JP2608152B2 - Cast iron pipe and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming an anticorrosion film on the outer peripheral surface of a cast iron tube and a cast iron tube having an anticorrosion film formed on the outer peripheral surface by the above method.

(Prior Art) In recent years, many cast iron tubes have been manufactured by using a centrifugal casting method, and usually, a receiving port for mounting another cast iron tube is formed at one end of the cast iron tube. . In order to manufacture the above-mentioned cast iron tube, the following procedure is usually performed.

First, for example, a cast iron pipe is cast-formed by a centrifugal casting apparatus shown in FIG. In the figure, reference numeral 21 denotes a mold, and a drive motor 22 is provided.
Are mounted on the rotating rollers 23, 23, and rotated at high speed. And a ladle 24 is poured into the mold 21 from a ladle 24
The molten cast iron is injected through 25, and a cast iron tube 26 is obtained by centrifugal force acting on the pouring. In the drawing, reference numeral 27 denotes a core for molding a receiving port of a cast iron tube.

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

Next, oxides (so-called scales) generated on the outer peripheral surface of the cast iron pipe by the annealing treatment are removed by a shot blast treatment, and then, usually, a zinc-rich paint having good anticorrosion properties is applied, and then an acrylic paint is applied. To finish the product.

The above-described anticorrosion coating is also applied to the inner surface of the receiving port of the cast iron pipe after the rust removal treatment. In addition, since concrete or mortar is applied to the inner surface of the straight pipe portion of the cast iron pipe, corrosion resistance is maintained.

(Problems to be Solved by the Invention) However, since the cast iron tube is exposed to the oxidizing atmosphere in the annealing furnace during the annealing heat treatment, there is a problem that the outer peripheral surface is oxidized and a thick scale is easily generated.

Since the thick scale has poor adhesion to the base and is porous, it cannot cover the outer peripheral surface of the cast iron tube and cannot be shielded from the external environment, and the outer peripheral surface of the tube is easily corroded. In addition, since it is porous, there is a drawback in that the watertightness of the joint is easily damaged when joining with another iron tube. Especially 250mm in diameter
This tendency is remarkable in the case of a small-diameter pipe having a diameter of φ or less. For this reason, the shot blast processing time becomes longer due to the removal of thick scale, and the productivity is reduced.

After the removal of the thick scale, the surface of the cast iron pipe is exposed, so that the above anticorrosive paint must be applied for anticorrosion. Since the anticorrosion effect and durability of the coating film of the zinc rich paint are sensitively affected by the degree of rust removal of the base, after the shot blasting, the base is subjected to a base treatment such as a grinder to sufficiently remove rust. Therefore, there is a disadvantage that the undercoating process is troublesome.

The present invention has been made in view of the above-described problems, and has a method for uniformly forming a good high hardness and high corrosion resistance film on the outer peripheral surface of a cast iron pipe with excellent productivity, and the outer peripheral surface by the above method. It is an object of the present invention to provide a cast iron pipe in which an anticorrosion film is formed.

(Means for Solving the Problems) The method of the present invention made to achieve the above-mentioned object is as follows. First, a cast iron pipe sprayed with Al or an Al alloy on the outer peripheral surface is placed in an annealing furnace in an oxidizing atmosphere. It is characterized in that the Al or Al alloy film is oxidized at the same time as the annealing treatment at an annealing temperature equal to or higher than the melting point of Al. Alternatively, an Al alloy is sprayed, and the cast iron tube is annealed in an annealing furnace in an oxidizing atmosphere at an annealing temperature equal to or higher than the melting point of Al, and at the same time, the Al or Al alloy film is oxidized.

Further, the cast iron tube of the present invention is characterized in that an Al or Al alloy film spray-coated on the outer peripheral surface is oxidized at an annealing temperature equal to or higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere to form an aluminum oxide film. And

(Action) In the present invention, simultaneously with annealing the cast iron tube, the Al or Al alloy film sprayed on the cast iron tube is oxidized in an annealing furnace in an oxidizing atmosphere at an annealing temperature equal to or higher than the melting point of Al. To oxidize the Al or Al alloy film at an annealing temperature higher than the melting point of Al, Al or Al
The alloy diffuses into the cast iron pipe, of course, and is oxidized from the surface layer in a high heat state and over time to a porous state, and the aluminum oxide film is formed to be thick and falls from the annealing temperature during annealing. At this time, the oxidation continues, and further oxidizes to the deep portion of the Al or Al alloy film to form an aluminum oxide film having a large thickness and a high bonding force.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic explanatory view of a centrifugal casting device for carrying out the present invention. In the figure, reference numeral 1 denotes a mold of a centrifugal casting device, which is located at a position near an end of the mold 1 opposite to the insertion side of the pouring gutter 2,
A plurality of nozzles 5, 5 of an arc spraying device for forming an Al or Al alloy film on the outer peripheral surface of the cast iron tube 3 are arranged at substantially equal intervals in the circumferential direction of the cast iron tube 3. The nozzle
In order to cover the outer peripheral surface of the cast iron tube 3 with an Al or Al alloy film without any gap, a number 5 and 5 are appropriately provided according to the outer diameter of the cast iron tube. In the drawing, reference numeral 6 denotes an arm of a drawing device (not shown) which can be moved forward and backward, and the distal end of the arm can be extended and contracted in the radial direction of the cast iron tube 3.

In the figure, the following procedure is used to form an Al or Al alloy film on the outer peripheral surface of the cast iron tube 3. First, the cast iron tube 3 is pulled out of the mold 1. To extract the cast iron tube from the mold 1, usually,
The pulling device is advanced to insert the arm 6 into the cast iron tube 3 from the center hole of the core 7, the distal end of the arm 6 is extended at a predetermined position in the pipe in the radial direction of the tube, and the distal end is cast iron. It is fixed to the inner surface of the tube 3 in a projecting manner. Then, if the drawing device is retracted in the direction of the arrow in the drawing in this state, the cast iron tube with the core 7 attached to the receiving end is pulled out. In order to facilitate the drawing of the cast iron tube, a support roller 8 which can be moved forward and backward in a direction perpendicular to the center axis of the tube is aligned with the drawing of the cast iron tube 3 on the lower surface side of the drawn cast iron tube. The cast iron tube may be appropriately advanced to support the drawn cast iron tube.

Next, an Al or Al alloy film 4 is formed on the outer peripheral surface of the cast iron tube 3. In order to form the film, when the cast iron tube 3 is drawn from the mold 1 by the drawing device, Al is passed through the nozzle.
Alternatively, the Al alloy may be sprayed on the outer peripheral surface of the cast iron tube. According to this method, the drawing of the cast iron pipe 3 and the formation of the coating 4 can be performed simultaneously, which is convenient. In addition, it is a matter of course that the thermal spraying of Al or the Al alloy may be separately applied to the outer peripheral surface after the cast iron pipe is completely drawn from the mold. FIG. 2 is an enlarged cross-sectional view of a receiving portion of the cast iron pipe 3 on which the Al or Al alloy film 4 is formed on the outer peripheral surface by the above-described procedure.

As the above Al or Al alloy, for example, industrial pure Al
(Al purity 99% or more), various casting aluminum alloys and wrought aluminum alloys
Alloys and the like can be raised.

The above-mentioned Al or Al alloy film 4 has a thickness of 1.0
It may be formed to a thickness of about 10 μm to 10 μm. If the thickness is less than 1.0 μm, it is difficult to sufficiently cover the outer peripheral surface of the cast iron pipe to prevent the formation of a thick scale. On the other hand, even if the thickness exceeds 10 μm, the effect of preventing scale generation and the Al ₂ O ₃ generated by annealing are reduced. No particular improvement in the anticorrosion effect of the film is observed.

In the present invention, an annealing heat treatment is performed on the cast iron pipe having the outer peripheral surface coated with the Al or Al alloy film as described above. As described above, the annealing heat treatment is usually performed at about 800 to 900 ° C. for 1 to 2 hours. It was attached to the outer peripheral surface during this process
The Al or Al alloy film protects the outer peripheral surface of the cast iron tube from the oxidizing atmosphere in the annealing furnace and oxidizes itself by being directly exposed to the oxidizing atmosphere to form a dense aluminum oxide film. The aluminum oxide film is usually 5 μm to 15 μm.
The thickness is about m.

Next, usually, an acrylic paint is finish-coated to obtain a product.

In the present embodiment, the case of the centrifugal casting apparatus in which the drawing apparatus moves is described. However, the present invention is not limited to this, and the mold that rotates with the pouring moves to the side opposite to the pouring gutter. Also applicable to casting equipment. In this case, the nozzle for thermal spraying is arranged on the frame of the mold, and as the mold returns to its original position, the cast iron tube fixed to the drawing machine is pulled out of the mold at the same time as the cast iron tube. Al or Al on outer surface
What is necessary is just to spray the alloy.

Further, on the outer peripheral surface of a cast iron tube cast by applying a coating agent such as resin sand to the inner surface of the mold, the above-mentioned coating agent may be attached even after being drawn from the mold. In this case, it is preferable to remove Al or an Al alloy by a suitable method such as light shot blasting before thermal spraying.

 Hereinafter, specific examples will be described.

Nominal diameter 150mmφ with JIS T type socket
Was cast by a centrifugal casting machine.

When the cast iron tube obtained in the above was pulled out of the mold, the outer periphery of the cast iron tube was subjected to arc spraying using a wire formed of JIS A1100 material. At this time, four nozzles for thermal spraying were arranged at substantially equal intervals in the circumferential direction of the cast iron pipe and sprayed.

By the above-mentioned thermal spraying, a film formed of the wire material was formed on the outer peripheral surface of the cast iron pipe with an average thickness of 5 μm.

Was placed in an annealing furnace, and kept at 950 ° C. for 1.5 hours to perform annealing heat treatment.

No thick scale was formed on the outer peripheral surface of the cast iron pipe after the annealing heat treatment, and a dense Al ₂ O ₃ film was formed.

When subjected to an atmospheric exposure test for 100 days to investigate the corrosion resistance of the cast iron tube, no red rust was found on the outer peripheral surface of the cast iron tube.

(Effects of the Invention) According to the present invention described in detail above, since the Al or Al alloy sprayed on the outer peripheral surface can be oxidized simultaneously with annealing the cast iron tube, the annealing and oxidation can be performed rationally and efficiently. , The productivity can be improved, and the coating of the cast iron pipe surface during annealing can be prevented by coating with the Al or Al alloy film, and
Since the Al or Al alloy film is oxidized at an annealing temperature higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere when annealing a cast iron tube, it can be deeply oxidized from the surface layer to the deep layer with high heat and time. In addition, even when the temperature drops from the annealing temperature during annealing, oxidation from the porous surface layer is continued, and oxidation to a deeper portion is achieved, so that a thick aluminum oxide film is obtained and the bonding strength with the cast iron pipe is increased. Can be

In addition, since the thermal spraying of Al or Al alloy on the cast iron tube is performed during drawing from the casting device, the Al or Al alloy film is applied to the cast iron tube in a high temperature state to diffuse the Al or Al alloy into the cast iron tube. It is possible to efficiently perform the diffusion at the annealing temperature during the annealing, and to prevent the oxidation of the cast iron tube from the casting device until annealing.

Furthermore, the cast iron pipe of the present invention is formed by oxidizing the Al or Al alloy film deposited on the outer peripheral surface at an annealing temperature equal to or higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere to form an aluminum oxide film. It is provided with an aluminum oxide film having a high hardness, a high density, and a high adhesion that is deeply oxidized to improve corrosion resistance and durability.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a centrifugal casting device for carrying out the present invention. FIG. 2 is an enlarged cross-sectional view of a receiving portion of a cast iron tube having an Al or Al alloy film formed on an outer peripheral surface, and FIG. 3 is a partial cross-sectional explanation showing a method of casting a cast iron tube by a conventional centrifugal casting device. FIG. 1 ... mold, 3 ... cast iron pipe, 4 ... Al or Al alloy film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mutsuo Uchida 2-26-2 Ohama-cho, Amagasaki City, Hyogo Prefecture Kubota Iron Works Co., Ltd. Mukogawa Works (56) References JP-A-48-18129 (JP, A) 53-33530 (JP, B2)

Claims (3)

(57) [Claims] The present invention is characterized in that a cast iron pipe having an outer peripheral surface sprayed with Al or an Al alloy is subjected to an annealing treatment at an annealing temperature higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere and at the same time, the Al or Al alloy film is oxidized. Method of manufacturing cast iron pipe. 2. After casting a cast iron tube, Al or an Al alloy is sprayed on an outer peripheral surface of the cast iron tube during drawing from a casting device, and the cast iron tube is annealed at a temperature higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere. A method for producing a cast iron pipe, wherein the Al or Al alloy film is oxidized simultaneously with annealing at a temperature. 3. An Al or Al alloy film deposited on the outer peripheral surface,
A cast iron pipe characterized by being oxidized at an annealing temperature higher than the melting point of Al in an annealing furnace in an oxidizing atmosphere to form an aluminum oxide film.