Runnability - the condition monitoring perspective

The term "runnability" is broadly used in paper manufacturing to describe the operating level or current ability to produce paper that meets quality requirements at maximum capacity. It is the result of a combination of many factors such as furnish, chemistry, process settings, condition of felts and nipped rolls, speed, etc. that are orchestrated by the paper maker in the practice of the art and science of paper making. In a sense it can be considered a balance between output (tonnage) and quality, since one affects the other. A consequence of "poor runnability", for example, are recurring sheet breaks, where the paper web tears (thus stopping production) and valuable time is lost in resuming production. During this time, the machine is still running (and consuming power, steam, etc.) but has no sellable output. Sheet breaks are a major cause of lost production time, and thus are of particular concern to operations (in contrast to, say, a failing bearing). Some types of problems can be traced back to mechanical sources especially in the wet section (i.e. approach, forming, and press sections). This paper focuses on high frequency variations (in the machine direction) and vibration as indicators of runnability problems. Condition monitoring, long recognised for its value in helping to achieve high levels of reliability, has an important role in alerting operations to mechanical problems that could negatively affect runnability. Applications include: Vibration from accelerometers mounted on the bearings in the nip direction to detect and diagnose: Felt barring Surface problems such as flat spots/barring in nipped rolls (e.g. press rolls, size press rolls, calenders) Excessive vibration at certain speeds due to resonance excitation Pulsation in the stock (from dynamic pressure sensors mounted in the approach piping) that can cause basis weight variations in the machine direction Frequency analysis of machine direction variability from scanner signals (typically basis weight, moisture, and caliper) that could pinpoint which mechanical sources upstream need attention Runnability information from Operator Driven Reliability (ODR) systems such as visual inspection for cleanliness, clogging, streaks, etc., gauge readings from pressure and temperature sensors, etc. The main advantage of using the ODR systems is that data from them is stored an analysed in the same software as on line systems