JPH0133504B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a heat exchanger made of a copper heat transfer member used in instantaneous water heaters, hot water supply equipment, heating equipment, and the like. Structure of a conventional example and its problems FIG. 1 shows a heat exchanger used in a conventional instantaneous water heater. As shown in the figure, the heat exchanger is composed of a copper heat transfer member including a drum 1 having a combustion chamber inside, a heat exchange tube 2 through which water to be heat exchanged passes, and heat absorption fins 3 provided on the top of the drum 1. is,
Furthermore, this surface is plated with molten metal whose main component is lead. In this configuration, NOx, SOx, CO contained in the combustion exhaust gas, and
CO ₂ , water vapor, and the like condense to produce acidic dew water, which causes severe corrosion of the molten metal plating and the copper base material. When such corrosion occurs, a large amount of corrosion products such as lead carbonate, lead nitrate, and patina are generated, which accumulate on the heat absorption fins 3 and drum 1, obstructing the flow of exhaust gas and causing incomplete combustion. This is unfavorable in terms of health and safety, as the heat exchange efficiency is significantly reduced due to the heat conduction to the water passing through the heat exchange tube 2 becoming worse, and the corrosion products peel off into powder, contaminating the surrounding area. It wasn't. Purpose of the Invention The present invention solves such conventional drawbacks, and improves the durability of the heat exchanger by preventing corrosion of the heat exchanger due to acidic condensation water in which combustion exhaust gas is dissolved. The purpose is to prevent a decrease in heat exchange efficiency and improve the reliability of the device. Structure of the Invention In order to achieve this object, the present invention provides a metal plating layer containing nickel or lead as a main component on the surface of a copper heat transfer member consisting of a drum in which a combustion chamber is formed, a heat exchange tube, and heat absorption fins. A coating layer consisting of a borosiloxane polymer, a titanium organic compound, and a filler having a thermal conductivity of 30 [kcal/m·hr·deg] or more is formed on this plating layer. With this configuration, even if acidic condensation water containing dissolved combustion exhaust gas is generated, the coating layer formed on the surface of the copper heat transfer member can prevent corrosion, thereby preventing incomplete combustion caused by the accumulation of corrosion products. Contamination of the surrounding area due to the scattering and falling of corrosion products can be prevented, and since the heat conduction between the metal plating layer and the coating layer is not impaired, a decrease in heat exchange efficiency can be prevented. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In the figure, numeral 4 indicates a drum heat absorption fin with a combustion chamber formed inside, and a copper heat transfer member of a heat exchange tube.A metal plating layer 5 is formed on the surface of the fin, and a coating layer 6 is further formed on the plating layer 5. . The metal used for the plating layer 5 is nickel or nickel because the operating temperature of the heat exchanger is 250 to 300°C at the highest point, and strong adhesion to the copper heat transfer member 4 is required. A metal whose main component is lead is preferable, and its formation methods include electrolytic, electroless (chemical), and fusion plating. On the other hand, the coating layer 6 is made by using borosiloxane polymer as a binder, and adding and dispersing a titanium organic compound, a filler with a thermal conductivity of 30 [kcal/m・hr・deg] or more, and a solvent such as toluene or xylene. It is formed by turning it into a paint, applying it, and curing it by heating. The titanium organic compound is used for the purpose of low-temperature firing of the borosiloxane polymer, and examples thereof include tetraisopropyl titanate, tetra-normal butyl titanate, and titanium acetylacetonate.
These may be used alone or as a mixture. In addition, the filler having a thermal conductivity of 30 [kcal/m・hr・deg] or more is applied to improve the thermal conductivity of the coating layer 6, and has a thermal conductivity of 30 [kcal/m・hr・deg]. hr・
There are no restrictions on the type of powder as long as the powder has at least 100 degrees, but from the viewpoint of cost and corrosion resistance, graphite powder, aluminum powder, and boron nitride powder can be used, and these powders can be used alone or in combination. . In this configuration, when the gas burner disposed at the bottom of the combustion chamber in the drum 1 of the heat exchanger shown in FIG. , NOx, SOx contained in the combustion exhaust gas,
A highly corrosive acidic condensed water (containing HNO ₃ , H ₂ SO _{4 ,} etc.) with dissolved CO and CO ₂ is produced, and the tip of the endothermic fin 3 reaches a high temperature of 250° C. or higher. Therefore, the tip of the heat absorbing fin 3 becomes high temperature, and the temperature is low at the contact portion of the drum 1 and the heat exchange tube 2 of the heat absorbing fin 3, but condensation of the acidic water, concentration of acid, and evaporation are repeated. This creates an extremely harsh environment, but the borosiloxane polymer used for coating layer 6
It has heat resistance of over 300°C and excellent acid resistance, so it does not deteriorate itself, and the surface is water repellent, and the film is dense, so it can be used as a coating layer for substances that cause corrosion such as acids and water vapor. 6, and excellent corrosion resistance and heat resistance can be achieved. Therefore, corrosion of the plating layer 5 and the copper heat transfer member 4 can be prevented, and the accumulation of corrosion products on the surfaces of the heat absorption fins 3 and the drum 1 is eliminated, thereby preventing incomplete combustion and contamination caused by this. can be prevented, and the safety of combustion equipment can be improved. Furthermore, the thermal conductivity within the coating layer 6 is 30.
Since graphite powder, aluminum powder, and boron nitride powder having a value of more than [kcal/m・hr・deg] are used as fillers, the coating layer 6 can achieve the same level of thermal conductivity as conventional lead plating. Furthermore, since there is no decrease in heat exchange efficiency due to corrosion as in the conventional method, excellent heat exchange efficiency can be maintained over a long period of time. The amount of the filler used in this example is preferably in the range of 30 to 50 wt% based on the solid content of the borosiloxane polymer, from the viewpoint of achieving both thermal conductivity and adhesion of the coating layer 6. The above-mentioned borosiloxane polymer is usually heated at 400℃ in order to achieve excellent corrosion resistance and adhesion as a coating film.
It is necessary to bake at a higher temperature than above, but in this case,
Copper, which is a heat transfer member, undergoes significant oxidation, and this oxide film is extremely brittle, resulting in delamination between the copper heat transfer member 4 and the plating layer 5, and when the copper heat transfer member 4 is in an annealed state. This has the drawback that the mechanical strength is significantly deteriorated, and that a metal material with a low melting point such as lead cannot be used as the metal material for the plating layer 5. Therefore, it is necessary to bake at 300°C or lower, but in this example, by using a titanium organic compound, the coating layer 6 has excellent corrosion resistance, heat resistance, and adhesion even when fired at 300°C or lower. I found out what I can do. This is considered to be because the titanium organic compound promotes the curing reaction (polymerization reaction) of the borosiloxane polymer.
This titanium organic compound can be any of tetraisopropyl titanate, tetra-n-butyl titanate, and titanium acetylacenate, and the amount of these added is 5 to 5 to 15wt%
is desirable. On the other hand, borosiloxane polymer has extremely poor adhesion to copper, which is a heat transfer member, and
Although it was not possible to directly form the coating layer 6 on the surface of the copper heat transfer member 4, this is achieved by providing the plating layer 5 made of nickel or a metal whose main component is lead, which has excellent oxidation resistance, on the surface of the copper heat transfer member 4. It has been found that excellent adhesion with the coating layer 6 can be achieved by this. Next, experimental results showing specific effects of this example will be explained. Heat exchanger (implementation product of the present invention) A Borosiloxane polymer (solid content 50wt%) 100
Graphite powder with weight part and average particle size of approximately 10μm
A paint was prepared by dispersing and mixing 20 parts by weight, 7 parts by weight of tetraisopropyl titanate, and 100 parts by weight of toluene in a ball mill for 24 hours. Next, electroless nickel plating is applied to the surface of the heat exchanger made of the copper heat transfer member shown in FIG.
It was sprayed to a thickness of 15 μm and baked at 280° C. for 1 hour to form a coating layer. Heat exchanger (implementation product of the present invention) B 100 parts by weight of the organosilicon polymer used in heat exchanger A, 10 parts by weight of flaky aluminum powder with an average particle size of about 10 μm, and nitride with a particle size of about 0.4 to 1 μm 10 parts by weight of boron powder and 5 parts by weight of titanium acetylacetonate
A paint was prepared under the same conditions as in heat exchanger A using parts by weight and 100 parts by weight of toluene. Next, on the surface of the heat exchanger used in heat exchanger A, a film thickness of approximately 10 μm was formed using 97 wt% lead and 3 wt% tin.
A coating layer was formed on the lead-tin alloy plating surface under the same conditions as heat exchanger A. Heat exchanger (product of the present invention) C 100 parts by weight of the borosiloxane polymer used in heat exchangers A and B, 10 parts by weight of graphite powder, 10 parts by weight of aluminum powder, 4 parts by weight of isopropyl titanate, and tetra-n-butyl titanate. Prepare a paint using 3 parts by weight and 100 parts by weight of toluene under the same conditions as heat exchanger A, and coat the surface of the nickel-plated heat exchanger used in heat exchanger A with the paint under the same conditions as heat exchanger A. formed a layer. Heat exchanger (sample not implementing the present invention) A. Among the paint compositions of heat exchanger A, a paint that does not contain tetraisopropyl titanate was used in heat exchanger A.
A coating layer was formed on the surface of the nickel-plated heat exchanger used in heat exchanger A under the same conditions as heat exchanger A. Heat exchanger (sample not implementing the present invention) (b) Using the paint used in heat exchanger A, a coating layer was formed on the surface of the heat exchanger that had not been plated under the same conditions as heat exchanger A. Heat Exchanger (Conventional Example) C. As a conventional heat exchanger, a heat exchanger made of a copper heat transfer member shown in FIG. 1 was used, the surface of which was plated with molten lead to a thickness of approximately 10 μm. The heat exchangers A to C and heat exchangers A to C of the present invention described above were incorporated into a gas instantaneous water heater (No. 5 type), and all were burned for 2 minutes under the same conditions.
A combustion experiment was conducted in which the fire was extinguished repeatedly for minutes. The results are shown in the table.

[Table] As seen from the above results, the conventional heat exchanger suffered severe corrosion, but the heat exchanger of this example showed excellent corrosion resistance. Also, in heat exchanger A,
The reason why the coating layer peeled off and the base plating layer corroded was because the paint used to form the coating layer did not contain titanium organic compounds.
This seems to be because the coating layer was not completely cured during baking at ℃ for 1 hour. Furthermore, peeling of the coating layer was observed in heat exchanger B, which is thought to be due to the extremely poor adhesion between the borosiloxane polymer binder and copper. In addition, the heat exchangers A to C of this example exhibited heat exchange efficiency equivalent to that of the conventional heat exchanger of heat exchanger C, and the coating layer of this example had excellent thermal conductivity. I confirmed that there is. Effects of the Invention As explained above, the present invention provides a plating layer with excellent oxidation resistance on the surface of a copper heat transfer member consisting of a drum in which a combustion chamber is formed, heat absorption fins, and a heat exchange tube, and a plating layer with excellent corrosion resistance and heat resistance. Since it forms a coating layer with excellent thermal conductivity, (1) corrosion of the copper heat transfer member is eliminated, greatly improving the durability of the heat exchanger. (2) Accumulation of corrosion products on the drum and heat absorbing fins is eliminated, preventing incomplete combustion and contamination of the surrounding area. (3) The initial heat exchange efficiency can be maintained over a long period of time. It has the following effects.

[Brief explanation of drawings]

FIG. 1 is an external perspective view showing a conventional heat exchanger for an instantaneous water heater, and FIG. 2 is a sectional view of essential parts showing an embodiment of the heat exchanger of the present invention. 4... Copper heat transfer member, 5... Plating layer, 6... Coating layer.

Claims (1)

[Scope of Claims] 1. A copper heat transfer member consisting of a drum with a combustion chamber inside, a heat exchange tube, and heat absorption fins, on the surface of which a metal plating layer containing nickel or lead as a main component and a borosiloxane layer on the surface of the copper heat transfer member. The polymer and titanium organic compound have a thermal conductivity of 30 [kcal/m・hr・
A heat exchanger formed by forming a coating layer consisting of a filler of more than deg]. 2. The heat exchanger according to claim 1, wherein the titanium organic compound comprises at least one of tetraisopropyl titanate, tetra-n-butyl titanate, and titanium acetylacetonate. 3. The heat exchanger according to claim 1, wherein the filler having a thermal conductivity of 30 [kcal/m·hr·deg] or more is comprised of at least one of graphite powder, aluminum powder, and boron nitride powder.