JP2003053478A - Lost foam pattern casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the recarburization by C residues accompanying expending of a foamed pattern material. SOLUTION: This method consists of steps of; forming a pattern by the foamed pattern material copolymerized with an EPMMA(expanded polymethyl methacrylate) and an EPS(expanded polystyrene), forming a mold coat attaining air permeability after drying of >=9.0 on the surface of the pattern, drying the mold coat applied to the surface of the pattern, packing the circumference of the pattern coated with the mold coat with molding sand and pouring molten steel. The gas produced by accompanying the pouring of the molten steel is sucked through the mold coat and the molding sand and is discharged outside the system.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a vanishing model casting method.

[0002]

2. Description of the Related Art In the disappearance model casting method, first, after processing or foaming beads into a desired product shape,
A mold is applied to the surface of the model to prevent seizure and dried to form a foamed model. The periphery of this foamed model is filled with foundry sand, and molten steel is poured into the model. When the foam model comes into contact with the molten steel, it disappears by gasification and is replaced by the molten steel. The gas generated when the model disappears becomes a so-called gas defect when it remains in the molten steel, and is discharged to the outside of the system by a suction pump in order to prevent this. The disappearance model casting method does not have the process of making a model by a wooden mold and removing the mold after matching the upper mold and the lower mold like the sand mold casting method, and further, molding such as kneading, filling and drying sand with a binder. There is an advantage that the number of man-hours related to can be significantly reduced.

[0003]

On the other hand, in the vanishing model casting method, the carbon (C) residue generated from the foamed model during casting is taken into the molten steel to cause carburization, resulting in C in the product.
The content increases. Therefore, in the conventional vanishing model casting method, applicable steel types are limited to cast iron parts that have a relatively high C content in the product and can tolerate some carburization.

An object of the present invention is to solve the above problems of the prior art, and an object thereof is to provide a disappearance model casting method in which carburization due to C residue due to disappearance of foamed model material is prevented or reduced. To do.

[0005]

The present invention according to claim 1 provides EPMMA (expanded polymethylmethacrylate),
8. The step of creating a model using a foamed model material that is copolymerized with EPS (foamed polystyrene), and the air permeability after drying is 9.
A step of applying a coating mold of 0 or more to the model surface, a step of drying the coating mold applied to the model surface, a step of filling the periphery of the model coated with the coating mold with molding sand, and pouring molten steel The gist of the vanishing model casting method is the step of performing the above-mentioned step and a step of sucking the gas generated by pouring the molten steel through the coating mold and the molding sand and discharging the gas out of the system.

The step of sucking and discharging the generated gas can be performed at a reduced pressure of 5.32 × 10 ^-2 MPa (value obtained by converting 400 mmHg into SI unit).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, a vanishing model casting test was conducted in order to obtain the relationship between the thickness of a coating mold and casting defects. EPMMA (expanded polymethylmethacrylate) with high gasification rate,
A foamed model material that is copolymerized with EPS (foamed polystyrene) that gives sufficient model strength is foam-molded in advance and cut into a predetermined shape, or a mold is used to foam-mold into the above-mentioned predetermined shape and the surface thereof is formed. A mold was applied to form a test piece.
The test piece had an air permeability of 1.1 × 10 ^{−3 to} 9.0 × 1.
0 ^-3 m ² / MPa min (0.11-0.9 ml / cmH ₂ O min SI
A test piece to which the coating type was applied once and a test piece to which the coating type was applied twice were prepared. After filling the periphery of this test piece with foundry sand, molten steel is poured into the test piece. When the foam model comes into contact with the molten steel, it disappears by gasification and is replaced by the molten steel. The gas generated when the model disappeared was discharged from the system by a suction pump.

The air permeability P (m ² / MPa min) of the mold used by the disappearance model casting was adjusted by changing the particle size of the aggregate added to the mold. The measuring method of air permeability of coating type is φ55
It is applied to a circular frame of mm so that the thickness of the mold is about 2 to 3 mm, and after molding and drying, according to the air permeability measurement method of JIS Z 2601, 0.002 m ³ (2000 ml) of air passage time and pressure difference. Was measured and calculated by the following formula (1).
The coating method was dipping.

P = 100 V × H / (p × A × T) (1) Here, V: amount of air passing through the coating film (0.002 m ³ ) H: thickness of test piece (m) p : Air pressure (MPa) A: Cross-sectional area of test piece (m ² ) T: Time required for 0.002 m ³ of air (V above) to pass (min)

The molten steel used in the test is ordinary cast steel (SC
Equivalent to 450: Chemical composition in molten steel C: 0.22%, Si:
0.36%, Mn: 0.69%, P: 0.013%,
S: 0.003%). The thickness of the coating film after drying was measured, and the surface sticking condition and internal gas defect condition of the test piece after the casting test were investigated. The test results are summarized in Table 1.

[0011]

[Table 1]

As a result of investigating the relationship between the thickness of the test piece and the coating mold cast by the above disappearance model casting method, the following effects were confirmed. When the number of times the coating type is applied is one, the thickness of the coating type is as thin as 0.5 mm or less, and as a result, the coating strength is insufficient, so that seizure occurs on the surface of the casting. Also,
The occurrence of seizure makes it difficult for the generated gas to be discharged to the outside of the system, so that a gas defect occurs. On the other hand, when the number of times the coating type is applied is 2, the thickness of the coating type becomes 0.9 mm or more, and since the coating has a sufficient coating strength, seizure and gas defects can be prevented. That is, when applying the disappearance model casting method to cast steel, use a foamed model material in which EPMMA and EPS are copolymerized and apply a coating mold to the model surface to prevent the casting surface from reacting with the casting sand and burning. Along with
It was found that it is necessary to maintain the strength of the model material as high as possible because the gas generated when the model disappears becomes the ventilation resistance when it is discharged to the outside of the system.

Further, when the disappearance model casting method is applied to cast steel, as described above, the problem is a carburization phenomenon in which the C residue generated during combustion gasification of the model material is dissolved inside the casting. is there. In order to reduce the C residue, it is necessary to use a model having a high gasification rate and efficiently discharge the generated gas out of the system. In order to discharge the gas out of the system,
It is necessary to suck through the mold and sand, but at this time the air resistance of the mold is reached, so the air permeability of the mold was changed and changes in the amount of carburization were confirmed by experiments.

In the experiment, the ordinary cast steel described above was used, and the air permeability after drying was changed by changing the particle size of the aggregate added to the coating mold.
1 × 10 ⁻³ , 3.4 × 10 ⁻³ , 7.0 × 10 ⁻³ , 9.0
A coating type was prepared and adjusted so that it would be x10 ^-3 and 13.0 x 10 ^-3 . EPMMA (expanded polymethylmethacrylate) and EPS (expanded polystyrene) 8 are used as model materials.
Using a foaming ratio of 40 times that was copolymerized at a ratio of 5:15, the above-mentioned coating mold was applied twice by a dipping method and dried. Decompression degree in the mold during casting is 5.32 × 10 ^-2
FIG. 1 shows the result of carrying out C analysis in the casting after casting as MPa (value obtained by converting 400 mmHg into SI unit).

Referring to FIG. 1, by applying a coating mold having a gas permeability of 9.0 or more to prevent carburization, the generated gas is effectively discharged to the outside of the system. It is understood that the amount of carburization in cast steel can be reduced. When the air permeability of the coating type applied to the model surface is 9.0 or more, the amount of carburization in the cast steel becomes 0.05% or less, and the desired C
It was possible to produce a concentration of cast steel. In addition, no gas defect is found in the casting.

FIG. 2 is a graph showing the amount of carbonization by analyzing the amount of C in the casting after the casting test by changing the degree of pressure reduction in the mold during casting. The mold was applied to the surface of a model formed from the same foam model material as in the experiment of FIG. As described above, it is necessary to reduce the pressure inside the mold in order to discharge the generated gas to the outside of the system, but in this test, the effect of the degree of pressure reduction on the amount of carburization was confirmed. In this test, the air permeability was 9.0 × 10 ^-3 and 13.0.
Two kinds of coating molds of × 10 ^-3 were applied twice on the model surface by the dipping method and dried to prepare test pieces. As the molten steel, the above-mentioned ordinary low alloy cast steel was used, and the degree of pressure reduction in the mold was monitored by a vacuum pump and a pressure gauge. In the test, casting was carried out in the same manner as described above by changing the degree of pressure reduction in the mold during casting, and the amount of carbon in the casting after the test was analyzed to investigate the amount of carburization.

Air permeability 9.0 × 10^-3And 13.0 x 1
0^-3In either case, increase the degree of vacuum in the mold.
Therefore, the amount of carburization in the casting decreases, and the degree of pressure reduction is 5.32 ×
10 ^-2MPa (400 mmHg was converted to SI unit
Value) or less, the amount of carburization in cast steel is 0.03% or less
Could be reduced to

[0018]

According to the present invention, the gasification rate is reduced in order to reduce the residue generated during casting in order to reduce carburization, which was a problem when applying the conventional disappearance model casting method to cast steel. High EPMMA (expanded polymethylmethacrylate)
And EPS (expanded polystyrene) that gives sufficient model strength
By using a foamed model material in which 85:15 was copolymerized and the air permeability of the coating type, which is the ventilation resistance, was 9.0 × 10 ⁻⁴ or more, C residue and gas defects could be obtained. The amount of carburization can be reduced to 0.03% or less, and a cast steel product with a small amount of carburization can be manufactured. Also, preferably, the degree of pressure reduction in the mold is 5.32 × 10 ^-2 MPa (400 mmHg is SI
(Converted into units), the generated gas can be more effectively discharged out of the mold system.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of carburization in a cast steel product and the air permeability of coating type.

FIG. 2 is a graph showing the relationship between the amount of carburization in a cast steel product and the degree of pressure reduction.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Ose             1-1 Satinoura Town, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries             Nagasaki Shipyard Co., Ltd. F-term (reference) 4E093 GA08 KB08

Claims (2)

[Claims] 1. A step of preparing a model from a foamed model material obtained by copolymerizing EPMMA (foamed polymethylmethacrylate) and EPS (foamed polystyrene), and a coating mold having an air permeability after drying of 9.0 or more. The step of exposing the model surface, the step of drying the coating mold applied to the model surface, the step of filling the periphery of the model coated with the coating mold with molding sand, the step of pouring molten steel, A vanishing model casting method, which comprises a step of sucking the gas generated by pouring through the coating mold and the molding sand and discharging it out of the system. 2. The step of sucking and discharging the generated gas,
The disappearance model casting method according to claim 1, which is performed at a reduced pressure of 5.32 × 10 ^-2 MPa.