What Is Blow Molding?
Look, forget the fancy brochures.
If you go to any real factory today (China, Europe, doesn't matter), the foreman will tell you there are only three machines that actually make money.
Plain old extrusion blow
The parison drops, mold closes, air goes in, part comes out. That's it. Everything bigger than a soda bottle and cheaper than a pharma vial is made this way. Jerry cans, detergent bottles, 55-gallon drums, kayak hulls, the plastic pallet with the nine legs - same damn process. You can buy a decent Chinese continuous machine for the price of a used BMW and start tomorrow.
Two-stage PET stretch blow
You already know it because you're holding one right now. Every water bottle, every Coke, every 500 ml iced tea in the convenience store fridge. Preform gets reheated, rod stretches it, air finishes the job. Nothing else on earth can hit 0.25 mm sidewall with that clarity and top-load strength at 70,000 bottles an hour. Period.
Injection blow (the one nobody loves)
10 ml eye drops, 30 ml nasal spray, 60 ml cough syrup with the measuring cap that has to seal perfectly. Neck finish has to be within two hundredths or the filling line in New Jersey rejects the whole truckload. So you keep one dusty three-station machine in the corner for those orders.
That's literally the whole industry
Everything else is just a footnote:
- Accumulator head? Still extrusion.
- Six-layer fuel tank? Still extrusion with more extruders.
- PC baby bottle? Still two-stage, just different resin and a lot more swearing.
- Tritan sport bottle? Same stretch blow machines, different temperature settings.
New machines are all servo now, electricity bill drops 40 %, great. Recycled resin runs fine if you dry it properly, also great. Doesn't change the fact that when the mold opens you still have one of the same three shapes you had in 1975.
So yeah. Three processes. Pick the one that matches your part size, volume, and budget. Done.
