Slitting and winding

The winder produces the rolls of the final product and can affect quality. The ease of use of the winder will dictate how much attention is given to it by the production 

The main function of a winder is to guide the film evenly into the roll form. To accomplish this, it must provide tension control on the film to produce evenly wound rolls. A secondary nip, either as part of the winder or just prior to the film entering the winder, is used to provide this tension control. Tension must be sufficient that the roll will not telescope when handled, but must not be so much that it causes crushed cores or center-roll bagginess. Tensions on center drive winders are generally tapered from the core to the outer wraps to compensate for the change in diameter of the roll. On a surface winder, the compensation is automatic because of the drive mechanism. When tension is being adjusted on a winder, it must be kept at or below 0.5% of the secant modulus of the film to avoid excessive stress in the film. One reason for this low value of recommended tension is that the film is not totally at equilibrium at the time it is wound into the roll. Dimensional changes occur as the film crystallizes or cools, and induce stress. 

Winders can use different methods of roll changing. Most winders used in the film industry are turret type, where the empty core is rotated into position by a turret mechanism and an automatic cutoff is made. 

Many variations in winder design are available from manufacturers, and one needs to determine the requirements of the products to be produced before winder selection. Knittel [1] and Loonsbury [2] have published discussions about winders that offer insight into the design parameters that are important. Winding technology is an area of study that has received more attention in the paper industry than in the film industry, but one can learn the principles from paper and apply them to film. One major difference between the two materials is the much greater elasticity of films, which must be considered in the analysis. 

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Downward extmsion of a bubble into a water bath and over an inner water-cooled mandrel is used in a few instances for polypropylene and polyesters. The water is removed prior to slitting and winding. 

In many extrusions film and coating operations the slitting and winding must be dealt with as one operation. Figure 18.5 highlights some of the factors that are involved where there is ... 

Then why is a looping pit necessary The looping pit is necessary to accumulate the apparent strand length differential, which is actually an illusion resulting from slitting and winding crowned strip. 

Figure 1.94 Multi-lamination flow pattern superposed by focusing in the slit-shaped interdigital micro mixer. Blurred zones indicate lamellae tilting and winding within the entire focusing zone [20] (by courtesy of AlChE).

Rubber in the form of fine threads produced by vulcanising a thin sheet of rubber compound, winding it on a drum and slitting it to the required size by revolving the drum against a number of sharp, wetted knives which revolve at high speed. Cyclised Rubber... 

Figures 3, 4, 5, 6, and 7. Method of Connecting a Branch to a Main Line of Cordeau. (Courtesy Ensign-Bickford Company.) Figure 3. Slitting the Branch Line. Figure 4. The Slit End Open. Figure 5. The Main Line in Place. Figure 6. Winding the Splice. Figure 7. The Finished Junction.

The amount of spray collected at each sampling site was conveniently determined fluorometrically when a suitable tracer was included in the spray liquid. Fluorescein was found to extract quantitatively from most deposits and could be determined easily to 0.1 p.p.b. This sensitivity allowed calculation of the fraction of spray collected at each sampling site if the amount of spray passing through the slit system and entering the wind tunnel in a given time period were known. Results from different sprays on the basis of equal droplet size then allowed us to make quantitative comparisons. 

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