JPH06106326A - Sand mold for vacuum casting - Google Patents

Abstract

PURPOSE:To improve the fluidity of a molten metal and prevent structural defects, such as mis-run and penetration, by removing the slag and gases intruded into the molten metal by a riser and/or run-off near a product cavity and connecting a vacuum pump to the suction port of the sand mold, then reducing the pressure in the cavity. CONSTITUTION:This sand mold 1 is formed with a casting plan part cavity 2, such as sprue 5, and the product cavity. The mold has the riser and/or run-off 10 provided near the final packing part of the molten metal 3 in the product cavity and the suction filter 8 which is provided near the riser and run-off and has the air passability higher than the air passability of the sand mold. The outside surface of the sand mold 1 is provided with a reduced pressure suction port 11 which opens outward and is connected from a suction filter 8 to the vacuum pump 15. The required part of the sand mold is subjected to mold coating 9. As a result, mass production is executed by providing the ordinary sand mold with the suction port, etc., and utilizing a transporting device, etc., and, therefore, the productivity is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is particularly useful for casting thin castings, in particular, castings such as stainless cast steel and heat-resistant cast steel with good productivity without casting defects such as non-rotation, blowholes and insertions. The present invention relates to a vacuum casting mold.

[0002]

2. Description of the Related Art A thin-walled casting partially having a wall thickness of 5 mm or less has a rapid progress of solidification after the molten metal is poured and comes into contact with a sand mold. For this reason, the fluidity of the molten metal deteriorates, and non-rotating defects and the like are likely to occur. Further, in a thin-walled casting having a complicated shape, during casting, air or gas generated from the mold is easily entrained in the molten metal, and gas defects such as blow holes are likely to occur in the solidified casting. Furthermore, thin-walled castings made of materials such as heat-resistant cast steel and stainless cast steel react with the sand mold due to the high temperature of the molten metal, insertion defects tend to occur, the surface roughness of the casting surface deteriorates, and it is extremely difficult to cast soundly. Is.

As a general method for solving this, there is a lost wax casting method. This lost wax casting method uses a ceramic mold, and the mold is 700 ° C during casting.
By heating to ~ 900 ° C, the cooling rate of the molten metal at the time of filling is slowed and the fluidity of the molten metal is improved. However, since the expensive ceramic mold is used, the manufacturing cost of the casting is considerably high.

In order to improve the fluidity of the molten metal, the pressure inside the mold cavity is reduced and the molten metal is suction-cast.
Japanese Patent Publication No. 60-35227 discloses a vacuum casting method "CLAS method" developed by Hitchener Co., Ltd. in USA, which has recently been used as a casting method for thin castings.

Further, in Japanese Patent Laid-Open No. 57-31463, the molten metal is sucked into the product cavity while sucking the inside of the product cavity of the mold through a ventilation hole provided at a position farthest from the sprue position in the product cavity. There is a disclosure of pouring and improving the fluidity of a molten metal to cast a thin wall casting. However, in this Japanese Laid-Open Patent Publication No. 57-31463, since the entire inner surface of the product cavity is sucked, the effect of sucking a necessary portion is small, and the molten metal is disturbed in the product cavity.
Casting defects due to the inclusion of air, slag, or slag are likely to occur.

As a countermeasure against this, Japanese Patent Laid-Open No. 60-
In Japanese Patent No. 56439, a refractory material filter having better air permeability than gypsum is provided from the vicinity of the final filling portion of the molten metal in the product cavity to the outer surface of the gypsum mold to enhance the depressurizing effect of the product cavity and perform suction casting. Due to
There is a disclosure of a gypsum mold for reduced-pressure casting, which is capable of obtaining a thin cast product having no hot water defects and gas defects caused by entrainment of air.

Further, in Japanese Patent Laid-Open No. 147760/1992, a suction guide which forms a suction passage is provided between the casting space and the outside of the mold, so that the portion where the depressurization is required is locally depressurized. There is a disclosure of a sand mold for suction casting, which has a large suction effect and also sucks a gas generated at the time of pouring to cast a thin casting without gas defects.

[0008]

However, in Japanese Patent Publication No. 60-35227, the structure for holding and immersing the mold for immersing the mold in the molten metal becomes complicated. Further, in JP-A-60-56439, since plaster is used as the mold, the molten metal is less likely to be inserted into the mold, but many steps are required to manufacture the gypsum mold, and the productivity is higher than that of the sand mold. Inferior. Further, since the gypsum mold itself has poor air permeability, the pressure (back pressure) in the cavity becomes large during casting, and the flowability of molten metal is poor as a whole.

Further, Japanese Patent Laid-Open No. 4-147760 discloses
The step of providing a suction guide for forming the suction passage in the sand mold is required, productivity is still insufficient, and the air permeability of the suction passage is not so large as compared with the sand mold, so the suction effect is small. It is an object of the present invention to provide a sand mold for vacuum casting, which has few casting defects such as non-rotation, blowholes and insertions and has good productivity.

[0010]

In order to achieve the above object, the sand mold for vacuum casting of the present invention is a sand mold in which a casting plan cavity such as a sprue and a product cavity are formed. A riser and / or a skein provided near the final filling portion of the molten metal, a suction filter having a higher air permeability than the sand mold provided in the vicinity of the riser and the skein, and an opening toward the outer surface of the sand mold. It is characterized by comprising a vacuum suction port connected from the suction filter to a vacuum pump. Then, a coating mold is applied to part or all of the inner surface of the plan cavity, the inner surface of the product cavity and the outer surface of the sand mold.

[0011]

The feeder provided near the final filling portion of the molten metal in the product cavity reinforces the molten metal against the solidification shrinkage of the poured molten metal. Or, in the case of vomiting, the excess molten metal is made to overflow from the feeder to remove the slag and the gas trapped in the molten metal. A suction filter installed near the feeder and skein that has a higher air permeability than the sand mold makes the depressurization degree on the feeder and skein side larger than the depressurization degree on the sprue side to secure and improve the fluidity of the molten metal. To do.

When the sand mold is at a predetermined position by the transfer device (not shown), the suction means vacuum-sucks it from the vacuum suction port which is opened toward the outer surface of the sand mold and connected from the suction filter to the vacuum pump.

Then, by coating a part or the whole of the inner surface of the design cavity, the inner surface of the product cavity and the outer surface of the sand mold, the suction effect is increased and the flow of the molten metal toward the final filling portion is required. And the surface roughness of the casting.

[0014]

The sand mold for vacuum casting according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a sand mold for vacuum casting of the present invention. In FIG. 1, a sand mold 1 comprises a hollow cylindrical cavity 2 having an outer diameter of 45 mm, a thickness of 2.5 mm and a length of 200 mm, and an outer diameter of 80 mm at both ends thereof.
Flange portions 1b and 1c having a width of 10 mm, and two boss portions 1 having a diameter of 10 mm and a height of 15 mm on the outer peripheral surface of the cavity 2.
a and 1d are formed. The sand mold 1 is a cold box type and uses silica sand No. 6. The sprue 5 is provided near one end of the sand mold 1, and the sprue 5 is provided with a spout bottom, a filter 6, and a weir portion 7 in succession. Flange 1 opposite the gate 5
A feeder 10 that also serves as a vomiting is installed in c. A suction port 11 that opens toward the bottom surface of the sand mold 1 is provided in the vicinity of the vase-use dual-purpose feeder 10 and the vase-use dual-purpose feeder 10 and the suction port 11 are provided.
Suction filter 8 with higher air permeability than sand mold
(No. 4 sand layer in this embodiment) is provided. Further, a coating mold 9 having a thickness of 0.15 mm is applied to the inner surface of the mold cavity. A flexible tube from the vacuum pump 15 is brought into close contact with the opening of the suction port 11 to perform vacuum suction. For depressurization, the optical scope 13 senses the time when pouring the molten metal from the ladle 4, starts preparation, and depressurizes after the melt level sensor 12 installed between the filter 6 and the weir 7 senses the entrance of the melt 2. To start. Regarding the degree of pressure reduction, the pressure reduction control means 14 controls the degree of vacuum of the vacuum pump 15 to inject the molten metal.

Table 1 shows the chemical composition of cast steel to be cast.

[Table 1] Chemical composition of cast cast steel (% by weight) C Si Mn P S Cr Fe 0.10 1.2 0.6 0.01 0.01 17.0 Remainder

After casting, the sand mold 1 is carried out on the roller conveyor to the next demolding station by an extrusion device. Further, the sand mold 1 of the present invention before casting is carried into the pouring station. The above steps are repeated to cast the required number of thin wall castings. When 50 cylindrical thin-walled cast steel castings with flanges were cast by the above-described vacuum casting sand mold,
There were no casting defects such as total number, non-rotation, blowholes, and insertion.

[0017]

As described above, according to the sand casting mold for vacuum casting of the present invention, the slag and the gas trapped in the molten metal due to the feeder and / or the spitting near the product cavity are removed,
Since the flexible pipe from the vacuum pump is brought into close contact with the suction port of the sand mold to reduce the pressure, the flowability of the molten metal is improved and casting defects such as improper rotation and insertion are reduced. Further, since a usual sand mold is provided with a suction port or the like and a carrying device or the like can be used for mass production, productivity is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a sand mold for vacuum casting of the present invention.

[Explanation of symbols]

1 sand mold, 2 cavities,
3 molten metal, 4 ladle, 5
Sprue, 6 filter, 7 weir,
8 suction filter, 9
Coating type, 10 feeder and / or vomiting,
11 suction port, 12 level sensor,
13 optical scope, 14 decompression speed control means, 15 vacuum pump

Claims (2)

[Claims] 1. A sand mold in which a casting part cavity such as a sprue and a product cavity are formed, and a feeder and / or a spout provided near the final filling portion of the molten metal in the product cavity, and the feeder. And a reduced pressure casting characterized by comprising a suction filter having a greater air permeability than the sand mold provided in the vicinity of the skein, and a reduced pressure suction port opened to the outer surface of the sand mold and connected from the suction filter to a vacuum pump. Sand mold. 2. A sand mold for vacuum casting according to claim 1, wherein a part or all of the inner surface of the plan cavity, the inner surface of the product cavity and the outer surface of the sand mold is coated with a coating mold.