Roving Machine Is Complicated, Liable to Faults, Causes Defects, Adds to Production Costs

SPEED FRAME

INTRODUCTION

Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. This machine is forced to use by the spinner for the following two reasons. 1. Sliver is thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this is around 300 to 500. Drafting arrangements of ringframes are not capable of processing this strand in a single drafting operation to create a yarn that meets all the normal demands on such yarns.

2. Drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame.

OPERATIONS OF SPEED FRAME 1. Attenuation- drafting the sliver into roving 2. Twisting the drafted strand 3. Winding the twisted roving on a bobbin  Fibre to fibre cohesion is less for combed slivers. Rollers in the creel can easily create false drafts. Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance. Therefore, a perfect drive to the creel rollers is very important.

 The drafting arrangement drafts the material with a draft between 5 and 15. The delivered strand is too thin to hold itself together at the exit of the front bottom roller.

 Bobbin and flyer are driven separately, so that winding of the twisted strand is carried out by running the bobbin at a higher peripheral speed than the flyer.

 The bobbin rail is moving up and down continuously, so that the coils must be wound closely and parallel to one another to ensure that as much as material is wound on the bobbin.

 Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after each completed layer.

 Length delivered by the front roller is always constant. Owing to the increase in the diameter of the package for every up and down movement, the peripheral speed of package should keep on changing , to maintain the same difference in peripheral speeds between package and flyer.

 There are two types of drafting systems. 1) 3/3 drafting system 2) 4/4 drafting system  In general 3/3 drafting system is used, but for higher draft applications 4/4 drafting system is used.

 The draft often has limits not only at the upper limit (15 to 20), but also at lower limit. It is around 5 for cotton and 6 for synthetic fibres. If drafts below these lower limits are attempted, then the fibre masses to be moved are too large, the drafting resistance becomes too high and the drafting operation is difficult to control.

 It is advisable to keep the break draft (predraft) as low as possible, because lower breakdraft always improves roving evenness.

 In general two condensers are used in the drafting arrangement. The purpose of this condensers is to bring the fibre strands together. It is difficult to control, Spread fibre masses in the drafting zone and they cause unevenness. In addition, a widely spread strand leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving. The size of condensers should be selected according to the volume of the fibre sliver.

 Flyer inserts twist. Each flyer rotation creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate.

Turns per metre = (flyer rpm)/(delivery speed (m/min)

Higher levels of roving twist, therefore, always represent production losses in Roving frame and possible draft problems in the ring spinning machine. But very low twist levels will cause false drafts and roving breaks in the roving frame.

 Centrifugal tension is created at the bobbin surface as the layers are being wound and is created by the rotation of the package. Each coil of roving can be considered as a high-speed rotating hook of roving on which centrifugal tension increases with increasing diameter of the package. centrifugal tension in the roving is proportional to the square of the winding surface velocity.

 In this context, centrifugal force acts in such a manner as to lift the top roving strand from the surface of the package so that the radial forces within the strand that hold the fibres together are reduced and the roving can be stressed to the point of rupture. Breaks of this type may occur at the winding-on Point of the presser or in strands that have just been wound on the top surface of the package.

 This phenomenon is known as "bobbin-bursting". This phenomenon will be prominent if the twist per inch is less or the spindle speed is extremely high when the bobbin is big.

 Apart from inserting twist, the flyer has to lead the very sensitive strand from the flyer top to the package without introducing false drafts. Latest flyers have a very smooth guide tube set into one flyer leg and the other flyer leg serves to balance the flyer.  The strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in the previous designs. Frictional resistance is considerably reduced, so that the strand can be pulled through with much less force.

 False twisters are used on the flyers to add false twist when the roving is being twisted between the front roller and the flyer. Because of this additional twist, the roving is strongly twisted and this reduces the breakage rate. Spinning triangle is also reduced which will reduce the fibre fly and lap formation on the front bottom roller.

 Because of the false twister, the roving becomes compact which helps to increase the length wound on the bobbin. This compactness helps to increase the flyer speed also.

 Roving strength is a major factor in determining winding limitations. It must be high enough for the fibres to hold together in a cohesive strand and low enough for satisfactory drafting at the spinning machine. The factors affecting roving strength are as follows: 1) The length, fineness, and parallelisation of fibres 2) The amount of twist and compactness of the roving 3) The uniformity of twist and linear density.

BUILDER MOTION

This device has to perform the following tasks : 1) To shift the belt according to the bobbin diameter increase 2) To reverse the bobbin rail direction at top and bottom 3) To shorten the lift after each layer to form tapered ends

 Shifting of the belt is under the control of the ratchet wheel. The ratchet wheel is permitted to rotate by a half tooth. The bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. The amount of shifting, which depends upon the thickness of the roving, is modified by replacement of the ratchet wheel or by other gears. If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it moves more rapidly, and vice versa.

 To form a package, the layer must be laid next to its neighbours. For that the lay- on point must continually be moved. The shift of the winding point is effected by moving the bobbin rail. This raising and lowering is done by rails. Since the package diameter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer.

 During winding of a package, the ratchet is rotated at every change over. Reversal of the bobbin layer occurs little earlier for every reversal. This gives a continuous reduction in the lift of the rail . Thus bobbins are built with taper.

PROCESS PARAMETERS IN SPEED FRAME Introduction Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. The following parameters are very important in SPEED FRAME. They are: 1. Feed hank 2. Delivery hank 3. Roving tension 4. Break draft 5. Drafting system 6. Bottom roller setting 7. Top roller setting 8. Condensers and spacers 9. Twist in the roving 10. Bobbin content 11. Flyer speed 12. Creel and creel draft 13. Drawframe sliver and can 14. Bobbin height 15. Breakage rate 16. Piecings

Drafting System

 Since modern Ringframes are capable of handling higher drafts in ringframe without quality deterioration. It is better to have coarser hanks in the speed frame.

 This helps to increase the production in speed frame. Investment cost will also be less, because the number of speedframes required will be less and the cost per machine is also high.

The following table can be a guide line for speed frame delivery hank.

Material Yarn Count Hank Total Draft Cotton combed 36s to 40s 1.2 10 Cotton combed 24s to 30s 1.0 10 Cotton combed 14s to 24s 0.7 to 0.8 9 Cotton karded 36s to 40s 1.3 9 Cotton karded 24s to 36s 1.1 8 Poly/cotton 36s to 45s 1.2 11 Poly/cotton 24s to 36s 1.0 10 Poly/viscose 36s to 40s 1.0 11 Poly/viscose 24s to 36s 0.85 10 Poly/viscose 16s to 20s 0.7 8 The above said details are for producing a good quality yarn. This is suitable for 4 over 4 drafting system with front zone as a condensing zone without a draft.  With 4 over 4 drafting system, the toal draft can be upto 13, whereas in the case of 3 over 3 drafting system , the draft can not be more than 11.

 The Roving thickness and Roving hairiness (yarn hairiness) will be less with 4 over 4 drafting system compared to 3 over 3 drafting system.

 In 4 over 4 drafting system, since the fully drafted material is just condensed in the front zone, if the stickiness in case of cotton or static in case of synthetic is high, then the lapping tendency will be very high on second top roller or second bottom roller. But in case of front roller, since the twist is penetrating upto the nip, lapping on the front bottom or top roller will be less.

 As long as stickiness, honey dew in cotton and static in synthetic fibres is less, 4 over 4 drafting system with front zone as condensing zone, will give better results upto even 51 mm fibre. Of course the humidity conditions should be good.

 4 over 4 drafting system can be described as follows; 1. Bottom roller diameter is 28.5 mm 2. Top roller diameter is 28 mm 3. Break draft is between 4th roller and 3rd roller 4. Main draft is between 3rd roller and 2nd roller 5. Bottom apron is run by a 3rd roller 6. Between front roller and 2nd roller is a condensing zone 7. front zone setting 35 mm (even for 51 mm fibre) 8. Main draft zone setting is 48 mm 9. Back zone setting depends on break draft, but it is normally 50 mm for cotton and T/c and 55 mm for synthetic fibres(44 to 51mm)

 3 over 3 drafting system is good for fibres longer than 51 mm. 30 or 32 mm bottom roller diameters will be used with this system.

 Feed hank depends upon the total draft in speed frame. The drafts mentioned in the above table can be considered as a guide line.

 While processing 51 mm synthetic fibres, if the delivery hank is coarser, and the delivery speed is very high, the break draft and the back zone setting to be widened. Break draft and break draft setting does not depend only on T.M and fibre properties, it depends on the total production also. If the total production is very high, with low break draft and closer setting, roving breaks due to undrafted strand will increase.

 Therefore, for very high production rate , higher break draft and wider break draft setting is required. This will result in very high "H" and "I" classimat faults (long thin faults). Therefore the breakage rate in spinning will increase.

 Break draft setting and break draft should be nominal. Abnormal break drafts and wider break draft settings indicate that there is a major problem in the process.

 Some times draw frame coiling is a very big problem with synthetic fibres . If kinks are formed in the sliver, the kink has to be removed before entering the draft zone.

 Kinks in the drawframe sliver depends upon; 1. Drawframe delivery speed 2. Delivery can diameter 3. Coiler type

 Higher the delivery speed, more the chances for kinks to be formed in the sliver. Lower the can diameter more the kinks. If a coiler which is meant for cotton is used, the kinks in the sliver will increase in case of synthetic fibres.

 While processing synthetic fibres if kinks are more, it would be better if the creel is stopped. Sometimes it would be recommended to use a rod between top arm and the first creel roll, so that the sliver takes a 90 degree bend before entering the top arm. This will help to remove the the kinks in the sliver.

 Otherwise, slubs in the roving will be more and the breakage rate in speed frame due to undrafted strand in the drafting zone will be more. Roving Tension  The roving tension depends on the delivery rate and the difference between peripheral speeds of flyer and the bobbin.

 If the delivery length and the peripheral speed difference are same, then the tension is ideal. If delivered length is more than the difference in peripheral speed, then the roving tension will be loose. If the delivered length by the front bottom roller is less than the difference in pheripheral speeds of flyer and the bobbin, the roving tension will be tight.

 Roving tension can be of three types; 1. Roving tension at the starting. It depends upon the Bare bobbin diameter and the Cone drum belt position. 2. Roving tension during build-up. It depends upon the Ratchet wheel and lifter wheel. The difference between peripheral speeds of flyer and bobbin should be same and it should be slightly more than the length delivered by the front roller. 3. Roving tension during up and down movement of the bobbin rail should be same. It depends upon the half tooth movement of the ratchet. If it is not exactly half tooth, then the tension will be different during up and down movement of the bobbin rail 4. With modern machines, cone drum is removed. Bobbin speed, bobbin rail speed and flyer speed is determined by the computer depending upon the tension settings. In some machines, it can be programmed and the tension sensor helps to control a bit. In some makes, the tension setting totally depends upon the sensing by sensors. The sensing accuracy depends upon the twist cap type, twist cape fixing, oil on top of twist cap etc. If only one roving tension is different due to various other reasons, then the entire machine tension will be altered. This is very dangerous. Enough care should be taken to avoid this problem. 5. If lifter wheel is changed, then tension during build up will also change, the ratchet has to be selected accordingly. For a particular roving hank, ratchet wheel depends on Lifter wheel also. 6. If the tension is low but uniform through out the bobbin, then the bobbin will be soft. Bobbin content will also be less. Chances of roving damages will be high. 7. If the roving tension is more, then the stretch on the roving will be more, thin places will be more. But it is better to increase the TPI little bit and increase the roving tension so that the bobbin content is more, roving damages are less, and creel stretch in the ring frame will also be less, because of higher TPI in the roving. Other Important Points in Speed-frame

 It is better to adopt group creeling in speed frame. Because every piecing of sliver will result in a thin and thick place. Therefore it is preferable to change 30 upto 60 cans together and remove the sliver piecing from the roving.

 Care should be taken so that no sliver piecing and roving piecing enters the ringframe and results in yarn. This yarn always results in thin and thick places from .6 to 2 meters length. This will not be cut by the yarn clearers if the difference in size is less.

 Roving Breaks in speed frame should not be more 1 to 2 per 100 spindle hours. If it is more than that, the reasons should be analysed and corrective action should be taken immediately.

 Spacers should be as small as possible, to improve yarn quality. If slubs and roving breaks due to undrafted is more, it would be better to use a bigger spacer(distance clip) instead of increasing the break draft and break draft zone setting to an abnormal level.

 It is better to use good quality apron and rubber cots , since the quantity produced by one apron and top roller is very high compared to ringframe. If the apron breaks and top roller damages are under control, It is always better to use the best apron and rubber cots available in the market. One should not think about cost saving in this machine. Cost saving for apron and cots can be considered for ring frames.

 Buffing should be done once in 3 months and the top roller shore hardness is around 80 to 85 degrees. After buffing, it is better to treat with acid or some special liquids which are being supplied to reduce lapping.

 Bottom and top clearers should rotate and should touch the top and bottom roller properly.  While processing cotton combed material, flyer speed is very critical. When the bobbin diameter is big, because of the centrifugal tension, surfact cuts will increase. i.e. roving breaks may occur at presser or in strand that have just been wound on the top surface of the package.

 To avoid this problem, it is better to use inverter drive system, to reduce the flyer speed, when the bobbin diameter is big. Otherwise the overall speed should be less for the entire doff, this will reduce the production of speed frame. Sometimes, higher Twist will also reduce the surface cuts.