Production hygiene for electrocoating systems

Good production hygiene is important to protect pipelines, rinsing zones and coating tanks in electrocoating lines (ETL). This includes the three points of basic cleaning, intermediate cleaning and continuous measures.

Bacterial growth in electrocoating lines (ETL) is unavoidable due to the environment and input from the various processes. In particular, the use of increasingly environmentally friendly systems and low-emission preservatives means that pipelines, rinsing zones and coating tanks can only be partially protected. This increases the importance and significance of good and careful hygiene throughout the entire coating process, from pre-treatment and the coating itself to waste water treatment and system maintenance.

For example, incrustations, deposits or other residues on the walls of the rinsing zones or in the ETL tank form ideal habitats for a large number of microbes. The microbes multiply in these habitats and form their own habitat, the biofilm, through their cooperation. Within this, the microbes can develop uninhibitedly and even protect each other from external influences. This is one of the most common sources of infection, because if biofilms are not removed, they cannot be successfully combated by chemicals such as biocides alone and lead to even greater growth.

To ensure that all this does not disrupt your coating process or even lead to production downtime, basic production hygiene is essential. The following points have proven their worth: Basic cleaning, intermediate cleaning and continuous measures.

The manufacturer FreiLacke recommends carrying out a complete system cleaning at least once a year. This involves pumping the ETL tank into the counter tank and removing sludge, residues and other impurities from the tank. The rinsing zones are also drained and intensively cleaned of incrustations and residues using suitable methods such as high-pressure cleaners. Attention must also be paid to the collection tanks under the rinsing tunnels, where deposits and thus breeding grounds for bacteria can form due to fluctuating fill levels. Pipes such as the cascades of the UF rinsing zones should also be checked and cleaned if necessary when cleaning the system.

Subsequent preservation using suitable biocides is extremely important, as this is the only way to achieve an optimum effect through a combination of mechanical and chemical treatment. It is essential to observe the relevant specifications regarding application quantities and exposure time.

During the course of the year and independently of basic cleaning, it is advisable to take preventative measures for system hygiene at an early stage. We therefore recommend draining and cleaning the UF flushing zones at regular intervals. This involves intensive mechanical and subsequent chemical treatment of the flushing tunnel and the collection trays of the flushing zones. The interval depends on the degree of production capacity utilization, the age of the system and the general degree of soiling; for many customers, a 1 to 3-monthly rhythm has proven successful.

During the course of the year, bacteria can and will occur despite all measures. In this case, a biocide treatment must be carried out at an early stage to prevent overgrowth, biofilm formation and coating problems.

The continuous measures include daily and weekly measures. The first step is to determine the daily bath values. Even here, signs of a possible bacterial infestation can be announced and recognized at an early stage. In particular, an increasing conductivity in the lacquer bath and especially in the ultrafiltrate are indicators and signs of a growing microbial infestation. The weekly routine also includes monitoring the bacterial situation using suitable immersion and dish culture media. DipSlides have proven their worth due to their ease of use and the wide range of bacteria they can detect and can be carried out by anyone after a brief introduction. Sampling should take place at least in the paint tank, the ultrafiltrate and the last rinse before the ETL and can be extended to other areas as required.

The new modern and more environmentally friendly coating systems contain significantly less solvent and can therefore be more susceptible to possible bacterial growth. Experience in recent years has shown that the ultrafiltrate rinsing zones and DI rinsing zones upstream of the ETL are often the origin or starting point of many bacterial infestations. Here, weekly preservation of the UF rinsing zones can lead to a significant extension of the service life of the ETL tanks and prevent rapid infestation.

As mentioned at the beginning, general cleanliness and order around the system is essential in the fight against constant microbial infestation. This starts directly in the system with the avoidance or regular removal of residues and continues in the rinsing zones, where standing water, incrustations and other things should also be avoided or regularly removed. However, the areas around the system, such as the filters, ultrafiltration tanks and paint post-dosing, also contribute to a good overall result. For example, soiling should be removed immediately and old filters disposed of so as not to provide a breeding ground for bacteria.

In summary, the following continuous measures help to prevent bacterial growth or to detect it early and react accordingly: Daily determination of bath values, monitoring by means of sampling with DipSlide, regular preservation of UF rinsing zones, demineralized water monitoring/preservation, cleanliness around the systems as well as last rinse pre-treatment, check and avoid carry-over.

As previously mentioned, microbial infestation can never be completely prevented, even with excellent system hygiene. However, the frequency and, above all, the consequences can be greatly influenced by system hygiene and maintenance. And in the event that preservation does have to be carried out, we have effective and efficient antidotes at hand with our biocide kit. The biocides have all been tested and approved for use in the ETL sector in the FreiLacke laboratory. Thanks to the possible combination of different active ingredients, a wide range of different bacteria, yeasts and fungi can be combated and possible adaptations prevented.

For all biocides, it is essential to observe the contact time of at least 48 hours. No production may take place during this time, as the biocides are disrupted in their effect and become unusable due to the application of tension and the coating process. A basic application rate of 0.2 % in relation to the tank volume has proven to be effective. In special cases, larger or smaller quantities may be appropriate and should always be discussed with AWT FreiLacke.

Only those who understand where the causes lie and recognize them can take targeted action and solve problems. FreiLacke supports its customers with a comprehensive service. The paint manufacturer therefore supports its customers with system cleaning, preventive maintenance concepts or root cause analysis by means of a hygiene audit. The latter is a "health check for the system" in which the entire process is put to the test with regard to microbiological infestation. A hygiene audit involves a systematic inspection of the various zones, from pre-treatment to the final rinse after ETL coating. The process liquids are sampled and swabs are taken from walls, undercuts, cover plates and deposits. All these samples are then spread on culture media and analyzed in a specialist laboratory for aerobic / anaerobic bacteria, yeasts and fungi.

Such a "health check for the system" provides a clear overview and a deeper understanding of the possible sources of contamination and starting points for recurring contamination. In addition, a systematic hygiene audit can be used to identify areas for action and take targeted measures to prevent constant contamination and ensure a stable and high-quality coating process (OM-8/25).