JP2015101041A - Inner surface corrosion protected cast-iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner surface corrosion protected cast-iron pipe whose inner surface corrosion protection of straight-tube type cast-iron pipe is easily achieved while suppressing the increase of pH of passing water.SOLUTION: The inner surface corrosion protected cast-iron pipe is subjected to corrosion protection by coating a solventless type epoxy resin coating to the inner surface of a straight section formed between an insertion port and a socket port in a straight-tube type cast-iron pipe, to form a coat film. When a cast-iron made by centrifugal casting is used as the object cast-iron pipe, it can be suitably used since the unevenness occurring on the inner surface during centrifugal casting can be leveled out. The type of cast-iron pipe is not particularly limited to, but a general type ductile cast-iron pipe or the like can be used.

Description

  The present invention relates to anticorrosion of a straight cast iron pipe.

  Cast iron pipes have higher strength than resin pipes and are widely used for water pipes including trunk water pipes. However, since it is made of cast iron, it will be corroded as it is cast, so it should be used after the anticorrosion treatment has been performed on both the outer and inner surfaces, including the joints.

  Of these, straight pipes are often manufactured by centrifugal casting mainly because of their ease of manufacture. However, the inner surface is not completely cylindrical, and it is inevitable that fine irregularities occur. If this unevenness remains, resistance is generated to the water to be passed and the water pressure is lowered. Therefore, it is desirable to make the inner surface as smooth as possible. For this reason, a method (for example, Patent Document 1, nominal diameter φ 50-1500 pipe) of applying an epoxy resin powder coating after polishing and smoothing the inner surface of the straight portion, or a method of performing mortar lining on the inner surface of the straight portion (for example, Patent Document 2, nominal diameter φ75 to 2600).

  On the other hand, as described in Patent Document 3, an epoxy resin powder coating is applied to the inner surface of a curved portion in a deformed pipe manufactured by pouring casting because the structure cannot be centrifugally cast.

JP 2011-72966 A JP-A-9-276794 JP 11-276949 A

  However, since a large-scale heating furnace is required to perform powder coating as in Patent Document 1, a burden on manufacturing is large. On the other hand, when mortar lining is performed as in Patent Document 2, cracks may occur on the surface, and the pH of water flow may increase due to the influence of the mortar covering the inner surface.

  Therefore, an object of the present invention is to carry out the inner surface anticorrosion of a straight pipe type cast iron pipe more easily while suppressing the pH increase of water.

  The present invention solves the above-mentioned problems by providing an inner surface anticorrosion cast iron pipe in which a coating film made of a solventless epoxy resin paint is formed on the inner surface of the direct iron portion of a straight pipe type cast iron pipe.

  By applying a solventless epoxy resin coating to the direct iron part that is not polished or mortar-lined, the anticorrosion work can be simplified and the construction period can be shortened. In addition, since the solvent does not evaporate, a heating furnace is not necessary, the storage period for evaporating the solvent in advance can be omitted, and the anticorrosive cast iron pipe can be used immediately after the resin has solidified. .

  In addition, scales are less likely to adhere as compared to cast iron pipes using mortar lining, odors are less likely to remain, pH increase in water flow can be prevented, and residual chlorine can be reduced.

Cross section showing the outline of straight pipe Axial sectional view showing the first coating method Radial cross section of the tube in the first coating technique Conceptual diagram of mixing procedure of solvent-free epoxy resin paint in the first coating method Axial sectional view of the second coating method

Embodiments of the present invention will be specifically described below.
In the present invention, a solventless epoxy resin paint is applied to the inner surface 13a of the straight portion 13 formed between the insertion port 11 and the receiving port 12 in the straight pipe type cast iron pipe 1 as shown in FIG. This is an inner surface anticorrosion cast iron pipe that has been subjected to anticorrosion processing by forming a coating film. When a cast iron pipe by centrifugal casting is used as the target cast iron pipe 1, unevenness generated on the inner surface during centrifugal casting can be leveled, which can be preferably used. The type of cast iron pipe is not particularly limited, and a general ductile cast iron pipe or the like can be used.

  The solventless epoxy resin paint includes at least an epoxy resin as a main component and a curing agent. In addition, pigments, fillers, and other additives may be included. However, the content of the solvent in which the main agent is dispersed is 1% by mass or less, preferably below the observation limit.

  The epoxy resin needs to be a liquid having a viscosity of 1000 mPa · s to 4500 mPa · s. As specific compounds, for example, epoxy resins such as bisphenol A type, bisphenol F type, novolac type, alicyclic type, glycidylamine type, and hydrogenated bisphenol A type can be used as the main agent. In addition, if necessary, C12 or C13 alkyl, polyethylene glycol, polypropylene glycol, neopentyl glycol, 1,6-hexanediol, glycidyl ether such as trimethylolpropane, xylene resin, petroleum resin, acrylic resin, Resin such as polyester resin, alkyd resin, polyimide resin, monoglycidyl ether, dioctyl phthalate, benzyl alcohol, etc. Can do.

  The curing agent is a compound that causes the epoxy resin to undergo a curing reaction. Specific compounds include polyamidoamines, epoxy resin amine adducts, aliphatic polyamines, modified polyamines, aromatic amines, tertiary amines, hydrazides, dicyandiamides, imidazoles, acid anhydrides, ketimines, acid-terminated polyester resins, phenol resins. , Urea resin, resol resin, amino resin, isocyanate, blocked isocyanate, and the like can be used alone or in combination.

  The filler and the pigment are materials that are added for ensuring the thickness of the coating film or imparting color. Specific compounds include silica, alumina, calcium carbonate, barium sulfate, magnesium oxide, talc, magnesium hydroxide, boron nitride, zinc oxide, titanium oxide, carbon black, mica, phthalocyanine blue, iron oxide, sulfur oxide, etc. They can be used alone or in combination.

  As said other additive, a thickener, a thixotropic agent, a coloring agent, a flow control agent, a catalyst, a hardening accelerator, an antifoamer, antioxidant, a ultraviolet absorber etc. can be used.

  The method of coating the cast iron pipe 1 with a solventless epoxy resin paint mixed with these is not particularly limited as long as smoothness can be ensured. For example, there is a method of coating while moving and rotating the cast iron pipe 1 (in the notation, the insertion port 11 and the receiving port 12 are omitted) by a method as shown in FIGS.

  In the method shown in FIGS. 2 and 3, the injection nozzle 6 for injecting the solvent-free epoxy resin paint 5 onto the inner surface 13a of the cast iron pipe 1 is set near the axial center of the cast iron pipe 1 and directed downwardly from the inner surface 13a. And spray. The cast iron pipe 1 is placed on two sets of rotating rollers 21 that are installed on a carriage 2A that moves the cast iron pipe 1 in the axial direction and that have an axis parallel to the axial direction of the cast iron pipe 1. . The cast iron pipe 1 is rotated by the rotation of the rotating roller 21, and the solventless epoxy resin coating 5 sprayed downward from the vicinity of the shaft center is applied to the entire circumference of the inner surface 13a. In addition, the carriage 2 </ b> A itself moves on the rail 22 arranged in the axial direction, so that the entire circumference of the inner surface 13 a can be applied over the entire straight portion 13.

  The solventless epoxy resin coating 5 supplied to the spray nozzle 6 includes a resin transport pipe 61 for introducing the epoxy resin 51, a curing agent transport pipe 62 for introducing the curing agent 52, a filler transport pipe 63 for introducing the filler 53, Additive transport pipes 64 for introducing other additives 64 are separately arranged in parallel with a length exceeding the entire length of the cast iron pipe 1 and introduced from a tank (not shown) outside the pipe. The mixture is prepared by a screw mixer 65 immediately before the injection nozzle 6 to prepare the solvent-free epoxy resin paint 5 and then injected from the mixing / transporting pipe 7 by the injection nozzle 6. This is because the curing starts with mixing with the curing agent 52, and therefore it is necessary to mix as soon as possible before the injection.

  Furthermore, in this invention, the silica sand 3 may be mixed together with the solventless epoxy resin paint 5 and applied to the inner surface 13a. By mixing silica sand, the thickness of the coating layer can be easily secured, and the smoothness of the plane can be further improved.

  The silica sand to be supplied is supplied from outside the pipe in the same manner as the transport pipes 61 to 64 described above. In the example shown in FIG. 2, the silica sand 3 is introduced into a hopper 42 placed on a fixed base 41 outside the pipe. By rotating the blades 43 in the hopper 42 and the screw conveyor 4 longer than the pipe length by the motor 44, the silica sand 3 is placed on the screw conveyor 4, and the inner surface of the pipe from the drop opening 45 at the tip of the screw conveyor 4. 13a. The drop opening 45 and the injection nozzle 6 are adjacently inserted in the vicinity of the center of the pipe, and the solvent-free epoxy resin paint 5 and the silica sand 3 are introduced while rotating the rotating roller 21 and moving the carriage 2A in the axial direction. By doing so, these can be mixed and applied to the inner surface 13a.

  Regardless of the presence or absence of the silica sand 3 described above, if the thickness of the protective layer coated with the solventless epoxy resin paint 5 is 300 μm or more, the inner surface 13a can be sufficiently protected against corrosion, and the unevenness caused by centrifugal casting can be sufficiently prevented. It can be leveled. Preferably it is 500 micrometers or more. However, it is easier to ensure the thickness by coating with silica sand 3. On the other hand, the coating thickness exceeding 800 μm is excessive for protecting the inner surface 13 a, so the thickness may be 800 μm or less.

  Before applying the solventless epoxy resin paint 5, a primer may be applied to the inner surface 13a of the cast iron pipe 1 as necessary. The primer increases the affinity of the solventless epoxy resin paint 5 for the inner surface 13a. The thickness is preferably 30 μm or more. On the other hand, even if the coating thickness exceeds 100 μm, the meaning as a primer is almost lost, so it may be 100 μm or less.

  As another embodiment, instead of moving the cast iron pipe 1 in the axial direction by the carriage 2A, a series of devices from the hopper 42 to the drop opening 45 and a series of devices from the transport pipes 61 to 64 to the injection nozzle 6 are provided. The carriage 2B may be moved in the axial direction. A cross-sectional view of this embodiment is shown in FIG. While the cast iron pipe 1 is rotated by the rotating roller 21, the carriage 2 </ b> B can be moved along the rail arranged in the axial direction, and can be applied to the entire inner surface 13 a from the injection nozzle 6 and the drop opening 45.

Hereinafter, the present invention will be specifically described with reference to examples of the present invention.
Nichika Co., Ltd .: NT-JW NS (F) (epoxy resin: as a solvent-free epoxy resin paint that mixes a hardener and epoxy resin with a screw mixer on the inner surface of a ductile cast iron pipe of φ1500 × length 6 m Curing agent = 2: 1 (volume ratio) was applied so as to have an average thickness of 550 μm. For the coating, a device in which the screw conveyor for silica sand and the dropping port were omitted from the apparatus of FIG. 2 was used.

  When the inner surface was confirmed after coating, a uniform coating film in which the resin was sufficiently cured was formed. A pinhole test was performed using a pinhole detector (voltage of 1200 to 1500 V), but no defects that generated sparks were found. Furthermore, although the coating film was picked up using a steel double-edged spatula, it was not easily peeled off. Also, no odor was observed during storage.

DESCRIPTION OF SYMBOLS 1 Cast iron pipe 2A, 2B Carriage 3 Silica sand 4 Screw conveyor 5 Solvent-free type epoxy resin paint 6 Injection nozzle 7 Mixing transport pipe 11 Insertion port 12 Receptacle 13 Direct part 13a Inner surface 21 Rotating roller 22 Rail 41 Fixing base 42 Hopper 43 Blade 44 Motor 45 Drop port 51 Epoxy resin 52 Hardener 53 Filler 54 Additive 61 Resin transport pipe 62 Hardener transport pipe 63 Filler transport pipe 64 Additive transport pipe 65 Screw mixer

Claims (2)

  Inner surface anticorrosion cast iron pipe with inner surface of straight pipe type cast iron pipe covered with paint film by solvent-free epoxy resin paint.   The inner surface anticorrosive cast iron pipe according to claim 1, wherein the coating film contains silica sand.

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