JPH08174145A - Forming method of lost wax mold - Google Patents

Abstract

PURPOSE: To provide a forming method of a lost wax mold to manufacture the long casting free from porosity by forming the lost wax mold which is long in shape and uneven in wall thickness. CONSTITUTION: A wax mold formed in the cavity shape to be formed is dipped in the slurry for forming the mold containing the refractory powder, and the slurry coated film is formed on the surface of the taken out wax mold. The thickness of the lower part of the coated film to be formed by the dipping in the slurry is larger than that of the upper part due to the sagging of the slurry by the gravity between the upper and lower parts when left standstill. After the difference in the thickness of the coated film is obtained, the refractory powder is scattered to change the attached amount of the refractory powder. By repeating these works, the mold having the directional solidification in the longitudinal direction is obtained. When the wax pattern is removed and the molten metal is poured, the cooling speed of the casting can be controlled to form the excellent casting free from porosity.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a lost wax mold. More specifically, the present invention relates to a method for forming a lost wax mold having a long shape and an uneven thickness.

[0002]

2. Description of the Related Art When obtaining a casting having a long shape such as an engine valve, it is difficult to give an appropriate cooling temperature gradient in the longitudinal direction of the long material when the molten metal filled therein solidifies. It was difficult to obtain sound castings because porosity was likely to occur inside. Therefore, as a method of ensuring the soundness of the inside of the cast product, a method of giving solidification directivity in the longitudinal direction or cutting many weirs has been adopted. For example, in the former case, there are cooling promotion methods such as installing cooling gold for cooling promotion at a shaft end portion, exposing a cooling burr (radiating plate), and providing a cooling device in a mold. However, this method requires a new device and a step of attaching the device to the mold. In addition, the latter method of providing a weir has a problem that cutting of the weir after mold separation is complicated and the number of processing steps is increased.

Therefore, such a method is not easy to introduce in the molding process of precision casting.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is a lost wax mold in which the mold thickness is changed in the longitudinal direction to prevent the formation of cavities in a cast product of a long product. Is intended to be formed.

[0005]

According to the method of molding a lost wax mold of the present invention, a wax model molded into a cavity shape to be formed is immersed in a slurry for molding a mold containing refractory powder and taken out to obtain a surface thereof. After performing a dipping step of forming a slurry coating layer, an adhesion step of sprinkling the refractory powder on the coating layer and then adhering the refractory powder to the coating layer, and then repeating the dipping step and the adhering step a plurality of times, A method for forming a lost wax mold by melting and removing the wax model by heating, wherein in the dipping step, the mold is dipped in the slurry and then pulled up, and the side of the mold to be thickened is left to stand down The step of thickening the slurry coating film in the lower portion, and the step of adhering is a step of sprinkling the refractory powder in a state of being left still in the dipping step.

The method for molding a lost wax mold of the present invention comprises a dipping step and an adhering step. In the dipping step, the wax model is dipped in the slurry for molding and then pulled up, so that the side where the wall pressure of the mold should be thickened is increased. Place it down and let it sit.
When left standing, the thickness of the lower portion of the wax model increases due to the slurry coating film dripping on the wax model. In the adhering step, a uniform refractory powder is sprinkled on the wax model slurry coating film in a stationary state. The sprinkled refractory powder is
The adhesion amount also changes according to the thickness of the slurry coating film.

By repeating these two steps a plurality of times so as to obtain a desired mold thickness, a thick wax model having a gradient between the upper side and the lower side when the wax model is allowed to stand can be obtained. A lost wax mold can be formed in which the wax model is heated to melt and remove the wax model and fired.

The wax or resin model of the wax model is removed by heating in an autoclave, for example. The obtained lost wax mold is a mold in which the mold thickness is uneven in the longitudinal direction, and is a mold in which the formation of porosity is suppressed.
A lost wax mold for precision casting, for example, a lost wax mold for an engine valve, is formed by assembling a plurality of wax models in a tree shape so that a plurality of cast products can be obtained by one casting. The wax model formed in the tree shape can be formed into a lost wax mold by the dipping and attaching steps as in the above.

[0009]

According to the method of the present invention, the wax model molded into the cavity shape to be formed is immersed in a slurry for molding a mold containing refractory powder and taken out to form a slurry coating layer on the surface thereof. After that, the adhesion step of sprinkling the refractory powder on the coating layer and adhering the refractory powder to the coating layer, the dipping step and the adhering step are repeated a plurality of times, and then the wax model is melted and removed by heating. And a lost wax mold is formed.

The coating film formed by immersing the wax model in the slurry for molding a mold becomes thicker in the lower portion than in the upper portion due to the dripping of the slurry between the stationary upper portion and the lower portion due to gravity. This degree depends on the characteristics of the slurry such as the viscosity of the slurry, but in the case of a long product, the thickness of the slurry coating film can be different between the upper part and the lower part only by standing. When there is a difference in the thickness of the coating film, the refractory powder is sprinkled to change the amount of the refractory powder deposited. Then, by immersing it again in the slurry and allowing it to stand still, a slurry coating film is similarly formed on the upper surface, and the operation of sprinkling the refractory powder is repeated until the desired mold thickness is obtained.

As a result, a mold having a solidification directivity in the longitudinal direction is obtained on the surface of the wax model. Then, the wax model is removed to form a lost wax mold having a desired coagulation directivity. When molten metal is poured using this lost wax mold, the mold has a direction of cooling from the thin side to the thick side, so that the cooling rate of the casting can be controlled and the occurrence of porosity can be prevented. For example, an engine valve can form a good cast product having no porosity.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. FIG.
Engine valve-shaped urea resin pattern wax model 3 with shaft diameter φ10 mm and total length 130 mm as shown in Fig. 3
One piece is fixed integrally under the beam-shaped runner model that forms the runner, and an inverted cone-shaped riser model is fixed in the upper center of the runner model and operated in the center of this riser model. A wax model with a fixed rod was prepared.

(Dip step) The slurry for dipping was 10 kg of ethyl silicate binder and zircon flour (#
325) was added to a solution having a viscosity of 20 sec (Zahn cup No. 5). The above wax model was immersed in this immersion slurry for 30 seconds. Next, as shown in FIG. 2, the valve was left stationary in the direction in which the shaft end portion of the valve was facing upward, and was cut off for about 40 seconds. It was confirmed that the thickness of the slurry coating film slightly increased due to the sagging during this period.

(Adhesion Step) Next, as a refractory powder, zircon sand having a particle size of 0.3 mm was sprinkled on the wax model. (Refer to FIG. 3) The work of the above-mentioned dipping process and adhesion process is 1
By repeating 0 times, as shown in FIG. 4, a wax mold for precision casting having a small thickness part at the shaft end part of the engine valve of 3 mm and a large thickness part at the shaft part directly above the umbrella of the lower part is 10 mm is produced. did.

The wax model of the engine valve molded as described above is demolded from the mold and then placed in an autoclave.
It was fired at 000 ° C. and dewaxed to obtain a lost wax mold shown in FIG. 110 in a furnace
Two minutes after heating to 0 ° C. and taking out from the furnace, an iron-based material at 1500 ° C. was poured into the mold with the shaft end of the engine valve facing downward as shown in FIG. The valve casting obtained from this mold was able to obtain a sound casting without generating internal porosity in the axial portion.

FIG. 6 is a graph showing mold temperatures of a thin wall portion (3 mm) and a large wall portion (10 mm) of a lost wax mold immediately after firing at 1000 ° C. and after 2 minutes. Therefore,
The thin portion has a high cooling rate, and the large portion has a slow cooling rate. As a comparative example, the above valve was cast under the same conditions using a conventional mold having a uniform thickness of 6 mm. The valve obtained had internal porosity.

[0017]

The lost wax mold produced by the production method of the present invention can impart cooling directivity from the side having a small thickness of the heat insulating wall to the side having a large thickness. Therefore, by using this lost wax mold, it is possible to obtain a good casting product of a long product (engine valve or the like) having no porosity.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a wax model of this example.

FIG. 2 is an explanatory schematic diagram illustrating a state of a slurry coating film in a still process of an example.

FIG. 3 is an explanatory schematic diagram for explaining an attaching step of this example.

FIG. 4 is a schematic cross-sectional view of a lost wax mold before dewaxing and firing in this example.

FIG. 5 is a schematic cross-sectional view of a lost wax mold of this example.

FIG. 6 is a line graph showing the results of measuring the temperature immediately after taking out the lost wax mold of the present embodiment from the firing furnace and the temperature after 2 minutes at different mold thickness sites.

Claims (1)

[Claims] 1. A dipping process in which a wax model formed into a cavity shape to be formed is dipped in a slurry for molding a mold containing refractory powder and taken out to form a slurry coating layer on the surface thereof, and then the coating layer is formed. Molding of a lost wax mold in which a refractory powder is sprinkled and an adhering step of adhering the refractory powder to the coating layer, and then the dipping step and the adhering step are repeated a plurality of times, and then the wax model is melted and removed by heating. In the method, the dipping step is a step of immersing in the slurry and then pulling it up, leaving the side of the resulting mold where the wall thickness should be thickened downward, and allowing it to stand, and thickening the slurry coating film in the lower part, The method for forming a lost wax mold, wherein the adhering step is a step of sprinkling the refractory powder in a state of being allowed to stand in the dipping step.