JP7061925B2 - Manufacturing method of sand mold for casting - Google Patents

Description

The present invention relates to a method for manufacturing a sand mold for casting.

In recent years, it has become possible to cast products of various shapes by manufacturing sand molds for casting by a laminated molding method. In particular, in the inkjet-type laminated molding method, a curing agent, which is a catalyst for curing a binder, is kneaded into cast sand to form kneaded sand, and the kneaded sand is spread by a blade mechanism to form an inkjet. Like the print head of a printer, the binder is discharged while moving the discharge head, and the binder is applied to a predetermined region of the thin layer to cure the kneaded sand. Therefore, according to the inkjet-type laminated molding method, a large model can be quickly modeled by using a large discharge head, and large products such as a cylinder head for a large engine and an impeller for a large pump can be advantageously manufactured. can do.

In such an inkjet-type laminated molding method, it is common to use cast sand made of natural silica sand. However, when cast sand made of natural silica sand is used, there is a problem that burr-like defects called vaning defects are likely to occur in the product after casting, and various measures are taken. For example, Patent Document 1 shows that the occurrence of vaning defects can be suppressed by preparing casting sand having a predetermined linear thermal expansion coefficient and a predetermined fluidity.

Further, as the casting sand, in addition to natural sand such as natural silica sand, artificial sand produced by a sintering method, a melting method (atomizing method) or a flame melting method is generally known. As described in Patent Document 2, for example, the sintering method is a method for producing artificial sand by spray-drying a raw material slurry and firing spherical granules obtained by firing with a rotary kiln or the like. Further, the melting method is a method for producing artificial sand by, for example, as described in Patent Document 3, the molten raw material is blown into the air by spraying or spraying air and spheroidized by surface tension. Further, the flame melting method is a method for producing artificial sand by melting a raw material in a flame and spheroidizing it, as described in Patent Document 4, for example.

Japanese Patent No. 5249447 Japanese Unexamined Patent Publication No. 5-169184 Japanese Patent Application Laid-Open No. 2003-251434 Japanese Unexamined Patent Publication No. 2004-202777

Since the artificial sand as described above has a lower coefficient of linear thermal expansion than that of natural sand, if such artificial sand can be used as casting sand in place of natural sand in the inkjet stereolithography method, it will cause vaning defects. It is thought that the occurrence can be suppressed. Here, when cast sand made of artificial sand by the sintering method is used, the fluidity of the kneaded sand in the recoater of the blade mechanism in the laminated molding apparatus is sufficiently ensured, and the layer of the kneaded sand is secured by the blade mechanism. As a result of investigation and research by the applicant, it has been found that the sand mold can be produced without any problem.

On the other hand, when cast sand made of artificial sand produced by the melting method and / or artificial sand produced by the flame melting method is used, the fluidity of the kneaded sand in the recoater is sufficient. It was not possible to manufacture sand molds. However, the foundry sand made of artificial sand produced by the melting method and / or the artificial sand produced by the flame melting method can obtain higher strength with a smaller amount of binder than the foundry sand made of artificial sand produced by the sintering method. Therefore, it is more desirable if it can be applied to an inkjet laminated molding method.

The present invention has been developed under such circumstances, and is a casting sand mold capable of reducing the amount of the binder used and improving the strength, and suppressing the occurrence of vaning defects in the cast product. The purpose is to provide a manufacturing method.

The method for manufacturing a sand mold for casting according to the present invention is
A casting sand preparation step for preparing casting sand having a median diameter d50 of 280 μm or more, including artificial sand produced by the melting method and / or artificial sand produced by the flame melting method.
A kneading step of kneading the casting sand with a curing agent, which is a catalyst for curing the binder, to obtain kneaded sand.
A laminating step of forming a sand mold for casting by applying the binder and hardening the kneaded sand layer by layer.
It is characterized by having.

Further, in the method for producing a sand mold for casting according to the present invention, the casting sand is preferably composed of artificial sand produced by a melting method and / or artificial sand produced by a flame melting method.

Further, in the method for producing a sand mold for casting according to the present invention, it is preferable that the particle size d80 of the total volume of the casting sand prepared in the casting sand preparation step of 80% is 400 μm or less.

According to the present invention, it is possible to provide a method for producing a sand mold for casting, which can reduce the amount of the binder used and improve the strength, and can suppress the occurrence of vaning defects in the cast product.

It is a flow chart which shows each process in the manufacturing method of the sand mold for casting which concerns on one Embodiment of this invention. (A) is a conceptual diagram showing a state in which the surface of sand particles is covered with a curing agent, and (b) is a partially enlarged view of (a). It is a graph of the experimental result which shows the relationship between the stacking pitch and the bending strength. It is a particle size distribution map of the foundry sand used in the experiment of FIG.

Hereinafter, a method for manufacturing a sand mold for casting according to an embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, in the method for manufacturing a sand mold for casting according to the present embodiment, first, a casting sand preparation step S1 for preparing casting sand is performed. Then, following the casting sand preparation step S1, a kneading step S2 is performed in which the casting sand is kneaded with a curing agent which is a catalyst for curing the binder to make kneaded sand. Then, following the kneading step S2, a laminating step S3 is performed in which the kneaded sand is laminated layer by layer, and a binder is applied to cure the kneaded sand to form a sand mold for casting.

As the casting sand prepared in the casting sand preparation step S1, a casting sand having a median diameter d50 of 280 μm or more, which contains artificial sand produced by the melting method and / or artificial sand produced by the flame melting method, is used. The melting method is a method for producing artificial sand by blowing a molten raw material into the air by blowing or spraying air and spheroidizing it by surface tension. The flame melting method is a method for producing artificial sand by melting a raw material in a flame and spheroidizing it. By using artificial sand produced by such a melting method and / or casting sand containing artificial sand produced by the flame melting method, the linear thermal expansion coefficient of the produced sand mold is suppressed, and thus Verneuil defects are generated. Can be suppressed. As the composition of the artificial sand, alumina (Al—O system), mullite (Al—Si—O system), mullite-zircon (Al—Si—Zr—O system) mixed system and the like are suitable. Further, as the artificial sand, at least one selected from fresh sand, recovered sand thereof and regenerated sand thereof can be used.

The casting sand prepared in the casting sand preparation step S1 is preferably composed of artificial sand produced by the melting method and / or artificial sand produced by the flame melting method. However, the casting sand prepared in the casting sand preparation step S1 is, in addition to the artificial sand produced by the melting method and / or the artificial sand produced by the flame melting method, the artificial sand produced by the sintering method and / or It may contain natural sand such as natural silica sand, and even in this case, the effect of containing artificial sand produced by the melting method and / or artificial sand produced by the flame melting method can be enjoyed. ..

The median diameter d50 is a particle size with a cumulative volume of 50% in the particle size distribution curve measured by the laser diffraction / scattering method. By setting the median diameter d50 of the casting sand to 280 μm or more, even when the artificial sand produced by the melting method and / or the casting sand made of the artificial sand produced by the flame melting method is used, the laminating step described later. In S3, the fluidity when the kneaded sand is filled in the recoater of the blade mechanism can be ensured, and a layer of the kneaded sand can be formed. The median diameter d50 of 100% natural silica sand cast sand, which is usually used in conventional laminated molding, is 140 μm. When using cast sand having a median diameter d50 of 140 μm, which consists of artificial sand produced by the melting method and / or artificial sand produced by the flame melting method, the kneaded sand does not sufficiently flow in the recoater, so that the sand mold (Laminated molding was possible when a predetermined amount of natural silica sand having a median diameter d50 of 140 μm was blended).

Here, the reason why the fluidity inside the recoater can be improved by increasing the particle size is presumed as follows. Artificial sand produced by the melting method or the flame melting method consists of sand particles having a smooth spherical surface. When such artificial sand is kneaded with a liquid curing agent, the surface of the sand particles is covered with the liquid curing agent as shown in FIG. 2 (a). At this time, as shown in FIG. 2B, the curing agent gathers at the contact points between the particles to form a liquid neck. In order for the sand to flow in this state, it is necessary to cut the neck and separate the sand particles from each other. The force that the sand in such a solid-liquid mixed state tries to flow inside the recoater is proportional to the weight of the sand particles, and is therefore proportional to the cube of the particle size. On the other hand, the force that the sand tries to aggregate is due to the surface tension of the hardening agent between the sand particles, and the force is proportional to the circumference of the neck, so that it is proportional to the particle size. Therefore, when the particle size of the sand exceeds a predetermined size, it is considered that the fluidity becomes superior to the force that the sand tries to aggregate.

Further, as the casting sand prepared in the casting sand preparation step S1, it is preferable to use casting sand having a cumulative volume of 80% and a particle size d80 of 400 μm or less. Here, the particle size d80 is a particle size with a cumulative volume of 80% in the particle size distribution curve measured by the laser diffraction / scattering method. By setting the particle size d80 of the casting sand to 400 μm or less, it is possible to advantageously manufacture a sand mold for casting having practically preferable strength. The reason is as follows.

The strength of the sand mold obtained by laminating molding tends to improve as the laminating pitch becomes thinner because the amount of the binder added increases. However, it has been found by the applicant's investigation that when the stacking pitch is reduced, the step-like strength decreases when the stacking pitch becomes thinner than the particle size d80. FIG. 3 shows the results of experiments conducted by the applicant. In FIG. 3, the horizontal axis represents the stacking pitch and the vertical axis represents the bending strength. In this experiment, cast sand produced by the melting method was sieved with 50 mesh. The result of measuring the particle size distribution using the laser diffraction scattering method is shown in FIG. Then, by laminating and modeling this cast sand, a sand mold having a size of 22.4 mm × 22.4 mm × 172 mm was produced, and the strength was measured by three-point bending with a span of 150 mm. From FIG. 3, it can be seen that the strength decreases when the stacking pitch becomes thinner than about 360 μm. It is presumed that this decrease in strength is due to an increase in the proportion of particles larger than the laminated thickness. Further, from the particle size distribution shown in FIG. 4, the d80 of the cast sand used in this experiment is about 360 μm. From these results, it is considered that the strength decreases when the stacking pitch becomes thinner than the particle size d80.

Further, in the range of the particle size and the stacking pitch that do not cause such a decrease in strength, it is necessary to set the stacking pitch to a thickness of 400 μm or less in order to obtain a sand mold having a practically preferable strength. Here, the practically preferable strength is a bending strength of about 2 MPa, which is usually required for a sand mold for casting a large cylinder block made of ductile cast iron, a large crankcase, or the like.

Therefore, in order to produce a sand mold having practically preferable strength without causing a decrease in strength due to an increase in the proportion of particles larger than the laminated thickness, the particle size d80 should be set to the stacking pitch or less and the stacking pitch should be 400 μm or less. Must be. As described above, in order to advantageously produce a sand mold having practically preferable strength, the particle size d80 needs to be 400 μm or less.

Further, as the curing agent to be kneaded into the casting sand in the kneading step S2, a conventionally known curing agent can be used as long as it is a catalyst for curing the binder, but for example, an acid such as furan resin can be used as the binder. When an organic resin that is cured by a dehydration-condensation polymerization reaction using a catalyst is used, it is preferable that the organic resin is cured at room temperature. For example, it is mainly composed of organic sulfonic acid such as xylene sulfonic acid and toluene sulfonic acid and sulfuric acid. The kneading ratio of the curing agent is preferably in the range of 0.01 to 1.0% by mass with respect to the total amount of kneaded sand. This is because when the curing agent is kneaded in this range, the moldability and fluidity of the kneaded sand are best balanced.

Further, as the binder to be applied to the kneaded sand laminated in the laminating step S3, it is preferable to use an organic resin, particularly a furan resin or a phenol resin. The furan resin may be, for example, one or more selected from the group consisting of furfuryl alcohol, a condensate of furfuryl alcohol and aldehydes, and a condensate of urea and aldehydes, or two or more condensates selected from the above group. Examples include furan resin composed of. Examples of the phenol resin include condensates of phenols and aldehydes.

In the laminating step S3, as described above, the sand mold for casting is formed by laminating the kneaded sand layer by layer and applying a binder to cure the kneaded sand. For example, based on the data obtained by 3DCAD designing the shape of the sand mold, first using an inkjet type three-dimensional laminated molding device (for example, Ex One S-15 (trademark), distributor: EX ONE Co., Ltd.). A thin layer of kneaded sand is uniformly spread on a flat surface by a blade mechanism in which the recoater is filled with kneaded sand, and then the discharge head (print head) is scanned based on the above-mentioned 3D CAD data to obtain the thin layer of the kneaded sand. The binder can be discharged and applied (printed) to a predetermined area.

The layer in the area where the binder is printed is in a bonded state and is also bonded to the already formed lower layer. Then, the steps of sequentially forming thin layers on the upper part and printing the binder are repeated until the entire sand mold is completed. Finally, the region to which the binder was not applied is in a non-bonded state, so that the kneaded sand can be easily removed from the sand mold. By the above operation, a sand mold having a desired three-dimensional structure can be manufactured. When a thermosetting phenol resin is used as the binder, the laminate containing the sand mold is heat-treated (preferably microwave heating) before the sand mold is taken out from the kneaded sand on which the binder is not printed. It is preferable to apply the above to completely cure the sand mold.

According to the method for producing a sand mold for casting according to the present embodiment, since artificial sand produced by a melting method and / or casting sand containing artificial sand produced by a flame melting method can be used, a binder is used. It is possible to reduce the amount and improve the strength, and it is possible to suppress the occurrence of vaning defects in the cast product.

Although various embodiments of the present invention have been described above, it goes without saying that the above-mentioned points are merely examples of the embodiments of the present invention, and various changes may be made as long as the gist of the invention is not deviated. stomach.

As an example of the present invention, when an attempt was made to manufacture a sand mold having a long rectangular parallelepiped shape under the following conditions, the sand mold could be manufactured without the kneaded sand staying in the recoater.
・ Three-dimensional laminating equipment: ExOne S-15 (trademark) (sold by: EX ONE Co., Ltd.) ・ Casting sand: Espal # 60 (sold by Yamakawa Sangyo Co., Ltd.) composed of 100% new sand ・ Amount of hardener added : 0.20% by mass
-Laminating pitch: 360 μm
Here, the median diameter d50 of the cast sand (Espearl # 60) was 280 μm.

From the results of this example, it can be seen that a sand mold for casting can be manufactured by an inkjet laminated molding method by using casting sand having a median diameter d50 of 280 μm or more, which is made of artificial sand produced by the melting method. Also, only when blended with artificial sand produced by the flame melting method or artificial sand produced by the flame melting method, which has the same sphericity and smoothness of the sand particle surface as the artificial sand produced by the melting method. It is presumed that the sand mold for casting can be manufactured by the inkjet type laminated molding method by setting the median diameter d50 to 280 μm or more even when the casting sand is similarly formed. Further, even when natural sand or artificial sand produced by a sintering method is blended, it is clear that sand molds can be produced if the median diameter d50 of the cast sand is 280 μm or more.

S1 Casting sand preparation process S2 Kneading process S3 Laminating process

Claims (2)

A casting sand preparation step for preparing casting sand having a median diameter d50 of 280 μm or more, including artificial sand produced by the melting method and / or artificial sand produced by the flame melting method.
A kneading step of kneading the casting sand with a curing agent, which is a catalyst for curing the binder, to obtain kneaded sand.
A laminating step of forming a sand mold for casting by applying the binder and hardening the kneaded sand layer by layer.
Have,
A method for manufacturing a sand mold for casting, characterized in that the particle size d80 having a cumulative volume of 80% of the cast sand prepared in the casting sand preparation step is 400 μm or less . The method for producing a sand mold for casting according to claim 1, wherein the casting sand is composed of artificial sand produced by a melting method and / or artificial sand produced by a flame melting method.

Images