ASTM D4120-07(2018)

5.1 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.

5.2 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.

5.3 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.

5.4 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.

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.