New trends in machinery development for technical textiles - I

Changing fashion among all age groups and new requirements in the fields of technical textiles have given rise to demand for highly application-oriented machinery, say Rupali S Chitnis & Dr R K Sarkar

The production of various types of industrial fabrics for filtration, conveyor belting, felts, tarpaulins and other application is almost as old as the mechanical weaving operation itself, and these end uses are important today. What is new and extremely attractive to the manufacturer is the growth in technical textiles and its application 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 specialised machinery serving the end purpose efficiently. In this paper various machinery used for manufacturing technical textiles have been reviewed.

Unconventional Spinning Machinery

1. Dref spinning

This process belongs to open end group because the fiber strand (Drawframe sliver) must be opened completely to individual fibers and reassembled to a new strand (yarn). In Dref 2 spinning one or two carded slivers after leaving from drafting arrangement are passed to the main opening roller (a drum clothed with saw teeth). While the drafting arrangement creates only a light drafting effect, the sawtooth roller opens the strand to individual fibers. The separated fibers are lifted off the roller by a blower and form cloud, descending towards two perforated drums. One suction stream per drum draws the fibers into the convergent region. The newly arriving fibers contact the rotating yarn and are thereby caught and twisted. This process is primarily suited for the production of coarser yarns and recycled yarns.

In Dref 5 individualized fibers from a single sliver are fed through a closed or partly open fiber duct into the spinning nip at a acute angle to the yarn axis, so that they are stretched as far as possible when fed into the nip. Good quality of yarns in count range of 16s-40s Ne is possible with speed of 200 m/min.

In Dref 2000 friction machine the rotating carding drum opening the slivers into single fibers and a specially designed inlet system used for sliver retention. The fibers are stripped from the carding drum by a centrifugal force and carried into the nip of the two perforated spinning drums. The fibers are subsequently twisted by mechanical friction on the surface of the drums, which rotate in the same direction. S & Z twist can be produced without mechanical alteration in the machine. Dref 2000 friction spinning machines are utilised for the recycling textile wastes as well as the spinning of technical and other yarns.

The Dref 3000 friction spinning machine, the latest model of the machine is utilised especially for the production of multi-component yarns (hybrid yams) The applications of Dref spun yarns are: Blankets for the hometex range and military uses, as well as for hotels, hospitals, camping plaids etc.; Secondary carpet backing for tufted carpets and filler yarns for carpet wefts; Filter cartridges for liquid filtration; Canvas for the military and civil sectors -Asbestos substitutes (e.g. heavy protective clothing and gloves, gaskets, packings, clutch- and brake linings, flame retardant fabrics etc.); Filler yarns for the cable, packaging, shoe and carpet industries; High-tenacity, core yarns for ropes, transport and conveyor belts; High tenacity fire resistant protective clothing ; Composites for the aviation, automotive and engineering industries etc.

2. Wrap spinning

A roving or sliver feedstock is drafted in three, four or five roller drafting arrangement. The fiber strand delivered runs through a hollow spindle without receiving true twist. In order to impart strength to the strand before it falls apart, a continuous filament thread is wound around the strand as t issues from the drafting arrangement. This thread comes from a small rapidly rotating bobbin mounted on the hollow spindle. Withdrawal rollers lead the resulting wrap yarn to a winding device. The wrap yarn consists of two components, one twist free staple fiber component in the yarn core and a filament wound around the core. Used mainly for making Home textiles, automotive textiles, outerwear, carpet yarns etc.

Weaving Machinery

1. Projectile weaving

Projectile weaving machines use projectile equipped with a gripper to insert the filling yarn across the machine. This unique principle allows the use of any yarns: cotton, wool, mono or multifilament and even hard fibers like jute and linen. Projectile weaving machines are available in two or four colour with working widths of 190-540 cm, central microprocessor control, electronically controlled progressive weft brake, automatic weft feed back-up which switches over to feeder head with intact weft thread in the event of weft break. Used for manufacturing cotton felts, agrotextiles, geotextiles, conveyor belts, cinema theatre screens, tarpaulins, paper machines clothing.

2. Rapier weaving

In this type of weaving a flexible or rigid solid element called rapier is used to insert the weft yarn across the shed. The rapier head picks up the weft yarn and carries it across the shed. After reaching the destination the rapier head returns empty to pick up next filling yarn, which completes the cycle. The conventional grippers are redesigned to ensure better clamping of the yarn and prevent rubbing of warp yarns. Rapier looms can weave very light fabrics of 20 gsm to heavy 850 gsm. The gripper heads can take a wide range of yarn count ranging from 5 to 1000 tex. Up to 16 different weft yarns can be inserted. In the latest machines rapiers are made of composites materials and the rapier guide is eliminated. Used for making automotive, aircraft defence industries, lightweight for sports wear.

3. Air-Jet weaving

Air-jet weaving is a type of weaving in which the weft yarn is inserted into the warp shed with compressed air. The main advantages of these looms are simple operation and reduced hazard because of few moving parts with a reduced space required. Air-jet machines can be used for weaving spun yarns ranging from gauze to dense woven fabrics and in filament sector from light weight linings to tape fabrics. Electronic let-off maintains consistent warp tension from full beam to empty beam. Automatic package monitoring system can be adopted on almost all airjet-weaving machines. This keeps the yarn flight time constant when changing from empty to full package. Low noise and vibration levels. Low spare part requirement, minimum maintenance. Used for manufacturing tent fabrics, airbags, parachutes etc.

4. Water-Jet weaving

Water-jet weaving machine inserts the weft yarn by highly pressurized water. The tractive force is provided by the relative velocity between filling yarn and water jet. This force can be affected by the viscosity of the water and roughness and length of the filling yarn, higher viscosity cause higher forces. Modern water jet looms have speed of 1500 ppm while the maximum reed width is 3m and filling insertion rate is 1800 mpm. The yarn must be wettable in order to develop enough tractive force. Lightweight tent/tarpaulin fabrics, Inter lining fabrics are made on these looms.

5. Circular weaving

In circular weaving machines the warp is circular and there are continuously circulating shuttles running around the periphery in a wave or ripple shed. Circular fabrics are tubular fabrics of varying diameter without a lateral fold or edge. Tubular fabrics woven on flat weaving machines have a folded edge as they are joined at selvedges. In this the shuttles require a continuous motion across the shed and cannot leave the shed. On circular weaving machines a ripple shed is formed in which warp is divided into segments which forms shed with small heddle frames or ires. An automatic shuttle change mechanism is used to remove the empty shuttle at a particular spot in the shed and a reserve shuttle is inserted. Drop wires pressing the filling yarns towards fell of the fabric perform the beat-up operation. Used for applications such as woven sacks, tubes, medical textiles.

6. Three dimensional (3D) weaving

The 3 Dimensional woven fabrics are fabricated by modifying the conventional weaving mechanisms. Harnesses with multi-eye heddles are used to arrange the warps into three sections in plane form for weaving convenience. Mainframe and flanges are interlaced by a set of warps moving to and fro as a joint. Weft passes through the clear warp sheds separated by multi-eye heddles to form the 3D woven fabrics in plane form. The differential feeding length between the warp yarns give rise to extra friction, and therefore hairiness may occur. In order to reduce this friction the warps are passed through the tensioner and weight with ceramic eyes individually between the creel and weaving loom. The thickness of the central portion of the flattened fabrics is different from the side portions. Therefore the cloth roller cannot be used to take up the flattened fabrics. The fabrics is clipped and pulled by pair of rollers set in front of the loom as a take-up device. Making preforms for construction, automotive, ballistic and various industrial uses; for marine applications like carbon fibre preforms for high-performance powerboats; in medical technology (artificial veins, arteries, orthopedic tubes); lightweight construction (reinforced section in automotive engineering and aeronautics); pipeline construction; in sports like shinguard for soccer, protective headgear for skydiving, high speed water sports etc.

7. Multiphase weaving

Multiphase weaving machine is one in which several phases of the working cycle take place at any instant such that several filling yarns can be inserted simultaneously. In this more than one shed is formed at a time. The multiphase can weave 190 cm width with 69 meters of fabric per hour. The weft is inserted continuously without interruption with an even pull off speed of around 20-25 m/s thus the stress on yarn is reduced. The system is more suitable for harsher bast fibers and cottons but unsuitable for weaving of continuous filament yarns. They have added problem of stopping the loom in the event of weft break in any of the sheds. As four sheds operate simultaneously the system is very complicated with many small parts operating together. Because of theses drawbacks these looms are not commercially popular. Mostly used for making geo-textiles, awnings.

Knitting Machinery

The development of knitting machines and their operating elements has moved hand in hand with latest technology in the field of precision machines. The use of Computer Numerical Controlled (CNC) machines has paved the way for production of high machine gauge with narrow tolerance and high density feeders to produce high tech products.

1. Circular knitting

The circular knitting is a method of forming a fabric by knitting in which the loops made by each weft thread are formed substantially across the width of the fabric. The machine is capable of processing a wide spectrum of yarn made from wide range of materials, blends and filaments on one and same machine. The new developments have resulted in different areas.

Instead of actuating the needles by means of conventional method an electromagnetic selection is employed. This provides greater versatility as regards to the design but also simplifies the pattern changing operations and in some cases the change can be made even while in motion. With increased speeds in knitting fibre-fly accumulation becomes a serious problem. In order to avoid accumulation of lint and dust blowing, suction and exhaust devices are employed.

2. Flat knitting

Flat knitting is a weft knitting machine having straight needle beds carrying independently operated latch needles. Presently compact machines having 1 to 4 feeders per carriage unit were developed. Movement of individual carrier is done separately. They are available from simple trimming to high-tech machine for the production of fully-fashioned knitted products.

The productivity has increased considerably with the introduction of traverse adjustments, automatic needle selection and automatic control in needle bed movement. Jacquard, computer control now offer additional assistance to the designer and can represent the knitting process virtually by means of video simulation. Elastic bandages, knee cap, seamless hand gloves, architecture & automotive industrial design are some of the common applications.

To be continued
(The authors are with SASMIRA, Mumbai)