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Edge alignment or picture frame effect

A coating defect can usually only be restored by a complete coating build-up. Bulging of materials at edges due to surface tension and/or overcoating.

  • Recognition characteristics:
    • Materials bunch up at the edges.
    • With metallic tones, a dark frame forms near the edges (picture frame).
  • Sources of error:
    • Incorrect spraying technique. Do not return or change direction on edges. Always try to guide a few centimeters beyond the object.
    • Edges on the object are too sharp or not well-ground. Edges, like those of a plate, are usually very sharp. This can be imagined as a break in the glass. Material rears up at these edges because it „flees“ from the edge. When you break these edges (they don’t have to be round), the material can pull up into the edge.
    • The layer thickness is too high. Material that is in the center of a plate, for example, pushes toward the outer edges. At this point, the inner presses against the adhesion forces to the edge, and the material „pile up“.
    • Material too diluted, viscosity too low.
    • The diameter of the nozzle size was selected as too large.
    • Hardener and/or thinner selected too long.
    • Flash-off times between courses are not observed.
    • Object temperature too low / temperature difference.
  • Error prevention:
    • Comply with material processing according to technical information.
    • Adapt spray technique. Paint over the object.
    • Adapt the hardener and thinner selection to the ambient temperatures and object sizes.
    • Reduce nozzle size or reduce material flow rate.
    • Flash-off times must be observed. If the preceding coating layer has not yet flash-off far enough, the layer will become too thick when further material is applied and will drift to the edges.
    • Break“ existing edges in the substrate preparation.
  • Repair path:
    • With stove: Only complete removal and repainting help here.
    • Without a stove in the uni material: Level the material with a scraper or hard block with sandpaper and prepare with the known finish method. Here you can see on the surface, just in the clear coat only a „bulge“ in the material. But here, too, an attempt to remove it may result in sanding through and repainting.
    • In the metallic basecoat: The only thing that helps here is to interrupt the painting process and „wash down“ the material. A visual disturbance in metallics cannot be eliminated in the clear coat. A „frame“ forming darkly at the edges cannot be changed by polishing. The metallic particles float towards each other and thus form a dark surface. This creates the „picture frame effect“.
    • What happens in this defect pattern?
      The material runs on the surface, pushes outward, and rears up again on the edges due to surface tension, away from the edge. This image is often seen on overcoated engine hoods.

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