Fixing Those Pesky Cold Spots in Glass Annealing
If you’ve ever worked with complex glass shapes, you know the nightmare of “cold spots.” You pull a piece out of a standard convection kiln, thinking you’re in the clear, only for it to shatter spontaneously a few days later. It’s frustrating. The problem is that hot air just can’t get everywhere. It struggles to reach deep recesses or tight curves, leaving internal stress trapped in the glass. We found a better way: we bring shortwave infrared (IR) lamps right into the bending and annealing cycle.
How to actually get full coverage
Here’s the thing about IR radiation—it doesn’t care about air movement. It just hits the glass surface directly. But if you just use one lamp, you get shadows. To fix that, we use a multi-lamp array. We stagger the emitters so the radiation cones overlap. It’s like using multiple flashlights to light up a dark room; the lamps fill in the gaps that the glass’s own shape would normally create.
Picking the right gear
For the heavy lifting, we usually go with quartz halogen tubes. They’re incredibly fast. You can hit your target temps in seconds, not minutes. Just keep an eye on your glass thickness. Thicker walls need more energy density, otherwise, you’ll end up with a surface that’s hot while the core is still shivering. We stick with standard R7s or Sk15 connectors. Why? Because they’re simple. When a lamp eventually burns out, you just pop it out and put a new one in. No need to tear apart your entire heater bank just to fix one bulb.
The trade-offs (because nothing is perfect)
Now, these high-wattage arrays pack a punch, but they’ll pull a lot of power. If you’re running a dense bank of 230V or 400V lamps, your control cabinet needs to breathe. If you don’t have proper ventilation, your switching relays and contactors will cook themselves and fail. And a quick tip on placement: watch your distance. If the lamp is too close, you’ll get “hot spots” that can warp your piece. It’s all about finding that sweet spot.