NADCA Die Casting Video News & Information
The material presented in this video include highlights from NADCA’s online webinar - The Role of Die Lubricants in Die Casting. Die lubricants are a necessary part of high pressure die casting. The lubricant provides a thin layer to protect the die steel from molten metal. This presentation will discuss what die lubricants are and characteristics important to die casting, how to apply die lubricants in operation, problems caused by improper use of die lubricants, and alternatives to conventional die lubricants.
So what does this have to do with the Leidenfrost effect? Well, the Leidenfrost effect is just the phenomenon in which a liquid in near contact with a mass significantly hotter than the liquid's boiling point produces an insulating vapor layer keeping that liquid from boiling rapidly. So as we talked about, that water is going to hit the metal. It's going to create that gas layer, and that's going to basically insulate the metal. It's going to keep any new cool water from getting to the metal and cooling it further. So due to the Leidenfrost effect, what we have are the droplets get repulsed from the surface of the die just by that gas layer. And it's going to hover over it rather than making physical contact. And of course, if that layer of water, which has less than half a percent of a concentration of lubricants in it is hovering above the surface, then that lubricant is not getting onto the surface and adhering to it. So, we're not getting the coverage that we need.
So, to give you a nice visual, let you see what's going on. As you can see, there's that gas bubble right in here that's preventing this drop of liquid from reaching the die surface. Or if you want to see it in different form, this is just showing the amount of heat removal during the process and you can see that it quickly cools. You have the film boiling and then it's going to start creating that vapor so you get less of the grade of heat transfer. Uh, then once it gets up to that transition boiling, this is where it's going to explode off the surface. You start getting a lot more heat transfer. That heats all being dissipated. Then, you get the nucleate boiling. And I know this is probably going a little bit in depth. Uh, it's just a different way of showing what we were talking about before. You have the different stages. Uh, obviously once you can get rid of that vapor barrier, you start cooling a lot faster
For information on purchasing a downloadable copy of this NADCA webinar in its entirety, please visit: http://www.diecasting.org/store/detail.aspx?id=WEB285
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