The Headache of “Cold Spots” in Glass Tunnel Kilns
Most infrared lamps stop at about a meter. That’s fine for small jobs, but when you’re running a glass tunnel kiln with a wide substrate, those short segments are a nightmare. Why? Because every time one lamp ends and another begins, you get a joint. And those joints create cold spots. If your temperature isn’t perfectly even, your glass is going to show it. That’s why we build custom continuous heating units that stretch past 2 meters.
The Trick to Long-Form Tubes
You can’t just stretch a filament and call it a day. It doesn’t work like that. As the tube gets longer, the internal resistance of the tungsten changes. If you aren’t careful with the voltage and wattage, you’ll end up with a “hot middle” and ends that never even reach annealing temperature. We spend a lot of time balancing the wattage per centimeter. The goal is a flat power density. We want the heat to be just as strong at the very edge as it is in the center. No guessing, no dead zones.
Getting the Heat Right
For big glass annealing jobs, we go with a continuous array. By overlapping the radiation zones of these long units, we basically kill off those thermal gaps you find in modular systems. We wrap everything in high-purity quartz to handle the heat load. The result? A steady stream of infrared flux that actually sinks into the glass instead of just hitting the surface.
A Few Things to Watch Out For
Here’s the reality: a 2-meter tube is a fragile piece of kit. We use heavy-duty connectors so the units don’t arc or snap when things start expanding from the heat, but you still have to be careful. If your kiln vibrates a lot or takes a few knocks, you’ll need to beef up your mounting brackets. Plus, keep an eye on your airflow. These high-wattage arrays dump a massive amount of heat into the kiln housing. If your cooling blowers aren’t up to the task, you’re risking a warped frame. It’s a lot of power, so make sure your cooling can keep up.