The main material for fabric construction is yarn. Knitting is the second most frequently used method, after weaving, that turns yarns or threads into fabrics. It is a versatile technique that can make fabrics having various properties such as wrinkle-resistance, stretchability, better fit, particularly demanded due to the rising popularity of sports wear and casual wears. As of present day, knitted fabrics are used widely for making hosiery, underwears, sweaters, slacks, suits and coats apart from rugs and other home furnishings.

 

 

Knitting Industry

Knitting industry is a very complex one. It has two primary areas having their own sub divisions of specialization. One of the key segment of knitting industry manufactures knitted goods for garment manufacturers, sewing centers, and consumers among others. The other one produces finished apparels such as hosiery, sweaters, underwear etc.

Basic Principle of Knitting

A knitted fabric may be made with a single yarn which is formed into interlocking loops with the help of hooked needles. According to the purpose of the fabric, the loops may be loosely or closely constructed. Crocheted fabric is the simplest example of knitting where a chain of loops is constructed from a single thread with the help of a hook. As the loops are interlocked in a knitted fabric, it can stretch in any direction even when a low-grade yarn having little elasticity is used.

Basic Construction Process of Knitted Fabric

The construction of knitted fabric is assessed by the number of stitches or loops per square inch. When the interlocking loops run lengthwise, each row is called a wale that corresponds to the direction of warp in woven fabrics. When the loops run across the fabric, each row is called a course that corresponds to the filling or weft in woven fabrics. A knitted fabric having 50 loops or stitches in one inch of width and 60 loops in one inch of length will be said to have 50 wales and 60 courses.

Importance of Needles in Knitting Process

The needle quality also affects the knitted fabric's quality. If the thickness of the hook differs from one needle to another then the stitches will also vary in width. Same is the case with loops which will vary in length with the needle lengths. Various types of needles are used for making different knitted fabrics including latch needle, spring-beard needle, and compound needle. Latch needle has a latch or swinging finger that closes onto the hook of the needle as it pulls the yarn through a loop in order to form a new loop. It is used for jersey and rib knitting. A spring-beard needle has a fine, springy hook looking like a beard. This hook has to be used with a sinker to hold the fabric down and a presser to close the hook as it forms the loop. It is used for making more fine fabrics with smaller loops. A compound needle made up of a hook and a sliding closing element is used for faster knitting with lesser fabric distortion.

Types of knitted Fabrics

There are various types of knitted fabrics and each type has different appearance and characteristics. The construction of a knitted fabric depends upon the type being constructed. A knitted fabric that has more wales will be rigid and stable in width while a fabric that has more courses will be rigid and stable in length. A fabric having many wales and courses per area will have better recovery from stretching than a fabric having lesser wales and courses. Such fabric that will have fewer wales and courses will be less rigid, stretch more easily, fit to body shape in a better way but will have poorer recovery ability. All the knitted fabrics are classified into two general categories:

• Weft knit fabric, where one continuous yarn forms courses across the fabric.
• Warp knit fabric, where a series of yarns form wales in the lengthwise direction of the fabric.

Weft Knitting

There are three basic stitches in weft knitting

• Plain-knit stitch
• Purl stitch
• Rib stitch

Any other stitch is a variation of these three stitches. Hand knitting is basically weft knitting. When done on weft knitting machines, individual yarn is fed to a single or multiple needles at a time.

Plain-knit stitch: Plain knit, the basic form of knitting can be produced in flat knit or in tubular (or circular) form. It is also called jersey stitch or balbriggan stitch. A row of latch or beard needles is arranged in a linear position on a needle plate or in a circular position on a cylinder. The side by side evenly spaced needles are moved by cams, which act on the needle butts. The spacing of the needles is called gauge, gage or cut which refers to the number of needles in one and a half inches, for example, a 60 gauge machine will have 40 needles per inch. The needles intermesh loops drawn to one side of the fabric, forming vertical herringbone like ribs or wales on the right side or technical face of the fabric. On the reverse side or the technical back, courses are visible as interlocking rows of opposed half circles. These fabrics have the tendency of curling up at the edges which is controlled to a level through certain finishes.

Plain knit allows the use of single or plied yarns produces comparatively lightweight fabrics than produced by other stiches. The production rate is higher, about 5 times more than weaving. It is inexpensive and a variety of designs may be produced including stripes, multicolored patterns, textured surfaces produced by raised designs and pile effects. Plain-knit fabrics stretch more in the width than in the length and as such, they are widely used for making underwear, gloves, hosiery and sweaters.

Purl stitch: Purl stitch, also called link-and-link stitch, is made on flat bed knitting machines and circular machines by needles using hooks on both ends to alternately draw loops to the front of the fabric in one course and to the back in the next course. The fabrics look similar on both the sides resembling back of the plain knit. Heavy, jumbo stitch is also possible which gives a bulky effect to the fabrics. However, It is comparatively slower and a costly technique. The fabric doesn't curl at the edges. Purl stitch is widely used in infant wear and kids clothing due to its crosswise stretch and excellent lengthwise stretch.

Rib stitch: Rib stitch produces alternate lengthwise rows of plain and purl stitches and as such the face and back of the fabrics are a lookalike. Rib stitch can be produced on a flat rib machine as well as circular rib machine. In the flat rib machine, one set of needles is placed opposite the other set of needles in an inverted V position. In the circular rib machine, one set of needles is placed vertically in a cylinder and the other set of needles is placed horizontally on a dial. In both the machines, one set of needles pulls the loops to the front and the other set of needles pulls the loops to the back of the fabric. Each set of needles alternately draws loops in its own direction, depending on the width of the rib desired. For instance, rib stitches can be 1X1, 2X2, 2X1, 3X1, and the like. Accordion rib is the combination of 1x1 and 2X2. As a greater amount of yarn is required for rib stitch and the rate of production is also slower, it is an expensive method of fabric construction. The fabric doesn't curl at the edges and as the fabric possess an excellent widthwise elasticity, it is widely used for making such clothing that needs an excellent fit such as wristbands of sleeves and waistbands of garments, underwear and socks for men and children.

Warp Knitting

Warp knitting is different from weft knitting in the sense that in it each needle loops its own thread. The needles of warp knitting machines produce parallel rows of loops that are interlocked in a zigzag pattern. The stitches on the front side of the fabrics appear vertically having a slight angle. The stitches on the backside appear horizontally as floats at a slight angle. These floats are called laps or underlaps and are a distinguished feature of warp knit fabrics.

Warp knitting machine may be flat or tubular that can produce a variety of patterns. It is a very fast technique that can produce fabric with a dimensional stability almost equal to that of a woven fabric. It can also use yarns of man made fibres very efficiently. There are basically seven types of warp knitting- Tricot knit; Milanese knit; Simplex knit; Raschel knit; Ketten Raschel knit; Crochet and Weft-insertion warp. Warp knit fabrics are very popular due to their many properties such as smoothness, sheerness, wrinkle resistance, shrink resistance, strength and abrasion resistance.

Comparison of Weft Knitting and Warp Knitting

Warp knit fabrics have certain advantages over weft knits

• Warp knit fabrics do not ravel easily.
• They are less prone to sagging.
• Quality is generally better than weft knits.
• Stitch definition, texture and fabric cover are also usually better than weft knits.
• Warp knits have superior dimensional ability.

3D woven and knitted fabrics

3-d textiles are those materials which have a system or systems in all the three axes of plane. These fabrics offer particular properties, such as interlaminar shearing force, and mechanical and thermal stability along all three axes of space, which are not achievable with other reinforcements.

Three-dimensional (3-D) textile fabrics hold a promising future. The demand for these types of fabrics is expected in to increase, especially in the area of high performance composites in housing, automobile industry, construction and reinforcement materials.

However, the reduction in the cost of manufacturing and raw materials has to be brought about in order to make these goods competitive in the current & future markets. In this context nonwovens, which are a major constituent of this class of textiles are becoming important because of their ease of manufacture and low production cost.