Yarn manufacture.Assignment. 01

Nalaka Sampath.

1. Discus the important of blow room in the Cotton Yarn Manufacturing process with regard to its objectives.

Cotton use in yarn manufacturing is always mixed with trash and dust particles and they need to be removed. Intensive cleaning is only possible process for this task. So bales are should be opened to remove containing impurities and other unwanted wastes. There are some methods to open the cotton bales into small tufts, before further processing. This process is knows as blow room process.There are some purposes of using a blow room in yarn manufacturing.

i). Opening of the baled cotton . In the spinning mills, used bales are highly pressed form to optimize the storage and transport conditions. So they can not be use as it comes to mills. They also contain impurities like leaves, husk, sands, stones, and broken seeds. So the highly pressed bales should be opened. This should be done under a minimum damaged to the fibres. There are two types of special machines to do this opening process better. A). Manual bale opener.

B). Automatic bale opener.

ii). Clean out impurities. It’s important to remove foreign particles of raw materials before the spinning process. Because vegetable and mineral impurities may cause to the damage of fabric and also to the machineries from dust and other foreign matters. Natural fibres can be cleaned in three various ways. Bt here discus only about the mechanical cleaning process and about the objects which are called Grid Bars and Mote knives, used to this purpose,. Grid bars are used to separate fibre flocks and impurities. Some times Grid can be used with one or two mote knives in front of the grid. The arrangements of grid in a machine are, one after one another to perform maximum task. These grids can be made from perfoted sheet or sloted sheet,

iii). Mix or   blend with other fibres.

The main purpose of this process is achieving uniformity to basic product. Even though man made fibres are homogenous for their characteristics, natural fibres are difference from fibres to fibres. That’s why we need blending and mixing processes during the yarn manufacturing to have a fine yarn.This can be defined as the combination of raw materials to achieve uniformed product. This combination of fibres allows fabrics to combine its properties with another type of fabrics which made out from difference type of fibres. As an example we can present the polyester and cotton are blended for achieve combined properties unique to them.

iv). Produce a uniformed   feed   to   the   carding   machine. Final raw materials take out from blow room, ensure that they are evenly delivered to the carding process. So the blow room prepare an even fibre format also.

1

2. What are the Drafting waves? Drafting waves can be defined as unevenness of sliver

dimensional property. A yarn, which has drafting waves, may appears some places are thick and some are thin. This is called drafting waves.

Drafting fault can occur due to the Roller nip movement and Roller speed variation. These faults are under he mechanical faults. Then other reason for drafting waves is floating fibres in drafting zone. Fibres not have been caught to the both front and back roller’s nips are cause to these floating fibres.

3. What cause drafting waves to occur and what are the techniques available to minimize the effect of drafting waves?

Drafting waves can adversely affect to the yarn’s properties. Most effective consequence of sliver evenness is variation of strength along the sliver. And also it’s difficult to make a fine yarn from these slivers under those conditions, which are so even. And these yarns will tend to break so easily when it’s used in weaving, spinning, knitting, or any kind of process where stress is high.

These drafting waves can be removed by applying some mechanical process. They are;

Doubling slivers. Apron drafting system. Auto leveling.

In Doubling method, two or more silvers are used to draft. Drafting machine feed from slivers, and in the drafting zone they combined together. But the final product comes as one sliver. The main purpose of this task to improve the evenness of sliver. And also it’s used as a blending method of fibre blending.

Apron drafting system can be preformed in two ways. Double apron and single apron drafting. These both systems are used to maintain the floating fibres during the drafting.

In double apron drafting there are two apron which guide fibres to rollers. These two aprons rotating with middle rollers. Single apron drafting also same as above but it’s using only one apron.

2

Auto leveling.

There are two types of Auto leveling systems. They area) Open loop system.b) Close loop system.d) Combined loop system.

Auto levelers are used to control linear density variation of uneven slivers. These levelers change draft according to variation of sliver to minimize unevenness. When auto leveler detects a thin place of a sliver, it apply low draft and, when it detects a thick place, auto leveler increases the speed of drafting rollers and corrects sliver’s unevenness.

In open loop leveling method sensors detect the fault of feeding sliver at feeding end, then it automatically change draft by adjusting speed of front or back rollers. This method is most commonly used auto leveling method in drafting machines, as it can be corrected fairly short term variations

Closed loop is used in earlier drafting machines. Sensors in both side of sliver, detect variation of sliver at the delivering end. Then it gives signal to drafting rollers to correct the variation. But the disadvantage of this method is, when sensors detect a variation of sliver, it already have passed the front roller. Then there is no way to correct the variation. In this reason, closed loop method is ideal in correcting of long term and medium term variations.

Combined loop is a combination of both above methods.

3