JPS61199543A - Coating method for casting mold - Google Patents

Abstract

PURPOSE:To improve the quality of a product by painting electrostatically refractory particles to a shielding part of a pattern and coating a fixing agent to said member thereby forming a mold coating material layer. CONSTITUTION:An electrically conductive paint is coated on the surface of a pattern 1 and the shielding member 2 is formed by heating and sucking. The shielding member 2 is then coated on the surface by using zircon powder, etc. and using an electrostatic powder painting machine to form the mold coating material layer 6. The fixing agent is coated on the surface 6a of the layer 6 to fix the layer 6 and a flask body 7 is placed thereon. Silica sand 8 is packed in the flask and is oscillated at the same time. A shielding film 9 is put to the upper part and the inside of the part 8 packed with the silica sand is sucked and evacuated. The inside of a box 3 is pressurized at the same instant. The upper and lower casting molds are thus respectively manufactured. A molten metal is poured into the mold. The generation of gas from the mold coating material and the cracking, etc. of the layer 6 are obviated and the quality of the product is improved.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a mold coating method for casting molds, and in particular, to a method for coating a casting mold, in particular, a method for shielding the molding surface of the mold with a shielding member, and filling the frame with refractory material particles for mold formation. The present invention relates to a method of forming a mold coating material layer by coating the surface of a shielding member with a mold coating material in the process of molding a mold that maintains the mold shape by reducing the pressure of the shielding member.

[Conventional technology]

Japanese Patent Publication No. 50-8409, Japanese Patent Publication No. 50-8410, etc. disclose that a shielding member on a film is brought into close contact with the surface of a model that is the original form of a cast product, and then a mold-forming member is placed on the shielding member in the frame. A method of maintaining the shape of the mold by filling the refractory particles and then depressurizing the refractory particle-filled part by suctioning from the outside of the frame, and also obtaining a casting mold that maintains the original shape by removing the model. is disclosed.

In this method, a mold coating material is generally used to prevent the mold-forming refractory material particles from sticking to the skin of the cast product. In the case of ordinary sand molds or metal molds, a coating material using alcohol or water as a solvent is applied directly to the molding surface of the mold. This method is performed as follows.

That is, a coating material made by suspending refractory material particles serving as a base material in a solvent such as alcohol or water together with a binder, a suspending agent, a thickening agent, etc. is used as a shielding member on a film that is closely adhered to the surface of the model. Spray the surface to a thickness of 0.1 to 1 m.

Next, after drying the coated mold material, mold-forming refractory material particles are filled thereon. Thereafter, by evacuating and reducing the pressure in the refractory particle filling section, the coating material layer coated on the surface of the shielding member together with the shielding member is attracted to the refractory material particle side, and the coating material layer is formed on the molded surface of the refractory material particles. A formed mold is obtained.

The composition of the coating material, which uses alcohol, water, etc. as a solvent, uses zircon, alumina, mullite, chromite, magnesia, silica, graphite, etc. as a fireproof material, and synthetic resin, natural resin, water glass, etc. as a binder. However, bentonite, starch, synthetic thickening agents, natural thickening agents, etc. are used as suspending agents and thickening agents.

[Problem that the invention seeks to solve]

Conventionally, as mentioned above, wet coating has been applied using alcohols, water, etc. as a solvent, but there have been the following problems.

(11) Since the mold coating material contains binders and other contaminants, it generates gas when it comes into contact with the molten metal during casting. Some of these gases get mixed into the molten metal and become part of the cast product. This can cause mold defects.Furthermore, there is a film-like shielding member on the outermost surface of the coating layer, and when it comes into contact with the molten metal and burns, it generates gas, so this mold cannot be used with ordinary sand molds. Cast cavity defects tend to occur more easily.

In order to prevent the occurrence of blowhole defects, it is necessary to reduce the amount of gas generated from the coating material and the shielding member, and the shielding member is an essential member. Therefore, consideration must be given to reducing the amount of gas generated from the coating material.

(2) After applying the coating material to the surface of the shielding member, it is necessary to dry it. This requires a process and time, so
This is an impediment to improving the efficiency of molding work, especially increasing speed.

(3) To speed up drying, mold coatings using solvents such as methyl alcohol, ethyl alcohol, or isopropyl alcohol are used, but this not only makes the coating materials expensive but also causes pollution of the working environment. .

(4) When applied thickly, cracks are likely to occur in the coating layer after the solvent has evaporated to dryness, and in severe cases, the coating layer may peel off locally. A product cast in a mold obtained in such a state suffers from burning due to the pouring of molten metal, resulting in poor casting surface.

[Means and effects for solving the problems] The present invention was completed by attempting to apply a basically dry electrostatic powder coating method in order to solve the various problems caused by the wet coating method. This is what I did.

The application of the electrostatic powder coating method to mold materials was first published in the 1970s.
It is disclosed in Japanese Patent No. 8-34218 and is well known.

However, in the technology described in the same publication, IN m
1#IJ 1/1-11L After molding, the refractory material particles are fixed on the molding surface by heating; (2) The molding surface is directly coated, and the electrical resistance value of the molding surface is 1Qn-am or less at 10KV. In contrast, the present invention is different.

Hereinafter, the present invention will be explained based on the accompanying drawings.

FIGS. 1 to 5 are explanatory diagrams sequentially showing the implementation process of the present invention.

First, in order to increase the chargeability of the refractory particles, which are the base material of the coating material, the refractory particles are coated with an electrically resistive substance. As in the case of the wet type, examples of refractory material particles include zircon,
There are alumina, mullite, chromite, magnesia, silica, graphite, etc., and examples of electrically resistive materials to coat include urethane resin, ester resin, epoxy resin, etc., but the key is to make it possible to perform electrostatic powder coating. Any refractory material particles for coated mold materials may be used.

Using a commercially available electrostatic powder coating device, the refractory material particles for mold coating prepared in this manner are coated on the surface of the film-like shielding member 2 that is in close contact with the surface of the model shown as 1 in FIG. Then, a mold coating material layer 6 shown in FIG. 2 is formed. In addition, the first
Although it is depicted that there is a gap between the model l and the shielding member 2 in FIGS. is in close contact with the surface of model 1.

Electrostatic powder coating cannot be applied unless the object to be coated is an electrical conductor and is grounded. The film-like shielding member 2 to which the present invention applies is made of electrically resistive synthetic resins such as ethylene vinyl acetate, polyethylene, vinyl chloride, polyvinyl alcohol, etc., and therefore cannot essentially be painted. However, if the model 1 under the shielding member 2 is an electrical conductor and is grounded,
It was experimentally discovered that it can be painted.

That is, although wood is usually used as the material for the model 1,
In this case, painting is not possible. However, it was discovered that it was possible to paint the wood model by applying water to the surface to make it electrically conductive. Furthermore, in the same way, when a graphite-based coating material is applied and dried, when an electrically conductive paint containing aluminum powder etc. is applied, and when a metal model such as an aluminum alloy is used, it can also be painted. can.

Next, mold-forming refractory material particles 8 such as silica sand are filled from above the coated mold coating material 1ii6 as shown in FIG. )). That is, since the coating material layer 6 coated with electrostatic powder on the shielding member 2 is not subjected to caking treatment, it falls off during the filling process with the refractory material particles 8. Furthermore, after filling, vibration is applied to the entire mold in order to increase the packing density of the refractory material particles 8. The coating material layer 6 also falls off due to the flow of the refractory material particles 8 due to this vibration.

In order to prevent these from falling off, the surface 6a of the mold coating material layer 6 is sprayed with, for example, an ethyl alcohol solution of vinyl acetate, a toluene solution of synthetic rubber, etc. to fix the refractory material particles for the mold coating material. As long as the solvent evaporates and the solute acts to fix the particles of the refractory coating material coated on the surface of the shielding member, it is sufficient.
It is preferable to have a fixing effect in a very small amount and dry immediately after spraying, and those that require heat treatment for fixing cannot be used because the film-like shielding member 2 will be damaged by heat. The fixing treatment can also be carried out by applying a fixing agent to the surface of the shielding member 2 and then electrostatically powder coating the refractory material particles for mold coating, but in this case, the refractory material particles for mold coating are applied to the surface of the shielding member. Since only the areas close to the area are fixed, this is not preferable when trying to obtain a thick coating agent layer.

In this way, the coating agent layer 6 made of refractory material particles coated and fixed on the surface of the shielding member 2 is formed by the refractory material particles 8 by suction and exhaust as shown by arrow B as shown in FIG. It is adsorbed onto the surface of the formed mold, and a mold having a coating material layer 6 as shown in FIG. 4 is obtained.

In addition, FIGS. 1 to 4 show the lower frame 11/I' of the two-split mold.
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〔Example〕

A mold for a cast product for a cast steel column base hardware having an as-cast weight of 156 kg was manufactured by the method of the present invention.

Referring to FIG. 1, first, a wooden model l was placed on the suction box 3. The surface of the model 1 was coated with an electrically conductive paint containing aluminum powder, and was grounded via a suction box 3. An ethylene vinyl acetate film was placed on the top of the model 1 as a shielding member 2, and was rendered plastic by a heating device (not shown). Next, the inside of the suction box 3 is depressurized by suctioning and exhausting from the vent 4 as shown by arrow A.
The shielding member 2 made of a plastic ethylene vinyl acetate film was brought into close contact with the model 1 through the ventilation hole 5, and the molding of the film-like shielding member 2 shown in FIG. 1 was completed.

On the other hand, as a coating treatment for refractory material particles for mold coating materials to impart charging properties, a solution prepared by diluting a xylene solution containing 40% by weight of urethane resin with methyl alcohol at a ratio of 1:1 by weight is used. It was added to zircon powder with an average particle size of 300 mesh. After cross-mixing, the dumplings were ground and dried in a stirrer blowing hot air to obtain zircon powder coated with urethane resin and having improved chargeability.

The zircon powder thus prepared was coated on the surface of the shielding member 2 shown in FIG. 1 using a commercially available electrostatic powder coating machine (not shown), and the coating material Fi6 shown in FIG. QJmm
It was formed thickly. The surface 6a of the mold coating material layer was further sprayed with an ethyl alcohol solution containing 5% by weight of vinyl acetate to fix mold coating material N6.

Next, as shown in FIG. 3, a frame 7 is placed on top of it, silica sand is filled as refractory material particles 8 for mold formation, vibration is applied, and an ethylene vinyl acetate film is placed on top as another shielding film 9. covered. By performing suction in the direction of arrow B from the suction port 10, reducing the pressure and tightening the silica sand-filled portion, which is the refractory material particles 8, and compressing air by sending compressed air into the suction box 3 from the ventilation hole 4, the model is removed from the closely-contact shielding member 2. 1
was separated and removed to obtain the mold shown in FIG.

In FIG. 4, since the suction from the suction port 10 was continued during the pouring operation, a casting mold having a mold coating layer 6 on the molding surface of the refractory material particles 8 was obtained.

Next, in the same process, the upper frame 12 shown in FIG. 5 was also produced and the two pieces were combined to complete a mold for column base metal fittings.

Molten cast steel was poured into this mold from the sprue 13 to obtain a cast product 14 of column base hardware. The casting surface of the cast product 14 had no defects and was in good condition. Furthermore, after finishing the casting, ultrasonic and
Internal defects were investigated using a wire, but the product was found to be in good condition, with no casting defects found in conventional products.

〔Effect of the invention〕

The dry coating method of the present invention solves the problems caused by the conventional wet coating method, and provides the following effects.

(11) Since the coating material does not contain a large amount of substances that can become a gas generation source unlike conventional molding materials, the occurrence of blowhole defects is prevented.

(2) Since the process of drying the mold coating material is no longer necessary, the molding work is speeded up.

(3) Regarding the use of organic solvents, for example, in the past, methyl alcohol, ethyl alcohol, isopropyl alcohol, etc. were used as a solvent for a mold coating agent, and in the embodiment of the present invention, ethyl alcohol was used as a solvent for a fixing agent. is about 10 to 20% of the conventional value.

The present invention not only saves the amount of expensive alcohol used, but also significantly reduces concerns about contamination of the working environment due to evaporation of alcohol.

(4) Since there is no cracking or peeling of the coating material layer, poor casting surfaces of cast products due to these are prevented.

(5) Since it is a dry powder coating, the occurrence of uneven thickness of the coating mold due to dripping of the coating material layer during the undried period immediately after the conventional wet coating mold is prevented.

(6) Since a powder is used directly instead of a coating material suspended in a solvent as in the past, it not only eliminates the need to manage suspension properties, but also has excellent long-term storage as it does not change in quality. .

(7) Since it uses electrostatic coating method, conventional spray 1,
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[Brief explanation of drawings]

FIGS. 1 to 5 are explanatory views showing the process of molding a casting mold when carrying out the present invention, in which FIG. 1 shows the molding of the shielding member, FIG. The figure shows the process of filling refractory particles for mold formation, sealing the mold, tightening the mold by reducing pressure, etc., Figure 4 shows the situation after removing the model, and Figure 5 shows the finished product after combining the upper and lower frames. FIG. 2 is a cross-sectional view showing a state in which a product is cast into a mold. 1: Model 2: Shielding member 3: Suction box 6: Coating material layer 7: Frame body 8 = Refractory material particles for mold formation 9: Shielding film 11: Lower frame 12: Upper frame 14: Casting product Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. In the process of manufacturing a casting mold that maintains the mold shape by shielding the molding surface with a shielding member and reducing the pressure in the mold-forming refractory material particle filling part in the frame, at least Particles of a refractory material for mold coating material coated with an electrically resistive substance to give the shielding member an electrically conductive surface are coated with electrostatic powder, and the electrostatic powder A mold coating method for casting molds, which comprises forming a mold coating layer by applying a fixing agent to prevent coated particles from falling off. 2. The casting mold coating method according to claim 1, wherein the surface of the model is coated with an electrically conductive material. 3. The casting mold coating method according to claim 1, wherein the model is entirely made of an electrically conductive material.