Internal corrosion-resistant cast iron pipes

Abstract

To simply perform corrosion prevention processing on a socket part of cast iron pipe in a high quality manner.SOLUTION: A zinc rich primer layer 31 covering an entire inner surface of a socket part 13 is formed. A coating film 32 with powdered paint is formed in contact with an inner surface side of the zinc rich primer layer 31. This coating film is set as a surface on an inner surface side.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to the corrosion resistance of cast iron pipes.

Background Art

[0002] In ductile iron pipes mainly used for water pipes, an epoxy resin powder paint with excellent corrosion resistance is applied to the inner surface other than the socket of the joint part. On the other hand, the inner surface of the socket has a complex structure, and in order to ensure the paintability even in such parts, a liquid paint and a powder paint are used in combination and applied.

[0003] For example, in Patent Document 1, a certain area from the socket end of the inner surface of the socket is painted with a zinc-rich primer, a certain area including a part of the inner surface of the socket from the straight pipe part is painted with a powder paint, a solvent-based paint is painted across the boundary between the zinc-rich primer and the powder paint, and further, a topcoat water-based paint is applied to the entire surface of the paint film, thereby proposing a method for preventing corrosion of the inner surface of the socket.

[0004] Also, in Patent Document 2, a method for preventing corrosion of the inner surface of the socket is proposed by applying a zinc-rich powder paint as a primer to the entire inner surface of the socket and applying another powder paint as a topcoat on the paint film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technology described in Patent Document 1, a zinc-rich primer is applied before applying powder coating. However, when the pipe is heated to approximately 200-300°C as preparation before applying the powder coating, the previously applied zinc-rich primer may deteriorate due to the heat, potentially reducing its adhesion to the topcoat water-based paint. To address this, a procedure was required to roughen the surface of the zinc-rich primer after applying the powder coating and before applying the water-based paint to improve adhesion. Furthermore, because the coating area of ​​the zinc-rich primer is limited to a portion of the inner surface of the socket, there was a risk of red rust forming in the area outside the coated area before applying the powder coating, requiring appropriate storage and other measures.

[0007] Furthermore, in the technology described in Patent Document 2, the zinc-rich powder coating used generally has a lower sacrificial anodic effect compared to liquid zinc-rich paint, and if the powder coating is damaged, the corrosion protection effect on the iron substrate of the cast iron pipe may decrease.

[0008] Therefore, the purpose of this invention is to simplify the procedure for corrosion protection of cast iron pipes, including the socket, to enable efficient manufacturing while also providing a high level of corrosion protection. [Means for solving the problem]

[0009] This invention solves the above problems by providing an internally corrosion-resistant cast iron pipe having a zinc-rich primer layer covering the entire inner surface of the socket portion of the cast iron pipe, and having a powder coating layer as the inner surface in contact with the inner surface of the zinc-rich primer layer.

[0010] Furthermore, in this invention, a heat-resistant zinc-rich primer can be selected as the zinc-rich primer used in the zinc-rich primer layer. [Effects of the Invention]

[0011] The internal corrosion-resistant cast iron pipe according to this invention improves the corrosion resistance of the inner surface of the socket before powder coating by applying a zinc-rich primer to the entire inner surface of the socket. Furthermore, because the zinc-rich primer covers the entire inner surface of the socket, a certain degree of corrosion resistance can be ensured even if the powder coating formed on top of it is damaged. Despite achieving these effects, it can be formed with only two layers: a zinc-rich primer layer and a coating layer, thus reducing the number of types of paints used compared to conventional methods and enabling the efficient production of internal corrosion-resistant cast iron pipes.

[0012] Furthermore, by selecting a heat-resistant zinc-rich primer, it is possible to prevent deterioration of the zinc-rich primer due to heat even when the pipe is heated before powder coating. This means that adhesion between the zinc-rich primer layer and the topcoat coating layer can be ensured without roughening the surface of the zinc-rich primer layer. In other words, the roughening process can be omitted, further simplifying the manufacturing procedure. [Brief explanation of the drawing]

[0013] [Figure 1] A cross-sectional view of a cast iron pipe processed according to this invention, showing the insertion end inserted into the receiving end. [Figure 2] 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. [Figure 3] (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. [Modes for carrying out the invention]

[0014] 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.

[0015] 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 insertion portion 12 is not inserted. In this invention, the socket portion 13 refers to the portion other than the straight pipe portion 14 (the area indicated by A). This socket portion 13 includes the area where the rubber ring 20 is fitted (rubber receiving portion 21: the area indicated by C) and the area where the insertion portions 12 of other pipes before and after it are introduced (enlarged diameter portion 22: the area indicated by B). The peripheral edge portion 23 (the 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 is the sum of 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 referred to here includes the insertion 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. There are no particular limitations on corrosion protection of the straight pipe portion 14.

[0016] Cast iron pipes produced by centrifugal casting are preferably used as the target cast iron pipes. The type of cast iron pipe is not particularly limited. In particular, it can be preferably used in cast iron pipes that have multiple irregularities on the inner surface of the socket portion 13, which conventionally required time-consuming corrosion prevention treatment.

[0017] 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 (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)).

[0018] The zinc-rich primer to be used preferably has heat resistance. Specifically, it is preferable that even when heated to about 200°C to 300°C for subsequent powder coating, the zinc-rich primer layer has heat resistance such that the surface modification of the zinc-rich primer layer is negligible. The zinc-rich primer is a liquid composition composed of zinc powder and a resin component. The specific component ratio is not particularly limited as long as corrosion resistance and adhesion can be ensured. For example, as a heat-resistant zinc-rich primer, a composition containing 65% by mass or more and 75% by mass or less of zinc powder and 7% by mass or more and 10% by mass or less of a resin component can be mentioned. Examples of the resin component in this case include a resin mixture containing 10 parts by mass or more and 20 parts by mass or less of an epoxy ester resin and 80 parts by mass or more and 90 parts by mass or less of a butadiene / styrene polymer resin. Further, the zinc powder is not limited to pure zinc, and any powder containing zinc and having a sacrificial anode effect on iron, such as a zinc-aluminum alloy powder or a mixed powder of zinc powder and aluminum powder, may be used.

[0019] The film thickness of the zinc-rich primer layer 31 is preferably 10 μm or more. If it is less than 10 μm, there is a high possibility that insufficient coating will occur at complex inner surfaces. On the other hand, the film thickness is preferably 50 μm or less. If it is too thick, it may be difficult to ensure the watertightness as expected in the design when the rubber ring 20 is fitted or when the insertion port 12 is inserted.

[0020] Furthermore, a powder coating is applied to form a coating film layer 32 on the inner surface side of the zinc-rich primer layer 31 (Fig. 3(c)). When a zinc-rich primer that is not heat-resistant is selected, roughening treatment needs to be performed before applying this powder coating in order to ensure the adhesion of the powder coating. When a heat-resistant zinc-rich primer is used, this roughening treatment can also be omitted and the powder coating can be applied. The range for applying the powder coating to form the coating film layer 32 may be the entire region where the zinc-rich primer layer 31 is formed.

[0021] As the powder coating to be used, the type is not particularly limited as long as the powder coating melts and then cures to form a coating film when the temperature of the pipe is about 200°C to 300°C. For example, an epoxy resin powder can be used. Further, the powder coating may contain other components such as silica sand in addition to the coating material.

[0022] The film thickness of the coating film layer 32 is preferably 100 μm or more. If it is less than 100 μm, there is a risk that the anticorrosion effect cannot be sufficiently exerted. On the other hand, the film thickness is preferably 300 μm or less. If it exceeds 300 μm, it may be difficult to ensure the watertightness as expected in the design.

[0023] The inner surface side of the receiving portion 13 is covered only with two layers of a zinc-rich primer layer 31 and a coating film layer 32, and the coating film layer is arranged on the surface of the inner surface side. For the inner surface anticorrosion cast iron pipe according to this invention, only two types of coating materials are required. Further, when a non-heat-resistant zinc-rich primer is used, the anticorrosion treatment is completed in three steps, and when a heat-resistant zinc-rich primer is used, the anticorrosion treatment is completed in two steps, saving the labor required for the anticorrosion treatment compared to the conventional method and making it easy to manufacture.

Example

[0024] Hereinafter, this invention will be shown more specifically by way of examples. First, the coating materials to be used will be described.

[0025] <Coating material for the first layer (zinc-rich primer layer)> It was applied to the inner surface of the cast iron pipe receiving port (the entire region E). The temperature of the pipe before coating was 60°C, and the target film thickness was 20 μm for coating. (1) Heat-resistant zinc-rich primer Name: "Crimoto Coat WZ-TH" manufactured by Dainippon Paint Co., Ltd., Components: Resin component (7.2% by mass with respect to the total coating material) among which {85 parts by mass of butadiene / styrene polymer resin, 15 parts by mass of epoxy ester resin}, zinc powder (70% by mass with respect to the total coating material) (2) Non-heat-resistant zinc-rich primer Name: "Kurimoto Coat WZ" Manufactured by Dainippon Paint Co., Ltd. Ingredients: Resin components (7.2% by mass of total paint) including {butadiene / styrene polymer resin 100 parts by mass}, zinc powder (70% by mass of total paint)

[0026] <Paint for second layer (paint layer)> The coating was applied to cover the entire area of ​​the first layer that encloses region E. (3) Epoxy resin powder coating Name: "V-PET#1600 Gray F" manufactured by Dainippon Paint Co., Ltd. (epoxy resin powder coating, JWWA G 112 standard product). The pipe temperature before coating was adjusted to 210-220°C. For coating, the heating oven temperature was adjusted to 270-280°C, and the heating time was 30 minutes. The target film thickness was 200 μm. (4) Water-based paint Name: "Kurimoto Coat WR Gaimen" manufactured by Dainippon Paint Co., Ltd. (water-based acrylic paint, JWWA K139 standard product). The pipe temperature before painting was adjusted to 60°C. The target film thickness was 80 μm. (5) Solvent-based paints Name: "Kurimoto Coat NT#100 New Gray" Manufactured by Dainippon Paint Co., Ltd. (Solvent-based two-component epoxy resin paint, JWWA K139 standard product)

[0027] The cast iron pipe used was a ductile iron pipe of nominal diameter 100GX type manufactured by Kurimoto Iron Works Co., Ltd. The first and second layers were formed on this cast iron pipe by combining (1) to (5) as shown in Table 1. In the table, ● indicates the paint used.

[0028] [Table 1]

[0029] Each internally corrosion-resistant cast iron pipe was evaluated as follows. The results are shown in Table 1.

[0030] <Adhesion Test> The test was conducted in accordance with JIS K 5600-5-6 "Cross-cut method". The specific conditions were as follows: First, each painted pipe shown in the examples and comparative examples was prepared for testing. On the painted surface where two layers had formed, 25 grid-like cuts were made with a cutter at 2 mm intervals. A peel test was then performed using cellophane tape, and the condition of the remaining grid was visually classified according to the following criteria. Classifications 0-2 were evaluated as ○, classification 3 as △, and classification 4 as ×. • Classification 0: The edges of the cut are perfectly smooth, and there is no peeling in any of the grid lines. • Classification 1: Small paint peeling at the intersection of cuts. The affected area at the cross-cut does not clearly exceed 5%. • Classification 2: The cut is peeling along the edge of the cross and / or at the intersection. The affected area in the crosscut is clearly more than 5%, but never more than 15%. • Classification 3: The paint film is partially or completely peeling along the edges of the cut, and / or various parts of the eye are partially or completely peeling. The affected area in the cross-cut is clearly more than 15% but not more than 35%. • Classification 4: The paint film is partially or completely peeling along the edges of the cut, and / or several areas are partially or completely peeling. The affected area in the cross-cut section does not clearly exceed 35%.

[0031] <Water resistance test> The tests were conducted in accordance with JIS K 5600-6-1, section 7, "Water Resistance." Specifically, each painted pipe shown in the examples and comparative examples was prepared for testing, immersed in deionized water for 30 days, and then visually evaluated as follows: ○: No rust, △: Spot rust present, ×: Red rust present.

[0032] <Pinhole property evaluation test> Test conditions: The entire painted surface of the painted pipe was inspected visually using a Holiday detector with a brass wire brush-type probe. A voltage of 1000V (JWWA G 112 Epoxy resin powder coating on the inner surface of ductile cast iron pipes for water supply) was applied, and the presence or absence of pinholes was checked. No pinholes were marked with ○, and pinholes were marked with ×.

[0033] <Overall assessment> In Example 1, all tests showed favorable results, confirming that two layers alone provided sufficient corrosion protection. In Comparative Example 1, the evaluation was unfavorable, strongly suggesting that roughening treatment is necessary after forming the zinc-rich primer layer using a non-heat-resistant zinc-rich primer. Comparative Examples 2-4, in which the second layer was formed using water-based or solvent-based paints, all showed insufficient water resistance, indicating that a powder coating layer is necessary when using only two layers for corrosion protection. [Explanation of Symbols]

[0034] 11 tube 12 Insertion port 13 Receptacle 14 Straight pipe section 20 rubber rings 21 Rubber receiving part 22 Expanded diameter part 23 Peripheral area 31. Zinc-rich primer layer 32 Coating layer

Claims

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, A cast iron pipe with internal corrosion protection, 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, a step is taken to form a coating layer of powder coating 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.

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