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BARRE IN FABRICS - Page 2

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  • VISUAL BARRE ANALYSIS:
  • The first step in Barre investigation is to observe and define the problem. Barre can be the cause of physical causes which can usually be detected, or it can be casued by dyeability differences which may be nearly impossible to isolate in fabric. Barre analysis methods that help to discriminate between physical barre and barre caused by dyeability differences incluede Flat Table Examination, Light source Observation, and the Atlas Streak analyser.
  • FLAT  TABLE EXAMINATION:
  • For a visual barre analysis, the first step is to lay a full width fabric sample out on a table and view both sides from various angles. Generally, if the streaky lines run in the yarn direction, color differences can be seen by looking down at the fabric in a direct visual line with the yarn direction, and the defect can be positively identified as a barre defect. Viewing the fabric with a light source in the back ground will show if the barre is physical.
  • LIGHT SOURCE OBSERVATION:
  • After completing an initial Flat Table Examination, a Light Source Examination may provide further useful information. Full width fabric samples should be examined under two light conditions, fluorescent and ultraviolet (UV) light. Observations that should be made while viewing under lights are:
  • frequency and direction of the barre
  • whether streaks are dark or light and
  • total length of pattern repeat.
  • Ultraviolet light, commonly referred  to as a "black light", allows the presence of mineral iols to be more easily detected, due to their radiant energy (glow). When observed under UV light, fabrics with streaks that exhibit glow suggest improper preparation. A change in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in scouring can create this problem.
  • PHYSICAL BARRE ANALYSIS:
  • When the  cause of barre is determined or presumed to be physical in nature, physical fabric analysis should be done. Physical barre causes are generally considered to be those which can be linked to yarn or machine differences. Methods of physical barre analysis include fabric dissection, microscopy, and the Roselon Knit Extension Tester.
  • FABRIC DISSECTION:
  • To perform accurate fabric dissection analysis, a fabric sample which contains several barre repetitions is required. First, the barre streak boundaries are marked by the placement of straight pins and/or felt markers. Individual yarns are removed from light and dark streak sections, and twist levels, twist direction, and cut length weight determinations are made and recorded. For reliable mean values to be established, data should be collected from at least two light/dark repeats. After compilation of yarn information, the numbers can be compared individually to adjacent yarns as well as by groupings of light and dark shades.
  • MICROSCOPY:
  • Microscopic examination is useful for verifying yarn spinning systems. Yarns from different spinning systems can have different light reflectance and dye absorption properties. Ring spinnning produces yarn that is smooth. Open end spinning produces yarn with wrapper fibres at irregular intervals. Air jet spinning produces yarn with more wrapper fibres than open end and inner fibres are more paralle. Microscopy can also reveal a shift in loop formation in knitted fabrics when twist direction (S and Z) differences are present.
  • Barre is noticed in a fabric when the visual perception of colour of a particular portion of a fabric is different from that of an adjacent portion. Numerous attempts have been made by research workers to arrive at a mathematical number which gives an equal change when a change in perceptible colour difference exists.
  • Reflectance differences have been considered by many researches to be indication of barre in fabrics. E.R.Cairns, H.A.Davis and J.W.Coryell 5 hypothesised that double knit barre is caused by textured yarn reflectance differences in the knit structure. Depending on the detailed arrangement of these differences, barre is seen as continuous or random and either as single end streaks or bands. Based on studies made with a research grade spectrophotometer, they also found that yarn reflectance differences are caused by differences in key textured yarn properties like bulk, cross section, loop size etc.
  • PREVENTION OF BARRE:
  • As outlined, Barre is caused by INCONSISTENCIES in materials, equipment, or processing. To prevent Barre form occuring, consistency must be maintained through all phases of textile production. Stock yarns should be properly and carefully labelled to avoid mixups. Fugitive tints can be useful for accurate yarn segregation. Inventory should be controlled on a First In/ First Out basis. All equipement should be properly maintained and periodically checked. Before beginning full scale production, sample dyeings can be done to check for Barre.
  • Salvaging a fabric lot with a Barre problem may be possible through careful dye selection. Color differences can be masked by using shades with very low light reflectance (navy blue, black) or high light reflectance (light yellow, orange, or finished white). Dye suppliers should be able to offer assistance in this area. Also, if the cause of the  barre is an uneven distribution of oil or wax, a more thorough preparation of the fabric prior to dyeing may result in more uniform dye coverage.
  • With close cooperation between production and quality control personnel, barre problems can be successfully analysed and solved.
  • EXPERIMENT:
  • The experiments  done by Mr.ANBARASAN of PREMIER POLYTRONICS is given below.
  • FIBRE PROPERTY INFLUENCE ON FABRIC BARRE:
  • EXPERIMENTAL PROCEDURE
    It was identified that the incidences of fabric barre was more common in knitted fabrics. So one of the most commonly used hosiery counts - 30s Nec Combed Hosiery was chosen for the study.
  • Preparation of basic yarn samples:
    Preparation of samples with different yarn count:

    The extent of influence of yarn count was studied by taking into consideration three levels of count. To avoid any abnormal conditions of spinning, one of the levels was maintained at the normal level used by mill for regular production. The other two samples were obtained by spinning counts differing by 2 Nec(6.7%) from the normal. The three count samples of 28, 30 and 32 Nec are designated as A, B and C respectively.
  •  The raw material and the process parameters maintained in all departments upto ring spinning were maintained the same for all the three samples. In ring frames, the count change pinion was changed to obtain the required count. All the other process parameters were maintained the same in ring frames as well.

    Preparation of samples from different micronaire cottons:
  • The samples for studying the influence of fibre micronaire were prepared by spinning yarn from cottons of micronaire values ranging from 3.8 to 4.32. The micronaire values of the samples are given in Table 1 along with their designations. The cottons were obtained by segregating samples of the same cotton variety to avoid influences of other varietal factors.
  • Serial No. Sample designation Micronaire
    1 P 3.8
    2 Q 3.95
    3 R 4.14
    4 S 4.32
  • Table : Micronaire Values of Basic Samples
  • Cottons with difference in micronaire readings of less than 0.15 were not taken up since 0.15 represented the measurement accuracy of the micronaire instrument. The spinnings were carried out using a miniature spinning system having the following sequential processing stages :

  • - Carding
    - Drawing
    - Sliver to Yarn Spinning
    About 50gms of cotton was processed from each sample to obtain yarns sufficient for the subsequent knitting process.

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