SU1072979A1 - Mix for producing cores and facing sand when casting magnesium alloys and method for preparing the same - Google Patents

Abstract

1. Mixture for the manufacture of cores and cladding layers in the casting of magnesium alloys, including refractory filler, carbamide-furan resin, orthophosphoric acid, boric acid and water, oj | jj and h with the aim of increasing the strength of rods and molds, improving the protection of magnesium alloys from oxidation and reducing the rejection of castings P6 gas defects, it additionally contains sodium thiosulfate in the following ratio: Research Institute of Components, May.%: Urea resin 1.5-3.0 Orthophosphoric acid 0.2-0 , 5 Borna acid 0, 3-0.5 Water 0.20-0.75 Sodium thiosulfate 0.4-1.5 Refractory filler Remaining 2. Method of preparing a mixture of i for the manufacture of rods and cladding layers of casting magnesium (L alloys, including an introduction to the refractory filler and mixing with it a carbash dofuran resin, orthophosphoric acid and boric acid, characterized in that, in order to improve the protection of magnesium alloys from oxidation, a previously prepared composition of orthophosphoric and boric acids is introduced into the refractory filler, and then carba Ido: furan resin, which predvaso | ritelno added 66-67% aqueous sodium thiosulfate solution. Kj co

Description

The invention relates to a foundry, in particular, to cold-hardening compositions of bio-resinous mixtures for the manufacture of cores and cladding layers during the casting of magnesium alloys, as well as to the method of preparation of these mixtures.

The use of cold-hardening sand-resin mixtures in the manufacture of casting molds and cores eliminates energy-intensive processes (for example, drying /, significantly shortens the production cycle and ensures that molds and cores of enhanced accuracy are produced by curing them directly in a snap.

The known cold-hardening mixture for casting magnesium alloys, containing a refractory filler, urea resin, p-phosphoric acid, water and boric acid 13.

However, when using this mixture to prevent oxidation of the melt at the first moment of its entry into the mold, it is necessary to apply a protective paint to the cavity of the casting mold that forms the casting and profitable system, the hot dust on the surface of the dry rods, which is an additional step.

Know the use of powdered sulfur, as a protective pripyla.

The resulting sulfur dioxide, interacting with the alloy, forms a protective film of magnesium sulfate on the surface of the C2D casting.

However, the use of powdered sulfur is extremely undesirable, since it is unevenly distributed on the surface of the mold, causes high gas evolution and does not eliminate the presence of oxide films and gas defects in the castings.

The closest to the invention according to the technical nature and the achievement of the MQMX result is a cold-hardening mixture for the manufacture of rods and cladding layers of casting magnesium alloys in the following ratio of compers, wt% amidofurans

resin (CSF-1) 3,0 Orthophosphrrna acid 0,4

Boric acid 0.5 Sulfur1,0

Bura0,2

Water2.0

Fireproof floor-. ., p.Otalnoe GZZ.

The method of preparation of the known resin consists in the sequential input with stirring into the beaker of phosphoric acid, water

boric acid solution, tar and powdered sulfur and borax GZZ.

However, a mixture prepared in a known manner is characterized by an uneven distribution of the protective additives of sulfur, boric acid. borax in powder form, which does not sufficiently protect the magnesium alloy from oxidation. Therefore, on the surface of the molds and cores it is necessary to additionally apply powdered sulfur or other pripyt. In addition, gas defects in castings are not excluded due to the high gas activity of the known mixture.

The purpose of the invention is to increase the TO4 ji of rods and molds to improve the protection of magnesium alloys from oxidation and reduce scrap casting for gas defects.

The goal is achieved by the fact that the mixture for the manufacture of cores and the Facing Layer Forms in the casting of magnesium alloys, including refractory filler, carbamidofuran resin, orthophosphoric acid, boric acid and water, additionally contains sodium thiosulfate in the following ratio of components, wt.%:

Carbamidofuranovs resin1.5-3.0

rtofosforna

acid0,2-0,5

Boric acid 0.3-0.5 Water 0.20-0.75

Sodium thiosulfate 0, 4-1.5 refractory

filler Else The goal is achieved by the fact that, according to the method, the introduction of urea resin, phosphoric acid and boric acid into the refractory filler and mixing with it, the previously prepared composition of orthophosphoric acid and boric acid, and then urea resin, in which a 66-67% sodium thiosulfate aqueous solution is added previously.

A 66-67% aqueous solution of sodium thiosulfate introduced into the mixture interacts with orthophosphoric and boric acids according to the following chemical reactions:

N "/ 2V W V V4 T V; a" j5203 2 PO - 3S 350j 2ftajpej 5 ",, 0. (And |

These reactions are accelerated by joining the forms with liquid metal.

The form and rods of sandy-cold cold-hardened mixture prepared by the above method, by the time they are filled with liquid magnesium

an alloy according to the reduced reaction media} and (2 ;, sulphide gas is released and it maintains uniformly distributed colloidal sulfur, due to which a protective sulfate film of magnesium is formed at the metal-form interface, which prevents the metal from oxidizing. wired pripilyov.

The resulting borax as a result of the above chemical reaction (2), as well as an excess of boric acid, prevents the metal from being oxidized in the form by precipitating during heating of the boron, which is introduced into the surface layers of the casting to a depth of 10 mm.

The content of the proposed mixture of sodium thiosulfate at the lower limit is due to the fact that the amount is below 0.4%. The effect of staioethe is ineffective, and its content above 1.5% can lead to the formation of gas sinks in the casting.

. . Since in the process of cooling the mold with the casting metal, only a layer of the molding mixture with a thickness of 20–40 mm interacts, the described sand-resin cold-hard mixture during the manufacture of the molds is expediently used as facing.

Example. In tab. 1 shows the compositions 1-3 of the proposed mixture and known, it is accepted as the basic object. The mixtures of l-3i prepared by the proposed method contain uniformly distributed protective additives in the form of colloidal sulfur and borax, a mixture of I 4, prepared in a known manner, contains porous sulfur and borax introduced into the mixture with stirring.

Table

Sand kvsch tsovyy 1KOE

containing clay

1.5-2.0

(GOST 2138-74)

Carbamidofuranova

resin KSF-1

{TU 6-05-02-26-79)

Orthophosphorus ajfi

acid.

Borna acid

Sulfur

Borax

The preparation of the proposed mixtures (9 1-3) was carried out as follows.

The sand is injected as a catalyst, a mash of orthophosphoric acid, previously mixed with boric acid, is stirred for 3 minutes, and a preformed resin composition CSF-1 and a 66-67% aqueous solution of sodium thiosulfate, pos93, are introduced 75

92.9

5.95

2.0

3.0

3.0

0.4

0.3

. 0.5 0.5 0.4 1.0 0.2

The mixing is continued for another 50–60 s.

Preparation of a known mixture, which is taken as the basic object,

carried out in a similar way with the difference that exclude the addition of an aqueous solution of sodium thiosulfate, boric acid is introduced into the mixture with water 2 minutes after the phosphoric

acids, and sulfur and borax are introduced into

the powder immediately after the introduction of the resin.

The test results of mixtures 1-4 are given in table. 2

table 2

32.0 41.0 64.0 56.0

Gas production

mixes

cm5 / D 11.8

12.5 16.6 21.0

Comparisons in terms of properties are subjected to a mixture with identical binder content (carbamide-furan resin), i.e. a mixture of 3 (proposed) and W 4 (prototype) ..

From the data table. 2 it follows that mixture 3, in contrast to mixture 4 (base object), with the same amount of binder, has reduced gas-tightness due to a decrease in the content of mixture 3 of colloidal sulfur resulting from the reaction and increased strength (15% higher than the strength of the base object). a) due to a decrease in water content. The protection of magnesium alloys from oxidation was evaluated by the pyro effect in the process of casting molds in the Kazan foundry to an electro-industrial manufacturing association.

From a mixture of 3 (proposed) and No. 4 (known), the cores and forms with a facing layer were made. When pouring 50 forms with a facing layer and cTepikHeM from a known mixture of W 4 with a magnesium alloy, an intense pyro effect was observed in three forms (b% of the filled forms). When pouring molds with a facing layer and a rod from the mixture (proposed) No. 3, there is no intense pyroelectric effect, which is explained by the protective effect of additives —fc1nomerically distributed throughout the volume of the rod.

Thus, the proposed mixture for manufacturing cores and cladding molds during casting of magnesium alloys, as compared with the base object, provides improved protection of magnesium alloys from oxidation while increasing the strength of molds and cores by 15% and reduces gas defects on castings. In addition, the proposed method of mixing the mixture, which includes sequential input into the floor; with stirring, at the beginning of the previously prepared composition of orthophosphoric boric acid, and then the composition of an aqueous solution of sodium thiosulfate and resin, in contrast to the base object, ensures an even distribution a sand mixture of protective additives evolving from chemical reactions in the form of colloidal sulfur and borax.

The economic effect from the introduction of the proposed invention is 30-35 thousand rubles. in year.

Claims (2)

MIXTURE FOR MANUFACTURE OF RODS AND FACING LAYER OF FORMS WHEN CASTING MAGNESIUM ALLOYS AND METHOD FOR PREPARING IT. ¹ (57) 1. A mixture for the manufacture of rods and a facing layer of molds for casting magnesium alloys, including a refractory filler, urea resin, phosphoric acid, boric acid and water, characterized in that: · with the aim of increasing the strength of the rods _t and molds , improving the protection of magnesium alloys from oxidation and reducing the rejects of πό castings to gas defects, it additionally contains sodium thiosulfate in the following ratio of components, May.%: Carbamidofuran resin Orthophosphoric acid Boric acid Water Sodium thiosulfate Refractory floor 1.5-3.0 0.2-0.5 0.3-0.5 0.20-0.75 0.4-1.5 carrier Else 2. A method of preparing a mixture for the manufacture of rods and a facing layer of molds when casting magnesium alloys, comprising introducing a urea-furan resin, phosphoric acid and boric acid into the refractory filler, characterized in that, in order to improve the protection of magnesium alloys from oxide In the refractory filler, a pre-prepared composition of phosphoric and boric acids is first introduced, and then urea: a furan resin, to which a 66-67% thios aqueous solution is preliminarily added sodium fata.