PAPER INDUSTRY WEB (PIW)

TNT - THE TOOLS OF WINDING

WHATEVER A WINDER MUST DO, it must have the ability to produce good salable shipping rolls. All else is secondary. If the winder in question cannot provide good quality shipping rolls to the customer-the customer will very quickly find another source.

The basic tools that are available to the operator to structure shipping rolls are TNT, an acronym for Tension-Nip and Torque. There are winders in present use that only have the tools of TENSION and NIP available by design intention or just the age of the equipment. There are additional tools available such as larger diameter winder drums, tractionizing of the winder drum surface, articulating rider rolls, the quality of the sheet and sheet properties, etc. but they are not available to the operator.

TENSION comes from the "holding back" of the sheet from the unwind brake. NIP is the sum of the external loads applied such station loads and rider rolls and in some designs the weight of the winding roll of paper on the winder drum(s). TORQUE is the rotational drive power applied at the winder drum (s).

In Part 2 in this series, Wound Roll Structure the basic shipping roll qualities were discussed as well as what happens inside a roll of paper when it is wound. To review, at the risk of being repetitive, just one more time to keep it fresh in our mind, "In the most basic definition an acceptable shipping roll must be hard enough at the core to support itself during unwinding, just hard enough at the OD to be handled and shipped without damage and a smooth transition in wound in tension (or hardness) from the core to the OD." Of course, the reality in the real world we live and work, the definition of a high quality shipping roll goes much farther than that. The axiom of roll quality is the same as that for any business: Build a better mouse trap and the world will beat a path to your door! The paper mill that can produce the best quality shipping roll to suit the end users' needs will get the bulk of and the most profitable business. To do this a winder must have all the tools available within the economics of the specific operations and just as importantly-know how to use them to advantage.

PAPER MACHINE REELS & REREELERS

Winding operations such as paper machine reels do not usually have the basic tools necessary for structuring high quality jumbo rolls either by design or age of equipment. Reels can be modified to include a tension sensing roll for full tension control and centerdrives for torque control to include such tools to improve their roll structuring capability.

Rereelers fall into the same category as reels. Basic rereelers do not usually have the basic tools necessary for structuring high quality jumbo rolls but can modified to include such tools centerdrive for torque control to improve their roll structuring capability.

TWO DRUM DUPLEX AND STANDARD TWO DRUM WINDERS

The two drum winders duplex or std have torque capability. All the core support two drum duplex winders were manufactured using a single drive motor and a harmonic drive tying the two drums together. This arrangement provided torque differential between the top and bottom winder drum.

The two major types of duplex winders are a mixed bag. When the core support duplex winder was first introduced in the 1960s to about the mid-1980s they were not equipped with a centerwind drive and therefor did not have TORQUE capability. Newer versions recently manufactured are equipped with centerwind drives and thus have the full TNT capability.

SINGLE DRUM DUPLEX WINDERS

The core support duplex winder is manufactured with or without centerwind drives on the individual windup stations. Those without centerwind drives have TENSION/NIP capabilities while those equipped with centerwind drives have the full TNT capability.

The debate still is going on concerning the value of centerwind drives on the core-support duplex winder. Only the quality of the shipping rolls and the breaks/100 rolls feedback from the pressrooms will finally determine if the extra complexity and additional maintenance of the centerwind drives will quantify the ROI for such equipment.

All standard two drum winders are capable of differential torque between the winder drums with the proper equipment. Early 2 drum winders used a single motor drive and a Vari-pitch sheave arrangement tying the two drums together to provide torque differential. Some of the early winders using two drum drives used field weakening to provide a small torque differential or in some cases a booster was added to the outside drum to give more positive torque differential control. Modern two drum winders use a two motor drive with torque capability designed into the electric drive.

In the world of paper machine reels, rereeler and supercalendar windups there appears to be acceptance of centerwind drives. There is a very high level of activity to retrofit centerwind drives on paper machine reels in both the primary and secondary winding position as well as an acceptance of new paper machine reel designs that inherently provide TNT in their design. In the case of rereelers, most new equipment includes centerwind drives and the retrofit activity in this area is high. In the case of supercalendar windups, the acceptance of centerwind drives appears to be universal. In stating this, one must recognize the complexity of a centerwind drive system for a multiple station duplex winder.

TENSION

Back tension is a contributing factor in the wound in tension in a shipping roll. Because the tension in the winder must be held reasonably constant during winding,  it is not considered a variable tool in controlling roll quality. An additional factor to consider is the reduction in the backstand tension level by the time the sheet gets to the back winder drum nip.

The amount of capstan wrap has an effect in isolating the tension. Venta-grooving a winder drum to eliminate entrained air tends to maintain more intimate contact between the sheet, increasing the the grip of the sheet on the drum further isolating the back tension seen at the drum nip. When conditions are appropriate, tapering tension as the wound roll diameter increases may be beneficial to roll structure but not significant.

NIP

This chart illustrates a typical control plot for a two drum winder. The winding tools of TNT are controlled to make the winding roll harder at the core and reduce the hardening effect as the roll forms on the drums. Note the difference of the roll weight curve (red) and the resultant curve (green).

Nip is the total load on the winder drums and has dramatic impact on wound roll structure. Nip is the product of the weight of the paper on the drums during winding and any external loads that are applied. In the case of a two drum winder it is the weight of the winding roll plus the external rider roll load. In the case of a duplex winder it the result of the rider roll loading at the start of winding plus the station loading. On drum support duplex winders, partial weight of the winding roll also effects the nip. The rider roll systems on both 2 drum and duplex winders and the individual winding stations of duplex winders permit varying the external load to compensate for the changing weight of the paper roll during winding.  The rider rolls used on duplex winders are generally programmed to lift completely from the winding rolls at approximately 10" to 12" diameter.(254 to 305 mm).

TORQUE

Torque as used in reference to roll structure control in this discussion is the driving of one drum of a two drum winder faster or with greater load than the second drum creating more tension in the web to make a tighter start at the core. With a duplex winder it is the ratio of driving effort applied by the center drum versus the centerwind drive of the the jumbo being wound. A demonstration of how torque tightens a winding roll is to wrap a sheet of paper around a finger, then twist the out wraps in a manner to tighten the sheet on your finger.

This chart indicates the drum load in PLI for a standard newsprint 50" (1270 mm) diameter shipping roll. Not all 2 drum winders, with the TNT precisely controlled, can produce this 50" diameter roll with a reasonable breaks/100 roll record at the printer. The shear weight of the roll being wound can, in some instances be beyond the capability of the winding tools.

TUNING THE TNT

There are no hard and fast rules or programs that will guarantee success winding various grades of paper and roll sizes. Assuming the winder is set up and tuned to produce reasonably good shipping rolls, adjustments beyond that point must be based on reject reports within the mill and documentation from the end user of the rolls in question. What problems are being encountered? The defect and complaint list is lengthy and there are many variations of each of the defects. "The customer is always right" couldn't be more true when it comes to winding and shipping roll quality. In today's competitive environment user complaints cannot be ignored.

Tuning the winder comes down to specific complaints: Bursts on the OD, core bursts, crepe wrinkles on newsprint? The problem has to be approached much like a detective at a crime scene. Hunt for clues, understand the clue and then solve the case. When adjusting the winder, understand the specific complaint. Get a sample of the defect. Where in the roll does the defect happen? At the OD, near the core, in machine direction, cross machine direction, at the roll edges or center? When you can answer these questions you are ready to start looking at the roll structure off the winder.

The roll must be examined both in the cross machine direction as well as from the core to the OD. The complaint you are chasing is your clue as to where to start in the roll.. Try to determine where in the cross machine and radial position the defect is occurring. If it can be isolated, say at the quarter point of the machine, or 6" (152 mm) from the core or 2" (51 mm) from the OD, it narrows down the search area significantly. Suppose your customer is experiencing core bursts that are causing breaks in the printing press, you should establish the distance from the core the breaks or bursts are happening.

There are hardness testers available that will permit the user to construct a picture of what the roll profiles look like. Both the Schmidt hammer and the Beloit Rhometer are hand held tools that permit measuring relative hardness across the face or from the core to the OD. The Smith meter is a tester that measures the penetration of a small needle that is inserted in the wraps along the roll edges. Any tester should be used with good judgment. When measuring across the face-draw a straight line and layout the increments of width to check. Mark the face of the roll in equal increments to measure the radial component. Hold the test instrument at right angles to the surface and try to apply the same trigger or actuating pressure for each reading. Criteria such as this must be followed to get uniform and reliable profiles. The Schmidt hammer and Rhomeer can perform a non-destructive roll test by unwinding the roll while supported in an unwind stand.

Another valuable test is the "gap" test developed by Cameron Machine Company. This test is a very reliable means to measure wound in tension from the core to the OD. It is not as popular as other test because it is a destructive test and time consuming. With this test, a roll is "cleaned up by removing all loose wraps. Then a single wrap is slit across the face until it "pops"., The wrap is allowed to relax and the gap is measured and recorded. This test is performed in equal increments down through the roll. An efficient way to perform this test is to load a program in a laptop computer using the formula for gap testing. Entering the gap data as the roll is tested will produce a nice picture of the wound-in-tension when the test is complete.

For more information on roll hardness testers click here.

There are shortcuts that can be used in this test to save work and time. Using the example of the core burst noted above. If it is established the core bursts are happening 10" (254 mm) from the core or less, slab the roll down being tested to about 15" (380 mm) and start the gap test at this point. Better yet, if the winder is a duplex winder, stop the winder at 15" (380 mm) diameter, remove the roll in question to test and the winder can be restarted. This saves the time, work and mess of slabbing the roll down to size before testing.

After the profile or wound in tension testing is complete a review of the data will determine which of the winding tools may need reprogramming. Make changes in small increments and try to run a few rolls with the converter or printer before making additional changes. If the problem is not a "crisis" it might be prudent to make the changes to the programs, run a few rolls, record the changes and return to the original winder settings until feedback is received from the converter. This will reduce the backlog of finished rolls that may not have good runnability if the changes made did not solve the defect.

There are a group of winder designs or modifications that are sometimes referred to as winder tools due to their impact on wound roll structure. These designs are usually provided on new modern winders and in most cases can be retrofit to existing winders.

DRUM SURFACE TREATMENT

There are many types of drum surfaces used on winders. Two treatments that have impact on roll structure are tractionizing and Venta-grooving. 

The purpose of tractionizing a winder drum is to increase the coefficient of friction to improve the differential torque transmission to the winding roll. When observing the amp meters of a winder, slippage can be noted by the amp reading variations. Tractionizing is a spray metal technique using tungsten carbide or molybdenum. In some instances, tractionizing winder drums will reduce vibration and bounce on grades with a rough surface. Tungsten Carbide is the most popular coating for tractionizing a winder drum and can be applied in the mill without dismantling the winder. Venta-gooving is a very narrow groove pattern that aids in eliminating the surface air that travels with the web from becoming entrained in the winding roll of paper. Eliminating the entrained air stabilizes the layer to layer slippage within the roll during winding. Venta-grooving can be used in conjunction with other surfaces or grooving patterns.

CORE CHUCK WEIGHT RELIEVING

Winders that do not have an efficient core chuck weight relieving system can cause "pinching" or loading of the A-Z rolls (front and back rolls of a set) causing defects in those rolls. Many early winders used hand wheel or chain and sprocket w/counterweight relief to unload the core chuck overhung loads, systems that are friction and maintenance intensive. The existing systems can be retrofitted with direct acting cylinder/programmed weight relief to improve the roll structure potential of the winder.

Luigi Bagnato-Paper Industry Web

CREDITS

References:

Kenneth G. Frye - Winding Technologies,
Marti Karttunen and Hans Ehrnrooth - New single drum winding concept for lightweight printing papers.
G. Forsberg - Modernization of Two Drum winders
S.M. Hussain and W.R Farrell - Roll winding-causes, effects and cures of loose cores in newsprint rolls.
Kenneth G. Frye - Winding Variables and Their Effect on Roll hardness and Roll quality