Roving Frame

 

 

 Roving frame

The roving frame is an intermediate machine between draw frame and ring frame the main objective of this machine is to convert sliver in to thinner sliver for the convenience of subsequent processes. The sliver we obtain from draw frame is still thicker sliver which is not good for yarn manufacture. So that the sliver  thickness or the yarn count is reduced by this machine to the required level. But in this operation main draw back is that the reduction is some what so high and cannot be obtained from roller drafting mechanisms. The solution for this is to reduce the yarn count in to a low level but not to the level required to the yarn manufacture which means the production of intermediate sliver which is called roving sliver. There are basic two reason which forces to the use of roving frame.

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 ring frames 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. Draw frame cans represent the worst conceivable mode of transport and  presentation of feed material to the ring spinning frame. The objectives of roving frame

1. Drafting the sliver in to a roving 2. Insert a twist in to the roving 3. Wind the roving in a bobbin Drafting

The drafting system used in this machine is four over four. This system improves the drafting and higher draft can be achieved. In this machine the drafting is very high than any of other machine. So that precautions are made to improve the draft. In the machine we can observe three drafting zones. Somehow after the drafting zone both material mechanical draft is required. 1. Break draft

In here the main objective of the break draft is to improve the fiber orientation instead of drafting itself in main draft the drafting operation take place. But for a

 

optimum draft the fiber orientation is very important factor. For achieve good draft fibers has to be straighten and parallel, this is done by break draft. 2. Main draft

Main draft is the drafting zone the real drafting is taken place. In here a draft in high magnitude is taken bars. place. For good fiber control many method s are used such as aprons pressure 3. Tension draft

The main objective of the tension draft is to maintain better and adequate tension to the sliver. In this zone actually the finer count for the roving frame is already achieved but after freeing from front roller nip twist has to be inserted for this it's important to keep good evenness throughout the sliver. In drafting we normally keep the front roller surface speed at a constant level  because during the winding process keeping that at a constant level improves the yarn quality and it helps to good control over roving sliver. In roving frame draft level often has its over and upper levels of drafting the drafting is done in between this limits if not each of the case tends to transfer high masses through the nips. So that the drafting resistance is high and difficult to get controlled draft. Always the break draft kept in low level because it only improves the evenness of the sliver. In this machine two condensers are used in the drafting arrangement. The purpose of these condensers is to bring the fiber strands together. It is difficult to control, Spread fiber masses in the drafting zone and they cause unevenness. In Addison, 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 fiber sliver. In main drafting zone aprons are used for further control of the drawing sliver. In the zone the number of fibers is less and they are given draft so that any floating fiber content would occur fabric defects and it has to be avoided. Further pressure is implemented on main drafting roller to improve the nip contact and higher nip. Since a high drafting is taken place the possibility to make slippages is somewhat high this is avoided and prevented to avoid long term variations in subsequent processes.

 

Cleaning is one another important aspect of drafting zone since high draft is given to the sliver short fibers can immune from the main flow of fibers and then may wind on rollers itself. If this process keep happening the drafting capability of the rollers are effected through how contact area and lose grip. So that tow aprons are used to clean reach and every roller during drafting. In this machine two top and  bottom cleaners are used. TORAL DRAFT = FRONT ROLLER SURFACE SPEED (RPM)/ BACK ROLLLER SURFACE SPEED (RPM) TOTAL DRAFT= INPUT MATERAL DENSITY/ OUT PUT MATERIAL DENSITY TOTAL DRAFT= INPUT MATERAIAL DENSITY/ OUTPUT MATERTAL DENSITY TOTAL DRAFT= 40 g/10m = 10 4 g/10m

TWISTING

Flyer inserts the twist to the sliver. The twist level is depended upon two factors they are flyer speed delivery speed The relationships between the twist and above factors are given below. TWIST = FLYER SPEED (RPM) / DLEIVERY SPEED (meters per min)

The insertion of the twist is done by the flyer when flyer rotates the twist in sliver  is put. Next end of the sliver is connected to the pressure finger and therefore next end of the yarn which is through fault twister has no choice than twisting around. 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 level of twist is somewhat very important is subsequent processes. The requirement of the twist in this level is that the roving sliver is quite thin as it cannot hold the fibers itself, this causes sliver breakages and small deformations and elongations in roving sliver may cause long term variations in ring frame. Therefore it's important that sliver has some strength to withstand deformation

 

forces and slacks during ring spinning. Even the unwinding in ring spinning machine also insert some tension on sliver the sliver tension must be adequate of  withstand to this forces But the excessive twist also influences the economics of the ring spinning machine. The twist has to be completely removed before the roving is taken to the main drafting zone of the ring fame. That means there should be a way of inserting higher breaking draft which is not that much god for the control of the system as well as the economics. 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 fiber 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. BOBBIN WINDING

In winding process there are several aspects has to be achieved. The buildup motion consists of several sub categories. To shift the spindle rail according to the diameter increase To reverse the trail motion direction at the top and bottom To shorten the lift length after each layer from tapered ends. The spindle diameter increases with the roving is being wound on the package tube. The rotating speed of the spindle has to be adjusting accordingly to reduce sliver breakages. Sliver breakages occur when the centrifugal force is increasing with the package diameter. 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 since the delivery speed is remaining as constant the only option is to speed down the spindle. If we reduce the delivery speed instead the economy of the machine goes down. This is undesirable and must be avoided. To differentiate the spindle speed according to the diameter special deferential mechanism is used. To form a package, the layer must be laid next to its neighbors. For that the lay-on  point must continually be moved. The shift of the winding point is affected 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. In bobbin winding three separate mechanisms are used to control the motions and there by achieve above objectives. 

Cone drum mechanism

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Reversing mechanism

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Buildup mechanism

DISCUSSION The operation of the speed frame is somewhat can be removed in staple yarn spinning process. We can understand this by looking at the objectives of the machine. After draw frame the slivers generated is parallel and can be used to  process yarns. But the problem is that the drawing action to convert draw frame sliver in to the yarn is difficult because high draft has to be inserted to the sliver. In conventional type roller drafting does not meet this level of success. Even though they can it's not economically viable. The basic problem occurs when a incident of high draft is that slippage and the weak control of the fibers. But using advance fiber controlling devices and using multiple roller systems there is a  possibility of achieving required higher draft. In multiple roller systems the draft can be distributed among different drafting zones in to a level of draft which is  possible with roller drafting. The material problems are another factor that influences the utilization of speed frame. Some staple fibers such as cotton has large verity of variations from one  batch to batch specially matured fiber content and short fiber content vary. If a sliver's made using this low quality raw materials many problems will occur even though high level of drafting can be achieved. Specially drafting waves will make long term variations. This effects can be avoided using critical carding conditions and thereby The draw frame sliver cans is a worst way to transform martial to other places and machines. These hardships are solved by using roving sliver packages which is small in size and other advantages. In industrial environment the mobility of   packages is very highly considered as a important aspect, because it has very high influence in economy of the factory. If draw frame sliver is wound on a package has convenience in transporting the slivers still there is a opportunity to remove speed frame in spinning machine line up.

 

Alternative definition 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. 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. Drawframe cans represent the worst conceivable mode of transport and  presentation of feed material to the ring spinning frame. TASKS OF ROVING FRAME: Attenuation- drafting the sliver into roving twisting the drafted strand 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 pakcage and flyer. There are two types of drafting systems. 3/3 drafting system 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(predarft) 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 addion, 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 rotaion 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 hool 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, ccentrifugal 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 arethe used on roller the flyers to add false twist when roving istwist, beingthe twisted between front and the flyer.Because of thisthe additional

 

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. 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: the length, fineness, and parallelisati parallelisation on of fibres the amount of twist and compactness of the roving the uniformity of twist and linear density. BUILDER MOTION: This device has to perform the following tasks to shift the belt according to the bobbin diameter increase to reverse the bobbin rail direction at top and bottom 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 layon 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 diamter is steadily increasing, 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.Revers change-over.Reversal al of the bobbin layer occurs little earlier for every reversal.This gives a conitnuous reduction in the lift of the rail . Thus bobbins are built with taper.