The size of the casting nozzle roll gap has a great impact on the quality of the cast-rolled strip product. In the process of adjusting the casting nozzle roll gap, the thermal expansion of the nozzle itself, the expansion when filled with molten aluminum, the radius of curvature of the oxide film, and the melting factors such as body surface tension.
When the gap between the nozzle rolls is too small, the distance between the casting roll and the caster tip is too close, and it is easy to form slag on the nozzle, so that the aluminum slag forms a small, uneven sticky aluminum tape on the surface of the roll in the circumferential direction, and the surface of the strip produces a phase. Corresponding, uneven lines along the length, this is the longitudinal stripes.
When the nozzle gap is too large, the oxide film will be broken, and the residual oxide will adhere to the roll and be brought into the gap between the nozzle rolls, so that the oxide film is clamped between the nozzle roll gap, causing local micro-compression of the casting nozzle here, causing melt distribution Inhomogeneous and sticky slag, so that the solidification rate of the strip surface will undergo periodic changes, the dendrite spacing will also undergo periodic changes, and longitudinal stripes will follow. Therefore, reasonable adjustment of the nozzle gap plays a vital role in product quality.
The aluminum melt forms a thin oxide film at the nozzle nip. The oxide film is arc-shaped. Because the liquid surface is curved and opened, the surface tension of the liquid surface gives the liquid metal a certain force to ensure that the metal does not leak from the gap between the nozzle rollers. Similarly, the metal melt gives the oxide film a reaction force, which is the static pressure of the liquid surface of the front tank acting on the liquid surface through the transfer of the liquid. Under the interaction between the surface tension of the oxide film and the static pressure of the liquid metal in the front box, the casting-rolling process reaches equilibrium.