JPS63260655A - Sand core for pressure casting - Google Patents

Abstract

PURPOSE:To prevent temp. drop of molten metal and to improve fluidity of the molten metal by coating surface of a core for pressure casting by the specific material having heat insulation. CONSTITUTION:Sand core body 2 is molded by using silica sand, zircon sand, etc., as an aggregate in the core 2 and phenol resin as an organic binder. Next, the material 3 having heat insulation, dispersing or dissolving poly metallocarbosilane and inorganic filler in an organic solvent, is applied on the surface of the sand core 2 by using a bar coater and baked. By this method, even if the core has complicated shape of under-cut shape or hollow shape, it can be effectively formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a sand core for pressure casting, particularly for use in forming undercut shapes or hollow shapes during pressure casting such as die casting. This invention relates to a suitable sand core for pressure casting.

[Prior Art] In general, when manufacturing various products by a casting method, a die-casting method is widely used as a pressure casting method due to its advantages in terms of improved productivity and the like. By the way, when manufacturing castings with complex cavities or undercuts in part of the product shape using the die casting method, it is not possible to use a drawn core as the core, and instead, a drawn core with good collapsibility is used. A sand core is used.

BACKGROUND ART Conventionally, as a collapsible sand core that forms an undercut portion or a cavity in a casting, a sand core made of molding sand hardened with a phenol resin or the like is generally used.

[Problems to be solved by the invention] This sand core has the contradictory functions of being able to withstand casting pressure and having good disintegration properties after casting. Good things are required.

Poor flow of the molten metal during casting is more likely to occur as the product shape becomes more complex.In addition, in casting using a core, the temperature of the core is lower than that of a preheated mold, so the flow of molten metal by the core is less likely. A drop in temperature is the cause of poor hot water flow.

In contrast, conventional sand cores have not been provided that can simultaneously satisfy the requirements of pressure resistance against casting pressure, disintegration properties after casting, and hot water running properties, and improvements are strongly desired.

[Means for Solving the Problems] The sand core for pressure casting of the present invention is characterized in that its surface is coated with a heat insulating material.

[Function] When the surface of the sand core is coated with a material having excellent heat insulation properties, a heat insulation layer is formed between the core sand and the molten metal during casting. Therefore, the heat of the molten metal does not escape to the core, preventing the temperature of the molten metal from decreasing due to the core, and improving the flow of the molten metal.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the sand core for pressure casting of the present invention.

As shown in the figure, in the sand core 1 for pressure casting of the present invention, the surface of the sand core body 2 is coated with a heat insulating material 3.

In order to manufacture the sand core 1 for pressure casting of the present invention, first, the sand core body 2 is molded using an organic binder or press molding according to a conventional method.

As the aggregate of the sand core body 2, silicic acid, zircon sand,
Chromite sand, high alumina sand, Cerabeads, or the like can be used. Further, as the organic binder, a shell mold binder such as thermosetting phenolic resin or unsaturated polyester resin, or a cold box binder such as chemical reaction hardening phenolic resin can be used.

The molded sand core body is coated with
A refractory powder such as mica or frogstone, which has lubricating properties and has no affinity with the coating metal, and is thermally and chemically stable, is dissolved in water containing phenolic resin, methyl cellulose, polyethylene oxide, etc. A slurry obtained by dispersion-mixing in a synthetic organic binder is applied, dried, and sealed.

On the surface of the sand core body formed in this way, a coating layer of a material that is elastic is formed. In the present invention, the heat insulating material is not particularly limited as long as it has a high heat insulating effect, has heat resistance to withstand the high temperature of the molten metal, and does not have any negative effects on the product, but there are no particular restrictions, such as , heat-resistant paint, A
Ceramic fibers such as fi203-5iO2 fibers or
Amorphous powder or the like can be used.

As the heat-resistant paint, a heat-resistant paint made by dissolving or dispersing polymetallocarbosilane and an inorganic filler in an organic solvent is preferred.

In this case, the polymetallocarbosilane preferably consists of a carbosilane bonding unit shown below (A) and at least one metalloxane bonding unit shown below (B), (provided that R1 and R2 are the same or different. (B): −+−M−o −← (However, M is selected from the group consisting of Ti, Zr%Cr, and MO. (In some cases, at least a portion of each of the above elements has at least one lower alkoxy group or phenoxy group as a side chain group.) Each bonding unit of (A) and (B) above a polymer randomly bonded in the main chain skeleton, and/or at least a portion of the silicon atoms of the bonding unit of (A) bond to each of the elements of the bonding unit of CB) via an oxygen atom; As a result, the polycarbosilane moiety obtained by linking the bonding units of (A) is a polymer crosslinked by the bonding units of (B), and the total number of bonding units of (A) is compared to the number of bonding units of (B). It is an organometallic polymer in which the ratio of the total number of bonding units is in the range of 1:1 to 10:1 and the number average molecular weight is 400 to 50,000.

The polymetallocarbosilane mentioned above is a carbosilane bonding unit and one type or 2f! ! A polymer mainly composed of the above metalloxane bonding units, in which the carbosilane and metalloxane bonding units are randomly bonded in the main chain skeleton, and/or at least a part of the silicon atoms of the carbosilane bonding units are It is a polymer in which a polycarbosilane moiety is bonded to each element via an oxygen atom and obtained by chaining carbosilane bonding units by kneading, and crosslinked by the metalloxane bonding units.

Inorganic fillers include oxides, borates, phosphates,
It is at least one selected from the group consisting of silicates, silicides, borides, nitrides, and carbides, and examples include the following.

Boron, magnesium, aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, zinc,
Zirconium, molybdenum, cadmium, tin, antimony, barium, tungsten, lead, bismuth oxides, carbides, nitrides, silicides, borides, lithium, sodium, potassium, magnesium, calcium, zinc borates, phosphates Contains salts, silicates, etc.

These may be used alone or in combination if necessary.

The polymetallocarbosilane and inorganic filler are dissolved or dispersed in a suitable solvent such as benzene, toluene, xylene, etc. to form a coating material.

In addition, the ratio of inorganic filler is polymetallocarbosilane 1
It is preferably 10 to 900 parts by weight, particularly preferably 50 to 500 parts by weight. If the amount of the inorganic filler added is less than 10 parts by weight, the adhesion of the baked paint film to the substrate will be poor, and if it exceeds 900 parts by weight, the flexibility of the paint film will be reduced.

The heat-resistant paint thus obtained can be applied to the surface of the sand core body by a method such as coating, roll coating, spray gun, dipping, etc., and then dried and baked to form a coating layer easily.

In this case, the amount of coating varies depending on the shape, size, purpose, etc. of the sand core body, but generally it is 20 to 100 g/m.
It is desirable to do so. If it is less than 20 g/rn', pinholes are likely to occur, while if it exceeds 100 g/rn', cracks in the coating film are likely to occur during baking.
Baking is carried out at a temperature of about 00 to 700°C, but below 400°C to prevent decomposition of the organic binder in the sand core body.

The above-mentioned polymetallocarbosilane is
Even after heat treatment at 000°C for 10 hours or more, the loss on heating is only 10 to 15% by weight. For this reason, shrinkage and cracking due to weight loss of the baked coating film are less likely to occur, and the formed coating film after baking becomes dense. Furthermore, when an inorganic filler is added to this polymetallocarbosilane, it adheres more firmly to the substrate than a coating film formed from polymetallocarbosilane alone, improves heat resistance, and has flexibility. A coating film is obtained.

However, this coating film has excellent heat insulation properties and mold release properties,
It is also effective in preventing molten metal from entering the core sand.

For coating with 1m ceramic fiber such as AjlOa-5iO21m fiber, for example, short fibers are processed and mixed with an inorganic or organic binder such as polyethylene oxide or polyvinyl alcohol, and then applied to the surface of the formed sand core. It can be coated on the surface of the sand core body by drying it evenly. The resulting coating layer generally has a thickness of about 60% to 9
It has a porosity of 0% and exhibits an excellent heat insulating effect during casting.The molten metal retains moisture during casting, and after casting, it takes on the shape of a product that has been cast into the product, preventing undercuts and cavities. The inner surface can be an FRM layer.

Further, as the amorphous powder, soot, glass powder, etc. can be used.

For example, in the case of soot, amorphous powder is produced by injecting and burning acetylene gas or the like together with a combustion auxiliary gas such as air toward the core surface using an injection nozzle, and causing the soot generated at this time to adhere to the core surface. In the case of glass powder, it can be coated on the surface of the sand core body by mixing it with a binder such as polyethylene oxide or polyvinyl alcohol and applying it to the surface of the core. When an amorphous powder is used, it exhibits an amorphous heat insulating property during casting, and then crystallizes due to the heat of the molten metal, thereby providing the effect of serving as a mold release agent after casting.

It is best to provide a coating layer of such a heat insulating material on at least the surface of the sand core that is likely to come into contact with the molten metal, but it is also possible to form it only on areas of the core where the hot water flows particularly poorly.
It may be formed on the surface of the core. In addition, the coating layer thickness is
It is determined as appropriate depending on the size, shape, etc. of the core, within a range that provides sufficient heat insulation and does not adversely affect costs or casting operations.

An experimental example will be explained below.

Experimental Example 1 The following polytitanocarbosilane xylene 50 A heat-resistant paint obtained by mixing 50 parts by weight of a weight percent solution and 50 parts by weight of talc was applied using a bar coater and baked. Baking was performed at 400° C. or lower to protect the organic binder in the sand core body. The thickness of the coating film formed was 0.5 mm.

Mainly H-3i -CH2-← bond unit and -f-
Part of the 5i-H bond in the organosilicon polymer (number average molecule gL470) consisting of bonding units and having hydrogen atoms and methyl groups in silicon side chains disappears, and the silicon atoms in this part disappear. is bonded to the titanium atom of titanium tetraisopropoxide through the oxygen atom, and a portion of the 10-Ti is bonded to the side chain of the organosilicon polymer.
A polytitanocarbosilane having three (OC3H7) groups and partially crosslinked with organosilicon polymers through H-Ti-0-← bonds. The reaction rate and/or crosslinking rate at the 5i-H bonding moieties in the polymer is 44.5%, and the -31-CH2-← bond unit H-s i -3i-← bond in the organosilicon polymer portion of the polymer. The ratio of the total number of units to the total number of -0-Ti (QC4H9)3 and -Ti-0- linking units is approximately 6:1.

The obtained sand core is set in a mold and JISADC12
Aluminum alloy was poured at a temperature of 750°C and a casting pressure of 200°C.
Die casting was carried out under conditions of ~400 kglCrd.

After casting, the product shape was inspected and it was found that the hot water flow was extremely good. Furthermore, after casting, the core sand could be easily and completely removed by sandblasting.

Experimental Example 2 In Experimental Example 1, instead of the heat-resistant paint film, Aj2
203 SiO;+ Casting was carried out in the same manner except that a core in which a coating of a fiber molded body was formed to a thickness of 2 mm was used.

As a result, the hot water flow was extremely good and core sand was easily removed. Note that the AjZ203-3 i 02 fiber molded body became FRM and formed the inner surface of the product.

Experimental Example 3 Casting was carried out in the same manner as in Experimental Example 1, except that instead of the heat-resistant paint film, a core was used in which a 30 μm thick amorphous film was formed using acetylene powder as an amorphous powder. .

As a result, the hot water flow was extremely good and core sand was easy to remove.

[Effects of the Invention] As detailed above, the sand core for pressure casting of the present invention has a surface coated with a heat insulating material, and this coating layer of the heat insulating material prevents molten metal from forming during casting. A heat insulating layer is formed between the sand and the core, preventing the core from lowering the temperature of the molten metal and improving the flow of the hot water.

Therefore, according to the sand core for pressure casting of the present invention, even products with complex shapes such as undercut shapes and hollow shapes can be manufactured extremely efficiently with good machinability. It is said that

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the sand core for pressure casting of the present invention. ! ...Sand core, 2...Sand core body, 3...Insulating material.

Claims (9)

[Claims] (1) A sand core for pressure casting, the surface of which is coated with a heat insulating material. (2) In the pressure casting sand according to claim 1, wherein the heat-insulating substance is a heat-resistant paint made by dispersing or dissolving polymetallocarbosilane and an inorganic filler in an organic solvent. Child. (3) Polymetallocarbosilane is the following (A) and (B)
A polymer in which each of the bonding units is randomly bonded in the main chain skeleton, and/or at least a portion of the silicon atoms in the bonding unit in (A) below are each of the above elements and oxygen atoms in the bonding unit in (B) below. is a polymer in which the polycarbosilane moiety obtained by linking the bonding units of (A) below is crosslinked by the bonding units of (B) below, and the total number of bonding units of (A) below is The ratio of the total number of bonding units in (B) below is 1:1 to 10:1, and the number average molecular weight is 40.
0 to 50,000, the sand core for pressure casting according to claim 2. (A): ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, R_ and R_2 may be the same or different and each independently represents a lower alkyl group, phenyl group, or hydrogen atom.) (B): -(M-O)- (However, M represents at least one element selected from the group consisting of Ti, Zr, Cr, and Mo, and in some cases, at least a portion of each element is lower alkoxy as a side chain group. or phenoxy group.) (4) Claim 2, wherein the inorganic filler is at least one selected from the group consisting of oxides, borates, phosphates, silicates, silicides, borides, nitrides, and carbides. The sand core for pressure casting according to item 1 or 3. (5) Any one of claims 2 to 4, characterized in that the ratio of the inorganic filler to 100 parts by weight of polymetallocarbosilane is 10 to 900 parts by weight.
The sand core for pressure casting described in 2. (6) The sand core for pressure casting according to claim 1, wherein the heat insulating material is an Al_2O_3-SiO_2 fiber molded body. (7) The sand core for pressure casting according to claim 6, wherein the Al_2O_3-SiO_2 fiber molded body is impregnated with molten metal during casting to become FRM and form the product surface. (8) The sand core for pressure casting according to claim 1, wherein the heat insulating material is an amorphous powder. (9) The sand core for pressure casting according to claim 8, wherein the amorphous powder is soot.