JP2001293537A - Method for manufacturing molding sand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing molding sand which is suitable to improve the dimensional stability in a casting, suitable to prevent the casting defect, such as mold cracking, veining, scab, burning, and has excellent heat- resistance, low thermal-expansion and regeneration efficiency in repeated use. SOLUTION: After adjusting alumina content in slag generated when producing a ferro-chromium to 31-50 wt.%, air-granulated to obtain the high alumina spherical slag obtained by grading. Since the high alumina spherical slag is excellent in heat-resistance, low thermal-expansion and high hardness, the casting excellent in the outward appearance can be obtained by using the mold molded with this slag and a binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing molding sand.

[0002]

2. Description of the Related Art Conventionally, the most common casting sand is high-purity silica sand having a silica (SiO ₂ ) content of 90% or more.
While high-purity silica sand is widely used for various castings,
Since the coefficient of thermal expansion is large, and a mold (especially a core) using this as an aggregate expands considerably by pouring, there is a problem that casting defects such as irregular dimensions of the casting, vaning, and hot cracks are caused. On the other hand, when low-thermal-expansion silica sand with low silica content is used, castings such as cast steel, high manganese steel, and stainless steel that are poured at a relatively high temperature or castings that can generate hot spots in the mold depending on the shape or plan are used. On the other hand, since the heat capacity and heat resistance are insufficient, the silica sand is melted before the molten metal solidifies, causing a seizure phenomenon. For this reason, chromite sand,
Zircon sand and mullite sand are used only on the mold surface (skin sand) or partially (pocket sand). However, these sands are expensive and economically disadvantageous. In addition, many foundries use thermal or mechanical regeneration of foundry sand for the purpose of environmental protection and resource protection, but silica sand has a square shape and lacks hardness. As a result, a part of the powder is crushed by the regeneration, and fine powder (bread) is generated. The bread cannot be used as a mold and is discarded for a fee, so that it is economically burdensome and has a negative effect on the environment. In order to solve such a problem, high-speed air is blown onto slag, which is produced as a by-product when producing high-carbon ferrochrome, and slag having a particle diameter of about 1 to 2 microns, which has been spheroidized (blasted), is cast into a mold sand. It was considered to be used as. (Ferroalloy vol. 36, No. 1, p. 114-11)
5) In this report, it is reported that the mold characteristics such as the transverse rupture force are improved as compared with the above-mentioned materials such as silica sand.

[0003]

In the above research, the evaluation of the mold characteristics was performed, but other characteristics such as thermal shock characteristics due to rapid thermal expansion and the like were not evaluated. It turned out that there were characteristics that needed to be improved. The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for producing a molding sand for obtaining a heat-resistant, low-thermal-expansion mold.

[0004]

SUMMARY OF THE INVENTION According to the present invention, the present invention has heat resistance enough to withstand casting of a high pouring temperature such as cast steel and alloy steel, has little rapid thermal expansion at high temperatures, and has a high yield. Focused on inexpensive and easily available refractory aggregates that can be recovered and recycled at the same time, as a result of repeated studies, we found a refractory aggregate that does not hinder practical use as molding sand and completed it. Reached. That is, the present invention, in a refractory aggregate used for mold molding applying various known binders to the refractory aggregate, air-crushed high alumina-containing slag generated when producing ferrochrome, and sized. An object of the present invention is to provide a method for producing a spherical slag (hereinafter, referred to as an air-crushed slag) which is excellent in heat resistance, low thermal expansion, and regeneration efficiency.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The novel refractory aggregate used in the present invention reduces the ore of ferrochrome produced naturally and separates and removes the metal component from the molten slag generated when producing ferrochrome, and then drops the molten slag. It is obtained by blowing high-speed air from a nozzle onto a falling slag to blow it off. The air-milled slag solidifies into a sphere due to surface tension in the air. Ferrochrome slag is made of SiO ₂ , Al ₂
It is mainly composed of three components of O ₃ and MgO, and has a dense structure composed of spinel, forsterite, and vitreous. The air-blasted slag of the present invention is characterized by using a molten slag in which an alumina component is added in excess to a slag component in advance.
It is adjusted to be about 50% by weight. If the alumina content is less than 30% by weight, the heat resistance and the low thermal expansion property are insufficient, so that there are cases where these characteristics are inappropriate for a mold that requires a high degree of these properties. Further, even if it exceeds 50% by weight, no further improvement effect can be obtained. This structure and composition are the origin of the characteristics of the air-crushed slag such as heat resistance, low thermal expansion, and high hardness.

When the above-mentioned crushed slag is used for foundry sand,
Since it contains high alumina and has a low coefficient of thermal expansion, expansion defects such as vaning, hot cracks and cracks can be prevented, and since it has excellent heat resistance, there is little baking, erosion, etc. during casting. In addition, it is possible to prevent poor appearance of the casting surface, and because of its high hardness, it exhibits good wear resistance and crush resistance in thermal or mechanical regeneration of aggregate, and aggregate can be collected with high yield. It has advantages such as

[0007] The air-blasted slag obtained by the present invention can be applied to a casting mold of light alloy, cast iron, ductile cast iron, steel, and alloy steel such as manganese steel, chromium steel, and stainless steel. In particular, it is suitable for molds such as cast steel and alloy steel, which have a high melting point and a high melt viscosity, that is, which require pouring at a high temperature.

The mold molding method to which the molding sand of the present invention can be applied is not particularly limited, but an acid-curing furan method, an acid-curing phenol method, an ester-curing phenol method, an urethane method, an ester-curing method which is self-curing at room temperature. Water glass method, diecal method, N process, amine cured urethane method as cold box, ester cured phenol method, phenol method, CO ₂ cured phenol method, CO ₂ cured water glass method,
As thermosetting, it can be applied to the shell mold method. However, since the air-milled slag is weakly alkaline, the acid curing method has a curing retarding effect, and the urethane method has a curing accelerating effect. Therefore, measures for curing adjustment are required.

[0009] Recycling and reuse of foundry sands are active for resource conservation, environmental protection and economic reasons. Although there are various regeneration techniques, it can be generally distinguished between thermal regeneration and mechanical regeneration. The regeneration method is selected depending on the molding method employed. In the thermosetting shell molding method, thermal regeneration or a combination of thermal / mechanical regeneration is used. In the case of room temperature curing, mechanical regeneration is generally used. In particular, mechanical regeneration uses frictional force between sand or between sand and a material constituting the machine (mainly iron) to peel off and remove the binder, so that damage and destruction of the sand in the casting are inevitable. The destroyed parts cannot be reused and are discarded. Since the crushed slag has a high hardness derived from its structure, the damage due to mechanical regeneration is extremely small as compared with the conventional foundry sand, and therefore the amount of sand replenishment and the amount of discarded damaged parts (hereinafter referred to as bread) are small. There are benefits both economically and environmentally. As described above, the present invention is a heat-resistant, low-thermal-expansion, reclaimed material obtained by subjecting slag generated during the production of ferrochrome to air-blasting and sizing, as a low thermal expansion, high hardness, high heat-resistant molding sand. Provided is a method for producing an air-crushed slag with excellent efficiency.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments.

[Example 1] As an aggregate for a mold, 5000 g of crushed slag having an alumina content adjusted to 40% by weight was used, and this was charged into a super mixer (manufactured by Naniwa Seisakusho Co., Ltd.). Then, a phenol resin for ester curing (TPA-36, manufactured by Gunei Boden Co., Ltd.) as a binder
100 g (2 parts by weight based on the weight of the crushed slag) and 18 g (18 parts by weight based on the binder weight) of an ester (ACE-535) are added, and the mixture is kneaded in a mixer for 60 seconds, and then sand is discharged and kneaded. Get the sand. Immediately after kneading, the kneaded sand was filled in a test piece forming die of 50 mmφ × 50 mmH, left at 25 ° C. for 30 minutes, and then punched out to obtain a test piece for compressive strength. Compressive strength and pot life are JACT test method H
Performed according to M-1 and HM-2. Measurement of thermal expansion coefficient is J
It carried out according to ACT test method M-2. The dimensions of the test piece were 30 mmφ × 100 mmH.

[Example 2] As an aggregate for a mold, 5000 g of crushed slag having an alumina content adjusted to 40% by weight was used, and this was mixed with a continuous mixer (manufactured by Nippon Casting Co., Ltd.).
As a binder, a phenol resin for curing an ester (TPA-36, manufactured by Gun-ei Boden Co., Ltd.) is 2 parts by weight based on the weight of the crushed slag, and an ester (ACE-535) is 18 parts by weight based on the binder weight. To obtain continuously kneaded sand. The kneading sand is continuously 55 kg in unit weight and 8 in casting weight.
A 0 kg, high-manganese steel "hammer" cast product was filled into a main mold and a core model to be obtained. Twenty-four hours later, alcoholic zircon coating was performed, the mold was assembled, and high-manganese steel was poured at a pouring temperature of 1520 ° C. After pouring, the mold was left to stand for 24 hours, and the high manganese steel product was evaluated. The air-blasted slag used for casting was regenerated with a rotary reclaimer (manufactured by Nippon Casting Co., Ltd.) in one stage of M type and five passes. The regeneration yield was determined by the following equation, and the characteristics were evaluated by using a mold according to Example 1. Yield (%) = (recycled sand weight, kg) / (sand input weight, k
g) x 100

[Comparative Example 1] The same procedure as in Example 1 was carried out using, as aggregates for a mold, air-blasted slag (hereinafter referred to as conventional air-blasted slag) and 5000 g of Iide silica sand without adding alumina to molten slag. .

[Comparative Example 2] The same procedure as in Example 2 was carried out using a conventional crushed slag and 5000 g of Iide silica sand as an aggregate for a mold. The test results are shown below.

[0015]

[Table 1] Characteristics of raw material sand

[0016]

[Table 2] Mold properties

[0017]

[Table 3] Casting and recycled sand evaluation

That is, it has been confirmed that the present invention, using the air-blasted slag as such a refractory aggregate, shows that the mold has a remarkable effect on casting defects such as vaning and baking and has excellent regeneration efficiency. Was.

[0019]

As is clear from the above description, since the mold using the high alumina-containing crushed slag of the present invention has excellent low thermal expansion, the rapid thermal expansion of the mold or core during casting is small. In addition to providing castings with excellent dimensional accuracy, casting defects such as mold cracking, vaning, squaring, and seizure can be prevented, and castings with beautiful casting surfaces can be provided. Further, the crushed slag in the present invention has a spinel structure, has a high hardness, and can be recycled economically and with less environmental load. It can be used as an alternative casting aggregate that is significantly cheaper than expensive special sand such as conventional zircon sand, olivine sand, and alumina sand, and has the advantage of contributing to resource saving of casting aggregate. ing. Thus, the crushed slag of the present invention is:
It is of extremely high industrial value in the casting manufacturing field.

Continued on the front page (72) Inventor Matsuo Kubota 1-1-1 Yoshioka, Takaoka-cho, Toyama-shi Nippon Casting Steel Co., Ltd. (72) Inventor Tsuyoshi Komori 1-1-1 Yoshihisa, Takaoka-cho, Toyama-shi Nichiju Casting Steel Co., Ltd. Company F-term (reference) 4E092 AA01 BA06 BA08 CA03

Claims (1)

[Claims] 1. A method for producing ferrochrome, the method comprising:
Slag having an alumina content of 31 to 50% by weight is air-crushed,
A method for producing molding sand, wherein a high alumina spherical slag obtained by sizing is used as molding sand.