reel

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

This chart displays the results of one such study. It is readily apparent that the defects in a jumbo are not uniformly distributed throughout the jumbo but disproportionately located in areas closer to the reel spool. This chart shows a roll tracking study of defects in the relative radial position as reported by a pressroom. In the way of explanation, if it is not obvious, the chart lists the defects in sets off the reel in order of unwinding the jumbo, first set being the outside set of a jumbo and the last set being the paper closest to the reel spool. Other studies on various grades of paper have produced similar results.

This chart dramatically illustrates the findings noted in the chart above. Fully 72% of the defects in this study occurred in the last set of paper off the jumbo, the paper closest to the reel spool. What does not show in this chart but is recognized in the details of the study is that many of the defects occur in the A & Z rolls of the winder (front and back side rolls) caused by over stressing the paper at the ends of the reel during the reeling process.

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

Operators discovering that leaving paper on the reel spool during the unwinding process to avoid breaks lead to the acceptance of this practice to improve overall general operating efficiency. As the problem became more severe, the product waste became an issue of concern. Several studies have been performed in mills to discover the extent of paper losses due to roll defects near the reel spool. The following study is only one of many. This is a study of a single LWC paper machine over a one year period. The operators were leaving several inches of paper on the reel spool at the rereeler not only to reduce breaks at the rereeler but more importantly to reduce breaks at the OMC.

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

When processing some grades of paper, the standard level rail reel as it exists is not a good winder In the development of winder designs to produce good quality rolls it is recognized that a minimum of sound tension and nip control is a basic requirement and in some instances, torque control is required as well. The standard level rail reel does not exhibit these minimum requirements. Tension on a standard reel is not a viable structure tool on a reel and the general configuration of the reel does not lend itself to efficient nip control.

A similar argument applies when considering the rereeler following the paper machine reel.

THE CAUSE OF LAST SET DEFECTS

Why does such a condition exist from a reel that has served the paper industry so well? The basic design of the present reel dates back to the mid 1940s. The first installations were on newsprint paper machines and designed for a maximum 72" (1829mm) diameter jumbo, with machine speed of 1800 FPM (550 MPM) and a trim range of 200" (5080mm). The paper weight on the spool was in the range of 9 tons (8 metric tons).

Today the same basic concept using swing arms for secondary loading in place of the horizontal secondary cylinders is widely used on paper machines approaching 400" (10.1 M) reel trim and machine speeds in excess of 4500 FPM (1370 MPM). It is not uncommon to see reel spools supporting paper weight of 40 tons, (36 metric tons).

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.

This chart illustrates a generic nip profile for the function described. The reel operators strive to minimize the changes in nip pressure as shown but can only accomplish this within the mechanical and control limits of the reel and the strength of the reel components.

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.

The reel is subject to the same laws of physics as other machines. In the process of increasingly demanding application for the level rail reel, this fact may have been overlooked. In the case of the reel, the reel spool, reel drum and winding paper on the spool all deflect at different rates. How much these elements deflect is dependent upon the mass, the stiffness of elements and external loading. This chart indicates the varying deflection in cross machine elements of the reel. The reel drum itself is reasonably stiff as compared to the reel spool and winding paper

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.

In addition to the deflections caused by gravity reacting to the masses involved, the mechanical operation of the reel introduces other forces that add to the complexity of the component deflections. A reel spool deflection component is present caused by the overhung primary hook loading at the time of turn-up through the primary arm movement to the load transfer in the secondary arms.

At the time the winding jumbo is transferred from the primary arms to the secondary rail, the secondary loading must be engaged before the primary arm loading is released. There is a time period when the two loadings are additive resulting in a spike in the nip profile unless the transfer of loading is performed in a smooth manner. The overhung load exerted by the secondary load system (in addition to the deflection caused by the primary arm loading) causes a horizontal deflection that couples with a vertical defection caused by the mass of the reel spool and winding paper complicating the issues.

A & Z ROLL DEFECTS

This chart illustrates a vertical component of reel spool deflection. Paper mills that operate very wide paper machines discovered that if jumbos are stored for an extended period without being rotated, the jumbo will be difficult to process. This same deflection occurs while the jumbo is resting on the level rails during the winding process.

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

Experience has taught us that left, on there own devices, winders will not make a shippable roll let alone a high quality shipping roll. Years of development in winding resulted in recognition of the mechanisms and controls required to produce a high quality shipping roll. In the case of a two-drum winder, the roll starts winding very soft and increases in hardness as the paperweight increases on the winder drums as represented by the red curve of the chart. Winder engineers and paper mills have developed a means to alter the hardness profile of the winding roll by carefully manipulating the TNT (tension-nip-torque) tools of winding.

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.

The machine reel presents the same challenge. The machine reel if nothing else is a continuous winder more likened to a duplex winder as opposed to a two drum winder. This chart attempts to portray the same scenario. The BLUE curve represents the nip profile of a standard primary arm reel. The GREEN curve represents the preferred nip profile. This preferred profile could possibly be attained with enhancements to the reel or in some case a replacement with one of the new generation reels.

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

The weight of the reel spool at turn-up can induce high nip loads that are detrimental to the hardness profile. Equipment is available in the form of reel spool weight relieving to reduce the tendency of high nip loads at start. Additionally, some installations can benefit by replacing sliding friction with anti-friction ways that can produce more predictable relief and load results.

REEL CENTERWIND DRIVES

Torque control has become a standard feature of two drum winding and becoming increasingly popular with duplex winding. The success of centerwind drives on super-calendar windups has been proven in many installation. Rereeler installations are beginning to demonstrate significant operational improvement with the addition of centerwind drives. Reels are presently operating in the field equipped with primary and/or secondary centerwind drives and in some installations at both positions. Centerwind drives are proving to be a beneficial addition on reels although in some cases the ROI has yet to be justified. Centerwind drives on primary and secondary winding positions should be carefully considered as a viable tool to improve jumbo runnability.

OTHER REEL IMPROVEMENTS:

Programmed primary & secondary arm control systems.
"Bumpless" transfer control of nip and centerwind drives.
Larger diameter reel spools. Reel drum surface-grooving and friction
Tension control systems
New turn-up devices.
Complete reel automation control packages.

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:

The Beloit TNT Reel. Some of the features described by the builder are:
1. Reel spool and winding jumbo are partially supported by the reel drum throughout the winding cycle.
2. The jumbo winds without transfers of nip loading or centerwind torque throughout the winding cycle.
3. Fully automatic operation with data logging, diagnostics and maintenance monitoring.

Picture and features from builder advertising literature.

The Valmet OptiReel. Some of the features described the builder are:
1. OptiReel increases mill's production and parent reel quality.
2. Eliminates broke and turn-up breaks.
3. Better runnability in downstream processes.
4. Larger parent reel diameters.

Pictures and features from builder advertising literature.

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.

Luigi Bagnato
Paper Industry Web

CREDITS

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"