JPH0428456B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to foundry sand for shell molds, and more particularly, to foundry sand made by using a compound (A) containing a urethane bond and an aromatic ring in the molecule together with a hardening agent as a sand binder. In particular, the present invention relates to foundry sand suitable for producing molds for castings whose pouring temperature is relatively low, about 700 to 800°C. When making castings of relatively low-temperature materials within the above-mentioned pouring temperature range, such as aluminum alloys,
Conventional shell mold cores have extremely poor disintegration properties when poured, and therefore require a lot of energy, labor and/or time, such as a special sand removal process. However, in view of the above-mentioned actual situation, the present inventors have developed a molding sand that has the same workability as conventional foundry sand for shell molds and is no inferior to conventional foundry sand for shell molds. We conducted extensive research with the aim of providing molding sand for shell molds that provides good properties and strength for castings, has good core collapse after pouring, and does not require a sand removal process even for aluminum alloy castings. As a result, they discovered that the above objective could be achieved by using a compound containing a specific atomic group called urethane bond in the molecule as a sand binder and coating the sand grains with it. He has completed his invention. That is, the present invention comprises a polyurethane (A) obtained from a phenol derivative having at least two hydroxyl groups and an isocyanate compound, a curing agent (B) consisting of hexamethylenetetramine or paraformaldehyde, and, if necessary, other thermosetting Foundry sand for shell molds obtained by coating sand grains with a resin or thermoplastic resin as a sand binder,
and the total weight of polyurethane (A) and curing agent (B) is equivalent to a grain of sand.
0.65 to 1.8 parts by weight per 100 parts by weight, hardening agent
The amount of (B) used is 15 per 100 parts by weight of polyurethane (A)
to 46 parts by weight, and polyuthalene (A) is 25 to 87% by weight in the sand binder. Here, suitable compounds as the above-mentioned urethane bond-containing compound (A) are:
It is obtained by reacting the phenol derivative (a-1) and the isocyanate compound (a-2), and first, the representative phenol derivative (a-1) is represented by the following formula. There are compounds like this.

【formula】

【formula】

【formula】

[Formula] or [However, n in the formula shall be zero or an integer from 1 to 20. ] Next, the isocyanate compound (a-2) includes all compounds having an isocyanate group at the end of the molecule, but in order to more effectively achieve the purpose of the present invention, at least Polyisocyanate compounds having two isocyanate groups are preferred, typical among which are hexamethylene diisocyanate, dicyclohexyl diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate or naphthalene diisocyanate,
or these polyisocyanate compounds and water,
Examples include polyisocyanate compounds obtained by reaction with amines or polyhydric alcohols. And such a urethane bond-containing compound (A)
These phenol derivatives (a-1) and isocyanate compounds (a
-2) should be selected so that the equivalent of the hydroxyl group in the derivative (a-1) far exceeds the equivalent of the isocyanate group in the compound (a-2). The conditions are no solvent,
Or, using a solvent that is not reactive with compound (a-2), (a-1) and (a-2) in the above-mentioned quantitative ratio.
Both compounds may be simply mixed together, or compound (a-2) may be added little by little to derivative (a-1), but in order to shorten the reaction time, it is recommended to It is effective to heat the mixture or to add a tertiary amine catalyst. However, if the amount of this catalyst added is too large or the reaction temperature is too high, side reactions may occur or gelation may occur, so special attention must be paid to this point. The compound (A) thus prepared is used as a sand binder in combination with a curing agent (B) consisting of hexamethylenetetramine or paraformaldehyde. The sand binder of the present invention hardens easily when heated to provide excellent foundry sand, but the core obtained using the foundry sand of the present invention is The reason for the good disintegration property is thought to be due to the mechanism in which the urethane bonding moiety in the compound (A), which is a sand binder, is decomposed by heat and reduces the sand binding effect. Therefore, the concentration of urethane bonds in the sand binder, that is, the urethane bond-containing compound (A)
The higher the concentration of the compound (A), the better the disintegration property is.Therefore, in the present invention, unless the compound (A) is present at least 20% by weight in the sand binder to coat the sand grains, the disintegration property is improved. It is not possible to obtain a sufficiently good foundry sand. The amount of sand binder used is polyurethane (A) and hardener.
The total weight of (B) is 0.6 to 1.8 per 100 parts by weight of sand grains.
Parts by weight. If the total weight of polyurethane (A) and curing agent (B) is less than the above range, the necessary mold strength will not be obtained, and if it is more than the above range, the collapsibility of the mold will deteriorate. The amount of curing agent (B) used is 15 to 46 parts by weight per 100 parts by weight of polyurethane (A). If the amount of curing agent (B) used is less than the above range, the curing speed of the mold will be slow and the necessary mold strength will not be obtained, while if it is more than the above range, the collapsibility of the mold will deteriorate. Among the various embodiments of the present invention as described above, particularly preferred embodiments from the viewpoint of economy, performance, and safety and hygiene are those having two or more hydroxyl groups, such as Resol Seal and bisphenol A, and A urethane bond-containing compound (A) is a reaction product of a phenol derivative (a-1) having 1 to 2 phenol nuclei and an isocyanate compound (a-2) with a low vapor pressure such as diphenylmethane diisocyanate. One method is to coat sand grains with a sand binder made of a mixture of a phenol resin and hexamethylenetetramine as a hardening agent. In obtaining the foundry sand of the present invention, the compound (A)
and curing agent (B) can be mixed in advance and the sand is coated with this mixture, or the sand is first coated with one of the components,
There is a method of further coating with the other component, and a method of coating with both components at the same time, but any method may be used. In obtaining the foundry sand of the present invention, the compound (A)
In order to coat the sand with the compound (A), it is best to adopt the so-called dry hot marling method, which involves kneading the compound (A) with hot sand and melting the compound (A) to coat the sand grains. There is a method of coating the sand, and a method of coating the sand by mixing a solution of the compound (A) with the sand and then evaporating the solvent. In the present invention, the compound (A) component and the curing agent (B) component, which can be involved in adhesion of sand grains after the mold is formed, are collectively referred to as a sand binder. Of course, when the binder consists of more components, foundry sand can be obtained by appropriately combining the various embodiments described above and coating the sand grains. Next, the present invention will be specifically explained with reference to Synthesis Examples, Examples, Comparative Examples, and Reference Examples, and unless otherwise specified, all parts and percentages are based on weight. The sand used in each example and comparative example has a SiO ₂ purity of 99% or more and is AFS (American Foundry Men's Society) sand.
This refers to silica sand with a grain size index of 60±3. Synthesis Example 1 115 parts of bisphenol A, 35 parts of tolylene diisocyanate, and 150 parts of ethyl acetate were stirred and mixed in a nitrogen stream, and reacted for 8 hours while refluxing the ethyl acetate to produce 300 parts of a urethane bond-containing compound. I got (A). Hereinafter, this will be referred to as the compound (A
-1). Synthesis Example 2 100 parts of "Foundrets TD-3402-B" (novolac type phenolic resin manufactured by Dainippon Ink and Chemicals Co., Ltd.) was kept at 130°C and dissolved, and then The obtained compound (A-
After adding 200 parts of 1) little by little and removing ethyl acetate etc. in this compound (A) by distillation,
198 parts of a mixture of a bisphenol A/tolylene diisocyanate reaction product, which is a urethane bond-containing compound (A), and a novolak type phenol resin, which is a thermoplastic resin, was obtained. Synthesis Example 3 110 parts of resorcinol, 68 parts of diphenylmethane diisocyanate, and 178 parts of ethyl acetate were stirred and mixed in a nitrogen stream, reacted for 2 hours while refluxing the ethyl acetate, and further added 0.1 part of triethylenediamine. The reaction was continued for 5 hours, and 356 parts of the urethane bond-containing compound (A)
I got it. Hereinafter, this will be abbreviated as compound (A-2). Synthesis Example 4 100 parts of "Foundlets TD-3402-B" was dissolved in advance at 130°C and kept at the same temperature, and the compound (A-2) obtained in Synthesis Example 3 was added thereto.
200 parts of this compound (A-2) were added little by little.
The ethyl acetate etc. inside are removed by distillation,
Urethane bond-containing compound (A) resorcinol
199 parts of a mixture of the diphenylmethane diisocyanate reaction product and a novolak type phenolic resin, which is a thermoplastic resin, was obtained. Synthesis Example 5 The same procedure as in Synthesis Example 4 was repeated except that the amounts of "Foundrets TD-3402-B" and Compound (A-2) were changed to 80 parts and 40 parts, respectively, and a urethane bond-containing compound was obtained. (A) 99 parts of a mixture of a resorcinol diphenylmethane diisocyanate reaction product and a novolak type phenolic resin as a thermoplastic resin were obtained. Example 1 100 parts of sand preheated to 90°C was placed in a mixer, and then the compound obtained in Synthesis Example 1 (A-
Mix and add 3 parts of 1) and 0.24 parts of hexamethylenetetramine, knead in a mixer for 2 minutes, and then add 0.1 part of calcium stearate powder.
and kneaded for 30 seconds to obtain molding sand for shell molds. Example 2 100 parts of sand preheated to 140°C was placed in a mixer, then 1.5 parts of the mixture obtained in Synthesis Example 2 was added and kneaded in the mixer for 1 minute, and then 0.45 parts of hexamethylenetetramine was added. After adding a solution dissolved in 1 part of water and kneading for 1 minute, 0.1 part of calcium stearate powder was added and kneaded for 30 seconds to obtain foundry sand for shell molds. Example 3 Foundry sand for shell molds was obtained in the same manner as in Example 1, except that the same amount of compound (A-2) was used instead of compound (A-1). Example 4 Foundry sand for shell molds was obtained in the same manner as in Example 2, except that the same amount of the mixture obtained in Synthesis Example 4 was used instead of the mixture obtained in Synthesis Example 2. Example 5 Foundry sand for shell molds was obtained in the same manner as in Example 2, except that the same amount of the mixture obtained in Synthesis Example 5 was used instead of the mixture obtained in Synthesis Example 2. Example 6 100 parts of sand preheated to 120°C was placed in a mixer, and then "Priamine P-364-BL" (urea resin manufactured by Dainippon Ink & Chemicals Co., Ltd.; non-volatile content =
67%) and kneaded for 30 seconds, then 1 part of compound (A-1) obtained in Synthesis Example 1 and 0.2 part of hexamethylenetetramine were mixed and added, and kneaded for 1 minute. Then, 0.1 part of calcium stearate powder was added and kneaded for 30 seconds to obtain foundry sand for shell molds. Example 7 100 parts of sand preheated to 140°C was placed in a mixer, and then 1.2 parts of the mixture obtained in Synthesis Example 4 was added and kneaded for 1 minute. 0.5 part of “60%)”
A solution of 0.36 parts of hexamethylenetetramine dissolved in 1 part of water was added and kneaded for 1 minute, and then 0.1 part of calcium stearate powder was added and kneaded for 30 seconds to obtain foundry sand for shell molds. Example 8 Instead of “Foundlets TD-3399”,
Foundry sand for shell molds was obtained in the same manner as in Example 7, except that 0.3 part of "Foundrets DA-405" (furan resin manufactured by the same company; active ingredient = 99% or more) was used. Comparative Example 1 The same operation as in Example 2 was repeated except that the same amount of "Foundrets TD-3402-B" was used instead of the mixture obtained in Synthesis Example 2, and a conventional shell mold for control was used. foundry sand was obtained. Reference Examples 1 to 9 Performance comparison tests were conducted using various foundry sands obtained in Examples 1 to 8 and Comparative Example 1. The results are summarized in Table 1. Each test was conducted in the following manner. First, the fusion point was determined according to JACT (Japan Casting Technology Promotion Association) test method C-1, and then the bending strength was determined according to JIS K-6910 "Powdered phenolic resin test method for shell molds". It is a thing,
Furthermore, the collapsibility was determined by heat-molding the resin-coated sand (foundry sand) to prepare a test piece with a size of 80 mmφ x 10 mm, and after holding this test piece in a reducing atmosphere at 450°C for 20 minutes. This was taken out and processed in a rotorp tester using a 10-mesh sieve, and the time until the test piece disappeared from the sieve was measured (however, if it took more than 5 minutes, the test was stopped at 5 minutes). By doing so,
The processing time in the testing machine was used as the disintegration data. The shorter the treatment time, the better the disintegration properties.

【table】

[Table] As is clear from the results in Table 1, all of the foundry sands of the present invention have significantly improved disintegration properties compared to Comparative Example 1, and in addition, there is no difference in other properties. I knew that it was comparable.

Claims (1)

[Claims] 1 A polyurethane (A) obtained from a phenol derivative having at least two hydroxyl groups and an isocyanate compound, a curing agent (B) consisting of hexamethylenetetramine or paraformaldehyde, and other thermosetting resins or thermoplastics as necessary. Foundry sand for shell mold obtained by coating sand grains with resin as a sand binder, and the total weight of polyurethane (A) and curing agent (B) is 0.65 to 1.8 parts by weight per 100 parts by weight of sand grains. The amount of curing agent (B) used is 15 to 46 parts by weight per 100 parts by weight of polyurethane (A), and the amount of polyurethane (A) in the sand binder is 25 to 87 parts by weight.
Foundry sand for shell molding in weight%.