Key points of LPDC process for sand mold low-pressure casting, sand mold permeability, sand core gas generation, parting, and coating selection

Key points of LPDC process for sand mold low-pressure casting, sand mold permeability, sand core gas generation, parting, and coating selection
Metal type low voltage is suitable for large quantities; Sand mold low-pressure is suitable for single piece, large, complex inner cavity, and short development cycle castings. Many engineers directly copy the parameters of metal molds to sand molds, resulting in high gas generation, porosity, sand holes, and sand flushing problems.
1、 Quantitative parameters of sand mold, sand core, and coating
Sand material: resin self hardening sand, sand mold permeability ≥ 80; The breathability of large thick walled components is ≥ 100; Low breathability, inability to release gas from the mold cavity, and high incidence of pores.
Resin addition ratio: 1.0-1.4%, curing agent ratio adjusted according to the resin; Resin too high, high temperature gas generation; The resin is too low, the sand mold strength is insufficient, and filling and sand flushing are required.
Control of sand core gas generation: Brush high-temperature resistant alcohol based coating on the sand core, with a coating thickness of 0.2-0.4mm; seal the gaps between sand particles with the coating to reduce sand core gas generation and aluminum liquid infiltration.
Sand casting temperature: 10-20 ℃ higher than metal mold, A356 conventional 710-730 ℃; Sand molds have poor heat storage, fast cooling, and are prone to cold insulation at low temperatures.
The low-pressure solution of Xinfeng Mechanical Sand Mold focuses on calculating the total amount of gas emitted from the sand core, matching slag collection and exhaust, controlling the filling speed, and avoiding sand erosion caused by gas entrainment.
2、 Key points of filling curve, exhaust, and anti sand flushing
The low-pressure pressure rise rate of sand molds is slower than that of metal molds, ranging from 0.6 to 1.0 kPa/s; Sand molds have weak resistance to erosion, and the pressure rise is too fast, causing turbulent flow at the front of the aluminum liquid, sand flushing, and sand holes.
Exhaust cannot rely solely on sand mold ventilation, additional slag collection exhaust channels should be set up at the highest point and sand core end; An exhaust rope is embedded inside the sand core to release the decomposed gas from the sand core.
Place a slag dam directly opposite the outlet of the liquid lifting pipe to prevent direct erosion of the sand mold wall by the aluminum liquid; Add refractory mortar reinforcement to weak areas and sharp corners of the sand mold.
The sand mold is fully solidified during static placement, but incomplete solidification leads to continuous gas generation and batch porosity during pouring; The moisture content of the sand mold should be controlled to be less than 0.3%.
3、 Low pressure differences in sand molds for overseas customers
Southeast Asian sand molds with low pressure are mostly used for small batch spare parts, with a high resin ratio and low cost. They accept more sand holes and pores and rely on grinding and infiltration.
Low pressure sand molds in North America are commonly used for construction machinery samples, and the total gas generation calculation is written into DFM. If the gas generation exceeds the standard, pouring is not allowed, and the sand core must be baked to remove gas.
European sand molds attach great importance to dimensional stability, low gas resin system, and multi-layer coating to reduce sand infiltration and surface roughness.
Large scale heavy sand casting in the Middle East, with thickened and reinforced sand molds, segmented filling and stabilizing to prevent long-term filling and erosion of the sand molds.
4、 Sand mold low-pressure defect chain
Excessive resin ratio, sand core not baked → high gas generation → pores;
Rapid pressure rise rate → Aluminum liquid flushing sand wall → Sand flushing and sand hole flushing;
Insufficient breathability, no pre embedded exhaust → gas retention in subcutaneous pores;
Insufficient solidification of sand mold, high moisture content → superposition of water vapor and resin gas, concentrated outbreak of defects.
5、 Long tail traffic layout ideas
Sand low-pressure casting, resin sand LPDC, sand core gas control, aimed at process engineers and sample development.
Keywords: sand mold low pressure casting LPDC, resin bonded sand core gas control;
Question class: sand mold permeability requirement for aluminum LPDC;
Comparison category: Sand Mold vs Metal Die Low Pressure Casting.
Suitable for sample development and sand mold low-pressure special pages.
6、 Common misconceptions in the industry
Misconception 1: The low-pressure parameters of metal molds are directly applied to sand molds, which have weak gas generation and erosion resistance. The pressure rise should be slowed down and the temperature should be raised.
Misconception 2: Natural breathability is sufficient for sand molds, and it is difficult for gases inside the sand core to be discharged through the sand mold, so exhaust must be pre embedded.
Misconception 3: Adding more resin results in higher strength. The higher the resin, the more gas will be emitted at high temperatures, and the risk of porosity will sharply increase.
FAQ
Q: What is the minimum requirement for breathability of resin self hardening sand?
A：≥80， Large items ≥ 100.
Q: What is the proportion of resin added?
A：1.0–1.4%。
Q: What is the temperature of low-pressure aluminum liquid in sand mold?
A: 710-730 ℃, 10-20 ℃ higher than the metal type.
Q: Sand mold pressure rise rate?
A：0.6–1.0kPa/s， Slow than metal type.
Q: What is the thickness of sand core coating?
A：0.2–0.4mm。
Q: What is the upper limit of sand mold moisture content?
A：＜0.3%。
Q: How to do sand core exhaust?
A: Pre embedded exhaust rope, with a slag collection bag set at the end.
Q: Short board of sand mold low-pressure core?
A: High gas generation and easy sand flushing, not suitable for stable mass production in large quantities.