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Tuesday, August 25, 2015

Processing Flowchart of Cotton Yarn

A yarn is a continuous and uniform mass of fibres bounded together by the insertion of twist. Yarns are raw material of the fabric. The thickness of the yarn varies to a wide range. Normally, the thickness of a yarn is expressed in terms of count. Count may be defined as the number which expresses the fineness or coarseness of a yarn. The yarns may be spun from staple fibre or continuous filaments. Normally majority yarns are produced from staple fibre. To produce yarns from staple fibres, a wide range of machines are needed, called spinning machines.

Flowchart of Cotton Yarn

A process flow chart of spinning machines and step – wise process sequence for producing cotton staple yarn is shown below:
Cotton in bale form
Blow room machine
Carding machine
Drawing machine
Roving machine
Spinning machine
Cotton yarn

Now I’ll describe the stages in brief as follows –
Cotton in Bale form
Bales are of raw cotton always contains a certain amount of impurities termed as ‘Trash’. The trash materials are broken seeds, husks, broken leaf, dirt’s, and short fibres etc. materials. The amount of trash varies from 1% to 15% depending on the quality of the fibres. Normally imported cotton fibrs are in bale form, which are highly compact form.
Blow room
Blow room is the starting section of a cotton yarn spinning mill. A series of different types of opening, cleaning, and mixing machines are used as per sequence in this section.
Carding
Carding may be defined as the reduction of an entangled or matted mass of fibres to a filmy web by working them between two closely spaced, relatively moving surfaces clothed with sharp points. A carding action is obtained when the teeth on the two surfaces are made to work point to point. When they are made to work point to back, the action is called stripping action.
Drawing Frame
The delivered sliver form the carding machine in coil form within the sliver can is fed in the drawing frame. The drawing frame may be 1, 2, 3, 4, or 5 headed machines. Two headed machine means two slivers will be delivered in that machine.  
Speed/Roving Frame
The delivered sliver from the drawing frame in the sliver can is fed in the speed frame. The speed frame is also called roving frame.
Ring Spinning
Ring spinning is a universal spinning system. The process involved in ring spinning is creeling, drafting, twisting, winding, building up and doffing. In normal ring frames, the number of spindles are 400-500, but 1000 delivery i.e. spindle per ring frame is also available. The delivered rovings in bobbin form is fed in the creels of the ring frame. The rovings are unwound by pulling action and passed through the drafting zone. At the front side of drafting rollers that is front roller, the drafted fibres become twisted and forms yarn.
Yarn
Delivery package that is yarn bobbin is situated on the spindle. The delivered yarn is wound on the yarn bobbin.

Sunday, January 4, 2015

Working Principle of Rotor Spinning

Now a day rotor spindles occupy at least 6% of the world’s total installation. This may seem as a small percentage, however, but when taken in the context of yarn production, this figure is large; as large percentage of yarn spun on this system is in the coarser to medium count range. Open end rotor spinning has become an inseparable part of spinning technology. Its many advantages from both the textile and economic view-point have been speedily recognized and exploited accordingly.

Rotor Spinning

In this process fibres from the draw frame sliver supply are separated from one another on an opening roller, taken over by an air stream, led through a fibre guide channel and fed to the rotor. In the revolving rotor housing the fibres lay themselves and form a ring. Out of this rotating ring the fibres are withdrawn in a plane more or less perpendicular to that of the fibre ring. The rotation of the rotor acts on the fibres in the form of twist when they just leave the fibre ring plane. This leads to a consolidation of the fibres amongst one another, i.e. to the formation of a yarn. This yarn is led away from the open end area and is subsequently wound on a cylindrical bobbin to form a cross-wound package. The yarn obtains ‘real’ twist. As a result of the fibre-yarn geometry during twist insertion the fibres do not have the idealized helicoidally configuration as in a ring yarn. Every now and then fibres also coil themselves on the yarn across the longitudinal yarn axis. These places are called wrappers. A further reference is made to them later in a direct comparison between open end and ring yarns.
This spinning has established itself so far in short staple spinning. The accent lies here in the course count range (3 Ne to 30 Ne or 20 Tex to 200 Tex). Due to improvements in the technique and machine construction, combined with the use of combed slivers, count up to 41 Ne is available in good quality. Even finer counts are not only being aimed at, but are also being presented to some extent.
In short staple spinning OE rotor spinning raises performance at this stage by about 5 to 6 times as compared to ring spinning.

Processing of Man-made fibres and Blends on Rotor Spinning

Ever since the rotor spinning established its superiority over conventional spinning, production of blended and man-made yarns has attracted spinners. One of the most important requirements of blended yarn is the degree of homogeneity in blending their components throughout the length yarns spun and uniform distribution of the individual fibre component in the cross section. In this spinning the fibres are separated down to single fibre stage and then are doubled in rotor groove before being spun into yarn, this result in a homogeneous fibre distribution in yarn can be manufactured economically. However, there are some properties of fibres which pose limitation on the use of rotor spinning.

Rotor Spinning

Raw material requirement
Fibre length
As in the case of cotton, here also the fibre length has direct influence on yarn strength, extension, irregularity CV%, U% handle, and running properties. But in the case of man-made fibres as the length increases it offers higher resistance to separation by opening roller and due to limitation of opening roller speed we cannot get desired fibre separation. As a result the quality of yarn decreases. Fibre length of 30-32 mm is the best suited to get optimum yarn quality economically. As shorter fibre length calls for smaller rotor diameter which can be worked at higher rotor speed.
Fibre Fineness
Finer fibres lead to more fibre/cross section, lower twist level, higher production and better yarn quality but extremely fine fibres pose lot of processing problems at preparatory stage and also at rotor spinning. Fine fibres not only increase rotor deposits but also offer more resistance to separation by opening roller, which affects yarn quality adversely. The optimum fineness to get good yarn as well as good working performance is 1.5 Denier.
Fibre Tenacity
Higher tenacity give higher yarn strength, minimize the strength loss of open-end yarns, suffer less fibre breakages during spinning and therefore, produce good quality yarn.
Fibre Crimp
Due to shortening of spinning process in case of rotor spinning it is very difficult to remove crimp in fibres prior to open end spinning. Highly crimped fibres perform very poorly in open-end because –
-        They offer great resistance to separation action by opening roller leading to fibre damage, deposits and poor yarn quality.
-        The fibres do not flow smoothly in transport channel and also deposition of fibres is not compact in rotor groove. Hence fibres with low crimp level performance must be selected.
Spin Finish
Spin finish affects the yarn parameters and running properties. The spin finish apart from acting as an antistatic has an influence on fibre to fibre friction and protects the fibre from mechanical damage in different process stage. Spin finish should include a lubricant and an antistatic agent but less for rotor spinning than for ring spinning. Excessive lubricant will cause polyester to adhere to combing rolls, points or pins creating fibre wraps and small slubs. Too little lubricant causes problems in carding and abrasion to open-end. When inorganic pigment, usually (TiO2) titanium oxide is included in synthetic fibres as delustring agents, they usually cause severe wear on various parts of the rotor spinning units, particularly the opening rollers and the open-ends. The content of titanium oxide in matt fibre is usually up to 0.5%, half matt or semi dull fibre containing considerable less TiO2 therefore is a better solution.

Sliver Preparation
For spinning good quality blending yarn apart from quality of sliver, the uniformity of blend requires special attention. The doubling that takes place in rotor will produce good fibre distribution in yarn cross-section; but is incapable of compensating for long term irregularity. The choice of blending system (Blow room or Draw frame) depends on whether the cotton components used are carded or combed. It is observed that use of combed cotton instead of carded does not improve yarn strength or other properties hence it is practicable to use carded cotton.
Both the systems of blending are good but blow room blend with one passage of draw frame gives good quality yarn. If draw frame blending is used, auto leveled carded sliver should be given two or three draw frame passages.

Rotor Spinning Parameters
For spinning 100% polyester or polyester cotton blends special type of opening roller suitable for processing man-made fibre is required. Because of greater adhesion in the case of man-made fibres the opening roller should be work at approximately 7,000 to 8,000 rpm. The rotor speed must not be excessively high otherwise molten spots will occur in yarn. The rotor speed should be approximately 10% less than in the case of 100% cotton under comparable condition. Apart from few exceptions this limit will presently be below 70,000 rpm, with low pill types the rotor speed must be reduced further. Only smooth chromium plated or ceramic navel should be used in order to achieve a yarn which is of the optimum smoothness and freedom from pilling. In order to get good quality and consistent good working, greater importance is needed to ensure that correct atmosphere conditions are maintained. Low dry bulb temperature must be maintained and relative humidity should be between 50 to 55%. Blends of polyester viscose can also be spun on similar lines.

Saturday, January 3, 2015

Open-end Rotor Spinning

Open-end Rotor is one of the most modern techniques of spinning and winding. Here spinning and winding are sensibly combined in one process. This process overcomes all the problems of Ring Spinning by separating twisting and winding in yarn manufacturing process. It has established itself alongside of Ring frame. On one hand, the success of rotor spinning is due to substantial increase in productivity and on other hand to the possibility of full automation of the spinning process. This is possible because it combines three manufacturing processes – Speed frame, Ring frame and Winding – into one single step. It was not only the economic advantages; but constant improvement in your parameter.

Open-end spinning

Steps in Process
Input Sliver
Drafting and fibre transportation
Twist insertion
Output yarn
Winding of yarn (Cheese/Cone)

Properties of Open-end yarn and Fabric

Because of the structural difference, some of the properties of this yarn are very different from those conventionally produced yarns. In some respects open-end yarns are indisputably better; in others they are inferior or at least may appear to be so when judged by the criteria normally applied to the ring spun yarns.
Yarn Properties
The tenacity of this spun yarn is 15-20% lower than that of equivalent ring spun carded cotton yarns and up to 40% lower than that of ring spun combed cotton or man-made fibre yarns. Factors affecting the degree of difference include linear density, material, preparatory process and type of machine. Even though the strength is low as compared to ring spun yarn the strength regularity is better in OE yarn which gives it an advantage in subsequent process.
-         Twist – OE spinning frames are built for ‘Z’ twist only. The level twist used in production of OE yarns is usually higher than ring and are necessary to give satisfactory performance.
-         Extension – OE yarns are more extensible and recover very quickly from short term stressing. The higher extensibility of OE yarn obviates or out-sets the disadvantages of lower strength.
-         Regularity – OE spun cotton yarns are superior in short term regularity to carded ring spun cotton yarns and there is complete absence of pronounced drafting weave type of irregularity that is the characteristic of the latter.
-         Imperfection – As for regularity the OE spun product is superior to ring spun equivalent for carded cotton yarn and is similar for combed cotton yarns.
-         Yarn Bulk – OE yarn is bulkier than the corresponding ring spun carded yarn. This is manifested in the yarn core where fibres do not adhere so firmly as in yarn spun on ring frames.
Fabric Characteristics
The major factors that determine the properties of fabrics are the yarn properties from which they are produced. It is therefore to be expected that fabrics produced from OE spun yarn will have lower tensile, tearing, and bursting strength and higher extension of breaks, than their equivalent. The actual differences however, are influenced by other factors like fabric construction etc.
-         Appearance – Yarn regularity, less fault content, absence of nep, hairiness and luster, all improve the appearance of fabric produced from OE spun yarn. The difference in appearance between fabric made from OE yarn and ring frame yarn is less when comparison is made with combed yarns in fabric or man-made fibre yarns.
-         Fabric Strength – The reduction of strength in OE yarns by 15-25% is reflected in fabric strength. This, however, can be adjusted by engineering the fabric, the weave, set and yarn count.
-         Fabric Shrinkage – With density set OE fabrics, shrinkage is approximately same as that of conventional fabrics. With loosely set woven fabrics, however, the shrinkage is about 0.5 - 1.0% higher in both warp and weft.
-         Mercerization – Because of difference in yarn structure the luster of mercerized OE fabric is less than ring spun fabric.
-         Creasing – The creasing behavior of OE fabrics is comparable with that of classical cloth.
-         Air Permeability – Air permeability of OE yarns is 15-25% greater; but after processing, when fabrics shrink this difference is reduced.
-         Hairiness – Evidence has shown that OE spun yarns are less hairy than ring spun yarns and the variation in hairiness that exists within ring spun package is not present in an OE spun package.
-         Fabric Drape – The fabric produced from OE yarns are stiffer than one produced from ring spun yarns because of greater space occupied by the yarns.
-         Fabric Handle – No marked difference in the handle of two types of fabrics is observed even when the OE yarns are bulky and are more twisted.
-         Fabric Cover – The cover of fabric made from coarser OE yarns is very good. Some types of fabrics from finer yarns have less cover as is also shown by greater air permeability. This may be due to lower yarn hairiness, difference in warp set, reed marks etc.

  Defects in Open-end yarn and their causes

-         Single thick place – Approximately 2-3 times than the normal yarn size and in length shorter than rotor circumference.
Causes – Insufficient fibre separation at opening roller due to worn or damaged opening roller. Quality of feed sliver and amount of short fibre% is more.
-         Thin Place – Are half the size of yarn cross section and are usually of length in excess of at least 60 cm.
Causes – Bunching of fibres in feed sliver (due to lack of homogeneous blending) faulty drafting during sliver feeding (can position, condition of can springs).
-         Chain of thick and thin faults – These faults are similar to those explained as above but differ due to fact that they are repeated along yarn at regular interval for few meters or km.
Causes
                              i.            Build up of dirt on rotor.
                            ii.            Sliver position is incorrect.
                          iii.            Air leakages in spin box.
                         iv.            Fibre accumulation in spin box, mainly in transport channel.
-         Moire – Thick places occur in conjunction with thin place. Their sizes is small i.e. thick place about 8-10% of average yarn count with length ranging from 5 – 10 mm but the most serious is their periodity.
Causes – Micro-dust accumulation in machine.
-         Over twisted yarn portion – Similar to crackers. They are placed in yarn which are of a high twist but are much longer.
Causes
                              i.            Lack of homogeneous mixing.
                            ii.            Fibres of varying properties blended.
                          iii.            More wrapper fibres.
                         iv.            UR% of fibres less.
                           v.            Rotor dia too small or wrong fitting.
-         Yarn hairiness
Causes -
                              i.            Rough, damaged navel.
                            ii.            Rough or damaged yarn guide.
                          iii.            Contaminated m/c.
-         Yarn spun too fine
Causes – Rotor position with respect to fibre channel plate wrong i.e. far away.
-         Flames and thick places
Causes – Wrong out twin discs, drops horizontally and disturb the position of rotor with respect to navel and fibre feed channel.
-         Poor twist in yarn
Causes – Yarn running out of take up roller, grip giving rise to fluctuating spinning tension.
-         Black or grey portions in yarn
Causes
                              i.            Soiled fluff of machine top falling in cans.
                            ii.            Dirt from winding head falling in cans.
                          iii.            Rotor stopped for long time gets soiled.
-         Trash on yarn
Causes
                              i.            High trash%.
                            ii.            Opening roller speed low.
                          iii.            Trash separation and collection poor (i.e. suction)
                         iv.            Trash belt speed low.
                           v.            Air leakage in one of spin box.

Wednesday, December 3, 2014

The main check points of machines from Blow room to Spinning

     Beginning from the fibre, if the section and blending of fibre is not proper, the yarn will be faulty and produce streaks and bars during weaving, dyeing or finishing. This factor, through not so prominent in exclusively cotton sorts, becomes a nuisance in the case of blended, regenerated or purely synthetic yarn fabrics. If there be variation in the intrinsic luster of two groups of fibres in a blend, the yarn will be faulty and is prone to produce streaks after weaving. The weighing of different fibres should be done accurately and there should be enough topping of the material in stack room to get as homogeneous a blend as possible. The moisture content of the blend should be checked and not allowed to exceed the limit, when feeding into scutchers.

The main check points of machines belonging to this section are as follows –

Machine
Check Points
Scutcher
-         Correct air drafts
-         Correct setting of piano feed regulator
-         Proper pressure during lap’s formation
-         Lap’s ejection mechanism should act at the right moment and in case of a 13 or 15 kgs lap, the variation between any two laps should not be more than 250 gms.
-         In case of the same scutcher is used for a different blend or fibre, it should be thoroughly cleaned so that any chance of fibre dilution is totally avoided.
-         Proper settings and speeds of cylinder, doffer and licker in.
-         The metallic clothings of all rollers should be undamaged and free from embedded, undesirable fibres or foreign matters.
-         Correct setting of flats, mote knives, under casings, and plates.
-         Drafting zone setting should be proper to suit the fibres being processed; as per machine makers directives.
-         Any eccentricity of rollers should be checked and corrected.
-         Any eccentricity of rollers should be checked and corrected.
-         Any roller slippage, which may occur due to wrong fitting, should be detected and corrected in time.
-         It has been found by experiment that if the number of draw frame passage is increased, streakiness is reduced.
-         Stop motions should be checked for proper functioning.
-         Singles should be avoided by the operatives.
-         Proper settings of drafting zone.
-         Drafts should not be more than recommended for a particular fibre length.
-         Accurate builder motion.
-         The break draft should be accurate.
-         Check the density of a rove package before any undesirable packages are formed.
-         Correct drafting zone setting.
-         Proper draft.
-         Correct passage of rove to the nip of the back roller.
-         Worn-out rings should be replaced in time and travelers changed before they are damaged.
-         Vibrations in ‘out of centre’ spindles should be checked and corrected.

Some important points relating to section –

-         Instead of the usual draw frame stage, if mixing be done at the earliest possible stage, the chances of streaks or bars are much less.
-         It should be noted that, in a mixing, the dull fibre contributes more to streakiness than its bright counterpart.
-         Upto a certain length, increased draw frame passages reduce the chances of streakiness.
-         If difference in fibre deniers be improper, then they will dye differently in the same dye liquor. In a 5% color strength, if two yarns, one composed of a 3d viscose mixing and the other of 5d viscose mixing, be dyed, then, due to higher capillary denier, the color yield of a 5d yarn will be higher and to get the same intensity of color for the 3d, whose strength will drop to about 80%; the amount of dye strength needed will be (5 X 100)/80 = 6.25%

Wednesday, November 20, 2013

Mixing, blending and bale management

Definition of Mixing and Blending | Lint and Linters | Bale management

Mixing: Mixing could be thought of combining of fibres together in somewhat haphazard proportion whose physical properties are partially known so that, the resultant mixture has only generally known average physical properties which are not easily reproducible.

Blending: Blending is based on the measurement of important fibre properties i.e, length, strength, cleanliness, e.t.c. Quantatively proportioning and combining the compatiable properties of the resultant blend can be predicted and reproducible.

Importance of mixing and blending:
  • To give the required characteristics to the end product.
  • To compensate for variation in the characteristics of the raw mtls.
  • To hold down raw material cost.
  • To achieve uniform quality.
  • To use waste cotton in mixing.
  • To meet functions and end use requirements.
Lint: The seed free cotton which is gotten after ginning is called ginning.
Linters: After ginning some short fibres are remained with the surface of the cotton seed which is called linters.
Bale management: The choice of cotton bales according to the fibre characteristics in order to achieve acceptable and economical processing condition and a constant yarn quality is called bale management.
Objects of bale management:
  • An evening out of the quality characteristics of a yarn.
  • A mean of avoiding quality jumps.
  • A possibility of reducing cost as a result of an improved knowledge of the fibre characteristics.
  •