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Abstract:
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In the manufacture of short staple yarns, many factors
affect the quality of the final product. These factors
range from fiber characteristics to machine settings and
even operator practices. To achieve quality yarn
manufacturing one must control all factors which cause
deteriorations in raw material, sliver, and resultant yarn
quality. One such factor which has been investigated since
the late 1940's is drafting force.
Drafting force is defined as the force necessary to
move fibers past each other in a drafting zone. Like yarn
quality itself, many factors such as fiber characteristics
and machine settings affect drafting force. Longer more
crimped fibers, higher fiber entanglement, and closer roll
spacings all lead to higher mean drafting force. Lower
levels of drafting force can be caused by wider roll
settings, higher fiber alignment, higher drafts, and lower
roving twist. Drafting force and drafting force
variability exist to different degrees in all types of
fiber assemblies. Many research articles have been written
relating fiber characteristics and drafting force; however,
few have gone the additional step to determine proper
machine settings as they relate to drafting force and
drafting force variability. Research associated with drafting force and drafting force
variability in roving was completed by Feil in the early
1980's. This research showed that drafting force and drafting
force variation affect the quality of ring spun yarn. Feil
related drafting force variation to actual spinning frame break
draft settings. Using the ITT Draftometer, Feil determined that
certain spinning frame break draft settings yielded a higher
degree of drafting force variability. This high force
variability area became known as the critical draft region.
When spinning break drafts are set in the critical draft region
fibers do not draft uniformly, but instead, draft in the sliding
and stopping motions, which in turn negatively affects ring yarn
quality.
It was the objectives of this research to determine if a
critical draft region exists in finisher drawn sliver, and if it
does, what effect does it have on yarn quality. In addition,
the effects of finisher drawn sliver drafting force and force
variability on ring and air-jet yarn quality was investigated.
This research was completed for four fiber blends, three of
which were ring spun, and one spun on an air-jet spinning
machine. All drafting force and drafting force variability data
were obtained using the ITT Draftometer which had been equipped
with a more sensitive measuring head capable of measuring the
small interfiber forces associated with finisher drawn sliver. Multiple correlation analysis on the data generated
concluded that critical draft as measured by the modified
ITT Draftometer does not exist in finisher drawn sliver.
However, finisher drawn sliver drafting force and drafting
force variability either seperatly or in conjuntion with
break draft did significantly correlate with both ring and
air-jet yarn quality. These correlations which show that
the modified ITT Draftometer can be used to predict both
ring and air-jet yarn quality are as follows:
1. Increases in the product or interaction of roving frame
break draft and mean sliver drafting force improves
yarn quality. As the interaction increases improvments
are witnessed such as lower ring yarn Uster CV, higher
adjusted single-end strength and break factor, better
yarn appearance, and lower levels of Uster thins, Uster
thicks, and Classimat minors.
2. Increases in drafting force variability of the finisher
drawn sliver lower the ring yarn elongation and the
degree of Uster neps.
3. Increases in the product of break draft and mean
drafting force increase the Uster CV, elongation
variability, and amount of Classimat thicks in
air-jet yarns.
4. Increases in the product of break draft and drafting force variability increases the Uster CV variability,
lowers the adjusted break factor and single-end
strength. Higher single-end variability, lower Uster
thicks, and higher Classimat minors and thicks are
noticed as increases in air-jet spinning break draft
and sliver drafting force variability.
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