Subrata Kumar Saha 1

Assistant Professor, DTE, AUST

▪ Most yarn is now produced on the ring frame. Ring spinning has been able to supplant
almost all other conventional spinning methods and has proved very resistant to
inroads by the newcomers. This can be attributed mainly to its:
▪ Flexibility

▪ Universal applicability

▪ Yarn quality.

▪ There are also problems associated with the ring spinning machine.
▪ Ring machine is difficult to automate.

▪ Ring frame productivity is currently limited by traveler speed (around 45 m/s)

▪ Yarn tension in the balloon and spindle speed (around 25 000 rpm)

▪ Major improvements above these levels are not easily imaginable.

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Main Problems Advantages
▪ Yarn character differing from that of ring-spun yarn, ▪ High production rates
▪ Characteristics occasionally bordering on the
▪ Elimination of processing stage
unusable
▪ a considerable reduction in:
▪ Difficulties in maintaining consistently uniform yarn
characteristics ▪ Personnel

▪ Greater demands on the raw material; ▪ Space

▪ Market segments limited to: ▪ Relative ease of automation.
▪ Narrow count range
▪ Specific raw material types
▪ Specific end products
▪ A high level of process know-how
▪ Expenditure on repair and maintenance

3
▪ 1937: Basic rotor patent by Berthelsen

▪ 1951:The first usable design proposed Meimberg at the Spinnbau company in Bremen,
but further development of the machine was discontinued because performance
proved unsatisfactory.
▪ 1960: The idea was taken up again in Czechoslovakia.

▪ 1965: The first machine really suitable for industrial application was shown at the Brno
fair.
▪ 1967: The presentation of the BD 200 machine at an exhibition parallel to the ITMA. The
rotor spinning process came into industrial use in spinning mills.
▪ 1970: Rieter, Schubert & Salzer and Platt formed a consortium to develop the rotor
spinning process.
▪ 1971: A number of prototypes at various stages of development.

4
▪ The rotor spinning machine itself is no longer just a
spinning machine in the traditional sense, but a highly
productive, computerized, and complex system for
converting sliver into yarn.
▪ The improvement in economics has been even more
remarkable than the technological advances.
▪ Since the introduction of rotor spinning in the 1960s
rotor speeds have increased from the original level of
around 30,000 rpm to that of 1,60,000 rpm in practical
use today.
▪ Nowadays (in 2005) rotor speeds of up to 170 000 rpm
are technically possible without any difficulty.
▪ A rotor spinning unit produces five to ten times as much
Development in achievable rotor speeds
as a ring spinning spindle. In countries with high wage since the launch of the rotor spinning system
levels, rotor spinning is more economical than ring
spinning for yarn counts up to Ne 60.

5
▪ With more than 8 million rotor spinning positions
installed worldwide, some 20 % of staple fiber yarns
have already been spun consistently for some years.
▪ In some countries (e.g., USA, Germany) the proportion
of rotor spun yarns is already around 50 % of total yarn
volume.
▪ Developments in fashion and textile applications, as
well as developments in spinning machinery
manufacturing, continue to expand and also reposition
the range of applications of rotor spun yarns.
▪ Air-jet spun yarns have been able to secure a certain
market share to date mainly in the USA. Despite Installed rotor capacity worldwide in 2007
intensive development effort, certain limitations in the (total of over 8 million), by ITMF region
processing of pure cotton remain a barrier to their
wider use.

6
▪ In recent years the share of automated rotor spinning machines world-wide is about 35 %.
▪ This figure is influenced by the huge number of not automared machines installed in China.
▪ In other parts of the world the share is much higher. The situation in Turkey, a big investor in rotor spinning during the last
decade. Shortly after introduction of automated rotor spinning, in Turkey within a few years the share increased over 80 %.
▪ Nowadays systems are also available for automatic can transport between the draw frame and the rotor spinning machine as
well as systems for package transport from the rotor spinning machine to the material store or directly to downstream
processing.
▪ This fact has contributed substantially to the improvement in the economics of rotor spinning.

Number of rotors installed, showing the proportion of automated machines

and new investment in rotors, using Turkey from 1979 to 2003 as an example
7
▪ The rotor spinning process enables fibers up to
60 mm (2.25˝) long to be processed and thus
covers the classical short staple cotton range.
▪ The machines developed by various
manufacturers (Schubert & Salzer, Duesberg
Busson) for processing longer fibers with
larger rotors were, however, unable to establish
themselves on the market.
▪ The main emphasis of rotor-spun yarns is in the
count range between Ne 6 and Ne 40, but
Installed rotor capacity (worldwide), by yarn count
covers the overall range from Ne 3 to Ne 60, (ITMF)
albeit with a small proportion of yarn volume.

8
The technological potential:
▪ Rotor spinning is a stable spinning process, i.e. it functions trouble-free under normal spinning
conditions, without variations in running behavior or yarn quality.
▪ The process is reproducible with standard spinning equipment and settings and transferable to a large
number of spinning positions. Quality consistency is therefore adequately assured both within the
spinning positions of a machine or a group of machines and over an extended period of time.
▪ Rotor spinning is a genuine open-end spinning process, i.e. a genuine twist is imparted to the yarn,
making it comparable to ring-spun yarn in its yarn structure and as regards its applications.
▪ Rotor spinning operates with normal draw frame sliver. Special preparatory passages are not required
here.
▪ Rotor spinning is appropriate for mill operations because technology can be implemented with
relatively simple spinning elements.
▪ The process imposes no special requirements on the atmosphere in the spinning mill as regards
temperature, humidity and air conditioning and in many cases is actually less critical in this respect
that ring or Air-jet spinning.

9
The economic potential:
▪ Rotor spinning was the first process that was capable of producing a cross-wound package ready for
processing or sale in a single process stage from a draw frame sliver. Roving frames and winders could
be dispensed with; there was thus a significant incentive from the very outset to utilize this process,
despite the higher cost of a rotor spinning position compared with a ring spinning position.
▪ In terms of manufacturing costs per kg of rotor-spun yarn, direct labor costs occupied a position
behind capital and energy costs.
▪ Rotor spinning operates with very high efficiency compared to ring spinning line. Machine efficiency
of up to 99 % is achieved in mill operations. Stopping the machine to remove packages, as on ring
Spinning machines, does not occur in rotor spinning.
▪ In many cases advantages in downstream processing in weaving and knitting mills result from longer,
faultless running lengths on the cross-wound packages, i.e. fewer malfunctions and stoppages in the
downstream process.
▪ Rotor spinning is more environmentally friendly in terms of dust and noise emissions compared with
ring spinning, despite its considerably higher output.

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1. Sliver feed: A card or draw frame sliver is fed through a sliver guide via a feed roller and feed table to a
rapidly rotating opening roller.
2. Sliver opening: The rotating teeth of the opening roller comb out the individual fibers from the sliver
clamped between feed table and feed roller. After leaving the rotating opening roller, the fibers are fed to
the fiber channel.
3. Fiber transport to the rotor: Centrifugal forces and a vacuum in the rotor housing cause the fibers to
disengage at a certain point from the opening roller and to move via the fiber channel to the inside wall of
the rotor.
4. Fiber collection in the rotor groove: The centrifugal forces in the rapidly rotating rotor cause the fibers to
move from the conical rotor wall toward the rotor groove and be collected there to form a fiber ring.
5. Yarn formation: When a spun yarn end emerges from the draw-off nozzle into the rotor groove, it receives
twist from the rotation of the rotor outside the nozzle, which then continues in the yarn into the interior of the
rotor. The yarn end rotates around its axis and continuously twists-in the fibers deposited in the rotor groove,
assisted by the nozzle, which acts as a twist retaining element.
6. Yarn take-off, winding: The yarn formed in the rotor is continuously taken off by the delivery shaft and the
pressure roller through the nozzle and the draw-off tube and wound onto a cross-wound package. Between
takeoff and package, several sensors control yarn movement as well as the quality of the yarn and initiate
yarn clearing if any pre-selected values are exceeded.

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Technological setting parameters:
Fiber length Natural and man-made fibers up to 60 mm
Sliver weight Nm 0.14 - 0.40; Ne 0.08 - 0.24; ktex 7.0 - 2.5
Yarn count range Nm 5 - 100; Ne 30 - 60; ktex 200 - 10
Draft range 40 - 400-fold
Twist range T/m 196 - 1 500/TPI 5 - 38
Winding helix adjustable between 30° and 40° in steps of 1°
Production-related setting parameters:
Rotor speed 35 000 - 160 000 rpm
Opening roller speed 6 000 - 10 000 rpm
Delivery speed, cylindrical up to 350 m/min (240 rotors), up to 270 m/min (500 rotors)
Delivery speed, conical up to 60 m/min (500 rotors)
Package weight, cylindrical up to 6 kg or 350 mm diameter
Package weight, conical up to 270 mm diameter
Machine data:
Number of rotors, total up to 500
Numbers of rotors/section 20 or 24 rotors depending on machine manufacturer
Number of sections up to 25 (with 20 rotors/section), up to 20 (with 24 rotors/section)
Number of robots up to 4
12
1. Functional units

2. Headstock

3. Tailstock

4. Spinning and winding units

5. Empty tube supply

6. 1 - 2 operating robots

7. Package conveyor belt

13
1. Sliver feeding via sliver funnel

2. Opening of the fiber sliver into

individual fibers by means of
opening roller
3. Trash removal

4. Fiber transport to and feeding into

rotor
5. Yarn formation and twist insertion in
rotor
6. Yarn take-off via draw-off nozzle and
draw-off tube

14
15
▪ Rotor spinning machines are capable of processing successfully fiber lengths
between 10 and 60 mm in virtually all natural and man-made fibers. Rotor
spinning thus offers a range of application that no other spinning process, except
for ring spinning, can even approach.
▪ Recycled cotton waste and noil are processed successfully on rotor spinning
machines. In mill operations the rotor spinning process has earned the reputation
of being especially „cotton-friendly“. This is also the reason why predominantly
carded rotor-spun yarns of 100% cotton or blends of cotton and man-made fibers
are currently produced worldwide.
▪ In addition to cotton, man-made fibers and/or their blends are successfully
processed on rotor spinning. Especially yarns made from polyester fibers and
their blends with cotton are used in a wide range of end products. The reasons for
this remarkable development are in particular:
▪ The outstanding physical and chemical properties of polyester fibers for use in
clothing;
▪ The low production costs for manufacturing polyester fibers and the resulting
economical raw material costs;
Share of fiber materials in the
total volume of rotor-spun yarns
▪ The limited availability of cotton in light of growing global fiber consumption; the
annual increase in fiber consumption of some 3% is now accounted for almost
entirely by man-made fibers, and here mostly by polyester fibers.

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 Cotton (CO)
100 % virgin cotton Cotton waste ≤ 7/8˝ Comber noil
• short and medium staple • secondary material, e.g. • rotor-friendly material
• carded and combed reclaimed by recycling because already cleaned

Man-made fibers (MMF)

Natural polymer, Cellulosic MMF Synthetic polymer, Synthetic MMF Bio polymer
• Viscose (CV) / rayon (term in • Polyester (PES) • Nature works (PLA)
Asia, USA) • Polyacrylic (PAN) and PAN high bulk
• Modal (modified viscose) • Polyamide (PA)
• Micromodal (fiber < 1.1 dtex) • PA-Aramide (Nomes, Kevlar)
• Lyocell (CLY) • Polypropylene (PP)
• Tencel • Polyvinyl chloride (PVC)

Other natural raw materials

Animal raw materials Bast fibres
• Angora wool • Jute
• Sheep‘s wool (sheared or teased, max. 60 mm) • Linen
• Wool noil (tow) • Ramie
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▪ In any spinning system, fiber properties exert a decisive influence on the processing of the
fibers and the resulting yarn. These influences are reinforced in the case of rotor spinning,
so that several remarks are appropriate here with regard to the raw material and its
preparation.

100 % Cotton yarns

Priority Rotor Ring Air-jet
1 Fineness Length Length
2 Strength Strength Cleanliness*
3 Length Fineness Fineness
4 Cleanliness* Strength

Priority of fiber properties for rotor-spun and ring-spun yarns

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Fibre count:
▪ The cottons used for rotor-spun yarns are mostly in the count
range of 3.5 to 4.6 Micronaire.
▪ In some applications very fine cottons from 2.8 Micronaire (for
very fine yarns) up to very coarse yarns up to 5.0 Micronaire (in
the coarse yarn range) are used. Careful selection of
correspondingly fine and well matured types of fiber, carded
cotton yarns up to Ne 60 can now be spun industrially.
▪ The availability of very fine man-made fiber fibers has enabled
yarn manufacturers to produce increasingly fine yarns with
increasingly high yarn quality. By using microfibers, man-made
fibers with counts of up to Ne 60 can also be spun on rotor
spinning machines.
▪ If finer fibers are used for coarser yarns, the number of fibers in
the yarn cross-section is increased, this has a positive influence Relationship between fiber count (B) and yarn
tenacity (A)
not only on the yarn characteristics; in particular, yarn twist can
be significantly reduced, which in turn substantially improves
the hand of the yarns in the end products.

19
Number of fibres in yarn cross section and Spinning limit:
▪ In rotor spinning fiber count and the number of fibers ▪ 𝑛𝑓 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑖𝑏𝑒𝑟𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑦𝑎𝑟𝑛 𝑐𝑟𝑜𝑠𝑠 −
in the yarn cross-section probably have the greatest 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
influence on yarn and spinning results. ▪ 𝑀𝑖𝑐 = 𝑀𝑖𝑐𝑟𝑜𝑛𝑎𝑖𝑟𝑒
▪ Fiber count (Micronaire or dtex) defines the spinning ▪ 𝑌 = 𝑌𝑎𝑟𝑛
limit. ▪ 𝐹 = 𝐹𝑖𝑏𝑟𝑒
▪ Yarn tenacity is some 15-25% lower than in ring-spun
𝑑𝑡𝑒𝑥 𝐹 ∗𝑛𝑓 𝑀𝑖𝑐∗𝑛𝑓
yarn. ▪ 𝑆𝑝𝑖𝑛𝑛𝑖𝑛𝑔 𝐿𝑖𝑚𝑖𝑡 𝑡𝑒𝑥 𝑌 =
10
= 25.4
▪ In order to ensure stable spinning conditions and
10000 25400
achieve good yarn tenacity, rotor-spun yarns must be ▪ 𝑆𝑝𝑖𝑛𝑛𝑖𝑛𝑔 𝐿𝑖𝑚𝑖𝑡 𝑁𝑚 𝑌 = =
𝑑𝑡𝑒𝑥 𝐹 ∗𝑛𝑓 𝑀𝑖𝑐∗𝑛𝑓
spun with a higher number of fibers (at least 90-110
(120)) in the yarn cross-section. 5917 15030
▪ 𝑆𝑝𝑖𝑛𝑛𝑖𝑛𝑔 𝐿𝑖𝑚𝑖𝑡 𝑁𝑒 𝑌 = =
𝑡𝑒𝑥 𝐹 ∗𝑛𝑓 𝑀𝑖𝑐∗𝑛𝑓
𝑡𝑒𝑥 𝑌 ∗ 10 5917 10000
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒𝑠 𝑛𝑓 = = =
𝑑𝑡𝑒𝑥(𝐹) 𝑁𝑒 𝑌 ∗ 𝑑𝑡𝑒𝑥(𝐹) 𝑁𝑚 𝑌 ∗ 𝑑𝑡𝑒𝑥 (𝐹)

𝑡𝑒𝑥 𝑌 ∗ 25.4 15030 25400

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒𝑠 𝑛𝑓 = = =
𝑀𝑖𝑐 𝑁𝑒 𝑌 ∗ 𝑀𝑖𝑐 𝑁𝑚 𝑌 ∗ 𝑀𝑖𝑐
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Spinning limit:
100 % Carded cotton MMF and blends

110 fibers/yarn cross-section 90 fibers/yarn cross-section

dtex Spinning limit Spinning limit

Micronaire dtex den
cotton (Ne) (Ne)

3.2 1.26 43 0.6 0.7 110

3.5 1.38 40 0.9 1.1 73
4.0 1.58 34 1.1 1.2 60
4.2 1.65 32 1.3 1.5 50
4.5 1.77 25 1.7 1.9 39
5.0 1.97 25 2.2 2.4 30

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Fiber length:
▪ The influence of fiber length on the processing
properties and the quality of the yarns produced is
less significant in rotor spinning than in ring spinning
but should nevertheless not be underestimated.
▪ Cotton and cotton waste with a high short fiber
content (< 1˝/25.4 mm) can be processed successfully
using the rotor spinning principle. Cotton waste is
therefore in demand as a raw material for certain
ranges of application.
▪ It should be borne in mind that yarn quality declines
alongside staple length; this affects yarn tenacity and
Relationship between staple length in inches (B)
yarn purity (imperfections) in particular. Yarns and yarn tenacity (A)
produced from shorter fibers usually also have to be
spun with higher twist multiplier.

22
Fiber length:
Relationship between staple lengths of cotton fibre and the yarn counts

100 % cotton / recycled cotton waste / comber noil

Cotton class Staple length (mm) Yarn count (Ne)
23.0 - 23.8 < 10
Short 24.6 < 12
25.4 ≤ 16
26.2 – 27.9 ≤ 40
Medium
28.3 – 29.4 < 60
Long > 30 no applications in rotor spinning
waste (recycled fibers) ≤ 22.2 5 - 17
comber noil ≤ 20

23
Fiber length:
▪ The influence of staple length compared to fiber count is also of secondary importance
for man-made fibers. The graduation of yarn count in accordance with fiber length
results from the fact that, in contrast to cotton, shorter fibers are supplied in finer counts
and longer fibers in coarser counts

Man-made fibres (MMF)

Fibre length (inch) Fibre length (mm) Yarn count (Ne)
1.18 - 1.4 30 – 36 24 – 50
1.5 - 1.58 38 – 40 20 – 30
1.9 -2.05 48 – 52 8.3 – 18
≤ 2.36 ≤ 60 ≤ 8.3

24
Fiber tenacity and fiber elongation:
▪ In order to achieve stable spinning conditions a sufficiently high number of fibers must be available in the yarn
cross-section in addition to adequate fiber tenacity. Yarn blends of cotton and polyester are increasingly being
used to manufacture rotor-spun yarns featuring particularly high tenacity and where the end product permits
this.
▪ Fiber elongation is at least as important. Only the product of fiber tenacity and fiber elongation, i.e. the work
capacity, enables a meaningful statement to be made regarding the further processing behavior of the fibers
and yarns in the spinning process.

Fibre Breaking strength (cN/tex)

Cotton 15 - 40
Cellulosic MMF
Viscose/rayon 23 – 30
Modal 32 – 38
Lyocell/Tencel 39 - 50
Synthetic MMF
Polyester 50 – 71
Polyacrylic 24 – 35
Polyamide 40 - 70 Relationship between fiber tenacity
(B) and yarn tenacity (A) in cN/tex 25
▪ Synthetic and cellulosic man-made fibers are usually clean and trash and extraneous
material free. Raw cotton always contains a certain amount of organic and inorganic trash,
dust, and vegetable and extraneous particles.
▪ Most disturbing impurities can be eliminated by efficient cleaning of the cotton with the
appropriate number of cleaning positions in spinning preparation and careful carding.
Modern blow rooms can remove up to 97% of the trash contained in raw cotton.
▪ Certain disturbing extraneous materials can survive the cleaning and carding process.
These are mainly:
▪ fine and very fine dust (especially critical when adhering tenaciously to the fibers)

▪ extraneous fibers (especially bale packaging material)

▪ vegetable residues (seed coats, leaves, cotton plant stems)

▪ larger trash particles when the cotton has not been adequately cleaned.

26
Effect of trash and extraneous material on rotor yarn:
▪ Rotor spinning machine is capable of effectively removing larger trash and extraneous
particles, but dust and other very light extraneous material can reach the rotor in the air
current and be deposited there in the rotor groove.
▪ Coarser particles (mainly seed coat fragments) stay caught in the rotor groove. They can prevent yarn
formation at this point, and this in turn can result in ends down, mainly when spinning finer yarn
counts. On the other hand, fiber agglomeration at the particle results in a thick place at the
agglomeration point, and immediately thereafter a thin place where the agglomerated fibers are
absent in the groove. The resulting defect (thick/thin place) is absolutely periodic and leads to a
moiré effect if the affected yarn is worked into a fabric.
▪ Small dust particles lead to slow but persistent filling-up of the collection groove in the rotor. If this is
originally narrow, it becomes steadily more open and wider as it fills up. The fiber bundle, which was
extremely condensed in the narrow groove to produce a compact yarn, becomes steadily less
compressed; the yarn thus becomes gradually more open and bulky. The yarn character and quality
thus change gradually and unnoticed over a long period. The same effect is observed in spinning
synthetic fibers if the spin finish can accumulate in the rotor.

27
▪ Clean raw material is a precondition for spinning yarn on the rotor spinning machine.
Rieter Ingolstadt recommends that the following residual trash content should not be
exceeded in the feed sliver:

Yarn count (Ne) Residual trash content in the feed sliver

up to Ne 6 0.3 %
up to Ne 20 0.2 %
up to Ne 30 0.1 5%
above Ne 30 0.1 %

▪ These requirements imply that the “cleanest possible” cotton should be sought out at the
purchasing stage and good preparation equipment, giving a high cleaning and dust
removal effect, is of great benefit for the rotor spinning process. In addition, several
machine manufacturers have fitted their machines with trash-removal devices.

28
Disturbing materials in the cotton:
▪ In addition to trash, dust and vegetable residues, cottons are unfortunately being
contaminated increasingly with other impurities, which in some cases can cause significant
processing or quality problems.
1. Organic and inorganic impurities
2. Yarn remnants
3. Quartz sand and mineral dust
4. Honeydew
Processing problems with man-made fibers
▪ In the case of man-made fibers (MMF), attention must be paid during processing in the
spinning mill not only to the coarse fibers, but especially to the spin finish and the titanium
dioxide used as a delustring agent on some types of fiber.
1. Spin finish (MMF)
2. Delustrants (MMF)

29
Disturbing materials in the cotton:
1. Organic and inorganic impurities:
▪ On the one hand, these are residues of cotton packaging (jute, polypropylene, etc.) that get into the
fiber material due to careless removal during bale feeding. However, more and more impurities, e.g.
remains of plastic sacks and other refuse, are already getting into the fibrous material during
harvesting in the cotton fields.
▪ These impurities and packaging residues are reduced in size by the various opening units in the blow
room and carding room to such an extent that it may no longer be possible to remove them. These
impurities either result in ends down on the spinning machine, which is the lesser evil, or they are
spun into the yarn, with much more serious consequences. Extraneous fibers (e.g. jute in the case of
cotton) usually display a different dyeing behavior from the original fibers. However, since the
extraneous fibers are also usually distributed over long lengths of yarn, this leads to a drastic
reduction in the value of the fabric produced.
▪ Increasing numbers of monitoring systems are therefore being used on rotor spinning machines to
detect and eliminate these impurities.

30
Disturbing materials in the cotton:
2. Yarn remnants:
▪ Recycled weaves, knits or fiber residues are processed on rotor spinning machines, since they
are especially suitable for this application.
▪ The crucial precondition for successful spinning of these very low-cost raw materials is the
opening of the materials used down to the individual fibers.
▪ Disintegration takes place in principle in several stages, starting with cutting up and then
tearing up the fabric or yarn residues down to the individual fibers. If the necessary care is not
devoted to this process, even the smallest remnants of fabric or yarn result in ends down if they
reach the rotor.
▪ In the case of very coarse yarns the remnants of fabric or yarn may not cause ends down but be
incorporated in the yarn and then inevitably appear as a thick place in the yarn.

31
Disturbing materials in the cotton:
3. Quartz sand and mineral dust:
▪ Quartz sand and mineral dust are present mainly in cotton from the latitudes of the desert regions (e.g.
West Texas cotton). They exert an abrasive effect, like sandpaper, and cause rapid wear on spinning
elements, such as opening rollers, rotors, and navels. If mineral dust is present, this effect is
reinforced.
4. Honeydew:
▪ Honeydew forms tenaciously adhering sticky deposits on spinning elements and thus makes spinning
more difficult while causing deterioration in yarn characteristics and an increase in ends down.
▪ However, if the use of cottons contaminated in this way is unavoidable, the speed of the spinning
machines must be reduced, and the room climate adjusted accordingly. In particular, relative humidity
should not exceed 45 to 50 % RH in order to limit the formation of sticky deposits on thread guiding
components.
▪ It is also necessary to clean all thread guiding components thoroughly after the passage of the
contaminated cotton (wash)! Wherever possible, the use of cottons containing honeydew should
therefore be avoided.

32
Processing problems with man-made fibers:
1. Spin finish (MMF):
▪ Quality and quantity of the spin finish of MMF are of considerable importance for spinning performance, shedding
and yarn quality. This also is one of the main reasons for speed limitations in high-speed rotor spinning. Rotor
spinning needs fibers with less finish application compared to ring-spun types.
▪ While the amount of spin finish for ring- spun yarn varies between 0.18% and 0.20%, fibers suitable for rotor
spinning require only 0.12% to 0.14%. Finish application above that level or insufficient adhesion may result in
troublesome deposits at the spinning elements and these in turn may cause ends down.

2. Delustrants (MMF):
▪ If luster and smoothness of MMF are to be suppressed in round fibers, this can only be done chemically. Titanium
dioxide (TiO2) is used for this purpose. However, this delustring agent is extremely aggressive, similar to mineral
dust, and results in premature wear of all fiber guiding components on the machine, and in particular the spinning
elements on final spinning machines (rotor, ring, Air-jet).
▪ While delustred fibers (titanium dioxide content ≥ 0.4%) should not be processed in principle, partially delustred
fibers with a titanium dioxide content ≤ 0.15% can be used in blends with natural and/or man-made fibers which
have not been delustred.

33
The processing stages:
1. Blow room:
▪ Since rotor spinning reacts less critically to short fibers than ring or Air-jet spinning, the main
task of blow room machinery is the efficient removal of trash and dust. The blow room line can
therefore be kept very short but calls for very effective cleaning and opening units.
2. Cards:
▪ The card usually has to reduce the dirt content to less than 0.1 - 0.2% and also to remove part of
the dust. The card is already capable of removing dust adhering to the fibers because significant
fiber/metal friction arises here, and the dust is rubbed off. The blow room, carding room and
draw frames are each expected to remove about one-third of the dust. Web crushing at the
delivery of the card often brings about a significant improvement in the cleaning effect for
cotton with medium to high dirt content.
▪ When the carded sliver is processed directly on the rotor spinning machine the card must be
equipped with a leveling device or a card with a draw frame module used.

34
The processing stages:
3. Draw frames:
▪ The draw frame is of crucial importance for the quality of the yarn and thus ultimately also for the quality of woven
and knitted fabrics. Defects which are not leveled out on the draw frame reappear undiminished in the yarn.
▪ An essential task of modern draw frames is to deliver defect-free draw frame slivers of maximum regularity to the
rotor spinning machine.
▪ Modern high-performance draw frames are currently equipped with highly efficient extraction systems which
reliable remove a substantial proportion of the dust still present in the fiber material. Dust, fiber fragments and
trash are effectively separated from the fibers by fiber/fiber friction during the drafting process in the draw frame
and can thus very easily be removed by the extraction system.
▪ In contrast to ring spinning, where in principle 2 draw frame passages, when processing blends even 3 draw frame
passages are used, rotor spinning operates with one or no more than two draw frame passages (even with blends).
▪ In rotor spinning the effect of fiber hooks is of secondary importance on the one hand, and additional blending
takes place in the rotor due to back-doubling on the other. Only 2 draw frame passages are therefore used, even
when manufacturing blended yarns, without loss of quality. Directly leveled carded sliver can also be fed to the
rotor spinning machine in certain applications.

35
The processing stages:

Rotor spinning systems with different sliver preparation depending on yarn quality requirements
36
The processing stages:
Two draw frame passages (leveling in the 2nd passage):
▪ for rotor-spun yarns in the fine count range (finer than Ne 20) and high demands on yarn count
constancy (e.g., for single jersey); the 2nd passage also serves for additional de-dusting;
▪ for rotor-spun blends with draw frame sliver and stock blending in the medium and fine count range;

▪ for rotor-spun denim yarns (branded goods) with high standards in terms of tenacity, elongation a nd
yarn purity.
One draw frame passage (with leveling):
▪ for rotor-spun yarns in the medium and coarse count range without very high demands on yarn
quality;
▪ for rotor-spun denim yarns (low-price products) without particular quality specifications by garment
manufacturers;
▪ for rotor-spun yarns with a high short-fiber content, where a second draw frame passage can even
result in a deterioration in sliver regularity;

37
The processing stages:
Direct processing of carded sliver (leveled card):
▪ for rotor-spun yarns in the count range coarser than Ne 12 without particular demands on yarn
quality;
▪ for rotor-spun yarns with a very high short-fiber content (e.g., cotton waste, recycled weaves or
knits).

Special case: card with draw frame module (with leveling):

▪ Range of application as for one draw frame passage with leveling. Exception: combed rotor-
spun or ring- spun yarns, since doubling cannot be dispensed with in this application.

38
The processing stages:
Combing:
▪ Although the processing of combed cotton on rotor spinning machines has not yet become
widely established to date, the results which can be achieved are noteworthy. Since the
advantages for rotor spinning lie mainly in the elimination of seed trash, fiber neps and seed
coats which interfere with the spinning process, and the short fiber content does not necessarily
have to be reduced, noil extraction rates of between 10 and 14% are adequate to ensure the
desired residual trash content of ≤ 0.04% for fine count yarns. The upgrading of available and
affordable cotton by means of combing has the basic advantage that, independently of
harvesting methods, environmental and ambient influences, the cotton properties (trash content,
short fiber content) can be adapted selectively and reproducibly to the spinning conditions.
▪ Processing combed slivers not only improves the machine ‘s running behavior (fewer stoppages
and higher efficiency), but also the quality of the yarn and the end product, as well as
downstream processing properties.

39
▪ The carded or drawn sliver being fed in is guided through sliver funnel and fed
between the feed shaft and spring-loaded feed table to the rotating opening roller.
Each spinning position is equipped with this combined feed shaft / feed table.
▪ The drive of the feed shaft for each spinning position is provided by a centrally driven,
rotating worm shaft. In the event of an end down or a switched-off spinning position the
feed shaft is disconnected from the worm shaft by an electromagnetic clutch and sliver
intake is stopped.
▪ However, the clutch wheel of the feed shaft remains engaged with the worm shaft even
if the spinning box cover is opened. This prevents damage to the clutch wheel when the
rotor cover is closed, which can occur in systems where the drive shaft and feed shaft
are disconnected when the cover is opened.
▪ Centralized setting of draft and delivery speed automatically determines the speed of
the feed shaft and thus the intake speed of the carded or drawn sliver.

40
▪ The opening point at the spinning box is comparable with the infeed at the
licker-in of the card. The rotating teeth of opening roller (a) pass at high
speed through the fiber beard and remove individual fibers from the sliver
clamped between feed table (b) and feed roller (c).
▪ The sliver beard in this case is being moved slowly forward by the feed roller.
By means of this continuous operation, the opening roller carries along by
friction all fibers emerging from the clamping point between the feed roller
and feed table. A fixed fiber beard support (d) provides uniform combing
even in the event of mass deviations in the sliver.
▪ After leaving the rotating opening roller, the fibers are transported to the
fiber channel. It is important to ensure that the speed of the air and fiber flow
at the opening roller is greater than the peripheral velocity of the roller itself.
If the roller velocity is equal to or higher than the air-flow speed, which can
occur with very high roller speeds, this leads to fiber buckling at the liftoff
point; this in turn causes deterioration in yarn quality and running
performance.
▪ When the fibers are detached from the opening roller clothing, the trash Opening roller housing with opening
included in the fiber material is removed via an opening under opening roller roller (a), sliver intake (b+c), fiber
(e). The degree of trash removal can be adjusted via a bypass system (f). beard support (d), trash removal (e)
and adjustable bypass (f)
41
Opening Roller:
▪ The opening roller task is to open the carded or
draw frame sliver fed to the spinning box into
individual fibers and at the same time to separate
the fibers from the trash.
▪ The shape, geometry and design of the opening
roller are, alongside the rotor, of the greatest
importance for faultless spinning results.
▪ The surface of the opening roller consist either of a
solid steel ring in which the appropriate tooth
design has been machined by grinding or of a
toothed wire which has been spirally wound on a
ring or a body.

42
Opening Roller:
Opening roller clothing:
▪ Opening rollers are available for every application to match both the thermal and
physical properties of the raw materials being processed, and the yarn properties
required. Their clothing differs mainly in the following respects:
▪ the shape of the teeth and their angle of inclination, tooth height and width of the tooth point;

▪ the density of tooth points;

▪ the geometric layout of the teeth; and

▪ different coatings.

43
Opening Roller:
The service life of the opening roller clothing :
▪ The point and front edge of the clothing tooth are exposed to wear. The wear is greater,
the more aggressive the raw material used.
▪ The service life of the opening roller clothing is significantly improved if the teeth are
coated. In this case the clothing is either given a nickel coating or diamond powder
with a grain size of several microns is embedded in the nickel layer for even better
wear resistance.
▪ The service life of nickel-plated clothing is about twice that of steel clothing that has
only been hardened, while diamond/nickel-treated clothing lasts about 4 times as long.
▪ Worn opening roller clothing must be periodically replaced, depending upon the rate
of wear. If this is delayed too long, yarn quality and spinning conditions deteriorate.

44
Opening Roller:
Range of application of the opening roller:
Clothing shape and opening roller speed must be coordinated with the raw materials being processed.
Clothing differs mainly in tooth shape, the gradient of the front edge of the clothing tooth and tooth
density (pitch) relative to clothing surface area:
▪ For carded and combed cottons and viscose, clothing with a large, i.e. more aggressive front edge, higher tooth
density and sharper points (type B174) is usually used.
▪ For critical cottons, also those containing a small amount of honeydew, the use of clothing type B174 - 4.8 is
recommended, which is characterized by a modified clothing shape and wider tooth spacing (4.8 mm instead of
2.5 mm as in B174).
▪ Clothing shape S 21 is characterized mainly by a less sharply inclined and thus also less aggressive front edge,
which is suitable for gentle processing of thermally more sensitive man-made fibers, especially polyesters and
their blends.
▪ Clothing with low tooth density and low tooth height, type S 43, is used for man-made fibers with a tendency to
lap due to high metal/fiber cohesion, such as polyacrylic. Especially gentle opening is possible with this clothing
and at the same time the fibers are more readily released from the clothing.

45
Opening Roller:
Tooth shapes of the opening roller clothing and their range of application :

46
Opening Roller:
Opening roller speed:
Special attention must also be paid to the setting of the opening roller speed. The opening roller speed range is
between 6000 and 10000 rpm; speeds between 6500 and 8000 rpm are usually used. Opening roller speeds that
are either too high or too low, always relative to the specific application, can have a negative impact on yarn
formation and yarn quality. Opening roller speeds that are too low can result in:
▪ inadequate separation of the sliver into individual fibers;

▪ inadequate opening of fiber neps and fiber clumps;

▪ inadequate trash removal;

▪ tendency toward lap formation on the opening roller.

Opening roller speeds that are too high can also have a negative impact. Excessively high opening roller
speeds result in:
▪ more or less severe damage of fibers;

▪ losses in yarn tenacity and the strength of the fabrics produced from them;

▪ an increase in fiber fly on the spinning machine and in downstream processing;

▪ melting points when processing man-made fibers.

47
Opening Roller:
Opening roller ideal speed:
The ideal speed for a given raw material and a given yarn is preferably defined by a series of
trials at several opening roller speeds. The most suitable speed can be chosen on the basis of yarn
quality. A series of trials of this kind can even provide a rough idea of running behavior. The
following factors apply in principle when specifying the opening roller speed:
▪ A higher opening roller speed should be selected, the higher the material throughput per unit of
time, for example with coarse yarns and/or high delivery speeds, or the more heavily contaminated
the raw material and the more effective trash removal.
▪ The opening roller speed selected should be lower, the more sensitively the fibers react to
mechanical and thermal stress and would be damaged at excessively high speeds.
▪ Certain raw materials, especially very fine and/or very long man-made fibers or fibers with high
fiber/metal adhesion, have a tendency to lap in the opening roller clothing. In these cases
especially careful definition of the opening roller speed is required, and this can ultimately only be
specified by spinning trials.

48
Opening Roller:
Trash removal:
▪ The high peripheral speed of the opening roller results in all particles heavier than fibers (trash and other extraneous
particles) being removed outward at this opening while the fibers continue with the roller, to be passed later into the fiber
channel.
▪ The expelled waste falls onto a conveyor belt, which carries it alternately to the headstock or the tailstock. At both sides of
the machine the collected waste is removed by suction nozzles and fed by vacuum to a central filter housing. Wipers on the
conveyor belt continuously clean the housing under the opening roller.
▪ Modern spinning preparation machines with the appropriate cleaning facilities can remove most extraneous, dust and trash
particles reliably from the raw cotton. However, a certain amount of organic and inorganic extraneous matter can survive the
cleaning process in the blow room and draw frame, depending on the susceptibility to cleaning of the cotton(s) being used
and due to the picking and ginning methods.
▪ Efficient trash removal is one of the most important preconditions in the rotor spinning system for stable spinning conditions
and high yarn quality. Unfortunately, the collecting groove of the spinning rotor not only collects fibers; particles, trash, dust,
etc., also accumulate in it, changing the groove‘s geometry and thus the yarn quality, and in the worst case causing a
deterioration in spinning stability. Due to the extremely high centrifugal forces, a tiny trash particle of only 0.2 mg can exert a
force of approx. 15 g on the fiber ring and thus prevent twist propagation, which results in a thread break. This clearly
illustrates the importance of effective trash removal for the operation of the rotor spinning machine.
49
Opening Roller:
Trash removal:
▪ Trash removal in the spinning box ensures that most of the extraneous matter still in the fiber sliver and disturbing the
spinning process is eliminated. However, trash removal in the spinning box can by no means replace careful cleaning of the
cotton during spinning preparation. The lower the residual trash content in the drawn or carded sliver fed in, the more
effectively can the remaining trash and extraneous particles be reduced in the spinning box.
▪ Trash removal systems with an adjustable BYpass, which enables the cleaning effect to be adjusted individually to the raw
material being used.
▪ The BYpass permits adjustment of the air flowing into the trash removal opening depending on the raw material. The larger
the amount of air provided through the bypass, the smaller the quantity of air drawn in at the trash removal opening, and the
easier it is to separate impurities.

BYpass open BYpass half open BYpass closed

(maximum trash removal) (medium trash removal) (minimum trash removal) 50
▪ After opening, the fibers must be supplied to the rotor. For this purpose, a closed fiber channel in the
shape of a flow passage serves as a means of guidance. Centrifugal forces of the opening roller and a
vacuum in the rotor housing cause the fibers to free from the opening roller. Transport of the
disengaged fibers through the fiber channel to the rotor is effected by an air current generated by
suction of air from the hermetically sealed rotor housing.
▪ The partial spinning vacuum on spinning systems with perforated rotors is generated by the rotors and
thus depends on rotor size and rotor speed. The partial spinning vacuum therefore declines as rotor
diameters become smaller or if dirt (trash, dust, fiber fragments) accumulates in the openings in the
base of the rotor.
▪ The shape of the fiber guide channel is crucial for fiber transport and the desired longitudinal
orientation of the fibers. The inlet and outlet openings of the fiber guide channel must be designed
and produced so that the transfer of fibers from the opening roller, fiber transport in the guide channel
itself and the transfer of fibers to the inside wall of the spinning rotor are trouble free. The fiber
channel narrows toward the rotor, which causes acceleration of the air and fiber flows. This
acceleration is of great significance because it leads to further separation of the fibers, down to
between one and five fibers in section, and straightens the fibers.

51
▪ The rotor is the main spinning element of the rotor spinning machine. The rotors, acting as fiber collecting
and at the same time twist inserting elements, are the most important and the most complex components in
yarn formation. Yarn quality, yarn character, operating performance, productivity, etc., all depend chiefly on
the rotor.

Structure and components of a spinning rotor:

▪ The rotor consists of

▪ rotor shaft (a)

▪ rotor cup (b)

▪ rotor groove (C)

▪ rotor wall (d)

▪ Rotors are made of steel. surface-treated or coated to give

them a longer useful life.
▪ diamond/nickel coating;

▪ boron treatment; or

▪ a combination of both processes.

52
Important rotor parameters:
▪ The most important parameters of the rotor that exert
influence are:
▪ the inclination of the rotor wall (a);

▪ the coefficient of friction between the fibers and the

surface conditions of the rotor wall (b);
▪ the design and the positioning of the rotor groove (c);

▪ rotor groove diameter (d)

▪ rotor speed.

▪ The rotor wall inclination is necessary so that fibers emerging from the feed tube and passing to
the wall can slide downward. Depending upon the material and area of use, the angle of the rotor
wall to the vertical ranges between 12° and 50°

53
Rotor groove:
▪ The configuration of the rotor groove determines whether the yarn is bulky or compact,
hairy, or lean, and whether the yarn quality is excellent or only adequate and the spinning
stability low or high. The groove also affects the extent to which dust and dirt tend to
accumulate in the rotor. Depending upon the raw material used, the desired yarn
characteristics and yarn values, different groove designs are used in practice.
▪ Wide grooves produce a soft, bulky yarn with rather low strength, while narrow grooves produce a
compact, strong yarn with low hairiness.
▪ Wide grooves are therefore used in the production of yarns for knitted fabrics, homespun type
fabrics and coarse articles;
▪ Narrow grooves are used for yarns required to produce stronger fabrics with a smooth appearance.

▪ A narrow groove is in most widespread use in classical short staple mills. The tendency to form
moiré effects is also greater with the narrower groove, because large dirt particles can jam in the
groove.

54
Configuration and properties of available rotor/groove shapes:

55
Configuration and properties of available rotor/groove shapes:
▪ Narrow groove angles and small groove radius (T and K rotors) are suitable for all raw materials and
are used to manufacture smooth weaving yarns with good regularity and high yarn tenacity.
▪ Narrow groove angles with large groove radius (G rotors) are also suitable for all raw materials and are
preferably used for bulky knitting yarns.
▪ Rotors with wide groove angles (U and DS rotors) are suitable for bulky knitting and denim yarns in
cotton and its blends with man-made fibers. The different groove shapes and groove radii are chosen
according to the type of denim yarn (weft or warp yarn, rope or beam dyeing, etc.).
▪ The TC rotor is outstandingly suitable for manufacturing high quality denim yarns and at the same
time is characterized by excellent running properties. Compared to the T rotor, groove angle and
groove radius are larger, but the groove shape has been retained. Especially shifting-resistant yarns
are produced when processing man-made fibers and viscose with the TC rotor.
▪ The GM rotor can be used very flexibly in the fine count cotton yarn sector, for both weaving and
knitting. Compared to the G rotor, groove angle and groove radius are larger, but the groove shape has
been retained.

56
Rotor speed and Rotor diameter :
▪ Rotor speeds have been increased from approx. 30 000 rpm originally to 160 000 rpm today. This has only
been possible by simultaneously reducing rotor diameter. The smaller the rotor diameter, the higher the
number of system related wrapper fibers.
▪ The rotor diameter should in any event be large enough to permit fiber formation in the groove without
technological disadvantages. A certain amount of space is needed for the fiber mass, i.e., larger rotor
diameters have to be used for coarser yarns and vice versa. Rotor diameter should not exceed 1.2 times
staple length, otherwise fiber integration in the rotor groove is disturbed. In mill operations staple lengths of
38 or 40 mm are also spun successfully on rotors in the 30 - 32 mm range.

Speed range and maximum rotor speed as a function of rotor diameter 57

Rotor bearing and drive:
▪ Nowadays, the rotors on all rotor spinning machines are driven using the friction drive
principle, i.e. by a tangential belt in contact with the rotor shafts on each side of the
machine. Other systems, such as driving the rotors by individual motors.
▪ Direct rotor bearing, in which tangentially driven
rotor shaft (a) is encased in ball bearing housing (b).
The ball bearing rotates at the same speed (rpm) as
the rotor shaft driven by the tangential belt. This
bearing principle limits rotor speeds to approx. 110000
rpm. Although direct bearings would be ideal,
individual motors have also been unable to establish
themselves for this rotor drive, on cost grounds.
Direct rotor bearing, with rotor shaft (a)
encased in ball bearing housing (b)
58
Rotor bearing and drive:
▪ Indirect rotor bearing, in which the rotor shaft, also driven tangentially, runs on two pairs of supporting discs
arranged side by side. With the support disc bearing the rotor speed is reduced at a ratio of 1:8 to 1:10 relative
to the bearing of the supporting discs, depending on the diameter of the discs, so that these bearings run at
speeds of only 16000 to a maximum of 20000 rpm (depending on the diameter of the supporting discs), even
at rotor speeds of 160000 rpm. For one thing, this bearing system permits much higher rotor speeds than
direct bearings, and at the same time the service life of indirect bearing systems is significantly higher than
that of directly driven bearing systems. High performance rotor spinning machines operating at speeds of up
to 160 000 rpm are therefore operated only with indirect rotor bearing.

Support-disc bearing (Twindisc bearing) with pressure roller (b) for tangential belt (a)
59
Various rotor bearing systems:
▪ The tangential arrangement of the rotors is important for the rotor drive, the axial positioning
of the rotor is the prerequisite for fiber feed to the rotor and thread take-off from the rotor.
Whereas both the tangential and the axial position of the rotor are defined by the fixed ball
bearing housing in the case of direct rotor drive, the rotor on support disc bearings also has
to be fixed in position in the axial direction. The rotor is fixed in position axially by slightly
crossing the pair of supporting discs, so that the rotor is pressed backward with some force
(toward the spinning beam). Various bearing systems are available for absorbing this
backward axial pressure:
1. Steel ball or hybrid bearings
2. Magnetic bearings
3. EC bearings
4. AERO bearings

60
Various rotor bearing systems:
Steel ball or hybrid bearings:
▪ The axial thrust of the rotor is absorbed by a steel ball rotating in an oil bath. The front
of the rotor shaft and the steel ball are subject to severe wear due to mechanical friction,
despite oil lubrication.
▪ In more modern bearing systems, the front of the rotor shaft is therefore ceramic coated.
This axial bearing system has been used by almost all machinery manufacturers in
recent decades.
▪ However, the fundamental drawbacks of this system high spare parts consumption, a
high level of cleaning and maintenance effort and severe soiling due to sticky deposits
in the axial bearing zone have encouraged the development of modern bearing
systems which are now used at least on high performance rotor spinning machines

61
Various rotor bearing systems:
Magnetic bearings :
▪ The end of the rotor shaft is fixed in position without contact in a magnetic field created by annular
magnets. Accurate radial positioning of the rotor shaft is the precondition for the functioning of this
system, which as far as is known to date has no speed limitations.

Axial rotor bearing with magnetic bearing Positioning the magnetic bearing
62
Various rotor bearing systems:
EC bearings :
▪ The end of the rotor shaft runs (in contrast to the oil bearing) on a steel ball embedded in grease. The
housing is sealed, grease can- not escape, and the bearing is largely maintenance free.

Axial rotor bearing with EC bearing Sealed grease cup of the EC bearing

63
Various rotor bearing systems:
AERO bearings :
▪ In this bearing system an air cushion provides axial support for the rotor. This air cushion is provided
by a compressed air supply of 6 bar to each spinning position. This system requires neither oil nor
grease, sticky deposits are avoided, and in the immediate vicinity of the air cushion the permanent
current of air ensures continuous cleaning (self-cleaning effect). Other advantages of this system are
low maintenance effort and spare parts consumption. The accurate, level surface of the end of the rotor
shaft is the precondition for trouble free operation.

Axial rotor bearing with AERObearing Airflow with the AERObearing; air pressure 6 bar
64
Rotor cleaning:
▪ An essential element of a functioning spinning unit is automatic rotor cleaning capability. This is one of
the major advantages of the rotor spinning system compared with other spinning processes, which are
unable to clean the raw material fed in again at the spinning position itself.
▪ Light trash particles and dust can reach the rotor in the air required for fiber transport and be
deposited together with the fibers in the fiber collecting groove of the rotor. These deposits can either
interfere with twist integration in the rotor groove to such an extent that thread breaks occur, or the
deposits continue to accumulate in the rotor groove without provoking thread breaks, but continuously
changing the groove geometry. This in turn results in a creeping change in yarn quality. Deposits in the
rotor groove which are not distributed uniformly over the rotor circumference, but occur at certain
points, result in periodic yarn defects known as moiré effect.
▪ In mill operations, rotor cleaning is performed automatically at each piecing operation at the spinning
position, i.e. at each end down, each quality stop and each package change.
▪ Two systems are used to clean the rotors:
▪ Pneumatic cleaning by means of compressed air

▪ Mechanical cleaning by means of scrapers.

65
Rotor cleaning:

66
▪ The rotors, acting as fiber collecting and at the same time twist
inserting elements, are the most important and the most complex
components in yarn formation. Transfer of the fibers fed from the
fiber guide channel into the rotor groove occurs via another
intermediate stage, the rotor wall.
▪ The peripheral speed of the inside wall of the rotor must be
significantly higher than the speed at which the fibers are
transferred to the rotor wall. This difference in speed ensures that
the fibers encountering the inside wall of the rotor are accelerated
to many times their transport speed.
▪ The fibers are transferred neatly, arranged in the longitudinal
direction, from the rotor wall to the rotor groove by the increasing
centrifugal force of the widening inside diameter of the rotor in the
direction of the rotor groove.
▪ The difference in speed between the fibers and the inside wall of
the rotor also ensures that the fibers are extended in the longitudinal Tangential fiber feed into the rotor and fiber
direction when they encounter the rotor wall, which in turn promotes transport to the fiber collecting groove of the rotor
the (desired) parallel arrangement of the fibers in the rotor groove.

67
Back doubling:
▪ The process of yarn formation in rotor spinning involves the separation by an opening roller of a fiber
bundle fed in into individual fibers or small groups of fibers (no more than 5 fibers), which are then
transported by the air current into the rotor, where they slide down the rotor wall.
▪ They are only combined again into fine layers of fibers in the rotor groove. A layer of these individual
fibers is deposited in the rotor groove with each revolution of the rotor until the yarn reaches the
required thickness.
▪ This buildup of fiber layers to the final yarn thickness is described as back-doubling, with the number
of fiber layers resulting from the (genuine) yarn twist set and the diameter/circumference of the rotor
used.
▪ Customary values are in the range of 60 – 90-fold back-doubling. Doubling of linear fiber formations
always improves the regularity of the resulting new product, an effect that is, of course, consciously
exploited in draw frames.
▪ The numbers of back-doubled fiber layers is calculated as follows:
𝑅𝑜𝑡𝑜𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑚𝑚 ∗ 𝑇𝑤𝑖𝑠𝑡 𝑝𝑒𝑟 𝑚𝑒𝑡𝑒𝑟 ∗ 𝜋
𝐵𝑎𝑐𝑘 𝐷𝑜𝑢𝑏𝑙𝑖𝑛𝑔 =
1000

68
▪ The collecting groove of the rotor combines the
fibers delivered to it into a ring of fibers which
changes into the twisted thread at the integration
point, while the integration point moves forward
relative to the rotor collecting groove at yarn
take-off speed.
▪ The integration point starts immediately after the
point at which the yarn is lifted out of the rotor
groove. The fiber ring formed in the rotor
consists of individual layers of fiber.
▪ When the required yarn thickness formed from
the individual fiber layers has been reached, the
Yarn formation and twist insertion in the rotor groove
yarn is withdrawn from the rotor groove.

69
▪ In the rotor spinning process fibers are continuously fed into the rotor
groove and the yarn is also continuously withdrawn from the rotor
groove. The fibers laid parallel and untwisted in the fiber collecting
groove of the rotor are given the necessary twist via the finished yarn
being withdrawn from the rotor.
▪ A finished end of yarn must therefore be fed into the rotor in the
opposite direction to yarn take-off at the start of the spinning process.
The yarn end is also twisted by the rotating rotor.
▪ The yarn end is pressed into the rotor groove by the rotor ‘s centrifugal
force and is thus connected to the fiber ring fed into the rotor groove.
▪ The yarn twist penetrates the fiber ring in the collecting groove, where
the fibers are to be bound together to form a yarn. Each revolution of
the yarn inserts one turn of twist.
▪ The exact twist formula for the yarn would thus have to be represented
Inserting twist in the rotor groove
as follows:
𝑟𝑜𝑡𝑜𝑟 𝑠𝑝𝑒𝑒𝑑 (𝑟𝑝𝑚)
Number of yarn turns per meter (T/m) =
𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑦 𝑠𝑝𝑒𝑒𝑑(𝑚/𝑚𝑖𝑛)

70
▪ Rotor spinning is an open-end process which generates a genuine yarn twist. In this case the component
imparting the twist is the rotor, which twists the thread around its axis. The resulting yarn twist is the decisive
factor for yarn tenacity. However, to maintain the spinning process, i.e. integrate the fibers in the rotor groove,
a spinning twist is required, which as a rule must be higher than the yarn twist required for yarn tenacity.
▪ This means that an additional twist must be imparted to the radial section of yarn (imparting false twist). This
false twist is imparted by the unrolling motion of the yarn on the draw-off nozzle, which is therefore much more
than a thread guide.
▪ Depending on spinning conditions, the false twist can be up to 60 % of the set yarn twist. The false twist effect
generated between the draw-off nozzle and the yarn unrolling from it has Z twist between the draw-off nozzle
and the rotor groove and S twist between the draw-off nozzle and the nip of the take-off shaft and the pressure
roller.
▪ At this nip the false twist effect has again reached its zero point and the yarn body has only the preset genuine
Z twist. The false-twisting effect of the draw-off nozzle can be increased by inserting a twist accumulating
element in the draw-off tube immediately following the draw-off nozzle.
▪ All rotor spinning machines are designed to spin yarns with Z twist. Z twist is the customary direction of twist
used in practice. Manufacturing yarns with S twist would imply redesigning the rotor drive, sliver feed into the
spinning box and fiber feed to the rotor.

71
▪ Genuine twist that is retained in the yarn is generated
when a length of yarn is clamped at one end and rotated
around its axis by a twisting element at the other end.
▪ Transferred to the spinning box of a rotor spinning
machine, this means that the yarn is clamped by the take-
off rollers and twist is imparted by the rotating rotor.
▪ One revolution of the rotor corresponds to one turn of the
yarn.
▪ The genuine twist therefore corresponds to the required
twist set.
▪ The number of required turns imparted to a yarn depends
on how long the length of thread remains in the rotor; the
longer this time, the higher the number of turns. Imparting twist to the yarn:
genuine twist in the Z direction

72
▪ A nip and a twisting element are also required to generate false twist, but an additional
passive or active twist element is also required. If additional turns, i.e. false twist, are
imparted to the yarn by this twist element, these are distributed to the left and right of
the twist element in mutually opposing directions of twist.
▪ When the yarn leaves the nip the length of yarn twists back into its original form by
exactly the number of additionally inserted turns. This is precisely what happens in
our rotor.
▪ The take-off rollers form the nip and the centrifugal force in the rotor groove acts as
the twist-generating element; these two forces act in opposition to one another. The
passive twist element in this case is the draw-off nozzle.
▪ The yarn is pressed onto the nozzle surface during take-off by the contrary tensile
forces and unwinds on this surface.
▪ A certain number of additional turns ‘the false twist’ are imparted to the yarn while it
unwinds on the nozzle surface.
▪ The false twist effect created between the draw-off nozzle and the yarn unwinding on it
has Z twist between the draw-off nozzle and the rotor groove, and S twist between the
draw-off nozzle and the nip of the take-off rollers.
▪ The higher the friction on the nozzle surface, the higher the number of additional, Imparting twist to the yarn:
reversible yarn turns inserted. additional twist due to the false
twist effect in the S and Z
direction
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▪ When it is removed from the rotor, the yarn is diverted virtually at right
angles by the draw-off nozzle protruding into the rotor and guided out
by the draw-off tube immediately following it.
▪ Meanwhile the yarn rolls continuously on the surface of the draw-off
nozzle. During the rolling motion the yarn is repeatedly raised briefly
in rapid succession from the nozzle surface due to the design of the
draw-off nozzle surface.
▪ This high frequency vibration together with the false-twist effect
created by the unwinding motion promotes twist propagation into the
rotor groove.
▪ The greater the false-twist effect and the more intensive the creation of
twist in the rotor groove, the lower the genuine yarn twist that can be
selected and the bulkier and softer the yarns that can be spun. Draw-off nozzles with ceramic
nozzle head and metal nozzle
▪ Spinning stability also improves with the increasing false-twist effect, of holder
course.

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Types:
▪ Draw-off nozzles are made of either ceramics or steel.
▪ Draw- off nozzles usually consist of two parts, a wear resistant ceramic nozzle head and a metal nozzle holder.
▪ Solid ceramic draw-off nozzles feature very low heat dissipation and can therefore hardly be considered for
processing man- made fibers.
▪ Metal draw-off nozzles feature excellent heat dissipation, would therefore also be ideally suitable for
processing man-made fibers, but due to short service lives are only used in certain cases for processing very
temperature sensitive man-made fibers, i.e. fibers with very low melt and softening point.
▪ The use of appropriate types of ceramic and the combination of ceramic head and metal holder create
conditions regarding heat dissipation that enable most common man-made fibers and their blends to be
processed successfully.
▪ The service life of ceramic nozzles can be several years, depending on raw material and material throughput.
▪ The service life of a ceramic nozzle is between 10000 hours (PES, CV, PAN) and 20000 hours (CO).
▪ Service lives with blends of cotton and man-made fibers are about in the middle of these ranges.
▪ The structure and design of the nozzle surface exert a decisive influence on surface structure and hairiness.

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Surface designs:
1. Nozzles with a smooth surface are suitable for producing
smooth warp yarns with low hairiness. This type of nozzle is
rarely used, since very high yarn twist has to be imparted due
to the low level of false twist created. Yarn values are not better
than with other nozzle types in every case. The use of a TWIST Smooth ceramic nozzle

stop draw-off tube is recommended for stable running

conditions.
2. Nozzles with a spiral surface are ideally suit- able for compact
and fine warp yarns in 100 % cotton with low hairiness and
good yarn values. High spinning stability.
Spiral nozzle

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Surface designs:
3. Nozzles with 3, 4, 6, 8 or more notches are universally applicable both for
cotton and also for man-made fibers and their blends. The nozzle with 4
mostly short notches is the universal nozzle with the widest range of
application: suitable for both warp and weft yarns (e.g. 4 notches) or
knitting yarns (4 - 8 notches, depending on the required hairiness).
Ceramic nozzles with 3, 4
Notched nozzles usually offer high spinning stability, the more notches, the and 8 notches
higher the false-twist effect and the higher the spinning stability but the
higher also the yarn hairiness and the tendency to generate fly in
downstream processing. Furthermore, the higher the number of notches,
the more aggressive their effect and the greater their influence on yarn
quality.
4. Externally knurled draw-off nozzles with additional notches in the nozzle
radius and an eddy insert in the nozzle throat are recommended solely for
manufacturing extremely hairy, very bulky, soft-twist yarns. „Yarn quality“
corresponds to the yarn structure.
Ceramic nozzle knurled
with additional notches

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Surface designs:
5. Nozzle surfaces with a small nozzle radius and 4
short notches feature a smaller contact surface
compared with the standard nozzle radius and are Ceramic draw-off nozzles
therefore especially suitable for processing PES Ceramic nozzle with small with normal radius (left)
nozzle radius and 3 notches and small radius (right)
and its blends at speeds up to over 100 000 rpm.
Rotor speeds are therefore up to 15 % higher than
those for other draw-off nozzles.
6. Spiral or notched nozzle surfaces combined with
an eddy insert in the nozzle throat are used solely
but very successfully for very hairy, bulky, and
very soft twist knitting yarns. The nozzles also offer
very good spinning stability. However, yarn quality
Eddy insert in nozzle throat (right)
is not priority with these nozzles.

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▪ The draw-off tube is positioned immediately behind the draw-off nozzle and is used to
guide the yarn on its removal from the spinning box. To divert the yarn being withdrawn
horizontally from the rotor to the take-up unit positioned vertically above it, the draw-off
tube is bent at an angle of between 30° and 60°, depending on the type of spinning box.
▪ This diversion zone in the draw-off tube acts as a second twist accumulation element and
supports the twist retention generated by the draw-off nozzle in the rotor. The greater the
angle of the bend, i.e. the angle of wrap of this diversion zone, the greater the twist
retention and the higher the spinning stability.
▪ This twist accumulation effect can be reinforced by fitting ceramic twist retention
elements of differing intensity on the contact surface in the radius of the bend.
▪ The greater the angle of diversion and the higher the friction caused by the additional
ceramic inserts, the greater the twist retention, the more intensive the twist propagation
into the rotor groove and the higher the spinning stability.
▪ This favors the manufacture of especially soft-twisted knitting yarns, since the high twist
retention enables low twist multiplyers to be set without adversely affecting spinning Thread draw-off tube (a) with
stability. interchangeable twist retention
element (b)
▪ The best spinning results as regards yarn quality, yarn structure and spinning stability
are always achieved when the draw-off nozzle and draw-off tube are ideally coordinated
with each other.

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▪ The yarn is taken from the rotor by the delivery shaft and
pressure roller, diverted virtually at right angles in the
process by draw-off nozzle (b) projecting into the rotor and
guided out by draw-off tube (c) immediately following this.
▪ At take-off the yarn continuously rolls off on the surface of
the draw-off nozzle due to the rotation of the rotor.
▪ This rolling-off temporarily inserts additional twist into the
yarn thus creating the false-twist effect required for
spinning stability, which can be up to 60 % of the set yarn
Yarn take-off with take-off rollers (a),
twist. draw-off nozzle (b) and yarn draw-off
tube (c)
▪ The greater the false-twist effect, the higher the spinning
tension.

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▪ A yarn‘s count is the product of the degree of draft applied to a
carded or draw frame sliver. This draft occurs on the rotor spinning
machine between the feed roller (for sliver in- take) and the delivery
roller (for the yarn), and results from the speed ratio of the two drives.
▪ The draft can therefore be changed by altering either the sliver
intake speed or the yarn take-off speed.
▪ However, since the take-off speed, i.e. delivery speed, is directly
responsible for imparting twist to the yarn, and therefore must not be
changed, the degree of draft can therefore only be changed by
adjusting the sliver intake speed.
▪ The drafts used in mill practice are between 60 and 400- fold.

▪ The drafting range of up to 400-fold on the rotor spinning machine Maximum flexibility with drafts of up to
400-fold
enables normal draw frame slivers in the range between 5 and 6 ktex
(Ne 0.12 to 0.10) to be fed in, even when producing very fine rotor-
spun yarns.

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In contrast to ring spinning, twisting during rotor spinning takes place from the inside
outwards.
Higher twist multiplyers are used,
▪ to increase yarn tenacity and yarn elongation;

▪ to produce lean yarns with low hairiness;

▪ to improve spinning stability;

▪ to obtain a clean-cut fabric appearance; and

▪ to improve the shifting resistance of the yarns.

Lower twist multiplyers are selected,

▪ presupposing adequate yarn tenacity,

▪ to achieve a soft hand in the final fabric;

▪ to produce bulky and more hairy yarns;

▪ to reduce a yarn‘s tendency to snarl; and

▪ increase output with the same rotor speed.

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▪ The rotor, and hence the fiber ring, revolve continuously under the stationary fiber
channel – as also does the spun yarn in the binding-in zone.
▪ A stream of individual fibers flows from the fiber channel and is deposited in the groove.
Normally, incoming fibers land on fibers that have not yet been twisted in, but in the
binding-in zone they strike an already-twisted yarn section rotating around its own axis.
▪ It cannot always be avoided that fibers arriving here wrap themselves around the yarn
core (so-called wrapper fibers).
▪ This is a typical characteristic, and simultaneously an identifying Feature of rotor-spun
yarns.
▪ The number of wrapper Fibers increases, among other things, the longer the binding-in
zone, the shorter the fibers relative to the rotor circumference and the higher the rotor
speed.

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▪ Rotor spinning machines produce packages ready for sale, which can be used
immediately in downstream processing without any detour via the winder.
▪ Waxing devices and quality monitoring sensors at each spinning position and
cylindrical package formats from ensure that the most suitable cross-wound packages
can be provided for any stage of downstream processing – knitting, weaving, yarn
dyeing or doubling.
▪ Almost all rotor spinning machines nowadays produce packages with a traverse of 150
mm (6˝), which results in the following package formats, depending on the winding unit
of the different types of machine:
▪ Cylindrical packages: max. diameter 350 mm; max. package weight up to 6 kg;

▪ Conical packages: max. diameter 280mm; package weight depends on package density.

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Rotor spinning machine cross-wound packages compared with those
from the winder:
▪ The number of piecings in the rotor spinning package is only 2-3% of the number in the
winder package.
▪ In rotor spinning, a continuously spun yarn is wound, whereas the winder package is
made up of yarn from small cops with a mass of 60-120 g, joined together by
corresponding splices;
▪ In rotor spinning, winding is carried out at speeds of up to 350 m/min, as compared with
1400 m/min in the winder; this gives a better package build, and the yarn lengths on the
individual packages can be kept more uniform;

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Requirements must be fulfilled by packages of yarn from modem rotor
spinning machines:
▪ Package density as uniform as possible from one package to another;
▪ The same yarn length on all packages; this will be achieved exactly with individual length-
measuring devices;
▪ Adaptable winding density attainable by means of adjustable yarn tension and above all by
a variable angle of intersection of the windings in the package;
▪ Packages free of patterning zones;
▪ Yarn waxing where necessary;
▪ Formation of an accessible yarn reserve on the tube so that, during unwinding, the thread
end can be knotted to the start of the yarn on the next package to be unwound before the
package runs out; this enables stoppages to be avoided at package change in further
processing.

86
Anti-patterning device:
▪ Normally, the yarn windings are distributed irregularly over the
whole surface of the package. However, it can happen that the turns
of a new layer are deposited exactly on top of the turns of the
preceding layer, and this process repeats itself for several
successive layers (turn on turn on turn, etc.).
▪ This generates uniformly intersecting ridges, so called pattern
windings or pattern zones. They reduce the take-up capacity of the
package and make unwinding difficult and are therefore to be
avoided at all costs.
▪ An anti-patterning device minimizes pattern winding (frequent
parallel layers) on the package.
▪ The anti-patterning device continuously varies the motion speed of
Variable stroke displacement
the traverse gear. Thus, the winding helix is changed continuously,
preventing the build-up of patterns to a large extent.

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Machine automation in rotor spinning:
▪ automatic gripping and introduction of the sliver end from a new can into the spinning
box (implemented only in certain cases to date);
▪ automatic cleaning of rotor, draw-off nozzle and draw-off tube after ends down, quality
stops or package changes;
▪ automatic piecing (start-up) after ends down, quality stops or package changes;
▪ automatic removal of full packages upon reaching the preset yarn length, and
replacement with empty tubes;
▪ automatic feeding of empty tubes to the operating robot for package change;
▪ programmable batch phase-out/batch change;
▪ automatic deposit of removed packages at the end of the machine;
▪ automatic or semi-automatic filter cleaning.

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Befits of machine automation:
▪ Machine automation reduces manual operations to a minimum and replaces them by monitoring tasks.
▪ The importance of automation is by no means confined to economies in operating personnel and labor costs.
▪ Automation also has a major influence on product quality, i.e. yarn quality, for example through automated
piecing after ends down:
▪ Manual piecing is no longer possible at high rotor speeds (> 100 000 rpm).

▪ Manual piecings have an average tenacity of no more than 40 %, whereas automated piecings have a yarn tenacity of up to
100 %.
▪ Since electronic yarn clearers are standard equipment on rotor spinning machines nowadays, it is only worth clearing yarn
defects as long as they are not replaced by a piecing of inferior quality (thick and of lower strength) than the cleared
defect, as a result of being produced manually. Only piecing systems featuring controlled fiber feeding and synchronized
yarn take-off can produce piecings that are virtually invisible in the yarn and the end product and thus permit fine clearer
settings.
▪ Consistent piecing quality is essential for economical downstream processing of rotor-spun yarns, and this can only be
assured by piecings produced with process control and reproducible setting parameters.
▪ Last but not least, thorough cleaning of the rotor groove inevitably takes place on automated machines after each end
down or package change, thus reducing the risk of a creeping decline in yarn quality.

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Concepts:
▪ Machine automation is represented in practice by two different concepts:
1. Integrated automation, in which all operating functions (rotor cleaning, repairing ends down,
package change) are combined (integrated) in a single robot. Package changing and the
subsequent restart of the spinning position occur as a single process.
2. Automation by means of units operating separately, with the operating functions of spinning
start-up (after ends down or package changes) being performed by a piecing robot, and the
transport of starter bobbins (instead of empty tubes) and package change by a second robot.
There is no system-imposed link between robots which operate separately and the use of
starter bobbins, but the greater technical complexity this concept entails in connection with
the pre-wound starter bobbin (additional starter bobbin unit, starter bobbin transport, etc.) is
system-imposed. This is probably also the reason why manufacturers which previously
supplied robots operating separately have switched to the integrated automation system on
their machines.

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Application options for operating robots:
▪ Rotor spinning machines can be equipped with up to 4 operating robots (up to 2 on
each side of the machine). Their travel strategy is usually coordinated in such a way that
the robots move to and fro within a certain working range, successively attending to all
spinning positions in the direction of travel where intervention is required. The travel
strategy can be optimized in accordance with the operating status of the machine.
▪ Machines with a single-operating robot

▪ Machines with a two-operating robot

▪ Machines with a three-operating robot

▪ Machines with a four-operating robot

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