JPS63168250A - Locally cooling method for lost-wax casting - Google Patents

Abstract

PURPOSE:To produce a casting having beauty surface and no shrinkage cavity by forming a mold, which executes coating under remaining one fase of chiller wax pattern, inserting the chiller into the part of no coating in the mold after de-waxing and burning, and executing casting and mold take-out. CONSTITUTION:The wax pattern having the same shaft with the product is injected and assembled together with each wax pattern 12, 13, 14 of a sprue, runner and gate. The chiller wax pattern 16 is sticked to the thick part in the wax pattern 11. Further, a plastic plate is stuck to the side face 17 of chiller wax pattern 16, Next, the coating is executed, and the de-waxing and burning are executed. Then, the face of plastic plate is not coated and the chiller 22 is inserted into the mold from this face. In this way, the casting having beauty surface and no shrinkage cavity is produced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a local cooling method for lost wax castings.

[Prior art] The lost wax method is the most representative precision casting method.The lost wax method can produce castings with excellent casting surface and dimensional accuracy, and is used in industrial machinery and automobiles.

It is widely used in the manufacture of parts for telecommunications, aircraft, etc.

The lost wax method consists of the following steps: ■ Injection ■ Assembly ■ Coating ■ Dewaxing ■ Sintering ■ Preheating ■ Casting ■ Demolding ■ Cutting. Here, (2) injection is a process of creating a wax pattern having the same shape as the product, and is usually performed by injecting molten wax into a mold.

■Assembly is the process of assembling gates, runners, sprues, etc. to the wax pattern created by injection. What is assembled in this way is generally called a tree.

■Coating involves immersing the tree in slurry (a liquid in which fine refractories are suspended in a binder such as water glass or colloidal silica), and coating the tree with refractories before the slurry dries.
It's J'J. This coating is repeated several times to achieve a desired thickness taking into consideration strength and other factors. This coating creates a mold with wax inside.

(2) Dewaxing is a process of removing wax from the coated mold, and is carried out by immersing the mold in molten wax or placing it in an autoclave.

- Firing is performed to burn out the wax remaining in the mold and completely remove the wax from inside the mold.

In other words, this is to avoid wax remaining in the mold, which would cause the surface of the product to become rough after casting.

Firing is usually carried out at a temperature around 800-900°C.

(2) Preheating is a process of heating the mold to 200 to 400°C, and is carried out to improve the stagnation and flow during casting.

Demolding is the process of removing the mold from the product after casting, and cutting is the process of separating the sprues, runners, and gates from the product.

(background) By the way, some products have thick parts.

When such a product is cast, the cooling rate in the thin-walled part is different from the cooling rate in the thick-walled part, and the cooling rate in the J'X-walled part is inevitably slower, so shrinkage cavities may occur in the thick-walled part. , and also lead to coarsening of crystal grains.

Such shrinkage cavities are detected by X-ray inspection, Zygro inspection, etc., and the portions become notch defects, causing stress concentration and deterioration of fatigue resistance.

Furthermore, products having coarse grains lead to a decrease in mechanical strength.

Furthermore, for example, stator vanes of turbine blades.

The inner shroud and outer shroud parts are thick, and if a drag cavity occurs in these parts, it may cause welding defects when the stator vane is assembled into the engine by welding.

To prevent such defects, adjust the sprue length and gate position.
Efforts have been made to design the mold, such as by selecting a cooling rate and adjusting the cooling rate by using an insulator, but there are limits to this, and the above-mentioned defects cannot always be sufficiently prevented.

[Prior Art] Therefore, the following techniques have been attempted in order to speed up the cooling rate of the thick-walled portion and prevent the occurrence of defects such as cavities.

■A technology that uses refrigerant (air, mist, liquid nitrogen, etc.) from the surface of the mold to cool areas where you want to increase the cooling rate.

■A technique in which cold metal is set in the mold before molding.

That is, this method involves adhering a cold metal to the wax pattern in advance, coating the wax pattern and the cold metal together, and then performing dewaxing, firing, and casting.

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

■In the technology that uses refrigerant, the #8 type has air permeability, so the refrigerant enters the surface of the molten metal and roughens the surface of the casting.

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

■After dewaxing, the cold metal remains in the mold, and if it is fired while remaining, the entire surface will be oxidized due to the high firing temperature of 900℃, and the oxide film created by oxidation will be inside the mold cavity. As a result, they become rough or get caught up in the molten metal during casting, causing defects in the product as non-metallic inclusions.

Furthermore, the mold and cold metal are removed during firing! However, since the coefficient of thermal expansion of the cooling metal is larger than that of the mold (made of refractory material), cracks occur in the mold during firing.

[Means for solving the problem] The above problem is solved by providing a chill wax pattern of approximately the same size as the chiller in the part of the product wax pattern where the chiller is used, and then applying the chiller to the wax pattern. A mold is created by coating leaving at least one side of the wax pattern, and then, after dewaxing and firing, inserting a cold metal into the #8 mold from the uncoated part of the mold, This problem is solved by a local cooling method for lost wax castings, which is characterized by casting, mold breaking, and cutting.

In the present invention, first, a chiller wax pattern having approximately the same size as the chiller is provided in a part of the product wax pattern where the chiller is used.

The cold wax pattern may be separate from the product wax pattern and bonded during injection and assembly, or it may be formed integrally with the product wax pattern.

Next, in the present invention, when coating is performed, at least one surface of the chilled metal wax pattern is left intact.

The reason why at least one surface is left open during coating is to serve as an entrance for inserting a cooling metal into the mold after dewaxing and firing.

In order to leave an uncoated surface, for example, a plastic plate, cellophane tape, etc. may be attached to that surface.

After coating, remove the wax. If plastic etc. is attached to the mj that is not coated,
If you remove it before removing the wax, the wax will escape from that surface, which is preferable to removing the plastic etc. after removing the wax.

After dewaxing, it is fired, and after firing, a cold metal is inserted from the uncoated side.

In addition, it is preferable to use a material with good thermal conductivity as the chiller. Copper may be used, and steel may also be used from a cost perspective. Considering expansion, it is preferable to use a cavity that is slightly smaller than the cavity of the PI type cooling full insertion section.

After cooling and fully inserting, preheat the mold. This preheating is carried out to improve high wave flow and prevent underfill defects due to poor hot water circulation, and is usually carried out at a temperature of 100 to 300°C. Therefore, this preheating does not oxidize the cooled gold.
As mentioned in the problem section, the problems of rough skin and inclusion of non-metallic inclusions do not occur, and since the preheating temperature is lower than the firing temperature, it is possible to eliminate the problems caused by the difference in thermal expansion coefficient between the cooling metal and the mold. It can also prevent cracking. This mold cracking can also be prevented by using a chiller that is smaller than the part of the chiller cavity, but this is also done by inserting the chiller later instead of putting it in from the beginning. This is made possible by the present invention. That is, in the method of adding a cold metal from the beginning, if a small cold metal is placed in the mold, the cold metal may move in the mold during dewaxing.

After preheating, it is cast by a conventional method. As for casting.

It does not matter whether it is air casting or vacuum casting.

Also, the type of alloy to be cast does not matter! The present invention is particularly effective for alloys having a wide solid temperature range.

After casting, the molten metal is left to stand to solidify (In the present invention, since there is a chiller, thick parts also solidify early, causing shrinkage and coarsening of crystal grains).

In addition, if it is desired to further accelerate the solidification rate, it is sufficient to cool the entire cooling body with a refrigerant, and the amount of cooling can be freely selected.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

An-4,5% Cu was used as the alloy.

An-4.5% Cu is an alloy that tends to cause shrinkage defects due to its wide solidification temperature range.

In this example, 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 sprue wax pattern 12, a runner wax pattern 13, and a gate wax pattern 14.

Next, a cold metal wax pattern 16 is adhered to the thick part of the product wax pattern 11. Furthermore, a plastic plate 4 is attached to the side surface 17 of this cold metal wax pattern 16.

In FIG. 3, the product wax pattern 11 and the chilled metal wax pattern 16 are shown as separate bodies, but a wax pattern in which they are integrated may be created at the time of injection.

Further, in this example, the plastic plate 4 is attached to the right side 17 of the cold metal wax pattern 16 in the drawing, but the upper surface 18, the lower surface 19, and the like in the drawing are the same. Alternatively, it may be attached to other locations.

After creating the tree 20, coating is performed, that is,
After soaking the tree 20 in the slurry, sand it (#big fish sprinkle), dry it, and repeat this process several times.

In this example, the surface of the plastic plate 4 is also subjected to slurry immersion and sanding, but if the adhering refractory material is removed before drying, the surface of the plastic plate 4 will not be coated.

Note that even if the plastic plate 4 is not used, if other means are used to prevent slurry from adhering to the right side surface 17 of the cold wax pattern, the right side surface 17 will not be coated.

The coating forms a refractory coating layer 30 on the surface of each wax pattern. FIG. 4 shows a cross-sectional view of the mold after coating and before the wax is removed.

After coating is completed, dewaxing is performed.

Dewaxing may be carried out by inserting the mold into a heating furnace or by using an autoclave. It is preferable to wax the area because the wax will escape from the area.

After dewaxing, firing is performed, for example, at a temperature of 700 to 90
It may be carried out at 0°C.

After firing, a cooling metal 22 was inserted into the mold as shown in FIG.

The mold was then preheated to 200 to 300°C and cast. No cracks were observed in the mold before casting.

After casting, No. 002 in Table 1 was left as is. The cooling rate in the thick part of the product between 642 and 548°C was measured and was 0.5°C/sec.

On the other hand, for No. 3, chilled metal 22 was sprayed with air. The cooling rate between 642 and 548°C at that time was 1.1θ°C/sec.

For comparison, the same product was manufactured using a conventional method that does not use any chilled metal, and was designated as No. 1 in Table 1.

For the samples No. 091 to No. 3 obtained in the above manner, the presence or absence of crystal grains, tensile cavities, and tensile strength in the thick portion were investigated. In addition, the nests were observed and detected by X-ray inspection, and the tensile strength was investigated after T6 treatment.

The results are shown in Table 1.

As shown in Table 1, in the examples of the present invention using a chilled metal (No. 2, No. 3), compared to the comparative example (No. 1) in which a chilled metal was not used, the crystal grain has become much smaller, the nest has become smaller, and the tensile strength has been greatly improved.

In particular, No. 3, in which the chilled metal was cooled with air, has N crystal grains.
o, less than half of 1, and there were no nests at all.

The casting surfaces of Nos. 2, 3, and 3 were no different from those of Nos. and 1, and there was no roughness or the like, and a beautiful casting surface unique to lost wax was obtained.

[Effects of the invention] ■ Castings can be obtained without damaging the beautiful casting skin characteristic of lost wax.

■Castings without inclusion of non-metallic inclusions etc. can be obtained.

■No mold cracks.

■If you pull it, #8 product without nests will be obtained.

■Castings with excellent mechanical strength can be obtained.

■Made from castings with fine crystal grains.

■The amount of cooling can be freely selected.

Table 1 The cooling rate of the main runner is in the temperature range of 642-548℃

[Brief explanation of the drawing]

1 to 5 are diagrams for explaining the present invention in detail.
The figure is a side view showing the state after the wax pattern is assembled.
FIG. 3 is a side view showing the uncoated surface, FIG. 4 is a sectional view showing the state after coating, and FIG. 5 is a sectional view showing the state after dewaxing and firing. 111.Product, 4-.Plastic plate, 11.-Product wax pattern, 12..Gate wax pattern, 13.
-.Truy wax pattern, 14..Gate wax pattern, 16..Cold metal wax pattern, 20.-Tree, 22..Cold metal. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A cold metal wax pattern of approximately the same size as the cold metal is provided in the part of the product wax pattern where the cold metal is used, and then a mold is formed by coating leaving at least one side of the cold metal wax pattern. A lost wax casting characterized in that after the casting is made, then dewaxed and fired, a cold metal is inserted into the mold from the uncoated part of the mold, and then the casting, mold breaking, and cutting are performed. local cooling method.