JPH04220133A - Desmoked mold material - Google Patents

Abstract

PURPOSE:To reduce the generating quantity of smoke and stimulative gas and to obtain the required mold strength by mixing an inorganic water holding material including a special water glass in the composing material to be normally used as the mold material in the shell mold method. CONSTITUTION:The mold material which is coated with the thermal setting resin 1, etc., as the base material 2 is mixed with an inorganic water holding material 3 which has the fine holes structure, whose water content capacity is more than 30% by weight, and which has the water absorbing or desorbing capability if the temperature is 100-250 deg.C, and also includes water glass. The mixing volume of the inorganic water holding material 3 is made to 1.5-4.5 volumetric % of the base material 2 of the mold material. As a result, the volume of the resin 1 absorbed in the fine holes of the inorganic water holding material 3 is properly controlled in the calcining process of the mold, the generating quantity of smoke or stimulative gas in reduced and the reduction of the mold strength can be decreased.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a shell mold material used in manufacturing the main mold and core of a casting mold used for casting metals such as cast steel, cast iron, and aluminum. .

More specifically, the smoke removal method generates less smoke, irritating odor, off-odor, and toxic gas (hereinafter referred to as irritating gas) due to heating during mold manufacturing, and reduces the decrease in the strength of the mold. This relates to mold materials.

[Conventional technology and its problems]

Traditionally, the shell molding method, which utilizes the property of synthetic resins such as phenolic resins to harden with heat, has been widely adopted as a manufacturing method for the main mold and core (hereinafter simply referred to as molds) of casting molds. has been done. By casting using a mold manufactured by this method, a casting having extremely high dimensional accuracy and a beautiful casting surface can be manufactured.

The mold material used in this shell molding method is a mold material base material such as silica sand, thermosetting resin such as phenolic resin, etc.
Resin-coated foundry sand (RCS), which is coated with a curing agent and a lubricant in that order, is commonly used.
Furthermore, a curing accelerator and other additives are added and mixed with the resin-coated foundry sand as needed.

However, when manufacturing molds using this resin-coated molding sand as raw material, the mold material is enclosed in the heating mold and fired and solidified, so when the heating mold is opened during the heating process, etc. When removing and transporting molds, strong irritating gases such as smoke and formaldehyde, phenol, and ammonia are generated, significantly deteriorating the working environment. Recently, when manufacturing molds in large quantities, a blowing method has been used in which resin-coated molding sand is blown into a mold using air pressure. In this method, calcium stearate is mainly used as a lubricant to improve the filling properties into the mold, and there is a problem in that the calcium stearate decomposes when the mold is made, generating a large amount of smoke.

In this way, with conventional mold materials, it is difficult to install smoke ducts around the mold manufacturing machinery, so the smoke and irritating gases generated during the mold manufacturing process can cause a deterioration of the working environment in the foundry. Reducing these problems requires enormous equipment costs and is not necessarily sufficient, so there is a strong need for fundamental countermeasures.

As a method to solve these problems, resin-coated foundry sand is made of hydrous magnesium silicate clay mineral, activated carbon, activated alumina, etc., which has many pores and has a specific surface area of 50 m2/g.
Mold material mixed with the above porous substances (Japanese Patent Application Laid-Open No. 63-60
No. 042) has been proposed.

From this, the amount of irritating gases generated during heating when molding a casting mold using the mold material or performing casting using the mold can be reduced by adsorption and catalytic action. It is said that it was created.

However, with this mold material, in order to completely remove smoke and irritating gases, it is necessary to mix a large amount of the porous material, which greatly reduces the strength of the mold and causes mold cracking during the casting process. This has the problem that this occurs. Furthermore, when a mold material mixed with a large amount of the porous substance described above is recycled and used, even after the regeneration treatment process, the porous material excluding carbides such as activated carbon is contained in the mold material base material (recycled sand) such as silica sand. The substance retains its shape and remains with pores, and when a mold is made using recycled sand containing the porous substance, there is a problem in that the strength of the mold decreases so much that it cannot be used as a mold. .

Therefore, the present inventors conducted intensive research to solve these conventional problems and conducted various systematic experiments, and as a result, they came up with the present invention.

[Purpose of the invention]

An object of the present invention is to provide a smoke-free molding material that generates less smoke and irritating gases when manufacturing casting molds, and provides the necessary mold strength.

In other words, the molding material used in the conventional shell molding method is resin-coated molding sand, which is made by coating a molding material base material such as silica sand with a thermosetting resin, and if necessary, resin-coated molding sand that is added to the resin-coated molding sand. - Consists of a mixed curing accelerator and other additives. Although this molding material made by mixing a porous substance with resin-coated foundry sand has the effect of reducing irritating gases, if the amount of porous substance mixed is increased to enhance this effect, There was a problem in that the strength of the mold was reduced and the mold collapsed during casting.

The present inventors conducted various systematic experiments and studies in order to elucidate the mechanism of generation of smoke and other irritating gases during mold manufacturing. As a result, there are two types of smoke generated during mold manufacturing: smoke generated by the curing reaction of thermosetting resin and smoke generated by the decomposition of calcium stearate used as a lubricant. It was found that the amount of generation was significantly increasing.

Therefore, the smoke generated by the curing reaction of thermosetting resin is caused by a portion of the resin component being absorbed into the pores of the porous material during the reaction, and the curing reaction is caused by a decrease in the ratio of resin to curing agent. We focused on the fact that acceleration reduces the generation of unreacted gases and that smoke caused by lubricants such as calcium stearate is decomposed into gases with smaller molecular weights by water or steam.

Then, water glass is absorbed into the pores of the porous material,
By creating pores of the necessary size, we released an appropriate amount of retained water during heating during mold production to promote decomposition of unreacted gases, etc., and also created pores that can absorb an appropriate amount of resin components in a fluid state. The above-mentioned problems have been solved by mixing an appropriate amount of an inorganic water retaining material with resin-coated foundry sand to prepare a mold material.

[Description of the first invention] Structure of the invention The smoke-free molding material of the present invention comprises a molding material in which a thermosetting resin or the like is coated on a molding material base material, and a molding material having a pore structure and a water absorption capacity of 30% by weight or more. and an inorganic water-retaining material that has the ability to adsorb and desorb moisture even at 100 to 250°C and contains water glass, and the amount of the inorganic water-retaining material is 1% of the foundry sand base material.
．． It is characterized by a content of 5 to 4.5% by volume.

Functions and Effects of the Invention The smoke-free molding material of the present invention generates less smoke and irritating gases such as irritating odors, off-odor odors, and toxic gases when manufacturing casting molds, and can maintain the necessary mold strength. Obtainable.

The mechanism by which the smoke-free molding material of the present invention exhibits the above-mentioned excellent effects is not yet fully clear, but it is thought to be as follows.

That is, in the present invention, the molding material used in the shell molding method is made by further mixing a water glass-containing inorganic water retaining material with a commonly used constituent material. This inorganic water retaining material has a pore structure, has the ability to adsorb and desorb moisture even at 100 to 250°C, and has a water holding capacity of 30% by weight or more. From this, smoke caused by lubricants such as calcium stearate during heating during mold manufacturing is decomposed into smaller molecular weight gases by the retained water released from the inorganic water retaining material, resulting in smoke and other irritating substances. It is thought that gas generation will be reduced. In addition, the smoke generated by the curing reaction of resins such as phenolic resins promotes the decomposition of curing agents such as hexamethylenetetramine by water or steam, and the formation of resins in the pores of the inorganic water-retaining material from which water is discharged. It is thought that the main component, such as phenol resin, is absorbed, and the curing reaction is accelerated due to changes in the amount of components in the resin and changes in the ratio of resin and curing agent, and the generation of unreacted gas is reduced. Furthermore, since the strength of the mold decreases due to the absorption of resin such as phenol resin into the pores of the inorganic water-retaining material, by incorporating an appropriate amount of water glass into the inorganic water-retaining material, the inorganic water-retaining material is added during the mold firing process. It is believed that the amount of resin absorbed into the pores of the water retaining material can be appropriately suppressed, the amount of smoke and irritating gases generated can be reduced, and the decline in mold strength can be further minimized.

Further, due to the firing step at 750 to 800° C. in the regeneration treatment, the inorganic water-retaining material containing water glass undergoes volumetric shrinkage due to vitrification of water glass, and the shape of the pores also becomes smaller. Therefore, it is thought that the amount remaining in the recycled sand during the sieving process is reduced, the resin absorption capacity is reduced, and the mold strength decrease is significantly reduced.

[Description of the second invention] Below, a second invention that is a more specific version of the first invention will be described.

The molding material used in the present invention, in which the molding material base material is coated with a thermosetting resin or the like, that is, the resin-coated foundry sand, has a thermosetting resin as a caking agent on the surface of the molding material base material (foundry sand) of the material. It is coated with a hardening resin, and if necessary, it can be used with a hardening material such as hexamethylenetetramine to accelerate the hardening of the resin, or to prevent the particles of foundry sand from caking together in the mold material manufacturing process and to improve fluidity. In order to increase the packing density, additives such as lubricants such as calcium stearate are added.

Here, the mold material base material is a refractory sand-like material that forms the base material of the shell mold, and specifically, it is made by crushing silica sand, zircon sand, chromite sand, olivine sand, sea sand, river sand, and rock. There are prepared sands, etc., and one or a mixture of two or more of them is used. This foundry sand has fluidity, filling properties, toughness,
Appropriate shape, size, etc. considering thermal expansion property, solidification rate, etc.
Choose a type. The particle shape of this foundry sand is preferably spherical, such as round or polygonal.

This is because, in this case, the sand has good fluidity, it is easy to obtain high mold strength with a relatively small amount of resin, and the mold has good air permeability.

In addition, thermosetting resin is a caking material that has the function of mutually bonding the foundry sand and inorganic water retaining material that serve as the base material of the shell mold material and forming it into a predetermined mold shape.・Use novolac-based phenolic resins such as formaldehyde resins and phenol/furfural resins.

Coating molding sand with resin can be done using the hot coat method, try-hot coat method, semi-hot coat method, cold coat method,
This is carried out by a conventional method such as a powder solvent method, adding appropriate additives as necessary.

Here, the blending amount of the resin is 1 to 10 w with respect to the mold material base material.
Preferably, it is t%. This amount is determined based on its purpose,
It varies depending on the amount of inorganic water-retaining material and other additives added and manufacturing conditions, but in general, when the mold material base material is silica sand, the amount of
6 wt%, and 1 to 4 wt% when zircon sand is used. In addition, the particle size of the mold material base material is 50 μm to 1 mm.
It is preferable that

Next, inorganic water-retaining materials release an appropriate amount of retained water during heating during mold manufacturing, etc., to promote the decomposition of hardeners, lubricants, etc., and have pores that can absorb resin components in a fluid state. It is an inorganic water retaining material that has the ability to adsorb and desorb moisture even at 100 to 250°C and has a water holding capacity of 30% by weight or more. By using such an inorganic water-retaining material, it is possible to reduce the generation of smoke and irritating gases during mold production, and to reduce the strength reduction rate of the mold to 20% or less. Specifically, hydrated magnesium silicate clay minerals and coconut husk charcoal may be mentioned, and one or more of these may be used. In addition, in addition to these, materials having the above-mentioned adsorption/desorption ability and water-containing ability, that is, natural porous inorganic materials, inorganic porous materials obtained by heat-treating inorganic materials or organic materials containing a large amount of fiber, and fine powders thereof. It may be used alone or in a mixture with an inorganic caking agent such as clay. Further, a calcined product of these materials may also be used.

Here, the hydrated magnesium silicate clay mineral has hydrated magnesium silicate as its main component, and has a diameter of 0.005 to 0.05 mm.
It consists of fibers of about 6 μm, and about 10 to 6
It has pores (channels) with a rectangular cross section of approximately Å, and has highly reactive hydroxyl groups on its surface. Note that a part of magnesium or silicon may be replaced with aluminum, iron, nickel, sodium, or the like. Also,
These materials may be calcined within a temperature range of 400 to 800°C.

Further, the inorganic water-retaining material may be used in any form as long as it has been pulverized to the extent that pores remain, but the size is in the range of 50 μm to 1 mm, which is about the same as the mold material base material. It is preferable. Among them, a particle size larger than or equal to the maximum particle size in the particle size distribution of the mold material base material is preferable, especially 14
It is more preferable that it is 9-500 micrometers. This is because the temperature rise of the inorganic water retaining material needs to be the same as the temperature rise of the resin-coated foundry sand. Furthermore, if the particle size is small, the strength of the mold obtained will be reduced and the smoke reduction effect will be reduced. In addition, the inorganic water retaining material contains not more than 10% by weight of particles having a particle size smaller than the maximum particle size in the particle size distribution of the foundry sand before being coated with the thermosetting resin, especially particles having a size of less than 149 μm. Preferably, the material is a granular material with a particle size distribution of . That is, in order to eliminate smoke in the curing reaction, it is necessary for the inorganic water retaining material to absorb the resin, but this resin absorption reduces the mold strength. Therefore, if there are many small particles, there will be many sites where the resin will be absorbed, and the amount absorbed will increase.
The strength of the mold decreases significantly.

It is preferable to reduce the number of particles with a smaller particle size. These crushers are jaw crushers, hammer mills, roller mills, crushing granulators, vibrating mills, pin mills,
This is done by wet or dry grinding using a crusher or the like.

When hydrated magnesium silicate clay mineral is used as an inorganic water-retaining material in a mold material, the mold strength decreases by approximately 20%.
It is large and remains in the recycled mold material base material, and when this recycled sand is used to produce resin-coated molding sand, it absorbs resin well and greatly reduces mold strength. In addition, when coconut shell activated carbon is added in an amount that achieves hardening with reduced smoke and irritating gases, the mold strength reduction rate cannot be kept within the allowable range of 20%.

Therefore, the inorganic water retaining material of the present invention, particularly the hydrated magnesium silicate clay mineral and coconut shell activated carbon, contain water glass. This contained water glass prevents the resin from being absorbed into the pores of the inorganic water-retaining material more than necessary during firing for mold production, thereby minimizing the decrease in strength of the mold, and further improving the recycling process. At this time, the inorganic water-retaining material shrinks and the amount remaining decreases, and the remaining material reduces absorption of the resin.

In addition, the water glass contains a water glass aqueous solution of 20 to 35% by weight, more preferably 25 to 30% by weight in terms of water glass solid content, which is less than the water holding capacity, that is, an amount that does not cause the surface of the inorganic water retaining material to become wet with water. It is preferable that the inorganic water retaining material contains the following. In this case, it was found that the solid content of water glass remained in the inorganic water retaining material in an amount of 20 to 35% by weight, depending on the weight change of the dry inorganic water retaining material before and after containing water glass. This means that in the case of a water glass aqueous solution with a solid content of less than 20% by weight,
In order to contain an appropriate amount of solid content in the inorganic water-retaining material, a large amount of water glass aqueous solution is required, which is not preferable because the aqueous solution remains on the surface of the inorganic water-retaining material.

In addition, in the case of a water glass aqueous solution having a solid content of more than 35% by weight, the viscosity of the aqueous solution is high and it is difficult to enter the pores of the inorganic water retaining material, and the water glass solution remains on the surface of the inorganic water retaining material, which is not preferable. . That is, when the water glass aqueous solution remains on the surface of the inorganic water retaining material in this way, even if the inorganic water retaining material containing water glass is dried at about 100° C., a large amount of solid water glass remains on the surface of the inorganic water retaining material. The water glass solid content on the surface of these inorganic water-retaining materials contains a large amount of water, and the same state occurs when water is adsorbed on the surface of the inorganic water-retaining material. For this reason, a mold material obtained by mixing the inorganic water retaining material and resin-coated molding sand has problems such as caking during mixing and a large decrease in mold strength.

In addition, it is particularly preferable that the water glass content of the water retaining material is 25 to 30% by weight in terms of water glass solid content.

The method for producing this water glass-containing inorganic water retaining material is not particularly limited, as long as the water glass solution containing the predetermined solid content is completely absorbed into the inorganic water retaining material. An example of a specific method for producing an inorganic water retaining material containing water glass is as follows. That is, a water glass aqueous solution with a solid content of 20 to 35% per 10 g of water retaining material
10 cc is absorbed into the inorganic water retaining material at room temperature to 50°C, and the water content in the water retaining material is a predetermined amount, preferably 5 to 20 cc.
% by weight. This is because the inorganic water retaining material needs to retain a certain amount of water before firing in order to reduce the generation of smoke during firing. That is, this is because water or steam is necessary to decompose calcium stearate and promote decomposition of hexamethylenetetramine.

If the amount retained is less than 5% by weight, the amount of water is insufficient relative to the amount of calcium stearate and hexamethylenetetramine mixed, and the effect of reducing smoke and irritating gases will not be sufficient.
If water comes out on the surface of the water glass-containing inorganic water retaining material, it is undesirable because it causes the resin-coated molding sand to solidify during mixing of the mold materials and causes a decrease in the strength of the mold. In addition, when an inorganic water-retaining material containing water glass is fired at a temperature of about 750 to 800°C for recycling treatment, the inorganic water-retaining material shrinks due to the vitrification and reaction with the water glass, causing the pores to collapse and forming granules. The shape also becomes smaller. Therefore, the amount remaining in the recycled sand after the recycled product is reduced, and the pores are made smaller, so that the amount of resin absorbed during the production of resin-coated molding sand is reduced, and a decrease in mold strength is suppressed.

The smoke-free molding material of the present invention comprises the resin-coated foundry sand and the water glass-containing inorganic water retaining material.

Here, the mixing ratio of the mold material (resin-coated molding sand), which is a mold material base material coated with a thermosetting resin, etc., and the water glass-containing inorganic water retaining material is determined based on the mold base material (foundry sand). 1 material
．． It is 5 to 4.5% by volume. This means that the mixing amount is 1.5
This is because if the amount is less than % by volume, it is difficult to sufficiently reduce the amount of smoke and irritating gas generated when manufacturing a smoke-free mold or during casting. Furthermore, if the amount of the inorganic water retaining material mixed exceeds 4.5% by volume, it is impossible to reduce the decrease in strength of a mold manufactured using the material. However, if the mold strength reduction rate is only 20%, the mixing amount may be 7.5% by volume or less.

In addition, when this mixing amount is 4.0-4.2 volume%, since the effect of this invention can be exhibited even more, it is more preferable.

Further, other additives may be appropriately added and mixed to the smoke-free molding material of the present invention to the extent that the excellent performance of the material is not impaired. Specifically, metal oxides such as zinc oxide, iron oxide, manganese oxide, titanium oxide, etc. are added to the mold after casting for the purpose of promoting hardening of the resin in the mold manufacturing process or thermal decomposition of the resin in the casting process. Halogen-based substances are added to the resin to improve the disintegration properties of the product, fillers such as steel balls, ballast, and silica sand are used to prevent the mold from forming during casting. Wetting agents such as kerosene are used to uniformly coat resin on the surface of foundry sand such as silica sand with flammable volatile substances such as pitch powder, coke powder, graphite powder, and gilsonite. Depending on the purpose, these additives may be included in the resin, or they may be mixed at an appropriate time, such as when coating molding sand with resin, or when mixing and adjusting smoke-free molding material. do.

A typical method for adjusting the smoke-free mold material of the present invention is briefly shown below.

First, resin-coated molding sand is prepared by sequentially coating a mold material base material with a resin such as phenol-formaldehyde resin, a hardening agent such as hexamethylenetetramine, and a lubricant such as calcium stearate in accordance with a conventional method.

Next, prepare an inorganic water retaining material that has a pore structure, has the ability to adsorb and desorb moisture even at 100 to 250°C, and has a water holding capacity of 30% by weight or more. Adjust accordingly. The shape and size of the inorganic water-retaining material may be appropriate, and the inorganic water-retaining material may be calcined at 400 to 800° C. before or after the pulverization step.

Next, an inorganic water retaining material having a predetermined moisture content is added in a predetermined amount of 1.5 to 4.5% by volume of the mold material base material, and mixed so as to be uniformly dispersed. Furthermore, appropriate additives are added to the mixture as necessary, and a mortar mixer is used.
The mixture is kneaded using a kneader such as a speed muller or a speed mixer so as to be uniformly dispersed, thereby obtaining a smoke-free molding material according to the present invention. Note that the additive may be added before the addition of the water glass-containing inorganic water retaining material. Further, necessary additives may be added to the resin for coating when producing the resin-coated foundry sand.

The thus obtained smoke-free molding material according to the present invention, as conceptually shown in FIG. 1, consists of foundry sand 2 coated with resin 1 and inorganic water retaining material 3 containing water glass.

〔Example〕

Examples of the present invention will be described below.

First Example A water glass-containing inorganic water retaining material was prepared by using hydrated magnesium silicate clay mineral and coconut husk activated carbon as an inorganic water retaining material, and adding various solid contents of water glass. After manufacturing a mold material using the water glass-containing inorganic water retaining material, a mold was formed using the material, and performance evaluation was performed.

First, as inorganic water retaining materials, hydrated magnesium silicate clay minerals (sample numbers 1 to 10) with a water holding capacity of 46.7% by weight and a particle size of 149 to 297 μm and a water containing capacity of 39.7% by weight and a particle size of 149 to 297 μm were used. Coconut shell activated carbon (sample number 11) was prepared. Next, the water glass aqueous solution with the solid content shown in Table 1 and the inorganic water retaining material were placed in a furnace at 40°C,
In the furnace, the amounts shown in Table 1 per 10 g of the inorganic water retaining material were added and mixed. Thereafter, it was dried in an oven at 100°C for about 40 minutes to produce water glass-containing inorganic water retaining materials having the water glass solid content and water holding capacity shown in Table 1 (sample numbers 1 to 11).
). The water content was expressed as the amount of water when approximately 40 mg of water was added to the inorganic water-retaining material dried at 100° C. and the surface of the inorganic water-retaining material became wet.

Next, commercially available silica sand (Mikawa Siliceki Co., Ltd.: particle size No. 6), 2% by weight of novolak phenol resin and 4% by volume of the water glass-containing inorganic water retaining material were added to the silica sand, and a small The smoke-free mold materials of this example were obtained by mixing with a mortar mixer (sample numbers 1 to 11).Next, using this smoke-free mold material, the mold temperature was adjusted using a mold capable of forming three pieces of 10 mm x 10 mm x 135 mm. A mold was produced under conditions of 250°C and a furnace temperature of 350°C for 1 minute.

At this time, the moldability of the mold was very good. In addition, as a result of observing the amount of smoke emitted during heating during mold production and conducting a sensory test on the odor generated, no smoke was observed, nor was any irritating odor or unusual odor observed. In addition, a strength test of the mold was conducted. The results are shown in Table 1. The strength of the mold without the addition of an inorganic water retaining material was 52 kg/cm2 on average. In addition, the inorganic water retaining material was added at a furnace temperature of 800°C.
The water holding capacity of the inorganic water-retaining material after firing and the mesh size of 48-100 (297 μm-149 μm
) to the amount before firing (residual amount) was investigated.

The results are shown in Table 1. Note that the size of the pores can be determined based on this water-retaining ability, and the state of contraction can be determined based on the remaining amount.

For comparison, a hydrated magnesium silicate clay mineral containing no water glass was used as an inorganic water retaining material (sample number C1).
), hydrated magnesium silicate clay mineral containing CaCl2 instead of water glass was used as an inorganic water retaining material (sample number C2), coconut shell activated carbon not containing water glass was used as an inorganic water retaining material (sample number C3) , water capacity is 30
For comparison, Kanuma soil with an inorganic water retention material of less than 30% by weight (sample numbers C4 to C7) and Akadama soil with a water content of less than 30% by weight using an inorganic water retention material (sample numbers C8 to C10) A comparative inorganic water retaining material and a comparative mold material were prepared using an inorganic water retaining material and the conditions other than Table 2 were the same as in the above examples, and the same performance evaluations were performed. The results are shown in Table 2. Further, a firing test of the comparative inorganic water retaining material was conducted in the same manner as in the above example. The results are shown in Table 2.

As a result, when the water glass-containing inorganic water retaining materials shown in sample numbers 3, 4, 7, 8, and 11 were used, the strength reduction rate was small and was 12% or less. This value is close to the variation range of 10 kg/cm 2 when the number of strength tests is increased with a mold material to which no inorganic water retaining material is added. These improved strength reduction by 40% or more compared to inorganic water retaining materials that do not contain water glass. The reason why the strength reduction rate is small but the water absorption capacity is large is because water glass contains a large amount of water. However, although small pores remain after the water has drained out of the water glass, it is thought that because less resin is absorbed, the strength of the mold is less likely to deteriorate. Furthermore, when these water glass-containing inorganic water retaining materials are fired at 800°C, those with a mesh size of 48 to 100 become less than 84% by weight of the weight before firing, which is thought to be due to volumetric shrinkage. Furthermore, the water holding capacity after firing was approximately 18% by weight or less, indicating that the number of pores was reduced.

Next, in sample number 5, absorption into the inorganic water retaining material was rather slow, probably due to the high viscosity of the water glass aqueous solution. Furthermore, if water glass No. 3 (solid content 38.5%) is used as is, the inorganic water retaining material will not be absorbed and will form large lumps. On the other hand, sample number 6 has a large amount of water glass aqueous solution and remains on the surface of the inorganic water retaining material. Since these materials have moisture on the surface of the inorganic water-retaining material, it seems difficult to reduce the decrease in strength.

Also, although the reason is not clear, sample numbers 1, 9, and 10
Those with a small water glass solid content, such as
The mold strength reduction rate increased.

On the other hand, Sample No. C2 of the comparative example contains CaCl2, which has a high solubility in water and is thought to leave a large amount of solid content in the pores of the inorganic water retaining material. In this case, although the mold strength reduction rate was very small, a strong chlorine-based pungent odor was generated even when the sample was small in size as in this comparative example.

In addition, when using comparative inorganic water retaining materials containing water glass in Kanuma soil and Akadama soil, which have a water-holding capacity of less than 30% by weight, the decrease in mold strength was approximately the same when the water glass content was low. However, as the water glass content increases, the mold strength decreases to a greater extent than that of a mold that does not contain water glass. This is thought to be because the water glass remains on the surface of the inorganic water retaining material because the water glass content is small due to the small number of pores.

As described above, in the case of an inorganic water-retaining material having a water-retaining capacity of 30% by weight or more, it can be seen that the reduction in mold strength is improved by containing water glass. In addition, unlike inorganic water-retaining materials, it cannot be determined by the water-retaining capacity alone, but by incorporating the inorganic water-retaining material so that the solid content remaining in the pores is 20 to 35% by weight, the reduction in mold strength can be improved. growing. Note that it is necessary to prevent an aqueous solution of water glass from remaining on the surface of the inorganic water retaining material, and no water glass from remaining on the surface after drying.

Second Example Using the water glass-containing hydrated magnesium silicate clay mineral obtained in Sample No. 3 of the first example, the water glass-containing inorganic water retaining material was fired once at 800°C for 5 hours (sample Sample No. 12), similarly fired three times (Sample No. 13)
), a comparative inorganic water retaining material (sample number C11) was prepared by firing a hydrated magnesium silicate clay mineral containing no water glass once in the same manner.

Next, foundry sand was prepared by mixing commercially available silica sand (Mikawa Siliceki Co., Ltd.: grain size 6) and each of the above-mentioned fired water glass-containing inorganic water retaining materials in an amount of 4% by volume based on the silica sand. Against 2.
5% by weight of novolak phenolic resin, 15% by weight of hexamethylenetetramine based on the resin, and 0.1% by weight of calcium stearate based on foundry sand were placed in a mix mara and mixed in order to obtain a mold material. .

Next, a mold was produced using this mold material in the same manner as in the first example. At this time, the moldability of the mold was very good.

Next, the strength test of the mold was conducted in the same manner as in the first example. As a result, the strength reduction rate of the mold was 2 for sample number 12.
8%, sample number 13 was 24%, and sample number C11 as a comparative example was 55%.

In this way, the rate of decrease in the sample containing water glass was less than half that of the sample without water glass. Furthermore, it can be seen that the mold strength reduction rate is smaller, albeit slightly, when the mold is fired three times than when it is fired once, and the number of pores in the inorganic water retaining material decreases with each repetition.

Furthermore, when recycled, it is difficult to separate and measure how much inorganic water retaining material remains in the mold material base material. Therefore, as shown in Table 1, the amount remaining as an inorganic water retaining material of the size to be used is 77% by weight of the added amount, and the mold material base material used as usual is 50% by volume of the new base material.
When using recycled base material at a ratio of 50% by volume and adding 4% by volume of inorganic water-retaining material containing water glass, the amount of inorganic water-retaining material that ultimately remains on the mold material base material after repeated use converges to approximately 1.6% by volume. However, considering that the amount is less than half of the newly added water glass-containing inorganic water retaining material and that the strength of the remaining inorganic water retaining material decreases each time it is repeated, the water glass-containing inorganic water retaining material of this example The material can be used practically without any problems.

Third Example A mold material was manufactured using foundry sand, a novolak phenolic resin, and an inorganic water-retaining material containing water glass, and then a mold was formed using the material, casting was performed, and performance evaluation was performed.

First, as an inorganic water retaining material, the water holding capacity is 46.7% by weight,
Hydrous magnesium silicate clay mineral with a particle size of 149 to 297 μm and a water-containing capacity of 39.2% by weight and a particle size of 149
An inorganic water retaining material made of coconut shell activated carbon with a diameter of ~297 μm was prepared. Next, the water glass aqueous solution having a solid content of 24% and the inorganic water retaining material were placed in a furnace at 40° C., and the water glass aqueous solution was mixed in the furnace at a ratio of 9 cc to 10 g of the inorganic water retaining material. After that, dry in a 100°C oven for about 40 minutes to
Water glass-containing inorganic water retaining materials having the water holding capacity, water content, and water glass solid content shown in the table were prepared (sample numbers 14 to 25).
).

Next, commercially available silica sand (Mikawa Siliceki Co., Ltd.: particle size No. 6), 2% by weight of novolak phenol resin based on the silica sand, 15% by weight of hexamethylenetetramine based on the resin,
0.1% by weight of calcium stearate was added to the silica sand in a small speed mixer and sequentially mixed to produce resin-coated foundry sand. Furthermore, the above water glass-containing inorganic water retaining material was added to the silica sand in the amount shown in Table 3, and mixed in a small mortar mixer to obtain smoke-free molding materials of this example (sample numbers 14 to 25).

Next, this smoke-free mold material was heated to 250°C in advance and was made into an outer diameter of 80 mm x inner diameter of 60 mm x height of 135 mm x bottom thickness of 1 mm.
It was placed in an iron mold for cup-shaped products with a diameter of 5 mm and a draft angle of 2 degrees, and the mold was heated and held at 400° C. for 2 minutes in a siliconite furnace, and then taken out from the furnace and the mold was removed to obtain a mold.

At this time, the moldability of the mold was very good.

In addition, the amount of smoke emitted during heating during mold production was observed and a sensory test was conducted on the odor emitted. The results are shown in Table 4. In the table, regarding the smoke generation status, "◎" indicates "no smoke is observed", "△" indicates "slight smoke is observed", and "x" indicates "a small amount of smoke is observed". In addition, in the table, regarding the irritating odor, "◎" indicates that "no irritating odor is observed" and "△" indicates that "the irritating odor is slightly felt." As is clear from Table 4, when the additive amount was 1.5% by volume or more and the water content was 5% by weight or more, no smoke was observed, and no irritating odor or abnormal odor was observed. Ta. Next, the strength of the mold was tested. The results are shown in Table 4.

As is clear from the table, the strength reduction of the mold was approximately 7%, which was well below the allowable range of 20%.

Furthermore, the mold material after casting was collected and evaluated as recycled sand. That is, in the resin-coated molding sand production process, 50% of the silica sand was replaced with the recycled sand containing the water glass-containing inorganic water retention material, and a smoke-free molding material was produced in the same manner as above, and evaluated in the same manner. I did it. As a result, the smoke generation and the level of irritating odor during the manufacturing of the mold were as good as those not using recycled sand, and the degree of decrease in mold strength was also approximately the same. Further, cast iron and molten aluminum were poured into the mold, but the mold did not lose its shape.

For comparison, the above-mentioned hydrated magnesium silicate clay mineral containing no water glass was used as an inorganic water-retaining material (sample number C12), and a water-glass-containing hydrated magnesium silicate clay mineral was used as an inorganic water-retaining material in an amount smaller than the specified amount. (sample number C13), water glass-containing hydrated magnesium silicate clay mineral in an amount greater than the specified amount as an inorganic water-retaining material (sample number C14), and water retention capacity of 30
Those using less than % by weight of inorganic water retaining material (sample number C15
~C22) were used as comparative inorganic water retaining materials, and the conditions other than those in Table 5 were the same as in the above Examples to produce comparative mold materials, and the same performance evaluations were performed. The results are shown in Table 6. 6th
As is clear from the table, the mold strength of the comparative examples of sample numbers C12 and C14 is significantly lower than that of the present example. In addition, in the case of sample number C13, although there was little decrease in mold strength, a small amount of smoke was observed after casting during mold production, and a pungent odor was also felt. Moreover, in the case of sample numbers C15 to C22, it can be seen that the mold strength is significantly lower than that of this example.

Claims (1)

[Claims] Claim 1: A mold material in which a mold material base material is coated with a thermosetting resin, etc., which has a pore structure, has a water-containing capacity of 30% by weight or more, and has the ability to adsorb and desorb water even at 100 to 250°C. It also consists of an inorganic water retaining material containing water glass.
The mixing amount of the inorganic water retaining material is 1.5 to 4.
A smoke-free molding material characterized by having a content of 5% by volume.