JPH0347942B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing resin-coated sand grains for shell molds, and more specifically, resin-coated sand grains with a substantially low nitrogen content suitable for manufacturing main molds or cores using liquid resin. Relating to a manufacturing method. [Prior art] For a long time, the mainstream method for producing resin-coated sand grains for shell molds was a dry hot coating method that uses novolac-type phenolic resin (hereinafter referred to as novolac) and hexamethylenetetramine (hereinafter referred to as hexamine) as a hardening agent. However, as a measure to improve the gas odor caused by nitrogen compounds caused by the thermal decomposition of hexamine and the gas defects that affect cast products, resol-type phenolic resins (hereinafter referred to as resols) that do not contain any nitrogen or have extremely low nitrogen content have been developed. ) has also been proposed. For example, there is a method in which a solid resol reacted in the presence of an ammonia catalyst is used as a curing agent for novolac (Japanese Patent Publication No. 14289-1989), and a method in which the same solid resol is used alone (Japanese Patent Application Laid-open No. 117591-1977).
However, all of these methods have the disadvantage of slow curing speed. In addition, in order to increase the number of functional groups in the solid resol and improve the curing speed, there is also a method of using a solid resol obtained by using an appropriate amount of an alkali metal catalyst together with an ammonia catalyst, and a method of using waxes inside the solid resol. There is also known a method (Japanese Patent Application Laid-open No. 78924/1983) in which the content is uniformly contained to further reduce the caking property. In this way, the flow of development of low-odor resins to replace hexamine has centered on solid resols based on ammonia catalysts, but due to the continuous improvement in productivity, faster curing and higher mold strength are being developed. I still haven't lost my desire to pursue it. [Problems to be Solved by the Invention] However, all of the above-mentioned methods for producing resin-coated sand grains are dry hot coating methods, which require the use of a solid resin and a high sand grain temperature (120 to 160°C) during kneading. Part of the problem lies in the fact that the reaction of the resin progresses during kneading and the functional groups, which are closely related to the curing rate, are consumed by the thermal covering period. In other words, even if the resin used is a resol designed to increase the number of functional groups by using a combination of the ammonia catalyst and alkali metal catalyst (hereinafter referred to as ammonia-alkali resol), since this is a solid resin, the manufacturing process is difficult. Not only is this difficult, but there is also a limit to extracting a relatively young resin due to the solidification properties of the resin itself.Furthermore, as mentioned above, the functional groups in the resin are affected by the thermal history during kneading. It disappears once. On the other hand, increasing the molecular weight of the resin in order to speed up the curing speed also poses similar restrictions, since the resin becomes a solid resin, resulting in poor flow of the resin during kneading and deterioration of coating properties. The present invention focuses on the problems of the dry hot coating method, and aims to reduce the influence of thermal history on the resin by using a liquid resin and lowering the sand temperature during kneading, thereby improving the productivity mentioned above. The technical problem to be solved is to create a method for manufacturing resin-coated sand grains that meets the desire for improvement. [Means for solving the problem] The liquid ammonia-alkaline resol used in the present invention uses 1 mol or more of formaldehyde per 1 mol of phenol, and contains an amine catalyst such as ammonia or an amine compound and an alkali metal catalyst. This is a resin made by dissolving a condensate reacted in the presence of an organic solvent. Here, phenol refers to phenol, alkyl phenols such as m-cresol, para-cresol, and xylenol, and mixtures thereof, and as formaldehyde, formaldehyde polymers such as paraformaldehyde and trioxane and mixtures thereof can be used in addition to formalin. Among amine catalysts, amine compounds include:
These include monomethylamine, dimethylamine, monoethanolamine, and monoethylamine. Alkali metal catalysts include sodium, potassium,
These are hydroxides or oxides of alkali metals such as lithium, and hydroxides or oxides of alkaline earth metals such as barium, calcium, and magnesium.
These alkali metal catalysts, unlike ammonia catalysts, contribute to the generation of functional groups without being incorporated into the resin, but if they are used in large quantities, the resin-coated sand grains will solidify, so 0.1 It is desirable to use less than a molar amount. The ammonia-alkaline resol and the liquid high ortho-oriented novolac are used as a mixed solution. High ortho-oriented novolacs are made by adding formaldehyde to the ortho position of phenol using lead acetate, manganese acetate, zinc acetate, etc. as catalysts, and are highly reactive. It is effective, but the desired mixing amount is 10% of the total resin amount.
~30% by weight. If the mixing amount is less than 10%,
The strength at room temperature is poor, and if it exceeds 30%, the strength at temperature decreases. Lubricants used in the emulsion include metal soaps such as calcium stearate and zinc stearate, fatty acid amides such as stearamide, methylene bis stearamide, ethylene bis stearamide, and ethylene bis amide, carnauba paraffin, Hydrocarbon waxes such as micro wax and polyethylene wax can be used. Any solvent can be used as long as it dissolves or disperses the lubricant, such as water or alcohol. The desired lubricant active ingredient concentration of the lubricant emulsion is:
It is 20-60% by weight. The amount of lubricant emulsion added is 0.01 to 0.09% by weight in terms of solid content, and 0.01% by weight
If it is less than 0.09%, there will be no effect of improving the strength, and if it is more than 0.09%, the strength will decrease. Preferably it is 0.05-0.08%. Next, a method for producing a mixed solution of liquid ammonia-alkaline resol and liquid high-ortho-oriented novolak used in the present invention will be outlined. First, 1 mole of phenol and 1 mole or more of formaldehyde are charged into a reaction vessel, and an amine catalyst and an alkali metal catalyst are added. Then, the mixture is heated to 50 to 100°C to carry out a condensation reaction for about 0.5 to 2 hours. Then 100℃
After concentrating under reduced pressure at the following temperature, an organic solvent is added and dissolved to obtain liquid ammonia alkaline resol. Next, 1 mol of phenol and 0.4 to 0.7 mol of formaldehyde are charged into the reaction vessel in the same manner, and an acidic catalyst is added. The condensation reaction is then carried out under reflux for about 3 to 6 hours. After concentrating under reduced pressure to 150-200°C, an organic solvent is added and dissolved to obtain a liquid high ortho-oriented novolak resin. These liquid ammonia alkaline resols and liquid high-ortho-oriented novolac resins are mixed to obtain a mixed solution. In the present invention, resin-coated sand grains for shell molding are manufactured as follows. After heating the sand grains to 70-110℃ and putting them into the kneading machine,
A mixed solution of liquid ammonia-alkaline resol and liquid high-ortho-oriented novolac resin is added to the sand grains in an amount of 1 to 3% by weight (in terms of resin solid content).
After kneading for 30 seconds, 0.05~
Add 0.15% by weight of lubricant emulsion and 0.4-0.5% by weight of cooling water and continue kneading until the sand collapses. Then, if necessary, a small amount of powdered calcium stearate is added to obtain resin-coated sand grains according to the method of the present invention. [Effects of the Invention] The resin-coated sand grains of the present invention are of course free from gas defects and odor, but (1) Since they are liquid resins, consideration for the solidification of the resin itself and difficult control for solidification are necessary. It is possible to easily take out a young resin whose polyfunctional groups have reacted, and because the functional groups are less likely to be consumed by the heat history during kneading, the curing speed is fast and the resin has high strength. . (2) Since the resin is less likely to be exposed to heat, it is possible to use a resin with a large molecular weight, and from this point of view, the strength at elevated temperatures can be improved. (3) By using a lubricant emulsion, the lubricant forms a uniform outer coating of the resin-coated sand grains, which not only prevents caking but also improves the filling properties of the sand grains, thereby improving their strength. [Example] Hereinafter, the present invention will be explained in detail by way of implementation. 1 Method for producing resin (1) In a three-necked flask equipped with a stirrer, reflux, condenser, and thermometer, add 1000 g of phenol, 620 g of 85% paraformaldehyde, and 4 zinc naphthenate.
Weighed 6 g of 20% sodium hydroxide aqueous solution, heated in a water bath while stirring, and heated to 90°C.
After reacting for 45 minutes, cool to 50°C, and add 180g of 25% ammonia water with stirring. The reaction was carried out at 70°C until it became cloudy, then concentrated under reduced pressure to 95°C, and then 650g of methanol was added and dissolved to form a liquid resin of ammonia alkaline resol.
A2150g was obtained. (2) Weigh out 1000 g of phenol, 115 g of paraformaldehyde, and 250 g of 37% formalin into a three-necked flask equipped with a stirrer, reflux condenser, and thermometer, and raise the temperature to 70°C while stirring to dissolve the paraformaldehyde. 10% zinc acetate aqueous solution
After adding 1.5 g of the solution, the temperature was gradually raised and a reflux reaction was carried out for 4 hours. Thereafter, the mixture was concentrated under reduced pressure to 170° C., and 430 g of methanol was gradually added to obtain 1430 g of a high ortho-oriented novolak liquid resin. Add 20 parts of this liquid resin to 80 parts by weight of the above liquid resin A.
A liquid mixed resin B was obtained by adding parts by weight and stirring. (3) After carrying out the reaction at 70°C until it becomes cloudy using the manufacturing method in (1), 60g of ethylene bisstearamide was added and concentrated under reduced pressure of -65 to -70cmhg until the internal temperature reached 95°C. At that point, it is discharged from the flask, cooled and solidified, and then crushed to produce 6 to 20 mesh solid ammonia-alkaline resol containing lubricant.
Obtained 1540g of C. (4) After carrying out the reaction at 70°C until it becomes cloudy using the manufacturing method in (1), add 75 g of calcium stearate and 530 g of the above-mentioned liquid resin of the high-ortho-oriented novolac, and use the same method as in (3) below to react with the lubricant-containing novolac mixture. Solid ammonia/alkaline resol
Obtained 1920g of D. 2 Production of resin-coated sand grains () 10 kg of Fuca sand heated to 90℃ and 214 g of resin B (1.5% solid resin content based on silica sand) were put into a speed mixer and mixed for 30 seconds with the lid closed, then the lid was opened. After adding 44 g of cooling water and 12 g of lubricant emulsion and kneading until the coated sand grains disintegrated, 10 g of calcium stearate was added and mixed for 20 seconds, and the sand was drained and aerated to obtain resin-coated sand grains. Note that calcium stearate a is used as the lubricant of the lubricant emulsion, and water is used as the solvent. The lubricant active ingredient concentration used was 50% by weight. () Resin-coated sand grains were obtained in the same manner as in () except that no lubricant emulsion was added and the amount of cooling water added was 50 g. () After putting 10kg of hookah sand heated to 150℃ and 150g of resin C or D (1.5% based on silica sand) into a speed mixer and mixing for 30 seconds,
After adding 150 g of cooling water and kneading until the coated sand grains disintegrated, 10 g of calcium stearate was added and mixed for 20 seconds, and the sand was discharged for aeration to obtain resin-coated sand grains. Among the resins used in A to D and the manufacturing methods of resin-coated sand grains in () to () above, the combination of B and () is Example 1, the combination of B and () is Comparative Example 1,
Table 1 shows a comparison of the characteristics of resin-coated sand grains produced using the combinations of 2, C and D and () as Comparative Examples 3 and 4.

[Table] It is clear from Table 1 that the room temperature bending strength and warm bending strength of the resin-coated sand grains of the Examples are higher than those of the Comparative Examples. It is clear that this is due to the effect of the present invention. The bending strength (Kg/cm ² ) is determined by JACT test method SM.
-1, sticking point (°C) is based on JACT test method C-1.

Claims (1)

[Claims] 1 For foundry sand grains heated to 70-110℃,
A mixed solution of a liquid resol type phenolic resin reacted in the presence of ammonia and an alkali metal catalyst and a liquid high ortho-oriented novolac resin in an amount of 10 to 30% by weight based on the liquid resol type phenolic resin is prepared.
1. A method for producing resin-coated sand grains for shell molds, which comprises adding 1.0 to 2.0% by weight and kneading, and further adding 0.05 to 0.08% by weight of a lubricant emulsion in terms of solid content and further kneading.