Structural design of slag blocking cap for LPDC riser, slag blocking, stable flow, anti suction, and optimized service life

Structural design of slag blocking cap for LPDC riser, slag blocking, stable flow, anti suction, and optimized service life
The slag blocking cap is a simple accessory installed at the bottom of the liquid lifting pipe, which is often omitted in many production lines; The sediment, oxides, and bottom slag at the bottom of the crucible enter the mold cavity through the rising liquid channel, causing periodic slag inclusion, which is sometimes good and sometimes bad, making it difficult to locate the root cause.
1、 Quantitative parameters of slag blocking cap structure, aperture, and aperture ratio
Material: Silicon carbide slag cap, matched with the liquid lifting tube, resistant to aluminum liquid erosion; Graphite is not recommended as it can easily peel off and form carbon inclusions.
Hole opening rate: 25-35%, hole diameter of φ 4-6mm; The opening is too small, the flow rate is insufficient, and the filling pressure is unstable; The opening is too large, and the slag blocking is ineffective.
Structural form: Bottom closed, side perforated, sediment settles at the bottom of the crucible, and aluminum enters smoothly from the side; Avoid direct suction of the bottom slag layer.
Assembly gap: The gap between the slag cap and the bottom of the liquid lifting tube is 0.5-1mm. If the gap is too large, slag may enter through the gap; Too tight, stuck due to thermal expansion, difficult to disassemble and assemble.
The inspection standard for Xinfeng Machinery's slag blocking cap includes direct replacement for deformation, cracking, and hole blockage, and synchronous matching of crucible slag removal frequency plan.
2、 Installation, preheating, slag removal, and maintenance standards
Preheat the slag blocking cap and the liquid lifting pipe in sections together. It is forbidden to directly lower the aluminum on the cold slag blocking cap, which may cause surface condensation and rapid blockage of the pores.
Immersion depth: The bottom of the slag cap should be 30-50mm away from the bottom of the crucible, leaving space for sediment to settle and not adhere to the bottom for slag suction.
Slag removal cycle: remove the sediment at the bottom of the crucible every 2-4 hours; If the slag is not removed for a long time, the slag layer will rise and enter the pipeline through the opening on the side of the slag cap.
Cleaning: Remove the slag cap from each shift and blow clean the alumina nodules in the pore channels; Tumor accumulation will reduce the effective opening and cause fluctuations in filling flow rate.
3、 Differences in slag cap control for overseas customers
The vast majority of production lines in Southeast Asia do not use slag blocking caps and rely on frequent slag removal, resulting in significant fluctuations in slag inclusions.
North American X-ray pressure parts are required to use silicon carbide slag blocking caps, and the structure is specified in the drawing process documents. Production is prohibited without slag blocking caps.
European customers have added a guide slope to the slag cap to further stabilize the flow and reduce the vortex induced slag entrapment in the aluminum liquid.
The Middle East has a large capacity deep crucible, with a raised slag cap and larger sedimentation space, suitable for long-term continuous production.
4、 Defect chain of slag blocking cap failure
No slag blocking cap/excessive opening → Bottom slag and oxide of crucible are sucked into the riser → Periodic slag inclusion and X-ray defects;
The slag cap is attached to the bottom of the crucible, and the slag layer directly blocks the opening, resulting in unstable filling flow and pressure curve drift;
The cold blocking slag cap is directly inserted into the aluminum → the inner wall of the hole is solidified with aluminum nodules, gradually blocked, insufficient filling, and cold isolation;
Graphite slag cap → graphite peeling, forming carbon inclusions and X-ray black spots.
5、 Long tail traffic layout ideas
Lift pipe slag cap, silicon carbide slag cap, low-pressure casting anti suction slag cap, aimed at equipment and smelting engineers.
Keywords: LPDC riser tube slab filter cap, SiC slab shuffle for low pressure casting;
Problem class: merger gap for riser slab cap;
Comparison class: SiC slab cap vs graphic slab cap aluminum casting.
Suitable for crucible conveying and slag removal system special pages.
6、 Common misconceptions in the industry
Misconception 1: The more holes in the slag blocking cap, the better. If the opening rate is too high, the slag blocking effect will be lost; The opening is too small and the flow is insufficient.
Misconception 2: Placing the slag blocking cap on the bottom can directly block the opening with sediment, making it easier to absorb the slag.
Misconception 3: Graphite is cheap and easy to use, graphite is prone to peeling off, carbon inclusions are introduced, and non-destructive testing parts are prohibited.
FAQ
Q: What is the recommended material for the slag blocking cap?
A: Silicon carbide (SiC).
Q: Reasonable opening rate?
A：25–35%。
Q: What is the distance between the bottom of the slag cap and the bottom of the crucible?
A：30–50mm。
Q: What is the diameter of the slag blocking cap opening?
A：φ4–6mm。
Q: What is the gap between the slag cap and the liquid lifting pipe?
A：0.5–1mm。
Q: What are the risks of graphite slag caps?
A: Graphite peeling and carbon inclusions.
Q: Is the slag cap blocked?
A: Unstable filling pressure, insufficient filling, and frequent occurrence of cold insulation.
Q: What is the core function of the slag blocking cap?
A: Block the sediment at the bottom of the crucible, ensure smooth flow, and reduce vortex induced slag entrapment.