Indeed, the management of release agents is one of the essence of die casting technology. Their double-edged nature is most pronounced in defects such as "cold shuts" and "porosity."
The essence of cold shuts lies in the front end of the metal flow being too cool to fuse. When release agents (especially water-based ones) are over-applied or poorly atomized, excessive liquid accumulates on the mold surface. At the instant of mold closure and pouring, the rapid evaporation of these liquids drastically absorbs heat from the mold, creating localized "over-cooled zones." The leading metal flow contacting these zones solidifies instantly, forming an extremely thin cold skin. When subsequent metal flow arrives, it fails to remelt this cold skin, resulting in distinct cold shut seams. This is the underlying physical process behind the document’s note that "excessive release agent usage" is a root cause of cold shuts.
Porosity forms when gas is entrained and trapped within the solidifying casting. Release agents contribute to this in two ways: First, their volatile components (moisture, carrier oils, etc.) vaporize at high temperatures. Second, excessive or uneven release agent films hinder the normal escape of air originally present in the cavity. As high-speed metal flow fills the cavity, these gases are entrapped, forming regular, smooth-surfaced voids. The document explicitly identifies "excessive release agent spraying" and "high volatile content in release agents" as direct causes of porosity.
Precision Spraying: Invest in advanced quantitative spraying systems to achieve the "less but uniform" principle. Ensure release agents are applied as ultra-fine mists evenly coating the cavity, rather than residue in droplet form.
Formulation Optimization: For critical components, select specialized release agents with low volatility, high lubricity, excellent film-forming properties, and high temperature resistance. These products form effective protective films while minimizing gas sources and thermal impacts on mold temperature.
Process Synergy: Treat release agent spraying as part of the overall thermal balance system. If mold temperature is low, prioritize raising mold temperature or reducing release agent dosage over increasing application volume to prevent sticking.
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