Problems on this page:
Glass breaking in the furnace
Hits OEE: Availability
Symptoms: Lites break in the heating section and the furnace has to be cleared.
Edge defects such as chips or shells
Check edge processing before tempering and remove damaged lites.
Heating too fast for the glass
Use the recipe for the glass type and thickness.
Glass thickness entered wrong
Check the thickness entered against the glass loaded.
Holes or notches too close to the edge
Check the design against the tempering rules for hole position.
Prevention: Breakages recorded by cause and recipe.
Roller wave distortion
Hits OEE: Quality
Symptoms: Tempered glass shows waves that distort reflections.
Heating time too long
Shorten the heating time to the minimum for good fragmentation.
Rollers worn, bent or dirty
Check the ceramic rollers and clean or replace them.
Oscillation settings wrong
Check the oscillation settings for the glass size.
Furnace temperatures too high
Check zone temperatures against the recipe.
Prevention: Distortion measured on sample lites.
Quench marks visible
Hits OEE: Quality
Symptoms: Iridescent patterns appear in polarised light or at certain angles.
Quench air uneven across the glass
Check the quench nozzles for blockage and the air distribution.
Nozzle boxes misaligned
Check the alignment of the upper and lower boxes.
Glass heated unevenly
Check heating zone balance.
Quench oscillation settings wrong
Check the quench oscillation.
Prevention: Visual check under polarised light on samples.
Bow or warp
Hits OEE: Quality
Symptoms: Lites are bowed or warped after tempering.
Top and bottom heating unbalanced
Balance the top and bottom heat for the glass.
Quench pressure unbalanced
Balance the top and bottom quench pressure.
Glass position on the rollers wrong
Load glass as the loading pattern shows.
Coated side facing the wrong way
Load coated glass coated side up unless the recipe says otherwise.
Prevention: Bow measured on sample lites.
Fragmentation test failing
Hits OEE: Quality
Symptoms: The break test gives too few fragments for the standard.
Quench pressure too low
Check the blower output and the quench pressure setting for the thickness.
Glass temperature at exit too low
Check the heating time and exit temperature.
Wrong recipe for the thickness
Check the recipe matches the glass thickness and type.
Delay between furnace and quench
Check the transfer speed so the glass reaches the quench while it is hot enough.
Prevention: Fragmentation tested as the standard requires.
Coated glass heating unevenly
Hits OEE: Quality
Symptoms: Low emissivity coated glass comes out under or overheated.
Convection not used for coated glass
Use the convection recipe, since coated glass reflects radiant heat.
Coating type entered wrong
Enter the coating type the glass supplier states.
Heating time too short for coated glass
Extend the heating time within the recipe limits until fragmentation passes.
Coating damaged before loading
Handle coated glass with clean gloves and suction cups made for coated surfaces.
Prevention: Recipes kept per coating type.
Roller marks or haze on the glass
Hits OEE: Quality
Symptoms: White haze or pick marks appear on the roller side.
Rollers dirty with glass particles
Clean the rollers on the interval the maker sets, and after any breakage.
Broken glass left in the furnace
Remove all fragments after a breakage before the next load.
Roller protection gas dosing wrong where it is used
Check the dosing against the maker setting.
Rollers worn or pitted
Replace rollers whose surface is worn or pitted.
Prevention: Roller condition checked weekly.
Heating zone cold
Hits OEE: Availability
Symptoms: One zone does not reach its temperature.
Heating element failed
Have the element tested and replaced by qualified staff with the furnace isolated.
Thermocouple faulty
Compare the thermocouple with a reference and replace it if it reads wrong.
Power controller fault
Check the zone power controller output.
Supply fuse open
Check the fuses for the zone and find why one opened.
Prevention: Zone temperatures logged.
Quench blower faults
Hits OEE: Availability
Symptoms: The blower trips or cannot reach pressure.
Blower inlet filter blocked
Clean or replace the inlet filter.
Damper stuck
Free and lubricate the damper and check its actuator.
Blower bearings worn
Check bearing temperature and vibration and replace worn bearings.
Blower drive fault
Read the drive fault log.
Prevention: Blower vibration trended; hearing protection used near the quench.
Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.
Related equipment guides: heat-treat furnace · industrial oven · waterjet cutter · overhead crane · fan / blower · tunnel kiln
Stop the same fault coming back
Recurring glass tempering furnace stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.
Book a Fabrico demo
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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary
Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover