Draw frame (1)
- 1. Draw frame Input: card sliver Output: Drawn sliver ##Difference between card sliver and Drawn sliver: Card sliver Drawn sliver Fiber orientation in all direction Fiber orientation in the parallel direction to the sliver axis Many fibers areprojected out from sliver Less fibers are projected out fromsliver Hooks (leading & trailing) are present Less hooks ( leading & trailing) are present Irregular wt./unitlength Regular wt./unit length Card sliver has less strength Drawn sliver has more strength ## Both input and output of a draw frame is sliver. Then why we use 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 hooked. They entangled with one another and their weight 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 draw 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.
- 2. Working principle of a draw frame: 1. Feeding of material: Four to eight card sliver can (feed can) are fed at below of creel frame. These slivers are the creeled and fed to the drafting arrangement through a feed roller pair located above each feed can to enable the feeding in a controlled manner. 2. Drafting of material: The slivers then run through the drafting arrangement where range of draft of 4 to 12 as required is applied. Here straightening, parallelization and attenuation operation take place. 3. Sliver formation: after leaving the draftingarrangementa packageof fiber is called drafted web, lacking significant cohesion between fibers is produced. In this condition the fibers do not form a transportable intermediate product in order to avoid disintegration of the web. The intermediate transportable product sliver is produced after condensing the drafting web passing through the condensing tube (trumpet) just after leaving the drafting arrangement. 4. Delivery of material: This sliver is then guided through a tube via a passageof the coiler tube gear into a delivery can in which it must be laid in clean coils with optimal utilization of the spacein the can. To enable the can to take up as much material as possible, the sliver is compressed by passing it through calendaring rollers. 5. Doffing of material: The filled can is prepared for the doffing operation. There is can track for feed-in of the empty can and delivery-outof the filled can.
- 3. Main objectives of a draw frame: 1. To remove majority of hooks present in card sliver 2. To increase uniformity of sliver Objects of draw frame: 1. To straighten the hooked fibers in the card slivers 2. To make them lie in a manner parallel to their neighbors and to the sliver axis. 3. To improve the uniformity and evenness of the slivers by doubling 4. To produce a more uniform sliver of definite weight/unit length. 5. To reduce weight per unit length of sliver 6. To remove dust from sliver 7. To make perfect mixing/blending of the sliver Tasks of draw frame: 1. Equalizing: one of the main tasks of the draw frame is improving evenness over short, medium and especially long term variation. Equalizing is always performed during drawing by a first process namely doubling and can optionally also be performed by a second process namely auto levelling. The slivers fed to the draw frame from the card contains variations in thickness that is they are not regular. The doubling process in draw frameimprovethe regularity of the final sliver by averaging out the weight variations existing in slivers fed to draw frame. 2. Parallelizing and straightening: To obtain optimum strength in yarn, the fibers mustbe arranged parallel in the fibers strand. Thedraw framehas the task of creating this parallel arrangement. Itfulfils this task by the way of the draft since every drafting step leads to straightening of the fibers. 3. Blending: Though a blending can be achieved in modern blow roomprocess, further blending after card improves the composition of fibers in the sliver. The practice of feeding several slivers ( doubling) side by side through the draw frameand recombining them at the frontgives a very good blending of fibers in the individual sliver and this makes the final sliver more uniform than card sliver in fiber composition. 4. Dust removal: The draw frame is a good dust removing machine because there are high levels of fiber to fiber and fiber to metal friction during
- 4. drafting. On high performance draw frames equipped with appropriate suction or removalsystemmorethan 80% of the incoming dust is extracted. Q. what is the influence of doubling on sliver quality? Q. what is the influence of drafting on sliver quality? Definition of different terms: 1. Drawing: A process in shortstaple spinning in which the slivers are blended, doubled, levelled and drafted by passing the slivers through a series of pairs of rollers each pair moving faster than the previous one. 2. Doubling: The process of combing two or more slivers, rovings or yarns into one is called doubling. 3. Drafting: The action of reducing the weight/unit length of the feed material by drawing is known as drafting. 4. Creeling anddoffing: The operation of replacing the cans of feed material at the back of the machine and joining the new can full of sliver to the old is known as creeling and that of removing the full delivery cans fromthe front of the machine is known as doffing. Features of modern draw frame: 1. Elimination of mechanical causes of irregularity. Provides electrical control auto levelling which givesand maintains higher degreeof regularity in drawn sliver. 2. High speed running 3. Pneumatic suction devices for dust removal 4. Stop motions at strategic points to stop the machine when needed 5. Automatic can changers 6. More machines per operative and little attention needed. So reduces labor cost 7. Improved top arm weighting system Elements of drafting arrangement: Bottomroller: 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.
- 5. a) Axial flutes b) Spiral flutes c) Knurled flutes Top roller:Thetop rollersare notpositively driven;they aremounted bythe means of ball bearings.These top rollers aremade of steel and they arecovered with thick coating of synthetic rubber. An importantmatter avoid this coating is its hardness. Softrubbers coating can grip the fiber strand moreperfectly than that of hard one, but soft coating of rubber wear out more quickly. Hardness of rubber coating on top rollers is specified in terms of degree shore. Soft coating -> 60-70 degree shore Medium coating -> 70-90 degree shore Hard coating-> Above 90 degree shore Top roller pressure: To clamp the fibers, the top rollers mustbe forced out at high pressure towards the bottom rollers. This pressure can be generated by:
- 6. 1. Loading by means of dead weight (now obsolete) 2. Spring weighting (the most usual form) 3. Hydraulic systems (hardly used) 4. Pneumatic weighting ( the Rieter company) 5. Magnetic weighting Types of drafting arrangement: Early draw frames had almost exclusively 4 over 4 roller drafting systems. The3 over 4 roller systemwas developed outof this earlier version and there after a multitude of new forms emerged. The drafting system may be classified based on the formof roller arrangementcan be described below: 1. Conventional 4 over 4 roller drafting system 2. 3 over 4 roller drafting arrangement 3. 3 over 3 roller drafting 4. 4 over 3 roller drafting 5. 5 over 4 roller drafting 4 over 3 roller drafting arrangement: This is the most widely used drafting arrangement for draw frames. Strictly speaking, this is also a 3 roller pressurebar drafting arrangementbut a fourth roller with somewhatlower loading is added to the delivery roller to act as a guide. This leads the web in curveround the grooved roller directly into the delivery trumpet, thereby facilitating the formation of the sliver. The top rollers are uniform in diameter and are large in order to keep the strain imposed in them low. Draft calculation: let, back roller rpm=500 & diameter=30mm Middle roller rpm= 900 & diameter= 30mm Front roller rpm=3000 & diameter= 40mm
- 7. We know, draft = surface speed of front roller surface speed of back roller = 3.1416×40×3000 3.1416×30×500 (surface speed=πdn) = 8 Back draft = surface speed of middle roller surface speed of back roller = 3.1416×30×900 3.1416×30×500 = 1.8 Front draft= surface speed of front roller surface speed of middle roller = 3.1416×40×3000 3.1416×30×900 = 4.44 Total draft = back draft × front draft = 1.8×4.44 = 8 Requirements of drafting arrangement: 1. Simple, uncomplicated construction 2. Stable design with smooth running of the roller 3. A mode ofoperation givinga high quality producteven athigh runningspeed 4. High degree of flexibility (suitability for all raw material, fiber length, sliver wt.) 5. Rapid and simple adjustability of roller spacing 6. Rapid and simple adjustability of draft level 7. Ease of maintenance and cleaning Q. what do you mean by roller setting/roller spacing/roller gauge? What is the importance of roller setting on drafting arrangement? Answer: In a draw frame it is necessary to space the rollers a certain distance apart. The distance from the centre of one roller to the centre of another is known as the roller setting/roller spacing/roller gauge. Roller setting mainly depends on the staple length of fiber. If fiber staple length is high then roller setting mustbe wide. On the other hand if fiber staple length is low then roller setting must be close.
- 8. Factors depending upon the drafting arrangement: 1. Diameter of the rollers 2. Hardness of top rollers 3. Pressure exerted by the top rollers 4. Surface characteristics of top rollers 5. Roller setting/roller spacing/roller gauge 6. Level of draft 7. Distribution of draft between various drafting stages Q. 1. A draw frame is running with 4-over-4 drafting system. Please distribute the draft between various drafting stages. (Sufficient data will be given) 2. A draw frame is running with 4-over-3 drafting system. Please distribute the draft between various drafting stages. (Sufficient data will be given) Necessities of auto stop motion: 1. The sliver run out from the creeled can 2. Sliver breaks in the creel 3. Lapping up on drafting rollers 4. If sliver is lapping between trumpet and calendar roller 5. If delivery can is filled with sliver If auto stop motion is absent: 1. Considerable damage may cause to machine 2. The output sliver may be thick or thin 3. Lapping up of drafting or calendar roller 4. Irregular drafting 5. Excess of full can 6. Too much waste produce 7. The yarn strength or roving strength may vary from place to place 8. Any operatormusthaveto attend the machine fulltime to stop it at anyfault Auto levelling: Auto levelling is an additional device which is meant for correcting the linear density variations in the delivered sliver by changing either the main draft or back draft of the drafting system, according to the feed variation. There are two types of auto levelling systems: 1. Open loop system
- 9. 2. Closed loop system Open loop auto levelling: In open loop auto levelers sensing is done at the feeding end and the correction is done by changing either a back draftor main draft of the drafting system. Most of the draw frame auto levellers are open loop auto levellers. Closedloopauto levelling: In closed loop system, sensing is at the delivery side and correction is done by changing either a back draft or main draft of the drafting system. Most of the earlier card auto levellers are closed loop auto levellers. But the latest cards have sensing at the feed rollers and as well as at the delivery calendar rollers. We can say, both closed loop and open loop systems are being used in such auto levellers. Let us discuss about an auto leveller system which is being used in most successful draw frames like RSB-951, RSB-D-30 etc. This system is an electronic levelling system. The major components in the system are scanning roller, signal converter, levelling CPU, servo motor, Differential gear box. Function of the scanning roller is to measure the variation in the feed material. All slivers fed to the machine pass through a pair of scanning rollers. Oneof the scanning rollers is moveableand another is fixed. The variations in sliver mass of the incoming slivers displacethe scanning roller. The distance moved by the scanning is proportional to the sliver mass fed. This displacement of scanning rollers is transformed into voltage by a signal converter and is fed to an Electronic Levelling processor. It is the Electronic Levelling processor which furnishesthecorrect target value to the servo motor.
- 10. Delivery speed of the machine and electric signalvalues arrived at by the slivers fed are the two important signals for the correction. Servo drive takes the information and is converted in such a way that servomotor RPM and direction is decided for appropriate correction. Differential gearing with its controlled output speed drives the middle and back roller. i.e. Sliver entry of the drafting system. Because the servo motor RPM and direction varies according to the feed variation and the servo motor generates a control speed of the differential gearing, the required change in main draft is accomplished, compensating for the weight variation of the sliver fed. If the slivers fed are too heavy, the entry speed (back and middle roller speed) is reduced i.e. draft increased If the slivers fed are too light, the entry speed is increased i.e. draft reduced Delivery speed (the frontroller speed) remains constantand hence the production remains constant. Mathematical problem: 1. Find out the draft of a draw frame if card sliver wt. is 70 gr/yd, drawn sliver wt. is 75 gr/yd, doubling ratio is 6:1. 2. If front roller rpm is 5000 and diameter is 40mm then what will be the delivery speed of this draw frame? 3. Find out the production/hr in kg of a draw frameif frontroller surfacespeed 650 m/min, drawn sliver wt. 75 gr/yd, efficiency 90%. 4. In a 4 over 3 drafting system, speed of back roller is 500, diameter of back roller is 35 mm and total draft8.45. If drawn sliver wt. is 75 gr/yd then what will be the production in kg/hr. let efficiency 90%. 5. Let, count of input sliver 72 gr/yd, doubling, total draft and front roller surface speed were set 8, 8.7 and 700 m/min respectively. Find out the production/day of this draw frame. (efficiency 88%). 6. Let, count of input sliver 70 gr/yd, doubling ratio 8:1, back draft 1.8, front draft 4.4, back roller rpm 500, diameter of back roller 30mm. find out the production/day of this draw frame. Assume efficiency 92%.