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.
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
TWO DRUM DUPLEX AND STANDARD TWO DRUM WINDERS
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.
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.
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.
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 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.
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
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.
CORE CHUCK WEIGHT RELIEVING
Kenneth G. Frye - Winding Technologies,