| A web can be defined as thin material manufactured and processed in continuous flexible strip form. A web is usually supported, guided and propelled by rollers. In order to make it travel through the process machine line, sufficient external machine direction force and velocity must be applied to web. The work presented here studies the mechanics and associated instabilities of webs running over the rollers which are not perfectly cylindrical in shape. Lateral and longitudinal behavior of web on concave, crown and tapered roller is studied. The exact boundary conditions are established. Several roller geometries, web materials and webline conditions are modeled using explicit finite element method for analyzing web-roller interaction. Instabilities in the form of troughs and wrinkles induced as a result of imperfection such as roller crown and taper are also studied. The simulation results are compared with available closed form solutions and experiments documented by previous researchers. A satisfactory agreement is observed for deflection, stress and overall behavior of web on such contoured (non cylindrical) rollers. This study revealed that normal entry condition is valid at the entry of web to a contoured roller. It is also found that web does not slip over its wrap on roller surface till the very exit from roller surface. These findings were then used to formulate computer code that predicts web behavior quite satisfactorily utilizing very few computational resources and time. |
