Why glass cracks in annealing

Tue, 09 Jun 2026 04:14:05 +0800

On the annealing line, a hairline crack in a 2 m² lite doesn’t come with a warning. It just shows up as yield loss, scrap, and a furnace that keeps running hot. More often than not, the root cause is thermal stress. Glass cracks during annealing when the hot zone isn’t even, or when the cooling profile forces the surface to pull against the core. Temperature spreads across the belt, emissivity shifts across the glass, and the stress finds the weakest edge to run. What matters, technically We set up annealing lehr heating with medium-wave infrared quartz emitters that match the glass absorption band. The point isn’t chasing peak temperature—it’s a stable, repeatable thermal field. We calibrate input per zone, holding setpoint within ±3 °C across the belt width by keeping voltage and current tolerances tight. Power density is tuned so the surface heats quickly, then soaks evenly, which cuts the transient gradients that drive crack initiation. Why it works in practice With annealing, the gains come from control. Fewer rejects from thermal shock. Fewer reworks driven by edge stress. You run the same schedule without over-tempering, and you stabilize the cooling curve so the surface and core come together instead of fighting. That means predictable flatness, consistent optical quality, and a line that hits throughput without constantly chasing setpoints. Energy use drops because the emitters deliver heat on demand—fast response, minimal parasitic loss. What you need to know up front This isn’t plug-and-play. You have to match lamp geometry to the furnace chamber, get the reflectors aligned, and confirm the power supply matches the load. Existing conveyors and control interfaces will likely need minor adaptation. Plan a short shutdown window for installation and re-commissioning, then recalibrate the annealing curve to match the new thermal profile.

Cracks on IR Glass Heating Technology

Why glass cracks in annealing