JP-7856463-B2 - Internal corrosion-resistant cast iron pipes

Inventors

• 冨田 直岐
• 明渡 健吾
• 柳谷 仁志
• 安東 尚紀

Assignees

• 株式会社栗本鐵工所

Dates

Publication Date

20260511

Application Date

20220329

Claims (2)

1. A cast iron pipe having a socket at one end and a receiving end at the other end into which the socket can be inserted, An internally corrosion-resistant cast iron pipe having a zinc-rich primer layer made of a liquid heat-resistant zinc-rich primer covering the entire inner surface of the socket portion, and having a coating layer of powder paint as the inner surface in contact with the inner surface of the zinc-rich primer layer.
2. A cast iron pipe having a socket at one end and a receiving end at the other end into which the socket can be inserted, A step of forming a zinc-rich primer layer consisting of a liquid heat-resistant zinc-rich primer that covers the entire inner surface of the receiving portion, A step of heating the tube to a temperature of 200°C or higher and 300°C or lower. After the heating step, the process involves forming a coating layer of powder paint in contact with the inner surface of the zinc-rich primer layer without roughening the inner surface of the zinc-rich primer layer. A method for manufacturing internally corrosion-resistant cast iron pipes.

Description

This invention relates to the corrosion resistance of cast iron pipes. In ductile iron pipes, primarily used for water supply, the inner surface of the pipe, excluding the joint sockets, is coated with epoxy resin powder coating, which offers excellent corrosion resistance. However, the inner surface of the joint sockets has a complex structure, and to ensure paintability in such areas, both liquid and powder coatings are used in combination. For example, Patent Document 1 proposes a method for preventing corrosion of the inner surface of a socket by coating a certain area from the socket end with a zinc-rich primer, coating a certain area including a portion of the inner surface of the socket from the straight pipe section with powder coating, coating a solvent-based paint across the boundary between the zinc-rich primer and the powder coating, and then applying a water-based topcoat paint to the entire surface of the coating. Furthermore, Patent Document 2 proposes a method for preventing corrosion of the inner surface of a socket by applying a zinc-rich powder coating as a base coat to the entire inner surface of the socket, and then applying another powder coating as a top coat on top of that coating. Japanese Patent Publication No. 2019-158113Japanese Patent Publication No. 2012-30156 A cross-sectional view of a cast iron pipe processed according to this invention, showing the insertion end inserted into the receiving end.This diagram shows an example of a cast iron pipe processed according to this invention, illustrating the region on the inner side of the receiving end.(a) Enlarged view of the surface of the socket, (b) Enlarged view of the surface with the zinc-rich primer layer formed, (c) Enlarged view of the surface with the coating layer formed. The embodiments of this invention will be described in detail below. This invention relates to an internally corrosion-resistant cast iron pipe having a socket portion 12 at one end of the pipe 11 and a receiving portion 13 into which the socket portion 12 can be inserted at the other end of the pipe 11. Figure 1 shows a cross-sectional view of this internally corrosion-resistant cast iron pipe with the socket portion 12 inserted into the receiving portion 13. During joining, the inserted socket portion 12 and the inserted receiving portion 13 are fixed together, ensuring watertightness, as a rubber ring 20 fitted into the receiving portion 13 comes into contact with the outer circumference of the socket portion 12. Figure 2 shows a cross-sectional view of the vicinity of the socket portion 13 of the internally corrosion-resistant cast iron pipe when the socket portion 12 is not inserted. In this invention, the socket portion 13 refers to the portion other than the straight pipe portion 14 (area indicated by A). This socket portion 13 includes the area where the rubber ring 20 is fitted (rubber receiving portion 21: area indicated by C) and the areas where the socket portions 12 of other pipes before and after it are introduced (enlarged diameter portion 22: area indicated by B). Furthermore, the peripheral edge portion 23 (area indicated by D) on the other end side of the rubber receiving portion 21 is also included in the socket portion 13. That is, the area indicated by E, which combines the areas indicated by B, C, and D in the figure, is the inner surface of the socket portion 13. On the other hand, the straight pipe portion 14 here includes the socket portion 12. The internally corrosion-resistant cast iron pipe according to this invention is particularly characterized by corrosion protection of the inner surface of this socket portion 13. The corrosion protection of the straight pipe portion 14 is not particularly limited. Cast iron pipes produced by centrifugal casting are preferably used as the target material. The type of cast iron pipe is not particularly limited. In particular, it is preferably used for cast iron pipes that have multiple irregularities on the inner surface of the socket portion 13, which conventionally required time-consuming corrosion protection treatment. The procedure for applying corrosion protection to the inner surface of the socket portion 13 will be explained with reference to Figures 3(a) to 3(c). Figure 3(a) shows an enlarged view of the socket portion 13 before corrosion protection after casting. Here, the top is the inner surface. A zinc-rich primer is applied to the entire inner surface of the socket portion 13 (the area indicated by E) to form a zinc-rich primer layer 31 (Figure 3(b)). The zinc-rich primer used is preferably heat-resistant. Specifically, it is preferable that the zinc-rich primer layer has sufficient heat resistance so that surface deformation is negligible even when heated to approximately 200°C to 300°C for subsequent powder coating. The zinc-rich primer is a liquid composition consisting of zinc powder and a resin component. The specific component ratio is not particularly limited as long as