JPS63317693A - Production of tube material for heat exchanger - Google Patents

Abstract

PURPOSE:To continuously produce an Al tube material for a heat exchanger with a Zn coating layer having superior adhesion and uniformity at a high speed and a low cost by tubularly extruding an Al material and subjecting the resulting tube material to degreasing, cleaning, Zn substitution treatment and contact plating. CONSTITUTION:An Al material is tubularly hot- or warm-extruded. The resulted tube material is well degreased and cleaned with trichloroethylene or the like. The clean material is subjected to Zn substitution treatment by immersion in a soln. contg. essentially NaOH and ZnO. Contact plating is then carried out with a graphite electrode coated with cotton cloth or the like impregnated with an electrolytic soln. contg. ZnO and ZnSO4. Thus, a Zn coating layer of 0.5-10mum thickness is formed on the surface of the extruded tube material and a tube material for an Al heat exchanger having superior pitting corrosion resistance is obtd.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing zinc-coated pipe material for an aluminum heat exchanger, and more specifically, to an aluminum heat exchanger whose surface is electrically galvanized after zinc substitution treatment. The present invention relates to a method of manufacturing a dexterous tube material.

(Prior Art) Heat exchangers for automobile air conditioners, ie, condensers and evaporators, are mostly made of aluminum. Most of these shapes are of the serpentine type as shown in Fig. 2, in which a tube material 1 is extruded into a tubular shape in a hot or warm state and is bent at a bending part 4 to form a serpentine shape. It is constructed by joining corrugated fins 2 made of ging sheets and further attaching connectors 3, and is manufactured by various brazing methods.

Aluminum materials are prone to corrosion in the form of pitting under high temperature and high humidity conditions, but the inner surface of heat exchanger tubes is in contact with the organic medium, so corrosion does not occur, but the outer surface does. Pitting corrosion occurs when exposed to hot and humid conditions and can be a serious problem that can lead to accidents due to penetration reaching the inner surface of the pipe.

To counter this pitting corrosion from the outside surface, each brazing method uses a different method. The brazing method using chloride-based flux (FB method) uses a flux containing zinc chloride as a component, and during brazing, zinc is diffused into the surface layer of the pipe material.1 Normally, the maximum concentration is 1 to 2%, and the diffusion depth is A zinc diffusion layer of 100-200 ILm is formed.

This layer is base with respect to the potential of the tube material and acts as an electrochemical sacrificial layer to protect the undiffused portions of Zn and prevent through-pitting corrosion. Further, in the vacuum brazing method (VB method), a plating sheet to which zinc or tin, etc., which has a base potential with respect to the pipe material is added, is used as the fin material, so that the fins are sacrificially corroded and the pipe material is protected. However, among these brazing methods, the FB method uses deliquescent and corrosive flux, so post-treatments such as wax punching hot water washing, nitric acid washing, and water washing are required, and the VB method requires post-treatment. However, it does require an expensive vacuum device, and due to the sacrificial effect of the fan material, it does not work on bent portions of the pipe material, such as the bent portion 4 in FIG. 2, and cannot be used in places with severe corrosive environments.

Recently, a method of brazing in a non-oxidizing atmosphere using a fluoride-based non-corrosive flux (NB method) has been adopted. Similarly, sacrificial fins are used in combination with a tube material coated with zinc in advance and brazed to prevent pitting corrosion of the tube material. The method currently employed for coating the pipe material with zinc is to chemically replace the zinc after bending the pipe material.

Since this replacement treatment method is based on the immersion method, it is necessary to separately seal the openings at both ends to protect the inside of the pipe material from the treatment solution, and since the solution is alkaline, the post-treatment rinsing process takes time. The manufacturing process for isothermal exchangers becomes complicated. For this reason, heat exchanger manufacturers desire that after extrusion, the material manufacturer coats the tube with zinc in the form of a long product, ie, continuously, by some method. Use of this tube material is advantageous when manufacturing a new heat exchanger for an air conditioner using the NB method, since conventional zinc coating equipment such as replacement treatment is not required.

Regarding techniques for coating pipe materials and the like with zinc, a thermal spraying method (Japanese Patent Laid-Open No. 58-204169) and a pressure melting method (Japanese Patent Laid-Open No. 58-157522) have been proposed as methods in place of the dipping method.

(Problems to be Solved by the Invention) However, the thermal spraying method and the pressure melting method for coating zinc disclosed in JP-A-58-204169 and JP-A-58-157522, respectively, do not Although it has the advantage of being able to perform continuous processing, there remains a difficulty in controlling the thickness or uniformity of the coating layer. Furthermore, there was a problem with the adhesion of the coating layer, and the bending process sometimes caused surface defects such as peeling, rough skin, and cracks at bent portions.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an improved method for manufacturing zinc-coated pipe materials for heat exchangers.

(Means for Solving the Problems) The present inventor has continued to conduct intensive research on a method for continuously coating the surface of aluminum pipes with a zinc layer, and found that if the surface of extruded aluminum pipes is coated with zinc by contact plating after pretreatment, the adhesion will be improved. It has been found that a zinc coating layer with good uniformity can be obtained continuously.

The present invention has been made based on this knowledge.

That is, in the present invention, an aluminum material is hot or warm extruded into a tubular shape, degreased and cleaned, and after zinc substitution treatment, contact plating is performed using an electrode covered with an electrolyte-impregnated body.
The present invention provides a method for manufacturing a heat exchanger tube material, which is characterized by forming a zinc coating layer on the surface of the extruded tube material.

In the present invention, the aluminum material refers to various aluminum alloy materials.

In the present invention, it is necessary to degrease and wash at least the part of the extruded material to be plated with an organic solvent before the plating process in order to ensure the uniformity and adhesion of the coating layer. This is necessary to further improve adhesion.

The zinc replacement treatment carried out in the present invention uses a general immersion method in a solution mainly consisting of sodium hydroxide and zinc oxide. Since the process is carried out continuously, the equipment and procedures can be relatively simple. Further, cleaning after replacement can be easily performed as long as it does not interfere with the subsequent contact plating.

In the present invention, the electrolytic solution used for contact plating can be any known zinc compound-containing electrolytic solution used for electroplating, but an electrolytic solution mainly containing zinc oxide and/or zinc sulfate is preferably used.

In contact plating, the surface to be plated is used as a cathode, and a graphite electrode covered with an impregnated material usually made of cotton cloth or soft felt impregnated with electrolyte is used as an anode, and plating is performed while moving the electrode in contact with the surface to be plated. This method is also called brush plating or brush plating, and this method can also be used in the present invention.

In the present invention, the thickness of the zinc coating layer is preferably 0.5 to
It is 10gm. If the thickness of the zinc coating layer is less than 0.5 gm, there is a risk that pitting corrosion will occur during actual use as a heat exchanger because a sufficient zinc diffusion layer will not be obtained after attaching fins to the pipe material and brazing the two together. If the zinc concentration exceeds 10 gm, the concentration of zinc in the diffusion layer becomes too high, and the effect of preventing pitting corrosion is saturated, and at the same time, general corrosion called white rust is likely to occur, which are both undesirable.

(Example) The present invention will be explained in more detail with reference to Examples below.

Example 1 Aluminum extruded pipe material 1 (
After degreasing A1050) with trichlorethylene, NaOH5
ZnO 40g/fL, ZnS after rinsing with water.
Using a graphite electrode covered with a cotton cloth impregnated with an electrolyte containing O480g/Jl, 25A/drn', 11
V, about 1.5 while rubbing under the condition of electrode contact time 25 seconds.
GM zinc plating was applied to the surface of the tube material. The obtained tube material was designated as sample 1.

In addition, as a comparative example, a pipe material sample was prepared which was subjected to contact plating under the above conditions without performing zinc substitution treatment after solvent degreasing, and this was designated as Sample 2. In addition, as a conventional example, pipe material samples were prepared in which zinc hot material, zinc hot-dip plating, and zinc replacement treatment were performed separately, and these were designated as samples 3, 4, and 5, respectively.

These five types of samples were tested for plating uniformity, adhesion, brazeability, and zinc diffusion distribution in the brazed thermal bridge.

These results are shown in Table 1.

The uniformity of the plating is determined by examining the zinc plating thickness at several locations, and if it is within the range of ±17 zm relative to the target plating thickness of 1.5 lm, it is considered "good", and if it is outside the range, it is "good". Not possible.”

Regarding adhesion, assuming the bending process of the pipe material shown in Figure 2, if the galvanized layer does not peel off on the surface bent 180 degrees with a radius of 8 mm, it is judged as "good", and if it peels off even slightly, it is judged as "unacceptable". ”.

Brazing properties were determined by combining each sample tube material with a plating sheet (BA12pc) with a plate thickness of 1 ms in an inverted T-shape.
! After immersing LF4/ in a solution of 2AiF5/H2O powder dissolved in water to a concentration of approximately 10% by weight, thoroughly drying to remove moisture, it was heated to 600°C in an N2 gas atmosphere with a dew point of -30°C or lower. Brazing was performed by heating for 3 minutes at °C, and the results were evaluated. In this evaluation, the state of fillet formation due to brazing, corrosion due to zinc, etc. was observed, and those that could be used as heat exchangers were rated "good," and those that had problems in use were rated "unacceptable."

The zinc diffusion distribution is the cross-sectional EP of the sample after the above brazing heat.
When analyzed by MA, if both the zinc peak concentration of 0.8 to 5% and the diffusion depth of 100 to 200 gm were satisfied at the same time, it was judged as "good", and in other cases, it was judged as "unsatisfactory".

As is clear from the results in Table 1, the zinc-coated aluminum pipe material produced by the method of the present invention has better uniformity, adhesion, brazability, and diffusion of zinc during solder punching than the comparative and conventional examples. This makes it an excellent tube material for heat exchangers.

Example 2 An extruded aluminum pipe material 1 (
After degreasing A3003) with trichlorethylene, NaOH5
Zinc replacement treatment was performed by immersing the sample in an immersion solution containing 00 g/l and 100 g/liter of ZnO at room temperature for 30 seconds, and after washing with water Zn040 g/l and 180 g of ZnSO4.
Seven types of tube material samples (No.
, 1 to 7) were prepared, and the samples were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

As is clear from the results in Table 2, the zinc coating layer thickness is 0.
The aluminum tube material produced by the method of the present invention having a weight in the range of 5 to 10 gm exhibits excellent properties as a tube material for a heat exchanger.

Example 3 Aluminum extruded pipe material lAl shaped as shown in Fig. 1
100) was degreased with trichlorethylene and then NaOH500
ZnSO,s
, using a graphite electrode covered with a cotton cloth impregnated with an electrolyte containing 180 g/fL, 1 IV, 24 A.
/drn', about 2 pm under electrolysis conditions with electrode contact time of 35 seconds
Thick galvanized. This was bent into a serpentine shape as shown in Figure 2, and a plating sheet 2 with a thickness of 0.16 mm was prepared.
(BA12pc) and brazing was performed under the same conditions as in Example 1 to produce a heat exchanger as shown in Fig. 2.

This heat exchanger was filled with argon gas at a pressure of 20 kg/crn', and the whole was subjected to a salt spray test for about 5,000 hours, but no gas leaked due to corrosion.

In addition, the pitting corrosion depth was examined by cutting it, but none of the pitting corrosion reached the zinc diffusion layer (200 pm), indicating that the zinc-coated 12 pipe material according to the present invention has excellent corrosion resistance.

(Effects of the Invention) According to the manufacturing method of the present invention, it is possible to continuously coat aluminum extruded pipes with zinc, and it is possible to obtain coating uniformity and adhesion that can sufficiently withstand bending after coating. It will be done. In addition, since contact plating is used, combined with the high speed of plating, it is possible to manufacture pipe materials at low cost. These quality and cost advantages greatly contribute not only to aluminum tube manufacturers but also to heat exchanger manufacturers.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an extruded aluminum tube material, and FIG. 2 is a perspective view showing an example of a heat exchanger for an air conditioner. Explanation of symbols

Claims (3)

[Claims] (1) After hot or warm extrusion of aluminum material into a tubular shape, it is degreased and washed, and after zinc substitution treatment, contact plating is performed using an electrode covered with an electrolyte-impregnated body, and the surface of the extruded tubular material is coated with zinc. A method for manufacturing a tube material for a heat exchanger, the method comprising forming a layer. (2) The method for manufacturing a heat exchanger tube material according to claim 1, wherein the electrolytic solution is a solution mainly containing zinc oxide and/or zinc sulfate. (3) The method for manufacturing a heat exchanger tube material according to claim 1 or 2, wherein the zinc coating layer has a thickness in the range of 0.5 to 10 μm.