JP3581687B2 - Sand core for casting and method for producing the same - Google Patents

Sand core for casting and method for producing the same Download PDF

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Publication number
JP3581687B2
JP3581687B2 JP2001393901A JP2001393901A JP3581687B2 JP 3581687 B2 JP3581687 B2 JP 3581687B2 JP 2001393901 A JP2001393901 A JP 2001393901A JP 2001393901 A JP2001393901 A JP 2001393901A JP 3581687 B2 JP3581687 B2 JP 3581687B2
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Japan
Prior art keywords
core
coating layer
slurry
layer
casting
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
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JP2001393901A
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Japanese (ja)
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JP2003191048A (en
Inventor
光明 上野
繁光 中林
哲司 梅本
篤 鈴木
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本田技研工業株式会社
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Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sand core for casting and a method for producing the same, and more particularly, it is possible to obtain a cast product having excellent dimensional accuracy, easily separate the cast product from the cast product, and easily collapse the product. And a method for producing the same.
[0002]
[Prior art]
Manufacture of an aluminum cast product by the die casting method is performed by placing a sand core in a cavity, closing a mold, introducing an aluminum melt into the cavity at high pressure and high speed, and then cooling and solidifying the melt. ing. At this time, a hollow portion having a shape corresponding to the shape of the sand core is formed in the casting.
[0003]
Sand cores are generally manufactured as follows. That is, first, silica sand (mainly composed of SiO 2 ), zircon sand (composite oxide of silicon and zirconium), chromite sand (mainly composed of composite oxide of iron and chromium), and high alumina sand (Al 2 O 3) Particles such as a main component) are mixed with an organic binder such as a phenol resin and molded into a predetermined shape to form a core body. This core body has a bending strength of about 4 to 6 MPa.
[0004]
Next, a coating layer is formed on the surface of the core body. This coating layer is for preventing the molten metal from penetrating into the core body. By the presence of the coating layer, it is possible to prevent the casting from being hardly separated from the core body and to prevent the casting from being rough.
[0005]
Various studies have been made on the material of the coating layer. For example, in Japanese Patent Publication No. 57-59013, it is obtained by drying and solidifying a first slurry which contains a powdery refractory and a water-soluble thermosetting resin, and whose pH and viscosity are adjusted with a water glass aqueous solution. It has been proposed that a first layer and a second layer obtained by drying and solidifying a second slurry containing mica or the like be a coating layer (hereinafter referred to as Conventional Technique 1).
[0006]
When the coating layer is too strong, it is not easy to disintegrate the sand core. In other words, the disintegration of the sand core decreases. Therefore, in the prior art 1, the amount of the organic binder in the core body is set to 2.95% by weight, which is smaller than the general amount, so that the core body is easily collapsed.
[0007]
In Japanese Patent Publication No. 3-36614, a first layer containing no organic binder is first formed, a low-temperature decomposable resin is applied on the first layer, and then a second layer containing flaky graphite or mica is formed. To maintain the disintegrability of the sand core (hereinafter referred to as Conventional Technique 2).
[0008]
[Problems to be solved by the invention]
However, in the above-mentioned conventional technology 1, when the molten metal is introduced into the cavity, the second layer may be separated from the first layer. When such a situation occurs, a portion corresponding to a portion where the second layer has separated from the cast product is protruded, so that dimensional accuracy is reduced. In addition, the water glass contained in the first layer reacts with the molten aluminum, and as a result, a composite layer of the first layer and aluminum is generated, so that it is difficult to separate the casting from the sand core. Invite.
[0009]
Further, as described above, in the prior art 1, since the amount of the organic binder is small, the core body is easily cracked. For this reason, if a crack exists at a location where the second layer has separated, when the molten metal is inserted into the crack and solidified by cooling, it is difficult for the casting and the sand core to separate.
[0010]
As a result, in the prior art 1, when the second layer is separated from the first layer, the dimensional accuracy of the casting is reduced, and it is difficult to remove the casting from the sand core.
[0011]
On the other hand, in the prior art 2, since the first layer does not contain the organic binder, the first layer and the core body may not be bonded with sufficient force. For this reason, cracks are likely to occur in the core body, so that the molten metal is easily inserted and the cast product and the sand core are unlikely to separate from each other, similarly to the prior art 1.
[0012]
The present invention has been made in order to solve the above-mentioned problem, and it is possible to avoid insertion of a molten metal, and therefore, it is possible to obtain a casting having excellent dimensional accuracy. And a method for producing the same.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention includes a core body in which aggregate particles are bonded to each other by a binder, and contains a powdered refractory and an organic binder , and coats a surface of the core body. With a coating layer,
As the powdery refractory, particles having different average particle sizes are blended with each other,
A part of the coating layer is connected to the core body while being buried in pores of the core body.
[0014]
As the coating layer is buried in the core body, pores existing near the surface of the core body are closed. Therefore, the permeation of the molten metal into the core body during the casting operation is significantly suppressed. In other words, it is possible to prevent the molten metal from being inserted into the core body, so that it is possible to obtain a cast product having good dimensional accuracy and less rough surface.
[0015]
In addition, since the molten metal does not enter the core body, the casting can be easily separated from the sand core.
[0016]
Here, it is preferable that particles having mutually different average particle diameters are blended as the powdery refractory. In this case, the pores existing in the vicinity of the surface of the core body can be reliably filled mainly with a small particle size. On the other hand, a coating having a large particle size can form a coating layer on the surface of the core body.
[0017]
As the sand core for casting, it is preferable that the second layer containing the lubricity-imparting substance is provided on the coating layer. This is because the presence of the second layer makes it easier to separate the casting from the sand core.
[0018]
Preferred examples of the lubricity-imparting substance include mica.
[0019]
Further, the core body preferably contains a composite oxide of aluminum oxide and silicon oxide as a constituent material. This composite oxide has a very low coefficient of thermal expansion. Therefore, the core body is unlikely to undergo thermal expansion, so that the internal stress generated in the core body due to the thermal expansion is significantly reduced. Therefore, it is possible to avoid the occurrence of cracks in the core body, and eventually, it is possible to further improve the dimensional accuracy of the cast product.
[0020]
Further, the present invention provides a first step of preparing a slurry for a coating layer containing a powdery refractory and an organic binder having different average particle diameters ,
A second step of penetrating the coating layer slurry into the pores of the core body and laminating the slurry on the surface of the core body;
A third step of drying and solidifying the coating layer slurry to form a coating layer;
It is characterized by having.
[0021]
According to such a manufacturing method, after the coating layer slurry permeates the core body and fills the pores existing near the surface of the core body, the remaining coating layer slurry is applied to the surface of the core body. Laminate. Therefore, it is possible to reliably obtain a coating layer partially buried in the core body.
[0022]
In this case, it is preferable to prepare and use a slurry for a coating layer in which powdered refractories having different average particle diameters are blended. The coating layer slurry is formed by leaving the pores, which are difficult to flow into the pores, on the surface of the core body, while the pores can be reliably closed mainly by the small particle diameter. This is because a layer can be provided.
[0023]
When a second layer for facilitating detachment of the casting is provided, in addition to the above first to third steps, a fourth step of preparing a second layer slurry containing a lubricity imparting substance,
A fifth step of laminating the slurry for the second layer on the coating layer;
A sixth step of drying and solidifying the second layer slurry to form a second layer;
Should be performed. In addition, mica can be used as the lubricity-imparting substance.
[0024]
The slurry for the coating layer and the slurry for the second layer preferably contain a wetting agent and an antifoaming agent. The slurry containing the wetting agent has improved wettability. That is, for example, the coating layer slurry spreads and adheres to the surface of the core body. For this reason, the layer made of the slurry for the coating layer, and eventually the coating layer, can be reliably formed on the surface of the core body. The same applies to the slurry for the second layer. The defoaming agent suppresses the generation of foam due to the incorporation of the wetting agent.
[0025]
Octyl alcohol is preferably further added to the slurry for the coating layer and the slurry for the second layer. This is because when octyl alcohol is present, the thickness of the finally formed layer is substantially uniform.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a sand core for casting and a method for producing the same according to the present invention will be described in detail with reference to the accompanying drawings.
[0027]
FIG. 1 shows a schematic overall perspective view of a sand core for casting according to the present embodiment (hereinafter, also simply referred to as a sand core). The sand core 10 is used when a cylinder block (not shown) constituting an internal combustion engine mounted on an automobile body is manufactured as a casting, and the hollow core formed in the cylinder block by the sand core 10 is used. The part is provided as a water jacket part.
[0028]
FIG. 2 shows an enlarged cross-sectional view of the vicinity of the surface of the sand core 10. As understood from FIG. 2, the sand core 10 has a three-layer structure in which a first coating layer 14 and a second coating layer 16 are laminated on the surface of a core body 12 in this order. In FIG. 2, reference numeral 18 indicates closed pores remaining without being filled with the first coating layer 14.
[0029]
In this case, the core body 12 is formed by bonding the particles 20 of the cera beads with a phenol resin (not shown). Here, Celabeads is a trade name of artificial sand sold by ITOCHU CERATECH CORPORATION and contains about 98% of a composite oxide of SiO 2 and Al 2 O 3 .
[0030]
Cerabeads have a significantly lower coefficient of thermal expansion than other common core sands such as zircon sand, chromite sand, silica sand and the like. In other words, the core body 12 is unlikely to undergo thermal expansion even when the molten metal is introduced. For this reason, the occurrence of cracks in the core body 12 is suppressed.
[0031]
The bending strength of the core body 12 is relatively high at about 20 MPa.
[0032]
The lower part of the first coating layer 14 is buried in the core body 12. Such a state can be achieved by filling the pores of the core body 12 with the first slurry to be the first coating layer 14 and then cooling and solidifying the first slurry, as described later. In addition, about 0.5 mm is sufficient for the burial depth D.
[0033]
The first coating layer 14 is formed by bonding zircon flour as a powdery refractory with a phenolic resin (organic binder). In this case, zircon flours having different average particle diameters are mixed. Specifically, a large-diameter zircon flower having an average particle diameter of about 10 μm and a small-diameter zircon flower having an average particle diameter of about 1 μm. The first coating layer 14 does not contain water glass.
[0034]
The distance H from the surface of the core body 12 to the upper end surface of the first coating layer 14 is set to such an extent that the molten metal can be prevented from being inserted into the core body 12 and the disintegration of the sand core 10 is not reduced. . Specifically, it is preferable that it is in the range of 0.1 to 0.3 mm. In the following description, the distance H from the surface of the core body 12 to the upper end surface of the first coating layer 14 is referred to as the thickness H of the first coating layer 14.
[0035]
The second coating layer 16 contains mica as a lubricity-imparting substance. As described later, the presence of the mica allows the cylinder block to be easily separated from the sand core 10. Note that the second coating layer 16 preferably contains an organic binder such as a phenolic resin. This is because the second coating layer 16 is firmly bonded to the first coating layer 14 with each other, so that the second coating layer 16 is hardly peeled off.
[0036]
The thickness T of the second coating layer 16 may be any value as long as sufficient lubricity can be imparted to the cylinder block 10 so that the cylinder block can be easily detached from the sand core 10. For example, the thickness T is about 0.1 mm. it can. In this case, since the first coating layer 14 has almost no pores, the second coating layer 16 is not buried in the first coating layer 14.
[0037]
The sand core 10 according to the present embodiment is basically configured as described above, and its operation and effect will be described next.
[0038]
When the cylinder block is manufactured by the die casting method, the mold is closed after disposing the sand core 10 in the cavity. Then, a molten aluminum at about 600 ° C. is introduced into the cavity at a pressure of about 100 MPa and a speed of about 2.5 m / sec.
[0039]
As described above, the core body 12 is covered with the first coating layer 14 and the second coating layer 16. Since the lower part of the first coating layer 14 is buried in the core body 12, the first coating layer 14 is firmly connected to the core body 12. Therefore, the first coating layer 14 does not flow out together with the second coating layer 16 due to the high-pressure and high-speed molten metal.
[0040]
Moreover, the lower portion of the first coating layer 14 is filled with pores existing near the surface of the core body 12 and is buried. That is, the pores near the surface of the core body 12 are closed by the first coating layer 14. Therefore, the infiltration of the molten metal into the core body 12 is suppressed, so that the molten metal does not flow into the pores existing inside the core body 12.
[0041]
Further, in the present embodiment, as the constituent material of the core body 12, celabeads having an extremely low coefficient of thermal expansion is used. In other words, since the thermal expansion of the core body 12 is extremely small, the internal stress generated in the core body 12 due to the thermal expansion is also extremely small. For this reason, it is possible to avoid the occurrence of cracks in the core body 12, the first coating layer 14, and the second coating layer 16.
[0042]
That is, in the present embodiment, since the first coating layer 14 that is hard to be washed off closes the pores existing near the surface of the core main body 12 and that the core main body 12 is hardly cracked, the molten metal is 12 can be reliably avoided. For this reason, a cylinder block which is a cast product can be obtained with high dimensional accuracy, and the occurrence of roughening of the cylinder block can be suppressed.
[0043]
After the introduction of the molten metal into the cavity is completed, the molten metal is cooled and solidified by being left for a predetermined time. Then, the cylinder block is taken out of the cavity together with the sand core 10, and then the cylinder block is easily separated from the sand core 10. Specifically, the sand core 10 is collapsed by a known technique such as a water jet method or a blast method. At this time, since the first coating layer 14 is provided with the appropriate thickness H, the collapse of the sand core 10 is not prevented.
[0044]
As described above, since the insertion of the molten metal into the sand core 10 is suppressed, a cylinder block having no part inserted into the sand core 10 is inevitably obtained. Further, since the first coating layer 14 does not contain water glass, there is no possibility that aluminum and water glass react to form a composite layer. Therefore, the cylinder block can be easily separated from the sand core 10.
[0045]
In addition, the second coating layer 16 contains mica that imparts lubricity. Therefore, when the cylinder block is detached from the sand core 10, the frictional force between the sand core 10 and the cylinder block becomes extremely small. That is, the cylinder block can be detached from the sand core 10 more easily.
[0046]
The sand core 10 can be manufactured as follows.
[0047]
FIG. 3 shows a flowchart of a method for manufacturing the sand core 10 according to the present embodiment. This manufacturing method includes a first step S1 for preparing a slurry for a first coating layer (hereinafter, referred to as a first slurry), a second step S2 for penetrating and laminating the first slurry to the core body 12, and A third step S3 of drying and solidifying the slurry to form the first coating layer 14, a fourth step S4 of preparing a slurry for the second coating layer (hereinafter, referred to as a second slurry), and applying the second slurry to the first coating There is a fifth step S5 for laminating on the layer 14, and a sixth step S6 for drying and solidifying the second slurry to form the second coating layer 16.
[0048]
First, in a first step S1, a first slurry is prepared. That is, a large particle zircon flour having an average particle diameter of about 10 μm, a small particle zircon flour of about 1 μm, a phenolic resin, a wetting agent, an antifoaming agent, and octyl alcohol are mixed together with water. In this case, the generation of foam due to the wetting agent is suppressed by the action of the antifoaming agent.
[0049]
Next, in a second step S <b> 2, the first slurry is penetrated into the core body 12 and is laminated on the surface of the core body 12. Specifically, the core body 12 may be immersed in the first slurry. The immersion time is set so that the first slurry sufficiently penetrates the core body 12 and the thickness H of the first coating layer 14 becomes about 0.1 to 0.3 mm. May be set in accordance with the viscosity of the first slurry so that are stacked.
[0050]
At this time, the small-diameter zircon flour contained in the first slurry mainly flows into the pores of the core body 12. Therefore, the pores can be filled with a high filling rate. On the other hand, most of the large-grain zircon flour does not flow into the pores and is stacked on the surface of the core body 12. Since the first slurry has good wettability by the wetting agent contained in the first slurry, it adheres well to the surface of the sand core 10. In addition, the action of octyl alcohol makes the lamination thickness substantially uniform. That is, octyl alcohol is a leveling agent that makes the lamination thickness of the first slurry, and thus the thickness H of the first coating layer 14, substantially uniform.
[0051]
As described above, by using the first slurry containing powdered refractories having different particle diameters, the pores of the core body 12 can be filled, and the surface of the core body 12 is formed of the first slurry. Layers can be formed.
[0052]
After a predetermined time has elapsed after the core body 12 has been immersed in the first slurry, the core body 12 is taken out, and the first slurry is dried and solidified in a third step S3 to have a thickness H of 0.1 to 0.1. The first coating layer 14 is about 3 mm. At this time, the powdered refractory is bonded to each other by the phenolic resin, and the core body 12 and the first coating layer 14 are firmly bonded to each other.
[0053]
While performing the above-described first to third steps S1 to S3, a second slurry is prepared in a fourth step S4. That is, mica, lubricates (lubricants), wetting agents, defoamers, and octyl alcohol are blended with water. If necessary, an organic binder such as a phenolic resin may be further added.
[0054]
Next, in a fifth step S5, the second slurry is laminated on the first coating layer 14. This lamination can also be performed by immersing the core body 12 on which the first coating layer 14 is formed in the second slurry. Alternatively, the second slurry may be laminated by various coating methods such as a spray coating method and a brush coating method.
[0055]
Next, in the sixth step S6, if the second slurry is dried and solidified, the sand core 10 in which the first coating layer 14 and the second coating layer 16 are laminated on the surface of the core main body 12 in this order. Leads to gain.
[0056]
In the present embodiment, the second coating layer 16 is provided over the entire surface of the first coating layer 14, but need not necessarily be provided on the entire surface. For example, it may be formed only at a portion where it is difficult to separate from the cylinder block. By partially providing the second coating layer 16 in this manner, the manufacturing cost of the sand core 10 can be reduced. In this case, in the fifth step S5, the second slurry may be applied only to the location where the second coating layer 16 is provided.
[0057]
In addition, if the cylinder block can be easily separated from the cylinder block without forming the second coating layer 16, it is not particularly necessary to provide the second coating layer 16.
[0058]
Further, in the present embodiment, the cylinder block has been described as an example of a cast product, but it goes without saying that the present invention is not particularly limited to this.
[0059]
【The invention's effect】
As described above, according to the sand core for casting according to the present invention, the first coating layer is buried in the core body, thereby closing the pores near the surface of the core body. Therefore, it is possible to prevent the molten metal from being inserted into the core body, and therefore, it is possible to obtain an effect that a cast product having good dimensional accuracy and less rough surface can be obtained.
[0060]
According to the method for manufacturing a sand core for casting according to the present invention, the first slurry to be the first coating layer penetrates the core body to fill the pores near the surface, and the first slurry is used for the core. It is laminated on the surface of the main body. For this reason, the effect that the 1st coating layer with a part buried in the core main body can be obtained reliably.
[Brief description of the drawings]
FIG. 1 is a schematic overall perspective view of a sand core for casting according to the present embodiment.
FIG. 2 is an enlarged cross-sectional view of the vicinity of the surface of the casting sand core of FIG.
FIG. 3 is a flowchart of a sand core for casting according to the present embodiment.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 sand core 12 core body 14 first coating layer 16 second coating layer 18 closed pores 20 particles

Claims (11)

  1. A core body formed by combining aggregate particles with a binder, and containing a powdered refractory and an organic binder , including a coating layer covering the surface of the core body,
    As the powdery refractory, particles having different average particle sizes are blended with each other,
    A part of the coating layer is bonded to the core body while being buried in pores of the core body.
  2. The casting sand core according to claim 1, wherein a distance from a surface of the core body to an upper end surface of the coating layer is 0.1 to 0.3 mm .
  3. 3. The sand core for casting according to claim 1, further comprising a second layer provided on the coating layer and containing a lubricity-imparting substance.
  4. The sand core for casting according to claim 3, wherein the lubricity-imparting substance is mica.
  5. The casting core according to any one of claims 1 to 4, wherein the core body contains a composite oxide of aluminum oxide and silicon oxide as a constituent material. Child.
  6. A first step of preparing a coating layer slurry containing a powdery refractory and an organic binder having different average particle diameters ;
    A second step of penetrating the coating layer slurry into the pores of the core body and laminating the slurry on the surface of the core body;
    A third step of drying and solidifying the coating layer slurry to form a coating layer;
    A method for producing a sand core for casting, comprising:
  7. The method according to claim 6, wherein the coating layer is formed so that a distance from a surface of the core body to an upper end surface of the coating layer is 0.1 to 0.3 mm. Child manufacturing method.
  8. The method according to claim 6 or 7, further comprising: preparing a second layer slurry containing a lubricity-imparting substance;
    A fifth step of laminating the slurry for the second layer on the coating layer;
    A sixth step of drying and solidifying the second layer slurry to form a second layer;
    A method for producing a sand core for casting, comprising:
  9. The method according to claim 8, wherein mica is used as the lubricity-imparting substance.
  10. The method according to any one of claims 6 to 9, wherein a wetting agent and an antifoaming agent are blended into the slurry for the coating layer and the slurry for the second layer. Manufacturing method.
  11. The method according to any one of claims 6 to 10, wherein octyl alcohol is further added to the slurry for the coating layer and the slurry for the second layer. Method.
JP2001393901A 2001-12-26 2001-12-26 Sand core for casting and method for producing the same Expired - Fee Related JP3581687B2 (en)

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EP2364795B1 (en) 2010-03-08 2012-07-18 Foseco International Limited Foundry coating composition
CN102343418B (en) * 2011-08-29 2013-07-10 西安西工大超晶科技发展有限责任公司 Casting method of three-dimensional flow aluminum alloy impeller casting
CN105149518A (en) * 2015-10-14 2015-12-16 河北天宇高科冶金铸造有限公司 Sand core and method for casting molding of deep holes with same

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