Development of a lining made from Karelian quartzites for crucible induction furnaces

Abstract

Factors are considered that increase the service life of a lining for a crucible induction furnace. Results are provided for laboratory studies and industrial tests of Karelian quartzites of Jotnian age of the Shokshinsk for- mation and Jatulian age of the Metchang'yarvinsk formation. The effect of impurities is quartzites on crucible induction furnace lining wear resistance is studied. Brief characteristics of quartzites are provided. The possi- bility is established of using waste materials from quarry production of Shokshinsk quartzites for preparing quartzite mixes. Crucible melting of cast iron, steel and non-ferrous met- als relates to the main requirements of casting-metallurgical technology and also exhibits economic advantages over cu- pola melting of cast iron, and it has a cheap and rapidly re- placeable acid lining. The economics of operating melting furnaces and the quality of melted metal depend on the qual- ity and service life of the lining. Specifications laid down for lining materials relate to refractories based on quartzite. A quartzite lining is favorably distinguished from magnesite and alumina materials by cheapness and the fact that shrink- age is balanced by growth of quartz during allotropic trans- formations. Domestically produced furnaces for melting cast iron, steel and alloys based on copper mainly operate on a quartz lining. This lining is also most widespread abroad. For exam- ple, in Germany about 90% of induction furnaces use it. Quartzites that during quartz inversion retain adequate strength and density are suitable for lining induction furnaces (1). In crucible induction furnaces (Fig. 1) metal has a ther- mal, chemical, and erosion effect on the lining. High metal- and slag-resistance of the lining is provided by minimum po- rosity of the sintered layer of the lining, for example of the Swedish lining mix Radanit (Fig. 2). An acid lining of a quartz mix has a constant volume or little growth within the limits of 1% during service. Between the sintered part of the lining and the inductor during crucible firing and its opera- tion a lightly-sintered (buffer) layer is created that prevents the spread of cracks deeper into the lining towards the induc- tor. Lining expansion gives rise to slow sintering of the rammed walls of the crucible due to which a powder buffer layer is retained for a long time. The safety of operating a furnace with an acid lining is provided by the fact that the buffer layer prevents breakthrough of molten metal to the in- ductor. An acid lining is quite inert with respect to molten cast iron and slag, and it exhibits the required refractoriness.