JPS5982153A - Production of composite casting - Google Patents

Abstract

PURPOSE:To produce easily and inexpensively a dense composite casting having uniformly distributed ceramic particles by subjecting a mixture composed of a molten metal and ceramic particles having the specific gravity larger than the specific gravity of said metal to heat replenishment by high-frequency induction heating in a casting mold. CONSTITUTION:A molten metal M or iron or the like is charged, via a charging hopper 5, from a ladle 8 into a casting mold 1 installed via backing sand 2 in a case 3. On the other hand, a prescribed amt. of ceramic particles P of WC or the like having the specific gravity larger than the specific gravity of said metal M are charged from a powder charger 6 provided with a flow rate control valve 7 for powder, via a feed port 61, into the metal M in the mold 1. The metal M is heated by a high-frequency induction heating coil 4 provided around the mold 1 to replenish the quantity of heat released by radiation, etc. whereby the fluidity of the metal M is maintained and the settling and deposition of the particles P are accelerated. The penetration of the molten metal into the clearances among the particles is made easy and the casting having the sound composite structure wherein the particles P are uniformly and densely distributed is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a composite casting made of a mixture of metal and tungsten carbide particles.

A material having a composite structure in which metal and ceramic particles such as tungsten carbide are mixed is a particle-reinforced material and is suitable as a wear-resistant material. Such a composite material can be manufactured more easily and at a lower cost by using a casting method than by a powder metallurgy method. That is, if a molten metal and ceramic particles having a higher specific gravity than the molten metal are poured into a mold, the ceramic particles in the solid-liquid mixture will settle and accumulate due to the difference in specific gravity, and then the molten metal will solidify. A casting having a composite structure consisting of ceramic particles and a base metal matrix filled between the particles is obtained.

In the above casting method, in order to form a composite structure with a dense and uniform distribution of ceramic particles and a strong bond between the metal base and the particles, it is necessary to make the molten metal viscous once during the sedimentation and accumulation process of the particles. The molten metal must be kept sufficiently hot and fluid so that accumulation is not hindered.

However, the molten metal in the mold loses a considerable amount of heat in a relatively short period of time due to heat radiation from the molten metal surface, heat transfer to the mold wall, and heat absorption by the applied particles. in this case,
If the amount of molten metal cast is large, there will not be much of an effect, but if the amount of molten metal cast is relatively small, such as for the purpose of casting, small articles, thin-walled items, etc., the viscosity of the molten metal will be affected early. f frequency/
Solidification begins, and subsequent sedimentation and accumulation of particles and penetration of the molten metal between the particles are prevented. As a result, the resulting casting has casting defects such as uneven particle distribution, local agglomeration, and microporosity between particles. Possible countermeasures for this include preheating the mold and ceramic powder, or increasing the casting temperature of the molten metal, or by preheating the mold and powder, it is hoped that preheating the mold and powder will provide enough heat to restore the fluidity of the molten metal. However, if the casting temperature is too high, problems with the material will occur, so neither of these measures can be taken as a sufficient measure.

This TM solves the above problem.

The method for manufacturing composite castings of the present invention replenishes heat by high-frequency induction heating to the molten metal in the mold during the sedimentation and accumulation process of ceramic particles in a solid-liquid mixture of molten metal and ceramic particles provided in the mold. While maintaining fluidity, it promotes the sedimentation and accumulation of particles and makes it easier for molten metal to infiltrate into the gaps between particles.This allows ceramic particles to be easily absorbed even in small articles, thin walls, or complex-shaped castings. This enabled the formation of a healthy composite tissue with uniform and dense distribution.

FIG. 1 shows an example of casting according to the method of the present invention. (1) is a mold, (4) is a high-frequency induction heating coil installed around the mold, (5) is a casting popper, and (6) is a ceramic powder throwing 1-1 device that has a powder flow rate control valve (7). be.

The mold (1) is, for example, a firing mold used for lost wax casting, and is installed in a case (3) with back sand (for example, magnesia stamp material) (2). In this device, a metal bath Ft) (M) melted in advance to a predetermined composition is poured from a ladle (8) into a mold (1) via a pouring potper (5), while a powder dosing device ( From step 6), a required amount of ceramic powder (P) is administered to the in-mold melt through the inlet (61). Ceramic particles (P) in the molten metal placed in the mold begin to settle due to the difference in specific gravity and gradually accumulate. During this particle sedimentation and accumulation process, the molten metal (M) is heated by the high frequency induction heating coil (4). Of course, the amount of heat supplied by heating must be sufficient to compensate for the amount of heat taken away by heat radiation from the scene, heat transfer to the mold wall, heat absorption by particles, etc., and to eliminate viscosity and solidification of the molten metal. It takes. After the particles are sufficiently settled and accumulated in this manner, the high-frequency induction heating is stopped and the solidification of the molten metal is waited for, thereby obtaining a solid cylindrical composite casting having a composite structure.

In the present invention, the high-frequency induction heating of the molten metal in the mold may be performed at an appropriate time after the start of casting the molten metal. For example, it may start after the completion of casting of the molten metal and ceramic powder, and may be continued continuously or intermittently at appropriate times to maintain a high-temperature fluid state in which sedimentation and accumulation can proceed smoothly until the required sedimentation and accumulation of particles is completed. Heat supply should be provided.

Alternatively, after the particles begin to solidify during sedimentation, they may be redissolved by high-frequency induction heating to restore sufficient fluidity.

FIG. 2 shows an example of manufacturing a hollow cylindrical casting.

Cast! l! (9) has an inner shape corresponding to the intended casting shape, and a high frequency induction heating coil (4) is attached around it. After molten metal is poured into the mold (9), ceramic powder (P) is dosed by a powder dosing device (6), and heat is supplied by a high-frequency induction heating coil (4) in a timely manner. . In the production of this hollow cylindrical casting, if the ceramic powder is dosed at one location in the mold (9), the powder will be localized in that location and cannot be distributed in the circumferential direction.

Therefore, the powder dosing device may have a plurality of dosing ports (62) along the annular open end of the mold, as shown, or an annular dosing port (62) along the open end of the mold.
2), it is necessary to uniformly distribute and administer in the circumferential direction within the mold. Alternatively, as shown in FIG.
By providing M) and powder (P) in the mold, it is also possible to achieve uniform dispersion in the circumferential direction.

In each of the above-mentioned casting examples, the metal powder and the ceramic powder were separately provided in the mold, but in addition to that, for example, in the examples shown in FIGS. Aim the tip of the molten metal (M,) toward the casting hopper (5).
and powder (P) may be mixed and cast into a mold.

In addition, instead of the method of casting a pre-molten metal as described above, a metal lump or metal powder is charged into a mold as a melting raw material, and it is melted using a high frequency induction heating coil, It is also possible to adopt a method of administering ceramic powder to the produced molten metal. Of course, even in that case, heat supply after powder administration may be performed in the same manner as described above, depending on the temperature drop of the molten metal.

The mold used in the casting of the present invention may be the precision casting mold described above or any other type of refractory mold.

The molten metal is a variety of ferrous or non-ferrous metals or alloys selected depending on the intended use and required performance of the casting. When melting a molten metal in a mold using a metal lump or the like as a melting raw material, if necessary, a ferroalloy or the like may be added to adjust the composition to a predetermined composition.

The ceramic powder is selected from carbide, nitride, ferride, silicide, etc. depending on the purpose. Of course, the particles must have a high melting point so that they do not easily dissolve and disappear in the molten metal, and must also have a specific gravity greater than that of the molten metal.

When the molten metal and the ceramic powder are separately cast into the mold, that is, when the ceramic powder is applied to the molten metal in the mold, the ceramic particles preferably have good wettability with the molten metal. This is because if the wettability is poor, it may not be immediately incorporated into the molten metal, but may float on the surface and locally aggregate. Furthermore, when the purpose is to make a casting for wear-resistant use, it goes without saying that the harder the ceramic particles themselves are, the more advantageous it is. For example, in the production of wear-resistant castings in combination with iron-based metals, tungsten carbide (W
2C, WC), tungsten titanium carbide and the like are preferably used. In addition, the particle size of the ceramic particles is approximately 300 ltm from the viewpoint of the material of the casting to be obtained.
It is preferable that it is below. However, if the particles are too fine, it will be difficult for them to settle and accumulate in the molten metal, so the lower limit of the particle size is usually about 50 μm).

The proportion of ceramic particles in the composite structure of the casting obtained according to the present invention (particle filling rate) C is approximately 60 to 75% by volume (particle:metal volume ratio - approximately 60:40), depending on the grain size structure of the particles. ~75:25). Therefore, the amount of molten metal and the amount of ceramic powder provided in the mold may be adjusted to the above ratio. Usually, when using this type of casting method, the amount of molten metal cast is larger than the above ratio, and the
1i As shown in Fig. 1, a cast body consisting of a composite structure part (A,) consisting of particles (P) and metal (M) and a single metal phase part (B) formed of surplus metal was obtained. After that, the metal single phase part (B) is cut and removed, and the composite structure part (A) is removed.
A procedure is required to extract the material as a product. This is intended to suppress the rapid temperature drop of the molten metal within the mold by increasing the amount of molten metal cast.

In contrast, in the present invention, the necessary heat is supplied by high-frequency induction heating, so there is no need to cast extra molten metal as described above, and the amount of molten metal can be reduced accordingly. However, in order to compensate for the amount of shrinkage that occurs during the solidification process, it is sufficient to give the feeder amount of ordinary casting and [Mr.

Next, examples of the present invention will be described.

Example 2) \-1.゛Cast iron molten metal (C8, 35%, Si 0.72%, Δin 0.68%) melted in a melting furnace as a molten metal.
, Ni4.85%, Cri, 52%, Mo0.88%)
and ceramic powder with a particle size of 150 to 250 μm (7
) Tungsten carbide (W2C) powder was prepared and cast using the apparatus shown in FIG.

5.4 hours of molten metal into a mold (precision casting IM) (9)
Casting temperature: 1600°C), high frequency coil (4
) was energized to maintain the temperature of the molten metal in the mold at 1600°ci, and then a powder dosing device (6) was used to add tungsten carbide powder 9.4. Kg was administered. The carbide powder (used at room temperature without preheating. After administering the powder, the temperature of the melt decreased,
Since the viscosity has become one round, heat it further and make it molten metal? 1 ship is 16
Stop heating when it reaches 00°C. After that, let it cool naturally and wait until the solidification is complete. +i4. .

Inner diameter LOOmm, wall thickness 20mm, length 1-0'O
A hollow cylindrical casting having a product shape of mm was obtained.

The distribution of carbide particles in the composite structure of the obtained casting is extremely uniform over the entire circumference of the product, and the particle filling rate is about 70%. Furthermore, the metal matrix between the particles is dense and no defects such as microporosity are observed.

As described above, according to the present invention, the heat compensation 16 for the metal welding field can be used not only for thick-walled and large-diameter castings, but also for small-diameter thin-walled castings, especially cylindrical bodies with a diameter of about 80 mm or less, or with a wall thickness of 30 tnm or less. Even when casting hollow cylindrical bodies or plate-like bodies, it is possible to obtain castings having a dense composite structure in which ceramic particles are uniformly distributed. Therefore, it is suitable for manufacturing small parts that require wear resistance, such as small diameter rolls and sandblasting nozzles.

[Brief explanation of drawings]

1 to 3 are longitudinal cross-sectional views showing examples of casting according to the present invention, and FIG. 4 is a cross-sectional explanatory view of the casting. 1.9: Mold, 4: High frequency induction heating Koinope 5: Casting hopper, 6: Powder dosing device, 10: Horizontal rotary table, P:
Ceramic particles, M: metal. Agent Patent Attorney Arata Miyazaki Dept. -3 4.・ , 4 Figure 2 Figure 4

Claims (1)

[Claims] (1) A solid-liquid mixture of molten metal and ceramic particles having a higher specific gravity than the molten metal is provided in a mold, and the ceramic particles settle and accumulate due to the difference in specific gravity, and are then solidified to produce a casting having a composite structure consisting of metal and ceramic particles. A composite casting characterized in that the manufacturing method comprises applying heat to the solid-liquid mixture in the mold by high-frequency induction heating to maintain the fluidity of the molten metal, thereby promoting sedimentation and accumulation of ceramic particles. manufacturing method.