JPH0516932B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for producing resin coated sand for shell molds. [Background Art] A shell mold is produced by bonding molding sand such as silica sand with a binder resin. This shell mold is widely used because it has excellent features such as a smooth casting surface and good dimensional accuracy. The binder for this shell mold is generally a novolak type phenolic resin made by adjusting the molar ratio of phenols and aldehydes to 1:0.6 to 0.9 and reacting them under an acidic catalyst, or a phenol and aldehyde resin. A solid resol type phenol resin is used, which is prepared by adjusting the molar ratio of 1:1 to 3 and reacting it under an alkali catalyst.For novolak type phenol resin, hexamethylenetetramine is blended as a curing agent, and resol type phenol resin is used. Leave the resin as it is,
A resin-coated sand coated with a coating layer of binder is created by mixing it with heated molding sand, and the resin-coated sand is sprinkled or filled into a heated mold to remove the binder. By melting and hardening it, it is molded into a shell mold. However, shell molds using phenolic resin as a binder generally have a problem in that cracks are likely to occur during pouring. This is thought to be due to the rapid thermal expansion of the resin and sand due to the high heat during pouring. In order to solve this problem, we added a substance with a cushioning effect to phenolic resin or resin-coated sand to make the shell mold more flexible and to reduce the coefficient of thermal expansion of the shell mold, thereby preventing the occurrence of cracks. Attempts are being made to do so. Conventionally, bisphenol A, petroleum resin, rosin, etc. have been used as this cushion material, but although these all have some effect in reducing the coefficient of thermal expansion of the shell mold and preventing the occurrence of cracks, There are drawbacks such as thermal decomposition and volatilization during pouring, producing a bad odor, and poor disintegration of the shell mold during pouring. Also, although this product is effective when casting aluminum or cast iron, when casting stainless steel or high manganese steel, which have high pouring temperatures, cracks are inevitable due to rapid thermal expansion during pouring. In addition, the decomposition and volatilization described above occur rapidly due to rapid heating, and decomposition gas is generated due to the oxidation of the phenol resin itself. It also has the disadvantage of causing defects in the casting surface. In order to suppress the thermal expansion of shell molds, attempts have also been made to modify the phenolic resin with bisphenol A, residues, or alkylphenols, to reduce the crosslinking density, or to mix iron oxide, etc. Although it has been shown to be effective to some extent, there are limits and high temperature hot water cannot be expected to be very effective. If a phenolic resin modified to suppress the crosslink density is used, the hot strength of the shell mold will be lowered, resulting in cracks due to insufficient strength, or the amount of gas generated due to carbonization during use of the resin will increase. It also has the disadvantage of worsening the casting surface. In order to improve this casting surface, conventional coating agents containing graphite, zircon, aluminum oxide powder, etc. have been applied to the surface of the shell mold in order to improve surface precision and strength. Since the agent contains some resin, the coefficient of thermal expansion of the surface of the shell mold that comes into contact with the hot water increases, making cracks more likely to occur. Since it is used after being dispersed, it has the disadvantage that it requires complicated operations such as coating, dipping, and drying. As mentioned above, in the past, it has not yet been possible to prevent shell mold cracks without deteriorating the casting surface of the casting. [Object of the Invention] The present invention has been made in view of the above points, and provides for the production of resin-coated sand for shell molds that can prevent cracks in shell molds without deteriorating the casting surface of castings. The purpose is to provide law. [Disclosure of the Invention] According to the method for producing resin-coated sand for shell molds according to the present invention, a phenolic resin binder containing the metal powder is prepared by mixing a liquid phenolic resin with a metal powder, and then By mixing this phenolic resin binder with molding sand, the surface of the molding sand is coated with a coating layer of the phenolic resin binder containing metal powder, and the following is described. The present invention will be explained in detail. As the phenolic resin, either a novolac type phenolic resin or a resol type phenolic resin can be used.The metal powder to be mixed with this phenolic resin is one that has a high affinity for oxygen and is easily oxidized, such as Al, Mg,
Examples include Si, Fe, Ni, Cr, Ti, Nb, and V, and one or more of these can be used in combination. Also, as metal powder, alloys consisting of two or more of the metals listed above, such as
Al-Mg, Al-Si, etc. can also be used. The particle size of the metal powder is preferably 10 μm or less from the viewpoint of uniform mixing and increasing the surface area to facilitate oxidation. This metal powder is mixed and dispersed with a phenolic resin to prepare a phenolic resin binder for shell molding, and the mixing is carried out by blending the metal powder into the liquid phenolic resin. Specifically, metal powder is blended and mixed during the process of condensing phenol resin and aldehydes to prepare phenolic resin, or metal powder is blended and mixed before taking out the condensation reaction product from the reaction vessel. Alternatively, after granulating and cooling the phenolic resin, it is heated and melted, and metal powder is added and mixed therein. Furthermore, the phenolic resin is dissolved in a solvent and in this state, metal powder is added and mixed. You can do it. The mixing ratio of phenolic resin and metal powder varies depending on the required performance of the shell mold, but generally 1 part by weight of metal powder is mixed with 100 parts by weight of the resin content of the phenolic resin.
It is preferably about 30 parts by weight. A phenolic resin binder for shell molds is prepared as described above, and coated sand for shell molds is obtained by mixing this phenolic resin binder with molding sand and coating it.
In coating the sand with the phenolic resin binder, a dry hot coating method, a cold coating method, a semi-hot coating method, a powder solvent method, etc. can be used. The dry hot coating method uses the above solid phenolic resin containing metal powder.
It is added to sand heated to 130-160℃ and mixed, the solid phenolic resin is melted by the heating by the sand, the surface of the sand is wetted with the molten phenolic resin and coated as a coating layer, and then this mixture is applied. It is cooled while being held to obtain granular and smooth resin-coated sand. In the cold coating method, the metal powder-containing phenolic resin is dissolved in a solvent such as methanol to form a liquid, which is added to sand and mixed, and the solvent is evaporated to obtain resin-coated sand. be.
In the semi-hot coating method, a liquid phenol resin dissolved in the above-mentioned solvent is added to and mixed with sand heated to 50 to 90°C to obtain resin coated sand. In the powder solvent method, the solid metal powder-containing phenolic resin is pulverized, the pulverized resin is added to sand, a solvent such as methanol is further added, and the mixture is mixed to obtain resin-coated sand. Although granular and smooth resin-coated sand can be obtained using any of the above methods, the dry hot coating method is preferred from the viewpoint of workability. The mixing ratio of sand and phenolic resin varies depending on the required performance of the shell mold, but in general, the ratio of phenolic resin to 100 parts by weight of sand is about 1 to 4 parts by weight in terms of resin solid content. preferable. Further, during this mixing, a curing agent and a silane coupling agent for making the sand and the phenol resin binder compatible may be added as necessary. The resin-coated sand thus obtained is sprinkled or filled into a heated mold according to a conventional method, and the phenolic resin binder is melted and hardened. A shell mold is formed by the bonding action of the two. Since this product contains metal powder, the low coefficient of thermal expansion of the metal powder suppresses thermal expansion during pouring into the shell mold and prevents cracks from occurring in the shell mold. In addition, metal powder easily reacts with oxygen and becomes oxidized, and the phenolic resin binder is oxidized during rapid heating during pouring, meaning that oxygen is consumed by the metal powder. This can be prevented by doing so. Next, the present invention will be specifically explained using examples. Example 1 Phenol 940 in a 2 liter four neck flask
g, 648 g of 37% formalin, and 5.6 g of oxalic acid were added and refluxed for about 90 minutes. After the reaction solution was emulsified, the reaction continued for another 90 minutes, and then atmospheric dehydration was started to dehydrate it to 150℃. did. Next, dehydration was further performed at a reduced pressure of 100 mmHg until the internal temperature reached 150°C. Next, 95 g of metallic aluminum powder with a particle size of 5 μm was carefully added, mixed well for 30 minutes, and then discharged into a vat, cooled, and coarsely crushed into particles with a particle size of 0.5 to 3 mm. The softening point of the obtained novolac-type phenolic resin binder containing metallic aluminum was 92°C, and the content of metallic aluminum powder was 10%. Next, 30 kg of flattery silica sand heated to 140°C was charged into a world mixer, and the novolac type phenolic resin binder obtained as described above was added to the world mixer.
After adding 750g and kneading for 30 seconds, 110g of hexamethylenetetramine dissolved in 300g of water was added.
The mixture was mixed until the clumps of sand grains were broken up. Next, 15g of calcium stearate was added to this,
After kneading for 30 seconds, the mixture was discharged and aerated to obtain resin coated sand. Example 2 A metal aluminum-containing novolac type phenolic resin caking with a softening point of 88°C and a metal aluminum powder content of 1% was prepared in the same manner as in Example 1, except that the amount of metal aluminum powder was changed to 9.5 g. obtained the drug. A resin-coated sand was obtained in the same manner as in Example 1 except that this novolak type phenolic resin binder was used. Example 3 1.5 kg of the novolac-type phenolic resin obtained in Example 1, which was not mixed with metal powder and had a softening point of 85°C, was placed in a 2-liter flask and melted by heating until the internal temperature reached
When the temperature reached 140° C., 165 g of the same metal aluminum powder as in Example 1 was carefully added, and the mixture was thoroughly stirred and mixed for about 30 minutes. The softening point of the obtained novolak-type phenolic resin binder containing metallic aluminum was 92.5°C, and the content of metallic aluminum powder was 10%. A resin-coated sand was obtained in the same manner as in Example 1 except that this novolak type phenolic resin binder was used. Example 4 Phenol 470 in a 2 liter four neck flask
g, 37% formalin 827g, 28% ammonia water 110g
was added, the internal temperature was raised to 80°C over about 60 minutes, and the reaction was continued for 4 hours. Next, perform vacuum dehydration at 70 mmHg, and the internal temperature will be 65.
When the temperature reached ℃, 40 g of metal silicon powder with a particle size of 6 μm was added, and vacuum concentration was further carried out to 90℃. Immediately this was poured into a vat, cooled, and then coarsely crushed to a diameter of 0.5 to 3 mm. The softening point of the obtained resol type phenolic resin binder containing metallic silicon was 83° C., and the content of metallic silicon powder was 5%. A resin coated sand was obtained in the same manner as in Example 1 except that this resol type phenolic resin binder was used and hexamethylenetetramine was not used. Example 5 Novolac type phenolic resin 1300 with a softening point of 90°C
Transfer g to a four-necked flask and add methanol to it.
700g was added and dissolved well. Next, 70 g of the same metal aluminum powder as in Example 1 was added to this and thoroughly mixed and dispersed. The viscosity of the obtained novolac type phenolic resin binder varnish containing metallic aluminum at 25℃ is
13 poise, and the content of metallic aluminum powder was 5% in terms of solid content. Next, 30 kg of flattery silica sand heated to 80°C was charged into a world mixer, and 1150 g of the novolac type phenolic resin binder varnish obtained as above was obtained.
A dispersion of 110 g of hexamethylenetetramine was added to the mixture, and the mixture was kneaded until the sand grains were disintegrated. Next, 15 g of calcium stearate was added, kneaded for 30 seconds, and then discharged for aeration to obtain resin coated sand. Example 6 1300 g of a solid resol type phenolic resin with a softening point of 78°C, which was prepared by reacting in the same manner as in Example 5 except that metallic silicon was not mixed, was placed in a four-necked flask, and 700 g of methanol was added to it to dissolve it well. I let it happen. Next, 70 g of metallic aluminum powder was added to this and well dispersed. The viscosity of the obtained resol type phenolic resin binder varnish containing metallic aluminum at 25°C was 13
Poise, and the metal aluminum content was 5% in terms of solid content. A resin-coated sand was obtained in the same manner as in Example 5, except that the resol type phenolic resin binder varnish thus obtained was used and hexamethylenetetramine was not used. Example 7 Same as Example 5 except that Al-Mg powder was used instead of metal aluminum powder.
A novolak type phenolic resin binder varnish containing Al-Mg was obtained. The viscosity of this material at 25℃ is 13
The content of Al-Mg powder was 5% in terms of solid content. A resin-coated sand was obtained in the same manner as in Example 5, except that the novolak type phenolic resin binder varnish thus obtained was used. Comparative Example 1 Resin-coated sand was obtained in the same manner as in Example 1, except that metal aluminum powder was not used. Comparative Example 2 A resin-coated sand was obtained in the same manner as in Example 4, except that no metal silicon powder was used. Various tests were conducted on the resin coated sand obtained in Examples 1 to 7 and Comparative Examples 1 and 2 above. The results are shown in the table below. In the following table, the melting point (°C) is according to JACT test method SM-1.
Room temperature bending strength (Kg/cm ² ) is based on JACT test method C-1, and rapid thermal expansion coefficient (%) is measured at a measurement temperature of 1000℃ in N ₂ gas based on JACT test method SM-7. Tests were conducted on each. Hot bending strength (Kg/cm ² ) is determined by placing a test piece prepared according to JACT test method SM-1 in an electric furnace set at 1000°C, and measuring the bending strength at 1000°C after processing for 1 minute. It was done by Oxidation resistance is
Test pieces (20φ x 50mm) prepared according to JACT test method SM-7 were placed in an electric furnace set at 1000℃ and treated for 5 minutes, then taken out, cooled, and placed on a vibrating sieve and vibrated for 1 minute. Afterwards, the weight was measured, and the weight percent of the residue was calculated using the following formula for evaluation. Weight after treatment / Weight before treatment x 100 (%) Casting surface is determined by measuring the inner diameter using resin coated sand.
Create a crucible with a diameter of 100 mm, a height of 100 mm, and a wall thickness of 20 mm.
This was done by pouring hot water at 1650°C into the mold and visually observing the surface of the finished casting after cooling.

[Table] ◎: Very good ○: Good △: Fair The results in the table show that the rapid thermal expansion coefficient of each example is lower than that of the comparative example, and is effective in preventing cracks from occurring in the shell mold. was confirmed, and it was also confirmed that the products of each example had excellent oxidation resistance and could be cast into castings with good casting surfaces. [Effects of the Invention] As described above, according to the present invention, since the metal powder is contained in the phenolic resin binder, the thermal expansion during pouring of the shell mold is reduced due to the low coefficient of thermal expansion of the metal powder. In addition, since metal powder easily reacts with oxygen and is oxidized, phenol resin caking occurs during rapid heating during pouring. The oxidation of the agent can be prevented by the consumption of oxygen by the metal powder, and the generation of gas components due to oxidative decomposition of the phenolic resin binder can be prevented from deteriorating the casting surface of the casting. This is something that can be prevented. And in the present invention,
A phenolic resin binder containing metal powder is prepared by mixing metal powder with liquid phenolic resin, and then this phenolic resin binder is mixed with molding sand to improve the surface of the molding sand. Since the metal powder is coated with a coating layer of a phenolic resin binder containing metal powder, the metal powder is uniformly dispersed in the liquid phenolic resin, and the phenolic resin binder containing the metal powder is uniformly dispersed in the liquid phenolic resin. The metal powder can be coated on the molding sand in a uniformly dispersed state, and the metal powder can be uniformly dispersed and contained in the shell mold, The effect of adding metal powder can be stably obtained.

Claims (1)

[Scope of Claims] 1. A phenolic resin binder containing metal powder is prepared by mixing metal powder with liquid phenolic resin, and then this phenolic resin binder is mixed with molding sand. A method for producing resin-coated sand for shell molds, which comprises coating the surface of molding sand with a coating layer made of a phenolic resin binder containing metal powder. 2 Metal powder is Al, Mg, Si, Fe, Ni, Cr, Ti,
The method for producing resin coated sand for shell molds according to claim 1, characterized in that the resin coated sand is one or more of Nb and V.