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Design principles of die-casting sprue, flow distribution, filling timing, and resistance control

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  • Release time: 2026-11-07

Design principles of die-casting sprue, flow distribution, filling timing, and resistance control
The sprue is the blood vessel for the flow of aluminum liquid, and many defects are not caused by the cavity, but by the unreasonable cross-section, direction, and flow distribution of the sprue. Xinfeng Machinery disassembles the underlying logic of the sprue design.
1、 Core design objective of sprue
Smooth conveying of aluminum liquid, control of sprue speed, uniform distribution of flow rate, reduction of gas entrapment and oxidation inclusions; Prevent aluminum liquid from splashing, colliding, and forming turbulence in advance. The alloy wheel hub belongs to a multi branch sprue, and the first difficulty is the balance of spoke flow. Uneven flow directly causes local material shortage and cold insulation.
2、 Classification of mainstream sprue structures
Fan shaped sprue: thin and large-area appearance parts, evenly spread aluminum liquid, suitable for flat shell; Branch sprue: hub, multi reinforced composite parts, more than one, gradually reducing the cross-section; Conical sprue: The material barrel is straight through, simple and small. The branch sprue follows the principle of equal flow rate, and each branch section matches the corresponding cavity volume.
3、 Sectional design and principle of decreasing cross-sectional area
The total cross-sectional area of the sprue is greater than the sum of each branch and the total area of all internal sprues, which is a convergent design. The inner gate has the smallest cross-section, and the aluminum liquid accelerates to the set speed here. Sudden changes in cross-section, sharp bends, and blind spots can all cause vortex entrainment, and corners should prioritize rounded transitions.
4、 Taboo for selecting the position of the sprue
Cannot directly face the core, thin-walled sharp corners, and exhaust slots; Priority should be given to the position of thick walled hot joints for easy expansion and contraction; Avoid direct impact of aluminum liquid on the cavity wall, which may cause oxidation and aluminum adhesion. The inner gate of A356 wheel hub is mostly placed at the root of the wheel hub, taking into account both filling and shrinkage.
5、 Hot balance of sprue and control of excess materials
The sprue itself is a heat carrier, and if the cross-section is too large, there will be excess heat, which will prolong the cooling cycle; The cross-section is too small and solidifies prematurely, resulting in insufficient filling. ADC12 has a lot of silicon slag, and the pouring channel should not be too narrow to prevent the accumulation and blockage of silicon slag. Low pressure casting has a low filling speed for the sprue, and the design logic of the sprue section is completely different from high-pressure die casting. Google's "die casting runner design principle" is aimed at mold designers.
FAQ
Is the larger the sprue, the more stable the filling?
No, the section is too large, resulting in high heat and prolonged beat, which increases costs.
How to ensure consistent flow in each branch runner?
Symmetric layout, step-by-step variable cross-section, CAE filling simulation verification.
How much is the speed of the sprue generally controlled?
Ordinary shell 30-45m/s, thin-walled exterior parts 45-60m/s.
Why does the corner of the sprue have to be enlarged?
A right angled corner is prone to generate eddy currents, entrainment, and oxidation inclusions.
Can the sprue suddenly narrow midway?
Try to avoid forced contraction as it can cause turbulence and impact.
What are the most common problems with wheel hub runners?
The flow rate of each spoke is uneven, with some spokes not fully charged and experiencing cold insulation.
Can the same product have both fan-shaped and branched runners at the same time?
Complex large items can be combined, but the timing of filling is difficult to control.
How to improve the residual aluminum slag in the sprue?
Smooth flow rate, polished surface of the sprue, and regular cleaning of the sprue.

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