JP3133273B2 - Composite centrifugal casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal casting method in which a metal or an alloy exhibiting a specific property is added to the whole or part of the metal to enhance the functionality.

[0002]

2. Description of the Related Art As a method of imparting corrosion resistance to a specific part of a cast product, there is a method of applying a surface treatment after casting, such as thermal spraying or partial quenching and carbonitriding, to the cast product itself. There is an increasing problem. Therefore, a hardening material layer containing a specific substance is provided at a desired portion of the cavity surface of the mold before casting, a molten metal is poured, the hardening material layer is welded by the heat, and hardened to a desired section after solidification. Various casting methods have been proposed to form layers.

In the prior art disclosed in Japanese Patent Publication No. 5-20184, for example, a filler made of a Ni alloy having a Ni content of 80% by weight or more is charged as a powder into a mold immediately before casting. The main point is to form a corrosion-resistant layer on the outer peripheral surface by pouring, and boron, silicon, chromium,
A filler having a melting point of 1300 ° C. or less was selected from copper.
Alternatively, an embodiment in which the melting point of the molten cast iron is selected to be 1150 ° C. or lower is also shown.

In the prior art disclosed in Japanese Patent Application Laid-Open No. 5-77019, a powder layer for accelerating solidification is placed in a mold for almost the same purpose.
It has been shown that it is formed by a mixed powder of i, Cr, or an alloy thereof and Ca, Si. It is stated that the heat insulation effect at the time of pouring by the powder layer prevents the occurrence of pinholes by preventing defects, protecting the mold, and rapidly solidifying the cast molten metal. That is, Ca and Si in this case are intended to have a kind of deoxidizing inoculation effect and an effect of lowering the melting point of the mixed powder layer.

[0005]

SUMMARY OF THE INVENTION In centrifugal die casting, a layer having excellent corrosion resistance is formed on the outer peripheral surface of a product.
The application or spraying of the corrosion resistant metal powder into the mold is already known, and the two prior arts cited above also belong to that category. However, the main point is to focus on controlling the components so that the melting point of the metal imparting corrosion resistance is shifted to the lower temperature side, and the reinforcement level of the outer peripheral surface protective layer itself to be coated is still perfect. Isn't it?

[0006] If it is primarily desired to lower the melting point of the powder layer, it must follow the form of a kind of metal brazing. It means that it diffuses into the metal and the concentration of components on the surface is greatly lost, and if the melting point is too high, there remains a question about the integral welding with the base metal.

[0007] The applicant of the present invention previously filed Japanese Patent Publication No. Hei 5-201.
No. 87 discloses a completely new composite integration by liquid phase sintering mainly aimed at locally strengthening wear-resistant steel. That is, by injecting a molten metal into the mold cavity and casting it into a desired shape after solidification, a specific metal or alloy imparting specific physical properties to A, and B is clearly lower than the metal constituting A. A metal powder having a melting point is used, C is an appropriate amount of an organic binder, and the three are kneaded together and attached at a desired position, and a molten metal having a higher melting point than the metal constituting B in the gap. Injecting casting method. With this configuration, first, the low melting point metal B is melted by the retained heat of the injected molten metal, and the three components A, B and the injected metal are integrated by liquid phase sintering, and then the injected metal and the layer are integrated. Diffusion welds through the surface.

[0008] Since the wear-resistant material is strong and is consumed from the outer surface with the passage of time, a certain thickness of the reinforcing layer is required.
Of Ni-Cr-Si-Fe powder as C and polyvinyl acetate as C, and pouring molten cast iron as a base material, especially in abrasion-resistant cast iron parts, the results of locally strengthening the wear surface Indicated.

On the other hand, regarding the corrosion-resistant material, the thickness itself of the reinforcing layer on the outer surface is not the main subject, and one point is how the protective layer integrally welded to the base material can form a dense and robust composite layer. Exhausted. An object of the present invention is to provide a method for most effectively improving the corrosion resistance of the above-described corrosion-resistant member, particularly the outer peripheral surface of a cast iron pipe formed by centrifugal casting.

[0010]

In the composite centrifugal casting method according to the present invention, a specific metal and an auxiliary agent are added to a mold in order to improve specific physical properties, and the molten metal is rotated at a high speed to form a molten metal. In a composite centrifugal casting method in which a molten metal is poured and the outer peripheral surface is compositely strengthened with a specific agent, Ni or Ni-based alloy, stainless steel containing Ni and / or Cr, or iron-based alloy containing at least 10% by weight or more of Cr One or a plurality of metal powders A selected from the group consisting of Ni-P and Ni-Cr- P metal powders B having a melting point distinctly lower than the metal powders A, and an organic binder C. It was mixed and coated on the inner surface of the mold, while rotating at high speed, than the melting point of the metal powder B is poured the molten metal of higher melting point, is first powdered metal B is the melt heat
Receiving and melting the powder metal A
Liquid phase sintering occurs in cooperation with the metal, and in this state
Strong mold inner surface by centrifugal force while holding each other
The above problem was solved by forming a strong and dense corrosion-resistant sintered layer integrally on the outer peripheral surface of the product by being pressed against the surface and rapidly cooling the product.

In the above configuration, instead of applying the mixture to the inner surface of the mold, a powder obtained by uniformly mixing the metal powder A and the metal powder B is injected into the mold immediately before the molten metal is injected into the mold. Alternatively, a composite casting may be cast in which A and B having higher specific gravity than the molten metal form an outer surface layer by spraying on a mold at the same time and exhibit physical properties of corrosion resistance. Further, in the composite centrifugal casting method described above, the mixing ratio of A and B is A
By setting / B = 10/100 to 90/10, the physical properties of corrosion resistance are exhibited.

When the target weld metal is poured into a mold having an attachment layer provided therein, the powder of B constituting the attachment layer reaches its melting point and begins to melt due to the heat of the molten metal. At this time, the powder metal A is dissolved by the compounded material,
There are three states, namely, the case where only a part is dissolved near the surface and the case where it is not dissolved at all. There are many different conditions depending on the composition of the powder metal A and the temperature of the molten metal to be injected, but these are elements that can be calculated and determined in advance. The most important feature of the operation is that, instead of dissolving and dispersing the entire adhering layer in the molten metal as it is to form a reaction layer straight, the low melting point powder metal B first melts by receiving the heat of the molten metal, This is so-called liquid phase sintering in which A is firmly embraced and welded in cooperation with the molten metal.
Therefore, as will be shown in a later embodiment, the reaction layer embraces the powder metal A, which controls the physical properties, and combines with the powder metal B and the molten metal base material. Diffusion bonding to the base material over a depth of The C component keeps the bonding of the mold surface when the adhering layer is formed, and at the time of pouring, plays a role of gripping until solidification starts from the surface without being pushed by the flow force to separate the layer.

An object of the present invention is to improve the corrosion resistance of the outer surface of a ductile cast iron pipe as a main object, as will be clearly described in embodiments described later. Specifically, the operation in this case will be described.
Melt of ductile cast iron into mold (melting point about 1150 ℃)
, The powder B (for example, Ni-P, melting point of about 1000 ° C.) is melted, and the molten cast iron begins to impregnate into the powder layer by centrifugal force, and the powder metal A (which has a higher melting point than the powder metal B) ( For example, microscopic liquid phase sintering starts in a state of enclosing nickel (melting point of about 1450 ° C.). In this state, they are strongly pressed against the inner surface of the mold while being held together by the centrifugal force, and are rapidly cooled to form a solid composite layer integrally. For example, when the heat capacity of the molten cast iron is large, a structure similar to a Ni-resist in which the base having a high Ni concentration is austenitized is obtained when the heat capacity of the molten cast iron is large. When the molten cast iron melts little, the diffusion of Fe, C, etc. in the surface layer is small,
An austenitic structure with a higher Ni concentration (specifically, 20% by weight or more) is obtained, and a corrosion-resistant outer layer is formed. The mixing ratio of powder metals A and B is A / B = 10 / 90-90.
With / 10, sintering by the heat of the molten metal is difficult with only A and does not completely dissolve, and only B dissolves and diffuses completely, and a layer having excellent corrosion resistance does not appear on the surface. When the mixed A and B are mixed and sprayed immediately before or during pouring, B is melted by the injection of the molten metal, and A is pressed against the mold surface due to the specific gravity, and the molten metal is melted therein. A causes liquid phase sintering through the liquid phase portion, and an A-rich layer is formed on the surface layer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to prove the corrosion resistance of the present invention, a confirmation test was performed in the following manner. FIG. 2 is a partial cross-sectional view of a centrifugal casting mold, in which a centrifugal casting mold 1 is horizontally supported by a rotary bearing 2, and while being rotated at a low speed, the mixed powder is sprayed from a supply pipe 4 to have a uniform thickness over the entire length. Thus, a powder layer 3 was formed. Using the mold shown in FIG. 2, a centrifugal cast iron pipe (outer diameter 169 m) was used.
m, length 1080 mm, thickness 7.5 mm).
The molten metal used was ductile cast iron at 1350 ° C. After casting, it was refined (980 ° C. to 730 ° C., 40 minutes), and then test pieces were cut out. The powder layers A and B were made to have a particle size of 150 microns or less, mixed, and scattered on the surface of a mold, and scattered so that the average thickness was about 500 microns. Table 1 shows the components of A and B and the mixing ratio in the examples. Binder C used polyvinyl acetate (PVAC).

[0015]

[Table 1] Note) In the case of spraying, the binder C was not used, but in the case of application, it was used at a ratio of about 5 with respect to A + B = 100. Table 2 is a list of chemical compositions of various materials used for forming the powder layer of Table 1.

[0016]

[Table 2]

The cast test piece was processed into an appropriate size, and the following test was performed. A, Quantitative analysis by EPMA, measuring the chemical composition ratio of elements contained near the surface. B, Corrosion resistance test According to the method described in JISK5400, JISZ2
371 at 35 ° C.
% NaClaq salt spray test. The test piece is 45mm x 45mm x 7.5mm thick,
The surface on which the coating layer was formed was exposed, and the other surface was sealed.

A brief description of the test results together with the charts will be given. The distance (μm) from the surface of the casting is plotted on the abscissa, and the quantitative analysis values of Fe, Na, and Cr components are plotted on the ordinate, and The relationship was shown. 3 shows the results of sample No. 1, FIG. 4 shows the results of sample No. 2, and FIG. 5 shows the results of sample No. 3. It clearly demonstrates that a composite layer containing Ni is formed from the surface to 500 to 600 μm each. FIG. 1 shows the relationship between the corrosion loss (mg / cm @ 2) and the immersion period (day) of each of the samples by a salt water (5% NaClaq) spray test. The difference in corrosion weight loss spreads proportionally with time with respect to cast iron (FCD), and it has been proved that the sample No. 1 of Ni / Ni-P has corrosion resistance of 10 times or more. It is clear from this figure that this difference increases significantly with the passage of time.

[0019]

According to the composite centrifugal casting method of the present invention, the prior art corrosion-resistant coating layer planned and implemented for almost the same purpose is mainly composed of a single coating, and has the following properties:
While some concerns had to be denied in consideration of the physical properties of the layer itself, the composite layer of the present invention is a dense layer with outstanding corrosion resistance based on the original idea of liquid phase sintering. In this case, the solid composite layer is integrally welded and formed, so that the durability after use is far superior.

[Brief description of the drawings]

FIG. 1 is a table comparing and displaying corrosion resistance by a salt spray test among the effects of the present invention.

FIG. 2 is a partially sectional front view of a centrifugal casting mold used for carrying out the present invention.

FIG. 3 is a table showing a relationship between a depth from the surface of sample No. 1 and components.

FIG. 4 is a table showing a relationship between a depth and a component from a surface of a sample No. 2;

FIG. 5 is a table showing a relationship between a depth from the surface of sample No. 3 and components.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Centrifugal casting die 2 Rotation bearing 3 Powder layer 4 Supply pipe

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Kitagawa 1-12-19 Kitahorie, Nishi-ku, Osaka-shi, Osaka Inside Kurimoto Ironworks Co., Ltd. (72) Kimio Nakamura 1 Kitahorie, Nishi-ku, Osaka-shi, Osaka No.12-19, Kurimoto Iron Works Co., Ltd. (72) Inventor Kiminori Yoshikawa 24, Hikita, Shinjo-cho, Kitakatsuragi-gun, Nara Pref. JP-A-5-77019 (JP, A) JP-A-1-148448 (JP, A) JP 5-20187 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 13/02 B22D 19/16

Claims (3)

(57) [Claims] 1. A composite centrifugal casting in which a specific metal and an auxiliary agent are added into a mold, a molten metal is poured while rotating at a high speed, and an outer peripheral surface is compositely reinforced in order to improve specific physical properties. In the method, Ni or a Ni-based alloy, Ni and / or Cr
At least 10% by weight of stainless steel or Cr containing
One or more metal powders A selected from the iron-based alloys contained above and N, which is a melting point at a lower temperature than the metal powders A,
The metal powder B of i-P or Ni-Cr- P and the organic binder C are mixed and applied on the inner surface of a mold, and the melting point of the metal powder B is increased while rotating at high speed. Pouring molten metal with a higher melting point, and powder metal B first releases the heat of the molten metal.
Receiving and dissolving the powder metal A firmly,
Liquid phase sintering occurs in cooperation with the
Strongly held inside the mold by centrifugal force while holding each other
A composite centrifugal casting method characterized in that it is pressed and rapidly cooled, and a solid, dense, corrosion-resistant sintered layer is integrally formed on the outer peripheral surface of the product. 2. A method according to claim 1, wherein the molten metal is poured into the mold by uniformly mixing the metal powder A and the metal powder B, instead of applying the mixture to the inner surface of the mold. A composite centrifugal casting method in which metals A and B having a higher specific gravity than the molten metal form an outer surface layer and exhibit physical properties of corrosion resistance by being sprayed on a mold immediately before or at the same time. 3. The mixing ratio of A and B is A / B = 10/9.
It is 0 to 90/10, the composite centrifugal casting method according to claim 1 or 2 wherein.