JPH04224043A - Shell mold - Google Patents

Abstract

PURPOSE:To provide a shell mold having difficult-to-develop heat decomposing material of resin, etc., and high mechanical strength. CONSTITUTION:Hole is arranged in the shell mold forming the resin as binder and powder or granules of porous material of seviolite, etc., is packed. Particularly, in the position producing much heat decomposition, the hole is arranged. The powder of porous material may be coated on surface of the mold. The producing material of resin, etc., is passed through the hole and absorbed and decomposed with the packed material. Further, in the case of arranging coating layer, this is absorbed and decomposed with the coating layer, too, producing quantity of the resin, etc., is restrained and gas defect is made to little. Lowering of strength in the mold is scarcely developed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shell mold made of resin and foundry sand, and more particularly to a casting mold that can reduce the amount of resin generated during casting.

0002

[Prior Art] Shell molding, which takes advantage of the property of synthetic resins such as phenol resins being hardened by heat, has traditionally been the most popular method for manufacturing the main mold and core (hereinafter simply referred to as molds) of casting molds. It has been adopted. A mold manufactured by this method is called a shell mold. As a mold material used in the shell molding method, foundry sand (resin coated sand), which is made by coating sand grains such as silica sand with a thermosetting resin such as phenol resin, is generally used. Further, there is also a method of manufacturing a mold using a resin that hardens at room temperature, such as a cold box.

However, using a shell mold made of molding sand coated with room-temperature curing resin or thermosetting resin (hereinafter simply referred to as resin), molds such as aluminum, magnesium, and their alloys, which have relatively low casting temperatures, are used. If casting is performed at a low molten metal temperature, the decomposition of these resins will be insufficient and tar will occur. Then, these resins adhere to gas vents and the like, causing clogging, and furthermore, the generated gas flows toward the cavity side, resulting in casting defects. In order to prevent this, the resin adhering to the vents must be cleaned frequently, which places a heavy burden on maintenance.

[0004] In order to solve these problems, a method of adding porous substances such as hydrous magnesium silicate, activated carbon, and activated alumina to resin-coated sand (Japanese Patent Laid-Open No. 62-4
5446, JP-A-63-60042) and a method of coating the mold surface (JP-A-1-202336). However, JP-A-62-45446, JP-A-6
Since the technique disclosed in No. 3-60042 mixes porous substances into the foundry sand, there is a risk that the strength of the resulting shell mold may be reduced. In addition, the technology disclosed in Japanese Patent Application Laid-open No. 1-202336 is applicable to areas where a large amount of gas is generated locally, where gas defects occur because the porous material exists only on the outermost surface of the mold, and where the mold wall thickness is large. It was not possible to completely suppress the generation of tar in areas where a large amount of gas was generated.

[0005]

[Problems to be Solved by the Invention] An object of the present invention is to provide a shell mold for casting that can further reduce the amount of resin generated from the shell mold during casting and also ensure sufficient mechanical strength of the mold. It is in.

[0006]

[Means for Solving the Problems] As a result of intensive research, the present inventors have come to invent a shell mold having a novel structure that solves the problems of the prior art.

[0007] The present invention provides a shell mold formed using a resin as a binder, in which holes are provided for filling with a porous substance that has an effect of adsorbing, absorbing, or decomposing the thermal decomposition products of the resin. Regarding the characteristic shell mold.

[0008] The pyrolysis product of the present invention refers to a substance produced by vaporization or decomposition of resin due to heat during casting.

[0009] The shape of the porous substance to be filled into the holes of the shell mold is preferably one that is easy to fill and matches the size and shape of the holes, such as powder, granules, or pellets. Furthermore, a shape and a filling method that allow good gas release and a large contact area between the gas and the filler are preferred. Furthermore, although the greater the number of holes in the present invention, the better the effect, if there are too many holes, the strength of the mold will decrease. Furthermore, the size and shape of the holes must be such that the strength of the mold is not reduced. The holes may be in either direction, but it is preferable to provide them in areas where gas generated from the mold is likely to be released to the outside, or in areas where the mold has a large wall thickness.

0010

[Function] The mold material used for shell molds is foundry sand (resin-coated sand), which is made by coating sand grains such as silica sand with thermosetting resin such as phenol resin or room temperature curing resin such as cold box. . When a relatively low-temperature molten metal such as aluminum or magnesium is poured into a mold made of such foundry sand, the coated resin becomes a thermal decomposition product and evaporates without being sufficiently decomposed. In conventional molds, these thermal decomposition products come into contact with low-temperature parts such as vents and adhere as tar, for example.

[0011] In the mold of the present invention, holes filled with a porous material that adsorbs or decomposes thermal decomposition products generated from the resin are provided in various parts of the mold. Since this hole also functions as a gas vent hole, thermal decomposition products generated within the mold collect in this hole without diffusing into the molten metal. The pyrolysis products collected in the pores come into contact with the porous material filling the pores. This thermal decomposition product is generated from the resin coated on the foundry sand and is mainly a polymer. A portion of these is adsorbed or absorbed by the porous material, or decomposed by the catalytic action of the porous material, and converted into low molecules such as H2O, CO2, and CH4.

0012

Effects of the Invention: As described in the above action, in the mold of the present invention, the porous material filled in the pores adsorbs, absorbs or decomposes the thermal decomposition products generated from the resin during casting. It is less likely that the gas will come into direct contact with the gas vent, etc. and adhere as tar and cause clogging. Therefore, the man-hours required for maintenance such as cleaning of resin can be greatly reduced. It helps protect the environment by reducing the release of products caused by other thermal decomposition products.

Furthermore, since the generated thermal decomposition products flow into the holes filled with porous material provided in the mold, they do not flow into the cavity side, thereby reducing the occurrence of casting defects. Furthermore, the mold of the present invention is provided with holes to the extent that its mechanical strength is not affected. Therefore, the mechanical strength of the mold itself is less reduced than when porous foreign matter is mixed into the molding sand.

(Other inventions) The thermal decomposition products of the present invention include tar, smoke, and bad odor generated during casting.

In the present invention, powdery porous substances include hydrous magnesium silicate clay minerals, activated carbon, activated alumina, etc., and one type or a mixture of two or more of these is used. Among these, hydrated magnesium silicate clay minerals are mainly composed of hydrated magnesium silicate and have a specific surface area of 1
It is large at 00-400m2/g. Specifically, the hydrated magnesium silicate clay mineral is sepiolite.
ite), this thing is commonly known as mountain cork (Mo
untain cork), mountain wood (Mo
untain wood), mountain leather (Mo
untain leather), meerschaum (Meers)
-chaum) etc. There is also palygorskite, which is a mineral whose main component is hydrated aluminum silicate, and is also called attapulgite.

[0016] Furthermore, activated carbon has a specific surface area of 400 to 200
It is as large as 0m2/g, and includes vegetable materials such as coconut shell charcoal and raw ash, and mineral materials manufactured from coal-based and petroleum-based raw materials. Activated alumina is obtained by heating hydrated alumina to a high temperature, and is an intermediate alumina in the process of becoming α-alumina, with a specific surface area of 50 to 400 m2/
There is g. This intermediate alumina is also called anhydrous alumina, and includes ρ, χ, η, γ, δ, θ, κ alumina, boehmite, and the like.

[0017] In the mold having the structure of the present invention, the surface of the mold may be coated with a porous material in order to further improve the effect of preventing tar formation. These porous substances are preferably used in powder form in order to coat the cavities between the sand grains and the surface of the mold, and preferably have a particle size of 200 μm or less. Also,
Methods for coating the cavity and surface of the mold with a porous substance as a coating material include a method of spraying or brushing with water, alcohol, etc. as a solvent, followed by drying, and a method of using a fluidized bed.

[0018]

EXAMPLES (Example 1) Hereinafter, the present invention will be explained in more detail using examples. This example shows an example in which aluminum alloy AC2B was cast using a core with holes filled with sepiolite powder, which is a hydrous magnesium silicate clay mineral (Fig. 1), and a CO2-type main mold made of silica sand. . The main mold is a CO2 mold, which is made by coating silica sand with sodium silicate and hardening it by spraying CO2.
mm, width 120mm, height 150mm, and a cavity with a diameter of 75mm and a depth of 135mm from the top surface.
The core 1 shown in FIG. 1 with a diameter of 30 mm is placed in the center of the cavity. Core 1 is made of novolac type phenol resin.
Made from 4 parts by weight coated silica sand. A hole 2 with a diameter of 4 mm is provided in the center of the core, and the average particle size is 100.
It was filled with sepiolite grains 3 having a diameter of .mu.m. 75 in this mold
Pour aluminum alloy AC2B at 0℃ and generate 1 liter of gas.
/min for 10 minutes, during which time the piping was cooled with water, and the resin adhering to the walls of the piping was dissolved with chloroform and collected. By measuring the transmittance of the collected chloroform solution with a spectrophotometer, the amount of tar attached was compared with a comparative example described below.

In addition, as a comparative example, a core of a shell mold without sepiolite-filled holes or a sepiolite coating layer was prepared, and an aluminum alloy was cast in the same method as above, and the resin attached to the pipe wall was removed. Transmittance was measured. The results are shown in Figure 2. As is clear from the figure, the transmittance of the mold with pores filled with sepiolite was superior to that of the comparative example, and the amount of tar generated could be suppressed to a considerable extent by using a mold structure with pores filled with a porous substance. Further, although the mold of this example had holes, it had sufficient strength for practical use.

(Example 2) This example has a core having holes filled with sepiolite powder, which is a hydrous magnesium silicate clay mineral, and whose surface is coated with sepiolite (Fig. 3), and a CO2 mold made of silica sand. An example of casting aluminum alloy AC2B using the main mold is shown below. The main mold is a CO2 mold, which is made by coating silica sand with sodium silicate and hardening it by spraying CO2, and its external dimensions are 120 mm in height.
Width 120mm, height 150mm, diameter 75mm from the top
It has a cavity with a diameter of 30 mm and a depth of 135 mm, and a core 1 shown in FIG. 3 with a diameter of 30 mm in the center of the cavity. Core 1 was made from silica sand coated with 1.4 parts by weight of novolak type phenolic resin. A hole 2 with a diameter of 4 mm was provided in the center of the core, and the hole 2 was filled with sepiolite grains 3 with an average grain size of 100 μm. Furthermore, the surface has a particle size of 5
Sepiolite powder 4 of 0 μm or less was coated with a fluidized bed.

[0021] Aluminum alloy AC2 at 750°C was placed in this mold.
B was poured and the generated gas was sucked in at 1 l/min for 10 minutes, during which time the piping was cooled with water, and the resin adhering to the walls of the piping was dissolved with chloroform and recovered. By measuring the transmittance of the collected chloroform solution with a spectrophotometer, the amount of tar attached was compared with Example 1 and Comparative Example. The results are shown in Figure 2. As is clear from the figure, the transmittance of the mold coated with sepiolite and provided with pores filled with sepiolite was even higher than in Example 1, and by providing the pores filled with a porous material in the mold, the amount of tar generated was reduced. We were able to suppress it further. Further, although the mold of this example had holes, it had sufficient strength for practical use.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a core used in Example 1.

FIG. 2 is a diagram showing the transmittance of a solution in which tar was eluted in an example.

FIG. 3 is a cross-sectional view of the core used in Example 2.

[Explanation of symbols]

1 Core 2 holes 3 Sepiolite grains filled in the pores

Claims (1)

[Claims] 1. A shell mold formed using a resin as a binder is provided with pores for filling with a porous substance that has an effect of adsorbing, absorbing, or decomposing the thermal decomposition products of the resin. shell mold.