• bulk
• stretch
• crepe

It is the intention of the papermaker to create the "optimum" roll in which the above variation is minimized, and bulk and stretch are conserved (i.e. maximized) as far as practical.

The influences causing this variation include

• incoming sheet tension
• gravity
• contact pressure against winding drums

Incoming tension is directly related to the paper properties. Above the core, weight of the outer layers will bear upon the layers underneath. Below the core, the layers will hang down unless they are supported. Neither sheet tension nor gravity is controllable. Thus, we cannot create a perfectly homogenous roll in which the paper properties are constant at all radii.

The only controllable element is the contact pressure. In a typical papermachine reel the secondary arm loading is controlled. In a 2-Drum rewinder it is the weighting or unweighting of the reel itself.

Equilibrium equations relate the applied load to the line load developed in the nip between the reel and the drums. For any nip load profile a table of psi values for the loading cylinders can be calculated.

The nip load profile, however, is the crux. It must satisfy the following criteria to create the optimum roll:

• the parent roll must not telescope or slip off the core,
• the bulk profile should be as flat as possible, and
• the roll must have a reasonably robust structure.

PM Reel 1

PM Reel 2

PM Reel 3

1. NIP LOADING OPTIMIZATION

WEBCON's method of optimizing reels:

• Procure/measure the geometry of the reel.
• Measure & plot cylinder psi vs. roll diameter.
• Compute nip line load as a function of roll diameter.
• Track the resulting bulk profile within the parent roll in converting.
• Modify the shape of line load curve using past experiences.
• Compute the new psi curve.
• Monitor the bulk profile in converting.
• Repeat the lst three steps as necessary.

Measure of Success:

• Consistency of finished product size and density as the parentroll is unwound from the outside to its core.
• Reduced slab wastage.
• Maintainability of sheet count at target.
• Improved bulk in the finished product.
• Reduced sheet breaks.
• Increased winding speed in converting.

Case Histories:

• In a through-dry (TD) process, the above method increased the throughput by as much as 5%.
• In a light-dry-crepe (LDC) process, the speed of the winders in converting increased by about 50 fpm.
• In a heavy-wet-crepe (HWC) process, perf breaks and wrap-ups were reduced.

2. REEL UPGRADE:

In a number of cases, especially with older reels, the kinematic analysis showed poor transmission angles of the linkage leading to an undesirably large range of mechanical advantage. This is further aggravated in the case of inclined rail reels, where the initial slant of the rail could result in an unusually high nip pressure. This would create a very tight initial wind especially for high bulk papers.

The upgrade program consists of the following:

• Measure the geometry of the reel.
• Kinematic analysis of the loading linkage.
• Relocate the Secondary Arm Pivot for best transmission angles.
• Adjust rail height if necessary.
• In case of inclined rails go horizontal.

This work is usually followed by Reel Loading Optimization described above.

3. REEL INSTRUMENTATION:

Methods of secondary arm loading pressure control:

• Fixed Pressure,

  as in a number of old machines,
  
  

• Mechanical:

  • Pressure regulator pushed by the secondary arm
  • Cam operated pressure regulator,
  
  

• PLC Control:

  • Rotary encoder on the secondary arm pivot,
  • Inclinometer mounted on secondary arm.
  
  

WEBCON can convert the old machines to either the mechanical or the electronic control. Again, the existing mechanical controls can be upgraded to PLC controls.

Experience has it that the optimal psi loading curves depend on the the bulk properties of the tissue, and the size of roll to be wound. Multiple psi tables are, therefore, stored in the PLC for quick selection by the papermaker.

4. PAPER CALIPER DISPLAY:

This feature can be available on machines with PLC controls. As the reel winds, real-time caliper of the sheet is continually updated and graphed on the screen. This caliper is essentially the thickness of the sheet as it resides in the roll as it is being wound. This is not the TAPPI Bulk which will usually be higher than the caliper reading.

Papermakers do like this reading because it gives them an indication of the TAPPI bulk. Any departure from linearity of the graph indicates instability of the papermachine. Any blips in the graphs, or a discontinuity, represents an abrupt change somewhere in the papermachine.

This tool has been very effective in making quick corrections. Otherwise, the papermaker has to wait till he measures the top of the reel bulk, which is too late. A printout of this graph helps the converter to tune his process for varying bulk, especially to the big changes across a sheet break, or from roll to roll.

5. LINEAR REEL

The linear reel is a mechanical variation of the conventional reel in which the secondary arm is of "infinite" length. This simplifies the mathematical calculations. However, winding of the optimum roll and the nip psi load control still follow the concepts discussed above.

WEBCON's optimization scheme for the nip psi control discussed above is also valid and directly applicable to a linear reel.