Roller nip deflections

Abstract

Rubber covered nip rollers are used in many web handling and processing applications. Successful use of these systems requires an accurate knowledge of the impact of various design and process parameters on key response metrics such as nip pressure and surface speed axial uniformity. These metrics are important since they are directly correlated to operational and functional requirements of nipping processes. Axial variations occur primarily due to roller shell bending, which arise from externally applied end loading forces. The non-linear radial compressive characteristics of elastomeric coverings that are often a part of such systems contributes to system complexity. Previous papers have presented a two-dimensional analytical model that relates force and deformations of rubber rollers in contact with other rollers. In the present paper, a three-dimensional model is presented that extends the previous model by incorporating shell bending deflections. In addition to the non-linearity due to the compressive characteristics of rubber coverings, the model also includes the ability to include other non-linear effects such as roller diameter non-uniformity and misalignment, or skew, of the roller's rotation axes. The model is used to demonstrate that the use of crowning or skewing must not only account for geometric effects but also for the nearly incompressible nature of rubber coverings to successfully mitigate axial nip pressure variation that otherwise is present in end-loaded nip roller systems.