JPH037859B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a water heater using electricity, gas, oil, or solar heat as a heat source. Conventional technology As shown in Fig. 6, this type of water heater conventionally has an iron can body 1 whose inner surface has been enameled, and an insoluble anode 2 disposed at a lower position to provide cathodic corrosion protection (hereinafter referred to as cathodic protection). . Problems to be Solved by the Invention However, the above configuration has the following problems. When the enamel is gradually eroded by the hot water and eventually eluted and the iron base of the can body is exposed, the cathodic protection becomes insufficient, the iron base corrodes, and the hot water turns red. In particular, the elution of this enamel is more pronounced in the upper part of the can where the temperature of the hot water is higher, so that the corrosion-preventing effect of the insoluble anode disposed in the lower part of the can becomes almost negligible, and the corrosion of the iron base becomes significant. In view of the above-mentioned problems, the present invention provides a water heater having an anti-corrosion function in which the anti-corrosion effect of cathodic protection is less reduced even when the enamel is gradually eroded by hot water and eventually eluted to expose the iron base of the can body. It is something. Means for Solving the Problems In order to solve the above-mentioned problems, the water heater of the present invention has an insoluble anode placed in a lower part of the iron can, and a sacrificial anode placed in the upper part of the iron can in an iron can whose inner surface is enameled. The structure was designed to provide cathodic corrosion protection. Effects According to the above configuration, the iron can body is protected from corrosion by cathodic protection using an insoluble anode during the initial period of use when enamel elution is difficult, but as enamel elution progresses, the iron base of the can body is exposed. At the same time, the heat-resistant and corrosion-resistant film on the surface of the sacrificial anode is also eluted, giving the sacrificial anode a corrosion-preventing effect and providing sufficient corrosion protection to the iron can body. Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In FIG. 1, an insoluble anode 4 and a sacrificial anode 5 are installed together on an iron can body 3 whose inner surface has been enameled for cathodic corrosion protection, and a heat-resistant and corrosion-resistant film 6 is provided on the surface of the sacrificial anode 5. In particular, the insoluble anode 4 is disposed at the lower part of the iron can body 2, and is made of platinum-plated titanium wire. The sacrificial anode 5 is placed in the upper part of the iron can body 3 and is made of magnesium, and its surface is coated with metal such as tin or nickel, resin (for example, melamine acrylic resin, epoxy resin) coated on these metal plating, magnesium It is covered with a heat-resistant and corrosion-resistant film 6 such as an anodic oxide film. Water flows into the iron can body 3 through a water supply port 7 provided on the bottom, is heated by a heater 8, and is discharged from a hot water supply port 9 as hot water. In the embodiment shown in FIG. 1, the insoluble anode 4 is placed above the heater 8, but it may be placed below the heater 8. The iron can body 3 of this water heater has a lower end surface 1
Because it is a structure with iron base welded at 0,
In order to sufficiently protect the lower end surface 10 from corrosion, an insoluble anode 4 was placed at the lower part of the iron can body 3, and a sacrificial anode 5 was placed at the upper part of the can body. In particular, the sacrificial anode 5 is placed laterally than directly above the insoluble anode 4. The effectiveness of the present invention was evaluated using an electric water heater shown in FIGS. 1 and 6. This electric water heater has a hot water storage capacity of 360 mm, and has a cover coat (average film thickness of approximately 250 μm) of silicate enamel (approximately 60% SiO ₂ ) and borosilicate enamel (SiO _{2 )} on the inner surface. 36-38%, B ₂ O ₃ 20%) undercoat (average film thickness 200 μm). To prevent corrosion of the water heater, an insoluble anode made of platinum-plated titanium wire is placed at the bottom of the can body to insulate the iron can body and the nickel-plated heater (base material is copper), providing cathodic corrosion protection for both. The corrosion protection potential shows the most noble value regardless of the conductivity of the water quality.
-850mV or less on the enamel of the iron can body (VS.SC
E.), the anti-corrosion voltage and current were adjusted using the heater to satisfy -450mV or less (VS.SCE). We attempted a laboratory simulation of the exposure of iron substrates due to elution of enamel in the market. The experiment involved hanging an iron plate on the inner surface of the enamel can of a water heater to change the exposed area of iron, and the iron plate was electrically connected to the iron can with a lead wire. <Experiment 1> City water (conductivity 100 μs/cm) was placed in the water heater shown in Figure 6, and an iron plate was suspended from the inner surface of the enamel can, which had been cathodically protected (hereinafter referred to as cathodic protection) by an insoluble anode, to expose the iron. The anticorrosion potential was measured by changing the area. The iron plates are electrically connected with lead wires and protected against cathodic corrosion. FIG. 2 shows the transition of the corrosion protection potential due to this cathodic protection. As the iron exposed area increased, the potential shifted towards higher values, and when the iron exposed area reached 500 cm ² , rust formed on the iron plate and corrosion protection became insufficient. <Experiment 2> A magnesium rod (φ19 mm, length approximately 900 mm, material Mg96%-Al3%-
Zn1%) was added to provide cathodic corrosion protection. Heat-resistant and corrosion-resistant coatings include tin (0.4 to 3 μm, average thickness 1.5 μm), nickel (3 to 65 μm, average thickness 25 μm), and magnesium anodic oxide coating (2.5 to 50 μm, average thickness 30 μm).
Figure 3 shows the results of measuring the anticorrosion potential while changing the exposed iron area in a water heater equipped with magnesium rods covered with these films.
In the present invention, rust occurs when the iron exposed area is ^2000cm2 ,
It can be seen that the corrosion protection performance is superior compared to conventional cathodic protection. <Experiment 3> A magnesium rod (φ19 mm, length approximately 900 mm, material Mg96%-Al3
%-Zn1%) for cathodic corrosion protection, and the corrosion protection potential was measured by changing the exposed iron area. Figure 4 shows the results. The combined corrosion protection method using cathodic protection and a magnesium sacrificial anode rod resulted in −0.77V vs. sce for an iron exposed area of 2000 cm ² and rust occurred, whereas the conventional cathodic protection method using only a magnesium sacrificial anode rod was In the method, -0.77V vs. iron exposed area of ^1000cm2 .
sec, and rust occurred. Comparing this result with the results of Experiment 2 described above, it can be seen that the present invention has corrosion protection properties that are relatively similar to the system that combines cathodic protection and an Mg sacrificial anode. <Experiment 4> Water was poured into the water heater shown in Figures 1 and 6, heated, and the 80°C warm water was allowed to stay there for 3 days to observe changes in water quality (PH
value, Mg ²⁺ amount) was measured. An iron plate (exposed area: 500 cm ² ) was suspended from the inner surface of the enamel can of the water heater, which was electrically connected to the iron can with a lead wire. In addition, city water has a pH of 7 and conductivity
A water quality of 100μs/cm is used. The results are shown in the table below. In addition, the conventional cathodic corrosion protection method using only a magnesium sacrificial anode rod has a pH value of 9.0 and a Mg ²⁺
Amount: 6.1 ppm, corrosion characteristics: slight rust occurred.

[Table] It can be seen that the present invention suppresses the elution of magnesium ions. It is presumed that this increases the lifespan of magnesium and extends its service life. The surface of the sacrificial anode is covered with a porous film, so there are pinholes. Dissolution of the anode rod occurs through this pinhole, and a sacrificial anode current is generated. Therefore, cathodic corrosion protection becomes possible. This means that
The anticorrosion potential characteristics shown in Figure 3 can be confirmed from the increase in magnesium ions (anode metal ions) in the water in this experiment. On the other hand, a porous coating with low solubility gradually dissolves and peels off over a long period of time when exposed to hot water, exposing the anode rod. By the time this low-solubility film dissolves and peels off, the iron base is exposed due to melting of the enamel at the top of the can body, so this anode anode rod protects the exposed part of the iron base from corrosion, and the corrosion protection of the top of the can body is also sufficient. This is the translation. Note that when an iron can body whose inner surface is enameled is cathodically protected with an insoluble anode, the enamel does not dissolve, so the anticorrosion effect is maintained for a long period of time. However, if the iron base is exposed due to melting of the enamel, corrosion protection is insufficient, so corrosion protection of the exposed part of the iron base is performed in combination with an anode anode rod. In other words, the purpose of covering the surface of the sacrificial anode with a film is to suppress its dissolution and consumption and to delay the consumption until the time when its anticorrosive effect is truly needed. If there is no film on the surface of the sacrificial anode, the sacrificial anode will begin to melt immediately, and by the time the enamel of the iron can melts and the base material of the iron can is exposed, there will be little left of the sacrificial anode and it will no longer be able to fulfill its original role. This will result in not fulfilling the purpose. <Experiment 5> In order to measure the degree of deterioration of the enamel, the amount of weight loss of the enamel test piece was measured in hot water at 100°C. The results are shown in FIG. The enameled test piece weighs 166g, and the area in contact with water is
It is ^26cm2 . The water used in the experiment had a pH of 7 and electrical conductivity.
100 μs/cm of water. The elution amount of enamel in this water quality is 0.113 mg/cm ² day, which indicates that enamel is gradually eroded by hot water and its components are eluted. Since the environment in which water heaters are used is more gentle than that of this accelerated deterioration test method, the degree of elution is still small, but it is expected that the exposed area of iron will be equivalent to 500 cm ² in about 6 years. Effects of the Invention As described above, the water heater of the present invention provides the following effects. An insoluble anode is installed at the bottom of the iron can whose inner surface has been enameled, and a magnesium sacrificial anode whose surface is covered with a film is installed at the top of the iron can to provide cathodic corrosion protection. The deterioration of the cathodic corrosion protection effect is reduced, and the iron can body remains free of red rust, extending its life. Furthermore, dissolution of the anode rod is suppressed and its lifespan is extended. The reason for this effect is as follows. The iron can body is
When the inner surface is enameled and further cathodically protected with an insoluble anode, the corrosion protection effect is maintained for a long period of time if enamel dissolution does not occur. However, if used for a long period of time in hot water, the enamel will dissolve and the iron base will be exposed, so there is a problem that the anti-corrosion effect of this insoluble anode alone will be limited and red rust will develop over time. The iron base is more exposed in the upper part of the can body, which is exposed to more hot water. Therefore, an insoluble anode that can maintain a long-term anticorrosion effect is placed in the lower part of the can where a heating source such as a heater is placed, and a sacrificial anode is placed in the upper part of the can. If the exposed portion of the iron base is protected against corrosion by using a sacrificial anode, the corrosion protection of the upper part of the can body will be sufficient and red rust will not occur on the iron can body. This has the effect of extending the life of the iron can body. On the other hand, corrosion protection using only a sacrificial anode has the disadvantage of a short lifespan as the anode rod gradually dissolves with use.However, if an insoluble anode is also used for corrosion protection and the surface of the sacrificial anode is covered with a porous film, This has the advantage of suppressing melting of the anode rod and extending its life. This is because a part of the anticorrosive current from the insoluble anode flows into the anode rod and cancels the current generated by the sacrificial anode effect through the porous film (this current causes the anode rod to melt), and the sacrificial anode This is because the surface area was reduced because the surface was porously covered with a film with low solubility. For the above reasons, the lifespan of the iron can body and the anode rod is extended. Furthermore, since magnesium is used as the anode rod, it has an excellent anticorrosion effect and provides safe water quality free from pollution. Further, there is an advantage that the coating with low solubility peels off after a long period of time, exposing the sacrificial anode metal.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of essential parts of a water heater according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of the corrosion protection performance of the cathodic corrosion protection method using an insoluble anode used in a conventional water heater, and Fig. 3 is a diagram of the anticorrosion performance of the cathodic corrosion protection method using an insoluble anode used in a conventional water heater. Figure 4 is a diagram showing the corrosion protection performance characteristics of the corrosion protection method used in a water heater in one embodiment. Figure 4 is a diagram showing the corrosion prevention performance characteristics when another cathodic corrosion protection method is applied to a conventional water heater. Fig. 6 is a characteristic diagram of the amount of weight loss of the enamel used in the water heater of the example in a hot water test, and is a sectional view of the main part of the conventional water heater. 3... Iron can body, 4... Insoluble anode, 5...
Sacrificial anode, 6... Heat-resistant and corrosion-resistant film.

Claims (1)

[Scope of Claims] 1. A water heater in which an insoluble anode and a magnesium sacrificial anode whose surface is covered with a film are arranged in an iron case whose inner surface is enameled. 2. The water heater according to claim 1, wherein the enamel comprises a silicate-based cover coat and a borosilicate-based undercoat. 3. The water heater according to claim 1, wherein the magnesium sacrificial anode is a magnesium alloy containing a small amount of aluminum and zinc.