JPH06190537A - Method for reforming casting surface - Google Patents

Abstract

PURPOSE:To obtain a reforming technique of a casting surface having improving characteristic of excellent wear resistance, etc.(in comparatively simple way by further developing the reforming technique of the casting surface with an internal chill method. CONSTITUTION:Metal powder having the characteristic corresponding to the reforming aim of wear resistance, heat resistance, etc., and wafer glass base deposited material are mixed to form raste-state. This mixed material is coated on the part corresponding to the surface reforming in a mold, and after hardening, molten iron-base metal is cast in the mold to form the reformed layer 3 on the surface of the casting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying the surface of a casting, and more particularly to a technology for modifying the surface of a casting which forms a modified layer having excellent wear resistance and heat resistance on the surface of the casting.

[0002]

2. Description of the Related Art Various surface modification methods have been conventionally proposed in order to improve wear resistance, heat resistance and the like at a specific portion of a casting surface.

For example, there are measures for improving wear resistance by surface quenching, carburizing, nitriding, etc., and measures for improving wear resistance and heat resistance by welding dissimilar metals such as spraying and brazing. The dissimilar metals used for thermal spraying and brazing differ depending on the required properties. For example, carbide constituent elements such as Cr are used to improve wear resistance, and N is used to improve heat resistance.
i, Mo, etc. are used.

[0004]

However, surface quenching, carburizing, nitriding, thermal spraying and the like of castings have the disadvantages that special equipment and complicated steps are required and the cost is high. In addition, since brazing includes a large amount of carbon in the casting, the adhesion with the casting is weak, and peeling easily occurs when a strong bonding pressure or impact is applied.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. Sho 60-82263, by utilizing the characteristics of castings, a welding material is applied to a predetermined shape formed in advance with a modifying alloy, and the resulting material is placed in a mold. There is known a so-called cast gurney technique in which a molten metal is set and cast into a casting to form a casting. In this method, the casting and the reforming alloy layer on the surface are integrated by solidification of the molten metal, and therefore the fixing force of the reforming layer is far superior to that of brazing.

However, in this method, it takes a lot of time to form the cast-in-stock material, and a large amount of expensive reforming alloys is required. In addition, since the welding material used is generally organic, it generates gas by contacting the molten metal during casting.
There are many problems such as the occurrence of defects such as pinholes at the boundary of the cast metal.

The problem to be solved by the present invention is to further develop the casting surface modification technology by the cast-girth method, and relatively easily and improve the casting surface modification technology having excellent wear resistance and the like. Is to get.

[0008]

In order to solve the above-mentioned problems, a method for modifying the surface of a casting according to the present invention comprises a metal powder and a water glass system having a characteristic such as wear resistance and heat resistance according to the modification purpose. Mixing with a welding material to form a paste, applying it to the surface modification equivalent part in the mold and hardening it, casting iron-based molten metal in the mold to form a modified layer on the surface of the casting Is characterized by.

Here, in order to improve the wear resistance of the casting surface, WC 70 to 98% by weight, Co 30 to 2% by weight,
Cemented carbide powder having a particle size of 100 μm or more can be used.

The Co content of 30 to 2% by weight is 30
This is because if it exceeds 5% by weight, the abrasion resistance becomes too low, and if it is less than 2% by weight, the strength becomes insufficient.

It is desirable that the water-glass type welding material be easily mixed when mixed with the metal powder and do not easily flow out by application to the mold, and have a molar ratio of 2.0 to 3.5%. Use one. The water glass and the metal powder are mixed at a weight ratio of 10: 1 to form a paste.

The paste can be applied by brush or spray, and the applied thickness is 1.0-6.
0 mm is desirable. If the coating thickness is less than 1.0 mm, the impact resistance becomes low, and if it exceeds 6.0 mm, it becomes difficult to form a sound superhard layer.

Further, for the purpose of improving heat resistance, a metal powder of Ni or Mo can be used, and for the purpose of improving corrosion resistance, a metal powder of Cr or Ni can be used.

In the case of heat resistance, the particle size is 10
Ni-Mo powder of 0-200 μm is mixed with water glass having the above molar ratio to form a paste, which is applied to a mold by brushing or spraying, and an iron-based molten metal is cast into the powder. 250 μm of Cr or Ni powder is applied to a mold and cast in the same manner as in the case of heat resistance.

[0015]

The paste-like mixture of the metal powder and the water glass-based welding material applied in the mold is securely held at the application site due to the viscosity of the water glass, and the metal powder applied by contact with the molten metal A modified layer is formed which is melted and integrated with the casting on the surface of the casting. At that time, the water glass-based welding material is dehydrated, melted into slag, flows out, and does not burn because it is an inorganic substance, and unlike conventional organic welding materials such as acrylic and phenol-based materials, gas generation is extremely small. In addition, there is no risk of pinhole or blowhole defects occurring at the boundaries of the base material.

In particular, the metal powder composed of WC and Co is
It alloys with the iron base material at the temperature of the molten iron-based casting. At that time, since WC has a relatively low solubility, most of it remains in the form of particles to become an aggregate, and Co alloys with Fe to form a solution, so that the WC as an aggregate is surrounded by Co in a stone wall. A surface-modified layer having a strong structure is formed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a mold used for carrying out the present invention.

In the drawing, 1a and 1b are organic self-hardening lower molds, upper molds, 2 are hollow parts for forming castings, 3 are modified layers, 4
Indicates the sprue, respectively.

In the modified portion of the lower mold 1a, WC93.
5% by weight, Co 6.5% by weight, particle size 125-250 μm
Cemented carbide powder of the above particles and water glass having a concentration of 50% and a molar ratio of 2.3 are mixed in a weight ratio of 10: 1 to form a paste, which is applied with a brush to a thickness of about 1.5 mm. Then, the modified layer 3 was formed.

Then, this is left at room temperature for about 5 hours to be hardened, and the upper mold 1b of the homogeneous material having the sprue 4 is covered to assemble the mold, and the melt of the ductile cast iron having the components (% by weight) shown in Table 1 is prepared. Was cast at 1320 ° C. by this,
A casting was obtained in which the modified layer 3 made of an alloy of WC and Co was welded to the entire surface.

[0021]

[Table 1] ★

FIG. 2 is a structural diagram of the modified surface, and FIG. 3 is an enlarged structural diagram of the cemented carbide portion.

As is clear from the figure, it can be seen that the hard WC is present in the form of lumps, and the Co alloyed with the base of the ductile cast iron fills the space between them with cement and is well welded.
Further, the water glass used as the welding agent remains spherical. The cemented carbide of this example is composed of WC and Co, and most of the C alloyed with ductile cast iron is crystallized as graphite, but when C is contained, its carbide is generated, contributing to wear resistance. Therefore, the cemented carbide component can be adjusted depending on the application.

As described above, when the cemented carbide powder comes into contact with the molten metal, most of the high melting point WC remains in the form of particles, and the low melting point Co dissolves in the base iron and WC.
The gap is filled up and it also diffuses into the ductile cast iron matrix to form a strong bond structure.

When a steel ball having a diameter of 3 mm was projected by shot blasting for a factory on the casting with improved wear resistance,
There was no peeling at all and no wear was observed.

Further, as shown in FIG. 4, a SiC polishing cloth having a roughness of # 60 (width 100 mm, length 1525 mm) 2
0 was moved at a speed of 920 m / min, sample A was placed on this, and a load of 3.0 kg / cm ² was applied, and the weight loss was measured at regular intervals. As a comparative example, the surface-chilled ductile cast iron of Table 1 component, AD which was austempered
A cemented carbide material having the same composition as in Example I and Example was brazed. The results are shown in FIG. 5, and it can be seen that this example is excellent.

FIG. 6 shows still another test example, in which the grain size 70-
20% by weight of 100 mesh flattery sand, about 1 in diameter
20x20 with a reforming layer on one side of a disk 25 equipped with a rotating shaft 24 in the center, in a liquid 23 that is mixed with 0 mm pebbles and placed in a container 22 and is soaked with water to the surface to form a mud × 10
The sample A of 0 mm is fixed by bolts 26, fixed and rotated. Further, the same comparative example as described above was fixed to the rotating disk 25 on a concentric circle. The rotation speed was set to 300 rpm, and the weight loss at every constant time was plotted in FIG. 7. In this test, the wear resistance of this example was excellent.

In any of the wear measurement examples, the brazed samples were not able to withstand the severe test conditions as in the present experiment because the cemented carbide portion was peeled off in a short time contact.

In this embodiment, the weight loss is much smaller than that of the chill casting and ADI, the surface structure after the test is stable as shown in FIG. 8, and there is no peeling and the surface modification layer effectively works. . Examples of applications of castings having such excellent wear resistance include teeth for construction vehicles and disk rotors.

For the purpose of improving the corrosion resistance, nickel was used as the metal powder in the same procedure as above. The particle size was 170 to 200 μm, and other conditions such as water glass were the same. As a result, a casting having excellent corrosion resistance could be manufactured.

Further, for the purpose of improving heat resistance, a grain size of 120
When molybdenum powder having a particle size of 170 μm was used, a casting having excellent heat resistance was similarly produced.

Although the ductile cast iron melt was used as an example in the present embodiment, it is natural that the same result can be obtained by using a normal cast iron melt or a low alloy cast iron melt.

[0033]

According to the present invention, the following effects can be obtained.

(1) Since the modified layer can be integrally welded to the surface of the cast iron casting by casting, it is inexpensive, unlike the conventional method of surface hardening or spraying or brazing a wear resistant alloy,
It is possible to obtain a casting that is strong and has excellent modifying properties without requiring extra steps.

(2) Since an inorganic water glass material is used as the welding material, there is no occurrence of pinholes at the boundary or the reforming layer due to combustion gas or the like.

(3) By using the metal powder composed of WC and Co, a strong surface modified layer having a stone wall structure in which WC as an aggregate is surrounded by Co is formed.

[Brief description of drawings]

1 is a cross-sectional view of a mold used to carry out the present invention.

FIG. 2 is a photograph showing the metal structure of the surface of the modified layer.

3 is a partially enlarged view of FIG.

FIG. 4 is a schematic diagram of a weight loss test apparatus.

5 is a test result by the test apparatus of FIG.

FIG. 6 is a schematic view of another test apparatus.

7 is a test result obtained by the test apparatus shown in FIG.

FIG. 8 is a structural diagram of the surface of the modified layer after the test.

[Explanation of symbols]

 1a Lower mold 1b Upper mold 2 Cavity for casting formation 3 Modified layer 4 Gate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Detsu 25-25 Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Automotive Foundry Co., Ltd.

Claims (2)

[Claims] 1. A paste is prepared by mixing a metal powder having properties such as abrasion resistance and heat resistance according to the purpose of modification and a water glass-based welding material, and applying this to a portion corresponding to surface modification in a mold. A method for reforming the surface of a casting, in which the molten iron is poured into the mold to form a modified layer on the surface of the casting. 2. The metal powder according to claim 1 is WC70-
A method for modifying the surface of a casting, which comprises a cemented carbide powder containing 98% by weight of Co and 30 to 2% by weight of Co.