ASTM D4120-07(2012)

This test method for the determination of cohesion in sliver, roving, or top in dynamic tests may be used for the acceptance testing of commercial shipments but caution is advised since information on between-laboratory precision is lacking. Comparative tests as directed in 5.1.1 may be advisable.

If there are differences or practical significance between reported test results for two laboratories (or more), comparative test should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, test samples that are as homogeneous as possible, drawn from the material from which the disparate test results were obtained, and randomly assigned in equal numbers to each laboratory for testing. The test results from the two laboratories should be compare using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If a bias is found either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

The cohesive forces overcome in continuous drafting of slivers, rovings, or tops are affected by surface lubricants and such fiber properties as linear density, surface configuration, fiber length, fiber crimp, and fiber-frictional characteristics.

The concept of drafting is one of the most important principles in the production of yarn from fibrous raw stock.

The values of force to maintain drafting determined by this method are induced by mechanical means similar to those used in textile processing.

The attenuation of textile fiber strands while in motion closely approximates actual textile processing conditions, and the relative values of force may be used to predict processing behaviors.

Fiber cohesion is affected by the alignment of fiber in the textile strand and strand compaction in addition to the factors listed in 5.2. Although fibers are more nearly aligned in draw sliver than in card sliver, the draw sliver is more compact. Thus, for a given production run, the drafting forces are higher for draw sliver than for card sliver.

In addition to the aforementioned effects on drafting forces, the direction of specimen movement through drafting rollers may give different drafting force. Fibers in slivers may have hooks of varying severity at one or both ends. Passage through drafting rollers results in higher drafting forces when the predominance of fiber hooks are oriented in the trailing mode of the strand.

1.1 This test method describes the measurement of fiber cohesion as the dynamic cohesive force required to maintain drafting in rovings, slivers or tops when they are subjected to stress induced by passing between pairs of drafting rolls of different surface speeds. The cohesive force is converted to cohesive tenacity based on the linear density of the material.

Note 1—For static tests refer to Test Method D2612.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.