Winding tension

One of the main drivers in moving to plastic substrates is that it opens up the possibility of roll-to-roll processing and the process and economic advantages that this brings. Under these conditions a winding tension will clearly be present and polymer film substrates with low moduli will be susceptible to internal deformation, particularly at elevated process temperatures. Figure 7.8 shows a comparison between poly(ethylene terephthalate) and poly(ethylene naphthalate) films. 

Tension Control Roil These type rolls provide the important function of material tension control. There is a proportional relationship between winding tension and lay-on-roll forces (eliminating areas were bumps, valleys, unwanted stretch, etc. develop). There are various tension control techniques available. The proper selection involves decisions on how to produce the tension, how to sense the tension, and how to control the tension. For instance, if the material has a very low tension requirement and if exact control is required, then perhaps, using a magnetic particle brake with an electrical transducer roll with appropriate electronic control is best. However, if the material is on large diameter rolls and moves at slow speed, then a roll follower system can be used effectively. 

Figure 12. Transmission losses of four optical fibers coated with different materials as a function of winding tension on a 25-cm diameter acrylic drum. The fibers are llO-um cladding diameter, 8-um core diameter single mode fibers. These fibers have a very small core-cladding refractive index difference and transmit only the fundamental, most axially directed light ray (mode). Coating thickness is 50 um. (Reproduced with permission from Ref. 28. Copyright 1981 Gordon and Breach Science Publishers.)...

Filament winding, tension The amount of tension on the reinforcement as it makes contact with the mandrel target is to have the required tension uniformly applied to all reinforcements. 

Blocking Inadequate cooling Excessive winding tension Excessive pressure on nip rolls Bad resin Use better cooling method Adjust tension Adjust pressure Check resin... 

Another purpose the wiper has is to provide some tension to the material when operating in a single-entry loop mode. Quite often, the tension created at the cut is inadequate to provide sufficient winding tension for the rewinder. In this case, the wiper pads can add tension to the cut tension and allow acceptable rewinding. 

There are many choices for wiper media. It can be felt, cloth, indoor carpet, outdoor carpet, leather, Scotch-Brite, or any similar material in sheet form. Care should be taken when selecting the basic unit to allow for quick and easy changing of the wiper media, as a conscientious operator will change the wipers frequently to ensure consistency in the winding tension. Another technique used... 

Fig. 9. Modulus of PpPTA fibers versus draw ratio in the air gap for a polymer viscosity of fiinh. = 4.5 and a concentration of the sulfuric acid solution of 19.3%. Estimated upper limit of the winding tension is 5 mN/tex [230]...

Fig. 9 presents the modulus of PpPTA fibers as a function of the applied draw ratio for air-gap spinning at a very low winding tension. This figure demonstrates the importance of the spin-stretch stage in the spinning process. It wiU be shown here that these results are in agreement with the affine deformation model [230]. 

The fibres conform to the mould surface by virtue of the winding tension. However, on a frictionless surface the fibres will take the shortest route between two points on the surface (this is the geodesic path). Therefore it is necessary either to wind a geodesic path or to generate sufficient frictional force to keep the fibres in the chosen path (by using a tacky resin or tacky prepreg). 

Hirai T, Program control system for winding tension force to obtain a uniform residual stress distribution in material. Proceedings of the 7 International Conference on Composite Materials, 1 Manufacture, Guangzhou, 101-106, 22-24 Nov 1989. 

Determination of winding tension. Substituting (fi)p for the second term of Eq. 15.64, we obtain the following equations. 

The re(juirerl winding tension, / , at radius r is obtained hy subtracting the change in. stress, A/, due to windings beyond mdius r fronj the residual hoop stress, /nrc.siituai)... 

Figure 10.21. Kinetic coefficient of Motion of polyethylene film containing 2,500 ppm eruc-amide vs. winding tension. [Data from Schumann, B. H. Wooster J. J., Soc. Plast. Eng., Inc., Antec, Conf Proc., paper 1081,1999.]...

Many other parameters influence performance of slip additives in polyethylene Figure 10.21 shows that when the winding tension of film increases, the coefficient of friction also increases.Aging temperature increases the degradation rate and volatile losses, and thus decreases the amount of active slip agent. 

Figures 11.17, 11.18 and 11.19 show the effect of erucamide loading and its surface concentration on static coefficient of friction of polyethylene film. Figure 10.21 shows that the winding tension also affects the coefficient of friction. At high winding tensions, slip agent does not migrate to the film surface, which contributes to increased coefficient of friction.

Coefficient of friction is influenced by many physical properties of surface, conditions under which it is measured, and material composition. These include temperature" " " time after processings-" " winding tension material thickness quality of mixing film density surface free energy surface adhesion force ... 

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