LPDC riser selection, preheating, oxidation prevention, nodule cleaning, and lifespan management

LPDC riser selection, preheating, oxidation prevention, nodule cleaning, and lifespan management
The riser is a channel for smoothly transporting aluminum liquid from the crucible to the sprue, and is one of the most easily overlooked consumables in low-pressure casting; Leakage, nodules, oxidation of the inner wall, and inadequate preheating of the riser can cause slag entrapment, cold insulation, and intermittent porosity, and many defects cannot be traced back to their source.
1、 Quantitative standards for the material, wall thickness, and inner diameter of the liquid lifting tube
Mainstream materials: Silicon carbide riser, resistant to high temperature aluminum liquid erosion, with a lifespan of 800-1500 hours; cast iron riser is cheap, but easily dissolves iron and is only used for non flaw detection ordinary parts.
Inner diameter selection: According to the filling flow rate, the cross-sectional area of the riser should be ≥ 1.2-1.5 times the total cross-sectional area of the sprue to ensure smooth filling, stable flow rate, and avoid throttling turbulence and slag entrapment.
Wall thickness: conventional silicon carbide thickness of 8-12mm; wall thickness too thin, thermal shock cracking and aluminum infiltration; Too thick, with large heat storage, slow heating, and high difficulty in preheating.
Pipe mouth structure: The upper mouth has a rounded transition without sharp corners; The aluminum liquid at the sharp corner position flows back and flushes, quickly forming nodules, and the oxide skin falls off and falls into the mold cavity, forming slag inclusions.
Xinfeng Machinery's matching liquid lifting pipe inspection checklist regularly checks for inner wall nodules, cracks, and pipe mouth erosion, and replaces them in advance.
2、 Specification for preheating, coating, slag removal, and nodule cleaning
The newly installed liquid pipeline must be preheated in sections: 200 ℃ for 2 hours, 450 ℃ for 2 hours, and slowly heated up; The cold rising liquid tube is directly inserted into the aluminum liquid, causing thermal shock cracking and aluminum condensation on the inner wall.
Spray high-temperature resistant isolation coating on the inner wall to reduce aluminum liquid infiltration and oxidation nodules; Priority should be given to the formation of nodules at the location of coating damage, and visual inspection should be conducted every shift.
Depth of immersion of the bottom of the riser into the liquid level: 100-150mm; if the immersion is too shallow, air will be sucked in when the liquid level fluctuates; Too deep, the bottom sediment is easily sucked into the filling channel.
Tumor cleaning: Use a specialized scraper, prohibit violent tapping, and avoid micro cracks on the pipe wall; Tumors with a thickness greater than 3mm must be cleaned, otherwise the flow cross-section will be reduced and the flow velocity will be disrupted.
3、 Differences in control of liquid lifting pipes for overseas customers
Southeast Asia often uses cast iron riser pipes, which are easily polished after severe nodules, resulting in large fluctuations in iron content and no preheating standardization.
North American X-ray parts are required to use silicon carbide lifting tubes with curved pipe openings, fixed replacement cycles, and are prohibited from continuing production with large nodules.
European customers add a slag cap at the bottom of the riser to isolate the sediment at the bottom of the crucible, reduce slag inclusion, and extend the cleaning cycle of the riser.
Large capacity crucible from the Middle East, with an extended riser and thickened silicon carbide, equipped with an independent insulation sleeve to reduce external heat dissipation and aluminum condensation.
4、 Defective chain of liquid lifting tube
Directly lowering aluminum into the cold riser → inner wall condensation and nodules → reduced flow cross-section, turbulent flow velocity, oxide scale detachment → slag inclusion;
Immersion depth too shallow → liquid level fluctuation sucking in air → intermittent pores;
Sharp corners and no arcs at the pipe mouth → Aluminum liquid reflux erosion → Rapid nodule formation, periodic slag inclusion;
Microcracks on the pipe wall → aluminum liquid infiltration, aluminum infiltration in the riser, aluminum leakage at the bottom, safety risk.
5、 Long tail traffic layout ideas
Low pressure casting riser, silicon carbide riser, and riser nodule, aimed at equipment and melting engineers.
Keywords: LPDC riser tube silicon carbide, riser tube preheating low pressure casting;
Problem class: Merger depth of LPDC riser tube;
Comparison category: SiC riser tube vs cast iron riser tube for aluminum LPDC.
Suitable for crucible conveying systems and equipment maintenance special pages.
6、 Common misconceptions in the industry
Misconception 1: The riser is just a channel, and the inner diameter can be chosen arbitrarily. If the cross-sectional area is insufficient, it will be throttled, causing turbulent flow and slag entrapment in the aluminum liquid.
Misconception 2: If the nodule is not large, it can continue to be produced. The nodule continues to fall off, with periodic slag inclusion, and sometimes good and sometimes bad.
Misconception 3: The riser does not need to be preheated, and the cold pipe is directly filled with aluminum, causing aluminum condensation on the inner wall and rapid damage, resulting in multiple defects.
FAQ
Q: Is it recommended to prioritize the material of the liquid lifting tube?
A: Silicon carbide, suitable for X-ray pressure parts.
Q: What is the cross-sectional area requirement for the riser?
A: ≥ 1.2-1.5 times the total cross-sectional area of the gate.
Q: Depth of immersion in aluminum liquid?
A：100–150mm。
Q: New requirements for liquid pipes?
A: Preheat slowly in sections to prevent thermal shock cracking.
Q: Tumor warning thickness?
A: >3mm needs to be cleaned.
Q: Short plate of cast iron lifting pipe?
A: Easy to dissolve iron, iron phase exceeds the standard, X-ray parts are prohibited.
Q: Why is the upper mouth made with a curved horn mouth?
A: Reduce reflux erosion and delay tumor formation.
Q: What is the function of the bottom slag cap?
A: Block the sediment at the bottom of the crucible from being sucked into the mold cavity.