YARN FAULTS AND CLEARING It is still not possible to produce a yarn without faults for various reasons. Fly liberation in Ring frame department is the major reasons for short faults in the yarn because of the fly gets spun into the yarn. Hence it is not possible to have fault free yarn from ring spinning, it is necessary to have yarn monitoring system in the last production process of the spinning mill. Depending upon the raw material, the machinery set up, production and process parameters, there are about 20 to 100 faults over a length of 100 km yarn which do not correspond to the desired appearance of the yarn. This means that the yarn exhibits a yarn fault every 1 to 5 km. These faults are thick and thin faults, foreign fibres and dirty places in the yarn. Faults Faults in fabric fabric due to yarn: 1) Neps 2) short thick 3) long thick 4) long thin 5) hairiness 6) count variation 7) contamination 8) splice fault 9) periodic fault 10)
1) Neps: This types of faults are extremely very short (a few mm) and
extremely thick (several times of the base diameter). Neps is generated during ginning and processing time. Neps is 3 types 1) Process neps, 2) Biological neps and 3) SCN. Shortt thic thick k plac places es are are thos thosee faul faults ts whic which h are are not not long longer er than than 2) Shor approximately 8 cms, but have a cross-sectional size approx. twice that of the yarn. These faults are relatively frequent in all spun yarns. yarns. (D : 1.8-3.8 1.8-3.8 of of base dia, dia, L : 0.5 to 10 10 cm) . Thick place place is generated around 50 % due to fly generated in process mainly in ring section. Optimum setting can prevent thick place.
3) Long thick places are much more seldom-occurring than the short
thick places places and usually usually have a length longer than 40cms. In some case cases, s, thei theirr leng length th can can even even reac reach h many many mete meters rs.. Thei Theirr cros crosss
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sectional size approx. + 40% to +100% and more with respect of the mean cross-section of the yarn. (D : 1.2-1.8 times of base dia and L: 5 – 200 cm) 4) Thin places occur in two length groups. Short thin places are known as imperfections, and have a length approx. three times the mean staple length of the fibre. Their frequency is dependent on the raw material and the setting of the drafting element. They are too frequent in the yarn to be extracted by means of the electronic yarn clearing. Long thin places have lengths of approx. 40cms and longer and a cross-sectional decrease with respect to the mean yarn cross-section of approx.30 to 70%. They are relatively seldomoccurring in short staple yarns, but much more frequentlyoccurring in long staple yarns. Long thin faults are difficult to determine in the yarn by means of the naked eye. Their effect in the finished product however, can be extremely serious. It is generated excess drafting in process.
The yarn faults are classified according to their length and cross-sectional size, and this in 23 classes.
FIG: CLASSIMAT FAULTS: •
The cross-sectional deviations are given +% or -% values. i.e. the upper limit, respectively, lower limit with respect to the mean yarn fault crosssection is measure in %. The fault length is measured in cms.
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FIG: YARN CLEARING CONCEPT OF USTER QUANTUM CLEARER N – NEPS, S- SHORT FAULTS, L-LONG FAULTS, CCP - COARSE COUNTS, CCM-FINE COUNTS The classes and their limits are set out according to the following: •
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Short thick place faults: 16 classes with the limits, 0.1 cm, 2cm, 4cm, and 8cm for the lengths and +100%, +150%,+250%, and +400% for the cross-sectional sizes are provided. The classes are indicated A1...D4. The classes A4, B4, C4, D4 contain all those faults, according to their length, whose cross-sectional size oversteps +400%. Spinners doubles: This refers to a class (with the indication E) for faults whose length oversteps 8cms and whose cross-sectional size oversteps +100 ( open to the right and upwards) Long thick place faults and thick ends: The long thin place faults are contained in 4 classes with the limits 8 cms and 32 cms for the lengths, and -30% , -45% and -75% for the cross-sectional sizes. The classes are designated H1.....I2. The classes I1 and I2 are open to the right i.e. they contain all those thin places having a size between -30 and -45%, respectively, -45% and -75% and whose lengths are longer than 32 cms.
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The classification of the shorter thin places is of no advantage in the analysis of the seldom-occurring faults. # Total clearer cut should be 70-100 per 100 km (as small sa better) # Splice less strength about 20% - 25 % of parent yarn # Hairiness increases 20% - 25 % in winding machine # Each splice two neps are generated # In loepfe, specific co-ordinate setting can not possible, to cut a particular point, the whole curb setting need to change which is possible in Uster quantum. # In loepfe, due to hairiness dia diff. setting say 10% for 30 count setting is required. Scanning is done outside of the 10% fine and course side. # for foreign cut no base cure is available. Only class cut is there. # No PP (white) clearing system is available. If we want to clear white PP setting need to close in such a way that total cut will be very high so machine efficiency will be low. # Surface index (SFI) fault are optional part of Yarn Clearer System but we don’t have
Types of Electronic Yarn Clearers
Electronic Yarn Clearers available in the market are principally of two types – capacitive and optical. Clearers working on the capacitive principle have ‘ mass’ as the reference for performing its functions while optical clearers function with ‘ diameter’ as the reference. Both have their merits and demerits and are equally popular in the textile industry. Besides the above basic difference in measuring principle, the bases of functioning of both the types of clearers are similar if not exactly same. Since most of the other textile measurements like, U% / CV%, thick and thin places etc., in various departments take into account mass as the reference parameter, the functioning of the capacitive clearer is explained in some detail in the following sections. Functioning Principle
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A) Capacitive Type: The yarn is measured in a measuring field
constituted by a set of parallel placed capacitor plates. When the yarn passes through this measuring field (between the capacitor plates), an electrical signal is produced which is proportional to the change in mass per unit length of the yarn. This signal is amplified and fed to the evaluation channels of the yarn clearing installation. The number and type of evaluation channels available are dependent on the sophistication and features of the model of the clearer in use. Each of the channels reacts to the signals for the corresponding type of yarn fault. When the mass per unit length of the yarn exceeds the threshold limit set for the channel, the cutting device of the yarn clearer cuts the yarn. Most of the lab machines are working this principle. B) Optical type: A light is passing through the measuring yarn from a light source. The yarn absorb some percentage of Light and the rest of passes through the yarn and the difference of absorbance is measured which indicated the diameter of the measured yarn. Advantage:
1) in high RH difference system is less affected. 2) This is also less sensitive compared with capacitative system 3) Cut is very flexible i.e. particular fault can be removed by specific setting.
Disadvantage:
1) Some times hairiness is treated as fault and cut excessive the measuring head. Yarn Clearer Settings
The yarn clearer has to be provided with certain basic information in order to obtain the expected results in terms of clearing objectionable faults. The following are some of them a. Clearing Limit: The clearing limit defines the threshold level for the yarn faults, beyond which the cutter is activated to remove the yarn fault. The
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clearing limit consists of two setting parameters - Sensitivity and Reference Length. i. Sensitivity - This determines the activating limit for the fault cross sectional size. ii. Reference Length – This defines the length of the yarn over which the fault cross – section is to be measured. Both the above parameters can be set within a wide range of limits depending on specific yarn clearing requirements. Here, it is worth mentioning that the ‘reference length’ may be lower or higher than the actual ‘fault length’. For a yarn fault to be cut, the mean value of the yarn fault cross-section has to overstep the set sensitivity for the set reference length. b. Yarn Count :
The setting of the yarn count provides a clearer with the basic information on the mean value of the material being processed to which the clearer compares the instantaneous yarn signals for identifying the seriousness of a fault. d. Winding Speed:
The setting of the winding speed is also very critical for accurate removal of faults. It is recommended that, instead of the machine speed, the delivery speed be set by actual calculation after running the yarn for 2-3 minutes and checking the length of yarn delivered. Setting a higher speed than the actual is likely to result in higher number of cuts. Similarly a lower speed setting relative to the actual causes less cuts with some faults escaping without being cut. In most of the modern day clearers, the count, material number and speeds are monitored and automatically corrected during actual running of the yarn. Fault Channels:
The various fault channels available in a latest generation yarn clearer are as follows: 1. Short Thick places 2. Long Thick Places 3. Long Thin Places 4. Neps 5. Count
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6. Splice 7. Hairiness The availability of one or more of the above channels is dependent on the type of the yarn clearer. Most of the modern clearers have the above channels. Besides detection of the various types of faults, with latest clearers, it is also possible to detect concentration of faults in a specific length of yarn by means of alarms (cluster faults).
Production of winding machine: It depends upon the following factors •
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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 Yarn 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 characteristics etc.
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WINDING PACKAGE DEFECTS:
Following are some of the package defects which will result in complaints •
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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
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