Phase composition of the products of encrustation of the channels of magnetodynamic feeders for aluminum alloys

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...

Interaction between molten aluminum and potassium fluorophlogopite

“…For example, the conducted experiments show that at 700-800~ the test specimens do not virtually interact (react) with molten aluminum [3]. However, the service life of the products exposed to the flowing metal (in particular, in magnetodynamic batching units) varies over a wide range (from 1.5 up to 8 months) [4]. The existing problems made it necessary to carry out dynamic tests on the fluorophlogopite materials in order to establish the reasons and the nature of their destruction.…”