JPH11197787A - Resin coated sand for shell mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve a trouble caused by static electricity at the time of transporting sand grain. SOLUTION: In the resin coated sand grain composed of the sand grain and the resin coating layer of thermosetting resin covering the surface of the sand grain, white carbon is stuck onto the surface of the resin coated layer. Since the white carbon contains crystal water under state of super fine powdery silicon dioxide (SiO2 .nH2 O), it is supposed that OH group and crystal water electrically discharge to the out of the system without storing. Further it is considered that the white carbon itself functions as lubricant and acts to reduce the friction of the resin coated sand grains to each other. Therefore, even in the case of using novolak type phenol resin having little free phenol content in order to improve the working environment in a molding work, the large electric charge preventing effect can be displayed by adding the white carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated sand particle used in a shell molding method, and more particularly to a resin-coated sand particle for a shell mold for preventing static electricity.

[0002]

2. Description of the Related Art A shell molding method conventionally known as a kind of a molding method is a method of forming resin-coated sand particles (Resin resin).
(Coated Sand (RCS)) is filled in a heated mold, the resin coated on the sand particles is melted to bond the sand particles, and the resin is cured by heating, and then the molded mold is separated from the mold. How to type. The resin-coated sand particles used in the shell molding method are composed of sand particles made of silica sand or the like, and a resin coating layer as a binding material made of a thermosetting resin such as a novolac phenol resin coated on the surface of the sand particles. ing.

When a mold is formed by such a shell molding method, the temperature of the mold is about 250 to 350 ° C. At this time, a bad smell is generated, and the working environment in the mold making factory is deteriorated. I have. The cause of this bad smell is a novolak-type phenol resin used as a binder for resin-coated sand particles. That is, it is considered that a bad smell is generated due to volatilization of low molecular components contained in the novolak type phenol resin, or generation of formaldehyde and ammonia by thermal decomposition of hexamethylenetetramine as a curing agent. In particular, low-molecular components of phenols such as free phenol are easily perceived by smell even at a low concentration, and are a major cause of malodor.

For this reason, in recent years, novolak-type phenol resins, in which the content of free phenol is reduced as much as possible, have been used as binders for resin-coated sand particles in consideration of the improvement of the working environment in mold making. Fairness 7-6
No. 4905).

[0005]

By the way, the resin-coated sand particles are usually used in a dry state, and the transfer of the resin-coated sand particles is carried out by means of a belt conveyor or air transfer using a transfer pipe. However, it has been clarified that resin-coated sand particles using a novolak-type phenol resin having a low free phenol content as a binder as described above generate static electricity at the time of transfer and cause inconvenience due to charging.

That is, in the case of transfer by a belt conveyor, there is a problem that charged resin-coated sand particles adhere to the conveyor surface, and thereafter, the resin-coated sand particles adhered to the conveyor surface fall in unexpected places, thereby deteriorating the working environment. is there. Further, in the case of air transfer, there is a problem that charged resin-coated sand adheres to the inner wall of the transfer pipe, causing pipe clogging.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a resin-coated sand particle for a shell mold which can eliminate the inconvenience caused by static electricity during transfer. Things.

[0008]

The resin-coated sand particles for a shell mold of the present invention for solving the above-mentioned problems have a resin coating comprising a sand particle and a resin coating layer made of a thermosetting resin coated on the surface of the sand particle. In the sand grains, white carbon is attached to the surface of the resin coating layer.

[0009] In a preferred embodiment, the amount of the white carbon is 0.00 0.00 parts by weight of the sand particles.
5 to 0.2 parts by weight.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The resin-coated sand particles for shell molding of the present invention comprise sand particles and a resin coating layer made of a thermosetting resin coated on the surface of the sand particles. The type of the sand particles is not particularly limited, but includes silica sand (SiO ₂ ), chromite sand, zircon sand, and the like, similarly to the conventional resin-coated sand particles for shell molding.

The type of the above-mentioned thermosetting resin is not particularly limited. However, in consideration of the improvement of the working environment in mold making, a novolak-type phenol resin having a reduced free phenol content (a free phenol content of (1% by weight or less of phenol resin). With such a novolak-type phenol resin, a bad odor is hardly perceived, so that the working environment is improved. In addition, when a novolak-type phenol resin having a reduced content of free phenol is used as a binder, OH groups of phenol, which is a hydrophilic group, are reduced and a charged charge is not easily released, so static electricity is generated at the time of transfer. According to the present invention, such static electricity can be prevented, so that it is possible to improve the working environment and eliminate the inconvenience caused by the static electricity at the time of transfer.

A feature of the present invention is that white carbon is attached to the surface of the resin coating layer. White carbon is made of ultrafine silicon dioxide (SiO ₂ .nH)
₂ O) contains water of crystallization. For this reason, although the reason is not clear, the OH groups and water of crystallization contained in the structure of the white carbon compounded in the resin coating layer do not accumulate the charged electric charge during the transfer of the resin coated sand particles or the like. It is presumed that the battery was discharged outside. Further, since white carbon has lubricity, it is considered that white carbon itself functions as a lubricating material and also functions to reduce friction between resin-coated sand particles.

This white carbon is relatively inexpensive, and can maintain the antistatic effect for a long time by adding a small amount of it. In addition, addition of white carbon does not significantly increase the number of steps and time. For this reason, the resin-coated sand particles of the present invention can be produced at extremely low cost and easily. Furthermore, since white carbon has water of crystallization in its structure, it can exhibit an antistatic effect even when used under low humidity.

The compounding amount of white carbon is 100
It is preferably 0.005 to 0.2 parts by weight based on parts by weight. If the amount of white carbon is less than 0.005 parts by weight, the effect of adding white carbon is not recognized, and the generation of static electricity cannot be suppressed. If it exceeds 0.2 parts by weight, the mold strength may be reduced. In the present invention, it is also preferable to add calcium stearate, which has been conventionally used for improving the lubricity of resin-coated sand grains, together with white carbon.
If calcium stearate is added together with white carbon, the antistatic effect is further improved. However, as shown in Examples described later, the strength decreases as the amount of calcium stearate added increases, and the antistatic effect of calcium stearate alone is small.

In order to produce the resin-coated sand particles for a shell mold of the present invention, for example, silica sand and a thermosetting resin heated to a predetermined temperature are put into a mixer, and after stirring for a predetermined time, an aqueous solution of hexamine as a curing agent or the like is added. It can be manufactured by adding and stirring, further adding white carbon (calcium stearate together with white carbon if necessary), stirring, and then cooling. Further, when producing a thermosetting resin as a binder, white carbon can be added as a substitute for an external lubricant.

[0016]

EXAMPLES Specific examples of the resin-coated sand particles for shell molding of the present invention will be described below. (Example 1) [Production of novolak type phenolic resin A] First, novolak type phenolic resin A as a binder was prepared by the following method.

<Reaction step> That is, phenol 100
0 parts by weight, 270 parts by weight of 37% formalin, and 115 parts by weight of 86% paraformaldehyde were charged into a reaction vessel equipped with a heating / cooling device, heated with stirring, and when the temperature reached 80 ° C., 2 parts by weight of oxalic acid was added. The temperature was gradually raised while stirring, and reacted at the reflux temperature. After 30 minutes, 60 minutes, and 90 minutes from the start of reflux, 3 parts by weight of oxalic acid was added, and the reaction was further allowed to proceed at the reflux temperature. The viscosity of the reaction solution was Z (25 ° C.) measured by a Gardner bubble viscometer. The reaction was continued until

<Primary dehydration reaction> Next, 12
The heating was continued while maintaining the pressure at 0 to 150 Torr.
As a result, water in the reaction system is gradually removed from the system, and the temperature of the reaction solution gradually increases. Under these conditions, the unreacted phenol inside is in a liquid state, and hardly escapes outside the system and contributes to the reaction.

<Secondary dehydration reaction> The temperature of the reaction solution is 120 ° C.
Was reached, the pressure in the reactor was reduced to 60 Torr or less, and heating was continued. In this state, unreacted phenol is vaporized and discharged out of the system together with water. Then, when the temperature of the reaction solution reached 230 ° C., the pressure was returned to normal pressure and cooled to 160 ° C., and 15 parts by weight of ethylene bisamide as an internal lubricant and 9 parts by weight of aminosilane as a coupling agent were added and dissolved. After that, take it out of the reactor and add calcium stearate 1 as an external lubricant.
Parts by weight were mixed. Thereby, weight average molecular weight: 14
Novolak-type phenol resin A having a free phenol content of 0.5% by weight was obtained.

[Production of Resin-Coated Sand Particles] Using the novolak-type phenolic resin A obtained, resin-coated sand particles according to the present example were produced by the following method. Silica sand heated to 160 ° C. was charged into a speed mixer, the novolak-type phenolic resin A was added thereto, and the mixture was stirred for 25 seconds. Then, an aqueous hexamine solution was added, and the mixture was stirred until the sand particles collapsed. Thereafter, an equivalent mixture of white carbon (trade name “Nip Seal VN3”, manufactured by Nippon Silica Kogyo Co., Ltd.) and calcium stearate was added, and the mixture was added for 20 minutes.
After stirring for 2 seconds, the sand was discharged and cooled to produce the resin-coated sand particles for the shell mold of Example 1. The mixing ratio of each material is as follows.

Silica sand: 100 parts by weight Novolak type phenolic resin A: 2 parts by weight Hexamine: 0.4 parts by weight Water: 1.5 parts by weight White carbon: 0.05 parts by weight Calcium stearate: 0.05 parts by weight (Examples) 2) In the same manner as in Example 1 except that calcium stearate was not added and the blending amount of white carbon was 0.1 part by weight during the production of resin-coated sand using novolak-type phenol resin A. is there.

Example 3 The same procedure as in Example 1 was carried out except that the mixing amounts of white carbon and calcium stearate were each 0.1 parts by weight during the production of resin-coated sand using novolak type phenolic resin A. The same is true. (Example 4) [Production of novolak-type phenolic resin B] Except for using white carbon instead of calcium stearate as an external lubricant, the same procedure as in Example 1 was carried out, and the weight average molecular weight was 1450 and the content of free phenol was as follows. : 0.
5% by weight of novolak type phenolic resin B was produced.

[Production of Resin-Coated Sand Particles] Instead of novolak-type phenolic resin A, novolak-type phenolic resin B
In the production of resin-coated sand using novolak type phenolic resin B, no white carbon was added, and the amount of calcium stearate was 0.1 part by weight. The same is true.

In the obtained resin-coated sand particles,
White carbon is 0.0
It is blended in 2 parts by weight of the resin coating layer. (Comparative Example 1) The above-mentioned Example 1 was repeated except that white carbon was not added and that the amount of calcium stearate was 0.1 part by weight during the production of resin-coated sand using novolak-type phenolic resin A. Is the same as

(Comparative Example 2) In the production of resin-coated sand using novolak-type phenolic resin A, except that white carbon was not added and the blending amount of calcium stearate was 0.2 parts by weight, This is similar to the first embodiment. (Comparative Example 3) [Production of novolak type phenolic resin C]
Only primary dehydration performed at a pressure of 20 to 150 Torr,
A novolak-type phenol resin C having a weight average molecular weight of 14,20 and a free phenol content of 2.5% by weight was produced in the same manner as in Example 1 except that the temperature was raised to 160 ° C.

[Production of Resin-Coated Sand Particles] Instead of novolak-type phenolic resin A, novolak-type phenolic resin C
In the production of resin-coated sand using novolak type phenolic resin C, no white carbon was added, and the blending amount of calcium stearate was 0.1 part by weight. The same is true.

(Comparative Example 4) [Production of novolak type phenol resin D] 2 parts by weight of benzoic acid were dissolved and mixed with novolak type phenol resin A prepared in Example 1, and the weight average molecular weight was 145.
Novolak type phenolic resin D having a free phenol content of 0.5% by weight was produced.

[Production of Resin-Coated Sand Particles] Instead of novolak-type phenolic resin A, novolak-type phenolic resin D
In the production of resin-coated sand using novolak type phenolic resin D, no white carbon was added, and the blending amount of calcium stearate was 0.1 part by weight. The same is true.

(Evaluation) The obtained resin-coated sand particles of Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated for the fusing point, room temperature strength and charge amount. Table 1 shows the obtained results. In addition,
In Table 1, the blending amount of white carbon indicates parts by weight based on 100 parts by weight of the sand particles of the white carbon contained in the whole resin-coated sand particles, and the blending amount of calcium stearate is from the novolac type to the calcium stearate contained in the whole resin-coated sand particles. It shows parts by weight based on 100 parts by weight of sand grains after subtracting calcium stearate added as an external lubricant during the production of the phenolic resin.

Here, the fusion point is determined by the C-Act of the JACT test method.
It measured by the method based on 1. The room temperature strength is determined by JI
It measured by the method based on SK-6910. further,
The charge amount is determined by rolling 10 g of resin-coated sand particles on an aluminum plate having a length of 30 cm, a tilt angle of 60 ° and a ground to frictionally charge, and an electrostatic charge meter (Kasuga Electric Co., Ltd., KQ-
431B) and the total charge was measured.

[0031]

[Table 1]

As is clear from Table 1, the resin-coated sand particles of Examples 1 to 4 in which white carbon having an antistatic effect is attached to the outer surface of the resin coating layer have a charge amount of 0.
20 to 0.50, indicating that the antistatic effect is greater than those of Comparative Examples 1 to 4 containing no white carbon. Also, the characteristics of the fusion point and the strength at room temperature do not decrease to a level that causes practical problems as compared with the case of Comparative Example 1 in which white carbon is not added.

When Examples 1 to 3 and Example 4 are compared, the antistatic effect of Examples 1 to 3 is higher than that of Example 4. This is because the blending amount of white carbon was
Although it is related to the fact that Example 4 is less than that of Examples 3 to 3, it is substantially related to the amount of white carbon adhering to the outer surface of the resin coating layer. That is, in Example 4, white carbon was added as a substitute for an external lubricant at the final stage of the production process of the novolak type phenolic resin so that most of the white carbon was attached to the surface of the phenolic resin. Is applied to sand particles to produce resin-coated sand particles. For this reason, although the white carbon is adhered to the outer surface of the resin coating layer, the amount of the adhered carbon is about half or less of the amount of the actually blended white carbon. In contrast, in Examples 1 to 3, white carbon was added at the final stage of the process of producing resin-coated sand particles. Specifically, when the novolak type phenol resin is coated on the sand particles, white carbon is added after the novolak type phenol resin is added to the heated sand particles and stirred. For this reason, almost all of the compounded white carbon adheres to the outer surface of the resin coating layer. Therefore, the antistatic effect can be exhibited more effectively. From the above, it is necessary to reduce the amount of white carbon, which may decrease the strength if the amount is too large, and to effectively exert the antistatic effect while suppressing the amount of white carbon to be applied. In order to increase the amount of white carbon that adheres to the outer surface of the layer and adhere to the outer surface, rather than adding white carbon at the final stage of the novolak-type phenol resin production process, the novolak-type phenol resin is converted into sand particles. It is more preferable to add white carbon at the final stage of coating. However, when white carbon is added during the production process of the novolak-type phenol resin, it is advantageous in that it is not necessary to modify the conventional process at all during the production process of the resin-coated sand particles.

On the other hand, in Comparative Example 1 in which only calcium stearate was added, the strength at room temperature was high, but the antistatic effect was small. In Comparative Example 3 using the novolak type phenol resin C having a high content of free phenol, the value of the charge amount was relatively small, but the phenol odor was strong. Furthermore, in Comparative Example 4 using novolak-type phenol resin D to which benzoic acid was added, the value of the charge amount was relatively small, but the pungent odor was strong.

Therefore, even when the novolak type phenolic resin A or B having a low free phenol content is used in order to improve the working environment in mold making, white carbon is adhered to the surface of the resin coating layer, A large antistatic effect can be exhibited without significantly lowering the properties of the fusion point and the room temperature strength.

[0036]

As described above in detail, the resin-coated sand particles for shell mold of the present invention exhibit a large antistatic effect due to the adhesion of white carbon to the surface of the resin coating layer. Using a novolak-type phenol resin having a small content, the working environment in mold making can be improved, and the inconvenience caused by static electricity during transfer can be effectively eliminated.

Further, white carbon is relatively inexpensive,
Since the addition to the resin coating layer is easy, the resin-coated sand particles of the present invention can be easily produced at low cost. Further, the antistatic effect by the addition of white carbon does not decrease with long-term storage, and is exhibited even under low humidity.

Claims (2)

[Claims] 1. A resin-coated sand particle comprising a sand particle and a resin coating layer made of a thermosetting resin coated on the surface of the sand particle, wherein white carbon is attached to the surface of the resin coating layer. Resin-coated sand particles for shell molds. 2. The resin-coated sand particles for a shell mold according to claim 1, wherein the blending amount of the white carbon is 0.005 to 0.2 parts by weight based on 100 parts by weight of the sand particles.