Rotor Spinning
Commercial rotor spinning was first introduced in 1969. Rotational speeds have gradually increased
up to 40 times their initial speed and continue to rise. Today’s rotor spinning machine has a linear
Rotor spinning eliminates the need for roving and after-spinning winding due to the large yarn package produced.
The amount of draft is substantially higher than that of ring spinning. Drafting in rotor spinning is accomplished using a comber roll (mechanical draft) which opens the input sliver followed by an air
stream (air draft). These two operations produce an amount of draft that is high enough to reduce the
20,000 fibers entering the comber roll down to as few 5 fibers. To produce a yarn, groups of fibers
emerging from the air duct are deposited on the internal wall of the rotor forming a fiber ring. The
torque generating the twist in the yarn is applied by the rotation of the rotor with respect to the point of the yarn contacting the rotor navel. The amount of twist is determined by the ratio of the rotor speed to the take up speed. The winding operation in rotor spinning is completely separate from the drafting and the twisting operations. The yarn is taken up at a constant rate. This separation between winding and twisting allows the formation of larger yarn packages than those in ring spinning.
As the opened fibers flow around with the combing roll, friction between the fibers and the comber roll metal chamber results in a fiber velocity lower than the surface speed of the combing roll. Those
fibers are normally in a disoriented shape. In this regard, fiber attributes such as fiber resilience,
fiber/metal friction, crimp, stickiness, and surface finish are of keen importance. The tendency to
increase the combing roll speed makes these fiber properties even more critical. Increasing comber
speed usually results in yarn hairiness and yarn imperfections. Normally, a wire-wound clothing is
recommended for cotton and cotton blends where pinned combing rolls are suitable for fragile fibers
such as acrylic and rayon.
Although the primary role of the combing roll is to open the fibers, it can also act as a cleaning unit by separating trash particles from cotton. Obviously, this additional function can easily overstress the
combing roll, making it wear rapidly. It is important, therefore, that the input sliver exhibit a great level of cleanliness.
Fibers coming out of the comb roller are airborne through an air duct. This zone of draft is of a special significance because of its impact on fiber orientation. To obtain such a fast airflow, the inside of the rotor is run at a vacuum which may be achieved by designing the rotor with radial holes to allow the rotor to generate its own vacuum; some use an external air supply.
Another approach to minimize fiber disorientation in the air duct is by designing it in a tapered shape
toward the rotor to allow acceleration of the fibers as they approach the rotor inside surface. This
action may also straighten the leading fiber hooks coming out of the opening roll. Fibers emerging
from the air duct come into contact with the rotor inside surface, which is typically faster than the
fibers. This also assists in straightening the fibers disoriented in the previous zones.
The air draft reduces the fiber strand down to few fibers (2-10 fibers). These fibers are then landed
into the inside surface of the rotor as it takes many layers of fiber to make up sufficient number of
fibers per yarn cross-section. As successive layers of fibers are laid into the inside surface of the
rotor, a doubling action occurs which tends to even out short-term irregularities in the yarn. Rotor
spinning requires very fine fibers.
Microscope examination reveals that the yarn axis of rotor-spun yarn has fibers that are not
completely tied into the yarn. Those fibers have a free end that wraps itself around the yarn periphery
and causes constriction of the yarn. This is an inevitable defect that is peculiar to rotor-spun yarns. It
is commonly called "fiber belts" or "wrapper fibers." They fail to contribute to the strength of the yarn and they provide no improvement to any quality aspect. In fact, they should be treated as waste fibers that happen to stick to the yarn body. The inevitability of wrapper fibers, however, has led many machine manufacturers to claim that they may have some merit including improvement of yarn
abrasion resistance.
Long fibers tend to form wrappers that are so tight that the belt looks more like a thin place. Short
fibers, on the other hand, form slack and loose belts. Other fiber attributes that may contribute to
wrapper fibers include fiber stiffness and fiber fineness; stiffer and coarser fibers tend to become
wrapper surface fibers.
Rotor spinning produces tighter fiber control due to the higher spinning tension. Fibers are not firmly
gripped at any point of their flow. The lack of significant tension also results in some fibers that are
only partially twisted, leading to inferior yarn strength. The yarn consists of three layers: a core that is
truly twisted (similar to ring-spun yarn), an outer layer that is partially twisted, and fiber wrappers.
The true twist in rotor-spun yarns results in a natural curling tendency, similar to ring-spun yarns.
However, this torque is partially balanced by a torque caused by the wrapping effect of the wrapper
fibers, particularly those that take an anti-clockwise direction. The more such anti-clockwise banding
fibers there are, the lower will be the curling tendency in the rotor yarn.
Rotor spinning has superior economical advantage over ring spinning in the coarse to medium yarn
counts. In recent years, there have been many attempts to push rotor spinning further into the area of
fine counts.
Fine counts are associated with high quality yarn (defect free and certainly trash free). This means
that the quality of the fibers must be upgraded to produce fine counts. The sliver fed to the machine
should be prepared carefully so that it exhibits the lowest irregularity possible, and the lowest trash
level possible. In case of light sliver, inter-fiber cohesion is critical. Fiber properties such as trash
content, short fiber content and inter-fiber friction are extremely important, not only for producing
acceptable quality levels, but also for minimizing end breakage during spinning.
In recent years, low level combing has been used to upgrade cotton fibers used in producing fine
rotor yarns. Combing upgrades the cotton quality by removing neps and short fibers, and by providing better fiber orientation in the fiber strand. The added-cost by combing is justified by lower endsdown during spinning, and slight reduction in twist.
Combing also provides the following benefits:
• Irrespective of raw material, yarn strength was found to increase by about 10% with combing and
yarn uniformity was improved.
• Combed rotor-spun yarns yield better filling insertion rates during weaving because of lower rates
of filling stops.
• Combed rotor-spun yarns result in better knitting efficiency because of the low fly deposition and
the smoothness of yarns. The uniformity and handle of single jersey knitted fabrics were
significantly improved as a result of using combed rotor yarns.
Important fiber properties in rotor spinning are:
• Fiber strength;
• Fiber fineness;
• Short fiber count;
• Variation in fiber length;
• Fiber to metal friction;
• Removal of unwanted residual materials.
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