JPS6316830A - Resin covered sand for shell mold - Google Patents

Abstract

PURPOSE:To improve the decay property of a core which has been brought to a low temperature treatment, by covering sand with a resin obtained by allowing phenol, etc., an organic compound or a resin having a low temperature thermal cracking property, and formaldehyde, etc., to react under an acidic catalyst or an alkaline catalyst. CONSTITUTION:Phenol, etc., and formaldehyde, etc., are allowed to react under an acidic catalyst or an alkaline catalyst, and an initial product of a phenol resin is formed. Subsequently, sand is covered with a resin obtained by allowing it to react by an organic compound or a resin for showing a low temperature thermal cracking property, and used as a resin covered sand for shell mold. In this regard, as for phenol or its derivatives, phenol or meta or para-alkyl phenol such as m-cresol, p-cresol, and 3-4 xynol, and a mixture of these phenol, etc. are exemplified. Formaldehyde, etc., are formalin, or parafomaldehyde, trioxane, and a mixture of their formaldehyde polymer, etc. As for the organic compound or the resin for showing a low temperature thermal cracking property,epsilon-caprolactam, nylon oligomer, a straight chain molecular structure of poly-vinyl acetate resin, etc., and that which scarcely has a carbon molecule is used.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to resin-coated sand for shell molding, particularly for aluminum alloy castings or light alloy castings with a pouring temperature of 700°C.
The present invention relates to resin-coated sand for shell molds that is used for castings of relatively low quality materials at ~800°C and improves the collapsibility of molds after casting.

[Conventional technology]

Generally, the mainstream method for molding mold cores for mass production is the shell molding method, which uses foundry sand that has been purified with phenolic resin. However, the pouring temperature for phenolic resin, like aluminum alloy, is 700 to 800℃, which is 100℃ for iron.
If the material is lower than 300 to 1400℃, the mold core will have poor collapsibility after pouring because it is not treated at high temperature, and it will be very difficult to remove sand, so a separate sand removal process will be provided. The current situation is that a great deal of cost and effort is expended in removing the sand.

As automobiles become lighter, the amount of light alloys used tends to increase, and light alloys have the physical properties necessary for shell molds.

Compared to conventional phenolic resins, there is a strong demand for improvements to easily disintegrating resins that thermally decompose at low temperatures.

The first method to improve disintegration properties is to use resins that have bonds that easily undergo thermal decomposition reactions at low temperatures.

JP-A-57-187142, JP-A-56-10913
No. 6, JP-A-55-165252 uses unsaturated polyester resin as a binder, compared to phenol resin.

Essentially, this method focuses on having ester bonds that are easily thermally decomposed at low temperatures, and although the disintegration property is improved, the strength of the core is low and it is not suitable for cores with complex shapes. Although it has historically had excellent disintegration properties at low temperatures, the thermal decomposition of the binder is accelerated during core molding and pouring, resulting in bad odors, deteriorating the working environment, and other negative effects on the human body, resulting in industrial pollution. The second method to improve the disintegration property due to the above problem is to add a thermal decomposition accelerator to the phenol resin, which is a conventional method.
No. 49043 splits Br or Br compound by heating with a bromine-containing organic compound, oxidizes and decomposes the phenolic resin, and improves the collapsibility of the mold. Since it generates a harmful odor and is highly corrosive to molds and machines, a disintegration promoter for post-molding molds that satisfies these conditions has not yet been developed.

A third method for improving disintegration properties is to modify conventional phenolic resins with polymeric substances or resins that are thermally decomposable at low temperatures, and many methods have been proposed in the past.

JP-A-56-114546 proposes a resin in which phenol, synthetic organic fibers, and formaldehyde are reacted under an acidic or alkaline catalyst to produce phenolic resin, but in order to improve the disintegration property, it is necessary to react at low temperature. Fibrous polymers that cause thermal decomposition have too high a molecular weight and are shaped like cores, and thermal decomposition is delayed in areas where heat is difficult to conduct, making it somewhat unsatisfactory to provide sufficient disintegration. be.

[Problem that the invention seeks to solve]

The object of the present invention is to eliminate the above-mentioned drawbacks of the conventional techniques, to eliminate the need for large costs and labor, and to provide mold strength and molding properties that are not as good as the conventional coated sand. It is an object of the present invention to provide resin-coated sand for shell molds, which has excellent collapsibility and is suitable for casting of low-temperature materials with a pouring temperature of 700 to 800°C.

[Means for solving the problem] As a result of intensive research, the present inventors have developed a method for producing phenolic resin for shell molds using organic compounds or resins that exhibit low heat resistance and low temperature thermal decomposition. By using the sand tested with a resin obtained by modifying or mixing the resin, the characteristics of the linear polymer are taken advantage of, and the crosslinking density during curing is relaxed, the thermal decomposition temperature is lowered, and it collapses after pouring. The present invention was completed based on the discovery that the properties are significantly improved.

The present invention is for shell molds, characterized in that the resin obtained by reacting phenols with organic compounds or resins exhibiting low-temperature thermal decomposition and formaldehyde under an acidic or alkaline catalyst is molded into sand. The present invention can be carried out by, for example, reacting phenols and formaldehyde under an acidic or alkaline catalyst to form an initial product of phenolic resin, which is then treated with low-temperature thermal decomposition. Resin coated sand for shell molding can be obtained by coating sand with a resin obtained by reacting with the organic compound or resin shown below.

The phenols used in the present invention are phenol or m-cresol, p-cresol, 3-4 xylenol, 3-5 xylenol, or paraalkylphenols, and mixtures of these phenols.

The first formaldehydes used in the present invention include formalin, paraformaldehyde, trioxane,
Mixtures such as polyoxymethylene, tetraoxymethylene and formaldehyde polymers thereof are prepared.

The amount of formaldehyde used is preferably in the range of 0.5 to 2.5 moles per mole of phenol.

The organic compound or resin exhibiting low-temperature thermal decomposition properties used in the present invention is ε-caprolactam.

Preferred examples include nylon oligomers, polyvinyl acetate resins, polyester resins, acrylic resins, and other linear molecular structures with particularly low carbon molecules.

The amount of the organic compound or resin exhibiting low-temperature thermal decomposition properties mixed into the resin and reacted is preferably in the range of 5 to 40% by weight;
If it is less than 40% by weight, the effect will be small, and if it is more than 40% by weight, the disintegration property after pouring will be improved, but the curing property during core molding will be slow and the practicality will be reduced.

〔Example〕

The present invention will be explained below with reference to Examples. Since the resin-coated sand for shell molds of the present invention is coated in the same manner as conventional phenolic resin cedar-coated sand, a modified phenolic resin with an organic compound or resin exhibiting low-temperature thermal decomposition will be described. The weight depends on the weight.

Example-1 Phenol 940 L? , ε-caprolactam 100
r.

465 f of 50% formalin and 6.62 f of oxalic acid were charged into a reaction vessel equipped with a reflux condenser and allowed to react under reflux for 3.0 hours.2Then, dehydration and concentration were performed under reduced pressure until the softening point was 85°C.
An ε-caprolactam modified phenolic resin was obtained.

Example-2 Nylon oligomer was used in place of ε-caprolactam in Example-1. Other than that, the same procedure as Example-1 was carried out.
A nylon oligomer-modified phenol resin with a softening point of 86°C was obtained.

Example-3 Polyvinyl acetate resin was used in place of ε-caprolactam in Example-1. Other than that, a polyvinyl acetate resin-modified phenol resin having a softening point of 84° C. was obtained in the same manner as in Example-1.

Example-4 Polyester resin was used in place of ε-caprolactam in Example-1. A polyester resin-modified phenol resin having a softening point of 88° C. was obtained in the same manner as in Example-1 except for the above.

Example-5 Acrylic resin was used in place of ε-caprolactam in Example-1. Other than that, the softening point was 8 as in Example-1.
An acrylic resin-modified phenol resin at 5°C was obtained.

Example-6 Phenol 940? , 50% formalin 450
f, 6.62 g of oxalic acid was charged into a reactor equipped with a reflux condenser and refluxed under reflux until emulsification was carried out, then ε-caprolactam 3002 was added and refluxed for 2.0 hours under backward flow. 9. Then, the pressure was reduced The resin was dehydrated and concentrated to obtain an ε-caprolactam-modified phenol resin with a softening point of 85°C.

Example 7 Nylon oligomer 4002 was used in place of ε-caprolactam in Example 6. A nylon oligomer-modified phenol resin having a softening point of 80° C. was obtained in the same manner as in Example 6 except for the above.

Example 8 In place of ε-caprolactam in Example 6, 35Of polyvinyl acetate resin was used. A polyvinyl acetate resin-modified phenol resin having a softening point of 82° C. was obtained in the same manner as in Example 6 except for the above.

Example-9 Polyester resin 5002 was used in place of ε-caprolactam in Example-6. A polyester resin-modified phenol resin having a softening point of 80° C. was obtained in the same manner as in Example-6 except for the above.

Example-10 Acrylic resin 6002 was used in place of ε-caprolactam in Example-6. Otherwise, an acrylic resin-modified phenol resin having a softening point of 80°C was obtained in the same manner as in Example-6.

Example-11 Phenol 940r, nylon oligomer 1002
was charged into a reaction vessel equipped with a reflux condenser and heated to dissolve, then 50% formalin 1200F and 2591I ammonia water 122F were charged and reacted at 80°C for 1.5 hours.2 Then, while removing the water content under reduced pressure, 90℃
When the temperature reached 95°C, the mixture was immediately taken out from the reactor and rapidly cooled to obtain a nylon oligomer-modified resol type solid phenol resin with a softening point of 80°C.

Example 12 In place of the nylon oligomer in Example 11, 100 tons of polyester resin was used. A polyester modified resol table solid phenol resin having a softening point of 82° C. was obtained in the same manner as in Example 11 except for the above.

Comparative example-1 Phenol 940f, 50% formalin 450
f, 6.62 g of oxalic acid was charged into a reactor equipped with a reflux condenser and reacted under reflux for 3.0 hours. 1. The mixture was then dehydrated and concentrated under reduced pressure to obtain a novolak type phenol resin with a softening point of 81°C.

Comparative example-2 Pheno-chishi 940 F, 50 thiformin 108
0 f '+ 35 1222 thiammonium water was charged into a reaction vessel and reacted at 80°C for 1.0 hour.1 Then, while removing the water content under reduced pressure, the temperature was gradually raised to 90°C, and when it reached 95°C. It was immediately taken out from the reactor to obtain a resol type solid phenol resin with a softening point of 78°C.

Test Example Table 1 shows the results of testing the properties of resin covering sand for shell molds of the present invention obtained by coating molding sand with the resins obtained in the Examples and Comparative Examples.

Silica sand heated to 140°C, 10 to 2, and 0.2Kr of resin were placed in a speed mixer for kneading foundry sand, and kneaded for 60 seconds. 1. Next, hexa water containing 0.03 parts of hexamine and 9 parts of water dissolved in 0.1 parts was added. After about 60 seconds, calcium stearate was added and the mixture was further kneaded for 20 seconds to obtain the resin-containing sand for shell molds of the present invention.

The characteristics of this resin test sand are shown, however, hexamine is not required for resol type resin.

Table 1 Note 1 Bending strength is based on JIS K-6910 test method for powdered phenolic resin for shell molds.

Note-2 The fusion point is based on JA (yr test method, C-1 fusion point test method).

Note-3 Disintegrability is 300×501+1++l core 500
6 m after being held in a reducing atmosphere for 1.0 hours
Shake for 60 seconds using a rotor tube tester using a θsh sieve.

〔Effect of the invention〕

As is clear from the table of Examples, it was observed that the disintegration properties of the cores treated at 500°C were significantly improved.

Claims (1)

[Claims] A shell mold characterized by coating sand with a resin obtained by reacting phenols with an organic compound or resin exhibiting low-temperature thermal decomposition and formaldehyde under an acidic or alkaline catalyst. resin coated sand.