How to balance anti sticking aluminum, porosity, and cost in the selection and spraying process of LPDC release agent?

How to balance anti sticking aluminum, porosity, and cost in the selection and spraying process of LPDC release agent?
Release agent is a thin film that isolates the aluminum liquid from the surface of the mold cavity, and is the easiest process to operate based on experience; The spraying amount, dilution ratio, and spraying position are incorrect, resulting in either aluminum sticking and pulling, or the outbreak of porosity and carbon deposition defects.
1、 Type, dilution ratio and applicable working conditions of release agent
Water based ink demoulding agent: dilution ratio 1:8-1:15, stable film formation, high temperature resistance, suitable for continuous mass production of shells and wheels; Excessive spraying can easily lead to carbon buildup and the formation of pores in the mold cavity.
Water based ceramic release agent: Diluted 1:10-1:20, the film layer is thinner and denser, the graphite content is low, the risk of porosity is significantly reduced, and the price is about 40% higher than graphite models. It is the mainstream choice for automotive parts.
Oil based demoulding agent: rarely used for LPDC, with high combustion gas production, only suitable for extremely low cycle, manual single piece trial production, not suitable for automated spraying.
Spray film thickness control: dry film thickness of 0.005-0.012mm; if the film is too thin, isolation failure may occur, and aluminum adhesion may cause scratches; The film is too thick, and it decomposes upon heating to produce gas, resulting in porosity in the casting.
Xinfeng Machinery provides a spray coating SOP for the delivery of molds, distinguishing the spray coating amount for the hot zone, thin-walled end, and parting surface.
2、 Specification for Automated Spray Coating Parameters
Spray gun atomization pressure 0.3-0.5MPa, spraying distance 150-220mm; too low atomization pressure results in coarse droplets and uneven film thickness; The pressure is too high, the atomization is too fine, and the release agent floats to the exhaust groove and accumulates, causing blockage.
Spray timing: mold opening → blowing air to clean dust → spraying → blowing air to dry, must be dried before closing the mold; Residual moisture in the mold cavity vaporizes instantly upon contact with high-temperature aluminum liquid, producing explosive pores.
Differentiated spraying strategy: increase spraying at gate and thick hot spot positions; Thin walled filling end and exhaust area should be sprayed with reduced amount to avoid blocking the exhaust.
Clean the carbon deposits on the spray gun nozzle and exhaust groove in each shift. The carbon deposits will adsorb the release agent, and the thicker the deposits, the more stable the process is broken.
3、 Differences in mold release agent preferences among overseas customers
Southeast Asian factories extensively use graphite water-based release agents, with high dilution ratios and low unit prices. They rely on manual spraying and tolerate small amounts of pores and carbon deposits.
Tier 1 mandatory low graphite/graphite free ceramic release agent in North America, graphite slag inclusion is a serious defect, and X-ray inspection directly determines waste. Spray records are included in process control.
European customers prioritize ceramic release agents, strictly control VOCs and internal impurities in castings, and many production lines are equipped with electrostatic spraying to achieve more uniform film formation and reduce waste.
The moisture evaporates quickly in the high-temperature workshop in the Middle East. Customers choose high solid content release agents to avoid rapid drying spots and intermittent adhesion of aluminum film after spraying.
4、 Defect chain caused by improper release agent
Insufficient spraying, excessive dilution → damage to isolation film → adhesion of aluminum to the mold cavity, tearing of the casting sidewall;
Excessive spraying, not dried → moisture+organic gas → pores and pinholes;
Long term spraying and accumulation of exhaust ducts → blockage of exhaust channels → accumulation of cold insulation and concentration of air holes at the end of the filling process;
Poor atomization due to nozzle blockage → local thick film, local no film, random fluctuation of defects, difficult to stabilize yield.
5、 Long tail traffic layout ideas
Release agents, spraying processes, and porosity defects belong to the category of process consumables, targeted at process engineers, workshop supervisors, and procurement.
keywords LPDC mold release agent spraying process、ceramic vs graphite release agent low pressure casting；
Problem class: Release agent dilution ratio for LPDC;
Tutorial class: How to reduce porosity from casting release agent.
Suitable for the topic of process consumables, undertaking inquiries for production line process optimization.
6、 Common misconceptions in the industry
Misconception 1: The more mold release agent sprayed, the less likely it is to stick to aluminum. Excessive spraying produces gas, causing a surge in porosity defects, which is not worth the loss.
Misconception 2: One of the most common causes of porosity in low-pressure casting is the vaporization of residual moisture without blowing dry after spraying.
Misconception 3: Graphite release agents are universal for all products, and high graphite formulas are prohibited for automotive X-ray parts, which can easily form slag inclusions.
FAQ
Q: What is the standard dilution ratio for graphite release agents?
A：1:8～1:15。
Q: What are the advantages of ceramic release agents?
A: Low graphite, lower risk of porosity and slag inclusion, preferred for automotive parts.
Q: Recommended dry film thickness?
A：0.005–0.012mm。
Q: Why is it necessary to blow dry after spraying?
A: Residual moisture vaporizes when encountering aluminum liquid, resulting in the formation of explosive pores.
Q: Spray gun atomization pressure?
A：0.3–0.5MPa。
Q: What are the spraying principles for the exhaust area?
A: Reduce spraying to prevent carbon buildup from blocking the exhaust duct.
Q: What are the release agent requirements for North American customers?
A: No/low graphite ceramic version, controlling graphite slag inclusion.
Q: Why are oil-based demoulding agents rarely used in mass production?
A: The combustion produces a large amount of gas and has a high risk of defects.