JPH0144423B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention provides a method for producing resin-coated sand for shell molds, which has superior strength and collapsibility when casting metals with low melting points compared to iron such as aluminum and magnesium. It is related to. <Prior Art> Recently, light metals such as aluminum and magnesium have been used in place of conventional iron to reduce the weight of automobile casting parts, but these materials have low melting points. It is expected that casting of these light metals will become increasingly popular in the future. In the case of iron-based metals, the internal temperature of the shell mold after pouring is 800 to 1000℃, so the phenolic resin used as a binder is exposed to high temperatures and almost thermally decomposes, causing the temperature to drop after pouring. Since the strength of the shell mold naturally decreases, it is easy to remove the shell core from the casting after casting in the form of sand. However, when casting low melting point metals such as aluminum and magnesium, The internal temperature of the shell mold remains at a low temperature of 300-400℃.
For this reason, the decomposition of the phenolic resin in the shell mold is insufficient, and since the shell mold maintains sufficient strength, it may be extremely difficult to efficiently remove the shell core from the casting from complex casting shapes. There is. Therefore, in such a case, in order to remove the cast shell core in the form of sand, it is necessary to heat it in a kiln or the like for a maximum period of time and then apply an impact to the core to disintegrate it. This is a major obstacle to improving product quality and saving energy when producing large quantities of aluminum castings. <Purpose of the invention> One method for causing the thermal decomposition of phenolic resin to occur at a low temperature of 300 to 400°C is thought to be effective by adding a substance that has a catalytic effect to lower the activation energy of thermal decomposition. . The present inventors have developed a resin-coated sand in which sand grains for foundry use are coated with a phenolic resin. It has been found that the presence of molten metal promotes the disintegration of the shell mold after pouring. (Special application 1982-
(No. 172137) The present inventors have completed the present invention as a result of intensive research on a method for further improving the disintegration properties after pouring while maintaining the strength of the shell mold at a high level. The present invention provides heated sand with
A solid resol type phenolic resin containing a lubricant and a solid novolak type phenolic resin having an unmodified lubricant content of 0.2 to 5 parts by weight per 100 parts by weight of solid resol type phenolic resin are mixed by weight of 85/15 to 45/55. Add in the ratio, and further add b, a, in the periodic table.
1 to 15% by weight of bromide of an element selected from groups b, a, b, based on the total resin addition amount;
and hexamethylenetetramine in an amount of 8% by weight or less based on the total amount of resin added to coat the sand, and this method improves the strength and collapse of the shell mold. It has become possible to achieve a high level of both gender and gender. <Structure of the invention> The lubricant-containing solid resol type phenolic resin used in the present invention is a solid phenolic resin obtained by reacting phenols and aldehydes in the presence of an alkali catalyst, and further using a lubricant in combination. . The solid novolak type phenolic resin used in the present invention is a solid phenolic resin obtained by reacting phenols and aldehydes in the presence of an acid catalyst. It is also possible to use a lubricant in combination with the solid novolak type phenolic resin. As the lubricant for carrying out the present invention, ordinary lubricants can be used, but in particular, ethylene bisstearamide, oxystearamide, stearamide, methylolstearamide,
Carnauba wax, montan wax, paraffin wax, polyethylene wax and the like are preferred. When the lubricant content of the solid resol is 0.2 to 5 parts by weight, it is particularly effective in improving the strength and disintegrability of the shell mold. If the slip mold content is less than 0.2 parts by weight based on 100 parts by weight of the solid resol, the effect of improving the strength and collapsibility of the shell mold will be poor, and if it exceeds 5 parts by weight, the hot strength will decrease. In addition, these lubricants are used during the production of solid resol type phenolic resin.
A solid resol type phenolic resin containing a lubricant can be obtained whether it is added before the reaction starts, during the reaction, or after the reaction ends. Phenols used as raw materials during the production of the phenolic resin of the present invention include phenol, cresol, xylenol, etc.
Catechol, hydroquinone, aniline, urea,
Those containing melamine, cashew nut shell oil, etc. can also be used. Further, as the aldehyde, an aldehyde substance selected from formalin, paraformaldehyde, trioxane, etc. can be used. The reaction catalyst for resol type phenolic resin is
Generally, basic substances such as ammonia, triethylamine, sodium hydroxide, barium hydroxide, etc. are used. Further, reaction catalysts for novolac type phenolic resins are generally acidic substances such as oxalic acid, hydrochloric acid, and sulfuric acid, and organic acid metal salts. The ratio of the lubricant-containing individual resol type phenolic resin to the solid novolac type phenolic resin is 85/15 to 45/55 by weight. If this ratio exceeds 85/15, the strength of the shell mold will decrease, and if it is less than 45/55, the collapsibility of the shell mold will decrease. In the present invention, the bromides particularly used are those of elements selected from groups b, a, b, a, and b in the periodic table, such as calcium bromide, manganese bromide, and dibromide. These include iron, triiron octabromide, cupric bromide, zinc bromide, and aluminum bromide. One or more of these bromides can be used. The amount of these bromides added is 1 to 15% by weight based on the total amount of the lubricant-containing solid resol type phenolic resin and solid novolak type phenolic resin. If the amount of bromide added is less than 1% by weight, the disintegrability of the shell mold decreases, and if it exceeds 15% by weight, the strength decreases. The bromide can be added before, after, or simultaneously with the addition of the phenolic resin during the resin-coated sand manufacturing process. Further, the bromide may be blended as it is or after being dispersed or dissolved in a medium. In the present invention, the amount of hexamethylenetetramine added is 8% by weight or less based on the total amount of resin added. Hexamethylenetetramine provides fast curing properties for resin coated sand and high strength for shell molds. When the amount of hexamethylenetetramine added exceeds 8% by weight, the disintegrability of the shell mold decreases. In order to carry out the present invention more effectively, it is desirable that the solid novolak type phenolic resin contains a silane coupling agent and an amide having a molecular weight of less than 500. Their inclusion further improves the strength and collapsibility of the shell mold. Silane coupling agents include aminosilane, epoxysilane and vinylsilane, and amides with a molecular weight of less than 500 include acrylamide, dimethylacrylamide, acetoacetanilide, formamide, dimethylformamide, N-methylbenzamide, N-phenyl Propionamide, methylolstearamide, N-phenylacetamide,
Dimethylacetamide, acetamide, stearylamide, propionamide, etc. are preferred. <Effects of the Invention> According to the method of the present invention, it is possible to achieve both high strength and good disintegration properties of shell molds, which were impossible with conventional methods, so resin-coated sand for shell molds for industrial light metals can be obtained. It is suitable as a manufacturing method. <Examples> The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. In addition, "parts" and "%" described in each example and comparative example all indicate "parts by weight" and "% by weight." Production Example 1 A flask equipped with a condenser and a stirrer was prepared, and 1000 parts of phenol, 1840 parts of 37% formalin, then 120 parts of 28% aqueous ammonia and 50 parts of 50% aqueous sodium hydroxide solution were added. The temperature gradually rises to 96
After reaching ℃, refluxing for 25 minutes, adding 50 parts of ethylene bisstearamide, dehydration under vacuum, discharging and quenching to obtain 1160 parts of solid resol type phenol resin containing lubricant, which is solid at room temperature. I got it. Production Example 2 A flask equipped with a condenser and a stirrer was prepared, and 1000 parts of phenol, 640 parts of 37% formalin, and then 10 parts of oxalic acid were charged therein. The temperature gradually increases until the temperature reaches 96
After reaching the temperature, the mixture was refluxed for 30 minutes, then dehydrated under vacuum, discharged, and rapidly cooled to obtain 640 parts of a novolac type phenolic resin that was solid at room temperature. Production Example 3 A flask equipped with a condenser and a stirrer was prepared, and 1000 parts of phenol, 1840 parts of 37% formalin, then 120 parts of 28% aqueous ammonia and 50 parts of 50% aqueous sodium hydroxide solution were added. The temperature gradually rises to 96
After reaching the temperature, the reaction mixture was refluxed for 25 minutes, followed by dehydration under vacuum, discharged, and rapidly cooled to obtain 110 parts of a solid resol type phenolic resin that was solid at room temperature. Production Example 4 A flask equipped with a condenser and a stirrer was prepared, and 1000 parts of phenol, 640 parts of 37% formalin, and then 10 parts of oxalic acid were charged therein. The temperature gradually increases until the temperature reaches 96
After reaching ℃, the mixture was refluxed for 30 minutes and then dehydrated under vacuum. 35 parts of methylene bisstearamide, 3 parts of γ-aminopropyltriethoxysilane, and 6 parts of propionamide were added, mixed, and then discharged and rapidly cooled to obtain 714 parts of a novolak type phenolic resin that was solid at room temperature. Example 1 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140°C was charged into a whirl mixer, and 105 parts of the solid resol-type phenolic resin containing a lubricant obtained in Production Example 1 and the solid novolac obtained in Production Example 2 were charged. After adding 70 parts of type phenolic resin, the mixture was kneaded for 45 seconds. Next, 14 parts of manganese bromide was added and kneaded for 10 seconds. Furthermore, an aqueous hexamethylenetetramine solution prepared by dissolving 7 parts of hexamethylenetetramine in 16 parts of water was added, and after kneading the coated sand until it disintegrated, 7 parts of calcium stearate was added. The mixture was mixed for 30 seconds, the sand was discharged, and aeration was performed to obtain resin coated sand. Example 2 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140°C was charged into a whirl mixer, and 96 parts of the solid resol type phenolic resin containing a lubricant obtained in Production Example 1 and the solid novolac obtained in Production Example 4 were charged. After adding 79 parts of type phenolic resin, the mixture was kneaded for 30 seconds. Next, a zinc bromide aqueous solution prepared by dissolving 18 parts of zinc bromide in 18 parts of water was added and kneaded for 15 seconds. Furthermore, an aqueous solution of hexamethylenetetramine in which 9 parts of hexamethylenetetramine was dissolved in 21 parts of water was added, and after kneading the coated sand until it disintegrated, 7 parts of calcium stearate were added. After mixing for 30 seconds, the sand was removed and aeration was performed to obtain resin coated sand. Comparative Example 1 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140°C was charged into a Whirl mixer, and 105 parts of the solid resol type phenolic resin obtained in Production Example 3 and the solid novolac type phenolic resin obtained in Production Example 2 were added.
After adding 70 parts, it was kneaded for 45 seconds. Next, 14 parts of manganese bromide was added and kneaded for 10 seconds. Furthermore, an aqueous hexamethylenetetramine solution prepared by dissolving 7 parts of hexamethylenetetramine in 16 parts of water was added, and after kneading the coated sand until it disintegrated, 7 parts of calcium stearate was added. The mixture was mixed for 30 seconds, the sand was discharged, and aeration was performed to obtain resin coated sand. Comparative Example 2 A resin-coated sand was obtained under the same manufacturing conditions as in Comparative Example 1, except that manganese bromide and hexamethylenetetramine were not added. Comparative Example 3 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140° C. was charged into a Whirl mixer, 175 parts of the solid novolak type phenolic resin obtained in Production Example 4 was added, and the mixture was kneaded for 45 seconds. Next, a hexamethylenetetramine aqueous solution prepared by dissolving 26 parts of hexamethylenetetramine in 88 parts of water was added, and after kneading until the coated sand disintegrated, 7 parts of calcium stearate was added.
part was added. The mixture was mixed for 30 seconds, the sand was discharged, and aeration was performed to obtain resin coated sand. Comparative Example 4 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140°C was charged into a Whirl mixer, 175 parts of the solid resol type phenolic resin obtained in Production Example 3 was added, and the mixture was kneaded for 45 seconds. Next, 66 parts of water was added, and after kneading the coated sand until it disintegrated, 7 parts of calcium stearate were added. The mixture was mixed for 30 seconds, the sand was discharged, and aeration was performed to obtain resin coated sand. Table 1 shows the characteristic values of each resin coated sand obtained in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4. The test method is as follows. Bending strength: Sticking point according to JACT test method SM-1: Hot tensile strength according to JACT test method C-1: Disintegration property according to JACT test method SM-10: Resin coated sand with a diameter of 29 m/m,
Fill an iron pipe with a length of 150m/m and heat it at 250℃ for 30 minutes.
Prebake for a minute. The pipe is covered with aluminum foil and treated at 370°C for 3 hours. After cooling, take out the pipe and apply an impact using the impact tester shown in Figure 1. After each impact, take out the collapsed sand, measure the amount of remaining sand, and determine the number of times of impact until the amount of remaining sand becomes 0. . In FIG. 1, A represents the sample and B represents the hammer portion. The hammer part is an arm that rotates around a fulcrum C. The fulcrum of the hammer part is height 30
cm, the hammer part is lifted horizontally and then allowed to fall naturally, applying an impact to the sample using the fulcrum as the center.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a side view of an impact tester for testing collapsibility. A is the sample, B is the hammer part, and C is the fulcrum to which the hammer part is attached.

Claims (1)

[Claims] 1. The heated sand has an unmodified lubricant content of 100 parts by weight of solid resol type phenolic resin.
0.2 to 5 parts by weight of a solid resol type phenolic resin containing a lubricant and a solid novolac type phenolic resin are added in a weight ratio of 85/15 to 45/55, and further, b, a, b, a, b in the periodic table are added. The sand is coated by adding 1 to 15% by weight of bromide of an element selected from the groups of , based on the total amount of resin added, and 8% or less of hexamethylenetetramine based on the total amount of resin added. A method for producing resin coated sand for shell molds, characterized by: 2 The lubricant is ethylene bisstearamide,
The claim 1 is one or more waxes selected from the group consisting of methylene bisstearamide, oxystearamide, stearamide, methylolstearamide, carnauba wax, Montan wax, paraffin wax, and polyethylene wax. The method for producing resin coated sand for shell molds according to item 1. 3. The method for producing resin coated sand for shell molds according to claim 1, wherein the solid novolak type phenolic resin contains a silane coupling agent and an amide having a molecular weight of less than 500.