Fixing Those Pesky Cold Spots in Glass Annealing
If you’ve ever dealt with glass containers that have weird shapes—think tight necks, sharp shoulders, or those chunky deep bases—you know the headache of “cold spots.” You’re running your annealing process, everything looks fine on paper, but then you start seeing breakage. Why? Because those tricky geometries create temperature dead zones. The heat just doesn’t get where it needs to go, leaving you with uneven internal stress and a lot of wasted product. Here is how we handle it. We drop shortwave infrared (IR) heating lamps right into the lehr or the inspection tunnel. It’s basically like giving the glass a targeted blast of heat exactly where the standard convection air just gives up. Getting the heat where it actually matters When you’ve got a complex shape, you can’t just “warm up the room.” You need a lot of power packed into a tiny space. We use quartz halogen tubes for this. The reason is simple: they put out shortwave radiation, which actually sinks into the glass instead of just bouncing off the surface. Depending on how fast your conveyor is moving, we can tweak the lamp length and the voltage. It’s all about matching the heat to the speed of your line. Just a heads-up: if you’re using high-wattage tubes to punch through thick-walled bases, keep an eye on your electrical panels. Adding a bunch of these lamps to one zone can really spike your current draw, so make sure your gear can handle the load. The nitty-gritty on the hardware We don’t mess around with flimsy connections. We use R7s or SK15 connectors because they stay put. The last thing you need is a connection vibrating loose while the machine is humming along. The quartz envelopes we use are tough. They let the heat through and can take a real beating in those brutal high-heat environments. And for the really strange shapes? We overlap the lamp patterns. It stops the “shadow effect,” which is when one part of the bottle basically blocks the heat from reaching the rest of the piece. A few things to watch out for The best part about shortwave IR is the speed. You can ramp up the heat almost instantly. But there is a catch. Because the heat is so intense and localized, you have to be careful. If the lamps are too close, you’ll end up with “hot spots” on the surface, and that’s a quick way to trigger thermal shock. It takes a little bit of tinkering with the distance and the angle, but once you find that sweet spot, you get full coverage without risking the integrity of the glass.