Issues in Knitting – Barre problem: Common causes and its understanding
One of the most common and frequent issues weavers today face is the problem of BARRE in the circular knitting industry in particular. The causes of the formation of barre are varied and diverse. So, the detection of the exact cause is the job of a skillful technologist.
This particular note is presented to dispel some of the unknown facts surrounding barre by providing a specific outline of possible reasons and their identifications. If one the fundamental cause is known, then appropriate steps can be taken for elimination and produce better quality fabrics.
As per ASTM literature barre is defined as “an unintentional repetitive visual pattern of continuous bars and stripes parallel to the filling of woven fabric or to the courses of circular knit fabrics. “In a warp knit barre normally runs in the length direction, following the direction of the yarn flow. But it is much chronic problem in circular knitting systems.
Barre can be created by physical, optical, or dye differences in the yarn, geometric differences in the fabric structure, or any of the combined of these differences.
Physical cause: – Flat table examination is practiced in the industry. It is primarily very easy to detect physical causes by dyeability differences. The fabric is dyed in an exhaust system in a pilot dyeing plant or sample dyeing machine. After that, the appearance is viewed. This may be difficult to remove from the fabric. The reflected as well as the transmitted light source can help in a visual examination. Viewing the fabric with a light source in the background will show if the barre is physical. The transmitted light source also reveals thick & thin places.
Further two light conditions fluorescence and U.V. light also help in determining barre. U.V. light source allows the presence of mineral oil easily to be detected. On this basis, the weaver can suggest the proper composition of contents of knitted oil. Knitter must select such a lubricating product with good scour ability.
Further physical barre analysis includes fabric dissection. Microscopy and Roselon knit tester. Also, few quality assurance departments use ATLAS STREAK ANALYSER.
Fabric dissection involves Individual yarn removal from the light and dark streaks pattern. After measuring count (BRITISH COUNT Ne) values of at least 8 to 10 streaks (defective area) and from the normal area, reliable mean values are calculated. The difference in values in terms of % can directly suggest the intensity of the barre problem straightaway. Directly it suggests the quality of yarn used and responsible for defects.
Atlas streak analyzer: – The instrument is also used for the detection of barre and its impressions over the thin plastic film that delivers the idea/judgment over the type of barre. The function of the Atlas Streak Analyzer is to isolate barré caused by physical differences.
Microscopic observation: It can reveal different spinning system yarn. Microscopic observation can also reveal a shift in loop formation in knitted fabrics when twist direction (S & Z). The principle applied is that different spinning systems can have different light reflectance and dye absorption properties. The mix-up can be from,
- Ring spinning
- O.E. spinning
- Air jet spinning
Yarn factors responsible for barre :-
- Inconsistency in micronaire/denier
- Failure to control yellowness index in the mixing stage.
- Too high a C.V. OF micronaire.
- Yarn supply chain management.
- Mixing of yarn different count.
- Mixing of yarn different suppliers.
- Mixing of yarn with different blend level.
- Mixing of yarn with different parameters e.g., thick/thin places.
- Mixing of yarn with different twist level/twist direction.
- Mixing of yarn with different hairiness index.
Fabric formation :- knitting machine factor responsible for barre problem
- Improper stitch length at a feed.
- Improper tension at feed.
Prevention barre :-
As outlined, barré is caused by inconsistencies in materials, equipment, or processing. To prevent barré from occurring, consistency must be maintained through all phases of textile production.
Stock yarns should be properly and carefully labeled to avoid mix-ups. Fugitive dyes can be useful for accurate yarn segregation. Inventory should be controlled on a First In/First Out basis. Before beginning full-scale production, sample dyeing can be done to check for barré. Salvaging a fabric lot with a barré 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). Also, if the cause of the barré is an uneven distribution of oil or wax, more thorough preparation of the fabric prior to dyeing may result in more uniform dye coverage.
The knitting lubrication oil must be checked on grey fabric by artificially putting oil drops and then oven dry and scouring with the bulk recipe. Finally, under a different light source, the spots can be assessed for their thorough removal.
With close cooperation between production and quality control personnel, barré problems can be successfully analyzed and solved.
