JPH0338020B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a centrifugal casting method for wear-resistant castings, particularly in casting castings such as cast iron or cast steel in which hard carbide particles such as tungsten carbide particles are mixed in the surface layer. This invention relates to a centrifugal casting method for wear-resistant castings that can be formed thickly.

By mixing hard particles such as tungsten carbide (WC, W ₂ C) particles in the metal, it is possible to impart a high degree of wear resistance that cannot be obtained with metal alone. Based on this knowledge, the present inventors first used centrifugal force casting to create an outer peripheral region (hereinafter referred to as "outer layer") in which metal M and hard particles P coexist, as shown in FIG. (referred to as "mixed layer")
We proposed a method for producing a casting having a two-layer structure: A and an inner region (hereinafter referred to as the "inner layer" or "metal layer") B consisting essentially only of metal M (Japanese Patent Application No. 1983).
-213860, 56-213861, etc.). in this way,
If a mixed layer is formed only on the surface layer where wear resistance is required, it is not only economical as it reduces the amount of expensive hard particles used, but also provides high wear resistance due to the mixed layer and the base layer due to the metal layer. It is possible to combine the inherent material properties of the material metal, such as toughness.

For example, as shown in FIG. 6, the above-mentioned casting is carried out by pouring metal into a mold 1 which rotates around its axis, through a pouring hole 3 in an end plate 2, and through a pouring trough 5 of a hopper 4. After casting the molten metal M', after finishing casting the molten metal, hard particles P having a higher specific gravity than the molten metal are scattered onto the surface of the molten metal using a hard particle adding jig 6 inserted through the hole 3' of the end plate 2'. This is done by Under the action of centrifugal force, the hard particles P administered to the surface of the molten metal,
Due to the difference in specific gravity between the molten metal and the molten metal, the molten metal layer is centrifugally transferred (sedimented) toward the inner wall surface of the mold 1 and concentrated in the outer peripheral area, forming a mixed layer, so the mold continues to rotate. By solidifying the molten metal, the above-mentioned casting can be obtained.

In the above centrifugal casting, in order to form a mixed layer with a uniform layer thickness over the entire length and circumference of the casting, it is necessary to uniformly disperse and administer the hard particles P to the molten metal layer M' in the mold. is necessary.

However, in actual casting, even though the hard particles are uniformly distributed along the axial direction of the mold, the thickness of the resulting mixed layer A is
As shown in the figure, it tends to be thinner in the central region in the axial direction and thicker near both ends. In particular, when forming a thick mixed layer (particularly a layer thickness exceeding about 5 mm), the above-mentioned tendency becomes more noticeable when the centrifugal force during casting is increased. The cause of this non-uniform layer thickness is considered as follows. In other words, hard particles such as carbides have poor adsorption to molten metal and are difficult to absorb into the molten metal, so even if they are sprinkled on the surface of the molten metal,
It is not immediately adsorbed into the molten metal layer and floats on the surface of the molten metal. Moreover, inside the mold, a small amount of molten slag mixed in with the molten metal is floating on the surface of the molten metal, and this slag has good wettability with hard particles, so it easily adsorbs and captures the hard particles applied. . This slag moves to the surface of the molten metal under the action of centrifugal force and tends to concentrate at both ends of the mold. Therefore, even if the hard particles are evenly distributed in the longitudinal direction, they are carried by the slag to both ends, where they are adsorbed by the molten metal and settle.
As a result, the resulting mixed layer becomes non-uniform, with thick layer thickness at both ends as described above.

The present invention provides a casting method that prevents the above-described local concentration and uneven distribution of hard particles and forms a mixed layer having a uniform layer thickness over the entire length in the axial direction.

The present invention adds hard carbide particles having a higher specific gravity than the molten metal to the molten cast iron or cast steel cast in a centrifugal casting mold, centrifugally transfers the molten metal, and concentrates the hard carbide particles in the outer peripheral area. In a method for casting a casting having a two-layer structure consisting of an outer layer containing a mixture of metal and coin carbide particles and an inner layer substantially consisting of metal, the molten metal surface in the mold is wetted with the molten metal and hard carbide particles. Form a molten flux layer with properties to cover the entire surface of the molten metal, and hard carbide particles are evenly distributed over the entire axial length of the molten flux layer, and the hard carbide particles are spread over the molten metal surface through the molten flux layer. It is characterized by being adsorbed to and incorporated into the molten metal.

The present invention will be explained in detail below.

According to the method of the present invention, a molten flux layer F is formed on the surface of the molten metal layer M', as shown in FIG. 1, prior to dispensing hard particles into the molten metal poured into the mold. The molten flux layer F needs to cover the entire upper surface of the molten metal. The hard particles P are administered to the molten metal M' through the molten flux layer F.

That is, the hard particles P dispersed and administered from above the molten flux layer F are once adsorbed by the flux layer F, then come into contact with the molten metal M', are adsorbed to the surface of the molten metal, are taken into the molten metal, and are then directed toward the outer periphery. Then, it is centrifugally transferred (sedimented) in the molten metal due to the difference in specific gravity between the molten metal and the molten metal. In this case, since the molten flux F covers the entire surface of the molten metal, it does not move greatly in the axial direction on the surface of the molten metal, but only oscillates in a substantially fixed position. Therefore, the hard particles adsorbed on this
It is not carried to the end of the mold as mentioned above,
It is adsorbed by the molten metal at approximately the position where it falls. After being adsorbed by the molten metal, it settles in the molten metal at approximately that position, although this depends somewhat on the movement of the molten metal.
In this way, the hard particles are virtually completely prevented from moving or being unevenly distributed at both ends of the mold, and if they are evenly distributed and administered along the axial direction, a uniform layer thickness can be obtained over the entire length and circumference of the casting. A mixed layer is formed.

Examples of the flux F that coats the molten metal surface include molten slag formed during refining of molten metal,
Another example is flux, which is used to prevent oxidation of molten metal in centrifugal casting, but in short, if it has wettability to both molten metal and hard particles, oxides, chlorides, fluorides, etc. Alternatively, any component system may be used, such as a mixture (solid solution or mixture) of two or more of these. Of course, it must not come into contact with molten metal and cause changes in the chemical composition of the molten metal.
Further, it is preferable that the material has a low melting point and exhibits sufficient fluidity even in a low temperature range near the freezing point of the molten metal. Furthermore, if the amount of flux on the molten metal surface is small,
Since the adsorption and capture effect of hard particles is insufficient, it is desirable that the amount is such that a layer thickness of at least 0.5 mm is formed.

The above-mentioned molten flux layer may be formed by a method in which a flux powder prepared to have a desired composition is injected into a mold and melted by the heat of the molten metal, or it may be injected as a molten flux in a high temperature state. . Needless to say, the latter method is advantageous in suppressing the temperature drop and viscosity of the molten metal in the mold. When the molten metal becomes extremely viscous, it becomes difficult for the hard particles added afterwards to settle in the molten metal layer by centrifugation, so casting of small-diameter or thin-walled castings with a small amount of molten metal is not recommended. Therefore, it is preferable to administer it as a molten flux.

Hard particles (carbides) that have a higher specific gravity than molten iron alloys such as cast iron and steel include tagsten carbide particles (WC, W ₂ C, etc.) (specific gravity: approximately 16 to 17), tungsten titanium double carbide ((W, Ti)C) (specific gravity: about 10-16), etc. These particles have extremely high hardness (tungsten carbide: Hv approx. 2400, tungsten titanium double carbide: Hv approx. 2000-2400)
Since it has a high melting point and does not easily dissolve and disappear in the molten metal, it is suitable. It has a higher specific gravity than the molten metal and has a high melting point that will not dissolve or disappear in the molten metal.
Other materials may be used as long as they have hardness that contributes to improved wear resistance. In addition, from the viewpoint of the effect of improving wear resistance, the particle size is suitably about 50 to 30 μm.

When hard particles are administered into a mold, the molten flux and molten metal lose heat to the particles, so when administering a large amount of hard particles relative to the amount of flux or molten metal, it is necessary to suppress the temperature drop and viscosity of these particles. For this reason, it is recommended that the hard particles be preheated before administration. The temperature is about 300°C or higher, preferably about 500°C or higher. If the particles are easily oxidized by heating,
For example, the above oxidation can be prevented by applying electroless nickel plating to the particle surface.

The material of cast iron or cast steel, which is the base metal, is selected depending on the intended use and usage conditions of the casting. For example, when heat resistance and strength are required, chromium-based cast iron or cast steel, chromium-based cast iron - Ferrous metals such as nickel-based cast iron or cast steel are preferably used.

In the casting method of the present invention, the administration of flux and the dispersion of hard particles into the mold can be carried out after the completion of casting of the molten metal. That is, after casting a predetermined amount of molten metal, a molten flux layer covering the surface of the molten metal may be formed, and hard particles may be dispersed into this layer. In this case, in order to smoothly concentrate the hard particles into the mixed layer by centrifugation,
It should be administered quickly while the melt temperature is high and fluidity is good. However, if a large amount of particles are administered at once in a short period of time, the surface of the molten metal will be rapidly cooled and partially solidified, which may impede centrifugal separation of the particles and cause the thickness of the mixed layer to become uneven in the circumferential direction. This will cause problems. Therefore, it is desirable to gradually administer the hard particles over a long period of time until the molten metal begins to solidify.

Another method is to coat the surface of the molten metal with a layer of molten flux by dispensing flux immediately before, simultaneously with, or at an appropriate time after the start of casting the molten metal, and to deposit the hard particles simultaneously with the casting of the molten metal. Dispersed administration can also be carried out. The timing to start administering the hard particles may be determined as appropriate, taking into consideration the time required for administration and the time required for casting the molten metal. Of course, the larger the dose of hard particles, the earlier the initiation of administration. However, if hard particles are applied at the early stage of casting when the amount of molten metal in the mold is small, the molten metal will solidify and it will be difficult to form a good mixed state. It is desirable to begin administering the hard particles at or after that point. It is preferable that the administration of the hard particles is completed before or simultaneously with the completion of casting of the molten metal, but it may be completed after the completion of casting as long as sufficient fluidity of the molten metal is maintained. In this way, if the hard particles are administered before the casting of the molten metal is finished, even if the dosage is large, the entire predetermined amount of the hard particles can be easily administered before the molten metal starts solidifying.

There are no particular restrictions on other casting conditions in the centrifugal casting of the present invention, and the rotation speed of the mold is controlled so that the centrifugal force on the mold wall is approximately 50 to 100 G, and the casting temperature of the molten metal is different from that of normal casting. There is no difference, and if necessary, the temperature may be adjusted to a slightly higher temperature in order to compensate for the amount of heat taken away by the hard particles. The amount of hard particles to be administered is, of course, appropriately determined depending on the desired thickness of the mixed layer.

The mixed layer of the casting thus obtained exhibits a mixed state in which each hard particle is densely dispersed and the interparticle gaps are filled with the base metal. The ratio (volume ratio) of hard particles in this mixed layer is preferably about 70
%.

Next, the method of the present invention will be specifically explained using examples.

Example 1 In a centrifugal casting apparatus as shown in Fig. 1, molten metal M' is cast from a ladle (not shown) into a mold 1 through a hopper 4, and the molten metal surface in the mold is cast over the entire circumference and length. It was coated with a molten flux layer F, and the hard particles P were dispersed and administered almost evenly over the entire length, and solidified as it was while the mold was rotating. Incidentally, the powder of the flux was added to the molten metal in the ladle and melted by the heat of the molten metal, and the flux was cast into the mold through a hopper at the same time as the molten metal was cast. The hard particles P are placed in the gutter-like body 7 of the addition jig 6.
(having a length that covers almost the entire length of the mold), the gutter-like body 7 is reversed as shown by arrow a by the rotating shaft body 8 that supports the gutter-like body, and is dropped onto the molten flux surface. administered. The casting conditions are as follows.

[] Mold (1) Inner diameter: 250mm, length: 100mm.

(2) Rotation speed: 650 rpm (centrifugal force on the inner wall of the mold)
60G) [] Molten metal (1) Ingredients: C3.36%, Si0.77%, Mn0.63%,
Ni4.38%, Cr1.51%, Mo0.48%, balance Fe and impurities.

(2) Casting temperature: 1600℃, (3) Casting amount: Molten metal layer thickness in mold approximately 3.5mm [] Molten flux (1) Components: SiO ₂ , 19%, Al ₂ O ₃ 6%, CaO 38%,
Na ₂ O 16%, B ₂ O ₃ 8%, fluorite 9.00%, others 4%, (2) Dosage: 1 mm layer thickness on the surface of the molten metal in the mold.

[] Hard particles (1) Tungsten carbide (W ₂ O). Particles with electroless Ni-P plating on their surfaces are preheated and administered. Temperature at the time of administration: 500°C.

(2) Particle size: 150-250μm.

(3) Dose: 9.1Kg.

(4) Administration timing: Starts 1 second after the end of molten metal casting,
The entire dose was administered in 2.5 seconds.

By the above casting, outer diameter 250mm x length 100mm x wall thickness
A 35 mm hollow cylindrical casting was obtained. For comparison, a hollow cylindrical casting of the same size was cast under the same casting conditions as above, except that the surface of the molten metal in the mold was not coated with molten flux.

As a result of examining the axial cross section of the castings obtained by each method, the thickness of the mixed layer of the comparative method castings was as shown in Figure 5 above, and was uneven, ranging from about 5 mm in the center to about 15 mm near both ends. It is. In contrast, in the castings obtained by the method of the present invention, as shown in Figure 4, there is almost no uneven distribution of hard particles, and the thickness of the mixed layer A is approximately uniform over the entire length and circumference, approximately 9 to 12 mm. It is. Further, the surface of each particle in the mixed layer is coated with metal M, and the gaps between the particles are filled with metal, creating a dense and good mixed state. Note that the ratio (volume ratio) of particles in the mixed layer is approximately 70%.

Example 2 Centrifugal casting was carried out in the same manner as in Example 1 using the apparatus shown in FIG. However, immediately after the start of casting the molten metal, flux powder was injected into the mold to form a molten flux layer, and when the molten metal layer thickness reached approximately 10 mm, 7.5 kg of hard particles were sprayed and administered simultaneously with the casting of the molten metal. . The administration time is approximately 8 seconds. All other casting conditions are the same as in Example 1. For comparison, casting was carried out in the same manner as above except that no flux was used.

As a result of examining the axial cross-section of each of the obtained castings (outer diameter 250 mm x length 100 mm x wall thickness 35 mm), the mixed layer thickness of the castings obtained by the comparative method was as shown in Fig. 5 above, and the center The castings obtained by the method of the present invention have almost no uneven distribution of hard particles, as shown in Fig. 4, and the mixed layer thickness is approximately 4 mm at both ends, and is extremely nonuniform, with approximately 15 mm at both ends. It is uniform at about 9 to 11 mm over the entire circumference. The ratio (volume ratio) occupied by hard particles in the mixed layer is about 70%, and the mixed state of particles and metal is also good as in the previous example.

As described above, according to the present invention, it is possible to obtain a casting in which a mixed layer consisting of hard particles and metal is formed in the surface region to a desired layer thickness that is uniform over the entire length and circumference, and the mixed layer This ensures reliable and stable high wear resistance. It also has high toughness due to the metal layer inside the mixed layer. For example, in applications such as rolling and conveyance rolls, wear and
It withstands impact well and exhibits durability that cannot be obtained with conventional materials. In other words, similar effects can be obtained as members for various devices and devices that require wear resistance.

[Brief explanation of drawings]

Fig. 1 is an explanatory axial cross-sectional view showing a specific example of the casting method according to the present invention, Fig. 2 is an explanatory cross-sectional view along V-V, and Fig. 3 is an explanatory front cross-sectional view of a hollow cylindrical casting. The enlarged explanatory drawings, FIGS. 4 and 5 are respectively axial partial cross-sectional views of a hollow cylindrical casting, and FIG. 6 is an axial cross-sectional view showing an example of a conventional casting method. 1: Centrifugal casting mold, 4: Molten metal casting hopper,
6: Hard particle addition jig, M: Metal, P: Hard particles, A: Mixed layer, B: Metal layer.

Claims (1)

[Scope of Claims] 1 Hard carbide particles having a higher specific gravity than the molten metal are added to the molten cast iron or cast steel cast in a centrifugal casting mold, and the molten metal is centrifugally transferred to concentrate the hard carbide particles in the outer peripheral area. In a method of casting a casting having a two-layer structure of an outer layer containing a mixture of metal and hard carbide particles and an inner layer substantially consisting of metal, the molten metal and hard carbide particles are deposited on the surface of the molten metal in the mold. A molten flux layer having wettability with the particles is formed to cover the entire surface of the molten metal, hard carbide particles are evenly distributed over the entire axial length of the molten flux layer, and the hard carbide is distributed through the molten flux layer. A centrifugal casting method for wear-resistant castings that is characterized by adsorbing particles to the surface of the molten metal and incorporating them into the molten metal. 2. The centrifugal casting of the wear-resistant casting according to item 1 above, characterized in that the thickness of the molten flux layer is 0.5 mm or more. 3. The centrifugal casting method for wear-resistant castings according to any one of the above items 1 or 2, characterized in that the hard particles are administered in a heated state. 4. The centrifugal casting method for wear-resistant castings according to any one of items 1 to 3 above, wherein the hard carbide particles are tungsten carbide or tungsten titanium carbide.