JPH0520187B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a casting method for obtaining a cast product having a desired shape after solidification by melting metal and injecting it into the voids of a mold, particularly a casting method for imparting specific physical properties only to desired parts. It is related to. [Prior Art] Depending on how the cast product is used, there are cases where it is desired to impart specific physical properties to only a desired portion of the cast product, rather than to the entire cast product. For example, parts such as the valve seat of a valve box, the throat of a casing of a centrifugal pump, and the vicinity of the blade of an impeller are subject to wear and tear due to sliding and cavitation, and must be replaced even though other parts are as good as new. Abrasion resistance, corrosion resistance,
As a method of imparting specific physical properties such as heat resistance,
There are methods of applying surface treatments to the cast product itself after casting, such as thermal spraying, partial hardening (for example, induction hardening), carburizing, and nitriding, but these require equipment and
There is a problem that the number of man-hours will definitely increase. Therefore, a hardening material layer containing a specific foreign substance is provided at a desired location on the cavity surface of the mold before casting, and molten metal is poured and the hardening material layer is welded by the heat. Various casting methods have been proposed to form a hardened layer at a desired location. There are quite a number of these conventional techniques, but examples include (1) "Surface hardening method using cast iron coating molds" (Japanese Patent Publication No. 18166/1983) (2) Method of manufacturing wear-resistant cast products (Japanese Patent Publication No. 18166/1983) 11026) (3) Hardening material for casting (Japanese Patent Application Laid-Open No. 177850/1982) (4) Method for joining cast iron and cermet (Japanese Patent Application Laid-open No. 60-206557) (5) Method for manufacturing composite castings (Japanese Unexamined Patent Publication No. 53-66824). The first cited example of conventional technology is a method in which a powder mainly composed of Te+Cu is mixed with an alcohol solution along with graphite powder, applied to a mold, and molten cast iron containing V and Ni is injected to harden the surface of the cast product. This is an improvement over the application of Te alone. The fourth reference is a method in which molten metal having the same composition as the chromium-containing cast iron is cast into a cermet that combines carbide particles and chromium-containing cast iron, thereby forming a joint with good wettability with the cermet. In the fifth cited example, a particle layer that enhances sliding properties and wear resistance is formed on the surface of the mold using a binder, and after the melt is solidified under pressure, metal is impregnated between the particles. [Problems to be solved by the invention] Conventional techniques commonly involve forming a coating film or cast-in body on the surface of a mold, and melting and dispersing metal or alloy powder into the molten metal using the heat of the injected molten metal. This is the basics. Except for the 5th citation, the molten metal listed here is limited to cast iron, and the carbon content is cementitized to partially form a white pig iron structure, so the purpose is to improve wear resistance through hardening. The hardening agents added are limited to specific substances that tend to whiten. However, in terms of realization requirements, cast products are not limited to cast iron, but include cast steel and non-ferrous metals, and the physical properties that are desired to be partially imparted are not limited to improving wear resistance through hardening, but also improving other types of wear resistance, There are also various improvements in corrosion resistance, cavitation resistance, corrosion resistance, etc. However, since conventional casting technology is based on the dissolution and diffusion of coating materials, the application of alloy powders with high melting points and combinations of metals and non-metals (e.g. carbides, oxides, nitrides, borides) is difficult. There are significant limitations, and it is difficult to form an alloy layer of a desired thickness using alloy powder that has poor reactivity with molten metal. Furthermore, relying only on resin as a bonding material has the disadvantage that pinholes and cavities are often generated due to gas generation after pouring, resulting in poor workability. There are organic and inorganic binders, but inorganic binders (such as water glass and ethyl silicate) have a strong binder effect and are less flammable, making it difficult for powdered metal to diffuse into the molten metal. This has the disadvantage that it is difficult to form the required reaction layer on the surface. In addition, the material powder that causes hardening is washed away when the molten metal passes through it, resulting in physical property changes in unexpected areas or loss of effectiveness. Generally, a coating film alone cannot be expected to have a great effect, and it also has the disadvantage that it is difficult to control the thickness of the cured layer. The fourth citation uses a cast-in instead of a coating method, and because it has good wettability with molten metal, it is used as a binder for forming ultra-hard carbides such as WC. It can be said that it is unique in that it uses the same ingredients as the chromium-containing cast iron, but for this purpose, for example, WC powder is pre-sintered in a vacuum to form a porous skeleton, which is then melted at 1300℃ in a vacuum. This requires a very complicated and sophisticated process of impregnating cast iron to obtain an integrated cermet. It must be said that this is a major problem when moving to actual production. In addition, the fifth reference does not specifically limit the use of cast iron as the matrix, but the purpose is to form a film with good sliding properties and wear resistance, and requires pressure solidification after pouring. It can also be interpreted as applying the idea of die casting to conventional technology. Naturally, material constraints, uniformity in shape and dimensions, equipment equipment, etc. all pose problems, so it cannot be said that this is a technology that can be directly applied to the production of a wide variety of cast products. In order to solve the above-mentioned problems, the present invention has developed a highly versatile new casting method that can meet the various demands of imparting desired physical properties to desired parts of a cast product and that can freely control the layer thickness. The purpose is to provide a method. [Means for Solving the Problems] The casting method according to the present invention A uses a specific metal, alloy, or metal that imparts specific physical properties (wear resistance, corrosion resistance, heat resistance, etc.) to the metal to be cast. A powder that is resistant to bonding with nonmetals, and a powder of a metal that has a clearly lower melting point than the metal constituting A.
An adhesion layer of a predetermined thickness is provided in advance at a desired location on the surface of the casting surface of the mold by binding an appropriate amount of an organic binder, and the metal constituting B is melted into the void. A third molten metal with a clearly higher temperature is injected and filled from the point, and the low melting point metal powder that makes up the impregnated layer is melted by the heat of the injected metal.
The three parts are integrated with each other by liquid phase sintering, and then the injected third metal is diffused and welded through the layer surface, but the metal constituting A remains unchanged and occupies the main part of the layer, and solidifies. Subsequently, the above-mentioned problem was solved by modifying the procedure for forming a reaction layer exhibiting specific physical properties at the desired site. In addition, as a specific embodiment of the present method, there is a method in which the three components A, B, and C are mixed in a slurry form and applied to the surface of the mold, or a method in which the three components are kneaded and then formed into a thin plate to form a casting surface. A mode of attaching it to a surface was also shown to make it easier to solve the above problem. [Operation] When a target molten metal is poured into a mold having an impregnated layer inside, metal B forming the impregnated layer reaches its melting point and begins to melt due to the heat of the molten metal. At this time, metal A (bond) can be dissolved in three ways depending on the blended materials: it may dissolve only partially near the surface, or it may not dissolve at all. There are many different conditions for this, depending on the content of component A (material and blending ratio) and the temperature of the molten metal to be injected, but all of these are factors that can be calculated and determined in advance. The most important feature of the action is that all of the impregnated layer does not dissolve and diffuse into the molten metal to form a straight reaction layer, but metal B, which has a low melting point, first receives the heat of the molten metal and melts, forming the A component. This is the point at which so-called liquid phase sintering occurs, where the metal is tightly held and welded to the molten metal. Therefore, as shown in the later examples, the reaction layer embraces the A component that controls physical properties and combines with the B metal and the molten metal matrix, and the A component is deposited at a predetermined depth according to the casting plan planned in advance. It is strongly diffusion bonded to the base material over a period of time. In addition, component C in the constituent requirements maintains the bond with the mold surface at the time of forming the attachment layer, and when pouring,
The layer does not separate due to the force of the flow, and solidification starts from the surface, so it plays a gripping role. On the other hand, with organic binders, the binder burns instantaneously, the powdered metal easily diffuses into the molten metal, and is easily soluble to form the desired reaction layer on the surface. Among organic binders, binders used in the production of ceramics are particularly suitable, as described in the Examples. [Example] Fig. 1 shows a cross section of a mold for a test piece prepared to confirm the effect of the present application, and molds 1 and 2 are silica sand and CO ₂ gas molds. (The mold has sprue 4,
(Providing a weir 5) The adhesion layer 3 is a mixture of three types A, B, and C kneaded and attached to the surface of the mold, and has a thickness of about 2 mm. Table 1 shows the components and compounding ratios of each compounding material A, B, and C of this example.

【table】

Dilute and mix according to [Table] to form an adhesion layer.
Next, Table 2 shows, for comparison, a conventional technique in which the mold has the same structure as that in FIG. 1, but the structure of the impregnated layer is only A+C.

[Table] Table 3 shows the composition of the base metal (ordinary cast iron) poured into two molds provided with the impregnated layers shown in Tables 1 and 2, respectively.

[Table] The casting temperature is 1450℃. FIG. 2 is a micrograph (×100) showing the structure of this example, and FIG. 3 is a micrograph (×100) showing the structure of the conventional technology carried out under the same conditions for comparison.
100). FIG. 4 shows the change in Vickers hardness at each depth from the surface toward the inside of this example and the comparative example (prior art), with the solid line representing the present invention and the dotted line representing the comparative example. Other examples were also tested using the specimen of FIG. That is, while the previous example was to confirm wear resistance, the second example aimed to add corrosion resistance, and Niresist was selected as a comparative material for confirmation. Table 4 shows the components and compounding ratios of each compounding material A, B, and C of the attachment layer 3.

[Table] Comparative example 1 is cut out of SS41, comparative examples 2 to 4 are
Niresist 1b, 2b, respectively specified by ASTM
A test piece corresponding to D ₂ was taken using the mold shown in Figure 1. Table 5 shows the second embodiment of the present invention and comparative examples 1 to 4.
The following shows the results of a corrosion resistance test under the same conditions. The test temperature was 45℃, the test time was 800 hours, and the corrosion test liquid was (a) 3% Nacl - 0.1% H ₂ SO ₄ (b) 3% Nacl. -0.3% H ₂ SO ₄ (c) 3% Nacl -0.5% H ₂ SO ₄ were used in a salt bath in continuous spray form. The numerical value of the test results is the average corrosion rate M (μ/
year) and the maximum plate thickness reduction rate R (mm/year).

[Table] As is clear here, in the second example of the present application, it has been proven that the corrosion resistance is far superior to that of ordinary carbon steel, and is in the range of Niresist, which has a reputation as a corrosion resistant material against seawater and the like. Figure 7 plots the results of Table 5 on a chart to visualize the degree of remarkable effect. Note that good results can be obtained by selecting the organic binder from among the materials listed below. Binding materials Cellulose acetate butyrate, nitrocellulose, petroleum resin, polyethylene, polyacrylic acid ester, polymetal methacrylate, polyvinyl alcohol, polyvinyl butyral, vinyl chloride, polymethacrylic acid ester, ethyl cellulose, abietic acid resin, and the metal A above In addition to the above, materials known as superhard materials such as metal carbides, nitrides, and borides, such as WC, TiC, and TiN, may be used as the system powder. Figure 5 shows an example of application as an actual cast product.
Figure 5A is a front view of a pump impeller.The area around the blade root (hatching area) is subject to severe wear, so conventionally the entire part was made of highly wear-resistant material (for example, 27% chrome cast iron). . FIG. 5B shows an embodiment of the present invention in which a core mold 2 is fitted into a main mold 1, and an adhesive layer 3 of the present invention formed into a thin plate having a thickness of 4 mm is pasted into the gap corresponding to the blade root of the core mold. 6 is a hot water path. Figure 6 is an example of a pump casing mold, main mold 1.
Of the core mold 2 to be fitted, the present application A mixed in a slurry form on the surface corresponding to the throat part of the casing;
Apply the B and C3 components to form the attachment layer 3 with a thickness of 2 mm.
It was formed over a period of time. [Effects of the Invention] Comparing an example of the effects of the present invention from the microscopic micrographs of the microstructures in FIGS. If you look at the hardened layer), you will see that the present application (second hardened layer)
It is clear that the method shown in Fig. 3 is more deeply expressed than the conventional technology (Fig. 3), and even if the same hardening material (Fe-Cr) is used, it achieves the purpose of hardening more effectively. In the end, it can be said that grasping the hardening material is more effective. This difference can also be seen from Figure 4, which shows changes in hardness. In addition, in the case of the impeller shown in Figure 5A, it has the effect of further increasing the wear resistance of the parts that are subject to severe wear, but in general wear-resistant materials are also typically difficult-to-cut materials, so machining of the impeller boss This results in a significant rise in processing costs. Therefore, the molten metal to be injected and filled into the void shown in Figure 5B can be made of a low wear-resistant material that is significantly lower than the conventional high wear-resistant (ultra-difficult-to-cut) material. Another effect is that it is possible to obtain a service life of . In addition, the embodiment shown in FIG. 6 can be expected to have the same effect, and has the advantage that this embodiment has a simple procedure and is easy to implement. Moreover, since the binder is limited to an organic type, the effect of reliably realizing the formation of the desired reaction layer on the surface can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of a mold showing an embodiment of the present application;
Fig. 2 is a micrograph showing the metal structure of the example of the present application, Fig. 3 is a photomicrograph showing the metal structure of the prior art example, and Fig. 4 is the hardened layer and hardness of the example shown in Figs. 2 and 3. and a graph showing the depth from the surface, Figures 5A and B are an actual cast product (front view) and a mold (plane sectional view) showing the embodiment of the present application, and Figure 6 is a plane sectional view showing another embodiment. . FIG. 7 is a graph illustrating the effect of the second embodiment of the present application. 1, 2...mold, 3...adhesive layer.

Claims (1)

[Scope of Claims] 1. A casting method in which a mold cavity is injected and filled with molten metal to obtain a cast product having a desired shape after solidification, which includes: A a specific metal and/or a plurality of metals that impart specific physical properties to the metal; A powder made of an alloy material of various types of metals and/or a combination of metals and non-metals; An impregnating layer of a predetermined thickness is prepared in advance at a desired location on the surface of the casting surface of the mold by kneading together the three materials, and an impregnating layer having a temperature clearly higher than the melting point of the metal constituting B is added to the void. The three molten metals are injected and filled, first the low melting point metal powder that makes up the impregnated layer is melted by the heat possessed by the injected metal, the three are mutually integrated by liquid phase sintering, and then The injected third metal is diffused and welded through the layer surface, but the A
A casting method characterized in that the metal itself that constitutes the layer remains the main part of the layer, and after solidification, a reaction layer that exhibits specific physical properties is formed at the desired location. 2. The casting method according to claim 1, wherein the attachment layer is a mixture of the three materials A, B, and C in the form of a slurry and is attached to a desired portion of the mold surface to a desired thickness. 3. The attachment layer is formed into a thin plate after kneading the three materials A, B, and C, and is attached as a thin plate of a desired thickness by following the desired area on the surface of the casting surface of the mold. casting method.