JPS5845343A - Surface treating material for heat exchanger - Google Patents

Abstract

PURPOSE:To obtain a surface treating material for a heat exchanger with superior corrosion resistance and high heat conductivity by preparing an Sn-Bi alloy contg. a specified amount of Bi. CONSTITUTION:The surface of a heat exchanger utilizing gaseous fuel such as town gas, liquefied gas or kerosene as a heat source is coated with an Sn-Bi alloy contg. 1-40wt% Bi. The Sn-Bi alloy as a surface treating material has heat conductivity about 2-4 times that of a Pb-Sn alloy, and the hot dipping temp. can be reduced by 50-100 deg.C.

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 and sulfur dioxide.

-Contains nitrogen oxide, nitrogen dioxide, etc. The corrosion phenomenon of the heat exchange surface is caused by components in the combustion gas being dissolved on the heat transfer surface due to rapid heat exchange. After the combustion gas burner is extinguished, the condensed water generated on the heat transfer surface evaporates, resulting in corrosion products such as metal carbonates, nitrates, and sulfates, which are scum components dissolved in the condensed water on the heat transfer surface. Precipitate. Corrosion on the heat exchanger surface progresses by repeating this cycle.

Conventionally, as a surface treatment material for the purpose of rust prevention of heat exchangers used in a combustion gas atmosphere, it is common to coat the surface of the heat exchanger with Snn content 1 positional plating. Ta. However, as the surface treatment material made of Pb-8n alloy is used in combustion gas, white corrosion products are formed due to repeated cycles of dissolving gas components in condensed water and precipitation of corrosion products as described above. is generated. In this way, corrosion gradually progresses, causing holes in the heat exchanger's surface treatment material, heat exchanger material fabric, and pipes wrapped around the heat exchanger, making them unusable, or causing holes in the heat exchanger surface treatment material, heat exchanger material fabric, and pipes wrapped around the heat exchanger, or making them unusable. There were problems such as the heat exchange fins becoming clogged due to the accumulation of corrosion products on the engine and causing incomplete combustion.

The present invention eliminates the above-mentioned drawbacks and provides a surface-treated material with excellent corrosion resistance against combustion gases such as city gas, liquefied gas fuel, and kerosene.

That is, the treated material of the present invention contains 1 to 40% B by weight i4%.
It is characterized by being made of a 5n-Bi gold alloy containing i.

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

First, a mother alloy was prepared by adding Bi in various proportions to molten Sn, and a test piece was prepared by hot-dip plating these mother alloys onto a copper plate.

Corrosion tests were conducted on the test pieces of Jl et al. as follows. As a corrosive gas, CO25%
, NO210ppm and 5o20. Air containing lppm 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, 4 corrosion of the heat exchanger occurs due to the condensation of water vapor in the combustion gas and the addition of a drying cycle.In order to approximately reproduce this condition,
The corrosion test was carried out in the above-mentioned gas atmosphere by condensing at 60° C. for 1 hour and then drying at 25° C. for 3 hours, one cycle of the steno knob, and repeating the kneading cycle.

The relationship between the amount of corrosion and the amount of corrosion after a 36-hour test is shown below. Note that the amount of corrosion is expressed as an increase in amount due to corrosion.

From Figure 1, it can be seen that B exceeds the amount normally contained as an impurity.
those containing i, that is, 5n with a Bi content of 1.0 weight or more
-Bi gold alloy, it can be seen that as the Bi content increases, the corrosion resistance improves.

Figure 2 shows alloy A consisting of 6% by weight Bi and the balance Sn.
and Pb with a S-n content of 1% by weight, which is a conventional surface treatment material.
-8n alloy B [This figure shows a comparison of the amount of corrosion when 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, 5n-Bi consisting of 6% by weight of Bi and the balance Sn
After alloy A and conventional Pb-8n alloy B were each melted into a copper base heat exchanger, this heat exchanger was installed in a gas instantaneous water heater and operated under normal usage conditions. The results are shown in FIG. Thirdly, it can be seen that it has corrosion resistance.

Moreover, FIG. 4 shows the relationship between B1 content and melting point in a 5n-Bi binary alloy. From the figure, it can be seen that as the Venus of Bi increases, the melting point decreases. 1. Generally, copper is used as the base material for heat exchangers, but copper surface II (when the surface treatment material is hot-dipped, the surface treatment material is However, the surface temperature of the heat exchanger is usually around 160°C, and it is desirable to use a surface treatment material with a melting point of 175°C or higher considering safety. From Figure 4, the Bi content of the alloy needs to be 4n weight or less.

From this, 1 to 40% of the weight of Bi and the balance of S
A material consisting of n 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, a suitable melting point, and a not too high melting dip temperature.

Comparing the thermal conductivity of the surface-treated material of the present invention with that of conventional surface-treated materials, the product of the present invention is about 2 to 4 times higher than the conventional product.

Furthermore, when the working temperature of the surface-treated material of the present invention is compared with that of the conventional surface-treated material, the product of the present invention melts at a temperature 50 to 100°C lower than that of the conventional product. This surface-treated material has superior corrosion resistance and higher thermal conductivity than conventional surface-treated materials, making it an excellent surface-treated material for heat exchangers.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the Bi content of the 5n-Bi gold alloy and the amount of corrosion, Figures 2 and 3 are diagrams comparing the amount of corrosion between the surface treated material of the present invention and the conventional product, and Figure 4 is 5 is a diagram showing the relationship between Bi content and melting point of a 5n-Bi gold alloy. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure B4 Total weight (weight t/l,) Figure 2 Trial cycle (1 cycle 4 hours) 0 211) # 6θ θρ 100 /2
θ 14ρ 16ρI length cap depth 57 @ (# and) Fig. 4 β44t (Fushimi weight)

Claims (1)

[Claims] ゛A surface treatment material for a heat exchanger made of a 5n-Bi gold alloy containing 1 to 40 layers of Bi.