Follow this checklist to troubleshoot CD moisture profiles

Nov 10, 2015

Poor CD moisture profiles can be caused by almost any paper machine section. The most common trouble areas are the press and forming sections, but the dryer section can play a role as well. The following areas should be checked when CD moisture profiles are not as good as desired.

  1. Basis weight profile: higher basis weight areas will carry more water down the machine.
  2. Press nip loading and crown settings: the higher the nip loading pressure, the lower the moisture will be in those areas. Press nip loading profiles generally are set up as slight smiles (slightly more load on the edges).
  3. Former, press and dryer clothing cleaning, conditioning and tension: high pressure needle showers and low pressure conditioning shower nozzles should be working properly with no plugging. Any discoloration streaks in the fabrics are an indication of fabric filling or burning. All clothing tensions should be at the supplier’s recommended values. Clothing tradelines should be straight across to keep fabric structure open. Dryer felts should be clean of fiber and oil contamination.
  4. Check for proper operation of former vacuum boxes (not flooded), press uhle boxes vacuums and flows, lube showers, etc.
  5. Steambox or re-wetting showering system profiles should be checked for clues of poor moisture profiles. Ideally, actuator profiles should be flat and no actuators should be at 0% or 100% output.
  6. Check dryer section condensate removal systems and pocket ventilation systems for proper operation and flow.
  7. Check moisture scanner calibration and historical moisture profiles to identify when moisture profiles changed. Single-point the scanner to check for MD moisture trends.
  8. Use thermography throughout the entire machine to look for clues. Temperature differences of only 1°F at the wet end may be significant, whereas temperature differences of 10°F are significant at the reel. Cooler temperatures at the reel are wetter, but at the press section center roll, cooler temperatures are drier (if steamboxes are used). Thermography is a good tool to see if steambox actuators are doing what they are told to do and if they are overheating the edges of the felt outside the sheet path.
  9. Higher moisture paper will calender easier, so roll structure may show a problem with poor moisture profiles. Here again, induction heater actuator profiles should be flat and no actuators should be at 0% or 100% output.

For more information on troubleshooting profile problems, contact your Valmet representative.