Spinning fault
1. Irregularity caused by raw material:
The natural
fibres have variable varieties. They have no true fixed length, fineness, shape
of cross- section, maturity, crimp, etc, which have effect on yarn properties
specially evenness These variations are due to different rates of cell
development due to changes in environmental conditions (nutrients, soil, and
weather)
In man-made
fibres, variations in mass/unit length occurs due to changes in polymer
viscosity, roughness of spinneret orifice, variation in extrusion pressure and
rate, filament take-up speed, presence of delustrant or additives, which can
modify the particular shape and fibre surface geometry
2. Irregularity caused by fibre arrangement:
Textile fibres
are not rigid. Their manipulation during conversion into yarn is an immensely
complex combination of mechanical movement which usually requires some degree
of compromise. The desirable results of relocating large number of fibres at
high speed and arranging in well ordered form tend to be difficult. Fibres
assembled into the form of a twisted strand constitute a yarn Fibres are not
precisely laid end to end. And gaps are present between them. As a result of yams
twist. fibres arrange in spiral form in a series of folds, kinks and doublings
3. Effect of fibre behavior :
Fibres shape
directly affects yarn regularity. The fibre cross section, arrangement of fibre
section and space between the fibres will vary from yarn section to section.
Hence the mass of each section will differ. A thin place in yarn will have
lower mass and less strength. In thin regions, yarn twist tends to be higher
since resistance to deformation is lower
4. Inherent shortcoming of machinery:
In many
engineering processes the by hand or machine and positioned with only a few
thousands of an inch tolerance.
In spinning it
is surprising how often the individual fibres are only negatively controlled at
times they are carried forward by air currents or jostled along by surrounding
fibres, or they are held in position by units from which the final product is
assembled are positively friction and twist .
Fibre
manipulation by rollers, aprons, gills, and other machine parts is hampered by
fibre variation, and the machines can only be set to give the best results
within the limitations imposed by the material. The drafting wave is one
example of irregularity due to the inability of a drafting system to control
each fibre. Where roller drafting is used, the distance from one nip to the
other is greater than the length of the shorter fibres.
These short
fibres 'float' in the drafting zone and move forward in an irregular but
cyclical manner which results in the drafted strand having thick and thin
places
The wavelength
of this type of irregularity is about 2-5 times the mean fibre length but it is
not necessarily constant for a particular strand. In addition to a varying
wavelength, the amplitude of the drafting wave is also variable.
5. Mechanically defective machinery:
machines even
in good condition produce irregular yarns, it is reasonable to assume that
defective machine will increase the amount of irregularity implementation of an
efficient maintenance system is essential if the level of irregularity is to be
kept in bounds.
Machines drift
out of adjustment, bearings become worn, components get damaged, and
lubrication system clog and dirt works its way into the mechanism. fault
rollers (top roller eccentricity) and gear wheels usually produce periodic
variation.
