• Rewinder to make smaller or spliced up larger rolls,
• Slitter to make sliced rolls of narrower width,
• Printer/embosser/decorator/laminator/coater,
• Combiner to make rolls of 2 or more plies.

In tissue operation there is always a loss of paper attributes through this process. The two main properties affected are

• bulk, and
• stretch.

The influences causing this variation include

• sheet tension through the rewinder,
• contact pressure against the winding drums.

A certain amount of tension is required to carry the sheet through the rewinder to maintain its stability: lateral drift, wrinkling, conveying over bowed rolls, etc. For best operations the rewinder is tuned to work at the minimum practical tension.

The only controllable element usually provided in a rewinder is the weight control of the rewinding roll. For denser papers, such as print and kraft papers, film and foil, the rider roller is weighed down to make a tight and dense roll.

In the case of tissue papers, it is necessary to minimize the "calendering" of the paper at the nips of the two rewinding rolls. In the tissue rewinders a means is usually provided to lift and unweight the rewinding roll to reduce the nip forces.

Equilibrium equations relate the unweighting 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 control is programmed to affect the following:

• the rewound 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 Rewinding 1

PM Rewinding 2

1. NIP LOADING OPTIMIZATION

WEBCON's method of optimizing reels:

• Procure/measure the geometry of the rewinder.
• Measure & plot cylinder psi vs. roll diameter.
• Compute nip line load as a function of roll diameter.
• Track the resulting bulk profile within the rewound 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 last three steps as necessary.

Measure of Success:

• Consistency of converted product size and density as the rewound rollis unwound from the outside to its core.
• Reduced of 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 light-dry-crepe (LDC) process, the target roll diameter in a Perini winderwas achieved without the need for extra sheets.
• In a recrepe process, the diameter/density consistency in the small roll winding operation significantly improved the wrapping operation.

2. REEL INSTRUMENTATION:

Methods of secondary arm loading pressure control:

• Fixed Pressure,

  as in a number of old machines,

• Mechanical:

  Pressure regulator activated by the unweighting mechanism,

• PLC Control:

  Rotary encoder activated by the unweighting mechanism.

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, store in the PLC for quick selection by the operator.

3. PAPER CALIPER DISPLAY:

This feature can be available on machines with PLC controls. As the roll 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.

This display reflects the measure of bulk in the rewound roll. When accompanied with the roll, it forewarns the converting operator what to expect in the roll. This helps him to fine- tune his operation.