JPH04339535A - Bonding composition for molding sand and production of mold - Google Patents

Abstract

PURPOSE:To provide the composition and manufacturing method improved to use to a gas curing mold. CONSTITUTION:This is related to the bonding composition for molding sand, containing alkali re-sol type bis-phenol-formaldehyde resin and boron compound or the bonding composition for molding sand further using silane coupling agent as the bonding agent. Further, the manufacturing method for mold having the peculiarity, in which at the time of manufacturing the mold by using refractory granular material, the bonding compound is used and cured with carbon dioxide, is provided. By this molding method, in which the bonding composition for molding sand is used and the mold is cured with the carbon dioxide, curing speed of the mold and mold strength are drastically improved, in comparison with use of the ordinary resol type phenol-formaldehyde resin solution, and the one having excellent storing stability of the bonding agent itself, is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved caking composition for foundry sand used in gas-curable molds and a method for producing molds.

0002

BACKGROUND OF THE INVENTION The self-hardening mold method, the cold box mold method, and the cloning method (shell method) are known as methods for producing molds such as main molds and cores using organic binders. In particular, organic self-hardening mold making methods have already become a general-purpose molding method, replacing inorganic ones, from the viewpoints of productivity, quality of castings, and safety and health, mainly in the field of mechanical casting.

On the other hand, conventionally, in order to manufacture molds at medium to high speeds, a cloning method has been widely used in which molds are manufactured by heating and hardening so-called coated sand, in which granular refractories are coated with phenolic resin.

However, in order to save energy during mold manufacturing, mold production speed, and improve the quality of molds and castings, the cold box molding method, in which gaseous or aerosol substances are used to cure molds at room temperature, is an alternative to the cloning method. The casting industry is seriously trying to introduce it as a molding method.

[0005] Recently, Japanese Patent Publication No. 1-224263 has been proposed as a gas-curing mold making method, particularly from the viewpoint of safety and health, as a process for manufacturing molds using carbon dioxide.

[0006]

However, in the above technique, it is difficult to obtain sufficient curing speed and strength of the mold, and a relatively large amount of binder must be used. or,
The viscosity of the binder itself changes over time during storage, resulting in poor storage stability, particularly in the summer.

[0007] The present invention aims to improve the above-mentioned problems, and provides a mold with sufficient hardening speed and strength even with a relatively small amount of binder, and the binder itself has good storage stability. An object of the present invention is to provide a method for producing a caking composition for foundry sand and a mold.

[0008]

[Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, the present inventors have developed a caking composition in which a boron compound is added to an alkaline resol type bisphenol-formaldehyde resin. The present inventors have discovered that when manufacturing a mold using a refractory granular material, the curing speed and strength of the mold can be significantly improved by curing it with carbon dioxide, and the present invention has been completed.

Specifically, the present invention relates to a caking composition for foundry sand containing an alkaline resol type bisphenol-formaldehyde resin and a boron compound.

[0010] Furthermore, the present invention provides a method for producing molds using refractory granular materials using alkaline resol bisphenol-
The present invention relates to a method for producing a mold, which comprises using a caking composition for foundry sand containing a formaldehyde resin and a boron compound, and curing it with carbon dioxide.

The alkaline resol type bisphenol-formaldehyde resin used in the present invention is represented by the following general formula.

0012

[Chemical formula 1]

(In the formula, M1 and M2 are H atoms or Li,
An alkali metal element consisting of one type or a combination of K, Na, etc., X and Y are H atoms or alkyl groups such as methyl groups, or a combination thereof, the sum of n and m is 1.2
~5.5. ) Such alkaline resol type bisphenol-formaldehyde resin is obtained by reacting bisphenol and formaldehyde in water in the presence of an alkali metal hydroxide by a conventional method, but the molar ratio of alkali metal hydroxide:bisphenol is 0. 7:1.0
~5.0:1.0, preferably 1
．． 0:1.0 to 4.0:1.0 is good. If the molar ratio is less than 0.7:1.0, the curing speed and mold strength will be insufficient, while if the molar ratio exceeds 5.0:1.0, the pot life will be shortened, which is not preferable.

[0014] The formaldehyde:bisphenol molar ratio is preferably in the range of 1.2:1.0 to 6.0:1.0, preferably 2.0:1.0 to 5.5:1.
．． 0 is good. If the molar ratio is less than 1.2, the compatibility with the boron compound will be poor as described above, and if the molar ratio is less than 6.
．． If it exceeds 0, the amount of unreacted formaldehyde remaining will increase.

Examples of boron compounds include boric acid and boric acid, sodium tetraborate decahydrate, potassium borate decahydrate,
Borate salts such as hydrate, sodium metaborate, potassium pentaborate and sodium pentaborate are preferred.

The boron compound:bisphenol molar ratio is preferably in the range of 0.01:1.0 to 2.0:1.0, preferably 0.05:1.0 to 1.0:
1.0 is good. If the molar ratio is less than 0.01, the curing speed and strength of the mold will be insufficient;
If it exceeds this amount, depending on the properties and water content of the alkaline resol type bisphenol-formaldehyde resin solution, the compatibility of boric acid and borates tends to deteriorate and precipitates tend to occur.

Specific compounds of the alkaline resol type bisphenol-formaldehyde resin represented by the above general formula used in the present invention include, in the case of bisphenol A, an addition condensate of formaldehyde in which X and Y are methyl groups; , in the case of bisphenol F, X and Y are H
It is an addition condensation product of the atom formaldehyde.

When manufacturing a mold using the caking composition containing a boron compound in the alkaline resol type bisphenol-formaldehyde resin solution of the present invention, the conventional resol type phenol-formaldehyde resin solution can be cured using carbon dioxide. A caking composition comprising a formaldehyde resin (Japanese Patent Publication No. 1-224263), which can provide sufficient curing speed and strength of a mold even with a relatively small amount of caking agent, and has good storage stability of the caking agent itself. can be obtained, resulting in a significant improvement. Further, the solid content of the caking composition solution containing the alkaline resol type bisphenol-formaldehyde resin and the boron compound in the present invention is preferably 25 to 75% by weight. 25% by weight
If it is less than 75% by weight, the mold strength will be low, while if it exceeds 75% by weight, the viscosity of the binder itself will increase, causing problems such as uneven kneading.

A silane coupling agent may be added to the caking composition of the present invention for the purpose of improving mold strength. Preferred silane coupling agents include γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)
Examples include aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and the like. The silane coupling agent is preferably 0.001 to 1 part by weight per 100 parts by weight of the binder.
A mold can be manufactured by a similar process using this binder composition by adding it in an amount of 0.002 to 0.5 parts by weight.

[0020] In the present invention, in order to produce a foundry sand mold, 0.4 to 15 parts by weight, preferably 0.6 to 8 parts by weight of a caking composition is added to 100 parts by weight of the refractory granular material. After the mixture is kneaded and filled into a mold model, it is hardened by gassing an appropriate amount of carbon dioxide. The amount of carbon dioxide, atmospheric pressure, etc. are not particularly limited.

[0021] The alkaline resol type bisphenol-formaldehyde resin used in the present invention may be co-condensed with a monomer capable of formalin condensation, such as urea, melamine, or cyclohexanone, to the extent that it does not become a main constituent unit by weight. Suitable alkaline substances used in the production of the alkaline resol type bisphenol-formaldehyde resin used in the present invention include sodium hydroxide,
Potassium hydroxide, lithium hydroxide and mixtures thereof, with potassium hydroxide being most preferred.

[0022] Examples of the refractory granular materials include silica sand containing quartz as a main component, chromite sand, zircon sand, olivine sand,
and alumina sand.

The resin may be produced by any known method, but for example, a bisphenol compound is heated and stirred in an optimal solvent (water) in the presence of an alkali metal hydroxide, while formaldehyde is added in portions or continuously. and convert it into a resin. If you use a method such as adding the boron compound and water separately to the generated resin, or making the resin into an aqueous solution (resin: water = 3:1 to 1:3) and then adding the boron compound, etc. good.

[0024]

[Examples] The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Bisphenol A 456g, water 781.5g
, 118.1g of 95% potassium hydroxide in a stirrer,
The mixture was placed in a flask, which is a well-known synthesis apparatus equipped with a condenser, a thermometer, and a heater, and kept at 80° C. with stirring, and 261 g of paraformaldehyde (purity 92%) was gradually added thereto, and the mixture was allowed to react for 90 minutes. Thereafter, it was cooled to room temperature. Based on 83 parts by weight of the obtained alkaline resol type bisphenol-formaldehyde resin solution, 7.3 parts by weight of 95% potassium hydroxide, 9.4 parts by weight of sodium tetraborate decahydrate, and 0.6 parts by weight of γ were added. -Aminopropyltriethoxysilane was sequentially dissolved to obtain the binder of the present invention [viscosity at 25°C was 150 cp]
s], and the change in mold strength over time (curing rate) was evaluated. For evaluation of mold strength, Fremantle silica sand 100
A mixture obtained by kneading 3 parts by weight of the above-mentioned binder per part by weight was filled into a 50 mmφ x 50 mmhφ gassing test piece model, and after aerating carbon dioxide (10 l/min), the change in coercive pressure over time was observed. was measured. Regarding the storage stability test of the above-mentioned binder, the change in viscosity over time was measured using a B-type viscometer when the binder was stored in a thermostat at 35°C (the viscosity measurement temperature was 25°C).

The results are shown in Table 1.

Comparative Example-1 800g of phenol, 701.3g of paraformaldehyde (purity 92%), and 40.85g of 50% aqueous sodium hydroxide solution were synthesized using a well-known synthesis apparatus equipped with a stirrer, a cooling tube, a thermometer, and a heater. The mixture was placed in a flask, heated to 65° C. while stirring, and maintained for 1 hour. 1 again
The temperature was raised to 75°C at a rate of 1°C per minute and held for 30 minutes. After that, the temperature was increased to 85℃ at a rate of 1℃ per minute.
The reaction was allowed to proceed for 70 minutes. Thereafter, it was cooled to room temperature. Obtained resol type phenol-formaldehyde resin 2
5 parts by weight of sodium tetraborate decahydrate and 35 parts by weight of 50% potassium hydroxide and 0
．． 4 parts by weight of γ-aminopropyltriethoxysilane were sequentially dissolved to obtain a binder [at this time, the viscosity at 25°C was 1
46 cps], and the change in mold strength over time (curing speed) was evaluated. That is, a mixture of 100 parts by weight of Fremantle silica sand and 3 parts by weight of the above-mentioned binder was mixed into a 50 mm diameter x 5
Fill a 0mmhφ gassing test piece model,
After aerating carbon dioxide (10 l/min), the change in coercive pressure over time was measured. Regarding the storage stability test of the above-mentioned binder, the change in viscosity over time was measured using a B-type viscometer when the binder was stored in a thermostat at 35°C (the viscosity measurement temperature was 25°C).

The results are shown in Table 1.

[0029]

[Table 1]

[0030]

Effects of the Invention: By using the caking composition for foundry sand prepared by adding a boron compound to the alkaline resol type bisphenol-formaldehyde resin solution of the present invention, it is possible to improve the molding method by hardening the mold with carbon dioxide. Compared to using a resol type phenol-formaldehyde resin solution, the curing speed and mold strength of the mold can be significantly improved, and the storage stability of the binder itself can be improved.

Claims (4)

[Claims] [Claim 1] Alkaline resol type bisphenol-
A caking composition for foundry sand containing formaldehyde resin and a boron compound. 2. The boron compound is one or more boron compounds selected from the group consisting of boric acid, sodium tetraborate decahydrate, potassium borate decahydrate, sodium metaborate, potassium pentaborate, and sodium pentaborate. The caking composition for foundry sand according to claim 1, comprising two or more types. 3. The caking composition for foundry sand according to claim 1, further comprising a silane coupling agent as a caking agent. 4. When manufacturing a mold using the refractory granular material, a caking composition for foundry sand containing an alkaline resol type bisphenol-formaldehyde resin and a boron compound is used, and the mold is cured with carbon dioxide. A method for manufacturing a mold.