Laser micrometer solves rapid thin fibre measurement

Testing the mechanical properties of different fibres is key to many manufacturers, especially those in the medical, textiles, electronics, cosmetics and personal care sectors. In cosmetics and hair care for example, regulations require that manufacturers have consistent, reliable data to support their product claims. Performance testing in this area also involves large-scale measurements of human hair strength and elasticity properties, both of which affect ease of combing. A key problem here for manufacturers, is that there is often a wide variation in the breaking force seen within a batch of hair samples. Researchers in these companies constantly seek out the small differences in hair strength caused by different treatment formulations. The problem appears to centre around the wide variation in sample cross sectional area (CSA) within a batch, showing that breaking stress is a better measure to use than pure breaking force and raises the need for automated machines that can accurately measure very small diameter fibres. Also, the time taken to process typical hair sample batches is between two days and one week, due to handling and preparation time. Andover-based testing machine maker DIA-STRON, has developed a fully automated machine, the Fibre Dimensional Analysis System (FDAS), which rapidly evaluates the tensile properties and enables the accurate measurement of the CSA of sub-micron thin fibres, including hair, cotton, Kevlar and carbon fibre, down to 5(m thicknesses. The machine uses a LSM-500H laser scan micrometer measuring unit from Mitutoyo. This is an automated, non-contact measuring system that measures thin fibres and coatings. A laser beam, which is rapidly swept through a 2mm wide band, detects the size of any object obstructing the beam in the direction of sweep. The system can be configured to measure outside diameters or gaps to a resolution of 0.01(m at an accuracy 0.4(m and transfers data to a PC via an RS-232C port. This means a fibre sample can be measured at just one point along its length or divided up and scanned in 24, 1mm slices. The FDAS allows a more accurate measurement of CSA by rotating a sample in the laser beam while taking multiple measurements at pre-determined angles. Nigel Winsey, director at DIA-STRON, explained: "Measuring the cross sectional area accurately can only be done with a laser instrument, as a hair tends to rotate to the position of least diameter between the anvils of a conventional micrometer."