JPH0454537B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in a casting method, and in particular to a process in which a model made of a polymer foam is buried in foundry sand, and molten metal is poured into the made mold. The present invention relates to an extinguishing model casting method in which the foam model is decomposed and vaporized by the heat of the molten metal, and the cavity thus formed is sequentially filled with the molten metal to produce a casting.

[Conventional technology]

As a vanishing model casting method, a full mold casting method using expanded polystyrene having a specific gravity of 0.015 to 0.025 (expansion ratio of about 40 to 70 times) as a polymer foam is generally well known.

This casting method produces the same shape as the desired cast product.
A model made of expanded polystyrene that has been integrally processed and molded to the desired dimensions (sometimes using a core made of foundry sand or metal) is placed in a sprue system (sprue system).
The mold is placed in a casting flask with a runner, a jar, etc., and refractory aggregate (generally silica sand is used, but sometimes special sand such as zircon sand, olivine sand, chromite sand, etc.) is used on and around (sometimes inside) the model. A mixture made by mixing and kneading a binder (sometimes a curing agent for the binder is also added)
For example, a mold is created by filling and solidifying inorganic foundry sand such as clay sand, water glass sand, and cement sand, or organic foundry sand such as Furan sand and cold box sand (sometimes, using only refractory aggregate, Non-caking sand without the addition of a binding agent is sometimes used in combination with a suction device, etc.) When the polystyrene foam model embedded in the mold created in this way is poured with the required molten metal without removing it from the mold, the polystyrene foam shrinks, melts, decomposes, etc. due to the heat of the molten metal. It vaporizes, and the cavity formed there fills with molten metal. As a result, it is a casting method that completes a cast product with the same shape and dimensions as the model.

However, the use of this full mold method is decreasing due to various problems caused by the chemical properties of polystyrene, which is the base resin of the foam used.

i.e. polystyrene is decomposed into hydrocarbons of c ₁ to cm by the heat of the molten metal,
Some of the decomposition products contain benzene rings, but due to their large binding energy, they are not completely decomposed and vaporized by the heat of the molten metal, and when they come into direct contact with the atmosphere (for example, in an open riser). installation),
Because benzene forms a polycyclic condensation structure and is released into the atmosphere as soot, the full mold method using expanded polystyrene uses a blind riser buried in the mold even when a riser is used.

The decomposed gas is released into the atmosphere through the gaps in the molding sand that makes up the mold, and it is recommended to increase the air permeability of the mold in order to prevent gas defects from occurring in the cast product. In addition, the method of increasing the particle size of the foundry sand to improve the air permeability of the mold has its limits because it becomes a gas passage and also promotes penetration of the molten metal that is cast, causing a sintering phenomenon. .

On the other hand, decomposition products containing benzene rings are not vaporized but are drawn into the molten metal, pushed toward the top of the mold as the molten metal rises and fills, and remain on the surface (particularly the upper part) of the casting as an unvaporized residue. This will damage your skin.

In this way, the amount of decomposed gas and unvaporized residue generated in the full mold method using expanded polystyrene is proportional to the weight of expanded polystyrene, so materials with low specific gravity (that is, high expansion ratio) are used. There is a tendency to A decrease in specific gravity induces a decrease in material hardness, which tends to cause deformation of the model during filling with molding sand, which in turn deteriorates the dimensional accuracy of the cast product after casting.

Since the main cause of the above problem is the presence of benzene rings, the present inventors investigated the foaming characteristics and casting characteristics of polyolefin hydrocarbon materials and developed foamed polypropylene resins and foamed polyethylene resins. , has succeeded in preventing casting defects caused by unvaporized residue. However, polyolefin-based resin foams have the disadvantage that if they are intended to prevent deformation during molding, they tend to cause blow-off due to gas pressure during casting because the amount of gas generated by their decomposition is greater than that of foamed polystyrene. In other words, the blowing phenomenon caused by decomposed gas during pouring occurs due to the correlation between the molten metal pressure of the poured molten metal, the mold air permeability, and the decomposed gas pressure.As a method to increase the molten metal pressure, increasing the sprue length, Pressurized pouring may be considered, but it is disadvantageous due to the casting method, on-site equipment, and product yield.

[Problem that the invention seeks to solve]

The present invention aims to provide an air casting method that allows foamed polyolefin resins such as foamed polypropylene resins and foamed polyethylene resins to be used as a disappearing model without reducing the surface hardness of the foamed polyolefin resins. be.

[Means for solving problems]

In other words, since blowing is likely to occur in the initial stage of casting, the present invention is designed to prevent blowing from occurring in the vicinity of where the molten metal comes into contact with the foamed polyolefin resin model, for example, in the push-up casting method. ), in the case of runners and weirs (same polyolefin resin foam), near the sprue, from the tip of the runner, or from the bottom of the model if there is a concern that there will be a large amount of decomposed gas (high gas pressure) due to the shape of the model. By installing a gas vent that connects directly to the atmosphere and releasing the gas generated by thermal decomposition of the polyolefin foam immediately after casting, the gas pressure is lowered and the penetration of molten metal into the mold is reduced. The feature is that even a polyolefin resin foam with a large amount of decomposed gas can be used as a casting model by promoting the decomposition and increasing the pressure of the molten metal.

That is, the present invention provides a means for direct connection of the lower part of the model to the atmosphere in vanishing model casting in which a foundry model made of polyolefin resin foam is buried in foundry sand containing a binder, and the foundry sand is solidified before casting. This is a casting method characterized by attaching a gas vent port to perform gas venting.

In the present invention, regarding the number and location of gas vents, it is desirable to install them in areas where blowing is likely to occur due to the volume and shape of the foam model. The exit position of the gas vent is not necessarily on the upper surface of the mold, but may be a vent that is inclined upwards from the entrance of the gas vent, and in this case, an inclination angle of 25° or more is preferable to prevent metal leakage.
Further, the number of gas vent ports can be appropriately set depending on the amount of decomposed gas, but the cross-sectional area also varies depending on the type of molten metal to be cast. When it is desirable to have a cross-sectional area that does not cause melt leakage, it is possible to take on-site measures such as blocking the outlet end of the gas vent with molding sand after the initial gas release.

The application of the present invention has the feature that it can be used even with materials having a high specific gravity (a large amount of gas generation) in order to prevent the deformation of the foamed polyolefin resin model and the deterioration of the dimensional accuracy of the casting. It is not limited to polypropylene resin and foamed polyethylene resin.

Hereinafter, the details of the present invention will be explained using examples.

〔Example〕

Example 1 A bead-method in-mold foam molded product (specific gravity 0.0280) of ethylene + propylene random copolymer (ethylene content 28% by weight) was prepared in Figures 1 A to C [Figure 1 A is a front view, Figure 1 A is a front view, Figure 1B is a view indicated by the a arrow in Figure 1A (side view), and Figure 1C is a view indicated by the b arrow in Figure 1A (plan view)]
A model 1 of 200 x 200 x 200 was made as shown in Figure 1, and a runner (30 x 20) 3 and a weir (15 x
After gluing 7 x 2) 4 with a vinyl acetate resin adhesive, place it in the casting flask 7 together with the sprue (30φ earthen pipe) 2, and place it 20 mm from the center of the sprue 2 on the side of the runner 3.
Gas vent port 5 with a diameter of 5 mm and an inclination angle of 25° is located at
Gas vent 5' with a diameter of 5 mm and an inclination angle of 30° at both ends of the runner 3, an angle of inclination from the bottom of the model 1 on the side opposite to the sprue.
After attaching a model for a 90°, 5mm diameter gas vent 5″, furan sand 6 (AFS55) is placed around it.
was filled and solidified. After that, open the gas vent port 5,
The 5' and 5'' models were cut out to complete the mold.

Molten cast iron (3.4% carbon, 2.2% silicon,
(0.7% manganese) was cast at 1340℃.

For comparison, we also created a mold using a model of the same shape and size without a gas vent, using a bead method in-mold foamed product (specific gravity 0.0280) of ethylene-propylene random copolymer (ethylene content 28% by weight). The same molten metal was cast.

Note that the properties of foamed polypropylene are shown in Table 1.

Table 1 Foamed poly Specific gravity Compression hardness ^*1 Gas generation amount ^*2 Proprene 0.0280 1.18 49cc *1 Compliant with JISK 6767 *2 Gas generation amount by foam 8cm ² (2 x 2 x 2) As a result of the casting test, gas In the mold without a vent (comparative example), the molten metal was violently blown back from the sprue immediately after the start of casting, and subsequent casting was stopped.

On the other hand, in the mold with a gas vent (example of the present invention), decomposed gas was released from the gas vent attached to the runner at the early stage of casting, but gas was released from the runner 2 seconds after casting. The ivy is falling. On the contrary, gas was temporarily released from the gas vent attached to the model, but
As the casting progresses, outgassing also ceases.
We were able to finish the casting smoothly.

After the casting was cooled, no gas defects due to decomposition gas were observed in its appearance or in the macroscopic condition of the central cut surface.

Example 2 Two molds similar to Example 1 (invention example and comparative example) were manufactured using bead-method in-mold foam moldings of high-density polyethylene having the characteristics shown in Table 2. Molten metal was cast.

Table 2 Foamed poly Specific gravity Compression hardness ^*1 Gas generation amount ^*2 Ethylene 0.0296 0.98 47cc *1 *2 Same as Table 1 As a result, in the mold with a gas vent (example of the present invention), the same as in Example 1 Casting was possible smoothly, and no gas defects were observed inside or outside the casting.

[Brief explanation of drawings]

FIGS. 1A to 1B are diagrams showing one embodiment of the method of the present invention.

Claims (1)

[Claims] 1. In the vanishing model casting method, in which a polyolefin resin foam casting model is buried in molding sand containing a binder, and the molding sand is solidified before casting, a gas vent is provided at the bottom of the model that connects directly to the atmosphere. A casting method characterized by the addition of a gas vent.