Coating Process Troubleshooting Guide
Technical guidance for diagnosing and correcting common coating process deviations to ensure consistent film quality and operational efficiency.
Process Deviation Management
Coating performance depends on precise alignment between formulation properties, equipment configuration and critical process parameters. Variations in spray rate, drying capacity, atomization pressure or tablet movement can result in surface defects and process inefficiencies.
This guide outlines common coating challenges, probable root causes and recommended corrective actions for controlled industrial application environments. By systematically identifying process deviations, manufacturers can restore operational consistency and ensure high-quality film formation.
Uneven Colour Distribution
Probable Causes
- Inefficient tablet rolling/mixing in the bed
- Improper baffle configuration or positioning
- Inconsistent spray pattern from nozzle
- Inadequate atomization uniformity
Recommended Corrective Actions
- Improve tablet bed mixing by adjusting pan speed
- Adjust baffle positioning for better tablet turnover
- Verify spray nozzle alignment and cleanliness
- Validate atomization uniformity across all spray guns
Excessive Drying Time
Probable Causes
- Low drying air temperature
- Reduced atomization pressure (large droplets)
- Low spray rate with insufficient wetting
- High suspension viscosity
Recommended Corrective Actions
- Maintain inlet air temperature within validated operating range (typically 50–60°C depending on formulation)
- Verify atomization pressure to ensure fine droplet distribution
- Adjust spray rate aligned with drying capacity
- Confirm suspension dilution and viscosity
Sticking or White Patch Formation
Probable Causes
- Over-wetting due to high spray rate
- Inadequate tablet rolling or bed movement
- Spray gun misalignment causing localized wetting
- Excess coating solution accumulation on pan surface
Recommended Corrective Actions
- Reduce spray rate to match drying capacity
- Ensure proper tablet bed movement and pan speed
- Clean pan surface if excessive accumulation occurs
- Optimize side air flow and drying parameters
- Verify spray gun alignment and coverage
Excessive Flying of Coating Material
Probable Causes
- Excessive side air flow
- High atomization pressure
- Spray gun positioned too far from tablet bed
- Excessively fine droplet formation
Recommended Corrective Actions
- Optimize side air flow to prevent premature spray drying
- Adjust atomization pressure to recommended levels
- Maintain appropriate spray gun distance (typically 9–12 inches)
- Align spray rate with drying capacity
Additional Process Considerations
- Suspension instability due to prolonged holding
- Inconsistent batch size impacting bed movement
- Equipment calibration deviations (pumps/sensors)
- Environmental humidity fluctuations in the coating area
- Core tablet moisture content variability
- Inadequate cleaning of spray gun nozzles