JPS6163334A - Production of resin coated sand for shell - Google Patents

Abstract

PURPOSE:To prevent the crack of a shell mold without making poor the casting surface of a casting by coating a coating layer consisting of a metallic powder- contg. phenolic resin on the surface of molding sand. CONSTITUTION:Either of a novolak type phenolic resin or resol type phenolic resin is usable for the phenolic resin as a binder. The metallic powder is, for example, Al, Mg, etc. which have high affinity to oxygen and are easily oxidized or the alloy of such metals, and 1 or >=2 kinds thereof are used in combination. The phenolic resin and the metallic powder are added and mixed to and with the molding sand such as silica sand to coat the coating layer of the phenolic resin binder contg. the metallic powder on the sand. The resin coated sand is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a method for producing resin-coated sand for shell molds.

[Background Art 1 A shell mold is obtained by forming molding sand such as silica sand by bonding it with a caking-resistant resin. This shell mold is widely used because it has excellent characteristics such as smooth casting surface and good dimensional accuracy. The binder for this shell mold generally contains 7 ethers and aldehydes in a molar ratio of 0.
The molar ratio of phenols and aldehydes is adjusted to 1:1 to 3 and reacted with an acidic catalyst. A solid resol type 7 el resin is used, and in the novolac type 7 el tδ1 resin, hexamethylenetetramine is blended as a curing agent, and resol type 7 el resin is used.
E/R resin is used as it is, mixed with heated molding sand to create resin coated sand coated with NM of phenolic resin binder, and this resin coated sand is sprinkled on the heated mold. A shell mold is created by melting and hardening the binder.

However, shell molds using phenolic resin as a binder generally have a problem in that cracks are likely to occur during pouring. This is thought to be due to the rapid thermal expansion of the resin component or the sand component due to the high temperature during pouring. Therefore, in order to solve this problem, we added a certain substance to the phenolic resin or resin-coated sand to make the shell mold flexible and to reduce the coefficient of thermal expansion of the shell mold, thereby preventing the occurrence of cracks. Attempts are being made to prevent this. This Kunonyon material is more bisphenol A and 5 oil based than before. J(
Although these substances have some effect in reducing the coefficient of thermal expansion of the shell solid and preventing the occurrence of cracks, they cause thermal decomposition and volatilization during pouring, resulting in bad odors. The drawback is that the mold may disintegrate easily after pouring. This method is effective when casting aluminum or cast iron, but when casting stainless steel or high manganese steel, which have high pouring temperatures, cracks inevitably occur due to sudden thermal expansion during pouring. Moreover, the above-mentioned decomposition and volatilization may occur suddenly and dangerously due to rapid heating.
It also has the disadvantage that decomposed gas is generated due to oxidation of the lubricating oil itself, and it causes defects in the casting surface of cast products such as r-shaped rods, -mi I, and orange nobeer. Also, the thermal expansion of the shell mold is i1! < In order to obtain IQ+, modifying the 7-er/7-el jH fat with bisphenol 8, residual liquid, or alkyl 7-er/-, increasing the crosslink density, or mixing iron oxide, etc. It has been tried and tested, and although it has some effect, there are limits and it is not very effective when used with hot water.
I can't hold it. In addition, if a 7 elastomer (5) is used, the hot strength of the shell mold will be lowered and slag will occur due to insufficient strength, or if There is also the disadvantage that a large amount of soot is generated due to carbonization when the fat is used, which deteriorates the casting surface.

In order to improve this casting surface, since the beginning of the ttt, a mold coating agent containing metal, norcon, aluminum oxide powder, etc. has been applied to the surface of the shell mold in order to improve surface accuracy and strength. There is some glue on the coating agent! Because it contains fat, the coefficient of thermal expansion increases when the shell mold comes into contact with hot water, making it more likely to cause scratches. Since it is commonly used, it has the disadvantage that it requires complicated work such as re-dipping and drying.

As mentioned above, in the past, it has not yet been possible to prevent cracks in shell molds without impairing the casting surface of castings.

[Objective of the Invention 1 In view of the above points, the present invention has been achieved by 'A':! A major object of the present invention is to provide a method for producing resin-coated sand for shell molds that can prevent cracks in shell molds without deteriorating the casting surface of castings.

[Disclosure of the Invention] According to the method for producing resin-coated sand for shell molds according to the present invention, resin-coated sand for shell molds is prepared by adding and mixing phenol (3) binder and metal powder to molding sand. The present invention is characterized by overturning VL currants on the surface of the sand using a phenolic oil containing a fractional powder.The present invention will be described in detail below.

As a 727-l resin as a binder, either borac type phenol O (fat) or resol type phenol (3) can be used. Easily oxidized, IN Ebohachi 1, MK, Si, Fe, Ni, Cr, T1, Nb
, V, or alloys of these metals such as A I-M
Among them, one or more of these can be used in combination.The particle size of the 4tM powder should be a uniform mixing layer and a large surface area for oxidation. The thickness is preferably 10 μm or less from the viewpoint of making it easier.

Then, the 7-el resin and the 8-genus powder were mixed into a 0-type bar 1 such as silica sand.
7 containing metal powder by adding it to the sand of 1lii
1MEL (resin-coated sand is obtained by coating sand with a layer of fat caking).

Phenol TL fat fl with metal powder contained in sand
Coating the '12+'+cut can be carried out by a dry hot coating method, a cold coating method, a semi-hot coating method, a powder solvent method, etc. The dry hot coating method uses metal powder and solid 7 el/tjl.
Add the oil to sand heated to 130 to 160°C and mix, then heat with the sand to melt the solid phenol (the fat is melted and the metal powder is mixed and melted. Wet the surface of the sand with phenol + l fat and apply metal powder-containing 7-el a (thin wave m M) 3
This mixture is then cooled while maintaining the mixture to obtain granular and smooth resin-coated sand. In the cold coating method, phenolic resin is dissolved in an H agent (such as methanol) to form a liquid, and this and 4R powder are added to sand and mixed, and the solvent is evaporated to obtain resin-coated sand. It is. In the semi-hot foot method, resin-coated sand is obtained by adding and mixing liquid 7-el resin dissolved in the above-mentioned solvent and metal powder to sand heated to 50 to 90°C. In the powder solvent method, solid phenol (2) is crushed, Hmr and metal powder are added to sand [7], and then a 78 agent such as methanol is added, and this is mixed to form a resin. Coated sand can be obtained. Although it is possible to obtain granular and smooth Lenoir Co-1 sand by the method of IzujI, 4!, etc.
1. A dry hot coating method is preferred. sand and 7
The proportion of 11L of 1Nol Pδ1 fat and metal powder varies depending on the required performance of the shell mold, but in general, 100 parts by weight of sand is mixed with 11L of phenol ljl.
Approximately 1 to 4 parts by weight of fat in terms of resin solid content, and 0 parts of metal powder.
．． The amount is preferably about 0.01 to 1 part by weight. Further, during this mixing, if necessary, a silane coupling agent may be added to make the sand or metal powder compatible with the phenol (M fat caking property).

The resin-coated sand thus dried is sprinkled or filled into a heated mold according to a conventional method, and the phenol resin is melted and hardened with the fat binder. It is molded into a shell mold by bonding sand by caking and cutting. Since this product contains metal powder, the low coefficient of thermal expansion of the metal powder suppresses thermal expansion during pouring of the shell mold and prevents cracks from forming in the shell mold. In addition, metal powder easily reacts with oxygen and becomes oxidized, and phenolic resin caking is oxidized during pouring and moderate heating.
This can be prevented by the consumption of oxygen by the metal powder.

Next, the present invention will be explained with reference to two embodiments.

7-borak type fer/- fat with a softening point of 90°C 1300g
into a Yotsuro flask and add 7 fl of methanol to it.
Q: I melted it well by adding more and more. The viscosity of the resulting 7-borane type 7-el resin varnish at 25°C was 8 poise.

On the other hand, put 30 kg of silica sand heated to 80°C into a whirl mixer, add 75 g of metal aluminum powder with a particle size of 5 μm, open for 30 seconds. 1075g of hexamethylenetetramine 11+1. A dispersed product was further added, and the mixture was kneaded until the sand grains disintegrated, which was then discharged and subjected to air tanning to obtain resin-coated sand.

′! 11Q-2- + 4fl 30kg of 7-ratari silica sand heated to ℃ was charged into a whirl mixer, softened], χ90℃/
Simultaneously add 700 g of Borac type 7enol + 61 fat and 5 g of the same metal aluminum powder as in Example 1;
31) Excerpt 1: After 11 mixing, hexamethylenthyl Ylamin I+ (+) was dissolved in 300H water for 71 minutes and kneaded until the sand grains collapsed.Next, this was further mixed with stearic acid calcium. Add 1115g, 3
() After one practice of Shakai City, it was taken out and aeration was performed to obtain resin-coated sand.

')', Shoulder f clause-L Practical Example 2; Resol type phenol with a softening point of 85°C instead of Kero/Borac type 7 el resin and metal aluminum powder! Resin-coated sand was rolled in the same manner as in Example 2, except that 700 g of No. 31 fat and 35 μm of metal silicon powder with a particle size of 6 μm were used, and hexamethylenetetramine was not used.

A solid resol type 7 elastomer with a softening point of 78°C (fat 13
Take nOg into a Yotsuro flask and add 70% methanol to it.
0.0 was added and the mixture was thoroughly dissolved.

This resol-type 71-norr JIFm face was used instead of the 7-volac type 7E/-le resin face of Example 1,
Resin-coated sand was obtained in the same manner as in Example 1 except for the case where hexamethylenetetramine was not used.

110 = Resin-coated sand was obtained in the same manner as in Example 2, except that the metal aluminum powder was not used.

Resin coated sand () was made in the same manner as in Example 3, except that the metal silicon powder was not used.

Various tests P and M were conducted on the resin-coated sand obtained in Examples 1 to 4 and 1 Comparative Example 1.2.9↑, 1. The Song Dynasty is shown in the table below. In the following table, the fusion point (°C) is based on 1△C' test method 5M-1, and the room temperature bending strength (K/cm2) is based on JACT test method C-1. Rate (%) 100 in N277 based on ACT test method 5M-7 to 11
(Each test was conducted at a measurement temperature of 1"C.

The bending strength (KF!/cm2) was determined by using a test piece prepared according to the JA CT test method 5M-1.
It was placed in an electric furnace set at 10°C, treated for 1 minute, and then measured for bending strength at 1°C. Oxidation resistance was measured using the JACT wiping test method 5M-7.
Test piece (20φX50+am) made using
+ +1 +1 (Set at 1'C), put them in an electric furnace and treat them for 5 minutes, then take them out, cool them, put them on a vibrating sieve and run them at FA for 1 minute, then measure the melons.
The weight percent of the residue was calculated using the following formula and evaluated.

ffl height after treatment j'1i/height before treatment X100 (
%) The casting surface is determined by resin coated sand.
1 inner diameter 1 tl Oφ, quotient 1n (1+*
Create a crucible with a wall thickness of 20+ws, and add 1650 m to this.
This was done by visually observing the casting surface of the finished casting after cooling it by pouring hot water at ℃.

◎: #lX'i Sound is good 0: Good b (△: As a result of the approval table, the thermal expansion coefficient of each example is 2. The coefficient of thermal expansion is smaller than that of the comparative example, and the shell mold has 1- cracks. It is confirmed that there is an effect of preventing the oxidation, and it is also confirmed that the products of each example have excellent oxidation resistance and can be cast into castings with good casting surfaces.

I Effect of the Invention 1 As mentioned above, according to the present invention, 7㎱/-L (
(b) By adding fat and metal powder and combining them for 1rL, the surface of the molding sand was coated with a layer of indium containing metal powder-containing 7-el resin. The JIt powder has a high thermal expansion coefficient that reduces the thermal expansion during pouring into the shell mold, and can prevent cracks from forming in the shell mold. Something that is oxidized,
Oxidation of the binder (7 er/-3) during sudden addition during pouring can be prevented by oxygen being consumed by the metal powder, and 71/- er resin. It is essential to prevent the casting surface of the casting from becoming defective due to the generation of large particles due to oxidative decomposition.

Claims (1)

[Claims] (1) A resin-coated product for shell molds characterized by adding and mixing phenolic resin and metal powder to molding sand to coat the surface of the molding sand with a coating layer of phenolic resin containing metal powder. How to make sand.