JPH0469844B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a mold manufacturing method, and more particularly to a mold manufacturing method that produces a non-stressed and undamaged molded product and allows reuse of mold material. [Prior Art] There are many methods for molding ceramics, and methods for molding products with complex shapes include the slip casting method and the injection molding method. The former is a method in which a slip containing ceramic powder dispersed in a medium (mainly water) is cast into a porous mold, and the medium is absorbed into the walls of the mold to obtain a green body. The injection method is a method in which thermoplastic resin powder is added to ceramic powder, heated to dissolve the resin, and this composition is injected under pressure into a cavity in a mold to obtain a green body. Among these methods, the slip casting method is superior in terms of manufacturing products with complex shapes. In addition, the injection method is superior in terms of continuous mass production of small parts with low complexity. However, ultra-small or ultra-thin parts (e.g.
(Size of 10×10×10mm or less, wall thickness of 1mm or less)
However, when considering the case of manufacturing products with more complex shapes, neither the current slip casting method nor the injection method can be said to be optimal. This is because as the slip passes through the mold cavity, the moisture in the slip is absorbed by the mold wall, causing the flow of the slip to stop instantaneously, resulting in what is known as "poor hot water flow" in metal casting. be. If pressure casting is performed to solve this problem, the problem of "poor hot water circulation" will certainly be resolved in many cases. However, on the other hand, there is a concern that cracks may occur in the green body when the mold and green body are separated, or that cracks may occur later due to excessive stress being applied. Another problem is that if the mold model has a reverse taper shape, it cannot be removed. Even in this case, if the mold is divided into a large number of parts, it is theoretically possible to form products of any complex shape. However, in practice, there are many cases where it is practically impossible to divide a small main mold or core into many pieces due to the reverse slope and large unevenness. The following method was proposed to make the mold easily collapsible. () Make a mold using hot water disintegrating gypsum, and after slip casting, place the green body and mold in warm water (80℃~
100℃) and remove only the green body. This method may provide better disintegration properties when applied to elongated cores. () A method in which a kneaded mixture of a water-soluble binder (K ₂ CO _3, etc.) added to refractory powder and a specified amount of water is used as a mold, and a slip is cast into the mold. () A method in which a slurry made by adding flammable organic substances such as cellulose to plaster and a specified amount of water is made as a mold, a slip is cast into this, the whole is heated to reduce the strength of the mold, and the green body is removed. . () In the above method, the mold before casting is
A method in which slips are cast after heating to ~500℃ to reduce strength. () A method in which after a slip is cast into a mold and a green body is formed, the entire body is heated to the sintering temperature of ceramic, and the mold material is then removed. In this method, stress is applied to the green body during the sintering process, which may cause cracks in the green body. The first representative conventional technology is the
Publication No. 28687 is mentioned. In the method disclosed therein, first, a part of the molded body having a complex shape is made of a non-water-absorbing organic mold, a part of a simple shape is made of a water-absorbing material, and a slip is cast into the formed cavity. The ceramic cup-containing slurry is then centrifuged by a water-absorbing mold placed on a rotating table. After the stub has solidified, the non-water-absorbing mold is removed by heating to obtain a green body. Furthermore, Japanese Patent Publication No. 57-28323 is based on the aforementioned Japanese Patent Publication No. 56
In Japanese Patent No. 28687, the mold after the slip has solidified is immersed in a solvent, and the absorbent organic mold is melted by the solvent. This melt permeates into the green body and improves its strength.
In the end, removal of the mold and improvement in the strength of the green body are achieved at the same time. [Problems to be Solved by the Invention] In all of the above conventional techniques, most of the inner surfaces of the mold cavity are non-water absorbent. Therefore, it takes a long time for the slip to solidify, and the efficiency is extremely low. It is also clear that skill is required, as the timing of casting is difficult, and if the timing is incorrect, cracks are likely to occur in the green body. Also, it is not suitable for mass production. An object of the present invention is to provide a mold manufacturing method that is excellent in production efficiency in terms of yield and production time. [Means for solving the problem] (Principle of the invention) In slip casting technology, a vehicle
Ceramic powder or metal powder suspended in the powder is poured into a mold. The medium is absorbed into the mold, leaving a solidified casting (green body) in the mold. The mold is then removed from the green body, which typically undergoes a sintering process to form a strong molded article.
Furthermore, final finishing processing is performed as necessary. As mentioned above, the slip solidifies when the mold absorbs water as a medium (sometimes a medium such as ethyl alcohol, methyl alcohol, or acetone), but what percentage of the medium in the slip is absorbed? It cannot be said that it has been quantitatively clarified whether or not the appearance of a green body will result. Originally, in order to form powders such as ceramics into slips, there is a desire to reduce the proportion of the medium as much as possible. This is because the smaller the proportion of the medium added (normally the medium is water, henceforth referred to as "water"), the less shrinkage occurs during solidification and the less likely cracks will occur.
This is also because it is suitable in terms of dimensional stability such as a small amount of shrinkage during sintering. If the powder is kept to a minimum amount of water to make it fluid, a green body will be formed by absorbing a minute amount of water, such as 0.5 to 1%. The inventor of the present application focused on this point and came up with the idea of a new molding method. For example, if the mold is thin-walled, the slip can solidify and form a green body even if the mold absorbs little moisture. However, since the width of the mold cavity of a thin-walled molded product is also thin, the possibility of slip casting becomes a problem. Immediately after the slip begins to flow through the thin cavity of the mold, almost instantaneously,
It solidifies. In other words, there is a high risk of causing "faulty hot water supply." That is, in the case of a thin-walled slip, the flow of the slip stops due to moisture absorption during pouring, and therefore the cavity is not completely filled. In order to prevent this, it is possible to perform high-speed casting using pressure casting or the like, but the pressurized method causes problems such as deformation and destruction of the mold, so it is not desirable to introduce it easily. Another possibility is vacuum casting, but in this case other problems such as filter equipment and conversion arise. For these reasons, the mold must be rigid and as strong as possible. However, if the mold is rigid, cracks are likely to occur in the green body during the process of solidifying the slip into a green body, or when separating the green body and mold, and in severe cases, this can lead to damage to the green body. There is also. In other words, if the thin body has a reverse taper, it will be completely damaged, and even if it has a forward taper, the green body will be subjected to unreasonable stress when separated from the mold, which will cause residual stress and hair cracks, resulting in baking. This often leads to cracks in the product. In the conventional slip casting method,
The medium in the slip was absorbed by the capillary phenomenon of the pores, which depended on the mold, and the medium was solidified to obtain a green body. A typical molding material is gypsum. In other cases, powder particles hardened with a binder and molded are used, and what they have in common is the presence of mold micropores to cause capillary action. In contrast, the mold manufactured by the mold manufacturing method of the present invention does not absorb moisture in the slip through capillary action, but through a chemical reaction. Therefore, the presence of micropores is unnecessary in the mold produced by the mold manufacturing method of the present invention.As the present invention relates to a molding method based on a new principle, the process is completely different from conventional methods. do. In the present invention, organic resin is suitable as the mold material. However, ordinary organic resins do not have absorbency and do not get wet due to their large contact angle with water, and therefore do not absorb any moisture in the slip, making them completely unsuitable as slip casting molds. It was hot. By the way, polyalkylene glycol, which is a long-chain dihydric alcohol with ester bonds, such as polyethylene glycol (molecular formula: HO (CH ₂ CH ₂ O) _o CH ₂ CH ₂ OH, hereinafter abbreviated as "PEG"), is used as a template material. The present inventors have found that this is extremely suitable, leading to the present invention. (Mold Model) The shapes of the mold models that can be used in the present invention can be roughly divided into those with a forward taper and those with a reverse taper. In the case of a reverse tapered shape, the mold is usually divided in consideration of removal of the model. Then, during casting, a mold is assembled and a slip is cast into the formed cavity. Such a concept is also valid in the present invention. Furthermore, another aspect, and a method that should be a feature of the present invention, is to PEG a reverse taper model.
It is made from low melting point substances such as. The method for manufacturing a mold using this method will be described below, but in this case, no matter how complicated the product is, it can be made into an integral mold. In the case of a forward taper, any rigid mold such as metal, wood, rubber, or synthetic resin can be used as the mold model. In this case, the model can be used repeatedly and has a semi-permanent service life. (Mold) The mold according to the mold manufacturing method of the present invention is a mold in which a slip containing a predetermined solvent as a dispersion medium is cast, and a green body is obtained by absorbing the dispersion medium from this slip, and at least the surface in contact with the slip is obtained. The material is preferably a material having a melting point lower than the heating collapse temperature of the green body, or a material in which particles are dispersed in the material. It is preferable that the contact surface forms a matrix surface and/or a core surface of the green body. It is desirable that the particles have a higher melting point or heat resistance than the green body. Further, the low melting point material is preferably a water absorbing low melting point resin or a mixture thereof with additives. In this case, the resin is preferably polyalkylene glycol. Polyalkylene glycols, particularly polyethylene glycol (PEG), have the properties described above, which can be summarized as follows. () Small contact angle with water, () Easily soluble in water, () Hygroscopic. () Melts at low temperatures; () Harmless to humans and animals. When the above-mentioned mold is used, the lubricity of the mold material allows the mold model to be easily removed, and the rigidity of the mold provides a mold cavity with high precision and high surface smoothness. The mold is made of aggregate and a binder, and the binder is the above-mentioned model material or a model material dissolved in a solvent. On the other hand, the aggregate differs between so-called slip casting and metal casting. In the former case, it is acceptable as long as the slip medium is insoluble and non-reactive, and heat resistance is not particularly required in this case. Examples include silica (SiO ₂ ), alumina (A ₂ O ₃ ), and resin powder. In the latter case, heat resistance suitable for each metal is required. In the case of aluminum, it is gypsum;
In the case of iron, etc., it is silica, alumina, magnesia (MgO) powder, etc. The holding force of the mold is not limited to the binder, but may also be achieved by using magnetic force or differential pressure (vacuum forming, etc.). (Mold manufacturing method) The mold manufacturing method according to the present invention is to form a cavity by filling dry particles around a mold model molded with heat-melting resin, and melting the resin by heating to infiltrate the gap between the dry particles. It is characterized by the formation of The resin is preferably a water-absorbing low-melting resin or a mixture thereof with additives. Moreover, it is desirable that the resin is a foamable resin. On the other hand, the particles preferably have a higher melting point or heat resistance than the resin. A typical embodiment of obtaining a cavity by the above mold manufacturing method is as follows. First, using the above-mentioned PEG as a template material,
This creates a mold model. Next, the model is melted by embedding it in resin powder or silica sand powder and heating it to around 70°C. After the molten material permeates into the surrounding powder, the whole is cooled and molded. Form a cavity. According to this method, removal of the model and hardening of the mold are performed simultaneously. Furthermore, it is possible to easily produce a one-piece mold even for a reverse taper model or a model with large irregularities. A slip is formed in the cavity of this mold, and the slip is solidified to obtain a predetermined molded product. (Casting material) The casting material is, for example, ceramics (SiC, Si ₃ N ₄ ,
sialon, A ₂ O ₃ , titania (TiO ₂ ), zirconia (ZRO ₂ ), etc.), slips of metal, glass, resin powder, etc., metal, molten metal (However, in this case, consideration must be given to the heat resistance of the mold) , melted plastic,
Liquid rubber, etc. The material of the slip may be any kind of ceramic powder such as A ₂ O ₃ , Si ₃ N ₄ , SiC, etc.
Metal powders such as Fe, A, Cu, etc. or alloys may also be used. Synthetic resin powder, carbon powder, etc. may also be used. In short, it may be a single particle or a composite particle that does not dissolve in water or alcohol as a solvent. Therefore, any mixture of ceramics, metals, synthetic resins, etc. may be used. Water is often used as the medium for the powder, but ethyl alcohol or the like may also be used in some cases. Additionally, a surfactant is added to reduce the surface tension of the slip, and a small amount of a peptizer is added to separate the particles. Starch to increase the strength of the green body,
A binder such as PVA is sometimes added, but since this tends to reduce the density of the sintered product, it is desirable to reduce it as much as possible. The contents of the slip described in this section, with some exceptions, are not essential only to the present invention, but are common to slip casting methods (modes of casting).Gravity casting, suction casting, and pressure casting. Either one may be adopted. When the mold cavity has a narrow gap, it is necessary to use suction, pressurization, or in other words differential pressure to fill the cavity with slip. In any case, it is desirable that the slip be subjected to a vacuum treatment to remove internal air bubbles before casting. In the present invention, since the template uses PEG itself or PEG as a binder, the water absorption rate is not as high as that of commonly used plaster. This brings about effects such as facilitating slip filling into the crevices of the mold cavity. Note that by appropriately selecting the molecular weight of PEG, the absorption rate of the slip medium can be varied over a wide range. The medium absorption rate can also be changed by adding fine powders of acrylamide, molecular sieve, CaC ₂ , or SiO ₂ gel to PEG. (Mold removal) “Heating” is the means for this. After the slip solidifies and a green body is formed, the entire body is heated to melt the PEG mold, and the mold is removed. PEG as a template material is collected and reused for repeated use. It is desirable that the heating of the mold is not rapid. In other words, when using PEG, it is
Hold for about a minute. In addition, the mold wall should be made as thin as possible (Shell
wall) is recommended. That is, if the walls are thin, the heating can be quickly distributed to the entire mold, and the mold removal time can be shortened. Furthermore, in the case of thin walls, if dry powder such as silica sand or resin is used as the mold backup material, solidification of the slip after casting can be promoted and the solidification rate can be controlled. Being able to control solidification globally or locally is effective in controlling coagulation. If the wall is to be made even thinner, it is conceivable to use the so-called "shell mold" method when molding the mold. As a mold model, we used one manufactured by Kogyo Co., Ltd., and heated it to coat the surface of the model with powder-like solid PEG.
Place. The PEG is melted by the heat of the model and adheres to the surface of the model to a certain thickness.The whole is then cooled by means such as air cooling, and then the model and PEG are molded into a "shell mold" using reduced pressure. It separates. (Cast-molded product) A cast-molded product (concept including green body, fired product, and sintered product) molded using a mold using the mold manufacturing method of the present invention has a heating collapse temperature higher than that of the mold-forming resin. It is made of a high quality material, has an inverted tapered part, is integrally molded, has no seams, adhesive layers, joints, etc., and has virtually no residual stress after the mold is removed. In this case, it is desirable that the material is further fired or sintered. (Green Body) Green bodies must be handled carefully and should not be left in the atmosphere or at low temperatures (60
It is necessary to completely dry it at around ℃. Here, handling carefully means not subjecting it to mechanical, scientific, thermal, or other shocks. In this regard, since a small amount of PEG is infiltrated near the surface of the green body molded using a mold using the mold manufacturing method of the present invention, this acts as a reinforcing material and may cause cracks during handling. This method has advantages over conventional methods, such as the fact that In the slip casting method, the natural drying time for the green body varies depending on the wall thickness and shape, but it usually takes about 2 to 10 days. However, since the surface of the green body manufactured using the present invention is thinly impregnated with PEG, there is little hope of moisture dissipation into the atmosphere, and the green body is dried by forced heating (about 60° C.). Moreover, even with such drying by forced heating, no cracks were observed in the green body. In other words, as heating progresses, the PEG on the surface of the green body dissolves and penetrates into the interior through capillary action.The presence of this substance, which has a higher viscosity than water, makes it extremely difficult for cracks to occur in the green body. It becomes difficult to wake up. Therefore, according to the present invention, the green body can be dried quickly before sintering, and the process can be significantly shortened compared to the conventional method. A further feature of the present invention is that pressure casting is possible. Therefore, it is possible to keep the amount of water as a slip medium to a minimum. As a result of the above two points, in the present invention, it is possible to greatly shorten the natural drying time of the green body by leaving it alone, or to make it nearly unnecessary. Furthermore, since the density (ie, filling rate) of the green body is increased by these, shrinkage during the sintering process is reduced. Therefore, cracks are less likely to occur,
It also has good dimensional stability and has the effect that the voids in the sintered product are close to zero. (Mold material) The mold material used in the mold manufacturing method of the present invention is a resin or resin composition that is applied alone or as a binder to a mold into which a slip with a predetermined solvent as a dispersion medium is cast, and is a resin or a resin composition that is obtained from the slip. It is characterized by having its melting point at a temperature lower than the heating collapse temperature of the green body, and having the property of absorbing the dispersion medium. Polyalkylene glycols such as PEG are particularly easy to handle as mold materials, but waxes based on paraffin and olefin are also possible. Specific examples of waxes include beeswax, spermaceti wax, Chinese wax, wool wax, canadilla wax, carnauba wax, wood wax, orikili wax, sugarcane wax, montan wax and its derivatives, ozotilite, ceresin, and lignite. wax, paraffin wax and its derivatives, microcrystalline wax and its derivatives, petrolatum, fissure tropism wax and its derivatives, low molecular weight polyethylene and its derivatives, cetyl alcohol, stearic acid, glyceryl stearate, polyethylene glycol Stearate, castor wax, opal wax, armor wax, acra wax, chlorinated hydrocarbons, synthetic animal waxes, alpha olefin waxes, and blended waxes. These materials are also mold material. (Sintering) As a mold material used in the mold manufacturing method of the present invention,
It is desirable to use PEG, which first becomes molten at 50 to 70°C and completely disappears by vaporization at 200 to 400°C when the temperature is further increased, and other vaporizable aggregates (synthetic resins, etc.), depending on the molecular weight. When such a mold material is used, even if some mold material remains in the case of a complex-shaped green body, there is no problem at all because it vaporizes and disappears during the temperature rise in the sintering process. In some cases, it is also possible to sinter the mold material together with the green body without removing it. When the wall thickness of the mold is thin, there is not much merit in recovering and reusing it, so it can be said to be effective to combine the three steps of mold removal, green body drying, and sintering as described above. (Finishing) There are two types of finishing for sintered products. () Finishing of sprue parts, etc. Removal and finishing of parts related to the casting method, such as sprues, drains, risers, etc., is usually done at the green body stage. Since such sprues are attached to any product, their removal is essential. Post-processing will be easier if the sprue is made as narrow as possible and a plastic pin gate concept is introduced. According to the present invention, the slip can be cast under pressure, so the sprue can be made narrower. This not only makes it possible to significantly reduce the number of man-hours, but also prevents excessive stress from being placed on the green body when cutting and removing the sprue system, which prevents cracks and deformation in the green body and products. can. (Relationship with the slip casting method and the injection execution method) According to the present invention, the slip casting method can be brought closer to the injection method.
One aspect of the present invention can be said to be a new molding process that eliminates the drawbacks of the slip casting and injection methods, leaves only the advantages, and is further improved. The reasons for this are shown in the table below.

[Effect]

When a slip is cast into a mold manufactured using the mold manufacturing method of the present invention, the dispersion medium in the slip is absorbed from the mold cavity, and at the same time, the slip solidifies. After that, when the solidified slip is heated together with the mold, the resin of the mold material is melted and removed, resulting in a green body. Therefore, this green body has never been under any stress. On the other hand, if a resin model is embedded in the mold particles and heated, this model melts and penetrates into the gaps between the particles, resulting in the above-mentioned cavity being obtained. Even if a slip is used, its properties allow for a reduction in moisture content compared to conventional methods. Next, regarding the properties of the mold, conventionally a porous mold such as gypsum was used. Although any type of material is acceptable as long as it is porous, gypsum is most widely used because of its fluidity, self-hardening properties, and smooth surface. On the other hand, the mold manufactured by the mold manufacturing method of the present invention exhibits water absorption, low melting point (mp = around 50 to 70°C), and water solubility. Pressure is used during casting, a method that has been used in some cases in the past. However, the effect is great in that it can be applied to thin-walled molded products. The removal of the mold manufactured by the present invention is characterized by using heating to liquefy the mold material and removing it dropwise, but conventionally, the mold has also been removed by heating the plaster mold to a temperature of 300 to 500°C. It was After reducing the strength of the mold, the mold was removed from the green body. However, when using a mold manufactured by the mold manufacturing method of the present invention, the (mold + green body) after casting is heated to a low temperature (approximately 80°C) above the melting point of the mold, melting the mold and removing it dripping. , no damage to the green body was observed, and the labor-saving effect was remarkable. [Examples] Examples of the present invention will be described below with reference to the drawings. (First Example) This example is a molding method used as a PEG mold model material. An embodiment will be described based on FIG. That is, the outline of the process is as follows. () Make and prepare template model 1 using PEG ((a)). () Set this in the center of the frame 3 placed on the surface plate 2 () Fill the frame 3 with synthetic resin powder 4 (polyethylene, etc.) and apply a vibrator to further increase the degree of filling (( b)). () Heat the whole and melt PEG model 1,
The melt is absorbed into the interparticle gaps of the dry synthetic resin powder 4, and the remainder is discharged outside the mold ((c)), ((d)).
Reference numeral 12 is a heater, 13 is a PEG melt, and 14 is a resin-impregnated particle layer. In addition,
When Model 1 is small, all of the PEG content is absorbed into the gaps between the dry particles. () A separately prepared slip 9 of ceramic or the like is injected into the mold cavity 6 obtained and stored as is ((e)). () The resin-impregnated particle layer 14 and the dry resin powder 4 behind it absorb moisture in the slip 9, forming a green body 10 ((f)). () After that, (green body + casting),
When heated above the freezing point of PEG ((h)), PEG
The resin mold impregnated with is gradually fluidized and separated to obtain the green body 10 ((i)). This embodiment is suitable for a model shape that is complex and has a reverse taper and cannot be removed from a rigid mold, but it goes without saying that it can be applied to any other shape. The advantage of using heat-disappearing synthetic resin powder as mold aggregate is that even if aggregate particles remain attached to the green body, the mold material will completely vaporize and disappear in the subsequent sintering process. Because there is. Inorganic powder such as SiO ₂ or A ₂ O ₃ may be used as the mold aggregate, but in that case, it is necessary to completely remove this inorganic powder from the green body before sintering. This is because it causes problems such as being fused to the green body during the sintering process and not being able to be removed from the sintered product. Conventionally, it has been said that ceramic slip casting products have a high occurrence of cracks and a low yield rate. The causes are complex, but one of the main factors is hair cracks before sintering. Even though this type of crack is minute and cannot be recognized with the naked eye, it grows during the sintering process, resulting in large crack defects in the sintered product. Furthermore, internal stress accumulated in the green body during the molding process is also a cause of cracking defects. The hair cracks and internal stress accumulation mentioned above are caused by the process of creating a green body. That is, as the slip hardens and becomes a green body, it receives stress from the rigid mold (mainly the plaster mold), and this stress accumulates inside. Furthermore, when the green body and mold are separated, since the mold is rigid, force is applied to the green body at this time as well, which tends to cause hair cracks and accumulate stress. On the other hand, according to this embodiment, since the mold is water-soluble, its surface slightly dissolves in the moisture in the slip, so no stress is generated between the mold and the green body. Also, when separating the green body and mold, approximately
By heating to about 60°C, the mold gradually softens and eventually flows, allowing the two to be separated under very mild conditions. Therefore, neither the accumulation of internal stress nor the generation of cracks can occur in the green body. As described above, it is clear that according to this embodiment, slip casting can be performed with high precision and high reliability no matter how complex the shape of the product. Next, I will touch on the properties of PEG. PEG is a long-chain dihydric alcohol with many ester bonds, as represented by the molecular formula HO(CH ₂ CH ₂ O) _o CH ₂ CH ₂ OH. As can be seen from the molecular formula, since it is made by polymerizing ethylene oxide using water or ethylene glycol as a raw material, the product has a unique molecular weight distribution, and is divided by average molecular weight. In this application, those having an average molecular weight of 200, 1000, and 20000 will be referred to as #200, #1000, #20000, etc., respectively. PEG #600 or less is liquid at room temperature, but as the molecular weight increases, it changes from a vaseline-like state to a solid state. PEG melts around room temperature. That is, the melting point of #1000, which is a white solid at room temperature (20℃), is 36
It is ℃. This lowers the melting point of those with low molecular weight, and the melting point of #400 is about 5°C. Conversely, those with higher molecular weights have higher melting points, but even #6000 has a melting point of 62°C at most. This can be said to be an advantageous property when using PEG as a template and removing it. When PEG is heated to 150-200℃, it thermally decomposes and disappears by vaporization. At this time, it does not carbonize or form into a gum to form sludge. This means that when PEG is used as a template, it can be easily vaporized at a temperature of about 200°C. It also suggests that even if PEG penetrates and adheres to the green body, it can be easily removed during the sintering process. Regarding hygroscopicity, the lower the molecular weight, the easier it is to absorb moisture. The surface tension of both aqueous solutions and solids is lower than that of water (76 dyn/cm), and slips tend to leak. This indicates that the slip easily penetrates into the slits of the PEG mold cavity, and that the corner portions are formed sufficiently well. Note that the surface tension of solid PEG is 45 to 46 dyn/cm, and there is almost no difference in molecular weight. Looking at the relationship between temperature and kinematic viscosity of PEG using PEG molecular weight as a parameter, the higher the temperature, the lower the kinematic viscosity, and the higher the molecular weight, the higher the kinematic viscosity. The above assumes an important position in this example.
The characteristics of PEG were described. However, the present invention is not necessarily limited to the use of PEG, and it should be understood that materials equivalent to PEG are included in the present application in terms of achieving the purpose of the invention. For example, from the perspective of achieving the purpose of the invention
Other organic resins with similar properties to PEG, PEG
An example of this is when other substances are added to the material without changing its properties. (Second Embodiment) This embodiment will be explained based on FIG. 2. () A mold model 5 made of metal, synthetic resin, etc. and having a predetermined shape is prepared (FIG. 2a, hereinafter abbreviated as a). () Place the mold model 5 on the surface plate 2 and install the frame 3 around it ((b)). () Fluid PEG11 melted by heating
is injected around the mold model 5 ((c)). () After the PEG has solidified due to the temperature drop, remove the surface plate 2, remove the mold model 5, and remove the mold 1.
Get 5 ((e)). () A separately prepared ceramic strip 9 is injected into the formed cavity 6 ((g)). Reference numeral 7 is a lid, and 8 is a casting spout. () The mold 15 made of PEG is attached to the slip 9
The water inside is absorbed and a green body 10 is formed. () Then, (green body + mold),
When heated above the freezing point of PEG, PEG gradually dissolves ((i)), and green body 10 is obtained ((j)). Reference numeral 12 is a heater for heating. Usually, this green body 10 is dried and further heated gradually to a high temperature to obtain a high-strength sintered product. (Third Example) The mold model 1 of PEG #1500 shown in FIG.
Installed in a frame 3 placed on a surface plate 2 shown in
Pour dry silica sand powder instead of synthetic resin powder 4,
Vibration filling was performed using a vibrator (not shown). Next, the whole is heated with the heater 12 shown in c,
The template model 1 was dissolved and removed ((d)). At this time, the PEG melt penetrates into the silica sand powder by capillary action, and the shell layer (resin-impregnated particle layer) 1
4 was formed. Next, as shown in e, a slip 9 of alumina powder was injected into the medium-sized cavity 6, and after solidifying, the whole was heated to 60°C by the heater 12. Since the melting point of PEG1500 is about 45°C, The shell layer was removed dropwise ((h)) to obtain an alumina green body 10. ((i)). Next, by sintering at a predetermined temperature, an alumina sintered product could be obtained. (Fourth Example) The mold model 1 of PEG #1000 shown in Fig. 3a,
A box-shaped electromagnet 17 installed on the surface plate 2 shown in b
Place it in the center and fill the surrounding area with iron powder 18 of approximately 400 mesh. By passing an electric current and applying a magnetic field, iron powder 18
magnetize and solidify the mold ((e)). Next, the mold model 1 is melted by flowing hot air at 120°C from the hot air inlet 19 and warming the entire body.
The PEG melt 13 is discharged from the handy pump 20 ((d)). A SiC slip 9 is cast into the formed cavity 6 ((e)), and after the water in the slip is absorbed into the mold and becomes a green body 10, when the current is turned off, the iron powder 18 is recovered without losing its mutual adhesion. ((f)). Next, a product was obtained by sintering the obtained green body 10 ((g)). (Fifth Example) Silica sand 21 that had leaked into water was longitudinally cut around the mold model 1 of PEG #1000 shown in FIG. 4a ((b)). When this was irradiated with microwaves in a microwave oven, the leaked silica sand 21 was heated, and the model material became molten due to this heat and was removed from the mold, yielding the mold cavity 6 shown in c. At this time, part of the melt from the model 1 entered the mold, and a resin-impregnated particle layer 14 was obtained ((c)). When the epoxy resin composition 22 to which a curing agent was added was cast into the cavity 6 ((d)), the mold material could be removed very easily by heating after the resin composition 22 had hardened, and the cured epoxy resin body 23 was obtained ((e)). (Sixth Example) A mold model 1 made of PEG #1000 (melting point 36°C) shown in FIG. Fill the surrounding area with dry silica sand 24, heat the whole, dissolve the PEG model 1, let the melt penetrate into the gaps between the sand grains, and let it cool.
A mold cavity 6 was formed ((c)). An acrylamide water supply port 26 was placed on the bottom surface of the mold 25 thus obtained, and a Si ₃ N ₄ slip 9 was cast into the mold cavity 6 thus formed. As a result, the acrylamide water-absorbing board 26 rapidly absorbed the moisture in the slip 9, and the green body 10 could be obtained in an extremely short period of time. After that, the water absorption board 26 is removed, the entire body is heated to 50° C., and the mold 25 is dripped and removed.
A green body 10 made of Si ₃ N ₄ shown in Fig. 1 was obtained. (Seventh Example) The mold model 1 made of PEG #1000 shown in FIG. 6a is placed on the surface plate 2 as shown in FIG.
The melting point of Model 1 was approximately 36 when placed in a container and filled with 28 styrene powder around it and heated to 70℃.
℃, it melted and was completely absorbed into the styrene powder, forming a mold 25 having a cavity 6. As shown in c, there is A ₂ O ₃ in the cavity 6.
After the slip 9 was injected and the slip 9 solidified, the whole was heated to 70°C, and most of the mold 25 was removed. However, as shown in d, a part of the mold remained deep inside the grain body 10. When this was sintered as it was, the remaining portion 29 of the mold was vaporized and disappeared during the sintering process, resulting in the desired sintered product 3 of A ₂ O ₃ quality.
0 was obtained. (Eighth Example) A mold model 1 of PEG #1000 (melting point 36°C) shown in Fig. 7a was placed in a frame (not shown), and silica sand and CaC ₂ were mixed at a ratio of 1:1 around it. Mixed particle powder 3
b filled with 1. Next, high humidity air 32 is passed through the chamber from the top.
(silica sand + CaC ₂ ) was humidified, and dry air was sucked in from the bottom c. As a result, the CaC ₂ in the mixed particle powder 31 generated heat by absorbing moisture, reaching a temperature of about 80°C. As a result, as shown in d, the model melted and was absorbed into the gaps between the sand grains by capillary action, yielding a mold 25 having a cavity 6. Thereafter, a two-component curable epoxy resin composition 22 was injected into the cavity 6 as shown in e, and after solidifying, the whole was heated with hot air to obtain an epoxy resin molded product 23. (Ninth Example) As shown in FIG. 8, a graphite coating mold 46 is placed on the surface of a casing model 45 made of wax with a melting point of 50°C.
The model 45 is coated with a thickness of 10 μm and placed in the frame 3 installed on the air intake box 47, and the area around the model 45 is filled with dry sand 48. The upper surface 47b of the air intake box 47 also serves as a filter, and has countless fine holes that do not allow sand to pass through, but allow air to pass through. The upper surface of the mold is covered with a 30 μm vinyl sheet 49. The mold is hardened by drawing air from the air inlet 51 using a vacuum pump (not shown) to remove air within the mold. By heating the whole to about 80℃, model 45
When melted, the molten wax quickly and extensively penetrates into the interstices of the sand grains due to the simultaneous effects of vacuum absorption and capillary action, resulting in a good mold cavity coated with graphite. Then, molten metal or liquid resin is poured into this cavity. (10th Example) As shown in FIG. 9a, a mold model 1 made of PEG #1000 is buried in resin-coated dry silica sand 52, and approximately
The whole was heated to 80°C. Due to this heating, the mold model 1 was melted and absorbed into the gaps between the sand grains. Next, after cooling the whole body, remove the frame 3.
Only the sand particles that have reached the PEG content remain, forming a shell-shaped mold 25 as a whole (FIG. 2b). Although a shell mold can be obtained by the above method, the model material in this case is not necessarily limited to PEG. It may be a resin or a metal as long as it can be absorbed into the gaps between the sand grains in a dissolved state. (11th Example) As shown in FIG. 10, a PEG model 1 was placed in a frame 3, and an iron stalk 53 was further placed on its lower end surface. The center of the sprue is a spherical melting chamber, into which granular aluminum 54 is inserted. The whole was covered with a frame 3, and dry sand 48 was injected and filled into the frame 3 from a charging port (not shown). Incidentally, an intake box 47 having a filter 55 is installed on the upper part of the frame 3. Next, the coil heater 12 was set at the lower part of the frame 3, and the whole was kept horizontal by moving it around the shaft 56 as the center of rotation. By passing a high frequency current through the coil heater 12, the iron stalk 53 is heated by induction, thereby melting the aluminum material 54. The model 1 is gradually melted by the heat of the induction-heated stalk and the heat of the molten aluminum, and the melt is absorbed between the sand grains. After that, the frame body 3 is
molten aluminum is cast into the cavity by moving around it at a predetermined angle. Since vacuum suction is continued during the entire heating and casting process, good aluminum molded products without gas defects can be obtained. (Twelfth Example) The surface of the PEG model 1 is coated with a graphite coating mold 46 to a thickness of about 50 μm, and the surrounding area is filled with dry sand 48 (see FIG. 11a). When the entire area is irradiated with microwaves, the coating part 46 is heated, and the model 1 is melted by the heat. Since the melt is absorbed into the dry sand through the coating film, a cavity 6 is formed (see b in the same figure). After the mold has cooled, a two-component mixture type epoxy resin liquid composition 22 is injected (see c in the same figure). After the epoxy resin has hardened, the mold material 25 is removed to obtain a resin molded product 23 (d in the same figure). (13th Example) As shown in FIG. 12, a screw rotor model 57 is made of PEG #1000, and glass particles 6 are placed around it.
0 is filled and heated as a whole to melt the model and penetrate into the gaps between the sand grains to form a mold cavity. Next, a photocurable resin is cast into this cavity, and light is applied to the cast resin through the glass particles to obtain a cured resin body 61 (the first
(See Figure 2 b). (Embodiment 14) A turbocharger and a casing were made of PEG #1000, and this model 62 was buried in iron powder 18 as shown in FIG. A coil (not shown) is placed around this mold,
Apply a magnetic field. Furthermore, by heating the model 62 by an arbitrary method, the model 62 is melted and this liquid material is added to the iron powder 18.
A slip made of carbon powder was injected into the impregnated cavity to obtain a carbon green body. (15th Example) As shown in FIG. 14, dry iron powder 18 is filled around the paraffin wax model 33, and the mold flask 3
A suction box 47 was installed at the bottom, and a hot air supply frame 63 was installed at the top. 100℃ from the top of the mold via the hot air supply frame 63
The hot air of
The interaction of capillary action and vacuum suction promotes cavity formation. At this time, an electric current is passed through the coil 64 to solidify the iron powder. After molding the cavity, molten aluminum is injected, but since the suction from the suction port continues at this time, the wax in the iron powder 18 is vaporized by the heat of the molten metal, and the gas is absorbed into the blown-out defects in the aluminum casting. There is no fear that this will happen. (16th Example) As shown in FIG. 15, a paraffin wax model 33 is placed in a frame 3 placed on a suction box 47, and the surrounding area is filled with dry sand 48 to which CaO has been added. After spraying a predetermined amount of water onto the top surface, a vinyl sheet 49 is immediately covered. Next, when suction is started from the suction port 51 of the installed suction box, the added moisture spreads throughout the mold, reacts with CaO in the sand, becomes high temperature, melts the model 33, and impregnates it into the sand, forming a cavity. . FIG. 16 shows a flowchart illustrating the recycling of materials for molds and mold models manufactured by the mold manufacturing method of the present invention shown in each of the above embodiments. In the figure, a shows a model, b shows the model buried in dry sand, c shows the model removed by heating and at the same time the mold is hardened, and b shows a liquid substance being injected into the cavity. (e) is the resulting green body, while the used sand and wax mixture is reheated at f.
and separated by suction. Then, the aggregate is returned to the pre-molding process, and the wax is returned to the pre-model manufacturing process, and the process can be repeated as many times as necessary, provided that the casting raw materials are supplied. [Effects of the Invention] The effects of the present invention are summarized as follows. (1) Particularly suitable for small, thin-walled products. (2) Suitable for continuous/mass production. (3) Mechanization and automation are easy. (4) No skill required. (5) Molds can be recycled.

[Brief explanation of the drawing]

Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 9, Fig. 11, and Fig. 12 are process diagrams showing embodiments of the present invention, respectively. , FIG. 8, FIG. 10, FIG. 13, FIG. 14, and FIG. 15 are sectional views of a model after filling the mold and a device including the mold according to still other embodiments of the present invention, and FIG. 16 is a cross-sectional view of the mold. FIG. 3 is a flowchart of recycling materials and mold materials. 1, 5... Mold model, 2... Surface plate, 3... Frame, 4... Synthetic resin powder, 6... Cavity, 7
... Lid, 8, 41 ... Sprue, 9 ... Slip, 1
0... Green body, 12... Heater, 13...
...PEG melt, 14...Resin-impregnated particle layer, 15,
25...Mold, 17...Electromagnet, 18...Iron powder,
19...Hot air inlet, 20...Handy pump,
21... Warm silica sand, 22... Epoxy resin composition, 23... Epoxy resin effect body, 24... Dry silica sand, 26... Water absorption board, 28... Styrene powder, 29... Mold residue, 30... ...Sintered product, 3
1...Mixed particle powder, 32...High humidity air, 33...
...Parafin wax model, 45... Wax casing model, 46... Graphite coating mold, 47... Intake box, 48... Dry sand, 49... Vinyl sheet,
51...Intake port, 52...Resin coated dry silica sand, 53...Iron stalk, 54...Grained aluminum, 55...Filter, 56...Shaft, 57...
...screw rotor model, 60...glass particles,
61...Resin cured body, 62...PEG turbocharger casing model, 63...Hot air supply frame,
64...Coil.

Claims (1)

[Scope of Claims] 1. Dry particles are filled around a mold model formed from a heat-melting resin, and a cavity is formed by heating to melt the heat-melting resin and infiltrate the gap between the dry particles. A mold manufacturing method characterized by: 2. The mold manufacturing method according to claim 1, wherein the resin is a water-absorbing low-melting resin or a mixture thereof with additives. 3. The mold manufacturing method according to claim 1, wherein the resin is a foamable resin. 4. The mold manufacturing method according to claim 1, wherein the particles have a higher melting point or heat resistance than the resin. 5. The mold manufacturing method according to claim 1, wherein the resin is polyalkylene glycol.