JPS61137646A - Manufacture of casting mold - Google Patents

Abstract

PURPOSE:To manufacture a casting mold sutable for precision casting of a large sized casting by inserting a pattern made of a foamed resin formed with a ceramic shell on the surface into a molding flask and packing sand to the circumference of said pattern then burning away the pattern and accelerating the curing of the ceramic shell to form a cavity. CONSTITUTION:The foamed resin pattern 1 having a pattern 1c, a sprue pattern 1a and a riser pattern 1b is manufactured of a foamed PST resin. A slurry 2 contg. a refractory binder such as silicate is sprayed by a sprayer 3 over the entire surface of the pattern 1 except the top surface of the pattern 1a and the top surface of the pattern 1b to form a slurry film 4 on the surface of the pattern 1. Dried Zr powder 5 is then sprayed by a sprayer 6 onto the film 4 to form the ceramic shell layer and further the spraying of the slurry 2 and the Zr powder 5 is alternately and repeatedly executed. The pattern 1 coated with the ceramic shell layer 7 is installed in the molding flask 8 and after the silica sand 9 is packed to the circumference thereof, the pattern is heated in a furnace to burn away the pattern 1. The casting mold of which the cavity 10 is coated with the layer 7 is thus completed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a mold suitable for a precision casting mold for large castings.

<Prior Art> Conventionally, the following methods for manufacturing precision casting molds have been known.

1) Lost Wax Method After making a model with the same shape as the casting to be cast using wax, the model is immersed in a fire-resistant slurry to adhere the slurry to the surface of the model, and then the surface is dried. By repeating the process of sprinkling sand, a fireproof shell with a length of 5 to 151 meters is formed around the model. Thereafter, the model is heated in a furnace to remove the model and dry the refractory shell, and the cavity into which molten metal is to be poured is formed of the refractory shell by removing the model.

II) Ceramic molding method This is a method typified by the Shaw process, in which a wooden or resin model is inserted into a casting flask, a refractory slurry is poured around the model, and after this slurry has hardened, the model is released. Make a mold.

Then, the mold formed from the hardened refractory slurry is fired to form a mold into which molten metal is poured.

<Problems to be Solved by the Invention> Each of the above manufacturing methods has the following problems.

1) Lost Wax Method ■ Since wax models are formed by injection molding, it is not possible to manufacture molds for making large castings (for example, 700 nm or more in length).

■ Because the model is immersed in a refractory slurry, molds for making large castings cannot be made.

11) Ceramic molding method ■ Castings are manufactured by fitting molds and pouring molten metal into the formed cavity, so burrs occur on the fitting surfaces of the castings and post-processing work is required. becomes.

■ Molds are made by pouring refractory slurry into the gap between the casting flask and the model, which results in thick molds that take a long time to dry and increase material costs.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a mold manufacturing method that is easy to manufacture and suitable for precision casting molds for large castings.

Means and Effects for Solving the Problems The method of manufacturing a mold according to the present invention consists of spraying slurry containing a refractory binder and refractory powder alternately on the surface of a foamed resin model to form a ceramic mold. After forming the shell, a foamed resin model whose surface is covered with a ceramic shell is inserted into a casting flask, and sand is filled around the foamed resin model. After this, the foamed resin model is placed in a furnace. The ceramic shell is burnt out and the hardening of the ceramic shell is accelerated to form a cavity into which the molten metal is to be poured.

<Example> Hereinafter, a method for manufacturing a mold according to an example of the present invention will be described with reference to the drawings.

First, as shown in FIG. 1, a model 1c of a cast product is made from expanded polystyrene resin.

A foamed resin model 1 is manufactured to which a sprue model 1a and a riser model 1b, which are also made of foamed polystyrene resin, are used as adhesives. Since these models 1c, #2 model 1a, and feeder model 1b can be fabricated by cutting out, for example, a foamed resin block, large-sized models 1 can also be easily fabricated. In addition, the model 1c, the hot water bath model 1a, and the feeder model 1b may be originally manufactured integrally, and the foamed resin may be made of other materials such as foamed polyethylene resin, foamed polypropylene resin, etc. can be used.

Next, as shown in FIG. 2, a slug containing a refractory binder such as ethyl silicate, colloidal silica, or silicate is applied to the entire surface of the model 1 except for the top surface of the sprue model 1a and the top surface of the riser model 1b. IJ-2 is sprayed using a spray 3 to form a slurry coating 4 on the surface of the model 1. As an example of slurry 2, ethyl silicate 40 binder (ethyl silicate 40 = 55 vat, alcohol = 37
VO1%, water = 6. OVOt'16, catalyst (0
, 11 hydrochloric acid) = 2 vot%) 350.9 g of zircon powder is used per 100 cc, or 350 g of zircon powder is used per 100 cc of colloidal silica (silica concentration 30% liquid), but zircon powder In addition, quartz (3ioz)-alumina (AI, t's
) may be used, and the composition of the slurry 2 can be set in various ways.

Next, dried zircon powder 5 as a refractory powder is sprayed onto the slurry coating 4 using a sprayer 6 to form a ceramic shell layer. Then, the spraying of the slurry 2 and the spraying of the zircon powder 5 are repeated alternately, and a third
As shown in the figure, a ceramic shell layer 7 with a thickness of 10 ann is formed on the surface of the model 1. The thickness of the ceramic shell layer 7 is usually about 5 to 15 inches, but is not limited to this and can be set as appropriate depending on casting conditions and the like.

In addition to the above-mentioned refractory powder, for example, quartz (5i
n2), alumina (Al, 03), zirconia (Z
r02), mullite (M, o3@8i0.), etc. can be used.

Next, as shown in FIG. 4, the model 1 covered with the ceramic shell layer 7 is placed in a casting flask 8, and the periphery of the model 1 is filled with silica sand 9 that does not contain a binder. In addition to silica sand, for example, zircon sand, chromite sand, etc. that do not contain a binder can be used as the sand, and since the ceramic shell layer 7 according to the present invention is strong, sand that does not contain a binder may be used. Of course, sand containing a binder may also be used. The flask 8 is usually made of mild steel. Next, the flask 8 is placed in a furnace and heated to 500°C.
The model 1 is burned out and removed, and a cavity 10 into which molten metal is poured is formed covered with a ceramic shell layer 7, as shown in FIG. 5, to complete the mold. The heating temperature for burning out the foamed resin model 1 is 100~
Although 200° C. is sufficient, the ceramic shell layer 7 is sufficiently hardened to have a bending strength of, for example, 50 kg/cnt.
It is preferable to heat the film to a temperature of 500° C. or higher in order to prevent gas defects such as those shown in 2.

When stainless steel (Sc813) was cast at 1480'C by pouring molten metal into 1° of the cavity of the mold produced as described above, it was possible to obtain a precision and good quality stainless steel casting.

<Effect of the invention> According to the present invention, the following effects can be obtained.

I) Since a foamed resin model that can be manufactured by cutting out is used instead of wax or the like as the burnout model, molds for large castings, such as 100 Yu or more, can be easily manufactured.

1:) Since the ceramic shell that covers the model surface is formed by spraying, there is no limit to the size of the model, and we can create molds that can produce large precision castings that could not be obtained using conventional precision casting methods. can be obtained easily.

111) Since the cavity of the mold is formed by an integrated burnt-out model, it is possible to easily manufacture a mold that has no mating surfaces and can produce large precision cast products without flash.

It goes without saying that the above effects can be obtained in the same way when manufacturing molds for small castings. Also, when the heating temperature is set to a high temperature of 500°C or higher, the model cannot be completely heated. By burning it out, a ceramic shell with high strength can be obtained. Furthermore, by making the ceramic shell stronger, it is possible to use molding sand that does not contain a binder, so it is possible to use molding sand that does not contain a binder. The separation step can be omitted and costs can be significantly reduced.

[Brief explanation of the drawing]

FIGS. 1 to 5 are explanatory diagrams for sequentially explaining one embodiment of the present invention, respectively. In the drawing, 1 is a model of the cavity. 1a is a model of a sprue, 1b is a model of a riser, IC is a model of a cast product, 2 is a slurry, and 5 is a zircon powder. 7 is a ceramic shell layer, 8 is a casting flask, 9 is silica sand, and 10 is a cavity. Patent applicant: Mitsubishi Heavy Industries, Ltd. Sub-agent Patent attorney: Shibu Mitsuishi (and 1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] After forming a ceramic shell by alternately spraying slurry containing a fire-resistant binder and refractory powder onto the surface of the foam resin model, the foam resin model whose surface is covered with the ceramic shell is placed in a casting flask. The foamed resin model was inserted into the furnace and filled with sand around the foamed resin model, and then the foamed resin model was burned out in a furnace and the hardening of the ceramic shell was accelerated to form a cavity into which the metal should be poured. A method for manufacturing a mold characterized by: