Performance Apparel Markets - Grado Zero Espace Srl

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Performance Apparel Markets, 1st quarter 2006 Seamless knitting and stitch-free technologies —polyester, polyethylene, polypropylene, urethanes and PVC At least 60% of the material must be thermoplastic, although thermoplastic tape or film can be used Some use tape or film to ensure seam integrity Welding takes place as a result of the high frequency mechanical motion of a vibrating horn and compression between it and a drum Welding by high frequency radiation uses electrodes to raise the temperature by dielectric heating But not all materials can be heated in this way The electricity causes molecules in dipolar materials to oscillate PVC and polyurethanes are the best Other terms are dielectric or radio frequency welding ● polyester; ● polyethylene; ● polypropylene; ● urethanes; and ● polyvinylchloride (PVC). Normally, at least 60% of the material to be ultrasonically welded must consist of thermoplastic materials. If not, seams produced using ultrasonic welding have to be reinforced with thermoplastic tape or film. However, some manufacturers use thermoplastic tape or film in any event during ultrasonic heating in order to ensure seam integrity. Materials are placed between a vibrating horn and a rotary drum which has a pattern of raised areas. Welding takes place as a result of the high frequency mechanical motion of the vibrating horn and compression between the horn and the drum. This action creates frictional heat at the point where the horn is in contact with the materials. WELDING BY HIGH FREQUENCY RADIATION Welding by high frequency radiation uses electrodes to raise the temperature by dielectric heating. Dielectric heating is the heating of an insulator—in this context the insulator is the fabric or the thermoplastic film—by a high frequency electric field. Such welding uses a frequency of 27.12 MHz. Not all materials can be heated in this way, however. The process relies on certain properties of the fabrics which cause the generation of heat in a rapidly alternating electric field. The electricity causes the molecules in dipolar materials, such as some thermoplastics, to oscillate. This oscillation may then be converted into heat, which facilitates the welding of the materials. Materials such as polyvinylchloride (PVC) and polyurethanes are the best types for this technique. High frequency welding is also known as dielectric welding, or radio frequency welding. SEAMLESS KNITTING Seamless knitting enables garments to be made with no or minimal sewing-up Overall, seamless knitting is an important development in and for the knitting industry. It provides the wherewithal to manufacture whole garments with no, or minimal, sewing-up. © Textiles Intelligence Limited 25
Performance Apparel Markets, 1st quarter 2006 Seamless knitting and stitch-free technologies This facilitates cost savings and faster production This means that cost savings and time savings can be made. Also, because of the time savings, production is quicker than traditional manufacturing (Table 1). Table 1: Potential benefits of seamless knitting Minimising or eliminating labour intensive cutting and sewing processes Savings in production times and costs Minimal yarn consumption Higher productivity Multi-gauge knitting Lightness and softness No bulky and irritating stitches and seams More constant product quality Better trimmability for finished edge lines Better look, better fit and greater comfort More creative possibilities for knitwear designers Quick response production for size and pattern changes Just-in time production Mass customisation Source: Journal of Textile and Apparel Technology and Management, Volume 4, Issue 3, Spring 2005. Seamless knitting is used for underwear, lingerie, nightwear and sportswear A complete garment can be produced on two types of knitting machines Seamless circular machines create a single tubular garment whereas V-bed machines can make multiple tubular pieces at the same time and then join them together Santoni is the largest producer of seamless circular knitting machines Shima Seiki and Stoll produce machines allowing different patterns to be combined in one garment Seamless knitting is used to produce underwear, lingerie, nightwear and sportswear. The biggest sector for seamless knitting is the lingerie market. A complete garment can be produced on two types of knitting machine: ● seamless circular knitting machines; and ● seamless flat V-bed knitting machines. The difference between the two types of machine is that seamless circular machines can be used to create a single tubular garment whereas V-bed machines are able to produce multiple garment panels and tubular pieces at the same time and then knit them together on the machine. Complete garments produced on circular machines are therefore not strictly seamless because they require some sewing-up. Companies which produce knitting machines for seamless knitting include the Italy-based companies Santoni and Sangiacomo. Santoni is the largest producer of seamless circular knitting machines. Companies which produce whole garment knitting machines include Japan-based Shima Seiki and Germany-based Stoll. Both of these companies’ machines allow different patterns to be combined in one garment. An example might be a jersey knit next to a mesh knit, next to a rib knit. 26 © Textiles Intelligence Limited
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