Singeing

Singeing is a process applied to both yarns and fabrics to produce an even surface by burning off projecting fibres, yarn ends, and fuzz. This is accomplished by passing the fibre or yarn over a gas flame or heated copper plates at a speed sufficient to burn away the protruding material without scorching or burning the yarn or fabric.

The process is usually to pass one or both sides of a fabric over a gas flame to burn off the protruding fibres. Other methods include infra-red or heat for thermoplastic fibers. Singeing of yarns is also called "gassing".
Cellulose fibres such as cotton are easily singed because the protruding fibers burn to a light ash which is easily removed. Thermoplastic fibres are harder to singe because they melt and form hard residues on the fabric surface.

When Singeing is done to fabrics containing cotton, this results in increased wettability, better dyeing characteristics, improved reflection, no "frosty" appearance, a smoother surface, better clarity in printing, improved visibility of the fabric structure, less Pill and decreased contamination through removal of fluff and lint.

Types of Singeing Systems

There are two types of systems in singeing 

 

Direct and Indirect.

Direct Singeing System

The action of burning away the protruding ends of the fibers is brought about by the direct action of the flame ensuing from the gas burners. In an alternative improved system, the fully combusted hot flue acts directly on the protruding fiber ends.The rates of fuel gas and air are carefully adjusted so that sufficient hair is removed without damaging the core.

Indirect Singeing System

In this system, the heat, in the forms of diffused infra-red radiations, produces a more even singeing effect. Owing to the indirect character of the singeing effect, this system is quite suitable for fabrics having wavy selvedges, such as those occurring in the case of fabrics coming out from shuttle-less types of looms.

Ply Yarns

For sewing threads as well as for some speciality industrial yarns , it is necessary to ply (to double or fold) the yarns to give them a smoother and less hairy character.

Doubling improves the evenness and plying balances torque if carried out correctly and binds some of the hairs on the component yarns.

Plying is a process used to create a strong, balanced yarn. It is done by taking two or more strands of yarn that each have a twist to them and putting them together. The strands are twisted together, in the opposite direction than that in which they were spun. When just the right amount of twist is added, this creates a balanced yarn, which is a yarn with no tendency to twist upon itself. Almost all store bought yarns are balanced, plied yarns.

A two-ply is thus a yarn plied from two strands, a six-ply is one from six strands, and so on. Most commercial yarns are more than a two ply. Embroidery floss is generally a six ply yarn

Regular Plying

Regular plying consists of taking two or more singles and twisting them together, the opposite way. This can be done on either a spinning wheel or a spindle. The most important thing to remember though is that the twist must go the opposite direction. If in spinning the single the wheel was spinning clockwise (which is called a "Z" twist, as on any given side the fibres appear to cross diagonally in the same direction as the diagonal of a "Z"), in order to ply it the wheel must spin counter-clockwise (an "S" twist). This is because otherwise you are not balancing the twist, just twisting it more. The concept is similar to when a heavily twisted piece of yarn is folded, and it twists up on itself. It is most common for singles to be spun with a "Z" twist, and then plied with an "S" twist.

Novelty Yarns

Many novelty yarns make use of special plying techniques to gain their special effects. By varying the tension in the strands, or the relative sizes of the strands, or many other factors different effects can be achieved. For example, when a soft, thick strand is plied against a tightly twisted thin strand, the resulting yarn spirals. Another example is bouclé, which is a yarn where one strand is held loosely and allowed to make loops on the other yarn while plying.

Splicing

A high degree of yarn quality is impossible through knot, as the knot itself is objectionable due to its physical dimension, appearance and problems during downstream processes. The knots are responsible for 30 to 60% of stoppages in weaving.

Splicing is the ultimate method to eliminate yarn faults and problems of knots and piecing. It is universally acceptable and functionally reliable. This is in spite of the fact that the tensile strength of the yarn with knot is superior to that of yarn with splice. Splicing is a technique of joining two yarn ends by intermingling the constituent fibres so that the joint is not significantly different in appearance and mechanical properties with respect to the parent yarn. The effectiveness of splicing is primarily dependent on the tensile strength and physical appearance.

Splicing satisfies the demand for knot free yarn joining: no thickening of the thread or only slight increase in its normal diameter, no great mass variation, visibly unobjectionable, no mechanical obstruction, high breaking strength close to that of the basic yarn under both static and dynamic loading, almost equal elasticity in the joint and basic yarn. No extraneous material is used and hence the dye affinity is unchanged at the joint. In addition, splicing enables a higher degree of yarn clearing to be obtained on the electronic yarn clearer.

Splicing technology has grown so rapidly in the recent past that automatic knotters on modern high speed winding machine are a thing of the past. Many techniques for splicing have been developed such as Electrostatic splicing, Mechanical splicing and Pneumatic splicing. Among them, pneumatic splicing is the most popular. Other methods have inherent drawbacks like limited fields of application, high cost of manufacturing, maintenance and operations, improper structure and properties of yarn produced.

Pneumatic Splicing

The first generation of splicing systems operated with just one stage without proceeding to trimming. The yarn ends were fed into the splicing chamber and pieced together in one operation. Short fibres, highly twisted and fine yarns could not be joined satisfactorily with such method. Latest methods of splicing process consist of two operations. During the first stage, the ends are untwisted, to achieve a near parallel arrangement of fibres. In a second operation the prepared ends are laid and twisted together.

 

Principle of Pneumatic Splicing

The splicing consists of untwisting and later re-twisting two yarn ends using air blast, i.e., first the yarn is opened, the fibres intermingled and later twisted in the same direction as that of the parent yarn. Splicing proceeds in two stages with two different air blasts of different intensity. The first air blast untwists and causes opening of the free ends. The untwisted fibres are then intermingled and twisted in the same direction as that of parent yarn by another air blast

Structure of Splice

Analysis of the longitudinal and transverse studies revealed that the structure of the splice comprises of three distinct regions/elements brought by wrapping, twisting and tucking / intermingling.

Wrapping

The tail end of each yarn strand is tapered and terminates with few fibres. The tail end makes a good wrapping of several turns and thus prevents fraying of the splice. The fibres of the twisting yarn embrace the body of the yarn and thus acts as a belt. This in turn gives appearance to the splice.

Twisting

The two yarn ends comprising the splice are twisted around the body of the yarn, each yarn strand twists on the body of the yarn on either side of the middle of the splice. The cross-section of this region distinctly shows the fibres of the two yarn strands separately without any intermingling of the fibres.

Tucking / Intermingling

The middle portion of the splice is a region (2-5 mm) with no distinct order. The fibres from each yarn end intermingle in this splice zone just by tucking. The studies on quantitative contribution of splice elements showed that intermingling/tucking contributes the most to the strength of splice (52%), followed by twisting (33%) and wrapping (about 15%). The lower strength of the splice is attributed to the lower packing coefficient of the splice zone. Spliced yarn has a lower breaking elongation than normal yarn. Breaking elongation is mainly affected by intermingling. Wrapping and twisting provides mainly transverse forces. The absence of fibre migration gives lower breaking elongation to splice.

Effect of Variables on the Properties of the Spliced yarn

Several studies have been conducted on the effect of various variables on the properties of the spliced yarn.

 

Effect of Fibre Properties and Blend

Fibre properties such as torsional rigidity, breaking twist angle and coefficient of friction affect splice strength and appearance. The lower torsional rigidity and higher breaking twist angle permit better fibre intermingling. Higher coefficient of friction of fibres generates more inter-fibre friction to give a more cohesive yarn. Thus, these properties of fibre contribute to better retention of splice strength. In blended yarn, usually the addition of polyester to other fibre blend like P/W, P/C both for ring and rotor spun yarn increases splice strength.

Effect of Yarn Fineness

Several studies on cotton, polyester and wool report that coarser yarns have higher breaking strength but a moderate extension. The coarse yarn cross section contains more fibres and provides better fibre intermingling during pre-opening, hence the splice is stronger than that of finer yarns.

Effect of Yarn Twist

An increase in the twist significantly increases the breaking load and elongation, even at higher pneumatic pressure. This could be due to better opening of the strands at higher pneumatic pressure. Splicing of twisted ply yarn is more complicated than single yarn due to the yarn structure having opposing twists in the single and doubled yarns. Twisted yarns also require a relatively longer time for complete opening of the yarn ends.

Effect of Different Spinning Methods

Yarn produced with different spinning methods exhibit different structure and properties. Therefore, these yarns show significant differences in splice quality. The ring spun yarn lent best splicing but the potential of splicing is affected by the spinning conditions. The breaking strength percentage of ring spliced yarns to a parent yarn is 70% to 85% for cotton yarn. However, the breaking strength and extension of splice vary with fibre and yarn properties. Rotor spun yarns, due to the presence of wrapper fibres, make it difficult to untwist and the disordered structure is less ideal for splicing. The breaking strength retention varies from 54% to 71% and is much lower compared to the splice of ring spun yarns. In case of friction spun yarns, the highest relative tensile strength obtained at the spliced joints can be above 80%, but a number of splicing failures occurs due to unfavourable yarn structure.

The air-jet-spun (MJS) yarn and the cover spun yarn are virtually impossible to splice. Only very low tensile strengths and elongation values can be attained due to the inadequate opening of the yarn ends during preparation of the splicing. The coefficient of variation of these properties is also generally high.

Effect of Opening Pressure

A study on 50/50 polyester cotton, 25 tex ring spun yarn shows a rise in tensile strength up to a certain opening pressure. However, long opening time deteriorates the strength. An increase in pressure up to 5 bar caused release of fibre tufts and fibre loss from the yarn ends in P/C blend which is due to intensive opening, but beyond this pressure, drafting and twisting in the opposite direction may also occur.

Effect of Splicing Duration

With a given splicing length, when the splicing is extended for a long period of time, the breaking strength of the spliced yarn and also their strength retention over the normal value of the basic yarn increases because of increased cohesive force resulting from an increased number of wrapping coils in a given length. The effects are more pronounced at higher splicing lengths. It is desirable however, that splicing duration be as short as possible. The splicing duration alone has no conclusive effect on elongation properties of splice yarn. It has also been observed that, for maximum splice strength, different materials require different durations of blast. These are between 0.5 to 1.8 seconds.

Effect of Splicing Length

Studies on splicing of flyer and wrap spun yarns spun with different materials, showed that regardless of the splicing material, the breaking strength and strength retention of both yarn types increase with the splicing length because of the increased binding length of the two yarn ends. Elongation at break and retention of elongation of both flyer and wrap spun spliced yarns increase with the splice length. Compared to the splicing duration, the splicing length has more pronounced effect on the load-elongation properties of the spliced yarn. It can be therefore be stated that the splices made on longer lengths and for longer period of time have more uniform strength.

Effect of Splicing Chamber

The factors like method and mode of air supply and pressure along with type of prism affect the splicing quality. It was observed that irregular air pressure has advantages over constant pressure for better intermingling in the splicing chamber, which varies with different staple fibres, filament yarns, and yarns with S and Z twists. It is not possible to make a general comment regarding potential of the splicing chamber due to the multiplicity of factors influencing splicing.

Comparison of Dry and Wet Splicing

The comparative studies on dry and wet splicing with water showed that the breaking load retention for wet spliced yarns are significantly greater than dry spliced yarns. In fact, wet splicing is more effective for yarn made from long staple fibres and for coarse yarn. This may be due to higher packing coefficient resulting from wet splicing.

Assessment of Yarn Splice Quality

The two important characteristics of a splice are appearance and strength. Although quality of splice can be assessed by methods like load-elongation, work of rupture, % increase in diameter and evaluation of its performance in down stream process etc., the appearance can be assessed either by simple visual assessment or by comparing with photograph of standard splice.

Bobbin Rejections and Quality Checking for Best Winding

A bobbin change occurs when yarn on the bobbin is fully exhausted during winding. But if a bobbin is changed with yarn still left on it, we call it ‘Rejected Bobbin'. The quantity of yarn on the bobbin may vary from full bobbin to only few layers of yarn.

The Various Reasons of Bobbin Rejections are as follows:

1. Bobbin Quality

• Long Tail End

• Kirchi/Lapetta

• Deshaped Bobbin

• Overfilled Bobbin

• Bottom Spoiled Bobbin

• Ring Cut Bobbin

• Soft Bobbin

• Sick Bobbin

2. Bobbin Feeding in Magazine

• Presence of under-winding and back-winding while feeding the bobbins in the magazine leads to rejection

3. Top Bunch Transfer Failure

• Top bunch position is lower with respect to bobbin tip.

• Blowing device does not come down to concentrate blow at the bobbin tip.

• Very few numbers of coils at the bobbin tip.

• Removal of top bunch due to fault in cutter at the bobbin preparatory or any other reason. Very few numbers of coils at the top bunch.

4. Fault in Winding Unit, Splicing Failure

5. Yarn Quality

• High degree of objectionable fault

• Count variation

• High Hairiness Bobbin

Bobbin Quality Checking for Best Winding

Whenever there is a count change in ring frame, the cop quality should be checked. Proper quality of cop ensures higher winding efficiency. The cop quality is checked as per the following parameters:

1. Bobbin Parameters

2. Cop Content : Depending on the spindle lift and ring diameter, the cop content (in gms) should be checked

3. Diameter of the Cop : The ‘Actual cop diameter' must be checked against ‘Standard cop diameter'. The standard cop diameter depends on the ring diameter. Standard Cop Diameter = Ring Diameter - 3mm.

4. Back Winding : The number of back winding coils should be around 1.5 to 2.5 and the maximum length of back winding should not be more than 80cms

5. Under Winding : The number of under winding coils should be around 2 to 3 and the maximum length of back winding should not be more than 20cm. As the under winding and back winding increases, more time is wasted to open them up before feeding in the magazine and also hard waste is increased.

6. Top Clearance : The clearance from bobbin tip to yarn body of a full cop should be approx 10 mm. If the top clearance is too less, it may cause slough off at the start of the bobbin unwinding.

7. Bottom Clearance : The clearance from bobbin bottom to yarn body of should be approx. 10mm. If the bottom clearance is too less, it may cause bottom spoiled bobbin.

8. Yarn Length per Chase : The length of yarn per chase should be around 3.5 to 5.5 m. If the length is too long, it may lead to slough of during high speed unwinding.

9. Bobbin Hardness : The bobbin hardness should be around 50° to 55°. Soft bobbins results slough off. Besides the above mentioned points, the cops should be also checked for long tail end, deshaped bobbin, kirchi & lapetta, ring cut, overfilled and bottom spoiled bobbin to ensure high production efficiency in winding.
Due to the ever-increasing emphasis on better quality of yarn for the competitive market and process performance, the normal parameters of yarn tenacity, unevenness and imperfections are not adequate to completely define today's quality. Besides the above mentioned traditional parameters, so many factors influence the performance of the yarn in the subsequent process such as process parameters in ring spinning & cone winding, work procedures in ring spinning & cone winding and ambient conditions. So to attain the expected quality for any applications such as weaving or knitting, one should focus mainly on the fault free feed material preparation because it contributes more than any other factor. Best winding capabilities can be achieved through best bobbin quality.

Winding Package Defects

Following are Some of the Winding Package Defects which will result in complaints

Yarn Waste in the Cones

This is due to loose yarn ends that are wound on to the cone

Stitch, Drop Over, Web

Yarn is visible on the small or on the big side of the cone either across the side , around the tube, or going back in the cone

Damaged Edges or Broken Ends on the Cone

The yarn is broken on the edges or in the middle of the cone.

Ring Formation

The yarn runs in belt formation on to the package, because it is misguided

Without Transfer Tail

The desired transfer tail is missing or too short

Ribbon Formation

Pattern or ring formation are made by the drum when rpm are staying the same

Displaced Yarn Layers

yarn layers are disturbed and are sliding towards the small diameter of the cone

Misguided Yarn

The yarn is not equally guided over the hole package

Cauliflower

On the smaller side of the package, the yarn shows a wrinkle effect

Soft and Hard Yarn Layer

Some layer of yarn are pushed out on the small side of the cone

Soft and Hard Cones

Great difference in package density from one winder head to another

Winding Tension, Bobbin Formation, Speed and Production

Winding Tension

If winding tension is selected properly, the following tensile properties are not affected

• Tenacity

• Elongation

• Work- to- break

But excessive tension in winding will deteriarate the above said tensile properties.

Characterestics Of Bobbin Formation

Stretch Length

It is the length of the yarn deposited on the bobbin tube during each chase (one up and down movement of ringrail ) of ring rail. The length should be around 3.5 to 5 meters. It should be shorter for coarser yarns and longer for fine yarns.

Winding Ratio

It is the ratio of the length of yarn wound during the upward movement of the ring rail and the length wound during the downward movement of the ringrail.

Bobbin Taper

The ratio of the length of the upper taper of the cop (bobbin with yarn) to the diameter of the bobbin must be 1:2 or greater. 

 

Winding Speed

It depends upon the following factors

• Count

• Type of Yarn, (type of fibre, average strength and minimum strength)

• Type and Charactersitics of Bobbin

• Package Taper

• Final Use of Package

The best winding speed is the speed which allows the highest level of production possible for a given type of yarn and type of package, and with no damage whatsoever to the yarn.(abrasion and breaks due to excessive tension)

Winding Production

It depends upon the following factors

• Winding speed

• Time required by the machine to carry out one splicing operation

• Bobbin length per bobbin( both bobbin weight and tpi to be considered, because TPI will affect the bobbin length). This decides the number of bobbin changes

• The number of faults in the yarn and the clearer settings, this decides the clearer cuts

• Count

• The number of doffs. It depends upon the doff weight. Higher the doff weight, lower the number of doffs

• The time taken for each doff either by the doffer or by an operator

• Down time due to red light. It depends upon, number of red lights, number of repeaters setting for red lights, clearer settings like off count channel, cluster setting which will result in red lights and others

• Bobbin rejections, it depends on weak yarn, wrong gaiting, double gaiting, bobbin characteritics etc.

Types Of Winding

1.Drum Winding

2.Precision Winding

Drum Winding

Drum winding machines rotate the forming package through surface contact with a cylindrical drum , and the yarn is traversed either by an independent traverse, typically by a wing cam or by grooves in the drum.

Precision Winding

Drum winding systems involves a significant contact between the yarn and the package forming device.Yarns that can be easily damaged by friction in particular filament yarns,are wound into packages using precision winders. 

 

With precision winders, the package is mounted onto a drive spindle, and a reciprocating yarn guide, driven by a cylindrical cam copled into the spindle drive, is used to move the yarn along the traverse length.The reciprocating yarn guide limits the winding speed because of the inertia on reversals. 

 

The term precision refers to the control of positioning each layer of yarn as it is wound on to the bobbin.

 

Different Packages Wound on Winding Machines

• Cones

• Cheeses

• Cops

• Pirns

Overview of Winding

Ring spinning produces yarn in a package form called cops. Since cops from ringframes are not suitable for further processing, the winding process serves to achieve additional objectives made necessary by the requirements of the subsequent processing stages.

Following are the Tasks of Winding Process

• Extraction of all disturbing yarn faults such as the short, long thick ,long thin, spinners doubles, etc

• Manufacture of cones having good drawing - off properties and with as long a length of yarn as possible

• Paraffin waxing of the yarn during the winding process

• Introduction into the yarn of a minimum number of knots

• Achievement of a high machine efficiency i.e high produciton level 

The winding process therefore has the basic function of obtaining a larger package from several small ring bobbins. This conversion process provides one with the possibility of cutting out unwanted and problematic objectionable faults. The process of removing such objectionable faults is called as yarn ‘ clearing'
Practical experience has proven that winding alters the yarn structure.This phenomenon does not affect yarn evenness, but affect the following yarn properties

• Thick Places

• Thin Places

• Neps

• Hairiness

• Standard Deviation of Hairiness