Dr. MIRELA BLAGA Faculty of Textiles and Leather Engineering, Iaşi, Romania - PowerPoint PPT Presentation

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Dr. MIRELA BLAGA Faculty of Textiles and Leather Engineering, Iaşi, Romania

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  1. Knitted Technical Textiles Dr. MIRELA BLAGA Faculty of Textiles and Leather Engineering, Iaşi, Romania

  2. Use of Non-Clothing Knitted Fabrics Textiles can be used mainly as: 1. Clothes and clothing components (underwear, outerwear, handkerchiefs, ties). 2. Interior textiles (furniture, decoration, bed linen) 3. Technical textiles (TT).

  3. Criteria Textile Classes 1. Types Open (porous) Closed 2. Geometry Longitudinal (1D) Plain (2D) Three dimensional (3D) 3. Technology Weaving Knitting Non-woven Classification of Technical Textiles[1]

  4. 4. End Uses Classes Domains Function Examples 1. Human and veterinary use TT 1.1. Health and medicine External protective Diapers, Surgical gauze, Sanitary towels External with mechanic effects Corsets Orthopedic textiles Internal Implants (sIurgical sewing yarns, arteries, bones) Classification of Technical Textiles

  5. 4. End Uses Classes Domains 1.2. Protective and safety Function Protection against fire Examples Non-flammable, insulation, fluorescent, reflective- textiles Anti-fire clothes Protection from accidents Bullet-proof, shrapnel-proof, anti-accident textiles Protection from radiation and radioactive contamination Classification of Technical Textiles

  6. 4. End Uses 2. Interior TT Classes 2.1. Interior of buildings Domains Floor covering Function Examples Separating textiles Mosquito nets Insulation 2.2. Interiors of means of transport Upholstery textiles Safety belts, airbags Safety 3. Exterior TT 3.1 Geo-textiles Water engineering, Drainage Communication Reinforcement 3.2 Textiles for buildings and light constructions Insulation and protection Dust, noise, water - protective clothes Classification of Technical Textiles

  7. 4. End Uses 4. Industrial Agricultural Technological Use Classes 4.1. Industry Domains Filtration Function Filters for wet and dry filtration Examples Material treatment Disks for polishing, cutting, sharpening belts Special textiles for industrial branches Electronics, paper, print, boot-and-shoe industry, driving belts, reinforcement of tires Handicraft and artistic needs Painter and projection screens, wicks, theatre and binding textiles Classification of Technical Textiles

  8. 4. End Uses Classes 4.2. Agriculture Horticulture Fishing Domains Agriculture protective Function Examples Nets, textiles for packing goods Fishing Nets, lines Ventilation Stables 4.3. Others Mountaineering Parachute textiles Toy textiles Bags, luggage Classification of Technical Textiles

  9. 4. End Uses 5. Construction materials Classes 5.1. Stressed via traction Domains Ropes Cords Function Examples 5.2. Stressed via bend Beams Panels 5.3. 3D products 6. Packing Classification of Technical Textiles

  10. Advanced Knitted Fabrics Advanced knitted fabrics, mainly those intended for the industrial market, are sometimes required to have some properties with marginal values. The two most frequently used extremities are [1] 1.Elongation and strength; 2.Voluminosity/thickness or lightness/permeability.

  11. 1. Knitted Fabrics with Extreme Elongation and Strength[1] Elongation relates to strength. Both properties depend on directional characteristics of yarn supply in textiles. A direct yarn ensures low elongation in the supplying direction and its strength is usually well used. It can be produced extremely firm and little tensile knitted fabrics due to the insertion of auxiliary yarns into one or several directions. Only straight yarns can facilitate longitudinal direction (wale direction), transverse direction (course direction) – so called mono-axial or longitudinal and transverse direction, both diagonals (bi-axial), diagonals and longitudinal/transverse direction (tri-axial), all directions (multi-axial textiles)

  12. Weft knitted fabric – there are possible interconnections of longitudinal or transverse yarns. Combination of both directions is simpler as for the structure shown below. Longitudinal yarns are over all sinker stitches, transverse ones over sides of all loops and transverse yarns over longitudinal ones. Structure with longitudinal and transverse yarns Diagonal yarns are inserted into weft knitted fabric still with more difficulties. They need special and complicated machine equipment.

  13. Warp knitting is by far the most versatile fabric production system in textiles. What make them so versatile? • Construction of knitting machines: needle type (latch, bearded, compound) needle bed number (1 or 2) • Patterning possibilities (special devices: yarn let-off, fabric take-up, jacquard device, fall plate) • Number of guide bars, yarn threading (full or partly) • Lapping (open or closed lap) • Knitted fabric geometry (plain or sandwich) and structure (closed, opened) • Raw materials (type, fineness) During the last few years, in spite of a permanent modest experience in the apparel industry, warp knitting is more and more identified with technical and other non-apparel fabrics.

  14. Directionally Oriented Structures The directionally orientated structures can be: • mono-axial structures (warp or weft direction), • bi-axial structures (perpendicular and diagonal), • tri-axial structures (diagonal and weft, diagonal and horizontal) • multi-axial structures.

  15. Mono-axial structures Weft insertion is used to achieve both aesthetic and technical advantages. The yarns introduced into the fabric do not enter the hooks of the needles and do not form loops. The yarns laying in the fabric horizontally from selvedge to selvedge, perform as weft yarns in a woven fabric, so the widthwise properties of the knitted fabric are similar to those of woven cloth.

  16. Warp Knitting Machines COPCENTRA HS (Horizontal Schusseintrag) Liba Co, Germany) [7] 1 - compound needles; 2 - closing element bar; 3 - guide bars; 4 - sinker bar; 5 - weft yarn insert element; 6 – weft yarns. RS4 MSU (Magazin Schuss Umkehrfaden)Karl Mayer Co, Germany) [3] 1 - trick plate; 2 - compound needles; 3 - closing element bar; 4 - sinker bar; 5 - weft yarn insert element; 6 - guide bars.

  17. Weft Technique [2] To introduce a weft yarn into the fabric, a special weft insertion mechanism should be used. The mechanism stretches the yarn segment across the whole width of the knitting machine outside and independent of the knitting elements. When the needles are about to ascend to the clearing position, the pre-prepared yarn is placed behind the backs of the needles. In this way, the yarn is securely positioned so that the back of the needle and the underlaps hold it in place. The figure shows the locking of the weft inserted yarn once the guide bars swing back from the overlap position. The warp yarns are now in the needle’s hooks so that the space in which the weft yarn is positioned is closed up. While the knitting elements are producing the knitting cycle, more weft yarns are being prepared across the back of the knitting machine. In the fabric, the weft yarn is held between the loops of the technical face and the underlaps. Since the yarn is not placed into the needles’s hooks is not even threaded in the guides, it is not restricted by size.

  18. Warp Technique [2] Warp insertion element can be formed with the following lapping movement.A set of yarns can easily be placed in a straight warp orientation by the ‘misslapping’ technique. In this case, three guide bars are required of which the middle one produces neither overlaps nor underlaps. By misslapping with the middle bar the yarn is placed in the construction. The straight yarns are blocked from reaching the technical back by the underlaps of the front guide bar and from the technical face by the underlaps of the back guide bar. The straight orientation of this set of yarns produces an increased stability in the length direction.

  19. Bi-axial structures Using both warp and weft insertion techniques, a very stable fabric can be produced. The fabric from the picture is made with three guide bars and a weft insertion mechanism. The front guide bar is knitting a 3 and 1 movement, the middle bar is misslapping and the back guide bar is knitting a tricot construction [2] • Advantages of mono- and bi-axial D.O.S. • The yarns in D.O.S. are absolutely straight and parallel • Yarn properties are fully utilized to withstand deformation forces • Optimally structured modulus • Fabric engineering is simple and fabric properties can be pre-calculated according to the intended end-use • Any yarn type can be processed -from low-twist soft staple yarns to high-tenacity filament yarns.

  20. Multi-axial structures [6] Multi-axial structures are fabrics bonded by a loop system, consisting of one or several yarn layers stretched in parallel. The yarn layers may have different orientation and different densities of single ends. Multi-axial multi-ply fabrics are used to reinforce different matrices. The combination of multi-directional fibre layers and matrices has proved capable of absorbing and distributing extraordinarily high strain forces. The typical feature of warp-knitted multi-axial multi-ply structures for substrates is the interlacing of single ends in line with the stitch courses and the associated almost smooth processing of fed yarns. These products are multi-ply structures with angles of 30° up to 60° and/or 90°/0°. A multi-axial multi-ply fabric demonstrating the two diagonal yarn sets in addition to the bi-axial yarn sets created by the misslapping guide bar (warp or ST-yarn) and the magazine weft insertion system (weft). Applications are: inflatable bodies, such as airships, inflatable boats, inflatable life-rafts, rescue tents, gas membranes, V-belts, flexible roofing membranes etc.

  21. Warp Knitted Fabrics from LIBA [4] Monoaxial Scrim Biaxial Scrim The fabric is designed to take force in two directions (0° and 90°). For this can be used rovings of glass, high tenacity polyester, aramide or carbon as pillar threads and weft threads. These fabrics are used for reinforced composites. The fabric is designed to take force in only one direction (0°). For this can be used rovings of glass, high tenacity polyester, aramide or carbon as pillar threads. These fabrics are used for reinforced composites.

  22. Multiaxial Scrim Open structure with +45° / 90° / -45° / 0° Carbon fabric Mixed carbon 45° and aramide 0° Glass fabric

  23. Grid Structures These fabrics are used as reinforcement for light weight coated fabrics or universally as reinforcement. For example in grinding discs and plaster. This kind of fabric especially in "fine" ranges, that means squares smaller than 10 mm, can be produced more effectively than wovens. By using weft threads in the fabrics an enormous tear resistance is achieved due to bundling effect (sliding of yarns)

  24. Warp Knitted Fabrics from KARL MAYER [5] Surgical bandages/ Furnishingfabrics/Adhesive tapes/Outerwear Geotextiles/Protective textiles/Tarpaulins/Construction textiles

  25. 2. Voluminous/thick knitted fabrics • Voluminous knitted fabrics can be obtained in different ways: • by using a material with a large diameter of yarns and a proper knitting machine (rough division) • by creating structures like two-or-multi-layer knitted fabrics (3D). Three-dimensional structures(3D) can be produced on a single needle bar warp knitting machines (pile fabric) and on two-needle bar Raschel machines (spacer or tubular fabrics). The use of two needle bars opened new horizons in warp knitting and different machine types are built for production of a wide variety of products ranging from packing sacks to artificial blood vessels [1]

  26. Knitting action of a double-needle bar Raschel machine The simplified knitting cycle [3]: 1 - The guide bars are positioned at the back of the machine, above the back needle bar. The front sinker bar is placed forward to secure the fabric while the front needle bar ascents to clearing position. The guide bars perform the underlap shogging movement for the needle bar and then swing to the hook-side. 2 - On the hook-side of the front needle bar, the guide bars shog an overlap according to the pattern mechanisms and then swing back. 3 - The swing back is completed, the yarns are wrapped within the needle hooks so that the front needle bar can start to descend. The front sinker bar retreats while the back one moves forward.

  27. Knitting action of a double-needle bar Raschel machine The simplified knitting cycle : 4 - Front needle bar descends, the previously formed loops which rested on the needle stems close the latches. The front sinker bar continues to retreat, the back one is now above its needle bar. The guide bar swing for the third time, this time to the front in order to clear the way above the back needle bar. Underlap shogging movement for the back needle bar can start. 5 - Front needle bar is at knockover position and the needles form new loops. Back needle bar, now with its fabric secured by the sinker bar, ascends to clearing position.

  28. Knitting options with two needle bars and more than two guide bars. a - the third guide bar is only threaded through one guide finger on one side, resulting two separate fabrics, produced by the fully threaded guide bars; b - by threading the middle guide bar through two guide fingers, one on each side, a tubular fabric is formed; c - a fully threaded middle bar is used to produce a sandwich of two fabrics connected by yarns.

  29. Applications [6] Horizontal tubes Vertical tubes

  30. Spacer fabrics [4] -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 structur - 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. 3D-Glass-textiles, manufactured on double needlebar high speed Raschel machines of Liba

  31. Applications of spacer fabrics [4] - Composite reinforcements/Container - Tanks/Boats - Aircraft/Sport shoes - Medical textiles/ Mattress

  32. 3. Light/permeable knitted fabrics Fishing nets are produced profitable onthe warp knitting machines, namely developed eight-guide-bar, high speed Raschel machine 1400/ 1400/ 1400 dtex Polyester, Diolen® 877 TN [4] 1880/ 1880/ 1880 dtex Polyester, Diolen® 877 TN The lapping movement of a typical six-guide bar fishing net[3]