JPH05305480A - Joining method for aluminum member by torch brazing - Google Patents

Abstract

PURPOSE:To greatly improve the torch brazability in atm. by using a flux contg. K2AlF5 at a specific ratio and consisting of the balance KAlF4. CONSTITUTION:The flux contg. 5-95wt.% K2AlF5 or K2AlF5.H2O and consisting of the balance KAIF4 is used. This flux consists of potassium pentafluoroaluminate hydrate (K2AlF5.H2O) having >=95wt.% purity and is easily and inexpensively produced by chemically synthesizing aluminum hydroxide [Al (OH)3] and potassium fluoride (KF). As a result, aq. fluoroaluminum acid and potassium compd. are mixed therewith and the mixture is chemically synthesized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of joining aluminum members made of aluminum and aluminum alloys by torch brazing in the atmosphere.

[0002]

2. Description of the Related Art Generally, heat exchangers such as aluminum equipment, for example, radiators and oil coolers for automobiles, condensers and evaporators for air conditioners are joined by a brazing method. In this brazing method, an Al-Si alloy brazing material is clad on the surface of an aluminum member in advance, or Al-Si is added between members to be joined.
Insert a thin plate of brazing filler metal and place them in the atmosphere to set a temperature slightly higher than the melting temperature of the brazing filler metal, i.e. 590 ~ 6
There is a method of heating to 20 ° C, a torch brazing method in which a brazing filler metal is placed on a portion to be joined and directly heated by an oxygen-acetylene flame (torch) in the atmosphere.

A flux is used in order to improve the fluidity and wettability of the Al—Si alloy brazing alloy by destroying the oxide film on the surface of the aluminum member during any brazing heating.

[0004] The brazing flux prior aluminum member, Na Cl, KCl, Li Cl , and chlorides such as _{Zn Cl 2, AlF 3, KF} , Na F, a fluoride such as Li F in a suitable composition A mixture is used. However, these fluxes must be removed by hot water or acid after brazing. This is because when the flux remains, the chloride becomes hygroscopic and becomes an electrolyte to corrode the aluminum member. In addition, removal by hot water or acid always involves waste liquid treatment for pollution reasons, which causes a high cost. Also, in order to braze one heat exchanger, 100 to 400 g of flux must be used, which causes higher cost.

Recently, in order to improve the above-mentioned drawbacks, a flux consisting only of fluoride, for example, AlF ₃ 53 to 55 wt% and a balance of KF (British Patent No. 1055914) and KAlF ₄ 65.6 to 99.9 wt%, the balance of A flux composed of K ₃ AlF ₆ (Japanese Patent Publication No. 58-27037) has been developed and put into practical use. In particular, the KAlF ₄ -K ₃ AlF ₆ flux has a very high activity, so a smaller amount than the above chloride-based flux has the effect of destroying the oxide film, and even a smaller amount if brazing in a non-oxidizing atmosphere, The amount of flux used is 10 to 30 g per heat exchanger, and even if the flux residue after brazing is left as it is, it does not absorb moisture and does not cause corrosion, so the flux removal treatment can be omitted. is there.

However, this flux has a drawback that the production thereof is difficult and the cost is high. For example
According to Japanese Patent Laid-Open No. 58-27037, a mixed flux of KAlF ₄ and K ₃ AlF ₆ is manufactured by melting AlF ₃ and KF and then pulverizing it. The material of the container is limited due to the erosion. In the above publication, a crucible made of graphite is used, but the graphite crucible is not preferable because the graphite crucible has a phenomenon of leaking to the outside. Further, a porcelain crucible made of alumina (Al ₂ O ₃ ) or the like is not corroded so much, but has a short life because it is brittle, and is destroyed by using it a few times. Further, since the flux which was melted and solidified was in the form of flakes, it was necessary to carry out a pulverization step for making it into powder.

The AlF ₃ -KF flux is Al
It is a mixture of F ₃ and KF, but the cost is low, but KAlF
_The brazing property was inferior to that of the _4- K ₃ AlF ₆ flux.

In view of this, the present inventors have made various studies,
We have developed and proposed a flux for brazing an aluminum member, which is easy to manufacture, inexpensive in cost, and has brazing properties similar to those of the above KAlF ₄ -K ₃ AlF ₆ flux in a non-oxidizing atmosphere. This flux has a purity of 95 wt
% Or more of potassium pentafluoroaluminate hydrate (K
₂ AlF ₅ · H ₂ O), hydrofluoric acid (HF),
It is easily and cheaply produced by chemically synthesizing aluminum hydroxide [Al (OH) ₃ ] and potassium fluoride (KF).

[0009]

However, although these fluoride-based fluxes can obtain good brazing properties in brazing in a non-oxidizing atmosphere, they are not always good in torch brazing in the atmosphere. There was a drawback that brazeability was not obtained.

[0010]

The present invention SUMMARY OF] As a result of various investigations in view to this, the aluminum member bets in the air - a method of joining by ozocerite with, which was significantly improved brazeability, K ₂ AlF ₅ or K ₂ AlF ₅ · H ₂ O 5
It is characterized by using a flux containing ~ 95 wt% and the balance KAlF ₄ .

[0011]

In other words, according to the present invention, K ₂ AlF ₅ or K ₂ AlF ₅
H ₂ O and KAlF ₄ are mixed, or aqueous fluoroaluminic acid (HAlF ₄ , H ₂ AlF ₅ , H ₃ Al
F ₆ ) and a potassium compound are mixed in an appropriate blending quantity and a flux easily obtained by chemical synthesis is used. This flux has suitable reactivity for torch brazing, and the torch in the air is used. The brazing property can be remarkably improved.

However, K ₂ AlF ₅ in the above flux
Or, the content of K ₂ AlF ₅ · H ₂ O is limited to the range of 5 to 95 wt% because the torch brazing property in the atmosphere is remarkably deteriorated even if it is less than 5 wt% or exceeds 95 wt%. This is because

The K ₂ AlF ₅ used in the present invention is obtained by mixing HF solution, KF and Al (OH) ₃ in an appropriate amount.
Those which are easily obtained by chemical synthesis, H ₂ O of 1 molecule K ₂ AlF ₅ is stable in the remaining _{K 2 AlF 5 · H 2 O} ( this state as water of crystallization by final drying conditions ), The same torch brazing property as K ₂ AlF ₅ can be obtained.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples. As shown in Fig. 1, the thickness of JIS3003 is 1.2 mm.
The Al plates (1a) and (1b) are butt-joined in a T shape, and JIS4047 (Al-12wt% Si alloy) is attached to one side of the joint.
Place the aluminum alloy brazing filler metal (2) with a diameter of 1.5 mm,
Apply a 40% aqueous solution of the flux shown in Table 1 to the above-mentioned joint and aluminum alloy brazing filler metal (2) with a brush, apply oxygen-acetylene combustion gas with a torch and braze it I checked the attachability. The results are also shown in Table 1. The brazing property is good when the brazing material flows sufficiently to the opposite side and the fillets are evenly formed on both sides, and when the brazing is uneven, the brazing does not turn to the opposite side at all. The case was disallowed.

[0015]

[Table 1]

As is clear from Table 1, the joining method No.
It can be seen that in Nos. 1 to 6, the torch brazing property in the atmosphere is good, and the brazing around is good. On the other hand, the comparative joining method N in which the composition of the flux used is out of the range specified in the present invention
Nos. 7 to 8 and No. 9 using the flux of K ₂ AlF ₅ · H ₂ O alone proposed above and the torch brazing of the conventional joining methods No. 10 to 12 all have poor or impossible brazing properties. It is understood that the torch brazing property is inferior to that of the present invention.

[0017]

As described above, according to the present invention, the brazing property can be remarkably improved in the torch brazing in the atmosphere, and it is practically used in the brazing in the condenser-core of the air conditioner. A bonding rate of 97% or more is required from the viewpoint of upper thermal efficiency, and it was extremely difficult to clear this by conventional torch brazing using a fluoride-based flux, but according to the bonding method of the present invention, It has an industrially remarkable effect such as easy clearing.

[Brief description of drawings]

FIG. 1 is a perspective view before brazing of a T-shaped joint material for examining torch brazing properties in the atmosphere.

[Explanation of symbols]

 1a 1b Aluminum plate 2 Brazing material

Claims (1)

[Claims] 1. A method of joining aluminum members by torch brazing in air, comprising the steps of K ₂ AlF ₅ or K ₂ Al.
A method for joining aluminum members by torch brazing, characterized in that a flux containing ₅ to 95 wt% of F ₅ · H ₂ O and the balance of KAlF ₄ is used.