WEFT KNIT FABRIC GEOMETRY

PRESENTATION ON

PRESENTED BY

• Name with ID:

• Nazmul Alam Pappu (020)

• Md. Enzamul Haque (022)

• Shawan Roy (023)

• Ahmmed Sharjin Sharif (024)

• Pankaj Roy (025)

• Kohinur (027)

• Saiful Hasan Sakib (030)

• Textile 5th Intake

• Section 1

• Bangladesh University of Business & Technology

DIMENSIONAL STABILITY

• Knitted fabric is so notorious for its tendency to change size and shape in wear and washing that to many people the phrase ‘ the dimensional stability of knitted fabrics’ will be contradiction in terms.

• The different dimensional stable states to which the knitted fabrics are imposed, and

• The loop length of yarn in the knitted loop.

DIMENSIONAL CHARACTERISTICS

• The lines of loops across the fabric are known as courses & the lines down the fabric as wales.

• One loop is referred as a

• W = wale spacing

• C = course spacing

• AB = stitch length, in mm

• S = number of stitches per square cm, stitch density

• W = wales/cm =

• C = course/cm =

DIMENSIONAL CHARACTERISTICS

• The dimension of plain knitted fabric is related as below:

1. Courses per unit length is inversely proportional to stitch length

• i.e., (or)

2. Wales per unit width is inversely proportional to stitch length

• i.e., (or)

3. Stitches or loops per unit area is inversely proportional to stitch length squared

• i.e., (or)

4. Loop shape factor;

• R = Courses per unit length / Wales per unit width

• Where are the geometrical constants for the plain knitted fabrics at different stable states.

DIMENSIONAL CHARACTERISTICS

Constants for geometry of plain worsted knitted fabrics at different stable states (imperial unit)

DIMENSIONAL CHARACTERISTICS

Constants for geometry of plain worsted knitted fabrics at different stable states (SI unit)

AREAL DENSITY

• By knowing the stitch density (loops/sq. m) loop length (mm) & yarn linear density, the areal density of the knitted fabric can be calculated as,

• Areal density (1Kmmm)

• If S is in stitches/, then

• Areal density

• Also,

• Therefore, Areal Density

FABRIC COVER

• The cover of the knitted fabric is also important for the study of their tightness.

• The total area covered by the yarn per

• Fractional cover =

• Where d is the yarn diameter in .

• As we know S =

• Fractional cover =

TIGHTNESS FACTOR

• By expressing the yarn diameter in terms of its linear density in tex & by deleting various constant by considering the fact that the yarn diameter is proportional to the square root of linear density, a new expression, cover factor known as tightness factor for knitted fabric is obtained.

• Tightness factor, K =

SPIRALITY

• Spirality is dimensional distortion in circular plain knitted fabric.

• The lengthwise rows of stitches, called wales or needle lines, should occupy a truly vertical line in the fabric & should always be at right angles to the cross-wise course of stitches.

• This perpendicularity of wales to the courses is frequently, not the case & many times the wales may skew to the right or left forming an angle, which appears in the form of a twilled surface.

• This geometrical defect has termed spirality of knitting in circular fabrics.

• The following fig. shows the fabrics with normal loop position & with spirality having wales skewness.

THEORY OF SPIRALITY

• The spirality occurred in knitted fabric is shown the figure. The fabric is assumed to be knitted with Z twist yarn on a multifeed circular machine, revolving clockwise.

• Let,

= total number of feeders, = courses per unit length

= total number of needles, = wales per unit length

• Let,

DD1 = position of a wale when total spirality occurs

BB1 = position of a wale when total spirality occurs due to number of feeders

XX = position of a course when total spirality occur

XA = position of a course when spirality occurs due to number of feeders

X1A = F/C = displacement between two consecutive courses knitted by the same feed

XX1 = n/w = Open width of fabric

THEORY OF SPIRALITY

• Total spirality

• Then,

• From the geometrical constant, as we know,

• and loop shape factor,

• Now, and

THEORY OF SPIRALITY

• The above relationship shows that the angle of spirality depends on

• 1.Number of feeders of the machine

• 2.Shape of the loop in a particular state of relaxation and

• 3.Number of active needles in the machine which depends on machine gauge and diameter

MEASUREMENT OF SPIRALITY

• The fabric sample is laid freely over a platform without any wrinkles and crimp.

• The spirality can be analyzed using a mini drafter/L-Square scale and the angle of deviation is calculated.

• The amount of spirality can be obtained using the following formula.

Degree of spirality,

Where d is the displacement of the course from a normal line to the wales of the fabric measured at a distance L from the identified wale line

• The spirality measurements can be taken for the three states of fabric samples such as dry relaxed wet relaxed and fully relaxed