JPH0241723A - Method for casting mold - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost of a metal mold and to reduce the casting deformation by setting a high heat conductive split projecting model to the movable platen of a vertical press, sinking it into a molten metal bath, then, taking the mold out of the split models. CONSTITUTION:A split movable projecting model 1 is set to a movable platen 4 of a vertical press and a molten metal bath 2 is laid on a bolster 3. Cooling water pipes 17a, 17b, 16a, 16b are provided in a split model 1 and thermo-couples 26-28 are arranged on the bottom part of the bath 2. The platen 4 is lowered, the projecting model 1 is sunk in the bath 2 to solidify the molten metal while the inside is cooled by water. After a recessed mold corresponding to the projecting model 1 is solidified and formed, the platen 4 is raised and the bath 2 is demounted to obtain a casting mold. Since the projecting model 1 having high heat conductivity can be used repeatedly, the manufacturing cost of the die is reduced and casting deformation, too, is reduced by uniformizing cooling shrinkage.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a mold casting method.

(Prior art) Conventionally, molds are generally made by injecting molten metal to be cast into a sand mold formed by solidifying amorphous particles such as silica sand with thermosetting resin such as phenol resin or urethane resin. It is manufactured by dismantling the sand mold after solidification. This sand mold has poor thermal conductivity, so the molten metal injected into the sand mold is slowly cooled, causing the alloy crystal grains to become coarse and the strength of the material to decrease, and the gas generated by the combustion of the resin to create blowholes in the casting mold. , pinholes, etc. occur.

It is clear from a comparison of the micrographs of the rapidly cooled structure in FIG. 11 and the slowly cooled structure in FIG. 12 that the slow cooling causes the alloy crystal grains to coarsen. Here, Fig. 11 shows zinc casting using a metal mold (iron mold), and Fig. 12 shows zinc casting using a sand mold.
This shows the aluminum alloy surface structure.

It is clear from the graph in FIG. 10, which compares the strengths of test pieces cast at various cooling rates, that the strength decreases with slow cooling. In this graph, Curve A is the result of casting by rapidly cooling the molten zinc-aluminum alloy using a 120°C mold, Curve B is the result of casting by slowly cooling the molten metal at room temperature using a sand mold, and Curve & IC is the result of casting by quenching the molten metal at 350°C. The tensile strength at each operating temperature of a mold cast by slow cooling in a furnace is shown.

In other words, in order to cast a mold with high strength, it is possible to use a mold that increases the cooling rate of the molten metal.

<Problems to be Solved by the Invention> As a mold material for increasing the cooling rate of molten metal, it is conceivable to use graphite, which has a large thermal conductivity coefficient as shown in the table.

However, there is a problem that the graphite casting surface hardens locally, causing flow wrinkles on the surface of the cast mold.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a mold casting method that does not reduce strength and do not cause flow wrinkles on the surface.

<Means for Solving the Problems> The mold casting method of the present invention, which can solve the above problems, uses a segment made of a highly rigid and highly thermally conductive material to form a mold concave shape on the movable platen of a vertical press. A movable convex model is attached, the model is allowed to settle in a molten metal bath set on the bolster of a press, and after waiting for the molten metal to solidify, the central model of the split movable convex model is lifted first, and the convex model is demolded. shall be.

In other words, there is a method in which a male mold is buried in a hardening material and after it descends, the male mold is removed to create a female mold. -2
(Refer to Publication No. 1816), which was thought to be difficult to adopt for casting molds.

As for the material for the above-mentioned convex model, it is better to use a material with higher thermal conductivity, or it is natural that it must have the necessary rigidity for a model for casting.For example, a preferable material that has both high thermal conductivity and high rigidity is One example is graphite.

A split movable convex model is a combination of multiple independent partial models, and has a convex shape that corresponds to the overall shape or the concave shape of the mold to be cast, and each partial model can be moved individually. This is a model that allows you to A preferred split movable convex model consists of a center model and an outer model (or even an intermediate model), the center model is wedge-shaped and can be pulled out upwards, and the outer model is shaped like a wedge in the direction of contraction due to solidification of the cast metal. One example is a mechanism that can be freely learned.

Such a convex model can be easily demolded even if it is tightened by solidified metal during casting. Furthermore, it is advantageous to arrange a plurality of independent water cooling pipes each having a valve within the split movable convex model so that the solidification region of the molten metal can be controlled depending on the shape of the mold to be cast.

The above-mentioned molten metal bathtub is made by making a sand mold (bathtub wall) in a casting flask (box) using shell sand, etc., and covering the inner surface of the sand mold, which has poor thermal conductivity and tends to generate gas, with a thin iron plate, etc. good. The use of organic substances that generate harmful gases in the bathtub should be avoided as much as possible.

Slag (oxides, impurities) is generated on the surface of the molten metal poured into the bathtub, but it is important to take appropriate measures to remove the slag so that the floating slag does not stick to or get caught up in the convex model. be. For example, slag can be conveniently removed by floating a flexible, fire-resistant net on the surface of the molten metal and pulling up the net immediately after the convex model descends and comes into contact with the molten metal surface. It would be a good idea to install a weir around the top of the bathtub to prevent the molten metal from overflowing with slag from scattering when the convex model is allowed to settle. The demolding timing of the split movable convex model may be determined by detecting the temperature of the molten metal using a thermocouple, for example.

Effects> If the mold casting method is configured as described above, the following effects will be achieved.

Since the convex model forming the concave shape of the mold is settled in the molten metal in the bath, no flow wrinkles will occur on the surface of the mold to be cast. Furthermore, since the convex model is made of a highly thermally conductive material, the molten metal that comes into contact with the surface of the convex model is rapidly cooled. This rapid cooling prevents the alloy crystal grains from becoming coarser and increases the strength of the mold. And since the convex model is movable in parts,
The mold can be easily removed by pulling out the wedge-shaped central model.

<Example> An example of the mold casting method of the present invention will be described based on the drawings, but the present invention is not limited thereby.

First, the casting apparatus used in this embodiment will be explained with reference to FIG. The casting device includes a movable platen 4 of a vertical press,
A molten metal bath 2 is placed on a press bolster 3 while a split movable convex model 1 for forming a mold concave shape is attached.

The split movable convex model 1 has an independent water cooling pipe 16a.

Iron frame 1 with 17a, 18.17b, 1.6b
Graphite around 4a, 15, 14b (model part) l
la, 1.2a, 13, 12b, and llb are fixed, and the central model l is attached to the elevating plate 10.
c, and the left model la attached to the floating plate 9a.
and a right model 1b attached to the other floating plate 9b. The central model 1c and the left and right side models la and lb are movable through vertically tapered dovetail grooves 19 and 19. The elevating plate 10 is moved vertically by a ball screw 7 of a servo motor 6. Although the plates 9a and 9b slide freely in the horizontal direction when engaged with the rails 8a and 8b (see also Figure 1a, which shows the part viewed from the side F), both plates 9a and 9
b are designed to be attracted to each other by coil springs 5. Therefore, the left and right models la and lb are in close contact with the center model IC.

In the molten metal bath 2, a sand mold 20 is made in a casting flask 29, and the sand mold 20 is
Its inner surface is covered with covering plates 24, 24, etc. made of thin iron plates or the like. Although the covering plate 24 expands due to the heat of the molten metal, slits 25 and 25 are provided to prevent deformation caused by the expansion.
...is provided. A weir 21 is provided on the outer periphery of the upper part of the machete molten metal bath 2 to prevent overflowing molten metal from scattering, and a bucket is placed under the notch 22 of the weir 21. Furthermore, thermocouples 26, 27, and 28 are provided in the molten metal bath 2, so that the temperature of the molten metal can be measured.

Next, the casting method will be explained. First, as shown in FIG. 2, molten metal 34 is poured into the molten metal bath 2. The inner surface of the bathtub 2 is heated with a burner immediately before pouring water, and volatile components are removed in advance. The molten metal 34 is poured from the tilting steel 33 through the pouring pipe 35 into the sprue 54 of the sand mold 20, and when the molten metal 34 passing through the runner 55 reaches a predetermined height 37, the pouring is stopped.

Then, as shown in FIG. 3, slag 44 is generated on the molten metal 34 in the bathtub, and a wire mesh 38, 39 with a handle 40, 41 for removing slag is floated. The wire meshes 38 and 39 are made by dividing a wire mesh made of ceramic-coated aluminum whose specific gravity is lighter than that of the molten metal into two parts, and are pressed down with metal fittings 42 and 43 so as to cover the entire surface of the molten metal.

Next, as shown in FIG. 4, the movable platen 4 of the vertical press is lowered, and the convex model 1 is submerged in the molten metal bath 2. At that time, the model portion 12a of the convex model bottom.

13.12b is in contact with the molten metal surface and the wire mesh 38.39 is pushed in the direction of arrow A, timing the timing to push the wire mesh 38.39.
, and move the glue 44 to the model parts 12a, 13, 12.
Remove from b. Due to buoyancy, the slag 44 is poured into the bucket 57 from the notch of the weir 21 along with the overflowing molten metal.

Here, as shown in FIG. 5, water cooling pipes 18-"+7a, +7b-+16a,
16b, and the valves (
(not shown) in sequence. The timing of opening the hartz is determined by the temperature measured by thermocouples 26, 27° 28 installed in the bathtub. When it melts and solidifies, a large "sink" 49 occurs, so the ladle 47 is used to replenish the pouring water 48. Fine crystals grow from the convex model 1 side, which has good thermal conductivity.

When the entire molten metal reaches the solidification temperature, the solid begins to contract as it cools and compresses the divided movable convex model l.
．． 28, the servo motor 6 is driven to rotate the ball screw 7 as shown in FIG. 6, and the central model IC is pulled up in the direction of arrow B. Left and right side model I
a and lb move slightly in the direction of arrow C, and the model part 11
a, llb, 12a, 12b, 13 and stress concentration parts 58, 58 of the casting mold are released.

As shown in FIG. 7, when the temperature reaches such a point that there is no need to worry about shrinkage deformation due to cooling of the casting mold 59, the movable platen 4 of the vertical press is raised and the split movable convex model 1 is demolded. Thereafter, the bathtub 2 is taken out from the press bolster 3, the casting flask 19 is opened, the sand mold 20 is dismantled, and the casting mold 59 is taken out.

When the dimensional error δ shown in FIG. 9 of the casting mold thus taken out was examined, it was found to be δ<lIIm.

When such a zinc-aluminum alloy mold is cast using a normal sand mold model, .delta.=6 to 7.times.I is reached, so the method of this embodiment can be said to be a casting method that causes very little casting deformation.

Moreover, unlike sand molds that use resin as a binder, the convex model is made from machined graphite, so there are no gas blowholes or pinholes on the surface of the cast mold.

In addition, if there is a concave shape 61 in a part of the bottom of the convex model, and there is a possibility that air will be drawn into the molten metal, as shown in Fig. 8,
This problem can be solved by providing an air vent 60.

<Effects of the Invention> According to the mold casting method of the present invention, a mold having a surface with a dense grain structure can be obtained, thereby increasing the strength and wear resistance of the mold.

Furthermore, since a mold with no flow and wrinkles on the surface can be obtained, by applying a high-precision finishing process to the surface of the graphite model, a mold that can be used immediately can be cast without the need for polishing.

Furthermore, preparing the model in parts creates parts that can be used repeatedly, such as supporting materials, and if two or more casting molds are made, the entire model can be used repeatedly. From the above, significant cost reductions can be achieved.

Furthermore, according to the method of the present invention, highly rigid graphite is used as the model material, and a plurality of independent water-cooled tubes are provided in the split movable model, so that the stress state caused by cooling contraction of the alloy is always maintained within a certain range. Since it is possible to control the inside of the mold, it also has the effect of reducing casting deformation.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a partial cross section of an apparatus used in an embodiment of the mold casting method of the present invention, Fig. 1a is a side view showing a part of the apparatus, and Figs. 2 to 7 are An explanatory diagram showing each step of one embodiment in succession, FIG. 8 is a partial sectional view showing a convex model according to another embodiment, FIG. 9 is a diagram showing the dimensions of a cast mold, and FIG. A graph showing a comparison of the relationship between temperature and tensile strength of test specimens cast under various conventional conditions. Figures 11 and 12 show the quenched structure and slow cooling of cast products using metal molds and sand molds, respectively. It is a micrograph of a metallographic structure showing a comparison of structures. In the figure: 1... split movable convex model la - left side model 1b...
・Right side model IC...Center model 2...Molten metal bathtub 3...Bolster-4...Movable platen 11a, llb, 12a, 12b, 13-Graphite (model part) 16a, 16b, 17a, 17b, 18...Water-cooled pipe 20...Sand mold 24...Coating plate 2
6.27.28--Thermocouple 34... Molten metal 38
．． 39...Wire net for sludge removal Patent applicant Toyota Motor Corporation

Claims (1)

[Claims] A split movable convex model made of highly rigid and highly thermally conductive material is attached to the movable platen of the vertical press to form the concave shape of the mold, and it is allowed to settle in the molten metal bath set on the press's bolster. A mold casting method characterized by waiting for solidification, lifting the central model of the split movable convex model first, and demolding the convex model.