Most dryer-section breaks aren’t freak accidents. They’re the predictable result of tension spikes meeting a heat‑weakened sheet — a profile modern sensors can spot before it tears.
Ask any production manager where uptime goes to die and they’ll point to the dryer section. Literature reviews conclude that dynamic tension surges colliding with the sheet’s strength limits are the primary culprits behind web breaks, while isolated flaws only trigger tears when they coincide with a tension spike (researchgate.net).
The dryer makes matters worse: heat and moisture gradients embrittle the “web” (the continuous paper sheet). Experiments show that even a few percent of additional draw (speed differential between sections that stretches the sheet) during drying can dramatically embrittle it — one study noted that a 4% total draw (press plus dryer) sharply reduces the paper’s strain‑at‑break, meaning the web tears under much lower stretch (researchgate.net).
Nonuniform moisture or basis weight (mass per unit area) compounds the risk. Cross‑direction thickness variation creates “baggy” zones that produce uneven tension profiles and slack edges that “cannot uniformly support web tension,” inviting breaks (valmet.com).
Then there’s adhesion and contamination on dryer cylinders. Sticky deposits or coating pickup make fibers grab and peel, raising tension erratically across the web; a Web Adhesion and Drying Simulator showed that surface contamination on dryer rolls markedly increases web breaks by pulling up the fiber web and forcing unscheduled stops for cleaning (researchgate.net).
Dryer‑section failure mechanisms
In high‑speed dryers, even small airflow disturbances or misregistrations can flutter the web and trigger breaks; modern sections often rely on active support like vacuum stabilizers and quick‑bend rollers. Quantitative audits show that tightening control of moisture profile, web cleanliness, and shock‑free draws reduces break frequency substantially (researchgate.net; researchgate.net).
Web tension control parameters
Maintaining the correct running tension is critical to web integrity. Too low and the sheet goes slack and flutters; too high and the hot, drying web tears. Industry guidance stresses tension accuracy on the order of 1–2% at steady speed (i.e., ±1% of setpoint), with a widely cited figure of ~1% accuracy at constant speed and a few percent during speed changes (blog.isa.org; blog.isa.org). In practice, even well‑tuned systems can see far greater error — distortions up to 10–200% have been observed — underscoring the need for robust sensors and control (blog.isa.org).
Tension uniformity across the machine width matters as much as the setpoint. Any “baggy” region (a slack edge or center) cannot sustain the intended load, and vendors explicitly warn that such nonuniform draw leads to “web tension difficulty” in the dryer (valmet.com). Mills counter this with closed‑loop tension control — dancer rollers (spring‑ or air‑loaded guide rolls used to stabilize tension) or load cells (force sensors) feeding back to drives. Field data also ties higher residual web tension (the tension remaining after relaxation) to better runnability: a furnish with higher residual tension needed less vacuum assist in the dryer (researchgate.net; pulpandpaper-technology.com). Tighter web control directly translates into fewer dryer‑section breaks (researchgate.net; researchgate.net).
Dryer‑roll alignment standards
Mechanical alignment of dryer and guide rolls is equally consequential. Any skew or out‑of‑parallel condition induces lateral forces that make the web wander, wrinkle, or telescope at the edges — concentrated stresses that precede tears. Expert guides call roll alignment “perhaps the single most critical factor influencing web runnability,” and misaligned rolls “silent destroyers” that induce uneven cross‑machine tension profiles (er88p.cn).
Even slight misalignment can overstretch one edge while leaving the opposite side slack; such caliper or profile mismatches easily initiate breaks at speed. Mills use laser alignment tools to keep each cylinder and support roll parallel (or intentionally skewed) to its neighbors, and periodic checks matter — adjusting a roller by fractions of a millimeter can eliminate “racing edges” or center spikes in tension. The payoff includes reduced vibration and less abrasion on cylinder wraps, while eliminating the lateral stresses that would otherwise “lead to wrinkles, tears, and edge variations” (er88p.cn).
Online monitoring and early warning
Because breaks still occur, modern dryer sections run with on‑line monitoring. Camera‑based web inspection systems (often paired with break sensors) watch for flutter, holes, or misalignment. One supplier claims a unified camera/WIS setup can reduce web breaks by at least 50%, even at speeds of up to 2,000 m/min (isravision.com).
Beyond cameras, mills deploy smart sensors and analytics for predictive maintenance: acoustic sensors, vibration probes on cylinders, and distributed tension measurement feed machine‑learning models. A recent industry study even published a large multivariate dataset from a pulp‑paper machine specifically for early break prediction, training classification models to flag the rare “paper break” events ahead of time (arxiv.org).
The trend is to catch drifts before they fail. Case studies report that real‑time monitoring and predictive algorithms yield substantial reduction in downtime because issues are fixed before a break forces a shutdown (pulpandpaper-technology.com). Implementations typically combine vision cameras, tension gauges, and humidity meters, with mills reporting far fewer breaks and faster recovery when these systems are active (isravision.com; pulpandpaper-technology.com).
Metrics and quantified payback
Each measure — precise tension control, correct roll alignment, and on‑line diagnostics — is data‑driven. Mills track break frequency per 10^5 tons produced and average downtime per shift, then analyze trends. In practice, adding a vacuum stabilizer or replacing a worn felt is cost‑compatible when the data show, for example, that a 50% drop in breaks saves hours (or hundreds of meters of paper) per week. Audits emphasize quantifiable outcomes: percent break reduction or KT/days of improvement. The throughline from literature and mill experience is consistent — improve tension control and roll alignment, and support both with real‑time monitoring, to achieve significant returns in uptime and quality (er88p.cn; isravision.com).
Source notes and definitions
Conceptual analysis reflects industry studies and expert literature: web‑break reviews highlighting tension swings and broken strength (researchgate.net); drying experiments quantifying how draw lowers break strain (researchgate.net); adhesion studies linking contaminants to higher break rates (researchgate.net). Technical guidelines stress 1–2% tension accuracy and precise roll alignment (er88p.cn; blog.isa.org). Recent papers document advanced monitoring, including a pulp‑mill dataset for break prediction (arxiv.org) and supplier claims of ~50% fewer breaks with camera systems (isravision.com), while manufacturer and trade sources (including Valmet) emphasize baggy webs and tension uniformity (valmet.com; pulpandpaper-technology.com).
