Application technology in painting systems encompasses the processes and systems used to atomize paint material and transfer it to workpiece surfaces. It significantly influences coating quality, material consumption, process stability, and application efficiency.
Automated painting systems utilize a variety of application systems. The choice of system depends on factors such as component geometry, paint material, production volume, and the requirements for surface quality and process stability.
Key technologies include high-speed rotary atomizers, air-atomizing spray guns, and electrostatic application methods.
Rotary Bell Atomizer
High-speed rotary atomizers are among the most efficient application systems in automated painting lines. The paint material is fed onto a rotating bell, on whose surface a thin film of paint forms due to the high rotational speed. At the bell's breaking edge, this film breaks into fine paint droplets, which are then transported to the workpiece.
In combination with electrostatic charging, high application efficiencies can be achieved under suitable conditions, as the charged paint particles are attracted to the grounded workpiece.
Typical characteristics
- very fine and reproducible atomization
- High surface quality with stable process parameters
- High material efficiency through electrostatic support
- Several independently controllable steering air paths allow for flexible adjustment of the spray pattern.
- Suitable for primers, base coats and clear coats
- Suitable for use with 2K and 3K paints as well as water-based and solvent-based paints.
- suitable for systems with color-changing or pigging technology
Due to their high reproducibility, high-speed rotary atomizers are primarily used in automated series processes, for example in the automotive industry or in industrial series painting.
Air atomizing paint guns (type INHP)
Air-atomizing spray guns are used in automated painting systems when flexibility in dealing with changing components, materials, or process requirements is paramount. They are suitable for both fully automated series painting systems and applications with frequently changing media or highly variable component geometries.
The coating material is atomized by compressed air. The air breaks the material flow into droplets, which are then transferred to the workpiece surfaces. The spray pattern and droplet size can be precisely adjusted via air pressure, material pressure, nozzle geometry, air cap design, and material flow.
Typical characteristics
- Uniform layer thicknesses with a stable spray pattern
- Highly diverse spray patterns thanks to numerous air cap and nozzle combinations
- separate regulation of horn and atomizer air
- Adapted air cap geometries support a high application efficiency.
- Compatible with water-based and solvent-based paints, adhesives, and 2K and 3K mixtures
- Suitable for systems with color change technology due to flow-optimized, short paint-carrying channels and good rinsability
- modular system for operation on robots and area automation systems
Electrostatic coating
In electrostatic painting, paint particles are electrically charged and attracted to the grounded workpiece. This so-called wrap-around effect improves material transfer, increases the application efficiency, and also enables the coating of hard-to-reach areas.
In practice, electrostatic methods are predominantly used in combination with high-speed rotary atomizers. Air-atomizing systems can also be operated electrostatically in principle, but require significantly more technical effort and are therefore mainly used in specific applications.
Two main variants are used in industrial painting facilities.
- Direct charging: The entire atomizer is at high voltage potential, and the coating is charged very efficiently as it flows through the direct contact. This method results in a particularly high application efficiency. At the same time, the demands on insulation, grounding, and system design increase, for example, the need for a potential isolation system for conductive coatings. An atomizer with direct or contact charging is a compact option that can operate even in confined spaces between components.
- External charging: Without direct contact between the coating and components at high voltage potential, charging occurs via external electrodes. This makes charging the coating less efficient, and the lower charge level results in comparatively lower application efficiencies. This method can also be used with conductive coatings with minimal technical effort because no potential isolation system is required. However, the electrodes being located externally on the atomizer make the atomizer larger and limit its usable area.
The use of electrostatic systems depends heavily on the material, system design, and safety requirements.
Steering air and spray pattern control
The shaping air, also called steering air, influences the shape, width and stability of the spray jet and thus the reproducibility of the spray pattern.
Several independently controllable steering air channels allow the spray pattern to be precisely adapted to different component geometries and process requirements.
Correctly adjusted steering air contributes significantly to:
- to achieve uniform layer thicknesses
- to reduce overspray
- to ensure a stable droplet path to the workpiece
Dirty or damaged steering air rings are among the most common causes of unstable spray patterns and should be checked regularly.
Paint bells – designs and selection
Paint bells form the central atomizing element of a high-speed rotary atomizer. The paint material spreads across the rotating bell surface as a thin film and breaks up into droplets at the breaking edge.
The geometry of the trailing edge significantly influences how the paint film divides and what droplet sizes are formed. This directly affects the spray pattern, droplet spectrum, and surface quality.
- Smooth tear-off edge: With a smooth tear-off edge, the paint film tears without any additional texturing. This results in droplets of varying sizes. This design is frequently used for applications with moderate surface quality requirements and is characterized by low wear.
- Lined edge: With knurled spraying, the paint film is divided into defined liquid threads before being torn off. This results in a more even droplet distribution and a better controlled spray pattern.
- Cross-knotted: The cross-shaped structure divides the paint film with exceptional precision, resulting in uniformly formed droplets. This design is frequently used for high-quality finishing applications, particularly in clear coats. It can also help reduce air inclusions and microbubbles in the paint, leading to a more homogeneous surface appearance.
Which tear-off edge is the best choice always depends on the interplay of several factors: paint material and viscosity, material flow, rotational speed of the bell, steering air, component geometry, desired surface quality, as well as bell diameter and process parameters.
Even minor contamination or damage to the demolding edge affects droplet size and spray pattern and can impair process stability.
Besides the tear-off edge, the bell diameter also influences the spray pattern. Smaller bells are often used for complex geometries or smaller components, while larger bells are better suited for large areas with higher material throughput.
Influence of application technology on order processing efficiency
The transfer efficiency describes what proportion of the applied coating material actually ends up on the workpiece. It is influenced by several factors: application technology, electrostatic assistance, spray pattern and droplet size, component geometry, system parameters, and process stability.
High-speed rotary atomizers can achieve high application efficiencies under suitable conditions. Air atomization systems, on the other hand, offer high flexibility for changing applications.
Choosing the right application technology therefore always involves a trade-off between material efficiency, process flexibility, surface requirements, technical effort, and investment costs.
When is high-speed rotary atomization a better choice than air atomization?
High-speed rotary atomizers are particularly suitable for automated, high-throughput production lines with stable process conditions. High deposition efficiencies can be achieved in combination with electrostatics. Air atomization, on the other hand, is often the better solution for varying media or complex geometries.
What influence does the choice of bell have on the coating result?
The bell diameter and the geometry of the trailing edge influence the spray pattern, droplet spectrum, and surface quality. Smaller bells are suitable for complex geometries, larger bells for larger areas and higher material throughput.
What is the difference between direct and external charging?
Direct charging generates the high voltage directly at the atomizer, enabling particularly high application efficiencies. External charging, on the other hand, uses external electrodes, making the system easier to integrate into existing systems.
What factors determine the application efficiency in paint shops?
The application efficiency is influenced by factors including application technology, electrostatic support, spray pattern, component geometry, and the stability of process parameters.
Which application technology is used in the automotive industry?
In the automotive industry, high-speed rotary atomizers with electrostatic assistance are predominantly used because they enable high surface quality and high deposition efficiency in stable series production processes.
Consulting on application technology
Selecting the right application technology is a crucial factor for stable painting processes, high surface quality and efficient material use.
INDUSTRA assists in selecting suitable application components and provides consulting services in the context of existing paint shops. Implementation is carried out on a project-specific basis in cooperation with plant manufacturers and integration partners.