A dome order of 500 pieces returned 130 with trapped bubbles after cure, a 26 percent reject rate that stopped shipment for two days. The cause was not the resin batch but the mixing and degassing routine around it.
This junior case guide covers the mixing sequence, vacuum degassing at -0.09 MPa, pot-life timing and the pre-cure checks that keep air out of every dome.
Common Mistakes and How to Avoid Them
| Mistake | Why It Happens | Practical Fix |
|---|---|---|
| 1. Fast mixer whips air | Air bubbles stay in the mix | Mix slowly, fold not whip |
| 2. Degassing skipped | Bubbles trapped in the dome | Vacuum 5-10 min at -0.09 MPa |
| 3. Vacuum released too fast | Air re-enters the mix | Release slowly after degassing |
| 4. Batch over pot life | Cloudy or tacky surface | Discard past working time |
| 5. Ratio guessed by eye | Under-cure and soft domes | Weigh both components |
| 6. Cold resin in winter | Thick mix holds bubbles | Warm to 25°C before mixing |
| 7. Moisture on parts | Pinholes at the interface | Dry parts before dripping |
| 8. Pour from height | Air trapped in the stream | Pour low and slow |
| 9. No bubble check before cure | Rejects found at packing | Check 10 pieces before cure |
Best Practices
- Weigh both components to the resin supplier's ratio
- Mix slowly until uniform, then degas
- Degas at -0.09 MPa until the foam layer collapses
- Release vacuum slowly and pour immediately
- Finish dripping inside the pot life window
- Hold a 10-piece bubble check before every cure
Implementation Roadmap
| Step | Frequency |
|---|---|
| Check resin and hardener | Batch number, expiry, ratio |
| Warm components | To 25°C working temperature |
| Mix slowly | Fold until clear and uniform |
| Degas | -0.09 MPa for 5-10 min |
| Drip and inspect | 10-piece check before cure |
Bubble-free dome flow
- Weigh - Both components per TDS. (Eye ratios under-cure.)
- Mix - Slow fold, no whipping. (Fast blades trap air.)
- Degas - -0.09 MPa until foam drops. (Fast release re-entrains air.)
- Check - 10-piece sample before cure. (Late checks waste the batch.)
Air is removed in the vacuum chamber, not in the cup. | Working time shrinks as temperature rises.
Dome dripping parameters
Reference values for two-component epoxy dome dripping.
| Parameter | Reference | Why It Matters |
|---|---|---|
| Mix ratio | 100 parts resin : 40-50 hardener | Weigh each batch per supplier TDS |
| Working viscosity | 300-1500 mPa·s at 25°C | Thick resin holds trapped air |
| Degassing | -0.09 MPa for 5-10 minutes | Until the foam layer collapses |
| Pot life | 30-60 minutes at 25°C | Past this, cure turns cloudy |
| Drip volume | 0.5-2.0 g per dome | Set by dome size and film need |
| Cure | 60-80°C for 2-6 hours | Follow the resin cure curve |
| Part dryness | No visible moisture | Moisture becomes pinholes |
Bubble fault map
| Symptom | Cause | Fix |
|---|---|---|
| Bubbles inside | Degassing skipped | Vacuum 5-10 min |
| Cloudy surface | Over pot life | Use fresh mix |
| Pinholes at base | Moisture on part | Dry parts first |
| Stream bubbles | Pour from height | Pour low and slow |
| Soft domes | Ratio wrong | Weigh components |
Degassing time by batch size
| Batch size | Degas time | Vacuum level |
|---|---|---|
| Up to 1 kg | 5 minutes | -0.09 MPa |
| 1-3 kg | 8 minutes | -0.09 MPa |
| 3-5 kg | 10 minutes | -0.09 MPa |
Case 1 - 26 percent bubble rejects traced to mixing and degassing
Scenario. A dome line rejected 130 of 500 pieces for bubbles; operators mixed with a fast drill and skipped the vacuum step to save time.
Action. Mixing was changed to a slow fold, a vacuum step at -0.09 MPa for 8 minutes was added, and a 10-piece check was placed before cure.
Result. Rejects fell to 3 of 500 in the next batch, and the check caught a rising-pot-life batch the same week.
Case 2 - pinholes on bag hardware from damp parts
Scenario. A bag hardware plant in Vietnam found pinholes on the underside of resin domes after the rainy season started.
Action. Parts were dried for 30 minutes at 40°C before dripping and kept in a covered tray during the drip cycle.
Result. Pinholes disappeared within two batches, and humidity became a line checklist item.
Frequently Asked Questions
Why do bubbles stay in the dome?
Air enters during mixing or pouring; degassing removes it before the resin gels.
What vacuum level is needed?
-0.09 MPa works for most two-component epoxies; deeper vacuum needs a stronger chamber.
How long should degassing run?
Until the foam layer collapses, usually 5-10 minutes depending on batch size.
Why release the vacuum slowly?
A fast release pushes air back into the mix and starts new bubbles.
What is pot life?
The working time after mixing; beyond it the resin thickens and cures cloudy.
Why weigh the ratio?
Eye-measured hardener under-cures the dome and leaves it soft and sticky.
Can cold resin be degassed faster?
No - warm it to 25°C first, because thick cold resin holds bubbles longer.
Why check before cure?
Bubbles are visible in liquid resin and fixable; after cure they are rejects.
How do I store components?
Sealed, dry and at 15-25°C; moisture in the container becomes pinholes.
What Would You Like to Solve?
Describe your dome size, resin type and current mixing routine, and a short parameter check can show where the air enters your batch.