Fixing the “Cold Spot” Problem in Long Glass Tunnel Kilns
Most infrared lamps stop at about a meter. That sounds fine until you’re running a massive glass tunnel kiln. When you string together a bunch of short lamps, you get these annoying gaps at every joint. Those gaps are “cold spots.” And in the glass world, cold spots are a nightmare. They cause uneven curing and build up internal stress in the glass, which usually ends in a crack you didn’t see coming. We figured out a better way: building custom medium-wave units that stretch past 2 meters.
The trick to keeping the heat even
You can’t just stretch a quartz tube and call it a day. If you do, the physics of the filament goes sideways. Here’s the thing: as the lamp gets longer, the internal resistance changes. If you just pump current through a long filament without balancing the voltage, you’ll end up with a glowing hot center and dim, useless ends. To stop that, we obsess over the winding density. We calibrate the voltage and wattage so the heat feels exactly the same at the first centimeter as it does at the very end.
Fighting the “Sag”
Quartz is great for heat, but it’s fragile. A 2-meter tube is basically a long, hot noodle that wants to bow under its own weight. To keep things straight, we use high-purity quartz with a very specific wall thickness. It gives the tube the backbone it needs to stay rigid. Plus, because it’s one continuous piece, the gaps are gone. You aren’t getting “stripes” of heat; you’re getting a solid wall of energy hitting your glass.
The honest trade-off
I won’t lie to you—these long units are a bit of a beast to handle. You can’t just toss a 2-meter lamp into a cardboard box and hope for the best. They’re awkward. You’ll need specialized jigs to drop them into place, otherwise, one wrong move and you’ve snapped a very expensive tube. And there’s the risk factor. Since one long lamp does the work of several small ones, a single filament break knocks out a bigger chunk of your kiln. My advice? Wire them into zoned controllers. It lets you balance the load across the whole tunnel and keeps things from becoming a headache if one unit goes down.