JPH0317577B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for manufacturing a mold suitable for casting a casting having a three-dimensional structure. [Background technology] The molds currently in use include ordinary molds that use clay as a binder, such as green sand molds, high-pressure molds, and high-speed molds, as well as thermosetting molds, self-hardening molds, gas-curing molds, and electron beam-curing molds. , special molds that use hardening binders, such as volatilization hardening molds and precision casting molds, and other molds, such as vanishing model molds, vacuum molding molds, and freezing molds. Ordinary molds are the most common type of mold, and because molding sand can be used repeatedly and are inexpensive, they are still the most popular type of mold. However, because ordinary molds, typically green sand molds, use clay or linseed oil as a binder, the mold is heated and set at a temperature of 170 to 180°C for several tens of minutes to several hours. It requires a long time and is low in productivity. Furthermore, a lot of gas is generated during casting, and the gas pressure can easily damage the mold or cause many defects in the casting, so a gas venting pipe must be installed. There is a problem. Additionally, molds are generally split horizontally or vertically, and if the surface of the object to be cast is two-dimensionally simple, the model can be easily extracted after molding. If the surface of the object to be cast is complicatedly curved three-dimensionally, such as a three-dimensional impeller, it may be impossible to extract the model.
Therefore, in this case, the model is divided into several to dozens of parts, each divided model is modeled manually, each model is pulled out, each model is reworked, and then they are combined. The molds are manufactured using the same technology. However, as mentioned above, ordinary molds use clay as a binder, and as it takes a long time to heat and set, there is a risk that the mold may become deformed, such as drooping or collapsing. It was necessary to insert a core metal into the core for reinforcement, which made the molding process extremely complicated. In addition, the special mold uses a curable binder and can quickly harden the binder by heat curing or room temperature curing using a hardening agent, resulting in high productivity and stable quality molding. This technology is rapidly progressing with the increase in the production of automobiles and motorcycles, and in particular, shell molds that use phenolic resin as a binder are rapidly gaining popularity as mold cores. This special mold is manufactured by hand molding, casting, blow molding, etc. to harden the curable binder, and then horizontally splitting, vertically splitting, dump box method, etc., to extract the model. However, since it is necessary to extract the model from a mold that has already been hardened, the surface of the object to be cast is not two-dimensionally simple, such as a three-dimensional impeller. If the surface of the object is complexly curved three-dimensionally, the model cannot be extracted.
In this case, the model is divided into several to dozens of parts, and each of the two parts is manually molded, the binder is hardened, and then each part is pulled out, as in the case of the ordinary mold. Efforts are being made to do so. However, in the case of this special mold, unlike ordinary molds, it is necessary to remove the model from the mold in which the binder has hardened, and it is difficult to release the model from the hardened binder, and the binder is in a hardened state. In some cases, it is difficult to extract a complicatedly shaped model from a non-plastic mold, and sometimes it becomes impossible to extract the model. [Object of the invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a mold that can easily manufacture a mold for casting a casting having a three-dimensional shape. It is something to do. [Disclosure of the Invention] However, the method for manufacturing a mold according to the present invention involves mixing sand with a liquid binder made of thermosetting resin containing a thickener, molding the sand, and extracting the model. It is characterized by hardening the binder immediately, and while making use of the ordinary molding method that makes it easy to extract models with complex shapes, it also uses a thickening agent to provide appropriate viscosity and a thermosetting resin. The rapid hardening of the binder makes it possible to prevent mold deformation without the use of a core metal, and the special molding method that can increase productivity can be utilized as is. The present invention will be explained in detail below. As the binder, thermosetting resins such as phenolic resins and furan resins that harden quickly are used. Among them, phenolic resins, which are commonly used in shell molds, are preferred. But that's fine. In addition, this thermosetting resin binder is used in liquid form, so if it is liquid at room temperature, it can be used as is, or if it is solid at room temperature, it can be used by dissolving it in a solvent or otherwise making it liquid at room temperature. . A thickener is added to this thermosetting resin binder to make it sticky and uniformly dissolved. The thickener is preferably one that dissolves well in the liquid thermosetting resin binder, does not separate, and does not significantly change the temperature-viscosity curve, especially one that reacts with the thermosetting resin binder used. More preferred. Further, even if the thermosetting resin binder is thickened, it is not preferable if it becomes too stringy or has high adhesion to the model. Furthermore, when low boiling point melting is used in combination, the viscosity can be changed arbitrarily by adjusting the volatilization of the solvent from the mixture mixed with sand, and one thickener can be used depending on the shape and size of the mold. It can be used as Specific examples of preferred thickeners include α-starch, β-starch, carboxymethyl cellulose (CMC), polyvinyl alcohol, polyethylene oxide, and guar gum. ), Cyryl (Chubuchi Chemical Industry Co., Ltd.), Pullulan (Hayashibara Biochemical Research Institute), Kanekazemurak (Chubuchi Chemical Co., Ltd.), etc. can be exemplified. Isoban is a copolymer of isobutylene and maleic anhydride, has a white appearance, and is generally used after being dissolved in an aqueous alkaline solution. Cylyl is a modified silicone liquid polymer whose main chain is polypropylene oxide and has a reactive silyl group at the end. It is a pale yellow transparent liquid with a molecular weight of approximately 8,000 and a viscosity of approximately 230 poise (at 23°C). This cylyl has reactivity with the phenolic resin, and even when the temperature becomes higher than room temperature, the thickening effect can be maintained due to the reaction with the phenolic resin as the temperature rises. Therefore, pyryl is one of the most preferred thickeners. Pullulan is a natural polysaccharide whose smallest unit is glucose, and is a non-gelling viscous aqueous solution with a linear structure in which maltotriose is repeated with α-1,6 bonds. Kanekazemurakku is an acrylic acid-modified silicone oligomer (Acrylic Silicone Oligomer).
Oligomer). However, when molding, a liquid thermosetting resin binder containing the above-mentioned thickener is kneaded with sand.
Fill the model with this sand. At this time, when the object to be cast has a three-dimensionally complex shape, such as a three-dimensional impeller, the model is divided into several to several dozen pieces, and each divided model is molded. A liquid thermosetting resin binder kneaded with sand acts to bind sand in the same way as a binder in ordinary molds such as green sand molds, and can impart shape retention to the sand mold. Therefore, unlike special molds such as shell molds, there is no need to harden the binder to maintain the shape of the sand mold, and the sand mold is bound by a thermosetting resin binder and has plasticity. The mold can be removed from the mold. In this way, because the model is removed before the binder hardens, as in the case of special molds, the hardened binder may adhere to the surface of the model, making it difficult to release the model, or molds with no plasticity. It does not make it difficult to pull out a model with a complex shape from a sand mold, and there is no risk that it will become impossible to pull out the model, and the model can be easily pulled out in the same way as a normal mold. It can be done. After the model is removed in this way, the thermosetting resin binder in the sand mold is hardened, but the thermosetting resin binder contains a thickener to increase its viscosity. This viscosity makes it possible to improve the shape retention of the sand mold, allowing the model to be removed without the risk of deformation such as sagging or collapse, and the process of curing the thermosetting resin binder. This can prevent deformation from occurring during the process. In particular, binders for thermosetting resins are rapidly cured by heating, etc., and there is a risk that the mold will collapse during this long period of time, as in the case of ordinary molds that require a long time to cure. Therefore, there is no need to use a core metal to prevent deformation as is the case with ordinary molds. Furthermore, since the binder is hardened quickly due to its hardenability, productivity can be increased as in the case of special molds. Here, the amount of the thickener is set within a range that increases the viscosity of the thermosetting resin binder to a viscosity that effectively prevents the sand mold from deforming. Although it cannot be determined unconditionally depending on the size, the amount is generally about 0.5 to 50 parts by weight per 100 parts by weight of the liquid thermosetting resin binder. After pulling out each divided model from the sand mold as described above, the binder is hardened and molded, and by assembling these, castings with complex shapes such as three-dimensional impellers are cast. It is then finished into a mold to be used. The invention will now be illustrated by examples. Production example of binder 1 658 parts by weight of phenol and 851 parts by weight of 37% formalin were placed in a reaction vessel, 40 parts by weight of 33% caustic soda water was added thereto, and the mixture was heated to 85°C over about 60 minutes with good stirring. The reaction was continued for 2 hours. After the reaction was completed and neutralized with boric acid, dehydration under reduced pressure was started and dehydration was carried out at 150 Torr until the internal temperature reached 70°C. The resol type phenolic resin thus obtained was reddish brown and had a viscosity of 180 poise at 25°C. Production example of binder 2 Resol type phenolic resin 900 obtained in production example 1
By adding 100 parts by weight of methanol to the parts by weight and stirring well, a product having a viscosity of 13 poise at 25°C was obtained. Production example of binder 3 940 parts by weight of phenol, 689 parts by weight of 37% formalin and 4.7 parts by weight of oxalic acid were charged into a reaction vessel,
It took about 60 minutes to reflux, and the reaction was continued for 2 hours. After the reaction is complete, start dehydration under reduced pressure, dehydrate at normal pressure to 150℃, and then reduce the pressure further.
Dehydration was performed at 100Torr until the internal temperature reached 150℃. The solid novolak type phenolic resin thus obtained had a softening point of 97°C. Next, 300 parts by weight of methanol was added to 700 parts by weight of this resin and dissolved well to prepare a liquid resin having a viscosity of 5 poise at 25°C. Production Example 4 of Binder 450 parts by weight of ethylene glycol was added to 550 parts by weight of the solid novolak type phenolic resin obtained in Production Example 3 and thoroughly dissolved to prepare a liquid resin having a viscosity of 60 poise at 25°C. Manufacturing Example 5 of Binder The liquid resins prepared in Manufacturing Examples 3 and 4 were mixed at a weight ratio of 1:1 to prepare a liquid resin having a viscosity of 28 poise at 25°C. Type of thickener: 25% aqueous solution of polyvinyl alcohol
...Thickener No.1 ・25% aqueous solution of Isoban #06 ...Thickener No.2 ・Cyril 5A03 ...Thickener No.3 ・25% aqueous solution of Pullulan ...Thickener No.4 Implemented Examples 1 to 4 Thickeners No. 1 to No. 4 were added and dissolved in the amounts shown in Table 1 to the binder obtained in Production Example 1, respectively. By adding this thickener, the viscosity of the binder at 25°C increased to the values shown in Table 1. Next, put 10kg of flattery silica sand into the whirl mixer,
A binder was added to this in the amount shown in Table 1 and kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand is
It was 1.08. Various tests were conducted using this mixed sand. The results are shown in Table 1. Adhesion to hands: After taking the mixed sand in one hand and squeezing it tightly, the hand was opened and rubbed with another hand to check for adhesion. Adhesion to wooden models The presence or absence of adhesion was examined by firmly pressing the mixed sand onto a wooden model and then rubbing it by hand. Moldability 200g of kneaded sand was filled into a 50mmφ pipe, hardened 5 times with a rammer, removed from the mold, and the bulk specific gravity was measured. The higher the bulk specific gravity, the higher the density and the higher the moldability, and the bulk specific gravity is 1.4.
If the moldability exceeds the above, the moldability is "good" and the bulk specific gravity is
If the value was less than 1.4, the moldability was evaluated as "poor."
At this time, the appearance was also observed and used as a factor in the evaluation. Green strength: 200 g of kneaded sand was filled into a 50 mmφ mold, molded using a press so that the bulk specific gravity was 1.50, and after demolding, the green strength was measured using an Amsler. Corner chipping property The test piece prepared in the above green strength measurement was placed in a blow dryer preset at 200°C, allowed to harden for 1 hour, and the state of corner chipping on the test piece was visually observed. Compressive strength The test pieces prepared in the above green strength measurement were placed in a blower dryer set at 150℃ in advance, and after 30 minutes, 1 hour, 3 hours, and 5 hours, the test pieces were taken out and tested for compressive strength using Amsler. was measured to investigate the drying and hardening speed of the binder. Amount of gas generated: Crush the test piece processed in the corner chipping test above, weigh approximately 5g accurately, place it in an electric furnace preset at 1000℃, measure the amount of gas generated, and calculate the maximum amount at that time. Indicated. Casting test A mold for a three-dimensional impeller was made using kneaded sand, dried and cured at 200°C for 30 minutes, and poured without applying a molding agent. After cooling, the casting surface was observed and evaluated using a casting surface roughness standard plate (JIS B 0601). Comparative Example 1 Kneading sand was prepared in the same manner as in Examples 1 to 4 except that no thickener was used. The bulk specific gravity of the kneaded sand was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 were conducted. The results are shown in Table 1. Examples 5 to 8 Thickeners No. 1 to No. 4 were added and dissolved in the blending amounts shown in Table 2 to the binder obtained in Production Example 2, respectively. By adding this thickener, the viscosity of the binder at 25°C increased to the values shown in Table 2. Next, put 10kg of flattery silica sand into the whirl mixer,
A binder was added thereto in the amount shown in Table 2 and kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand is
It was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 were conducted. The results are shown in Table 2. Comparative Example 2 Kneading sand was prepared in the same manner as in Examples 5 to 8 except that no thickener was used. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, the above Examples 1 to 4
We conducted various tests similar to those in the case of . The results are shown in Table 2. Examples 9 to 12 Thickeners No. 1 to No. 4 and hexamethylenetetramine were added to the binder obtained in Production Example 3 and dissolved in the amounts shown in Table 3, respectively. By adding a thickener, the viscosity of the binder at 25°C increased to the values shown in Table 3. Next, 10 kg of flattery silica sand was placed in a Whirl mixer, a binder was added in the amount shown in Table 3, and the mixture was kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 above were conducted. The results are shown in Table 3. Comparative Example 3 Kneading sand was prepared in the same manner as in Examples 9 to 12, except that no thickener was used. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, the above Examples 1 to 4
We conducted various tests similar to those in the case of . The results are shown in Table 3. Examples 13 to 16 Thickeners No. 1 to No. 4 and hexamethylenetetramine were added to the binder obtained in Production Example 4 and dissolved in the amounts shown in Table 4, respectively. By adding a thickener, the viscosity of the binder at 25°C increased to the values shown in Table 4. Next, 10 kg of flattery silica sand was placed in a Whirl mixer, a binder was added thereto in the amount shown in Table 4, and the mixture was kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 above were conducted. The results are shown in Table 4. Comparative Example 4 Kneaded sand was prepared in the same manner as in Examples 13 to 16 except that no thickener was used. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, the above Examples 1 to 4
We conducted various tests similar to those in the case of . The results are shown in Table 4. Examples 17 to 20 Thickeners No. 1 to No. 4 and hexamethylenetetramine were added to the binder obtained in Production Example 5 in the amounts shown in Table 5 and dissolved therein. By adding a thickener, the viscosity of the binder at 25°C increased to the values shown in Table 5. Next, 10 kg of flattery silica sand was placed in a Whirl mixer, a binder was added in the amount shown in Table 5, and the mixture was kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 above were conducted. The results are shown in Table 5. Comparative Example 5 Kneading sand was prepared in the same manner as in Examples 17 to 20, except that no thickener was used. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, the above Examples 1 to 4
We conducted various tests similar to those in the case of . The results are shown in Table 5. Examples 21 to 23 Cylyl No. 3 was added as a thickener to the binder obtained in Production Example 2 in the amount shown in Table 6 and dissolved. By adding this thickener, the viscosity of the binder at 25°C increased to the values shown in Table 6. Next, put 10kg of flattery silica sand into the whirl mixer,
A binder was added to this in the amount shown in Table 6 and kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand is
It was 1.08. Using this kneaded sand, the above Example 1
Various tests similar to those in cases 4 to 4 were conducted.
The results are shown in Table 6. Examples 24 to 26 Thyryl No. 3 and hexamethylenetetramine as thickeners were added and dissolved in the amounts shown in Table 6 to the binder obtained in Production Example 5. By adding a thickener, the viscosity of the binder at 25°C increased to the values shown in Table 6. Next, put 10 kg of flattery silica sand into the whirl mixer, and add the binder to it.
The amounts listed in the table were added and kneaded for 10 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand was 1.08. Using this kneaded sand, various tests similar to those in Examples 1 to 4 above were conducted. The results are shown in Table 6. Conventional example: Put 10 kg of flattery silica sand into a whirl mixer, add 150 g of linseed oil, 1 g of lead naphthenate,
After adding 1 g of cobalt naphthenate and kneading for 3 minutes, 15 g of Abrazin was added and kneaded for 7 minutes to prepare kneaded sand. The bulk specific gravity of the mixed sand was 1.08.
Using this kneaded sand, various tests similar to those in Examples 1 to 4 above were conducted. The results are shown in Table 6.

【table】

[Table] *The mold could not be made due to missing corners.

【table】

[Table] *The mold could not be made due to missing corners.

【table】

[Table] *The mold could not be made due to missing corners.

【table】

[Table] *The mold could not be made due to missing corners.

【table】

[Table] *The mold could not be made due to missing corners.

【table】

[Table] As shown in Tables 1 to 6, each example using a phenolic resin binder containing a thickener had better adhesion and moldability than each comparative example. It has been confirmed that it is excellent in corner notch shape and casting tests, and can easily manufacture molds for casting three-dimensional castings. In addition, compared to the conventional method corresponding to the green sand mold method, each example has excellent moldability, corner chipping resistance, hardenability (see compressive strength column), casting test, etc.
It is confirmed that it is possible to easily manufacture a mold for casting three-dimensional castings. [Effects of the Invention] As described above, in the present invention, a liquid binder made of a thermosetting resin containing a thickener is mixed with sand,
The binder is hardened after the sand is molded and the model is extracted, so the binder of liquid thermosetting resin is used in sand in the same way as the binder in ordinary molds. It has a caking effect and can give shape retention to the sand mold, and there is no need to harden the binder to retain the shape of the sand mold, and it is suitable for thermosetting resin binders. As a result, the mold can be easily removed from the sand mold, which is caked and has plasticity, and the caking agent contains a thickener to increase its viscosity.
This viscosity makes it possible to improve the shape retention of the sand mold, allowing the model to be removed without the risk of deformation such as sagging or collapse, and the binder of the thermosetting resin hardens quickly. There is no risk of mold deformation occurring during this long period of time, unlike in the case of ordinary molds, which require a long time, and therefore there is no need to use a core metal to prevent mold deformation, as in the case of ordinary molds. It's something that doesn't exist. Furthermore, since the binder is hardened quickly due to its hardenability, productivity can be increased as in the case of special molds.

Claims (1)

[Claims] 1. A liquid binder made of a thermosetting resin containing a thickener is mixed with sand, and the binder is hardened after the sand is molded and a model is extracted. Characteristic mold manufacturing method. 2. The method for manufacturing a mold according to claim 1, wherein the binder is a phenolic resin. 3. The mold manufacturing method according to claim 1 or 2, wherein the thickener is reactive with a thermosetting resin binder.