The short answer: Not very well. But before we evaluate the results, let's talk about mechanics.

The root cause, which may justify slip-core winding, is caliper variations across the width. If one roll has a thicker gauge material than another in a set, its diameter will build larger. If both the large and small diameters are forced to rotate at the same RPM, as is the case with locked-core winding, the large-diameter roll in the set will have a higher surface speed. The higher speed results in higher "draw" and thus tension.

The problem, however, is with the small-diameter roll. It may have insufficient tension, or possibly none at all. In extreme cases, the web puddles on the floor under the small roll.

How do you know that caliper variations are the root cause? You could check diameter variations carefully with a PI tape. Alternatively, you could check for hardness variations with an instrument or by sounding the roll with a stick. If the small or soft roll in the set is also the loose one, you have confirmation that manufacturing is the root cause.

However, manufacturing is going to be quite reluctant to accept blame for this. They are going to say they are within spec. They are going to say the product is level as measured by lab test or scanner. They are going to tout impeccable die design or coater maintenance. They are going to want more proof. The final proof is to show that you can temporarily tighten any loose roll in a set merely by throwing in "shims" of paper or whatever to fill out the low spots made by manufacturing.

Even if you get buy-in that the root cause is indeed manufacturing, variations does not mean the pressure is off the winderman. Manufacturing will then say that this is the best they can do. Like it or lump it, you've got to wind it. All the winderman can do now is pull like hell and pray. Sometimes you can tension things enough to pull up the slack roll. Sometimes you have to rebuild the winder to give more tension capability, assuming the web and tight roll will tolerate it.

Next, we can think about slip-core winding. In this arrangement, the rolls are tensioned by over-speeding the shaft and transferring torque to the rolls through a slip-clutch arrangement. Slip clutches allow the varying diameter rolls to turn at their own speeds. The need for this treatment increases when all of the following are present: high caliper variations, stiff ZD modulus (roll rings when struck with a stick) and multiple rolls (the more rolls, the more risky).

However, slip-core winding is not without issues. Setup time and skills increase. Shafts are very expensive and require a lot of maintenance. If you over-speed the shaft too much, you can generate heat and debris from the friction of rubbing. Lubricants can contaminate product. Also you lose closed-loop control. When in locked-core mode, the average tension of the set is often regulated by load cells, while variations across the width are caused by caliper variations. In slip-core winding, you often lose closed-loop average tension depending on the design.

More to the point, the tension variations across the width are now caused by variations in clutch frictions. It is not at all unusual to have 2:1 tension variations across a set of clutches on even the best shafts. It can get much worse if operators use lubricants or if the friction elements get glazed.

In other words, the tension variations of the cure may be more deadly than the tension variations of the disease. You must evaluate, on a case-by-case basis, which mode works best. It is done by comparing roll-hardness variation of slipped-core versus locked-core mode on a particular grade.