Molten metal bath chemistry analyzer for continuous hot-dip galvanizing lines

With standard methods of bath chemistry monitoring, a bath sample is taken at a specific location in the bath at a given time and then analyzed in a laboratory. Between sampling, the operators have no information about the concentrations and the ensuing actions to take. Since the Galvalibs 2.0 continuously monitors the molten metal flowing under the probe, operators benefit from comprehensive volumetric information about the bath chemistry. The Galvalibs 2.0 measurement directly conveys the concentration of dissolved elements, so there’s no need to correct the recorded values for temperature, eliminating error due to inaccurate temperature readings.

Laser-Induced Breakdown Spectroscopy (LIBS) is a laser-based compositional analysis method of solids or liquid matter. In its basic principle, a high-energy laser pulse heats a small volume of the target to plasma level. The light emitted by this plasma is then collected and analyzed by an optical spectrometer. Since each individual element, such as Al, Fe and Zn, only emits light at specific optical wavelengths, or colours called optical spectral lines, isolating and measuring the intensity of selected spectral lines can detect the presence and concentration of elements in the plasma. The method makes it easy to measure Al and Fe concentrations in a galvanizing bath.

The Galvalibs 2.0 LIBS signal is recorded in a controlled, inert environment: a high-quality Argon bubble. No external contamination can skew the measurement. In addition, continuous recordings, as many as 1,000, are combined to reject outliers and reduce noise. This results in higher-accuracy spectral line intensities and, in turn, the concentration values of each element analyzed.

Studies have shown that bath chemistry is fairly well distributed in a standard galvanizing bath, except near where ingots and steel coils are inserted in the bath (dross formation). As a result, the Galvalibs 2.0 can be inserted at any location in the bath, except downstream, in the flow of molten metal from the feed ingot. With robotic drossing, care must be taken with the robot’s path. However, the unit is typically inserted in the bath next to the side of the snout away from the robot's path.

In its standard operation, the Galvalibs 2.0 probe beam focuses on a small spot inside a bubble of inert Argon gas, deep within the volume of the molten bath. This microsampling of the bubble wall vaporizes the liquid phase. The small beam spot limits the possibility of solid particles (dross) in the probed volume, yielding a measurement of the dissolved phase only. If a dross particle is detected in the microsample, a higher-than-normal signal intensity for intermetallic elements is recorded. With its shot-per-shot signal processing, the Galvalibs can sort the data and produce reliable, independent solid and dissolved content measurements.