JPH04305364A - Pretreatment for vacuum brazing - Google Patents

Abstract

PURPOSE:To drastically reduce the lining cost of equipment by completely removing the working oil sticking to the surfaces of aluminum materials constituting a heat exchanger with plural specified stages. CONSTITUTION:The greater part of the working oil sticking to the surfaces of aluminum materials W constituting a heat exchanger is removed by ultrasonic oscillation in water or hot water in a prewashing stage 3. The oil remaining on the surfaces of the aluminum materials W is then removed by a weakly alkaline degreasing agent of 7 to 11pH and the formation of oxide films and smut is suppressed in a degreasing stage 4. The residues of the degreasing agent stuck with the aluminum materials W during the degreasing stage 4 are then removed by ultrasonic oscillation in water at ordinary temp. in a rinsing stage 5 and thereafter the aluminum materials W are dried by a drying stage 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating aluminum core plates and fins before vacuum brazing when manufacturing a heat exchanger by vacuum brazing aluminum core plates and fins.

0002

2. Description of the Related Art As shown in FIG. 2, an aluminum heat exchanger has a complicated shape in which a core plate 1 and fins 2 are joined together by vacuum brazing. When performing vacuum brazing, the core plate 1 and fins 2 have traditionally been assembled as a pre-process.
However, in recent years, it has been discovered that chlorine-based solvents destroy the ozone layer, and the amount of chlorine-based solvents used has been regulated for the purpose of environmental protection and pollution prevention. becomes impossible. Other pretreatment methods include cleaning with an acidic agent as disclosed in JP-A-61-108466, but since this cleaning corrodes equipment and jigs, acid-resistant treatment and elution are required to prevent this corrosion. It is necessary to consider the treatment of Cr-containing wastewater, which causes an increase in costs. Furthermore, alkaline degreasing agents used in furnace brazing have been studied, but if this is used as a pre-treatment agent for vacuum brazing the core plate 1 and fins 2, the amount of etching will increase and the core An oxide film is formed on the surfaces of the plate 1 and the fins 2, causing smut, making vacuum brazing difficult.

0003

[Problems to be Solved by the Invention] This invention suppresses the formation of oxide films and smut on the surfaces of the core plate and fins (hereinafter referred to as aluminum materials) that constitute a heat exchanger, and provides a vacuum solder of excellent quality. It is an object of the present invention to provide a vacuum brazing pretreatment method that can be used to perform vacuum brazing, and that can significantly reduce equipment costs and running costs compared to conventional methods. In addition to the above-mentioned JP-A-61-108466, there is also JP-A-62-54091 as a prior art document related to the present application.

0004

[Means for Solving the Problems] In order to solve the above problems, the present invention removes most of the oil adhering to the surface of the aluminum material constituting the heat exchanger by ultrasonic shaking in water or hot water. A pre-washing process to remove the oil remaining on the surface of the aluminum material after the pre-washing process to a pH of 7 to 1.
A degreasing process in which the formation of an oxide film and smut is suppressed while being removed using a weakly alkaline degreasing agent in step 1, and a washing process in which the residue of the degreasing agent adhering to the aluminum material during this degreasing process is removed by ultrasonic shaking in water at room temperature. and a drying process of drying the aluminum material that has undergone the water washing process.

[0005]

[Operation] In the pre-cleaning step, most of the oil adhering to the surface of the aluminum material is removed by ultrasonically shaking the aluminum material in water or hot water. In the degreasing process, pH is 7~
The weak alkaline degreaser No. 11 removes oil remaining on the surface of the aluminum material and suppresses the formation of an oxide film and smut. In the water washing step, the residue of the degreasing agent adhering to the aluminum material during the degreasing step is completely removed by ultrasonically shaking the aluminum material in room temperature water. In the drying process, the aluminum material is heated at a wind speed of 2 m/sec or more.
Since it is dried within 20 minutes with an air flow at an ambient temperature of 100°C or higher, it prevents the formation of an oxide film and improves vacuum brazing properties.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to drawings showing examples. As shown in FIG. 1, this invention is comprised of a preliminary cleaning process 3, a degreasing process 4, a water washing process 5, and a drying process 6. Between each process, there is a draining process using air blow.

In the pre-cleaning step 3, the aluminum material W is immersed in water or hot water, and most of the machining oil adhering to its surface is removed by the physical action of ultrasonic vibration by the ultrasonic oscillator 7. This pre-cleaning step 3 reduces the load on the next degreasing step 4 and extends the life of the liquid degreaser. In the degreasing step 4, residual machining oil on the surface of the aluminum material is removed by the chelation, emulsification and dispersion of the alkali builder and surfactant in the degreaser, and substances such as Al on the surface of the aluminum material are removed by the etching action of the degreaser. and the oxide film are removed.

In the washing step 5, the aluminum material W is subjected to the physical action of ultrasonic vibration in water at room temperature, so that the residue of the degreasing agent is removed. In the drying step 6, the aluminum material W
When the moisture on the surface of the
It is removed within 20 minutes with air at temperatures above 0°C.

[0009] Next, key points for obtaining good vacuum brazing properties will be explained with regard to each of the above steps. Good vacuum brazing properties mean that there is little leakage of the refrigerant in the heat exchanger, that the brazing fillet is large enough to withstand the pressure of the refrigerant, and that there is no residual adhesion of foreign matter in the appearance. There is no discoloration caused by In addition, the key points of pre-treatment for vacuum brazing are (1) that processing oil is sufficiently removed from the aluminum material, (2) that the oxide film formed on the surface of the aluminum material is thin (approximately 200 angstroms), (3) There is no change in the composition of the surface layer of the aluminum material, and no impurity residue is attached to the surface layer of the aluminum material.

Regarding the importance of degreasing step 4. degreaser p
In the case of alkalinity where H is 11 or more, there is a region where Mg in the brazing material becomes a hydroxide such as Mg(OH)2, and the dissolution rate (etching amount) of Al increases as the pH of the degreasing agent increases. Therefore, Al is selectively etched, increasing the exposure of Si in the aluminum material, causing a change in the composition of the surface layer of the aluminum material, exposing Mg increasing the oxide film layer, and impurities such as Fe in the brazing material. precipitates on the surface as smut, impairing brazing properties. Furthermore, if an acidic degreasing agent with a pH of 1 to 3 is used, not only will a large amount of Al be etched, but as mentioned above, equipment such as SuS, etc.
Corrosion of the jig and elution of Cr occur, and costs increase when measures to prevent these are taken into account. Also, since degreasing agents in the neutral range have low degreasing power, it is necessary to increase the proportion of surfactant in order to increase the degreasing power. Problems arise in processability, and furthermore, there is a drawback that the oxide film cannot be made thin due to lack of etching power. Considering the above points, a degreasing agent in a weakly alkaline range (pH 7 to 11) is suitable.

Regarding the importance of water washing step 5. The purpose of this step is to completely rinse off the residue of the degreasing agent from the previous step, that is, degreasing step 4. However, if hot water is used for washing, as shown in Figure 4, the longer the immersion time, the more oxidation will occur on the surface of the aluminum material. The growth rate of the film becomes faster, and the effect of removing the oxide film in the degreasing step 4 is wasted. Therefore, it is necessary to use room temperature water. There are also experimental results showing that the more pure water is used, the thicker the oxide film becomes.

Regarding the importance of drying step 6. For the same reason that it is undesirable to use hot water in the washing process, an oxide film will grow if the drying time is long, that is, if heated moisture comes into contact with the surface of the aluminum material for a long time. For this reason, it is important to dry in a short time, as shown in Figure 3 (b).
It is necessary to dry within 20 minutes. This time varies depending on the size and shape of the product, but as shown in FIG. 3(a), a wind speed of 2 m/sec or more and an ambient temperature of 100° C. or more are required.

The amount of etching is preferably 20 g/m 2 ·hr or less, but since the total amount of etching matters, it is not necessarily limited to this value. As another example, the basic process is the same, but the amount of etching is controlled by controlling the type of degreaser and processing time, and it can also be used as a pretreatment for other brazing methods such as brazing using fluoride flux. Adaptable.

[0014]

[Effects] Since the present invention has the above structure, it has the following excellent effects. (a) To provide a heat exchanger with vacuum brazing of excellent quality since processing oil on the surface of the aluminum material constituting the heat exchanger is completely removed and the formation of oxide film and smut is suppressed. (b) Equipment costs compared to conventional vacuum brazing pretreatment methods;
Running costs are significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a perspective view of an aluminum heat exchanger.

[Figure 3] (A) is a diagram showing the relationship between the drying conditions of aluminum material and the drying time (min) when the residual moisture content becomes zero and the ambient temperature (°C) in the brazing pretreatment method. . (b) is the thickness of the oxide film formed on the aluminum material (
FIG. 3 is a diagram showing the relationship between drying time (min) and drying time (min).

FIG. 4 is a diagram showing the relationship between the immersion time (min) of the aluminum material and the thickness (Angstrom) of the generated oxide film in the brazing pretreatment method.

[Explanation of symbols]

3 Preliminary cleaning process 4　Degreasing process 5　Water washing process 6 Drying process

Claims (1)

[Claims] 1. A pre-cleaning step in which most of the oil adhering to the surface of the aluminum material is removed by ultrasonic shaking of the aluminum material constituting the heat exchanger in water or hot water, and the aluminum material that has undergone the pre-washing step. The oil remaining on the surface of
A degreasing process that removes with a weakly alkaline degreaser of H7-11 and suppresses the formation of oxide film and smut, and removes the residue of the degreaser that adheres to the aluminum material during this degreasing process by ultrasonic shaking in water at room temperature. A vacuum brazing pretreatment method consisting of a water washing process and a drying process of drying the aluminum material that has undergone the water washing process.