Press Section Troubleshooting Flashcards
Why are extra HP showers put at press felt edges
To tackle all kinds of edge issues including edge drop off under pick up
Edge wrinkling
Edge cracking
Edge napping
Sheet stealing
What can cause moisture variations to the sheet at the press felt
PLugged showers
What devices can be used to monitor press felts
Moisture meter - uses resonance frequency to determine moisture content
Permeability meter - water fed at constant pressure into the felt, water velocity is measured - this shows if there is change in flow resistance//permeability
Air speed through felt at uhle box - determines openess of felt. (plugging level and conditioning level)
What does air speed measurements through the felt at the uhle box tell you?
Plugging level and conditioning level
What is something you can do on the machine to improve start up dewatering in the press section
Have start up showers that saturate the the felt - this will increase hydraulic pressure and therefore nip dewatering will be better at the start
What is analysed in the lab for a used press felt
Basis weight, thickness, void volume, permeability, ash %….
How does geometry of nip affect speed
If the felt is not angled out of the nip rewetting can occur and the machine speed cant be increased
In the felt is angled there is some rewetting but its possible to increase machine speed and runnability
What factors affect sheet release in press
Geometry
Forces
- Pressure differences
- centrifugal
What are some reasons for fibre shedding? (Press felt)
*At the uhle box:
Cover smoothness
Vacuum level
Width of slots
*Hp showers
*Abrasive filler
*Rough rolls
What are some causes of felt wear
Uhle boxes
Uneven nip loading
Speed difference of rolls
Save all touching
What are some causes of uneven moisture profile
Misalignment of press roll
Condition of uhle box and showers
Steam box profile
Plugged grooves on belt or roll or wear on either
What are some influencers for edge issues
low dry content
Poor alignment
Bad edge cutters
What can bad aerodynamics in press cause
Horse shoe defect
Air bubbles
How can you do a nip profile measurement
Can put pressure sensitive film through the nip. Here you will see pressure pulses
How can air blades be used in the press
Helps push water away from rolls which means we can lower rewetting crushing and wrinkles
Helps with profile and runnability
