Weaving Processing

Weaving Process

The weaving process consists of 5 basic operations, shedding, picking, and beating-up, left off and take up.

Shedding: Separating the warp yarns into two layers by lifting and lowering the shafts, to form a channel known as the ‘shed’.

Picking or Filling: Passing the weft yarn (pick) crossways the warp threads through the shed.

Beating-up: Pushing the newly inserted fill yarn back into the fell using the reed.

Let off: The warp yarns are relaxed from the warp beam during the above three processes.

Take up: The woven fabric is wound on the cloth beam during the above 3 processes.

The above operations must be matched to occur in the accurate sequence and not interfere with one another. The full sequence is repeated for the insert and interlacing of each weft yarn length with the warp yarns, and is therefore called ‘The Weaving Cycle’

Shedding Mechanisms:

All weaving machines regulator the warp yarns to create a shed. This can be expert with the following systems:

• Crank shedding

• Cam shedding or tappet shedding

• Dobby shedding

• Jacquard shedding

Crank, cam and dobby machines regulator the harnesses which lift the shafts. Jacquard machines regulator the individual warp yarns. Each system is outlined below:

Crank Shedding:

Crank shedding mechanisms are simple and relatively economy to use. However it can only be used for plain weave fabric productions. In this system the harnesses are measured by the crank shaft of the weaving machine. For each crank shaft revolution a wheel is rotated half a turn, which changes the harness position. This system is only used in air-jet and water-jet machines where high speed is reached.

Cam Shedding:

Cam shedding is also simple and cheap. A cam is a disk which has grooved or conjugated edges which links to the lifting plan. The lifting plan controls which harnesses are lifted. The difficulty of cam shedding is that when the woven design has to be changed the cams have to be reorganized to suit the new design. Pattern design is too limited due to the quantity of harnesses the cams can control.

Dobby Shedding:

Dobby shedding is more difficult than crank and cam systems. The main benefit of dobby looms is that more difficult designs can be produced. Older dobby looms were operated by wood lags with pegs, which rotated around a roller overhead the loom. The pegs in the lags correspond to the lifting plan, which controls which harnesses are lifted. Punched paper or plastic pattern cards can also be recycled. Recently modern dobby looms are controlled via an electric system. The disadvantage of dobby systems is that faults are more likely to occur due to their complexity.

Jacquard Shedding:

In jacquard weaving a means called a ‘jacquard’ selects and lifts the warp yarns separately. This type of machine is used for larger more complete patterns, where all or most of the yarns in a recap, move freely. There are single or double lift machineries which use either mechanical or electric systems, using CAD to resistor the harness lifting and lowering. Modern jacquards are skillful of control over 1200 harness cords which control the lifting and lowering of the warp yarns.

Weft Insertion Methods:

Modern automatic looms do not involve a shuttle to carry the weft yarn crossways the shed. In its place the weft yarn is inserted by either one of the following techniques:

Rapier:

A shuttle less weaving loom in which the filling yarn is passed through the shed of warp yarns by fingerlike carriers called rapiers. There are two types of rapiers.

1. A single long rapier that scopes crossways the loom’s width to carry the filling to the other side.

2. Two small rapiers, one on each side. One rapier conveys the filling yarn halfway through the shed, where it is chanced by the other rapier, which carries the filling the rest of the way across the loom. The insertion rate of picks can be up to 1000 m min-1.

Projectile:

Projectile machines convey yarn through the shed using a small bullet shaped object known as a ‘projectile’. The yarn must be open to the projectile in order for it to hold this. This process can happen in the following ways:

1. A single projectile is dismissed from each side of the machine alternately and requires a joint yarn supply.

2. A yarn supply from one side of the machine is open to the projectile. It conveys the fill yarn crossways the machine and is then conveyed back to the other side by a conveyor belt. Several projectiles are in use at the similar time to enable rapid pick insert. Pick insert rate can be up to 1300m min-1.

Air jet:

In air-jet weaving machines the weft yarn is inserted pneumatically. It is approved through the shed by compressed air flow supplied from a chief nozzle and send nozzles. This is the firmest type of weaving qualifying pick insertion of 3000 m min-1.

Water jet:

Water jet weaving is the similar principle as air jet weaving, water is used in its place of air and a similar speed is achieved. One disadvantage is that only hydrophobic yarns can be recycled.

Multiphase

All of the upstairs methods are classified as single phase weaving, where by the fill yarn is laid crossways the full width of the warp yarns and beat-up takes place. Multiphase weaving includes several phases of the weaving taking place at the similar time, so that several picks can be injected simultaneously. The shedding machines of the weaving disturb this process:

1. Wave shed machineries convey the yarn in either straight or circular paths. Parts of the warp are in dissimilar stages of the weaving cycle at any one moment. It is possible for a series of weft transporters to move along in successive sheds in the same plane.

2. In parallel shed machines numerous sheds are formed simultaneously. Each shed extends across the full width of the warp and passages in the warp direction.

Limitations and Energy Consumption:

Although air and water jet machines can weave fabric at higher speeds matched to the projectile and rapier looms, the high power consumption effects in higher costs. The flow of the air is also hard to control and waste heat formed by the compressors is sometimes wasted when it could be used for other operations in the factory. However cooling of the factories via air Conditioning? Is not always needed with air and water jet looms and so energy costs are avoided in this way. The rapier and projectile looms produce a lot more heat and so air Conditioning? Is often installed to keep temperatures dejected within the factory. Multiphase wave shed looms affecting in a straight path have not been commercially successful as maintaining a fresh shed has proved very hard. The fill insertion rate of 2200 m min-1 was very elegant they became obsolete when simpler air jet machines started to surpass this speed.