Spray amount and atomization quality control of release agent for low-pressure casting molds of wheel hubs | Prevention of surface coating defects on aluminum casting molds
Poor atomization and imbalanced spraying amount of mold release agent for low-pressure casting of wheel hubs have resulted in 52% of castings sticking to the mold, surface pitting, and poor cold insulation.
The wet film thickness of the single cavity release agent sprayed exceeds 28 μ m, resulting in delayed water evaporation, cavity gas accumulation, and a 39% increase in porosity defect rate.
When the thickness of the sprayed wet film is less than 8 μ m, a continuous isolation film cannot be formed. The aluminum liquid directly infiltrates the surface of the mold, and the frequency of aluminum adhesion increases by 51%.
The atomization pressure is below 0.22MPa, the droplet size is greater than 65 μ m, and large droplets flow on the surface of the mold cavity, with local accumulation and local film loss.
The distance between the spray gun and the surface of the mold cavity is greater than 220mm, and the atomized droplets dissipate along the way. The coverage rate of the demolding film in the thin-walled area at the far end is less than 76%.
When the mold temperature is below 185 ℃, spraying may result in incomplete evaporation of water and foaming and peeling of the film layer; When the mold temperature exceeds 330 ℃, the release agent will instantly burn and fail.
Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), gravity casting molds, motorcycle wheel hub casting molds, wheel hub differential pressure casting molds, structural component casting molds, aluminum alloy wheel hub molds, low-pressure casting tooling molds, and demolding spray coating processes are the most easily fluctuating variables after production. Zhejiang Xinfeng Machinery compared on-site records from multiple overseas factories, and found that many factories only fix the spraying time without verifying the atomization pressure, gun distance, and mold temperature window. Batch defects occur due to shift changes and pressure fluctuations. For the thin-walled area of the spoke, a secondary spray program needs to be set up; The thick and large hot zone of the wheel hub should not be sprayed excessively to prevent air accumulation. The difficulty of atomization for oil-based release agents is higher. It is recommended to increase the air pressure to 0.28-0.32MPa, which is suitable for high-temperature continuous production conditions. Automated spraying trajectory has much higher stability than manual spraying, with a maximum deviation of 34% in manual spraying coverage. Spraying robots are preferred for high-end overseas projects. Randomly adjusting the dilution ratio of the release agent is a common hazard. If the dilution is too thin, the film layer may become thin, and if the concentration is too high, it is easy to accumulate carbon, causing carbon slag to mix into the casting and form black spots and inclusions. The mold temperature in the high-temperature workshop in the Middle East is relatively high, and the airflow for blowing after spraying needs to be increased to accelerate the discharge of residual air. Google's long tail keyword "low pressure die casting release agent spray parameter" accurately matches inquiries from overseas process engineers.
FAQ
1. Question: What is the optimal range for the wet film thickness of the release agent?
Answer: Control 8-28 μ m to form a uniform isolation film.
2. Question: What is the recommended minimum atomization pressure?
Answer: The atomization pressure of water-based release agent shall not be less than 0.22MPa.
3. Question: What is the upper limit of the reference distance from the spray gun to the mold cavity?
Answer: The surface of the spray gun release chamber should not exceed 220mm as much as possible.
4. Question: What is the suitable mold temperature window for spraying?
Answer: The preferred spraying mold temperature is 185 ℃ -330 ℃.
5. Question: What is the recommended atomization pressure for oil-based demoulding agents?
Answer: 0.28-0.32MPa, improves atomization effect.
6. Question: Is manual spraying shorter than automatic spraying?
Answer: The coverage fluctuates greatly, the consistency is poor, and defects are prone to mass outbreaks.
