JPS6147619B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating agent for microwave-curable molds. The present inventors first filled a model made of a material that easily transmits microwaves with a mold material made of a refractory material containing a thermosetting binder and a microwave-resistant dielectric material, and then the mold By irradiating the material with microwaves, the dielectric substance contained in the mold material generates heat, and this heat hardens the binder. After the mold material is cured in this way, We are proposing a mold making method in which molds are manufactured by cutting out molds. The present invention relates to a mold coating agent used in this mold making method. The present inventors also developed a liquid mold coating agent consisting of refractory particles, phenolic resin, and water or alcohol as a mold coating agent used in the above-mentioned mold making method, since ordinary powder mold coating agents have various problems. (Patent Application No. 53-102930). However, as a result of further intensive research by the present inventors, the coating mold used in the above molding method needs to have the following properties. (1) The coating mold and mold material heat and harden at the same time by microwave irradiation, but the coating mold must be in close contact with the mold at this time. That is, if the coating film of the mold coating agent does not adhere closely to the mold, the mold may peel off, causing scuffing or vening to appear on the product surface. (2) The coating film of the coating agent forms a hard layer with a thickness of about 0.1 to 0.5 mm and adheres to the mold, so the coefficient of thermal expansion of the coating film (coating mold) and the mold are almost similar. Must be a value. If the two differ significantly, it will cause vaning. (3) The model used in the above modeling method is required to have low microwave energy loss and appropriate heat resistance and elasticity.
The above-mentioned silicone rubber or base material is coated on the mold side surface of a substrate made of silicone rubber, fluorocarbon rubber, dried wood, epoxy resin, acrylic resin, styrene resin, or these resins filled with a substance that imparts rigidity such as glass fiber. Manufactured from raw rubber coated. Therefore, the material of the surface layer of the model, such as silicone rubber, must be sufficiently coated (applicability of the liquid mold coating agent to the heat-resistant rubber layer). A coating mold made of refractory particles (100 parts of 300 mesh silica), water-soluble resol type phenolic resin (10 parts) and water (60 parts), which was proposed in The coating properties of the surface layer, such as silicone rubber, are poor, and molds formed by microwave heating molding often have a mottled coating. In addition, other specific examples of refractory particles (400 mesh alumina fine powder 100
parts), phenolic resin (5 parts), methanol (30 parts)
Although the coating mold consisting of part) had no problems with respect to its applicability to silicone rubber, it had the disadvantage that the adhesion between the sand layer of the mold and the coating film was poor, and the coating layer easily peeled off. Therefore, an object of the present invention is to provide a mold coating agent suitable for microwave-curable molds that satisfies the characteristics that a coating mold should have as described above. According to the research conducted by the present inventors, the above object is basically achieved by a mold coating agent made by blending refractory particles with a thermosetting resin, iron sand, and water or alcohol. By using a coating agent consisting of this basic composition, the adhesion to the heat-resistant rubber layer of the model is significantly improved, the occurrence of vaning of the coating layer is completely prevented, and the occurrence of scooping can also be almost prevented. . However, the above-mentioned coating agent may cause slight scratches in the coating layer. This problem is completely solved by the second mold coating agent of the present invention, that is, the mold coating agent made by blending refractory particles with a thermosetting resin, iron sand, vinyl acetate, and water or alcohol. The refractory particles used in the mold coating agent according to the present invention serve as a base material for the mold coating, and include, for example, zircon powder, fused silica powder, alumina powder, and silica powder. The thermosetting resin is used as a binder, and for example, phenolic resin, urea resin, etc. can be used, but resol type phenolic resin is particularly suitable. In the mold coating agent according to the present invention, iron sand (Fe ₃ O ₄ ) is added in addition to the above components. This can significantly prevent vaning of the coating layer. The first mold coating agent according to the present invention is obtained by using an appropriate amount of water or alcohol as a solvent, adding the above-mentioned components to this, and kneading for a predetermined period of time. Considering the characteristics that the coating mold should have as described above, the blending ratio of each component is 20 to 40 parts by weight of thermosetting resin and 20 to 40 parts by weight of iron sand to 100 parts by weight of refractory particles.
20-30 weight is the most preferred range. In the second mold coating agent according to the present invention, vinyl acetate, particularly vinyl acetate emulsion, is added in addition to the above-mentioned components. This vinyl acetate acts as a cushioning agent against thermal expansion of the coating film,
By adding vinyl acetate to the coating mold, it can be made to follow the expansion of the mold that occurs when molten metal is cast, and it is possible to make it follow the expansion of the mold that occurs when molten metal is cast. The scuffing of the paint film layer, which had previously been caused, can be completely prevented. The most suitable blending ratio of vinyl acetate is 0.5 to 1.0 parts by weight per 100 parts by weight of the refractory particles. The mold coating agent thus obtained is then applied to the surface of the model by a mold coating method such as injection, dipping, or spraying. When applying a mold coating agent to the model surface by injecting the mold coating agent into the model cavity or by so-called dobuzuke,
From the viewpoint of coating the surface layer of heat-resistant rubber such as silicone rubber, water is used as a solvent, and 75B′e or higher,
Preferably, a concentration of 80 B'e or more is required. To explain this with reference to the attached drawing, the drawing is a graph showing the wettability (therefore, it means the spreadability) of the liquid mold coating agent to the heat-resistant rubber layer by soaking. As is clear from the drawing, 100% wetted area (Wet
Approximately 80B′e or more is required to obtain a Similarly, when a spray method is employed, either water or alcohol may be used as the solvent, but the concentration is preferably about 70 B'e or more. Each of the above concentrations can be easily adjusted by adjusting the amount of solvent. Preferred specific examples of the mold coating agent according to the present invention are shown below. Coating agent 1 Zircon powder (JIS particle size index 500) 100 parts by weight Phenol resin 30 Iron sand 20 Vinyl acetate 0.5 Water 10 Kneading is performed for about 3 minutes under stirring. The concentration of the mold coating obtained was approximately 82 B'e. As a method for applying this mold coating agent to the model surface, the core removal method is suitable. In addition, this coating agent contains 20 parts by weight of iron sand, and molds manufactured using this coating agent can be used not only as molds for aluminum alloys and cast iron, but also as molds for cast steel. However, no burning occurs. Coating agent 2 Fine fused silica powder (JIS particle size index 490) 100 parts by weight Phenol resin 30 Parts by weight Sand Iron 30 Parts by weight Vinyl acetate 0.5 Water 31.5 Kneading is performed for about 5 minutes under stirring. The concentration of the mold coating agent obtained was 80B'e, and it is suitable mainly as a coating mold for cast iron molds. As a method of coating the model surface, both the core-dipping method and the spray method are possible. Coating agent 3 Alumina powder (JIS particle size index 500) 100 parts by weight Phenol resin 40 Sand Iron 20 Vinyl acetate 1.0 Alcohol 28 Kneading is performed for about 4 minutes under stirring. Coating agent 4 Silica powder (JIS particle size index 490) 100 parts by weight Phenol resin 35 Sand Iron 20 Vinyl acetate 0.5 Alcohol 35 parts by weight Knead for about 5 minutes with stirring. The model whose surface has been coated with the mold coating agent according to the present invention as described above is then subjected to the mold forming process using the microwave heating described above. That is, by filling a model coated with the above-mentioned molding agent with molding material (foundry sand) and then irradiating the molding material with microwaves, the dielectric substance contained in the molding material is heated. The binder in the mold material and coating agent is cured by this heat, and in this way, the mold material and coating mold are hardened in a close contact state, and the mold is removed to obtain a mold equipped with a coating mold. . The mold material used in the above mold making method is made of a refractory material containing a thermosetting binder and a microwave-resistant dielectric material, and can be made of any material that generates heat and hardens when irradiated with microwaves. may be used, but more preferable specific examples will be described below. Note that the term "thermosetting binder" as used herein also includes one made thermosetting by blending a curing agent with a thermoplastic resin. First, as an example of the first specific mold material,
Examples include materials containing 2 to 5 parts by weight of thermosetting resin per 100 parts by weight of dry recycled sand containing 0.5 to 6% clay content and 0.3 to 5% carbonaceous organic matter. This mold material stores recovered sand generated in large quantities in a foundry in an inclined rotating container, gives the recovered sand a compound circulation motion by the rotation of the rotating container, and
Dry cleaning the recovered sand for a predetermined period of time by imparting an impact friction effect to the recovered sand in the circulating motion state by rotation of an agitator disposed in a rotating container and rotating in a direction opposite to the rotational direction of the container; After classification and removal of fine powder, a thermosetting resin can be added and kneaded to the recovered sand thus recycled. The recycled sand produced as described above is characterized by containing some clay content and loss on ignition. The clay content plays a role in moderately mitigating the thermal shock that the mold receives when pouring the molten metal, while the ignition loss is mainly carbonaceous organic matter, so it can play an effective role as a dielectric material that contributes to microwave heating. Therefore, the recycled sand obtained as described above can be used as it is as a raw material for a mold material for microwave curing. The thermosetting resins used in this mold material include resol type phenolic resin, resol type + novolac type mixed phenolic resin, and novolac type phenolic resin (However, since this resin is thermoplastic, hardening of hexamethylenetetramine etc.) It is necessary to normally contain about 10 to 15% of a thermosetting agent to make the resin thermosetting. In addition, thermosetting resins such as furan resins can also be used. When these thermosetting resins are mixed with new sand, they generally have a
In the case of recycled sand obtained as described above, 2 to 5 parts by weight is sufficient for 100 parts by weight of recycled sand. For example, 100 parts by weight of recycled sand is mixed with powdered phenolic resin (contains 15% hexamethylenetetramine based on the resin, melting point is 70-97℃, gel time is 35-35%).
A mold material can be produced by blending 3 parts by weight (67 seconds/150°C) and 0.2 parts of white kerosene and kneading for 3 minutes using a kneader. A second preferred example of the mold material is one made by adding a phenol resin (aqueous solution) to a water-soluble graphite dispersion, mixing it with new sand, and heating and drying the mixture, so that carbonaceous material is formed on the surface of the new particles. Examples include mold materials that are in a coated state.
This mold material consists of fresh sand, water-soluble graphite dispersion and phenolic resin (a few percent of the weight of the graphite dispersion).
and mix the sand with a mixer for several minutes, then heat and dry it, and the sand that has become granular due to the hardening of the phenolic resin during heating is crushed into sand granules by crushing with a muller etc. be able to. Although specific examples of preferable mold materials have been shown above,
In addition, there are mold materials made by kneading new sand, thermosetting resins (including thermosetting resins made by adding a hardening agent to thermoplastic resins), and dielectric substances such as graphite, and thermosetting resins. It is also possible to use a mold material made by mixing new sand with carbonized sand that acts as a dielectric substance against microwaves. The mold material may be filled into the model by any method such as pouring, damping, or blowing. The model, coating agent, and mold material used in the manufacturing method of microwave-curable molds have been explained in detail above.
By irradiating microwaves of 2450MHz and 6KW output for 2 to 3 minutes, it has the same precision as the mold surface.
A mold with excellent mold surface can be manufactured.
Furthermore, by using this mold, it is possible to manufacture molded products of extremely high quality. Table 1 below shows the effects when molds are manufactured using various mold coating agents according to the present invention in comparison with cases where conventionally known various mold coating agents are used. A silicone rubber coated model was used as the model, and microwave irradiation was performed at 2450 MHz x 6 KW at a rate of 1 minute per 1 kg.

【table】

[Table] As mentioned above, by using the mold coating agent of the present invention, (1) Since the coating film itself is a hard film, the influence of the aggregate of the foundry sand is relatively small, and it can be used as a low-grade coating material. (2) Since it is hardened together with foundry sand in the mold, the coating surface itself can transfer the model surface. (3) Compared to conventional coating molds, it requires less binder. (4) By adding thermoplastic vinyl acetate to the coating mold, the molten metal can be easily cast. It is possible to provide followability to the expansion of the mold that occurs when the mold is heated, and it is possible to prevent the coating layer from being scooped out. (5) By adding iron sand (Fe ₃ O ₄ ) to the coating mold, various advantages can be obtained, such as being able to prevent veining of the coating layer. Therefore, by using the coating mold according to the present invention in a molding method using microwave heating, a mold with an excellent mold surface can be manufactured.

[Brief explanation of the drawing]

The drawing is a graph showing the wettability of a liquid mold coating agent to a heat-resistant rubber layer by soaking.

Claims (1)

[Scope of Claims] 1. A microwave-curable mold after applying a coating agent to the mold surface, which is characterized by being made by blending refractory particles with a thermosetting resin, iron sand, and water or alcohol. A microwave-curable mold coating agent that is filled with material and simultaneously cures the mold material and coating agent by microwave irradiation to transfer a coating film to the mold surface. 2. The mold coating agent according to claim 1, wherein the refractory particles are zircon powder, alumina powder, silica powder, or fused silica powder. 3. The mold coating agent according to claim 1, wherein the thermosetting resin is a resol type phenolic resin. 4. The mold coating agent according to claim 1, which has a Baume degree of 70 B'e or more and is suitable for spray use. 5. The mold coating agent according to claim 1, which has a Baume degree of 80 B'e or more and is suitable for dobuzuke. 6 Characterized by blending refractory particles with a thermosetting resin, iron sand, vinyl acetate, and water or alcohol, a coating agent is applied to the surface of the mold model, and then a microwave-curable mold material is filled. A microwave-curable mold coating agent that simultaneously cures the mold material and coating agent by microwave irradiation and transfers a coating film to the mold surface. 7. The mold coating agent according to claim 6, wherein the refractory particles are zircon powder, alumina powder, silica powder, or fused silica powder. 8. The mold coating agent according to claim 6, wherein the thermosetting resin is a resol type phenolic resin. 9. The mold coating agent according to claim 6, which has a Baume degree of 70 B'e or more and is suitable for spray use. 10. The mold coating agent according to claim 6, which has a Baume degree of 80 B'e or more and is suitable for pickling.