JPS6214227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of applying rust prevention treatment to the inner surface of an iron heat pipe.

Steel heat pipes can operate in a wide temperature range from low temperatures (70 to 130 degrees Celsius) to high temperatures (200 to 400 degrees Celsius), and are cost-effective compared to copper ones, as well as being stronger. Since it is satisfactory, it has been used in a wide range of applications including exhaust heat recovery equipment. In this type of heat pipe, water is the most suitable working fluid because it has a wide operating temperature range, a high latent heat of vaporization (540 cal/g), and a critical heat flow (109 W/cm ² ). ing.

Prior Art When water is used as the working fluid and the heat pipe container is made of iron, hydrogen gas is generated by the reaction between water and iron. The generated hydrogen gas then diffuses within the walls of the steel container in an atomic state, and some of it is released outside the container at a constant rate, but most of it accumulates in the condensation section inside the container, which improves the performance of the heat pipe. decrease. Conventionally, in consideration of these points, a NaOH aqueous solution, other alkaline aqueous solution, or vanadate aqueous solution was sealed in a container as the working fluid, and a corrosion-resistant coating made of Fe ₃ O ₄ was formed on the inner surface of the container (specially (Refer to Publication No. 86391 of 1983). However, the film formed in this way is not perfect, and a certain amount of hydrogen gas is generated due to corrosion on the inner surface of the container, and the rate of hydrogen gas generation cannot be suppressed below the rate at which hydrogen gas is released outside the container. It was not possible to avoid hydrogen gas accumulating in the container.

Purpose of the Invention The present invention was made in view of the above-mentioned circumstances, and provides a method for rust-preventing iron heat pipes that can completely prevent the generation of hydrogen gas due to the reaction between water and iron. The purpose is to

Structure of the Invention The method for rust-preventing iron heat pipes according to the present invention includes cleaning the inner surface of an iron container with an aqueous solution of an organic acid as a pretreatment when forming a rust-preventing film on the inner surface of the iron container with an aqueous solution of vanadate. It is characterized by the fact that

As the iron container of the heat pipe according to the present invention, a container made of stainless steel, carbon steel, etc. is used.

The outer surface of the iron container may be aluminized for the purpose of imparting corrosion resistance and vacuum brazing with aluminum fins having a brazing layer.

Before cleaning with an organic acid aqueous solution, the inner surface of the container is
Usually, it is degreased with an inorganic acid and then an organic solvent.
It is then polished with a stainless steel brush.

In pretreatment with an organic acid aqueous solution, the organic acid
It is a weak acid in the pH range of 3 to 8, and examples thereof include oxalic acid, citric acid, tartaric acid, and benzoic acid. The concentration of organic acid aqueous solution is usually
It is 0.5-50% by weight. If the amount is less than 0.5% by weight, the cleaning effect will not be sufficient, and if it exceeds 50% by weight, the formation of a film by the vanadate aqueous solution will not be sufficient. The preferred concentration is 1% by weight.

The conditions for cleaning with an aqueous organic acid solution vary depending on the concentration, but the standard conditions are room temperature to elevated temperature and a time of about 10 to 60 minutes.

As a result of cleaning with an organic acid aqueous solution, gentle etching progresses, the oxide film on the inner surface of the container is removed, and the inner surface remains activated. On the other hand, when cleaning is performed using an aqueous solution of a strong inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, the etching performance is so good that an oxide film is formed on the treated surface again after cleaning, and the inner surface is likely to become inert. be.

In the rust prevention film forming treatment using a vanadate aqueous solution, ammonium metavanadate, sodium metavanadate, potassium metavanadate, lithium metavanadate, and the like are often used as the vanadate, but are not limited thereto.
The concentration of vanadate is preferably 0.1% by weight to saturation concentration. If the amount is less than 0.1% by weight, a rust-preventing film of sufficient thickness will not be formed.

An aqueous solution of vanadate can be prepared in advance by dissolving vanadate in deionized water, or it can be prepared in a container by first adding vanadate to the container and then adding deionized water. It may be something you have done. Furthermore, if the vanadate aqueous solution is sealed in a container and then heat treated at a high temperature range of 160 to 200°C, the formation of a rust-preventing film can be promoted.

The water as working fluid is replaced with an aqueous vanadate solution after treatment with the same. Further, the vanadate aqueous solution used in the rust-preventing film forming treatment may be used as the working fluid as it is.

A linear hydrogen permeable member made of palladium or an alloy thereof is provided in a penetrating manner at the condensation side end of the heat pipe container, and is soldered with silver. A small amount of corrosion may occur on the inner surface of the heat pipe container, and a small amount of hydrogen gas may be generated. In this case, the hydrogen gas that has diffused inside the wall of the container is blocked from being released outside the container by the aluminized film formed on the outer surface of the container, but is released to the outside through the hydrogen permeable member. In addition, by using a wire-shaped hydrogen permeable member and protruding into and out of the container, corrosion of the container caused by the battery action between the hydrogen permeable member and the container wall can be minimized. .

Example A pipe made of STB35 steel with an inner diameter of 25 mm, a length of 3000 mm, and a thickness of 4 mm was prepared, and an end wall having a palladium wire extending therethrough was welded to one end to close the same end. Then, only the outer surface of the tube material was aluminized, and the inside was degreased with nitric acid and then acetone, and then the tube material was heated and dried.

After polishing the inner surface of the tube with a stainless steel brush, the tube was soaked in a 1% oxalic acid solution at 50°C.
Soaked for 30 minutes. The tube material was then taken out from the aqueous solution and washed with water.

In addition, an end wall with a working fluid injection nozzle was fixed to the other open end of the tube material by welding to produce a heat pipe container. Next, an aluminum fin having a brazing layer was attached to this container by vacuum brazing, a 0.5% by weight ammonium metavanadate aqueous solution was injected into the container, and the nozzle was closed.
In this way, a heat pipe with fins was manufactured.

For comparison, the same operation as above was repeated except that the washing treatment with oxalic acid was not performed.

After each of the two heat pipes produced in this way was heated at 150° C. for 1000 hours, the temperature difference (ΔT) between the heated part, that is, the evaporation part, and the non-heated part, that is, the condensation part was measured. the result,
In the heat pipe obtained in the example, ΔT was 1° C., and no deterioration in performance due to hydrogen gas generation was observed. On the other hand, in the heat pipe obtained for comparison, ΔT was 3°C.

Effects of the Invention As described above, according to the present invention, when treating the inner surface of an iron container with an aqueous solution of vanadate to form a rust preventive film, the inner surface is cleaned with an aqueous solution of an organic acid as a pretreatment. The vanadate aqueous solution treatment makes it possible to make the rust preventive film formed on the inner surface of the container denser and to significantly increase its weight, resulting in a rust preventive film that does not easily deteriorate over a long period of time. Obtainable.

Claims (1)

[Claims] 1. A method for rust-preventing iron heat pipes, which comprises cleaning the inner surface of an iron container with an aqueous solution of an organic acid as a pretreatment before forming a rust-preventing film on the inner surface of the iron container with an aqueous solution of vanadate.