated

Through holes of the associated tube sheet mixed and thereby leads to local cracks.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated

Description of the figures with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

Show, in each case schematically,

Fig. 1 is a sectional view of an inventively produced

 heat exchanger tube,

Fig. 2 shows an apparatus for carrying out the inventive

 Manufacturing process

Fig. 3 is a sectional view through a possible embodiment of a heat exchanger according to the invention.

According to FIG. 1, a heat exchanger tube 1 according to the invention has an inwardly arranged turbulence plant 2. Such a heat exchanger tube 1 according to the invention is used in a heat exchanger 3, for example an exhaust gas heat exchanger 4 (see FIG. 3).

According to the invention, the heat exchanger tube 1 is now made of an austenitic material, for example a stainless steel, whereas the

Turbulence insert 2 made of a preferably ferritic material,

for example, also a stainless steel is formed. The difference between the two materials can only in their

Magnetizability lie. By forming the turbulence insert 2 from a preferably ferritic material and the heat exchanger tube 1 made of an austenitic material, in particular a completely new

Manufacturing process for the heat exchanger tube 1 are made possible, which in particular known from the prior art disadvantages, such as For example, a loss of strength by annealing in a brazing furnace, avoids.

The heat transfer tube 1 according to the invention is produced as follows: First, the austenitic heat transfer tube 1 and the

preferably ferritic turbulence insert 2 is provided, wherein subsequently the turbulence insert 2 is inserted into the heat exchanger tube 1. Now, the turbulence insert 2 is soldered to the heat exchanger tube 1 by means of induction soldering, for which purpose in particular an inductor 5 (cf. FIG. 2), for example an induction coil 6, is used. In FIG. 2, the induction coil 6 is arranged such that the heat exchanger tube is moved through it. In this case, also arranged above and below and designed as a flat coils inductors 5 are conceivable. Before, during and / or after induction soldering, the heat exchanger tube 1 is still pressed against the internal turbulence system 2, as a result of which the

Solder connection can be fixed more reliably. The pressing of the

Heat exchanger tube 1 against the turbulence insert 2 can thereby

For example, by means of a pair of rollers 7 (see Figure 2).

So far, the turbulence inserts 2 were also fixed in the heat exchanger tube 1 by soldering, but the soldering was done in a brazing furnace, in which both the heat exchanger tube 1 and the turbulence insert 2 were heated for hours and experienced by soft annealing a not to be underestimated strength drop. This can now be done with the

Induction brazing according to the invention can be reliably avoided, since the soldering required heat input takes place only briefly and locally, without a long-term heating of the turbulence insert 2 and the

Heat exchanger tube 1. Soft annealing does not take place at all. On the only local heating is also a much faster cooling of the finished brazed heat exchanger tube 1, which is of course still optional can be supported by, for example, that after the inductor 5 arranged roller pair 7 is cooled. For this purpose, a corresponding cooling device is then arranged in the roller pair 7 or connected thereto.

When inductive heating of the heat exchanger tube 1 is the

alternating electromagnetic field, which is registered by means of the inductor, partially or completely shielded in the tube interior by the inventively preferably ferritic material, so that the heating of the solder takes place only via the contact with the heated heat transfer tube 1. At a

austenitic stainless steel, which is not ferromagnetic and has a relatively poor electrical conductivity, this penetration depth is about 1 mm or more at the usual for the inductive soldering frequencies of 50 to about 200 kHz. With a wall thickness of the heat exchanger tube 1 of at most 0.5 mm, a direct heating of the solder or the turbulence insert 2 is thus possible. The inventive design of the turbulence insert 2 of a preferably ferritic material (steel) shifts the

Power input of the alternating field further in the direction of

Turbulence insert 2, what the temperature differences between

Heat exchanger tube 1 and turbulence insert 2 and thus further reduced internal stresses.

The heat exchanger tube 1 according to the invention is used, for example, in an exhaust gas heat exchanger 4, wherein the individual heat exchanger tubes 1 are fixed at their respective longitudinal ends 8 in each case in an associated tube plate 9 or in this arranged passages. A fluid-tight fixation of the heat exchanger tubes 1 in the associated passages of the tubesheets 9 takes place by means of laser welding, for which purpose a laser welding device 10 is used. As a result, the production of a heat exchanger block 1 1 with heat exchanger tubes 1 and the longitudinal end thereof arranged Tube bottoms 9 are carried out in a conventional manner, whereby a comparatively robust heat exchanger block 1 1 can be created without causing a feared by the so far in the brazing furnace resulting strength drop.

In order to avoid a negative influence of a solder 12, which is applied for example as a solder foil 13 or solder paste 14 on an inner side of the heat exchanger tube 1 and / or on the turbulence insert 2, with respect to the laser weld joint 17, it is preferably provided that a with the tube sheet 9 welded longitudinal end 8 of the

Heat exchanger tube 1 is lot-free. In this way, in particular access of the nickel-containing solder material to the welding area and at the same time the associated negative influences can be avoided.

A soldering with the induction soldering method and / or the laser welding used according to the invention can take place under a protective gas atmosphere, which in particular prevents undesired access of oxygen to the solder connection or to the laser welding connection 17.

With the invention produced by induction soldering

Heat exchanger tube 1 and the laser welding associated with tube sheets 9 can be avoided in particular the hitherto the strength decrease causing soft annealing of the steel in the brazing furnace, whereby the entire heat exchanger block 1 1 and in particular the tube sheets 9 have a higher strength in the long term. By the laser welding connection 17 of the heat exchanger tubes 1 in the passages of the tube plates 9 also a small local heat input can also be achieved, which in turn does not lead to soft annealing of the tube plate 9 and the heat exchanger tubes 1 and thereby not caused thereby in the soldering oven Strength loss caused. With the induction brazing method according to the invention and also the laser welding according to the invention, the areal thermal load during the joining of the turbulence insert 2 in the

Heat exchanger tube 1 and 9 are considerably reduced when joining the heat exchanger tube 1 with the associated tube sheet 9, whereby the

Steel structure and thus the strength remain intact. To further increase the rigidity of the heat exchanger tubes 1, this can

optionally have longitudinal corrugations 15 (see FIG. 1) or transverse corrugations 16.

The method according to the invention can be used in particular as a continuous production process, resulting in very short throughput times and costs for producing the heat exchanger tube 1 with it

induction soldered turbulence insert 2 can be achieved in comparison to a Ofenlötung. In addition, a proven

Tube bundle technology with laser welded in tube sheets 9

Heat exchanger tubes 1 and their known advantages are maintained.

It is conceivable that the provided heat exchanger tube 1 is open on the long side, so that the turbulence insert 2 can be better inserted / pushed together with a brazing foil 13. After inserting the turbulence insert 2, the heat exchanger tube 1 is closed by means of a laser welding process and then soldered by means of induction soldering. In this case, the solder foil 13 on both sides of the turbulence insert 2, for example, top and bottom, be attached, which significantly simplifies the manufacturing process, since so far the problem was to insert the solder foil 13 clean together with the turbulence insert 2. This is done with a brazing foil 13 which is folded over at the front around the turbulence insert 2, that is to say a long brazing foil 13 which is longitudinally wound around it

Turbulence insert 2 is placed. This has the disadvantage that the solder foil 13 first once the heat exchanger tube 1 on one side completely closes and must be completely melted during the soldering process. It also has unnecessary Lot 12 in the heat exchanger tube. 1

*****

Claims

claims 1 . Manufacturing method of a heat exchanger tube (1) with a  internal turbulence insert (2) for a heat exchanger (3), characterized by the method steps,  Providing an austenitic heat exchanger tube (1) and a preferably ferritic turbulence insert (2),  Inserting the turbulence insert (2) into the heat exchanger tube (1), Soldering the turbulence insert (2) and the heat exchanger tube (1) by means of induction soldering,  - Pressing the heat exchanger tube (1) to the turbulence insert (2) before, during and / or after induction soldering. 2. The method according to claim 1,  characterized,  a solder (12) is applied as solder foil (13) or as solder paste (14) on an inner side of the heat transfer tube (1) and / or on the turbulence insert (2). 3. The method according to claim 1 or 2,  characterized,  the pressing of the heat exchanger tube (1) against the turbulence insert (2) takes place before, during and / or after the induction brazing, in particular by means of at least one pair of rollers (7). 4. The method according to any one of the preceding claims, characterized,  - That for the heat exchanger tube (1) an austenitic stainless steel is used, and / or  - That for the turbulence insert (2) a ferritic or austenitic  Stainless steel is used. 5. The method according to any one of the preceding claims,  characterized,  that the induction brazing is carried out under a protective gas atmosphere. 6. Heat exchanger (3) with at least one heat exchanger tube (1) produced according to one of the preceding claims, which has a  Laser welding connection (17) is fixed in an associated tube sheet (9) of the heat exchanger (3). 7. Heat exchanger according to claim 6,  characterized,  a wall thickness of the heat exchanger tube (1) is smaller than 0.5 mm. 8. Heat exchanger according to claim 6 or 7,  characterized,  that the heat exchanger tube (1) consists of a formed and  laser-welded steel strip is made. 9. Heat exchanger according to one of claims 6 to 8,  characterized, the heat exchanger tube (1) has at least one longitudinal bead (15) and / or one transverse bead (16). 10. Heat exchanger according to one of claims 6 to 9,  characterized,  - That one with the tube sheet (9) welded longitudinal end region (8) of the heat exchanger tube (1) is solder-free, and / or  - That the heat exchanger (3) is designed as an exhaust gas heat exchanger (4).