Patent Application
20100270361
The invention relates to an apparatus and a process for applying a flux for brazing parts, in particular for producing plate-type radiators as used in motor vehicles, in accordance with the preamble of claim 1 or or 13 or 14. The invention also relates to a heat exchanger using a corresponding process.
It is currently customary to use special brazing processes, in particular what is known as NOCOLOK® brazing, to braze solder-plated individual parts in particular for heat exchangers, i.e. in particular of radiators, evaporators, condensers, etc. as used in the automotive sector, if the base material used is aluminum or aluminum alloys.
NOCOLOK® brazing is described in principle in DE-A 26 14 872 as a process for joining aluminum components using an aluminum brazing alloy with a melting point below that of the aluminum components, by heating the assembled components to a temperature above the melting point of the brazing alloy and below the melting point of the components in the presence of a potassium fluoroaluminate flux which is substantially devoid of unreacted KF. This known process is distinguished by the fact that the flux and the brazing alloy are applied to the surfaces of at least one of the components as an aqueous suspension of finely dispersed flux and metal powder, the film of suspension is dried and the dust-free inert gas atmosphere (if appropriate after the parts have been assembled) is used for brazing, with the application of the flux/brazing alloy suspension being controlled in such a way that from 40 to 150 g/m2 are applied and the ratio of flux to brazing alloy is selected in such a way that at least 5 g/m2 of flux are deposited.
On account of the special materials properties of aluminum or aluminum alloys, in the known brazing process it is necessary to apply a noncorrosive, non-hygroscopic flux. In the NOCOLOK® brazing process (CAB—Controlled Atmosphere Brazing), a flux based on potassium fluoroaluminate of the empirical formula K(1-3)AlF(4-6) is used for this purpose. This flux is in the form of a eutectic, melts at a temperature of 562° C. to 572° C. and removes the aluminum oxide which is always present as a surface impurity on the aluminum itself. As a result, the surface of the Al material is for a brief time rendered accessible to further processing steps, such as brazing, which is also known in the specialist field as “activation of the surface”.
The non-hygroscopic flux mentioned above wets the surface, and the solder, when the solder plating starts to melt at a temperature of 577° C., can be drawn freely into the soldering gaps through capillary action. Therefore, completely sealed brazing in a reliable manufacturing process is not possible without an application of flux appropriate to the brazing situation.
It is usual for the flux mentioned to be applied in the following ways, a process known in the specialist field as fluxing:
The variant of applying the flux described under a) is primarily used for the fluxing of heat exchanger meshes, for fin/tube brazing or, as illustrated in
However, conventional fluxing still leaves something to be desired; in particular excess quantities of flux may be supplied, which leads to increased costs.
It is an object of the invention to provide an improved apparatus for applying flux. A further object is to provide a process for more optimum fluxing. Another object of the invention is to provide heat exchangers which have an optimized fluxing.
This object is achieved by an apparatus having the features of claim 1. This object is also achieved by an apparatus having the features of claim 3. This object is also achieved by a process having the features of claim 13. Furthermore, this object is achieved by a process having the features of claim 14. The object according to the invention is also achieved by heat exchangers as described in claim 18. Advantageous configurations form the subject matter of the subclaims.
The invention provides an apparatus having a fluxing apparatus for the automated application of flux to a material surface using a spraying apparatus, such as for example a spray nozzle or spray gun which is arranged, inclined at an angle of 30° to 60° with respect to the material surface, preferably at an angle of approximately 40°, in a region in the vicinity of an edge of the material surface.
This apparatus is used in particular for the targeted spraying of plates of a plate-type heat exchanger with flux, during which process the material surfaces which have been provided with flux are then joined to suitably treated other material surfaces by means of NOCOLOK® brazing.
The earlier application DE 101 41 883, the disclosure of which is hereby expressly incorporated by reference in the content of disclosure of the present application, has disclosed flux compositions which can preferably be used for the process according to the invention.
It is preferable for the material surface to be arranged horizontally. In this case, the plate which is to be fluxed is preferably positioned with its finned side facing upward on a conveyor apparatus, for example a conveyor belt, and successively passes through various stations, such as a spraying station, a drying station, a monitoring station. The spray gun is slightly laterally offset with respect to the plate in the vicinity of a cup-like region of the plate which is located in the vicinity of an edge of the plate.
In an exemplary embodiment of the invention, the arrangement of the spraying apparatus can be selected in such a manner that the component is sprayed or coated in such a manner that the higher quantity of flux required for tightly sealed brazing is applied in a defined region of the component, whereas a reduced quantity of the flux, for example for the fin brazing, is applied in another region of the component.
The apparatus preferably has a monitoring apparatus which is used to monitor the flux coating. This monitoring apparatus is preferably formed by one or more monitoring units which, for example, monitor the spray jet and in particular also the presence of a sufficient flux coating, which is not too thick, in one or more defined regions of the component.
The monitoring apparatus is preferably an optical monitoring apparatus. This has the advantage of accurate yet rapid monitoring in production at a high process rate. This optical monitoring apparatus may in particular be a laser apparatus with at least one emitter and at least one receiver. A two-channel laser is preferably provided for monitoring the layer thickness or layer weight, which is preferably in a range from 0.01 to 0.15 g/cm2, and in particular in the range from 0.02 to 0.1 g/cm2.
In the text which follows, the invention is explained in more detail on the basis of an exemplary embodiment and with reference to the drawing, in which:
The plate has a cup-like region 4, which is indicated by “cup” in
To ensure reliable brazing, according to the invention a spraying apparatus, such as a spray nozzle or spray gun, 5, comprising a spraying apparatus, such as spray nozzle or spray gun, which sprays the flux 3 to be sprayed as a spray fan jet, is arranged at an angle of approximately 40° to the horizontal. The spray jet comprising flux 3 from the spray gun 5 is fanned out in such a manner that flux is sprayed beyond the workpiece 2 on the right-hand and left-hand sides (“overspray L” and “overspray R”). The core zone of the spray jet in this case strikes the cup-like region 4 of the plate, which is arranged in the vicinity of the spray gun 5.
The flux 3 which is sprayed as “overspray R” and is substantially in the form of a mist is used to ensure sufficient fin brazing. Excess quantities of sprayed flux 3, in particular the flux 3 which is sprayed as “overspray L”, is collected by means of funnels or the like at the bottom and returned to the fin-side flux circuit.
The process described above reduces the quantity of flux per unit area on the finned side of the plate to a defined value of approx. 0.01 to 0.15 g/cm2, in particular approx. 0.02 to 0.09 g/cm2, while nevertheless ensuring reliable brazing.
The fluxing of the studded side, i.e. of the opposite side of the plate from the finned side, facing downward in the figures, is carried out by means of a second fluxing apparatus (not shown in the figure) via a separate circuit, since the pump and spraying apparatus settings for the finned-side coating should be set to a different, preferably lower value compared to the other side. The studded-side fluxing apparatus can be formed in a conventional way. However, it may also be advantageous to perform nonuniform, heterogeneous fluxing or coating on this side, if the preconditions for the brazing require or permit this.
A monitoring apparatus 10 with a plurality of monitoring units 10a, 10b, 10c is provided for monitoring the fluxing operation and therefore the flux thickness. Referring to
A second monitoring unit 10b monitors whether there is sufficient flux 3 on the studded side, the laser belonging to this unit being provided at the exit of the dryer. In this case, monitoring involves determining whether or not a white coloration is present. The result of the monitoring, i.e. of whether a predetermined white color is present, i.e. sufficient flux has been applied, or the white color is insufficient, i.e. the studded side is still silver/aluminum-colored and consequently insufficient flux has been applied, is digitized and transmitted to the monitoring apparatus 10. The latter outputs a corresponding signal, so that if necessary the corresponding part can be removed and the spray jet intensity corrected accordingly, or any other malfunction can be eliminated.
Furthermore, there is a third monitoring unit 10c, which monitors whether sufficient flux 3 is present on the finned side in the region indicated in
In this case, the control is carried out as follows:
If the first channel responds, i.e. the predetermined layer weight is exceeded, statistical measured value evaluation of a number of subsequent measured values/measurements is carried out. An automatic setting of the spray time and/or spray quantity is set as a function of the evaluation of these measured values, for example a reduction in spray time, i.e. it is possible to lower the quantity of flux applied. If a plurality of, for example four successive, measurements with measured values in the desired value range are carried out, the statistical evaluation is commenced again.
When the second channel responds, the quantity of flux is too high. The quantity of flux is automatically adjusted downward.
A corresponding two-channel laser can also be used on the studded side in order to optimize the thickness of flux coating there too.
According to the invention, it may be advantageous if the quantity of flux is distributed inhomogeneously over the component. In this case, regions with an even distribution may be present next to regions with an uneven distribution and/or with the same distribution but a different quantity. In this case, by way of example, a region comprising 50% by weight may be present next to regions comprising 30% by weight and 20% by weight. This may be advantageous in heat exchangers having a collection manifold on one side. According to the invention, it may also be advantageous if two regions comprising approx. 40% by weight are present next to a region comprising 20% by weight or two regions each comprising 10% by weight. This may be expedient in the case of a heat exchanger with two collection manifolds on two opposite sides.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03-004-158.6 | Feb 2003 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/12763 | 11/14/2003 | WO | 00 | 1/23/2008 |
