Tunnel Kiln Troubleshooting: Causes & Fixes

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Problems on this page:

Uneven firing across the car Cracks from heating or cooling too fast Kiln car problems Fuel use high Refractory damage Burner faults Fan failures Stack emissions above the limit

Uneven firing across the car

Hits OEE: Quality

Symptoms: Products on some positions of the kiln car are under-fired or over-fired.

Burner settings or flames uneven

Check each burner zone and its flame.

Setting pattern blocking gas flow

Check the setting pattern on the kiln cars against the standard.

Kiln car seals or sand seals leaking

Check the sand seals and car side seals.

Pressure profile along the kiln wrong

Check the kiln pressure profile and the fan dampers.

Prevention: Product shrinkage or colour checked at several car positions.

Cracks from heating or cooling too fast

Hits OEE: Quality

Symptoms: Products crack in the preheating or cooling zones.

Preheating zone temperature rising too fast

Check the temperature profile in the preheating zone.

Push rate faster than the firing curve allows

Check the push rate against the approved firing curve.

Cooling air too strong at the start of cooling

Check the cooling fans and dampers.

Products entering with too much moisture

Check the dryer exit moisture.

Prevention: Cracked pieces counted per car.

Kiln car problems

Hits OEE: Availability

Symptoms: Kiln cars derail, jam or push unevenly.

Car wheels or bearings worn

Replace worn wheels and bearings during car maintenance.

Rails damaged or out of line

Check the rail alignment and joints.

Car superstructure damaged

Repair cars before damaged parts fall into the kiln.

Pusher pressure or stroke wrong

Check the pusher settings and its hydraulics.

Prevention: Kiln cars inspected on a rota.

Fuel use high

Hits OEE: Performance

Symptoms: The kiln uses more gas per tonne of product than before.

Air leaking in at seals and doors

Check the sand seals, car seals and doors for leaks.

Burners out of tune

Have the burners tuned for the right air-to-gas ratio.

Heat recovery to the dryer not working

Check the hot air transfer to the dryer.

Insulation damaged

Repair damaged insulation found in a thermal survey.

Prevention: Gas use per tonne trended monthly.

Refractory damage

Hits OEE: Availability

Symptoms: The kiln lining cracks, spalls or shows hot spots on the casing.

Repeated heating and cooling from stops

Plan production to avoid unnecessary kiln stops.

Kiln cars hitting the walls

Check car alignment and loads that stick out.

Lining at the end of its life

Plan the relining at a planned shutdown.

Hot spots not followed up

Run thermal surveys of the casing and track hot spots.

Prevention: Casing thermal survey on a fixed schedule.

Burner faults

Hits OEE: Availability

Symptoms: Burners trip or fail to light.

Flame sensor dirty

Clean the flame sensor; never bypass flame supervision.

Gas pressure outside the switch limits

Check the gas train pressure and switches.

Combustion air fan fault

Check the combustion air fan and its pressure switch.

Igniter worn

Replace the igniter electrode.

Prevention: Burner trips recorded by zone.

Fan failures

Hits OEE: Availability

Symptoms: Kiln fans stop or vibrate, and the pressure profile is lost.

Fan bearings worn

Check bearing temperature and vibration on a route.

Belts worn or loose

Check the belts and their tension.

Impeller out of balance from deposits

Clean the impeller with the fan isolated and locked off.

Motor fault

Test the motor insulation and check its protection.

Prevention: Fans checked on the maintenance plan.

Stack emissions above the limit

Hits OEE: Quality

Symptoms: Stack monitoring shows emissions above the permitted level.

Combustion not tuned

Have the burners tuned and record the flue gas readings.

Raw material releasing more fluorine or sulphur

Check the raw material analysis for a change in the clay or additives.

Scrubber not working as designed

Check the scrubber reagent supply, its flow and the filter condition.

Monitoring instrument drift

Check the stack analyser calibration with test gas.

Prevention: Emissions reviewed against the permit.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: rotary kiln · fan / blower · industrial oven · glass tempering furnace · tile press

Stop the same fault coming back

Recurring tunnel kiln 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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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover