JPH07155929A - Production of corrosion resistant cast iron tube - Google Patents

Abstract

PURPOSE:To easily and economically obtain a cast iron tube having good corrosion resistance without needing annealing heat treatment. CONSTITUTION:A corrosion resistant metal 3 such as Al, Cu, Ni, etc., enabling the alloying with iron is stuck on the inner peripheral surface of a master mold 1A (or the outer peripheral surface of a core mold 1B) in a mold 1, and the molten cast iron is cast into the mold 1. By this method, the corrosion resistant metal 3 is melted with the molten metal heat and the corrosion resistant alloy layer composed of iron-aluminum alloy is formed in the outer peripheral surface (or the inner peripheral surface) of the cast iron tube, and the corrosion resistance is secured in the as-cast condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a corrosion-resistant cast iron pipe such as a deformed pipe cast by a sand mold.

[0002]

2. Description of the Related Art Conventionally, most cast iron pipes have been manufactured by utilizing a mold centrifugal casting method. After casting, the cast iron pipes are usually subjected to ferritic annealing heat treatment. Since it is exposed to the oxidizing atmosphere inside, the outer peripheral surface is easily oxidized and thick scale is easily generated. Therefore, in order to prevent the formation of thick scale on the outer peripheral surface of the cast iron pipe and form a film having excellent corrosion resistance, an Al or Al alloy film is deposited on the outer peripheral surface of the cast iron pipe before annealing, A method has been proposed in which a cast iron pipe is annealed and heat-treated to oxidize the film to form an aluminum oxide film on the outer peripheral surface (Japanese Patent Application No. 1-2.
88535).

On the other hand, in a cast iron pipe having a comparatively thick wall such as a deformed pipe cast in a sand mold, since the matrix is ferritic in the as-cast state, it is customary not to perform ferritic annealing. Therefore, in order to improve the corrosion resistance of the surface of such cast iron pipe, a sprayed metal layer may be formed on the pipe surface. Since the sprayed metal layer is porous and does not have sufficient corrosion resistance, it is possible to form the sprayed metal layer into a dense oxide layer by annealing.

[0004]

However, in the case of a sand casting cast iron pipe, an annealing heat treatment is required to improve the corrosion resistance although the ferritic annealing is not necessary originally, which is extremely uneconomical and costly. There is a drawback. The present invention has been made in view of the above problems, and an object thereof is to provide a method capable of easily and economically producing a sand cast iron pipe having good corrosion resistance. .

[0005]

In order to achieve the above object, the present invention takes the following technical means. That is, the present invention, a part or all of the surface of the sand mold for casting iron pipe, a corrosion-resistant metal that can be alloyed with iron is attached, and by casting the cast iron molten metal into the sand mold, the heat of the molten metal It is characterized in that a corrosion resistant metal is melted to form a corrosion resistant alloy layer on a part or the whole of the surface of the deformed cast iron pipe.

[0006]

According to the present invention, the corrosion-resistant metal adhered to the surface of the main mold and / or the core mold constituting the sand mold by thermal spraying, coating, etc. It is melted and alloyed with cast iron to form a corrosion resistant alloy layer. On the outer peripheral surface and / or inner peripheral surface of the cast iron pipe thus cast, a corrosion resistant alloy layer is formed in the as-cast state.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. The drawing shows a deformed cast iron pipe 2 using a sand mold 1.
FIG. 3 is an explanatory view of an embodiment of the present invention for manufacturing a mold 1 in which the mold 1 is composed of a main mold 1A and a core mold 1B.
On the inner surface of A, Al3, which is a corrosion resistant metal capable of alloying with iron, is sprayed to a thickness of about 150 μ, and then the core mold 1B is set.

In this way, in the mold 1 sprayed with Al3, ductile cast iron (C: 3.53%, Si: 2.
A molten metal 4 (75%, Mg: 0.035%) is cast at 1370 ° C. (see FIG. 2A), and the cast iron pipe 2 as a product is 30
The mold was removed when it was cooled to 0 ° C. By casting the molten metal 4, Al3 is melted and alloyed with iron.
As shown in (b), the iron / aluminum alloy layer 5 is formed in a film shape on the outer peripheral surface of the cast iron pipe 2.

Then, the cast product cast iron pipe 2 was cut and microscopically observed in the wall thickness direction, and it was confirmed that an iron / aluminum alloy layer 5 of about 185 μ was formed on the outer peripheral surface side of the pipe. did it. In addition, the microscope sample of the cast iron pipe 2 is EPM.
When the aluminum concentration analysis by A is performed, the alloy layer 5
It was found that 58% of aluminum was detected on the outermost peripheral surface and 13% of aluminum was detected on the innermost surface, forming a good corrosion-resistant metal film.

Corrosion resistant metal (including alloy) 3 in the present invention
In addition to Al, Cu, Ni, Cr or the like can be adopted. Instead of thermal spraying, powder can be applied to the surface of the mold. In the case of powder, even if a metal powder is mixed with an organic binder and applied, Good. The thermal spraying or coating thickness of the corrosion-resistant metal 3 is 80 to
It may be about 300 μm. In the above embodiment, the corrosion resistant metal 3 was sprayed on the inner surface of the main mold 1A of the mold 1, but a portion where corrosion resistance is required, for example, the surface of the core mold 1C or both the inner surface of the main mold 1A and the core mold 1C, May have a corrosion-resistant metal deposited on the entire surface of the mold.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that the present invention can be applied to ordinary cast iron other than ductile cast iron.

[0012]

As described above, according to the present invention, a corrosion-resistant metal capable of alloying with iron is adhered to a part or all of the surface of a sand mold for casting a cast iron pipe, and cast molten iron is cast in the sand mold. By incorporating the corrosion-resistant metal by melting heat to form a corrosion-resistant alloy layer on a part or all of the surface of the deformed cast iron pipe, the cast iron pipe having good corrosion resistance can be very easily formed. In addition, it can be economically obtained without requiring annealing heat treatment, and the productivity is significantly improved.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view of a sand mold according to an embodiment of the present invention.

FIG. 2 is an enlarged view of part A in FIG. 1, in which (a) shows a state immediately after the molten metal is cast into the mold, and (b) shows a state before mold separation.

[Explanation of symbols]

 1 Mold 1A Main type 1B Core type 2 Cast iron pipe 3 Corrosion resistant metal (Al) 4 Molten metal 5 Iron / aluminum alloy layer

Claims (1)

[Claims] 1. A corrosion resistant metal capable of alloying with iron is adhered to a part or all of the surface of a sand mold for casting iron pipe, and the cast iron molten metal is cast into the sand mold so that the corrosion resistance is caused by the heat of the molten metal. A method for producing a corrosion-resistant cast iron pipe, which comprises melting a metal to form a corrosion-resistant alloy layer on a part or all of the surface of the deformed cast iron pipe.