JP2843243B2 - Manufacturing method of corrosion resistant cast iron tube - Google Patents

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 tubes are manufactured using a centrifugal force casting method. After casting, the cast iron tubes are usually subjected to a ferrite annealing heat treatment. Since the inner surface is exposed to the oxidizing atmosphere, the outer peripheral surface is oxidized and a thick scale is easily generated. Therefore, in order to prevent the formation of a thick scale on the outer peripheral surface of the cast iron tube and to form a film having excellent corrosion resistance, an Al or Al alloy film is applied to the outer peripheral surface of the cast iron tube before the annealing treatment. A method has been proposed in which a cast iron tube is annealed and heat-treated, and the film is oxidized to form an aluminum oxide film on the outer peripheral surface (Japanese Patent Application No. 1-2).
88535).

On the other hand, a relatively thick cast iron pipe such as a deformed pipe cast in a sand mold is generally not subjected to ferrite annealing because the base is ferritized in an as-cast state. Therefore, in order to improve the corrosion resistance of the surface of such a cast iron tube, a sprayed metal layer may be formed on the surface of the tube. Since the sprayed metal layer is porous and has insufficient corrosion resistance, the sprayed metal layer can be formed into a dense oxide layer by annealing.

[0004]

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

[0005]

According to the present invention, the following technical measures have been taken in order to achieve the above object. That is, the present invention adheres aluminum or an aluminum alloy, which is a corrosion-resistant metal capable of being alloyed with iron, to part or all of the surface of a sand mold for casting a cast iron tube, and forms a molten cast iron in the sand mold. By casting
The corrosion-resistant metal is melted by the heat of the molten metal to form a part or all of the surface of the deformed cast iron pipe , the iron having a different aluminum content in its thickness direction.
-It is characterized by forming a corrosion-resistant alloy layer made of an aluminum alloy .

[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, or the like is cast by casting the molten cast iron in the sand mold. It is melted and alloys with cast iron to form a corrosion resistant alloy layer. On the outer peripheral surface and / or the inner peripheral surface of the cast iron pipe thus cast, a corrosion-resistant alloy layer is formed in an 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 tube 2 using a sand mold 1.
FIG. 1 is an explanatory view of one embodiment of the present invention for manufacturing a mold. 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 that can be alloyed with iron, is sprayed with a thickness of about 150 μ, and then a core 1B is set.

In this way, ductile cast iron (C: 3.53%, Si: 2.
The molten metal 4 of 75%, Mg: 0.035%) is cast at 1370 ° C. (see FIG. 2A), and the product cast iron pipe 2 is 30
When the temperature was cooled to 0 ° C., the mold was disintegrated. 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 on the outer peripheral surface of the cast iron pipe 2 in a film form.

Therefore, when the cast product cast iron pipe 2 is cut and observed with a microscope in the thickness direction, it is confirmed that an iron / aluminum alloy layer 5 of about 185 μm is formed on the outer peripheral surface side of the pipe. did it. In addition, a microscope specimen of the cast iron tube 2 was subjected to EPM.
When the aluminum concentration was analyzed by A, the alloy layer 5
And 58% of the aluminum was detected on the outermost surface and 13% on the innermost surface, indicating that a good corrosion-resistant metal film was formed.

[0010] Corrosion resistant metals (including alloys) 3 in the present invention
It can be applied to the mold surface in place of the morphism solvent as a powdery, if the powder form may be applied by mixing an organic binder to the metal powder. The sprayed or applied thickness of the corrosion resistant metal 3 may be about 80 to 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 requiring corrosion resistance, for example, the surface of the core 1C or both the inner surface of the main mold 1A and the core 1C, May be made to adhere a corrosion-resistant metal to the entire surface of the mold.

The present invention is not limited to the above-described embodiment, 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, aluminum or an aluminum alloy , which is a corrosion-resistant metal capable of being alloyed with iron , is adhered to part or all of the surface of a sand mold for casting cast iron pipes. By casting the molten cast iron into the inside, the corrosion-resistant metal is melted by the heat of the molten metal, and the thickness of the molten metal is partially or entirely formed on the surface of the deformed cast iron pipe.
Iron and aluminum alloys with different aluminum contents in the
Forming a corrosion-resistant alloy layer because characterized in that, a good cast iron pipe of corrosion resistant, extremely easily and economically obtained it can without requiring annealing heat treatment, greatly improved productivity I do.

[Brief description of the drawings]

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

FIGS. 2A and 2B are enlarged views of a portion A in FIG. 1, wherein FIG. 2A shows a state immediately after casting a molten metal in a mold, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 1A Main type 1B Core type 2 Cast iron tube 3 Corrosion resistant metal (Al) 4 Molten metal 5 Iron and aluminum alloy layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) B22D 19/00 B22C 3/00 B22D 19/08

Claims (1)

(57) [Claims] An aluminum or aluminum which is a corrosion-resistant metal which can be alloyed with iron is partially or entirely provided on a surface of a sand mold for casting a cast iron tube.
By attaching a Lumi alloy and casting a cast iron melt in the sand mold, the corrosion resistant metal is melted by the heat of the melt, and a part or all of the surface of the deformed cast iron pipe has an aluminum content in the thickness direction thereof.
A method for producing a corrosion-resistant cast iron pipe, comprising forming a corrosion-resistant alloy layer made of different iron and aluminum alloys .