Simple Solutions That Work! Issue 13

Continued on next page 13 DEFECT PREVENTION FRANÇOIS AUDET SOLUTIONS FONDERIE ARTICLE TAKEAWAYS: • Grain refining/cleaning flux additions to liquid aluminum prevent casting defects • Grain refiner additions without measuring the melt properties is counter-productive • Thermal analysis measures the solidification properties of your liquid aluminum • You might not need to add grain refiner at all - let’s use data-driven decisions! MEASURE YOUR MELT PROPERTIES: Variations of your melt properties need to be minimized and measured from shift to shift if you want to grow your business into higher value casting jobs or just decrease your cost of operation. The Reduced Pressure Test (RPT) density gives a melt quality index: a mixed value of the hydrogen and oxide content of your melt that contribute to porosity formation. The spectrometer tells you the chemical presence % of a given element in the liquid alloy. A thermal analysis system measures the solidification properties of the shop- floor alloy within 8 minutes; is what your casting simulation software uses? Are the chemical elements measured by the spectrometer available to participate in the solidification events as measured by the thermal analysis system? For example, the titanium % value given by your spectrometer might not be active in the form you need it to be to perform effective grain refining; thermal analysis will let you know about that. The goal is to always start with the same quality melt. After that, we know our efforts for melt properties control are often wasted around the world by a dirty furnace, turbulent transfer, air aspiration from the pouring basin of the mold and a bad gating design. Each day the environment in the foundry can change, affecting the process parameters like the mold thermography, pickup of moisture by the melt, reoxydation and the fading of properties like the grain refinement or nucleation potential. Why do you need to degas more today than yesterday? Let’s record the process data to understand and discuss as a team. What’s happening on the shop floor today that is causing more scrap than 6 months ago? With data, we’ll have the first step accomplished to prevent defects scientifically and win higher value jobs. THERMAL ANALYSIS OF ALUMINUM-SILICON ALLOYS: All thermal analysis systems are not the same. Make sure to ask how the solidification events are calculated during your demonstration of a thermal analysis system to confirm GRAIN REFINEMENT AND THERMAL ANALYSIS OF LIQUID ALUMINUM; DON’T HURT YOUR MELT! SOLUTIONS FONDERIE Figure 1. A liquid aluminum sample being taken for thermal analysis of its so- lidification properties with the SF system. The thermocouple is surrounded by liquid metal.