Methods To Prevent Barre In Knitted Fabric

Methods To Prevent Barre In Knitted FabricIn textile production, peerless of the most common and perplexing tonus issues is barr. The factors that earth-closet cause or contribute to barr be varied and diverse. For this reason, when a barr problem is detected, the skills of a sleuth may be required to expose the problem and eliminate its cause. Once a cause is place, steps throw out be taken to minimize or eliminate the barr, and better graphic symbol textiles can be produced. This discussion will mettle on knitted fabrics.DISCUSSIONSThe noun barr is defined by ASTM1 as an unintentional, repetitive visual excogitation of continuous bars and stripes usually parallel to the filling of distort fabric or to the courses of circular knitted fabric. In a warp knit, barr normally runs in the length direction, following the direction of screw thread flow. Barr can be caused by physical, optical, discolor related differences in the yarn, geometric differences in the fabric struct ure, or by whatsoever combination of these differences. A barr stripe can be one or several courses wide. A typical characteristic of barr is that it generally consists of stripes that repeat. Isolated or intermittent defects may or may non be barr.1 ASTM D123-96a Standard Terminology Relating to Textiles1Various aspects of barr argon important for consideration and discussion. The first is the identification of barr. Secondly, how can barr be analyzed? What are the causes of barr, and finally, how can it be prevented?IDENTIFICATION OF BARRThe first step in a barr investigation is to observe and define the problem. Barr can be the result of physical causes that can usually be detected, or it can be caused by optical or colourability differences that may be nearly impossible to isolate in the fabric. Barr epitome methods that help to discriminate between physical barr and barr caused by other reasons include Flat remand Examinations, Light Source Observation, and the telamon Streak Analyzer.Flat Table ExaminationFor a visual barr analysis, the first step is to lay a full-width fabric render out on a table and view both sides from various angles. Generally, if the streaky lines run in the yarn direction that is in the course direction, apparent color differences can be seen by looking follow out at the fabric in a direct visual line with the yarn or course direction, and the defect can be positively identified as a barr defect. Viewing the fabric with a easygoing source in the background will show if the barr is physical.Light Source Observation aft(prenominal) completing an initial Flat Table Examination, a Light Source Examination may provide further useful in random variableation. Full width fabric samples should be examined2under two come in lighting conditions, ultraviolet (UV) and fluorescent light. Observations that should be do duration viewing under lights are1. the absolute frequency and width of the barr,2. whether the streaks are dark or light, and3. the total length of pattern repeat.Ultraviolet light, comm hardly referred to as black light, allows the presence of mineral oils to be to a greater extent easily detected, due to their radiant energy (glow). When observed under UV light, fabrics with streaks that exhibit glow suggest improper or insufficient preparation. A form in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in cleaning can create this problem. light lighting simulates the mode of observation that is common to most inspection tables in mill around and will highlight whether the barr is perceivable in an industry quality influence setting.Atlas Streak AnalyzerThe function of the Atlas Streak Analyzer is to isolate barr caused by physical differences. A fabric swatch is combined with polystyrene sheet film, and the Atlas Streak Analyzer produces a malleable impression of a fabric surface by incorporating specific conditions of pressure and heat. The absence of color on the plastic impression ensures that only physical streak effects will be seen. The plastic impression is examined to determine whether the streak alignment matches the3streaks observed on the fabric. However, impressions made from spun yarns such as cotton can be difficult to read due to the inherent yarn variation characteristic of spun yarns. Also, a excessively rapid cooling of the test specimen after making an impression can produce a moir pattern. From a valid plastic impression, the barr source can be identified as1. physical with all streaks showing on the impression,2. optical or dyeability variations where none of the color streaks are aligned on the impression, and3. a combination of physical and dyeability differences where some streaks align with those on the impression, and some do non.Fabrics with combination causes present the greatest challenge for analysis.If the streak analyzer indicates the same barr pattern as seen in the fabric, then the b arr stripes are physical in nature. This can relate to several physical causes such as yarn tensenesss, secure length, yarn compute, twist differences, etc.Yarn tension causes can be found by raveling adjacent courses and measuring the lengths of yarn extirpated from all(prenominal) course. If all the lengths raveled from the fabric are the same, the pieces can be weighed to determine if the yarn counts are the same.4If the plastic replica shows no stripes, then the barr is due to chemical substance causes or to light reflectance differences. Chemical causes relate to improper preparation, and light reflectance differences relate to non-uniform dyestuff penetration or reflectance. The next step is to remove the color and evaluate the stripped sample in front re-dyeing to determine if the removal of dye was complete and if the barr is notwithstanding present. An uneven or incomplete stripping can indicate an additional strip. If the color is stripped uniformly and the barr is gone, then the sample should be re-dyed. If after stripping and over dyeing the fabric no perennial has barr, then the barr was caused by improper preparation. If the barr remains, then the problem is related to optical or light reflectance problems.PHYSICAL BARR ANALYSISWhen the cause of barr is determined or presumed to be physical in nature, physical fabric analysis should be done. Physical barr causes are generally considered to be those which can be linked to yarn or mechanism differences. Methods of physical barr analysis include fabric dissection, microscopy, and the Roselon Knit Extension Tester.Fabric DissectionTo perform accurate fabric dissection analysis, a fabric sample that contains several barr repetitions is required. First, the barr 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 level, twist direction, and cut length5weight determinations are made and r ecorded. For reliable mean values to be established, data should be smooth from at least two light/dark repeats. After compilation of yarn information, the numbers can be compared individually to adjacent yarns as strong as by groupings of light and dark shades.MicroscopyMicroscopic examination is useful for verifying yarn-spinning forms. Yarns from divers(prenominal) spinning systems can fill contrary light reflectance and dye absorption properties resulting in barr when mix. Ring-spinning produces yarn that is smooth with all qualitys twisted in a tight helix. Open-end spinning produces yarn with wrapper fibers that form a belt around the diameter of the yarn at irregular intervals. Air jet spinning produces yarn with more than wrapper fibers that form a continuous spiraling band around the inner fibers that are more parallel to the axis of the yarn. Microscopy can in any case reveal a shift in loop formation in knitted fabrics when twist direction (S and Z) differences are present.Roselon Knit Extension Tester2Barr produced by knit stitch machinery is relatively common, is the easiest to see in the greige, and is the easiest to correct. a good deal uneven yarn tension during knitting may be a cause. To test for uneven tension, the Roselon Knit Extension Tester can be used. For this test, a fabric sample is cut and raveled to yield yarn samples from light and dark streak areas. The yarn ends are taped and clamped2 Source Spinlon Industries Incorporated, 18 S. fifth Street, Quakertown, Pennsylvania 189516to the tester. As each yarn is stretched to the maximum extension point, the points are plotted on graph paper. Comparisons are usually made visually rather than mathematically.CAUSES OF BARRThe varied and diverse causes of barr can generally be summed up in one word INCONSISTENCY. An inconsistency that leads to barr can originate in one or more of the following categories fiber quality/raw material management, yarn formation/supply management, k nitting processes, and preparation and dyeing techniquesFiber tone of voice/Raw Material Management1. Failure to control fiber diameter (micronaire or denier) from laydown to laydown.2. Too high a C.V. of micronaire in the laydown for a given mills opening line blending efficiency.3. Failure to control the fiber color in the mix (grayness Rd, yellowness +b).4. Failure to control maturity/fineness in a laydown5. Most, if not all, fiber barr can be controlled by the above four items however, under certain unusual circumstances, it may be beneficial to also select mixes using ultraviolet reflectance information for each bale of cotton.7MicronaireAverage micronaire must be controlled within a laydown and from laydown to laydown. Controlling ordinary micronaire in the laydown may not be sufficient to completely eliminate barr. Other micronaire related causes of barr are 0.2 difference in micronaire. 0.1 change in mix-to-mix fair micronaire. 12.0 % CV of micronaire within the laydow n.It may be necessary to change the laydown averages periodically to make use of all the bales in the warehouse. This must be done late with no more than a 0.1 change in mix-to-mix averages. Figure 1 shows acceptable changes in micronaire from laydown to laydown.No barr from micronaire differences should show in knitted fabrics when yarns are mixed on the knitting machine from full-strength laydowns. However, if laydowns vary more than 0.1 micronaire, for example laydowns 1 (4.3 mic.) and 6 (4.6 mic.) in Figure 1, then barr is much more possible to occur.8Figure 1 Slowing Changing Micronaire Average in Laydown Acceptable Change in Micronaire From Laydown to Laydown3.53.63.73.83.94.04.14.24.34.44.51234567891011121314Laydown NumberMicronarieFigure 2 shows a high CV% in the micronaire for bales within a laydown. The laydown shown has 24 bales with an average of 4.1 micronaire and a CV% of 17.7. The change in micronaire from bale to bale is more than a 0.1 change. Also, the CV% is mo re than 12.0% and would probably result in barr. High Micronaire CV% in Laydown3.53.73.94.14.34.54.7123456789101112131415161718192021222324Bale NumberMicronaireAvg. 4.1 CV% 17.7 *Figure 2 Results of Changing the Micronaire Average too RapidlyMax +/- 1.0 mic9Maturity and FinenessAlthough micronaire gives an indication of fiber maturity, it does not directly measure that property. Maturity and fineness related causes of barr include Blending cotton from contrasting harvest-festival areas or seed varieties. Immature fiber content such as white specks, neps, etc.Yarn Formation/SupplyEven with proper fiber selection to reduce raw material effects on barr, techniques in the opening, cleaning, blending, and carding areas can have an impact on barr. These variations can occur at carding where different amounts of non-lint content removal from card to card can be a problem. Poor blending of fiber from opening through finisher drawing cannot be overlooked. In ring spinning, the running of d ifferent types of spindle tapes and the use of different cots or revolutionary and used cots mixed together on the same framing can create barr.Faulty management in the spinning plant can result in the following yarn related causes of barr1. Yarn count variations.2. Yarn twist variation.3. Wrong yarn size, color, blend level, twist direction.4. Mixed yarn lots.5. Mixed shipment dates of same dye lot.106. Uneven wax or oiling of yarn7. Improper conditioning.Knitting Processes and Yarn ManagementThe set-up and operation of a knitting machine is complex and requires precision settings to produce first quality goods. Machine related causes of barr include1. Different stitch settings (stitch lengths).2. Improper tension at a feed.3. Faulty cylinder or dial cam settings.4. Malfunctioning of retentiveness or tape feeders.5. Improper threading of yarn.6. Variations at take-down or spreader system.7. Machine vibration.8. Dirt, lint, and/or yarn fragments in the camming system, tricks, ne edles, or sinkers.9. Variation in oil content.10. have on needles, which generally produce length direction streaks.11. Uneven cylinder height needles (wavy barr).12. Worn cylinder and/or dial.Even with a properly set-up machine, barr can still occur at knitting due to poor yarn management. Examples of poor yarn management at knitting include111. Mixing yarns of different counts.2. Mixing yarns from different spinning systems.3. Mixing yarns with different blend levels.4. Mixing yarns from different suppliers.5. Mixing yarns with different twist level/twist direction.6. Mixing yarns with different degrees of hairiness.7. Mixing yarns with different amounts of wax.8. Mercerization differences.9. Excessive backwinding or abrasion during this process.10. If yarns are conditioned, then each lot must be uniformly conditioned.Preparation and Dyeing TechniquesNormally, dyehouses have standard preparation procedures and formulas that work very well in terms of removal of non-fibrous contam inants and natural fiber pigmentation. However, some fabrics can exhibit barr that is caused by either optical or dyeability issues. Often, the barr is not created in dyeing, but can be highlighted. In this scenario, the dyeing is not the cause but the messenger of the problem.Typically, barr is not a problem in whites, only in dyed fabrics. Therefore, if a fabric is known to have barr, then that roll should be processed into a white.12Preparation can help mask barr, but cannot and will not eliminate it. The cause of the barr must be eliminated for future rolls to be free of the defect.The scour and/or bleach procedure can be intensified to mask the barr. This can be done by combinations of using a higher temperature or longer processing times. Usually the chemistry will remain the same however, in some cases, it may have to be increased or changed.If any changes are made in the preparation procedure, the fabric and resultant shade will possibly change in whiteness, strength, and a ppearance. In fact, the whiteness will closely always change. If whiter, the elderly dye formula will need to be adjusted. The strength of the fabric may be affected to the point where it becomes a problem. Finally, the surface of the fabric may change so that it may not match previous lots. As a result of more aggressive preparation to contend barr, it is important to evaluate such changes on small samples in the lab or a sample machine.Tension can play an integral usance in not only the formation of the fabric, but also during preparation, dyeing, and finishing. As with all variables, it must be controlled to known parameters and be consistent. Any inconsistencies in tension could change the morphology of the cotton (i.e. during mercerization), level of dye pick-13up, or surface appearance (i.e. during mechanical finishing such as brushing or sanding).PREVENTION OF BARRAs discussed in the text, barr is caused by inconsistencies in materials, equipment, or processing. To preven t barr from occurring, consistency must be maintained through all phases of textile production. sway yarns should be properly and carefully labeled to avoid mix-ups. Fugitive tints and/or marked cones can be useful for accurate yarn segregation. Inventory should be controlled on a first in/first out basis. All equipment should be properly maintained and periodically checked. In spinning and knitting before beginning full-scale production, sample dyeings can be done to check for barr. Knit machine operators should be trained to look for barr as it occurs in the greige. If spotted, the machine should be stopped until the cause is eliminated.Salvaging a fabric lot with a barr problem may be possible through careful dye selection. subterfuge 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 barr is an uneven distribution of oil or wax, a more double-dyed(a) preparation of the fabric before dyeing may result in more uniform dye coverage.14With close cooperation between production and quality control personnel, barr problems can be successfully analyzed and solved. Recommendations to minimize barr include Knit an entire dye lot from the same knitting machine. Use only yarn from the same spinning lot. Use only from the same shipment date if possible. If yarn shipment dates must be mixed, then use consecutive shipment dates. line up through laboratory analysis and experience if the preparation procedures are sufficient or can they be modified to eliminate the problem. Determine if some shades and dyestuffs are less susceptible to showing barr, and apply those to problem fabrics. Make use of yarn/fabric analysis systems such as CYROS. Identify those rolls within a dye lot that have mixed yarn shipment dates so that it is known when the fabrics go through the dyehouse. Identify dye lots that have rolls from different yarn shipments before dyeing.CASE STUDY IN BARRA 100% cotton, ring-spun single jersey style T-shirt is knitting in production with a yarn that does not have a barr problem. This style has been knitting for numerous days and no more of the yarn is usable for creeling on the machine as the yarns are knitting out. Some yarn packages are skinners and others are full five-pound packages. The machine is 24-inch diameter with 80 feeds.15When the impertinent yarn is creeled onto one of the 80 positions, the mixing of yarn shipment dates begins to take place. For this discussion, we will assume that this new yarn will cause barr when mixed with the old yarn. Once all positions are knitting the new yarn, there will be no barr. How more rolls of fabric will have barr when both these yarns are present in the rolls?If the knitter is making 50 pound rolls, then each yarn package will supply 1/80th of the 50-pound roll or 0.625 pounds of yarn. T herefore, the new yarn will make 8.0 rolls of fabric with barr (5-pound package divided by 0.625 pounds per package for a 50 pound roll). It is important to realize that while this new package is knitting, other old yarn positions on the creel are also being re primed(p) by new yarns. By the time the first new package has knitted out, all feeds will be using the new yarn. When the last old package is replaced and all positions have new yarn, the barr will disappear.Often, many machines will be knitting the same style. If ten machines are knitting this style and are using the old yarn and new yarns are placed on these 80 feed machines, then the total number of rolls knitted with barr will be 80. A total of 4,000 pounds of fabric will be made with barr. If the style in question weighs 5.8 ounces per linear yarn, then a total of 11,035 chiliads of fabric will be made. Further, if it can be assumed that each yard of fabric can make 1.2 shirts, then a total of 13,240 defective T-shirts will be made. This is 1,103 dozen16garments. If the cost per shirt is $2.05 per unit, then a loss of $27,142 plus is realized.If open-end yarn was used for this case study instead of ring-spun yarns, then 8-pound packages of yarn could be used. This would result in 128 rolls containing 6,400 pounds and 17,655 yards of fabric. From this, 21,186 T-shirts (1766 dozens) would have been made. Based on a cost per shirt of $1.86, the loss would be $39,405. The result is that bigger packages mean bigger losses.The best methods to reduce the possibility of this catastrophe are listed to a lower place1. When mixing yarn shipment dates of only one week, try to reduce the number of machines using the old and new yarns.2. As more machines are use the old yarn, consolidate the old packages to fewer machines. This means removing the yarns from one creel and using them on other machines that are still knitting the old yarn.3. Knit dye lots from a single machine if possible.4. When a roll is known to have mixed yarns, a laboratory dyeing should be done on a swatch from the roll to determine if barr is present. If not, then proceed as normal. If barr is present, then the roll should be processed in17shades that are not known to be barr sensitive or prepared with more aggressive chemistry.CONCLUSIONSIt is evident that barr is a problem that results from inconsistencies and is a result of poor management of fiber, yarn, and/or related knitting processes. The spinner, the knitter, and the dyer must communicate and work as a team to reduce the potential for barr to occur. A well planned and executed system of monitoring the spinning, knitting, dyeing, and finishing systems in the mill can provide for defect free fabrics.18