2.2 - Quality

2.2 Quality

2.2.1 Keeping spraying and drying areas clean

The look of the paint finish depends not only on the paint material and processing, but also on the state of the spraying and drying chambers and the work equipment. Paint should be applied at a room temperature of between 18 and 25° C. The spraying air must be oil and water-free (check oil separator every day). The spray pressure must be constant. It is important to choose the correct nozzle and to keep the nozzles and air caps clean because otherwise you will not achieve an even finish.

Keeping the spraying and drying areas dust-free serves first and foremost to allow ventilation and extraction systems to function properly, which is necessary for safety reasons to prevent explosive solvent vapor/air mixture concentrations.

Apart from the spray technique, a proper ventilation and extraction system is particularly important for the quality of a vehicle paint finish. Air consumption in spraying chambers is approx. 20,000 m3/h; removal from the workshop is not advisable because of the increased dust filter performance which is also required.

The incoming air must be routed via filter and heating units. This applies, in particular, to colder times of the year and particularly for combined model versions, i.e. when the spraying box is also used as the drying box.

The incoming quantity depends on the size of the spraying area as well as the outgoing air quantity. In any event, sufficient air must be supplied to produce overpressure in the spraying area. An outgoing/incoming air ratio of around 1:1.05 is sufficient.

A vacuum causes fresh paintwork to become soiled because the outside air that is streaming in takes the most convenient route through cracks in doors, gaps in walls, etc., thereby carrying along dust deposits. The air will not automatically choose the inconvenient route via the ventilation system filters. Of course, the appropriate filters must be used and must always be kept clean. The micro-filters must have a minimum dust extraction level of 99.8%. It is particularly important that the air supply is routed via suitable distributors that are used to prevent the formation of excessively strong air currents. This would not only irritate the sprayer, but would also cause air whirls in which paint dust would be retained for a long time. Gradually, it would come to rest on the fresh paintwork there and dirty it.

The air speed must not be too high because the paint would harden too quickly on the surface. This would result not only in flow disturbances, but would also produce pinholing because the paint mist can no longer be absorbed, but accumulates on top. In addition, the gloss may be reduced and the paint can wrinkle if the surface dries too quickly. If conditions in the workshop allow, it is always a good idea to set up the air supply and distribution from the entire ceiling area. An air gradient, i.e. an air speed of 0.3 m/s measured in any cross-section of the spraying chamber, is generally sufficient (approx. 350x change of air/h).

Air extraction is carried out most effectively using extraction pipes on the floor of the spraying box. It is a good idea to arrange the floor in the form of a water trough fitted with grates so that the paint dust can settle on the surface of the water. The paint dust deposit on the water prevents premature blockages of the extraction channels, thereby assuring a constant pressure in the chamber.

2.2.2 Protective measures for vehicle parts

To protect vehicle parts from damage or from malfunctions caused by soiling that could have been prevented, particular attention must be paid to the components - sanding dust, paint mist, temperature - which occur with every paint job.

2.2.2.1 Protection against sanding dust, paint mist and temperatures

Sanding dust

The amount of sanding dust involved can be reduced considerably by wet-sanding or by performing dust extraction during dry-sanding.

Paint mist

Carefully covering up and masking any areas that do not need to be painted not only protects them, but also cuts down on the time and cost-intensive tasks of subsequently cleaning and polishing.

Temperature

The maximum permitted temperature burden must be observed in the specified time period, particularly because of plastics and the electronic control units.

2.2.2.2 Protection for electronic control units, tires and door and lid locks

Electronic control units

While drying following painting work, the temperature burden on electronic control units must not exceed two hours at a maximum temperature of 80° C.

Tires

The temperature burden during drying can result in irreversible flat spots on the tires. Given this, the tires must be removed and the vehicle raised during oven drying (drying chamber).

Door and lid locks

During painting, the door and lid locks must either be removed or covers must be used to protect them against:
- grinding dust
- sanding water
- paint mist
- solvents
- lubricant removal

2.3 - Environmental Protection