No abstract
In the boundaries of plants of various branches of industry, the MDN-6A standard magnetodynamic feeder [1][2][3][4], which is an induction channel furnace with an an additional electromagnet, is widely used for mechanization and automation of the process of pouring aluminum alloys into the casting mold.The feeder includes a rectangular crucible holding 250 kg of aluminum alloy to which is fastened a vertical UJ-shaped channel (Fig. i).The channel lining is a double-layer one (Fig, 2). The inner portion is made of a shaped part with a wall thickness of 15 mm, which is produced from molten oxyfluorides by casting in a sand-clay mold using a method developed in the Institute of Problems of Casting of the Academy of Sciences of the Ukrainian SSR [5]. The primary phase of the casting material is potassium fluorophlogophite KMgs(SisAl01o)F2, which is a synthetic analog of natural phlogopite in which the [OH]-: group is replaced by fluoride ions. Other crystalline formations and also free glassy phase may be present in the material.The properties of the fluorophlogopite part are apparent density 2.68-2.71 g/em s, open porosity 0.5-3.8%, compressive strength 50-120 N/mm 2, and heat resistance in the 293-973 K range more than 200 thermal cycles [6,7].The outer layer of the lining is made of various materials including SKM-97 silica compound to TU 14-8-92--74 and chamotte-magnesia heat resistant concrete or concrete based on crushed chamotte with a portland cement binder filling the space between the fluorophlogopite casting and the metal shell of the channel.As a rule the crucibe lining is made of the same materials.Encrustation of the channel occurs in service of the feeder.The formation of the crust leads to a breakdown in feeding of the metal and is the main reason for compulsory shutdowns of the equipment.In connection with this a study of the character of encrustation and the structure and composition of the crust is of important value in searching for means of increasing the service life of the lining and stability of operation of magnetodynamic feeders, This article presents the results of investigation of the condition of the cavity and composition of the crust of the channels of MDN-6A feeders in operation under the conditions of two different plants for 1.0-8.5 months casting AL2 and AK7 alloys, which contain 5-13%* silicon, 0.5-1.0% magnesium, and 1.0-1.5% iron. After service of the feeder the fluorophlogopite parts were removed from the shell, freed from the layer of thermal insulation, and cut with a diamond saw on a plane coinciding with the vertical axis of symmetry.This made it possible to reveal the condition of the inner surface of the lining element (Fig. 2).It was established that regardless of the operating time encrustation of the channel cavity has a local character.The crust is formed in one of its side vertical portions at the level of the feeder inductors.Here the thermal insulation layer of the lining is frequently fused.Failure of the fused and cast fluorophlogopite material is observed not rar...
The foundries of a number of plants and production unions of the country are equipped with standard magnetodynamic furnaces designed for automatic proportioning of aluminum and zinc alloys in casting machines. The MDN-6 furnace is an induction channel furnace with an additional electromagnet and includes a rectangular crucible to which is fastened a vertical | channel [1][2][3]. The channel lining is made both as a double-layer one with cast inserts [3, 4] and as a single-layer one of a rammed refractory compound. In service of a furnace with a rammed lining there are frequently cases of compulsory shutdowns revealing of the reasons for which this investigation is devoted to.The MDN-6A-0.16 furnace has been in service under production conditions for 25 years in proportioning of an aluminum alloy into the casting mold of a casting machine under pressure. The composition of the alloy* is 0.2-0.4 Mg, 6.0-8.0 Si, 0.1 Mn, 0.1 Cu, 0.2 Zn, 0.005 Sn, 0.03 Pb, and remainder A1. The crucible and channel lining was made of semidry ramming compound by ramming. The composition of the compound was 45% magnesite, 40% chamotte, 13% water glass, and 2% sodium fluosilicate. After service the lining was cut lengthwise and one of the side branches perpendicular to the vertical axis of symmetry, which made it possible to conduct the required observations (Fig. 1).tVisual inspection showed that within the channel in one side channel and in the area of the active zone there are crusts. Their thickness differs and in the active zone they have the tbrm of stalactites. The lining is permeated with a multitude of cracks, most of which are filled with aluminum alloy. In places they have penetrated to the shell.At the contact with the aluminum the lining material undergoes transtbrmations revealed in a change in structure and color (Fig. 2). The metal penetrating through the pores and microcracks reacts with the binder, forming thin (30/xm) white borders around the filler grains. Petrographic analysis in combination with x-ray diffraction data made it possible to establish that these formations are low-temperature quartz (d/n 3.34, 2.12, 1.81, 1.54, and 1.37). As the result the zone adjoining the contact surface acquires a light and in places white color (Fig. 2), which makes it possible to determine the depth of penetration of aluminum. The thickness of the changed layer in the horizontal portion of the channel is 10 mm and in the vertical up to 20 ram. Particles of chamotte and magnesite do not react with the metal alloy, remaining unchanged but sometimes with a dark color.The structure and phase composition of the crusts tbrmed in the channel were studied. In the side channel the height of the crust is 160 mm. Its thickness differs and is greatest close to the crucible. Along the walls perpendicular to the plane of the channel cross section the crust thickness is the least, 2 tO 5-7 mm (Fig. 1). On the walls parallel to the cross section plane the crust is significantly thickner, up to 20-30 ram, which leads to a decrease in the cross se...
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