Manufacturing Worsted Yarns | Manufacturing Woolen Yarns

Manufacturing Worsted Yarns: Now, we would learn the steps involved in manufacturing worsted yarns. In the manufacturer of worsted yarns, the Different steps involved are:

• Carding


• Gilling and combing


• Drawing


• Roving


• Spinning

Carding: The carding process for worsted yarn production is intended to disentangle and lay them as parallel as possible. The fibres are passed between rollers covered with fine wire teeth. Since worsted yarns, however, should be smooth, the fibers are made to lie as parallel as this process will permit. Following this operation, the wool goes to the gilling and combing processes.

Gilling and Combing: Gilling is carried out before (preparative gilling) and after (finisher gilling) combing. The preparative gilling is mainly to align the fibers in a parallel direction, further blend the wool through doubling and to add moisture and lubricants. Whereas finisher gilling is mainly aimed to remove the mild entanglement introduced to the combed sliver. The carded wool, which is to be made into worsted yarn, is put through gilling and combing operations. The gilling process removes the shorter staple and straightens the longer fibers. This process is continued in the combing operation, which removes the shorter fibers of 1 to 4 inch (25 – 100 mm) lengths (called combing noils), places the longer fibers (called tops) as parallel as possible, and further cleans the fibers by removing any remaining loose impurities.

Drawing : Drawing is an advanced operation which doubles and redoubles slivers of wool fibers. The process draws, drafts, twists, and winds the stock, making the slivers more compact and thinning them into slubbers. Drawing is done only for worsted process.

Roving : This is the final stage before spinning. Roving is actually a light twisting operation to hold the thin slubbers intact.

Spinning : The type of spinning explained here is applicable both for woolen and worsted yarns. In the spinning operation, the wool roving is drawn out and twisted into yarn. There are two main methods used to produce woolen-spun yarns. These are:

• Ring spinning


• Mule spinning

Mule-spun yarns generally are superior to ring-spun yarns but they tend to be much more expensive due to the slow production rates and high labor input.

Worsted yarns are spun on any kind of spinning machine – mule, ring, cap, or flyer. The two principle systems of spinning worsted yarns are the English system and the French system.

· In the English system (Bradford), the fiber is oiled before combing, and a tight twist is inserted. This produces smoother and finer yarns. The more tightly twisted yarn makes stronger, more durable fabrics.

· In the French system, no oil is used. The yarn is given no twist; it is fuzzier, and therefore suitable for soft worsted yarns.

Manufacturing Woolen Yarns: In the manufacture of woolen yarns, the fibers are passed through two stages such as:

• Carding


• Spinning

The objective of carding process is to disentangle the fibers. In this process the wool fibers are passed between rollers covered with thousands of fine wire teeth. The wool fibers are disentangled by the action of the wires and are arranged in parallel fashion. This makes the woolen yarns smooth. Since the production of woolen yarns is intended to be rough or fuzzy, it is not desirable to have the fibers too parallel. By use of an oscillating device, one thin film, or sliver, of wool is placed diagonally and overlapping another sliver to give a crisscross effect to the fibers. This process helps in obtaining a fuzzy surface on the yarn.

The next stage is spinning which is similar to that of worsted production process. We would learn the spinning process is the next section.

Manufacturing Processes for Wool Based Yarns | Production Processes for Wool Yarns

Wool is the fiber derived from
the hair of domesticated animals, usually sheep. Wool is classified
according to the source from which it is obtained. The fleece or the
wool which is collected is kept to the different stages of manufacturing
process which starts with the preparation of the fiber. The different
stage through which it is taken depends upon whether the fiber is intended for worsted or woolen yarns. The flow chart for the manufacturing process is as follows:

Preparation Wool

Fleeces
vary from 6 to 18 pounds (3-8 kg) in weight. The best quality wool is
obtained from the sides and shoulders and is treated as one fleece.
Similarly, the wool obtained from the head, chest, belly, and shanks is
treated as a second fleece.

Preparation Wool

The
raw wool or newly sheared fleece is called grease wool because it
contains the natural oil of the sheep. When grease wool is washed, it
loses from 20 to 80 percent of its original weight. The wool obtained
should be carefully sorted into different grades.

Sorting and Grading: In
sorting, the wool is broken up into sections of different quality
fibers, from different parts of the body. The best quality of wool or
one fleece is used for clothing; the lesser quality or second fleece is
used to make rugs. Each grade is determined by type, length, fineness,
elasticity, and strength. The wool may be graded according to the type
of merino sheep or according to fineness or diameter which is otherwise
called as United States System and British System.

The
classification according to the United States System or according to the
type of merino sheep from which it is obtained is as follows:

• First quality wool is identified as fine and is equivalent to the
  quality of wool that could be obtained from a full-to
  three-quarter-blood Merino sheep.


• Second quality is equivalent to the kind of wool that could be obtained from a half blood Merino.


• The
  poorest qualities are identified as common and braid; they are coarse,
  have little crimp, relatively few scales and are somewhat hair like in
  appearance.


• The grading system on the world market is based upon
  the British numbering system, which relates the fineness, or diameter,
  of the wool fiber to the kind of combed, or worsted, yarn that could be
  spun from 1 pound of scoured wool.


• The first in quality would be
  that wool which is fine enough for and capable of being spun into the
  highest wool yarn counts of 80s, 70s, and 64s (No. of 560 yards in 1 
  pound).


•  The second quality is fine enough to be capable of being spun into yarn counts of 62s, 60s, and 58s.
  
  


• The poorest grade is capable of being spun into yarn counts of only 40s and 30s.

TableComparative Wool Grading Table

United States System	British System
Fine (full-to-three-quarter-blood)	80S, 70S, 64S
Half – blood	62S, 60S, 58S
Three – eights – blood	56S
Quarter – blood	50S, 48S
Low – quarter – blood	46S
Common	44S
Braid	40S, 36S

Scouring: Wool taken
directly from the sheep is called “raw” or “grease wool.” It contains
sand, dirt, grease, and dried sweat. The weight of these contaminants
accounts for about 30 to 70 percent of the fleece’s total weight.
Wool
scouring is the first step in the conversion of greasy wool into a
textile product. It is the process of washing wool in hot water and
detergent to remove the non-wool contaminants and then drying it. The
scouring machine contains warm water, soap and a mild solution of soda
ash or other alkali. They are equipped with automatic rakes, which stir
the wool. Rollers between the vats squeeze out the water. If the raw
wool is not sufficiently clear of vegetable substance after scoring, it
is put through the carbonizing bath of dilute sulfuric acid or
hydrochloric acid to burn out the foreign matter.

Drying: Wool
after scouring should not be allowed to become absolutely dry. About,
12 to16 percent of the moisture is left in the wool which would enable
handling of the fibers in further processing.

Oiling: Wool
is unmanageable after scouring and hence the fiber requires to be
treated with various oils to keep it from becoming brittle. Oiling of
the fibers also helps to lubricate it for the spinning operation.

Carding:
From this stage, further processing depends on whether woolen or
worsted yarns are to be produced. The main objective of carding is to
disentangle and to open the scoured wool. Carding also forms a web of
disentangled fibers that are formed into sliver.

Sewing Thread Winding System | Different Types Winding | Precision winding | Parallel winding

A transformer winding in which all the turns are arranged on a bobbin instead of in the form of a disk. Generally used for the high-voltage windings of small transformers.

Different types of Sewing Thread winding system

Precision winding: 

• Constant winding ratio

• Winding angle reduces with increasing diameter

• No pattern areas

• Good off-winding characteristics

• High package density

Step precision or digicone winding:

• Almost constant winding angle

• The wind ratio is reduced in steps

• Combines the advantage of random and precision winding

• No pattern areas

• Higher consistent package density

• Perfect unwinding characteristics

• Straight sided packages

Random winding: 

• Winding angle is kept constant since the winding ratio reduces with increasing diameter

• Stable packages

• Even density

Pineapple winding:

• Winding traverse reduces to produce packages with tapered edges

• Required for filament winding operations

• All three types of winding applicable

Parallel winding:

• Very high package density

• Thread vertical to package axis

• Relatively short lengths of thread

• Suitable for side unwinding

• No pattern areas 5,6

Ball winding:

• Very easy unwinding 

• Winding takes place in 4 stages:

1. Rough base winding

2. Form winding

3. Surface layer winding

4. Circumferencial winding

Skein winding:

• Easy unwinding

• Very small parallel strand of soft twisted thread.

Uses of Sewing Threads, Embroidery Thread | Necessities of Sewing Threads

Sewing thread is a flexible, small diameter yarn or strand usually treated with a surface coating, lubricant or both, intended to be used to stitch one or more pieces of material or an object to a material. It may be defined as smooth, evenly spun, hard-twisted ply yarn, treated by a special finishingprocess to make it resistant to stresses in its passage through the eye of a needle and through material involved in seaming and stitching operations.

Applications of sewing threads

Approximately 80% of all sewing threads produced are used by the clothing industries. sewing, embroidery, applique and serging thread that needlecraft hobbyists and professionals need. We carry product lines from Aurifil, Floriani, Gutermann, Isacord, Mettler, Presencia, Robison Anton, Signature, Superior, Wonderfil, YLI, and more. We also carry the entire line of Floriani Embroidery Stabilizers, and a wide selection of quilting patterns and sewing notions.

Importance of Sewing Threads

The sewing thread is of considerable importance, playing a major role in retaining the fabric appearance, look, and life of the garment in the long run, even though it usually represents much less than 1% by mass of a garment. 

Nowadays, a numerous variety of sewing threads are available in the market due to diverse demands from the sewing industry, increasing use of different types of fibres in the garment industry and expanding application of textile materials in various fields like apparels, technical applications as well. Better understanding of the sewing process and its requirements as obtained through studies by modern instrumentation techniques has also greatly contributed to the development of new threads. It is also very much required and appreciable to have different types of sewing threads, which can suit various applications, since various end-uses demand specific property requirements.

It is beyond anybody’s doubt that the success of garment manufacturing process mainly depends upon the operation of sewing, though a very better quality of fabric is selected for the garment manufacturing process. Again, the sewing threads play a vital role in the success of sewing operation, since a wrong thread may ruin a very high quality fabric and even a best sewing machine used for the sewing, and the whole process will fail. It can add to waste of both time and money. Hence, it is very much imperative to select a right type of sewing thread which can suit one’s requirements exactly. This is possible by the correct understanding of the type of fibre used to manufacture, manufacturing processing sequence & properties of different types of sewing threads existing on earth, which was touched upon in this technical article to a greater extent.

Sewing Threads | Different Types of Sewing Threads

Sewing Threads

Sewing threads can make or mar a garments, and hence a through understanding of their processing and properties is vital for the industry to choose the right type of the threads. According to the definition given by ASTM, sewing thread is a flexible, small diameter yarn or strand usually treated with a surface coating, lubricant or both, intended to be used to stitch one or more pieces of material or an object to a material. It may be defined as smooth, evenly spun, hard-twisted ply yarn, treated by a special finishing process to make it resistant to stresses in its passage through the eye of a needle and through material involved in seaming and stitching operations1.

Sewing threads are used in garments, upholstery, air-supported fabric structures and geotextiles to join different components by forming a seam. The primary function of a seam is to provide uniform stress transfer from one piece of fabric to another, thus preserving the overall integrity of the fabric assembly.

Seam can be formed by the following techniques:

- Mechanical: stapling, sewing.

- Physical: welding or heat-setting.

- Chemical: by means of resins2.

The formation of seams by physical and chemical methods is restricted to a few specialised applications, as these processes tend to alter certain properties of the textile material. Among mechanical sewing techniques, sewing maintains its prevailing position by virtue of its simplicity, sophisticated and economical production methods and the controllable elasticity of the seam produced.

Different types of sewing threads

Usually, sewing threads are manufactured from either natural or manmade fibres in either staple or filament form3. A broad classification of different types of sewing threads is given below:

Classification of Sewing Thread

Properties of Sewing Threads | Essential Properties Required for Sewing Threads

Essential properties required for sewing threads: Industrial sewing techniques make specific and often very exacting demands on the threads involved in the sewing process. The sewability of sewing threads is of major importance6, having a very profound effect on seam quality and production costs. The sewing and the seam performance of a sewing thread are largely influenced by the material to be sewn, the sewing technique and the end-use for which the sewn material is intended. These requirements can be defined as:

* The ability of the sewing thread to meet the functional requirements of producing the desired seam effectively.

* The ability of the sewing thread to provide the desired aesthetics and serviceability in the seam.

* The cost of sewing thread and that associated with producing the desired seam.

The different important properties required by a sewing thread are discussed below:

1. Needle thread must pass freely through the small eye of the needle; consequently they must be uniform, knot-free, non-torque and fault free.

2. Tensile strength/breaking strength is one of the essential properties of the thread. It must be capable of withstanding several kinetic/lateral movements during sewing. The strength of the sewing thread must be higher than that of the fabric so that the thread does not rupture during use. During sewing at high speeds, the needle thread is subjected to repeated tensile stresses at very high rates. The thread also comes under the influence of heat, bending, pressures, torsion and wearing. The value of these stresses depends on the sewing speed, machine settings and the thread used. The stresses created within the thread have a negative effect on the processing and functional characteristics of the thread, and there is significant reduction in the thread strength after sewing.

This is a function of the dynamic and thermal loading of the thread and is influenced by the thread frictional properties, thread tensioning during sewing, needle size, stitch length and number of fabric layers in the seam. The thread should therefore possess adequate strength and elongation in order to perform satisfactorily during sewing and in seam 7.

3. For good performance in a sewing machine moderate to low extension-at-break of the thread is usually preferred. Needle thread with different elongation-at-break has been found to behave quite differently during stitch formation. The determinants of success of sewing a thread with certain elongation per cent without any problem are the machine setting and special properties of the sewing thread itself 6.

4. The elasticity of the sewing thread must be uniform along its length in order to enable equal length stitches to be formed, and it must closely match the elasticity of the fabric being sewn; otherwise either seam thread fracture, or tearing of the adjacent fabric may arise during garment use. Clearly, the requirements of woven and knitted fabrics will be different.

5. The forces that are developed in the sewing thread are mostly due to the friction between the thread and machine parts, the most severe action taking place between:

- The thread and the needle.

- The thread and the fabric being sewn.

A controlled level of both static and dynamic friction is required; this must not be too high, which could cause lack of thread control. High static friction values are necessary to allow the stitches to lock and prevent “run-back” of seams. Spun threads are particularly good in this respect when compared with filament thread. The worst is the monofilament threads. The frictional properties are affected by lubrication. The factors that influence the frictional properties are:

• Uniform application of lubricating agents.
• Adhesion of the finishing agent on the thread.

The quantity and quality of finishes are very important. Special finishes like silicone compounds have been found to exhibit clear advantage over standard paraffin wax.

6. Good abrasion resistance is essential for good sewing performance. The thread is under tension condition, especially when the stitch is being set. The thread must be resilient enough to return to shape after the distortions, and then must maintain its physical properties to provide good performance in the seam after the sewing process is complete. Nylon and polyester offer the best resistance to abrasion.

7. Good resistance to heat is a very important requirement of a sewing thread. The temperature reached by the sewing needle during sewing very much depends on:

* the nature of the fabric to be sewn (density, thickness, finish)

* the speed of the sewing machine

* the type of needle used (size, shape, surface finish)

* size and finish of the sewing thread.

The needle temperature is especially critical for fabrics and sewing threads of thermoplastic fibres, where it may exceed their melting temperature. Needle heating causes sewing thread breakage, cross-thread, skipped stitches, seam damage and physical damage to the needle.

Various studies show that the sewing thread influences the needle temperature significantly. Its movement through the needle reduces the needle temperature by an average of 21- 45%, the amount of reduction depends on the sewing condition and the structure, fineness and composition of sewing thread.

Lubrication of sewing thread with a mixture of wax, emulsions with synthetic resins, and silicon based products may minimise heat generation, and the fibres surface of spun yarns may be an advantage in that a thin layer of the surrounding air will move with the thread and promote needle cooling.

8. The hairiness of sewing thread also affects the appearance of the seam. Sewing threads for decorative seams are singed, squeezed and gloss-brushed.

9. The final direction of twist insertion may be important to enable the stitch forming mechanism of the sewing machine to perform correctly; most sewing machine require Z twist, but there are a few where performance is better with S twist.

10. Colour fastness is a general requirement for sewing thread. It is important that the selected shade retain its colour throughout the life of the garment. Two aspects of fastness are important:

• The thread must not change colour.

• The thread must not stain any material adjacent to the seam.

11. Low shrinkage during washing and ironing is required. Shrinkage due to fibre swelling causes seams to pucker, especially if the fabric exhibits less shrinkage than threads. Synthetic threads suffer less from this problem than cotton threads owing to their much lower moisture absorbency; however they are liable to residual shrinkage problems if unsuitable manufacturing processes are employed. Synthetic threads can suffer from the problem of thermal shrinkage during ironing but this difficulty can be solved by the use of high temperature setting, which stabilises the thread at temperature above those normally encountered during the ironing process.

The sewing threads should possess better evenness and should contain minimal number of knots, faults and neps, etc. Thread should have very low level of imperfections and classimat faults.

12. Good lustre in the thread improves appearance of the seam. 

13. Threads must be uniformly dyed in a good match to the materials being sewn and also the dyed thread should have properties like colourfastness to washing, light, perspiration, and sublimation.

14. The ability of the thread to perform efficiently in the sewing machine is defined sewability. It can be assessed by the number of breaks that occur during the sewing of a certain number of stitches. However, owing to the generation of needle heat in high-speed sewing, the threads could be damaged without breaking. The long knot-free evenner yarns in case of rotor and air-jet can give better sewability.

15. The characteristics of properly constructed seam are strength, elasticity, durability, stability and appearance. The relative importance of these qualities is determined by the end-use of the sewn product. The factors that govern these properties are seam and stitch type, thread strength and elasticity, stitches per unit length of seam, thread tension, seam efficiency of the material. The hairiness of sewing thread is important to decide seam appearance. The shrinkage potential of the thread and hence the seam is also major importance for proper seam appearance. The serviceability of a garment depends not only on the quality of the fabric but also on that of the seam. The seam quality is measured by stitching parameters of the threads and seam parameters such as size, slippage and strength. 

The failure of seam produced by traverse loading can generally be classified as: Type I: the failure due to thread breakage, Type II: the failure due to fabric breakage, Seam breakage: the failure due to the slippage of cloth yarns at right angle to the seam. 

Seam slippage is the most probable cause for seam failure that leads to garment rejection in wear. The durability of a seam depends largely on its strength and its relationship with elasticity of the material. It is measured in terms of seam efficiency, where Seam Efficiency = (Seam tensile strength/fabric tensile strength) x 100, generally ranges between 85 to 90%. The minimum loop strength correlates well with the stitch breaking strength. Further resistance to abrasion and wear of the seam during everyday use, including laundering is also essential for the longer seam.

16. Seam pucker can be defined as a differential shrinkage occurring along the line of a seam and is mainly caused due to seam instability, due to high tension imposed during sewing. Though currently available threads have a certain amount of controlled elasticity and elongation they get over-stretched when the sewing tensions are high. During relaxation the thread recovers its original length, thus gathering up the seam. Threads for use in apparel are also required to have good stability to laundering, ironing and other treatments since differential shrinkage between the sewing thread and the fabric of a garment can cause puckering.

Further, Seam pucker can be determined by measuring the differences in fabric and seam thickness under a constant compressive load. The seam-thickness strain is calculated by using the formula:

Thickness strain (%) = (seam thickness – 2 x fabric thickness) x 100 / 2x fabric thickness {ref}

Torsional Properties of Fiber | Torsional Properties of Textile Materials

It is the property of fibre or material when a Torsional force is applied on it. Here Torsional force is a twisting force that is applied on the two ends of the material in two opposite direction. The behaviors which are shown by a textile material when it is subjected to a torsional force is called torsional property.

1. Torsional rigidity

2. Breaking twist 

3. Shear modulus

1. Torsional rigidity:  

Torsional rigidity can be defined as the torque required against twisting is done for which torque is termed as torsional rigidity.Mathematically, torsional rigidity = ηET2/ρ

Where, 

η = shape factor, 

E = specific shear modulus (N/tex)

Specific torsional rigidity: Specific torsional rigidity can be defined as the torsional rigidity of a fiber of unit linear density.Mathematically, specific torsional rigidity = ηE/ρ

Unit: N-m2 /Tex

2. Breaking twist:  

The twist for breaking of a yarn is called breaking twist. It also can be defined as the number of twists required to break a yarn. Breaking twist depends on the diameter of fiber and it is inversely proportional to its diameter.That is, Tb ∞ 1/d

Where, 

Tb = Breaking twist, 

d = diameter of fiber

Breaking twist angle: This is the angle through which outer layer of fiber are sheared at breaking. Mathematically, α = tan-1(πdTb)

Where, 

α = breaking twist angle, 

d = diameter of fiber, 

Tb = breaking twist per unit length 

Frictional Property of Textile Fiber

When the textile materials are processed, then friction is developed between the fibers. The properties which are shown by a textile material during friction is known as frictional property. This properties are shown during processing. Too high friction and too low friction is not good for yarn. Therefore it is an important property when yarn manufacturing and processing.

Frictional properties depend on-

1. Composition of the material

2. State of the surface of the material

3. Pressure between the surfaces

4. Temperature

5. Relative humidity %

Co-efficient of friction:  

Frictional force is proportional to the normal or perpendicular of a material due to its own weight.That is, F ∞ N Or, F = μ N Or, μ = F/NWhere, F = Frictional force, N = Normal / perpendicular forceHere, μ is the proportional constant known as “co-efficient of friction”.So, co-efficient of friction can be defined as the ratio of frictional force and perpendicular force.

Methods of measuring co-efficient of friction:  

Capstan method is most commonly used to measure co-efficient of fraction. Capstan method can be classified into two classes-

1. Static capstan method

2. Dynamic capstan method

Other methods- 

1. Buckle & Pollitt’s method

2. Abboh & Grasberg method

3. Gutheric & Olivers method

Influences of friction on textile material:

Friction holds the fibers in a sliver and hence the sliver does not break due to its’ own weight. Friction helps in drafting and drawing.· Uniform tension can be maintained during winding & warping because of friction.· Friction helps to make yarn by twisting during spinning.· Friction increases lusture and smoothness of the yarn and the fabric.· Friction makes more clean material. 

Demerits of friction on textile material:· 

Friction causes nap formation.· High static friction causes high breakage of yarn during weaving.· If the frictional force is high, the handle properties of fabric will be low.· Friction generates temperature and therefore static electricity is developed which attracts dust, dirt etc. and the materials become dirty.· Sometimes due to over friction materials may be elongated.· Friction increases yarn hairiness.· Friction worn out parts of machine.

Minimization of friction intensity:  

1. Sizing is done in warp yarn before weaving to reduce frictional intensity. As a result, yarn damage will be reduced.

2. Emulsion, oil, lubricants etc. are specially applied on jute fiber to reduce friction.

3. Chemical treatment is done on wool fiber to reduce scale sharpness and thus reduce friction during processing.

4. By calendaring frictional intensity of cloth is reduced.

5. Sometimes resin finish is applied on fabric to reduce friction.

Mechanical Properties of Textile Fibers | Mechanical Properties of Textile Materials

The mechanical properties of textile fibers include fiber strength, elongation, elasticity, abrasion resistance, modulus of elasticity. Fiber strength is the ability of fiber resistance to external damage, which largely determine the durability of the textile goods. Fiber strength is the absolute strength fibers to said fibers in a row it is under increasing load until fracture can bear the maximum load. Lecturer in units of its statutory Newton (N) or PCT Newton (cN). Over the past practice of using chocolate or kilograms force said.

Fiber strength with the thickness of fiber is related to the different thickness of the fiber so absolutely not comparable strength, so often used to indicate the relative strength of the fiber strength. Relative intensity is the unit linear density (per special or every once) fibers can bear the greatest tension. Legal units of measurement for the cow / special (N / tex), or determining cattle / Special (cN / tex). Over the past practice of using Chris / Dan said. The mechanical properties of Textile fibres is the response to applied forces and deformation. But we should know the strength of yarn can not be greater than the sum of the maximum strength of its component’s fibres.

Mechanical Properties of Textile Fibers

1. Tensile Properties.
2. Flexural Properties.
3. Torsional Properties.
4. Fictional Properties

1. Tensile Properties.
Tensile properties indicates how a material will react to the forces being applied in Tension. Fibers usually experience tensile loads whether they are used for apparel or technical structures. Their form, which is long and fine, makes them some of the strongest materials available as well as very flexible. This book provides a concise and authoritative overview of tensile behaviour of a wide range of both natural and synthetic fibres used both in textiles and high performance materials.

2. Flexural Properties.
Flexural properties is one of the mechanical properties of textile material. It is the property or behaviour shown by the fibre or material when we bend it. The importance of Flexural properties is required when we wear cloth. The flexural test measures the force required to bend a beam under three point loading conditions. The data is often used to select materials for parts that will support loads without flexing. Flexural modulus is used as an indication of a material’s stiffness when flexed.

3. Torsional Properties.
The behaviors which are shown by a textile material when it is subjected to a torsional force is called torsional property. It is the property of fibre or material when a Torsional force is applied on it. Here Torsional force is a twisting force that is applied on the two ends of the material in two opposite direction.

4. Fictional Properties
Frictional properties is due to the friction between the fibres. This properties are shown during processing. Too high friction and too low friction is not good for yarn. Therefore it is an important property when yarn manufacturing and processing.

Flexural Property of Textile Fiber

 Flexural properties is one of the mechanical properties of textile material. The flexural test measures the force required to bend a beam under three point loading conditions. The data is often used to select materials for parts that will support loads without flexing. Flexural modulus is used as an indication of a material’s stiffness when flexed. Since the physical properties of many materials (especially thermoplastics) can vary depending on ambient temperature, it is sometimes appropriate to test materials at temperatures that simulate the intended end use environment.

Flexural Property of Textile Material

 
The behavior which shows by textile material during bending is called flexural property.

1. Flexural rigidity 

2. Bending recovery

3. Bending modulus

1. Flexural rigidity:  

Flexural rigidity is the stiffness of a textile fiber. It can be defined as the couple needed to bend a fiber.Mathematically, Flexural rigidity = (1/4π) (ηET2/ρ) 

Where, 

η = shape factor, 

E = specific shear modulus, 

T =linear density (Tex), 

ρ = density (gm/cm3)

Specific flexural rigidity: 

Specific flexural rigidity can be defined as the flexural rigidity of linear density.

Mathematically, Specific flexural rigidity = (1/4π)(ηE/ρ)

Where, 

η = shape factor, 

E = specific shear modulus, 

ρ = density (gm/cm3)

2. Bnding recovery:  

The recovery from a given curvature is called bending recovery.Say, nylon shows 100% recovery from small curvature of 15D, where it shows 20% recovery from large curvature.

Unit = N-m2/ Tex.

3. Shape factor:  

Shape factor is a number that indicates the shape of a fiber. Shape is expressed by “η”.If, η = 1, it indicates the shape of fiber is round.

If, 

η > 1, it indicates the shape of fiber is increased.If, 

η

Tensile Properties of Textile Material ( Fiber or Yarn or Fabric ) | Tenacity | Breaking Extension | Work of Rupture | Initial Modulus | Work Factor | Work Recovery | Elastic Recovery | Yield Stress | Yield Strain | Yield Point | Breaking Load | Creep

Fibers usually experience tensile loads whether they are used for apparel or technical structures. Their form, which is long and fine, makes them some of the strongest materials available as well as very flexible. This book provides a concise and authoritative overview of tensile behaviour of a wide range of both natural and synthetic fibres used both in textiles and high performance materials.

Tensile Properties of Textile Material

1. Tenacity

2. Breaking extension

3. Work of rupture

4. Initial modulus

5. Work factor

6. Work recovery

7. Elastic recovery

8. Yield stress

9. Yield strain

10.Yield point

11. Breaking load 

12. Creep

Description of each is given below:

1. Tenacity:  

The ratio of load required to break the specimen and the linear density of that specimen is called tenacity.Mathematically, Tenacity = Load required to break the specimen / Linear density of the specimenUnit: gm/denier, gm/Tex, N/Tex, CN/Tex etc.

2. Breaking extension:  

The elongation necessary to break a textile material is a useful quantity. It may be expressed by the actual percentage increase in length and is termed as breaking extension.Mathematically, Breaking extension (%) = (Elongation at break / Initial length) × 100%

3. Work of rupture: 

 Work of rupture is defined as the energy required to break a material or total work done to break that material. Unit: Joule (J)

4. Initial modulus:  

The tangent of angle between the initial curve and the horizontal axis is equal to the ratio of stress and strain.
In engineering science the ratio is termed as Young’s Modulus and in textile we use the terms as Initial Young’s Modulus.

Initial modulus, tan α = stress / strain Tan α ↑↓ → extension ↓↑

5. Work factor:  

The ratio between work of rupture and the product of breaking load and breaking elongation is called work factor. Work factor = work of rupture / (breaking load × breaking elongation)

6. Work recovery: 

 The ratio between work returned during recovery and total work done in total extension is called work recovery.Total extension = Elastic extension + Plastic extension Total work = work required to elastic extension + work required to plastic extension.

7. Elastic recovery: 

The power of recovery from a given extension is called elastic recovery. Elastic recovery depends on types of extension, fiber structure, types of molecular bonding and crystalline of fiber. The power of recovery from a given extension is called elastic recovery. Elastic recovery depends on types of extension, fiber structure, types of molecular bonding and crystalline of fiber. 

8. Yield point. 

The point up to which a fiber behaves elastic deformation and after which a fiber shows plastic deformation is called yield point.

9. Yield stress 

The stress at yield point is called yield stress.

10. Yield strains:  

The strain at yield point is called yield strain.

11. Breaking load: 

The load which is required to break a specimen is called breaking load.

12. Creep:  

When a load is applied on the textile material an instantaneous strain is occurred, but after that the strain will be lower with the passing time. This behavior of the material is termed as creep. 

There are two types of creep:

 

i. Temporary creep

ii. Permanent creep

 

Here, AB = initial length of the specimen 

AD = final length after recovery 

BD = total extension 

CD = elastic extension 

BC = plastic extension 

Total extension = Elastic extension + Plastic extension
So,Elastic recovery (%) = (Elastic extension/total extension) ×100% = (CD/BD) × 100% 

So, Plastic recovery = (plastic extension/total extension) ×100% = (BC/BD) ×100%

Feature of Yarn Ring Spinning frame | Drafting Zone | Ring & Traveller | Rubber Cots and Apron | Yarn Twist

Yarn Ring Spinning frame Technology is a simple and old technology, but the production and quality requirements at the present scenario puts in a lot of pressure on the Technologist to select the optimum process parameters and machine parameters, so that a good quality yarn can be produced at a lower manufacturing cost.

Following are the Points to be Considered in a Ring Frame

• Draft distribution and settings
• Ring and travellers
• spindle speed
• Twist
• Lift of the machine
• Creel type
• Feed material
• Length of the machine
• Type of drive

Raw material chracteristic plays a major role in selecting the above said process parameters in Ring Frame.
Technical information and guidelines are given below based on the learnings from personal experience and discussions with Technologists. This could be used as a guideline and can be implemented based on the trials taken at site. Some of this information can be disproved in some other applications, because many of the parameters are affected by so many variables. A same machine or rawmaterial cannot perform in the same way in two different factories. This is because of the fact that no two factories can be identical.

DraftingThe break draft should depend upon the following,

• Fibre type
• Fibre length
• Roving T.M
• Main draft

Main Draft Zone

Mostly for cotton fibres, short cradles are used in the top arm. Front zone setting is around 42.5 mm to 44 mm depending upon the type of drafting system. The distance between the front top roller and top apron should be around 0.5to 0.7mm when correct size top roller is used. This is normally taken care of by the machinery manufcturer. If a technician changes this setting, this will surely result in more imperfections, especially with karded count the impact will be more. Therefore when processing cotton fibres, care should be taken that the front zone setting should be according to the machinery.

Ring & Traveller

Ring diameter, flange width and ring profile depends upon the fibre, twist per inch, lift of the machine,maximum spindle speed, winding capacity etc.

• Operating speed of the traveller has a maximum limit, because the heat generated between ring and traveller should be dissipated by the low mass of the traveller with in a short time available.
• If the cotton combed yarn is for knitting, traveller speed will not be a limiting factor. Since yarn TPI is less, the yarn strand is not strong enough. Therefore the limiting factor will be yarn tension. Following points to be considered

1) For 12s to 24s , 42mm ring with 180 mm lift can be used 

2) For 24s to 36s, 40 mm ring with 180 lift can be used

3) For 36s to 60s , 38 mm ring with 170 mm lift can be used4) For 70s to 120s, 36 mmring with 160 mm lift can be used.
5) If winding is a problem, it is better to go for reduced production with bigger ring dia.
6) Anti-wedge ring profile is better, because of better heat dissipation
7) Elliptical traveller should be used, to avoid start-up breaks in hosiery counts
8) Special type of travller clearer can be used to avoid accumulation of fibre on the traveller as traveller with waste does not perform well during start-up.

• For polyester/cotton blends and cotton weaving counts yarn strength is not a problem. The limiting factor will be a traveller speed. For a ring diameter of 40 mm, spindle speed upto 19500 should not be a problem. Rings like Titan(from Braecker), NCN(bergosesia) etc, will be able to meet the requirements.
• For spindle speeds more than 20000 rpm, ORBIT rings or SU-RINGS should be used. As the area of contact is more with this rings, with higher speeds and pressure, the heat produced can be dissipated without any problem. Normal ring and traveller profile will not be able to run at speeds higher than 20000 to produce a good quality yarn.
• ORBIT rings will be of great help, to work 100% polyester at higher spindle speeds. Because, of the tension, the heat produced between ring and traveller is extremely high. But one should understand, that ,the yarn strength of polyester is very high. Here the limiting factor is only the heat dissipation. Therefore ORBIT RINGS with high area of contact will be able to run well at higher spindle speeds when processing 100% polyester.
• While running 100% cotton, the fibre dust in cotton, acts like a lubricant. All the cottons do not form same amount of lubricating film. If there is no fibre lubrication, traveller wears out very fast. Because of this worn out or burn out travellers, microwelding occurs on the ring surface,
• Lubrication is good with west african cottons. It may not be true with all the cottons from West africa. In general there is a feeling, cottons from Russia, or from very dry places, lubrication is very bad. If the fibre lubrication is very bad, it is better to use lighter travellers and change the travellers as early as possible.
• Traveller life depends upon the type of raw material, humidity conditions, ringframe speeds, the yarn count, etc. If the climate is dry , fibre lubrication will be less while processing cotton.
• Traveller life is very less when Viscose rayon is processed especially semi dull fibre, because of low lubrication. Traveller life is better for optical bright fibres.
• Traveller life is better for Poly/cotton blends, because of better lubricatiion between ring and traveller.
• Because of the centrifugal force excerted by the traveller on the yarn, the particles from the fibre fall on the ring where the traveller is in contact. These particles act like a lubricating film between ring and traveller. 

Rubber Cots and Apron

• For processing combed cotton, soft cots (60 to 65 degree shorehardness) will result in lower U%, thin and thick places
• There are different types of cores (inner fixing part of a rubber cot)available from different manaufacturers. Aluminimum core,PVC core,etc. It is always better to use softer cots with aluminium core.
• When softer cots are used, buffing frequency should be reduced to 45 to 90 days depending upon the quality of the rubber cots, if the mill is aiming at very high consistent quality in cotton counts.
• If the lapping tendency is very high when processing synthetic fibres for non critical end uses, It is better to use 90 degree shore harness cots, to avoid cots damages. This will improve the working and the yarn quality compared to working with 83 degree shore hardness.
• If rubber cots damages are more due to lapping, frequent buffings as high as once in 30 days will be of great help to improve the working and quality. Of course,one should try to work the ringframe without lapping. 

The basic reasons for lapping in the case of processing synthetic fibre is

• End breaks
• Pneumafil suction
• Rubber cots type
• Fibre fineness
• Oil content(electrostatic charges)
• Department temprature and humidity 

Almost all the lappings orginate after an end break. If a mill has an abnormally high lapping problem the first thing to do is to control the end breaks,

• After doffing
• During speed change
• During the maximum speed by optimising the process paramters.
• It is obvious that fine fibres will have a stronger tendency to follow the profile of the roller. Therefore lapping tendency will be more.
• If the fibre is fine, the number of fibres in the cross section will be more, therefore lapping frequency will be more.
• If the pressure applied on the roller is more, then lapping tendancy will be more. Hence fine and longer fibres will have more tendency for lapping because of high top roller pressure required to overcome the drafting resistance.
• If the pneumafil suction is less, the lapping tendency will be more both on top and bottom roller. But the pneumafil suction depends on the fan diamater, fan type, fan speed, duct design, length of the machine, profile of the suction tube etc. If any one of the above can be modified and the suction can be improved, it is better to do that to reduce the lapping.
• The closer the setting between the suction nozzle and the bottom roller, the higher the suction efficiency and lower the lapping propensity
• Higher roving twist will reduce the lapping tendency to some extent. Therefore it is better to have a slightly higher roving twist, provided there is no problem in ringframe drafting, when the lapping tendency is more
• With Softer rubber cots lapping tendency will be more due to more surface contact.
• The most minute pores, pinholes in the rubber cots or impurities in the cots can cause lapping. Therefore the quality of buffing and the cots treatment after buffing is very important. Acid treatment is good for synthetic fibres and Berkolising is good for cotton.
• Electrostatic charges are troublesome especially where relatively large amount of fibre are being processed in a loose state e.g drawframe, card etc.Lapping tendency on the top roll increases with increasing relative humidity. The frequently held opinion is that processing performace remains stable at a steady absolute relative humidity, i.e. at a constant moisture content per Kg of dry air. 

TWIST:
The strength of a thread twisted from staple fibres increases with increasing twist, upto certain level. Once it reaches the maximum strength, further increase in twist results in reduction in yarn strength

• Coarser and shorter fibres require more Twist per unit length than finer and longer fibres
• Twist multiplier is a unit which helps to decide the twist per unit length for different counts from the same raw material.This is nothing but the angle of inclination of the helical disposition of the fibre in the yarn. This is normally expressed as TWIST PER INCH = TWIST MULTIPLIER * SQRT(Ne)
• If the two yarns are to have the same strength, then the inclination angles must be the same
• For 40s combed knitting application, if the average micronaire of cotton is 3.8 and the 2.5% span length is around 29 mm, Twist multiplier of 3.4 to 3.5 is enough . If the average micronaire is around 4.3, it should be around 3.6 to have better working in Ring frame.
• cotton combed knitting T.M. = 3.4 to 3.6 
• cotton combed weaving T.M. = 3.7 to 3.8 
• cotton carded knitting T.M. = 3.8 to 4.0 
• cotton carded weaving T.M. = 3.9 to 4.2

The above details are for cottons of 2.5% span length of 27 to 30 mm and the average Micronaire of 3.7 to 4.4. For finer and longer staple, the T.M. will be lower than the above.

• In general for processing poly/viscose , the T.M. is as follows
• 51 mm, 1.4 denier fibre : T.M. = 2.7 to 2.9 for knitting application
• 51 mm, 1.4 denier fibre : T.M. = 2.9 to 3.1 for weaving application
• 44 mm, 1.2 denier fibre : T.M. = 2.9 to 3.0 for knitting application
• 44 mm, 1.4 denier fibre : T.M. = 3.0 to 3.1 for knitting application
• 38 mm, 1.2 denier fibre : T.M. = 3.1 to 3.3 for knitting application

Others

The following ROVING parameters will affect the ring frame process parameters
1) Roving T.M.
2) Bobbin weight
3) Bobbin height

• Higher the roving T.M., wider the back bottom roller setting or higher the break draft in ring frame
• For combed material the creel height should be as low as possible in ringframe
• Very long creel heights in ringframe, lower roving T.M. and heavier roving package will result in many long thin places in the yarn.(especially in combed hosiery counts)
• In general 16 x 6 ” bobbins are used. This helps to increase the spare rovings per machine with higher creel running time. Therefore one should aim at increasing the bobbin weight as well as increasing the number of spare rovings in the ring frame.
• Normally 6 row creels are used in modern ring frames. Six row creels will accomodate more spare rovings compared to 5 row creels.(around 150 rovings for 1000 spindle machine.) Creel height should be as low as possible for cotton combed counts.Spare rovings will improve the operators efficiency.
• Shorter machines are always better compared to longer machines. But the cost per spindle will go up. For cotton , polyester/cotton blends, poly/viscose(upto 44mm length), number of spindles upto 1200, should not be a problem. But maintenance is more critical compared to shorter machines.
• For synthetic fibres with very high drafting resistance, it is better to use shorter machines, because the load on break draft gears and on second bottom rollers will be extremely high. If long machines are used and the maintenance is not good for such application, the bearing damages, gear damages, bottom roller damages etc. will increase. This will result in coarse counts, higher count C.V., long thin and thick places.
• Four spindle drive is always better compared to Tangential belt drive. Because small variation in machining accuracy of bolster , spindle beam etc will affect the spindle speeds, thereby the twist per inch. Waste accumulation between contact rollers, bent contact rollers, damaged contact rollers, oil spilling from any one spindle etc. will affect the spindle speeds and thereby TPI. The spindle speed variation between spindles in a 5 year old ringframe will be verh high incase of tangential belt ? drive compared to 4 spindle drive.
• Noise level and energy consumption will be low in 4 spindle drive compared to Tangential belt drive
• Compared to Contact rollers, Jockey pully damages are nil. I have worked with 20 year old ring frames with Jocky pulleys,but the variations in spindle speed between spindles is very less compared to a 5 year old ringframe with Tangential belt drive. I have made this comment based on my personal experience.
• When processing coarse counts at higher speeds, the air current below the machine is a big problem with 4 spindle drive . This is due to the more running parts like tinrollers and jockey pullys. This will lead to more fluff in the yarn, if humidification system is not good enough to suck the floating ,fluff.
• If spindle speeds is high for cotton counts, every end breaks will result in more fluff in the department due to the free end of the yarn getting cut by the traveller when the distance between traveller and the bobbin with the yarn is less. Higher the delay in attending the end break , higher the fly liberation.If the number of openings of return air system for a ringframe is less and the exhaust air volume is not sufficient enough, then fly liberation from an end break will increase the endbreaks and thereby will lead to multiple breaks. End break due to a fly entering the traveller will get struck with the traveller and will result in heavier traveller weight and that particular spindle will continue to work bad.
• Multiple breaks are very dangerous, as it will result in big variation in yarn hairiness and the ringframe working will be very badly affected due to heavier travellers because of the fluff in the traveller.
• Dry atmosphere in ringframe department will result in more yarn hairiness, more fly liberation and more end breaks
• It is a good practice to change spindle tapes once in 24 months.Worn out spindle tapes will result in tpi variations which is determinetal to yarn quality.

Yarn Twist | Twisting Process of Yarn | Mechanism of twist insertion to the strand

Twisting is a very essential process in the production of staple yarn, twine, cord and ropes. Twist is inserted to the staple yarn to hold the constituent fibres together, thus giving enough strength to the yarn, and also producing a continuous length of yarn. The twist in the yarn has a two-fold effect; firstly the twist increases cohesion between the fibres by increasing the lateral pressure in the yarn, thus giving enough strength to the yarn. Secondly, twist increases the helical angle of fibres and prevents the ability to aooly the maximum fibre strength to the yarn. Due to the above effects, as the twist increases, the yarn strength increases up to a certain level, beyond which the increase in twist actually decreases the strength of staple yarn. The continuous filament yarn also requires a small amount of twist in order to avoid the fraying of filaments and to increase abrasion resistance. 

However, twisting the continuous filament yarn reduces the strength of the yarn . Yarn is often ply-twisted in a direction opposite to a single yarn twist to improve evenness, strength, elongation, bulkiness, lustre and abrasion resistance, and to reduce twist liveliness, hairiness and variation in strength .

The twisting of fibres strands are carried out on a roving frame, ring frame, rotor spinning and DREF spinning machines etc. This twisted strand has to be wound on the delivery package in a certain form for easy withdrawal of these strands in the next process. Since the open end of the yarn is rotated in the rotor and DREF spinning systems, the delivery package has to be rotated axially to wind the yarn. The twisting and winding operations are separated in the open-end spinning . However, this is not possible on a roving frame or a ring frame.

There should be two rotating elements (the spindle and traveller or flyer and bobbin) in order to twist and wind the strand on the package. The winding rate should be equal to the delivery rate from the drafting device. As the winding on the diameter of the package varies continuously throughout the process, the difference in speed between the two elements also has to be varied continuously. Since the delivery rate is constant, the product of winding on diameter and the speed difference between the two rotating elements should be kept constant. On a roving frame, this is achieved by adjusting the bobbin speed continuously and keeping the flyer speed constant, whereas in ring spinning, only the spindle is rotated at a constant rate and the traveller is dragged around the ring by the yarn. Due to the frictional force between the ring and traveller, the required speed difference between the spindle and traveller is automatically adjusted. In both the ring and roving frame of the short-staple spinning system, the bobbin lead is used. For calculating twist in the roving, the flyer speed is taken into account, whereas in ring spinning, the spindle speed is considered .

Twist/cm in the roving = flyer speed in rpm)/ delivery rate in cm/min 

Twist/cm in the yarn = spindle speed in rpm/ delivery rate in cm/min

The reasons for the above, and the mechanism of twisting strands on a roving frame and ring frame are not explained in textbooks or literature. In the present paper, the mechanism of twisting strands on a roving frame and ring frame is explained. 

Mechanism of twist insertion to the strand

Twist insertion to the yarn when the spindle is stationary. We assume that the spindle is stationary and the traveller rotates in the ring frame. Each revolution of the traveller winds one coil of yarn onto the cop. This is similar to gripping and winding the yarn on a cop by hand. The yarn will rotate 3600 per coil wind while winding the yarn onto a stationary cop by hand; hence the winding causes yarn twisting.

Length of yarn wound per revolution of traveller = πd

Turns/cm due to winding = 1/πd 

where d – Winding on diameter of cop or bobbin in cm.

If the yarn is unwound in parallel from the cop, the yarn will retain all the twists present in the yarn, whereas if the yarn is over-end unwound, unwinding a coil removes one turn of twist. The unwinding causes twisting. So, the twists inserted into the yarn during winding are removed during over-end unwinding. The over-end withdrawal may be from any side of the cop. If the traveller rotates in a clockwise direction to wind the yarn onto the cop, each coil of wind inserts one turn of ‘Z’ twist to the yarn. When the same is over-end unwound, every unwinding coil inserts one turn of twist in an ‘S’ direction, and so the resultant yarn will not have any twist.

Twist insertion into the yarn when the traveller is stationary. We assume that the traveller is fixed on a stationary ring and that the spindle is rotating at a constant speed. Every revolution of spindle winds one coil of yarn onto the cop. Here winding does not cause twisting, and hence the yarn in the cop will not have any twist. But if the yarn is over-end unwound, every unwinding of a coil of yarn inserts one turn of twist into the yarn.

Turns/cm due to over-end unwinding = 1/πd

The direction of twist insertion during over end unwinding depends on direction of yarn winding. If the spindle rotates in an anticlockwise direction to wind the yarn onto the cop, during over-end unwinding a ‘Z’ twist will be inserted into the yarn. But if the same yarn is unwound in parallel, the yarn will not receive any twist.

Twist insertion onto the yarn when both spindle and traveller rotate in opposite direction. It may be wondered why it should be necessary to rotate the traveller and spindle in the opposite direction, and also how to rotate the traveller in the opposite direction. This is only to enable the reader to clearly understand the mechanism of twisting. When both the spindle and traveller rotate in the opposite direction, each revolution of the spindle and traveller winds one coil each. The length of yarn wound per min and twist/cm can be calculated.

Length of yarn wound per min = π d (NS+NT)

Twist/cm due to winding = - NT/ π d (NS+NT) where

NS – spindle speed in rpm,

NT – traveller speed in rpm.

If the spindle and traveller rotate in clockwise and anticlockwise directions respectively, the direction of twist insertion due to winding would be ‘S’. But during over-end unwinding, the direction of twist insertion would be ‘Z’. + and - signs are used to represent the Z and S twist directions respectively.

Twist/cm due to over-end unwinding = (NT/ π d (NS+NT)) + (NS/ π d (NS+NT))

Twist/cm in the yarn after over-end withdrawal = (NS/ π d (NS+NT) 

Twist insertion onto the yarn when the spindle leads the traveller. In ring spinning, both the spindle and traveller rotate in the same direction. However, the spindle rotates at a higher speed than the traveller. If both rotate at the same speed, only the twisting of yarn takes place without winding. Due to the difference in their rotational speeds, the winding of the yarn takes place on the cop.

Length of yarn wound on the cop per min = πd (NS –NT)

Due to rotation, both spindle and traveller insert twists onto the yarn. If both the spindle and traveller rotate in a clockwise direction, a ‘Z’ twist is inserted to the yarn.

Turns/cm in the yarn = NT/πd (NS –NT)

The winding rate should be equal to the delivery rate.

Length of yarn delivered (cm/min) = πd (NS –NT)

Here winding takes place in similar conditions to when the traveller is stationary and the spindle is rotating; hence winding does not insert any twist onto the yarn. On the other hand, during over-end unwinding one turn of twist is inserted for every unwound of coil.

Turns/cm for unwinding = 1/πd

Total twist present in the yarn after over-end unwound = NT/πd(NS –NT) + 1/πd = NS/πd(NS-NT)

Since yarn from the ring cop is normally over-end withdrawn during the winding process, the spindle speed is taken for calculating the turns/cm in the yarn instead of using traveller speed. However, turns/cm in the roving is calculated by taking the flyer speed into account. This is due to the parallel withdrawal of roving during spinning.

Twist insertion onto the strand when flyer leads bobbin. Due to the difference in the speeds of the flyer and the bobbin, the winding of roving takes place on the bobbin.

Twist/cm due to twisting = NB / πd(NF-NB)

Twist/cm due to winding = (NF-NB)/ πd(NF-NB)

Twist/cm in the roving = NF / πd(NF-NB) where

NF - flyer speed in rpm,

NB - bobbin speed in rpm.

If the roving is unwound in parallel, the roving will have the same amount of twist as in the bobbin, but if it is over-end withdrawn, it will lose a certain amount of twist during unwinding.

Turns/cm due to over-end withdrawal = - (NF-NB)/ πd(NF-NB)

Turns/cm in the roving after over-end withdrawal = NB/πd (NF-NB) 

Summary and conclusion

• Yarn will rotate 3600 per coil wound while winding yarn onto a stationary cop by hand. When it is over-end unwound from the cop, all twists present in the yarn are removed. Hence both winding and over-end unwinding cause twisting, but in opposite directions.
• If the yarn is wound onto the cop by feeding the yarn perpendicular to the cop and rotating it, winding the yarn will not cause any twisting. But if the yarn is over-end withdrawn, the yarn will receive one turn of twist per coil unwound.
• If the flyer leads the bobbin in the roving frame, twisting of the roving takes place due to both twisting and winding.
• Since the yarn from the cop is over-end withdrawn during winding, the spindle speed is taken for calculating the twist in the yarn, whereas the flyer speed is taken for calculating the twist in the roving, due to parallel unwinding of the roving during spinning.
• The over-end unwinding of yarn helps in getting extra twist to the yarn, and the parallel unwinding of roving will not introduce any extra twist to the roving. If the roving is over-end withdrawn during spinning, every coil unwound will insert one turn of twist onto the roving. Hence the break draft and the setting of the back roller have to be increased to facilitate the breakage of the twist present in the roving. Otherwise, undrafting of the strand will occur during drafting. Hence the roving is normally unwound in parallel from the bobbin during ring spinning.