JPH11192533A - Casting mold for precision casting and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart the sufficient strength to counter a molten metal pressure at the time of casting to a casting mold and to eliminate the misrun in thin parts by welding a porous ceramic piece to an intermediate layer, thereby increasing the air permeability and strength to the casting mold. SOLUTION: The first layer which is an inner side among the layers constituting the casting mold 2 comes into direct contact with the molten metal and since there is a need for precisely transferring a product shape, a fine powder refractory slurry and stucco are used. The intermediate stage after the second layer is coated with the slurry and stucco and is dried, following which the porous ceramic piece 1 having the good air permeability is tightly adhered thereto and the next layer is executed. The porous ceramic piece 1 is preferably adhered to the place where the misrun occurs. The materials which do not differ much in thermal expansion are selected to meet the kinds of the refractories of the casting mold material. As a result, the strength enough to counter the surface pressure of the molten metal at the time of production may be imparted to the products, such as, for example, turbine blades, having the portions of large surface areas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold used mainly for a lost wax precision casting method, and more particularly to a mold having a wing shape and a large surface and a thin wing tip. The present invention relates to a mold capable of preventing a mold breaking phenomenon due to insufficient mold strength and a method for manufacturing the mold.

[0002]

2. Description of the Related Art Among the precision casting methods, particularly, the lost wax precision casting method can obtain a cast product with high dimensional accuracy, so that it is often used for manufacturing various members having complicated shapes which cannot be machined. Has been adopted. In addition, a usual lost wax precision casting mold is a method in which a slurry type refractory is coated on a vanishable model (wax model), and a powdery or granular refractory (stucco) is formed on the slurry by utilizing the viscosity of the slurry. The slurry and the refractory are alternately coated alternately to obtain a mold having a predetermined thickness. Therefore, the term "granular" as used in the present invention is a general term for powder, granular, and a state in which both are mixed. This mold usually contains powder for refractory slurries such as zircon, zirconia, alumina and fused quartz, mullite and zircon for powdery and granular refractories (hereinafter also referred to as stucco), and colloidal silica and ethyl silicate as binders. Used.

[0003] The process of manufacturing the lost wax precision casting mold is called a coating operation. After the final coating is completed, the wax model is sufficiently dried, and the wax model is generally eluted in an autoclave. Use as a mold. Further, the mold is fired for casting such as burning off residual wax adhered to the mold, removing residual moisture, developing mold strength, and the like.

However, in the conventional precision casting mold, when the target product has a blade shape such as a turbine blade and has a large area portion and a thin portion, the pressure of the molten metal during casting is large, so that the thickness of the mold is increased. That is, it is necessary to increase the number of layers of the mold. In this case, the number of layers of the mold is usually 5 to 7 layers, but 9 to 11 layers, and in some cases, 10 layers or more. There is a point.

[0005] Furthermore, since the air permeability of the mold is reduced as the thickness of the mold is increased, the thin portion at the tip of the blade is not filled with molten metal at the time of casting, so that there is a problem that the molten metal runs short.

[0006]

As a measure for preventing insufficient running of the molten metal during casting as described above, Japanese Patent Laid-Open Publication No.
And Japanese Patent Application Laid-Open No. 57-11748 discloses a method of manufacturing a mold after adding a gas-permeable substance on a vanishing model in advance. A method for improving the air permeability by adding a foaming or heat-dissipating substance is disclosed. However, many of these methods are insufficient to simultaneously satisfy the strength and air permeability of the mold.

The present invention solves the above-mentioned problems, and provides a casting mold for precision casting which has sufficient strength to withstand the pressure of the molten metal at the time of casting and which does not cause insufficient running of the molten metal in a thin-walled portion, and a method of manufacturing the same. With the goal.

[0008]

SUMMARY OF THE INVENTION The present inventor has made various studies to solve the above-mentioned problems, and has focused on the fact that the mold has both strength and air permeability.

Specifically, the present invention relates to a precision casting mold in which a slurry-like refractory and a powder-granular refractory are alternately coated on a vanishing model, and the vanishing model is removed.
A precision casting mold and a method for producing the same, characterized by increasing the air permeability and strength of the mold by bonding a porous ceramic piece to the intermediate layer, and further characterized in that the vanishing model is a wax model. This is a precision casting mold.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that the inner first layer of the mold must directly contact the molten metal and transfer the product shape precisely. For this purpose, use the fine powder refractory slurry and the fine powder granular refractory stucco, but after coating the slurry and the stucco in the intermediate stage of the second layer and subsequent layers, drying and bonding the porous ceramic pieces with good air permeability, Characterized in that the layers are implemented. At this time, it is desirable that the porous ceramic be adjusted to the shape of the product and adhered to a place where a shortage of hot water occurs. Adhesion may be performed with a normal sticky refractory, but may be performed with a thin metal wire such as a wire.

The step of bonding the porous ceramic piece includes:
Any stage may be used as long as it is the second layer or later and before the final layer, but it is desirable to perform the third or fourth layer, which has a sufficient thickness of the mold and has a certain strength.

The material of the porous ceramic piece must be a material that does not greatly differ in thermal expansion according to the type of refractory of the mold material.

[0013] The bonding of the porous ceramic makes it possible to provide a product having a large surface area, such as a turbine blade, with strength sufficient to withstand the surface pressure of the molten metal during casting. The number of layers can be made the same as the normal number of layers. Further, since the porous ceramic is used, a sufficient air permeability can be obtained. At this time, if a part of the mold material coated on the porous ceramic piece is scraped off, the air permeability is further improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to an embodiment and drawings. 600mm x 200mm and 0.5mm thickness
A wax model of a turbine blade having a single blade shape of 35 mm is prepared, and this wax model is assembled in a tree shape. Hereinafter, the assembled wax model is referred to as a tree. Next, the mold was manufactured by coating the slurry-like refractory and stucco on the tree. At this time, the number of mold layers was seven, and a porous ceramic piece bonded to the third layer and a normal-coated one were prepared for comparison. After drying, the wax model was melted by heating in an autoclave and taken out to obtain a mold.

The slurry of the first layer used as described above was prepared by adding 1.00 of water-soluble colloidal silica having a silica content of 30% by weight as a binder, and Zr powder of 350 mesh or less as a filler at a ratio of 3.00. As mixed. The slurry of the second and subsequent layers was the above-mentioned colloidal silica 1.00, and the filler was a mixture of 2.00 of Zr powder of 350 mesh or less and 0.80 of fused silica powder. As a stucco,
For the first layer, zircon (120 mesh or less) was used, and for the second and subsequent layers, a mixed powder of silica (Si02) and alumina (Al2O3) (60 to 100 mesh) was used.

In the coating operation, the tree was immersed in the refractory slurry contained in the container to coat the slurry, and then the stucco was coated using a sanding device to form a first layer. The sanding device used had a structure in which a ventilated floor was provided at the lower part of the container, and air was blown from below the floor to float the stucco stored above the floor.

Next, the slurry of the second and subsequent layers contained in another container is coated on the first layer, and the slurry is stored in another sanding device having the same structure, and the stucco of the second and subsequent layers is coated. To form a second layer. Thereafter, a refractory slurry and a stucco were alternately coated in the same manner to obtain a seven-layer mold. In the mold of the present invention, after the third layer is completed and dried, FIG.
A porous ceramic piece was adhered to the location shown in FIG. Then, after alternately coating up to seven layers and drying, the tip of the porous ceramic was scraped off and heated in an autoclave to melt and discharge the wax model to obtain a mold. FIG. 2 shows a main cross section of the completed mold.

The obtained mold was fired at 1000 ° C. for 2 hours to cast JIS SCS13. As a comparative example, SCS13 was cast in the same manner using a conventional mold to which the porous ceramic piece was not bonded.

As a result of the casting, in the example of the present invention, there is no shortage of hot water at a position of 0.5 mm at the tip of the blade. In the comparative example, the shortage of hot water shown in FIG. 3 occurred at the same location.

In the present embodiment, the slurry and the stucco to be coated are specified, but the use of another slurry depending on the product shape is effective. Further, although the sanding device has a structure in which the stucco is floated using air, a structure in which the stucco is dropped from above and sprinkled may be used.

[0021]

As described above, when the mold of the present invention is used, a mold having the same number of layers as in the prior art and having the strength of the mold and the air permeability can be manufactured, so that the cost is low and the reliability is low. Since a high precision casting product can be obtained, it is an invention that produces a very large industrial effect.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a tree according to the present invention. However, the porous ceramic pieces adhere during the coating operation.

FIG. 2 is a view showing a main cross section of a mold according to the present invention.

FIG. 3 is a view showing a situation of insufficient running of a hot water in an example of a product according to the present invention.

[Brief description of reference numerals]

1. 1. Porous ceramic piece Mold 3. Elution part of wax model Lack of hot water

Claims (2)

[Claims] 1. A precision casting mold in which a slurry-like refractory and a powder-granular refractory are alternately coated on a fugitive model, and a porous ceramic piece is placed on an intermediate layer in the precision casting mold from which the fugitive model is removed. A precision casting mold and a method for producing the same, characterized by increasing air permeability and strength of the mold by bonding. 2. The precision casting mold according to claim 1, wherein the fugitive model is a wax model.