JPS60145237A - Binder composition for molding sand - Google Patents

Abstract

PURPOSE:To provide a binder composition for molding sand having good warm strength and collapsing property by adding a specific amt. of an ammonium phosphate compd. to a mixture composed of a resol phenolic resin and melamine resin at a specific ratio. CONSTITUTION:An ammonium phosphate compd. is added at 1-30pts.wt. to 100pts.wt. a mixture composed by mixing 10-90pts.wt. a resol phenolic resin and 90-10pts.wt. a melamine resin. The resol phenolic resin is prepd. by adding excessively formalin to phenol and bringing the same into reaction in the presence of an alkali catalyst. The softening point thereof is made about >=60 deg.C. The melamine resin refers to the melamine prepd. by providing a methylol group to the molecule by the reaction of melamine and formalin or the oligomer which is initial resultant product of condensation. Ammonium primary phosphate, ammonium polyphosphate, etc. are used for the ammonium phosphate compd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Summary Related to the Invention) The present invention relates to a caking composition for foundry sand used for manufacturing molds or cores.

(Prior art) Regarding conventional molds and cores, regardless of the type of alloy, as a mold binder, for example, "Plastic Technology Complete Book Vol. 15 Phenol Resin" published by C Co., Ltd. Kogyo Choshokukai, No. 180
As described on pages 1 to 185, the shell mold method using phenol resin is widely used as a molding method. In particular, cores are mostly manufactured by shell molding and are widely used because of their excellent productivity and dimensional accuracy. However, in this conventional shell molding method, a part of the phenolic resin undergoes a thermal change due to the heat of the molten metal, changing into an extremely strong graphite structure, resulting in extremely high residual strength of the core, which is difficult to maintain after casting. , each casting is heated at a high temperature of about 500°C for a long period of 5 to 10 hours, called ``sand baking'', to burn off and discharge the residual binder, which has a graphite structure. Consumes energy.

On the other hand, based on research results showing that the formation of graphite structure is due to benzene rings in phenolic resins, a search is being made for thermosetting resins that do not contain benzene rings. For example, JP-A-5'6-59560 discloses a resin using unsaturated polyester. However, when thermosetting resins that do not contain benzene rings are used, their heat resistance is poor, resulting in low strength when heated, and the resin's thermal decomposition properties are too good, making it easy for gas defects to form in the mold. ,
The mold yield is extremely poor.

(Disclosure of the Invention) As a result of intensive research focusing on the above points, the inventor found that resol phenol resin has a large amount of benzene rings in its molecules, so it has high strength when heated, but when heated. Melamine resin tends to form a graphite structure and has poor disintegration properties.On the other hand, melamine resin has a triazine ring in its molecules, so rapid thermal decomposition occurs at around 880℃, so it has excellent disintegration properties but poor heat resistance. is inferior. However, both resol phenol resin and melamine resin have many methylol groups in the molecule and are hardened by heating condensation reaction, so their reactivity is extremely high. By reacting sol phenol resin and melamine resin, a benzene ring with strong heat resistance and a triazine ring with excellent thermal decomposition properties are introduced into the molecule, so the blended resin of sol phenol resin and melamine resin has strong strength when heated. Furthermore, when a specific amount of ammonium phosphate compound was added as a disintegration aid to this blended resin, the disintegration properties were further improved without reducing the strength at elevated temperatures. It was discovered that a caking composition for foundry sand can be obtained, and the present invention was accomplished.

In the above blended resin of resol phenol resin and melamine resin, if the resol phenol resin is more than 90% by weight, the disintegration properties will be extremely poor, and the melamine resin will be 90% by weight.
If the amount exceeds 0% by weight, the hot strength tends to decrease dramatically, so to make a resin binder that is easily disintegrated and has excellent hot strength, it is necessary to add 10 to 90 parts by weight of the resol phenol resin. 90 to 10 parts by weight of melamine resin must be blended.

Further, the disintegration properties of the ammonium phosphate compound improve as the amount is added, but if the amount is too large, a large amount of decomposed gas is generated, which may cause the core to break. In addition, since it may be a cause of inhibiting the curing of the blend resin during core production, the amount of ammonium phosphate compound to be added is preferably 1.0 to 80 parts by weight per 100 parts by weight of the blend resin. Considering the balance between 5.0 and 15 fi, it was confirmed that 5.0 to 15 fi was more preferable.

Therefore, the caking composition for foundry sand of the present invention contains 10 to 90 parts by weight of resol phenol resin (I) and melamine resin (B
)" is characterized in that 1 to 80 parts by weight of ammonium phosphate compound (C) is added to 100 parts by weight of resin mixed with 90 to 10 parts by weight.

The resol phenol resin (A) used in this invention is made by adding an excess of formalin to phenol and reacting it under an alkaline catalyst.
The softening point of A) is preferably 60°C or higher.

Next, the melamine resin (B) used in this invention refers to melamine with a methylol group added to the molecule by the reaction of melamine and formalin, or an oligomer that is an initial condensation product thereof, and the resin-coated sand is In order to prevent blocking, the softening point of these melamine resins (B) is 60.
℃ or higher is preferable.

Also, the ammonium phosphate compound used in this invention (
C) refers to, for example, primary ammonium phosphate, secondary ammonium phosphate, tertiary ammonium phosphate, and ammonium polyphosphate. Among these ammonium phosphate compounds, ammonium polyphosphate is particularly preferable because it has a large amount of ammonium bound in its molecule, so it generates a large amount of ammonia gas with a small amount of addition, which improves the disintegration property. .

Hereinafter, the action of the ammonium phosphate compound (C) in the caking composition for foundry sand of the present invention will be explained using primary ammonium phosphate as an example.

Ammonium monophosphate NH, .H, PO, begins to rapidly thermally decompose at around 800°C, generating ammonia gas, and then successively generating water before decomposing into phosphorus pentoxide.

Therefore, the mold binder made by adding monoammonium phosphate to the blended resin of resol phenol 4iJ resin and melamine resin has a low strength at high temperatures during core production (20θ to 260°C) due to the heat resistance of the blended resin. The molding yield is also good. In addition, after pouring metal hot water, the poured hot water cools down and heats the core, but generally the core has poor heat conductivity, and during pouring, the inside of the mold is removed except for a thin layer that comes into contact with the hot metal. Because the temperature of the hot water is not sufficiently transmitted to the inside of the mold, it is strong enough to maintain its shape even as the mold changes. After that, as the hot water continues to cool, the temperature inside the mold rises, and when it reaches around 800°C, the primary ammonium decomposes, generating ammonia or water, which causes cracks in the binder layer due to gas pressure. In addition to reducing strength, the blend resin itself also begins to thermally decompose.
The strength of the core decreases and the collapsibility improves significantly. At this point, the hot water has solidified and has sufficient strength by itself, so even if the strength of the core decreases, the shape of the solidified hot water will not be affected in any way.

From the above, the caking composition for foundry sand in which an ammonium phosphate compound is added to the blended resin has extremely good strength and disintegration properties when heated, has no gas defects, has a high molding yield, and has high sand discharge properties.

The caking composition for foundry sand of the present invention may contain auxiliary agents, inorganic fillers other than silica sand, etc. for the purpose of improving the slipperiness of the resin-coated sand, as long as they do not impede the purpose of the present invention. is also possible.

When producing Resin #1 sand using the caking composition for foundry sand of this invention, the caking agent of this invention is usually added to and mixed with sufficiently preheated silica sand, and the mixture is cooled and applied to the sand surface. A method is used in which the binder is fused, but there is also a method in which the binder of the present invention is dissolved or dispersed in a solvent, water, etc., mixed with silica sand, and dried.

The resin-covered sand obtained by the above method is usually 150°
It is possible to pour the mixture into a mold heated to a temperature above C, preferably 180-250''C, and then remove it from the mold after 80 seconds to 8 minutes to obtain a core.

(Examples of the Invention) Next, the present invention will be explained with reference to Examples, Comparative Examples, and Test Examples.

Example l 4 kg of No. 6 silica sand preheated to Q 00 'C was put into a speed mixer, and when the temperature reached 1 'I O'C, resol phenol resin 0Gun Jo Kagaku Co., Ltd., product name °Regitop was added. , softening point 90°C, OH equivalent 11.0) 72I
and melamine resin (Nippon Carbide 4 stocks) H1 product name
Nikaresin 5805, softening point 110°C, OH equivalent 11
0) Pour the resin mixed with 8.9, and add 0.8 g of primary ammonium phosphate at 180°C, 4.9, 8.9
．． After adding , , 16.9 or 24.9 g, in each case when the sand grains started to block, 4 g of calcium stearate was added, giving five types of resin-coated sand.

Similarly, resol phenol resin 64.17゜5
6.9.48, 9, 40, 9. '8! II, 9, 24J
7, 16g, 8g, melamine resin 16, 9, 24g, 82.9, 40.9°, 48.9.56g, 64g, respectively as shown in Table 1. ! Eight types of resins were prepared by mixing i' and 72 Jil, and monoammonium phosphate was added to these resins at 0.89, 49, and 8.9, respectively.
.

By adding 16g and 24g, 40 types of resin-coated sand were created.

Comparative Example 1 Eighteen types of resin orange sand were prepared, the only difference being that in Example 1, no ammonium monophosphate was added and 82.9% of ammonium monophosphate was added.

Example 2 In Example 1, ammonium polyphosphate (manufactured by Monsando, trade name PH) was used instead of ammonium monophosphate.
O8OMEOK F/80) It1 other than Woyo Ita
41jlK and 45 types of resin coatings were created.

Comparative Example 2 Eighteen types of resin-coated sand were prepared in the same manner as in Comparative Example 1 except that ammonium polyphosphate was used instead of ammonium monophosphate.

Test Example l The resin-coated sand prepared in Examples 1-2 and Comparative Examples 1-2 was immediately fired at 280'C for 70 seconds to create a test piece, and at the firing temperature, the resin-coated sand was tested using a shell sand high temperature tensile tester. A strength test was conducted.

The high temperature tensile strength measurement results are shown in the upper row of Table 1 for Example 1 and Comparative Example 1, and in the upper row of Table 2 for Example 2 and Comparative Example 2.

Test Example 2 Resin-coated sand of Examples 1-2 and Comparative Examples 1-4 was heated at 200°C.
Pour into a mold heated to 280℃ and hold for 5 minutes.
A test piece of 0x50x20 was prepared.

This test piece was wrapped in aluminum foil with dimensions of 170 x 125s+i and placed in an oven at 500°C, and after 21.5 minutes it was taken out of the oven and cooled. This heat treatment is actually carried out from resin-coated sand@
This heating condition corresponds to the state in which the mold is normally the least likely to disintegrate.

The thus heat-treated test pieces were passed through a rotor-tub type sieve and the relationship between the rotor-tub time and the amount of sand falling was measured using a machine.

Here, the amount of sand falling is 12, which covers only the sand that passed through the wire mesh of mesh 4. The measurement results are shown in the lower part of Table 1 for Example 1 and Comparative Example 1, and in the lower part of Table 2 for Example z1 and Comparative Example 2.

The machine for the rotary tube type sieve mentioned here is JISZ2.
The test piece was placed in a 4-mesh sieve using a machine used in the particle size test method No. 602, and sieved for 8 minutes with a saucer placed underneath. As a result, the collapsibility was defined as the weight percent of the sand that fell into the tray relative to the weight of the test piece.

Table 1 Table 2 (Effects of the Invention) As has been explained and clarified above, the caking composition for foundry sand of the present invention includes an ammonium phosphate compound added to the blend resin of resol phenol resin and melamine resin to aid in disintegration. By adding it as an agent, it has extremely good strength at high temperatures and crumbling properties, does not cause gas defects in the mold, has a high molding yield, and has extremely good sand drainage. It will be done.

Patent applicant: Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1 A caking composition for foundry sand characterized by adding 1 to 5 solid parts of an ammonium phosphate compound to 100 parts by weight of a mixture of 90 parts by weight of resol phenol resin 10S-90 and 90 to 10 parts by weight of melamine resin. thing.