Getting Your Heat Right in PET Blow Molding
Ever pull a batch of PET bottles off the line only to find some walls are paper-thin while others are thick and clunky? It’s a nightmare. Usually, it comes down to uneven heating in your KHS or Sacmi SBF 12 machines. It happens a lot. Your OEM lamps get old, or you swap them out for replacements that just don’t put out the same kind of light. When that happens, your thermal field goes wonky, and your bottles start failing.
The Power Balance
On a Sacmi SBF 12, it all comes down to the wattage and voltage of the lamp. If you go with a high-wattage shortwave IR lamp, you’re packing a lot of energy into a tiny space. That’s great because it speeds up your cycle times. But you’ve got to be careful. The voltage has to match your machine’s transformer exactly. If the voltage is too low, you’ll never hit that sweet spot—the glass transition temperature—where the PET actually becomes moldable. But push it too high? You’ll end up burning your preforms. It’s a delicate balance.
The Secret is in the Glass
We use high-purity quartz because it can handle the “thermal shock” of turning on and off rapidly without cracking. Inside, we use a halogen cycle. It basically stops the tungsten filament from evaporating too fast, which means your lamps actually last longer. Some of our top-tier tubes even have special coatings. Instead of just scorching the surface of the plastic, these coatings help the heat sink deeper into the preform wall. It makes a world of difference in the final strength of the bottle.
Installation and the “Catch”
The good news? These are drop-in replacements. You just pull the old tube, wire in the new one, and you’re done. No need to tear apart your oven housing. But here’s the thing: if you crank up the heat density to fix a patchy thermal field, your cooling blowers are going to feel it. If you’re using higher wattage to make up for a reflector that’s seen better days, the whole machine is going to run hotter. Keep a close eye on your cooling system. You don’t want to find out the hard way that your lamp sockets have melted because the heat had nowhere to go.