Applications of Knitted Fabrics for Industrial Purposes
DKTE Society’s Textile and Engineering Institute, Ichalkaranji
The production of various types of industrial fabrics for industrial application is almost as old as the mechanical weaving operation itself, and these end uses are important today. What are new and extremely attractive to the manufacturer are the growth in industrial textiles and their applications in the sectors such as agriculture, construction, geotextiles, automotive, protective apparel, electronics etc. This rapid increase in market potential has led these high profile manufacturers to develop specialized fabric for knitting and serving the end purpose efficiently. In this paper focused various knitted fabrics used for manufacturing of industrial textiles have been reviewed.
Knitting is one of several ways to turn thread or yarn into cloth (compare to weaving, crochet). Unlike woven fabric, knitted fabric consists entirely of horizontal parallel courses of yarn. The courses are joined to each other by interlocking loops in which a short loop of one course of yarn is wrapped over the bight of another course. Knitting can be done either by hand, described below, or by knitting machine. In practice, hand knitting is usually begun (or “cast on”) by forming a base series of twisted loops of yarn on a knitting needle. A second knitting needle is then used to reach through each loop (or stitch) in succession in order to snag a bight of yarn and pull a length back through the loop. This forms a new stitch. Work can proceed in the round (circular knitting) or by going back and forth in rows. Knitting can also be done by machines, which use a different mechanical system to produce nearly identical results.
The knitting process consists of interconnecting loops of yarn on powered automated machines. The machines are equipped with rows of small, hooked needles to draw formed yarn loops through previously formed loops. The fabric is designed to take force in two directions (0° and 90°). For this can be used roving of glass, high tenacity polyester, aramid or carbon as pillar threads and weft threads. These fabrics are used for reinforced composites. Considering though orientation of the force taking yarns (0°, 90°) this fabric is comparable to a woven fabric. However, there is the advantage that yarns are directly oriented and lie absolutely straight in the fabric. This means that there is no loss of tenacity as in the woven due to its crimp effect. Furthermore, the yarn-protective inlay system prevents all fiber damage.
3D-Glass-textiles, manufactured on double needle bar high speed Raschel machines of LIBA find ever more fields of application within the area of composite materials, technical textiles.
1.2. Manufacturing properties
Made of 100% e-glass, one uses the capillary function of the glass, i.e. when absorbing the resin, the commodity sets up itself automatically to the desired height.
Whether as isolation layer in the boat- and container construction or as double-walled tanks, these so-called spacer fabrics perform particularly well. Caused by the fabric construction, after laminating, a more stable, lightweight and ductile composite develops.
Depending on the final product, the thickness of the fabric can be adjusted between 3mm to 15mm directly at the machine. By using a special design technique, a thickness of even 25 mm can be achieved.
- Composite reinforcements (Sandwich-constructions)
- Sport shoes
- Medical textiles and Mattress.
2. Geotextiles Application
Geotextiles are permeable textile materials which are designed for use in civil engineering applications such as erosion control, soil reinforcement, separation, filtration and drainage etc. Geotextiles are forecast to be the fastest growing sector within the market for technical textiles. At least 70% of all geotextile fabrics fall into the category of nonwoven geotextiles and at least 25% are woven both warp knitted and weft knitted structures are used in the manufacture of geotextiles.
Warp knitting is well established in this area and an extremely wide range of structures spanning from nets and grids to monoaxial, biaxial, triaxial, multiaxial as well as composite and three-dimensional spacer materials are all used as geotextiles. Grid shape structures grip the soil more effectively than plain smooth fabrics. Also, for extremely high performance and critical applications – such as land reclamation, construction of high walls and water reservoir embankments – high strength (up to 1000 k N m-1) biaxial raschel structures are more suitable. These fabrics have high strength, low extensibility, and high modulus, above all, high tear strength.
A new and novel technology has been developed and commercialized at Bolton Institute, which enables the manufacture of monoaxial and biaxial specialist natural fiber geotextile structures for soil reinforcement. The technology is based on flat knitting, in which high strength coarse and hairy natural fiber yarns such as sisal, coir etc can be inlaid in the machine or cross, or both directions and incorporated within a knitted structure made from jute, flax and other natural fiber yarns, such as cotton, viscose, Tencal, wool etc. It is possible to manufacture designer natural fiber geotextile structures for specific short-term solutions. These Directionally Structured Textile Fabrics have been patented, and are currently being commercialized for mass production. Figures 1 and 2 illustrate the novel weft knitted structures and Figures 3, 4 and 5 shows the modified mechanically operated flat machine which enables either warp or weft or both threads to be incorporated within the fabric structure. It is also used with foundations, soil, rock, earth or any other related material as an integral part of human man-made project, structure or system. This specification covers circular-knit geotextiles for use on the outside of perforated pipes and Class B geo-composites in subsurface drainage applications. Material covered by this specification comprises Type A and Type B fabric geotextiles, which have been used extensively as filtration geotextiles in combination with subsurface drainage pipes.
The geotextile can be manufactured from polymeric materials by a circular-knit process, which will ensure a consistent, continuous fabric without seams. Tests for water permittivity, apparent opening size, and puncture strength shall be performed and shall conform to the requirements specified. Per service requirement, additional tests for chemical resistance and durability may be performed as well. This specification covers circular-knit geotextiles for use on the outside of perforated pipes and Class B geo-composites per Specification D 7001 in drainage applications.
The tests used to characterize the geotextile are intended to ensure good workmanship and quality, and are not necessarily adequate for design purposes in view of the importance of environmental factors and specific performance objectives. Tests have been selected with essentially neutral aqueous systems in mind. Other tests may be necessary to establish chemical resistance and durability under the conditions of a particular application.
This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
Geotextiles are permeable textile materials, which are designed for use in civil engineering applications such as erosion control, soil reinforcement, separation, filtration and drainage, etc. Geotextiles are forecast to be the fastest growing sector within the market for technical textiles. At least 70% of all geotextile fabrics fall under the category of nonwoven geotextiles and at least 25% are woven both warp knitted and weft knitted structures are used in the manufacture of geotextiles.
Warp knitting is well established in this area and an extremely wide range of structures spanning from nets and grids to monoaxial, biaxial, triaxial, multiaxial as well as composite and three-dimensional spacer materials are all used as geotextiles. Grid shape structures grip the soil more effectively than plain smooth fabrics. Also, for extremely high performance and critical applications – such as land reclamation, construction of high walls and water reservoir embankments – high strength (up to 1,000 k N m-1) biaxial raschel structures are more suitable. These fabrics have high strength, low extensibility, and high modulus, above all, high tear strength.
A new and novel technology has been developed and commercialized at Bolton Institute, which enables the manufacture of monoaxial and biaxial specialist natural fiber geotextile structures for soil reinforcement. The technology is based on flat knitting, in which high strength coarse and hairy natural fiber yarns such as sisal, coir, etc, can be inlaid in the machine or cross, or both directions and incorporated within a knitted structure made from jute, flax and other natural fibre yarns, such as cotton, viscose, Tencal, wool, etc.
It is possible to manufacture designer natural fiber geotextile structures for specific short-term solutions. These Directionally Structured Textile Fabrics have been patented, and are currently being commercialised for mass production.
2.1. Knitted Spacer Fabrics
Warp and weft knitted spacer fabrics continue to find new and novel product applications and it is generally recognized that spacer fabrics will be extensively used in the future in a wide range of products, mainly due to the fact that an extremely wide range of possibilities are available to tailor make their aesthetical, functional and technical properties for applications
2.1.1. Warp Knitted Spacer Fabrics
Warp knitted spacer fabrics are structures that consist of two separately-produced fabric layers which are joined back to back. The two layers can be produced from different materials and can have completely different structures. The yarns which join the two face fabrics can either fix the layers directly or space them apart. It is this three-dimensional space which is the special feature of these structures. Typically, spacer fabrics can be from 1 to 15 mm thick, with the two faces being from 0.4 to 1 mm thick. The major single feature of warp knitted spacer fabrics is that virtually any thickness can be obtained, depending upon the type of machinery used and the type of yarns and structures used. The warp knitted spacer fabric with a thickness of over 100 mm (4 inches) for use as a seating fabric for sports cars.
Spacer structure manufactured in one process:
- Up to 15 mm spacer distance
- Up to 3, 3 m full fabric width
- Large pattern variety for outside cover fabric and
- Spacer structure
3. Karl Mayer spacer machine RD6N:
In which guide bars 1 and 2 knit the front base fabric on the front needle bar only and guide bars 5 and 6 knit the other separate base fabric on the back needle bar only. Guide bars 3 and 4, which carry the spacer threads knit on both needle bars in succession. The thickness of the spacer depends upon the distance between the two needle bars and can be varied between 1 and 15 mm. In theory the material used in guide bars 1 and 2; 3 and 4; and 5 and 6 can be different, as well as the structure of the two base fabrics can be completely different. It is possible to vary the structure from an inelastic, elastic, solid, net or a specific textured surface independently in each face fabric. Furthermore, the compression and resilience properties of the spacer can be altered at will, depending upon the material and the pattern chains of the threads in guide bars 3 and 4.
The major benefit of using spacer material is to replace polyurethane, neoprene and other types of foams which are laminated to textile fabrics for creating bulk, softness, flexibility, resilience etc. These foams, however, have some serious drawbacks. For instance, foams are generally flammable; they are extremely uncomfortable due to extremely small cavities. Their thermo physiological properties are poor, their compression and resilience properties deteriorate with time and their mouldability, delamination, maintenance of original thickness when moulded into complex three-dimensional shapes, washing and drying properties are often poor and not up to the standard required. Relatively stiff monofilaments generally used as spacer material, more or less overcome the above-mentioned drawbacks associated with laminated structures
The major product applications for warp knitted spacer materials are: car seat covers (both solid or net structures in the face or back or both surfaces); automotive interiors (lining for doors, roofs, convertible hoods etc); seat heating systems for cars; mud flaps for lorries and buses; insoles and face fabric for sports and other shoes; lining for rubber and other boots; protective inner lining; mattress underlays and mattress covers for prevention and management of incontinence, pressure sores as well as for children’s beds; diving and surfing suits; sports equipment; high-performance sportswear; reinforcement for composite structures; bras; underwear; swimwear; shoulder pads; fluid filters; geotextiles; bandages; plaster casts; braces; controlled release of drugs, antimicrobials, cosmetics etc; and finally heat and moisture regulation fabrics.
3.1.1. Weft Knitted Spacer Fabrics
Weft knitted spacer fabrics can be produced on circular double jersey machines as well as electronically controlled flat machines. The major advantages of these structures are:
- Plain as well as color and design and surface texture effects can be produced on the face of the fabric knitted by the cylinder needles; and
- Shaped and true three-dimensional structures can be produced on electronically controlled flat machines.
The major limitations of weft knitted spacer fabrics are:
- The thickness of the spacer is normally limited to between 2 and 10 mm
- The basic structure of the spacer fabric is limited to either knitting the spacer threads on the dial and tucking on the cylinder, or tucking the spacer threads on the dial and cylinder needles.
It is obviously more practical to use tuck stitches with spacer monofilament yarns in order to ensure that the spacer yarns lie correctly inside the knitted fabric and prevent the face and back of the fabric from having a rough or harsh feel.
The structure of a circular knitted monofilament spacer fabric is Produced on circular interlock gaited machines are shown in Figures. Three different yarns are required for each course:
- Yarn for the dial needles
- Yarn for the cylinder needles
- Spacer yarn, normally monofilament yarn.
The future scope of fabric science is very broad. Only innovative products will be able to open up new markets and new horizons for the textile industry. To achieve this, it is essential to invest in future research and researches. In the coming years, knitted fabrics will increasingly take on industrial functions. Knitted fabrics will combine the functions of medium, carrier and interface for an extremely wide range of industrial applications. This new generation of industrial fabric makes considerable new demands on the innovative ability within the clothing industry. What is needed is not simply the conveyance of knowledge but the development of truly creative researchers. The textile industry needs to shift its emphasis from ‘quantity, quality; to ‘functionality’ in the new millennium of Global Competition Era.
- S. C. Anand, Developments in Technical Fabrics – Part 1, Knitting International, July 2000, page 32
- M. Hard castle, In the Driving Seat, Knitting International, July 2001, page 52
- T. Shah and S. C. Anand, Geotextiles: A Growing Market for Technical Textiles, Technical Textiles Markets, 2nd Quarter 2002, page 34
- S. C. Anand, Developments in Technical Fabrics – Part 2, Knitting International, August 2000, page 53
- S. C. Anand et. al., Directionally Structured Textile Fabrics, UK patent Number GB2339803, published on 27th November 2002
- Double-Layer, Circular Weft Knitted Fabrics with Monofilaments (Spacer Fabrics), Knitting Technique, 16, 5, 1994, page 306
- J. Millington, Do We Have Lift Off, Knitting International, October 2002.
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