Friday, December 27, 2019

DRAWING ( DRAW FRAME) , A SPINNING PROCESS, OBJECTS OF DRAWING (DRAW FRAME) PROCESS

DRAWING ( DRAW FRAME ), A SPINNING PROCESS, OBJECTS OF DRAWING ( DRAW FRAME PROCESS:

Drawing is one of the processes which comes after carding in the manufacturing of yarn.

As far as the share of the drawing in yarn cost is concerned, it has very little effect on the production cost of yarn but the drawing process (draw frame) plays a very big role to improve the quality of yarn in many respects such as evenness, strength, elongation at break and degree of hairiness. 

Draw frame process avails the last chance to improve the sliver irregularities and to eliminate the dust and impurities present in the carded sliver. 
There is no other chance to eliminate the irregularities and impurities left in the sliver in the further process of yarn manufacturing.

Two actions are taken place in the draw frame process.

One is doubling and another one is drafting. 

The doubling process helps to improve the evenness of the sliver and drafting helps to achieve the maximum parallelisation of fibre along the sliver length and reduce the linear density of the sliver too.

Since the carded sliver contains a large percentage of hooked and curled fibres so that these fibres necessitate to straighten properly. The drafting process allows straightening these fibres.

Doubling: 

In the process of doubling, two or more carded slivers are taken and they are fed together. 

After the drawing process, a combined sliver of the same linear density is obtained. 

Mostly 6 or 8 slivers are combined together in the doubling process and a single sliver is produced. 

The resulting sliver has improved uniformity and linear density. 

How the evenness of the sliver is improved during doubling? It can be understood by the law of doubling.

Law of doubling:

As we know that two or more slivers are combined (doubled) together at the input side of the draw frame sliver during the drawing process.  

According to the law of doubling, if N number of slivers are combined (doubled) together, the overall irregularity of the resulting sliver after doubling is reduced as per the following law:



The above equation shows when the value of N increases, the value of CVI decreases. Therefore, the doubling process always reduces the overall irregularity of the carded sliver.

Drafting:

The weight per unit length of the input sliver is reduced in the process of drafting. 

The hooked and curled fibres are straightened and fibre arrangement in the sliver is improved by making fibres parallel along the sliver length. 

The fibres are blended together in the drafting process. The drafting also helps to eliminate dust from the sliver. 

The drafting action is performed with the help of pairs of drafting rollers. 

In the drafting process, the rollers rotate higher than the previous one.

OBJECTS OF DRAWING ( DRAW FRAME) PROCESS:

The main objectives of the draw frame process are given below:

To improve the uniformity (linear density) of sliver up to optimum level.

To improve the fibre arrangement in the sliver and to make the fibres parallel to the sliver length.

To straighten the hooked, curled and crimped fibres present in the sliver.

To draft the material and to reduce the weight per unit length of sliver.

To mix or blend the components of sliver to each other and to find homogeneous material output.

To eliminate the dust and impurities present in the sliver.
                               
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