Parametric study of nip load control on a pope reel
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The secondary arms on a conventional pope reel control the nip load between the winding parent roll and the reel drum. As the parent roll grows, the secondary arms pivot away from the reel drum changing the angle of contact on the spool bearing housing. This changes the magnitude of the component of force that contributes to nip load. The moment caused by the secondary arm weight also changes as the roll grows. These two effects combine with actuator geometry to create a sinusoidal relationship between cylinder pressure and nip load.Older reels typically relied on constant pressure control to maintain the nip load. Operators could manually adjust the pressure if they thought it was required. Once programmable logic controllers (PLCs) became popular, the changing geometry of the secondary arms could be easily compensated for which made automatic nip load control practical. A look up table or polynomial in the PLC was used to create the pressure versus diameter function required for the desired nip load curve.A comparison of the effects these two control methods have on radial and circumferential parent roll stresses has not been publicly documented to this authors knowledge. The purpose of this work was to perform this comparison and gain insight into the benefit of automatic nip load control. The question of whether the differences cause or solve any winding defects was beyond the limited scope of this study.