The individual stages of surface pre-treatment – including degreasing, phosphating and rinsing – are standard processes in cathodic electrocoating. However, the final coating quality also depends on the ability to maintain the long-term stability of all process baths. This directly affects coating adhesion, coating uniformity and the corrosion resistance of finished components. At Automotive Painting Partners (APP), we manage process baths through precisely defined parameters, regular process evaluation and rigorous control of the entire process.
Precise laboratory control of process parameters, where every stage influences the final result
The surface pre-treatment process consists of several sequential stages, each of which contributes to the final coating quality.
- Degreasing bath – uses an alkaline phosphate-based cleaner designed for steel, galvanised steel and aluminium. To enhance cleaning efficiency, it is supplemented with a cleaning accelerator.
- Pickling bath – a sulphuric acid solution used for pickling and deoxidising metal surfaces. The bath also removes mill scale and silicates formed during previous manufacturing operations.
- Activation bath – prepares the component surface for the formation of a fine, uniform crystalline phosphate layer during the subsequent phosphating process.
- Phosphating bath – uses a trication zinc phosphating solution that forms a microcrystalline zinc phosphate layer on the metal surface, providing the material with its primary corrosion protection.
- Passivation bath – a chromium-free acidic solution used as the final post-passivation rinse. It minimises the risk of underfilm corrosion and improves the adhesion of the final cathodic electrocoating layer.
- Demineralised water rinse – produced using a reverse osmosis water treatment system, with additional water softening where required. It serves as the final rinse, ensuring consistent surface properties across the entire pre-treatment process.
”At Automotive Painting Partners, we do not view the individual process baths as isolated stages, but as an integrated system in which the stability of every phase directly influences the final quality of the surface treatment,” explains Ondřej Lukášek, Head of Maintenance and Technology at APP.
Thorough laboratory analysis as the foundation of process stability
The objective of laboratory analysis is to keep all critical parameters of the process baths and the entire pre-treatment system within defined operating limits. This enables us to identify undesirable conditions at an early stage, such as process bath carry-over or contamination by foreign substances, and prevent them from affecting the quality of the final coated surface.
Quality control begins directly on the cathodic electrocoating line during sample collection. Laboratory technicians continuously assess the condition of each process bath, assessing not only their visual appearance but also monitoring temperature, liquid circulation, the quantity and nature of contaminants captured by the filtration systems, and operating pressures. These inspections are followed by laboratory analysis using titration methods, pH and conductivity measurements, and determination of solids content by the gravimetric method.
If any deviations from the specified operating parameters are identified, clearly defined escalation procedures are initiated to enable rapid assessment of the situation and the implementation of appropriate corrective actions. An equally important part of the process is the validation of the in-house laboratory results. These are regularly verified in cooperation with accredited expert laboratories operated by our suppliers of process chemicals and coating systems. Based on the data obtained, we adjust process bath parameters, optimise chemical dosing rates and refine our long-term chemical maintenance strategy.
The laboratory’s role extends well beyond the operation of the pre-treatment process itself. APP also manages the disposal of process baths at the end of their service life, including supervision of the in-house wastewater treatment plant, analysis of discharged wastewater, and the administration of all related documentation, regulatory reporting and statutory compliance requirements.
Autonomous online monitoring minimises the risk of human error
APP’s cathodic electrocoating lines are equipped with sensors that continuously monitor key process parameters, including temperature, pH, conductivity and the operating pressures of the pumping systems. The control system incorporates both warning and critical alarm thresholds, providing operators with continuous real-time visibility of the process status.
If predefined limits are exceeded, the system automatically alerts operators and continuously records all events for traceability. This autonomous online monitoring of the process baths significantly reduces the risk of human error, enables a rapid response to process deviations and provides historical data for long-term trend analysis and process optimisation. Process stability is routinely verified through corrosion testing and periodic requalification.
“This enables us to respond quickly and precisely to any process deviations while maintaining complete traceability of changes in key process parameters over time. The data we collect also provides a solid foundation for modelling the behaviour of process bath systems and their further optimisation, including future AI-driven optimisation,” says Lukášek.
Corrosion resistance for every component and compliance with OEM standards
At Automotive Painting Partners, we consider the integration of laboratory analysis with online process monitoring to be one of the key tools for maintaining long-term process stability. This integrated approach ensures consistent product quality throughout the entire production cycle while meeting the requirements of OEM standards. The result is consistently high surface treatment quality and long-term verified corrosion resistance for every component we produce.
Looking for a partner in cathodic electrocoating with a strong focus on process stability and OEM-quality standards? Get in touch with us. Together, we’ll find the right solution for your project, from individual requirements to high-volume series production.
