JP2005319474A - Method for drying, dewaxing, and firing plaster mold for precision casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively drying a plaster mold, in which a large-size resin pattern is embedded, without breaking the pattern. <P>SOLUTION: A method for drying, dewaxing, and firing method for a plaster mold for precision casting comprises: a plaster mold forming step (A), wherein a resin pattern (a), to which a gate pattern is attached, is set in a mold form, plaster for precision casting is poured into the mold form, and the plaster is cured; a drying step (B), wherein the mold form is removed after curing the plaster, and then a plaster mold (P), in which the resin pattern (a) is embedded, is dried under a pressure reduced condition (I): a dewaxing step (C), wherein the plaster mold (P), in which the resin pattern (a) is embedded, is subjected to stepwise heating (II) with the gate (O) turned downward, and thermally melted, decomposed, and liquefied components of the resin pattern (a)is allowed to flow out from the gate (O); and a firing step (D), wherein the resin pattern (a) is burnt and extinguished, and further an excessive moisture in the plaster is removed. In addition, the stepwise heating in the dewaxing step is preferably conducted at a temperature zone of ≤250°C, and, in the firing step, the resin pattern (a) is preferably burnt and extinguished at a temperature of 300°C-750°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gypsum mold drying, dewaxing and firing method in a precision casting plaster mold method.

Typical methods for precision casting are the lost wax method and the plaster mold method. With the lost wax method, a wax model with a gate is immersed and dried in a slurry that is a dispersion containing a refractory filler and colloidal silica. The wax model is covered with a fireproof coating layer. Next, the pouring gate is lowered and heated to 150 to 300 ° C., the wax model is melted and discharged, and the remaining wax component is burned and burned out. Next, the temperature is raised to around 1000 ° C., and the refractory coating layer is made into a ceramic by firing, thereby forming a high-strength mold having a hollow portion similar to a wax model. Next, the molten metal is cast with the gate facing upward, the mold is collapsed after cooling, a metal body having a similar shape to the wax model is taken out, and is processed into a metal product by post-processing.

  In the plaster mold method, a wax model with a gate is placed in a mold, and gypsum is poured into it, and the wax model is buried in the gypsum and cured. After the plaster is fully cured, it is removed from the mold and allowed to air dry for several days. Next, heat the pouring gate down to 150-250 ° C to melt and flow out the wax model, and then raise the temperature to 300-750 ° C to burn and burn off the wax component remaining in the gypsum. A plaster mold having a model-shaped hollow part is manufactured. This is a method in which molten metal is cast with the gypsum mold gate facing upward, and after cooling, the gypsum mold is collapsed to take out a metal body having a wax-wax model-like shape and form a metal product by post-processing.

  In the lost wax method, a high melting point alloy such as titanium alloy, nickel alloy, cobalt alloy or cast steel is used. On the other hand, in the plaster mold method, a low melting point alloy such as an Al alloy, Mg alloy, or Zn alloy is used.

  The lost wax mold is ceramic, and has high strength and heat resistance that can withstand precision casting of high melting point alloys. When the mold collapses, a strong impact is applied to the surface of the metal body, but since the metal body has high strength, the metal body can be taken out with little damage. On the other hand, the plaster mold of the plaster mold method is plaster and does not have high strength and heat resistance enough to withstand precision casting of a high melting point alloy. However, it has sufficient strength and heat resistance to withstand precision casting of low melting point alloys. When the gypsum mold collapses, the metal body is impacted, but the gypsum mold is weaker than the ceramic mold and can be disintegrated relatively easily, so even a low melting point alloy that is inferior in strength to a high melting point alloy has almost no damage. The metal body can be taken out.

  The drying of precision casting plaster molds is described in the casting manual, Japan Foundry Association. The casting manual discloses a temperature rise curve of the drying furnace and a temperature curve of the central portion of the gypsum mold regarding drying of the gypsum mold. After about 20 hours at a drying furnace temperature of 230 ° C., the gypsum mold center temperature reaches the drying furnace temperature of 230 ° C.

According to the catalog of gypsum maker Sanes Gypsum Co., Ltd. for precision casting, gypsum is dried by (1) natural drying at room temperature for 3 hours, (2) from room temperature to 100 ° C for 1 hour, and (3) 100-150 ° C. 1 hour, and (4) drying at 150 to 250 ° C. for 1 hour in the dryer.

As for the low-pressure casting method using a sand mold or a gypsum mold, there is a “manufacturing method of a thin large casting” disclosed in Patent Document 1. There are “a casting method of a metal casting using a modeling resin as a master” and “a manufacturing method of a mold for precision casting and a model used therefor” disclosed in Patent Document 3.
JP 2004-82211 A JP-A-9-66344 JP 2002-153943 A

  However, as described above, the gypsum drying process takes the longest time among all the processes in the precision casting plaster mold method. This is because it is necessary to sufficiently dry the central part of the precision casting gypsum mold, and the time required for drying becomes longer as the gypsum mold increases.

  In addition, when the gypsum mold is not sufficiently dried, there is a risk that a steam explosion will occur if molten metal is cast. Precision casting method Japan Foundry Association Precision Casting Section edited by p-197, it is stated that a gypsum mold is not suitable for Mg alloy precision casting because it causes a chemical reaction with the dry moisture of the gypsum mold. .

  On the other hand, if heating and drying in a gypsum drying furnace is rushed, it will cause cracking and warping of the gypsum mold. In particular, in the case of a resin model rather than a lost wax model, the phenomenon is remarkably expressed.

  Therefore, the inventors of the present invention have reached the present invention as a result of earnestly examining a method for efficiently drying a gypsum mold in which a large resin model is embedded without breaking.

  Accordingly, the present invention provides a plaster mold manufacturing process (A) in which a resin model (a) having a gate model is placed in a mold frame and a plaster for precision casting is poured and cured in a plaster mold method in precision casting, After curing, the mold is removed, and a drying step (B) for drying the gypsum mold (P) in which the resin model (a) is buried in a reduced pressure state (I); and a gypsum mold (P) in which the resin model (a) is buried A dewaxing step (C) in which the gate (O) is stepped and heated in a stepped manner (II), and the hot melt decomposition liquefaction component of the resin model (a) flows out from the gate (O), and the resin model (a) This is a drying, dewaxing, and firing method for a precision casting plaster mold comprising a firing step (D) that burns and burns and removes excess moisture from gypsum. The stepwise heating in the dewaxing process is preferably performed in a temperature range of 250 ° C. or less, and in the baking process, the resin model (a) is burned off at a temperature of 300 ° C. to 750 ° C. Is desirable.

  Furthermore, the resin model (a) is preferably a polystyrene powder layered modeling model. The resin model (a) may be a two-component reaction curable polyurethane resin model containing a wax component (b) and / or a plasticizer component (c).

  Furthermore, the reduced pressure state (I) is preferably a state in which dry gas can flow into the space where the gypsum mold (P) is disposed from the pore capillary (CP). The space is preferably at a temperature within a temperature range of room temperature to 80 ° C., and the pressure is preferably a pressure within a pressure range of 200 mmHg to 750 mmHg.

  Further, the stepwise heating (II) undergoes a heating process such that the stepwise heating (II) is held for a predetermined time in the first temperature band and is held for a predetermined time in a second temperature band that is higher than the first temperature band by a predetermined value. It is desirable. The first temperature zone is preferably 150 ° C. or lower, and the second temperature zone is preferably 150 ° C. to 250 ° C. The predetermined time is preferably at least 30 minutes.

  Furthermore, the wax component (b) contained in the resin model (a) is preferably a fine powder having a melting point of 50 to 130 ° C.

  Furthermore, it is desirable that the plasticizer component (c) contained in the resin model (a) is liquid at 0 ° C.

  As explained above, how quickly the gypsum mold is dried in the entire precision casting process is the rate-determining method for short delivery. It is necessary to dry and remove excess free water from the gypsum mold and to remove the crystal water of gypsum. It takes a long time for water removal to dry and remove excess free water.

  According to the method of the present invention, by drying under reduced pressure and heating while passing a dry gas in the initial stage of drying, drying of the gypsum mold is promptly promoted, and a short delivery time can be achieved. It also has the effect of preventing cracking due to rapid drying of the gypsum mold.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the precision casting plaster mold method, the model is buried in a plaster mold and dried, dewaxed, and fired. The gypsum mold is not reusable because the gypsum mold collapses after casting and the metal body is taken out to form a product. In order to manufacture a plurality of cast products having the same shape, as many models as the number of products are required. Since casting products similar to each model are produced, the shape of the model must be tightly controlled.

  FIG. 1 is an overall perspective view of a model (M) of a two-cylinder suction port used as an embodiment of the present invention. This three-dimensional shape data was introduced into an optical modeling machine to produce an optical modeling master model. Next, it was inverted with silicon rubber to produce a silicon rubber split mold. A two-component reaction-curable urethane resin solution was vacuum cast into this silicon rubber mold to prepare a two-cylinder suction port-shaped resin model (a). The overall perspective view of the created two-cylinder suction port-shaped resin model (a) is the same as FIG.

Here, first, an embodiment of the resin model (a) will be described. Manufacturing is not suddenly mass-produced, and generally starts with several to several tens of prototypes in the initial stage. There is also a precision casting product. In recent years, when receiving orders for castings from customers, the form of receiving orders using three-dimensional data has increased rapidly. Rapid prototyping is the fastest model manufacturing method in which this three-dimensional data is sent to a laminated powder molding machine to produce a resin model by three-dimensional solid modeling.

  The resin model (a) for precision casting is optimally a resin that melts and flows out by heating, and polystyrene fine powder beads are also used in the present invention. The polystyrene model formed by powder lamination molding is made of a thermoplastic resin having a softening point of 150 to 200 ° C., and is softened and melted away in the dewaxing step (I). In addition, as the heating conditions progress, the thermal degradation decomposition combustion burns away. If burnt down enough, the ash remaining in the gypsum mold will be very small. A small amount of ash remaining in the model-shaped space in the plaster mold can be easily removed by blowing air.

  If it is about several models, it can be manufactured by powder additive manufacturing, but if you make tens or more models, the occupying time of the modeling machine will be longer, so one 3D stereo modeling model will be the master model, Dozens of replicated resin models are produced by inverting the silicon rubber mold and vacuum casting the liquid resin into the silicon rubber mold. If one master model is produced firmly, it is not so difficult to produce several hundreds of replicated resin models (a) in a short time with a plurality of silicon rubber molds.

  The resin model (a) is provided with a casting gate shape. The addition of the gate shape may be a three-dimensional three-dimensional model that is integrally added to the resin model during powder additive manufacturing or optical modeling, or the gate model is pre-manufactured and bonded to the resin model (a) with an adhesive. Also good. Preferably, it is the fastest method to form in an integrally added state.

  The replicated resin model (a) is one in which a two-component reaction curable urethane resin is used. In general, a urethane resin has a heat resistance of about 80 ° C., is a resin that easily decomposes, melts, flows out, and is highly compatible as a precision casting model. In this two-component reaction-cured urethane resin solution, a wax component (b) and / or a plasticizer component (c) are blended and used. Thus, in the dewaxing step (I), the wax component (b) and / or the plasticizer component (c) are first washed away, and the urethane resin remains in the gypsum mold (P) in a contracted state. To do. Next, as the heating conditions progress, the urethane resin is thermally decomposed and melted, a part of which is liquefied and discharged, and a part of it is burned and burned out. If it is burnt down sufficiently, the amount of ash remaining in the gypsum mold (P) will be very small. A small amount of ash remaining in the model shape space in the plaster mold (P) can be easily removed by blowing air.

  The two-component reaction curable resin is used as a replica material for an industrial prototype design model, and has excellent manufacturing workability, curability, shape retention, and cutting workability. It can be rapidly cured and demolded by adding a catalyst for acceleration of curing, and a liquid plasticizer can be added as a plasticizer component (c), and a fine wax wax component (b). It is also possible to mix powder.

  Details of the resin model for precision casting using such a two-component reaction curable urethane resin are disclosed by the present inventors in Japanese Patent Application Laid-Open Nos. 2003-212257 and 2003-290871.

  Next, an embodiment of the gypsum mold manufacturing process (A) will be described.

  Various types of precision casting plaster have been put on the market, and the representative plaster used is “Caster 8” of San-S Gypsum Co., Ltd. Mixing with gypsum / water = 100 parts / 50 parts, placing the resin model (a) in the mold, pouring the gypsum / water mixture as shown in FIG. 2, and burying the resin model (a) . The gypsum was allowed to stand for several hours at room temperature, and then the mold was removed and the resin model-embedded gypsum mold (P) was taken out.

  When installing the resin model (a) on the mold (F), the gate (OP) added to the resin model (a) was lightly fixed and installed on the mold bottom (FB) with an instantaneous adhesive. Now, as shown in FIG. 3, the air vent hole (O) and the gate (OP) are exposed on the bottom surface (PB) of the gypsum mold (P) from which the mold (F) has been removed. It becomes a state. In addition, D is a saucer for casting ports.

  Next, an embodiment of the step (B) for drying the gypsum mold (P) will be described.

  The gypsum needs only to have water necessary for a chemical reaction, but it must have sufficient fluidity and workability that can be poured into a mold. Therefore, it is inevitably necessary to have excess water, and it is necessary to remove this excess water from the gypsum mold.

  The initial drying of the gypsum mold, which removes excess water from the gypsum mold lump, is allowed to stand at room temperature. Free water molecules present between the gypsum crystal particles gradually evaporate from the surface of the gypsum mold. When free moisture on the gypsum mold surface is scattered, capillaries are formed between the gypsum crystal particles, and the free moisture present in the lower layer of the gypsum surface moves to the surface through the capillaries and is sequentially scattered into the air. The scattering drying process is repeated to gradually dry the gypsum mold.

  In order to dry the gypsum mold quickly, the surface area may be increased. However, the outer shape of the gypsum mold is determined by the mold, and the frame for injecting the gypsum / water mixture in which gypsum and water are mixed is a wooden frame or a metal frame, with four sides and five sides. It is a configured box type. The five faces that make up the formwork can be easily assembled with screws. Therefore, the plaster mold is manufactured as a rectangular parallelepiped, which is the simplest manufacturing method.

  If the shape of the gypsum mold is made complex so as to increase the surface area, the mold itself becomes complicated, and it takes a long time to produce the mold, and no merit can be found.

  The rectangular gypsum mold in which the resin model (a) is embedded has a small surface area as described above.

  In the case of the resin model (a) having a large and complex shape, the gypsum mold also becomes large, the surface area per weight becomes smaller and the drying of the central part of the gypsum mold becomes very disadvantageous. In particular, when the shape of the resin model (a) is a hollow body having an opening, the gypsum that has entered and hardened into the hollow portion from the opening of the model is eventually almost covered with the material of the model. Since the material of the model consists of a resin component that hardly absorbs water, the free water present in the gypsum located in the hollow part of the resin model (a) is in a very disadvantageous state for moving to the gypsum surface and evaporating to dryness. It is in.

  For these reasons, it is very difficult for the large hollow complex resin model (a) to rapidly dry up to the central part of the gypsum mold under room temperature drying conditions for several days.

  As a result of intensive studies on a method for promptly accelerating drying without impairing the curability of the gypsum, as shown in FIG. 4, the gypsum mold (P) demolded from the mold (F) is removed from the decompression tank ( V) was found to be most effective when it is dried by heating under reduced pressure at a temperature of 20 to 80 ° C. for several hours at a reduced pressure of 200 to 750 mmHg while flowing nitrogen gas from a capillary (CP).

  That is, after the gypsum mold (P) is cured, the free water on the gypsum surface is quickly evaporated and scattered by placing the gypsum mold (P) in a reduced pressure state. In addition, free moisture inside the gypsum mold (P) is to be sucked out to the surface under reduced pressure. Moisture scattered from the gypsum surface is transported out of the system on a dry gas flowing from the capillary (CP). Since the surface temperature of the gypsum mold (P) decreases due to free water scattering from the surface of the gypsum mold (P), and the evaporation and scattering of free water decreases, it is effective to keep the gypsum mold (P) slightly heated. is there. In order to keep the gypsum mold (P) in a heated state, the decompression tank (V) itself is heated by an electric heater (H). Irradiation is applied to the gypsum mold (P) from the glass window of the decompression tank (V). A method of heating the gypsum mold (P), a method of heating dry gas introduced from the capillary (CP), and the like are effective. In this embodiment, a heat transfer heater (H) is used. Moreover, in FIG. 4, (HR) is a holding stand for holding the plaster mold (P).

  A capillary (CP) is easily manufactured by cutting a glass tube by heating and melting it with a burner and stretching it at a stretch, forming a thin enamel wire at the stretched portion. As long as the capillary (CP) is manufactured from the glass tube by the above method, the capillary tube (CP) is tubular. When the tip of the capillary (CP) is put into water and air pressure is applied to the other end, air is released from the tip of the capillary (CP) into the water and bubbles are generated, confirming the completion of the capillary (CP).

  Next, an embodiment of the dewaxing step (C) will be described.

  In the dewaxing step (C), the resin model (a) to which the gate (OP) is added is melted and liquefied and melted and discharged from the gate part (B) of the gypsum mold (P). ). Naturally, the drying of gypsum also proceeds in parallel.

  Therefore, as shown in FIG. 5, the gypsum mold (P) is installed in the combustion furnace (FN) with the bottom surface from which the pouring gate (OP) comes out facing down, and is heated by electricity or gas.

  When the resin model (a) is a polystyrene powder layered product, it is dewaxed at a furnace temperature of 150 to 200 ° C. above the softening and melting temperature of polystyrene, but the furnace temperature is rapidly raised to 150 to 200 ° C. Then, since the remaining free water or crystal water is vaporized inside the gypsum and the gypsum mold (P) may be broken by the pressure, it is necessary to raise the temperature stepwise.

  When the resin model (a) is a two-component reaction curable resin, the furnace temperature is maintained for 30 minutes or more at a higher temperature of 120 to 150 ° C. near the blended and melted liquid, and the resin model (a) is waxed with the liquid plasticizer (c). -The wax component (b) is liquefied and discharged. Thereafter, the temperature in the furnace is raised stepwise to promote dewaxing.

  When the temperature in the furnace is 120 to 150 ° C., the gypsum mold (P) is taken out, cooled and cut, and the cross section is observed. As a result, the wax component (b) and the liquid plasticizer component (c) are the gate (OP). Further, it was confirmed that it started to be slightly washed away by natural fall and penetrated into the gypsum mold (P) inner wall. In the resin model (a), the wax / wax component (b) and the liquid plasticizer component (c) were removed, so that a resin skeleton contracted in a sponge shape remained.

  From these observation facts, it is possible to clarify the behavior change of the resin model (a) embedded in the plaster mold (P) due to heating. That is, this is because when the resin model (a) is heated, the wax component (b) and the liquid plasticizer component (c) contained in the resin model (a) are transformed into the resin model (a). It exudes from the inside of a) and impregnates the gypsum mold (P) inner wall. The resin skeleton of the resin model (a) contracts in a sponge shape that retains the trace of the wax / wax component (b) and the liquid plasticizer component (c) oozing from the inside of the resin model (a). The internal pressure at which the resin model (a) tries to expand by heating is relieved by this phenomenon. When the heating is further continued, dewaxing starts from the gate shape part attached to the resin model (a), and the wax and wax component (b) oozing out from the resin model (a) in the inside and the liquid plasticizer component ( It was reached that c) was smoothly interpreted as flowing out of the gypsum mold (P) having a gate shape.

  Gypsum releases a portion of crystal water around 130 ° C. and turns into hemihydrate gypsum. Therefore, at a stage where the temperature in the furnace is slightly higher than 150 ° C. and is maintained for 30 minutes, crystal water will be released and become semi-hydrated gypsum. At this point, the resin model (a) buried in the gypsum mold is in a dewaxed state, and the release of crystal water generated from the center of the gypsum mold (P) pushes out the dewaxed component via the dewaxing passage. However, it is discharged from the gate (OP) of the plaster mold (P) into the heating furnace (FN). In FIG. 5, (FH) is a heater, (MP) is a metal tray, and (AB) is an effluent during the dewaxing process.

  That is, the water vapor released from the gypsum mold (P) can eliminate internal pressure in the gypsum and prevent the gypsum mold (P) from cracking as long as the stepwise heating proceeds reliably. In particular, in the case of a resin model (a) made of a two-component reaction curable urethane resin containing a liquid plasticizer (c) having a lower melting point than commercially available lost wax and a wax component (b), a plaster mold (P) It can be said that it can be said that it is excellent in performance capable of avoiding cracking.

  Next, an embodiment of the firing step (D) will be described.

  After the dewaxing step (C), the furnace temperature is gradually raised to 700 to 750 ° C., and the liquid plasticizer (c) and wax / wax of the resin model (a) embedded in the plaster mold (P) The contracted resin skeleton which is the shell of component (b) is burned. At this time, the liquid plasticizer (c) impregnated and adhered to the inner wall of the plaster mold (P) and the wax component (b) are also combusted. Further, the free water and the released crystal water present in the gypsum mold (P) itself are removed, and a gypsum mold that can be used for casting is completed.

  Air is injected into the interior from the gypsum mold (OP) to remove trace ash remaining in the gypsum mold (P). Immediately install in casting equipment and prepare for casting molten metal.

  In particular, it is important to remove moisture from the gypsum mold (P). If the molten metal is cast in a state where moisture removal from the gypsum mold (P) is insufficient, the water in the gypsum mold (P) reacts with the molten metal to cause explosion. Sufficient care is required as it will occur.

1 is an overall perspective view of a model of a two-cylinder suction port used as an embodiment of the present invention. FIG. 3 is a cross-sectional view of a state in which a two-cylinder suction port-shaped resin model to which a gate has been added is installed in a mold and a gypsum / water mixture is poured into the mold. It is sectional drawing of the gypsum type | mold with which the 2-cylinder suction port shape resin model was embed | buried. It is sectional drawing which is carrying out the reduced pressure heating drying of the gypsum type | mold with which the 2-cylinder suction port shape resin model was buried below the pouring gate. It is sectional drawing which is implementing the dewaxing process in a heating furnace.

Explanation of symbols

a Resin model F Formwork FB Frame body bottom FN Heating furnace O Air vent OP Opening gate P Gypsum mold V Depressurization tank

Claims (7)

In the plaster mold method in precision casting,
Placing a resin model (a) with a gate model in the mold (P), pouring gypsum for precision casting and hardening the plaster mold (A),
After the gypsum is cured, the mold is removed, and a drying step (B) for drying the gypsum mold (P) in which the resin model (a) is buried in the reduced pressure state (I),
The gypsum mold (P) in which the resin model (a) is buried is heated stepwise with the gate (O) facing downward (II), and the hot melt decomposition liquefaction component of the resin model (a) flows out from the gate (O). A dewaxing step (C);
A method for drying, dewaxing and firing a plaster mold for precision casting, comprising: a firing step (D) for burning and burning the resin model (a) and removing excess water from the gypsum.   The method for drying, dewaxing, and firing a plaster mold for precision casting according to claim 1, wherein the resin model (a) is a polystyrene powder additive manufacturing model.   2. The precision casting according to claim 1, wherein the resin model (a) is a two-component reaction curable polyurethane resin model containing a wax component (b) and / or a plasticizer component (c). Plaster mold drying, dewaxing and firing methods.   4. The reduced pressure state (I) is a state in which dry gas can flow into a space where a gypsum mold (P) is disposed from a pore capillary (CP). Drying, dewaxing and firing methods for precision casting plaster molds.   The stepwise heating (II) passes through a heating process such that it is held for a predetermined time in the first temperature zone and is held for a predetermined time in a second temperature zone that is higher than the first temperature zone by a predetermined value. The method for drying, dewaxing, and firing a plaster mold for precision casting according to any one of claims 1 to 4.   The precision casting according to any one of claims 1 to 4, wherein the wax component (b) contained in the resin model (a) is a fine powder having a melting point of 50 to 130 ° C. Plaster mold drying, dewaxing and firing methods. The plasticizer component (c) contained in the resin model (a) is in a liquid state at 0 ° C, and the plaster mold for precision casting according to any one of claims 1 to 4, is dried. Dewaxing and firing method.

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