JPS6010792B2 - How to apply metal tubes - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of coating a metal tube.

For metal pipes, such as cast iron pipes, baking paint such as epoxy resin paint is usually used for the inner surface coating, and a metal that is electrochemically less base than the base material of the cast iron pipe is used for the outer surface coating, based on so-called galvanic pmtection. For example, paints containing zinc, so-called zinc-rich paints, are used.

However, in the substructure, the internal and external coatings are performed in separate processes, which is disadvantageous in terms of work efficiency.

For this reason, it is required to perform the above-mentioned internal and external coatings at the same time, but for internal coating, the metal tube must be heated to a high temperature of 150 to 350 degrees Celsius to enable the paint to smudge. There is a problem in that even if the zinc-rich tint is applied at such high temperatures, a satisfactory coating film cannot be formed.

In other words, there are solvent-based and water-based zinc rich paints, but when applied to a substrate at a high temperature of 150 to 350 degrees Celsius,
Solvent or water evaporates rapidly from the paint, and binder film formation progresses before the zinc powder and resin binder are combined, making it impossible to avoid problems such as uneven distribution of the zinc powder on the substrate. Thermal spraying is a well-known method for coating metal pipes with zinc, and according to this method, the higher the temperature of the substrate, the better the adhesion of the zinc coating, and the above-mentioned problems with zinc-rich vents can be solved.

However, if the inner surface of the metal pipe is coated with zinc at the same time as the outer surface coated with zinc by thermal spraying, the sprayed zinc powder that is sprayed on the outer surface of the tube end will invade the inner surface of the tube end, causing competition on the inner surface of the tube end. When zinc powder is mixed into the coating film, pinholes occur in the coating film, which inevitably deteriorates the quality of the coating film. The coating method for metal pipes according to the present invention is a method that makes it possible to perform baking coating on the inner surface of the tube and spraying zinc on the outer surface of the tube at the same time without the above-mentioned problems. The metal tube is coated with a metal that is electrochemically more base than the metal tube base material, and then the metal tube is heated and the inner surface of the metal tube is coated with a dazzling coating. This method is characterized by spraying the electrochemically base metal.

The present invention will be explained below with reference to the drawings.

The present invention can be applied to metal tubes made of various materials, but the following:
The described embodiment relates to cast iron pipes and uses zinc as the electrochemically base metal.

To carry out the present invention, first, as shown in FIG. 1, the outer surfaces of both ends of a cast iron pipe 1 are coated with zinc 2.

This coating material is made of cast iron pipe with 150%
A zinc powder mixed paint can also be used as long as it does not cause quality deterioration in the coating film even when heated to 350 to 0. Zinc is usually coated by thermal spraying. Also, the length 1 of the pipe end to be coated is usually 50
〜100 佽. After coating the outer surface of both ends of the cast iron pipe with zinc, the metal pipe is heated to 150 to 350 o'clock, and while the heated cast iron pipe is rotated, resin 3 is coated on the entire inner surface of the pipe 1, as shown in Fig. 2. At the same time, zinc 20 is applied by thermal spraying to the remaining portion 10 of the outer surface of the tube excluding the above-mentioned both ends. For competitive painting of the inner surface of the tube, a powder coating machine is used, in which a long arm a2 that is inserted into the tube is supported on a cart a, and a resin powder spray nozzle a3 is attached to the tip of the arm a2. During painting, the nozzle a3 is moved into the pipe 1 by running the truck a.

For the zinc spraying on the outer surface of the pipe, flame spraying methods such as a gas wire method, a powder method, and a crab wire method can be used.

The method of coating metal pipes according to the present invention is as described above. When baking the inner surface of the tube and spraying zinc on the outer surface of the tube at the same time, the outer surfaces of both ends of the tube are coated with zinc in advance, and then When painting at the same time, there is no need to spray zinc on the outer surface of both ends of the tube, so it is possible to prevent zinc powder from getting mixed into the baked coating on the inner surface of the tube end, and the quality of the late-applied coating can be ensured.

Therefore, according to the present invention, baking painting of the inner surface of the metal tube and painting of the outer surface by zinc spraying can be performed simultaneously, and the efficiency of the painting work can be improved. The zinc coating on the outer surface of both ends of the metal tube has a coating area of 4.
Despite the fact that zinc coating occupies a small proportion of the total painting time, work efficiency can be sufficiently improved.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are explanatory diagrams for showing the present invention. In the figure, 1 is a metal tube, 2 is a zinc coating on the outer surface of both ends of the tube, 2 is a zinc spray coating on the outer surface of the tube, and 3 is a frosted coating on the inner surface of the tube. 72 of

Claims (1)

[Claims] 1. Coat the outer surface of both ends of the metal tube with a metal that is electrochemically more base than the metal tube base material, then heat the metal tube and bake paint the inner surface of the metal tube, and at the same time coat the outer surface of the metal tube. A method for coating a metal tube, characterized in that the electrochemically base metal is sprayed onto the remainder of the tube except for the two ends.