View Workout (Chris Kelly)
LMF
September 17, 2013 (Morning)
Exercise Type: Run
Comments:
So I forgot to mention yesterday what I was doing in the melt shop. So yesterday I was at the EAF (Electric Arc Furnace). This is the first step in the melting process. Scrap metal is brought in by conveyor and fed into the furnace. The metal is preheated using the off gasses from the furnace its self. Before they are taken to the bag house the gasses pass over the scrap raising its temperature to about 1000F before it actually enters the furnace.
In the furnace the scrap is melted. It is melted using an electric arc. Imagine welding on a massive scale. A graphite electrode about a foot in diameter and 20 feet tall arcs to the scrap metal. The arc is about 10000F. It takes about 45ish minutest to melt all the scrap and fill up the furnace. The furnace holds about 200 tons when full. During the melting process impurities in the form of slag are poured off periodically. Lime is added to the furnace to form this slag and make it float to the top to be poured off. Also oxygen in injected into the furnace to both lower the carbon level of the steel and help form this slag.
After the melting process is complete the furnace is "tapped." This is how the steel is removed from the furnace so it can be further processed. It is poured out from a hole in the bottom into a large container called a ladle. About 120 tons are removed when the furnace is tapped. This 120 tons is now called a "heat" and has a specific heat number to identify it. This leaves 80 tons in the furnace that helps speed up melting the new scrap for the next heat.
As the heat is tapped into the ladle alloying elements are added. This is the first step in a two step process that turns the scrap into the grade it will become when we sell it.
This occurs about 15 times a shift. That's typically what happens at the EAF. Once a shift the furnace is "tapped out." Here after the 120 ton heat is poured into a ladle another ladle is brought in and the last 80 tons are removed completely emptying the furnace. The furnace lining is then inspected and ceramic powder is used to coat the lining. This preserves the lining of the furnace and makes it last longer. Also the electrode is changed. Then the furnace is "charged" By dumping about 10-20 tons of cold scrap into the furnace. This is a very violent process. The furnace is restarted and melts this small amount of scrap. Once this charge has been melted the 80 tons of molten steel that was poured off is poured back into the furnace. Again a violent process. Once this has occurred the top is placed back on the furnace and the process runs smooth again.
So that was the EAF. We will now follow the ladle to the LMF (Ladle Melting Furnace).
The ladle that contains the heat that has been tapped from the LMF is on a large rail cart. This cart is slowly moved from under the LMF to under a stationary crane. This crane then lifts the ladle slightly when the first car is moved back to under the furnace and another cart is slid in. The ladle is placed back down and that car moves it on to under the LMF.
The LMF has three graphite electrodes. They break through the slag and begin to heat up the heat again. It has not solidified just cooled some. After that initial heating more alloying elements are added. This is where the small additions end up making the final chemistry of the heat. During the process a lot of samples are taken and checked for chemistry so see where the heat chemistry is at and what needs to be added to get it to where its chemistry needs to be. Also many temperature readings are taken as well. This is important as the amount the steel is over its solidification temperature is very important for the casting process. It's honestly very hard to describe why this is important without pictures. But it is and this is the last place the temperature of the heat can be controlled. Once it goes to the caster it out of the operators hands.
Once the chemistry and temperature of the heat is right it is sent on to the caster.