JPH0890150A - Self-curing mold for cast steel and method for regenerating molding sand - Google Patents

Abstract

PURPOSE: To prevent the generation of harmful components from self-curing molds for cast steels, to prevent the burn of molten steel and to effectively regenerate and recover molding sand from this kind of the casting molds. CONSTITUTION: A water-soluble phenolic resin and a hardener are used for the binder of the self-curing molds for cast steels for which a one-process two- sand system is used. Mullite base ceramic sand 8 of spherical grain shapes having grain size of 0.5 to 1.5mm, Knoop hardness of sand grains of >=900 and a grain size constant of <=1.1 is used for the base sand thereof. Chromite sand 9 of a grain size of <0.5mm which can be sieved from the ceramic sand 8 is used for the chromite sand 9 of pocket sand to be used for the thermally severe facing sand. Such molding sand is subjected to removal of the residual resins by a regenerating machine of a scrubbing system by a high-speed revolving rotor. The iron-components of iron beads are simultaneously removed and are classified by a vibration sieve. The coarse grains are reused as ceramic sand and the fine grains of minus sieve are reused by taking out the chromite sand which is a weakly magnetic material by a magnetic separator.

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 and a method for reclaiming foundry sand, which uses a 1-process 2-sand system in a foundry.

[0002]

2. Description of the Related Art In recent years, a water-soluble phenol sand process has become widespread as a next-generation furan sand process for self-hardening molds for cast steel. The water-soluble phenol sand process uses a water-soluble phenol resin as a binder as a binder and an organic ester as a curing agent, the binder does not contain sulfur and nitrogen harmful to castings, and the water-soluble phenol is mixed with the binder. Phenolic sand has advantages such as a mold with higher heat resistance and thermoplasticity than conventional furan sand, and is a new sand process that reduces hot cracking of cast steel products, casting defects such as gas and inclusions. With the same binder,
It is expected that the application will be expanded due to the progress of low price and high strength products year by year.

As a method of applying the water-soluble phenol sand process to a casting steel mold, "1 process 1 sand system", "2 process 2 sand system", and "1 process 2 sand method"
Is used, and the flow of each method is shown in FIG. 6, FIG. 7 and FIG.
Shown in

In the "1 process 1 sand method" shown in FIG. 6, a water-soluble phenol mold is used as a relatively fine particle of ceramic sand (trade name; Cera beads, spray-dried granulated and kiln-fired relatively fine particle, and high). By constructing a single sand of spherical mullite sand with hardness, the sand processing equipment in the sand kneading, recovery, regeneration and supply system is simplified and the molding work is mechanized. Also, due to the good crush resistance of ceramic sand, it is possible to prevent the sand from becoming fine-grained due to strong sand regeneration, to reduce the waste sand of the casting, to stabilize the sand quality, and to realize a low thermal expansion mold.

In the "2 process 2 sand method" shown in FIG. 7, a chromite sand is used as a mold skin sand, a water-soluble phenol resin and an organic ester are used as a binder, and a furan resin and a sulfonic acid are applied to silica sand as a back sand. . The characteristics of this method are that water-soluble phenol chromite sand is used for the skin sand that most affects the quality of cast steel to prevent casting defects, and cheap furan silica sand is used for the back sand to reduce sand costs. In addition, the sand reclaiming method for the skin sand and the back sand is adapted to each process. In other words, the water-soluble phenol binder, which requires strong regeneration, is applied to skin sand that is easily thermally decomposed by the heat effect of molten steel, and the furan binder, which is easily regenerated, is used in areas where the back sand has little heat effect. Furthermore, as an effect of two processes,
The steam generated from the water-soluble phenol binder of the skin sand at the time of casting is covered by the back sand of the furan binder, which generates less steam.

The "1 process 2 sand method" shown in FIG. 8 is a method which is not limited to the size of the casting to be applied, and has a relatively good air permeability to the base of the water-soluble phenol mold and is available at low cost. Is the most common method using chromite sand, which is expensive special sand, as a pocket sand at locations where heat is severely affected.

[0007]

As described above, the water-soluble phenol mold is a sand process suitable for improving the quality of cast steel products that are prone to casting defects, but the existing methods have the following problems.

"1 process 1 sand system" The system shown in FIG. 6 is the simplest closed system for the sand circulation system, and it is necessary to satisfy all the conditions required for the mold with 1 sand. There is a problem. Generally, using fine-grained sand can prevent seizure, but there is a concern of gas defects. With fine-grained sand, gas defects can be dealt with, but seizure easily occurs, and the applicable range is small heat capacity and quick solidification. Limited to goods. In addition, the water-soluble phenolic resin is about 50
% Of water, large amount of water vapor is generated at the time of pouring, and the current spray-dried ceramic sand (Cera beads) is a relatively fine-grained sand with a sand particle size of 0.1 to 0.35 mm. is there. Therefore, although it is possible to apply fine-grained ceramic sand to small cast steel products, application to large cast steel molds may cause gas defects due to reduced air permeability, and the ceramic sand is due to sintering of sand such as chromite sand. There is no function for preventing molten steel from being inserted, and seizure is likely to occur at locations where heat effect is significant, such as skin sand above the solidification temperature of molten steel. The same applies to silica sand as well as to ceramic sand, and the tendency becomes more remarkable as the particle size of sand increases, so the range of application of single sand is limited to small articles.

[2 process 2 sand method] When water-soluble phenol chromite sand is applied to the skin and furan silica sand is applied to the back sand by the method 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 countermeasure for the separation of the sand on the back of the skin, and it takes time for molding work, and the amount of new sand replenished increases as the amount of expensive chromite sand used for skin sand increases. . In addition, the area of the upper mold is large in a large mold, and there is concern that the mold removal resistance of the model during molding and the thermal expansion of the skin sand layer due to the radiant heat during casting may cause the skin sand layer to fall, which is a problem in terms of productivity. The range is limited to small and medium products. Further, since there are two processes, two series of sand kneading equipments are required, and there is a drawback that the installation cost and maintenance of the sand treatment equipment including the binder supply equipment become high.

"1 process 2 sand system" The system shown in FIG. 8 is usually a water-soluble phenol mold based on No. 5 silica sand, and chromite sand is applied as pocket sand to heat-affected skin sand, It is the most general method that is not limited by size. As a drawback, there are various problems related to casting quality and sand reclamation, such as crushing of silica sand due to strong sand reclamation. Even if there are some problems, the "1 process 1 sand method" and "2 process 2 sand method" are available. ]
Has been applied to prevent the spread of the water-soluble phenol sand process to cast steel products.

The disadvantages of the one-process, two-sand method shown in FIG. 8 are as follows. (1) The residual resin of water-soluble phenol sand is tenacious. In the recovered sand, a viscous, tough and water-soluble phenolic resin solidified with ester remains. (2) When there is a large amount of residual resin in the recycled sand. Water-soluble phenolic sand has a moisture absorption capacity similar to that of residual resin, and if there is a large amount of residual resin in the reclaimed sand, not only will sand reproduction be difficult due to moisture absorption, but also it will be suspended from the sand bin during the rainy season, and it will Trouble such as clogging is likely to occur, and there is concern about gas defects in terms of casting quality. In addition, water-soluble phenol sand
The sand strength decreases in proportion to the increase in the amount of residual resin in recycled sand,
This tendency is significantly accelerated when the sand absorbs moisture. (3) Powerful regeneration is required to remove the residual resin in the recovered sand. In order to obtain the required strength of the mold, water-soluble phenolic sand requires about twice as much binder as conventional furan sand, and water-soluble phenolic 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 residual resin amount control value of alkali phenol regenerated sand for cast steel is about 0.5%, which is half of the conventional furan reclaimed sand residual resin amount control value, which is strict due to the reason in the above item (2), and residual resin is removed. Requires strong regeneration. Generally, in sand regenerators that use a rotor-type scrubbing method for alkaline phenol sand, double the energy for furan sand is set as the high-speed rotation required for strong regeneration, and the residual resin amount control value for alkaline phenol sand is set. Because of low and severe, multistage regenerators are often used to increase the number of regeneration 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, crushing of the sand easily occurs due to strong regeneration, and the yield of the sand deteriorates. This may raise the sand cost due to the increase in the amount of new sand replenishment, and may worsen the amount of industrial waste due to the 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, it is necessary for workers to take measures against silicosis. (5) It is necessary to remove fine-grain crushed silica sand from the silica sand.
In order to maintain the sand grain size of the system sand, it is necessary to install a sieve, a fluid tank, etc. after the sand reclamation device to remove the crushed silica sand by powerful sand reclamation. (6) An expensive and powerful magnetic separator is required to separate silica sand and chromite sand. When recovering a part of chromite sand from a large amount of silica sand used as the base sand, silica sand and chromite sand are mixed in a large particle size distribution, which makes it difficult to classify with a sieve and has a strength of 20,000 gauss or more. A magnetic separator is used. The magnetic separator in this case 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 by the existing silica sand. When silica sand is reused for a long time, a molten steel silicate (FeSi ₂ ) having a low melting point is generated due to a reaction with molten steel, which may cause gas defects and seizure. The application of silica sand for casting steel molds is almost limited by the physical properties such as particle size, shape, composition, etc., and generally available silica sand No. 5 is often used. No. 5 silica sand has a particle size index of AFS 30-40 and air permeability of 500-
Since it is 900, it is necessary to degas the complex core of a large mold due to insufficient air permeability of the mold, which complicates the mold. When a higher grade cast steel product is sought, 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 method.

Although many self-hardening molds for cast steel are desired in terms of moldability, cast size applicability, cast steel quality, sand reclaimability, etc., the above-mentioned three conventional methods have the above-mentioned drawbacks. Accordingly, it has hindered the spread of the water-soluble phenol sand process for cast steel. The present invention intends to provide a self-hardening mold for casting steel and a method for reclaiming casting sand, which can solve the problems of the above-mentioned conventional methods by improving the "1 process 2 sand method" which is the most practically applicable. To do.

[0014]

The present invention has taken the following means. (1) The self-hardening mold for cast steel of the present invention is a self-hardening mold for cast steel using a 1-process, 2-sand method, in which a water-soluble phenolic resin and a curing agent are used as a binder, and the particle diameter of the base sand of the foundry sand is 0. Chromite sand, which is a pocket sand used for thermally severe skin sand, is made of spherical mullite ceramic sand having a Knoop hardness of 900 to 1.5 mm and a grain size of 1.1 or less. It is characterized by using chromite sand having a particle size of less than 0.5 mm, which can be separated from ceramic sand by screening. (2) Further, the method for reclaiming foundry sand of the present invention comprises: ceramic sand having a particle size of 0.5 to 1.5 mm as a base sand;
When regenerating the alkali phenol recovered sand using chromite sand with a particle size of less than 0.5 mm as the pocket sand, a strong scrubbing type regenerator with a high-speed rotating rotor was used to remove the residual resin of the coarse-grained ceramic sand and chromite sand. In addition to removing iron, iron particles of iron beads deposited on the surface of chromite sand were classified, and both sands were classified by a vibrating sieve.The coarse particles on the sieve were reused as regenerated ceramic sand, and the fine particles under the sieve were fined. Uses a magnetic separator of 20000 Gauss or more to remove medium magnetic material that is precipitating iron beads, ferromagnetic material such as iron, and non-magnetic material such as runner brick scraps, and remove chromite sand that is a weak magnetic material. The feature is that it is taken out and reused.

[0015]

The self-hardening mold for cast steel according to the present invention (1) is a water-soluble phenol mold using water-soluble phenol and a hardening agent as a binder, and a coarse-grained ceramic as a refractory granular aggregate used as foundry sand. This is a simple mold composition using sand and chromite sand, which results in the following improvements in cast steel quality.

The action of the resin. The water-soluble phenol resin is first solidified by the neutralization reaction by the organic ester of the curing agent, and further polymerized and cured by the heat at the time of casting to be secondarily solidified. Further, since the water-soluble phenol resin has a benzene ring and is easily carbon-bonded by heat, it is expected that a mold having high heat resistance is formed to reduce seizure and sand trapping due to sand washing. Further, since the binder using the water-soluble phenol and the curing agent does not contain sulfur, hot cracking hardly occurs, and since it does not contain nitrogen, gas defects related to nitrogen can be prevented.

The action of chromite sand. As a special sand, by applying chromite sand as pocket sand to skin sand at locations where the mold temperature of the core and outer mold corners is 900 ° C. or higher, for example, it is a pocket sand.
In the chromite sand surface layer in contact with molten steel, the chromite sand [(Fe, M
g) Iron components are reduced and precipitated on the sand surface from O. (Fe, Cr, Al) ₂ O ₃ ]. This phenomenon occurs because the iron content contained in the chromite sand in the extent of 25-29% due to the reduction reaction due to the high heat at the time of receiving hot water is deposited on the chromite sand surface as metallic Fe in the state of sweat having a particle size of 2 to 20 μm, and is usually iron. Precipitates called beads are visible. Also, in chromite sand that has been significantly affected by heat for a long time, a large number of iron beads are connected to each other and the particle size is less than 0.5 mm (average particle size 150-
Chromite sand surface of (350μ is desirable) 5-10μ
Cover with a thick iron coating. This iron coating forms a bead shape on the sand surface and is called an iron bead. During casting, intergranular sintering occurs due to the above-mentioned precipitates from chromite sand, and the outermost surface layer of chromite sand that comes into contact with molten steel forms a solid mold wall, which suppresses penetration of molten steel and prevents seizure. At the same time, these precipitates reduce the porosity between the chromite sand grains in the outermost surface layer of skin sand, suppress the gas pressure from the rear of the skin sand to the molten steel to some extent, and have the effect of reducing gas defects.

The action of ceramic sand. As the base sand, coarse-grained ceramic sand granulated with a pelletizer is applied. The ceramic sand is crushed and mixed with a kaolinic raw material and an alumina raw material, pelletized into a spherical shape with a pelletizer, and then fired at a high temperature in a kiln to form a mullite. It is a fine ceramic sand, and like fused silica, it causes gas defects and seizure due to the reaction with molten steel.
i ₂ ) is unlikely to occur. As the grain size setting of ceramic sand, "coarse grains that can be sorted by chromite sand""Sand grain size with normal distribution, low thermal expansion coefficient, and seizure resistance against infiltration type seizure like No. 5 silica sand It is preferable that the chromite sand having a particle size of less than 0.5 mm and the above-mentioned coarse-grained ceramic sand that can be sieved are used as the base sand, so that the combustion gas from the mold surface sand that the molten steel comes into contact with Also, by letting water vapor escape backwards, gas that enters the molten steel is prevented as much as possible to reduce gas defects, and a cast steel product with high dimensional accuracy can be obtained by a mold with high fire resistance, low expansion and little thermal deformation. It is possible.

Synergy of resin and sand. By using the water-soluble phenolic resin and a curing agent such as an organic ester as a binder, and applying coarse ceramic sand to the base of the refractory granular aggregate and chromite sand as the pocket sand where the heat effect is significant, high-grade cast steel products A mold having low expansion, high air permeability, and high heat resistance, which is necessary for the production of, is constructed.

Further, the method (2) of the present invention for reclaiming foundry sand has the following effects.

Easy to regenerate sand. By using high hardness ceramic sand and chromite sand as the mold base material, it is possible to regenerate the pair of mixed and recovered sands by removing the residual resin with a powerful scrubbing type regenerator using a high-speed rotating rotor. . Iron beads and solid iron beads are formed on the surface of chromite sand that has been significantly affected by heat.
Of these, 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.

Easy classification of ceramic sand and chromite sand. Coarse-grained ceramic sand of base and chromite sand of special sand are
As described above, there is a difference in sand particle size, and this difference in sand particle size enables classification with a simple vibration screen. This sieve-classified coarse-grained ceramic sand can be reused as it is, and the fine-grained sand mainly contains chromite sand.

Impurities in chromite sand can be removed with a small magnetic separator. The composition of the sieve-classified fine sand is as shown below. Non-magnetic material: crushed runner sleeve that cannot be reused, crushed ceramic sand, resin exfoliated from the sand surface Weak magnetic material: Mainly composed of fine-grained sand, good chromite sand that is relatively unaffected by heat and has not deteriorated, and Chromite sand that can be reused after removing iron beads Medium magnetic material: chromite sand that is hard to reuse with solid iron beads in the sand surface layer Ferromagnetic material: Sand particles with molten steel attached, chromite sand surface by sand regeneration Iron components such as more separated iron beads, hot water balls, and fine cast burrs The weak magnetic material, which is the main component of the fine-grained sand, is selected by a strong magnetic separator of 20,000 gauss or more and reused. In addition,
At this time, the capacity of the magnetic separator can be small enough to process the applicable chromite sand.

Furthermore, the following effects are exhibited by the self-hardening mold for cast steel according to the present invention (1) and the method for reclaiming foundry sand according to the present invention (2).

Reduction of Waste Sand By applying the ceramic sand as described above to the base sand of the mold, it becomes possible to remove the solid residual resin by strong regeneration, and to minimize the grain refinement of the sand to improve the yield. Improvement and reduction of waste sand amount can be realized.

Reduction of Dust Dust, which is coarser than silica sand used in the present invention, is unlikely to be crushed unlike silica sand, which improves the pneumoconiosis to sand processing operators. Further, silicosis can be prevented by using ceramic sand whose main component is mullite containing no free silicic acid.

[0027]

EXAMPLES Examples of the present invention will be described below. First, as shown in Table 1, Iwami No. 5 silica sand was used as raw material sand to investigate the gas composition of the furan binder and the water-soluble phenol binder, as shown in Table 1, It was confirmed that the gas composition from the water-soluble phenol sand had no sulfur and nitrogen gas components.

[0028]

[Table 1]

As the ceramic sand, three types of particle sizes A, B, and C having the particle size distribution shown in FIG. 1 were examined as the particle sizes capable of separating chromite and sieve. First, in selecting the particle size of the ceramic sand, as shown in Table 2, the air permeability of the comparative ceramic sands B and C is significantly higher than that of Iwami No. 5 silica sand, but the kneading sand strength is inferior and the molding surface is hindered. B, C
It was judged that it was difficult to apply because of the large average particle size and concern about penetration type seizure.

[0030]

[Table 2]

As shown in Tables 2 and 3, the ceramic sand A has a fire resistance, a grain shape, a hardness, an air permeability, which are higher than those of Iwami No. 5 silica sand.
Excellent in rapid thermal expansion. Inferior to Iwami No. 5 silica sand, 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 permeation type seizure, and the test piece cast by the mold shown in FIG. The anti-seizure property was investigated by using, 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 the Iwami No. 5 silica sand, and penetration-type seizure occurs at the heat-affected part of the convex part of the test piece, and the flat part is good. I got good results. This means that although the particle size is larger than that of Iwami No. 5 silica sand, the amount of rapid thermal expansion of ceramic sand A is small, so that the movement of the outermost surface skin sand layer is small and the coating layer is less destroyed. It is highly probable that the results were shown in.

An example of application to an actual product based on the above test results is shown in FIG.
Shown in FIG. 3 is a cross-sectional view of a cast steel mold for a compressor casing, in which a water-soluble phenolic resin and a curing agent are used as a binder, and a refractory granular aggregate applied as foundry sand and chromite sand shown in Tables 1 and 2 are used. Using ceramic sand A,
A coating material is used on the outermost surface of skin sand that comes into contact with molten steel.

FIG. 4 is a sectional view of a cast steel mold for a compressor casing according to an embodiment of the present invention. 1 is a casting frame, 2 is a surface plate, 3 is a mold space portion, 4 is a riser, and 4-a is a Feeder heat retaining sleeve, 5 runner, 5-a runner sleeve, 6 outer mold, 6
Reference numeral -a indicates an outer skin sand flat surface portion, 6-b indicates an outer skin sand convex portion, 7 indicates a core, 8 indicates ceramic sand, and 9 indicates chromite sand.

Outer mold skin convex portion 6-b of the mold severely affected by heat
Chromite sand 9 having good seizure resistance is used for the skins of the core and the core 7 in an amount of about 10% of the total sand, and the heat effect is not severe. Ceramic sand 8 is used as the base sand for the back sand. Molten steel enters the mold space 3 via the runner 4 and is poured up to the riser 4, and since the ceramic sand 8 has good air permeability, degassing of the core 7 has been eliminated. It was possible to realize a low-expansion mold that is a breathable mold and that has little thermal expansion.

Further, the self-hardening mold for cast steel shown in FIG. 4 uses a water-soluble phenolic resin and a hardening agent as a binder, has a particle size of 0.5 mm to 1.5 mm as a base sand of foundry sand, and , Mullite ceramic sand having a spherical particle size with a Knoop hardness of 900 or more and a particle size number of 1.1 or less is used, and chromite sand of pocket sand used for heat-harsh skin sand is classified into the above-mentioned ceramic sand and a sieve. It is a one-process, two-sand mold using chromite sand with a possible 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 chart of the 1-process 2-sand method and is an explanatory view of a sand circulation system mainly for reclaiming sand.
In this example, cast steel is poured into a water-soluble phenol mold using chromite sand and ceramic sand A shown in Tables 1 and 2, and the unfolded sand is recovered and then the following regeneration is performed.

As a reclaiming device for the unraveling sand, water-soluble alkali phenol recovery sand (residual resin amount: 1.4%) obtained by mixing chromite sand in ceramic sand is used at a peripheral speed of 50 m /
A powerful scrubbing type regenerator with a high-speed rotor of sec is used. The residual resin removal rate for each pass is 23
It is ˜25% / pass, and the residual resin in the recovered sand is removed with an increase in the number of passes, and 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 was 0.6%, which was a remarkably good value. In chromite sand, if the angle of the sand grains is removed to some extent, the sand hardness is high, so that the grain size does not become extremely fine and the particle size distribution becomes stable. Moreover, when the removal process of the iron beads on the chromite sand surface was investigated with a scanning electron microscope,
It was confirmed that the resin can be almost removed by 4 passes within the control value of the residual resin. It was also found that the iron beads on the surface of the chromite sand, which were significantly affected by heat, remained without being removed by intensive regeneration. It should be noted that the residual resin polished from the sand during the sand reclamation, the iron beads of 2 to 20 μm, and the abrasive powder of the sand were removed as much as possible from the duct provided with the recycling apparatus.

The ceramic sand and chromite sand used in this example have a mesh size of 35 mm and a mesh size of 35 mesh.
The pair of sands was classified by using the vibrating screen of. Coarse grains of 0.5 mm or more remaining on the sieve are reusable recycled ceramic sand, and fine grains of less than 0.5 mm that have passed through the sieve account for 12% of the total amount of sand.

The fine-grained sand that has passed through the 35 mesh vibrating screen is sorted according to the strength of magnetism by a 20000 Gauss two-stage roll-type magnetic separator. The magnetic separator used at this time is a small model that processes about 15% of the total sand. First, the upper magnetic separator separates the non-magnetic material from the magnetic material to take out the magnetic material, and the lower magnetic separator selects the effective magnetic material, which is a weak magnetic material and has relatively little heat effect and has not deteriorated. Good chromite sand and reusable chromite sand with iron beads removed are removed. In addition, medium magnetic materials include chromite sand that is hard to reuse due to solid iron beads generated in the sand surface layer, sand particles with molten steel of ferromagnetic material attached, and some iron particles separated from the chromite sand surface during sand regeneration. Iron components such as beads, hot water balls and fine cast burrs are removed by a magnetic separator as an object to be removed. The composition ratio of the fine-grained sand subjected to magnetic separation is non-magnetic material; 9%, weak magnetic material; 74%, medium magnetic material and ferromagnetic material; 17%.

As a result of the regeneration, the yield of fresh sand was 0.6% for ceramic sand and 19% for chromite sand. The yield when used as a system sand for a long time is about 2% with ceramic sand, including loss such as casting adhesion,
Chromite sand is estimated to be about 30%, and it is possible to greatly reduce industrial waste. Both ceramic sand and chromite sand have high sand hardness and are difficult to crush, which greatly reduces dust at the time of unraveling, which is the most problematic problem in a foundry, and ceramic sand and chromite that do not contain free silicic acid (SiO ₂ ). The sand can prevent silicosis.

[0045]

As described above in detail, the self-hardening mold for cast steel using the 1-process 2-sand method of the present invention,
In a water-soluble phenol mold for cast steel using a water-soluble phenol resin and a hardening agent, the particle size of the base sand is 0.5 to 1.
Spherical ceramic sand having a hardness of 5 mm and a Knoop hardness of 900 or more is used, and chromite sand having a particle size of less than 0.5 mm that can be sieved from the ceramic sand is used as a pocket sand. be able to. (1) Due to the water-soluble phenolic resin and the binder, the gas from the mold at the time of casting does not contain harmful components such as sulfur, which is the main cause of hot cracking, and nitrogen, which contributes to gas defects. (2) By using chromite sand as pocket sand for the skin sand of the mold where heat is significantly affected, inter-sand grain sintering occurs due to iron components reduced and precipitated from chromite, and molten steel can be prevented from penetrating and seizure can be prevented. (3) A low expansion mold is realized by applying mullite ceramic sand to the base sand, and molten silicate, which is a reaction product with molten steel, is unlikely to be produced. (4) By using coarse-grained ceramic sand, degassing is unnecessary and a simple high-permeability mold is obtained.

Further, the method for reclaiming foundry sand of the present invention can exert the following effects. (1) High-hardness ceramic sand and chromite sand suppress sand crushing due to strong scrubbing to improve sand yield, reduce the amount of new sand replenishment and the amount of waste sand, and prevent pneumoconiosis and silicosis. . (2) Coarse-grained ceramic sand and chromite sand can be used for classification with a simple sieve, and chromite sand can be recovered by an inexpensive small magnetic separator.

As a result of the above, according to the present invention, the water-soluble phenol sand process can be used for cast steel by the new one-process-two-sand method, and it is possible to realize a large-scale high-grade cast steel product in accordance with the times.

[Brief description of 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 mold for a test piece in a seizure test.

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

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

FIG. 5 is a flow chart showing a 1-process 2-sand method showing a method for reclaiming foundry sand according to an embodiment of the present invention.

FIG. 6 is a flowchart showing a conventional 1-process 1-sand method.

FIG. 7 is a flowchart showing a conventional 2-process 2-sand method.

FIG. 8 is a flowchart showing a conventional 1-process 2-sand method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting frame 2 Surface plate 3 Mold space part 4 Hot water 4-a Hot water heat retaining sleeve 5 Runway 5-a Runway sleeve 6 Outer mold 6-a Outer skin sand plan view 6-b Outer skin sand convexity 7 Core 8 Ceramic sand 9 Chromite sand

Claims (2)

[Claims] 1. A self-hardening mold for cast steel using a 1-process 2-sand method, wherein a water-soluble phenolic resin and a hardening agent are used as a binder, and a particle diameter of 0.5 is used for the base sand of the foundry sand.
Spherical-grain type mullite ceramic sand with a Knoop hardness of 900 to 1.5 mm and a grain size of 1.1 or less is used, and the above-mentioned ceramic is used for chromite sand of pocket sand used for thermally harsh skin sand. 0.5 that can be divided into sand and sieve
A self-hardening mold for cast steel, which is characterized by using chromite sand having a particle size of less than mm. 2. A base sand having a particle size of 0.5 to 1.
The grain size is 0.5 mm as 5 mm of ceramic sand and pocket sand.
When regenerating the alkali phenol recovered sand using less than 5 mm of chromite sand, a strong scrubbing type regenerator with a high-speed rotating rotor was used to remove the residual resin of the coarse-grained ceramic sand and chromite sand and to remove the chromite sand. Iron particles of iron beads deposited on the surface are removed, both sands are classified by a vibrating screen, coarse particles on the screen are reused as recycled ceramic sand, and fine particles under the screen are magnetic separators of 20000 Gauss or more. By, medium magnetic substance that is precipitating iron beads, ferromagnetic substance such as iron,
And a method for reclaiming foundry sand, characterized by removing non-magnetic runner bricks and the like, and taking out and reusing the weak magnetic material chromite sand.