For paper tray manufacturers running wet pressing lines, surface quality is the main selling point, but it is also the main source of production headaches. The good news is that the most frequent defects have well-established solutions.
Defect one: cracked hot pressing nets. When the mesh tears during hot pressing, the tray surface picks up a visible impression of the crack. The fix starts with prevention: choose a softer mesh and pre-shape it to the product contour before pressing. If a tear does occur, spot welding can repair the mesh quickly, avoiding a complete replacement.
Defect two: stripes on the tray surface. These lines appear because the forming mold absorbs slurry unevenly, leaving some areas with different fiber density. Adjusting the mold by using a smaller drill bit for the suction holes, or raising the pressure of the hot press, usually smooths out the problem. Adding extra mesh layers to the mold is another effective way to distribute the vacuum more evenly and prevent localized striping.
Defect three: blackened areas on the product. This occurs when slurry builds up in the narrow parts of the mold, making those sections thicker than intended. During hot pressing, the excess thickness compresses and darkens. The same effect can come from too much press pressure or too long a pressing cycle. Removing the excess material with a file or adjusting the press parameters resolves the issue.
Wet pressing is a precise process, but it is forgiving when problems are diagnosed correctly. By paying attention to net condition, mold geometry and press settings, manufacturers can produce smooth, uniform trays with minimal waste.
