Assignment on Different Spinning System

Introduction:

From the very beginning of human era, man has given importance to various things. The best among them after food is “Clothing”. Man always wanted to protect himself from the rude weather and for this, the concept of “Clothing” has blasted into human brain. Since, then men have come a long way. They have seen various phases of clothing. From animal skin to luxurious dresses we see today. Men had to work very hard.

“Spinning” is the first step to enter into the world of clothing. It is the process through which a fibre is turned into yarn. The biggest textile sector “Spinning” is the most important part of making a garment. Textile technology in spinning covers blow room, carding, draw frame comber, speed frame, ring frame, winding, fibre testing, yarn testing etc. For thousands of years, fiber was spun by hand using simple tools, the spindle and distaff. Only in the High Middle Ages did the spinning wheel increase the output of individual spinners, and mass-production only arose in the 18th century with the beginnings of the Industrial Revolution. Now in modern era Man made fibre is vastly used to produce fabric. But the production of man made fibre is simply different. Most synthetic & cellulosic manufactured fibres are created by the different spinning system, such as wet, dry, melt & gel spinning process etc. We are textile engineering students, we tried our level best to create a reports on Different spinning process of MMF and hence this attempt. With our limited knowledge, we would like to share some information with you.

v What is spinning?

The term “Spinning” is used to describe any process used in producing continuous yarns or threads. Confusion is often caused by the fact that it refers to two different techniques.

ü In its original textile sense, Spinning is an ancient textile art in which plant, animal or synthetic fibers are twisted together to form yarn (or thread, rope, or cable). In spinning, separate fibers are twisted together to bind them into a long, stronger yarn. Characteristics of the yarn vary based on the material used, fiber length and alignment, quantity of fiber used and degree of twist.

ü In making man made fibres a liquid fibre forming material is extruded from holes in a spinneret. The liquid polymer is converted first to a rubbery state and then solidified. The process of extrusion and solidification of endless filaments which may be virtually any length. A number of them twisted together to form a yarn, is too called spinning.

THE HISTORICAL DEVELOPMENT OF SPINNING

Spinning » Early spinning methods:

Spinning is the process of drawing out and twisting fibres to join them firmly together in a continuous thread or yarn. Spinning is an indispensable preliminary to weaving cloth from those fibres that do not have extreme length. From early times through the Middle Ages spinning was accomplished with the use of two implements, the distaff and the spindle. The distaff was a stick on which the mass of fibres was held. The drawn-out length of fibre was fastened to the weighted spindle, which hung free. The spinner whirled the spindle, causing it to twist the fibre as it was drawn from the distaff. As a length was drawn out the operation was halted, the new yarn wound on the spindle and secured by a notch, and the operation repeated. The spinning wheel, invented in India and introduced to Europe in the Middle Ages, mechanized the process; the spinning of the wheel supplanted the whirl of the weighted spindle, and after each operation the spinner wound the new yarn on the spindle. This was accomplished simply and speedily by holding the yarn outstretched with the left hand and feeding it as the wheel was spun in the reverse direction.

An important advantage conferred by the spinning wheel was the fact that it tended to add more twist at thin places in the forming yarn and to draw out the thicker places, giving a more uniform yarn.

The spinning wheel continued in use into the 19th century, receiving an important improvement in the 16th century in the form of the Saxony wheel, which made possible continuous spinning of coarse wool and cotton yarn. With this improvement in speed, three to five spinning wheels could supply one loom with yarn, but Kay’s flying shuttle (described below under Woven fabrics) greatly increased the output of the loom and created a demand for spinning machinery. James Hargreaves’ spinning jenny (patented 1770) operated a number of spindles simultaneously, but was suitable only for making yarn used as filling.

Arkwright's First Spinning machine

Sir Richard Arkwright, making use of earlier inventions, produced a better machine, capable of making stronger yarn than Hargreaves’ jenny. Still a third machine, Samuel Crompton’s “mule” (1779), vastly increased productivity, making it possible for a single operator to work more than 1,000 spindles simultaneously; and it was capable of spinning fine as well as coarse yarn. Several further modifications were introduced in Britain and the United States, but the Crompton mule effectively put yarn spinning on a mass production basis.

Spinning » Modern spinning methods:

In modern spinning, slivers or rovings are fed into machines with rollers that draw out the strands, making them longer and thinner, and spindles that insert the amount of twist necessary to hold the fibres together. Tightness of the twist determines the strength of the yarn, although too much twist may eventually cause weakening and breakage. When the spirals formed by twisted yarns are similar in slope to the central portion of the letter Z, the yarns are described as Z-twist; when the spirals conform in direction to the central portion of the letter S, the yarns are described as S-twist. Crepe yarns, producing a crinkled effect in fabrics, are made with a very high degree of twist, producing a kink. Shadow effects can be produced in finished fabrics by the use of yarns combining opposing twists, producing differing light reflections. The spinning process is completed by winding the yarn on spools or bobbins.

Most synthetic and cellulosic manufactured fibers are created by “extrusion” — forcing a thick, viscous liquid (about the consistency of cold honey) through the tiny holes of a device called a spinneret to form continuous filaments of semi-solid polymer.

In their initial state, the fiber-forming polymers are solids and therefore must be first converted into a fluid state for extrusion. This is usually achieved by melting, if the polymers are thermoplastic synthetics (i.e., they soften and melt when heated), or by dissolving them in a suitable solvent if they are non-thermoplastic cellulosics.

If they cannot be dissolved or melted directly, they must be chemically treated to form soluble or thermoplastic derivatives. Recent technologies have been developed for some specialty fibers made of polymers that do not melt, dissolve, or form appropriate derivatives. For these materials, the small fluid molecules are mixed and reacted to form the intractable polymers during the extrusion process.

THE SPINNERET

The spinneret, which is used in the production of all man-made fibers, This is the most important part of a man-made fibre producing machine. It is made in the principle, to a bathroom shower head. A spinneret may have from one to several hundred holes. The tiny openings are very sensitive to impurities and corrosion. The liquid feeding them must be carefully filtered (not an easy task with very viscous materials) and, in some cases,

the spinneret must be made from very expensive, corrosion-resistant metals. Maintenance is also critical, and spinnerets must be removed and cleaned on a regular basis to prevent blockage.

Spinneret was first invented by OZANAM at 1862 A. D. It is made of Platinum, Iridium, Rhodium, Stainless steel, Tantalum.

Types of spinning process:

There are four methods of spinning filaments of manufactured fibers:

1. Wet spinning.

2. Dry spinning.

3. Melt spinning.

4. Gel spinning.

Wet spinning :

Wet spinning is the oldest process. It is used for fiber-forming substances that have been dissolved in a solvent. The spinnerets are submerged in a chemical bath and as the filaments emerge they precipitate from solution and solidify. Because the solution is extruded directly into the precipitating liquid, this process for making fibers is called wet spinning. Acrylic, rayon, aramid, modacrylic and spandex can be produced by this process.

Wet spinning is carried out by the following steps:

1. Dope preparation

2. Extrusion

3. Spinning.

4. Stretching.

5. Spin finish.

6. Drying & steaming.

Wet spinning process:

1. At first solid polymer and suitable solvent is dissolved in a solution vessel.

2. The solution is then heated in heat exchanger.

3. The solution is passed / extruded to spinneret which immersed in a coagulation bath / spin bath by pump.

4. The polymer is then precipitated or is chemically regenerated and it is converted into the filament of solid form.

5. The filament is converged & wound on bobbin.

6. The wended filament is then drawn and finally it is washed & dried and is also wound on suitable package.

Figure 1: Stages in the wet spinning of polymeric fibres.

Wet spinning solvent & coagulant:

Fibre	Solvent	Coagulant
Viscose	Alkaline water	Dill H₂SO₄ + Na₂SO₄+ ZnSO₄
PVA	Water	Aqueous NaOH
PAN	DMF/DMC+60%ZnCl₂	Aqueous DMF/DMC+40%ZnCl_2..

Advantage:

Ø Suitable for staple fibre.

Ø Both organic and inorganic solvent can be used.

Ø Low temperature required.

Ø Higher production due to continue spinning.

Ø Soften process.

Ø Investment cost is low.

Disadvantage:

Ø Slow spinning speed.

Ø Washing & bleaching of fibres are needed.

Ø Toxic .

Dry spinning:

In dry spinning, the fibre forming polymer dissolved in a volatile solvent is introduced into a heated drying chamber where the solvent is evaporated and solid fibre is obtained through spinneret. This process may be used for the production of acetate, triacetate, acrylic, modacrylic, PBI, spandex, and vinyon.

Dry spinning process:

1. Firstly the solid polymer and suitable solvent is dissolved together in a solution vessel.

2. The solution vessel is filtered and stored to a feed vessel.

3. The solution is slightly heated by a heat exchanger to a temperature above the boiling point of the solvent.

4. Then it is pumped to the filter and to spinneret at specific rate of pressure. The number of holes in the spinneret typically does not exceed 2000.

5. The spinning cabinet has pre-heated gas (air, nitrogen, carbon dioxide, superheated steam, or solvent vapor) entering at the bottom of the spinning cabinet. The gas flows around the spun fibers and the solvent is rapidly removed from the fiber and the solvent rich gas exits out of the top.

6. The evaporated gas is passed to the solvent recovery plant.

7. Solid filament is treated to spin finish and then wound on a suitable package.

Dry spinning solvent:

Fiber	Solvent	Polymer Concentration (%)
acetate	acetone + 2-6% water	20-30
triacetate	methylene chloride + 5% methanol	20-22
acrylic	dimethylformamide	25-32
modacrylic	acetone	25-30
	dimethylformamide	25-30
PVC	carbon disulfide + acetone (40:60)	35
	acetone + benzene
vinyl chloride-vinyl acetate copolymer	acetone
elastane	dimethylformamide	20-35
	dimethylacetamide	20-25
Poly (m-phenylene isophthalamide)	dimethylformamide + 5% LiCl	15-20
polybenzimidazole	dimethylacetamide

Advantages:

Ø Suitable for producing fine denier fibres.

Ø No need of washing of fibre.

Disadvantages:

Ø Investment cost is high.

Ø Toxic and risk of explosion.

Ø Heat input is very high.

Ø Can not be used for staple fibre production.

Ø Produce low dye ability fibre.

Melt spinning:

The process of spinning by which fibre or filament is produced from melted polymer chips by extruding through spinneret is called melt spinning. Continuous filament produced here. It is the preferred method of manufacture for polymeric fibres. Number of filament depends on number of holes in spinneret. In melt spinning, the fiber-forming substance is melted for extrusion through the spinneret and then directly solidified by cooling. Nylon, olefin, polyester, saran and sulfar are produced in this manner. Melt spun fibers can be extruded from the spinneret in different cross-sectional shapes (round, trilobal, pentagonal, octagonal, and others). Trilobal-shaped fibers reflect more light and give an attractive sparkle to textiles.

Pentagonal-shaped and hollow fibers, when used in carpet, show less soil and dirt. Octagonal-shaped fibers offer glitter-free effects. Hollow fibers trap air, creating insulation and provide loft characteristics.

Melt spinningprocess:

1. At first the fibre forming polymer / polymer chips are fed into a hopper then to the melter.

2. At the melter the polymer is heated over melting point.

3. The full chamber is filled by N₂or inert gas.

4. The polymer solution is pumped to the filter to removing impurities.

5. The polymer is then extruded through the spinneret holes.

6. Cold air is passed over the filament to bring solid form.

7. Then the solid filaments are converted by converging guide to give a slight twist.

8. Apply spin finish.

Advantages:

Ø This process can be used for both staple & continuous filament.

Ø Direct and simple process.

Ø No environmental pollution occurs.

Ø No solvent required.

Ø Non toxicity and no risk of explosion.

Ø High production speed. (2500-3000 ft/min )

Ø Low investment cost.

Disadvantages:

Ø Required more proper maintenance of the machine.

Ø For flat yarn separate stretching operation is required.

Ø Heat of input is high.

Typical melt spinning system:

Polymer	Melting point	Spinning temperature
Nylon – 6,6	264˚C	280 -290
Nylon – 6	220˚C	270 -280
PET	264˚C	280-300
Polypropylene	167˚C	250-300
Polyethylene	125˚C	250-300

Gel spinning process:

Gel spinning is a special process used to obtain high strength or other special fiber properties. The polymer is not in a true liquid state during extrusion. Not completely separated, as they would be in a true solution, the polymer chains are bound together at various points in liquid crystal form. This produces strong inter-chain forces in the resulting filaments that can significantly increase the tensile strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis by the shear forces during extrusion. The filaments emerge with an unusually high degree of orientation relative to each other, further enhancing strength. The process can also be described as dry-wet spinning, since the filaments first pass through air and then are cooled further in a liquid bath. Some high-strength polyethylene and aramid fibers are produced by gel spinning.

Conclusion:

As a textile engineer, learning “Spinning” or “Yarn manufacturing” is must for us. In this assignment we were able to bring only one drop of spinning knowledge from the spinning ocean. But one thing is for sure, each and everyone of this group has tried their heart out to enrich this assignment.

This assignment has helped us in two ways. First of all, we have learnt quite a lot about different spinning system with the help of modern technology/Internet and various books. Secondly, it encouraged us to work as a group. Now we know the power of unity which looked quite impossible when we started but now have become a reality. It has been possible only because of working as a team. At last, thanks to almighty ALLAH, who has bestowed us with some of His knowledge.

Contribution: