JP3238166B2 - Manufacturing method of precision casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a precision casting mold used for manufacturing a precision casting of an active metal material such as titanium or a titanium alloy.

[0002]

2. Description of the Related Art Titanium and titanium alloys are extremely active metal materials in a molten state. Therefore, even if graphite with high chemical stability is used as a mold for producing a cast product of titanium or a titanium alloy, the casting surface of the cast product that has been in contact with the mold has several hundred μm of titanium. And a reaction layer of carbon and carbon.

[0003] Therefore, a zirconia coating layer was formed on the surface of a mold in contact with a molten metal by using zirconia fine powder having higher chemical stability than graphite and low reactivity with titanium in a molten state and a titanium alloy. A method for manufacturing a precision casting mold has been proposed (if necessary, Japanese Patent Application No. 62-30872).
No. 0).

[0004]

The conventional method for manufacturing a precision casting mold has the following problems. That is, when the thickness of the precision casting is thick, if the zirconia coating layer on the surface of the mold is as thin as 20 to 30 μm, a few hundred μm of titanium and carbon are added to the casting surface of the casting which has been in contact with the mold. A reaction layer is created.

In order to solve this problem, in the method of manufacturing a precision casting mold, the zirconia coating layer may be thickened. However, if the zirconia coating layer is made thicker, the zirconia coating layer may be cracked. And the zirconia coating layer is peeled off from the wax pattern, so that a reaction layer of several hundred μm is also formed on the surface of the casting surface of the casting which has been in contact with the mold.

The present invention has been made in view of the above problems, and has as its object to form an extremely small reaction layer with the mold on the casting surface of the casting which has been in contact with the mold. It is an object of the present invention to provide a method for manufacturing a precision casting mold capable of manufacturing a precision casting.

[0007]

Means for Solving the Problems In order to achieve the above object, a method of manufacturing a casting mold for precision casting according to the present invention comprises the steps of adding a water-soluble polymer substance and a solvent to a zirconia fine powder as a main aggregate. Immerse the wax pattern in the slurry,
The slurry is applied to the wax pattern, and the wax pattern to which the slurry is applied is dried to form a zirconia coating layer on the wax pattern. In the same manner, after forming the backup shell layer and then removing the wax pattern, the shell mold is baked to produce a precision casting mold having a zirconia coating layer on its surface. Is characterized by adding 1 to 50% by weight of zirconia fiber to the zirconia fine powder as described above to increase the thickness of the zirconia coating layer.

[0008]

According to the method for manufacturing a precision casting mold of the present invention, a wax pattern is immersed in a slurry obtained by adding a water-soluble polymer substance and a solvent to a zirconia fine powder as a main aggregate as described above. And apply the slurry to
Dry the wax pattern with this slurry attached,
A zirconia coating layer is formed on the wax pattern, and then a backup shell layer is formed on the outside of the zirconia coating layer in the same manner as when manufacturing the precision mold shell mold, and then the wax pattern is removed. In firing the shell mold to produce a precision casting mold having a zirconia coating layer on the surface, zirconia fibers are added to the zirconia fine powder, which is the main aggregate of the slurry, in an amount of from 1 to 3.
By adding 50% by weight, the thickness of the zirconia coating layer is increased .

[0009]

【Example】

(First Embodiment) Next, a method for manufacturing a precision casting mold according to the present invention will be described with reference to a first embodiment. A zirconia fine powder having an average particle diameter of 1 μm or less is used as a main aggregate, and the diameter is 1 to 100 μm.
zirconia fiber with a length of 0.1 to 10 mm
５０50% by weight to obtain a mixed powder.

On the other hand, water or an alcohol is added as a solvent to one of high molecular compounds such as an alkali acid ester copolymer, polyvinyl chloride, polyvinyl butyral, polyvinyl alcohol, and polycarboxylic acid to form a polymer having a concentration of 5 to 2%.
A 0% by weight solution is added, and this solution is added to the above mixed powder in an amount of 5 to 20%, and stirred and mixed to obtain a slurry.

Next, the wax pattern is immersed in the slurry, the slurry is adhered to the wax pattern, the wax pattern is pulled up from the slurry, and the wax pattern to which the slurry is adhered is naturally dried to obtain the wax. A zirconia coating layer is formed on the pattern. The maximum thickness of this zirconia coating layer is about 500 μm
It is about.

Next, a back-up shell layer is formed on the outer side of the zirconia coating layer in the same manner as in the production of the shell mold for the precision mold. For example, a slurry is obtained by adding zircon flour to an aqueous colloidal silica solution. In addition, the wax pattern having the zirconia coating layer formed thereon is immersed in the slurry, and then pulled out of the slurry and air-dried to form a zircon flower backup layer. Then, using a slurry (slurry obtained by adding zircon flour to the above-mentioned aqueous colloidal silica solution) as a binder, a back-up shell layer of coarse particles such as mullite is formed.

Next, the wax pattern is removed from the mold using the autoclave, and the shell mold is fired at a temperature of 1000 ° C. for 1 hour in a firing furnace to produce a precision casting mold having a zirconia coating layer on the surface. I do. FIG. 1 shows the particle structure of the precision casting mold obtained according to the first embodiment. In FIG. 1, 1 is a zirconia coating layer and 4 is a back-up shell layer.

(Second Embodiment) Next, a method for manufacturing a precision casting mold according to the present invention will be described with reference to a second embodiment. The wax pattern is immersed in the slurry obtained in the same manner as in the first embodiment, and the slurry is adhered to the wax pattern. The wax pattern is pulled up from the slurry, and the mesh pattern is dried before the slurry is dried. 100 (particle size 150 μm)
A degree of zirconia particles are sprinkled on the slurry, and the zirconia particles are adhered while being partially embedded in the slurry to form a first zirconia coating layer on the wax pattern.

Next, after the wax pattern to which the slurry is attached is naturally dried, the wax pattern on which the first zirconia coating layer is formed is immersed again in the slurry to form the first layer. A slurry is deposited on the zirconia coating layer, and the wax pattern is pulled up from the slurry.
(Particle size: 400 μm) to mesh # 100 (particle size: 150 μm)
m) Sprinkle the zirconia particles on the slurry and adhere the zirconia particles in a state of being partially embedded in the slurry to form a second zirconia coating layer on the wax pattern. During the above manufacturing process, about 1 mm for each layer
A zirconia coating layer having the following film thickness can be obtained, but the above steps are repeated as necessary to increase the thickness of the zirconia coating layer.

Next, a back-up shell layer is formed on the thickened zirconia coating layer in the same manner as in the first embodiment, and then a wax pattern is removed and the shell mold is fired. A mold for precision casting having a zirconia coating layer having a thickness of several mm is manufactured. FIG. 2 shows the particle structure of the precision casting mold obtained according to the second embodiment. In FIG. 2, 1 is a zirconia layer, 2 is a zirconia slurry layer, 3 is a zirconia particle layer, and 4 is a back-up shell layer.

In the conventional method for forming a zirconia coating layer, a wax pattern is immersed in a slurry containing zirconia fine powder, a water-soluble polymer substance and a solvent as main components.
The wax pattern attached with the thriller is dried to form a zirconia coating layer on the wax pattern.However, when the thickness of the zirconia coating layer is increased, in the drying process of the slurry, The shrinkage of the zirconia coating layer becomes too large, causing cracks in the zirconia coating layer or peeling of the zirconia coating layer from the wax pattern.

In order to prevent this, in the method for producing a precision casting mold of the present invention, a zirconia fiber is added as an aggregate of the slurry, in addition to zirconia fine powder, and a water-soluble polymer substance and a solvent are added. To obtain a slurry. Then, a wax pattern is immersed in the slurry, the slurry is adhered to the wax pattern, and the thickness of the conventional adhered slurry having an upper limit of about 30 μm is increased to about 500 μm by adding the zirconia fiber. , Let it dry naturally, cause cracks,
A zirconia coating layer that does not peel off from the wax pattern is formed on the wax pattern.

When a zirconia coating layer having a thickness of 500 μm or more is required, the zirconia particles are deposited on the slurry after the slurry is applied to the wax pattern as described above and before the slurry is dried. After sprinkling and attaching, air dry. By repeating this step, a thick zirconia coating layer is formed on the wax pattern.

After forming the zirconia coating layer composed of the zirconia slurry alone or the zirconia slurry and the zirconia particles on the wax pattern, a general method of manufacturing a precision casting mold is provided outside the zirconia coating layer. Zircon sand, alumina, quartz sand,
A shell mold is formed using mullite or the like as a backup material. Thereafter, the wax pattern is removed to obtain a precision casting mold having a thick coating layer of several tens μm to several μm formed of only zirconia on the surface.

[0021]

As described above, in the method for producing a precision casting mold of the present invention, 1 to 50% by weight of zirconia fiber is added to zirconia fine powder which is the main aggregate of the slurry. This zirconia fiber has a role of suppressing the slurry shrinkage rate during slurry drying and improving the film strength by entanglement of the zirconia fiber when drying is completed.

The zirconia coarse particles sprinkled on the slurry attached to the wax pattern together with the zirconia fiber further suppress the slurry shrinkage during the drying of the slurry, thereby generating cracks in the zirconia coating layer during the drying of the zirconia coating layer, and It has the role of suppressing the peeling of the zirconia coating layer from the wax pattern. In addition, zirconia fiber and zirconia coarse particles also have a role of suppressing the zirconia shrinkage at the time of shell mold firing low and suppressing the occurrence of cracks in the zirconia coating layer at that time,
According to the present invention, it is possible to produce a sound precision casting mold having a thick zirconia coating layer in which cracks are unlikely to occur, and by using this precision casting mold, it is possible to cast a casting in contact with the casting mold. It is possible to manufacture a precision cast product in which a very little reaction layer with a mold is formed on the skin surface. That is, the thickness of the zirconia coating layer of the precision casting mold is 20 to
When the thickness is as thin as about 40 μm, the colloidal silica contained in the backup shell penetrates into the casting through the thin zirconia coating layer, and becomes 250 to 400 μm into the thick precision casting.
When the thickness of the zirconia coating layer of the precision casting mold is as thick as about 180 μm as in the present invention, the colloidal silica contained in the backup shell is cast through the thick zirconia coating layer. Difficult to penetrate, thick
Only a reaction layer of about 30 μm is formed on a precision casting of meat .

[0023]

[Brief description of the drawings]

FIG. 1 is a photograph showing the particle structure of a mold obtained by a first embodiment of the method for producing a precision casting mold according to the present invention.

FIG. 2 is a photograph showing a particle structure of a mold obtained by a second embodiment of the method for manufacturing a precision casting mold according to the present invention.

[Description of Signs ] 1 Zirconia coating layer 2 Zirconia slurry layer 3 Zirconia particle layer 4 Backup shell layer

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masami Maeda 1-1 1-1 Wadazakicho, Hyogo-ku, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Minoru Yanagisawa, Hyogo-ku, Hyogo-ken 1-1-1 Wadazakicho Inside Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Hirofumi Furukawa 2-1-1, Niihama, Araimachi, Takasago-shi, Hyogo Pref. Hei 1-150428 (JP, A) Japanese Patent Publication 54-28293 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22C 9/04 B22C 1/00-3/00 B22D 21 / 02

Claims (1)

(57) [Claims] 1. A wax pattern is immersed in a slurry obtained by adding a water-soluble polymer substance and a solvent to a zirconia fine powder as a main aggregate, and the slurry is adhered to the wax pattern. To form a zirconia coating layer on the wax pattern, and then form a backup shell layer on the outside of the zirconia coating layer in the same manner as when the shell mold for the precision mold is manufactured. After removing the zirconia, the shell mold is fired to produce a precision casting mold having a zirconia coating layer on the surface. In the zirconia fine powder which is the main aggregate of the slurry, 1 to 50% by weight of zirconia fiber is added. A method for producing a casting mold for precision casting, characterized in that the thickness of a zirconia coating layer is increased by addition of the zirconia coating layer.