Tuesday, 20 October 2009

Animation- Weaving Principles and Fabric Structure

1. Relationship between Draft, Peg Plan, Denting Plan and Design- Click Here

2. Weave and Color Combination - Click Here

3. Principle of Double Cloth Formation- Click Here

4. Principle of Tubular Fabric - Click Here

5. Double Cloth based on Exchange Principle- Click Here

6. Principle of Terry Towel Weaving- Click Here

7. Principle of Weaving Leno Fabric- Click Here

8. Principle of Weaving  Velvets and Corduroys- Click Here

9. Principle of Jacquard- Click Here

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A Few Notes About Fiber Chemistry

1. All fibers are formed from polymers, are not the only products containing polymers

2. Polymer means many units. Each individual molecule is known as monomer and the process of joining all the monomers together to form long chain molecules (polymers) is known as polymerisation.

3. The degree of polymerisation is the number of monomers units in the polymer. These may be of same type ( a homopolymer ) or two different randomly arranged monomers ( a copolymer)

4. There are two types of polymerisation: addition polymerisation, where all the atoms present in the monomers are also present in the polymer and condensation polymerisation where some small molecules are eliminated during polymerisation.

5. Polypropylene and acrylic polymers are produced by addition polymerisation.

6. Polyester, polyamide, wool, silk, cotton, flax, jute and viscose polymers are produced by condensation polymerisation.

7 There are three types of intermolecular forces. In decending order of strength: they are hydrogen bonds, polar bonds and Van der Waal's forces.

8. The properties of polymers for good fiber formation are: high degree of polymerisation, good intermolecular forces, linear and regular arrangement of monomers, high orientation of molecules and an inflexible repeat unit.

9. Crystalline regions are highly ordered areas within the fibers. They give the fiber its tensile and rigidity properties.

10. Amorphous regions are where the molecules are not closely packed within the fibers. They give the fiber its flexibility, extensibility and elasticity.

11. In natural fibers, crystalline regions develop as the fiber grows. In MMF, the ratio of crystalline to amorphous regions can be altered by drawing and heat setting.

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Sunday, 18 October 2009

Cloth setting and Fabric Geometry Theories

1. Fractional Cover is defined as d/p where d is the diameter of the yarn and p is the thread spacing.

2. There are various theories for calculation of yarn diameter. According to Law yarn diameter d is equal to 1/ sqrt (Fn) where F is 500 for worsted yarn, 800 for cotton yarns, 530 for woolen n being worsted and cotton and Yorkshire count respectively. According to Ashenhurst yarn diameter d = 1/(F sqrt(N)), where F is .95, .9,.84 for cotton, worsted and woolen yarns respectively and n= yds/lb. According to Pierce, yarn diameter is 1/(28 sqrt(N) where N is the English count.

3. Ashenhurst Diameter  intersection theory says that when the count of warp and weft are the same, it is assumed that an intersection takes up as much space as a thread. Then Threads/inch (T) can be determined as equal to D x W/ (W+I) where D is the diameter per inch of yarn, W is the threads in one repeat of weave and I are the intersection in one repeat of weave. For plain weave W =2, I=2 for 2/1 twill weave, W=3 and I = 2.

4. Curvature theory says that T = D x W/ ( W +.732 I), the notations being the same as in point 3.

5. Armitage Maximum Setting Theory says that cloths which are similarly built are equally firm. For regular twill weaves Threads per inch (T) = Sqrt (6 x C(F+4)) where C are the counts of worsted yarn and F is the average float of weave. For other weaves, Armitage gave the following “setting ratio” instead of (F +4). For plain weave it is 4.75, for 2/2 hopsack it is 6.25, for 4 end satin it is 6.5 for 5 end, 6 end and 8 end satin it is 7.5, 7.75 and 9.0 respectively.

6. Laws Maximum Setting suggests that T = ((D x F)/ (F+1) )+ various percentages where F is the average float and D is the diameter per inch. For common weaves like plain weave T = ( D X 1)/(F+I), for twill weave T= ((DF)/(F+1))+ 5% for each float exceeding two, for satin weave T = ((DF)/(F+1))+5.5% for each float, for hopsack weaves T= ((DxF)/(F+1))+ 4.5% for 2 floats and 9.5% for floats exceeding two.

7. Brierjey’s Maximum Setting suggests that square settings vary according to the formula T= sqrt (KC x (F)^m) where C is the average count of yarn, F is the average float, K is a constant varying according to kind of yarn and numbering system: it is 134 for worsted yarn, 200 for cotton yarn and 60 for york shire yarn. m is a constant varying according to the type of weave: For twill weaves it is 0.39, for Satin weaves it is 0.42 and for plain and hopsack weaves it is 0.45.

An amazing treatment on fabric geometry is done in this presentation.

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Wednesday, 14 October 2009

Why Wool Feels Warm

Long and short hair wool at the South Central ...Image via Wikipedia
Why Wool is Warm to Wear- Heat of Sorption

When a fiber absorbs water, heat is evolved. It results from the attractive forces between the fiber and water molecules. The phenomenon occurs due to the fact that when moisture vapour is absorbed into fiber’s internal structure, it transforms from gas to liquid and the phase change produces the rise in temperature.

It is calculated by heat of wetting. It is the heat evolved when a specimen of the material at a given regain, whose dry mass is one gram is completed is completed wetted.

It is expressed in joules per gram ( of dry material)

The heat of wetting is greatest for the more highly absorbing fibers and is very small in the non-hygroscopic fibers. Thus it is 113 J/g for wool, 106 for viscose, 69 for silk, 55 for flax, 46 for cotton , 73 for mercerized cotton and only 34, 31,5 and 7 respectively for Acetate, Nylon, Polyester and Acrylic.

As we can see from the figures above, wool has the highest heat of sorption. And this heat raises the temperature of the wearer which makes the wool feel warmer. In fact “the heat of sorption from a kg of Merino can be equivalent to the output from an electric blanket over eight hours” (Source ).

You can also find some discussion on Heat of Sorption here.

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Tuesday, 13 October 2009

Why Fiber Fineness is so Important

Why Fiber Fineness is So Important

It has been known since long that fiber fineness plays an important role in determining the quality of resultant yarn and hence that of the resultant fabrics. In general fiber fineness is important due to the following factors:

1. It affects Stiffness of the Fabric

As the fiber fineness increases, resistance to bending decreases. It means the fabric made from yarn of finer fiber is less stiff in feel. It also drapes better.

2. It affects Torsional Rigidity of the Yarn

Torsional rigidity means ability to twist. As fiber fineness increases, torsional rigidity of the yarn reduces proportionally. Thus fibers can be twisted easily during spinning operation. Also there will be less snarling and kink formation in the yarn when the fine fibers are used.

3. Reflection of Light

Finer fibers also determine the luster of the fabric. It is so because they there are so many number of fibers per unit area that they produce a soft sheen. This is different from Hard glitter produced by the coarser fibers. Also the apparent depth of the shade will be lighter in case of fabrics made with finer fibers than in case of coarser fibers.

4. Absorption of Dyes

The amount of dye absorbed depends upon the amount of surface area accessible for dye out of a given volume of fibers. Thus finer fibers leads to quicker exhaustion of dyes than coarser fiberes.

5. Ease in Spinning Process

Finer fibers leads to more fiber cohesion because the number of surfaces are more so cohesion due to friction is higher. Also finer fibers lead to less amount of twist because of the same increased force of friction. Which means yarns can be spun finer with the same amount of twist as compared to coarser fibers. Which also means that the yarns will be softer.

6. Uniformity of Yarn and Hence Uniformity in the Fabric

Uniformity of yarn is directly proportional to the number of fibers in the cross fibers. Hence finer the fiber, the more uniform is the yarn. When the yarn in uniform lit leads to other desirable properties such as better tensile strength, extensibility and luster. It also leads to fewer breakages in spinning and weaving. In fact fiber fineness is one of the dominant factor in determining the limiting count to which a yarn can be spun.

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Saturday, 10 October 2009

8 Things to Remember While Spreading Fabric

Things to remember While Spreading

1.      Mark the Splice Zone on the Spreading Table

Spreading is an operation in which bolts of fabrics are unrolled on a table in such a way in order to produce a multi-layer stack, so as to facilitate cutting.

Fabrics usually contain many defects. The defects in pieces which are cut into patterns are highly undesirable. To avoid this, the spreading operator must identify and cut out defects as the material is being spread on the table. However, if the material is cut in the mid of the pattern, it will lead to more material wastage.

To avoid this, zones are defined called splice zones, where cuts can be made by the spreading operator. Also it is also required to decide about the overlap of the next section of cloth. Thus there are two lines in a splice zone: One line shows how far the previous piece of cloth must extend, and one line shows where the next piece of the cloth must begin, ie how much overlap is needed.

Thus when a flaw is encountered, the spreader is stopped, the operator moves back to the nearest splice point, cuts the flaw out and moves the spreader back to overlap the cut line with the required overlap.

Apart from cutting out defects, splices are also used to achieve proper shade matching when starting a new roll of cloth.

Thus the splicing points are marked by means of a chalk or paint.

2.      Use Paper for the first ply in case the table surface is rough or when fine fabrics are being spread

3.      Identify the defects noticed in the fabric by means of stickers

4.      Use lubricated paper for separating layers
a.       To prevent scorching in the natural fibers ( coarse fabrics)
b.      To prevent fusing in the synthetic fabrics

5.      Ensure that decided number of ply count and height of the spread is achieved.

6.      How to spread
a.       Mount the bolt on the machine
b.      Pull the fabric to far end position
c.       Position the fabric at the far end ( with our without weight or pins)
d.      Align the ply ( width on one side)
e.       Cut the ply after each lay
f.       Repeat this process from b-e until the entire bolt is spread.
g.      Check ply count
h.      Repeat a and then b to g till the decided number of ply are spread
i.        Mark the remnants of the bolts with length in meters and bolt number and stack separately at the given place.

7.      How to Splice
a.       When the ends of the patterns in a marker are joined on both sides by straight line then use the single line splicing. Make sure that overlapping at this point should be about 2”
b.      When the ends of the patterns in a marker interlock at a common vertical line across the width then use two line marking with a diagonal indicating common area that must be overlapped when patterns in a marker interlock at a common vertical line across the width.

8.      When the required height of lay is achieved, place the marker on the spread and secure it by means of brass pins on each pattern section.

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Additional Reading: Indian Textile Journal

Friday, 2 October 2009

Comparison of Various Printing Techniques

Comparison of Various Printing Techniques

There are various printing techniques available. All have their unique points as well as shortcomings. It would be worthwhile to compare them in order to appreciate and use them for a particular end use.

Handblock Printing: It yields very low production, there is more downtime of ‘machine’. The cost of set up is very less. Very skilled personnel is required to do such printing. The cost of making a design is very less, however durability of design is very low, being defined by durability of block, usually made of wood. The variety of designs is dictated by the skill of the woodworker who carves those designs. The size of design pattern repeat can be larger. There is a limitation of width of the fabric- which is dictated by the width of the table. The printing can be very bold or subdued. In fact, in India there are numerous techniques based on a twin combination of natural dyes and block printing.

Roller Printing: Yields more production , machine downtown is very less, however cost of setup is high- as investment is needed for the maching. The space required is less. Again very skillful operators are required. The cost of making a design is more, as roller has to be carved. The durability of the design is more than a handblock print. Very elaborate and fine designs can be carved on a roller printing. The repeat size is limited to upto 42 cm. Again it has a limitation of fabric width. Very bold and lustrous prints cannot be done on a roller printing.

Flat Bed Screen Printing: Yields more production but less than roller printing as the process is not continuous. There is very less downtime of the machine. The cost of machine and installation is very high. The space requirement is also very high. Very less skilled workers are needed for this printing method. The cost of making a design is less as compared to a roller printing. The durability of the design however is very less, as new screen has to be made after few uses. The quality of designs can be very fine. The repeat of pattern can be very high. Also even a higher width cloth can be printed. The colors can be very bright and bold.

Rotary Printing: It has the maximum production among all printing techniques. The machine downtime is very less. The cost of machine and space requirement is again very high. Less skilled workers can be employed to operate this machine. Cost of making a design is very high. Compared to this the durability of the design is very less. The variety of design it offers and the quality of reproduction is the best among all techniques. Also fabric width can be high for it to be printed. It can yield bright colors.

Transfer Printing: It can do printing only on synthetic fibers such as polyester. One cannot get a ‘tone effect’ in this printing. Even unskilled workers can be used for this technique. However 100% color is not transferred so reproducibility is affected. Paper can’t be used again after one printing therefore its durability is the minimum of all techniques. The cost of making a design is very high. The production is about equal to that of flat bed. There is very less downtime of the machine. Space requirement is very less, infact, less than any other printing technique.

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