Fundamentals of Knitting:
Knitting is a process of converting the yarn into fabric similar to the weaving process. However, the knitting process uses a different method over warp and weft. Here the fabric formation happens by successive loop formation with the help of single yarn. The knitting process is also capable of creating different stitches and so, produces different structures like weaving. But the fabric production in this process is measured in terms of weight. The general process flow of the knitting is provided below.
Receipt of yarn from the spinning / winding process
↓
Selection of design according to the requirement
↓
Knitting process
↓
Fabric formation and output of roll in tubular form
↓
Fabric inspection and dispatch
The term knitting describes the technique of making textile structures by forming a continuous length of yarn into columns of vertically and horizontally intermeshed loops. Interlooping consists of forming yarn into loops, and these loops are held together by the yarn passing from one loop to the next loop. Knitting requires a relatively fine, smooth, strong yarn with good elastic recovery properties. The knitted structure gives good elastic properties to fabrics. Nowadays, Lycra is used to increase the elastic properties of knitted garments.
The potentials of knitting technology are varied. The unique loop structure of knitting provides opportunities for using a minimum number of yarns to make a fabric. By varying the size of loops, fabrics with different textures can be produced. Under tension, the shape of the loop will get distorted. Knitted fabrics can be engineered for extensibility and tailorability. Different types of yarns can be used to produce fabrics with different properties on each side.
Types of Knitting:
There are two types of knitting:
- Weft knitting
- Warp knitting
Weft knitting is further classified into circular knitting and fat knitting. Again there are three types of circular knitting, namely plain, rib and interlock. Tricot, raschel, crochet and Milanese are the further classification of warp knitting. Figure 2 shows the detailed classifications of knitting.
1. Weft Knitting:
Weft knitting is the process in which the loops are formed progressively in the widthwise direction of the fabric. This is similar to inserting weft in a woven fabric and, hence, its name as weft knitting. In weft knitting, the needles form the loops sequentially in the same yarn one after another. Weft knitting produces softer, more elastic fabrics that are ideal for applications requiring stretch, such as t-shirts and sweaters. See Figure 1.
2. Warp Knitting:
Warp knitting is the process in which the loops are formed progressively in the lengthwise direction of the fabric. This is similar to the movement of warp yarn in weaving and, hence, its name warp knitting. In warp knitting, all the needles form the loops at the same time. Warp knitting creates stronger, more stable fabrics that are less prone to unraveling, making them suitable for technical textiles and sportswear. See Figure 1.
Comparison of Weft and Warp Knitting:
Both weft knitting and warp knitting offer distinct advantages based on their unique structures and yarn movements. Differences / Comparison of weft and warp knitting is point out below.
a) In weft knitting, yarn feeding and loop formation occur at each needle in succession, whereas in warp knitting, yarn feeding and loop formation occur simultaneously in all the needles in a knitting cycle.
b) Weft knitted fabrics are mostly produced as tubular fabrics having a constant diameter. Warp knitted fabrics are knitted at constant width.
c) Weft knitting is more versatile and cost-effective, whereas warp knitting is limited to certain applications and more expensive.
d) Staple fiber-spun yarns and textured continuous filament yarns can be knitted in weft knitting machines, but knitting them in warp knitting machines is diff cult.
e) Even with a small quantity of yarn, weft knitted fabrics can be produced, but warp knitting requires a beam of yarn.
f) The yarn does not require sizing for weft knitting, whereas for warp knitting, the yarn has to be sized. However, waxing of the yarn is sometimes preferred for weft knitting.
g) Compared to weft knitted fabrics, warp knitted fabrics have more dimensional stability.
h) Both fine and coarse fabrics can be produced in weft knitting, whereas in warp knitting, generally fine fabrics only are produced.
References:
- Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
- Handbook of Textile and Apparel Costing by Dr. R. Rathinamoorthy, Dr. R. Surjit and Dr. K. J.Vishnu Vardhini
- Understanding Textiles for a Merchandiser By Shah Alimujjaman Belal