Fibre Testing
A 38 mm cut length measures 33 mm in the bale, and both numbers are correct.
— %
How much shorter the crimped fibre measures than its extended length
The crimp is modelled as a two-dimensional sine wave of uniform amplitude and frequency. Real mechanical crimp from a stuffer box is a sawtooth with variable amplitude and some three-dimensional character, so measured contraction on a specimen will scatter around this figure - use it as the design value for a crimper setting rather than as a prediction of an individual test. Amplitude is the hardest input to obtain: it is half the peak-to-trough height and is usually inferred from the contraction rather than measured directly, so working the calculation backwards from a measured contraction is often the more useful direction. Production and cut rate assume continuous running with no doff or changeover; cutter loss covers blade dust and short cuts only, not the tow preparation losses upstream.
Staple Cut-Length, Crimp Contraction & Tow-to-Staple Yield — free, with the formula and a worked example, at Textile School.