JPH0357549A - Pressure reduction/suction casting method - 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] The present invention relates to a vacuum wicking casting method known as one of precision casting methods.

[Conventional technology]

The vacuum wicking casting method is an improvement on the casting method of the well-known loss 1 wax casting method, as disclosed in Japanese Patent Publication No. 52-38924-1 or Japanese Patent Publication No. 60-35227. It was developed by Hutchner, a major US manufacturer of stowage products.

First, the outline of this vacuum casting method will be explained with reference to FIGS. 3a to 3C. In Fig. 3a G, ■ is a bath for storing molten metal heated to below its melting point, 2 is a chamber supported above it so that it can be raised and lowered, and 3 is a chamber for firing foundry sand. It is a breathable mold made by Mold 3
The sprue part 4 is centered around the sprue part 4.
A large number of cavities 6 are formed radially and communicate with each other via gates 5. The upper end of the sprue portion 4 is closed, and a cylindrical snout 7 extends downward, with a suction port 8 opening at the lower end. The mold 3 is set in the chamber 2 so that the snout 7 hangs downward from the bottom opening 9 of the chamber 2. However, chamber 2 is
As shown in Figure b, when the inside of the chamber 2 is suctioned by immersing the molten metal in the hot water tank 1 and the air inlet 10 of the chamber 2 into a clean air pump, the mold 3 Since it is breathable, even the air inside the mold is sucked into the suction port 8.
The molten metal is drawn into the sublube part 4, and the molten metal further passes through the gate 5 and fills the cavity 6. After the predetermined holding time has elapsed and the molten metal in parts 1-5 has solidified, the reduced pressure in the chamber 2 is released, and the unsolidified molten metal in part 4 flows out under its own weight, as shown in FIG. 3C. Empty the sublu portion 4 as shown in FIG.

Therefore, if you break the mold 3 and take out the products formed at 4-Yabitei 6, each product can be taken out as a separate item without being connected in a row.There is an advantage that it does not take time to separate the products, and from the sprue part 4. The molten metal returned to the tundish tank 1 can be used without wastage for the next casting process, resulting in a high yield.Furthermore, the molten metal is not contaminated and its quality is improved, among other advantages.

[Problems with the conventional technology] However, in the vacuum suction casting method described above, it is better to suck the molten metal in the molten metal tank 1 into the mold 3 in the shortest possible time to reduce the fluidity caused by the cooling of the molten metal. This has the advantage of improving the circulation of the hot water even down to the minute parts since there is no fear of it falling, and for this purpose, air is instantly sucked from inside the chamber 2 in a short period of time to instantly suck up the molten metal. However, if the molten metal is sucked up too rapidly, the thermal and mechanical shocks applied to the mold will be strong, and the mold may be destroyed. For this reason, the speed at which air is sucked out from the chamber is an important factor that determines the success or failure of this type of casting, but in the past, this suction speed was not given much importance and was simply determined from experience. It was leaning on me.

Therefore, there are many failures caused by inappropriate intake speed, and improvement of these problems has been desired.

[Purpose of the invention]

The present invention solves the above-mentioned problems, clarifies the required intake speed of the air in the chamber in vacuum casting in relation to the air permeability of the mold, eliminates casting defects due to excessive or insufficient intake speed, and improves the vacuum wicking casting method. The aim is to improve yield.

[Means to achieve the purpose]

In order to achieve the above object, the vacuum wicking casting method of the present invention sets an air permeable mold in a chamber, and immerses the wicking port formed in the mold into molten metal by hanging from the bottom opening of the chamber. However, in a vacuum wicking casting method in which the molten metal is sucked up into the mold by suctioning the air in the chamber, the permissible maximum airflow per unit time of the mold, which is determined by the air permeability of the mold, is exceeded. This is characterized in that the air in the chamber is sucked at a predetermined speed to prevent the air from entering the chamber.

[Example] Next, an example of the present invention will be described. First, the vacuum casting mold shown in FIG. 1 will be explained. This mold is manufactured by applying a slurry, which will be described below, to the surface of a master mold (not shown) made with wax, and coating the slurry in multiple layers with molding sand using its viscosity. Zircon flour and dissolved silica are used as the slurry, and ethyl silicate or colloidal silica dissolved in pure water is used as a hinderer, and a small amount of a surfactant and an antifoaming agent are added to this slurry. Viscosity can be controlled by changing. The surface of the prototype has a viscosity of 400
A relatively high viscosity material of 0 to 5000 cps is applied to this, and a highly heat resistant zircon sand (100 mesh 1 to 3%, 1140 mesh 34 to 37%, 2
00 mesh is 58-62%, 270 mesh is 2-5
%) is attached. Then, a relatively low viscosity slurry with a viscosity adjusted to about 100 to 300 cpS is applied onto the zircon sand, and the particle size is 0.2 to 0.5 m.
Attach the chamotte of m. Adhesion of chamotte sant using this low viscosity slurry can be carried out in two steps as necessary.
Repeat ~3 times. Next, the surface has a viscosity of 1000~
A slurry of 3000 cps was applied, and the particle size was 0.5 to 1.
Serve 4 servings of chamotte sandwich {;J. Repeat this 2 to 3 times as necessary. After coating the molding sand in multiple layers in this manner, the molding sand is heated to melt the wax inside to form a hollow shell mold 3 as illustrated in FIG. 1. The various parts of the mold 3 include a sprue part 4, a gate 5, a cavity 6, a snout 7, as described in FIGS. 3A to 3C.
A suction port 8 is formed.

The air permeability of the mold 3 can be adjusted by adjusting the viscosity of the slurry used in the mold manufacturing process, the particle size of the foundry sand, the number of times it is repeatedly deposited, etc.

The mold 3 manufactured in this manner has the maximum permissible air flow rate per unit time. In other words, the air permeability of a mold is determined by the materials used in the mold's manufacturing process, wall thickness, and surface area, but the maximum permissible air flow per unit time of the mold is determined by the pressure, machine, and pressure of the mold. Determined by the strength of the objective. According to the present invention, the air inside the chamber 2 is sucked into the vacuum tank 11 via the flow rate regulating valve 17 as shown in FIG. 2 so as not to exceed this permissible maximum ventilation view per unit time.

In FIG. 2, 12 is an intake pipe connected to the chamber 2, 13 is a flow rate sensor that detects the air flow rate in the intake pipe 12 and outputs the signal to the controller 14, and 15 is a vacuum tank II. A vacuum pump 16 is a popular suction valve for pressure recovery provided in the intake pipe 12 to keep the negative pressure constant. The maximum permissible air flow rate of the mold 3 set in the chamber 2 is input into the controller 14 in advance as data, and the flow rate adjustment valve 17 controls the amount of air flowing through the intake pipe I2 according to the command from the controller 14. . The flow rate sensor 13 detects the flow rate of air flowing through the intake pipe 12, and the signal is fed back to the controller 14 to readjust the opening degree of the flow rate regulating valve 17. When the air is discharged from the chamber 2 in this way, the air in the mold 3 is also sucked into the chamber 2 through the air-permeable shell wall, and accordingly, the molten metal in the tundish 1 can be sucked up and cast into the mold.

〔Effect of the invention〕

In this way, in the vacuum suction casting of the present invention, air is sucked from inside the chamber so as not to exceed the maximum permissible air flow rate of the mold, so there is no risk of mold destruction and the yield of vacuum suction casting is improved. It has a beneficial effect.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional perspective view showing an example of a mold used in the vacuum wick casting method of the present invention, and Fig. 2 is a piping diagram of the intake system also used in the vacuum wick casting method. , Figure 3a,
Figure 3b. FIG. 3C is a longitudinal sectional view showing the process of vacuum wick casting. ]...Tank, 2...Chamber, 3...Mold, 4...
... Sprue part, 5... Game 1, 6... Cavity, 7... Snow 1, 8... Suction port, 9... Bottom opening.

Claims (1)

[Claims] A breathable mold is set in a chamber, and a suction port formed in the mold is suspended from the bottom opening of the chamber, immersed in the molten metal, and the air in the chamber is sucked, thereby causing the molten metal to flow into the mold. In the vacuum suction casting method, the air in the chamber is sucked at a predetermined speed so as not to exceed the maximum permissible air flow per unit time of the mold, which is determined by the air permeability of the mold. A vacuum wick casting method characterized by: