CS272045B1 - Cold-hardenable foundry mixture - Google Patents

Abstract

Liquid organic compound esters, lactones, carbonates, and or of methyl formate vapors, is characterized by ascending the onset of strength, increased reproducibility, reduced viscosity, easier regenerability, prolonged processability and exhibits higher strength and surface the quality of foundry molds and cores for which it is intended. Includes on 100 wt. parts of refractory granular material 0.7 to 4 wt. parts of an aqueous solution phenolic resins of 45 to. 65 wt. %, with a molar ratio of phenol: formaldehyde greater than 1: 1.8, with content of 7 up to 17 wt. % of alkali hydroxides; \ tor carbonates, with a miscibility greater than 1:10 at 20 ° C; it further comprises 1 to 20 % wt. diols 02 to Og based on the content phenolic resin solution.

Description

The invention relates to a cold-curable foundry composition with an organic hardener for the production of molds and cores.

Known and utilized curable binder systems for the cold fenolformalde- hydových based binders modified with furfuryl alcohol alone or, curing in the presence of strong inorganic acids, such as sulfuric acid, or organic sulphonic acids nejčastě- ⁵ it as paratoluenesulfonic, xylenesulfonic have the disadvantage that that they contain sulfur. During the thermal decomposition of the binder in the period of casting of liquid metal, solidification and cooling of castings, sulfur dioxide is released, adversely affecting the working environment and the environment by exhalations into the atmosphere. In addition, there are adverse effects on sulfur-sensitive alloys, which prevent carbon precipitation in the desired globular form and cause the formation of undesirable lamellar or other structures, depending on the sulfur content, even in the entire cross section of the casting. Other processes use even sulfur dioxide in the gas phase to cure. It combines with the peroxides present in the molding composition to form sulfuric acid, which has similar disadvantages, in addition to the increased occupational safety risks associated with the use of peroxides and sulfur dioxide. More modern methods use curing mixtures at room temperature by reactions between a strongly alkaline phenol-formaldehyde resole and a carboxylic acid ester or gaseous methylformate, characterized by a molecular weight of 600 to 2000, a molar ratio of potassium hydroxide: phenol = 1.2 to 2.6: 1. strength immediately after curing, lower binder stability, and thus changing properties, and further deteriorated regenerability after casting. Another disadvantage is the decrease in strength up to 80% of the initial value in the period of 2 to 4 hours after curing for mixtures cured with gasified ester, which requires a delay in the completion of molds with delays in production. Also another mixture containing unmodified resoles, e.g. with a potassium hydroxide: phenol ratio = 0.9: 1, hardened with butylene glycol diacetate or with butyrolactone, or in the gas phase again with methyl formate, but catalyzed by sodium hydroxide or cured with propylene carbonate, have similar disadvantages. An increase in strength is achieved by using a phenol-formaldehyde binder modified with a mixture of glycerin and polyethylene glycol. One of the newest processes with gas phase curing using acetals has a disadvantage in the field of ecology. The reactants decompose to free formaldehyde. Another disadvantage is the need to keep the elevated core temperature in a narrow range of 30 to 35 ° C. Although the consumption for heating is lower than with hot processes, one of the main advantages, which is the simpler construction of the cores, and the problems with temperature control in a narrow temperature range, are eliminated. In other mixtures, unmodified phenol-formaldehyde resoles are used again, differing only in the use of strong alkalis KOH and NaOH in a suitable ratio. Another option is to process using such phenolic resin binders soluble in an alcohol in the presence of hydroxides or oxides of polyvalent metals and alkali metal, water and organic solvents curing 00 ₂ cold. The big disadvantage of this system is the very low initial compressive strength immediately after curing - less than 10 kg.cm ² .

The above-mentioned disadvantages are eliminated by a cold-curable foundry mixture with liquid organic esters, lactones, carbonates and / or methyl formate vapors according to the invention, containing per 100 parts by weight of 0.7 to 4.0 parts by weight of refractory granular material, 45 to 4.0 parts by weight of aqueous phenolic resin solution. 65 wt.%, having a molar phenol: formaldehyde ratio greater than 1: 1.8, containing 7-17% by weight, alkali metal hydroxides or carbonates and míčitelností water exceeding 1 _t at 10 temp <JTE »20 5c. The essence of the invention consists in the fact that the mixture further contains 1 to 20% by weight of diols C ₂ to Og, based on the content of the phenolic resin solution, i

The higher technical effect of the mixture according to the invention is manifested by the achievement of higher strengths, a favorable, mainly increasing, tendency of the onset of strength, elimination of the initial decrease, increased reproducibility. The diol does not have the function of a phenolic resin solvent, due to the presence of water and the excellent solubility of the type of phenol formaldehyde resin used in water, nor the function of a chemically crosslinking agent, as in the case of e.g. iso-f-cyanate; at low temperatures, i.e. normal temperatures in the range of usually 17 to 35 ° C, no reaction with the phenol formaldehyde present occurs during the curing process with organic esters

CS 272 045 B1 hydro resin, but for the incorporation of diols into the gaps of the polymer network of the phenolic resole in the physical process of its precipitation from aqueous solution by decomposition of the organic esters present. This filling of the phenolic branched network manifests itself as indicated. The mixture further exhibits increased flowability, manifested by improved packing of the cores due to reduced viscosity in the presence of the modifying component. The high content of polar groups present in the mixture influences the positive increase in adhesion to refractory sands. Furthermore, the presence of diols and surfactant during the period of thermal exposure during cooling of the castings causes the desired embrittlement of the binder envelope around the grains, which results in easier regenerability. Also typical is the improved stability of the mixture before curing, resulting in prolonged workability with a steeper rise in strength, further increased resistance of the surface of the cores and molds to drying, and finally their high surface quality. The mixture can be prepared on conventional mixers, both continuous and discontinuous.

The advantages of the composition according to the invention are illustrated in the following examples.

Example 1

A mixture of 100 parts by weight of parts of quartz sand with a mean grain size d50 = 0.27 mm, 2 parts by weight of an aqueous solution of phenolic resin with a dry matter content of 60% by weight, with a molar ratio of phenol: formaldehyde = 1: 2.15, with unlimited miscibility in water, containing 16% by weight. KOH. 0.4 part by weight of a portion of glycerol triacetate was further homogeneously mixed into the mixture, and the mixture was immediately compacted. The test specimens had a density of 1.58. The course of compressive strength depending on the curing time is given for individual samples in Table 1.

Samples 1 to 3 according to the invention with different diols:

sample 1 .. <sample 2 ... sample 3 «· <sample A is Table 1 Sample no. .................. 10 parts by weight of ethylene glycol 10 hmn-h. / Κ1Λ 1. inrnnvl ΑησΊ -vířní n 10 hmn + r. parts triethylene glycol comparative. Curing time (h) 1 2 4 24 48 120 AND fixed st in pressure (MPa) 0.7 1.4 2.1 3.4 4.6 3.6 1 • - »1 - ’, 4 2.5 3.0 4.8 5.5 6.2 2 - tt - 1.2 2.2 2.6 4.1 4.9 5.5 3 - tt - 1.1 2.3 2.4 3.9 4.5 5, ’

Example 2

A mixture of 100 parts by weight of parts of zirconium sand with a mean grain size d50 = 0.14 mm, 1.2 parts by weight, of a part of an aqueous solution of phenolic resin with a dry matter content of 55% by weight, with a molar ratio of phenol: formaldehyde = 1: 2, containing of alkali hydroxide 11% by weight, with a miscibility with water greater than 1:10. 0.4% by weight of alkali hydroxide was further mixed into the mixture. -aminopropyltriethoxysilane and 1% by weight of a nonionic surfactant in the form of ethoxylated nonylphenol, based on the phenolic resin solution. Sample B is comparative, samples 4, 5, 6 according to the invention contain 1% by weight, 10% by weight, and 20% by weight, of ethylene glycol, based on I. to water. phenolic resin solution. The ·· mixture was compacted after mixing. The density of the packed test specimen was 2.86 to 2.90. Table 2 shows the achieved results as a course of values of compressive strengths as a function of time. The test specimens were cured by purging with methyl formate vapor at 22 ° C at a constant time.

Table 2

CS 272 045 B1

Sample no. Curing time (h) immediately 2 4 24 48 120 B compressive strength (MPa) 3.95 3.2 3.1 3.9 4.05 4.1 4 _ - 4.0 4.1 4.2 4.3 4.35 4.4 5 _ - 4.9 5.3 5.5 5.8 5.9 6.0 6 - ° - 4.5 5.05 5.1 5.1 5.2 5.2

OBJECT OF THE INVENTION

Claims (1)

OBJECT OF THE INVENTION Foundry mixture, cold curable with liquid organic esters, lectons, carbonates and / or methyl formate vapors, containing per 100 parts by weight of refractory granular material 0.7 to 4 parts by weight of aqueous phenolic resin solution with a dry matter content of 45 to 65% by weight, with phenol molar ratio : formaldehyde greater than 1: 1.8, containing by weight 7 to 17% of alkali hydroxides or carbonates and more than 1:10 miscible with water at a temperature of 20 ° C, characterized in that it contains 1 to 20% by weight of C _{2 diols} to Cg, based on the content of the phenolic resin solution.