Winder vibration: Causes, defects, and remedies

Web process machines employ various winder types depending on the web being wound. These winders have various rolling contacts between machine elements and the winding roll which give rise to complex vibration phenomena. Consequences of the vibration vary from wear of the machine elements and web material defects to wound rolls being thrown catastrophically from the winder. The type of the vibration excited is very much dependent on the web material properties. Hence, the remedies for vibration problems can differ depending on the web. Despite recent advances in reducing the vibration, roll vibration continues to be the major obstacle to increasing winding equipment speeds.The web properties which contribute to vibration sensitivity are discussed as well as various mechanisms which can cause wound rolls to become out-of-round and compound vibration problems. When the basic dynamic features of the winding process are studied with elementary or more detailed mathematical models the influence of the damping enhancement of the winder components can be simulated. Some typical vibration types are described together with commercially available solutions

Study of CD elongation of core in winding

In this paper the elongation of a core in a roll bottom is studied experimentally and theoretically. The CD elongation effects are of interest especially because they are known to contribute prominently to a two-drum winder vibration or roll instability phenomenon called bouncing in the paper industry.Analytical and numerical calculation models are used to study the effect of different geometrical, material, etc., parameters on the core and paper CD elongation. If the free lateral elongation and rotation is allowed and the friction between paper and the core is neglected, the radial and tangential stresses of the core are due to the radial pressure only. The lateral and shear stresses are equal to zero and the elongation depends on the pressure, Poisson's ratios in the thickness-machine and thickness-cross directions, elastic modulus in the thickness and tangential directions and the geometry. If the lateral frictional farces between the paper and core are also taken into account, another, equally effective elongation mechanism is introduced.The measurements of the paper and core elongation are in accordance with the calculated results. In practice, cores expand typically +/-1 mm/m depending on the tightness of the roll bottom and core properties. This study shows that the core elongation increases linearly with the radial pressure. Small diameter cores lengthen less than large cores. Cores with thicker wall thickness lengthen less than thinner cores, and cores with a bigger winding angle lengthen less than cores with a smaller winding angle (conventional cores).The radial moduli of paper and the core wall also play an important role in the elongation of the core. Preliminary studies suggest that the softer the paper the more it tends to widen. According to paper stack modulus measurements, the radial modulus of paper layers in the roll bottom can be less than 100 MPa, even with high winding pressures. The radial elastic modulus of the core wall is usually 100 - 200 MPa or even greater depending on the core type. It is possible that the frictional force between the core and paper could force the core to elongate more than it would without paper

Contact mechanical approach to the winding nip

A contact mechanical model for the winding nip, consisting of the wound roll, winding drum and the intervening sheet, is presented. The roll and drum are modeled as linear, orthotropic, homogeneous cylinders with a rigid core. The elastic solutions for the cylinders are derived analytically in a series form. The sheet is modeled as a linear and orthotropic material as well. An approximate elastic solution for the sheet is obtained by assuming an internal stress distribution compatible with the boundary conditions (thin sheet approximation). The governing contact mechanical equations are presented and the appropriate form of the wound-on-condition of the sheet is presented

Development of web tension in a winding nip

Today practically all winding devices apply a nip to the wound roll. In this winding method, radial pressure is applied by a winding drum to the wound roll at the point where the web enters the roll. This reduces the air entrainment into the roll and increases the tension of the web entering the roll. The wound roll internal stress profile is determined by this Wound-On-Tension (WOT). If the WOT along with the elastic moduli of the web are known, the internal stresses of the wound roll can be calculated. A winding simulation model predicting the internal stresses of a wound roll would provide a valuable tool for the optimal selection of the winding control parameters. When the incoming web enters the nip area its state of stress and strain changes significantly. An evaluation of these changes without any presumptions necessarily calls for a rigorous contact mechanical solution. The aim of the present paper is to calculate the surface tractions and the WOT due to the winding nip and, hence, provide means to predict the wound roll stresses as a function of the winding parameters.The contact mechanical model is based on the plane strain elastic solutions of the wound roll, winding drum and the wrapping and intervening web, combined with the indentation, stick and slip equations. A homogeneous elastic orthotropic material law for the roll, drum and web is used. The incoming web may slip with respect to the roll and drum, whereas slippage of the layers in the roll is not allowed (solid roll model). The stick-slip pattern within the contact zone is iterated using a variant of the Panagiotopoulos Process. Numerical calculations revealed a typical mechanism for the development of the nip-induced tension when the winding drum is hard and the coefficient of friction between the drum and web is larger than that between the web and roll. Due to the appearance of a double-sided slip zone in the vicinity of the trailing edge of the nip, the web moves faster than the wound roll and winding drum and, hence, the web tension increases, It is also shown that for a winding drum covered with a thin rubber cover, most of the web tension increase occurs at the winding drum wrap. In addition, the dependence of the nip-induced tension on the winding force, layer-to-layer friction, wound roll and winding drum radii, drum cover compliancy and the elastic constants of the web was studied numerically. The calculated results were in good qualitative agreement with the experimental ones

Two-drum winder run simulation model

A dynamic, analytical model for winder run simulations is presented. The model consists of elastic drums, deformable paper rolls and a rigid rider roll beam. A paper roll nip flexibility model is derived and a profound influence of paper roll properties on winder dynamics is demonstrated. The origin of winder vibrations due to specific vibrating paper grades is explained in detail. Winder drum design aspects against vibrations are studied. Finally, some practical measures to reduce winder vibrations are presented

Wound roll generated unstable vibration on a two-drum winder

Nip contact between the paper roll, winding drum and rider roll or some other nip roller may cause that the wound roll is deformed into a convex polygon. This deformation process is accompanied with a strong vibration. The conditions under which this phenomenon occurs depend very much on the web properties. For example, in the paper industry some bulky grades with a high layer-to-layer coefficient of friction are known to be prone to this unstable vibration.In this paper a simple wind-up model of a two-drum winder, capable of capturing quite comprehensively this phenomenon, is developed. The pattern formation is modelled via viscoelastic surface deformation. This results in a system of linear delay differential equations. Performing Laplace transformation to the system equations enables to study the stability of the system as a function of the web properties, nip drum stiffness, wind-up geometry and damping. The model parameters related to the viscoelastic surface deformation are measured experimentally for several paper grades.The paper is concluded by studying the system stability in a certain resonance condition. It is demonstrated that the system can be stabilised by changing the structural parameters of the winder

Study of stress-strain relation for paper roll

In the present method a wound roll of paper is loaded against a nip roller and the measured values of the nip width and the roll indentation are compared with the corresponding calculated values of the non-linear problem. The nip width is measured by a sensitive sensor film and the roll indentation by a laser displacement sensor. The nonlinear numerical problem is solved using the Finite Element Method with four-node isoparametric quadrilateral elements and Newton-Raphson-type iteration. A suitable form of the constitutive equation and the stress state dependence of the moduli of the incremental stress-strain law will be discussed. A least squares fit to the experimental results determines the values of the paper roll elastic moduli

Wound roll generated unstable vibration

Nip contact between the wound roll and the winding drum, rider roll or some other nip roller may cause that the wound roll is deformed into a convex polygon. This deformation process is accompanied with a very strong vibration. The conditions under which this phenomenon occurs depend much on the web properties. For example, in the paper industry some bulky grades with a high layer-to-layer COF are known to be prone to this unstable vibration.In this paper a simple wind up model, capable of capturing quite comprehensively this phenomenon, is developed. The polygonal pattern formation is modeled as a viscoelastic surface deformation. This results in linear delay differential equations. In order to analyze the stability, the Laplace transformation is performed for the system equations. The inspection of the root locus shows several zones of instability during the winding cycle. In an example, it is shown how the model can be utilized to explain some well-known winder vibration phenomena.The paper is concluded by stating general beneficial trends for the wind up design and by explaining how to determine the susceptibility of certain webs to unstable vibration by simple laboratory measurements