Topic 2 Shedding mechanisms 3rd tt BY-SHAILU

 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.

 •The way the warp sheet is separated depends  on the weave design of the fabric.

General requirements on shed 

  • Smallest possible: lowest possible additional warp tension •Clear enough: preventing faults

 •Proper shed welling:convenient for weft Proper shed dwelling: convenient for weft insertion Smooth movement of the heal frames

 • Smooth movement of the heal frames (mechanism dependent) : low noise, low parts damage and less fabric falt this parts damage, and less fabric faults, this also affects the loom speed

 Types of shedding mechanisms 

 • Four different types of shedding mechanisms are available for looms: –Crank shedding mechanism (simplest) –Tappet shedding mechanism  –Dobby shedding mechanism –Jacquard shedding mechanism(most complex) Jacquard shedding mechanism (most complex) 

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

Features of crank shedding 

 The simplest •No need for maintenance No need for maintenance •Does not put limit on loom speed

 •Controlling only 2 heald frames –plain weave (and weft backed weaves) only

•No shed dwelling, working width of loom limitedto200cm limited to 200 cm

Howdoestappetmechanismwork 

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

 Feature softappet shedding

•Simple principle, easy maintenance

 •Low installation cost

 •Low installation cost

 •Mechanism robust and reliable

 •No limit on loom speed Controlling28healdframesthusonly

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

 •Inconvenience for frequent pattern changes 

Featuresof dobby shedding

•Controlling large number (2-36) of heal 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 loom speed

 •Posing limit on loom speed •Occasional shedding errors (early versions)

Types of Jacquard

•Coarse pitch (English pitch) –200, 400, 600, 800 needles ,,, •Fine pitch (French pitch) Vii8801320dl – Vin : 880, 1320 needles –: 896, 1344, 2688 needles  

Features of jacquard shedding
•Capable of weaving all types of fabrics, from the simplest to the most complex pp 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 mechanism Complex mechanism