Aerodynamic Web formation (Air-lay)

Non woven fabric

Nonwoven Fabric is a fabric-like material made from fibers, bonded together by chemical, mechanical,heat or solvent treatment. 

Web formation

Nonwoven manufacture starts by the arrangement of fibres in a sheet or web. The fibres can be staple fibres packed in bales, or filaments extruded from molten polymer granules.

Methods of forming a web

   — Drylaid

   — Spunmelt

   — Wetlaid

   — Other techniques

 

Aerodynamic web formation 

•       Drylaid web forming method.

•       Short fibres are used to form the web.

•       Compared with other drylaids, airlaid webs have a lower density, a greater softness and an absence of laminar structure 

 Aerodynamic web forming machine

 Process

• Lap or plied card webs are fed by a feed rollers.

• The fibers are separated by a licker-in or spiked roller and introduced into an air-stream.

• By the force generated by the air stream (suck or blew), single fibres are collected to form a web on a perforated surface of the cylinder.

• The web is delivered to a conveyor for transporting to the bonding area. 

 Features of the Air-laid

• The length of fibers used  varies from 2 to 6 cm. 

• The shorter lengths allow higher production speeds. Longer fibers require higher air volumes to avoid tangling.

• Due to uniformity problems, it has not been practical to make isotropic webs lighter than 30g/m2.

• Air-laying is slower than carding ,hence more expensive.

Advantages

•         Isotropic structure of the web.

•         Vast webs can be produced.

•         Wide variety of processable fibers such as natural, synthetic, glass, steel, carbon, etc.

•       Possibility of processing waste fibres 

Disadvantages

• Low level of opening fiber material by licker-in.

• Variable structures of web in width of layer due to irregular air flow close to walls of duct.

• Possible entanglement of fibers in air stream.

 

Open-End Rotor Spinning

This system differs to that of ring spinning in many ways. Unlike the conventional drafting and

spinning system there is a break in the continuity of the material and an open end is produced.

This open end must be rotated to introduce the necessary twist for the yarn formation. 

The fibre flow should be separated into individuals before being reassembled.

This system eliminates the ring, traveler, and spindle.

There is no ballooning to introduce problems in the air-drag. 

 It is rotate the yarn package at high speed is eliminated so power needed is thereby reduced.

      

Rotor Spinning 

Features

•         Ability to Automate
•         Rotor speed up to 150,000 rpm
•         Production speed up to 235 m/min
•         High speed, high strength piecing
•         Package size up to 5Kg
•         Flexibility – variable adjustment of draft, twist, and tension and rotor speed
•         High processing efficiency and lower downstream cost weaving/knitting
  Principles of OE spinning
  §Opening of feed sliver into individual fibres 
  §Assembling of individualized fibres 
  §Twist insertion 
  §Withdrawal of resultant yarn and winding onto a package  
  
  
  
  
  Opening/ Individualization and Fibre Feeding

  
  
  •Opening roller called opener or the beater
  •Opening roller speed =6500 – 9000 rpm
  •Surface speed =800 – 2500 m/min
  •Sliver count = 30 – 300 thicker than yarn count (draft)
   Fibre Assembling/Transport
           •The individual fibres are carried forward from the opening roller by an air

    current through the feed tube or transport tube. 

  •The conical shape of tube accelerates the air current leading to improved fibre 

    orientation and straightness.

  •The fibres carried by the air current are deposited at the grove in the form of a

    ring.

   
  
   
  

  Drafting
  
  
  •drafting from sliver to Final yarn count

  •Assembly of fibres in the spinning groove to give the linear density of yarn

    required.
  
  
                Twist Insertion
  •Centrifugal forces presses the fibre band against the inner peripheral surface

    of the rotor causing it to rotate and thereby inserting twist to the fibre assembly.

  •Rotor speed may vary between 50,000- 150,000 rpm depend on the fibre and

    yarn count

  •Theoretically one turn of twist is introduced for each revolution of the yarn end.

  •Direction of the twist is determined by the direction of rotation of the rotor.

   
  
  
  
  Twist (tpm) = Rotor speed (rpm) / Yarn delivery speed (m/min) 

  
  

  Yarn Piecing

  Yarn Properties

  •Structure

  –Fibres in the Rotor yarn are not well oriented as in the ring spun yarn

  –Core more twist, Sheath less twist

  –Bipartite Structure, Core contribute to strength and sheath for bulkiness

  –Wrapper fibres in the surface gives dull appearance

  
  

  •Strength and Extension

  –Due to inferior orientation, the fibre length utilization is lower, and therefore less strength than equivalent ring spun yarn (80-85%).

  –Higher extension at break than ring spun yarn

  
  

  •Yarn count

  –Yarn 15 tex or coarser.

  –Finer fibres are preferred. 

   
  

  •Unevenness and imperfection

  –Rotor yarn is relatively evener than equivalent ring spun

  –Fewer imperfection than ring

  
  

  •Flexural Rigidity

  –Higher flexural rigidity than ring spun (1.5-2.5 higher than ring spun)

  –Higher stiffness

  
  

  •Hairiness

  –Less hairy than ring spun

  
  

  •Abrasion Resistance/ Pilling

  –Higher abrasion resistance than ring spun.

  –Lower pilling resistance

  End uses of Rotor Spun Yarns

  
  

  
  

  
  

  •The rotor spinning has established very well in coarser and medium count

    sector to spin yarns economically in the range of 15 tex to 100 tex.

  
  

  •The marked evenness, abrasion resistance, and surface look enables these 

    yarns to find applications extensively in various products, like:

  –Denims, Jeans, knit fabric for inner wear, leisure wear, outer garments, T-shirts, sweaters, furnishing etc.

  
  

   

Composite Yarn Manufacturing & Their Applications

  Definition

         Composite yarns are structures consisting of at least two strands, one forming the center axis, or core, of the yarn, and the other strand forms the covering or wrap One strand is usually composed of staple fibers and the other is of filaments

 Classification

 Covering Process

• Covered yarns have a central yarn (core) which is completely covered by fiber or another yarn
• The core might be an elastomeric fiber, such as rubber or spandex, or a hard fiber such as polyester or nylon.

 Single Covering Process 

Double Covering Process

 

Core Spun Yarn

Definition

• Core-spinning is a process by which fibers are twisted around an existing yarn, either filament or staple spun yarn, to produce a sheath– core structure in which the already formed yarn is the core. 

• Core-spun yarns are two-component structure with Core and sheath. Generally continuous filament yarn is used as core and  the staple fibers used as sheath covering.                                

 Method of production

The production of Core-spun yarns done successfully by many spinning systems. 

1.Conventional core spinning attachment with ring spinning systems

2.Core-twin spinning system

3.Composite electrostatic spinning system

4.Rotor spinning system

5.Friction spinning system and

6.Air jet spinning system

 Conventional core spinning attachment in Ring spinning

 The conventional ring spinning is simple and economy but  the core positioning in the center is difficult and major strip back problem may arise during subsequent process and the core filaments get twisted

  Effect of Process variables on Ring Core-spun yarn properties   

    The process variables that affect the core-spun yarn properties are: 

1) Core - sheath ratio

2) Pre-tension applied to the core materia

l3) Spinning draf

t4) Number of roving feed and

5) Twist

 

Core Twin Spinning system   and Composite yarn by Electro static filament charging method 

                                    

 

        A minimum pre-tension is necessary to avoid filament flung out in to the rotor-collecting surface. The core is not twisted during this process. It is economical to produce coarse core-spun yarns through rotor machine than the ring core-spun yarns Any types of material, including metallic wires high tensional rigidities can be used as cores                                                                                                                Core-spun yarn production by MJS spinning system 

 

        The Air-jet spinning could be used for producing core yarns after optimizing process parameters. A relatively higher first nozzle pressure is advantageous for improving sheath-slippage resistance. The use of higher spinning speed and wider condenser markedly improves the tenacity, breaking extension, initial modulus and sheath-slippage resistance and affects the yarn hairiness, mass irregularity and flexural rigidity. However, yarn properties deteriorate at high spinning speed especially for finer yarns.   

           Core-spun yarn production by Friction spinning system

         The sheath fires are attached to the core fires by false twist generated by the rotating action of the drums. In DREF III the core positioning can be set accurately and used to produce the industrial and conductive yarns. 

 

         Strength of the DREF III core-spun yarns have direct relationship with the strength of core filaments and number of sheath fires that are active in generating radial pressure due to their structural helical configurations

         The effectiveness of wrapping of sheath fires depends on physical and mechanical characteristics of fires, configuration, length variations, firmness of the wrap and wrap angle

 WRAPPED YARNS

 Filament-Wrapped Spun Yarns

 Untwisted, parallel staple fiber strand in the center of the yarn, and a filament wrapped around the center strand. Combines spun yarn aesthetics with filament yarn durability.  Wrap spinning with a filament replaces the insertion of twist to produce a yarn. It is also economical and has good evenness, strength, elongation, appearance, and abrasion properties   
                                                                        
      Filament-Wrapped with Staple Fibers  

  •Bundle of filaments wrapped with staple fibers.

–Coarse filaments - strength

–Fine broken filament - softness 

  •Production of these yarns is very fast.  These yarns give better texture and hand to fabrics

Filament-Wrapped with Filament Yarns • 

•For better strength purposes 

• Heavy applications 

•Speeder than conventional ring spinning•Ease of core slippage -
Composite properties, depended on filament frictional properties &   yarn packing density.