01How the process works
In extrusion blow moulding, a tube of molten plastic (parison) is extruded, closed by the mould and inflated with air. In stretch blow moulding, an injection moulded preform is heated, stretched and blown into bottles.
Wall thickness distribution is the key quality feature: thin corners fail drop and pressure tests. The pinch-off seam at the bottom of extrusion blow moulded parts is another weak point.
- Parison or preform. Material extruded or preforms heated.
- Mould closing. Mould closes around the parison.
- Blowing. Air inflates the part against the mould.
- Cooling. Part cools in the mould.
- Trimming and testing. Flash removed; leak and wall checks.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Thin walls | Parison programming, stretch ratio | Ultrasonic or magnetic wall gauge |
| Weak pinch-off | Mould design, temperature | Drop test, section |
| Leaks | Pinch-off, contamination | Leak test |
| Rocker bottoms | Cooling | Visual, stability |
| Dimensional deviation of necks | Mould, trimming | Gauges |
| Contamination | Material handling | Visual |
03Where an inspector should look
01
Before production
- Mould and preform approval
- Material grade
02
During production
- Wall thickness sampling
- Weight checks
03
After production
- Leak test
- Drop and top load tests
- Neck dimensions
04Standards and references
Customer specifications for containers; UN packaging tests for dangerous goods containers.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of blow moulding parts
Independent Quality ControlIncoming, in-process and final quality control performed independently at the supplier, with measured results and clear acceptance decisions.
Pre-Shipment InspectionFinal random or complete inspection of finished goods before shipment: quantity, conformity, workmanship, packing and marking.