How to troubleshoot aluminum adhesion defects in aluminum alloy casting molds from the mold end

How to troubleshoot aluminum adhesion defects in aluminum alloy casting molds from the mold end
Aluminum sticking is a common fault in aluminum alloy casting molds, which is mainly caused by three factors: mold surface condition, temperature control, and exhaust design, affecting continuous production.
When the thickness of the nitride layer on the surface of the mold is less than 0.08mm, the affinity between the aluminum liquid and the mold substrate increases, and the probability of aluminum adhesion increases by more than 60%.
The nitride layer serves as an isolation barrier, which can prevent aluminum liquid from infiltrating the mold substrate and is the basic protective measure for wheel hub casting molds.
The local temperature of the mold cavity remains above 620 ℃ for a long time, and the stability of the mold release agent film formation deteriorates, losing its isolation effect and easily forming sticky aluminum deposits.
These high-temperature areas are mostly concentrated near the sprue and at the location of thick and large section hot nodes, which are also key areas that need to be optimized in cooling design.
After the exhaust groove is blocked, the gas inside the mold cavity compresses and heats up, causing an abnormal surge in local temperature and simultaneously inducing dual defects of aluminum adhesion and porosity.
Türkiye hub foundry feedback that aluminum deposition in exhaust slot after continuous production of 300 molds is a time node with high incidence of aluminum sticking.
Insufficient spraying amount or offset spraying position of release agent, unable to form a continuous protective film on the surface of the mold cavity, and the aluminum liquid directly adheres to the surface of the mold.
The spraying parameters need to be matched with the mold temperature. Excessive spraying at low temperatures can cause water vapor to be trapped, which in turn can lead to porosity defects.
Xinfeng Machinery will provide corresponding spraying point references for the mold cavity during mold delivery to assist customers in standardizing spraying operations.
Many factories encounter aluminum sticking and directly polish the mold cavity. Repeated polishing will quickly consume the nitride layer and shorten the overall service life of the mold.
If the depth of a single polishing exceeds 0.05mm, the original nitride protective layer will be damaged, and subsequent aluminum adhesion problems will repeatedly occur.
If the cooling circuit of the water-cooled LPDC mold is blocked and the cavity temperature continues to rise, the problem of aluminum adhesion will show intermittent batch outbreaks.
The dust in the Middle East factory area is large, and impurities in the mold release agent and cooling water are more likely to adhere to the mold cavity. Therefore, it is necessary to increase the frequency of daily inspections.
The flow rate at the gate position of gravity casting molds is higher, the aluminum liquid is more washed away, and the frequency of aluminum adhesion in the gate area is higher than other positions in the mold cavity.
Aluminum mold sticking is a pain point term frequently searched by process engineers in Google's keyword planning tool.
This type of pain point content can undertake casting factories that have already started production but are currently plagued by defects, with a strong intention to convert.
The surface of the mold is excessively polished, with a surface roughness lower than Ra0.2, and the adhesion of the release agent decreases, making it more prone to aluminum adhesion.
The appropriate surface roughness range Ra0.8-1.6, taking into account the adhesion of release agents and the quality of casting surface forming.
Some customers will simply rely on increasing the concentration of release agent to solve aluminum adhesion, and excessive concentration will cause surface inclusion defects in castings.
The priority for defect management should start with temperature control, exhaust, and nitride layer status, and then fine tune the release agent scheme. The order cannot be reversed.

## FAQ

Q: What is the safe thickness of nitride layer for casting molds?
A: The recommended thickness for the nitride layer is 0.08-0.15mm.
Q: What is the temperature of the mold that can easily induce aluminum adhesion?
A: The local temperature of the cavity remains above 620 ℃, and the risk of aluminum adhesion increases significantly.
Q: What are the drawbacks of repairing bonded aluminum by polishing the cavity?
A: Excessive polishing can damage the nitride layer and cause repeated recurrence of aluminum adhesion.
Q: Will blocking the exhaust duct cause aluminum adhesion?
A: The compressed gas heats up, causing local overheating and simultaneously triggering pores and aluminum adhesion.
Q: Is it better to have a smoother cavity polishing?
A: No, Ra0.8-1.6 is more conducive to stable adhesion of release agents.
Q: Which area of the mold is prone to aluminum adhesion?
A: Gate, thick hot spot position, strong aluminum liquid flushing, high temperature.
Q: Which overseas customers have reported more issues with aluminum adhesion?
A: Türkiye hub factory has prominent problems under continuous mass production conditions.
Q: Is the higher the concentration of release agent, the better the anti sticking effect on aluminum?
A: Excessive concentration can easily lead to inclusion defects, and it is necessary to match the mold temperature.