JPH0390246A - Coated sand for manufacturing mold - Google Patents

Abstract

PURPOSE:To shorten hardening time and to lower hardening temp. by applying compound, which can generate combination by coming into reaction with the specific compound as resin component and the other resin component, on sand. CONSTITUTION:As the resin component (a), in (1) compound having two or more of aldehyde group in molecule induced from starch, (2) polyaldehyde shown with the formula 1, (3) polyaldehyde shown with the formula 2 and (4) polyaldehyde shown with the formula 3, one or more kinds of polyaldehyde compound are used. The resin component (b) is solid-state at the room temp. and has active hydrogen, and the compound, which can generate the combination (X: aldehyde remained group) shown with the formula 4 by reacting the resin component (a) and the above (b), is used. In the case of using the coated sand for manufacturing the mold by coating the resin components (a), (b) and hardening agent on the surface of refractory aggregate, the hardening time is shortened and the hardening temp. can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to coated sand that is heated and hardened to form a mold.

[Conventional technology and its problems]

Conventionally, as a method for manufacturing heat-curing molds, there is a so-called shell molding method in which refractory granular aggregate is coated with a phenol novolak resin and heated and cured at around 300° C. using hexamethylenetetramine as a catalyst. This heat-curing method is currently the most commonly used heat-curing mold manufacturing method due to its simple equipment and ease of use. However, since the curing time was long and the curing temperature was high, there were many mold distortions and mold distortions, mold deburring work was indispensable, and dimensional accuracy was insufficient. Furthermore, the working environment is extremely poor due to the high curing temperature, and the working environment is extremely polluted due to the odor of thermal decomposition of the phenol resin and hexamethylenetetramine, and it has been desired to significantly improve these conditions.

In addition, acid-curing resins such as furan resin, phenol resol resin, phenol or urea/formalin-modified furan resin, and curing catalysts such as ammonium chloride and oxalic acid are added to the refractory granular aggregate at temperatures between 150°C and 250°C. There is a method of producing a mold by heating and hardening the mixed mixture. This method has a shorter curing time than the shell mold method, and is also improved in terms of temperature-induced distortion, dimensional accuracy, and thermal working environment.

However, acid-curing resins such as furan resins, phenol resol resins, and phenol- or urea/formalin-modified furan resins are liquid at room temperature, so when mixed with refractory aggregate for foundries, the kneading sand becomes wet. Compared to dry sand such as the shell mold method, the filling properties are inferior, so measures such as blow blowing are required.

As described above, each of the molding sands used in the conventional heat-hardening mold making method has its advantages and disadvantages, and there is a desire for an even better molding sand that combines these advantages.

[Means to solve the problem]

As a result of intensive research to solve the above problems, the present inventors manufactured a mold by pre-coating the surface of fire-resistant granular aggregate with a specific resin component and curing agent component to form a solid resin coating layer on the surface of the aggregate. The present inventors have discovered that the coating sand can significantly improve the curing speed and filling properties of molds without deteriorating other properties, and have completed the present invention.

That is, the present invention provides coated sand for mold production in which the surface of a fire-resistant aggregate is coated with the following resin components (a) and (b) and a curing agent.

(i) A compound derived from starch and having two or more aldehyde groups in its molecule (ii) A polyaldehyde represented by the following 2 (in the formula,
m represents 0 or 1%, n represents 0 or 1, and l represents a number from 1 to 5. However, when 1ll-0, n-1, when m-1, n-
It is 0. ) (tii) Polyaldehyde R+ represented by the following formula (wherein m and n are 2 or 3, k and f represent numbers from O to 50, R, and R2 are each H- or C)! Represents 3-. ) (iv) Poly"aldehyde represented by the following formula (in the formula, m represents a number of O to 4, n represents a number of 2 to 3, R is H-, CH
s-, CJs-1C3H? -, 80-, H3CO-.

At least one of HOOC-, H, and N-. ) One or more polyaldehyde compounds selected from the above (i) to (iv).

00- A compound that is solid at room temperature, has active hydrogen, and can react with the resin component (a) to form -CI (-bond (X: aldehyde residue)).

Examples of the resin component (b) used in the present invention include tjunol monomers, phenol resins, amino compounds, amino resins, and aromatic hydrocarbon resins. Preferred examples include phenolic monomers such as bisphenol A1, bisphenol F, lusorcinol, and xylenol, as well as phenolic resins, urea, urea resins, and xylene resins.

Furthermore, at least one of conventionally known modifiers may be mixed or co-condensed with the resin component used in the present invention.

Specific examples of conventionally known modifiers include coumaron/indene resin, petroleum resin, polyester, alkyd resin, polyvinyl alcohol, epoxy resin, ethylene/vinyl acetate, polyvinyl acetate, polybutadiene, polyether, polyethyleneimine, and polychloride. Vinyl, polyacrylic ester, polyvinyl butyral,
Polymers and oligomers such as phenoxy resin, cellulose acetate, xylene resin, toluene resin, polyamide, styrene resin, polyvinyl formal, acrylic resin, urethane resin, nylon, lignin, lignin sulfonic acid, rosin, ester gum, vegetable oil, bitumen , heavy oil, cashew nut shell liquid, vanillin, natural products such as tannins, saccharides and their derivatives such as starch, cornstarch, glucose, dextrin, resorcin residue, cresol residue, 2.2.4-trimethyl-4-( Reaction residues and by-products such as reaction by-products of hydroxyphenyl) coumarone and isopropenylphenol, reaction by-products of terephthalic acid and ethylene glycol, polyhydric alcohols such as polyethylene glycol, ketones such as acetone, cyclohexanone, acetophenone, etc. Condensates with aldehydes, amino or imino compounds such as dicyandiamide, acrylamide, and thiourea, and their aldehyde condensates, aldehyde compounds such as furfural and glyoxal, and ester compounds such as isocyanuric acid esters and unsaturated fatty acid esters. be.

The resin components (a) and (b) used in the present invention are both solid at room temperature, but they can be finely pulverized, put into heated molding sand as a lump, or dissolved in a solvent and then By pouring it into foundry sand, it is made to adhere uniformly to the surface of the refractory aggregate.

In the present invention, resin components (a) and (b) are blended in a total amount of 0.5 to 8 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the fire-resistant aggregate. .

Among them, the resin component (a) is blended in an amount of 0.1 to 5 parts by weight, preferably 0.3 to 3 parts by weight, per 100 parts by weight of the refractory aggregate.

Although the resin components (a) and (b) of the present invention may be partially reacted in advance and coated on the sand, they are generally coated on the sand without being reacted. Since the sand is heated during coating,
Part of the reaction may proceed due to the heat.

In order to further enhance the effect of the present invention, the resin components (a) and (b) in the present invention contain a silane coupling agent.
For example, T-ureidopropyltriethoxysilane), a lubricant (for example, calcium stearate), etc. may be added.

Further, as the curing agent in the present invention, at least one acid such as oxalic acid, salicylic acid, maleic acid, boric acid, benzenesulfonic acid, toluenesulfonic acid, organic sulfonic acid such as xylene sulfonic acid, or oxalic acid, salicylic acid, Organic sulfonic acids such as maleic acid, boric acid, toluenesulfonic acid, xylene sulfonic acid, benzenesulfonic acid, etc. and copper, iron, argonium, zinc, urea, melamine,
Acids or salts that are solid at room temperature, such as salts with amines, copper chloride, iron chloride, and other Lewis acids, are used, and the blending amount is 0°5 to 0.5 to the total amount of resin components (a) + (b). 50% by weight
, preferably 10 to 40% by weight. By coating the sand with this curing agent together with the resin component, the curing time of the coated sand during mold making can be shortened.

The refractory granular aggregate used in the present invention includes, but is not particularly limited to, silica sand containing quartz as a main component, zircon sand, chromite sand, oripin sand, and the like.

(Examples) The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Examples 1 to 8 100 parts by weight of Australian flattery silica sand was added with the table below.
After adding 2 parts by weight of a 20% methanol solution of the curing agent shown in Table 1 and 5 parts by weight of a 20% methanol solution of the resin component (b) shown in Table 1, kneading them in a mixer and evaporating the solvent. , 5 parts by weight of a 20% methanol solution of the resin component (a) as shown in Table 1 was added and kneaded in a mixer, the solvent was evaporated, and 0.1 part by weight of calcium stearate was added and kneaded to obtain a fluidized A coated sand with good properties was obtained.

This coated sand was heated to 180°C in advance in a 25 x 2
A mold of 5×250 m/m was filled by blowing with pressurized air and baked for 10 seconds to form a mold.

The bending strength and bulk specific gravity of the mold were measured 10 seconds after the mold was removed. The results are shown in Table-1.

Comparative example 1. 2 For 100 parts by weight of Australian flattery silica sand,
2 parts by weight of novolac type phenolic resin with a softening point of 85°C and an average molecular weight of 1150, 1.5 parts by weight of a 20% hexamethylenetetramine aqueous solution, and 0.1 parts by weight of calcium stearate.
The resin-coated sand coated with the weight part was blown and filled with pressurized air into a 25 x 25 x 250 m/m mold that had been preheated to the temperature shown in Table 2, and was fired for the time shown in Table 2 to form the mold. It was molded and evaluated in the same manner as in Example 1. The results are shown in Table-2.

Comparative Examples 3 and 4 Table 2 in 100 parts by weight of Australian flattery silica sand
A coated sand prepared by using 0.45 parts by weight of a 20% aqueous solution of a curing agent as shown in Table 2 and 1.5 parts by weight of a urea-modified furan resin was heated in advance to the temperature shown in Table 2.
The mixture was blown into a mold of X 250-/m and filled with pressurized air, fired for the time shown in Table 2 to form a mold, and evaluated in the same manner as in Example 1. The results are shown in Table-2.

Claims (1)

[Scope of Claims] 1. A coated sand for mold manufacturing, in which the surface of a refractory aggregate is coated with the following resin components (a) and (b) and a curing agent. Resin component (a) (i) Compound having two or more aldehyde groups in the molecule derived from starch (ii) Polyaldehyde represented by the formula below ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (in the formula , m is 0 or 1, n is 0 or 1, l is a number from 1 to 5. However, when m = 0, n = 1, and when m = 1, n =
It is 0. ) (iii) Polyaldehyde represented by the following formula ▲ Formula,
There are chemical formulas, tables, etc. ▼ (In the formula, m and n represent 2 or 3, k and l represent numbers from 0 to 50. R_1 and R_2 each represent H- or CH_3-.) (iv) Below Polyaldehyde represented by the formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, m represents a number from 0 to 4, n represents a number from 2 to 3, and R represents H-
, CH_3-, C_2H_5, C_3H_7-, HO-
, H_3CO-, HOOC-, and H_2N-. ) One or more polyaldehyde compounds selected from the above (i) to (iv). Resin component (B) It is solid at room temperature, has active hydrogen, and reacts with resin component (B) ▲There are mathematical formulas, chemical formulas, tables, etc.▼
A compound that can form a bond (X; aldehyde residue).