False-twist texturing converts suitable polyester feed yarn into a bulkier, more textured yarn. In friction-disc texturing, the relationship between disc surface motion and yarn running speed is often described by the D/Y ratio. This setting helps engineers understand how the discs interact with the yarn, but it must be assessed together with twist, tension, draw ratio and heater conditions.
How friction-disc texturing works
Polyester yarn passes through a controlled route that can include drawing, heating, friction-disc twisting, cooling and winding. The discs insert temporary twist into the running yarn. Thermal treatment and yarn movement determine the structure that develops; when the twist is removed downstream, the filament bundle retains a textured character.
Definition of the D/Y ratio
A simplified D/Y ratio is friction-disc peripheral surface speed divided by yarn running speed. The same units must be used for both velocities. For example, 600 metres per minute disc surface speed over 300 metres per minute yarn speed gives a nominal D/Y of 2.0. This is an arithmetic example, not a recommended equipment setting.
Why disc diameter matters
The surface speed of a rotating disc depends on its diameter and rotational speed. For a given rotational speed, a larger effective diameter produces a higher peripheral speed. Wear or a change in disc geometry can modify yarn-disc contact, so the ratio alone does not fully describe twisting force.
D/Y versus draw ratio
Draw ratio compares different yarn transport speeds to describe deliberate extension. D/Y compares disc peripheral velocity with yarn speed. They are separate quantities even though both are dimensionless ratios. A texturing recipe should record them separately, including actual measured line speeds.
What disc contact contributes
Friction discs transmit motion to the yarn through contact. The effectiveness depends on disc material, number and arrangement of discs, contact angles and yarn surface friction. Nominal D/Y does not reveal the actual twist inserted into every filament.
Effect on crimp development
Changes in disc operation can change twisting conditions, tension and the textured yarn's appearance. Crimp contraction, crimp stability and bulk must be measured on finished yarn with a consistent method. More disc speed does not automatically generate higher useful crimp throughout an unlimited range.
Importance of heater temperature
False-twist texturing relies on a suitable thermal history to stabilise the temporary deformation. A disc adjustment without reviewing the heater profile may create breaks or inconsistent crimp. The relevant filament temperature can differ from the heater's displayed setpoint depending on contact, speed and path.
Tension before and after the texturing zone
Tension is a diagnostic signal of how the yarn interacts with discs and transport rollers. Compare positions and historical baselines. A tension difference can also arise from POY quality, feed variation or mechanical alignment, so avoid changing D/Y on the basis of one force reading alone.
How uneven texturing appears in polyester fabric
Changes in textured yarn bulk, dye response or filament condition may become visible as stripes, texture differences or other defects after knitting and dyeing. Not all such defects originate in texturing; lot mixing, knitting feeder variation and dyeing process factors can also contribute.
Trial and acceptance procedure
Run the intended POY lot at a documented combination of yarn speed, disc geometry, D/Y, draw ratio and heater condition. Sample across texturing positions and test linear density, crimp, tensile properties and dyeing uniformity. Select a setup from measured final quality, not the nominal ratio alone.
FAQ
Is D/Y the same as twist per metre? No. Does D/Y have units? No, if both input speeds use matching units. Can different machines use the same D/Y and produce identical DTY? Not necessarily. Does higher D/Y always improve bulk? No.
Conclusion
D/Y is a useful descriptor of yarn–disc motion during friction texturing. It gains meaning when linked to equipment geometry, thermal processing, yarn tension and finished polyester DTY tests.
Related Technical Articles
Explore polyester textile manufacturing and wholesale fabric supply with Walrus – Yes India Can; enquiries: +91 90420 77722.
