Topic 2 Shedding Mechanisms[1]

Topic 2 Shedding Mechanisms vs F bi Fabrics

What 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. p sheet is separated p depends p • The wayy the warp on the weave design of the fabric.

General requirements on shed • S Smallest ll t possible ibl : lowest l t possible ibl additional warp tension • Clear enough : preventing faults • Proper shed dwelling : convenient for weft insertion • Smooth movement of the heald frames (mechanism dependent) : low noise, low parts damage, damage and less fabric fa faults, lts this also affects the loom speed

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

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

How does crank mechanism work

Features of crank shedding • • • •

The simplest No need for maintenance Does not put limit on loom speed Controlling only 2 heald frames – plain ea e (a (and d weft e t bac backed ed weaves) ea es) o only y weave • No shed dwelling, working width of loom limited to 200 cm

How does tappet mechanism work N Negative ti

Tappet is also known as cams cams. Basic principle: p p Cam followers follow the cam p profiles

How does tappet mechanism work Positive - 1

How does tappet mechanism work Positive - 2

Features of tappet shedding • • • • •

Simple principle, easy maintenance Low installation cost Mechanism robust and reliable No limit on loom speed Controlling 2 2-8 8 heald frames frames, thus only suitable for fabric with simple weaves • Inconvenience for frequent pattern changes

D bb Dobby

How does dobby mechanism work Negati e Negative

How does dobby mechanism work

How does dobby mechanism work

Positive

Features of dobby shedding • Controlling large number (2-36) of heald g wide frames,, therefore suitable for weaving range of fabrics – Plain and simple weaves – Weaves with medium complexity

• Convenient for pattern change • Posing limit on loom speed • Occasional shedding errors (early versions) 5 October. Next time – jacquard mechanism

Jacquard

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

• Fine pitch (French pitch) – Vincenzi: Vi i 880, 880 1320 needles dl – Verdol: 896, 1344, 2688 needles

How does a jjacquard q work English E li h y type

How does a jjacquard q work

How does a jjacquard q work French type

Harness management g

Features of jacquard shedding • Capable of weaving all types of fabrics, p to the most complex p from the simplest fabrics – Mostly used for weaving complex fabrics – Not economical for weaving simple fabrics

• Posing speed limit on loom • Complex mechanism

Mechanical and electronic jacquard

Electronic jacquard

Comparison 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 2-8 ends 2-36 ends 2-1000s Collective Collective Collective Individual

Fabric types

Plain w fabrics

Simple w Fancy fabrics fabrics

Complex fabrics

Shed geometry

Equal tension

Unequal tension

Unequal tension

Shed timing 90°

0° 0

180° 180

Late shedding

Early shedding

270°

Effect shed timing •

Early shedding – – – – – –

larger shed angle at beatup helpful in weaving fabrics with high weft density clear shed better fabric hand (fullness) more likely to produce end breaks used for plain fabrics

11 October 2010

•

Late shedding – small shed angle at beatup – small resistance to beatup – lower end breakage – clear weave pattern on fabric – less likely to achieve higher weft density – used for twill and satin fabrics