TL;DR
A sticking slice actuator creates a fixed CD basis weight hump that does not respond to control commands. Identify the stuck actuator from position feedback, lubricate or replace it at the next outage.
What you might see
- one CD zone showing a persistent hump or hollow in basis weight
- slice actuator position feedback not matching the command
- actuator drive current higher than adjacent actuators
- CD profile improvement stops at one location regardless of adjustment
Likely causes
Stock infiltration and hardening around the actuator stem and seal
Corrosion binding the actuator screw from prolonged exposure to wet stock
Failed actuator motor or gearbox preventing movement
Wiring fault preventing the actuator from receiving the control signal
Required tools
- DCS slice actuator diagnostic interface
- Multimeter for wiring check
- LOTO kit for outage work
- Recommended actuator stem grease
- Replacement actuator (if needed)
Safety first
- The headbox is under stock pressure during operation. Never remove actuators or open the headbox without full LOTO and depressurization.
- Slip hazard from stock around the headbox. Use non-slip footwear.
Procedure
- 1
From the DCS, command each slice actuator in the suspect zone to move 2 steps up and then 2 steps down. Observe position feedback and motor current.[1]
- 2
An actuator that shows no position change and elevated current is mechanically stuck. An actuator with no current change is electrical.
- 3
For an electrical fault, check the actuator field wiring and terminal connections at the junction box for looseness or corrosion.
- 4
For a mechanical fault, schedule replacement or cleaning at the next planned headbox outage.[1]
- 5
During outage, isolate and depressurize the headbox, then remove the stuck actuator per the headbox design documentation.
- 6
Clean the actuator stem and bore of any hardened stock deposits. Inspect threads for corrosion damage.
- 7
Lubricate the stem with the recommended food-grade grease or replace the actuator if corrosion damage is severe.
Sources
Voith Paper Voith MasterJet Pro Paper Machine / Headbox general technical documentation, Voith Paper
Paper machine headbox slice actuator maintenance and diagnostics, general paper machine practice (general)
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