Published research has indicated that cotton strength increases as the specimen loading rate increases when measured by Stelometer and Pressley methods. This report describes an instrument designed to test 1/8 gauge bundles at constant rates of extension from 0.05 to 50 cm/min. A computer analyzes voltage signals from force and displacement transducers. Pressley jaws hold the fiber bundles, and a Stelometer vice is used to load them in the jaws. Specimens are selected with a mechanized sampling and combing procedure. The method provides measurements of strength, elongation, modulus, and two forms of toughness.A new class of fiber testing instruments is evolving to meet the demand for increased information and better precision while measuring the quality of cotton enroute to market. The quality evaluation procedure involves removing or cutting two small samples from each cotton bale, which are delivered to a USDA marketing service office for testing in a controlled laboratory. At the laboratory, they are opened and exposed to circulating air for a time sufficient to assure proper temperature and moisture content. In ofhces where the new high volume instruments (HVI) are being used, fiber length, length uniformity, strength, fineness, lint color, and trash content are measured.There are two manufacturers of HVI systems, Motion Control, Inc. (MCI) of Dallas, Texas, and Spinlab/ Uster Inc., of Knoxville, Tennessee. Both measure cotton fiber length with tapered bundles (a collection of fibers each grasped at a random position along its length with its ends free to extend parallel to each other from a clamp). Prepared specimens (5.1 to 6.4 cm wide) are measured at several distances from the clamp to form fibrograms for length analyses. A point (some distance from the clamp) is selected for strength testing.HVI strength measurements are made at a jaw displacement speed much faster than conventional laboratory instruments, but laboratory instruments are used to check strength values obtained with the HVI methods. The Cotton Division of the Agricultural Marketing Service (AMS) has reported higher HVI strength values for some cottons when compared to Stelometer values [8]. Brown [2] demonstrated the speed problem by modifying an HVI to operate at two extension speeds. He reported no average strength difference when the HVI was recalibrated at each speed, but there was a 9% loss in the strength of his calibration cottons when tested at the increased extension speed.Hertel and Phillips [3,5], on the other hand, reported strength gains with an increasing rate of loading for Stelometer and Pressley methods.The precise extension speed of HVIs is loosely controlled, and jaw displacement is not routinely calibrated. Taylor [7] measured the extension speed of a research model (MCI) at 19.8 cm/min, and Brown [2] reported the speed of an MCI 3000 system at 13.6 cm/ min. Others have studied the effect of testing time on cotton strength for Stelometer and Pressley methods [4, 5], but the literature does not reveal sufficient informat...
Short-term exposure of small cotton specimens to nonstandard atmospheric conditions can cause errors in their strength measurements. Experiments were conducted to evaluate the effect of local humidity changes on strength measurements. Two production model high volume instruments were equipped with humidity sensors near their specimen brushing stations. The system from one vendor was more sensitive to short-term humidity cycles (1.15 compared to 0.6 %gf/tex/%RH), while the other system was more sensitive to humidity changes including sample conditioning (1.81 compared to 1.42 %gf/tex/%RH). Both instruments showed a wide range of strength-humidity sensitivities for the 57 cottons surveyed.
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