JP2000254760A - Lost foam pattern casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the development of surface defect by adding a projection having the same material as a pattern and the shape gradually reducing the cross sectional area toward the end part of molten metal stream or reducing step by step to the last reaching portion of the molten metal stream in a lost foam pattern, executing casting and removing the portions except the cast product shape after casting. SOLUTION: The lost foam pattern 2 is embedded in molding sand 4 filled in a molding flask 3. The poured molten metal reaches the lost foam pattern 2 through a sprue 5, runner 6 and gate 7, and the lost foam pattern is burnt and lost and gasified to form the cast product having the same shape as the lost foam pattern 2. This lost foam pattern casting method has comparatively small cross sectional area and can effectively be applied to the cast product having high height. In the case of arranging the conical projection 10 shrunk at the upper part in the upper end of the lost foam pattern 2, when the molten metal surface raises the portion of this projection 10, the molten metal pouring speed is reduced and shock is releaved, and on the surface of the cast product, the defect is not developed. This projection 10 is cut off and removed and can be used as a columnar body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vanishing model casting method for casting cast iron and cast steel.

[0002]

2. Description of the Related Art In a vanishing model casting method, a model of a cast product shape is made from a material which is thermally decomposed or burned by the heat of the molten metal when approaching or in contact with the molten metal, and the model is embedded in a mold sand. This is a casting method in which a mold is formed, a molten metal is supplied to the mold to thermally decompose the model, and the generated gas is discharged out of the system to replace the molten metal with the model to produce a product-shaped casting. As a material thermally decomposed by the heat of the molten metal, for example, expanded polystyrene, polymethyl methacrylate, or the like is used. Since there is no need to form a cavity in the mold, the vanishing model casting method has an advantage that a casting having a complicated shape can be easily manufactured. Also,
There is no need to make the mold into a structure that can be die-cut, and there is no need for operations such as mold division, mold matching, core molding, and core insertion. This is an advantage of the vanishing model casting method.

[0003] However, there are disadvantages. In casting methods other than the vanishing model casting method, a gas vent hole called `` rise '' is located downstream of the molten metal flow, and the molten metal flows into that hole, so that the molten metal flow does not stop suddenly at the completion of molten metal filling,
Due to the kinetic energy of the molten metal, there is no shock when the molten metal is stopped, and no problem occurs.

On the other hand, in the vanishing model casting method, since there is no "rise", gas is discharged out of the system through the coating / molding sand. Thus, the molten metal is filled and the energy of the flow becomes a pressure change or a local disturbance of the flow when the flow stops. When the fluid stops,
Water hammers are well known. This turbulence in the flow becomes a surface defect of the casting product.

Although it is conceivable to provide "rises" even in the vanishing model casting method, there are the following disadvantages, and usually there is no provision. (1) It is necessary to provide the rises to a height at which the molten metal does not overflow outside the mold. There are many parts that do not become products, so the yield decreases.

(2) In the case of vanishing model casting, since a flammable gas exists at a positive pressure in a mold, there is a possibility that a high-temperature gas or a molten metal may blow out, which is dangerous.

(3) The workability is poor because an object is set outside the mold frame during molding.

(4) In order to connect a pipe used for “rise” to a model, it is necessary to newly provide a connection part outside the product shape.

[0009]

In the vanishing model casting method, since it is difficult to provide air vents, there is a problem that a surface defect of a cast product is easily generated. An object of the present invention is to develop and provide a vanishing model casting method that solves the above problems.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its technical means is to use a material similar to the model and cut off toward the end of the molten metal flow in the vanishing model casting method. It is characterized by adding a projection having a shape with a gradually decreasing area or a stepwise decreasing shape to the final reaching part of the molten metal flow of the disappearing model, casting and removing parts other than the casting product shape after casting. I do. By this technical means, it is possible to prevent the occurrence of surface defects of the cast product. Even if the cross-sectional area of the projection has a shape that is gradually reduced, it is effective. The material of the projection may be the same as or similar to the model, as long as it is thermally decomposed or burned by molten metal and gasified.

The projection in the present invention is a shock absorbing portion, and the generation of the shock is dispersed by gradually or stepwise stopping the flow of the molten metal at the end of filling the molten metal, thereby reducing the impact at one time. Prevent surface defects that occur in products.

In a casting having a small weight, the energy of the molten metal flow itself is small and the influence is small, but when the weight is large, the energy of the molten metal flow at the end of the molten metal flow is large and the influence of the impact is large. According to experience, the effect is significant for castings that are long in the direction of the melt flow. This is because the force applied to each part due to the stoppage of the flow is substantially proportional to the length of the part upstream of the part.
In addition, a casting product having a long length has a long casting time, which causes a decrease in the temperature of the molten metal and causes defects such as poor running of the molten metal and rough skin. If an attempt is made to reduce the casting time to prevent this, the impact is increased because conditions are selected for increasing the casting speed even within the range of the appropriate casting speed.

[0013] Among the prior arts, there is a technique in which a part other than the shape of a cast product is cast together and then removed. A typical example is a feeder for casting cast steel. This is to prevent the shape change and defects of the cast product due to shrinkage that occurs during the temperature change from the molten metal to room temperature at the time of casting. Is concentrated on the riser to prevent defects in the cast product.
The riser is often provided at the end of the flow. The solidification time of the feeder needs to be longer than the solidification time of the cast product, and the shape and size of the feeder are restricted in order to increase the yield of the molten metal, and the cross-sectional area must be at least a certain size. .
Therefore, the flow rate of the product component when the surface of the hot water passes through the riser is high, the area of the final flow reaches a large change, and the impact when the flow stops is large. Can not. In this case, an impact can be absorbed by providing an impact absorbing portion at the final flow of the hot water in the riser. The projection of the present invention differs from the riser in that the cross-sectional area gradually or stepwise decreases toward the end of the flow.

The impact in the vanishing model casting method of the present invention is considered to occur at the following locations.

(1) A portion where the cross-sectional area from the cast product to the projection decreases, and (2) A portion where the cross-sectional area at the projection changes.

Ideally, the area from the cast product to the protrusion should be gradually reduced from the cross-sectional area of the cast product. However, even if the area is changed stepwise, there is an effect. This is advantageous in terms of cost because the work load when removing the protrusion later can be reduced. The area change rate at which no defect occurs when the cross-sectional area is changed stepwise and the area of the final location of the molten metal may be determined according to the shape of the casting product, the composition of the molten metal, and the velocity of the molten metal.

The shape of the cast product itself has a portion where the cross-sectional area changes abruptly, and a surface defect may occur even when the flow rate of the molten metal changes, and a shock is absorbed by providing a projection near the position. be able to.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a technique for preventing a surface defect of a cast product caused by an impact in a final stage of pouring of a vanishing model casting method. Usually, since a casting mold is provided with a weir at the lower end of a casting product for casting, pouring is completed when the molten metal surface reaches the top surface of the casting product. The rise in the level of the molten metal in the mold depends on the burn-off rate of the disappearance model (eg, disappearance volume / second).
Is governed by Therefore, if the cross-sectional area of the top of the model is small, when the level of the molten metal reaches the top, the inflow of pouring water decreases,
Shock generation is reduced. The present invention reduces the pouring speed in the final stage of pouring by this principle.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a vanishing model 2 according to a first embodiment of the present invention.
It is a figure which shows the casting_mold | template 1 of the casting method using. Vanishing model 2
Are buried in the molding sand 4 filled in the mold frame 3.
The pouring metal reaches the vanishing model 2 through the sprue 5, the runner 6, and the weir 7, and burns and disappears to be gasified, and is discharged to form a cast product having the same shape as the vanishing model 2.

The vanishing model casting method of the present invention can be effectively applied to a cast product having a relatively small cross section and a high height. FIG. 1 shows a vanishing model 2 provided with a conical projection 10 whose upper part is reduced at the upper end. When the level of the molten metal rises above the projection 10, the pouring speed decreases,
The impact is reduced, and no surface defects occur in the cast product. The protrusion 10 is cut and removed later.

FIG. 2 shows a second embodiment, in which a projection 10 composed of a stepped pillar is provided at the upper end of the vanishing model 2. The projection 10 having the stepped column has a shape in which the cross-sectional area is smaller than the top surface of the model and the cross-sectional area of the upper part of the column is reduced. Therefore, no impact is generated at the end of pouring, and no defects are generated on the surface of the cast product. The protrusion 10 is cut and removed later.

[0023]

As described above, the vanishing model casting method of the present invention has an excellent effect that the casting speed in the final stage of pouring is reduced and no surface defects occur in the cast product.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment.

FIG. 2 is an explanatory diagram of a second embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 vanishing model 3 mold frame 4 casting sand 5 gate 6 runner 7 weir 10 protrusion

Claims (1)

[Claims] In the method of casting a lost model, a protrusion having a shape similar to that of the model and having a shape whose cross-sectional area gradually decreases toward the end of the molten metal flow or a shape that gradually decreases is used to reach the final flow of the molten metal flow of the lost model. A vanishing model casting method characterized by performing casting in addition to a part, and removing a part other than a cast product shape after casting.