Once the wetting temperature is reached by a hot die (< 400˚C), the die lube droplets sprayed into the die do not bounce off the hot die surface anymore. Instead, the water component of the die lube is vaporized, while the lubricating agents, or solids, adheres to the die cavity surface to form a thin film that acts as a barrier between the die and the injected molten metal.
By having a barrier, soldering, or the phenomenon of a casting, or certain portions of the casting, sticking to the die is prevented.
The release of the casted product is thereby performed. This is not straightforward though, since soldering as a defect is still common in die casting factories. There are just too many variables that prevent the formation of a consistent uniform film on the die surface. These factors include,
- Differing die cavity geometry depending on the parts produced,
- Varying surface temperatures within one (1) die, in different areas or portions of a die,
- Consistency (or inconsistency) of die lube spray volume, spray time, and spray position,
- Die lube quality, chemistry and dilution ratios, and,
- The behavior or characteristic of the metal alloys to be casted.
Nonetheless, the experienced die caster should be able to control the variables to an extent that soldering is reduced to an acceptable and economical level.
Other than providing the release function, the solids or the barrier film will have an impact on casting appearance, and to a smaller extent, the casting’s structural integrity. On a best-case scenario, the barrier film should enhance the casting appearance, as bright, shiny, and stain-free castings are always desired by the casters.
In our succeeding discussion, the different chemicals and oils utilized as lubricating agents, or solids, in die lube formulations shall be broken down. The author shall also elaborate on the pros and cons of each raw material.
See Release Agents for High-Pressure Die Casting Part 2 here.