JPH0729177B2 - Method for producing locally cooled lost wax casting - Google Patents

Description

The present invention relates to a method for producing a locally cooled lost wax casting.

[Prior Art] The lost wax method is the most typical casting method as a precision casting method.

The lost wax method is capable of producing castings with excellent casting surface and dimensional accuracy, and is widely used for producing parts for industrial machines, automobiles, telecommunications, aircraft and the like.

The lost wax method comprises the steps of injection, assembly, coating, dewaxing, firing, preheating, casting, demolding, and cutting. Here, the injection is a step of forming an Ikiwax pattern having the same shape as the product shape, and is usually performed by injecting molten wax into a mold.

Assembly is a process of assembling gates, runners, gates, etc. on the ikiwax pattern created by injection. Those assembled in this way are generally called a tree.

The coating consists of immersing the tree in a slurry (a solution of fine refractory suspended in a binder such as water glass or colloidal silica), and immediately sanding (sprinkling refractory) before the slurry dries. This is a step of coating a refractory material by performing and drying. This coating is repeated several times to give a desired thickness in consideration of strength and the like.
By this coating, a mold (shell mold) containing wax inside is created.

Dewaxing is a step of removing wax from the coated mold, and is performed by immersing the wax-containing mold in molten wax or by placing it in an autoclave.

The firing is performed to impart strength to the mold, burn the wax remaining in the mold, and completely remove the wax from the mold. That is, if the wax remains in the mold, it may cause roughening of the surface of the product after casting, and this is to avoid this.

Usually, firing is performed at a temperature near 800 to 900 ° C.

Preheating is the process of heating the mold to 200-400 ° C,
This is done to improve the flow of molten metal during casting.

Unmolding is a step of removing the mold from the product after casting, and cutting is a step of separating the sprue, runner, and gate from the product.

(Background) By the way, some products have a thick part.
When such a product is cast, the cooling rate in the thin portion and the cooling rate in the thick portion are different, and the cooling rate in the thick portion is inevitably slow, so that porosity is generated in the thick portion, and the crystal is also formed. It may cause grain coarsening.

Such shrinkage cavities are detected by X-ray inspection, zygul inspection, etc., and the portions become notch defects, which causes stress concentration and causes deterioration in fatigue resistance.

Further, a product having coarse crystal grains leads to a decrease in mechanical strength.

Furthermore, for example, in a turbine blade stator blade, the inner shroud and the outer shroud portion are thick, and if shrinkage cavities occur in this portion, when this stator blade is installed in an engine by welding, it may cause a welding defect. To become.

In order to prevent such defects, ingenuity is made by designing the mold such as adjusting the sprue length, selecting the gate position, and adjusting the cooling rate by using the insulator, but there is a limit to that, and the above defects are not always sufficiently prevented. .

Therefore, in order to accelerate the cooling rate of the thick portion and prevent the occurrence of defects such as shrinkage cavities, the following techniques have been tried.

Technology that uses a coolant (air, mist, liquid nitrogen, etc.) from the mold surface to cool the part where you want to increase the cooling rate.

 A technique to set a cool metal in the mold before molding.

That is, this is a method in which a chill is adhered to the wax pattern in advance, the wax pattern and the chill are coated together, and then dewaxing, firing and casting are performed.

[Problems to be Solved by the Invention] However, the above technique has the following problems.

In the technique using a refrigerant, the mold has air permeability, so that the refrigerant enters the surface of the molten metal and roughens the surface of the casting.

Further, since the cooling amount cannot be freely selected, it is not always possible to prevent the occurrence of shrinkage cavities.

After the dewaxing, the chilled gold remains in the mold, and if it is baked while it remains, the baking temperature is as high as 900 ° C, the surface of the gold is cooled and the surface of the gold is oxidized, and the oxide film generated by the oxidation remains inside the mold cavity As a result, the surface is roughened or, as a result, it is caught in the molten metal during casting and causes defects as non-metallic inclusions in the product.

Further, the mold and the chilled gold thermally expand during firing, but the coefficient of thermal expansion of the chilled gold is higher than that of the mold (comprising a refractory material), so that the mold is cracked during firing.

[Means for Solving the Problems] The above-mentioned problem is that a chill wax pattern having substantially the same size as that of the chill is provided on a portion of the product wax pattern where the chill is used, and the chill wax is also used. A plastic plate is attached to cover one surface of the pattern, leaving the outer surface of the plastic plate to form a mold by coating, followed by dewaxing and baking, and then coating of the mold. The problem is solved by a method for producing a locally cooled lost wax casting, which is characterized by inserting a chill into the mold from an absent portion, and then casting, demolding and cutting.

According to the present invention, first, a chill wax pattern of substantially the same size as the chill is provided on a portion of the product wax pattern where the chill is used.

The chill wax pattern may be separated from the product wax pattern and adhered at the time of injection and assembly, or may be integrally molded with the product wax pattern.

Next, in the present invention, when coating is performed, a plastic plate is adhered to at least one surface of the cold gold wax pattern and coating is performed.

Since the surface is covered with the plastic plate, there is no adherence of slurry sand to the surface, and it is possible to prevent the occurrence of non-metallic inclusion defects (shell bite) in the casting product due to the adhered slurry sand. it can.

After coating, dewaxing is performed. The plastic plate attached to the uncoated surface should be removed before removing it. Since the wax escapes from that aspect, it is preferable to remove the plastic or the like after removing the wax.

After dewaxing, baking is performed, and after baking, cooling metal is inserted from the uncoated surface.

As the chill, it is preferable to use a material having good thermal conductivity. Copper may be used, or steel may be used in terms of cost. In consideration of thermal expansion during preheating, which will be described later, it is preferable to use a mold slightly smaller than the cavity of the chill insert portion of the mold.

After inserting the chill, preheat the mold. This preheating is carried out in order to improve the flow of the molten metal and prevent the lack of wall defects due to the defective running of the molten metal, and is usually carried out at 100 to 300 ° C. Therefore, the preheating does not oxidize the chill, and the problems of rough skin and inclusion of non-metallic inclusions as described in the problems do not occur. Further, since the preheating temperature is lower than the firing temperature, it is possible to prevent the mold from cracking due to the difference in the coefficient of thermal expansion between the chill and the mold. In addition, the crack of this mold is
It is also prevented by using a chiller that is smaller than the chill cavity part, but this is also possible by the present invention that the chill is inserted after the chill is not inserted from the beginning. is there. That is, in the method in which the chill is put in from the beginning, if a small chill is put, the chill may move in the mold at the time of dewaxing.

After preheating, casting is performed by a conventional method. The casting may be atmospheric casting or vacuum casting.

The present invention is particularly effective for alloys having a wide solidification temperature range, regardless of the type of alloy to be cast.

After casting, it is left to solidify the molten metal. In the present invention, since there is a chill, the thick portion does not solidify at an early stage, and shrinkage cavities and coarsening of crystal grains do not occur.

If it is desired to further increase the solidification rate, it is sufficient to cool the chilled gold itself with a refrigerant, and the amount of cooling can be freely selected.

EXAMPLES Examples Examples of the present invention will be described below with reference to the drawings.

Al-4.5% Cu was used as the alloy. Al-4.5% Cu is an alloy that easily causes shrinkage cavity defects because it has a wide solidification temperature range.

In this embodiment, the product 1 shown in FIG. 1 is manufactured.

First, a product wax pattern 11 having the same shape as the product 1 is injected, and as shown in FIG. 2, this product wax pattern 11 is assembled together with a spout wax pattern 12, a runner wax pattern 13, and a gate wax pattern 14.

Next, a cold gold wax pattern 16 is bonded to the thick portion of the product wax pattern 11. Further, the plastic plate 4 is attached to the side surface 17 of the chilled wax pattern 16.

In FIG. 3, the product wax pattern 11 and the cooled gold wax pattern 16 are separate bodies, but a wax pattern in which both are integrated may be created at the time of injection.

Further, in this example, the plastic plate 4 is cooled and attached to the right side surface 17 of the gold wax pattern 16 in the drawing, but it may be attached to the upper surface 18, the lower surface 19 or another place in the drawing.

Coating is performed after the tree 20 is created. That is, the tree 20 is dipped in the slurry, sanded (sprinkled with a refractory material), dried, and this process is repeated several times.

In this example, the surface of the plastic plate 4 is also immersed in the slurry and sanded. However, if the adhering refractory is removed before drying, the surface of the plastic plate 4 is not coated.

Even if the plastic plate 4 is not used, the right side surface 17 is not coated if it is cooled by other means so that the slurry does not adhere to the right side surface 17 of the gold wax pattern.

The coating forms a refractory coating layer 30 on the surface of each wax pattern. A cross-sectional view of the mold after coating and before dewaxing is shown in FIG. After coating, remove the wax.

The dewaxing may be performed by operating the mold in a heating furnace or using an autoclave. In addition, the plastic plate 4 is cooled and a gold wax pattern
It is more preferable to remove it from 16 and then remove it, because the wax escapes from that part.

Bake after dewaxing. The firing may be performed, for example, at 700 to 900 ° C. After firing, as shown in FIG. 5, cooled gold 22 was inserted into the mold.

Then, it was preheated at 200 to 300 ° C. and cast.

Before casting, no crack was found in the mold.

After casting, No. 2 in Table 1 was left as it was.
When the cooling rate between 642 and 548 ° C in the thick part of the product was measured, it was 0.5 ° C / sec.

On the other hand, with regard to No. 3, a chill 22 was blown with air. At that time, the cooling rate between 642 and 548 ° C was 1.10 ° C / sec.

For comparison, the same product was manufactured by the conventional method without using any chill and designated as No. 1 in Table 1.

With respect to the No. 1 to No. 3 samples obtained as described above, the crystal grains, the presence or absence of shrinkage cavities, and the tensile strength in the thick portion were investigated. The cavities were observed by X-ray examination, and the tensile strength was examined after T6 treatment.

The results are shown in Table 1.

As shown in Table 1, in the examples (No. 2 and No. 3) of the present invention using a chill, compared to the comparative example (No. 1) not using a chill, the crystal grains are It is significantly smaller, shrinkage cavities are smaller, and the tensile strength is greatly improved.

In particular, No. 3 in which the chill was cooled with air had less than half the crystal grains of No. 1, and there were no shrinkage cavities at all.

The No. 2 and No. 3 casting surfaces were completely the same as No. 1 without any rough skin, and a clean casting surface peculiar to lost wax was obtained.

(Comparative Example) In this example, the plastic plate is not adhered, the slurry is soaked and sanded, then the right side surface of the chilled wax pattern
The slurry sand adhering to 17 was removed at each coating step. Other points H The same as in Example No. 3 above.

When the final casting was surface-inspected with a microscope of this example and No. 3, the number of shell (non-metallic inclusion) biting defects was larger in this example than in No. 3.

[Effects of the Invention] A casting that does not impair the clean casting surface specific to lost wax can be obtained.

It is possible to obtain a casting that is free from inclusion of non-metallic inclusions.

No mold cracks.

Castings without shrinkage cavities are obtained.

A casting having excellent mechanical strength can be obtained.

A casting with fine crystal grains can be obtained.

The cooling amount can be freely selected.

[Brief description of drawings]

1 to 5 are views for explaining an embodiment of the present invention, FIG. 1 is a perspective view showing the shape of a product and a chill, and FIG. 2 is a state after a wax pattern is assembled. Side view, FIG. 3 is a side view for showing a surface not coated, FIG. 4 is a sectional view showing a state after coating, FIG.
The figure is a cross-sectional view showing a state after dewaxing and firing. 1 ... Product, 4 ... Plastic plate, 11 ... Product wax pattern, 12 ... Gate wax pattern, 13 ... Runner wax pattern, 14 ... Gate wax pattern, 16
…… Cold money wax pattern, 20 …… Tree, 22 …… Cold money.

Claims (1)

[Claims] 1. A chill wax pattern having substantially the same dimensions as the chill is provided at a portion of the product wax pattern where the chill is to be used, and one surface of the chill wax pattern is covered so that a plastic is formed on the surface. A plate is adhered, a mold is created by coating, leaving the outer surface of the plastic plate, and then, after dewaxing and firing, a chill is applied from the uncoated portion of the mold to the mold. A method for producing a locally cooled lost wax casting, which comprises inserting into a sheet, casting, demolding, and cutting.