JPH0813400B2 - Precision casting method for castings having a narrow hollow portion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a type of precision casting method, the lost wax method in investment casting.
The present invention relates to a method for casting a casting having a hollow portion with a narrow hole.

[Prior Art] The lost wax method is the most typical precision casting method and is widely used in industrial machinery, automobiles, telecommunications equipment, parts for aircraft, etc. because of its excellent casting surface and dimensional accuracy. .

FIG. 2 is a schematic view conceptually showing each step of this lost wax method. First, in step 1, a brazing material is injected to obtain a brazing mold. Then, in step 2, after assembling this wax pattern to obtain a wax pattern, step 3
Is immersed in a slurry, and in step 4, sand as a refractory material is sprinkled to cover the refractory material and dried. This slurry dipping and refractory material coating are repeated to form a mold layer having a predetermined thickness.

And in the solid molding method, step 5a
At step 6a, the periphery of the refractory material mold layer is filled and backed up, and in step 6a, dewaxing is performed by heating, and the wax is completely burned and removed. Next, in step 7a, the molten metal is poured and left until the solidification is completed.

Then, in step 8, sanding, cutting and finishing are performed to obtain a product as shown in step 9.

In the ceramic shell molding method, as shown in step 5b, without backing up,
As shown in step 6b, heating and dewaxing treatment are performed, and then in step 7b, molten metal is cast.

[Problems to be Solved by the Invention] However, in the conventional casting method, in the case of a casting having a long casting hole or a casting having a blind hole, the slurry and the refractory are formed on the inner surfaces of these holes. Hard to adhere and hard to dry. For this reason, the mold strength becomes low, the mold is broken during dewaxing and firing, or the mold cannot withstand the thermal shock when casting the molten metal, and cracks occur in the narrow-mouth hollow part, resulting in hot water leakage or Penetration tends to occur, so that a sound casting cannot be obtained.

A technique of using a ceramics mold in the narrow-mouth hollow portion or injecting gypsum into the narrow-mouth hollow portion to solve the above-mentioned drawbacks has been proposed, but the ceramics mold is expensive and As-cast property is also poor.
Furthermore, gypsum has insufficient mold strength and cracks occur during dewaxing or firing, which makes it difficult to produce a sound casting, and the drying process requires a long time. There is also a drawback.

As described above, in the conventional casting method using the lost wax method, it is extremely difficult to manufacture a casting having a narrow hollow portion.

The present invention has been made in view of such problems, there is no crack in the narrow-mouth hollow portion, it is possible to mold a mold having excellent erosion property, cast metal without defects such as leaking It is an object of the present invention to provide a precision casting method for a casting having a hollow portion with a narrow mouth, which can be manufactured stably, quickly and at low cost without performing.

[Means for Solving the Problems] A method for precision casting of a casting having a narrow-neck hollow portion according to the present invention includes a step of depositing a mold layer on the surface of a wax mold having a predetermined shape having the narrow-neck hollow portion, and the narrow-neck hollow portion. A step of inserting a fusible resin through the inside of the part, a step of filling the narrow-mouth hollow part with ceramics, a step of dewaxing, and a step of firing the template layer and eliminating the fusible resin. It is characterized by including a step and a step of injecting a molten metal into the space from which the wax has been removed and casting.

[Operation] In the present invention, a fusible resin is arranged so as to be inserted through the wax-shaped narrow-mouth hollow portion, and then the narrow-mouth hollow portion is filled with ceramics. Then, after dewaxing treatment, the mold layer covering the wax mold is fired. Then, the fusible resin also melts, vaporizes and disappears, so that a hole is formed in a portion occupied by the fusible resin. After that, when the molten metal is poured into the space where the wax is removed and casting is performed, a desired cast product is obtained. In this case, since the hollow part is filled with ceramics at the time of pouring the molten metal, the mold strength is high and damage to the mold is prevented. Further, since the fusible resin disappears during firing to form a hole, the hole functions as a gas vent hole, and a sound casting can be manufactured.
In addition, this hole promotes the erosion of ceramics,
Improves the as-cast property of the narrow mouth hollow part.

[Examples] Hereinafter, examples of the present invention will be specifically described with reference to the accompanying drawings. 1 (a) to 1 (d) are schematic views showing an embodiment method of the present invention in the order of steps.

As shown in FIG. 1 (a), first, a wax mold 11 having a narrow hollow portion 12 is formed. Next, as shown in FIG. 1 (b), the surface of the wax mold 11 is coated with a first layer and a second layer of refractory material in the same manner as in the prior art to form a coating layer 13. Then, after the coating layer 13 is dried, the fusible resin 14 vertically attached to the cored bar 15 is placed in the hollow portion 12 by inserting the hollow portion 12 therethrough. The fusible resin 14 is made of polyvinyl alcohol, for example, and has a string shape. The cored bar 15 is a linear one having a diameter of 2 to 3 mm, and a soft fusible resin 14 is added to the cored bar 15 to support the fusible resin 14 in a linear posture. And this fusible resin 14
And the core metal 15 is inserted into the narrow-mouth hollow portion 12 and arranged so as to be coaxial with the wax mold 11 at the center thereof.

After that, as shown in FIG. 1 (c), a fluid ceramics 16 containing silicic acid sol as a binder and an alkaline curing agent is poured into the hollow portion 12, and the ceramics
Fill the hollow part with 16. Then this ceramics
After 16 is dried and cured, normal coating is repeated. Since the ceramics 16 is dried by alcohol evaporation, the drying speed is fast.

Next, a dewaxing process is performed by heating, the wax mold 11 surrounded by the coating layer 13 is melted, vaporized, and removed. Then, the coating layer 13 forms a mold shell in which the region occupied by the wax mold 11 serves as an injection space.

Then, as shown in FIG.
The whole including the (mold shell) is heated to, for example, 800 to 850 ° C., and the coating layer 13 is baked. As a result, the coating layer 13 is cured, and the fusible resin 14 is melted and further vaporized and disappears. Therefore, a thin vent hole 17 is formed in the portion occupied by the fusible resin 14. After preheating the mold thus produced, it is taken out of the furnace and the coating layer 13
When the molten metal is poured into the space surrounded by and then left to stand, it solidifies to produce a casting having a narrow-mouth hollow portion. In the step of pouring the molten metal, since the ceramics 16 supports it behind the mold shell formed of the coating layer 13, the mold shell may be broken due to thermal shock at the time of injection,
The occurrence of cracks is avoided. Further, since the hole 17 is formed in the portion where the fusible resin 14 was present and the hole 17 functions as a gas vent hole, it is possible to obtain a sound casting without cracks.

After the injection of the molten metal and the solidification thereof are completed, the mold shell and the ceramics 16 on the inner surface are removed. This ceramic 16 can be removed by applying vibration to the entire casting or by
This can be done by applying water pressure to 16. In this case,
The holes 17 functioning as gas vent holes promote the erosion of ceramics in this as-casting process. Therefore, in this embodiment, the casting time is short.

Next, the result of producing the magnesium alloy casting by the method of the present invention will be described in comparison with the comparative example.

Table 1 below shows the casting conditions and the results of Examples and Comparative Examples.

In Comparative Example 2, only the mold shell made of the coating layer was provided as in the conventional method, but in this case, the mold collapsed and casting was impossible. On the other hand, in Comparative Example 1, since the ceramic was poured into the hollow portion 12, molding was possible in the molding process of the hollow portion with a narrow mouth, but cracking (incorporation of oxide) occurred. However, when the fusible resin was arranged as in this example, a sound casting product was produced, and the casting time was short.

EFFECTS OF THE INVENTION In the present invention, a fusible resin is placed in a wax-shaped narrow-mouth hollow portion, and the hollow portion is filled with ceramics. The shell can be shaped to produce a sound casting with no defects.

[Brief description of drawings]

1 (a) to 1 (d) are schematic diagrams showing the method of the present invention in the order of steps, and FIG. 2 is a schematic diagram showing a conventional method. 11; wax type, 12; hollow portion with narrow mouth, 13; coating layer, 14; fusible resin, 15; core metal, 16; ceramics, 17; hole

Claims (2)

[Claims] 1. A step of depositing a mold layer on the surface of a wax mold having a predetermined shape having a narrow hollow portion, a step of inserting a fusible resin through the hollow portion of the narrow opening, and a hollow portion of the narrow opening. A step of filling with ceramics, a step of dewaxing treatment,
Precision of a casting having a narrow-necked hollow portion, characterized by having a step of firing the mold layer and causing the fusible resin to disappear, and a step of injecting a molten metal into the space from which the wax has passed and casting. Casting method. 2. The precision casting method for a casting having a hollow portion with a narrow mouth according to claim 1, wherein the fusible resin is attached to a core wire and arranged.