What is Rotor? | Principle of Rotor Spinning | Tasks of the Rotor Spinning Machine

The Rotor:
The rotor is the main spinning element of the rotor-spinning m/c. Yarn quality ,character working performance of yarn productivity, & costs etc. all depend chiefly on the rotor. The most important parameters of the rotor that exert influence are
  •  The rotor form
  •  The groove
  •  The rotor diameter
  •  Rotational speed along with
  •  The rotor bearing
  •  Co-efficient of friction b/w the fiber & the rotor wall.
  •  The air-flow conditions inside the rotor
  •  Liability to fouling
Rotors are replaceable element in the m/c.

Tasks of the Rotor Spinning Machine:
The basic tasks of the rotor spinning machine are
  •  Opening (& attenuating) almost to individual fibers (fiber separation).
  •  Cleaning.
  •  Homogenizing through back doubling.
  •  Combining i.e. forming a coherent linear strand from individual fibers.
  •  Ordering (the fibers in the strand must have an orientation as far as possible in the longitudinal direction).
  •  Improving evenness through back-doubling.
  •  Imparting strength by twisting
  •  Winding.
Principle of Rotor Spinning:
The general principle of rotor spinning is shown in Figure. The input fiber strand is a drawn sliver. A sliver may have more than 20,000 fibers in its cross-section. This means that a yarn of 100 fibers per cross-section will require a total draft of 200. This 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 few fibers (5-10 fibers). In order to produce a yarn of about 100 fibers per cross-section, the groups of few fibers emerging from the air duct are deposited on the internal wall of the rotor and a fiber ring is formed inside the rotor.

The total draft in rotor spinning is, therefore a combination of true draft from the feed roll to the rotor (in the order of thousands) and a condensation to accumulate the fiber groups into a fiber ring inside the rotor. The total draft ratio is the ratio between the delivery or the take-up speed and the feed roll speed. This should approximately amount to the ratio between the number of fibers in the sliver cross-section and the number of fibers in the yarn cross-section. 
Rotor Spinning process
Consolidation in rotor spinning is achieved by mechanical twisting. 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 (turns per inch) is determined by the ratio between the rotor speed (rpm) and the take up speed (inch/min). Every turn of the rotor produces a turn of twist, and a removal of a length of yarn of 1/tpi inches.

The winding operation in rotor spinning is completely separate from the drafting and the twisting operations. The only condition here is that 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.

Sequence of Operation:
The feed stock in form of either card sliver or draw frame sliver from first or second passage drawing. The sliver runs from a can beneath the spinning unit into the feed trumpet. A feed roller grips the sliver & pushes it over the feed through into the region of the opening roller. A spring ensures firm clamping of the sliver by urging the trough towards feed roller. In the event of an end-break, the feed unit is stopped either by stopping the feed roller rotation or by pivoting the in feed trumpet, in each case sliver feed stops automatically. The signal pulse causing this effect is generated by a yarn-sensing arm.

In the in conventional spinning processes, the fiber strand at in feed is maintained as a coherent structure & is merely attenuated during spinning. In rotor spinning, the fiber strand is opened to individual fibers. This task is performed mainly by the opening roller. This small roller which is clothed with needles or saw teeth, combs through the fiber beard projecting from the nip between the feed roller & the tough it transports the plucked fibers to the feed tube. An air flow is needed for further transport of the fibers to the rotor. This is generated by central fan that draws air by suction through leads from each rotor box. To facilitate generation of this under pressure, the rotor box must be hermetically sealed as far as possible. The suction stream in the feed tube lifts the fibers off the surface of the opening roller & leads them to the rotor. In the course of this movement, both the air & the fibers are accelerated because of the convergent form of the feed tubes. This represents a second draft following the nip trough/ opening roller & giving further separation of the fibers. Moreover partial straightening of the fibers is achieved in this air flow. A third draft arises upon arrival of the fibers on the wall of the rotor because the peripheral speed of the rotor is several times as the speed of the fiber. This is a very important feature because it contributes significantly to good orientation of the fibers. The last straightening of the fibers occurs as the fiber slides down the rotor wall into the groove under the influence of the enormous centrifugal forces work within the rotor.

Speed Interrelationship:
Normal & maximum revolutions & speeds are
  •  Rpm of opening roller :5000 -10000 rpm
  •  Rpm of rotor up to 100000 rpm
  •  Delivery speed: up to 200m/min.
Technical Data of Rotor Spinning Machine:
  •  Number of spinning positions per m/c           up to 220
  •  Count range                                                12- 125 Tex (5 – 50 Ne)
  •  Draft                                                           25- 400
  •  Speed of rotation of opening roller               6000- 11000 rpm
  •  Rotation speed of rotor                                up tp 120000 rpm
  •  Rotor diameter                                            32 -65 mm
  •  Delivery speed ( m/ min)                              up to 200
  •  Package mass                                             up to 5 kg
  •  Angle of taper                                             2° - 4° 20’
  •  Winding angle                                             29° – 45° 
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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