Argon Bubble Behavior in Slide-Gate Tundish Nozzles During Continuous Casting of Steel Slabs

"Argon injection into a tundish nozzle is an efficient and widely employed method to reduce nozzle clogging in the continuous casting process. It also affects casting operation and product quality by changing the flow pattern in the nozzle and mold. The current work combines mathematical modeling and experiments to investigate the argon bubble behavior in slide-gate nozzles and to analyze phenomena related to product defects and operational problems during the continuous casting of steel slabs. Water model experiments are performed to study bubble formation behavior, including bubble size, frequency, mode and effects of variables such as liquid velocity, gas injection flow rate, gas injection hole size and gas density. An analytical model is developed to predict the average bubble size. Argon gas bubbles are predicted to be 1--5mm. This is larger than air bubbles in water, especially at low speed. A three-dimensional finite difference model is developed to study the turbulent flow of liquid steel and argon bubble in the slide-gate nozzles. Experiments are performed on a 0.4-scale ""water caster"" to verify the model by comparing the model prediction with the measurements using PIV (Particle Image Velocimetry) technology. A weighted average scheme for the overall outflow is developed to quantify jet characteristics such as jet angle, jet speed, back flow zone fraction, turbulence and biased mass flow. Swirl is generated at nozzle ports. The validated model is employed to perform extensive parametric studies to investigate the effects of casting operation conditions such as gas injection, slide-gate orientation, casting speed, gate opening and bubble size and nozzle port design including port angle and port shape. The interrelated effects of nozzle clogging, argon injection, tundish bath depth, slide gate opening and nozzle bore diameter on the flow rate and pressure in tundish nozzles are quantified using an inverse model, based on interpolation of the numerical simulation results. The results are validated with measurements on operating steel continuous slab-casting machines, and presented for practical conditions. Suggestions to improve argon injection practice are proposed based on the modeling results. During ladle transitions and at other times when either casting speed or tundish level is low, argon flow should be turned off or at least severely reduced. The optimum argon flow rate required to avoid air aspiration in the nozzle is derived from the model."

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Bai, Hua

Contributors dc:contributor

• Thomas, Brian G.

• Engineering, Metallurgy

Language dc:language

eng

Identifier

(MiAaPQ)AAI9971018

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/84002