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Design of overflow tank and slag collection bag, collaborative logic of slag capture, exhaust, and replenishment

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  • Release time: 2026-11-07

Design of overflow tank and slag collection bag, collaborative logic of slag capture, exhaust, and replenishment
The overflow tank is not a simple waste tank, but serves multiple functions such as capturing oxide slag, carrying cold materials, assisting in exhaust, and locally supplementing shrinkage. Many mold overflow tanks are only made in appearance and do not work at all.
1、 The difference between overflow tank and slag collection bag
The slag collection bag is located near the sprue, prioritizing the capture of the low-temperature oxidized cold material that flows out first; The overflow groove is arranged at the end of the material flow and the final filling position to remove the end inclusions and wrapped gases. Overflow grooves must be arranged at the end of the spoke and the edge of the wheel rim of the alloy wheel mold to capture cold slag at the end.
2、 Design rules for overflow tank capacity
The volume of a single overflow channel is generally 10% -25% of the local volume of the corresponding casting; The capacity is too small, and the slag and gas cannot fit properly, so they flow directly back into the casting; Excessive capacity wastes aluminum material and prolongs the cooling cycle. Multiple overflow channels are allocated in size according to the flow of materials, with the overflow at the end usually being larger.
3、 Key parameters of overflow tank connection interface (overflow neck)
The overflow neck is a weak section, thinner than the overflow tank body, and solidifies first to prevent aluminum liquid from flowing back into the mold cavity from the overflow tank. Once reversed, inclusions and gases in the groove return to the casting, resulting in batch defects. The thickness of the overflow neck is generally 0.8-1.5mm, adjusted according to the product wall thickness.
4、 Prioritize the placement order
The endpoint of the material flow, the location where two material flows converge and collide, the thin-walled end, the blind spot where gas is easily trapped, and the area where cold separation is prone to occur. Do not add overflow at the hot spot randomly, as it will take away heat and exacerbate shrinkage.
5、 Overflow groove paired with exhaust groove
The overflow groove must be connected to the exhaust groove behind it, and the gas enters the overflow first before being discharged from the exhaust. Only overflow without exhaust, the pressure inside the tank increases, and the aluminum liquid cannot flow smoothly into the overflow tank. Low pressure casting has a smooth filling process, with minimal use of overflow slots and more reliance on liquid lifting tubes and cavity exhaust. Google's "die casting overflow and slab well design" is aimed at mold engineers.
FAQ
Is it harmful to add more overflow slots?
Aluminum loss increases, pouring spout remelting increases, and the pace slows down.
What will happen if the overflow neck becomes thick?
The overflow neck solidifies late, causing aluminum liquid to reflux and slag gas to flow back into the casting.
3. Should the slag collection bag be placed before or after the sprue?
After the sprue, it comes into contact with the first wave of cold material first.
4. Do we have to add overflow at the intersection of two materials?
Priority is given to adding, as the intersection is most prone to air entrainment and slag inclusion.
Can the overflow groove replace the exhaust groove?
No, the overflow mainly stores slag, and the exhaust groove is responsible for discharging gas.
6. Should the surface of the overflow channel be polished?
Suggest polishing to reduce slag adhesion and facilitate cleaning.
7. Where is the hub overflow groove usually placed?
End of spoke and sealing position of wheel rim.
Can the overflow tank be replenished later?
Sure, but the cost of mold modification is high, and CAE prediction is optimal in the early stage.

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