JPH07171655A - Method for modifying resin for reconditioning casting sand in mold with water soluble resol type phenol resin as binder - Google Patents

Abstract

PURPOSE:To provide the plasticity to withstand the compressive strength of a mold, the hardening crack and the thermal stress during the molding by adding polyethyrene glycol of the molecular weight to meet the nature of an intended mold to the water soluble resol type phenol resin. CONSTITUTION:When a mold where the water soluble resol type phenol resin is the binder is reconditioned and recycled, the resin is modified by adding 20-5 pts. polyetherene glycol (molecular weight: 400-600) to 80-95 pts. of water soluble resol type phenol resin. This resin is fully stirred to be reacted, added to silica sand for molding and mixed therewith, and the resin is filled into a molding flask, and hardened with CO2 gas to make a mold. For example, by weight, 7% polyetherene glycol and 3% methyl alcohol is added to 90% water soluble resol type phenol resin, and mixed, and gaseous CO2 is blown into this resin to be solidified.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] A process of kneading a water-soluble resol-type phenolic resin with silica sand as a binder for a casting mold, filling the flask with a CO ₂ gas, and hardening the mold. The phenol resin used for this is modified to improve the initial strength of the mold and to recover and reuse the foundry sand.

[0002]

2. Description of the Related Art A water-soluble resol-type phenolic resin is used as a binder, which is kneaded with silica sand, molded and then cured by bubbling CO ₂ gas into a mold. However, this mold has a low initial strength, and if the mold is applied immediately after the molding, the components near the surface of the mold are destroyed by the components in the mold coating agent and the function as the mold cannot be maintained. This tendency is particularly remarkable when recycled sand is used.

[0003]

Were cured according to the preceding paragraph [0008] mold, in conjunction with that the initial strength is low is contained in the coating agent in the next mold wash Engineering the (-CH ₂ -CHR'-) Due to the action of the adhesive containing, for example, polyvinyl alcohol, vinyl acetate, or a phenol-based adhesive, the cross-linking of the cross-linked phenol resin is released and the mold surface is destroyed, and the strength near the mold surface cannot be maintained. Therefore, the phenol resin is modified in advance and treated so that the initial strength is not increased and the crosslinking of the phenol resin is not destroyed in the coating process.

[0004]

Means for Solving the Problems To 95 to 80 parts of a water-soluble resol type phenol resin, 5 to 20 parts of polyethylene glycol is added and mixed and stirred to modify the resin to obtain a mold resin. After adding this resin to silica sand and kneading and molding, C
It is cured by bubbling O ₂ gas.

[0005]

[Function] Phenol resin is CO _{2 in} the environment of OH ⁻
When gas is aerated, COOH group is substituted at the 2 or 4 position of the phenol ring shown in FIG. 1 to form hydroxybenzoic acid, and an ester is formed from the ester. The ester is hydrolyzed to crosslink the phenol resin. Since the crosslinked structure contains polyethylene glycol, the crosslinked structure can be retained and the mold strength can be improved. Also, the strength of the mold and the plasticity of the mold can be controlled by adjusting the molecular weight from the chain structure of polyethylene glycol.

(Example 1) Polyethylene glycol 7 against water-soluble resol type phenol resin 90 (WT%)
(WT%) and methyl alcohol 3 (WT%) were added and mixed, and CO ₂ gas was blown into the resin to solidify it by the experimental apparatus shown in FIG. 2. The crosslinked phenolic resin was analyzed by an infrared spectrophotometer. The IR spectrum obtained is shown in FIG.

[0007] (Example 2) The phenol resin is contained in the coating agent in the next mold coating process _(-CH 2 -CHR '
-) It becomes difficult for the terminal group crosslinked by the monomer to be removed. In addition, since polyethylene glycol has a long chain structure in its molecular structure, the resin can have plasticity.

Example 3 Polyethylene glycol having a molecular weight of 600 and methyl alcohol were mixed at a ratio of 5: 5 to 10:
The solution was mixed at a ratio of 0, and then this solution and the water-soluble resol-type phenol resin were mixed at a ratio of 1: 9 to prepare a modified phenol resin. This resin was added to No. 6 silica in a ratio of 3.5% to the sand, and after kneading with a Simpson muller, it was filled in a test mold making frame (inner diameter 50 mm, length 150 mm), and then CO ₂ gas was aerated for 20 seconds. Then, it was cured to obtain a test mold. An alcohol coating mold containing a phenolic adhesive was applied to this mold by dip coating, and immediately after that, it was ignited and dried. The result of measuring the compressive strength of this mold by an autograph is shown in FIG. From this figure, the metamorphic effect of phenolic resin can be confirmed.

(Example 4) FIG. 5 shows changes in the compressive strength of a mold and the strain at the time of pressurization by a resin in which the molecular weight of polyethylene glycol to be added is changed. From this, it has become clear that by controlling the molecular weight of polyethylene glycol to be added, it is possible to adjust the compressive strength of the mold, absorb shrinkage cracks during molding, and absorb deformation of the mold due to thermal stress during pouring.

(Example 5) Regarding a mold using recycled sand, in order to confirm the modification effect of the resin by the coating operation, a mixture of recycled sand and 50% of fresh sand was used for the modification treatment and the conventional resin. After adding 3.5% to each sand ratio and kneading,
It was cured with CO ₂ gas, used as a mold, and subjected to a test of compressive strength. FIG. 6 shows changes depending on the presence or absence of modification and the presence or absence of a coating type. As can be seen from this figure, the mold strength of the resin using the unmodified resin was significantly reduced by applying the mold.

According to the present invention, it is possible to adjust the strength of the mold after coating and the plasticity of the mold. In addition, it is possible to save resources by recovering and reusing silica sand after pouring, and reduce industrial waste.

[Brief description of drawings]

FIG. 1 is a chemical reaction formula when a CO ₂ gas is passed through a phenol resin.

FIG. 2 is an explanatory view of an experimental device for aerating CO ₂ gas in a phenol resin.

FIG. 3 is a graph showing an IR spectrum obtained by analyzing a crosslinked and solidified phenol resin with an infrared spectrophotometer.

FIG. 4 is a diagram showing a relationship between a ratio of polyethylene glycol added to a resin and a compressive strength of a mold 2 hours after baking and drying.

FIG. 5 is a diagram showing changes in the compressive strength and strain of a template when the molecular weight of polyethylene glycol used for modifying a resin is changed.

FIG. 6 is a diagram showing changes in compressive strength before and after coating, depending on whether or not resin is modified when recycled sand is used.

Claims (1)

[Claims] 1. A water-soluble resol-type phenolic resin 80
Polyethylene glycol (molecular weight 400 to 95 parts)
To 600) 20 to 5 parts by weight of the resin to modify the resin, and a method for modifying the resin for mold binder, which enables recovery and reuse of molding sand.