User:Jasmin Proulx/AlSCAN

Hydrogen gas porosity is an aluminium casting defect under the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas in the aluminium at the liquid phase before freezing.

Aluminum smelters and aluminum foundries want to produce high quality aluminum and shape castings. This can be obtained by reducing the amount of hydrogen in the liquid aluminium alloy.

The hydrogen problem
Hydrogen forms whenever molten aluminium comes into contact with water vapor, and easily dissolves into the melt. The gas tends to come out of the solution and forms bubbles when the melt solidifies.

The detrimental effects arising from the presence of an excess of dissolved hydrogen in aluminium are numerous. Hydrogen causes porosity in aluminum products leading to many casting defects, reduced mechanical properties like fatigue and lower corrosion resistance. Several methods are used to reduce the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degassing equipment during the casting process.

An on-line method of measuring hydrogen in aluminum is then required to characterize and optimize the process, which helps ensure the quality of outgoing products and monitors the performance of these degassing processes. Traditional laboratory methods, such as hot extraction, are too expensive for routine quality assurance, and too slow for effective process control. Reduced pressure tests often used on the production floor are only semi-quantitative and do not provide enough accuracy.

Hydrogen measurement
Hydrogen measurement is required in aluminium foundries.

from experience and measurement, systematic measurement, enabling control on the melt quality at all stages of the manufacturing process.

The AlSCAN technology is a proven solution that directly monitors hydrogen in molten aluminum. The AlSCAN analyzer is an on-line quantitative measurement technology based on the well known closed-loop recirculation method and a proven probe design.

AlSCAN Hydrogen Analyzer
Since its introduction in 1989, the AlSCAN technology has been used more and more by all major aluminum producers. They appreciate its outstanding reproducibility and its rugged probe.

Operation principle
The closed loop recirculation is a proven method of directly monitoring hydrogen in molten aluminium. A small volume of carrier gas, usually nitrogen, is brought in contact with the melt by means of an immersed probe, and is continuously recirculated in the closed loop until its hydrogen content reaches equilibrium with the vapor pressure of H2 in the melt. The H2 concentration in the gas is measured and converted into a reading of the gas concentration in the metal. This method is fast, reproducible and accurate, and can be used “on-line” on the cast shop floor. The amount of H2 in the gas loop of the instrument is determined by a thermal conductivity sensor, which provides high reproducibility and a broad measurement range. The analyzer has a built-in microprocessor which controls its operation and processes data.