Special Feature | November 2019
Knitting technologies & developments
Knitted fabrics, due to their properties like shape fitting, softer handle, bulkier nature and high extensibility at low tension, which are being extensively used for dress materials, are now gaining strong ground in the area of technical textiles, says Jeyaraman Anandha Kumar.
Throughout the knitting industry, circular knitting machines are one of the most widely used knitting machines. For producing the fabric, we commonly use the circular knitting machines. India efficiently manufactures these knitting machines in almost every reasonable diameter. We can build the circular knitting machines even in a small diameter of up to five which we commonly use for producing the fabrics to wear.
Introduction to seamless knitting: We can achieve the seamless garment knitting either by using the circular knitting machines or by using the v-bed flat knitting machines. Seamless circular knitting machines are different from seamless flat knitting machines. By using the seamless circular machines, we can create only a single tubular type of garment whereas when we use the seamless flat knitting machines, we produce more than one tube, which we have to join together on a machine. The complete or single tubular type of garment, which we knit on the circular knitting machines, requires a minimal cutting operation.
Moreover, if we want to make any significant change in the size of the garment, then we require different diameters in case of the seamless circular knitting machines whereas in seamless flat knitting machines we can change to the different sizes of the garments on the same machine. Therefore, the seamless knitting which we achieve on the circular machine is not the true seamless knitting. On the other hand, V-bed seamless machines produce the truly seamless garments because they do not need any cutting or sewing of the fabric.
Automatic seamless circular knitting machine: It is essential to control the manufacturing functions of the machine to manufacture an excellent quality knitted garment. For successfully producing new products in the knitting industry, it is necessary that the designers, as well as the manufacturers, effectively communicate with each other. Most of the times, the designers complain that the technicians do not accurately create the designs that they specify, whereas the technicians are of the opinion that the designers do not understand the technical problems that they have to face in the knitting feasibility. However, to solve the communication problem between the designers and the technicians, it’s always better to make use of intelligent CAD systems. When we use the CAD system, then the designers, as well as the manufacturers, can specify and evaluate their designs more correctly without requiring technical expertise and taking much time investment.
To facilitate communication between the designers and technicians we have diverse computer controlled systems such as CAD/CAM controlled knitting machines. At present, knitting machine manufacturing companies also have a facility for several new types of CAD systems. The new types of the CAD systems use two different monitors as well as have a design window for designers and a separate technical window for the manufacturers because both of them require different information even for making the same design.
Ultra-fine gauge knitting machines: We use fine gauge circular knitting machines for producing the fine knitted fabrics, which we call as the ‘second skin’. For creating the fine circular knitted fabrics, we commonly use polyester, cotton and viscose yarns of 90 to 120 Ne. The fine knitted fabrics have an appearance similar to that of the woven fabrics, but they are more flexible as compared to the woven fabrics.
Ultra-fine gauge elements of circular knitting machine: To complement the company’s premium range of needles and system parts, we have high-grade circular knitting cylinders. High-grade knitting cylinders help us in creating a perfect knitting system from a single reliable supplier. Circular knitting machines can attain their full potential for giving high-performance operation on the factory floor only because of the consistently outstanding durability and high standard of component quality. We always ensure to install every component of the existing knitting machines with utmost precision. The precise installation of the individual element not only improves the capacity utilisation in production but also simplifies the work flow.
Pai Lung ultra fine gauge knitting machines consist of the fine gauge double cylinders, which we use to produce the fine gauge automotive fabrics called as woven-like fabrics. Ultra-fine gauge knitting machines make use of the pile technology, and the fine gauge of loop makers is present near to the sinkers.
Loop transfer technology in circular knitting machines: Stitch transfer is an essential operation in the process of knitting. Higher the number of transfer modes, more are the possibilities of making structured designs and shaped fabrics. For creating the structured designs, we transfer the stitch within the same cylinder or from one cylinder to the other. The high-quality knitted fabrics have a homogeneous appearance, and they don’t have any holes and barring in them. To produce high-quality fabric, we require a smooth knitting process as well as the application of certain technical solutions.
Concerning the needle used, the Italian knitting machines have latch needles incorporated in them, which operate by the drowned butt principle. In Italian machines, the needle remains in an idle position. The heel of the needle remains wholly drowned in the needle bed groove and do not involve in the action of the cams. The heel also retains the loop, which in this case is not subject to any strain.
Pile and sliver insertion mechanism: The sliver knitting process locks the individual fibres directly into a lightweight knit backing. The sliver insertion mechanism makes the fibres free from the backing and allows them to stand upright; thus forming a soft pile on the face of the fabric. This technique helps in making the comfort pile fabrics softer, more resilient, warmer and more drapeable as compared to the fabrics made from yarns. The fibres, which we commonly use, include high-tech micro-fibre-acrylics, mod-acrylics and polyesters along with that of the natural fibres like wool.
Loop transfer tool: We carefully choose each blend to gain the specific results. By engineering the fibre mix, we can quickly produce the comfort knit pile fabrics in an incredibly wide range of colours, density, weight, texture, patterning and performance features.
Needle with spring for high-speed loop transferring: After the process of knitting, we shear the pile fabric to the desired level of height. The fabric then undergoes a series of technical finishing processes specially developed to control the special characteristics as well as the surface texture of the final fabric.
Use of knitting technologies in manufacture of technical textiles
Studying the objects exhibited on fairs and the articles published in technical papers and on the Internet, we have the experience that various kinds of warp knitted fabrics play the most important role among knitted technical textiles. These fabrics are made on tricot, raschel, crochet and knit braiding machines. Products of these machines can be used in themselves like nets or bandages, but also as reinforcement materials in composites or backing materials for laminated or coated fabrics. However, besides warp knitting technology, important products are made also on weft knitting, mainly on circular knitting machines but V-bed flat knitting must not be neglected either.
Nets: Application field of nets is extremely wide. Agriculture, fishing, packaging, transport, sports, shading technology, construction, healthcare, surgery, safety technology and military present many good examples for that. Many of these nets are made by raschel or crocheting technology the great advantage of which is that they do not contain knots. This makes the nets easier to handle because the layers do not tangle up and there are no knots that could harm the good packed into the net. Warp knitted nets—both flat and tubular ones—can be produced with very high productivity.
Materials used for net manufacture are very different, depending on the end use. Spun yarns or filament yarns, narrow plastic tapes are commonly used for this purpose. Elastic nets are made with using of elastane yarns. Width of flat nets knitted on raschel or tricot machines may reach as well 5 to 6 m, while to make narrower variants (up to 100 to 120 cm width) crochet machines are also available. Raschel machines with two needle bars are able to produce wide tubular net fabrics. To manufacture tubular nets of smaller diameters (from 1 or 2 cm to about 20 cm) knit breading machines can be used very effectively but their final diameter can be extended in the practice if they contain elastane yarns.
Knitted fabrics with orientated behaviours: Knitted fabrics with orientated behaviours are made usually with lots of yarns laid lengthwise, crosswise and/or diagonally into the fabric. Their keeping together is performed by warp knitted loops. Aim of these structures is mainly to reduce the stretch and/or to increase the forth of the fabric in one or more directions. If this effect is realized only in one direction (lengthwise or crosswise) the fabric is called “unidirectional” or “monoaxial”. If this behaviour asserts itself in both directions, the fabric is called “biaxial”. “Multiaxial” or “multidirectional” fabrics have almost the same behaviour in every direction.
To manufacture such fabrics, special tricot and raschel machines have been developed completed by equipment to prepare and lead the lots of reinforcing yarns into the place of loop formation. In these fabric constructions, the laid-in yarns play the main role; the loops only link them together. There are a great number of end users for these fabrics. Biaxial fabrics with PVC coating, for instance, are used for manufacture of stressed roof constructions by which very wide spaces can be covered. Fabrics with directed behaviours are available also as reinforcement materials of composites or for geo grids.
Spacer fabrics: Among knitted fabrics, perhaps the most spectacular development can be registered in case of spacer fabrics. This is already the product of the 21st century, their development began only several years ago but it has made great progress since then. Though the principle of the fabrication is not new, it goes back to the manufacture of plush fabrics on raschel machine; the adaptation of this technology to make a completely new type of fabric is very ingenious. At the beginning they were developed really on two needle bar raschel machines but now there are also circular knitting machines on the market for manufacturing of such products and, of course, Vbed flat knitting machines are al so able to make spacer fabrics of some kinds.
The two surface layers of spacer fabrics are usually linked by relatively thick monofilaments which make the fabric elastic when pressed in thickness direction. This is the most important reason why spacer fabrics have found many fields of application. They can substitute foam in seats or beds, in orthopaedic support devices, in bras and shoes. It can serve in smart clothes as heat insulation or for forming of ventilation passages. As a type of geo textiles, spacer fabrics can be used to lead off water from the soil. In manufacturing of composites used in the motor industry or ship building they can work as reinforcement inlay.
Using proper yarns or with application of special treatment they can be electrically conductive, flame retardant, antibacterial, etc. As we see at this moment, most spacer fabrics used are made on raschel machines or, in recent times, also on crochet machines. Needle bed distance on these machines can be varied within wide range and fabric thickness can reach even 60 mm. On circular knitting machines needle bed distance is much more limited, only thinner (thickness of some millimetres) spacer fabrics can be made on them. However, these variants are also very important and can be found in many products.
Stitch bonding: Stitch bonding machines combine knitting and sewing. They have grown from warp knitting technology and their products occupy an intermediate position between knitted and nonwoven fabrics. This fabric contains a carded web which is reinforced by yarns or loops formed from fibres pulled out from the web itself. Needles of the warp knitting machine pierce holes through the web and work like a sewing needle when forming a seam of chain stitching (called pillar stitch in warp knitting technology) or zigzag seam where stitches made on neighbouring needles couple with each other (called tricot lap in warp knitting technology). These fabrics have great importance in almost each class of technical textiles. They are used very often as reinforcing materials in composites or for heat or sound insulation, filling materials in clothes or furniture, etc.
A further variant of such fabrics is when not only carded web but lots of yarns are laid in various directions over the web and all of these are stitched together. This formation may be called “composite fabric” since it is a composition of various types of textiles (web and yarns). They find application fields among filters, geo textiles, reinforcement materials in composites, etc. Advantage of these fabrics is that the carded web may be made of various fibres, which, because of their length or quality, cannot be spun, even in various blending, fabric thickness and stitch density (number of stitches in length unit) as well as yarn counts (in accordance with machine cut) can be varied in relatively wide range. The fabric can be easily formed. At the end of its lifetime it can be torn and recycled.
Knitted fabrics in construction: Construction industry is a great market for textiles and also for knitted fabrics among them. Around buildings being under construction or renovation the scaffold is usually covered by raschel knitted net made of polypropylene foil tapes.
Knitted fabrics can be used also to reinforce wall coverings, both outside and inside. Some types of geo textiles and geo grids are also knitted structures. Many buildings, and not only provisional ones, have roofs made of textile fabrics (sports stadiums, air terminals, halls for various functions, etc.). If this roof is made from knitted fabric bi or multi-axial knitted structures are used with waterproof and weatherproof coating. Huge areas, many hundreds of square metres can be covered by such fabrics.
Another possible application of knitted fabrics in construction is textile reinforced concrete. There are warp knitted structures developed especially for this purpose. Textile reinforced concrete has the advantage that it is much lighter than the one reinforced by steel bars.
Knitted fabrics in medical treatment: Many kinds of textiles are used in medical treatment. It is not surprising that a great part of clothing worn by doctors and nurses in hospitals and clinics is product of the knitting industry (e.g. undershirts, socks). But sometimes they are not conventional ones, they are made from yarns or with finishing that make them antibacterial against infections or against of rising of unpleasant sweaty smell. Various types of bandages (both rigid and elastic), surgical stockings, certain parts of orthopaedic equipment (or theses) (like knee, wrist and elbow braces, calf and lumbar supports, etc.) are also made by knitting technology. An important application field for spacer fabrics is manufacturing of mattresses for beds, operating tables and wheel chairs. Knitted products find application field also among implants: artificial blood vessels (they can be circular knitted or warp knitted, the latter is made on double needle bar raschel machine and can be made also in Y form), surgical meshes (made on tricot machine), coverings of artificial heart valves, etc.
Thus, development and application of textiles open interesting possibilities for medical sciences and vice versa: manufacture of textiles for medical treatments offer important possibilities for the textile industry. Cooperation of doctors and technical experts of the textile industry can lead to development of new surgical technologies. Structure of the textiles used as implants is determined by its material composition, fibres’ behaviour and features of degradation. Materials of sutures and implants having biologically good properties, designable absorption and degradability and that endure the sterilization process are continuously subjects of research. At the same time, continuous development of textile technologies and machines enables to develop newer and newer methods in surgery and medical treatment. For this mutual development textile technologists and doctors must closely cooperate, while all the administrative procedures concerning manufacturing and trading of such products must be strictly respected.
Knitted fabrics in functional clothes: Knitted fabrics may be important components of functional clothes, too. For example, spacer fabrics can be used here as lining that, due to its hollow structure, enables ventilation inside the garment or, due to its elastic behaviour in thickness direction, protects against pressure or hit. This is why this fabric is a penchant for lining of motorcyclists’ protective garments. The speciality of a spacer fabric that there is a distance between its two surfaces but they can be springily pressed together enables to use them as electric switch if electrically-conductive yarns are used in the two isolated surfaces. When they connect to each other under pressure an electric signal can be created. Also pressure sensor can be built in between the surfaces. Cables can be led in the inside hollow.
Undershirts, trousers, socks made from elastic knitted fabrics fit close to the body and if sensors are fastened on them they can transport signals of the movements and the state of the body (perspiring, pulse, breath frequency, etc.).Remarkable developments are going on – also in Hungary – with knitted fabrics containing metallic fibre components for manufacture of protective underwear against electromagnetic radiation as well as with other types of underwear that contain modacrylic or carbon fibres to make the knitted garments flame retardant.
Socks made from heat resistant aramide fibres do good service on hot workplaces. On the recent Techtextil in 2019, a knitting factory presented a complete set of knitted underwear (long sleeve shirt, trousers, socks, hoods) made of a special blending of modacrylic, aramide and cotton fibres to be worn in hot work environment. Another set of knitted underwear was made of antistatic polyester completed by antibacterial treatment.
Innovations that redefine the future of knitting
- MES – Intelligent manufacturing: In addition to monitoring production efficiency using POMS, being able to exercise complete control is one of the most critical aspects of Industry 4.0. Rather than manually changing machines’ knitting parameters, MES allows machines to be adjusted through computers — both ensuring consistent knit quality and type, while also streamlining production and achieving strict quality control standards.
- Spinit: Replacing the traditional method of spinning raw materials into yarn, Spinit creates textiles directly from raw materials, significantly shortening the yarn spinning step. This helps save raw material cost, accelerate production, and create high quality fabrics that are soft and light, ideal for polo shirts and other golfing attire.
- Knitted 3-layer high pile (KDFPS-HW): As the name suggests, the knitted 3-layer high pile technology simultaneously knits three layers on a single machine, completely avoiding the laborious process of producing the laminated three-layer high pile and reducing production time by 60 per cent. At the same time, KDFPS-HW solves the two-layer high pile loss issue — both accelerating production and improving fabric quality.
- Segue Jacquard (KRTDCJ6): Equipped with state-of-the-art technology that releases yarn as needed—rather than all at once—KRTDCJ6 can knit up to eight different types of yarn with varying colours, materials, and denier values, without thickening the knit. Segue Jacquard knits vibrant patterns that last longer than printed designs, and can create knits with embossed patterns.
- Sculpted Spacer (ISP203): Spacer has played a revolutionary role in the fabric industry, and sculpted spacer is bringing it to the next level. ISP203 can knit a single piece of spacer fabric with various thicknesses, offering an alternative to padded bras and other apparel. The sculpted spacer not only embraces wearers in a snug fit, it also significantly reduces production time by completely eliminating the cutting and patching step that was previously required for shaping.
Jeyaraman Anandha Kumar is a lecturer with the Department of Textile Processing, G.R.G. Polytechnic College, Kuppepalayam, Sarkar Samakulam, Coimbatore. He can be contacted at: Email: firstname.lastname@example.org
- Liba – New double needle bar knitting machine for technical textiles. Melliand International, 2008. No. 2. p. 105
- Kanakaraj, P.; Anbumani, N.: 3D knitted spacer fabrics and their application. Melliand International, 2007. No. 1. pp. 47–52.