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Dhaka University of Engineering and Technology(DUET), Gazipur
Department of Textile Engineering
Prepared by
MD MAHBUBAY RABBANI MIM
DHAKA UNIVERSITY OF ENGINEERING AND
TECHNOLOGY(DUET),GAZIPUR
Contact number:-01767281858
Presentation about
Shed Geometry and Shedding
Definition
• On a weaving loom warp yarns are divided into two half for forming a
shed. This division makes a geometrical structure. This geometrical
structure is called shed geometry.
Significance of shed Geometry
Shed geometry plays an important role for controlling the warp yarns:-
I. Tension
II. Elongation
III. Friction between them
Resultantly it helps in controlling :-
●The pick penetration in the warp density of the fabric
●Warp and filling yarn breakage
●Morever it helps to avoid the fabric fault control.
 Different Possible Shed Geometry
Impact of shed angle in a loom
• Shed angle↓elongation↓ tension ↓friction breakage↓ production↑
Elements of shed geometry
• Frame depth
• Frame height
• Frame rest height
• Back rest height and depth
• Front shed
• Back shed
• Top shed line
• Bottom shed line
• Virtual shed dividing line
• Dropper box and droppers movements
Shedding Parameters
Details about components of shed
geometry
 Frame Depth:-
• The distance between the maximum height position and lowest height
position in the frames is called frame depth or lever height.
Example:- amplitude of a heddles frame movement.
 Frame height
• It is the distance between two reference points.one reference point is
on loom stationary structure and other one is on the heddle frame.
Back rest or Deflecting roller
• It is the most rear or back roller in the loom from where warp yarns
are forming shed.It is used as most frequent element in shed
geometry. Because it controls the warp tension and for this
controlling tension pick density is produced in a fabric.
Virtual shed dividing line
• It is the line which divides the frame shed equally and parallel to the
machine horizontal.
Clear shed and Unclear shed
• For clear shed the shed heights are all shed is
not equal and the shed angle also different with
each other. That means any kinds of weft
insertion is possible especially jet.
• For unclear shed the shed heights are same and
the shed angles are also equal
Classification of shed geometry
Shed Geometry
Symmetric shed
Symmetrical
shed
Asymmetrical
shed
Slightly asymmetric
shed
Strongly asymmetric
shed
Reverse asymmetric
shed
Shed vibration Shed clearance Shed staggering
Symmetric shed
In that shed
• Top shed and bottom shed are identical.so advantageous for picking.
• The whip roller height is almost zero.
• Whip roller and cloth support roller are at same height with respect
to each other.
Symmetric shed
Symmetric shed
Effects of symmetric shed
As top and bottom shed are identical so the warp tension in both sheds
is same and therefore adjustment of warp thread is very easy.
It can be noted that there has no rocking action in the adjustment.
Otherwise the shed looks like flatter.
Application:-
For very light fabric such as voil, fabric with lower cover factor etc.
Yarns with little or no elongation.
Very weak yarns
Handkerchief fabrics.
 Asymmetrical shed
• It is formed when back rest and cloth roller are not at same height.
That means they are up or down with respect to each other. In that
shed top shed and bottom shed are not identical.
Effect of asymmetrical shed
i. When the back rest is raised then hypothetical line of minimum
tension will move up and for this reason the strain of bottom
shed is increased.
ii. Cloth cover is improved.
iii. Vertical axis and horizontal axis of the lift of the heald shaft is
asymmetrical.
Slightly asymmetrical shed
• Here cloth support is at normal height but the back rest is slightly
above to the normal height.
Effects of slightly asymmetrical shed
i. Bottom shed is get more tensioned as upper shed is slacker.
ii. A slightly rocking effect is occurred.
iii. The fabric takes more picks.
Slightly asymmetrical shed
Application
• For all light weight to medium weight fabrics.
Strongly asymmetrical shed
• Here cloth support is completely raised above to the normal and back
rest is raised to a vey high position.
Effect of strongly asymmetrical shed
• There is an extremely height adjustment occurred between cloth
supporting plate and whip roller and for this reason a strong rocking
action is created in bottom shed and due to this rocking action a very
high weft density can be attained.
• It can be noted that if the upper shed is extremely slack , more warp
breakage is occurred.
Strongly asymmetrical shed
Application
• A heavy fabric with high warp density like as denim , sail cloth ,
awining fabrics etc.
Reverse asymmetric shed
• In this shed the cloth supporting plate is at normal height and the
back rest position is below to the normal.
Effect of reverse asymmetric shed
1.Due to adjustment the upper shed is more tensioned.
2. Jacquard harness and Rubber returning motion is better treated.
Reverse asymmetric shed
Application
Jacquard fabrics , satin weaves etc.
Types of back shed
3 kinds :-
i. Short back shed
ii. Middle back shed
iii. Long back shed.
Short back shed
• In this shed the whip roller is adjusted so that it has a minimum
depth.
• Here the tesion is act on the short range and for this reason warp
tension is more.
• Again due to short range the warp separation is better obtained here.
 Effects of short back shed
• High warp tension.
• Better separation of warp is obtained.
Application
Fabric demanding high warp tension.
Hairy warp that separate badly.
Heavy fabrics of all kinds of yarns.
Middle Back Shed
• In this case the roller is adjusted so that it has a medium depth,
• In this shed the warp tension is better and warps are sag less.
 Effects of Middle Back Shed
• As the tension is better so warp yarns are sag less.
• Warps are better treated due to better tension.
Application
• Light to medium weight fabrics
• Jacquard fabrics.
• Yarn with little elongation and little breaking strength.
• Fabrics woven with more than 10 shafts.
Long Back Shed
• Whip roller is adjusted so that it has maximum depth . In this shed
the warps are sag less as the tension is work out in long range.
• Due to long range working tension less stress is created on the back
shed.
• For less tension the warps are less extend.
 Effects of Long Back Shed
• Warps are sag less due to long range tension.
• Warps are even out better.
• Less degree of tension is occurred due to less tension.
Application
• silk weaving
• For extremely warp yarns.
• Man made fiber weaving.
 Effects of Back Rest
• If the back rest is raise (25-30) mm above to the normal
warp crimp ↓ weft crimp ↑
• Lowering the back rest above to the normal
warp crimp ↑ weft crimp ↓
• There is no effect of back rest changing position on breaking strength.
• But effect of changing position of back rest is existed on fabric
elongation at break.
 Shed and Shedding
 Shed
Dividation of warp threads into two parts for insertion of weft threads
is called shed.
 Shedding
The mechanism of shed is called shedding. It is the first primary motion
of weaving.
 Types of shed
I. Bottom close shed
II. Centre close shed
III. Semi-open shed
IV. Open shed
TYPES OF SHED
After inserting a pick, both the lines meet at the center
between the highest and lowest line of a divided warp
This kind of shed is known as a stationary bottom
with a rising and falling top
A stationary bottom line is refined, but threads from the top
line either pass to the bottom at one movement or carried out
to the top. The remaining threads move down.
In this types of shed, the warp threads from two
stationary lines, one at the top and another at the
bottom. After inserting a pick change are made by
carrying threads from one fixed line to other.
Center close shed
Bottom close shed
Semi open shed Open shed
 Bottom close shed
• This type of shedding is produced by giving motion only to threads
that are to form the upper line. Under this condition, the warp is level
on the bottom line. Hence in order to form a top shed, it is necessary
to move some threads through a space equal to twice the depth of a
shed, once up and down, before a fresh selection is made. A shed of
this kind is known as stationary bottom with a rising and falling top.
A → Bottom line of warp
B → Rising and falling line
C → An arrow showing the space passed through
Center close shed
• This type of shed is produced by imparting an upward movement to
those threads which are to form the top line and the downward
movement to the threads which are to form the bottom line. Then
after inserting a pick, both the lines meet at the center between the
highest and lowest lines of a divided warp.
A → Closed warp line
B, C→ Upper and lower lines of a divided warp
respectively
D → Arrow showing the half distance of a shed in an
upward direction
E → Arrow showing the half distance of a shed in a
downward direction
Semi-open shed
• In this shed, the stationary bottom is retained but threads for the top line
either passes to bottom at one movement and again carried to the top mid
way and again carried to top. In this shed close and open shed occurred
simultaneously. In it the stationary bottom line is retained, but threads for
the top line either pass to the bottom at one movement, or are arrested
midway and again carried to the top. Such a shed can be formed as
expeditiously as an open shed, for the upward movement begins and ends
with the downward through movement, and the arrested downward
movement is converted into an upward movement immediately the falling
threads are in the same plane as the rising ones. They all reach the top
together but the strain upon them is not equally distributed.
A → Stationary bottom line
B → Top point
C → The point where downward movement ceases in
threads
D, E → Showing the movement of through healds
F → Arrow showing the threads which are to lift for the
next pick
Open shed
• In open shed, the warp threads form two stationary lines, the top line
and the bottom line and changes are made by carrying the threads
from one fixed line to the other without any interval.
A, B → Stationary warp line
C, D → Arrows which show the movement of rising and
falling warp to equal the distance between A & B
Uses of various shed
• Bottom shed - used in hand loom and single lift jacquard.
• Centre close shed- for lino fabrics, still used in some jacquards.
• Open shed- ideal type of shed so used in most purposes.
• Semi-open shed- used in double lift jacquards.
Early shedding and late shedding
• If the crank shaft comes to 0 or 360 degree and heald
shafts are the same level then it is known as normal
shedding.
• If the crank shaft comes to 5 degree after the
shedding and heald shafts are at the same level then
it is known as late shedding.
• If the crank shaft comes to 355 degree before top
centre then it is known as early shedding. In early
shedding the insertion of pick is done after opening
the shed completely.
Advantage of Early Shedding
• Getting the closer pick spacing and redistribute of warps is more
even.
• Beat up with larger shed angle.
• Form clear shed.
• Better fabric hand.
• High warp density.
Effect of raising Back Rest and Early
Shedding
• Obtain closer pick spacing.
• Improve warp cover and better fabric appearance.
• Reed marks remove and so better fabric appearance.
Geometrical View of various shed
 Some Questions with their answers
Question:- Why short back shed is used in hairy yarn used in
weaving?
• we know hairy yarn tends to entangled with each other and causes
warp breakage during weaving. Due to entangle tendency it very
difficult to warp separation in processing. If we use short back shed,
then the tension act on the short range and due to short range
working tension we get the better warp separation in the loom and
for this reason the warps can’t entangled and warp breakage
tendency is decreasing. That’s why short back shed is used for hairy
yarn fabrication.
Question:- Why long back shed is used in silk fibre weaving ?
• We know silk yarns is more lustrous and because of lustrous effect
they are more used. If any tension is act on the yarn the surface of
the fibre is ununiformed and for this reason the luster effect will
decrease. If we used long back shed then the tension less occurred in
the shed and due to less tension the luster effect is remain same and
which is more desirable for the weaver and also consumer. that’s why
we used long back shed in silk fibre weaving.
Question:- Why back rest is away from the healds in silk weaving
as compared to cotton weaving ?
If the back rest is not away from the healds the tension will more
occurred in weaving and due to tension increasing the yarn elongation
will more occurred. For this reason the luster effect will decrease.
That’s why the back rest is away from the healds in silk weaving as
compared to cotton weaving.
The End

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Shed geometry by Mim

  • 1. Dhaka University of Engineering and Technology(DUET), Gazipur Department of Textile Engineering
  • 2. Prepared by MD MAHBUBAY RABBANI MIM DHAKA UNIVERSITY OF ENGINEERING AND TECHNOLOGY(DUET),GAZIPUR Contact number:-01767281858 Presentation about Shed Geometry and Shedding
  • 3. Definition • On a weaving loom warp yarns are divided into two half for forming a shed. This division makes a geometrical structure. This geometrical structure is called shed geometry.
  • 4. Significance of shed Geometry Shed geometry plays an important role for controlling the warp yarns:- I. Tension II. Elongation III. Friction between them Resultantly it helps in controlling :- ●The pick penetration in the warp density of the fabric ●Warp and filling yarn breakage ●Morever it helps to avoid the fabric fault control.
  • 5.  Different Possible Shed Geometry
  • 6. Impact of shed angle in a loom • Shed angle↓elongation↓ tension ↓friction breakage↓ production↑
  • 7. Elements of shed geometry • Frame depth • Frame height • Frame rest height • Back rest height and depth • Front shed • Back shed • Top shed line • Bottom shed line • Virtual shed dividing line • Dropper box and droppers movements
  • 9. Details about components of shed geometry  Frame Depth:- • The distance between the maximum height position and lowest height position in the frames is called frame depth or lever height. Example:- amplitude of a heddles frame movement.
  • 10.  Frame height • It is the distance between two reference points.one reference point is on loom stationary structure and other one is on the heddle frame.
  • 11. Back rest or Deflecting roller • It is the most rear or back roller in the loom from where warp yarns are forming shed.It is used as most frequent element in shed geometry. Because it controls the warp tension and for this controlling tension pick density is produced in a fabric.
  • 12. Virtual shed dividing line • It is the line which divides the frame shed equally and parallel to the machine horizontal.
  • 13. Clear shed and Unclear shed • For clear shed the shed heights are all shed is not equal and the shed angle also different with each other. That means any kinds of weft insertion is possible especially jet. • For unclear shed the shed heights are same and the shed angles are also equal
  • 14. Classification of shed geometry Shed Geometry Symmetric shed Symmetrical shed Asymmetrical shed Slightly asymmetric shed Strongly asymmetric shed Reverse asymmetric shed Shed vibration Shed clearance Shed staggering
  • 15. Symmetric shed In that shed • Top shed and bottom shed are identical.so advantageous for picking. • The whip roller height is almost zero. • Whip roller and cloth support roller are at same height with respect to each other.
  • 17. Symmetric shed Effects of symmetric shed As top and bottom shed are identical so the warp tension in both sheds is same and therefore adjustment of warp thread is very easy. It can be noted that there has no rocking action in the adjustment. Otherwise the shed looks like flatter. Application:- For very light fabric such as voil, fabric with lower cover factor etc. Yarns with little or no elongation. Very weak yarns Handkerchief fabrics.
  • 18.  Asymmetrical shed • It is formed when back rest and cloth roller are not at same height. That means they are up or down with respect to each other. In that shed top shed and bottom shed are not identical. Effect of asymmetrical shed i. When the back rest is raised then hypothetical line of minimum tension will move up and for this reason the strain of bottom shed is increased. ii. Cloth cover is improved. iii. Vertical axis and horizontal axis of the lift of the heald shaft is asymmetrical.
  • 19. Slightly asymmetrical shed • Here cloth support is at normal height but the back rest is slightly above to the normal height. Effects of slightly asymmetrical shed i. Bottom shed is get more tensioned as upper shed is slacker. ii. A slightly rocking effect is occurred. iii. The fabric takes more picks.
  • 20. Slightly asymmetrical shed Application • For all light weight to medium weight fabrics.
  • 21. Strongly asymmetrical shed • Here cloth support is completely raised above to the normal and back rest is raised to a vey high position. Effect of strongly asymmetrical shed • There is an extremely height adjustment occurred between cloth supporting plate and whip roller and for this reason a strong rocking action is created in bottom shed and due to this rocking action a very high weft density can be attained. • It can be noted that if the upper shed is extremely slack , more warp breakage is occurred.
  • 22. Strongly asymmetrical shed Application • A heavy fabric with high warp density like as denim , sail cloth , awining fabrics etc.
  • 23. Reverse asymmetric shed • In this shed the cloth supporting plate is at normal height and the back rest position is below to the normal. Effect of reverse asymmetric shed 1.Due to adjustment the upper shed is more tensioned. 2. Jacquard harness and Rubber returning motion is better treated.
  • 25. Types of back shed 3 kinds :- i. Short back shed ii. Middle back shed iii. Long back shed.
  • 26. Short back shed • In this shed the whip roller is adjusted so that it has a minimum depth. • Here the tesion is act on the short range and for this reason warp tension is more. • Again due to short range the warp separation is better obtained here.
  • 27.  Effects of short back shed • High warp tension. • Better separation of warp is obtained. Application Fabric demanding high warp tension. Hairy warp that separate badly. Heavy fabrics of all kinds of yarns.
  • 28. Middle Back Shed • In this case the roller is adjusted so that it has a medium depth, • In this shed the warp tension is better and warps are sag less.
  • 29.  Effects of Middle Back Shed • As the tension is better so warp yarns are sag less. • Warps are better treated due to better tension. Application • Light to medium weight fabrics • Jacquard fabrics. • Yarn with little elongation and little breaking strength. • Fabrics woven with more than 10 shafts.
  • 30. Long Back Shed • Whip roller is adjusted so that it has maximum depth . In this shed the warps are sag less as the tension is work out in long range. • Due to long range working tension less stress is created on the back shed. • For less tension the warps are less extend.
  • 31.  Effects of Long Back Shed • Warps are sag less due to long range tension. • Warps are even out better. • Less degree of tension is occurred due to less tension. Application • silk weaving • For extremely warp yarns. • Man made fiber weaving.
  • 32.  Effects of Back Rest • If the back rest is raise (25-30) mm above to the normal warp crimp ↓ weft crimp ↑ • Lowering the back rest above to the normal warp crimp ↑ weft crimp ↓ • There is no effect of back rest changing position on breaking strength. • But effect of changing position of back rest is existed on fabric elongation at break.
  • 33.  Shed and Shedding  Shed Dividation of warp threads into two parts for insertion of weft threads is called shed.  Shedding The mechanism of shed is called shedding. It is the first primary motion of weaving.
  • 34.  Types of shed I. Bottom close shed II. Centre close shed III. Semi-open shed IV. Open shed
  • 35. TYPES OF SHED After inserting a pick, both the lines meet at the center between the highest and lowest line of a divided warp This kind of shed is known as a stationary bottom with a rising and falling top A stationary bottom line is refined, but threads from the top line either pass to the bottom at one movement or carried out to the top. The remaining threads move down. In this types of shed, the warp threads from two stationary lines, one at the top and another at the bottom. After inserting a pick change are made by carrying threads from one fixed line to other. Center close shed Bottom close shed Semi open shed Open shed
  • 36.  Bottom close shed • This type of shedding is produced by giving motion only to threads that are to form the upper line. Under this condition, the warp is level on the bottom line. Hence in order to form a top shed, it is necessary to move some threads through a space equal to twice the depth of a shed, once up and down, before a fresh selection is made. A shed of this kind is known as stationary bottom with a rising and falling top. A → Bottom line of warp B → Rising and falling line C → An arrow showing the space passed through
  • 37. Center close shed • This type of shed is produced by imparting an upward movement to those threads which are to form the top line and the downward movement to the threads which are to form the bottom line. Then after inserting a pick, both the lines meet at the center between the highest and lowest lines of a divided warp. A → Closed warp line B, C→ Upper and lower lines of a divided warp respectively D → Arrow showing the half distance of a shed in an upward direction E → Arrow showing the half distance of a shed in a downward direction
  • 38. Semi-open shed • In this shed, the stationary bottom is retained but threads for the top line either passes to bottom at one movement and again carried to the top mid way and again carried to top. In this shed close and open shed occurred simultaneously. In it the stationary bottom line is retained, but threads for the top line either pass to the bottom at one movement, or are arrested midway and again carried to the top. Such a shed can be formed as expeditiously as an open shed, for the upward movement begins and ends with the downward through movement, and the arrested downward movement is converted into an upward movement immediately the falling threads are in the same plane as the rising ones. They all reach the top together but the strain upon them is not equally distributed. A → Stationary bottom line B → Top point C → The point where downward movement ceases in threads D, E → Showing the movement of through healds F → Arrow showing the threads which are to lift for the next pick
  • 39. Open shed • In open shed, the warp threads form two stationary lines, the top line and the bottom line and changes are made by carrying the threads from one fixed line to the other without any interval. A, B → Stationary warp line C, D → Arrows which show the movement of rising and falling warp to equal the distance between A & B
  • 40. Uses of various shed • Bottom shed - used in hand loom and single lift jacquard. • Centre close shed- for lino fabrics, still used in some jacquards. • Open shed- ideal type of shed so used in most purposes. • Semi-open shed- used in double lift jacquards.
  • 41. Early shedding and late shedding • If the crank shaft comes to 0 or 360 degree and heald shafts are the same level then it is known as normal shedding. • If the crank shaft comes to 5 degree after the shedding and heald shafts are at the same level then it is known as late shedding. • If the crank shaft comes to 355 degree before top centre then it is known as early shedding. In early shedding the insertion of pick is done after opening the shed completely.
  • 42. Advantage of Early Shedding • Getting the closer pick spacing and redistribute of warps is more even. • Beat up with larger shed angle. • Form clear shed. • Better fabric hand. • High warp density.
  • 43. Effect of raising Back Rest and Early Shedding • Obtain closer pick spacing. • Improve warp cover and better fabric appearance. • Reed marks remove and so better fabric appearance.
  • 44. Geometrical View of various shed
  • 45.  Some Questions with their answers Question:- Why short back shed is used in hairy yarn used in weaving? • we know hairy yarn tends to entangled with each other and causes warp breakage during weaving. Due to entangle tendency it very difficult to warp separation in processing. If we use short back shed, then the tension act on the short range and due to short range working tension we get the better warp separation in the loom and for this reason the warps can’t entangled and warp breakage tendency is decreasing. That’s why short back shed is used for hairy yarn fabrication.
  • 46. Question:- Why long back shed is used in silk fibre weaving ? • We know silk yarns is more lustrous and because of lustrous effect they are more used. If any tension is act on the yarn the surface of the fibre is ununiformed and for this reason the luster effect will decrease. If we used long back shed then the tension less occurred in the shed and due to less tension the luster effect is remain same and which is more desirable for the weaver and also consumer. that’s why we used long back shed in silk fibre weaving.
  • 47. Question:- Why back rest is away from the healds in silk weaving as compared to cotton weaving ? If the back rest is not away from the healds the tension will more occurred in weaving and due to tension increasing the yarn elongation will more occurred. For this reason the luster effect will decrease. That’s why the back rest is away from the healds in silk weaving as compared to cotton weaving.