"ACTION ON REMOVAL of EFFECT of WINDING of SCALE ROLLERS ÌÍËÇ AT POURING LONG SERIES"
Formation of scale at continuous casting is observed in spray cooling chamber and in zone of refrigerator; however processes, occurring in the crystallizer, can exercise a significant influence on scaling.
In the crystallizer surface of preparation is formed oxygenation protection -- how it is possible to consider proof light external type of hard file, got at breaks.
In the meantime in the crystallizer on surfaces of preparation some layer of slag-forming mixture of (slag) is formed, that is then kept on the surfaces in spray cooling chamber. Thickness of layer of slag forming mixture depends from whole number of parameters: speeds of pouring, geometrical form of preparation, physical and chemical properties of mixture (temperature of melting and softening, viscosity in area temperatures of casting and other.) In process of movement on spray cooling chamber part slag forming mixture decrepit ate and partly forces down with water from surface of preparation.
Growth of scale, consisting in steels (Fe3 O4) are primary from wustite with small additives of magnetite and hematite (Fe2 O3), it is accompanied with its cracking on measure progress of preparation and actually brought to that on surfaces of preparation, that on surfaces of preparation local areas, covered with layer of scale are formed, where certain quantity of slag forming mixture is present.
Fluctuations of temperature of scale, connected with cyclic spraying with water in spray cooling chamber, cause surface stresses, bringing to partial destruction of scale and its removing from surface of preparation. Between those, in the presence mixtures of scale and slag, last can be present in softened type, what, per se, promotes to hardening of layer of scale behind account of increase of its plasticity and degree of sticking to surface of preparation.
Hence, on the surfaces sites, covered with layer of scale with blobs of slag can be formed by continuous cast blank. These sites have somewhat other strength properties, that classical layer of scale, formed on surfaces of preparation at secondary oxidation.
In first turn this concerns to durability of scale and its propensity to sticking to metal surface. On measure progress of preparation in spray cooling chamber escalating of layer of scale on surfaces of preparation occurs. So in zone of unbending of preparation enough thick layer of scale is accumulated (several millimeter), that by the action stretching (small radius) and compressing (smooth radius) in addition decrepit ate and it softens.
On plateau scale, arranged on top side of preparation, does not practically leave, continuing to be thickened. In addition in zone of air cooling of preparation are conditioned for not enough intensive cooling of supporting rollers (accumulation of scum in shank bore water-cooler rollers), what actually causes temperature of surface of rollers on line contact with slab on the level 650-700 oÑ and more.
Such temperature surfaces of rollers it is rendered sufficient for display of effect of sticking of scale to them surfaces, that in fact it is confirmed with external type of surface of samples of scale, selected directly from rollers (surface "bubbly" rough). Development of effect of sticking of scale to supporting rollers, probably, is strengthened in case, when, for example, offset of position of roller concerning nominal point occurs .
Findings
1. In the presence mixtures of scale and slag, slag can be present in softened type, what promotes to hardening of layer of scale behind account of increase of its plasticity and degree of sticking to surface of preparation.
2. In zone of air cooling of preparation because of accumulation of scum are conditioned for not enough intensive cooling of supporting rollers, what causes temperature of surface of rollers on line contact with slab on the level 650-700îÑ and more.Äàíûé temperature of surface of rollers is sufficient for display of effect of sticking of scale to surface.
3. Reinforcement of effect of sticking of scale to supporting rollers, occur at offset of position of roller concerning nominal point.
4.Installation above roller of injector, giving on its surface cooling water in type flat disperse jet effect of "winding" of scale how at pouring on working speed, and at non-stationary modes of pouring exclude let.
DonNTU| Master's portal | Electronic library | Report on search