The secret Capabilities of Release Agents

You might think that some foundries even “recycle” their wastewater from the DCM containing the release agent. So, it cannot be too dramatic? It depends on the expected properties. Is the requirement “not being plastic”? Take whatever you want. But as soon as requirements like mechanical properties with high elongation, weldability, and rivetability become relevant, the release agent plays a vital role.

For all applications, the most important role of the release agent is to make the casting demoldable from the die. Therefore, chemistry is added to ensure a constant film layer between the die steel die and the aluminium of the cast part. This film layer must stay on the die during the filling of the mold. But after casting, eventually, the thermally decomposed release agent remains should be removable, so it doesn’t impact post-casting processes. Some issues (like buildup) can be avoided by the optimal setting of the temperatures and spray pattern regulation.

In addition, its job is to overcome the Leidenfrost effect to enable cooling capabilities. You might have seen the Leidenfrost effect in action with the water droplet dancing on the hot surface. The water doesn’t instantly turn into a gas because it doesn’t contact the surface. It forms an insulating steam layer between the steel and the water. Therefore, the heat exchange is massively delayed. This is, for example, the reason why you can let liquid nitrogen run over your hands. Adding the right chemistry to the release agent reduces the surface tension and enables direct contact of the sprayed water with the die. So the impact on cooling is massive.

Release agents can, depending on their formulation, extract very different temperature levels from the mold. You can see the difference in the thermal images. The only difference is the release agent. Still, the temperature difference is between 20 and 45 Kelvin.

Now it comes down to the application of the release agent. You can see a lot of foundries washing their tools at spraying the release agent on the die surface. By washing, I mean spraying way too much release agent. This might be because they actively want to reduce the lifetime of their tool ;-), or they use the wrong release agent setting. The reason for the reduction in lifetime is thermal fatigue. During the casting cycle, the surface temperature increases drastically with the liquid metal. Then, the spraying cools the die surface. If you “wash” your die tools, you reduce the temperature to a low level. The delta of these temperatures is in relation to the stress on the surface. The mechanical stress on the tool surface, which results in nasty cracks, is squared. So, a doubling of the temperature delta results in four times the mechanical stress on the surface.

So, finding the sweet spot between cooling your hot spots and maintaining the temperature in colder areas is important. As you can imagine, your tool’s cooling and heating capabilities are vital to an effective casting process and die life.

You need to pick your release agent wisely and on a part-to-part basis. Don’t treat it as a commodity that works for everything. It is worth spending more on the “white water” to increase the part quality, reduce the rejection rate, and prolong the lifetime of your die tool. All these factors translate directly to your profits. Therefore, be aware of where you save money and where you spend it.

Implementing new release agents and spray methods the right way can be challenging. With the Casting Expert on Demand you get Casting-Campus GmbH on your site in the development phase and in the casting trails on-site.

A special thank you to Darko Tomazic and Branislav Serbin from Chem-Trend for the thermal images and the fact-checking!