JPH03150343A - Cast-iron pipe and its production - Google Patents

Abstract

PURPOSE:To form an Al2O3 film on the outside peripheral surface of a cast-iron pipe and to produce the cast-iron pipe excellent in corrosion resistance by previously allowing an Al or Al-alloy film to adhere to the outside peripheral surface of a cast-iron pipe and then carrying out annealing at the time of annealing a cast-iron pipe. CONSTITUTION:Molten cast iron is poured through a pouring spout 2 into a mold 1 while rotating the mold 1 at high speed, by which a cast-iron pipe 3 is cast on the internal surface of the mold 1 by means of centrifugal force. An arm 6 is inserted into the cast-iron pipe 3 via a core 7 and turned to draw out the cast-iron pipe 3 from the mold 1 in the direction of an arrow. In the course of the above drawing out, molten Al or Al alloy is sprayed through many nozzles 5 provided to the outside peripheral part of the cast-iron pipe 3, by which a thin film of Al or Al alloy is closely formed on the outside peripheral surface of the cast-iron pipe 3. This cast-iron pipe is subjected to annealing treatment, e.g. at 800-900 deg.C for 1-2hr to oxidize the thin film of Al or Al alloy into an Al2O3 film, followed by finishing by means of acrylic paint. By this method, the cast-iron pipe having the corrosion protective film excellent in corrosion resistance can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming an anti-corrosion coating on the outer circumferential surface of a cast iron pipe, and a cast iron pipe having the anti-corrosion coating formed on the outer circumferential surface by the method described above.

(Prior art) In recent years, many cast iron pipes have been manufactured using the centrifugal casting method, and usually a socket is formed at one end of the cast iron pipe for attaching another cast iron pipe. .

To manufacture the cast iron pipe described above, the following procedure is generally followed.

First, a cast iron pipe is cast by, for example, a centrifugal force casting apparatus shown in FIG. In the figure, 21 is the mold, and the drive motor 2
It is placed on rotating rollers 23, 23 which are rotated by 2 and rotated at high speed. Then, a ladle 24 is placed in the mold 21.
Molten cast iron is injected through the pouring gutter 25, and a cast iron pipe 26 is obtained by centrifugal force acting on the molten metal. In addition, 27 in the figure
is a core for molding sockets of cast iron pipes.

After casting, the cast iron pipe is taken out from the mold 21 by a drawing machine, placed in an annealing furnace, and usually maintained at a temperature of about 800 to 900° C. for 1 to 2 hours to undergo an annealing heat treatment.

Next, oxides (so-called scale) generated on the outer peripheral surface of the cast iron pipe by annealing are removed by sitat blasting, and then a zinc-rich paint with good anti-corrosion properties is applied, followed by acrylic paint. The product is made by applying a final coat of paint.

Note that the above-mentioned anticorrosion coating is also applied to the inner surface of the socket of the cast iron pipe described above after the rust removal treatment. Furthermore, since concrete or mortar is applied to the inner surface of the straight part of the cast iron pipe, corrosion resistance is maintained.

(Problems to be Solved by the Invention) However, since cast iron pipes are exposed to an oxidizing atmosphere in an annealing furnace during annealing heat treatment, there is a problem in that the outer circumferential surface is easily oxidized and thick scales are easily formed.

Thick scale has poor adhesion to the substrate and is porous, making it impossible to cover the outer circumferential surface of a cast iron pipe and shielding it from the outside environment, making the outer circumferential surface of the pipe susceptible to corrosion. In addition, since it is porous, it has drawbacks such as the fact that the watertightness of the joint part is likely to be impaired when joining it with other iron pipes. Especially the diameter is 250m
This tendency is remarkable in the case of small diameter pipes of mφ or less. For this reason, the shot blasting process takes a long time to remove thick scales, resulting in a decrease in productivity.

In addition, after removing thick scale, the base of the cast iron pipe is exposed, so the above-mentioned anti-corrosion paint must be applied to prevent corrosion. Since it is sensitively affected by the degree of rust, it is necessary to thoroughly remove the rust by applying a surface treatment such as grinding after the shot blasting process, which has the disadvantage that the surface treatment is time-consuming.

The present invention has been made in view of the above-mentioned problems, and provides a method for forming a coating that prevents the formation of thick scale on the outer circumferential surface of a cast iron pipe and has excellent anticorrosive properties, and The purpose of the present invention is to provide a cast iron pipe with an anti-corrosion coating formed on its surface.

(Means for Solving the Problems) The method of the present invention achieved in order to achieve the above object is as follows:
In a method for manufacturing a cast iron pipe in which a cast iron pipe is cast and then subjected to annealing heat treatment, an AII or A1 alloy coating is applied to the outer peripheral surface of the cast iron pipe before the annealing heat treatment, and the cast iron pipe is annealed. , a method of oxidizing the film to form an aluminum oxide film on the outer peripheral surface. Further, the cast iron pipe of the present invention has an aluminum oxide film formed on its outer peripheral surface by the method described above.

(Function) In the present invention, an annealing heat treatment is performed on the cast iron pipe after an Al1 alloy film is deposited on the outer peripheral surface of the cast iron pipe before the annealing heat treatment. Therefore, since the outer circumferential surface of the cast iron pipe is covered with the above-mentioned film, it is not directly exposed to the oxidizing atmosphere in the annealing furnace, and thick scale can be prevented from forming on the outer circumferential surface.

On the other hand, since the Al or Al alloy film is directly exposed to the oxidizing atmosphere in the furnace, it is oxidized and can form a dense aluminum oxide film with excellent corrosion resistance on the outer peripheral surface of the cast iron pipe.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory schematic view of a centrifugal casting apparatus for carrying out the present invention. In the figure, 1 is a mold for a centrifugal casting device, and AII or A! is attached to the outer peripheral surface of a cast iron pipe 3 near the end of the mold 1 on the opposite side to the insertion side of the pouring gutter 2. A plurality of nozzles 5, 5 of an arc spraying apparatus for forming an alloy coating are arranged at approximately equal intervals in the circumferential direction of the cast iron pipe 3. The nozzles 5, 5 are provided in an appropriate number depending on the outer diameter of the cast iron pipe in order to cover the outer peripheral surface of the cast iron pipe 3 with the ^l or Al alloy film without any gaps. Further, reference numeral 6 in the figure is an arm of a drawing device (not shown) which is movable forward and backward, and the tip thereof is extendable and retractable in the radially outward direction of the cast iron pipe 3.

In the same figure, the following procedure is used to form a 1 or A1 alloy coating on the outer circumferential surface of a cast iron pipe 3. First, to pull out the cast iron pipe 3 from the mold 1, and to pull out the cast iron pipe from the mold l, normally,
The drawing device is advanced to insert the arm 6 into the cast iron pipe 3 through the center hole of the core 7, and at a predetermined position inside the pipe, the tip of the arm 6 is extended in the radial direction of the tube, and the tip is inserted into the cast iron pipe. It is abutted and fixed to the inner surface of the tube 3 in a tensioned manner. Then, in this state, if the drawing device is moved backward in the direction of the arrow in the figure, the cast iron pipe with the core 7 still attached to the socket end will be drawn out. In order to facilitate the drawing of the cast iron pipe, a support roller 8, which is movable forward and backward in a direction perpendicular to the central axis of the pipe, is placed on the underside of the drawn cast iron pipe in accordance with the drawing of the cast iron pipe 3. It is recommended that the cast iron pipe be moved forward as appropriate to support the drawn cast iron pipe.

Next, an Af or A1 alloy coating 4 is formed on the outer peripheral surface of the cast iron pipe 3. In order to form the above-mentioned coating, Af or A1 alloy may be thermally sprayed from the nozzle onto the outer peripheral surface of the cast iron pipe when the cast iron pipe 3 is pulled out from the mold 1 by the above-mentioned drawing device. This method is convenient because it is possible to simultaneously pull out the cast iron pipe 3 and form the skins 1!4. In addition, AIl or AIl
Of course, the alloy may be thermally sprayed separately on the outer circumferential surface of the cast iron pipe after it has been completely pulled out from the mold. Figure 2 shows AIl or AI! Alloy film 4
FIG. 3 is an enlarged cross-sectional view of the socket portion of the cast iron pipe 3 formed with the above.

As the above-mentioned Al or Al alloy, for example, industrially pure An! (^l Purity 99% or more) and other types of Al for casting
Aj for alloys and elongation! Alloys, etc. can be listed.

The above-mentioned AIl or AIl alloy coating 4 may be formed on the outer circumferential surface of the cast iron pipe to a thickness of about 1.Ot1m-107/III.If it is less than 1.Oa■, the outer circumferential surface of the cast iron pipe is sufficiently covered and a thick scale is formed. It becomes difficult to prevent the generation of 10. Even if it is formed beyond the cr layer, it has the effect of preventing scale generation and the A j! , No particular improvement was observed in the anticorrosion effect of the 03 coating.

In the present invention, in the above-described manner, AIl or AIl is applied to the outer circumferential surface.
As mentioned above, the annealing heat treatment in which the cast iron pipe coated with the alloy film is subjected to annealing heat treatment is usually held at about 800 to 900°C for 1 to 2 hours. The Al or A1 alloy film deposited on the outer circumferential surface during this treatment protects the outer circumferential surface of the cast iron pipe from the oxidizing atmosphere in the annealing furnace, and is directly exposed to the oxidizing atmosphere and oxidized, forming a dense structure. Produces an aluminum oxide film. The aluminum oxide film is usually formed to have a thickness of about 5mm to 15mm.

Next, the finished product is usually coated with acrylic paint.

In this embodiment, the case of a centrifugal force casting device in which the drawing device moves is described, but the present invention is not limited to this, but can also be applied to a type in which the mold that rotates as the metal is poured moves to the side opposite to the pouring gutter. It can also be applied to casting equipment. In this case, the thermal spraying nozzle is placed on the flask of the mold, and as the mold returns to its original position, the cast iron pipe fixed to the drawing machine is pulled out of the mold, and at the same time the cast iron pipe is pulled out from the mold. N or N alloy may be thermally sprayed onto the outer circumferential surface of the material.

In addition, the outer circumferential surface of cast iron pipes that are cast by applying a coating agent such as resin sand to the inner surface of the mold may still have the coating agent attached to it even after being pulled out of the mold. In some cases, it is advisable to remove the Al or ^1 alloy by a suitable method such as light thickening before thermal spraying.

Specific examples will be described below.

0 Joint type is JIS T type receiver has opening and nominal diameter 1
A 50-φ cast iron pipe was cast using a centrifugal casting machine.

(2) When pulling the cast iron pipe obtained in (2) from the mold, arc spraying was applied to the outer peripheral surface of the cast iron pipe using a wire made of JIS A1100 material. At this time, four nozzles for thermal spraying were arranged at approximately equal intervals in the circumferential direction of the cast iron pipe to perform thermal spraying.

As a result of the above thermal spraying, a coating made of the wire material was formed on the outer circumferential surface of the cast iron pipe with an average thickness of 5p.

■ The cast iron pipe obtained in (■) was charged into an annealing furnace and heated to 950°C for 1.
Annealing heat treatment was performed by holding for 5 hours.

No thick scale was observed on the outer peripheral surface of the cast iron pipe after the annealing heat treatment, and a dense Al203 film was formed.

0 In order to investigate the corrosion resistance of the above cast iron pipe, it was subjected to an atmospheric exposure test for 100 days, and no red rust was observed on the outer peripheral surface of the cast iron pipe.

(Effects of the Invention) In the present invention, Al is preliminarily applied to the outer peripheral surface of the cast iron pipe before annealing heat treatment.
Alternatively, since an Al alloy film is applied and annealing heat treatment is performed, it is possible to prevent scale from forming on the outer circumferential surface during annealing heat treatment of a cast iron pipe. Therefore, shot blasting for removing scale can be omitted. Further, the Al or Al alloy film is oxidized by annealing heat treatment to form a dense aluminum oxide film with excellent corrosion resistance, so that anticorrosive coating on the outer peripheral surface can be omitted. Therefore, surface treatment associated with anticorrosive coating can be omitted, and productivity is greatly improved.

do.

Furthermore, as described above, the cast iron pipe of the present invention has an aluminum oxide film on the outer circumferential surface that has extremely excellent anticorrosion properties, and therefore has improved anticorrosion properties and excellent durability.

[Brief explanation of the drawing]

FIG. 1 is an explanatory general view showing a centrifugal casting apparatus for carrying out the present invention. Figure 2 shows eight on the outer circumferential surface! Also; FIG. 3 is an enlarged cross-sectional view of a socket portion of a cast iron pipe on which an alloy film is formed. FIG. l...Mold, 3...Cast iron pipe, 4...^l or Al
Alloy film.

Claims (2)

[Claims] (1) In a method for producing a cast iron pipe in which the cast iron pipe is cast and then subjected to annealing heat treatment, an Al or Al alloy coating is applied to the outer circumferential surface of the cast iron pipe before the annealing heat treatment, and the cast iron pipe is A method for manufacturing a cast iron pipe, comprising performing an annealing heat treatment and oxidizing the film to form an aluminum oxide film on the outer peripheral surface. (2) A cast iron pipe manufactured by the method according to claim (1).