Weaving process and advancement in weft

insertion system

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Weaving processWeaving of any fabric is simply done by

three main mechanisms.warp let-offssheddingPickingBeatingFabric take up

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The weaving process can be explained as :Firstly the warp yarn are let off by warp let-off

mechanism Shed formation is there to separate the sheets

of warp yarns into two sheets upper and bottom. Then a weft yarn is passed into the middle of the

two sheets of warp yarn by means of any weft inserting media whether shuttle projectile or jet mechanism (air, water)

After the picking completed beat up of weft yarn to the feel of cloth done by means of reed

After wards fabric wounds on the cloth roller which is take up mechanism.

Weaving process

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Advancement in weft insertion system

Projectile weaving machineRapier weaving machineAir-jet weaving machineWater-jet weaving machineMultiphase weaving machine

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Projectile Weaving MachineThe Projectile weaving machine introduced into

market in 1952 by Sulzer as the first successful shuttle less weaving machine.

Projectile machine uses a projectile equipped with a gripper to insert the filling yarn across the machine.

The unique principle of this machine is that we can practically insert the any kind of yarn like cotton ,wool, filament yarn, poly propylene or even jute as well, this is because all the finer or coarser yarns are securely grip by a gripper and inserted by the projectile

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Projectile motion

Fig: Hitting of Projectile with torsion rod and picking lever6

The principle operationThe projectile draws the filing yarn into the

shed.Energy requires for picking is build up by

twisting a torsion rod.On release the rod immediately returns to

initial position smoothly accelerating the projectile by means of a picking lever.

The projectile slides through the shed in rake shape guide and braked into the receiving unit.

Projectile is then conveyed into the original position by a transport device (belt) installed under the shed . 7

Advantages of projectile weaving machine

Low power consumption Reduced waste of filling insertion due to

unique clean ,tucked in selvagesQuick warp and change styleEasy operation ,maintenance and low spare

parts requirements More than one width of fabric woven at a

time due to large machine width such as 33-540cms

Energy savingDifferent designs and color sequences can

be woven. 8

Rapier weaving machineRapier weaving machineIn this type of weaving, a flexible or rigid solid element, called rapier, is used to insert the filling yarn across the shed.

The rapier head picks up the filling yarn and carries it through the shed.

After reaching the destination, the rapier head returns empty to pick up the next filling yarn, which completes a cycle.

A rapier performs a reciprocating motion.

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Single Rapier Double Rapier

TYPES OF RAPIER WEAVING MACHINES

Flexible RapierRigid Rapier

Dewas system Gabler System

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Single rapier weaving machinesA single, rigid rapier is used in these machines.

The rigid rapier is a metal or composite bar usually with a circular cross-section.

The rapier enters the shed from one side, picks up the tip of the filling yarn on the other side and passes it across the weaving machine while retracting.

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Fig: Single rapier transfers the yarn in one way12

A single rapier carries the yarn in one way only and half of the rapier movement is wasted.

The single rapier’s length is equal to the width of the weaving machine; this requires relatively high mass and rigidity of the rapier to ensure straight movement of the rapier head.

For these reasons, single rapier machines are not popular. However, since there is no yarn transfer from rapier to rapier, they are suitable for filling yarns that are difficult to control.

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Double rapier weaving machinesTwo rapiers are used in these machines one

rapier, is called the giver, takes the filling yarn from the yarn accumulator on one side of the weaving machine, brings it to the centre of the machine and transfers it to the second rapier which is called the taker.

The taker withdraws and brings the filling yarn to the other side.

Similar to the single rapier machines, only half of the rapier movements is used for filling insertion.

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Double rapier machines can be rigid or flexible.

Double rigid rapiers are further classified into two types: Dewas system and Gabler system.

In Dewas system the giver grip the tip of the yarn, brings it to the centre and transfers it to the taker which retracts and carries the yarn to the other side of the weaving machine. 15

In the Gabler system, the yarn is not gripped. The giver extends the yarn in the form of “U” shape to the centre of the weaving machine.

The yarn is then transferred to the taker, which extends the yarn to the other side of the weaving machine by straightening it.

since both rapiers extend to the out side of the weaving machine, the space requirement of the double rigid rapier machines is high. 16

In flexible rapier machines the rapier has tape-like structure that can be wound on a drum.

This saves space and allows narrower machine widths compared to the double rigid machines.

The yarn is gripped both by giver and taker.

Double flexible rapier machines are more common than the rigid rapier machines.

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Versatility of rapierRapier weaving machine produces top- quality

fabrics from spun yarns such as cotton-wool, camel hair, silk, synthetic fibers and fancy yarns.

Rapier weaving machine are fast and exceptionally flexible.

It offers a choice of various reed widths, shedding motions, selvedges and filling insertion colors.

This makes it suitable for weaving an extended range of articles: fashion fabrics, shirting, denim, suiting, industrial or furnishing fabrics, in one to eight or twelve filling colors or yarns, with a maximum weight of 500 g/m2.

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Versatility of rapierToday's rapier weaving machine is designed with

modern electronics, with total automation of weaving and central microprocessor control system, also ensuring maximum reliability, amazing user-friendliness, ease-of-operation, shorter style changing time, excellent fabric quality, low energy consumption.

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Water jet weaving machineThe water-jet weaving machines inserts the filling

yarn by highly pressurized water.The tractive force (pulling force) is provided by the

relative velocity between the filling yarn and water jet.

if there is no velocity difference between the water and yarn then there would be no tension on the yarn which would be result in curling and snarling of the yarn.

The tractive force is affected by the viscosity of the water and roughness and length of the filling yarn; higher viscosities cause higher retractive forces.

The viscosity of water depends on the temperature.20

Water jet weaving machineWater jet weaving machines have the same basic

functions of any other type of weaving machines.the principle of weft insertion with a water jet is

similar to the filling insertion with an air jet: they both use a fluid to carry the yarn.

however there are some differences has affect the performance and acceptance of water jet weaving machines.

For example, the yarn must be wettable in order to develop enough tractive force.

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Water jet weaving machineThe flow of water has three phases:1. Acceleration inside the pump prior to injection into the nozzle.2. Jet out let from the nozzle3. Flow inside the shed. The water flow inside the shape has conical shape with three

regions; Compact, split and atomized. Compact and split portions are

better for yarn insertion. due to water weight the jets axis forms a parabola which necessitates adjusting the axis of the nozzle upward by some angle. the flow of water then flows the motion of angular projection.

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Water jet weaving machineThe width of the water-jet weaving machine

depends on the water pressure and diameter of the Jet.

Since water is not compressible it is relatively easy to give enough pressure to water-jet for insertion.

The diameter of Jet is around 0.1 cm and the amount of water used for one pick is less than 2 cc.

Double pump system, with two nozzle at will filling insertion, is suitable for weaving fabrics with two different fillings. 23

Air- Jet weaving machineAir-jet weaving machine is a type of weaving in

which a filling yarn is inserted into the warp shed with compressed air.

Yarn is drawn from a filling supply package by the filling feeder and each pick is measured for the filling insertion by means of a stopper, the filling is feed into the feed tunnel via tandem and main nozzles.

The tandem and main nozzle combination provides the initial acceleration, where the relay nozzles provide the higher air velocity across the weave shed.

Profiled reed provides the guidance for the air and separates the filling yarn from the warp. 24

Air- Jet weaving machineA cutter is used to cut the yarn when the insertion

is completed.The air-jet weaving machine combines high

performance with low manufacturing requirements.It has an extremely high insertion rate, due to its

exceptional performance.Air-jet weaving machines are used primarily for the

economical production of standard fabrics, covering a wide range of styles.

Meanwhile, more and more special fabric segments are covered: heavy cotton fabrics such as denim, terry fabrics, glass fabrics, tire cord, etc.

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Principle operation of air jet weft insertion system

Profiled reed 26

Multi-phase weavingFurther increases the production rates of woven

fabrics(woven area/machine hour) require new technologies such as multi-phase 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 these machines more than one shed is formed at a time, there fore they are also called Multi-shed weaving machines.

This concept is drastically different than single shed weaving machines in which each of the five functions takes place subsequently.

Therefore it is appropriate to consider the multi-phase weaving machines as the third generation of weaving machines. 27

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VERSITILITY OF MULTIPHASEWith the Multi-phase weaving, weft insertion rates of up to

2800 picks/min (5400 m/min) are possible -meaning that up to 1500 linear m of printing ground fabric can be produced daily.

On the basis of practical experience it is known that a complete style change on the multiphase is possible in less than 3 hours.

The style-dependent parts required, such as beat-up combs, weft channels and warp positioner can be held in stock by the customer.

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DEVELOPMENTS IN PROJECTILE MACHINES

1) COLOUR SELECTION1 X 1, 2, 4 and 6 colors can be used in weft direction. The system is freely programmable and operated by servo controller. No limitations on feeder position shifting.2) ELECTRONIC WEFT BRAKER  This device keeps a uniform tension on weft.  The braking force and the braking duration are programmable. Program can be given for each pick.The device is driven by stepper motor.3) Pre-acceleration to weft yarn is given by compressed air, which

relieves extra tension in weft while inserting.4) K3 Synthetic projectile can be used for weaving of delicate yarns.

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5)The no. of heald shafts operable by cam motion is extended to 14.

6)Speed has been increased upto 470 rpm due to improvement in many related mechanisms.

7)LED display at signal pole for machine speed, projectile arrival time, angle of machine stop, etc. which helps in monitoring of process.

8)Automatic weft brake repair motion enables shifting of feed package to a reserved one in the event of weft break between package and accumulator, no stopping of machine which increases the machine efficiency.

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DEVELOPMENTS IN AIR JET WEAVING

Modification In Weft Insertion System The multi nozzles are divided into two zones and connected directly

with separate tanks.The weft yarn requires higher pressure at later part of its flight, and this separation has helped greatly in optimization of pressure in duration of Jet opening.The weft insertion, based on a precise electronic control that

includes ATC (automatic timing control), also uses newly developed nozzles, which guarantees optimum weft insertion conditions.

Independent pressure tanks make it possible to set weft insertion pressures at optimal levels, this makes a significant contribution to energy conservation.

All settings regarding picking is done by microprocessor keyboard, which reduces machine down time.

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Tandem Nozzles: - In tandem nozzles, the two main nozzles are arranged in

series so called tandem nozzles. Advantages: -

It reduces the nozzle pressureSaving in energyAlso use of wider weft count range. Low pressure weft insertion to occur, making effective for super

high-speed operation accommodating yarns with low breaking strength.    

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Tapered Sub-Nozzles: - It consists of a tapered hole to prevent air dispersion. Advantages: -

It enables stable weft insertion with lower air volumes. It stabilizes air injection angles during weft insertion. The weft insertion is more stable and requires less air.

Tapered Tunnel Reed: - A tapered shape has also been applied to the tunnel selection of reed

blade. Advantages: -   It helps in preventing air dispersion.   The weft insertion is more stable and requires less air. Electronic Braking System: - One of the serious drawback of Air-jet picking was tension peak in

weft when brake is applied. The electronic braking system can precisely control braking time and brake stroke, which significantly reduces tension pick, thereby reduction in weft breaks.   34

  Automatic Pick Controller: -For smoother working, all machines have weft

arrival time sensing and correction of pressure at nozzles but when package is changed from empty to full package, the arrival time will be delayed and this would be beyond the capacity of such a correction system. With APC (Automatic pick controller), this problem is attended.

It instantly corrects the main nozzle’s air pressure for timing control during full cheese changes.

It adjusts automatically nozzle air jet pressure, which compensates for variations in the travel timing of weft yarn. 

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OTHER DEVELOPMENTS: -Weft feeder threading is comparatively time consuming and, now the

self-threading by pneumatic system is done.The weft cutter is electronically controlled and operated by steeper

motor By this, cutter can easily adapt to any cutting time to the accuracy of 1°. Style changing time is saved.

With the help of mechanopneumatic tucking device can hold the weft at both selvedges firmly during beating and then tuck-in. this eliminates auxiliary selvedge and weft waste is zero. The system can work upto 850 rpm.

Almost every machine manufacturer supplies positive easing motion for maintaining constant tension during shedding and beating.

There is a new shedding concept introduced, in which the heald shaft is directly controlled by Servo Motor. Thus the total motion of heald shaft can be independently programmed.

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Developments in rapier weaving machines Programmable filling tensioner lamellae

(PFL)The PFL is a device ensuring a correct yarn tension at

any time during the insertion.During the insertion cycle, the rapier accelerates from

rest to maximum speed causing peak tensions in the pick being inserted.

Peak tensions are the main cause of yarn breakages.The mounting of a PFL at the exit of the prewinder

allows you to keep those peak tensions under control and avoids yarn breakages.

With the PFL the overall basic minimal filling tension can be drastically reduced because tension is added at the right moments: when the yarn is presented and when it is transferred from the left to the right rapier and at this time only! A low basic tension is an enormous advantage when weaving weaker yarns.

The PFL is equipped with an automatic cleaning system requiring conditioned air.

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QUICK STEP FILLING PRESENTER The filling can be presented at low tension, which avoids

unnecessary filling breakages.The quick step-filling presenter operates with independent

modules.Each consists of electronically controlled stepper motor with

presenter needle and the system handles upto 8 colors.The weaver can enter color pattern through microprocessor

keyboard or at jacquard control unit.

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ELSY (False Selvedge Device)The unique ELSY full leno false selvedge motion is

electronically driven by individual stepper motor. They are mounted in front of harness so all harness remain available for fabric pattern.

This only Rapier machine that allows selvedge crossing to be programmed on microprocessor independently of shed crossing even while machine is in operation. So result of resetting can be checked immediately.

The easiest position of rethreading can be set by a simple push button. When machine starts, the selvedge system automatically comes to original position.

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PSO (Prewinder Switch Off)PSO is the system by which the machine does not stop

immediately after a bobbin breakage, but continues to weave, until the weaver is available to repair breakage.

The weaver is informed by flashing orange light that the machine carries PSO action.

Consequently the waiting period for intervention of weaver reduced to zero, weaver can decide himself when breakage must be repaired, for this Piezo-Electric filling detector is used.

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ELECTRONIC TAKE-UP AND LET-OFF MOTIONIt plays important role. Required pick density can be

programmed on microprocessor keyboard. No pick wheel required. The accuracy of settings make it easy to adjust pick density of fabric with optimum fabric weight and minimum yarn consumptions. By ETU make it possible to weave fabric having various pick densities.

The electronic link between let-off and take-up is an additional tool to manage the fabric marks. Warp beam driven by electric let off motion through separate drive wheel that stays on loom, ensures trouble free operation of let-off system and improve fabric quality.

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FDEI (Filling Detection At The End Of Insertion) When weaving ‘lively’ yarns, use FDEI system. It checks

the presence of filling at the end of insertion. The system detects short picks, rebounding fillings and prevent faults in fabric at right end.

At filling breaks, the machine stops and only the harness are moved automatically to free the broken pick for removal of weaver. The is outstanding since automatic pick finder is not driven by separate motor but monitored by hydraulic system. In this way a two speed slow motion become a standard luxury to the weaver. The transfer position of filling yarn in center of fabric is always correct even after changing the cloth for new style. 42

Development in multiphase weaving machine

Weft insertion The channel in the shed forming elements guide in insertion of

weft. The weft is inserted by nozzles are similar to Air jet weaving. Additional nozzles between shed forming elements further support the weft. Four wefts are inserted at a time. The weft measuring, clamping, cutting, sensing and controlling are similar to air jet machines.

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Beat-UpThe combs located behind shed forming element perform the function

of conventional reed. The lower shed, which rises after insertion of weft, lift the weft out of channel over the entire weaving width. The beat-up comb then catches the weft and beats up.

The modular design concept adopted has helped to change warp beam within 20 min. the warp beams upto 1600mm diameter can be used. The inclusion of batching motion for cloth winding has reduced change intervals.

Many machines are in operations since 1997- 98 and this might be the machine for mass production in future.

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