The presence of non-metallic impurities which are released into the melt during the melting process and casting the liquid metal affects the quality of smelted metal. It is known and the steel industry and the foundry and metal processors.
Overwhelmingly non-metallic inclusions are refractory oxides with melting temperature above the melting point of steel. This is mainly oxides of magnesium, calcium, aluminum and silicon included in the slag and lining material. A significant portion of non-metallic inclusions formed in the melt as a result of the deoxidation of steel . The solubility of oxides in pure iron with little or no.
Non-metallic inclusions, often presented in the form of compact solid particles. Oxide films in the melt are in the liquid state, but have a much higher viscosity of the molten metal. The content of the mentioned impurities can be significantly reduced. This can be achieved in a whole set of activities including qualitative cutoff of slag, reducing erosion of the lining of steelmaking stalevich gutters, steel-teeming and intermediate ladles, purging the melt with inert gases and by filtering of the metal, using various options and methods of filtration.
Due to the fact that the fractional composition of nonmetallic inclusions is in a very wide range - from fractions of a micron to tens of millimeters, the degree of purification of the metal and therefore its quality depends on what methods of cleaning were used in its production.
Oxide and gas bubbles, having a density significantly less than the liquid iron, under certain conditions, which are described by known physical laws, is able to switch completely to the melt surface. However, these conditions practically is not possible. In particular, increased time spent resplablanovo metal in the steelmaking facilities and reduced viscosity, increased wear of the lining and the secondary saturation of liquid metal non-metallic inclusions. Intensive treatment of the melt with an inert gas allows to remove not more than 15% of non-metallic inclusions, while most particles smaller than 50 microns remain in the liquid metal.
We would like to highlight some of the most delicate method of cleaning of metal, when saturation of the melt of non-metallic impurities is unavoidable. This method consists in filtering the metal through the ceramic foam filters and ability to remove almost all existing non-metallic inclusions and gas bubbles.
Filters are volume Panoramico of high-refractory materials with a specified number of holes and a certain specific surface.
The mechanism of purification of the melt with the ceramic foam filters is quite complex and poorly understood, but, nevertheless, the efficiency of cleaning by this method can be called unique. This can be confirmed by casters who have the ability to apply the same materials of foreign production to obtain high-quality castings.
Depending on the filter material and configuration can be performed both full and selective degassing of the melt. With the passage of the contaminated metal through the filter, inside the ceramic base is induced EMF, which can adjust the phase and chemical composition and specific surface of the ceramic and the flow rate of the metal. Flowing through the ceramic filter, the flow of molten metal, except that it is cleaned, it is additionally homogenized. This, of course, affects the quality of castings.
Existing experience of applying ceramic foam filters for cleaning of low-melting metals and filtration of steel by the method of precision casting, with respecstuudy structural modifications, can clean a much larger volume of liquid metal.
We propose to consider several options for the use of ceramic filters:
in the continuous casting of steel,
in the case of casting steel into molds,
in the casting of iron and steel in sand molds, the molds and investment casting.
In the continuous casting of steel, the filters are installed in filter walls in different levels, as shown in the figure.
As overgrowth of the filters at the same level, the metal rises to the next level of filters, which may be different from the previous structure and the number of holes. The upper level of holes in the partition does not have filters. Thus the casting of metal according to his level, you can control the quality of ingots for the content of non-metallic inclusions. In the existing bulkhead hole there is the possibility of setting of filters, "coarse" and "fine" cleaning.
Currently together with a number of metallurgical enterprises have carried out preparatory work for testing this method of purification of liquid metal from non-metallic inclusions and development of compositions and parameters of ceramic filter.
1. Korotich, V. I., Bratchikov S. G. the metallurgy of ferrous metals. M., metallurgy, 1987, p. 240 .
Published in the journal "Steel" № 7, 2005 (p. 43)
Addition to the article
Within three years after publication in the journal "Steel", No. 7, 2005 article "the Possibility of removing non-metallic inclusions from the melt using a ceramic Filtrow" views on the problems of filtration of liquid metal has changed significantly.
Held jointly with JSC "Chelyabinsk tube rolling plant" and JSC "Seversky pipe plant" work on the use of ceramic foam filters for casting steel into molds not give a positive result. The reason in this case, one is a chemical interaction of liquid iron with the ceramic material of the filter. What would be the melting point or had ceramics, with available thicknesses of lintels filter (up to 2 mm), the speed of its dissolution in the liquid metal were not significantly different. Thus, filters made from aluminum oxide, magnesium oxide, zirconium dioxide and titanium carbide is able to retain its shape for 7-15 seconds, and to a greater extent time until complete dissolution of the filter depended on the thickness of the bridges between the cells of the ceramic foam.
On the basis of their studies, to talk about the possibility of applying ceramic foam filters to clean the steel from non-metallic inclusions at the time of operation of the filter more than 7 seconds prematurely, especially when using filters of this type in the continuous casting of steel.
All of the above provisions in the article relating to the work of ceramic foam, correct only for cleaning non-ferrous metals with melting points much lower than the melting point of steel, or for short-term use.
A particularly effective ceramic foam filters to remove non-metallic inclusions from molten aluminum and when used with the same purpose in the case of casting of iron and steel in foundries with a casting weight up to 700 kg.
With regard to the removal of nonmetallic inclusions in continuous casting of steel and casting it in a mold, it needs a fundamentally different approach. As one of the options we are considering further refining with the use of vibrations of ultrasonic frequency. Work in this direction lead usll received some positive results and we hope that soon this method of cleaning steel and cast iron will find wide application metallurgists and machinists. (See the article "the effectiveness of the refining of molten aluminum when exposed to the melt, vibrations of ultrasonic frequency")