The up percentage T% = L – P/

The
Role Of Crimp In The Textile Process

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

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.

      
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 :

i.       
Ladies and children knitted outer wear

ii.     
Sweaters

iii.   
Ladies blouse