This article analyzes the causes of porosity defects in the green sand casting process of engine cylinder blocks and proposes corresponding solutions. By optimizing the local structure, improving the pouring system, and increasing the pouring temperature, the porosity defect problem in the cylinder block was effectively solved, reducing the scrap rate from 6.8% to 0.
1. Formation Mechanism of Cylinder Bore Porosity
Porosity Feature
Description
Reason
Location
Inside the casting, between two cold cores, at the cylinder bore wall
The flat and large plane formed by the gap between the two cold box cores is conducive to gas accumulation
Shape and Surface
Large volume, smooth inner surface, approximately pear – shaped
Caused by gas intrusion during metal solidification
Formation Reason
Inability of invading gas to escape during metal solidification
External gas entrainment, vapor and combustion gas generation, and poor bubble discharge conditions in the flat space
2. Solutions to Cylinder Bore Porosity Defects
2.1 Casting Structure Optimization
Original Structure Problem
Optimization Measure
Effect
Large and flat plane where gas easily accumulates and cannot be discharged
Add small bosses (width 15mm, height 2mm) to break the flatness
Reduce surface tension, lower gas entry/exit resistance, and prevent porosity
2.2 Pouring System Optimization
Original Pouring System Problem
Optimization Measure
Effect
Poor filling ability at the porosity defect location, gas accumulation, and lack of internal runner
Add an internal runner (thickness 6mm, width 12mm)
Accelerate filling, prevent sand core gas from entering the molten metal, and reduce porosity
2.3 Increasing Pouring Temperature
Original Pouring Temperature Range
Optimized Pouring Temperature Range
Effect
1385℃ – 1405℃
1400℃ – 1420℃
Improve metal fluidity, extend solidification time, and facilitate gas escape
3. Conclusion
Solution Method
Key Points
Effect on Porosity Defect
Add bosses at porosity location
Destroy the flat structure, reduce surface tension
Facilitate gas discharge and prevent porosity
Optimize the pouring system
Add runners at appropriate positions to enhance filling ability
Suppress porosity defect generation
Increase pouring temperature
Improve metal fluidity and extend solidification time
