JPH0829396B2 - Method for manufacturing filter for casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for manufacturing a filter for castings which is inexpensive and has excellent filtration efficiency.

(Prior Art and Problems Thereof) When casting a molten metal into a mold, a filter is set on a runner to remove solid foreign matters such as slabs and oxides. In recent years, a technology has been developed in which a high silicate glass fiber woven fabric, that is, a fabric made of high-purity silica glass long fibers as a woven fabric is used as a filter. Adsorption, removal of minute solids by chemical reaction, and adsorption / separation of dissolved foreign substances such as oxides, sulfides, nitrides, phosphides, or dissolved gas are effectively performed, and the quality of castings is greatly improved. It turned out to do.

The high-purity silica glass long-fiber woven fabric is lighter and thinner than the conventional refractory mesh filter or honeycomb filter, and has a large filtration area and a large adsorption surface area. A material having a high heat resistance and a silica purity of 97% or more can withstand a high heat of 1700 ° C. for a short time, and has improved surface activity, and is suitable as a casting filter.

However, since it is a woven fabric, it has no rigidity, and since it is a high-purity silica material, its strength as a fiber is insufficient, and it must withstand the initial dynamic pressure of the molten metal and must be reinforced for fixing.

Therefore, as an improvement measure, it has been proposed to impregnate and reinforce with a phenol resin having high heat resistance. The phenolic resin used in the reinforcement with the phenolic resin is
It is roughly classified into novolac prepared by condensation reaction of phenols and aldehydes under acidic catalyst and resole prepared by condensation reaction under alkaline catalyst.

Novolac is generally a solid at room temperature and has high condensation (▲
▼ = 600 to 1500, ▲ ▼ = 1000 to 5000), high melting point (100
~ 150 ℃), it is possible to prepare those with a small amount of unreacted monomer remaining, but it is necessary to use hexamethylenetetramine in combination for thermosetting, and to contain nitrogen which causes gas defects in the casting, In addition, there are drawbacks such as poor solubility of hexamine in the solutionization for reinforcing the impregnation into the silica glass woven cloth, and a problem in storage stability after solutionization.

On the other hand, resol is a thermosetting type and can be easily concentrated and solubilized, but its molecular weight is small (▲ ▼ = 500max, ▲
▼ = 3000max), it is difficult to remove unreacted monomer, and 5% or more of the monomer is contained in the resin, so it is necessary to consider odor and work hygiene. Also, the softening point cannot be increased.

From the above, as the phenolic resin used for reinforcing the high-purity silica glass long-fiber woven fabric, resol is particularly desirable from the viewpoint of heat resistance of the cured product, but on the contrary, it forms carbides and impairs the surface activity of silica glass. There is a fear.

(Problems to be Solved by the Invention) The present inventors have made investigations to solve the problems caused by the phenol resin in the reinforcement of the above-mentioned high-purity silica glass long fiber woven fabric as a filter material for castings.

That is, the present inventors demand that the reinforcing binder have the following properties: 1) Folding resistance and thermal rigidity that can withstand the initial dynamic pressure of 10 to 100 kg of molten metal (approximately the size of one casting).

2) At the same time when the molten metal pressure changes to static pressure, the thermal decomposition of the reinforcing binder proceeds promptly to develop the activity of the silica glass surface. That is, at a pouring temperature of 1400 to 1750 ° C, it should decompose promptly and do not cause residual charcoal (do not form carbide on the silica glass surface).

3) The decomposition of the binder does not adversely affect the molten metal and the silica glass surface. That is, it is desirable that the resin binder does not contain components other than C, H, and O such as alkali metal, nitrogen, and sulfur content. Also, do not generate combustion or black smoke as much as possible when disassembling.

4) The temperature around the filter rises (max200) until the molten metal passes through and solidifies in the filter periphery that is held in the sand mold without contacting the molten metal.
), Yet maintain sufficient rigidity.

As a result of earnest research to develop a low cost product satisfying the above conditions, it was found that a novolac / resole mixed type phenol resin is most suitable as a reinforcing binder, and the present invention has been completed.

[Structure of Invention]

(Means for Solving the Problems) The present invention will be summarized. The present invention is characterized by treating a high silicic acid glass woven fabric filter for casting with a novolac / resole mixed type phenol resin as a reinforcing agent. An object of the present invention is to provide a method for producing a high silicate glass woven fabric filter for casting.

 Hereinafter, the configuration of the present invention will be described in detail.

Phenolic resin as a reinforcing agent used in the present invention,
It is prepared by subjecting phenols and aldehydes to condensation reaction. Phenols as raw materials are not particularly limited, but phenol, cresol, bisphenol A and the like, and fractionated tar acids containing phenols and the like can also be used. Of these, phenol, which is the cheapest in terms of cost and has stable quality, is preferable. Similarly, the aldehydes are not particularly limited, and formaldehyde, acetaldehyde, furfural and the like are used. Of these, formaldehyde is the cheapest and formalin as an aqueous solution is preferable.

It is desirable that the phenol resin has both thermal rigidity after curing and quick thermal decomposability, and a solution of a mixture of high molecular weight novolac and low molecular weight resole is suitable.

As a desirable novolac, ▲ ▼ = 400 or more, ▲
▼ = 1000 or more, softening point of 100 ° C. or more, and the less unreacted monomer is desirable. As a catalyst for the preparation of novolac, an organic carboxylic acid system, which rarely remains in the resin, is preferable, but purification by washing, extraction, etc. after resinification is also one method. As a desirable resole, a binding molar ratio (formaldehyde / phenol binding molar ratio) of 1.0 to 1.5 by NMR analysis, a polystyrene-converted molecular weight of HGPC ▲ ▼ = 200 to 300, and ▲ ▼ = 400 to 800 are preferable.
If the amount is less than this range, the amount of unreacted phenols increases in the resin liquid, which causes problems of odor and chemical damage, and further lowers thermal rigidity. In the opposite case, the amount of unreacted formalin is large, the odor is strong, and the impregnating workability deteriorates. It is desirable to use a volatile amine containing no active hydrogen, such as triethylamine, as a catalyst for the preparation of the resol and remove it by concentration distillation, or to carry out a condensation reaction using an alkaline earth hydroxide and then perform neutralization filtration. Alkali metals impair the heat resistance and activity of silica glass, and ammonia and the like are not preferable because they are likely to bond between resins and cause gas defects during pouring.

The mixing ratio (weight ratio) of the novolac and the resole is 8: 2.
~ 4: 6 is desirable, and 6: 4 is optimal. It was surprisingly found that by using a mixture of novolac and resol, both high thermal rigidity and thermal decomposability of the filter can be achieved. The amount of resin required for reinforcement is preferably 15 to 40% by weight, and the optimum amount is 25 to 30% by weight. When the amount of resin is small, the effect of reinforcement is poor, and when it is too large, the activity of the filter surface due to residual carbon may be impaired.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples. Unless otherwise specified, all components used are on a weight basis.

Example 1 A formaldehyde / phenol molar ratio of 0.85 and 0.3% of oxalic acid as a catalyst to phenol were added, and the mixture was refluxed 1
The reaction was carried out at 00 ° C for 3 hours. Next, under normal pressure or reduced pressure, 18
Distill to 0 ℃ to remove water and unreacted phenols and purify, softening point 125 ℃, ▲ ▼ = 900, ▲ ▼ = 350
A novolac resin having an unreacted phenol content of 0.1% or less was obtained. This was dissolved in methanol to prepare a varnish having a nonvolatile content of 50%. (Varnish A).

Next, a formaldehyde / phenol molar ratio of 1.3,
Add 2% of calcium hydroxide to phenol as a catalyst, react at 80 ℃ for 2 hours, blow carbon dioxide gas to pH = 7.5
Neutralized. Further vacuum distillation up to 700mmHg, 80 ℃,
Immediately, methanol was added to adjust the nonvolatile content to 60%, and the neutralized salt was filtered to obtain a varnish. (Varnish B).

This varnish had ▲ ▼ = 300, ▲ ▼ = 1000, and unreacted phenol was 3% / Solid.

As shown in Table 1, the varnish A and the varnish B were used alone or in combination to prepare a high-purity silica glass woven fabric substrate with a solid resin content.
Impregnate and adhere to 25%, dry, and then 150 ℃ 0.5-2
It was cured for a time and subjected to performance evaluation. 150 as curing condition
If the temperature is less than 30 minutes, the resin will not cure sufficiently and will be deformed during pouring. Further, at 150 ° C for 2 hours or more, the cured product becomes brittle and may be damaged by the dynamic pressure of the molten metal.

Comparative Example-1 Formaldehyde / phenol molar ratio 1.1 As catalyst, 25% ammonia water was added to phenol at 4%,
The mixture was reacted at ℃ for 5 hours, distilled under reduced pressure to 700 mmHg, 80 ℃, and added with methanol to adjust the nonvolatile content to 60%. Further, heating and refluxing were continued to obtain high molecular weight resol of ▲ ▼ = 650, ▲ ▼ = 3500. 7% of unreacted phenol remained per resin solid content. A high purity silica glass woven fabric was impregnated and heat treated in the same manner as in Example 1 to prepare a filter, but a phenol odor was strongly felt.

Comparative Example-2 Hexamethylenetetramine previously dispersed and dissolved in water was added to the novolak varnish of Example 1 in an amount of 3% based on the resin solid content.
In addition, in the same manner as in Example 1, a high-purity silica glass woven fabric was impregnated and heat-treated to prepare a filter. Table 1 shows the results of performance tests of various filter materials prepared as described above.

(Note) Base material: High-purity silica glass woven fabric (manufactured by Nippon Inorganic Fiber Co., Ltd., BCM-940) Binder amount: 25% / Solid, Curing condition: 150 ° C, 1Hr Flame resistance: Test piece width 17m / m, UL.9 cut to a length of 150 m / m
Tested by 4V-O method and expressed by afterflame time.

Rigidity: Test piece cut to 17m / m width, center of Span 200mm
A load of 10 g is applied and the amount of strain is expressed.

Folding resistance: The test piece in the preceding paragraph was repeatedly bent 180 ° on one side, and the number of times of reciprocal repeated bending until breakage was displayed.

Residual coal: The filter was kept at a predetermined temperature for a predetermined time in a reducing atmosphere furnace, and the amount of adhered carbides was measured.

Pouring test: 1400 ° C. 70 kg of cast iron was poured.

Thermal rigidity: Since the reinforcing cloth used in the test cannot be measured thinly, it was judged in the state of the cloth by the pouring test.

〔The invention's effect〕

It was prepared by impregnation with a novolac / resole resin as a reinforcing agent. The high silicate glass woven fabric filter material for casting according to the present invention has a flame resistance, as compared with a case where a novolac or resol type phenol resin is used alone.
Not only are properties such as rigidity and folding endurance well balanced, but they are also excellent in high thermal rigidity and thermal decomposition properties (residual coal properties) in the high temperature environment during pouring.

(Reference: Foundry Technical Information, '85 -No. 3 (60 years 8
Moon))

Claims (2)

[Claims] 1. A method for producing a high silicate glass woven fabric filter for casting, which comprises treating the high silicate glass woven fabric filter for casting with a reinforcing agent composed of a novolac / resole mixed phenolic resin. 2. A method for producing a high silicate glass woven fabric filter for casting according to claim 1, wherein the mixing ratio of the novolac and the resol type phenol resin is 8: 2 to 4: 6. .