JP3268137B2 - Self-hardening mold for cast steel and method for reclaiming foundry sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-hardening mold for cast steel using a one-process two-sand system in a foundry and a method for reclaiming foundry sand.

[0002]

2. Description of the Related Art In recent years, a water-soluble phenol sand process has been widely used as a next furan sand process for a self-hardening mold for cast steel. The water-soluble phenol sand process uses a water-soluble phenol resin as a binder and an organic ester as a curing agent, and the binder does not contain harmful sulfur and nitrogen in a casting, and is a water-soluble mixture kneaded with the same binder. Phenolic sand has the advantage of obtaining a mold with higher heat resistance and thermoplasticity than conventional furan sand, and is a new sand process that reduces casting defects such as hot cracking, gas, inclusions, etc. in cast steel products. At the same time, the binder is
Improvements to low-price, high-strength products are progressing year by year, and application expansion is expected.

[0003] As a method of applying the water-soluble phenol sand process to a mold for cast steel, there are a "1 process 1 sand system", a "2 process 2 sand system", and "1 process 2 sand method"
Are used, and the flow of each method is shown in FIG. 6, FIG. 7, and FIG.
Shown in

[0004] In the "one process, one sand system" shown in FIG. 6, a water-soluble phenol mold is made of relatively fine-grained ceramic sand (trade name; Celabeads, spray-dry granulated and kiln-fired, and relatively high-grained). By using a single sand of a spherical mullite sand having hardness, the sand processing equipment in the sand kneading, collecting, regenerating and supplying system is simplified and the molding operation is mechanized. In addition, the excellent crushing resistance of the ceramic sand prevents the sand from being refined due to strong sand regeneration, reduces the casting waste sand, stabilizes the sand quality, and realizes a low thermal expansion mold.

In the "two-process two-sand method" shown in FIG. 7, a water-soluble phenol resin and an organic ester are used as a binder in chromite sand as a mold sand, and a furan resin and sulfonic acid are applied to silica sand as back sand. . As a feature of this method, casting defects are prevented by using water-soluble phenol chromite sand for skin sand that most affects cast steel quality, and sand costs are suppressed by using inexpensive furan silica sand for back sand. In addition, the method for regenerating the sand of the skin sand and the back sand is made to correspond to each process. In other words, a water-soluble phenol binder that requires strong regeneration is applied to skin sand that is easily thermally decomposed by the heat of molten steel, and a furan binder that is easy to regenerate is used in places where the back sand is less thermally affected. Furthermore, as an effect of two processes,
The water vapor generated from the water-soluble phenol binder of the skin sand during casting is covered with the back sand of the furan binder which generates less water vapor.

[0008] The "one process and two sand system" shown in FIG. 8 is a system which is not limited to the size of the casting to be applied, and has a relatively good permeability to the base of a water-soluble phenol mold and is available at a low cost. This is the most common method using expensive special sand chromite sand as pocket sand in places where heat is severely affected.

[0007]

As described above, the water-soluble phenol mold is a sand process suitable for improving the quality of a cast steel product in which casting defects are likely to occur, but the existing system has the following problems.

"One process, one sand system" As a sand circulation system, the system shown in FIG. 6 is the simplest closed system, and it is necessary to satisfy all the conditions required for a mold with one sand. There is a problem. In general, sedimentation can be prevented by using fine-grained sand, but there is a concern about gas defects.Small-grained sand can cope with gas defects, but sedimentation is likely to occur. Limited to articles. The water-soluble phenol resin is about 50
% Of water, a large amount of water vapor is generated at the time of casting, and the ceramic sand (cerabies) granulated by current spray drying is a relatively fine-grained sand having a sand particle size of 0.1 to 0.35 mm. is there. Therefore, application of fine-grained ceramic sand to small cast steel products is possible, but application to large cast steel molds is concerned about gas defects due to reduced air permeability, and the ceramic sand is obtained by sintering sand such as chromite sand. There is no function to prevent the molten steel from being inserted, and seizure is likely to occur in places where there is a remarkable thermal effect such that the skin sand is at or above the solidification temperature of the molten steel. The same applies not only to the ceramic sand but also to the silica sand, and the tendency becomes remarkable as the sand particle size increases, so that the applicable range of a single sand is limited to small articles.

[2 Process 2 Sand Method] When water-soluble phenol chromite sand is applied to the skin sand and furan silica sand is applied to the back sand in the manner shown in FIG. 7, the skin sand becomes alkaline and the back sand becomes acidic. Since the reaction form is completely different, it is necessary to provide a "tie" as a measure to separate the sand behind the skin, which takes time for the molding work, and the amount of fresh sand replenishment increases as the amount of expensive chromite sand used for the skin sand increases . In addition, large molds have a large upper mold area, and are likely to drop the skin sand layer due to the resistance of the model to mold removal during molding and the thermal expansion of the skin sand layer due to radiant heat during casting. The range is limited to small and medium products. Furthermore, two processes require two lines of sand kneading equipment, and the installation cost and maintenance of sand treatment equipment including binder supply equipment are disadvantageously high.

[1 Process 2 Sand Method] The method shown in FIG. 8 is a method in which chromite sand is applied as a pocket sand to skin sand that is severely affected by heat, usually using a water-soluble phenol mold based on No. 5 silica sand. This is the most common method that is not limited by size. As disadvantages, there are many problems related to casting quality and sand regeneration, such as crushing of silica sand due to strong sand regeneration, and even if there are some problems, the "1 process 1 sand system" and "2 process 2 sand system" 』
Has been applied, which has hindered the spread of the water-soluble phenol sand process in cast steel products.

The disadvantages of the one-process two-sand system shown in FIG. 8 are as follows. (1) Residual resin of water-soluble phenol sand is sticky. A sticky and hard water-soluble phenol resin solidified by the ester remains in the recovered sand. (2) When the residual resin in the recycled sand is large. Water-soluble phenol sand has the same level of moisture absorption as the residual resin.If there is a large amount of residual resin in the recycled sand, not only will it be difficult to regenerate the sand due to moisture absorption, but it will also be suspended in the sand bin during the rainy season, Troubles such as clogging are likely to occur, and gas defects may occur in casting quality. Water-soluble phenol sand is
The sand strength decreases in proportion to the increase in the amount of residual resin in the recycled sand,
This tendency is greatly accelerated when the sand absorbs moisture. (3) Strong regeneration is required to remove the residual resin from the recovered sand. In order to obtain the required strength of the mold, the water-soluble phenol sand requires about twice as much binder as the conventional furan sand, and the water-soluble phenol sand has a high heat resistance. A large amount of solid resin remains in the recovered sand after the frame, and strong sand regeneration is required to remove the residual resin. Normally, the control value of the residual resin content of the alkali phenol regenerated sand for cast steel is as strict as about 0.5%, which is about half of the conventional control value of the residual resin content of the regenerated furan sand, for the reason of the above item (2). Requires strong regeneration. In general, a sand reclaimer using a rotor type scrubbing method for alkali phenol sand sets twice the energy of furan sand as the high-speed rotation required for strong regeneration, and further controls the residual resin amount of alkali phenol sand. Therefore, multistage regenerators are frequently used to increase the number of reproduction passes. (4) Silica sand is easily crushed by strong sand regeneration, and the working environment deteriorates. When silica sand is used as the base sand, the sand is easily crushed due to strong regeneration, and the yield of sand is deteriorated. This may lead to an increase in sand costs due to an increase in the amount of fresh sand replenishment and a deterioration in the amount of industrial waste due to an increase in crushed sand. Further, the silica sand used for the cast steel mold is required to have a high heat resistance of about SK33, and the SiO ₂ component is generally 95 to 99%.
High purity silica sand is used. Silica sand in contact with the molten steel easily quartz transformation is crushed occurred at 575 ° C. The thermal shock, with concerns pneumoconiosis occurs during sand reclamation, SiO ₂
Due to the high content of silica sand dust, workers need to take measures against silicosis. (5) It is necessary to remove finely crushed silica sand from silica sand.
In order to maintain the sand particle size of the system sand, it is necessary to provide a sieve, a fluidized tank and the like after the sand regenerating device to remove crushed silica sand by strong sand regenerating. (6) An expensive and powerful magnetic separator is required to separate silica sand and chromite sand. In recovering a part of chromite sand from silica sand used in large quantities as base sand, silica sand and chromite sand are mixed in a large particle size distribution. A simple magnetic separator is used. In this case, the magnetic separator requires a large processing capacity to process the entire system sand, and is a large and expensive facility. (7) There is a limit to the improvement of casting quality with the current silica sand. When silica sand is reused for a long time, low-melting molten silicate (FeSi ₂ ) is generated by reaction with molten steel, which may cause gas defects and burning. The application of silica sand for casting steel molds is almost limited by physical properties such as particle size, shape, components, etc., and commonly available silica sand is commonly used. Particle size index of No. 5 silica sand is AFS 30-40 and air permeability 500-
It is 900, and it is necessary to perform degassing on a complicated core of a large mold due to insufficient air permeability of the mold, and the mold becomes complicated. When seeking a higher-grade cast steel product, it is necessary to improve the air permeability, the amount of thermal expansion, the fire resistance, etc. as the mold shape, but as long as the silica sand is used, significant improvement of the mold by the raw material sand cannot be expected. .

The above items (6) and (7) also apply to the two-process two-sand system.

[0013] For the self-hardening mold for cast steel, many things are desired in terms of moldability, applicability of casting size, cast steel quality, sand recyclability and the like. As a result, it has hindered the spread of the water-soluble phenol sand process for cast steel. The present invention seeks to provide a self-hardening mold for cast steel and a method for reclaiming foundry sand, which can improve the "one process and two sand system" which is the most practical and can solve the problems of the conventional system. Is what you do.

[0014]

The present invention takes the following measures. (1) A self-hardening mold for cast steel according to the present invention is a self-hardening mold for cast steel using a one-process two-sand method, wherein a water-soluble phenol resin and a hardening agent are used as a binder, and a particle diameter is zero in a base sand of molding sand. Knoop hardness of sand grains with ceramic sands more than 900 particle shape coefficient number 1.1 mullite following spherical particle shape in .5～1.5Mm, chromite sand pocket sand used in thermally severe skin sand Chromite sand having a particle size of less than 0.5 mm, which can be sieved with the ceramic sand, is used. (2) Further, the method for reclaiming foundry sand of the present invention comprises the steps of:
In regenerating alkali phenol recovered sand using chromite sand having a particle size of less than 0.5 mm as a pocket sand, using a strong scrubbing type regenerator with a high-speed rotating rotor, the residual resin of the coarse-grained ceramic sand and chromite sand was used. While removing iron from the iron beads precipitated on the surface of the chromite sand, classifying both sands with a vibrating sieve, reusing coarse particles on the sieve as regenerated ceramic sand, and fine particles under the sieve. By using a magnetic separator of 20,000 gauss or more, the medium magnetic substance, the ferromagnetic substance such as iron, and the non-magnetic substance, such as runner brick debris, that have precipitated the iron beads are removed, and the chromite sand, which is a weak magnetic substance, is removed. It is characterized by taking out and reusing.

[0015]

The self-hardening mold for cast steel according to the present invention (1) is a water-soluble phenol mold using a water-soluble phenol and a hardening agent as a binder. It is a simple mold configuration using sand and chromite sand, and the following improvements in cast steel quality are achieved.

The action of the resin. The water-soluble phenol resin is primarily solidified by a neutralization reaction by an organic ester as a curing agent, and is further polymerized and cured by heat at the time of casting to be secondarily solidified. In addition, since the water-soluble phenol resin has a benzene ring and is easily carbon-bonded by heat, it can be expected to form a mold having high heat resistance to reduce baking and reduce sand biting due to washing of sand. In addition, since the binder using a water-soluble phenol and a curing agent does not contain sulfur, it is difficult to generate hot cracks, and since it does not contain nitrogen, gas defects related to nitrogen can be prevented.

The action of chromite sand. As special sand, by applying chromite sand as pocket sand to skin sand in thermally severe places where the mold temperature of the core and outer corners is 900 ° C or higher, for example.
In the chromite sand surface layer that comes into contact with molten steel, chromite sand having a spinel structure [(Fe, M
g) From O. (Fe, Cr, Al) ₂ O ₃ ], an iron component is reduced and precipitated on the sand surface. This phenomenon is caused by a reduction reaction caused by high heat at the time of receiving hot water, and iron contained in about 25 to 29% in chromite sand precipitates on the chromite sand surface in the form of sweat having a particle diameter of 2 to 20 μm as metal Fe, and is usually iron. Precipitates called beads are seen. In addition, in chromite sand that has been significantly affected by heat for a long time, a large amount of iron beads are connected to each other to have a particle size of less than 0.5 mm (average particle size of 150 to
Chromite sand surface of 5-10μ
Covered with thick iron coating. This iron coating forms the sand surface in a bead shape and is called an iron bead. At the time of casting, inter-grain sintering occurs due to the precipitates from the chromite sand, and the outermost surface layer of the chromite sand in contact with the molten steel forms a solid mold wall, thereby suppressing penetration of the molten steel and preventing seizure. In addition, these precipitates reduce the porosity between chromite sand grains in the outermost surface layer of the skin sand, suppress the gas pressure from the back of the sand to the molten steel to some extent, and also have the effect of reducing gas defects.

The action of ceramic sand. As the base sand, coarse ceramic sand granulated by a pelletizer is applied. The ceramic sand is obtained by pulverizing and mixing kaolin raw material and alumina raw material, granulating them into a spherical shape with a pelletizer, and then firing at high temperature in a kiln to form mullite, which has a small thermal expansion and good crush resistance without a thermal transformation point. The molten silicate (FeS), which causes gas defects and seizure by reaction with molten steel like silica sand
i ₂ ) is less likely to occur. As the particle size setting of ceramic sand, "coarse particles that can be screened for chromite sand""Sand particle size showing normal distribution and low coefficient of thermal expansion Preferably, by using the coarse-grained ceramic sand having a particle size of less than 0.5 mm as a base sand so that it can be sieved with the chromite sand having a particle size of less than 0.5 mm, the combustion gas from the mold skin sand with which molten steel comes into contact. In addition to reducing gas defects by preventing gas entering the molten steel by leaking water vapor backward, it is possible to obtain a cast steel product with high dimensional accuracy by using a mold with high fire resistance, low expansion and little thermal deformation. It is possible.

Synergy between resin and sand. By using a hardener such as the water-soluble phenolic resin and an organic ester as a binder, a coarse-grained ceramic sand as a base of a refractory granular aggregate, and chromite sand as a pocket sand at a location where heat influence is remarkable, a high-grade cast steel product A mold having a low expansion, a high air permeability and a high heat resistance required for the production of is manufactured.

The method for reclaiming molding sand of the present invention (2) has the following effects.

Regeneration of sand is easy. By using high hardness ceramic sand and chromite sand as the mold base material, the pair of mixed and recovered sand can be regenerated by removing the residual resin with a powerful scrubbing type regenerator using a high-speed rotating rotor. . In addition, iron beads and solid iron beads are formed on the surface of chromite sand that is significantly affected by heat,
Of these, the iron beads are generated in the form of sweat on the surface of the chromite sand, and most of them can be removed by the strong sand regeneration at the time of removing the residual resin.

[0022] Classification of ceramic sand and chromite sand is easy. The base coarse ceramic sand and the special sand chromite sand
As described above, there is a difference in the particle size of the sand, and the difference in the particle size of the sand enables classification with a simple vibration screen. The coarse-grained ceramic sand classified by the sieve can be reused as it is, and the fine-grained sand mainly contains chromite sand.

[0023] Removal of impurities in chromite sand is possible with a small magnetic separator. The composition of the fine sand classified by sieve is as shown below. Non-magnetic material: crushed runner sleeve that cannot be reused, crushed ceramic sand, resin separated from the sand surface Weak magnetic material: good chromite sand that is mainly composed of fine-grained sand, has relatively little heat effect, and has not been altered Chromite sand that can be reused by removing iron beads Medium magnetic material: Chromite sand that is difficult to reuse with solid iron beads on the sand surface layer Ferromagnetic material: Sand particles with molten steel attached, chromite sand surface when sand is recycled Iron components such as iron beads, hot water balls, and fine cast burrs which are more separated The weak magnetic material that is the main component of the fine-grained sand is sorted and reused by a powerful magnetic separator of 20,000 gauss or more. In addition,
At this time, the capacity of the magnetic separator can be small enough to process the applied chromite sand.

Further, the following effects can be obtained by the self-hardening mold for cast steel of the present invention (1) and the method for reclaiming molding sand of the present invention (2).

Reduction of Waste Sand By applying the above-mentioned ceramic sand to the base sand of the mold, it becomes possible to remove firm residual resin by strong regeneration, and to minimize the fineness of the sand and reduce the yield. Improvement and reduction of waste sand volume can be realized.

Reduction of Dust The ceramic sand coarser than the silica sand used in the present invention, unlike silica sand, is hard to crush and improves pneumoconiosis to sand treatment operators. In addition, silicosis can be prevented with ceramic sand mainly composed of mullite containing no free silicic acid.

[0027]

Embodiments of the present invention will be described below. First, as a survey of the gas composition from the mold that has a large effect on the quality of molten steel, as shown in Table 1, using Iwami No. 5 silica sand as raw material sand, a survey was performed on the generated gas composition of furan binder and water-soluble phenol binder. It was confirmed that there was no sulfur or nitrogen gas component in the gas composition from the water-soluble phenol sand.

[0028]

[Table 1]

For the ceramic sand, three types of particles A, B and C having a particle size distribution shown in FIG. 1 were examined as particle sizes which can be separated from chromite and sieve. First, when selecting the particle size of the ceramic sand, as shown in Table 2, the air permeability of the comparative ceramic sands B and C was significantly higher than that of Iwami No. 5 silica sand, but the kneading sand strength was inferior and hindered the molding surface. B, C
Has a large average particle size and is considered to be difficult to apply due to concerns about infiltration type baking.

[0030]

[Table 2]

As shown in Tables 2 and 3, ceramic sand A has a higher fire resistance, grain shape, hardness, air permeability, and
Excellent rapid thermal expansion. In addition, the inferiority to Iwami No. 5 silica sand is that the kneading sand strength is slightly lower and the average particle size is as large as 1.4 times, so it is necessary to pay attention to infiltration baking, and FIG . 3 cast by the mold shown in FIG. The seizure resistance was investigated using the test pieces shown in Table 4 and the results shown in Table 4 were obtained.

[0032]

[Table 3]

[0033]

[Table 4]

According to Table 4, the seizure resistance of the ceramic sand A is not much different from that of Iwami No. 5 silica sand. Results were obtained. This indicates that despite the fact that the grain size is larger than Iwami No. 5 silica sand, the amount of rapid thermal expansion of the ceramic sand A is small, so the movement of the outermost skin sand layer is very small, and the coating layer is hardly destroyed. It is presumed that the results shown in the above were obtained.

FIG. 4 shows an example of application to an actual product based on the test results .
Shown in FIG. 4 is a cross-sectional view of a cast steel mold of a compressor casing. A water-soluble phenol resin and a hardening agent are used as a binder, and the refractory granular aggregate used as a molding sand is made of chromite sand shown in Tables 1 and 2. Using ceramic sand A,
A coating material is used on the outermost surface of the sand in contact with the molten steel.

FIG. 4 is a sectional view of a cast steel mold of a compressor casing according to an embodiment of the present invention, wherein 1 is a casting frame, 2 is a platen, 3 is a mold space, 4 is a feeder, and 4-a is Heater sleeve, 5 is a runner, 5-a is a runner sleeve, 6 is an outer mold, 6
-A indicates an outer mold sand flat surface part, 6-b indicates an outer mold sand convex part, 7 indicates a core, 8 indicates ceramic sand, and 9 indicates chromite sand.

Outer skin sand protrusion 6-b of a mold severely affected by heat
Chromite sand 9 having good seizure resistance is used for about 10% of the total sand for the skin sand of the core 7 and the outer mold sand plane 6-a and the outer mold 6 and the core 7 which are not severely affected by heat. As the back sand, ceramic sand 8 is used as a base sand. The molten steel enters the mold space 3 via the runner 4 and is poured up to the feeder 4. Due to the good air permeability of the ceramic sand 8, the gas vent of the core 7 is eliminated and the simple molten steel is removed. A low-expansion mold having low air-expansion and being a mold with air permeability could be realized.

The self-hardening mold for cast steel shown in FIG. 4 uses a water-soluble phenol resin and a hardening agent as a binder, and has a particle size of 0.5 mm to 1.5 mm as a base sand of molding sand. Knoop hardness of sand using a ceramic sand over 900 particle shape coefficient number 1.1 mullite following spherical particle form, chromite sand pocket sand used in thermally severe skin sand, the ceramic sand and sieve This is a one-process two-sand mold using chromite sand having a particle size that can be divided and having a particle size of less than 0.5 mm.

FIG. 5 shows a method for reclaiming foundry sand according to an embodiment of the present invention, and is a flow diagram of a one-process two-sand system and is an explanatory view of a sand circulation system mainly for reclaiming sand.
In this embodiment, cast steel is poured into a water-soluble phenol mold using chromite sand and ceramic sand A shown in Tables 1 and 2, and after the unsealed sand is collected, the following regeneration is performed.

As an apparatus for reclaiming cracked sand, water-soluble alkali phenol recovered sand (residual resin amount: 1.4%) in which chromite sand is partially mixed with ceramic sand is used.
A powerful scrubbing type regenerator with a high-speed rotating rotor of sec is used. Residual resin removal rate per pass is 23
２５25% / pass, and as the number of passes increases, the residual resin in the recovered sand is removed, and the target control value becomes 0.5% of the target control value in 4 passes.

Ceramic sand having a high sand hardness and a good grain shape is such that the sand surface is slightly polished and removed by sand regeneration.
The reproduction yield showed a remarkably good value of 0.6%. In the case of chromite sand, if the corners of the sand grains are removed to some extent, the sand hardness is high, so that a stable particle size distribution can be obtained without limitless fineness. In addition, when the process of removing the iron beads on the chromite sand surface was investigated with a scanning electron microscope,
It was confirmed that the resin could be almost removed in four passes within the control value of the residual resin. Iron beads on the surface of chromite sand which were significantly affected by heat were found to remain without being removed by strong regeneration. In addition, the residual resin polished from the sand in the sand regeneration, the iron beads of 2 to 20 μm and the sand polishing powder were removed as much as possible from the duct provided with the regeneration device.

The ceramic sand and the chromite sand used in the present embodiment are 35 mesh having an opening size of 0.5 mm.
The pair of sands was classified using a vibrating sieve. The coarse particles of 0.5 mm or more remaining on the sieve are recycled ceramic sand that can be reused, and the fine sand of less than 0.5 mm that has passed through the sieve accounts for 12% of the total sand amount.

The fine-grained sand that has passed through the above-mentioned 35 mesh vibrating sieve is separated by a 20,000 gauss two-stage roll type magnetic separator according to the strength of the magnetism. At this time, a small-sized machine that processes about 15% of the total sand amount is used as the magnetic separator. First, the upper magnetic separator separates the non-magnetic material and the magnetic material to take out the magnetic material, and the lower magnetic separator, among the magnetic materials, is an effective weak magnetic material with relatively little heat influence and has not been altered Good chromite sand and reusable chromite sand without iron beads are removed. In addition, for the medium magnetic material, chromite sand, which is hard to reuse due to the formation of solid iron beads on the sand surface layer, sand particles with molten steel of ferromagnetic material, and some irons separated from the chromite sand surface by sand regeneration It is iron, such as beads, hot water balls, and fine cast burrs, and is removed by a magnetic separator as an object to be removed. The composition ratio of the fine-grained sand subjected to magnetic separation is 9% for non-magnetic material, 74% for weak magnetic material, and 17% for medium magnetic material and ferromagnetic material.

As a result of the regeneration, the yield of fresh sand was 0.6% for ceramic sand and 19% for chromite sand. Yield when used as a system sand for a long time is approximately 2% with ceramic sand, adding loss such as adhesion of castings.
It is estimated to be about 30% for chromite sand, and it is possible to greatly reduce industrial waste. Ceramic sand and chromite sand both have high sand hardness and are not easily crushed. They greatly reduce dust during framing, which is the most problematic problem in foundries, and can also be used with ceramic sand and chromite that do not contain free silicic acid (SiO ₂ ). Sand can prevent silicosis.

[0045]

As described above, the self-hardening mold for cast steel using the one-process and two-sand method of the present invention is as described above.
In a water-soluble phenol mold for cast steel using a water-soluble phenol resin and a hardener, a particle diameter of 0.5 to 1.
5 mm, high hardness spherical ceramic sand having a Knoop hardness of 900 or more is used, and chromite sand having a particle size of less than 0.5 mm, which can be sieved with the ceramic sand, is used as a pocket sand, and the following effects are obtained. be able to. (1) The gas from the mold at the time of casting with a water-soluble phenol resin and a binder does not contain harmful components of sulfur which is a main cause of hot cracking and nitrogen which is a cause of gas defects. (2) By using chromite sand as pocket sand for skin sand in places where the heat effect of the mold is remarkable, intergranular sintering occurs due to iron components reduced and precipitated from chromite, thereby preventing penetration of molten steel and preventing seizure. (3) By applying mullite ceramic sand to the base sand, a low expansion mold is realized, and molten silicate, which is a reaction product with molten steel, is hardly generated. (4) By using coarse-grained ceramic sand, degassing is unnecessary and a simple high-permeability mold can be obtained.

The method for reclaiming foundry sand of the present invention has the following effects. (1) High-hardness ceramic sand and chromite sand can suppress sand crushing by strong scrubbing to increase the yield of sand, reduce the amount of fresh sand and reduce the amount of waste sand, and prevent pneumoconiosis and silicosis. . (2) Classification can be performed with a simple sieve using coarse-grained ceramic sand and chromite sand, and chromite sand can be collected with an inexpensive small-sized magnetic separator.

As a result, according to the present invention, the water-soluble phenol sand process can be used for cast steel by a new one-process two-sand system, and it is possible to realize a large-sized high-grade cast steel product suitable for the times.

[Brief description of the drawings]

FIG. 1 is a particle size distribution diagram of raw material sand studied in an example of the present invention.

FIG. 2 is a cross-sectional view of a test piece mold for a baking test.

FIG. 3 is a perspective view of a baking test piece.

FIG. 4 is a sectional view of a cast steel mold of a compressor casing according to the embodiment of the present invention.

FIG. 5 is a flowchart showing a one-process two-sand system showing a method for reclaiming foundry sand according to an embodiment of the present invention.

FIG. 6 is a flowchart showing a conventional one-process-one-sand method.

FIG. 7 is a flowchart showing a conventional two-process two-sand system.

FIG. 8 is a flowchart showing a conventional one-process two-sand system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting frame 2 Surface plate 3 Mold space part 4 Feeder 4-a Feeder heat insulating sleeve 5 Runner 5-a Runner sleeve 6 Outer mold 6-a Outer skin sand plan view 6-b Outer skin sand convex part 7 Core 8 Ceramic sand 9 Chromite sand

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22C 1/22 B22C 1/00 B22C 5/00 B22C 9/02 103

Claims (2)

(57) [Claims] 1. A self-hardening mold for cast steel using a one-process two-sand system, wherein a water-soluble phenol resin and a hardening agent are used as a binder, and a base sand of molding sand has a particle size of 0.5.
Knoop hardness of sand grains with ceramic sands more than 900 particle shape coefficient number 1.1 mullite following spherical particle shape with 1.5 mm, said the chromite sand pocket sand used in thermally severe skin sand 0.5 that can be separated from ceramic sand
A self-hardening mold for cast steel, characterized by using chromite sand having a particle size of less than mm. 2. The base sand having a particle size of 0.5 to 1.
Particle size of 0. 5mm ceramic sand and pocket sand.
In regenerating alkali phenol recovered sand using chromite sand of less than 5 mm, while removing the residual resin of the coarse-grained ceramic sand and chromite sand using a strong scrubbing type regenerator with a high-speed rotating rotor, The iron content of the iron beads deposited on the surface is removed, both sands are classified by a vibrating sieve, the coarse particles on the sieve are reused as regenerated ceramic sand, and the fine particles under the sieve are magnetic separators of 20,000 gauss or more. Thus, a medium magnetic substance that has precipitated an iron bead, a ferromagnetic substance such as iron,
And a method for reclaiming foundry sand, comprising removing non-magnetic runner brick debris and the like, extracting and reusing chromite sand, which is a weak magnetic substance.