JPS6043420B2 - Surface treatment material for heat exchangers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface treatment material that imparts corrosion resistance to a heat exchanger that uses fuel gas such as city gas, liquefied gas, and kerosene as a heat source.

Combustion gas from fuels such as city gas, propane gas, and kerosene contains large amounts of nitrogen, oxygen, carbon dioxide, water vapor, and trace amounts of carbon monoxide, sulfur dioxide, nitrogen monoxide, and nitrogen dioxide.

The corrosion phenomenon of the heat exchange surface is caused by water vapor in the combustion gas condensing on the heat transfer surface due to rapid heat exchange, and components in the combustion gas dissolving into the condensed water. After the combustion gas burner is extinguished, the condensed water generated on the heat transfer surface evaporates, resulting in the formation of corrosion products such as metal carbonates, sulfates, and nitrates, which are gas components dissolved in the condensed water, on the heat transfer surface. Precipitate. As this cycle is repeated, corrosion on the heat exchanger surface progresses. Conventionally, S
A Pb-Sn alloy with an n content of about 1% by weight was used, and it was common to coat the surface of the heat exchanger by hot-dip plating.

However, as surface treated materials made of Pb-Sn alloys are used in combustion gas, white corrosion occurs due to repeated cycles of dissolving gas components in dew condensation water and precipitation of corrosion products as described above. Products are formed, and corrosion progresses gradually, causing holes in the heat exchanger surface treatment material, heat exchanger material fabric, and pipes wrapped around the heat exchanger.
There were problems such as the heat exchanger becoming unusable or clogging due to precipitation of corrosion products on the heat exchange fins, resulting in incomplete combustion. The present invention eliminates the above-mentioned drawbacks and provides a surface-treated material that has excellent corrosion resistance against fuel gases such as city gas, liquefied gas, fuel, and kerosene.

That is, the treated material of the present invention is characterized by comprising 0.01 to 4% by weight of river, 0.01 to 15% by weight of Mg, and the balance Sn.

Hereinafter, the present invention will be explained with reference to examples thereof.

First, Al was added in various proportions to molten Sn to create a master alloy, and Mg was added to this to create an Al-Sn-Mg alloy. A test piece was prepared by hot-dip plating this alloy onto a copper plate. Corrosion tests were conducted on these test pieces as follows.

As the corrosive gas, air containing Co, 5%, N0010 pμm and 5020.1 pμm was used. This gas composition was set based on the analysis results of city gas combustion gas used in gas instantaneous water heaters. In addition, as mentioned above, corrosion of heat exchangers is caused by condensation of water vapor in combustion gas.
This occurs due to the addition of a drying cycle, and in order to approximately reproduce this condition, the corrosion test was performed in the gas atmosphere described above, after condensing at 50'C for 1 hour, at 25°C.
The step of drying for 3 hours was defined as one cycle, and these cycles were repeated.
Figure 1 shows the Mg content of A1-Sn-Mg alloy at 1% by weight.
The relationship between the A1 content when changed to 5% by weight and 10% by weight and the amount of corrosion after 20 cycle tests under the above test conditions is shown.

Note that the amount of corrosion is expressed as an increase in amount due to corrosion. From Figure 1, it can be seen that N-Sn contains more than the amount of N normally contained as an impurity, that is, N-Sn with an A1 content of 0.01% by weight or more.
It can be seen that the -Mg alloy has improved corrosion resistance as the A1 content increases.

Furthermore, as the Mg content increases, corrosion resistance tends to deteriorate. Figure 2 shows alloy A consisting of 1% by weight N, 1% by weight Mg, and the balance Sn, and the conventional surface treatment material Sn.
The amount of corrosion is compared when Pb-Sn alloy B having a content of 1% by weight was tested in the same manner as above.

From FIG. 2, it can be seen that alloy A of the present invention has significantly better corrosion resistance than conventional product B. Next, 5% by weight of A
A1-Sn- consisting of 1 and 1% by weight of Mg and the balance Sn
After hot-dipping Mg alloy A'' and conventional alloy B onto a copper-based heat exchanger, the heat exchanger was installed in a gas instantaneous water heater and operated under normal operating conditions.

The results are shown in Figure 3. From Figure 3, it can be seen that the surface treated material A'' of the present invention has significantly higher corrosion resistance than conventional surface treated materials. Figure 4 shows the N content in the NxSn-Mg alloy and Shows the relationship between melting points.

From FIG. 4, it can be seen that increasing the Al content increases the melting point. Copper is generally used as the base material for heat exchangers, but when hot-dipping a surface treatment material onto a copper base, there are problems such as the copper softening and deforming if the temperature of the molten surface treatment material exceeds 600'C. Therefore, in consideration of safety, it is desirable to use a surface treatment material with a melting point of 55 (s) or lower. Considering this point, as shown in FIG. 4, the Al content of the surface treatment material of the present invention needs to be 40% by weight or less. On the other hand, increasing the Mg content tends to increase the amount of corrosion, and considering that Mg is more expensive than A1 and Zn, Mg, which is usually included as an impurity,
The content is desirably 0.01% by weight or more and 15% by weight or less. That is, a material consisting of 0.01 to 4 weight percent N, 0.01 to 15 weight percent Mg, and the balance Sn is suitable as a surface treatment material for a heat exchanger.

Conditions that a surface treatment material for a heat exchanger should have include good corrosion resistance, good thermal conductivity, and a somewhat high melting point.

Comparing the thermal conductivity of the surface treated material of the present invention with that of the conventional surface treated material, the conventional product has a thermal conductivity of 26% at 250°C.
~30Kca1/M. hr·°C, whereas the product of the present invention has a heat resistance of 50 to 160 Kcal/m-Hr·°C, which is about 2 to 5 times larger than that of the conventional product.

As described above, the surface-treated material of the present invention has superior corrosion resistance and higher thermal conductivity than conventional surface-treated materials, and has excellent characteristics as a surface-treated material for heat exchangers.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between A1 content and corrosion amount of N-Sn-Mg alloy, FIGS. 2 and 3 are diagrams comparing the corrosion amount between the surface treated material of the present invention and a conventional product, Figure 4 shows N-Sn
- Shows the relationship between A1 content and melting point of Mg alloy.

Claims (1)

[Claims] 1 0.01-40 weight Al and 0.01-15 weight M
A surface treatment material for a heat exchanger characterized by comprising g and the remainder Sn.