AUTOMATIC SYSTEM TO CONTROL THE ANISOTROPY OF NONWOVEN FELTED WEBS

摘要

The webs produced using a card as former system generally keep the fiber orientation. This effect is not very important for a great number of applications. But if an even pore distribution is necessary or the mechanical properties are to be uniform in all directions, then this system doesn't work very well. Some years ago, it has been introduced a drafting operation of the web between the pre-needling and the final needling operations, as a solution. However, this alternative has a problem: there is no way to adapt it to variations in fiber orientation in the web. Taking into account these considerations, a new technological solution has been specifically devised to control the fibre orientation during the drafting operation in pre-needled felts. A prototype is used as drafting unit with the rolls driven by stepper motors and controlled by computer. Two video cameras collect images of the surface of the web, before and after the drafting operation, and process them in a computer. The values of the images textural descriptors, are calculated and compared. It is intended an increase in entropy which means that the web become less ordered and this is the situation we are aiming for. A computer program will adjust automatically the speed and pressure of the drafting cylinders so as to ach ieve the best possible situation in terms of the isotropy of the final product and, consequently, MD:CD ratio close to 1.