JPS61212442A - Casting method - Google Patents

Abstract

PURPOSE:To make possible the use of a polyolefin resin foam for a pattern in consumable pattern casting in which the pattern made of the polyolefin resin foam for a casing is used by attaching gas vent ports communicating with the atm. to a runner and/or the bottom surface of the pattern. CONSTITUTION:The pattern 1 is formed of the foamed-in-place molding of an ethylene-propylene random copolymer by a bead method and is adhered to a runner 3 and gate 4 made of the same material by a vinyl acetate resin adhesive agent. The assembly is installed together with a sprue 2 into a molding flask 7 and is attached with the patterns for the gas vent port 5 on the side face of the runner 3, the gas vent port 5' at both top ends of the runner 3 and the gas vent port 5'' having a prescribed angle of inclination from the bottom surface of the pattern 1 on the counter sprue side. Furan sand is packed to the periphery thereof and is solidified. The patterns for the ports 5, 5', 5'' are thereafter removed and the casting mold is formed.

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 casting method in which a model made of a polymeric foam is buried in foundry sand and cast into a mold. The present invention relates to a vanishing model casting method in which the foam model is decomposed and vaporized by the heat of the molten metal during immersion, and the cavity thus formed is filled with the molten metal to produce a casting.

[Conventional technology]

In the vanishing model casting method, specific gravity Q,
(A full mold casting method using expanded polystyrene of M5 to 1025 (expansion ratio of about 40 to 70 times) is generally well known.

This casting method uses a mold made of expanded polystyrene that has been integrally processed and molded into the same shape and dimensions as the desired cast product (sometimes a molding sand or metal core is partially used). , runner, weir), etc., in the casting flask, and on and around (sometimes inside) the VC
Refractory aggregate (generally silica sand, sometimes special sands such as zircon sand, oripin sand, furomite sand, etc.) with a binder (sometimes a hardener for the binder is added) A mold is created by filling and solidifying a mixture, such as 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. With only fire-resistant aggregate,
Non-caking sand without adding a binding agent is sometimes used in combination with a suction device, etc.) The foamed polystyrene model embedded in the mold thus created is removed from the mold. In particular, when the required molten metal is poured into the mold, the foamed polystyrene shrinks, melts, decomposes, and vaporizes due to the heat of the molten metal, and the molten metal fills the cavity formed there. As a result, this full molding method, which is a casting method that completes a cast product with the same shape and dimensions as the model, has problems due to the chemical characteristics of polystyrene, the base resin of the foam used. Therefore, its use is gradually decreasing.

In other words, polystyrene/ is decomposed into 01 to On hydrocarbons by the heat of the molten metal, and some of it is gasified, but the decomposition products containing benzene rings have a large bond energy, so they are not completely decomposed and vaporized by the heat of the molten metal. In cases where K comes into direct contact with the atmosphere (for example, in the installation of an open riser), K forms a benzene polycyclic condensation structure and is released into the atmosphere as soot. Even when hot water is used, a blind riser buried in the mold 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 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 naturally has its limits because it becomes a gas passage and also promotes penetration of the molten metal into the casting, causing a casting phenomenon. .

On the other hand, decomposition products, including benzene, do not vaporize and are drawn into the molten metal, causing the molten metal to rise.

As the liquid is filled, it is pushed toward the top of the gun mold and remains on the surface of the casting (at the top at tVf) as an unvaporized residual liquid, damaging the casting surface.

As shown in the figure, 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. tends to be used.

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 a foamed polypropylene resin and a 2-cell polyethylene resin. This method has been successfully used to prevent casting defects caused by unvaporized residue. However, polyolefin resin foams have the drawback that, if they are intended to prevent deformation during molding, the amount of gas generated by their decomposition is greater than that of foamed polystyrene, which tends to cause blowing due to gas pressure during casting. 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, there are methods such as increasing the length of the sprue, Pressurized pouring may be considered, but due to the casting method and on-site equipment.

There are advantages in terms of product yield, etc.

[Problem that the invention seeks to solve]

The present invention aims to provide a casting method that can use a foamed polyolefin resin as a disappearing model without reducing the surface hardness of the foamed polyolefin resin such as foamed polypropylene resin 9 foamed polyethylene resin. 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 near the area where the molten metal comes into contact with the foamed polyolefin resin model, for example, in the casting method using the push-up method.
In general, if a clay pipe is used (in a cavity), or in the case of a runner and weir (made of the same foamed polyolefin resin), it is near the sprue.

If there is a concern that there will be a large amount of decomposed gas (high gas pressure) from the tip of the runner or due to the shape of the model, we will install a gas vent that connects directly to the atmosphere on the bottom of the model, and use polyolefin foam immediately after casting. Polyolefin resin foam with a large amount of decomposed gas by releasing gas generated by thermal decomposition of the body, reducing gas pressure, promoting penetration of molten metal into the mold, and increasing molten metal pressure. However, it has many features that allow it to be used as a casting model.

That is, the present invention is characterized in that, in the vanishing model casting method in which casting is performed using a casting model made of polyolefin resin foam, a gas vent is provided in the runner system and/or the lower surface of the model to directly communicate with the atmosphere. This is a casting method.

In the present invention, regarding the number and location of the 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 box. The exit position of the gas vent is not necessarily on the top of the mold, but may be a vent that is slanted upward from the gas vent inlet.In this case, an inclination angle of 25 mm or more is preferable to prevent hot water from leaking. .

Further, the number of gas vent ports can be appropriately set depending on the amount of decomposed gas, but the cross-sectional area thereof also varies depending on the type of molten metal to be cast. It is desirable to have a cross-sectional area that does not cause melt leakage, and in some cases, on-site methods such as blocking the outlet end of the gas vent with molding sand after the initial gas release may be taken.

The application of the present invention has the characteristic that it can be used even with materials having a high specific gravity (a large amount of gas generation) in order to prevent deformation of foamed polyolefin resin models and deterioration of dimensional accuracy of castings.
In terms of materials, the foamed polyethylene resin is not limited to the foamed polyethylene resin.

Hereinafter, the details of the present invention will be explained with reference to examples.

〔Example〕

Example t Bead method indoor foam molded product of ethylene-based propylene random copolymer (ethylene content 2.8 weight
O2BG), Figure 1 (4) to (0) [Figure 1 (4)
is a front view, Figure 1 (B) is a view indicated by the a arrow in Figure 1 (4) (side view), and Figure 1 (C) is a view indicated by the b arrow in Figure 1 (4) (plan view)] A model 1 of 200 x 200 x 200 as shown in the figure was manufactured, and a runner (30
0) After gluing the 5p weir (15X7X2) 4 with a vinyl acetate resin adhesive, install it in the casting flask 7 together with the sprue (30φ earthen pipe) 2, and insert the sprue 201111 from the center of the sprue 2 on the side of the runner 5. Diameter at position s m # Inclination angle 25
5. Diameter 5 m at both ends of runner 5.
After attaching a model for a gas vent hole 5' with an inclination angle of 30' and a diameter SW of 5'' from the bottom surface of the model 1 on the opposite side of the hot water tank, furan sand 6 is placed around it. (AF
855) was filled and solidified. After that, remove the gas 5
．． The 5' and 5' models were cut out to complete the mold.

Molten cast iron (carbon 54, silicon 2.2%, manganese 17%) was poured into the mold at 13400 mol.

In addition, for comparison, a model of the same shape and size without a gas venting port was made using a bead method in-mold foamed product (specific gravity 1028G) of an ethylene-propylene random copolymer (ethylene content 2.8 weight x). A mold was made and the same molten metal was poured into it.

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

Table 1 Book 1 Compliance rate with J Engineering 8 K 4767 2 Gas generation amount with foam 8c [2 The molten metal was violently blown back, and further casting was halted.

On the other hand, in a mold with a gas vent (example of the present invention), decomposed gas is released from the gas vent attached to the runner at the beginning of casting, but gas is released from the runner 2 seconds after casting. It subsided. On the other hand, gas was temporarily released from the gas vent attached to the model, but as the casting proceeded, no gas was released and the casting was completed smoothly.

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

Example 2 Two molds (one inventive example and a comparative example) similar to those in Example 1 were manufactured using in-mold foam molded products of high density polyethylene having the characteristics shown in Table 2. Molten metal was cast.

Table 2 Foamed polyethylene 10296 0.98 4
7cc$1. $2 Same as Table 1 The results were as follows: In the mold equipped with a gas vent (example of the present invention), casting could be performed smoothly as in Example 1, and gas defects inside and outside the casting were also observed.

[Brief explanation of the drawing]

1) to (B) are diagrams showing one embodiment of the method of the present invention.

Claims (1)

[Claims] A casting method in which a casting model made of a polyolefin resin foam is used for casting, which is characterized in that a gas vent is attached to the runner system and/or the bottom surface of the model to directly communicate with the atmosphere.