JP2000246392A - Molding method of wax model having ceramic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a model which does not generate core cracks by installing a solid wax between a ceramic core surface and a mold inner face in advance, before the molten wax is injected inside the mold. SOLUTION: A molten wax is injected between the core outer surface of a wax model ceramic formed from a product drawing and a mold inner surface. Then, the face of the ceramic core is checked to see which face of the core is pressured by interrupting injection or the like. The solid wax with the same thickness as a space between the ceramic core surface opposed to the pressure applied face and the mold inner surface is adhered on the ceramic core surface opposed to the pressure applied face. The solid wax is made to be a sheet with an adhesive. During injection of the molten wax, if the pressure is applied to the ceramic core, the mold inner surface holds the ceramic core via the solid wax so as to prevent fracture of the core. It is suitable for the wax model having an expensive ceramic core such as a moving blade or the like for a gas turbine by a lost wax precise casting method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast product manufactured by a lost-wax precision casting method and having a space inside, and in particular, a wax model for a gas turbine moving blade and a stationary blade having an air cooling hole therein. And a method for molding the same.

[0002]

2. Description of the Related Art Conventionally, moving blades and stationary blades for gas turbines are:
Manufactured by lost wax precision casting. Since the blade is exposed to high-temperature combustion gas, a cooling hole is provided inside the blade and the blade is forcibly cooled. And the cooling hole is very complicated and the gap is several mm.
And it is designed to be thin.

[0003] When manufacturing a rotor blade and a stationary blade for a gas turbine having the cooling hole by the lost wax precision casting method, a ceramic core having a cooling hole shape is placed inside the rotor blade and the stationary blade shaped wax to be manufactured. It is necessary to mold the embedded model. Specifically, it can be obtained by placing a ceramic core held by a baseboard in a mold having a cavity in the shape of a moving blade or a stationary blade to be manufactured, and thereafter injecting a molten wax.

[0004]

SUMMARY OF THE INVENTION A wax model of a moving blade and a stationary blade shape for a gas turbine obtained by the above-described method is as follows.
There is a problem that cracks may occur in the internal ceramic core and the molding yield is low. As a method of preventing such a crack of the core, for example, a method of increasing the strength of the ceramic core by mixing zircon in a core usually made of silica or impregnating with an organic resin is proposed. Have been.

[0005] However, the above-mentioned molding method has insufficient strength and is not sufficient to suppress breakage of the core. Also,
Since the ceramic core after metal casting is finally melted and removed from the product with an alkaline solution, there is also a problem in that the removal of the core takes a long time if it contains anything other than silica that is melted with alkali. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of molding a wax model such as a moving blade or a stationary blade for a gas turbine which is low in cost and does not cause core cracking.

[0006]

The inventor of the present invention has analyzed the cracks in the ceramic core in detail, and found that the cracks in the core were caused by the pressure of the ceramic core during the injection of the molten wax into the mold. Was found to be the result of unbreakable breakage. In other words, taking the rotor blades and stationary blades for gas turbines as an example, the core cracks occur in the situation shown in Figs. 3 and 4, and the reason is that the ceramic core is thin to make thin cooling holes. In addition to the above, there is no portion other than the baseboard for holding the ceramic core in the mold, and the molten wax cannot withstand the pressure during the injection and breaks.

Accordingly, the present inventor has focused on the above-mentioned factor of the occurrence of core cracking, and has found a method for obtaining a ceramic core having strength that can withstand wax pressure caused by injection of molten wax. That is, the present invention is a method for molding a wax model in which solid wax is previously provided between the surface of the ceramic core and the inner surface of the mold before the molten wax is injected into the mold.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The feature of the present invention is that, as compared with the conventional method of simply increasing the strength of the core itself, as a result of focusing on the fact that the core cracking occurs at the time of injection of the molten wax,
By providing the reinforcing member in accordance with the pressure applied to the core, breakage of the core can be efficiently suppressed at low cost.

As described above, the core cracking occurs in a situation as shown in FIGS. 3 and 4, and one of the causes is that the molten wax cannot withstand the pressure during injection and breaks. is there. In other words, if the molten wax is completely filled in the mold, the force that breaks the ceramic core does not work, but the mold cavity has a complicated shape during filling, or the position of the injection port is not sufficient. As a result, pressure acts on only one side of the ceramic core and breaks.

In this case, as a measure for preventing the breakage of the ceramic core, it is conceivable to eliminate the above-mentioned cause of breakage, that is, to apply the pressure of the molten wax uniformly over the entire surface of the ceramic core. However, in order to satisfy such conditions, a very complicated mold and injection machine are required, such as providing a plurality of wax injection ports and controlling the flow rates of the respective wax injection ports.

The present inventor has conducted various experiments and studies to prevent breakage of the ceramic core, and as a result, has found a molding method that does not cause cracks in the ceramic core, and has reached the present invention. Specifically, before injecting the molten wax into the mold, it is a method of molding a wax model in which solid wax is previously provided between the ceramic core surface and the mold inner surface,
The details are described below.

First, an example will be described as a flow for carrying out the molding method of the present invention. First, the shapes of the mold and the ceramic core and the position of the wax injection port are determined from the target product drawings such as the moving blade and the stationary blade for the gas turbine.
Next, the temperature of the molten wax, the injection pressure, the injection speed, and the like are determined while observing the state of the surface skin, shrinkage, and the like, using the wax model under these determination conditions.

When all the conditions are determined, the flow of the molten wax filled between the outer surface of the ceramic core and the inner surface of the mold is examined to examine which surface of the ceramic core is subjected to pressure. Specifically, the injection may be stopped halfway and the filling state may be checked, or a different kind of wax may be mixed into the molten wax, and the judgment may be made while leaving a striped pattern on the injected model.
FIG. 5 shows an example of the result of the investigation using the stationary blade for a gas turbine. In this case, the injected molten wax has a shape in which either surface precedes each surface of the ceramic core. . That is, pressure acts on the surface of the ceramic core that is delayed from the preceding surface (B in FIG. 5).
Department).

From the flow of the molten wax thus obtained, it is possible to determine in which direction the pressure acts on the ceramic core placed in the mold cavity. The point of child reinforcement is determined. Next, the distance between the inner surface of the mold and the surface of the ceramic core on the opposite side to which pressure acts (that is, the dimension A in FIG. 5) is determined. Then, a solid wax having a thickness of this dimension is prepared and attached to, for example, the surface of the ceramic core on the opposite side where pressure acts. By doing so, even if the ceramic core is under pressure during the injection of the molten wax,
Since the inner surface of the mold holds the ceramic core through the solid wax, and the solid wax itself has sufficient strength,
It is possible to prevent the core from being broken.

Since the solid wax used in the present invention becomes a part of the wax constituting the wax model as a result, it does not hinder the subsequent lost wax process. The solid wax is preferably an easily available sheet wax with an adhesive, but is not particularly limited. In addition, the dimensions of the solid wax cannot be adapted to the dimensions of the cavity, which continuously changes in a tapered shape if the dimensions are too large, so that the dimensions do not match the dimensions of the inner surface of the mold and the surface of the ceramic core. Or break. On the other hand, if it is too small, the strength of the solid wax is insufficient, and the effect of the present invention is reduced. Desirably, 5.0
2 mm square to 8 mm for a thick part of a wax model such as a rotor blade and a stationary blade for a gas turbine.
A size having an area of mm square is good.

When a plurality of solid waxes are required, the number and spacing may be determined appropriately according to the shape of the model to be molded and the shape of the ceramic core. In this case, the larger the number and the narrower the interval, the higher the effect of preventing core cracking, but the number of steps for arranging the solid wax increases, so that it should be minimized.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. In the present embodiment, a wax model of a gas turbine stationary blade having dimensions of a blade length of 200 mm, a cord length of 230 mm, and inner and outer shrouds is formed. First, the ceramic core has a baseboard at the inner and outer shroud portions, and the dimension in the blade length direction including the baseboard is 250 mm. The wing trailing edge also has a baseboard, and the cord length including the baseboard is 252 mm. The maximum blade thickness formed by the inner surface of the mold and the surface of the ceramic core is 3.5 mm,
The minimum is 1.4 mm. The thickness of the ceramic core is 30 mm at the maximum and 1.2 mm at the minimum. At the trailing edge of the ceramic core, there are formed holes for forming pin fins and partition walls by casting.

First, the ceramic core was set in a mold without sticking a solid wax, and injection conditions were determined. Thereafter, 1/5 of the amount of the molten wax to be injected was injected, the amount was sequentially increased by 1/5, and the flow of the molten wax was grasped by a total of 5 injections. As a result, it was found that the surface on which pressure acts upon injection of the molten wax is the portion B in FIG. According to this result, the solid wax was attached to the part C in FIG. The solid wax used is a sheet wax with an adhesive which can be easily obtained.

The dimensions of the solid wax used are two types, the height dimensions of which are 1.8 mm and 2.3 mm corresponding to the blade thickness previously determined from the drawings, and the cross-sectional dimensions are 2.8 mm and 2.3 mm.
5 × 2.5 mm. The number of each was eleven, and the interval was equally divided in the blade length direction. FIG. 2 shows a ceramic core to which solid wax has been attached. Then, the ceramic core to which the solid wax was attached was set in a mold, and the wax temperature was 74 ° C., the injection pressure was 8 kgf / cm 2, and the injection speed was 2
The molten wax was injected into the mold at 30 cubic cm / sec.

As a result of X-ray transmission inspection of the molded wax model, no crack was found in the ceramic core. Further, the model was placed in an electric heating furnace at 150 ° C., the wax was melted and removed, the ceramic core was taken out, and a detailed check for cracks was made by color check. In the present embodiment, the stationary blade for gas turbine is used as an example. However, the present invention is not limited to the stationary blade, and is applicable to all lost wax precision casting methods using a ceramic core.

[0021]

According to the present invention, it is possible to mold a wax model without breaking the ceramic core. As a result, the occurrence of core breakage and the like can be suppressed by molding a wax model having an expensive ceramic core such as a rotor blade or a stationary blade for a gas turbine by a lost wax precision casting method, and at a low cost and a high yield. Therefore, its industrial value is high.

[Brief description of the drawings]

FIG. 1 is a view showing an example of the present invention before a molten wax is injected into a mold.

FIG. 2 is a view showing an example of the present invention in a core set inside a mold before molten wax is injected.

FIG. 3 is a view showing an example of cracks generated in a core of a wax model of a moving blade for a gas turbine.

FIG. 4 is a diagram showing an example of cracks generated in a core of a wax model of a stationary blade for a gas turbine.

FIG. 5 is a diagram showing an example of a filling state of wax injected into a mold.

Claims (1)

[Claims] 1. A method of molding a wax model having a ceramic core, wherein a solid wax is provided between the surface of the ceramic core and the inner surface of the die before injecting the molten wax into the die.