Monday, December 5, 2011
Sunday, December 4, 2011
Fabric PPI & EPI Calculation
The General formula to calculate Maximum EPI and PPI for a Given count of Warp and Weft
Now
in a plain weave in a repeat there are 2 threads and 2 intersections.
For 2/2 Twill in one repeat of 4 threads there will be 4 threads and 2
intersections.
Also as a rule please remember that 40s count yarn diameter is 1/165 of an inch.
To convert it to the yarn diameter of 50s warp we use the following formula
Which means for 50s PV Warp the diameter will be
Thus the Maximum Threads per inch for a plain weave will be 184 as this will be the diameter of the Yarn.
For 2/2 Twill be they will be ( From the Formula above)
Which means x will be equal to 122 threads per inch
Similarly for Satin weave one can find out the maximum ends and picks per inch
Please remember however that this is theoretical construct. Actual threads per inch are generally less than that.
To Calculate the Cotton Equivalent of 150 D, We use the formulaà count= 5315/denier, Which means it is equal to 35.43 or 35 count.
The Diameter for 35 count yarn will be ( Using the formula above) = 154.34 th of an inch
Then you can use the same equation to calculate the Maximum EPI and PPI
In these examples there is no allowance for bending, shrinkage or compression, the threads should be reduced or increased proportionately in case the fabric is subjected to bending, shrinkage or compression.
Fabric Parameters
Woven fabric parameters
There are four basic parameters that are essential for every woven fabric.
1. Ends per Inch and Picks per inch (EPI and PPI).
2. Yarn count
3. Crimp
4. Weave or Fabric Structure or Design
1. Ends per Inch or Picks per Inch
It is a measure of thread density. The normal method used to determine thread density is to use a pick glass.
2. Yarn count
EPI and PPI affects the compactness of the fabric. It is also known as thread count or cloth count. Thread counts range from as low as 20 threads per inch as used in tobacco cloth to as high as 350 threads per inch, found in type writer ribbon fabrics. Normally EPI and PPI of a fabric are described as EPI×PPI. Thus a fabric of 74×66 means 74 EPI×66 PPI.
Balanced constriction
A fabric is said to be well balanced if the number of warp yarns and weft yarns per inch are almost equal.
3.Crimp
Crimp refers to the amount of bending that is done by thread as it interlaces with the threads that are lying in the opposite direction of the fabric. Crimp is defined as the ratio of difference of length of yarn (Ly) taken from length of fabric (Lf) to the length of fabric (Lf).
Crimp = (Ly-Lf)/Lf
Often it is more convenient and preferable to use percentage values. Thus we can define crimp percentage as:
Crimp% = (Ly-Lf)/Lf
A crimp will normally give values ranging from 0.01 to 0.14 ie. (1% to 14%).
Crimp is related to many aspects of the fabric. It affects the cover, thickness, softness and hand of the fabric. When it is not balanced it also affects the wear behaviour and balance of the fabric, because the exposed portions tend to wear at a more rapid rate than the fabric. The crimp balance is affected by the tensions in the fabric during and after weaving. If the weft is kept at low tension while the tension in warp directions is high, then there will be considerable crimp in the weft and very little in the warp.
4. Weave
It refers to the arrangement of warp and weft in the fabric.
OTHER FABRIC PROPERTIES
1. Fabric weight (W)
It is the weight of the yarn per square meter in the woven fabric, which is the sum of the weight of the warp (W1) and weight of the weft (W2).
Weight of the warp is calculated as (per square m):
W1= [n1 x 100 (1+c1%)/100] x [N1/1000] g
Where
n1 = Ends per cm
N1 = Warp count in Tex
C1% = Warp crimp percentage.
Similarly weight of the weft is calculated as (per square m)
W2= [n2 x 100 (1+c2%)/100] x [N2/1000] g
Total weight per square meter = W1+W2
weight/piece = (W1+W2) × piece length × piece width in gram.
Example
A fabric 120m long, 1.3 m wide and having 30 ends per cm of 12 tex warp and 24 picks per cm of 15 tex weft. The warp and weft crimp percentages are five percent and eight percent respectively. We describe these fabric particulars as
30×24; 12 tex × 15 tex; 5%×8%
Warp weight per square m = [30 x 100 x (1+5)/100] x [12/1000] = 37.8 gms
Weft weight/square m = [24 x 100 x (1+8)/100] x [15/1000] = 38.8 gms
Piece weight
= total weight per m × piece length × piece width
= 76.68 × 120× 1.3
= 11962.08 gm or 11.96 kg.
2. Cover factor
(K) it is defined as the area covered by the yarn when compared with the total area covered by the fabric.
The warp cover factor can be found by using the formula.
k1= n1 x sqrt(N1)/10
Where
n1 = Ends/cm
N1 = Count of warp in tex
Similarly the weft cover factor can be found by the formula
k2 = n2 x sqrt(N2) /10
So the total cover factor is
K = K1 + K2
Thus with fabric (30×24; 12 tex×15 tex) the values are
k1= (30 x sqrt12)/10 = 10.39
k2 = (24 x sqrt15)/10 = 9.30
K = K1+K2 = 10.39+9.30 = 19.69
3. Fabric Thickness
For a wide range of fabric, this parameter is not important, but it becomes critical for fabrics that are to be used as belts and felts.
Twill fabric Structure
Introduction to Twill Weave
The twill order of interlacing causes diagonal lines to be formed on the cloth.
Comparison with plain weave
As comparison to plain weave, twill weave has greater weight, closer setting and better draping quality
Construction of simple twill- Step-by-Step
Step – 1 : We use a minimum of three threads (i.e. warp and weft) to construct a twill. We first try the twill 1/2 (1 up 2 down). We make a 3x3 square as:
Step – 2 : Now we start from the first end and first pick we make our first mark here (it represents the point of interaction).
Right Hand Twills and Left Hand Twills
The twills can be produced from Right to left (also called as left hand twill) as shown in fig.
The Twills can be
1. Warp faced Twill: In which quantity of warp is more on the face of the fabric eg 3/1 twill.
2. Weft faced twill: In which quantity of weft is more on the face of the fabric (e.g 1/3 twill)
3. Warp and Weft faced twill: In which warp and weft are in equal quantity on the face of the fabric (eg. 2/2 twill).
Angle of Twill
The angle formed in the cloth by a twill weave depends upon:
(a) The relative ratio of ends and picks per cm.
(b) The rate of advancement of interlacing
If the EPI and PPI are equal, a regular twill runs at an angle of 45º as shown:
In fact the angle of the twill with the horizontal can be calculated by the formula:
Tangent ( Angle) = ((Rate of Advancement of twill upwards x ends per cm)/(Rate of advancement of twill outwards x pics per cm))
Thus if
Step upward = 2
Step onward = 1
Ends/cm = 42
Picks/cm = 21
Then tan(angle of twill) = ((2 x 42)/(1x21)) thus the angle would be = 76º
As in the following twill
Factors influencing the prominence of twills
The relative prominence of twills is chiefly determined by:
(a) The character of weave
(b) The character of yarn
(c) The number of warp and weft threads per inch
(d) The direction of twill in relation to the direction of twist imparted to the yarn.
(a) The Character of Weave
A twill weaves will be relatively more pronounced if developed from longer than from shorter floats of yarn.
(b) Character of yarn
A more pronounced twill will result either from coarse spun of soft spun yarn than from fine spun or hand spun yarns; also from folded yarn than from single yarn.
(c) Number of Threads per inch
A twill will be relatively more or less pronounced in proportion to the number of warp threads and picks of weft per inch.
(d) Direction of twill with relation to the direction of twill in the yarn
If twills are produced in the reverse direction to that of the twist in the yarns, they will be more pronounced and if twills are produced in the same direction as that of the twist in the yarn, they will be less pronounced.
Denim Manufacture
Manufacturing of Denim
For manufacturing Denim and Grey Fabric, the process is same up to the level of weaving, but in case of Denim Fabric, dyeing is done at the stage of sizing where as for Grey Fabric it depends upon the finished product. The details of each process are given below:
1. Fabric Weaving
a. Grey Yarn on ConesNormally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:
o Warp yarn
o Weft yarn
Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.
b. Warping on Sectional/ Direct Warping
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine.
c. Sizing of yarn in Set/ Beam to Beam Position
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.
d. Drawing–in
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.
e. Beam Gaiting or Knotting on Loom
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.
f. Weaving
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:
o Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
o Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile
Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttle less Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms. These looms are distinguished by weft insertion method, which is briefly discussed hereunder.
Airjet Looms
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.
Finishing
a. Grey Fabric
The finally woven fabric or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out from weaving machines at certain intervals and checked on inspection machines for possibilities of any weaving fault. If such faults are seen anywhere in fabric during inspection, certain corrective steps are taken at weaving, warping, sizing, etc so that they can be minimised in subsequent product. This is a quality control exercise.
b. Denim Fabric
Denim Fabrics woven of 100% cotton would be very strong and durable.
Traditionally Blue Denim is warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in a solid colour and weft left un-dyed. The look and quality of the Denim Fabric shall improve after dyeing, the process of which differs from plant to plant. Normally the process of dyeing dictates the technology of Denim manufacturing.
The dyeing for Denim Fabric happens at the sizing stage. Generally there are two most popular methods of dyeing Denim Fabric. They are:
o Rope Dyeing
o Sheet Dyeing
A company can adopt any of the methods. In countries like India Sheet Dyeing Method is commonly used for manufacture of its Denim Fabrics, which has following advantages over Rope Dyeing Method:
o The technology is less capital intensive.
o The technology is a proven one.
o The cost of production is lower.
o The process time is lower.
o The Sheet Dyeing machines are very easy to operate.
For manufacturing Denim and Grey Fabric, the process is same up to the level of weaving, but in case of Denim Fabric, dyeing is done at the stage of sizing where as for Grey Fabric it depends upon the finished product. The details of each process are given below:
1. Fabric Weaving
a. Grey Yarn on ConesNormally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:
o Warp yarn
o Weft yarn
Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.
b. Warping on Sectional/ Direct Warping
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine.
c. Sizing of yarn in Set/ Beam to Beam Position
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.
d. Drawing–in
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.
e. Beam Gaiting or Knotting on Loom
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.
f. Weaving
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:
o Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
o Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile
Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttle less Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms. These looms are distinguished by weft insertion method, which is briefly discussed hereunder.
Airjet Looms
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.
Finishing
a. Grey Fabric
The finally woven fabric or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out from weaving machines at certain intervals and checked on inspection machines for possibilities of any weaving fault. If such faults are seen anywhere in fabric during inspection, certain corrective steps are taken at weaving, warping, sizing, etc so that they can be minimised in subsequent product. This is a quality control exercise.
b. Denim Fabric
Denim Fabrics woven of 100% cotton would be very strong and durable.
Traditionally Blue Denim is warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in a solid colour and weft left un-dyed. The look and quality of the Denim Fabric shall improve after dyeing, the process of which differs from plant to plant. Normally the process of dyeing dictates the technology of Denim manufacturing.
The dyeing for Denim Fabric happens at the sizing stage. Generally there are two most popular methods of dyeing Denim Fabric. They are:
o Rope Dyeing
o Sheet Dyeing
A company can adopt any of the methods. In countries like India Sheet Dyeing Method is commonly used for manufacture of its Denim Fabrics, which has following advantages over Rope Dyeing Method:
o The technology is less capital intensive.
o The technology is a proven one.
o The cost of production is lower.
o The process time is lower.
o The Sheet Dyeing machines are very easy to operate.
The only defect in Sheet dyeing is that their is a problem of center to selvedge shade variation.
c. Sheet Dyeing Process
This process eliminates a few intermediate processes of the rope dyeing. The yarn sheet is washed with chemicals such as caustic and washing soda and after squeezing the excess water; the yarn sheet is allowed to pass through Dyeing Troughs one time for oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed again with fresh water for two-three times and finalIy squeezed before allowing it to pass through six drying cylinders. The dyed yarn enters the starching device and sizing is done. After sizing, the sized warp beam goes for weaving. After weaving, the woven Denim Fabrics goes for various finishing processes consisting of brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing should eliminate impurities and help to even the surface of the fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking regulates its dimensional stability.
Even today Denim Fabric without Indigo Dyeing is not called authentic Denim. Initially when Denim Fabric entered the fashion market, Denim manufacturers were using Natural Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers still prefer the latter and attract premium after branding them “Natural Dye Used”.
d. Making-Up
Weaving of fabrics on such multi sizes is not economical, hence a standard width fabrics is then sent to making up. Fabrics are cut into the desired width as per size required on this machine. Denim Fabric and Grey Fabric are thoroughly checked for various types of defects such as:
o Weaving Defects
· Uneven Dyeing
o Bleaching and Dyeing Defect
o Oil Stain
o Patches
Here the final product is categorised quality-wise. The products then found okay are segregated and sent to packaging department whereas defective ones are sent for correction. After inspection, the sets are wrapped with polythene covers and sent for despatch as per buyer’s specifications.
Despatch
Rolls and sets so formed and packed as per buyers’ requirements are then sent for final despatches.
c. Sheet Dyeing Process
This process eliminates a few intermediate processes of the rope dyeing. The yarn sheet is washed with chemicals such as caustic and washing soda and after squeezing the excess water; the yarn sheet is allowed to pass through Dyeing Troughs one time for oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed again with fresh water for two-three times and finalIy squeezed before allowing it to pass through six drying cylinders. The dyed yarn enters the starching device and sizing is done. After sizing, the sized warp beam goes for weaving. After weaving, the woven Denim Fabrics goes for various finishing processes consisting of brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing should eliminate impurities and help to even the surface of the fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking regulates its dimensional stability.
Even today Denim Fabric without Indigo Dyeing is not called authentic Denim. Initially when Denim Fabric entered the fashion market, Denim manufacturers were using Natural Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers still prefer the latter and attract premium after branding them “Natural Dye Used”.
d. Making-Up
Weaving of fabrics on such multi sizes is not economical, hence a standard width fabrics is then sent to making up. Fabrics are cut into the desired width as per size required on this machine. Denim Fabric and Grey Fabric are thoroughly checked for various types of defects such as:
o Weaving Defects
· Uneven Dyeing
o Bleaching and Dyeing Defect
o Oil Stain
o Patches
Here the final product is categorised quality-wise. The products then found okay are segregated and sent to packaging department whereas defective ones are sent for correction. After inspection, the sets are wrapped with polythene covers and sent for despatch as per buyer’s specifications.
Despatch
Rolls and sets so formed and packed as per buyers’ requirements are then sent for final despatches.
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