Release Agents also called Die Lubes, are an essential ingredient in the high-pressure die casting process. Composed mainly of water (>99%) and lubricating agents (<1%), the release agents, and sprayed by mist into the mold cavity prior to the injection of molten metal such as aluminum, the release agents serve the following purposes.
Cools the die
Since the dies run pretty hot in pressure die casting (due to heat transfer from the 600˚C plus molten metal to the die cavity), cooling protects the die from excessive thermal stresses that can shorten the expected economical life of the die. The cooling function is provided by the water component of the die lube.
In addition, cooling the die down to temperatures of around 250˚C allows the adhesion of the <1% lubricating agents into the cavity surface. The film at the die cavity (to be formed by the lubricating agents) will be critical to providing casting release.
Releases the casting
This is a function of the lubricating agents in the die lube formulations. While very little by volume, the thin film formed at the die cavity serves as a barrier between the molten metal and die, preventing soldering or adhesion of the casting, thus ‘releasing’ a usable and functional casting without distortion or defects.
This is not straightforward or easily achieved though, as many factors come into play in trying to create a ‘good, uniform’ barrier. Some of these factors include variations in temperatures along the die surfaces (some spots are hotter than others), die lube chemistry, dilution ratios, spray volumes, spray times, and mold designs.
Lubricate components of the die
The dies have moving components, such as ejector pins, that requires lubrication to reduce any friction that can wear out the mechanical parts prematurely. The mineral-based oil or synthetics in the die lube formulation addresses this requirement to lubricate.
Since die lubes are fairly complicated, the next chapters shall detail each of the functions stated above, as well as die-lube chemistries & ingredients, usage tips, and casting defects.