topic 2 shedding mechanisms[1]
TRANSCRIPT
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Topic 2 Topic 2 Shedding Mechanisms vs Shedding Mechanisms vs
F b iF b iFabricsFabrics
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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.
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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
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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
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How does crank mechanism workHow does crank mechanism workHow does crank mechanism workHow does crank mechanism work
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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
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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
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How does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism work
Positive - 1
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How does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism work
Positive - 2
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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
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D bbD bbDobby Dobby
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How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work
Negati eNegative
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How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work
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How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work
PositivePositive
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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
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JacquardJacquardJacquardJacquard
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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
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How does a jacquard workHow does a jacquard workj qj q
E li hEnglish typey
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How does a jacquard workHow does a jacquard workj qj q
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How does a jacquard workHow does a jacquard workj qj q
French type
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HarnessHarnessHarness Harness managementmanagementgg
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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
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Mechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquard
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Electronic jacquardElectronic jacquardElectronic jacquardElectronic jacquard
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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
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Shed geometryShed geometry
Equal tension Unequal tension Unequal tension
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Shed timingShed timingShed timingShed timing
90°
180°0° 1800
270°
Late shedding
270°Early shedding
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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