Sizing

 

Introduction :

Size is a gelatinous film forming substance in solution or dispersion form, applied normally to warp yarns. It can sometimes be applied to weft yarns.Sizing is the process of applying the size material on yarn.A generic term for compounds that are applied to warp yarn to bind the fiber together and stiffen the yarn to provide abrasion resistance during weaving. Starch, gelatin, oil, wax, and manufactured polymers such as polyvinyl alcohol, polystyrene, poly-acrylic acid, and poly acetates are employed. 2. The process of applying sizing compounds. 3. The process of weighing sample lengths of yarn to determine the count.

 

Objects of Sizing :

 

1. To protect the yarn from abrasion 

2. To improve the breaking strength of the yarn

3. to increase smoothness of yarn

4. To increase yarn elasticity

5. To decrease hairiness

6. To decrease the generation of static electricity

 

Types of sizing :

 

Pure sizing: when the size pick up % is about 3 – 10 % it is called pure sizing.

 

Light sizing: when the size pick up % is about 11 -16% it is called light sizing.

 

Medium sizing: when the size pick up % is about 17 – 40 % it is called medium sizing.

 

Heavy sizing: when the size pick up % is above 40 % then it is called heavy sizing.

 

Disadvantages of Sizing :

• Cost of land and machine is high 
• Requires lot of labors 
• Requires utility like gas, electricity etc and their cost is high 
• Cost of ingredients 
• The process is long and it takes time 
• There is a risk of degradation of yarn 
• The yarn diameter is increased 
• Requires robust loom 
• It increases yarn stiffness 
• The fabric needs to be desized before use 
• Need knowledge and information about the size ingredients 
• There is a risk of pollution 
• Sizing changes the shade of colored yarn 

 

Why Sizing is Called The Heart Of Weaving ?

When the yarns are placed in loom machine then it comes to contact with the machine that causes friction. For this reason yarn breakage & yarn rupture may be occurred. As a result, the fabric quality becomes lower so the production also becomes lower. To prevent this problem sizing is done. Sizing gives a protective coating on yarn surface to tolerate the friction on loom machine. The size yarn may reduce the yarn breakage & yarn rupture during weaving process. As a result, fabric quality becomes better & production becomes higher.

Technological Changes Due to Sizing :

1. Increasing in breaking strength: Inter fibre bonding system during increase the strength of yarn. It increases the breaking strength up to 20-40%.
2. Increase abrasion resistance: After sizing the gap between fibres are filled with size & coating on the outer surface of the yarn takes place.
3. Increase in stiffness: In sizing process stiffness of yarn is increased.
4. Increase in elasticity: Due to sizing the extensibility of sized yarn decreased, more force has to be applied to extent the yarn. Hence elasticity increases.
5. Increase frictional resistance: Hairs protruding from one yarn in the warp do not entangled with the hairs protruding from a neighboring yarn. It occurs because of sizing. Hence smoothness of the outer surface of the yarn increases. As a result less friction takes place.
6. Increase in yarn diameter: Application of sizing material on the warp yarn i.e. adhesive coating of the yarn increase the diameter of the yarn.
7. Decrease in extension: After sizing the gap between the fibers is filled by the size material hence the slippage between the fibers does not take place. So the extension in decreased.
8. Decrease in electrostatic charge: Due to friction between yarn & roller electrostatic charge is formed. But the application of size material reduces the friction hence electrostatic charge formation is decreased.
9. Decrease hairiness: Application of size material on the yarn parallelizes the protruding fiber with the yarn axis so yarn hairiness decreases.
10. Decrease yarn irregularity: Sizing process makes the projecting fiber to adhere together. Hence yarn irregularity decreases.

Effects of Sizing on Yarn Properties :
The following properties of yarn are affected by sizing:

• Yarn elasticity.
• Yarn strength.
• Hairiness of yarn.
•  Flexibility of yarn.
• Smoothness of yarn.
• Irregularity of yarn.
• Yarn diameter.
• Yarn weight.

 

Sizing Chemicals & Their Importance :

Film forming materials:
Starch is the oldest film forming material used in sizing of cellulosic fibers. It is also the most widely used in the world due to its low cost and ease of availability. In Pakistan, mostly maize starch is used, whereas, potato starch is more popular in Europe. 

PVA is the second largest film former used in sizing. It is mostly used on synthetic yarns such as polyester and poly/cotton blends. PVA coating is strong, abrasion resistant and can easily be de sized in hot water. Its strength is greater than starch and also more flexible than most standard starches. PVA is less prone to setup in the size box compared to starches. PVA can form foam in the size box which is controlled with a de former. PVA may be too strong for some sizing applications. In this case, some weaker film forming polymers such as starch are added to modify the mixture, which also reduces the cost, since PVA is more expensive than starch.

The most widely used size materials are starch and PVA. However, other size materials have been developed and used for specific purposes. Carboxymethyl cellulose (CMC) is produced from wood pulp and cotton lint and has good adhesion to cotton. 

Poly acrylic acid based sizes (poly acrylates and poly acrylamides) are used to size hydrophobic fibers and their blends such as nylon, acrylics, polyester, etc because of their good bonding.

Properties of a Good Sizing Material :

1. Environmentally safe.
2. Good film former.
3. Reasonable use economics.
4. Penetration of yarn bundle.
5. Elasticity.
6. Good film flexibility.
7. Good specific adhesion.
8. Good frictional properties.
9. Transparency.
10. Bacterial resistance.
11. Reasonable strength.
12. Controllable viscosity.
13. Water soluble or water dispersible.
14. Good hygroscopicity characteristics.
15. Uniformity.
16. Clean split at bust rods.
17. Improves weaving efficiencies.
18. No effect on drying.
19. Reasonable extensibility.
20. Recoverable and reusable
21. Low static propensity.
22. No skimming tendency.
23. Easily removed.
24. Easily prepared.
25. Lack of odor.
26. No beam blocking.
27. Compatible with other ingredients.
28. Good abrasion resistance .
29. Neutral pH.
30. High fold endurance.
31. Insensitive to high heat.
32. Low BOD.
33. No build up on dry cans.
34. Reduced shedding.
35. Rapid drying.
36. No re-deposition of size
37. Insensitive to changes in relative humidity.

The functions of the sizing operation are :

1. To lay in the protruding fibers in the body of the yarn and to cover weak places by encapsulating the yarn by a protective coating of the size film. The thickness of the size film coating should be optimized. Too thick a coating will be susceptible to easy size shed-off on the loom.

2. To increase the strength of the spun warp yarn without affecting its extensibility. This is achieved by allowing the penetration of the size into the yarn. The size in the yarn matrix will tend to bind all the fibers together. The increase in strength due to sizing is normally expected to be about 10 to 15% with respect to the strength of the unsized yarn. Excessive penetration of the size liquid into the core of the yarn is not desirable because it affects the Flexibility of the yarn.

3. To make a weaver’s beam with the exact number of warp threads ready for weaving.

Sizing variables :
A good sizing depends on various factors. During sizing the following variables should be checked and controlled where necessary:

1. Viscosity of the size solution.·
2. Sizing machine speed.·
3. Size add-on levels.·
4. Concentration of the size mixture.
5. Volume of the size box.·
6. Threading arrangements.·
7. Condition of squeeze rolls.
8. Squeezing pressure.·
9. Hardness of squeeze rolls.
10. Diameter of squeeze rolls.
11. Number of size boxes.·
12. Yarn count and size box warp density per unit space.
    
    

Causes of Faults of Sizing :

Underslashed Warps:
Causes:

• Due to insufficient size concentration
• Improper size feed to the size box
• Variable size level
• Dilution of size
• Strong squeezing of warp

Overslashed Warps:
Causes:

• Due to insufficient splitting of starch at size preparation
• Weak squeezing
• Too deep immersion of the warp into the size box

Sticky Warps:
Causes:

• High sizing speed
• Low drying temperature

Over Dried Warps:
Causes:

• Low sizing speed
• Long stoppage of machine during sizing
• Very high temperature in the drying section

Gum Spots and Smears:
Causes:

• Splashes of size get on the squeezed warp
• Bad stirring of starch at preparation
• Improper coating of felts on the squeezing rollers

Non Uniform Size Regains:
Causes:

• Irregular heating of the size in the box
• Dilution of the size with live steam
• Non uniform pressure of squeezing rollers

Crossed and Lost Ends:
Causes:

• Lease rods are set too far apart
• Broken ends are improperly pieced up
• Bad warping.

Improper Build of Beam:
Causes:

• Incorrect spreading of yarn ends in the reed dents

Incorrect Warp Length:
Causes:

• Disarrangement of the measuring and marking mechanism
• Improper adjustment of measuring and marking mechanism

Dirt Stains in Warp:
Causes:

• The size boxes and machine metal parts are dirty
• The size is cooked in non-galvanized iron kettles.

Shinnery:
Causes:

• Due to the friction between the yarn and drying cylinder

Sandy Warp:
Causes:

• Due to not crushed or grind the size material

Hard Sizing:
Causes:

• Excessive application of size material

Size Dropping:
Causes:

• Due to not optimum viscosity of the size solution

 

Conclusion :

sizing is very important for our yarn manufacturing .so in the above we explained how and what is the sizing and how it is works.

Reference :

http://www.bdtextileblog.com/2011/12/yarn-count-types-of-counting-system.html

http://www.davytextiles.com/glossary_of_terms_and_definition.htm

http://textilelearner.blogspot.com/