RU2705823C1 - Cold-hardening mixture for production of casting cores and molds - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to metallurgy, particularly, to production of molds and rods from cold-hardening sand-resin mixes. Mixture includes carbamide or carbamidofuran resin and refractory filler, and the hardening catalyst used is liquid waste of chemical cleaning of zinc plated steel cut from zinc coating in form of an aqueous solution containing zinc chloride, at following ratio of components, wt%: refractory filler 100; carbamide or carbamidofuran resin 2.0–2.2; liquid waste of chemical cleaning of galvanized steel cutoff from zinc coating in form of an aqueous solution containing zinc chloride, 0.8–1.2.

EFFECT: higher durability of mixture while maintaining strength of molds and rods.

1 cl, 2 tbl

Description

Cold-hardening sand-resin mixtures are widely used in foundry in the manufacture of molds and cores. Cold hardening mixtures (CTS) consist of a filler (silica sand), a synthetic binder, a curing catalyst and various additives improving the mixture. Urea, carbamidofuran, phenolofuran resins and a catalyst, in the presence of which the mixture is hardened, are introduced into the composition of CTS as binders. Inorganic materials have become widespread as catalysts for urea and urea-urea-furan resins. Depending on the required hardening rate of CTS, determined mainly by serial production, complex or single-component inorganic hardeners are used. The most important property of sand-resin mixtures is the survivability of the mixture - the time during which the prepared mixture remains technologically usable. The survivability of mixtures based on furan and urea-furan resins is determined by the reaction rate of these resins with the catalyst and depends on the exposure time and ambient temperature.

Known cold-hardening mixture containing a refractory filler, urea resin 1.8-2.0 wt.% And phosphoric acid 0.6-0.8 wt.%, A concentration of 1.56-1.58 g / cm ³ as a catalyst [ one].

The disadvantage of this mixture is the low value of survivability (5-10 minutes) [1].

The closest in technical essence and the achieved effect is a mixture for the manufacture of foundry molds and cores [2], including a refractory filler, urea resin, phosphoric acid and ethanol in the following ratio of ingredients, wt.%:

refractory filler - 100;

urea resin 2.16-2.64;

phosphoric acid 0.6-0.8;

ethanol 0.54-0.66.

Orthophosphoric acid is used here as a curing catalyst. Ethanol is used as an additive to improve the survivability of the mixture, however, the use of ethanol is associated with additional fire safety risks in production, in addition, ethanol is an expensive material.

The objective of the invention is to provide a cold-hardening sand-resin mixture, which would provide increased survivability of the mixture in comparison with the prototype while maintaining the strength of the molds and cores.

The technical result consists in creating a cold-hardening sand-resin mixture, providing increased survivability of the mixture while maintaining the strength of the molds and cores.

The technical result is achieved by the fact that the mixture for the manufacture of foundry molds and cores, comprising as a binder urea or urea-furan resin, a refractory filler, according to the invention, as a curing catalyst use liquid waste chemical cleaning of galvanized steel trim from a zinc coating in the form of an aqueous solution containing zinc chloride, in the following ratios of components, wt.%:

refractory filler - 100;

urea or carbamidofuran resin 2.0-2.2;

liquid waste of chemical cleaning of galvanized steel trim from zinc coating in the form of an aqueous solution containing zinc chloride 0.8-1.2.

The invention consists in the following.

In the modern automotive and machine-building industry, galvanized steel sheet with a zinc coating thickness of 20-60 microns is widely used as the main material. Therefore, a large amount of edged galvanized steel sheet is accumulated, the use of which for smelting cast iron is difficult if the melting sections of machine-building enterprises are equipped with induction melting units. To prepare the galvanized steel trim for induction remelting, it is necessary to remove the zinc coating from the steel base. According to the source [3], as a by-product of the zinc coating separation from galvanized steel trim, a liquid waste product is formed that contains an aqueous solution of zinc chloride, a residual amount of hydrochloric acid, and hexamethylenetetramine.

The average composition of the liquid waste cleaning galvanized steel trim, wt.%:

dissolved zinc chloride 10.5-12.5;

hydrochloric acid (conc.) 2.8-4.2;

hexamethylenetetramine 2.5;

water is the rest.

Urea or carbamidofuran resin refers to acid curing resins, in relation to which acid catalysts have a decisive effect on the pH of the medium, but do not enter into the curing reaction themselves [1].

As a catalyst for curing urea or urea-urea-furan resins, it is proposed to use liquid waste from the chemical cleaning of galvanized steel trim from a zinc coating in the form of an aqueous solution containing zinc chloride. Zinc chloride solutions have an acid reaction, the pH of the solutions usually corresponds to values from 1.5 to 3.5. Hydrochloric acid in the composition of the catalyst has an additional catalytic effect on the curing process of the mixture [1]. Thus, the liquid waste resulting from the removal of the zinc coating from galvanized steel trim has a pronounced acid reaction and is able to serve as a curing catalyst for synthetic acid-cured resins, such as urea and urea-furan resins.

The water contained in the introduced component slows down the curing of the resin, which leads to an increase in the survivability of the mixture. At the same time, hydrochloric acid, which is part of the introduced component, is stronger than orthophosphoric acid, which is part of the prototype mixture, and a significant content of zinc chloride (10.5-12.5 wt.%) In combination with it ensures the completeness of the process curing urea and urea-formaldehyde resins with a mixture strength sufficient for technological processes of manufacturing molds and cores. The vanishingly low content of hexamethylenetetramine in the composition of the input liquid waste from the cleaning of galvanized steel trim cannot affect the technological properties of the mixture.

In comparison with the prototype, the number of components of the mixture is reduced, which simplifies the process of mixing.

The use of galvanized steel scrap cleaning process mixtures as part of cold-hardening waste mixtures contributes to the utilization of foundry waste and helps to prevent environmental pollution, which positively affects the environment.

Narrowing the interval to a lower binder content in comparison with the prototype allows you to save expensive synthetic resin.

An example implementation of the invention.

To prepare the mixture, carbamidofuranic resin SVHK-40BSLTU-2223-007-14559685-2006 with a density of 1.245 g / cm ^{3 was} used as a binder resin, and dry quartz sand of grade 2K ₂ O ₃ 03 GOST 2138-91 was used as a refractory filler.

The mixture is prepared as follows. Quartz sand and a binder are loaded into the mixing runners, the mixture is mixed for 5-8 minutes. Then the catalyst is added, and stirring is carried out for another 5-8 minutes until a homogeneous mass is obtained, after which the mixture is ready for molding.

The content of the refractory filler was taken equal to 100 wt.%, The content of the remaining components was taken in excess of 100 wt.%. The amount of binder was 2.0 wt.%. The catalyst content ranged from 0.4-1.4 wt.% In increments of 0.2 wt.%. Samples for controlling tensile strength were made from a mixture of each variant.

The strength of the samples was determined on a Centrozap LRu molding and bar mass strength apparatus 1 hour and 24 hours after their manufacture.

Samples rods in the form of cylinders with a diameter of 50 mm and a height of 50 mm were made from a mixture of each variant.

The survivability of the mixture was determined as follows. First, the compaction of the mixture was determined by changing the height of the sample after compaction with three strokes of the copra with a constant weight of the sample. Next, survivability was found at the inflection point on the curve of the dependence of the compressibility on the exposure time, which corresponds to a loss of strength of not more than 30%.

The compositions of the tested mixtures are shown in table 1, the results are presented in table 2.

Table 1 The compositions of the tested mixtures

Name of ingredients The content of ingredients in the examples, wt.% 1 (prototype) 2 3 4 5 6 7 Refractory filler one hundred Binder 2.16-2.64 2.0 2.0 2.0 2.0 2.0 2.0 Ethanol 0.54-0.66 - - - - - - Orthophosphoric acid 0.6-0.8 - - - - -

Catalyst (liquid chemical cleaning waste
galvanized steel scrap from
zinc coating in the form of water
solution containing zinc chloride) - 0.4 0.6 0.8 1,0 1,2 1.4

Table 2 Control Results

Name of properties Composition Test Results 1 (prototype) 2 3 4 5 6 7 Vitality, min 12-15 98 74 22 25 32 110 Tensile strength after 1 hour, MPa (kgf / cm ² ) 0.06-0.1 (0.6-1.0) 0.002 0.008 0.08 0.12 0.10 0.004 Tensile strength after 24 hours, MPa (kgf / cm ² ) 0.98-1.18 (10-12) 0.8 1,1 1.19 1.22 1.24 1.36

From table 2 it is seen that when the content of the catalyst in the mixture in an amount less than 0.8 wt.% And more than 1.2 wt.%, The survivability of the mixture exceeds the value of this characteristic of the prototype on average twice. The tensile strength of the mixture after 1 hour is not lower than that of the prototype, and after 24 hours it exceeds it.

Repeated testing of the mixture with a changed binder content of 2.2 wt.% Confirmed the stable nature of the results in terms of survivability and strength of the mixture.

Thus, a mixture with a binder content of 2.0-2.2 wt.% And a catalyst in the range of 0.8-1.2 wt.% Provides improved survivability of the mixture while maintaining the strength of the molds and rods in comparison with the prototype.

Quoted sources:

1. Foundry technology: Molding and core mixtures. // Ed. S.S. Zhukovsky, A.N. Boldina, A.I. Yakovleva, A.N. Poddubny, V.L. Krokhotina. Textbook for universities. - Bryansk: Publishing House of BSTU, 2002. - 470 p.

2. USSR author's certificate SU 681648A, MKI B22C 1/22. Cold hardening mixture for the manufacture of foundry cores and molds. G.P. Tolkacheva, E.I. Mantrova, S.L. Ivanova.

3. RU 2599061 C1 Method for removing zinc from galvanized steel I.O. Leushin, A.Yu. Subbotin, M.A. Geiko.

Claims (2)

A mixture for the manufacture of foundry molds and cores, comprising a urea or urea-urea-furan resin as a binder, a refractory filler and a curing catalyst, characterized in that a liquid waste of chemical cleaning of galvanized steel trim from a zinc coating in the form of an aqueous solution containing zinc chloride is used as a curing catalyst , with the following ratios of components, wt.%: refractory filler one hundred carbamidofuran binder 2.0-2.2 liquid waste chemical cleaning galvanized steel trim from zinc coating in the form of an aqueous solution of zinc chloride 0.8-1.2