YARN AND YARN MANUFACTURING-Doubling and Drawing-4.7.1

DOUBLING AND DRAWING

Doubling and Drawing : 

In preparing the fiber tufts for spinning, doubling and drawing represent two essential
operations and their combined effect permits a sliver with a more regular section to be
obtained(through doubling) equipped with parallel fibers (through drawing) as well as the
count requested by the spinning plan. 

The drawing operation done with the machine called the draw frame, permits a homogeneous
blend both with fibers of the same nature as well as fibers with a different nature; the doubling
steps are usually between four and eight.

On a par with fiber characteristics such as length and fineness, a sliver with parallel fibers
permits a yarn with better regularity and resistance. The drawing depends on some factors such
as the number of doubling carried out and the value of the count of the entry sliver and
delivery sliver. With drawing, curls, crimps and hooks are also eliminated, meaning the fibers
folded in on themselves, present in the carded sliver. 

Drawing is a process in which the sliver is elongated by passing it through a series of pair of
rollers, each pair moving faster than the previous. This permits combination of several slivers
and drawing and elongating them to straighten and create greater uniformity to form a regular
sliver of smaller diameter. This action pulls the staple lengthwise over each other, thereby
producing longer and thinner slivers. Finally the sliver is taken to the sliver can.

The main objects of the Draw-Frame are below: 

• Crimped, curled and hooked fibers are straightened;  
• Parallelism of fibers; 
• Reduction of sliver weight per unit length; 
• Reduce irregularities of fibers by doubling and drafting 
• Remove remaining dust from sliver.
• Blending of fiber to provide compensation of raw material variation.

There are two passages of drawing are uses

• Breaker drawing and 
• Finisher drawing

The main difference between them, like on the card, there are also auto levelers on the finisher
draw frames, whose job it is to correct the draft in function of variations in the fibrous mass, to
maintain the section of sliver as even as possible and therefore reduce the frequency of
breaking threads in spinning and in successive operations.