Airway streaks are mainly caused by too high melt hydrogen content and blocking of foreign objects in the nozzle cavity. The casting nozzle is relatively humid, the melt stays in the smelting furnace or the standing furnace for too long, or the temperature of the aluminum liquid is too high, which causes the hydrogen content to increase. During the rolling process, the gas in the liquid cavity for rolling is not easily dispersed in the solid belt The billet is always suspended in the liquid cavity. Over time, the accumulated gas will form more and more small bubbles. Where there are bubbles, the flow of the melt is hindered and the continuous supply of the melt is affected, so a white channel appears on the surface of the strip.
In addition, if metal or non-metal impurities stay in the nozzle cavity during the vertical plate or production process, it will cause partial blockage and produce a low-pressure zone. The gas (mainly hydrogen) will be concentrated here and gradually grow into a gas cone. Hinder the normal flow of aluminum melt. At this time, increase the strip speed and appropriately increase the front box temperature and liquid level. Under the action of static pressure, long pores will be formed on both sides of the stripes and move. When the two “air channels” are closer together There seems to be an attraction between the two, making them gradually close together, and finally merge into one, forming an air triangle at the confluence, exposing a hole on the surface; or sticking paper tape and steel sheet to the corresponding position of the stripe on the roller, and then rotating to the roller. In the two-phase zone, the surface hard shell that forms the gas cone is broken, and the gas is released, and the airway stripes gradually disappear.
Airway Streaks Treatment Measures
(1) The spout sheet material can be installed and used after being fully dried, which shortens the preparation time of the vertical board to prevent moisture absorption.
(2) Shorten the residence time of the molten metal in the smelting furnace and the standing furnace, and re-refining must be performed if it exceeds 4 hours. When the temperature is over-temperature or the molten aluminum stays for more than 8 hours, it is modified and re-sprayed for refining to reduce the hydrogen content of the molten metal.
(3) Take ceramic foam filter filtering measures to filter out the suspended solid inclusions in the melt.
(4) Clean up the front box and base, feeding pipe, and metal transfer launder system after the machine stops, to prevent metal and non-metal impurities from being brought into the casting nozzle when the slab is erected.
(5) Ensure the purity, pressure, and flow rate of the refined gas to avoid polluting the melt quality.