JPH03291160A - Heat exchanger for hot-water supply - Google Patents

Abstract

PURPOSE:To obtain the heat exchanger which is excellent in low temperature corrosion resistance and to prevent the fin from being closed up by a corrosion product by brazing and joining a tube made of iron and a fin made of Al at a specific temperature through a specific brazing filler metal. CONSTITUTION:A tube 1 made of iron and a fin 2 made of Al are brazed and joined at a temperature of <=570 deg.C through an Al - Si - high Zn compound brazing filler metal 24. In such a way, heat exchanger for hot-water supply in which an intermetallic compound layer of brittle FeAl3, etc., is not generated in the joint interface, or it is suppressed is obtained. Also, by covering the tube 1 with an Ni or Cr layer 7 in advance, generation of the intermetallic compound layer is further suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a heat exchanger for hot water supply used, for example, in bathtubs, instantaneous water heaters, water heaters, and the like.

In this specification, the term iron is used to include not only pure iron but also stainless steel, common steel, and base metal alloys. Furthermore, the term aluminum is used to include aluminum alloys.

BACKGROUND OF THE INVENTION Heat exchangers for hot water supply as described above generally have a configuration in which a plurality of plate-like fins are arranged in parallel in the longitudinal direction of a tube, and heat applied to the surface of the fins by combustion gas is absorbed. The system heats the water by transmitting it to the water flowing inside the tube.

Conventionally, steel materials have been used for the tubes and fins of such heat exchangers for hot water supply. The tube is made of copper because it has good corrosion resistance against water, and the fins are also made of steel because it has excellent thermal conductivity and can maintain sufficient bonding with tubes made of the same material. be.

Problems to be Solved by the Invention However, the heat exchanger for hot water supply in which both the tubes and fins are made of steel has the following drawbacks.

In other words, when the tap water temperature decreases during use, condensation water is generated on the surface of the heat exchanger, and impurities in the combustion gas mix and dissolve in the condensation water, becoming acidic water that corrodes copper (low-temperature corrosion), and its corrosion. The disadvantages were that the products clogged the fins, causing non-combustion, ignition failure, and reduced thermal performance. Furthermore, since the entire structure is made of copper, it has the drawbacks of increased weight and cost.

The present invention has been made in view of this technical background, and an object of the present invention is to provide a lightweight, low-cost heat exchanger for hot water supply that is excellent in low-temperature corrosion resistance and can prevent fin clogging due to corrosion products.

Means for Solving the Problems In order to achieve the above objectives, it is conceivable to construct the tubes and fins with aluminum, which is relatively strong against low-temperature corrosion and lightweight in terms of TL quantity. From the viewpoint of corrosion resistance, it is problematic to use aluminum for the tube. Furthermore, when only the fins are made of aluminum, there is a problem in joining the copper tube and the fins. That is, when mechanically joining a copper tube and an aluminum fin by expanding the tube or the like, the thermal resistance becomes large and heat conductivity decreases, and the joint becomes loose due to repeated use.

Also, direct brazing of copper and aluminum causes erosion.

Therefore, in this invention, the fins are made of aluminum, and the tube is made of iron containing stainless steel, etc., which has relatively good corrosion resistance against circulating water and has good low-temperature corrosion resistance. The idea is to braze the fins together. However, when brazing, when using AQ-8i brazing filler metal, which is used for brazing two materials together, the brazing temperature is 595 to 610℃ because the melting point of the brazing filler metal is generally high. However, if the brazing temperature is high, a hard and brittle intermetallic compound layer such as FeA [3, Fe2 A, Q5, etc. Another drawback is that the joint surface cannot have sufficient strength. Therefore, the heat exchanger for hot water supply according to the present invention suppresses the formation of brittle intermetallic compounds at the joint interface, and brazes an iron tube and an aluminum fin in a state that has sufficient joint strength.

That is, the gist of the present invention is a heat exchanger for hot water supply, characterized in that an iron tube and an aluminum fin are brazed together at a temperature of 570°C or less via an Ap-5i high Zn brazing filler metal. shall be. In this case, Ni or Cr coated on the tube is placed at the joint interface between the tube and the fin.
By interposing a layer, there is a further effect of suppressing the formation of an intermetallic compound layer.

Since the working tube is made of iron such as stainless steel and the fins are made of aluminum, they have excellent low-temperature corrosion resistance.
It can also be made lighter. In addition, A, Q-5i-high Zn brazing filler metal exhibits a low melting point, and since the tube and fin are brazed together at a temperature of 570°C or less using this brazing filler metal, the bonding interface z: is brittle. This provides a hot water supply heat exchanger in which the formation of metal open compound layers such as FeA and Q3 is eliminated or suppressed. Further, by coating the tube with a Ni or Cr layer in advance, the formation of the intermetallic compound layer is further suppressed.

Example Next, this invention will be explained in detail.

In FIGS. 1 to 7, (1) is a tube, and (2) is a plate-shaped fin.

The tube (1) is made of stainless steel such as 5U3304, and has three straight pipe sections (lla) (llb) (IIC) arranged in parallel in the vertical direction, and is meandering. One end of the tube is a water inlet (12) and the other end is a hot water inlet (13).

On the other hand, the plate-shaped fin (2) is made of aluminum. As shown in Figures 6 and 7, this plate-like fin (2) has a tube (1) in its center.
Three sheave insertion holes (21) having a diameter slightly larger than the outer diameter of the tube are arranged in parallel, and a cylindrical fin collar (22) is provided upright on the periphery of each insertion hole (21).

Then, by inserting a plurality of plate-like fins (2) into each straight pipe portion (lla) (Hb) (llc) of the tube (1) in each tube insertion hole (21), the fin collar ( 22), the outer surface of the straight pipe part is covered in a manner parallel to the length direction of the straight pipe part in a manner that continuously covers the outer surface of the straight pipe part. The reason why the outer surface of the straight pipe portion is covered with the fin collar (22) in this way is to provide even better low-temperature corrosion resistance by covering it with an aluminum material. The purpose is also to secure as large a joint area as possible between the fin (2) and the tube (1) to further increase the joint strength. Such a fin (2) has a core made of A3003 alloy etc. (IMb) with one aluminum brazing sheet coated with a brazing filler metal (24) on one side of T1.
j2, and the fin collar (22) is formed with its inner surface facing the brazing metal layer side. The fin collar (22) and the tube (IB) made of stainless steel are brazed together via a brazing filler metal (24). Here, the above-mentioned brazing material is an AΩ-5i-high Zn-based brazing material containing about 0.5 to 12vt% of Si and about 15 to 80vt% of Zn. In this way, by using a high Zn-containing brazing filler metal, it is possible to lower the melting point of the brazing filler metal, which in turn makes it possible to braze at a low temperature without forming a brittle intermetallic compound layer such as FeAQ3, Fe2 AU5, etc. at the bonding interface. Become.

An example of a specific composition of the brazing filler metal is as follows.

That is, basically, S i :0. 5-12wt%
, Zn: 15 to 80 νt%, and the balance is aluminum and unavoidable impurities. In the above, Si is necessary for lowering the melting point of the brazing material and increasing its fluidity. However, if the content is less than 0.5 wt%, there is a risk that these effects will be poor.

On the other hand, if the content exceeds 12 νt%, the melting point will rather increase sharply, and there is a possibility that it cannot be used as a brazing filler metal. A particularly preferred content of Si is 4wt% or more, especially 5 to 8vt%. The Zn is an extremely effective element for lowering the melting point of the brazing filler metal. However, the content is 15νt
If it is less than 80%, there is a risk that the effect will be poor;
If it exceeds vt%, there is a risk that processability will deteriorate. A particularly preferable Zn content is 55 νt% or less, especially 20 to 50
It is about wt%.

In addition, as other high Zn-containing brazing materials, the above-mentioned Si; Zn
In addition to 8e from 1-1.02 to 1. You may use the one containing within the range of Ovt%. Be contributes to improving the mechanical properties such as strength and elongation of the brazing filler metal without impairing the low melting point effect of Si and Zn, and also improves the mechanical properties of the brazed joint after application. It has the effect of improving. However, if it is less than 0.02 νt%, there is a risk that the above effect cannot be exhibited, while if it exceeds 1°Ovt%, the effect will be saturated, which may lead to economic waste.

A particularly preferable range when containing Be is 0.10 to 0.
．． It is 5vt%.

Furthermore, with other high Zn-containing +'f brazing filler metals, the above 5i
In addition to SZn °'C, Cu: 0. 2-2. 0v
You may use the thing containing t%. Cu plays the role of preventing the natural electrode potential after brazing from becoming base due to the high concentration of Zn, and preventing corrosion of the joint by shifting the potential to the noble side. However, if the content is less than 0.2vt%, the above effects may be poor, and if it exceeds 2°0w1%, there is a risk of deterioration in workability. The preferred range when containing Cu is 0.5
~1.5vt%. In addition, when Cu is contained, Be may be contained in an amount of about lvt% or more F, preferably in the range of 0.05 to 1vt%, in order to improve the mechanical properties of the joint.

Furthermore, as another high Zn-containing brazing filler metal, in addition to the above-mentioned St%Zn, I n : 0. 02~0. 2vt%, Sn
: 0.05-0.4vt%, Bi: 0.05-0.
Examples include those containing one or more of 4vt%. In the above, InsSnsBi is an effective element for making the oxide film on the surface weak and defective and achieving good brazing when the molten brazing material spreads during brazing.

All of these are evaluated as equivalent in terms of such effects, and it is sufficient that at least one of them is contained. However, In is less than 0.02wt% and Sn is 0.05wt%.
If the Bi content is less than 0.05 wt%, the above effects may not be exhibited. On the other hand, In exceeds 0.2vt%, Sn exceeds 0.4vt%, and Bi exceeds 0.4vt%.
There is a danger that even if the amount is exceeded, the effect will be saturated, resulting in economic waste. In, 1f of 5nSBf! 11i or 2
A particularly preferable content range when containing tIf or more is I
n: 0.03~0.15vt%, Sn: 0°10~
0.30ν196, Bi: 0.10 to 0.30vt%.

The heat exchanger according to the illustrated embodiment was manufactured as follows. That is, each straight pipe section (
la) (lb) (lc) with plate-like fins (
After 2) is sheathed, the tube is expanded to improve the adhesion between the tube (1) and the fin collar (22). Note that instead of expanding the tube, the insertion hole (21) of the plate-shaped fin (2) may be formed to have a slightly smaller diameter, and the fin may be press-fitted into the tube to bring them into close contact.

Next, a suspension of flux in water or an organic solvent is applied to the finned tube by a dipping method and then dried. The flux may be either chloride-based or fluoride-based, but since the melting point of the brazing filler metal is as low as about 540°C or less, it is desirable that the flux has a melting point of about 500°C or less.

Next, brazing is performed in an atmosphere such as N2 gas, and the brazing temperature must be regulated to 570° C. or less. At brazing temperatures exceeding 570°C, thick FeAU3 is formed at the joint interface between the tube (1) and the plate-like fin (2)
This is because an intermetallic compound layer such as the like is formed, resulting in a decrease in bonding strength. Since this intermetallic compound layer grows over time, it is preferable to keep the soldering time as short as possible within a range that provides good bonding.

In particular, when the brazing temperature is set at a high temperature of 540 to 570°C, the brazing time is preferably 10 minutes or less, preferably 5 minutes or less. By this brazing, the pre-fertilized brazing material (24
) is a fin collar (22) as shown in Figures 4 and 5.
) and the outer circumferential surface of the tube (1) without any gaps, and the two are firmly joined.

Note that (4) shown in FIGS. 1 and 2 indicates that the straight pipe portions (lla) (llb) (
This is the number of brazing parts when the U-shaped connecting part (5) and the L-shaped water supply part (6) are connected to the L-shaped connecting part (5) and the L-shaped water supply part (6) by brazing.

In the illustrated heat exchanger for hot water supply, water flowing in from the water inlet (12) flows along the tube (1), but during this time it is heated by the combustion gas applied to the part where the plate-shaped fins (2) are present. , the water becomes hot water and flows out from the hot water supply port (13).

FIGS. 8 and 9 show other embodiments of this invention,
The outer surface of the stainless steel tube (1) is coated with a Ni or Cr layer (7) in advance by plating or other means, and the tube (1) is coated with a Ni or Cr layer (7) through this Ni or Cr layer (7).
) and the plate-shaped fin (2) are joined by brazing.

In this way, the presence of the Ni or Cr layer (7) suppresses the formation of the A, Q-Fe intermetallic compound layer at the bonding interface, and provides a heat exchanger with even better bonding strength. . In addition, in Figures 8 and 9, Figures 1 to 7
Components that are the same as those in the figures are given the same reference numerals, and their explanations will be omitted.

Incidentally, in order to demonstrate the superiority of the present invention, the following tests were conducted. That is, a tube made of 5US304 and A3
A plate-shaped fin made of an aluminum plating sheet with a thickness of 0.4 mm is used, and one side of the 00B alloy core material is clad with a brazing filler metal layer having various compositions shown in Table 1 at a cladding ratio of 10%. Multiple heat exchangers for hot water supply were assembled. Regarding tube No. 9.10,
The surface was coated with a Ni plating layer and a Cr plating layer. Further, the melting point (liquidus temperature) of the brazing filler metal alone was as shown in Table 1.

Next, each of the heat exchanger assemblies described above was immersed in a suspension of water with a flux having a melting point of 480°C, and then dried, and then heated at the heating temperature shown in Table 1 in an N2 gas atmosphere. The tube and plate-shaped fin were brazed by heating for 5 minutes each.

For the heat exchanger manufactured as described above, the tube was cut and the F at the joint interface between the tube and the plate-like fin was measured.
The presence or absence of an intermetallic compound layer such as eAf13 was examined using a microscope. The results are also shown in Table 1.

[Margins below] As can be seen from the results in Table 1, the formation of an intermetallic compound layer at the joint interface is suppressed in the products implemented in the present invention, whereas the formation of an intermetallic compound layer at the joint interface is suppressed, whereas No.1 used
1, a thick intermetallic compound layer was formed.

In addition, for the implemented products No. 1 to 10 shown in Table 1 and the conventional product where both the tube and plate-like fin are made of copper, 1
When we investigated the occurrence of corrosion by conducting an actual machine test in which 7 minutes of operation and 10 minutes of stopping were repeated 104 times, only a small amount of corrosion products were observed on the fins of the tested product, whereas
In conventional products, corrosion products caused a blockage between the fins. Therefore, it was confirmed that the product according to the present invention is effective against corrosion.

Effects of the Invention This invention is based on the above-mentioned method. First, the tube is made of iron such as stainless steel, which has excellent corrosion resistance against water and low-temperature corrosion resistance, and the fins are made of iron, such as stainless steel, which also has excellent resistance to low-temperature corrosion. Since it is made of aluminum and both parts are brazed together, the heat exchanger as a whole has improved low-temperature corrosion resistance compared to conventional products that are entirely made of copper, and can eliminate concerns about fin clogging. . Furthermore, the fin portion, which accounts for most of the weight of the product, can be made of lightweight and inexpensive aluminum, making it possible to reduce the weight and cost of the heat exchanger. Furthermore, as a brazing material for joining the tube and fin, /J-5i-High Zn
Since a Si type material is used, the melting point of the brazing filler metal can be made much lower than that of conventional A, Q-Si type materials while maintaining good brazing properties. Furthermore, since the brazing filler metal contains a high concentration of Zn, it has good wettability with the iron tube, allowing for good bonding. In addition, after ensuring good brazing properties and lowering the melting point of the brazing material, brazing is performed at a temperature of 570°C or less, so FeAR3 at the joint interface between the tube and the fin is The formation of brittle intermetallic compound layers such as It can be done.

[Brief explanation of drawings]

Fig. 1 is a front view of a heat exchanger for hot water supply according to an embodiment of the present invention, Fig. 2 is a bottom view, Fig. 3 is a side view, and Fig. 4 is a sectional view showing the state of connection between tubes and fins. , Figure 5 is the fourth
6 is a front view of the fin alone, FIG. 7 is a sectional view taken along the ■-■ line in FIG. 6, and FIG. 8 is a state where the tube and fin are joined in another embodiment. FIG. 9 is a sectional view taken along the line IX-IX in FIG. 8. (1)...Tube, (2)...Fin, (24)
...brazing filler metal, (7)...Ni or Cr layer. Figure 6 above

Claims (2)

[Claims] (1) The iron tube and aluminum fin are
- A heat exchanger for hot water supply, characterized in that it is brazed and joined at a temperature of 570° C. or lower via a Si-rich Zn brazing filler metal. (2) The heat exchanger for hot water supply according to claim 1, wherein a Ni or Cr layer coated on the tube is interposed at the joint interface between the tube and the fin.