It must be understood those release agents or die lube, as provided by various chemical companies, are supplied in the form of an emulsion, a ‘mixture’ of water, and oils & chemicals (called solids), wherein the solids would comprise 10-30% of the totality. These emulsions are then further diluted before use at the die-cast machine from ratios as low as 1:20 to ratios as high as 1:250. The water component acts as a coolant.
Protecting the die by cooling
Therefore, the die lube as sprayed into the die cavity is mostly water and thus, has a high ability to absorb the heat at the die surface. When sprayed properly and at the right volumes, die temperatures as high as 500˚C may be lowered down to > 200˚C, though other mechanisms such as the cooling system of the die and convection play a role in lowering temperatures. In cooling the die, the die lubricant prevents premature failure or wearing of the die due to thermal stresses, especially important in this age of mass production, and the need for lower manufacturing costs.
Promoting lubricant and barrier-firm formation at the die cavity
At temperatures higher than 400˚C, the die lube particles (including the solids) hitting the hot die mostly bounce-off due to the heat, a phenomenon called the Liedenfrost effect, while at lower temperatures, a significant portion of the sprayed die-lube particles will have a tendency to leak down from the die.
Consequently, cooling the die down to what is called the ‘wetting’ temperature is the next phase — wetting temperature being the temperature range at which the solids in the die lube adhere to the die cavity surface to form a thin and ideally uniform lubricating and barrier film. Wetting temperatures normally starts a bit below 400˚C and ends at around 150˚C.
In the next discussion, we shall tackle the release function of the die lubes.