RU2271262C2 - Large-size ingot mold working surface alloying method - Google Patents

Abstract

FIELD: manufacture of large-size ingot molds cast with use of sand-clay mixture.

SUBSTANCE: method for alloying working surface of large -size ingot molds with mass in range 15 - 25 t comprises steps of applying pickup preventing paint onto surface of core of sand-clay mixture; drying core and applying onto it aluminum containing composition. Said composition contains, mass. %: cryolite, 6.0 - 7.0; sodium chloride, 7.5 - 9.1; refractory clay, 10.0 -15.0; potassium chloride, 2.0 - 3.0; sodium bicarbonate, 2.0 - 3.0; aluminum powder, the balance. Content of sodium chloride in relation to cryolite is in range 1.1 - 1.3. Composition with density 1.6 -1.8 g/cm³ is applied at flow rate 1000-1500 g/cm³ onto core having temperature 50 - 100°C . Alloyed layer with thickness 500-700 micrometers containing aluminum up to 20% is formed on ingot mold.

EFFECT: enhanced strength of large-size ingot molds.

1 tbl, 18 ex

Description

The invention relates to ferrous metallurgy, in particular to foundry, and can be used to reduce burns, up to the complete elimination of longitudinal cracks and increase the resistance of large molds weighing 15-25 tons (TU 14-12-14-84) cast using sand-clay mixture rods.

A known method of alloying the working surface of medium (8-15 tons) and small (3-8 tons) molds, which consists in the fact that on the surface of the rod of sand-clay mixture, after applying non-stick paint on it and drying it in a drying device, a layer of aluminum-containing paint containing wt.%: cryolite - 2-4, sodium chloride 6-8, potassium chloride 4-8, refractory clay 10-18, aluminum powder - the rest, while the paint is applied with a density of 1.30-1.80 g / cm ³ and a flow rate of 600-2000 g / m ² [1].

The known method is unacceptable for large molds, because the mass of the molds is large, slow cooling occurs, which leads to the resorption of the diffusion (alloyed) layer on the mold weighing 15 tons or more. In addition, the low cryolite content leads to an increase in aluminum loss by oxidation. The total loss of aluminum reaches 67% of the total mass of aluminum contained in the paint. The parameters of the doped layer are reduced. So the concentration of aluminum in the layer reaches 3%.

The resistance of the mold differs slightly from the resistance of the ordinary mold.

In addition, a known method of alloying the working surface of a mold, comprising applying to a rod of sand-clay mixture after coating it with non-stick paint and holding in air for 20-60 minutes, an aluminum-containing composition, in the following ratio of components, wt.%: Cryolite 2.0- 5.0, sodium chloride 9.0-11.0, refractory clay 8.0-12.0, dextrin 1.4-1.8, water glass 1.5-5.0, inhibitor 0.02-0, 04, aluminum powder - the rest, the composition is diluted with water to a density of 1.56-1.70 g / cm ³ at a flow rate of 800-1900 g / m ² [2].

This method has been used at the Chelyabinsk Metallurgical Plant since 1993 in the production of molds SS-6.2 and LS-6.2. Consumption ratio reduced to 4 kg / t.

The known method of alloying the working surface of the mold is unacceptable for a large mold weighing 15 tons or more, the composition for alloying the mold is ineffective. With a mass of 15 tons or more, cooling occurs slowly, the doped layer exfoliates. The content of cryolite and sodium chloride, having a melting point of about 700 ° C, with such a mass of molds contributes to this. The resistance of the mold practically does not differ from the resistance of the ordinary mold.

This method is the closest in technical essence and is taken as a prototype.

The problem to which the invention is directed, is to increase the operational stability of a large mold weighing 15-25 tons

This object is achieved by the fact that the proposed method of alloying the working surface of a large mold, including applying a non-stick paint to the core from a sand-clay mixture, and after drying it, applying an aluminum-containing composition that contains aluminum powder, cryolite, sodium chloride, refractory clay, while the composition is additionally introduced sodium bicarbonate and potassium chloride in the following ratio of components, wt.%:

Cryolite 6.0-7.0 Sodium chloride 7.5-9.1 Potassium chloride 2.0-3.0 Refractory clay 10.0-15.0 Sodium bicarbonate 2.0-3.0 Aluminum powder rest, moreover, the ratio of sodium chloride to cryolite is 1.1-1.3,

The composition is applied with a density of 1.6-1.8 g / cm ³ at a flow rate of 1000-1500 g / m ² at a surface temperature of the rod 50-100 ° C.

The essence of the invention is the quantitative content of cryolite and sodium chloride, which reduces the temperature of cryolite to 780-820 ° C and thereby limits the time of alloying the surface of the mold without resorption of the already formed alloy layer. Potassium chloride, which increases the fluidity of the melt aluminum - aluminum oxide - cryolite - sodium chloride, promotes the formation of a compact alloyed layer.

Experimentally established:

- when the ratio of sodium chloride to cryolite 1.1-1.3, an alloyed layer is formed with a thickness of 500-700 microns with an aluminum content of up to 20%. Such an alloyed layer provides an increase in the resistance of the mold by 20-25%. If the ratio of sodium chloride to cryolite is different, for example, as in the prototype, 1.8-5.5, resorption of the alloyed layer reduces the aluminum content in the layer to 2.0-3.0% with increasing layer thickness to 1000-1500 microns. The durability of such a mold does not practically differ from the ordinary mold;

- it was found that the formation of a compact doped layer is achieved by introducing 2.0-3.0% potassium chloride into the paint, which increases the fluidity of the melt aluminum - aluminum oxide - sodium chloride. For this purpose, the introduction of 2.0% potassium chloride into the composition is quite sufficient. An increase in the content of potassium chloride to 3.0% has little effect on fluidity. The content of potassium chloride in excess of 3.0% does not affect fluidity at all;

- refractory clay, a binding component of the composition, as well as the protection of aluminum powder from oxidation when cast iron is cast into a mold. In addition, clay provides the necessary density of the composition. When the clay content is less than 10.0%, the covering power of the composition decreases, the density of the composition decreases, and aluminum powder may settle. With a clay content of more than 15.0%, burns may occur. The density can go beyond the declared range, the quality of the working surface of the mold is reduced, application of the composition by the atomizer is difficult, which leads to a decrease in the resistance of the mold. Sodium bicarbonate is used to reduce the oxidation of aluminum in the composition during its manufacture and storage. It is known that 1 kg of aluminum powder in water emits up to 10 liters of hydrogen per hour. The resulting air bubbles reduce the density of the composition. The quality of the applied layer is reduced, which leads to a decrease in the resistance of the mold. The optimal density of the composition of 1.6-1.8 g / cm ³ . At such a density, there is no flow around it from a rod having a surface temperature of 50-100 ° C. With a lower density, this is possible. When the composition density is more than 1.8 g / cm ³ , irregularities and tubercles are formed, which reduces the surface quality, an uneven thickness of the alloyed layer is formed, and the resistance of the mold is reduced.

The claimed consumption of the composition of 1000-1500 g / m provides the formation of a doped layer with a thickness of 500-700 microns with an aluminum content of up to 20%. It is impossible to obtain an aluminum content of more than 20% + 1% in this way.

When the composition consumption is less than 1000 g / m ^2, it is impossible to obtain an aluminum content of 20% due to a lack of aluminum.

Consumption of a composition of more than 1500 g / m ^{2 is} impractical, an increase in the doped layer does not occur. Part of the composition creeps on the surface of the rod during application. Sections with a small layer thickness are formed, which reduces the size of the doped layer and, therefore, the resistance of the mold.

An analysis of technical solutions in the studied and related fields allows us to conclude that there are no signs in them that are similar to signs in the claimed object, and to recognize them as meeting the criterion of "significant differences".

The pilot industrial application of the method took place at the Magnitogorsk Iron and Steel Works in the molds shop on the molds UN-18, UN-19, UN-20, UV-16.9 (deaf). Earlier, at MMK, a method was used to increase the resistance of molds weighing 8 tons. But this method turned out to be completely unsuitable for molds of large sizes over 15 tons

The table shows the data of industrial tests of the method of alloying the working surface of the mold according to the prototype and according to the invention.

Example 1. The example shows the application of the previously used method with an aluminum-containing composition of the prototype for molds weighing 8 tons

Example 2. The content of cryolite is less than the declared, while changing the ratio of sodium chloride to cryolite. The durability of the mold practically does not change.

Example 3. The cryolite content is more than stated. The ratio of sodium chloride to cryolite is changing. The durability of the mold at the level of the ordinary mold.

Example 4. The content of potassium chloride is less than stated. The durability of the mold is reduced.

Example 5. The content of potassium chloride is greater than the declared limit. The mold does not affect the durability.

Example 6. The content of refractory clay is less than the declared limit. A creep of the composition occurs, areas with a thin layer appear. The durability of the mold is reduced.

Example 7. The content of refractory clay is greater than the declared limit. The surface quality is reduced. Tubercles form, the mold resistance decreases.

Example 8. The content of sodium bicarbonate is less than the declared limit. Air bubbles form during preparation and storage of the composition. Difficulty applying the composition. In places, unevenness of the layer is formed. The durability of the mold is reduced.

Example 9. The content of sodium bicarbonate is greater than the declared limit. Practically does not affect the durability of the mold.

Example 10. The density of the composition is less than declared. A flow around the composition is observed, in places a thin layer forms. The durability of the mold is reduced.

Example 11. The density of the composition is higher than stated. In some places, a layer of a composition thicker than normal is observed, and a thick layer creeps in. Surface sections are exposed, mold resistance is reduced.

Example 12. Consumption of the composition is less than stated. The aluminum content in the composition is reduced. The durability of the mold is reduced.

Example 13. Consumption of the composition is more than stated. Part of the composition is sliding. A thin layer remains in places. The resistance of such sections decreases to the level of an ordinary mold; the resistance of the mold as a whole decreases to the level of an ordinary mold.

Examples 14-18. All parameters are within the specified limits. The durability of the mold increases.

The proposed method, which passed pilot industrial tests at the Magnitogorsk Iron and Steel Works on the molds UV-16.9, UN-18, UN-19, UN-20, allowed to increase the resistance of the molds to 30%. The method is acceptable for industrial use.

Claims (1)

A method of alloying the working surface of a mold, comprising applying a non-stick paint to a rod from a sand-clay mixture, and after drying it, applying an aluminum-containing composition containing aluminum powder, cryolite, sodium chloride, refractory clay, characterized in that potassium chloride and bicarbonate are additionally introduced into the composition sodium in the following ratio, wt.%: Cryolite 6.0-7.0 Sodium chloride 7.5-9.1 Fire-clay 10.0-15.0 Potassium chloride 2.0-3.0 Sodium bicarbonate 2.0-3.0 Aluminum powder Rest the ratio of the content of sodium chloride to cryolite is 1.1-1.3, the composition is applied with a density of 1.6-1.8 g / cm ³ at a flow rate of 1000-1500 g / m ² at a surface temperature of the rod 50-100 ° C .