Needle | Needles are the heart of the needlepunching process. The schematic diagram of a typical needle is shown in Figure 3.2. As shown, a needle has the following parts: crank, shank, taper, blade, barb, and point. The shank locates in the hole in the needleboard and the crank is clamped between upper surface of the needleboard and the needlebeam, thus holding it firmly and vertically aligned in the loom. Traditionally, the cross-section of a needle is triangular and carries a total of nine barbs, three per apex. The dimensions of the barbs and their relative arrangement vary depending on the application and machine operation. | | | Figure 3.2 | Figure 3.3 | | In general, the nonwoven industry uses two types of needles, known as single reduction needle and double reduction needle. They are shown in Figure 3.3. The single reduction needle has two sections, shank and blade. But the double reduction needle has an intermediate section in-between the shank and the blade. This is a transition stage between the different diameters of the shank and the blade. The single reduction needle is much stiffer than the double reduction needle. The single reduction needle is usually made only for coarser gauge needles. The single reduction needle is used for stiff fibres (waste fibres, shoddy, etc.) | | Figure 3.4 | | | Figure 3.5 | | The barb is known to be the main working component of a needle. The schematic diagram of a barb along with its important parts is shown in Figure 3.4. A barb is characterized primarily by kick-up, spacing, angle, and depth. As far as the kick-up is concerned, there exist high kick-up (‘K’ barb), low kick-up (‘NK’ barb), and no kick-up (‘B’ barb). These barbs are shown in Figure 3.5. The fibre carrying capacity decreases from ‘K’ barb to ‘NK’ barb to ‘B’ barb. Based on the spacing, the barbs are categorized by regular barb (RB), medium barb (MB), close barb (CB), and high density barb (HDB). These barbs are shown in Figure 5.6. The high density barb provides maximum aggressive punching, followed by the close barb, medium barb, and regular barb. At the same time, the surface of the fabric is found to be maximum uneven with the high density barb, followed by the close barb, medium barb, and regular barb. There exist barbs with different angles, as shown in Figure 3.6. | | Figure 3.6 | | | In nonwoven industry, a wide variety of needles are used. They vary in their cross-sectional shape as well as the geometry of the point of the needle. The blade cross-section of classical needles is triangular, with three barbs formed on the apex. This is shown inFigure 3.7(a). The star bladed needles have four apices and a cruciform cross-section. This needle is intended to carry an increased number of fibres per penetration as compared to the standard triangular needle, which can increase fabric strength. This is shown inFigure 3.7(b). | | Figure 3.7 | | Figure 3.8 | | Besides there are fork needles used for structuring and patterning pre-needled fabrics. The crown needles are designed to be used in conjunction with random velour needleloom to introduce fibre loops that protrude from the surface of the fabric. These needles are shown in Figure 3.8 . | Selection of needle | The selection of needle is very important for getting good quality nonwoven fabrics. It is decided by many factors, discussed earlier, along with the fineness of the fibres required to be processed. | Fibre linear density (denier) | Needle gauge (SWG) | 0.5-1.5 | 42 | 1.5-6.0 | 38-40 | 6-10 | 38 | 10-18 | 36-34 | 18-30 | 36-32 | >30 | 30-coarser | | Table 3.1 | | Table 3.1 lists the gauge of the needles for different finenesses of fibres. The higher is the gauge of the needle, the finer is the needle and vice-versa. |