JPS6365414B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a binder having appropriate moldability, heat resistance, and thermal decomposition properties. Specifically, it relates to a binder whose maximum weight loss rate is 25% by weight or less when heated in air at a heating rate of 20°C per minute, and whose weight loss at 450°C is 30% by weight or more and 75% by weight or less. It is something. Binders are used to give granular materials, such as carbon materials such as coal powder, charcoal powder, and coke powder, and inorganic materials such as sand, stone powder, clay, silica gel, and ash, a specific size and shape for industrial use. Sometimes. That is, for applications such as fuel, ceramics, metallurgy, and molded products, special thermal properties are often required for these binders. The binder for casting sand cores must provide physical strength to the core molded product so that it can maintain its shape during the process up to the process of pouring molten metal. It is desirable that the material disintegrates easily when a slight amount of stress is applied. For relatively low melting point alloys such as aluminum alloys, the molten metal temperature for casting is around 700℃;
When pouring water with a sand core in place, the temperature of the core is approximately 450.
℃, and the temperature decreases over time. Therefore, in order to easily remove sand from the core after casting is completed, a binder that undergoes thermal decomposition at a temperature of 450° C. or lower is preferable as the core binder. Among the binders used industrially, inorganic binders generally have poor thermal decomposition properties at temperatures below 400 to 500°C, so organic binders are preferred. On the other hand, when an organic compound is heated in air, its thermal decomposition generally results in the generation of gases such as CO, CO ₂ and H ₂ O (water vapor), and the decomposition occurs within a narrow temperature range. It often occurs suddenly over a short period of time. If a large amount of gas is generated in the caking material of the sand core due to such rapid thermal decomposition, the surface condition and dimensional accuracy of the core itself and the cast metal will be impaired. It is extremely difficult to find a binder that meets the above requirements, that is, a binder that has bond formability at low temperatures and slow thermal decomposition at high temperatures. As a result of intensive research, the present inventors have noticed that binders that require specific thermal properties can be evaluated by analyzing weight loss curves on a thermobalance. That is, the weight loss rate is measured in air at a heating rate of 20°C/min, and the weight loss at 450°C, that is, the amount of thermal decomposition, is 30% by weight or more and 75% by weight or less, and the maximum thermal decomposition is achieved over the entire range. It has been found that samples whose speed does not exceed 25% by weight/min are suitable as binders. If the amount of thermal decomposition at 450℃ is less than 30% by weight, the disintegration property when used as a sand core binder is insufficient, and if it is more than 75% by weight, the binding property during pouring is insufficient. Neither is suitable as a binder. Moreover, those whose peak of the thermal decomposition curve indicating the maximum thermal decomposition rate reaches 25% by weight or more are accompanied by rapid gas generation, and are therefore unsuitable as bonding substrates. It is difficult for a single compound to satisfy the requirements for a binder exhibiting the thermal behavior described above.
A composition consisting of at least two components that are mutually miscible and capable of reacting with each other by heating is heated at a relatively low temperature for a short period of time, e.g.
Those that are partially reacted by heating at 150 to 300°C for about 30 seconds to 5 minutes exhibit good properties. The first component of the binder is an organic compound having a hydroxyl group or a carboxyl group, such as cellulose derivatives such as acetylcellulose and nitrocellulose; monosaccharides and oligosaccharides such as glucose, fructose, xylose, sucrose, and starch. and polysaccharides; polyvinyl alcohol, partially saponified products of ethylene/vinyl acetate copolymers; synthetic polymers such as liquid polybutadiene with hydroxyl group terminals;
It can be selected from polyhydric alcohols such as pentaerythritol, trimethylolpropane, ethylene glycol, and glycerin, and their initial condensates; and phenols such as pyrocatechol and resorcinol. The other component is
Thermosetting resin initial condensates reactive with hydroxyl groups, such as melamine/formaldehyde initial condensates and alkyl ethers thereof, urea, formaldehyde initial condensates and alkyl ethers thereof, furfuryl alcohol or initial condensates of furfural and formaldehyde, epoxy resins It can be selected from initial condensates and the like. The manufacturing method and the application method of the binder will be explained below using a sand core binder for casting as an example. That is, the organic compound as the first component and the thermosetting resin initial condensate as the second component were selected as a combination in which a common solvent existed, and this was dissolved in the solvent and mixed with the foundry sand. Thereafter, the solvent is removed by volatilization to obtain sand coated with a mixture of the two components. Next, this coated sand is filled into a mold for molding the core and heat-treated at 150 to 300°C for about 30 seconds to 5 minutes, so that the two components partially react and at the same time bond the sand together to form a core molded product. obtain. This core molded product will be used in a normal casting process and will be evaluated in practice. on the other hand,
Two components are mixed without using sand, and after the solvent is removed, the sample is heated for a short time and the loss on heating is measured using a thermobalance. The present invention will be explained below with reference to Examples. In the examples, all parts indicate parts by weight. Example 1 32.5 parts (77% aqueous solution) of methylated methylolmelamine (Sumimar M30W manufactured by Sumitomo Chemical Co., Ltd.) was added to 250 parts of a 30% aqueous solution of glucose, and the resulting binder solution was stirred for 10 minutes at 70°C. The sample was dried in a hot air dryer and heat-treated at 200°C for 1 minute, which was designated as Sample 1 for thermobalance measurement. Also this binder liquid 8.5
and 100 parts of silica sand (flattary) were placed in an open tank mixer and kneaded while blowing warm air at approximately 70°C. After 30 minutes, 0.1 part of calcium stearate was added as a lubricant to create coated sand. did. The thermobalance measurement results of Sample 1 are shown in FIG. 1st
The curve in the figure is a graph showing the relationship between weight loss (W%) and heating temperature, and the curve also shows the relationship between weight loss rate (weight loss w divided by time t, expressed by the differential formula dw/dt). It is a graph showing the relationship with heating temperature, and the curves are drawn at the same time. In addition, the second
The same applies to FIGS. 9 to 9. Also, the covering sand
JISK6910 “Powdered resin test method for shell mold”
The transverse rupture strength of the molded test piece was measured according to . However, the mold temperature during molding was 270±10°C, and the heating time was 1 minute. Furthermore, in order to compare the disintegration properties of each coated sand and the disintegration properties determined by thermal balance, the test pieces were wrapped in aluminum boxes and treated in an electric furnace at a predetermined temperature (520℃) for 3 minutes, and the residual transverse rupture strength was measured after cooling. , the strength residual rate (strength residual rate=residual transverse rupture strength÷transverse rupture strength) was determined. The high temperature strength was determined by measuring the tensile strength of the test piece at 280℃.
Expressed qualitatively. These results are shown in Table-1. Example 2 100 parts of a 20% acetone solution of cellulose acetate (manufactured by Daicel Chemical Industries, Ltd., degree of acetylation 55.5%, intrinsic viscosity measured in an acetone solution at 25°C is 0.80) and methylated methylolmelamine (Sumimar, manufactured by Sumitomo Chemical Co., Ltd.)
104 parts (77% aqueous solution) of M30W) were added and stirred for 10 minutes, and the resulting binder liquid was used in the same manner as in Example 1 to prepare Sample 2 for thermobalance measurement. The thermobalance measurement results are shown in Figure 2. In addition, coated sand was prepared in the same manner as in Example 1 except that 6.1 parts of this binder liquid was used.
Table 1 shows the results of evaluation as coated sand for core molding. Example 3 Methylated methylolmelamine [Sumitomo Chemical Co., Ltd.] was added to 150 parts of a 20% acetone solution of cellulose acetate [manufactured by Daicel Chemical Industries, Ltd., degree of acetylation 51.0%, intrinsic viscosity measured in an acetone solution at 25°C: 0.63]. 91 parts (77% aqueous solution) of Sumimaru M30W manufactured by the company were mixed in the same manner as in Example 1 to obtain Sample 3 for thermobalance measurement. Further, coated sand was prepared in the same manner as in Example 1 except that 7.2 parts of this binder liquid was used. The thermobalance measurement results are shown in Figure 3, and the coated sand evaluation results are shown in Table 1. Example 4 A portion of the binder liquid obtained by adding 15.5 parts of a 77% aqueous solution of methylated methylolmelamine (Sumimar M-30W manufactured by Sumitomo Chemical Co., Ltd.) to 93.3 parts of a 30% aqueous solution of glucose and stirring for 10 minutes. Sample 4 for thermobalance measurement was prepared in the same manner as in Example 1. In addition, 8.2 parts of this binder liquid and 100 parts of silica sand (Mikawa No. 6) were placed in an open tank mixer and kneaded while blowing hot air at about 70°C, and after 30 minutes, 0.1 parts of calcium stearate was added as a lubricant. A coated sand was prepared by adding 100% of the above amount. The thermobalance measurement results are shown in Figure 4, and the evaluation results of the coated sand are shown in Table 1. Comparative Example 1 A 30% methanol solution of a commercially available phenolic resin for shell molds was dried and heat treated in the same manner as in Example 1 to obtain Sample 4 for thermobalance measurement. Further, coated sand was prepared in the same manner as in Example 1 except that 10 parts of this binder liquid was used. The thermobalance measurement results are shown in Figure 5, and the coated sand evaluation results are shown in Table 1. Comparative Example 2 A 20% acetone solution of cellulose acetate (manufactured by Daicel Chemical Industries, Ltd., degree of acetylation 55.5%, intrinsic viscosity 0.80 measured with an acetone solution at 25°C) was dried and heat treated in the same manner as in Example 1. This was designated as sample 5 for balance measurement. Further, coated sand was prepared in the same manner as in Example 1 except that 15 parts of this binder liquid was used. The thermobalance measurement results are shown in Figure 6, and the coated sand evaluation results are shown in Table 1. Comparative Example 3 A methylated methylol melamine resin (Sumimar M30W manufactured by Sumitomo Chemical Co., Ltd., 77% aqueous solution) was dried and heat treated in the same manner as in Example 1 to obtain Sample 6 for thermobalance measurement. Further, coated sand was prepared in the same manner as in Example 1, except that 3.9 parts of this binder liquid was used. The thermobalance measurement results are shown in Figure 7, and the coated sand evaluation results are shown in Table 1. Comparative Example 4 317 parts of a 30% acetone solution of a commercially available phenolic resin for shell molds and 25 parts of a 20% acetone solution of cellulose acetate used in Comparative Example 2 were mixed, dried and heat treated in the same manner as in Example 1. Sample 7 for thermobalance measurement
And so. Further, coated sand was prepared in the same manner as in Example 1 except that 10.2 parts of this binder liquid was used. The thermobalance measurement results are shown in Figure 8, and the coated sand evaluation results are shown in Table 1. Comparative Example 5 Furan resin for commercially available molds (Hitafuran manufactured by Hitachi Chemical)
40 parts of a phosphoric acid curing agent was added to 100 parts of VF603K), and the mixture was reacted and cured at 20°C for 24 hours, and this was used as Sample 8 for thermobalance measurement. In addition, 100 parts of silica sand (flattary) was added to Example 1.
Place in the stirrer described above, add 0.57 parts of phosphoric acid curing agent about 10 seconds after starting stirring, and stir for about 60 seconds. After this, 1.43 parts of the above Hitafuran VF603K was added and the amount of
Mix and stir for seconds. The coated sand thus obtained
JISK6910 “Powdered resin test method for shell mold”
A test piece was prepared by filling the mold described in 1 and curing at room temperature for 24 hours. The thermobalance measurement results are shown in Figure 9, and the coated sand evaluation results are shown in Table 1.

[Table] The coated sands of Comparative Examples 1, 4, and 5 had poor sand disintegration properties after casting. On the other hand, the coated sand of Comparative Example 2 generated significant gas during heating and was deformed during pouring. The coated sand of Comparative Example 3 produced a significant amount of gas accompanied by an irritating odor when heated. All of the examples of the present invention were excellent as core binders for aluminum alloy casting.

[Brief explanation of drawings]

FIGS. 1 to 9 are graphs showing thermobalance measurement results in Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] 1. Consisting of an organic compound having a hydroxyl group or a carboxyl group and a thermosetting resin initial condensate having reactivity with the hydroxyl group, the maximum temperature under heating conditions of a heating rate of 20°C per minute in air The weight loss rate is 25% by weight or less and the weight loss at 450℃ is 30% by weight.
A pyrolyzable binder for foundry sand that is 75% by weight or less. 2 The organic compound having a hydroxyl group or a carboxyl group is selected from the group consisting of cellulose derivatives, monosaccharides, oligosaccharides, polyvinyl alcohol, partially saponified products of ethylene/vinyl acetate copolymers, liquid polybutadiene having a hydroxyl group end, and phenols. A pyrolyzable binder for foundry sand according to claim 1. 3 The thermosetting resin initial condensate reactive with hydroxyl groups is selected from the group consisting of melamine/formaldehyde initial condensates and their alkyl ethers, urea/formaldehyde initial condensates and their alkyl ethers, and epoxy resin initial condensates. A pyrolyzable binder for foundry sand according to claim 1 or 2.