JPH0223321B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for thermoforming ceramics. (Prior art) Various ceramic products such as tableware, sanitary ware, crafts, tiles, electrical and electronic parts, etc. are made by molding a hydrous ceramic material (slip) into a desired shape using a mold, processing it, drying it, and then firing it. It is made by Widely used methods for forming this slip include a casting method using discharge casting or solid casting, and a plastic forming method using a potter's wheel. Conventionally, in this type of molding method, a setkou mold is generally used as the mold, and in cast molding, after the mold is assembled, the slip is poured at room temperature, and the mold adheres to the material by water absorption, and the parts that do not adhere to it are drained ( discharge casting) or no mud discharge (solid casting)
The method used was to compact the soil and then remove it from the mold. In addition, in plastic molding, a slip is placed on a mold at room temperature, and a trowel such as a roller is applied to the mold while rotating the mold to form the desired shape. (Problems to be Solved by the Present Invention) However, in the above-mentioned molding method, the deposition speed is slow because the molding method uses only the natural water-absorbing force of the sagging mold, and it takes a long time to dry the absorbed moisture after molding. Since it takes time, there are problems in that productivity is low and molding costs are high. In addition, the settsukou type is subject to severe wear and lacks mechanical strength such as compression and bending, so it tends to chip at the corners and peel off the surface in a short period of time. Therefore, it has poor durability and can only be used a few hundred times at most, and it also has problems in that it cannot be easily molded into large, complex and precise shapes due to its strength and wear and tear, and it is easily attacked by acids. Therefore, there was a problem in that it interfered with the molding of fine ceramic products. (Means for Solving the Problems) The present invention was created through repeated research in order to eliminate the problems of the conventional ceramic molding method as described above, and its purpose is to improve molding efficiency ( A ceramic molding method that can improve mold deposition speed, mold release time), shorten mold drying time, and mold various ceramic products with large or complex shapes at low cost and with high productivity. Our goal is to provide the following. In order to achieve the above object, the present invention uses a special mold as a mold, and actively utilizes the characteristics of this mold to cast the slip under heating conditions and perform plastic shaping or pressure forming. It is something. That is, when molding ceramics, the present invention involves mixing and kneading ceramic powder with metal powder and a binder containing a component that evaporates or burns out to form a slurry, which is poured into a mold, solidified, and then fired to form an air-permeable composite. A firing mold is used to mold ceramics while heating this breathable composite firing mold to a required temperature. The heating method for the above-mentioned breathable composite firing type can be atmospheric heating and/or direct heating (conduction heating), and the heating temperature is generally 30°C or higher, although it depends on the moisture content in the slip. The molding method of the present invention is generally applied to discharge casting, cast molding represented by solid casting, and plastic molding represented by roller machine, but may also be applied to pressure molding. (Function) The breathable composite firing mold according to the present invention uses at least ceramic powder and metal powder or reinforcing fibers added thereto as an aggregate, and a binder containing an evaporable or burnable component that does not remain after firing. It can be obtained by firing the mixture. This mold has a dense hardened layer in which metal powder oxide is dispersed on at least the surface, and the evaporated or burned-out component in the binder escapes from the surface layer during drying or firing, resulting in countless fine particles. Open pores are formed throughout the mold, and these vents create good water absorption. Moreover, it has high compressive strength and bending strength due to the shell effect of the hardened layer, has good heat resistance because it is fired at a high temperature, and has excellent thermal conductivity due to the combination of metal powder. Furthermore, since a hardened layer is formed by mixing and firing metal powder and ceramic powder, it has significantly higher abrasion resistance than slat molds or resin molds, and will not chip or peel at the corners even after repeated use. It also has good chemical resistance and is not easily attacked by water or acid. Also, mold shrinkage (dimensional change) is small, and this effect is particularly great when reinforcing fibers are added as aggregate. In the present invention, a ceramic material is molded using the above-mentioned breathable composite firing mold. During this molding, the breathable composite firing mold is actively heated. Since metal powder oxide is dispersed inside and has good thermal conductivity, a sufficient amount of heat is accumulated within the mold, and this acts on the ceramic material through the mold surface. Therefore, when the ceramic material comes into contact with the mold surface, water is rapidly absorbed from the mold surface, evaporates vigorously, and is discharged outside the mold through the ventilation holes. In addition, because the wettability of water improves, the water absorption capacity of the mold itself increases significantly compared to when it is at room temperature, and a high water removal effect continues. Since the temperature of the ceramic material itself increases due to heat conduction, water removal during mud removal during casting is also accelerated. Due to these features, the ink deposition speed is much faster than that of the conventional settsukou type. In addition, the moisture contained in the inking layer or molding layer quickly permeates from the center to the surface layer and is efficiently absorbed from the entire surface of the heated mold, and the moisture inside the mold also passes through the ventilation holes. It is forcibly removed by evaporation. Therefore, soil compaction is good, good mold release properties are imparted even though the mold does not have an ion exchange function, and mold release time is shortened. Furthermore, even after the mold is released, heat has already been applied to the mold from the molding process, and the absorbed moisture is successively discharged.Moreover, the mold has good heat resistance, so it dries quickly. can be carried out, and the amount of heat required for drying can also be reduced. (Example) Examples of the present invention will be described below based on the accompanying drawings. First, the present invention involves molding ceramic materials.
A special mold called a breathable composite firing mold is used as the mold. Figures 1 to 5 illustrate a mold 1 according to the present invention, in which Figure 1 is for discharge casting, Figure 2 is for solid casting, Figure 3 is for plastic molding, and Figure 4 is for processing. Indicates pressure molding. The ceramic molds shown in Figures 1 to 3 are
It is made of an air-permeable composite fired body made of metal powder and ceramic powder as aggregates, and a dense hardened layer 2 is formed on the outer shell portion including at least the mold surface 11.
In this example, the hardened layer 2 reaches the center of the wall thickness, but in some cases, the hardened layer 2 does not reach the center, and the inside is made of an unfired mixed structure of metal powder and ceramic powder. It may have a packing layer. In FIG. 4, a mold 1 is made of a composite sintered body made of metal powder, ceramic powder, and reinforcing fibers 4 as aggregates. It goes without saying that the molds shown in FIGS. 1 to 3 may have a reinforcing fiber dispersed structure similar to that shown in FIG. 4. Furthermore, in the case of a split type, one side may have a conventional structure. The above-mentioned breathable composite firing mold includes a step of mixing and kneading ceramic powder and metal powder or a binder containing a component that evaporates or burns out reinforcing fibers at a predetermined mixing ratio to obtain a slurry sample, and It is made by pouring a sample into a mold and shaping it into a desired mold shape, and drying the molded body and then firing it at a high temperature. Here, the "metal powder" may be ferrous metal powder, non-ferrous metal powder, or a mixed powder or alloy powder thereof, depending on the type of ceramic material to be molded, molding conditions, etc. As the iron-based metal powder, iron powder such as cast iron powder, electrolytic powder, pure iron powder, or steel powder is used. Among these, cast iron powder has the advantage of promoting pore formation by burning free carbon during firing. As the cast iron powder, gray cast iron, ductile cast iron, alloy cast iron, etc. can be used, and alloy cast iron has improved heat resistance and corrosion resistance. Nonferrous metal powders mainly include nickel powder, chromium powder, manganese powder, molybdenum powder, titanium powder,
Almost any metal can be used, such as copper powder, cobalt powder, tungsten powder, etc. Each of these may be used as a single powder, a mixed powder of two or more kinds, an alloy powder, or a composite powder. If necessary, non-ferrous metal powders other than those mentioned above, such as zinc powder, tin powder, lead powder, etc., can also be used, but properties such as strength and heat resistance will deteriorate. Iron-based metal powders are generally inexpensive and are often used, but the chemical stability of their oxides tends to be poor, so if even a small amount of iron-based rust components cannot adhere, non-ferrous metal powders are used. Powder should be used. By appropriately selecting the nonferrous metal powder, strength, heat resistance, and corrosion resistance are improved, and dimensional accuracy and surface quality are improved. For example, chromium powder is suitable for pressure molding where strength is required as a ceramic mold, and when heat resistance and corrosion resistance are particularly required as a ceramic mold. , chromium powder, nickel powder, and molybdenum powder are effective. As the "ceramic powder", one that has a small deformation rate at high temperatures and is easily bonded to metal powder is used. For example, neutral types such as mullite, calcined alumina, activated alumina, fused alumina, chromite, and sillimanite, and acidic types such as fused silica, zirconia, and fused zircon are generally suitable. Basic materials such as magnesia and talc can also be used, but if the binder is something like silica sol, it is generally stable at a pH of 2 to 4. A neutral or acidic refractory powder would be appropriate. Generally speaking, steel-based fibers are suitable as the "reinforcing fibers." In particular, since stainless steel fibers do not corrode during the firing process, they have a high reinforcing effect on both the hardened layer and the packing layer. Other reinforcing fibers, such as ordinary steel fibers such as free-cutting steel, ceramic fibers such as glass fibers and alumina fibers, and carbon fibers, can also provide a reinforcing effect, and have the advantage of preventing cracks and preventing ceramic powder from falling off. is obtained. For example, glass fiber can be expected to have a great reinforcing effect because it has good adhesion with a binder, and is also useful in cases where iron oxides are to be extremely avoided. The particle size of metal powder when unmolded is generally 2 to 500 .mu.m in maximum dimension, and the particle size of ceramic powder is preferably 10 to 300 .mu.m in maximum dimension. The lower limit was specified because, although from the standpoint of transferability and surface roughness of the mold surface, the smaller the particle size, the better, but on the other hand, cracks are more likely to occur. The upper limit was specified because of the need for strength and because excessive porosity would deteriorate the surface properties of the mold. The particle size is appropriately selected between an upper limit and a lower limit depending on the specific ceramic molding application and usage conditions (molding shape, surface roughness of the mold surface, etc.). In addition, depending on the size of the mold, the reinforcing fibers may be, for example, 0.05 to 30 mm long and 5 to 30 mm thick (in terms of diameter).
It is sufficient to appropriately select one within the range of 400 μm.
Among the reinforcing fibers, for example, stainless steel fibers and steel fibers are preferably produced directly from blocks using a self-excited vibration cutting method, but fibers produced by other methods are not prohibited. When reinforcing fibers are used in combination, the amount added should be approximately 1 to 20 vol%, although it depends on the fiber material and dimensions.If it is less than 1 vol%, effects such as improved strength and dimensional stability cannot be expected. However, no matter what material the reinforcing fibers are made of, if they are added in excess of 20 vol%, fiber balls are likely to occur and the moldability is reduced. Further, excessive precipitation on the surface of the hardened layer deteriorates the skin and is also disadvantageous in terms of cost. For metal fibers such as stainless steel with a large aspect ratio, the upper limit is generally 10 vol%.
Small aspect ratio, e.g. thickness 0.03, length
In the case of glass fibers such as 0.1 mm, it can be added up to nearly 20 vol%. Next, “binder containing evaporated or burned-out components” means:
It is a substance used to bond metal powder particles and ceramic particles and to provide fine pores to the composite fired body. Typical binders containing evaporable components include silicon compounds, especially silica sol (colloidal silica) SiO ₂ .nH ₂ O. Silica sol is a stabilized colloidal solution of silica. Examples include SiO ₂ concentration 20-21%, Na ₂ O concentration 0.02% or less,
PH3~4, viscosity (20℃) 3cp or less, specific gravity (20℃)
There are properties of 1.10 to 1.16. In this case, water evaporation is the factor that creates porosity. Particularly suitable binders for the present invention are organosilicate binders, especially alcoholic solvent-borne silica sols based on ethyl silicate. Ethyl silicate is ethyl monosilicate (etlhy ortho
silicate), and is a stable substance with no binder properties when used alone. To obtain the binder, ethyl silicate is mixed with an alcoholic solvent and water and hydrolyzed. As the alcohol solvent, ethanol and isopropanol are mainly used. Then, an acidic substance (hydrochloric acid, phosphoric acid, oxalic acid) is added as a catalyst to promote the reaction and stabilize the silica sol. As a blending example, 80 parts by weight of ethyl silicate,
Alcohol solvent 13 parts by weight, water 6 parts by weight, catalyst 1
Examples include parts by weight. This results in a silica concentration of 32%.
of silica sol is obtained. Further, as the binder containing a component that burns out, room temperature curable resins such as urethane resins, polyester resins, and epoxy resins can be used, and those whose viscosity has been lowered with a solvent are particularly preferred. In addition, appropriate amounts of known substances such as water glass may be added to the binder. The mixing ratio of the metal powder, ceramic powder, and binder is preferably (1 to 5):(1 to 5):1 by weight, and particularly recommended is 2:2:1 to 5:5:1. Ru. The reason for setting the blending ratio in this way is to obtain a good balance of various properties such as strength, water absorption, thermal conductivity for making mold heating effective during ceramic molding, and surface texture. The lower limit of the blending ratio is 1:1:
1 because this level is necessary to obtain the minimum strength that can be used as a mold. The reason why the upper limit was set at 5:5:1 is that if there is too much aggregate relative to the binder, the covering ability of the binder will be reduced, resulting in a decrease in strength and deterioration of the stability of the mold surface. be. The reason for setting the upper limit for metal powder is that even if the blend of ceramic powder and binder is appropriate, if the metal powder is in excess, sufficient strength will not be obtained and the porosity will be higher than necessary. At the same time, the surface quality deteriorates, and transferability, which is important for ceramic molds, is impaired. The reason why the upper limit of the ceramic powder is limited is that the strength will be impaired by excessive blending. Caking agents are necessary for bonding the aggregates together and are necessary to provide air permeability. However, excessive addition makes the fired body more porous than necessary, resulting in a decrease in strength. Preferred formulation examples according to the present invention are shown in Table 1 below.

[Table] Next, the process moves on to manufacturing the ceramic mold to obtain the desired shape. This step is performed by pouring and solidifying the slurry mixed sample obtained in the previous step. That is, for example, as shown in FIG. 6, the mixed sample 5 is poured into a mold 7 in which mold surface elements 6 such as a model, a master model, or an actual ceramic product are set, and the mixture is left to stand for a predetermined period of time. In this casting process, it is effective to add a hardening agent to promote solidification, to apply vibration to promote filling properties, and to perform squeezing. By selecting the good fluidity of the mixed sample 5 and the appropriate particle size of the metal powder and ceramic powder, the shape and shape of the mold surface element 6 can be adjusted.
Patterns can be transferred accurately. Then, by inserting pins and pipes into the formwork during this modeling, the second
The casting hole and mold heating mechanism shown in the figures and FIG. 4 are obtained. Next, in the present invention, after the shaped body obtained in the previous step is removed from the mold, it is subjected to natural drying and/or ignition drying. This is to prevent the occurrence of cracks and distortion, as well as to make it porous (pore formation) by evaporating the alcohol and moisture contained in the binder.The former (natural drying) Appropriately select from a range of 1 to 48 hours depending on mold dimensions, etc. Further, in order to accelerate drying, a high temperature atmosphere, hot air, etc. can also be used. The latter (ignition drying) may be performed by directly igniting the molded body with a torch lamp or the like and burning the evaporated components vaporized from the molded body. The molded body after this drying process has air permeability throughout and can be used as is for cast molding or the like. However, it has low mechanical strength and poor durability. Therefore, in the present invention, as shown in FIG. 7, the molded body 8 that has undergone the drying process is placed in a heating furnace 9 and fired in an oxidizing atmosphere using a heat source such as a resistance heating element or gas. The oxidizing atmosphere may be air or may be so-called oxygen-enriched air in consideration of oxygen supply. The firing conditions depend on the metal powder type, compounding ratio, mold dimensions, desired water absorption rate, etc., but generally the firing temperature should be 400 to 1500°C and the firing time should be 1 hour or more. Lower limit of firing temperature is 400℃, lower limit of firing time is 1
The reason why the time is set is because the firing is insufficient and the dense hardened layer, which is a feature of the present invention, is not formed, and the strength necessary for a durable type cannot be obtained. The reason why the upper limit of the firing temperature was set at 1500° C. is that although a hardened layer is formed, the surface becomes rough, impairing transferability and reducing dimensional accuracy. If the metal powder is iron-based powder, the upper limit of the firing temperature is approximately
A temperature of 1000°C is best, especially a temperature of 850 to 950°C. The longer the firing time, the higher the strength, but it also causes surface roughness and reduced productivity. Through this firing step in an oxidizing atmosphere, firing of the ceramic powder and oxidative sintering of the metal powder in the molded body proceed, and a hardened layer 2 is gradually generated from the surface of the molded body toward the inside. At the same time, volatile components of the binder and burned-out components remaining in the molded body are burned and removed, so that the formation of porosity is promoted. Upon completion of the firing process, a breathable composite firing mold as shown in FIGS. 1 to 4 can be obtained by further applying a stopper or attaching a cover or box as necessary. In the air permeable firing mold according to the present invention, the mold surface 11 is composed of the hardened layer 2 as described above, and this hardened layer 2 consists of oxide particles 20 of metal powder dispersed as shown in FIG.
The surface and inside of the hardened layer 2 have fine particles (0.1
50 μm, average 1 to 20 μm) are formed, and due to these fine ventilation holes, the surface has a porous yet dense and smooth surface. The porosity is generally 5 to 60 vol%, but the type and particle size of the metal powder and ceramic powder, the mixing ratio of the metal powder, ceramic powder, and binder, vibration and squeezing conditions during pour molding, firing conditions, etc. It can be freely adjusted by setting it as desired while taking mold strength etc. into consideration. The mold has a compressive strength of 100 to 1000 Kg/cm ²
In general, the expansion coefficient is 0~1.5% and the thermal conductivity is 0.7~
1.5Kcal/m・h・℃, heat resistance 900℃, hardness Mohs 6-7, thermal spalling for more than 24 hours (5 at 800℃)
It has the characteristics of heating for 5 minutes and cooling for 5 minutes. Next, the present invention involves molding ceramics.
The breathable composite firing mold made in the above process is heated, and while maintaining this state, a slip is placed and molded into the desired shape. The heating method for the breathable composite firing mold may be any method such as direct heating or indirect heating. Typical heating methods include placing the entire mold in an oven or heating chamber as shown in Figure 8A, and heating the atmosphere with a heater or hot air; A method of heating (conduction heating) by inserting a heating element such as nichrome wire or a heating fluid into a mold heating mechanism 10 installed in advance, in which a heating element 12 is placed outside the mold 1 as shown in Fig. 8C , this heating element 1
Possible methods include a method of heating the mold 1 using 2, or a method of heating the mold 1 by embedding it in a fluidized heating layer. Of course, it is also possible to use two or more of the above heating methods in combination. Which heating method to employ may be determined depending on the type of molding method, the water content of the ceramic material, etc. The heating temperature of the mold 1 may be set appropriately depending on the amount of moisture in the slip, the molding method, etc., but if the heating temperature is too low, the moisture removal effect, which is a feature of the present invention, will be insufficient and demolding will also be difficult. So at least
A temperature of 30℃ or higher is required. However, if the heating temperature is too high, too much moisture will be removed from the slip, resulting in loss of fluidity and deterioration of quality. Therefore,
For example, in the case of cast molding, it is best to set the temperature to about 100°C or less. The heated state of the mold 1 is maintained from the slip loading process to the demolding process. For example, in the case of casting molding, the mold is heated during each step of pouring, inking, compacting, and demolding, as shown in FIG. 9A to D. The heating temperature may be constant in each step or may be changed in each step. Furthermore, while heating the mold 1, suction force may be applied from the entire mold or a part thereof. Mold 1 has high heat resistance because it is fired at a high temperature, and is porous as a whole, with metal powder oxides dispersed therein. Therefore, a sufficient amount of heat is accumulated inside by heating, and the water absorption capacity is significantly improved. In this state, water is absorbed by the slip 13 being injected into the mold 1, but in the present invention, water is not simply absorbed naturally through the ventilation holes, but as described above, the amount of heat accumulated inside the mold acts synergistically. Therefore, the moisture 14 in the slip is rapidly sucked through the air holes as the molding process progresses by the mold surface 11, and is heated and evaporated vigorously while passing through the mold, so that the slip is quickly molded. Particularly in the case of cast molding, which has a high moisture content, not only is the evaporation of moisture from the mold accelerated, but the slip itself is also heated, which accelerates the evaporation of moisture on the side that is not in contact with the mold surface. As a result, the deposition speed (the amount of deposit) is significantly increased compared to the settsukou type. Moreover, since the mold surface 11 is porous but dense and smooth, transferability is extremely good, and even fine uneven patterns can be molded with high precision. The moisture 14' absorbed into the mold after mud removal is also
When heated, they evaporate one after another, and the conductive heat uniformly heats the entire molded layer, causing it to shrink uniformly in a short time. Therefore, mold releasability is good. In the mold drying process after mold release, the mold 1 is heated during molding in the present invention, so the temperature rise can be reduced, and since the mold has good heat resistance, high temperature drying is possible. The time required for the drying process is very short. When applied to plastic molding, it becomes possible to omit the use of a drying oven or at least significantly reduce the drying process. Further, the ceramic mold used in the present invention has high mold strength due to the hardened layer 2, and has particularly good wear resistance. Therefore, there will be no cracking, chipping, or crumbling caused by repeated rapid heating and cooling, repeated mold clamping pressure, etc., and chipping at corners, which is important in ceramic molds, will not occur. For this reason, even if the durability of the mold is not as good, it is much more durable than existing plaster molds, resin molds, etc., and the number of molding times can be dramatically increased compared to molding with a settsukou mold. can. A specific example of molding ceramics according to the present invention will be shown. A mold having the shape shown in FIG. 1 was used. Dimensions are total height 75mm, cavity depth 60mm,
The bottom diameter is 35mmφ and the opening diameter is 50mmφ. The mold is a mixture of mullite powder, nickel powder, and ethyl silicate in a ratio of 1:1:0.45, and a slurry sample made by mixing and kneading these is poured into the mold, and after being ignited and dried, it is fired at 1200℃ for 6 hours under atmospheric conditions. obtained by doing so. The water absorption rate of the mold at room temperature is approximately 30%
As a result of the taper wear test in accordance with JIS A 1453, the Setsukou type was 0.11cm ³ /
100 rpm, it was 0.01 cm ³ /100 rpm, indicating extremely good abrasion resistance. Discharge casting was performed using the above mold. The slip was a ceramic slurry with a moisture content of 29%, and the casting conditions were 10 minutes. The mold was preheated prior to molding and kept heated from the pouring process to the mold release process. The heating method used was radiation atmosphere heating using an electric furnace, and the heated state was maintained from pouring to demolding. The amount of ink deposited at each heating temperature of 20 to 100℃ is compared with that of the Setsukou type under the same conditions except for heating.
As shown in Figure 0. It can be seen from FIG. 10 that the present invention can significantly improve the amount of ink deposit. In addition, in the case of the present invention
A good product was obtained even after 20,000 moldings. Similar durability was obtained when a suction force of 700 mmHg was applied to the mold, and the amount of ink deposit increased by more than 10%. Similar results were obtained when the molds shown in Table 1 above were used. (Effects of the Invention) According to the present invention as described above, moisture in the slip can be removed extremely efficiently, so that the inking speed and demolding time can be greatly improved.
Furthermore, the drying time of the mold can be shortened, and as a result, various ceramic materials including fine ceramics can be molded at low cost and efficiently, which is an excellent effect.

[Brief explanation of drawings]

Figures 1 to 4 are cross-sectional views showing a mold used in the heat forming method of ceramics according to the present invention, Figure 5 is a partially enlarged view thereof, and Figures 6 and 7 are manufacturing steps of the mold. 8A to 8C are sectional views illustrating the mold heating method, FIGS. 9A to 9D are sectional views showing state changes when the present invention is applied to cast molding, and FIG. It is a graph showing the relationship between the amount of deposited material and temperature when ceramic molding is performed according to the present invention. 1...Mold, 5...Slurry sample, 11...Surface mold, 13...Slip, 14, 14'...Moisture.

Claims (1)

[Scope of Claims] 1. When molding ceramics, ceramic powder is mixed and kneaded with metal powder and a binder containing a component that evaporates or burns out to form a slurry, which is poured into a mold, solidified, and then fired. 1. A thermoforming method for ceramics, which uses an air-permeable composite firing mold and molds the ceramic while heating the air-permeable composite firing mold to a required temperature. 2. The method of thermoforming ceramics according to claim 1, wherein the heating method for the breathable composite firing mold is conduction heating. 3. The method of heating ceramics according to claim 1, wherein the heating method for the breathable composite firing mold is atmospheric heating. 4. The method for thermoforming ceramics according to claim 1, wherein the heating temperature of the breathable composite firing mold is about 30°C or higher. 5. The method of thermoforming ceramics according to claim 1, wherein the molding method is any one of cast molding, plastic molding, and pressure molding.