Shedding mechanisms

Topic 2 Topic 2 Shedding Mechanisms vs Shedding Mechanisms vs

F b iF b iFabricsFabrics

What does shedding doWhat does shedding doWhat does shedding doWhat does shedding do

• Shedding is one of the 5 loom motions– The others are weft insertion, beat-up, take-up, and

let-off• Shedding separate the yarn sheet delivered

from the weavers beam into two levels to form a space (shed) to allow a pick of weft yarn to be inserted.

• The way the warp sheet is separated depends y p p pon the weave design of the fabric.

General requirements on shedGeneral requirements on shedGeneral requirements on shedGeneral requirements on shed

S ll t ibl l t ibl• Smallest possible : lowest possible additional warp tension

• Clear enough : preventing faults• Proper shed dwelling : convenient for weftProper shed dwelling : convenient for weft

insertionSmooth movement of the heald frames• Smooth movement of the heald frames(mechanism dependent) : low noise, low parts damage and less fabric fa lts thisparts damage, and less fabric faults, this also affects the loom speed

Types of shedding mechanismsTypes of shedding mechanismsTypes of shedding mechanismsTypes of shedding mechanisms

F diff t t f h ddi• Four different types of shedding mechanisms are available for looms:– Crank shedding mechanism (simplest)– Tappet shedding mechanismpp g– Dobby shedding mechanism– Jacquard shedding mechanism (most complex)Jacquard shedding mechanism (most complex)

• Choice of shedding mechanisms determines the scope of fabrics that can bedetermines the scope of fabrics that can be made

How does crank mechanism workHow does crank mechanism workHow does crank mechanism workHow does crank mechanism work

Features of crank sheddingFeatures of crank sheddingFeatures of crank sheddingFeatures of crank shedding

• The simplest• No need for maintenanceNo need for maintenance• Does not put limit on loom speed• Controlling only 2 heald frames – plain

weave (and weft backed weaves) onlyea e (a d e t bac ed ea es) o y• No shed dwelling, working width of loom

limited to 200 cmlimited to 200 cm

How does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism work

N tiNegative

Tappet is also known as camsknown as cams.

Basic principle:p p

Cam followers follow the cam profilesp


Positive - 1


Positive - 2

Features of tappet sheddingFeatures of tappet sheddingFeatures of tappet sheddingFeatures of tappet shedding

• Simple principle, easy maintenance• Low installation cost• Low installation cost• Mechanism robust and reliable• No limit on loom speed

Controlling 2 8 heald frames thus only• Controlling 2-8 heald frames, thus only suitable for fabric with simple weaves

• Inconvenience for frequent pattern changeschanges

D bbD bbDobby Dobby

How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work

Negati eNegative


PositivePositive

Features of dobby sheddingFeatures of dobby sheddingFeatures of dobby sheddingFeatures of dobby shedding

• Controlling large number (2-36) of heald frames, therefore suitable for weaving wide , grange of fabrics

Plain and simple weaves– Plain and simple weaves– Weaves with medium complexity

• Convenient for pattern change• Posing limit on loom speed• Posing limit on loom speed• Occasional shedding errors (early versions)

5 October. Next time – jacquard mechanism

JacquardJacquardJacquardJacquard

Types of JacquardTypes of JacquardTypes of JacquardTypes of Jacquard

• Coarse pitch (English pitch)– 200, 400, 600, 800 needles, , ,

• Fine pitch (French pitch)Vi i 880 1320 dl– Vincenzi: 880, 1320 needles

– Verdol: 896, 1344, 2688 needles

How does a jacquard workHow does a jacquard workj qj q

E li hEnglish typey


French type

HarnessHarnessHarness Harness managementmanagementgg

Features of jacquard sheddingFeatures of jacquard sheddingFeatures of jacquard sheddingFeatures of jacquard shedding

• Capable of weaving all types of fabrics, from the simplest to the most complex p pfabrics

Mostly used for weaving complex fabrics– Mostly used for weaving complex fabrics– Not economical for weaving simple fabrics

• Posing speed limit on loom• Complex mechanismComplex mechanism

Mechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquard

Electronic jacquardElectronic jacquardElectronic jacquardElectronic jacquard

Comparison of the 4 mechanismsComparison of the 4 mechanismsComparison of the 4 mechanismsComparison of the 4 mechanisms

Crank Tappet Dobby Jacquard

Mechanism Simplest Simple Quite complex

Most complex

Installation cost

Low Low Medium High

Yarn control 2 endsCollective

2-8 endsCollective

2-36 endsCollective

2-1000sIndividual

Fabric types Plain w fabrics

Simple w fabrics

Fancy fabrics

Complex fabrics

Shed geometryShed geometry

Equal tension Unequal tension Unequal tension

Shed timingShed timingShed timingShed timing

90°

180°0° 1800

270°

Late shedding

270°Early shedding

Effect shed timingEffect shed timingEffect shed timing Effect shed timing

• Early shedding– larger shed angle at beat-

up

• Late shedding– small shed angle at beat-

upup– helpful in weaving fabrics

with high weft density

up– small resistance to beat-

up– clear shed– better fabric hand

(fullness)

– lower end breakage – clear weave pattern on

fabric(fullness)– more likely to produce

end breaks

fabric – less likely to achieve

higher weft density– used for plain fabrics – used for twill and satin

fabrics

11 October 2010

Shedding mechanisms

Engineering

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