JP2983416B2 - Mold structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to the structure of a casting mold, and in particular, by using a molding sand having high resistance to crushing due to heating and abrasion, even after repeated use. The present invention relates to a structure of a mold improved so that mixing of crushed fragments of back sand into a skin sand layer can be suppressed, and the amount of foundry sand discarded during regeneration processing can be reduced as much as possible.

[0002]

2. Description of the Related Art Conventionally, as one of molds frequently used in the production of castings, a molding cavity is formed at a substantially central portion of the mold, and a sand layer in contact with a predetermined molten metal,
There is a back sand layer which is provided behind the sand layer to reinforce or support the sand layer.

In general, in such a mold, inexpensive silica sand having a relatively large particle size is used as the back sand forming the back sand layer, and the back sand is formed as the skin sand and core sand forming the skin sand layer. Alumina sand, mullite sand, zircon sand, chromite sand, olivine sand, having relatively high fire resistance than sand, or natural sand or synthetic sand with a relatively small particle size such as ceramic particles,
Then, after a predetermined binder, an auxiliary material, and the like are added to the molding sand, the molding sand is formed into a desired shape, thereby being formed. And, as is well known, in such a mold, after casting, a predetermined treatment such as mold release and sand removal is performed, whereby the molding sand constituting the mold is removed from the casting, and furthermore, ,
This foundry sand is collected, and thereafter, subjected to a predetermined regeneration treatment, so that it can be reused.

However, such a mold has various problems as described below. That is, in such a mold, when performing a molding sand reclaiming process for the purpose of reuse, for example, the molding sand removed from the casting is caused to collide with the rotating blades by an air moving method, and the sand is isolated by the particle isolation and the polishing effect. A method such as a rotary clayer for cleaning the surface and a method for removing the deposits on the sand surface of the foundry sand by a fluidized roasting furnace have been adopted. Since the sand surface is cleaned by applying mechanical and thermal force to the foundry sand, during the process of reclaiming such foundry sand, destruction of the foundry sand particles is caused and reused. It was inevitable that a large amount of impossible fine particles were generated. Moreover, those fine particles are hardly used effectively,
Most of it is disposed of as waste sand.

[0005] In particular, when various molding sands having a higher fire resistance than the silica sand constituting the back sand layer are used as the skin sand layer as described above, the fire resistance of the skin sand layer at the time of reuse is increased. In order to prevent the drop of the casting sand, after the casting sand is removed from the casting by removing the mold and removing the sand, it is necessary to separate the casting sand into skin sand, core sand and back sand, and collect it. It is very difficult to separate and collect skin sand, core sand, and back sand that merely differ in fire resistance. Therefore, skin sand and core sand mixed with this back sand are actually disposed of in the same manner as the above-mentioned waste sand.

In short, in the case of using a conventional mold, a large amount of molding sand, particularly expensive skin sand and core sand, must be discarded every time casting is performed. It was difficult to save costs.

Further, in such a mold, in order to enhance the fluidity of the sand particles, the air permeability and strength of the mold itself, and to prevent the surface of the molding cavity from being roughened, the surface sand and the medium forming the skin sand layer are required. Desirably, spherical sand is used as the child sand. However, as described above, if the reproduction and reuse are repeated, the back sand is crushed, and the crushed sand having an irregular shape or section shape is obtained. Debris is formed, and the incorporation of such crushed debris into the skin sand layer significantly impairs the excellent mold properties as described above obtained by the use of spherical skin sand and core sand. There has also been a problem that the quality of the casting to be manufactured is deteriorated.

To solve these problems, Japanese Unexamined Patent Publication (Kokai) No. 4-4942 discloses a method of using back sand having a large particle size and skin sand having a small particle size to remove the skin sand and the like after the mold is separated. There has been proposed a method of recovering the back sand and the like by separating them by sieving during the operation of collecting the back sand and the like.

However, even if such a method is adopted,
It is very difficult to reduce the amount of waste sand inevitably generated during reprocessing and to prevent crushed fragments of back sand from mixing into the skin sand layer. And the skin sand are both worn or crushed, the particle size of both is gradually made uniform, and it becomes difficult to separate and collect by sieving. Therefore, such a method is still insufficient to solve the above-mentioned problems caused in the conventional mold.

[0010]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to minimize the amount of waste sand generated during a regeneration treatment. At the same time, it has been improved so that the crushed fragments of the back sand can be prevented from being mixed into the skin sand layer, and even after repeated use, the skin sand and the core sand and the back sand can be more reliably separated and recovered. To provide an improved mold configuration.

[0011]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, as the back sand constituting the outer layer of the mold, the skin sand constituting the inner layer forming the molding cavity, and By using refractory particles having a larger particle size than core sand and having high resistance to particle destruction by heating and abrasion, all problems caused by the conventional ones are eliminated. I found what I could do.

That is, the present invention has been completed on the basis of such findings, and is characterized by forming a molding cavity surface of a mold and forming a skin sand layer in contact with a predetermined molten metal with a particle size. Is less than 0.5 mm and has an apparent porosity of 20% or less, while the back sand layer behind and behind the skin sand layer for reinforcing or supporting the skin sand layer has a particle size of Spherical mullite ceramic particles having a size of 0.5 to 3 mm and a crushing rate of 135% or less
In the template structure constituted by refractory particles made from the child.

Further, in the present invention, refractory particles having a fire resistance of SK35 or more are advantageously used as the back sand.

[0014]

The mold structure according to the present invention as described above comprises a sand layer as an inner layer and a sand layer as an outer layer surrounding the sand layer. And in such a mold structure, of those two layers,
The skin sand layer is composed of mullite ceramic particles.

[0015] This sand layer forms a molding cavity having a shape corresponding to the outer shape of the product at an inner portion thereof, that is, a substantially central portion of the mold, and is brought into contact with a high-temperature molten metal on the surface of the molding cavity. Things. Therefore, the skin sand and the core sand which provide such a skin sand layer are required to have characteristics such as a small volume change with respect to a temperature change and excellent heat resistance. Therefore, high mechanical strength at high temperatures that can withstand the above is also required.

On the other hand, as is well known, the mullite ceramic particles have both of these characteristics, and also exhibit excellent characteristics in abrasion resistance.

Therefore, the mold structure according to the present invention can satisfy all the above-mentioned requirements by using such mullite ceramic particles as skin sand and core sand. In addition to improving the dimensional accuracy and quality of the casting, the abrasion or crushing of the sand particles can be prevented or suppressed as much as possible at the time of casting or at the time of mold release and sand removal. -ing

Further, in such a mold structure, such mullite ceramic particles must have a spherical particle shape. Thereby, excellent fluidity can be obtained in the skin sand and the core sand, the filling property at the time of molding can be enhanced, and thus high moldability can be ensured, and it can be obtained by molding this In the mold as well, excellent degassing properties and disintegration, as well as strength, can be obtained, and roughening of the molding cavity surface can be prevented, and a high-quality casting without rough skin, gas holes, cracks, etc. can be manufactured. It becomes.

Further, such spherical mullite ceramic particles must have a dense structure having an apparent porosity of 20% or less, and preferably 10% or less. When the apparent porosity exceeds 20%, not only the particle strength is low and the mechanical strength of the obtained mold is reduced, but also the crushing rate described below is reduced, and the crushing resistance to heating and abrasion is reduced. This is because a problem such as a reduction in the amount of light is caused.

In the mold structure according to the present invention, such spherical mullite ceramic particles as the skin sand and the core sand must have a particle diameter of 0.5 mm or less. Because, when such spherical mullite ceramic particles are composed of those having a particle size of more than 0.5 mm, the surfaces of the mold and the core become rough, and as a result, in the castings produced,
This is because rough skin is caused.

The spherical mullite ceramic particles having the above-mentioned characteristics can be produced according to a conventional method. For example, a predetermined amount of an SiO ₂ raw material and an Al ₂ O ₃ raw material are blended to prepare a slurry. Then, the slurry is granulated into spherical particles by a spray dryer or the like, or the slurry is dehydrated and dried, and then granulated into a spherical shape by a bread granulator or the like, and thus obtained. It is obtained by sintering the granulated material at a predetermined temperature.

On the other hand, as the back sand constituting the back sand layer, any of natural or artificial refractory particles which have been conventionally used can be employed. However, as described above, the back sand layer has a high temperature on the surface of the molding cavity. It is desirable to have excellent heat resistance and high mechanical strength because it is located behind the sand layer in contact with the molten metal and functions to reinforce or support the sand layer. From that point, in the present invention, natural sand such as zircon sand, chromite sand, high alumina sand, mullite sand and the like and synthetic sand such as mullite ceramic particles having those characteristics are used as such backing sand. It can be suitably used. In the casting mold structure according to the present invention, one or more kinds are appropriately selected from such foundry sands, and each of them is used alone or in various combinations to serve as a back sand. It is.

In such a mold structure, desirably, among these refractory particles, those having a fire resistance of SK35 or more are used. It ’s S
In those having a fire resistance of less than K35, when the temperature becomes high, the crushing rate, which will be described later, sharply rises, the wear resistance and crush resistance are significantly reduced, and the mechanical strength of the mold at high temperatures is low It is because it becomes.

Further, in the mold structure according to the present invention, the particle shape of the back sand is not particularly limited, but it is preferable that the back sand has a rounded shape, and a spherical shape. Is more preferable. Thereby, in such a template structure, compared to other parts,
The sharp corners on the surface of the back sand that are relatively easy to crush can be removed in advance, and the crush resistance and wear resistance of the back sand can be advantageously increased. Then, as a result, the amount of crushed fragments generated by crushing or abrasion of the back sand can be reduced, and at the time of molding or the like, mixing of the crushed fragments of the back sand into the skin sand layer can be more effectively suppressed. At the same time, the amount of the non-reusable crushed fine powder generated from such crushed debris can be further reduced at the time of casting or during the regeneration treatment. Further, in the mold structure according to the present invention, in particular, if the back sand is configured to have a spherical shape, the strength of the mold and the quality of the casting to be manufactured are enhanced by the cooperative action with the above-mentioned spherical sand and core sand. Can be further improved.

In order to obtain such rounded or spherical back sand, when synthetic sand is used as the back sand, a spray drier or a pan-type granulator is used during the production. And granulate it into spherical particles.
Also, when using natural sand, the back sand after pulverization, sizing treatment, for example, the surface is polished with a rotary clayer, sand shine, sand fresher, hybridizer, etc., The sharp corners are removed, and then they are sieved and sized.
In particular, when using sintered alumina clinker or band shale as back sand, crushed fine powder is more likely to be generated than other materials, so that spherical particles are to be formed by the method described above. Is more desirable.

Further, in such a mold structure, the crushing rate of such back sand needs to be 135% or less, and particularly preferably 115% or less. For refractory particles with a crushing rate exceeding 135%,
When the refractory particles are used as backing sand, the crushing or abrasion during repeated use is remarkably crushed or worn due to poor crushing resistance to heating and abrasion, achieving the intended purpose. It is very difficult to do so.

Here, the crushing rate of the back sand specified in the present invention is defined as JACT (Japan-ese Association of Japan).
Casting Technology: Casting Technology Promotion Association) Test Method S-
AF of the sand after the crushing test obtained by repeatedly performing the crushing test three times in accordance with the friability test method by thermal treatment and mechanical treatment of the molding sand specified in 6-II
It is expressed as a ratio (%) of the average value of S (American Fundry Society) particle size index: F to the AFS particle size index: F of raw sand before the crushing test.

Such a crushing ratio is specifically determined as follows. That is, JACT
First, based on the friability test method by thermal treatment and mechanical treatment of molding sand specified in Test Method S-6-II, first, a predetermined amount of sample is heated in a heating vessel at a predetermined temperature for a predetermined time. Then, air-cool and cool to room temperature. Next, the sample is taken out of the heating container, and the sample is put into a ball mill together with a specified amount of balls. Then, after rotating them for 1 hour, the sample is taken out of the ball mill, and the sample is reduced and divided to obtain 50 g as a sample for measuring the particle size distribution. Such an operation is repeated three times, and a sample for measuring the particle size distribution is collected each time. Thereafter, the three types of samples for measuring the particle size obtained in this manner are mixed with the original sand before the crushing test is performed. And for 1
Using a 4-mesh to 36-mesh sieve, a sieving test is performed to measure the particle size distribution of each.

The apparatus conditions and the like in the crushing test and the sieving test are as follows. Heating container: a porcelain container capable of holding about 500 g of a sample. Heating device: a heating furnace capable of keeping the temperature at about 1000 ° C. and containing the above-mentioned heating container. Porcelain pot for ball mill: outer diameter 90-300mm (capacity 5
~ 6l). Rotating machine for ball mill: Rotating speed of about 33 to 333 rpm. Sieve: JIS Z 8801- ₁₃₈₇ that passed the "standard sieve". Sieving tester: rotation speed 240-280 times / min, number of hits 13
0 to 150 times / minute. Upper balance: weighing 100 g, sensitivity 100 mg.

Next, the three kinds of AFS particle size index: F are calculated by substituting the three types of particle size distribution measurement samples obtained as described above and the measured values of each particle size distribution of the raw sand into the following equation 1. Then, the average value of the AFS particle size index: F of the three types of particle size distribution measurement samples is calculated. _{F = Σ (W n × S} n) / ΣW n ··· ( Equation 1) where, W _n: In sieve analysis, the weight of the remaining sand on each sieve surface (g) S _n: particle size coefficient

The obtained calculated value is used to calculate the AF of the sand after the crushing test against the AFS particle size index: F of the original sand.
The ratio of the average value of the S particle size index: F is determined as a percentage, and this is defined as the crushing rate. In short, the crushing rate defined in the present invention is an index indicating the resistance to crushing caused by refractory particles due to heating or abrasion.

In the mold structure according to the present invention,
The backing sand having the above-mentioned characteristics must be constituted by one having a particle size of 0.5 to 3 mm. In the case where particles with a particle size of less than 0.5 mm are mixed, when the casting sand is recovered after the mold is removed or the sand is removed, the same as the back sand is used. It is because it becomes difficult to reliably separate skin sand and core sand composed of those having a particle size range by sieving,
This is because, in the case where particles having a particle size of more than 3 mm are mixed, not only is it difficult to form a mold having a complicated shape, but also there is a problem that the strength of the mold is reduced.

As described above, in the mold structure according to the present invention, since the back sand layer is formed of the back sand having extremely high resistance to crushing due to heating and abrasion,
The crushing or abrasion of the back sand during casting or reprocessing can be significantly reduced, and at the same time, the amount of crushed fragments generated can be reduced, so that such crushed fragments are mixed into the skin sand layer. Can be effectively avoided or suppressed.

In this mold structure, the skin sand layer is also excellent in heat resistance and mechanical strength at high temperatures, and furthermore has skin sand and core sand made of spherical mullite ceramic particles having high wear resistance. The crushing and abrasion of not only the back sand but also the skin sand and the core sand can be reduced at the time of pouring or during the regenerating process, so that the crushing and The amount of crushed fines produced by abrasion can be reduced, so that the generation of non-reusable waste sand can be significantly reduced.

Further, in the mold structure according to the present invention, the back sand having such excellent crush resistance against heating and abrasion has a larger particle size than the skin sand and the core sand which also have such excellent properties. Because it is composed of refractory particles with a diameter, even after repeated use, the back sand, skin sand, and core sand are more reliably separated by sieving after mold release and sand removal. Can be recovered.

Therefore, when the casting structure is manufactured by employing the mold structure according to the present invention, the fluidity, strength, and air permeability of the skin sand layer are reduced due to the incorporation of the crushed fragments of the back sand into the skin sand layer. Roughness of the molding cavity surface and the like can be effectively prevented, and the quality of the casting to be manufactured can be effectively improved.In addition, the amount of casting sand discarded at the time of regeneration processing and the like is significantly reduced. As a result, the material can be saved, and the cost can be effectively reduced.

[0037]

EXAMPLES Hereinafter, some examples of the present invention will be described to clarify the present invention more specifically. However, the present invention imposes no restrictions on the description of such examples. It is needless to say that it is not something to receive.
In addition, in addition to the following examples, the present invention, in addition to the above-described specific description, various changes, corrections, and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that improvements can be made.

First, as raw materials, a predetermined amount of band shale and aluminum hydroxide are prepared, and these are shale: 93
% By weight and aluminum hydroxide: 7% by weight to obtain a blend. Then, this composition was put into a ball mill, and water was further added thereto.
The mixture was pulverized for an hour and mixed to obtain a slurry. Thereafter, the thus obtained slurry was taken out of the ball mill, and after dehydration and drying, the particle size was reduced to 0.5 to 0.5 by a bread granulator.
Granulation was carried out so as to be 3.5 mm spherical particles.

Next, in order to prevent the spherical granules thus obtained from adhering to each other, 0.5 parts by weight of a high alumina powder is added to 100 parts by weight of the spherical granules, and mixed. Then, the mixture was obtained. Thereafter, the mixture was put into a rotary kiln and fired at a temperature of 1680 ° C. for 2.5 hours to obtain a fired product having a partly lump. Then, the fired product was put into a stirrer to disintegrate the lump, and then the high alumina powder was removed to obtain spherical mullite ceramic particles in which all particles were isolated.

Subsequently, the spherical mullite ceramic particles thus obtained are sieved to have a particle size of 0.5 to 3.
It was adjusted to be 0 mm. Separately, a predetermined amount of chromite sand and imported silica sand were prepared, and each was sieved to prepare a powder having a particle size of 0.5 to 3.0 mm. Spherical mullite ceramic particles, chromite sand and imported silica sand composed of particles having the same particle size range are used as back sand, and they are used as back sand 1, back sand 2 and back sand 3, respectively.
And The chemical composition of the back sands 1 to 3 is shown in Table 1 below, and the physical properties thereof are shown in Table 2 below. In addition,
In the physical properties of the back sands 1 to 3, the powder bulk density was measured using a powder bulk density measuring instrument, and the coefficient of thermal expansion was measured as the back sand 1
2% by weight of phenolic resin and 1% by weight of phenolic resin to back sands 2 and 3 respectively, and the thermal expansion coefficient when heated at 1000 ° C. for 300 seconds in an electric furnace is RCS
It was measured using a thermal expansion coefficient measuring instrument.
IS R2204 Test method for fire resistance of refractory brick ".

[0041]

[Table 1]

[0042]

[Table 2]

Subsequently, the back sands 1 to 3 obtained as described above were subjected to the JACT test method S-6 described in detail above.
The crushing test was repeated three times in accordance with the friability test method by thermal treatment and mechanical treatment of the molding sand specified in II. That is, first, 600 g of each of the back sands 1 to 3 was weighed, and these were used as samples and placed in three porcelain containers. Next, these samples were heated at a heating rate of 5 ° C./min, kept at a temperature of 700 ° C. for 30 minutes, air-cooled, and cooled to room temperature. Then, those 3
Samples of various kinds, pot material: porcelain, pot diameter: outer diameter 2
20 mm, inner diameter 190 mm, pot volume: 5 l, number of revolutions: 1
10rpm, ball material: made of alumina, ball diameter: 20m
m, number of balls: in 40 ball mills,
They were charged separately and rotated for 60 minutes.

After the completion of the rotation treatment, the three kinds of samples were taken out of the ball mill and subjected to a screening test using a sieve of 14 mesh to 36 mesh to measure each particle size distribution. Then, the measured values thus obtained were substituted into the above-mentioned formula 1, respectively, to obtain an AFS particle size index F of the back sands 1 to 3 after the friability test. Further, such an operation was repeated three times, and the AFS particle size index obtained each time:
The average value of F was calculated. Further, along with that, the particle size distribution of the back sands 1 to 3 not subjected to any friability test was measured in the same manner as above, and the AFS particle size index: F was calculated.
Based on the calculated values, the crushing rates of the back sands 1 to 3 were determined. The particle size distribution of each of the back sands 1 to 3 before and after the crushing test, the AFS particle size index: F, and the crushing ratio are shown in Table 3 below.

[0045]

[Table 3]

As is apparent from the results shown in Table 3, the back sand 1 composed of spherical mullite ceramic particles and the back sand 2 composed of chromite sand have a crushing rate of 135% or less as specified in the present invention. On the other hand, it was found that the back sand 3 made of imported silica sand had a crushing rate much higher than that.

Next, using such back sands 1 to 3, each of the four back sands was subdivided into a predetermined amount to prepare a total of 12 samples. And, based on the JACT test method as described above,
At room temperature, 700
C., 1000.degree. C., and 1300.degree. C., respectively, were subjected to crushability tests at different heat treatment temperatures, and the respective crushing rates were determined. FIG. 1 is a graph showing the relationship between the heat treatment temperature and the crushing ratio thus obtained.

As shown in FIG. 1, the back sand 1 and the back sand 2 having a fire resistance higher than specified in the present invention.
Irrespective of the heat treatment temperature, the crushing rate shows a substantially constant value, whereas the back sand 3 having a fire resistance smaller than specified in the present invention, with the increase of the heat treatment temperature, The crushing rate is also increasing. From this, the back sand 1 and the back sand 2 are excellent in crush resistance by heating, and at the same time, the back sand 3 outside the scope of the present invention is extremely poor in crush resistance by heating. It is confirmed that.

Subsequently, in the same manner as in the production of the spherical mullite ceramic particles as the back sand 1, sand shale and aluminum hydroxide were blended, and this was pulverized and mixed by a wet method to obtain a slurry. The slurry was dehydrated and dried, and then granulated into a sphere. Thereafter, the spherical granules thus obtained are put into a rotary kiln, and at a temperature of 1500 ° C. for about 3 hours.
Baking was performed for 0 minutes to obtain spherical mullite ceramic particles fired at a temperature lower than that of the back sand 1, and this was designated as back sand 4.
Then, the physical properties of the back sand 4 and the back sand 1 are measured, and the crushing rate of the back sand 4 is obtained by the same method as described above. Were compared. The results are shown in Table 4 below. The physical properties of the back sand were measured according to “JIS R2205-74 Method for measuring apparent porosity, water absorption and specific gravity of refractory brick”.

[0050]

[Table 4]

As is clear from the results in Table 4, the back sand 4 having a porous structure with an apparent porosity of 22.1% was obtained.
In this case, the crushing ratio is a value exceeding 135%. From this, it is confirmed that even if the particles are made of the same spherical mullite ceramic particles, if the apparent porosity exceeds 20%, the crush resistance against heating and abrasion is reduced. It is.

Next, apart from the friability test based on the JACT test method described above, a friability test was performed on the back sands 1 to 3 by a regenerating treatment using a rotary cramer similar to the on-site operation. That is, first, a predetermined amount of the back sand 1 to 3 is prepared, exposed and heat-treated at a temperature of 1300 ° C. in a shaft kiln, and then cooled. Repeatedly, a friability test corresponding to 15 regeneration treatments in the field operation was performed. Then, the back sand 1 after the crushing test is performed in the same manner as in the crushing test based on the JACT test method described above.
A sieving test was performed on the samples No. 3 to No. 3. Then, the ratio of the sum of the amount of crushed sand of 36 mesh under and the amount of dust generated during the rotary crema treatment to the amount of each back sand 1 to 3 subjected to the crushability test, and the ratio of the remaining portion In other words, the crushed sand crushed to the particle size of the normally used skin sand and the ratio of the recovered sand that can be reused as the back sand are shown in Table 5 below, and crushed by the JACT test method performed earlier. The ratio of the crushed sand of 36 mesh under after the crushability test to the amount of the back sand 1 to 3 subjected to the crushability test and the balance thereof was determined by the crushability test generated by the JACT test method as described above. The ratio of sand to recovered sand is shown in Table 5 below. In the table, crushing test A
Indicates a crushing test by the JACT test method, and crushing test B indicates a crushing test by a rotary Kramer treatment.

[0053]

[Table 5]

As is clear from Table 5, back sand 1
In Examples 3 to 3, a proportional relationship was observed between the rate of occurrence of crushed sand and recovered sand after the crushability test based on the JACT test method and that after the crushability test by the rotary crema treatment, and thus, based on the JACT test method. It is confirmed that the crushing rate obtained by the crushing property test can sufficiently function as an index of the crush resistance of the back sand in the on-site operation.

Then, as shown in Table 5 above,
The back sand 1 and the back sand 2 having a crushing rate specified in the present invention can be used in a crushability test based on the JACT test method.
Even in the crushability test by the rotary kramer treatment, the amount of the back sand crushed to the grain size of the skin sand by the both tests is small, and along with that, a large amount of sand that can be reused as the back sand can be recovered It is recognized that. On the other hand, the back sand 3 having a crushing rate which greatly exceeds the specified range in the present invention generates 1.6 times or more of the back sand 2 and 16 times or more of the crushed particles as compared with the back sand 1. doing. That is, this is such back sand 3
When a mold is used to form a mold, a large amount of non-reusable waste sand is generated, and further, it is proved that a large amount of crushed debris of the back sand is mixed into the skin sand layer. .

Next, spherical mullite ceramic particles having a particle size of less than 0.5 mm were produced in the same manner as when the spherical mullite ceramic particles as back sand 1 were produced. And while using this as skin sand,
Using the above-mentioned back sands 1 to 3, although the skin sand is the same, three kinds of molds with different back sand types are prepared according to the conventional method, and then the production of castings, regeneration treatment, and sieving fractionation. , And the operation was repeated 15 times.

Then, three types of molds having different back sands were prepared using the skin sand and the back sands 1 to 3 thus repeatedly used 15 times, and the performance test of these three types of molds, ie, The calculation of the mixing ratio of the back sand into the skin sand layer, the measurement of the mold strength and the air permeability, and the observation of the casting surface condition were performed. The results are shown in Table 6 below. For comparison, a mold was prepared from unused spherical mullite ceramic particles used as skin sand, the strength and air permeability of the mold were measured, and the results of observation of the casting surface were shown in Table 6 below. Are shown together. In preparing such a mold, 30% by weight of skin sand and 70% by weight of each of back sands 1 to 3 were used, and a curing agent [C-30A: Kobe] was used in the skin sand in a ratio of 25 parts by weight. Phenolic resin [Phoenix 610: manufactured by Kobe Rika Kogyo Co., Ltd.]
It was added in an amount of 1.5 parts by weight to the skin sand to prepare a mold. In addition, in the performance test of the mold thus produced, the mixing ratio of the back sand into the skin sand layer is calculated as a value obtained by subtracting the occurrence rate of the pan from the reduction ratio of the back sand, as the estimated value. After the mold was prepared, the pressure resistance was measured 24 hours later, and the air permeability was measured according to JACT test method SM-6.
The measurement was carried out according to the test method for air permeability specified in "1. Further, in the table, ◎ indicates that the casting surface condition was extremely good,
Indicates good, and Δ indicates substantially bad.

[0058]

[Table 6]

As is clear from the results in Table 6, the backing sand 1 having the particle size and the crushing ratio specified in the present invention was obtained.
And the mold made using the back sand 2, the mixing ratio of the back sand into the skin sand layer is small, the mold strength is excellent, and it is recognized that the casting surface condition is good. It is confirmed that the mold having both back sand and spherical mullite ceramic particles exhibits extremely excellent mold performance on all surfaces including the air permeability. On the other hand, a mold produced using the back sand 3 having the particle size specified in the present invention but having a crushing rate outside the scope of the present invention is inferior in all aspects of the mold performance. Is confirmed.

[0060]

As is clear from the above description, in the mold structure according to the present invention, the sand layer is composed of spherical mullite ceramic particles having excellent wear resistance and crush resistance, while Since the sand layer has a particle size larger than that of the spherical mullite ceramic particles constituting the skin sand layer, and is composed of refractory particles having excellent crush resistance due to heating and abrasion, it is used during casting or during regeneration. The generation of crushed fine powder that cannot be reused during processing and the like, and the generation of crushed fragments of back sand can be significantly reduced, and in the collection operation of molding sand after mold release and sand removal,
Separation of skin sand, core sand and back sand can be performed more reliably.

Therefore, by employing such a mold structure, the incorporation of the crushed fragments of the back sand into the skin sand layer can be effectively prevented or suppressed, and the mold performance can be remarkably improved. It is possible to produce a simple casting, the amount of foundry sand that is discarded at the time of regeneration processing, etc. can be effectively reduced as compared with the conventional method, saving material in the production of castings and Cost reduction can be achieved very effectively.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows each heat treatment temperature when refractory particles satisfying the conditions specified in the present invention and refractory particles not satisfying the conditions are subjected to crushability tests based on JACT test methods having different heat treatment temperatures. 6 is a graph showing a change in the crushing rate of each refractory particle with respect to the temperature.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Matsubara 4-11, Shiosagusa-cho, Seto-shi, Aichi Prefecture Inside Lamix Co., Ltd. (72) Inventor Fumio Toda 4-11-4, Shiogusa-cho, Seto-shi, Aichi Prefecture Lamix Co., Ltd. (56) References JP-A-4-4942 (JP, A) JP-B-3-47943 (JP, B2)

Claims (2)

(57) [Claims] 1. A surface sand layer which forms a molding cavity surface of a mold and is in contact with a predetermined molten metal is composed of spherical mullite ceramic particles having a particle diameter of less than 0.5 mm and an apparent porosity of 20% or less. On the other hand, the back sand layer behind or behind the skin sand layer for reinforcing or supporting the skin sand layer has a particle size of 0.5-3.
mm at and crushing of not more than 135%, the spherical mullite Sera
A mold structure comprising refractory particles composed of mixed particles . 2. The mold structure according to claim 1, wherein the back sand layer is made of refractory particles having a fire resistance of SK35 or more.