When performing the “powder in powder” process, the use of corona charging is strongly recommended for the application of the primer and the use of tribo charging is strongly recommended for the application of the top coat. All standard devices with corona and tribo charging can be used. In doing so, the use of classic tribo guns or so called tribo lances is insignificant. The only advantage of tribo lances is the ability to comfortably coat areas at a greater distance when dealing with larger workpieces. The primer and the top coat can also be processed with tribo charging for both powders. However, this reduces the efficiency of the coating and increases the risk of both powders mixing during the application process. Coating using the corona charging method should not be applied as this method generates a less appealing surface and quickly leads to a sprayback effect and a mixing of the powders. As is the case with all electrostatic powder coatings, sufficient earthing must also be ensured when processing using the powder in powder effect. The correct earthing of the components should be regularly monitored during the entire coating process. An insufficient earthing can lead to a significant worsening of the coating result and efficiency.

No special aspects need to be taken into account when coating with the primer powder. The applicants can be performed in a similar manner as when coating using the conventional two-coat structure. However, limiting the current and adjusting the high voltage to <80 kV may make the later application of the top coat easier and reduce the probability of spray-back effects or powder mixing. Furthermore, primer coating thicknesses >100 μm should be avoided as they can have a negative impact on the subsequent coating thickness. Once the primer has been coated, the top coat should be applied immediately as the primer is not cured.

The recycling mode should not be utilised if the coating of the primer and the top coat takes place in the same chamber and the entry of the primer powder into the powder circuit of the top coat or the entry of the top coat into the powder circuit of the primer powder cannot be prevented during the coating process. The recycling can be utilised when processing the primer and top coat in separate coating chambers. However, it should be ensured that the lowest amount of overspray is generated as the processability of the  powder can slightly decrease over time due to the high stress generated in the recycling process. The dosage of recycled powder into the fresh powder should take place in constant volumes (and automatically where possible). This ensures a constant ratio of fresh and recycled powder in the powder container.