This document discusses different types of shedding mechanisms used in looms: crank, tappet, dobby, and jacquard. It explains how each works and their features. Crank is the simplest but can only produce plain weaves. Tappet controls 2-8 heald frames for simple weaves. Dobby controls more frames for medium complexity weaves. Jacquard is the most complex but can produce all fabric types by controlling thousands of heald frames individually. The timing of shed opening, early vs late, also affects weaving properties.

1. Topic 2Topic 2
Shedding Mechanisms vsShedding Mechanisms vs
F b iF b iFabricsFabrics

2. 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 dependsy p p p
on the weave design of the fabric.

3. 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
insertion
Smooth 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

4. 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

5. How does crank mechanism workHow does crank mechanism workHow does crank mechanism workHow does crank mechanism work

6. 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

7. 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

8. How does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism work
Positive - 1

9. How does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism workHow does tappet mechanism work
Positive - 2

10. 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

11. D bbD bbDobbyDobby

12. How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work
Negati eNegative

13. How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work

14. How does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism workHow does dobby mechanism work
PositivePositive

15. 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, g
range 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

16. JacquardJacquardJacquardJacquard

17. 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

18. How does a jacquard workHow does a jacquard workj qj q
E li hEnglish
typey

19. How does a jacquard workHow does a jacquard workj qj q

20. How does a jacquard workHow does a jacquard workj qj q
French
type

21. HarnessHarnessHarnessHarness
managementmanagementgg

22. 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 complexp p
fabrics
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

23. Mechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquardMechanical and electronic jacquard

24. Electronic jacquardElectronic jacquardElectronic jacquardElectronic jacquard

25. 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 ends
Collective
2-8 ends
Collective
2-36 ends
Collective
2-1000s
Individual
Fabric types Plain w
fabrics
Simple w
fabrics
Fancy
fabrics
Complex
fabrics

26. Shed geometryShed geometry
Equal tension Unequal tension Unequal tension

27. Shed timingShed timingShed timingShed timing
90°
180°0° 1800
270°
Late shedding
270°
Early shedding

28. Effect shed timingEffect shed timingEffect shed timingEffect 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