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Fundamental Fundamental Operations in WeavingOperations in Weaving

Fundamental Fundamental Operations in WeavingOperations in Weaving

Dr Jimmy LamDr Jimmy LamInstitute of Textiles & ClothingInstitute of Textiles & Clothing

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Learning Objectives• Four fundamental operations in weaving

1. Shedding1. Tappet2. Dobby3. Jacquard

2. Picking

3. Beating up

4. Taking up and letting off

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Shedding

• A process of raising and lowering of warp yarns by hardnesses to make an opening for the filling (weft) yarn to pass through

• The raised and lowered form of warp yarns is called shed

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Shedding

Three types of shedding motions (opening) are available for different type of fabrics. They are:

1. Tappet shedding2. Dobby shedding3. Jacquard shedding

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Tappet shedding• Tappet shedding uses tappets and cams to control

the up/down movement of shafts.• The bulkiness of its mechanical movement limits

the loom to control up to 8 shafts (repeat not more than 8)

• Therefore, tappet shedding is the simplest and least versatile shedding motion.

• The design is restricted to plain weave, simple twill and simple sateen or satin weave.

• Any design more than 8 shafts requires dobby loom.

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Dobby Shedding• This is a compact, electronically guided shedding

motion and capable of having up to 28 shafts.• More complex and versatile shedding motion.• A dobby loom, therefore, can have up to 28 shafts,

and much greater weave repeat is possible.• Design may be woven with two or more basic

weaves and their variation.• Such fabrics may be referred as dobby cloths or

dobby weave, towels ususally show geometric designs when pattern is provided by dobby.

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Jacquard Shedding• To provide with unlimited design width, jacquard

shedding is needed.• This shedding motion has no shafts, instead, a

hardness consisting of as many cords as there are ends in the warp sheet connects each end individually to the jacquard machine.

• Each warp could weave independently of all others.

• Complex and most versatile shedding motion.• Biggest weave is possible with jacquard shedding

as each warp yarn may be individually controlled.

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Picking(weft insertion)

• Inserting filling (weft) yarn through the shed by carrier device.

• In shuttle loom, the weft carrier is the shuttle

• Whereas in the shuttleless looms, the projectile, air jet or water jet carriers the weft yarn.

• The weft insertion determines the production of weaving looms

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Weaving Speeds

Type of loom Insertion per minute

Shuttle 300

Flexible rapier 950-1,300

Rigid rapier 1,000-1,300

Projectile 1,200

Water jet 1,800-2,000

Air jet 1,100-2,200

Multiphase 5,400

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Production rate (meter per 8 hours)

Rpm Meters/8 hours

Handloom 20 4

Ordinary loom 160 24

Modern auto shuttle loom

220 40

Rapier loom 400 73

Projectile loom 600 110

Air jet loom 800 146

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Beating up

• Beating up pushes each loose filling yarn into cloth by the reed, after the shuttle has moved through the shed.

• The reed determines the sett (density) of the warp and weft.

• Beating-up gives the fabric firm and compact construction.

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Conclusion• Discuss three different types of

shedding motions in weaving• What are the advantages of dobby

shedding over tappet shedding?