RU2238168C1 - Additive for molding sands - Google Patents

Abstract

FIELD: foundry, namely casting of magnesium alloys to sand molds.

SUBSTANCE: additive for molding sands contains boric acid, 14 - 20 mass %; aluminum fluoride, 8 - 18 mass % and urea, the balance. Additive may contain in addition manganese carbonate, magnesium carbonate, copper sulfate, ammonium sulfate, aluminum sulfate or magnesium sulfate in quantity 4 - 8 mass %.

EFFECT: improved protection of magnesium alloys against oxidation and pickup, enhanced sanitary condition at operation.

2 cl, 2 tbl

Description

The invention relates to foundry, and in particular to a protective additive for molding mixtures used in shaped casting of magnesium alloys in sand forms.

Known typical formulations of molding compounds for shaped casting of magnesium alloys include sand of various grades, bentonite and a protective additive.

Molding sand mixtures serve to fill foundry molds that are filled with liquid magnesium alloys. The molten liquid magnesium alloy poured into the mold in the air of the mold cavity is oxidized and therefore, to protect the liquid magnesium alloy from oxidation, a protective additive is added to the molding mixture, which protects the molten metal in the mold from oxidation and thereby prevents the formation of oxide defects on the surface of the hardened casting (details ) and burnout.

The principle of the protective action of additives is based on thermal decomposition, hydrolysis of its components, the formation of gases neutral to the melt of magnesium alloys, and their partial interaction with the metal with the formation of protective films on the surface of the castings.

Known additive for molding mixtures containing sulfur pyrite and boric acid in the ratio in wt.% (2.0-9.0) :( 0.5-3.0) (AS USSR No. 1228418).

The disadvantage of this additive is the likelihood of the formation of hydrogen sulfide in the process of filling sand molds with liquid metal and the lack of protection of the liquid metal from oxidation until the sand-borne layer of the sand mixture is heated to 350-400 ° C.

Known additive, consisting of urea ,, boric and sulfuric acid in a ratio of 2: 1: 2 (AS USSR No. 330899). It has a laborious, insecure cooking technology due to the presence of acids and has not found industrial application.

The closest in composition and purpose, taken as a prototype, is a VM additive having the following chemical composition in wt.%:

Boric acid 13-17

Aluminum sulphate crystalline hydrate 15-19

Urea Else

(Magnesium alloys II. Reference “Production technology and properties of castings and deformed semi-finished products.” Moscow, Metallurgy, 1978, p. 109).

A disadvantage of the known additive is its low protective properties, especially in the temperature range 100-300 ° C of the boundary layer of the sand mixture containing the protective additive with the metal.

The technical task of the invention is the creation of additives for molding mixtures of casting molds of magnesium casting, which reliably protects molten magnesium alloys in the mold from oxidation - burning and burning in a wide temperature range of the mold (150-700 ° C).

The solution to this problem is achieved by the fact that the proposed additive for sand foundry forms of magnesium casting, including urea, boric acid, which additionally contains aluminum fluoride in the following ratio of components in wt.%:

Boric acid 14-20

Aluminum fluoride 8-18

Urea Else

The additive may additionally contain one component from the group comprising carbonic manganese, magnesium carbonate, copper sulfate, aluminum sulfate, ammonium sulfate, magnesium sulfate in the following ratio of components in wt.%:

Boric acid 14-20

Aluminum fluoride 8-18

One component from the group including:

Manganese Carbon

Magnesium carbonate

Copper sulfate 4-8

Aluminum sulfate

Ammonium sulfate

Magnesium Sulfate

Urea Else

The difference between the proposed additive composition and the prototype composition is the introduction of aluminum fluoride, which can have no more than 3 molecules of crystallization water, while the aluminum sulfate contained in the prototype additive has 18 water molecules, and the weight ratios of these two components in the additives are approximately equal. For this reason, and due to the inherent hygroscopicity of this substance, the prototype additive is moistened during transportation and storage. High humidity additives adversely affects the quality of castings obtained by sand casting, as it pollutes the surface and sections of the castings with oxides and slags.

The aluminum fluoride contained in the proposed additive is not hygroscopic, and its partial interaction with liquid magnesium forms a film of magnesium fluoride on the surface of the castings, which has a positive effect on the surface cleanliness of the castings and their corrosion resistance.

To improve the technological characteristics of the additive and molding mixtures, when obtaining critical parts of aerospace engineering, one substance from the group is introduced into its composition: manganese carbonate, magnesium carbonate, copper sulfate, aluminum sulfate, ammonium sulfate, magnesium sulfate.

Each of these substances has different decomposition temperatures and more effectively protect the surface of the casting from the formation of oxides and burns during the filling and crystallization of liquid metal in the mold.

The proposed additive formulations and molding compounds, including it, have been tested in laboratory and factory conditions. In runners-mixers, a typical molding mixture was prepared in an amount of 40-400 kg from sand with the addition of one of the compounds listed in table 1, in which the proposed compositions are listed by serial number 1-9, and the composition of the prototype additive under number 10 . Additive to all formulations of the molding sand was added in an amount of 6% of the total weight of the molding sand. In total, nine compositions of the molding mixture with various additives were prepared (table 2).

The manufactured sand casting molds were poured with ML5 liquid magnesium alloy and, after cooling, metal shaped castings and samples were extracted from them.

The surface properties of castings and samples were evaluated for the protective properties of the used molding sand compositions and protective additives. From the data of table 2 it follows that all tested compositions of protective additives allow you to get the best quality in cleanliness (oxide inclusions) of the surface of the castings compared with the protective additive prototype, which confirms the increased protective properties of the proposed additives. The number of defective castings is reduced by about 2-4 times. With the exception of additives No. 7, 8, all of them do not contain aluminum sulfate, which, due to the content of 18 water molecules in it, greatly moisturizes the additive and, in contact with liquid metal, hydrogen sulfide may be released. However, the composition of additives No. 7, 8 contains aluminum sulfate less than the composition of the prototype and therefore the possible release of hydrogen sulfide is also less.

When using additives of compositions No. 1, 2, 3, 4, hydrogen sulfide is not released and this improves sanitary and hygienic working conditions and the environment.

The number of defective samples during their use in comparison with the additive prototype is reduced by 2-4 times, which will allow to obtain an economic effect.

Thus, the application of the invention will allow to obtain high-quality castings from various magnesium alloys, reduce labor and energy costs to eliminate defects in the castings (parts) and improve sanitary conditions.

Claims (2)

1. Additive for the molding mixture of casting molds of magnesium casting, including urea, boric acid, characterized in that it additionally contains aluminum fluoride in the following ratio, wt.%: Boric acid 14-20 Aluminum fluoride 8-18 Urea Else 2. The additive according to claim 1, characterized in that it additionally contains one component from the group comprising carbonic manganese, magnesium carbonate, copper sulfate, ammonium sulfate, aluminum sulfate, magnesium sulfate, in the following ratio, wt.%: Boric acid 14-20 Aluminum fluoride 8-18 One component from the group: carbon dioxide manganese, magnesium carbonate, copper sulfate, ammonium sulfate, aluminum sulfate, magnesium sulfate 4-8 Urea Else