Differences between weft knitting and warp knitting process

  

Comparison between weaving and knitting process

Comparison between weaving and knitting process

 

An introduction about shuttleless weaving method( non-conventional weft ...

An introduction about shuttleless weaving ( a non-conventional weft insertion system)

The weft insertion in the shuttleless loom is carried out without using the shuttle. Since the pirn winding process does not occur in the shuttleless weaving method so that the manufacturing cost is reduced. The loom revolutions per minute are also increased comprehensively. The weft insertion in these looms is carried out from one side. The yarn package is directly used in weft yarn so that the loom stoppage time due to weft package change is reduced many times in comparison to the shuttle loom. The multicolour weft fabric is woven effectively. Eight colours in the weft may be used successfully without any problem in the rapier loom. Four colours in weft can be used successfully in the projectile looms and air-jet looms. There is no selvedge wastage in the projectile loom. The selvedge waste occurs in the jet looms and rapier loom. Since the weft insertion is carried out from one side of the loom so that ordinary selvedge does not form in shuttleless weaving. Leno selvedge, tuck-in selvedge, and melt selvedge are formed in shuttleless weaving. 

The shuttleless loom can be classified into the below categories according to the weft insertion mechanism used in the shuttleless loom:

1 - Projectile loom

2 - Rapier loom

3 - Air jet loom

4 - Water jet loom

Projectile loom: 

The weft insertion is carried out in a projectile loom with the help of a projectile. The small gripper is fitted in the projectile. the weft yarn package is mounted on the weft creel. The weft yarn first passes through the weft accumulator. This weft accumulator ensures the continuous supply of weft yarn at regular tension. The weft accumulator neutralises the effect of irregular yarn tension to be created due to a change in the package size. The weft yarn passes through the yarn tensioner. Now weft yarn passes through the compensator which brings the weft back as required. The weft yarn next passes through the filling sensor. Finally, weft yarn passes through the weft selection finger.

The projectile is projected from picking a side to receiving side with the help of picking shoe which hits the projectile hardly. The projectile travels in between the projectile guide. The number of projectiles depends upon the reed space used on the loom. When the projectile reaches the receiving side, the micro procedure controlled projectile brake breaks the momentum of it. Since the projectile gets crossed the required mark during its journey so that the compensator brings it in its correct position. Now the gripper grips the tail of weft yarn. The projectile falls on the conveyor chain which has projections at regular interval. The projectiles circulate from receiving side to the picking side with the help of a conveyor chain. The difference between the two projections in the conveyor chain is kept 10 inches.

The projectile lifter brings the projectile in front of the picking shoe. The projectile opener opens the gripers jaws. When the tail of weft yarn enters between the gripper jaws the opener comes out and the projectile gripper holds the weft yarn firmly. Now the picking shoe hits the projectile and sends it from the picking side to receiving side. A release opener now opens the jaws of the gripper and weft yarn gets released. this insertion cycle gets repeated continuously.

Rapier loom:

This is the most versatile loom. It has a very wide weft count range. You can insert from very coarse to very fine yarn without making a big change. The weft yarn package is mounted on the creel. The weft yarn passes through the weft accumulator first. The weft accumulator ensures continuous yarn supply at regular yarn tension. Now the weft yarn passes through the filling tensioner, weft sensor, and the yarn guide. The weft sensor keeps continuous watch on the weft movement. If weft yarn gets failed to reach the destination, the weft sensor stops the loom immediately.  Finally, the weft yarn passes through the eye of the weft selector finger.  

The weft insertion is carried out by grippers fitted on the ribbons made of Teflon and carbon fabrics. These. ribbons make a reciprocating motion with the help of sprocket wheels and drive gears. When the weft insertion cycle begins, both the grippers start to move toward the sley centre. The receiving gripper starts to moves first. The weft selection finger falls down over the rapier guide. Now the insert gripper holds the weft yarn between the gripping jaws. The weft cutter cuts the weft yarn now. The receiving gripper arrives first and rests in the dwell period. When the insert gripper travels toward the sley centre and the yarn gripped by the insert gripper crosses the hook of receiving gripper, the receiving gripper begins to move outside of the shed. The insert gripper also moves back after the dwell period. The weft transfer takes place in the centre of the shed. When the receiving gripper comes out of the shed, the gripper opener releases the weft yarn near the fabric selvedge. This cycle is repeated continuously.

Air-jet loom:

The air jet loom is a very high-speed loom. The weft insertion is carried out with the help of compressed air. The weft yarn travels from one selvedge to another selvedge through the reed profile guide The weft yarn package is mounted on the weft creel. First of all, the weft yarn passes through the weft pre-winder. The main objective of the pre-winder is to ensure continuous weft supply at constant tension and to release accurate pick length for weft insertion. A magnetic brake is used to control the required pick length accurately. This yarn brake is controlled electronically.  The required number of yarn coils is fed in the control computer. The weft yarn enters into the main air jet nozzle and rests there. The relay nozzles are mounted on the sley at a definite interval of distance. The number of relay nozzles depends upon the reed space used in the loom. The main nozzle and relay nozzles are connected to a compressed airline through flexible pipes. The operation of the main nozzle and relay nozzles get controlled electronically through a control computer. The opening and closing of the nozzles are carried out with the help of magnetic valves. air regulator valves regulate air pressure in the loom. A filling detector is mounted at the end of the profile reed opposite side of the main nozzle. A weft stretch nozzle is also mounted near the filling detector. A filling cutter is mounted on the filling insertion side close to the end of the reed. 

When the reed begins to move from the front dead centre to the back dead centre position, the filling cutter cuts the last inserted  pick at 0 - 10 degree. when the shed gets almost opened, the air supply in the main nozzle gets opened. The compressed air carries the weft yarn from one selvedge to another selvedge. The main nozzle can not inset the weft yarn alone. The relay nozzles activate one by one according to the program and help to accelerate the weft insertion. When the yarn reaches near the selvedge opposite of the insertion side, it is detected by a filling detector. If the yarn is short or too long than required, it stops the loom immediately. The weft stretch nozzle sucks the tail end of the weft outside of the shed. This cycle is repeated continuously. The fabric quality of the air-jet loom is better than the projectile loom and rapier loom.

water jet loom:

The water pressure is used to insert the weft yarn into the shed in the water jet loom. This loom also has high productivity.  Low moisture content yarns can be woven on the water jet loom. The water jet nozzle is used to insert the weft yarn. A high-pressure water pump generates high water pressure. The water jet nozzle gets connected with the high-pressure water pump. The opening and closing of water pressure in the water jet nozzle are carried out with the help of a microprocessor-controlled magnetic valve. The pressure regulator valve regulates the water pressure in the water jet nozzle. A filling detector is mounted at the end of the reed opposite side of the water jet nozzle. A stretch nozzle is also mounted near the filling detector. A filling cutter is mounted near the end of the reed at the picking side. Weft pre-winder ensures the continuous weft yarn supply at regular yarn tension. The pre-winder also regulates the required pick length. The weft yarn rests inside the water jet nozzle.

When the sley starts to move toward the back dead centre position, the filling cutter cuts the last inserted pick. When the shed gets almost opened, the water jet nozzle controlled by the magnetic valve is opened. The very fine stream of water emerges from the jet of the nozzle. This water stream carries the weft yarn with it. The filling detector feels the weft yarn. If the weft insertion gets failed or gets short of the required length, the filling detector stops the loom immediately. The stretch nozzle sucks the end of inserted weft simultaneously. This cycle is repeated continuously.

Hollow spindle spinning method ( wrap spinning process) l Structure and ...

Hollow spindle spinning method ( wrap spinning process ):

Wrap spinning process:

The wrap spinning is a process in which a drafted strand of parallel fibres is wrapped by either surface fibres protruding from the fibres strand or by a continuous filament or filaments. The wrapping filament imparts coherence and strength to the resulting yarn in the wrap spinning process.
The high-quality specific yarns with a wide range of applications are produced in the wrap spinning process.

The wrapped yarn consists of two components. The first component contains a drafted strand of staple fibres in the yarn core. The second component is a filament which is wrapped around the drafted fibres strand.
The hollow spindle spinning method is most commonly used to produce wrapped yarn.

Hollow spindle spinning method:
The complete mechanism of the hollow spindle spinning method can be divided into four sections:
1 - Roller drafting mechanism.
2 - Hollow spindle.
3 - Pair of delivery rollers and package building mechanism.

Roller drafting mechanism:

The drafting roller mechanism consists of a series of rollers. These drafting rollers reduce the linear density or weight per unit length of the fibre strand getting processed.

The 3 or 4 roller drafting assembly allows selection of either the clamping point or draft methods with a draft range of 5 - 59. Fibre length between 50 - 220 mm can be processed effectively. Electronic monitoring used to identify faults and improves yarn quality. Special features of the drafting assembly include self-alignment of the spinning triangle to the centre of the spindle and continuous suction at the draft rollers, which eliminates roller lapping and assist in self-cleaning in the spinning zone. Pneumatic threading is an optional attachment to the hollow spindle and speeds up the operating time. A photoelectric cell monitor equipped to detect end-breaks to stop the spindle when a break occurs.

Hollow spindle mechanism:

The hollow spindle is designed as a false twisting assembly. The fibre strand does not pass directly after entering the vertical spindle instead, shortly after entering the spindle; this strand is led out again and back around the spindle with a wrap of about one-quarter of the spindle periphery. In this way, as the spindle rotates, the strand is provided with a twist between the drafting arrangement and the head of the hollow spindle. These turns of twist are cancelled out again in the spindle head in accordance with the false twist principle. This twist prevents the strand from falling apart in the length prior to filament staple fibres wrapping with filament.
A wrap spun yarn consists of a non-twisted parallel bundle of staple fibres held together by helically wrapped filament as shown in Figure 2. The proportion of the filament in the yarn is about 2 - 5%. Due to the helical wrapping of the filament and radial pressure, necessary cohesion between the individual staple fibres is improved. This imparts desired strength to the yarn. The number of wraps per unit length in a standard PL yarn is approximately the same as the amount of twist in a comparable ring spun yarn.

Pair of delivery roller and package building mechanism:

There is a pair of delivery rollers used to take the yarn forward

The yarn received by delivery rollers is wound on the yarn package. Once the yarn leaves the hollow spindle and delivery rollers, it passes through a traverse guide. This traverse guide distributes the yarn along with the package horizontally from one side to another side. When one layer is completed, the next layer gets started. The traverse guide is used as a connection between the hollow spindle and the bobbin where the yarn is stored.

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