Knitting Technology Fundamentals

Knitting Technology

• Knit fabric quality depends on several physical parameters
• These parameters include GSM (grams per square meter)
• Loop dimensions (loop length, wales, and courses per unit length)
• Fabric width
• Dimensional stability
• Fabric defects

Introduction

• Current knit fabric quality assessment focuses on physical parameters

• Aesthetic value, customer appeal, and overall satisfaction are not considered

• Comfort properties like smoothness and loop fluidity, and their impact on shear and low-stress mechanical properties, are not adequately addressed by existing parameters

• Knit fabrics often show poor dimensional stability. Localized variations in dimensions can impact appearance and useful life

Parameters Of Fabric Quality

• Fabric quality at a micro level can be determined by loop-to-loop variations in dimensions (including loop shape geometry and loop density), rather than just GSM.

• Key loop dimensions include length, width (wale spacing), and height (course spacing)

• Uniformity in loop dimensions improves fabric appearance by reducing the blurring effect of irregular dimensions. This leads to a more elegant, lustrous, smoother, softer, and stable fabric.

• Uniformity in loop shape geometry affects fabric elegance and fluidity

• Distorted loops during relaxation, chemical processing, or usage can result in dullness, roughness, or ridging in the fabric

Parameters Of Fabric Quality

• Examples of standard loop shapes are shown graphically

• The geometrical shape of a standard loop should have consistent curvature for crown & sinker loops – Generally, sinker loops are larger than crown loops.

• Both loop arms should be in the same plane, and bending of crown & sinker loops should be equal without twisting

• Shape factor (ratio of loop width to height) should be approximately 1.3

• Yarn contact points in loop interlacement should occur at the junction of the loop arm and crown/sinker loop (indicated in the diagrams with A, B, C, & D)

• Minimum variation in loop shape and dimensions are ideal, leading to improved dimensional stability as loops can readily adjust during fabric deformation

Machine Parameters

• Machine parameters and technology affect fabric quality and yarn demand.

• Key machine parameters include needle type, gauge, cam type, yarn feeding system, number of feeders, take-down system (cloth rolling or spreading), and monitoring/control systems.

• Machine selection for a particular yarn with a given GSM (grams per square meter) is crucial. Ideally, the gauge and count range should be carefully chosen. Coarser gauges are often easier to operate for any given yarn compared to finer gauges.

Process Parameters

• Process parameters significantly impact fabric quality.

• Relevant process parameters include cam settings, speed, yarn tension, sinker settings (single jersey), delay time (double jersey), stitch length, take-down rate, and machine condition.

• Similar input yarn and machine conditions with similar process parameters can still lead to different fabric qualities, often beyond acceptable levels in industry. This indicates the importance of factors other than those considered in current practices.

Process Parameters

• Variations in strain and relaxation across different loops cause loop-to-loop variations in dimensions and loop geometry.

Yarn Quality

• Yarn purchase considerations for knitting include count, U%, imperfections, strength/elongation, and TPM (threads per meter).

• Many SMEs (small and medium enterprises) in the knitting industry focus primarily on count to determine the GSM (grams per square meter) of the fabric, neglecting other important yarn parameters.