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The
Role Of Crimp In The Textile Process

Texturing:  means by
which luxurious bulk , greater absorbancy and improved hand are combined with
rugged performances through permanent introduction of crimp, loops, coils or
wrinkles into an otherwise continous filament.

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Advantages:

Higher bulk
Greater water
absorption
Increased warmth
Good draping
capacity
Better air
permeability
Better dimensional
stability
Higher covering
power
Higher hygienic
characteristics
Pleasing hand and
appearance

Disadvantages:

Increased
hairiness
Reduced
strength and abrasion resistance

 

Crimp :   is waviness introduced in staple fibres to be
spun into yarn.

Take Up
Percentage or Crimp Rigidity:

 

Take up percentage or crimp
rigidity is a measure of the ability of textured yarn to receive from stretch.
It is the ratio of reduced length to original length, expressed as percentage.
Thus, take up percentage T% = L – P/ L × 100.

Crimp rigidity tester:

There are three methods:

1. Mechanical method

2. Chemical method

3. By using bio components

 

1. Mechanical method

In order for staple fibres to be spun into yarn,
they must have a waviness, or crimp, similar to that of wool.

Crimp may be introduced mechanically by passing
the filament between gear like rolls.

2. Chemical method

It can also be produced chemically by controlling
the coagulation of a filament.

3. By using bio components

A similar effect can be produced from bio
component fibers. When the filament is drawn, the two polymers extend to
different degrees, producing a helical crimp when the strain is relaxed.

 

Types of crimping:

1. Edge crimped yarns

2. Stuffer box crimping

3. Gear crimping

1. Edge crimped yarns

Stretch and modified stretch yarns can
also be produced by a process known as 
“edge crimping”.

The use of edge crimped yarn has been
extended to heavy denier yarns for the use in carpet, knitted outer wear, men’s
hosiery etc.

 

Knife edge crimping:

•       
In this
process yarn is tensioned, stretched, heated , bent and drawn around an edge ,
followed by shrinking and cooling step.

•       
Crimp
development in a filament is caused by bilateral compressional deformation,
extensional strain deformations  induced
in the heated filament as it is being pulled over a blunt knife edge.

•       
The
filament touching the knife edge is under compression where as that on the
outside experiences extension.

•       
The region
pressed against the knife edge is deformed into a flat and a filament cross
section appears.

•       
Final
crimp development is thus a function of:

temperature
bending curvature
dwell time on edge

•       
Compression
zone : rupture of crystals, disruption of molecular orientation .

•       
Region
farthest from edge :  stretched to
develop a crimp in the filament.

•       
The strains
thus induced are relaxed by subsequently relaxing and heating the yarn under
controlled conditions.

•       
Relaxation
is carried out either in steam or in dry heat.

•       
When
strain is released crimpage takes place .

•       
Filament
form coils in almost helical configuration.

 

Crimp
structure:

2. Stuffer box crimping

 

The crimping unit consists of two feed rolls and
brass tube stuffer box and a brass tube stuffer box. By compressing the yarn
into the heated stuffer box, the individual filaments are caused to fold or
bend at a sharp angle, while being simultaneously set by a heating device.

 

 

•       
The process of
texturing by the stuffer box method is based on the principle of  heat setting filaments held in a confined
space in compressed state and then drawing them in their crimped form. The
chamber in which the filaments are stuffed is known as the stuffer box.  The
stuffer-box method is a fast and inexpensive method for carpeting yarn.

•       
Properties :
zig-zag to wavy crimp, low elasticity.

•       
Crimp structure:

•       

      
3. Gear
crimping :

In this method filament is run between a pair of
intermeshing gear wheel. The resultant yarn is left with the impression of the
gear wheel teeth.

 

•       
Bulk can be produced
in a continuous filament yarn when it is passed through closely meshed gears.

•       
The gear head is
heated so that the crinkle produced in the yarn is permanent.

•      
 

End use applications :

Ladies and children knitted outer wear
Sweaters
Ladies blouse

 

4. Air jet texturing method:

·       
The
air jet texturing process consists of subjecting an overfed bundle of filaments
to the action of a turbulent air steam in a venture tube.

·       
 Air jet is basically a mechanical process and
can be used for both thermoplastic and non thermoplastic  filament yarns as well as their blends.

·       
Yarns
produced by this process resemble the natural fiber spun yarn both in
appearance and physical characteristics.

·       
Yarns produced by the air-jet
texturising are totally different structures in that they much more closely
simulate spun yarn structures

      There
are two basic types of texturing jet

                            
i.           
Axial

                          
ii.           
Radial

·       
Properties:

 

        
i.           
High yarn stability

      
ii.           
  Low and uniform package take-off tension

     
iii.           
High bulk

    
iv.           
Reduced boiling water shrinkage

      
v.           
Improved soft hand of fabrics

    
vi.           
Elimination of the Velcro effect
of fabrics

   
vii.           
High pilling resistance

  viii.           
Uniform appearance of the fabric

    
ix.           
Sizing of warp beams may not be
necessary for slower running looms

 

Crimp structure:

 

 

5. Knit and
de knit:

In this
method, the flat yarn is first knit, then heat set and unraveled to produce a
crinkle type structure.

·       
Properties:

                               
i.           
Excellent stretch

                             
ii.           
Full hand

                           
iii.           
Yarns are torque free

                          
iv.           
Wavy crimp

                            
v.           
Elongation

                          
vi.           
Crepe effect

 

Crimp structure:

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