This machine tutorial explains how to operate and troubleshoot stack flexo inline corona treatment placement and dyne level verification on stack-type flexographic printing presses. It is written for shift supervisors, maintenance technicians, and application engineers who need repeatable procedures—not theory alone.
Machine scope and operating context
Yaoshg field teams use this discipline on presses and converting lines built in Wenzhou—from early stack flexo units through CI, gravure, laminating, slitting, bag making, and paper container equipment. The steps below assume normal safety lockout rules, OEM manual limits, and documented substrate specifications for each job.
Inline corona placement on stack flexo presses determines whether treatment energy improves ink adhesion or merely oxidizes surface before print while introducing static and tension transients. Optimal position is immediately before the first printing deck with minimal intervening idlers that could regenerate weak boundary layers.
Set corona power relative to line speed using the treater watt-density formula from equipment supplier. Increasing speed without proportional power increase drops dyne level and produces adhesion failure mistaken for ink fault. Log speed-power pairs in job recipe for repeatability.
Step-by-step machine procedure
Verify dyne level with test pens or contact angle measurement at production speed using offline sample tap if inline measurement is unavailable. Target dyne should match ink supplier specification, typically 38 to 42 dynes for film flexo, without exceeding substrate damage threshold that causes brittleness.
On stack flexo presses, color decks are vertically arranged—each unit adds web wrap and potential misalignment. Thread the web at crawl speed and confirm nip engagement on idle decks before bringing impression to print stations. Yaoshg stack platforms from the Nova series onward use documented torque references for plate locks and anilox saddles; record these values so repeat jobs do not depend on one senior operator.
Bring ink to viscosity specification while decks are off impression. Start with the lightest color or smallest coverage area when possible so register marks remain visible. After the first stable proof, ramp speed in steps of 10–15 m/min and observe register error trend—not only print density.
Operator shift checklist
- Confirm web path, dancer position, and unwind brake before threading.
- Log ink viscosity, cup temperature, and anilox ID at shift start.
- Run kiss-impression proof on one color before engaging full color set.
- Record impression reference and plate mount torque after stable print.
Common defects and corrective adjustments
Q: Treat before or after primer? A: Follow ink system architecture—some structures need primer print then corona on second pass, rare on standard stack flexo. Q: Metalized film? A: Corona on metalized side is usually wrong; treat non-metalized face or use adhesion promoter ink.
Tension control through corona station requires stable web wrap on earthed roller electrode. Flutter reduces treatment uniformity and creates lateral dyne bands visible as density variation in the first print station.
Yaoshg stack line layouts specify corona mounting frame location relative to unwind distance for surface recovery time. Some PE grades benefit from 30 to 60 seconds post-treatment before impression; commissioning should validate adhesion against time-delay trials, not only immediate print.
If register drifts only on upper decks, suspect web stretch between lower and upper units before adjusting mark sensors. Heat from lower dryers can change film length enough to disturb upper-color phase. Temporary relief by lowering dryer load on early colors often confirms the diagnosis.
Gear backlash in older stack drives shows as repeating error every cylinder revolution. Compare error period to gear ratio documentation. Servo-enhanced stack units reduce this pattern but still require clean mark signal and correct tension into each deck.
Maintenance records and when to call service
Weekly maintenance on stack flexo should include anilox inspection under magnification, blade edge review, and unwind brake calibration. Store setup sheets with substrate gauge, ink batch, anilox ID, and impression reference. These records shorten changeover on the next repeat order and support warranty discussions with clear data.
If mechanical adjustment, drive parameter changes, or repeated defects exceed on-site scope, log serial number, job recipe, and photos before contacting Yaoshg service. Commissioning engineers can remote-review HMI trends when VPN or data export is available—faster resolution when shift records are complete.