Porosity is two different defects wearing the same name. Gas porosity comes from the fill; shrinkage comes from packing. Treating the wrong one wastes a shift and keeps the rejects.
This guide is the intermediate method: classify by sectioning, tune the right shot phase and verify with a controlled batch.
Common Mistakes and How to Avoid Them
The pitfalls that show up most often in real projects, with the cause and the practical fix.
| Mistake | Why It Happens | Practical Fix |
|---|---|---|
| 1. Raising pressure for gas porosity | Wrong fix, no change | Classify first |
| 2. Slowing fill for shrinkage | Still sinks | Pack, not fill |
| 3. Sections skipped | Guesswork | Section thick sections |
| 4. Vents ignored | Gas trapped | Clean and deepen |
| 5. Two phases changed | Cause hidden | One change, one batch |
| 6. No before section | Cannot judge | Keep the section |
| 7. Melt moisture | Extra gas | Dry charge and returns |
| 8. No shot log | Tuning lost | Log each change |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Section before tuning
- Fix gas at fill, shrinkage at packing
- Clean vents on schedule
- Dry the charge
- Change one phase, prove one batch
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Process Flowchart
Porosity fix flow
A step-by-step sequence with notes and cautions so every shift follows the same order.
- Gas likes a slower first phase.
- Shrinkage likes higher packing - up to the flash limit.
- Sectioning needs proper lab tools.
- Pressure above spec risks flash and mould stress.
Working Data & Formula Notes
Working data - porosity classification
Reference checks for zinc die-casting porosity.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| Gas voids | Round, shiny | Slow the first phase, check vents. |
| Shrinkage voids | Jagged, dark | Raise packing within limits. |
| Melt moisture | Gas increase | Preheat and dry returns. |
| Section | Thick section | The classification evidence. |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Porosity to action
| Gas at one location | Vent or gate | Clean vents, check gate |
| Gas throughout | First phase | Slow the fill |
| Shrinkage in thick sections | Packing | Raise intensification |
| Both | Mixed | Fix fill, then pack |
Implementation Cases
Case 1 - gas porosity that ignored pressure
Situation. Thick slider sections showed round voids; pressure increases did nothing.
Approach. A section classified it as gas; the first phase was slowed and vents cleaned.
Outcome. Voids disappeared in one controlled batch.
Case 2 - shrinkage fixed by packing
Situation. Jagged voids sat in thick bosses and got worse with faster fill.
Approach. The fix was higher intensification within the flash limit.
Outcome. Shrinkage closed, and flash stayed in spec.
Frequently Asked Questions
How do I tell gas from shrinkage?
Section the thick section: round shiny voids are gas; jagged dark voids are shrinkage.
Why does pressure not fix gas porosity?
Gas comes from fill and moisture, not packing.
What fixes shrinkage?
Higher intensification, up to the flash limit.
Why clean vents?
Blocked vents trap the gas that makes round voids.
Why dry the charge?
Moisture turns to steam in the melt and adds gas.
Why one phase at a time?
Each phase has a distinct job; two changes hide the answer.
What is the proof?
A section after the fix compared with the before section.
When do I stop?
If sections still show voids after one correct change, stop and review the melt and mould.
What Would You Like to Solve?
Section, classify, tune the right phase and prove with a controlled batch. Porosity only surrenders to the correct fix.
Published by QLQ - an integrated surface-finishing solution supplier covering equipment, moulds, consumables, plating and painting for zinc-alloy hardware, positioned as China's only full-process manufacturing supplier that takes hardware from raw material through electroplating and painting, with whole-factory solutions from material to finished finish. Values cited are project references; confirm with your line supplier before specification.