PAPER INDUSTRY WEB (PIW)
PAPER MACHINE REEL TECHNOLOGY UPDATE
THE EFFECT OF MARKET CHANGES ON WINDING
In the recent past, market demands have encouraged papermakers to develop many new grades of paper with very specific characteristics to meet user requirements. Not only have papermakers developed new grades but are producing those grades at increasingly higher paper machine speeds. This coupled with the demand for larger, higher quality shipping rolls from the pressrooms present both winder builders and paper mill finishing operations with unique challenges. Paper mill finishing rooms and builders, working together have developed new winding systems to meet the demands. The reality is, that even with the great progress in winding, new challenges and obstacles keep occurring that require changes in operation that are outside the area of finishing room responsibility.
The need for higher winder productivity effects other elements of the paper machine. One element is the paper machine reel. To attain more productivity from operations that follow the paper machine such as off machine coaters, supercalenders and winders, mills process a greater number of sets from the jumbo. To do this, the jumbo has become increasingly larger. Jumbos to 90" (2286 mm) diameter processing coating grades and 120" (3048 mm) on other grades are common. This trend has occurred slowly over the years and only recently recognized as a problem.
Winder builders and winder operators were first to feel the effects of this trend by facing situations that challenged their technology and expertise. In an effort to understand their inability at times to produce shipping rolls with fewer defects, they looked to the end user for help. Investigations with end users of shipping rolls, in this case the pressroom, revealed that defects in shipping rolls originated in specific areas of the jumbo from the paper machine reel.
DEFECTS BY POSITION IN JUMBO
Once this phenomena was recognized, questions came immediately to mind. What causes it? How wide spread is the problem? What can be done to relieve the situation? In looking at winder operations in general, it is not uncommon to see operators slowing down when winding the last set off the reel. It was also observed that many times the operator will leave as much as 2" to 3" of paper on the reel spool. Operators discovered by experience that the last set off the reel does not run as well in the winder as the other sets and many times a winder break will occur in the last couple of inches of paper near the reel spool. Both of these observations are clues to the seriousness of the problem
The losses shown in this study represented millions of dollars at current product prices at the time of the study. In addition to product losses there are other losses to consider. The breaks at the off machine coater attributed to over-stressed paper at the reel spool of the machine reel represent about 16 1/2 calendar days of lost coater use. Add to that the energy cost to re-pulp the 7000 tons of paper tossed into the broke pit and the extra work required by the operators to slab and clean up each reel spool the magnitude of the problem becomes apparent.
Simple cures were tried such as additives in the stock, making smaller jumbos or the use of larger reel spools. All these type cures yielded some marginal return but the cure is not a simple one. The consensus seemed to be to look at the machine reel itself.
The winders that efficiently produce the large shipping rolls today are technologically advanced when compared to only a few years ago. To produce high quality shipping rolls with a minimum number of defects, it was discovered that success was not only using the tools of TNT (Tension-Nip-Torque) to the utmost precision during winding but an understanding of the laws of physics and how they effect weight distribution in the winder was needed to control the nip forces that were unmanageable in some winder configurations.
THE PAPER MACHINE REEL AS WE KNOW IT
THE CAUSE OF LAST SET DEFECTS
When winding shipping rolls on a paper machine winder it is universally accepted that nip control is a significant factor when structuring a high quality shipping roll. The winder operator strives for a uniform transition in nip and roll hardness from the core to the OD of the winding set. Unfortunately, the geometry of a reel using primary arms does not lend itself to the precise nip control required for this uniform transition to optimize roll quality.
In normal reel operation the reel spool, at turn-up, contacts the reel drum somewhere near top center of the reel drum and immediately after turn-up, the primary arms rotate in a clockwise manner around the reel drum to the horizontal level rail. In this process, timing is important to insure the large jumbo winding on the level rails is moved horizontally on the rail towards the dry end to make space for the new reel spool being rotated to the level rails. In addition, when the reel spool arrives at the level rail position, the loading must be transferred from the primary to secondary arms. The transfer of load from the primary to secondary position is critical to attain a uniform nip.
The conventional reel has difficulty when producing large jumbos of newsprint, light weight coated papers and some fine papers. It is important when studying reel operation to understand the interaction of reel spools, maximum jumbo weight, winding parameters and paper properties The criteria for sizing reel spools in the past for the most part considered journal and shell stresses, critical speed or to duplicate existing reel spools used in a given operation. Unfortunately this selection, in many cases, did not directly relate to the winding process.
A result of the variation in deflection is a non-uniform nip profile between the winding drum and the roll, tight at the ends and light in the center.
A & Z ROLL DEFECTS
The above chart illustrates the paper being stressed due to the deflections during the reeling operation. As the winding paper rotates in a mass around the axis of the reel spool that is deflecting at a different rate than the paper being wound, stresses occur in the web at the 9 and 3 o'clock position at each end of the jumbo. This action is considered to be the cause of many of the defects in the A and Z rolls (front and back rolls) of the set off the winder.
THE CHALLENGES OF ROLL BUILDING ON A REEL
This set of curves illustrates how back tension, rider roll nip and drive torque can be programmed to produce the most desirable wound roll for a two drum winder. There is also a recognition that as the "resultant" curve goes off scale, the limitation of the mechanics of the winder should be questioned and another mechanical mechanism should be considered such as an enhancement to the two drum winder or a duplex winder.
Click here to see an animation of a standard reel equipped with primary and secondary arms. Note the nip profile progression as the jumbo forms in the reel.
AVAILABLE MODIFICATIONS TO IMPROVE THE REELING PROCESS
In recognition of the need to improve the winding process on the paper machine reel, machinery builders have developed designs to attain higher quality jumbos with better runnability in subsequent processes. The paper mill can choose the feature that will give the best ROI consistent with their specific needs. A few of the improvements available are described. Due to the grade of paper, variations in sheet characteristics, vintage and original design of equipment, careful consideration must be given to insure the promised results can be attained.
PRIMARY ARM NIP RELIEVING
REEL CENTERWIND DRIVES
OTHER REEL IMPROVEMENTS:
Programmed primary & secondary arm control systems.
NEW TECHNOLOGY REELS
Builders are offering new designs to better serve the need for improved jumbo runnability and reel efficiency. A couple of new designs follow:
An additional new technology reel is the Beloit ATR (Advanced Tissue Reel). The ATR reel is similar in many respects to the TNT Reel , a major difference is a fixed position reel drum.
The descriptions and images of the new technology reels are from builders brochures and advertising literature. There are probably additional new design reels from other builders than those noted. Builders are encouraged to submit information suitable for inclusion in this article. Current designs may be greatly different from that shown. Check with machinery builders for current information as to availability and design.
Literature cited and recommended as follow up reading:
Smith, P., & Bagnato, L., 1993 TAPPI Finishing & Converting Conference Proceedings, "Relationship of the Paper machine Reel to the Winding Process"
Frye, K.,TAPPI Journal, "Winding Variables and Their Effect on Roll Hardness".
Pfeiffer,D., TAPPI Journal, " Nip Forces and Their Effect on Wound Roll Hardness".
Frye, K.,1989 TAPPI Finishing & Converting Proceedings, "Runnability in the Pressroom".
Roth, D., 1993 CPPA Conference Proceedings, "How to Build a Jumbo Roll and Other Winding Tricks"
Dorfel, W., Papier Carton Cellulose, "Theory of Winding"
Daly, D., Paper Trade Journal, "Study of Defects in Wound Rolls lead to Better Winding Control"
Bagnato, L., University of Maine, Summer Institute, 1996 "Paper Finishing & Winding"