Need for roving frame:

In conventional ring spinning system, conversion of sliver into yarn through a single step has not succeeded

since the total draft needed is in the range 300-500 which is very difficult to apply on sliver in a single

step and obtain good quality yarn .

Draw frame cans represent the worst conceivable mode of transportation and method of feeding material to

the ring spinning frame as it occupies large space in comparision to the space of one spinning position of

ring spinning frame

Sliver is a thick, untwisted strand that will lead to more hairs and fly while converting it directly to yarn

when high draft is applied.

With ring spinning technology, the use of the roving frame is still remaining.

While using other newer spinning methods, the roving frame has been made as superfluous.

Disadvantages :

The system is lengthy with more number of machines.

Possibility of creating faults is more

Requires more space.

Advantages :

As compared to earlier method, the number of processes are less.

Possibility of creating faults is less

Requires less machines and space, hence less expensive

Objective of the roving frame :

Attenuation of the sliver

Protective twist insertion.

Winding the roving on a suitable package.

Conversion of sliver to roving

Operating Sequence in a roving frame:

Draw frame slivers presented to the roving frame is in large cans.

Driven transport rollers draw the slivers from the can and forward them to the drafting arrangement.

A draft of 5 to 20 is applied.

Protective twist in the range 30-65 turns per meter is imparted by a rotating flyer to provide

strength to the drafted stand of fibers in the unsupported zone.

The twisted stand passes through the flyer top and the hollow flyer leg, and is wrapped 2-3 times

around the pressure arm before being wound on the bobbin.

Winding is done as coils placed just next to each other. This needs continuous raising and lowering

of the bobbing rail which supports all the bobbins.

Introduction to roving operation :

Figure .2 shows schematic diagram of the cross section of a roving frame. Drawn slivers from the

draw frame section are fed through driven creel rollers to drafting arrangement from the sliver

can . This driven rollers guide the sliver to drafting arrangement which is at a considerable distance

from the cans. In order to avoid variation created in this passage, smooth and correct amount of drive

should be given to the rollers so that the slivers do not get stretched unduly. In the drafting system,

silver is converted into roving form by means of suitable draft. Mostly 3 over 3 drafting system is

used in the roving frame with break draft and finisher draft being applied in the first and second

zones of drafting. In the drafting system aprons are used to guide and transport the fibers during drafting

and they exert a very significant amount of control over the short fibre movement.

Figure 2. Side view of roving frame machine

Condensers used in the drafting system help to bring the fibre strand together again, since during drafting

fibres may tend to spread apart. Twist is inserted by means of flyer setup and the roving is wound onto

bobbin through pressure arm. The spindle is simply a support and drive element for the flyer

without any ancillary function. Bobbin rack moves up and down so that roving coils are placed

adjacent to each other on the surface of the bobbin.

Figure 3 Pattern of coil winding on roving bobbin

Figure.3 represents the pattern of winding coils on the roving bobbin. Roving ends are placed layer by

layer on the bobbin surface in such a manner that it will create tapered ends at top and bottom of the

bobbin. Pressure arm which is attached to lower end of hollow flyer leg assists in placing the coils.

The arm guides the roving from the exit of the flyer leg onto the package surface. The roving is

wrapped two (or) three times around the yoke and the number of turns determines the roving tension.

Figure 4 Packing of coils on bobbin surface

Figure.4 represents the placements of coils on bobbin surface. The coils should be just touching each

other and there should not be any space between the coils which will create problems in packing and

during unwinding. The angle of taper of the ends normally lies between 80° & 95°, depending upon

the count of the roving and adherence of the fibres. The angle is made as large as possible, so that

maximum roving is wound onto the package. However, angle must be small enough to ensure that the

layers do not slide apart.

CREEL:

Drawn slivers used in creel section, especially combed slivers have high degree of fibre parallelization

and low strand coherence. If these slivers are not handled properly in the creel section of the roving frame,

it will produce more mass variations in the roving because of uneven and uncontrolled stretching of the

slivers which is also called as ‘false draft’. In order to avoid this, following steps should be taken.

Sliver feed cans should be arranged in a simple manner so that the operator can access every can

easily, in case of sliver breakage, replacing empty cans and any other work in the feed creel section.

Slivers should be drawn vertically out of the cans. The relative placement of the cans and the guide

rollers should be such that the slivers are withdrawn vertically from the cans. If not, slivers will rub

against the edges of the cans leading to sliver damage and increased mass variation.

Guide rollers should run smoothly.

DRAFTING ARRANGEMENT

3/3 system with double apron is quite commonly used in roving frame.

Figure 1 : 3/3 Double Apron Drafting System

Figure.1 shows the placement of the top and bottom aprons in the drafting arrangement of roving

frame. Pressure is applied by top aprons on the lower aprons and the distance between them

decides the intensity of fibre clamping and fibre guidance. The apron arrangement must permit

precise adaptation of the minimum distance to the fibre volume. It is done by placing “spacers”

between the nose bar of the lower apron and the cradle edge of the top apron, i.e at the exit

opening M(Figure.2) .

Double apron enables draft up to 20 with proper fibre control during drafting.

Bottom rollers are fluted metallic rollers and the top rollers are rubber covered with hardness 800 to 850 shore.

(Top rollers over which aprons move have hardness slightly above 600 shore.)

Brake draft of 1.1 for cotton and slightly higher for synthetics (up to 1.3)

Aprons:

Figure 2 : Components of Double Apron Drafting System

Two types of aprons are used

Top aprons which is smaller

Bottom aprons which is larger

Both aprons are having thickness of 1mm.

Aprons cooperate with each other to guide and transport the fibres during drafting.

Aprons should extend as closely as possible to the nip line of the front rollers.

Cradle length must be adapted according to the fibre staple length.

Top roller loading:

100- 300 N load per roller is normally applied depending on raw material and volume of fibres.

Adjustment: steps or continuous.

Usually pneumatic weighting system is used.

Condensers:

'Infeed' condensers are mounted on a reciprocating bar.

Reciprocating movement helps to spread the wear over the whole width of the roller coating.

Condensers are provided in the break draft as well as main draft zones.

Presence of condensers reduces ‘hairiness’ of the rovings.

Spacers:

Spacers are used between top and bottom aprons to create space between them. The gap between the

top and bottom aprons at the front end decides the pressure existed on the fibres and the fibre control.

Flyers :

Components and structure of flyer :

s

Figure 3 : Components and structure of the flyer

The flyers are made of light alloys instead of steel.

Reduces the spread of legs ensures controlled bobbin build.

Reduces power consumption

Figure 3 represents the structure and components of the flyer used in roving frame. Flyer is doing a

major part that it has to lead the very sensitive strand from the flyer top to the package without

introducing the false drafts. Because,

Fiber strand has only protective twist and is very liable to break.

It is passing through flyer which is rotating more than 1500 rpm, so it should be protected

against air current.

To overcome this problem, one of the flyer legs (4) is usually hollow as shown in figure 3, with a deep

guide groove roving is passed. If guide groove is very smooth then occurrence of false draft is reduced.

However piecing of broken strands is very difficult

Various designs of flyers are

Spindle mounted flyer

Top mounted flyer

Closed flyer

Figure 4 shows schematic diagram of top mounted and closed flyer. In most of the industries, top

mounted flyer is used since it allows automation of the doffing operation. The flyer is supported at top

and driven by gear wheel running by toothed belts.

Closed flyers are mainly used for high speed operation. It also has advantages of reduced spreading of

the legs at high operating speeds.

Figure below represents the roving path geometry for flyers located in the front and back rows as in the

case of conventional roving machines. Bobbins placed in these front and back row spindles will the

following differences in the spinning conditions following variations.

The angle of approach of the roving to the flyer top is different for the two rows. This

will create different rolling conditions at the entry point of the roving to the flyer top.

Both rows of spindles will have different spinning triangles (Figure 6).

Difference in the unsupported lengths (L), i.e the lengths between the drafting

arrangement and the flyer top.

Difference also occurs in twisting of roving which leads to variation in fineness between

the front and rear ends.

The top mounted flyers also enable to have constant angle of wrap and similar spinning triangles for the

roving with the front delivery roller for both front and back rows of spindles. This is obtained by having

longer extension sections on top of the back row of spindles.

Flyer top

The passage of roving at the entry point of the flyer (Figure 8) determines the degree of

twist and the winding tension.

If the roving has only low twist or is coarse, so that there is a risk of false drafts the strand passes through the flyer top to

the guide groove without wrapping (A) [Figure (8)].

Earlier model flyers had smooth flyer tops made out of metal. But most modern flyers have

rubber insert formed with grooves, notches or indentations. These flyer inserts exert a strong

influence on the level of twist in the roving in the unsupported zone by introducing false twist.

This also has strong influence on winding conditions.

False twist

The additional false twist reduces the roving break in the Spinning.

Spinning triangle is reduced so that quality of roving is improved.

Fly and lap formation also reduced.

False twist enables compact rovings which increases the bobbin capacity and leads to

higher flyer speeds.

Spindle

It is simply a support and drive element for the flyer.

Mounted at its lower end in a bearing and the bobbin tube acts as neck bearing.

Flyer:

Leads the sensitive strand from the flyer top to the bobbin without introducing false draft

Guide groove

Guide tube

Guide groove – ‘service friendly’

Guide tube – ‘better protection of roving’s.

THE PRESSURE ARM

The pressure arm made up of steel yoke is attached to the lower end of the hollow flyer

leg.

It guides the roving from exit of the flyer leg to the package.

The roving is wrapped two (A) or three (B) times around the yoke.

No. of turns determines the roving tension and package hardness.

If this is high, then a hard, compact package is obtained. If it is too high, false drafts or

roving breaks may happen.

Number of turns depends upon the fibre type and twist level.

Spindle & flyer :

Turns / meter =

Flyer rotation(rpm)

----------------------------------

Delivery speed(m/min)

High twist level ----> Production loss

.......................------> Drafting problem in ring Spinning.

Low twist level -------> false drafts

....................................Roving break

Figure above shows the relationship between the TPI and count. As the count increases, in order to hold

the fibres, twist multiflier also increases, so that corresponding twist per inches also increases.

Builder Mechanism-

Builder Motion :

Builder motion is used to wind the roving in a parallel wound package with conical ends as shown in

Figure 1. The package is formed layer by layer. The lift of each layer is shortened by a small length which

decides the taper angle ‘α’.

Figure 1. Roving package Animation A1 Roving package formation

The rovings are wound in coils around the bare bobbin to start with. The winding of coils starts from the

bottom position determind by the position of the bobbin rail. As the bobbin rail moves up the coils are

wound upwards forming the first layer of rovings on the bare bobbin. After reaching the top position of

the lift for the first layer, the bobbin rail reverses the direction of movement and starts to move

downwards. Now the coils are placed downwards and second layer of roving are wound on the first

layer of rovings. This time the bobbin rail does not go all the way to the starting point of the first layer.

Instead, it returns and start to move upwards from a level just above the starting level of the first layer,

the difference in these levels is called as ‘shift’ (S). The third layer of roving is wound over the second

layer of rovings upwards. Again the bobbin rail does move all the way up to the starting level of the

second layer but returns from a level just lower by ‘S’ and starts forming the fourth layer. The distance

‘S’ decide the taper angle. Higher is S, smaller will be α.

The roving can be wound onto the bobbin using either Flyer lead method or Bobbin lead method.

Flyer Lead

Flyer surface speed is faster

Flyer winds the roving on the bobbins surface

Bobbins Lead

Bobbins surface speed is faster

Bobbins winds the roving onto itself

Advantages of Bobbins Lead

In case of roving break, the direction of roving on the bobbins provides stable outer layer

The drive to the spindle is shortest hence it starts faster than the bobbins.

This leads to more roving breaks in flyer lead while staring.

Figure 2 : Spindle speed and Bobbin speed for different Winding methods

In both the cases, the spindle speed remains constant through out the winding process, since changing the spindle

speed will change the twist density in the roving. The bobbin speed is changed according to the requirement.

Figure 2 shows the manner in which the bobbin speed has to be changed in case of bobbin lead and flyer lead

methods.

In both the cases, the roving delivery speed is constant decided by the surface speed of the front pair of drafting

rollers. But, as the bobbin builds up the diameter and the circumference of the bobbin increases. If the bobbin rotates

at a fixed speed, then the roving will get stretched more and more in case of bobbin lead method since the bobbin is

leading and winding the roving on to itself as the winding proceeds; the roving will get slackened more and more

in case of flyer lead method as in this case the flyer is leading and winding the roving onto the bobbin. The difference

between the peripherals speeds of the flyer and the bobbins needs to be kept constant for proper winding.

Hence, in case of bobbin lead method the bobbin speed has to be gradually decreased and in the case of flyer lead

the bobbin speed has to be gradually increased in order to keep the roving tension constant while winding the rovings

on the bobbin.

For cotton system, because of the advantages of bobbin lead method and the difficulties associated with flyer lead

method, the bobbin lead method is always used.

REQUIREMENTS FOR BOBBIN BUILDING :

Based on the above discussions, in order to have proper winding of the rovings on the bobbins, the following

requirements should be met:

The rotational rate of the bobbin should be reduced for layer formation

Shorten the lift after each layer to form tapered ends on the bobbin

Reverse the direction of movement of the bobbin rail after each layer formation

The speed of the movement of the bobbin rail should be reduced after formation of every layer, as it will take

more time to lay one coil as the bobbin builds up.

Drive system in Roviing Frame :

Figure 3 : Typical drive system in a roving frame

The main shaft received the drive from the motor and rotates at a constant speed. It provides the

constant drive to the differential gear assembly, top cone, drafting system and the spindle as shown in

Figure 3. The bobbin rails gets it motion directly from the bottom cone drum. The bobbins get their drive

from the output of the differential drive which combines the fixed speed from the main shaft and the

variable speed from the bottom cone drum. The operating principles of cone drums and the differential

drive are explained below.

Cone drive transmission :

The reduction in the rotational rate of the bobbin and the reduction in the speed of movement of

bobbin rail are obtained with a cone drive mechanism. In this mechanism, shown in Figure 4 there are

two cone drums out of which the top cone drum receive a constant rate of rotation from the motor.

Depending up on the position of the drive belt between them, the speed of the bottom cone drum

changes. Hence, at any given position of the belt the sum of diameter of the top cone drum (d1) and

diameter of the bottom cone drum (d2) should be a constant.

Cone Profile

-Variation in bobbins rotation rate occurs in small steps owing to shifting of the cone belt after each lift

stroke.

Figure : 4 Cone belts shifting mechanism

-The bobbins winding speed reduces in a hyperbolic fashion as the bobbins building up. If the shifting

of belt is constant for each lift stoke then the cone profile should be

(i) Convex for top (driving cone)

(ii) Concave for bottom (driven cone)

Top cone drum rotates at fixed speed of U1 rpm. Speed of bottom cone drum depents upon D1 and

D2 which depend on L.

Moving belt in direction X increases U2

Moving belt in direction Y increases U2

Figure 5 : Differential gearbox mechanism

Figure 5 represents speed of flyer and wind-on speed with differential gear box. Over the cone pulleys

belts are shifted, due to which differential speed is obtained from differential gear box as U output = U1≠

U2 rpm.

Figure 6 : Principle of winding on roving bobbin

Winding Speed profile

Let us take the following parameters and calculate the winding speed for different bobbin diameters

and plot it.

Bare bobbin dia=50mm Spindle speed=1000 rpm

Roving =1.2 mm TPI =1.68

Delivery = 15 m.min

Figure 7 : Effect of bobbin diameter on winding speed

Figure 7 represents relationship between winding speed and bobbin diameter. As the diameter of the

package increases, winding speed is decreases to maintain the same same winding rate.

BOBBIN DRIVE

The continuously reducing rotational rate from the bottom cone drum is combined with the constant

speed of main shaft using a differential mechanism. The output of the differential gear mechanism is

provided to the bobbins which are housed in the bobbin rail which is moving up and down. Since the

bobbin rail is moving up and down, there is a need for a flexible drive. One example of such drive

known as knee swinging joint is shown in Figure 1.

Figure 1 : Swinging knee joint at the bobbin drive shaft

The swinging knee joint method causes additional revolutions that are either added or subtracted from

the basic package rotation, depending on the direction of the lift stroke. This leads to tension variation.

On the bobbin rail, bevel / helical gears fixed on the longitudinal shaft drive the bevel / helical gears of

the bobbin support.

The other method is to use chain and sprocket with suitable mechanism to adjust the varying tension in

the chain because of the movement of the bobbin rail.

Cone drum types and belt shifting:

The cone drums can be of two types. In first type which is conventional one, a pair of convex and concave

cone drums are used and in second type a pair of cone drums having straight surface is used. In the first

type, the belt is moved a constant length every time to get the required speed profile for the bobbin. In

the second case, the belt is shifted through different lengths through out the bobbin build up.

Figure 2 : Shifting the belt with hyperbolic and straight sided cones

Hyperbolic cones are difficult to design (Figure 2).

During the winding operation the belt is moved on surface of varying inclination.

To-day the cones are made straight sided. The belt is shifted through varying magnitude.

Shifting of the Belt:

Shifting of belt is under the control of ratchet wheel, which is permitted to rotate by half tooth for

each lift stroke

This half tooth movement is transferred to the cone drum belt through gear train, changes gear and

wire rope.

The bobbin diameter increases depending on the roving hank the change wheel ‘Tension change wheel’

is provided in the gear train to accommodate the changes in the roving hank.

Shifting and Shorting of cone belt :

Metal brackets (3/7) and rods (5/6) induce all changes for the bobbin building mechanism.

Figure 3 : The reversing gears of the lifter motion

The mechanism is fixed to the bobbin rail and raised and lowered as a unit.

Striking of a stationary pin by rods (5/6) makes the micro switch to emit a pulse, which permits

the ratchet wheel to rotate by ½ tooth (Figure 3).

Correction Rail:

Useful when the required bobbin speeds are not attained by changing the change wheel only.

Normal position of this rail is parallel to belt guide.

If this rail inclination is more steep, the extension of the wire rope is not completely transferred to

the belt guide. Shifting of the belt taken place through smaller steps than those corresponding

directly to paging out of the rope in the builder motion.

Reverse effect if the rail inclination is made less steep

Figure 4 : Reversing mechanism for bobbin rail movement

From Figure 4, reversal of the rail movement originates from the reversing gear (1/2/3).

An electrically operated valve pressurizes the left and right chambers of the double acting cylinders

alternatively.

So that, the left hand clutch (1) and right hand clutch (2) are operated successively so that the

pinion (3) is meshed either with gear wheel 1 (or) gear wheel 2.

The shaft 10, on which gear wheels 1 & 2 are mounted, always rotates in the same direction.

Accordingly, operation of clutch (1) or (2) causes left or right hand rotation of the pinion 3 and

shaft 4. The bobbin rail is correspondingly raised or lowered via the bevel gear 5, pinion 6,

sprocket 7 and lifting chain 8.

Cone drum change wheel: If the diameter of the tube is altered. The starting speed of the bobbin

must be adapted correspondingly. Since the ratchet wheel has not been operated at this stage, the

adaptation cannot be performed by way of the builder motion.

Ratchet change wheel determines the amount by which the belt is shifted upon each operation of

the ratchet and therefore must be adapted precisely to increase in the bobbin diameter.

LIFTER MOTION

Bobbin are raised and lowered to place the coils placed next to each other.

Lifter motion work with levers or with racks.

To compensate for the increase in bobbin diameter the lift speed is reduced after each lift stroke.

Drive to the bobbin rail is provided from driven cone drum, but not through the differential gear

mechanism.

Figure 5 : Lifter motion with levers

Figure 6 : Lifter motion with racks

Lifter motion is used to wind the roving on the package layer by layer i.e placing new coils near to

neighboring layers by moving bobbin package up and down, so that winding point is continuously

varied.

The required raising and lowering can be carried out by means of several racks secured to the rail

(Figure 6).

However several manufactures mount the bobbin rail on a lever and move the rail by an up and

down movement of that lever (Figure 5).

As diameter increases, lift speed must be reduced by a small amount after each completed layer.

Developments in roving frames-

The speed frame is the machine that has gone least change. This can be realised from the fact

that a spindle speed of 1,500 rpm as on date as compared to 600 rpm in 1950s. Still there are

certain changes that have been carried out for better production and quality like, increase in the

roving bobbin diameter from 4" to 7" and lift from 8" to 16", use of straight cone drum instead of

hyperbolic cone drum for better control over the roving tension etc. Now all closed (AC Type)

flyers are used to overcome the problem of air drag on roving.

These flyers are aerodynamically balanced and are of light weight. The roving frames are

equipped with auto doffing system that, apart from avoiding manual handling, reduces doffing

time. Roving bobbins auto doffing and transportation, to the ring spinning through over head

rails, becomes a standard feature of the roving frame. Apart from above, some of the

developments those are really significant will be discussed in subsequent sections.

Equal roving geometry for front and back row roving

Deposition of roving spindles in two rows leads to variation in roving twist and count in front

and back row due to different level of twist attained by roving in front and back row. This is

due to change in roving path geometry . Modern speed frames have raised flyer top of the

back row as compared to the front row to maintain the roving delivery angle. Rieter F15/F35

roving frame, Zinser 668 roving frame, Marzoli FTN roving frame and Lakshmi LFS 1660

speed frame incorporate this development in their machines.

Drive System

Main drive changed from loose/fast pulley system to centrifugal clutches.

To reduce noise and vibrations spur gears are replaced with helical gears with thrust

bearings.(smooth & gradual engagement of teeth)

For same speed reduction ratio helical gears are smaller in size – less pitch line velocity of

gears.

Self-aligning ball bearings for top drafting rollers and use of needle bearings for bottom

drafting rollers.

Replacement of bush bearings by ball bearing for creel rollers and gear shafts.

Latest trend is to use timing belts:

Greater flexibility in location of elements.

Power transmission efficiency as good as gears.

Less power consumption and noise compared to gears.

Simple drive system.

Less maintenance.

Individual motor drive

In multi-motor drive system, drafting rollers, flyers, bobbins and bobbin rail are driven

directly by individual servomotors and are synchronised throughout package build by the

control system. The advantages of this system are like, no need of heavy counter weight for

bobbin rail balancing and differential gear, reduced maintenance, lower energy consumption,

etc. All machine manufacturers incorporate four-motor-drive system except Toyota that uses

three servomotors on FL100 roving frame. One motor for drafting system and flyer while one

motor each for bobbin drive and bobbin rail.

Figure 1 : Schematic of the multi-motor drive system.

Microprocessor controlled Building Mechanism

Technological parameters like length of roving in first layer, taper angle, no of layers,

count, type fibers- are fed to the control panel.

Bobbin speed and Bobbin rail position are sensed by electronic sensors.

Tapering, rail movement etc. are controlled by Computer.

Operator is lead by operating menus and has all important information all the time.

Adjustments can be stored, and transferred to other machines.

Roving tension sensors Roving tension sensors measure and control the roving tension (constant) through out the bobbin build. These tension sensors do not actually contact the roving while measuring the tension. The tension is measured at periodic intervals and the required change in tension is actuated by changing the bobbin speed through servomotor. Rieter F15/F35 roving frame, Zinser 668 roving frame, Marzoli FTN roving frame, Lakshmi LFS 1660 speed frame and Toyota FL100 roving frame have incorporated roving tension sensor on their machines. Figure 2 shows the roving tension sensor used in Rieter roving frame.

Figure 2 : Roving Tension sensor (Rieter F15/F35 roving frame)

Luwa Pneumastop

Pneumatic suction system in delivery of drafting system

To avoid series of roving breaks

Suction system draws the drafted strand into a large collector duct, extended in full m/c length

Suction system draws the drafted strand into a large collector duct, extended in full m/c length

Change in capacitance generates a signal to stop the m/c.

Sr.No. Defects Remedies

1. Roving

tension

Roving tension is directly related to machine. The roving tension depends

upon delivery rate and the difference between flyer speed and bobbin. For

preventive action we should keep the delivery length and the speed

difference constant then the tension in this case will be ideal.

2. Improper

handling of

material

Roving material is very sensitive regarding to quality point of view.

It is necessary to take care of material. The material should be

handled in such a way that fine dust must not affect the material. It

must be avoided touching because of its sensitivity. Fresh material

should be used for next process. This material should not be keep for

long time. If it will be kept for long time then it will create variation.

C.V% increases if material is not used .

Supervisor must treat its worker in a proper way so that handling of

material should be according to policy of mill.

3. Improper

piecing in

roving

Supervisor should train his workers in a proper way. If end breakage is

disturbed then its treatment should be proper. If piecing will not be proper

then it will affect the next process.

4. Roving

breakage

This problem is caused due to maintenance problem. Maintenance required

machine stoppage but it is against the production. To enhance the quality of

product, the machine maintenance is the chief requirement. For the proper

solution of roving breakage, speed of machine, trained operator and proper

management should be must otherwise it create severe problems in ring

section.