Tempering Troubleshooting

BOWING

Cause and countermeasures:

1. Heating balance:

• Water holding: Reduce top temperature (convection or IR- heaters)
• Water shedding: Increase top element power ( convection or IR- heaters)

2. Quench air balance

• Water holding: Increase top quench pressure
• Water shedding: Increase bottom quench pressure

BI-STABLE BOW

Cause and countermeasures:

1. Hot edges and cold center

• Decrease Furnace temperature and/or increase cycle time
• Reduce edge heating
• Increase convection pressure

CHILL CRACK

Possible Cause and countermeasures:

1. High quench pressure setting -> Reduce
2. Too cold exit temperature -> Inrease
3. Moisture in quench air -> Reduce air intake outside
4. Glass stopped during quenching
5. Excessive blowback to furnace -> Check
6. Cover last furnace rollers with Kevlar

WHITE HAZE

Possible Cause and countermeasures:

1. Excessive Bottom Temperature -> Reduce (roller bed temperature)
2. Varying temperature conditions due to incosistent loading -> Run consistent full loads
3. Bowing at heating ->Adjust heating:
   a. Haze at edges decrease top heating
   b. Haze in center parts of glass increase top heating
4. Roller contamination -> Clean the roller bed

QUENCH BREAKAGE

Cause and countermeasures:

1. Edge work:
   • Review and correct cut & grind process
2. Glass oscillation stop at quench:
   • Review and adjust quenching conditions
3. Glass exit temperature:
   • Low furnace exit temperature -> increase heating time
4. Quench air cool or moist:
   • Reduce outdoor air intake
5. Glass thickness:
   • Measure glass thickness

IRIDESCENCE

Cause and countermeasures:

1. Furnace conditions:
   • Decrease Furnace temperature
   • Increase the oscillation lenght to max
2. Quench conditions:
   • Nozzle distance & field temp condition
   • Quench pattern test -> clean?
   • Maximum oscillation time to first stop.

ROLLER DISTORTIONS

Possible Cause and countermeasures:

1. If ‘wave’ peak to peak=roll spacing distance:
   • Excessive glass temperature at exit
   • Glass “stop” on oscillation reversals
2. If wave peak to peak=circumference of the roller
   • Twisted roller in furnace or quench
3. Glass End Kinks
   • Check furnace-quench levelling.

FRAGMENTATION ISSUES

Possible Cause and countermeasures:

1. Excessive Fragment Count:
   • Reduce quench pressure or glass temp
2. Low Fragmentation:
   • Increase quench pressure or/and glass temp
3. Elongated spline-type fragments:
   • Review heating conditions ->uniform temp
   • Review quench conditions, quench nozzle field condition, top-bottom cooling rate (balance).