Simple Solutions That Work! Issue 8

In my 37 years of traveling all over the world one thing has become increasingly apparent. Some die casters and foundries have lost the basic understanding of molten metal management. I have been asked to talk to companies about this subject more in the last three years than in all years combined with The Schaefer Group, Inc. If you ask 10 different melt shop managers what molten metal management is you may get 10 different answers? Molten metal management is “managing the workers ability to deliver clean, hydrogen free, inclusion free aluminum to the casting equipment on time and at temperature”! Pretty straight forward isn’t it? But amazingly this concept has been pushed aside to increase production, reduce manpower and because of the lack of qualified workers, an acceptance of poorer quality workmanship. Customers are demanding higher and higher quality parts and so rejects are up scrap rates are high and this trend gets worse when our industry is overwhelmed with work like we all have been for the last three years. It all starts with leadership. Someone in the company has to take ownership of the aluminum. There are people being put in melt shop management positions with little or no experience and being told to do it the way we always have done it. There is usually a better way. About 40% of my time now is spent training companies on how to clean metal, clean furnaces so the linings last 5-7 years and molten metal management. What is the most important aspect of casting aluminum parts? Is it not the metal quality, metal temperature and on time delivery to the holding furnaces? That last one baffle me the most and it is a simple fix. How can you expect molten metal handlers to deliver metal on time if no one knows how much metal is needed per hour per machine? When there is no daily plan then metal gets delivered too often or not often enough and both scenarios cause issues. Melt shop managers need to know how many pounds of aluminum is required for each machine that is running each day. It can vary day to day depending on downtime and part weights being cast that day. You can obtain better utilization of your melters, holders and people with this basic knowledge. This is my point: if you have radiant burners in the roof or electric elements in the roof of a holder or even a high headroom side fired melter (fig. 1), molten metal management is critical to their operation and efficiency. For example if you draw your melters down 6-8” before refilling them then chances are they are not at specified set point temperature anymore. They have to work much harder to get the heat to the aluminum. Same thing applies to radiant roof holders. If you draw them down 5-6” before refilling them chances are they will start to lose temperature. Stefan–Boltzmann Law of Radiant Heat says “that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (also known as the black- body radiant emittance or radiant existence), is directly proportional to the fourth power of the black body’s thermodynamic temperature”. In English it is basically the greater the temperature difference between your heat source and the media (aluminum) when there is a slight oxide film, the faster the transfer of BTU’s into that load to the 4th power. Also the closer they are to each other enhances that transfer. So by limiting the draw down to a couple of inches you can make your furnaces run more efficiently and guarantee better temperature control. The best practice is whatever you take out of a furnace in 15-20 minutes you replace with more metal to bring it back up full again. DAVID WHITE National Sales Manager THE SCHAEFER GROUP ARTICLE TAKEAWAYS: 1. Back to basics starts with leadership 2. Control of the metal melting and delivery process 3. Saving metal 6 MOLTEN METAL MANAGEMENT BACK TO BASICS Figure 1. High headroom central melter with preheat hearth!