JPH0199742A - Method for preventing crack in mold for precision casting - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention aims to prevent mold cracking due to thermal stress generated during dewaxing in a precision hammer making method for manufacturing molds using wax master molds. It's about how to do it.

[Prior art] As is well known, the lost wax casting method involves making a model using wax, coating its surface with molding sand with a binder, drying it, and then putting it into a steam waxing machine and heating it to about 160°C. A hollow shell-shaped breathable mold is produced (heated to melt the wax and dewax), and then fired at a high temperature in a furnace.

In addition, in the CLA method, in order to save wax, 8 rods (usually iron pipes are used) are embedded in the part corresponding to the sprue in the prototype made with 1 normal wax, and these 8 rods are removed at the same time when dewaxing. I have to.

[Problems with conventional technology] However, when the mold was being heated for dewaxing.

Since the coefficient of thermal expansion of the wax when it is solid is more than 10 times greater than that of the refractory material forming the shell-shaped mold, minute cracks may occur in the mold. For this reason, there is a problem that hot water leaks during spinning, which may lead to deterioration of the quality of the product.

[Means for Solving the Problems] This invention attempts to solve the above-mentioned problems by combining an elastic material on the inner circumferential surface of the sprue and molding a wax master mold, so that the mold during dewaxing can be easily removed. This is a method for preventing cracks in precision casting molds, characterized by preventing cracks.

[Function] When the elastic material is heated for dewaxing, it absorbs the thermal expansion of the solid wax, prevents excessive thermal stress from being applied to the spinning mold shell, and prevents it from cracking.

[Example] Next, an example of the present invention will be described regarding a mold used in a vacuum wicking precision casting method. This vacuum wicking precision casting method is an improvement of the casting method in the lost wax casting method disclosed in Japanese Patent Publication No. 52-38924, and was developed by Hutchner, a major American manufacturer of lost wax products, and was developed by one inventor. rCLA method, which takes the initials of the name
It is also called a new technology and is attracting attention in this field.

In the figure, ■ is a bar made of a certain length of iron pipe with both ends closed, and a female screw body 2 is integrally fixed to one end of the bar. A foamed polyethylene pipe 3, which is an elastic material, is inserted into the outer periphery of the 8-rod 1, and the outer peripheral surface of the 8-rod 1 is covered with the foamed polyethylene. Then, this is set in a predetermined mold (not shown) and wax is injected into the cavity to form a wax master mold 4 shown by solid lines in FIG. 2.

Then, a mold 5 is formed by applying a binder to the surface of the master mold 4 and coating it with molding sand.

Note that 5a is the product molding part of the mold, and 5b is the goo 1 to part.

5c is a part of the sprue, 5d is a molten metal suction pipe extending downward from the sprue part, and 5e is formed at the upper end of the molten metal suction pipe to have an abacus-shaped bulge. The cup portion 5f is a robot gripping portion extending above the sprue portion 5C, and a large diameter portion 5g for preventing slipping is formed at the upper edge of the gripping portion.

After drying the binder, this mold 5 is placed in a steam dewaxing apparatus and heated with steam. In the heating process, the amount of thermal expansion of the wax and the eight rods 1 when solid is larger than that of the mold 5, which is the outer shell, but the thermal expansion of the wax and the eight rods 1 is greater than that of the foamed polyethylene pipe 3, which is an elastic material. is absorbed by contraction. In addition, since the lower end of the 8-piece 1 is exposed to the outside, it tends to rise in temperature before the wax when heated from the outside, but the foamed polyethylene pipe 3 delays the temperature rise of the wax due to its heat insulating effect. For this purpose, thermal stress is also alleviated. In this way, the entire body is heated to the melting temperature of the wax under low thermal stress, and the wax flows out of the mold. At the same time, a screw (not shown) is screwed into the female screw body 2, and the 8 rods 1 are pulled out of the mold. .

When the mold 5 is set in a depressurizing chamber and the molten metal suction pipe is suspended from the bottom opening of the chamber to suck up the molten metal, the navel knob 5e is formed between the inner periphery of the bottom opening and the outer periphery of the molten metal suction pipe. It is formed to provide an airtight seal.

The foamed polyethylene pipe 3 is melted by heating during dewaxing and flows out of the mold together with the wax. The liquefied polyethylene and wax are separated and reused. Foamed plastics such as zero-foamed polyethylene are suitable as materials due to their high elasticity and heat insulation properties, but other elastic materials such as fibrous materials may also be used. good. However, it goes without saying that it is preferable to use a material that does not react with the wax and does not hinder the later reuse of the wax. Further, in this embodiment, the entire length of the 8 rods 1 is covered with the elastic material, but the elastic material may be placed only on a portion that is likely to cause cracks.

In a mold formed by coating an elastic material on the outer circumferential surface of the eight rods in this way, the incidence of mold cracking during soldering as described above could be significantly reduced. In particular, the mold cracking rate of the 1eJ hot water intake pipe upper pipe d and the grip portion 5f, which were common in the past, could be reduced to less than one-tenth of that in the conventional method.

[Effects of the Invention] As described in the embodiments above, according to the present invention, the elastic material absorbs the thermal expansion of the wax and prevents excessive thermal stress from being applied to the mold, thereby reliably preventing cracking of the mold and improving yield. It has a remarkable effect of significantly improving

[Brief explanation of the drawing]

The drawings show one embodiment of this invention, and FIG.
A perspective view of the rod, and FIG. 2 is a vertical sectional view of the prototype. l...8 dedication, 3...polyethylene pipe (elastic material), 4...prototype, 5...mold, 5c...
Part of the sprue. Figure 2

Claims (1)

[Claims] 1. A precision casting mold characterized in that mold cracking during dewaxing is prevented by combining an elastic material on the inner peripheral surface of the sprue and forming a wax master mold. How to prevent cracking. 2. The method for preventing cracking of a precision casting mold according to claim 1, wherein the elastic material is a foamed plastic.