JPH05277699A - Method for casting thin casting - Google Patents

Abstract

PURPOSE:To cast a sound thin casting by forming a specific thickness of sand layer in between a metallic mold and a plastic film to which a pattern is transferred. CONSTITUTION:In a casting method for pouring molten metal into a cavity 3 in the mold in a reducing pressure box 2 by vacuum action, by varying the layer thickness of the sand 9 filled in between the metallic mold 8 and the plastic film 6 to which the pattern is transferred in the range of 0-100mm, the coefficient of the thermal conductivity of the mold 1 is varied and the poured molten metal is directionally solidified toward feeder head 5 direction. By this method, the sound thin casting without casting defect of misrun and shrinkage cavity, etc., in thin stainless steel and heat resistant casting can be cast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a casting having a good quality, such as a stainless casting or a heat-resistant casting, which is free from casting defects such as non-rotation and shrinkage cavities.

[0002]

2. Description of the Related Art Stainless cast steel and heat-resistant cast steel have a high melting point, so that they are poured and come into contact with a mold to solidify immediately. Therefore, the fluidity is poor and non-rotating defects are likely to occur. Further, particularly in the case of a thin-walled casting having a complicated shape, air or a gas generated from a mold is easily entrained, and gas defects such as blowholes are easily generated. Further, since the molten metal has a high temperature and easily reacts with the sand mold, insertion defects are likely to occur, the surface roughness of the casting surface is deteriorated, and it is extremely difficult to manufacture a sound casting.

[0003]

As a general method for solving this problem, the lost wax casting method is used. In this method, a ceramics mold is used, and the mold is heated to 700 ° C. to 900 ° C. at the time of casting, thereby slowing the cooling rate of the molten metal at the time of filling and improving the fluidity. However, since the expensive ceramic mold is used, the manufacturing cost of the casting is considerably increased.

On the other hand, as a method for improving the fluidity, there is a method of reducing the pressure in the mold to perform casting (reduced pressure molding mold, CLAS method, etc.), which has recently been used as a method of manufacturing a thin cast product. However, in these conventional vacuum casting methods, since the mold is depressurized by a vacuum pump, the molten metal is disturbed during pouring, air or slag or ladle entrainment occurs, and casting defects occur, Repairing this increases the manufacturing cost and deteriorates the quality. Further, in the reduced pressure molding mold (V process mold), only sand is used as an aggregate without containing a binder, and the mold shape is maintained by the pressure difference from the atmospheric pressure through the plastic film. Since the plastic film sometimes burns and disappears, the mold holding force is lost, and insertion defects and mold deformation defects are likely to occur.

It is an object of the present invention to provide a method for producing high quality thin wall castings with low casting defects and at low cost.

[0006]

In order to achieve the above object, a casting method of a thin casting according to the present invention is a casting method in which molten metal is injected into a mold cavity in a depressurization box by a vacuum action. , The step of adhering the plastic film to the model having the feeder and casting transfer part,
(2) A step of setting a mold having a vent hole communicating with the outside in a volume larger than the outer shape of the model by 100 mm while closely adhering a plastic film to the model, (3)
A step of filling sand containing no binder between the plastic film and the mold, (4) a step of releasing the adhesion of the plastic film to the model, (5) a vacuum from the vent holes of the mold And (6) a step of releasing the model from a plastic film, (7)
A step of disposing a core on the filled sand and a plastic film, if necessary, (8) a step of assembling another mold of the above steps (1) to (7), if necessary,
(9) By depressurizing with a vacuum pump from the opening of the depressurization box, the sand of the mold is hardened by the pressure difference from the atmospheric pressure, and the molten metal is vacuumed in the cavity of the mold with the sprue exposed to the outside. The step of injecting is characterized by comprising the combination of the above (1) to (9).

The thickness of the sand layer is changed so that the injected molten metal is directionally solidified in the direction of the feeder.

[0008]

Since the thickness of the sand layer filled between the mold and the plastic film is as thin as 0 to 100 mm, the reduced pressure reaches the end of the sand layer, the mold becomes strong, and the casting is less deformed and a precision casting can be made. Moreover, the thickness of the sand layer is 0 to 100 mm.
By changing the heat conductivity coefficient of the mold by changing in the range of, the injected metal melt is directionally solidified in the direction of the riser, and it is possible to soundly manufacture a casting having a thin portion with a wall thickness of 5 mm or less. . In the part where the thickness of the sand layer is 0 mm, the molten metal is in direct contact with the mold, so the solidification progresses quickly, and the thickness of the sand layer is 1 mm.
The length of 00 mm makes the progress of coagulation relatively slow. If the thickness of the sand layer exceeds 100 mm, the vacuum suction force decreases and the strength of the mold decreases, so it is set to 100 mm or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 is a plan view of a parting portion of a mold for casting an exhaust manifold using the casting method for a thin cast product of the present invention, and FIG. 2 is a plan view showing a state after pouring molten metal into the mold of FIG. 1 as well. Is. As shown in FIGS. 1 and 2, a cast steel exhaust manifold having a branch portion 11 having a wall thickness of 2.5 mm is cast. Mold 8 is FC
25 pieces of flake graphite cast iron are used, and the vent hole 7 is formed by driving a commercially available vent hole. First, a vent hole is formed in a wooden model for an exhaust manifold (not shown), and the plastic film 6 is placed on a suction box (not shown) to cover the heated plastic film 6 so that the plastic film 6 is shaped according to the model. Transform it.
Then, the mold 8 with the decompression box 2 is installed at a predetermined place, and the sand 9 is filled between the plastic film 6 and the mold 8 while vibrating. As sand 9, silica sand No. 7 is used. The lower opening of the decompression box 2 is connected to a decompression device, and decompression suction is performed by the vacuum pump 12. In the casting method, the riser 5 is provided on the outlet flange side 13, the sprue 4 is provided above the riser 5, and four weirs 15 are provided on the outlet flange side 13 from the riser 5. There is no riser on the inlet flange 14, and the die 8
The thickness of the sand 9 between the plastic film 6 and the plastic film 6 is set to 0, and the mold 8 is directly used as a chiller. Figure 2 shows the state when pouring is completed. The injection of the molten metal replaces the plastic film 6 and the cavity 3 with metal. In the present invention, unlike the conventional vacuum molding mold, the sand 9 layer has a thickness of 100 mm or less only between the plastic film 6 and the mold 8. For this reason, even if the plastic film 6 burns and disappears during pouring, the sand 9 layer is held by the pressure of the air flow, and insertion defects and mold deformation defects do not occur. Table 1 shows the chemical composition of the cast steel.

[0010]

[Table 1] When the cast steel exhaust manifold having the chemical composition shown in Table 1 is cast by the above method, there are no non-rotating defects, leak defects, entrapment of air, blow holes, and no shrinkage cavity defects due to the cooling effect of the mold. Can be manufactured.
By using No. 7 silica sand containing no binder, a product having a surface roughness (indicated by Rmax) of 70 μm or less and a good casting surface was obtained.

[0011]

As described above, according to the casting method for a thin casting of the present invention, since the molten metal is injected at a high speed because the mold is depressurized, there are few non-rotating defects, and because the sand layer is thin, cooling can be performed. It is easy to control and has few shrinkage cavity defects by directional solidification. Further, since fine sand containing no binder can be used, a casting having a good casting surface can be manufactured.

[Brief description of drawings]

FIG. 1 is a plan view of a parting portion of a mold for casting an exhaust manifold using the casting method for a thin casting of the present invention.

FIG. 2 is a plan view showing a state after pouring a molten metal into the mold of FIG.

[Explanation of symbols]

 1 Mold 2 Decompression Box 3 Cavity 4 Gate 5 Riser 6 Plastic Film 7 Vent 8 Mold 9 Sand 10 Core 11 Branch 12 Vacuum Pump 13 Outlet Flange 14 Inlet Flange 15 Weir

Claims (2)

[Claims] 1. A casting method in which molten metal is injected into a mold cavity in a depressurization box by a vacuum action.
A step of bringing a plastic film into close contact with a model having a sprue, a feeder, and a casting transfer part, (2) keeping the plastic film in close contact with the model,
A step of setting a die having a ventilation hole communicating with the outside with a volume of 100 mm, (3) a step of filling sand containing no binder between the plastic film and the die, (4) to the model Of releasing the close contact of the plastic film of (5), applying a vacuum from the ventilation hole of the mold, (6) releasing the model from the plastic film, (7) filling as necessary Placing the core on the sand and plastic film,
(8) A step of assembling another mold in the above steps (1) to (7), if necessary, (9) a mold by a pressure difference from the atmospheric pressure by decompressing with a vacuum pump from the opening of the decompression box. A step of injecting a molten metal into the cavity of the mold with the sprue part exposed to the outside while hardening the sand, by a combination of (1) to (9) above. Casting method. 2. A method for casting a thin casting, wherein the thickness of the sand layer is changed so that the poured molten metal is directionally solidified in the direction of the feeder.