Draw Frame
Drawing
Drawing is the operation by which slivers are blended, doubled and leveled. In short staple spinning the term is only applied to the process at a draw frame. In drawing slivers are elongated when passing through a group of pair rollers, each pair is moving faster than previous one. This permits combing, drawing and elongating of several slivers to make them strong and uniform.In most modern worsted drawing sets there are 3 passages of pin drafting and roving process.
Objects of drawing
1. To straighten the crimped, curled and hooked fibers.
2. To make the fiber parallel to their neighbors.
3. To improve uniformity of fibers by drafting and doubling.
4. To reduce weight per length unit of sliver.
5. To remove dust from slivers.
6. To blend raw material of same hank perfectly.
Necessity of Draw frame
To parallelization of fiber and blending the carded sliver, draw frame is needed.
In carded sliver, fibers are present in hook form i.e. trailing hooks and leading hooks. To parallel these hooks raw frame is used.
Majority of the fiber hooks in a carded sliver are trailing hooks while leading hooks are comparatively less. Trailing hooks are also known as major hooks, while leading hooks are known as minor hooks.
Tasks of Draw frame
· Equalizing
· Parallelizing
· Blending
· Dust removal
Equalizing: One of the main tasks of draw frame is improving evenness over short, medium and especially long terms. Carded slivers are fed to the draw frame have degree on unevenness that cannot be tolerated in practice and slivers from the comber contain the “infamous” piecing. It is obscured by draw frame.
Equalizing is always performed by a first process, namely doubling and can optionally also be performed by a second process, namely auto leveling. The draft and the doubling have the same value and lie in the range of 6 to 8.
Parallelizing: To obtain an optional value for strength in the yarn characteristics, the fibers must be arranged parallel in the fiber strand. The draw frame has the tasks of creating this parallel arrangement. It fulfills the task by way of the draft, since every drafting step leads to straightening the fibers.
Blending: In addition to the equalizing effect, doubling also provides a degree of compensation of raw material variation by blending. Their results are exploited in particular way in the production of blended yarns comprising cotton or synthetic blends. At the draw frame metering of the individual components can be carried out very simply be selection of the number of slivers entering the machines.
Dust Removal: Dust is steadily becoming a greater problem both in processing and for the personnel involved. It is therefore important to remove dust to the greatest practical extent at every possible point within the overall process.
Dust removal can only be carried out to a significant when there are high levels of fiber. Since a large function the smallest particles adhere relatively strong to the fibers. High performance draw frame is equipped with appropriate suction removal systems; more than 80% of the incoming dust is extracted.
Actions involved in Draw Frame
Drafting: It is the process of increasing length per unit weight of sliver. It is mainly due to peripheral speed of the rollers.
Doubling: The process of combing two or more carded sliver into a single form is called doubling. In draw frame m/c generally six slivers are fed to convert into one i.e. six doubling.
Drawing: In the cotton industry the term is applied exclusively to processing on the draw frame, where the operation is one of doubling and drafting. Drawing= Drafting + Doubling.
Operating Devices
· Creel (Sliver Feed)
· The drafting Arrangement
· Suction systems for the drafting arrangement
· Coiling
· Can charger
Creel
The creel must be designed so that:-
· False Drafts are avoided.
· The machine stops upon accordance of the sliver break.
· Sliver breaks can be dealt with easily, comfortably and safely.
In this purpose it is necessary to provide a rotable roller or roller pair above each can. A guiding device for leading the rollers into the drafting arrangement is also required.
Requirements of drafting arrangement
The drafting arrangement is the heart of the draw frame. Drafting arrangement exerts most decisive influences on sliver quality. The requirements placed on the drafting arrangements are mentioned bellow:-
1. Simple, uncomplicated construction.
2. Stable design with smooth running roller. IT means rollers should be centric and smooth running.
3. A mode of operation giving a high quality product at even high running speeds.
4. High Degree of flexibility, suitability for all raw materials.
5. Optimal control over the movement of the fibers during the drafting operation.
6. High precision in both of operation and adjustment.
7. Rapid and simple adjustability of roller spacing and draft levels.
8. Ease of maintenance of cleanings.
9. Optimal ergonomic design.
Factors dependent upon the fiber materials
1. Mass of the fibers in the strand cross section.
2. Degree of order of the fiber.
3. Shape of cross section of the fiber strand.
4. Compactness of the fiber strand.
5. Length of fiber.
6. Adhesion between the fiber depends upon:-
· Surface structure
· Crimp
· Lubrication
· Compression of the strand.
7. Evenness of distribution of fiber length.
8. Twists present in the fiber strands.
Factors depending upon the drafting arrangement
1) Diameter of the rollers.
2) Hardness of the top rollers.
3) Pressure exerted by the top rollers.
4) Surface characteristics of the top rollers.
5) Fluting the bottom rollers.
6) Type and form of fiber guiding devices, such as pressure rods, pin bars, aprons, condenser etc.
7) Clamping distance.
8) Level of the draft.
** Both input and output of draw frame is sliver, then what is done in draw frame?
Answer: From a purely commercial point of view draw frame is of little significance. But its influence on quality and evenness is greater. The carded sliver contains fibers which are oriented in various directions and they are crimped, hooked or curled. They entangled with one another and their height per unit length is high. They are irregular and contain some impurities. So they need a process for eliminating these errors.
In cotton spinning line raw frame is the definitive compensation point for eliminating errors. This draw frame:-
· Straighten the fibers in sliver.
· Make the fibers more or less parallel.
· Reduce the weight per unit length of sliver.
· Remove dust from sliver.
· Make very perfect blending of fibers.
So, the carded sliver is actually made perfect in quality and evenness of draw frame.
Elements of drafting arrangements
Bottom roller: Bottom rollers are made of steel and are mounted in roller strands or in frames by means of needle or ball bearings. They are positively driven from main gear transmission.
On order to improve their ability to carry the fibers along, they are formed with flutes of one of the following types.
· Axial flutes
· Spiral flutes
· Knurled flutes
Top roller: The top rollers are not positively driven; they are mounted by the means of ball bearings. These top rollers are made of steel and they are covered with thick coating of synthetic rubber. An important matter avoid this coating is its hardness. Soft rubbers coating can grip the fiber strand more perfectly than that of hard one, but soft coating of rubber wear out more quickly.
Hardness of rubber coating on top rollers in specified in terms of degree shore.
Soft coating -> 60-70 degree shore
Medium coating -> 70-90 degree shore
Absorb coating-> Above 90 degree shore
3 over 3 drafting Arrangement
Blow room is the first section of spinning line for spinning cotton yarn from fiber. It consists of a number of machines which are used one after another for opening and cleaning cotton fiber from its bale to a required degree. Besides these fibers can also be mixed or blended in this section. In this section from cotton bale, we produce lap of specific length and width.
