Possibilities of filter-refining of metals and the required characteristics of the filter elements: A review

Abstract

The level of the physical and mechanical properties of steels and alloys can be improved by decreasing the degree of their contamination with nonmetallic inclusions. Among the methods and the technological routes available for solving this problem, the filter-refining method appears to be promising. This method involves passing a molten metal through a filtering unit in which the particles of the nonmetallic phase are separated out and are arrested at the developed surface of the filter. This concept is not new; in the Soviet literature, the process is known as the "Firam-process." This method reduces the extent of contamination due to nonmetallic inclusions during the process of pouring molten metals into the ingot molds and the molds used for continuous casting or in foundry.At the present time, a large volume of experimental data is available on this subject. Systematization of these data is required mainly for evaluating the prospects of application of this method for refining steels and alloys under the conditions of mass-scale production.A filter element (filter-assembly) forms the main technological component of any filtering unit. Under industrial conditions, two basically different designs of the filter elements have been tried out. The first design includes a refining chamber having a granular (lump) sorbent. The sorbent granules are obtained by fragmenting (dispersing) large lumps of a refractory ceramic. A ceramic filter element forms the main component of the second design. Different methods are used for producing it (in particular, compaction, slip casting, extrusion of a refractory body, compaction of ceramic granules into a single block containing a developed system of pore channels, and braiding of glass fibers or the fibers of a plastic ceramic material). In recent years, the so-called 'foam' filter elements have gained in importance. They are obtained by impregnating foamed polyurethane with a ceramic suspension, squeezing out the excess suspension, drying, and firing. The filter elements are located in the intermediate spaces during top-pouring of steels [i, 9], in the channels of the bottom-pouring lines [13], in the intermediate ladles [2, 6-8, I0, 14], in the channels of the immersible nozzles (downtubes) used during continuous casting [15], in the short pipes (nozzles) of the RH and DH installations [16], and in the casting equipment [17]. Figure 1 shows the dispositioning of the filter elements during top and bottom pouring and continuous casting.The method proved to be highly effective when refining the plain-carbon steels that were deoxidized (killed) using A1 [5,8,12,14] The maximum weight of the alloy being refined amounted to 250 tons [6] at a pouring rate of 2.5 ton/min [14].The effectiveness of the filter-refining process is indicated by the decrease in the contamination due to nonmetallic inclusions [5,8,9] and the total oxygen content in the alloy [i, 2, 5, 18] and, in a number of cases, by the decrease in the sulfur content [ii]. All et al. [5] and Fukudo [7] observed a decrea...

Functionalized Carbon‐Bonded Filters with an Open Porous Alumina Coating: Impact of Time on Interactions and Steel Cleanliness

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Carbon‐Bonded Alumina Spaghetti Filters by Alginate‐Based Robo Gel Casting

“…[11][12][13][14][15] Steel melt filtration is a promising method to remove these last detrimental inclusions prior to casting. [5,[16][17][18][19][20][21][22][23][24] Commonly, ceramic filters are produced by the so-called replication technique.…”

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