JPH0417741B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a binder composition for molds. In particular, it is used in a method of manufacturing molds by injecting gaseous or aerosol sulfur dioxide into a sand mold made by adding acid-curing resin as an essential component to fire-resistant granular material and then kneading it with peroxide. , which relates to an improved mold binder composition. [Conventional technology] Conventionally, in order to manufacture medium to large quantities of molds, the shell molding method was used, in which a refractory granular material was coated with phenol resin, and this was filled into a mold using air pressure, etc., and thermoset molded. I've been However, in order to save energy during mold manufacturing, mold production speed, and improve the quality of molds and castings, the cold box mold manufacturing method, which hardens at room temperature using gaseous or aerosol substances, has been introduced as a mold manufacturing method that replaces the shell molding method. Serious attempts are being made to introduce it in the foundry industry. The cold box method uses an acid-curing resin, typically a furan resin, as a binder and a peroxide as an oxidizing agent, and is cured with sulfur dioxide.The cold box method uses an acid-curing resin, typically a furan resin, as a binder and hardens it with sulfur dioxide, using peroxide as an oxidizing agent. There is a urethane cold box that cures using amine as a catalyst. Among these, molds using urethane cold boxes have drawbacks such as poor disintegration of casting sand during casting production, and the tendency to cause casting defects such as sand trapping, scooping, pinholes, and soot defects. On the other hand, Francold Boxing has been rapidly attracting attention in recent years as a method to solve the above-mentioned difficulties. The present invention relates to a mold binder composition suitable for use in the Franco cold box method, and is used to improve curing behavior such as initial strength of cold boxes that harden instantly by injecting gas at room temperature. The present invention relates to a binder composition for molds that is mainly composed of an acid-curable resin. [Problems to be solved by the invention] Conventionally, automatic molding machines have been used to manufacture medium to large quantities of molds, and acid-curing resin and peroxide are added and kneaded to fire-resistant granular materials to make them fire-resistant. The surface of the particulate material is coated, and filling, molding, curing, and removal are performed continuously in a cycle of less than one minute automatically using air pressure or the like. Therefore, in the cold box method, in order to further improve mold productivity, it is desired to improve the initial strength so that the mold can be sufficiently mechanically handled within one minute after molding. [Means for solving the problem] As a result of intensive research, the present inventors have developed a binder composition for molds that greatly improves the initial strength within 1 minute after molding and further improves mold productivity. As a product, a binder composition for manufacturing cold box molds consisting of an acid-curing resin combined with a specific compound was discovered, and the present invention was achieved. That is, the present invention provides a binder composition used in a cold box mold manufacturing method in which a mold is formed using sulfur dioxide using an acid-curable resin as a binder and a peroxide as an oxidizing agent, the composition comprising: is below a)
~e) a Polycondensate of ketone and aldehyde b Polycondensate of aromatic hydrocarbon and aldehyde c Polycondensate of resorcin and aldehyde d Polycondensate of alkylresorcin and aldehyde e Oxirane ring in one molecule A resin component consisting of at least one type of epoxy resin or at least one type of copolymer thereof containing two or more of the following, and having a molecular weight of 100,000 or less, and at least one of a furan resin, a phenol resin, a urea resin, and a melamine resin. The content of the resin component () consisting of at least one of the above a) to e) or at least one copolymer thereof is 3 to 50.
% by weight of the mold binder composition. The content of the component () in the binder composition of the present invention is preferably 5 to 30% by weight. Moreover, the molecular weight range of the above component () is preferably
It is preferably 5,000 or less, more preferably 1,000 or less, and is selected in consideration of the viscosity, workability, etc. of the binder composition. When the molecular weight exceeds 100,000, the viscosity of the binder composition becomes high, the fluidity of the kneaded sand deteriorates, and the strength of the sand core decreases. As a result, the initial strength immediately after molding is greatly improved compared to the case of conventional acid-curable resins consisting only of the components (). The reason for this is that the peroxide accelerates the initiation of the polymerization reaction, and the chemical reaction product of peroxide and sulfur dioxide causes a polycondensation reaction of free methylol groups between the composition components, resulting in a block polymerization reaction. It is possible that For this reason, it is thought that a strong bonding network is formed between the components of the composition, which tightly envelops the refractory granular material, resulting in improved adhesive strength. Among the resin components () used in the present invention, acetophenone-formaldehyde resin is exemplified as the polycondensate of ketone and aldehyde in a). As the polycondensate of aromatic hydrocarbon and aldehyde b), xylene-formaldehyde resin is exemplified. Examples of the polycondensate of resorcin and aldehyde c) include resorcin-formaldehyde resin and resorcin-cresol-formaldehyde resin. An example of the polycondensate of alkylresorcin and aldehyde (d) is methylresorcin-formaldehyde resin. Examples of the epoxy resin containing two or more oxirane rings in one molecule e) include bisphenol A type epoxy resin and epoxidized novolak resin. Examples of copolymers of a) to e) include acetone-formaldehyde-glyoxal resin, methylresorcinol-acetone-formaldehyde resin, and xylene-formaldehyde-acrolein resin. If the content of these resin components a) to e) in the binder composition is less than 3% by weight, it will not have the effect of significantly improving the initial strength immediately after molding, and if it exceeds 50% by weight, the initial strength will decrease. is significantly improved, but because the molecular weight of the binder does not increase, the final strength after the mold is left to stand deteriorates. In the present invention, as for the form in which the above two components are used together, the component () may be stirred and mixed separately with the component () in the refractory granular material when manufacturing the mold; The above components () may be incorporated into the reaction system, or
After producing the component (), it may be mixed with the component (). A silane coupling agent is added to the binder composition of the present invention for the purpose of improving the surface stability and moisture resistance of the mold.
In order to improve viscosity, workability, etc., known additives such as solvents and diluents may be used in combination. In addition to silica sand containing quartz as a main component, zircon, chromite, olivine sand, etc. may be used as the refractory granular material when manufacturing molds using the binder of the present invention, but there are no particular limitations. isn't it. Further, as the peroxide, organic peroxides such as ketone type and aromatic type, and inorganic peroxides such as hydrogen peroxide are used, but are not particularly limited. [Examples] Hereinafter, in order to explain the present invention in more detail, the advantages of the present invention will be described using Examples, but the scope of the present invention is not limited by the following Examples. Examples 1 to 11 Urea-formalin-modified furan resin containing the substances according to the present invention shown in Table 1 based on 3000 parts by weight of silica sand
40 parts by weight of methyl ethyl ketone peroxide and 15 parts by weight of methyl ethyl ketone peroxide were kneaded in a Shinagawa-type rotation-revolution type batch mixer, filled into a mold for a mold bending strength measurement test piece, and sulfur dioxide gas was blown in for 1 second to remove excess dioxide. The sulfur was washed away with pressurized air for 5 seconds and the mold was molded. The initial strength is measured using a bending strength tester 30 seconds after the start of sulfur dioxide injection, and the initial strength of a mold made of urea-formalin-modified furan resin that does not contain the substance of the present invention is similarly measured.
Expressed as a ratio. These results are shown in Table 1. As shown in Table 1, compared to the blank, the initial bending strength was improved in all the examples, and the increase rate was 120 at the lowest and 165 at the highest, indicating a sufficiently remarkable effect on the development of the initial bending strength. It was seen.

[Table] Examples 12 to 17, Comparative Examples 1 to 6 Using the same test method as Examples 1 to 11, the substances according to the present invention listed in Table 2 were added in the stated amounts, and the initial strength was measured. The bending strength ratio was determined in the same manner as in Nos. 1 to 11. In addition, the final strength is determined by measuring it with a bending strength tester one day after the start of sulfur dioxide blowing, and the final strength of the urea-formalin-modified furan resin that does not contain the substance according to the present invention is taken as 100 and expressed as a ratio. did. The results are shown in Table 2. From the results in Table 2, it can be seen that the content of resin component (I) in the binder composition in the present invention is 3% by weight.
If it is less than
It can be seen that when the content exceeds 50% by weight, the final strength decreases.

【table】

Claims (1)

[Scope of Claims] 1. A binder composition used in a cold box mold manufacturing method in which a mold is formed using sulfur dioxide using an acid-curable resin as a binder and peroxide as an oxidizing agent, the binder composition comprising: Polycondensates of ketones and aldehydes b Polycondensates of aromatic hydrocarbons and aldehydes c Polycondensates of resorcinol and aldehydes d Polycondensates of alkylresorcinols and aldehydes e A resin component () consisting of at least one type of epoxy resin containing two or more oxirane rings in one molecule or at least one type of copolymer thereof and having a molecular weight of 100,000 or less, and a furan-based resin, a phenol-based resin, or a urea-based resin A resin component () consisting of at least one type of resin, a melamine resin, and a resin component () consisting of at least one of the above a) to e) or a copolymer thereof has a content of 3 to 50
% by weight of a mold binder composition.