TL;DR
A temperature zone deviation causes glass breakage from residual stress. Identify whether the zone is overheating or underheating, then check the heating element and thermocouple before adjusting the setpoint.
What you might see
- glass breakage at the lehr exit
- thermocouple in one zone reading outside the set point
- residual stress in finished glass above quality limit
- heating element burn-out alarm
Likely causes
Heating element burned out, causing an undertemperature in that zone
Thermocouple failed open or shorted, feeding the controller a false temperature
Zone control relay or solid-state relay failed, causing full-on or full-off heating
Lehr conveyor belt gap in that zone disrupting the temperature uniformity
Required tools
- Multimeter for thermocouple and element continuity check
- mV calibration source
- Replacement thermocouple or heating element
- LOTO kit
Safety first
- Lehr interior and zones operate at temperatures up to 700 degC. Use heat-resistant gloves and face shield for any access.
- Lock out lehr heating power and conveyor drive before any internal inspection.
Procedure
- 1
Read the zone temperature setpoint and actual value from the lehr controller. Identify the direction and magnitude of the deviation.[1]
- 2
Compare the zone heating element current draw to the rated value. Zero current with a setpoint indicates a failed element or relay.[1]
- 3
Test the thermocouple by substituting a known-good thermocouple or a mV source at the same temperature range. If the controller responds to the substitute, the original thermocouple is failed.
- 4
Check the solid-state relay or contactor for the zone. A failed SSR can leave the element permanently on or off.
- 5
Inspect the heating elements visually during a planned stop. A broken element shows an open section in the coil.
- 6
Replace the failed component and verify the zone temperature stabilizes at the setpoint within the expected time.
Sources
Pennekamp Pennekamp Profile / Mosaik Annealing Lehr general technical documentation, Pennekamp
General glass annealing lehr temperature control and maintenance procedures (general)
More guides for Pennekamp Pennekamp Profile / Mosaik
How to diagnose atmosphere control faults on a Pennekamp Profile / Mosaik annealing lehr
Glass surface staining in the lehr means the protective atmosphere has been disrupted by air ingress or a gas control fault. Check the lehr seal curtains, gas supply, and O2 sensor calibration.
How to fix conveyor belt tracking faults on a Pennekamp Profile / Mosaik annealing lehr
A belt tracking to one side is almost always a tension imbalance or a crown alignment issue on the end rollers. Adjust the tracking roller in small increments and allow the belt several belt lengths to respond before adjusting again.
Stop fixing the same fault twice.
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