Tablet Coater Troubleshooting: Causes & Fixes

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Problems on this page:

Tablets sticking or twinning Rough or orange peel coating Picking or peeling of the coat Uneven colour between tablets Spray guns blocking or dripping Chipped or eroded tablets Air handling faults Coating cycle taking too long

Tablets sticking or twinning

Hits OEE: Quality

Symptoms: Tablets stick together in pairs or to the pan wall.

Spray rate too high

Reduce the spray rate to what the drying air can remove.

Pan speed too low

Raise the pan speed within the validated range.

Bed temperature too low

Check the inlet air temperature and exhaust temperature.

Flat tablet faces

Discuss the tablet shape with the formulation team.

Prevention: Bed temperature and spray rate trended for every batch.

Rough or orange peel coating

Hits OEE: Quality

Symptoms: The coating surface is rough or dull instead of smooth.

Spray drying before it reaches the tablets

Reduce the atomising air or bring the guns closer to the bed.

Bed too hot

Lower the inlet temperature.

Coating suspension too thick

Check the solids content and mixing of the suspension.

Prevention: Coating appearance checked on samples during the run.

Picking or peeling of the coat

Hits OEE: Quality

Symptoms: Pieces of coat or tablet surface are pulled off, leaving marks.

Over-wetting of the bed

Lower the spray rate or increase the drying air.

Spray guns too close or misaligned

Set the gun distance and angle to the validated setup.

Tablets sticking briefly to each other

See the causes of sticking and correct them.

Prevention: Gun setup checked with a template at each batch.

Uneven colour between tablets

Hits OEE: Quality

Symptoms: Some tablets are darker or lighter than others in the same batch.

Poor mixing in the pan

Check the baffles and the pan speed.

Spray pattern uneven between guns

Check each gun pattern and flow.

Coating time too short for the weight gain

Coat to the validated weight gain.

Prevention: Spray pattern test before each batch.

Spray guns blocking or dripping

Hits OEE: Availability

Symptoms: Guns stop spraying, spray unevenly, or drip onto the bed.

Suspension not stirred

Keep the suspension stirred during the whole run.

Coating dried in the nozzle

Flush the guns at pauses and clean them after each batch.

Worn gun needle or seat

Replace worn gun parts.

Prevention: Guns stripped, cleaned and inspected after every batch.

Chipped or eroded tablets

Hits OEE: Quality

Symptoms: Edges and logos wear away or tablets chip in the pan.

Pan speed too high

Reduce the pan speed.

Tablet cores too soft or friable

Check core hardness and friability before coating.

Long tumbling before the first coat

Start spraying as soon as the bed reaches temperature.

Prevention: Core hardness and friability released before coating starts.

Air handling faults

Hits OEE: Availability

Symptoms: Inlet air temperature, flow or humidity alarms stop the batch.

Air filters blocked

Replace the filters on the differential pressure reading.

Heater or chilled water fault

Check the air handling unit.

Exhaust fan or damper fault

Check the fan and the dampers.

Prevention: Air handling unit on the planned maintenance schedule.

Coating cycle taking too long

Hits OEE: Performance

Symptoms: Batches take longer than planned to reach the weight gain.

Spray rate held low because drying is limited

Check the inlet air temperature and volume.

Batch size above the validated load

Load the pan to the validated batch size.

Frequent stops to clear guns

Fix the causes of gun blocking.

Prevention: Coating time recorded per batch and reviewed weekly.

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

Related equipment guides: tablet press · fluid bed dryer · capsule filler · blister pack machine · air handling unit · high shear granulator

Stop the same fault coming back

Recurring tablet coater 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