Momentary measurement of force exerted on individual fork needles in random-velour needling

摘要

Random-velour needling can be regarded as a modified technique of conventional needling process. This modified technique results in the occurrence of fundamental changes in initial orientation of fibers within the preconsolidated fibrous assembly. As the consequence of these changes a dual fibrous structure comprising base and pile layer is created. It is evident that momentary analysis of forces exerted on fork needles is vitally important in the design of both needle and machine. In this research, momentary forces experienced by individual fork needles were precisely measured. A novel force measuring system enabling the momentary sensing of the forces was designed and developed. The results were analyzed by purposely written MATLAB-based software hereafter named as force analyzing software. Results showed that fork needle experiences various forces due to its vibration and inertia and also frictional resistances offered by preconsolidated fibrous assembly and brush conveyor during a complete needling cycle. Furthermore, fork needle is subjected to an additional force due to contact of fork needle with fibers of preconsolidated fibrous assembly during dwell of needle board at the bottom dead center. It is concluded that total force on the fork needle includes contact and noncontact components. Quantification of results showed that, noncontact forces arc due to fork needle vibration and inertia. These comprise significant proportion of total force experienced by individual fork needles. Magnitudes of these forces are strongly dependent on stroke frequency of the needle board. It was found that contact component of the total force is dominated by preconsolidated fibrous assembly characteristics.