Thursday, September 10, 2009
At simplex, drawn slivers are converted into roving form. The roving differs from sliver in wt/length, twist and storage form. As compared to sliver, wt/l of roving is less, twist is more and unlike sliver it is stored in package form. Coarse count yarn 2.5-5 can be obtained from simplex and can not be spun on ring frame. This yarn is used for carpet manufacturing. So we can say that yarn production starts from simplex machine.
The roving frame is an intermediate machine between draw frame and ring frame the main objective of this machine is to convert sliver into 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 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 into 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.
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. “Simplex is a necessary evil”, even than 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/OBJECTIVES OF ROVING FRAME:
Attenuation- drafting the sliver into roving
twisting the drafted strand
3. winding the twisted roving on a bobbin
4. package building
PARTS OF SIMPLEX &THEIR FUNCTIONS
Bottom steel fluted rollers
Top & bottom cleaners
9. Bobbin Rail
1. BOTTOM STEEL FLUTED ROLLERS:
ü The bottom rollers are made of steel and are mounted in roller stand.
ü These are positively driven from the main gear transmission.
ü For better carrying of the material in forward direction, these rollers are fluted.
i. Axial fluted
ii. Spiral/inclined fluted
iii. knurled fluted
ü Nowadays axial flutes are replaced by inclined flutes which result in better grippage of fibers as well as less wears of top rollers.
ü Knurled flutings are on those rollers on which apron revolves.
ü There are two parts of top rollers,
a. Arber (top rollers without rubber cot)
b. Rubber cot
ü These are actually twin rollers having rubber cots for better grippage of fibers during drafting.
ü Hardness of top rollers depends upon the type of material. Normally for cotton, less hardness is recommended as compared to polyester fiber.
ü For polyester more hardness is better to avoid wear of the top rollers.(Rollers are replaced after 15-20 years)
ü For better grippage, these rollers are grinded after certain period.
ü So with the passage of time, diameter of these rollers will be reduced and behind the limits, these can’t be used. Hence old cots are replaced by new cots
ü With the result of reduction of top roller diameter, arm pressure will be reduced which will result in less/undrafted material.
ü With the result of grinding, surface of top rollers become rough. Hence on processing of sensitive fibers, rough roller surface result in wrapping effect. To overcome this problem a chemical treatment is required which will smooth the surface.
ü The upper aprons are short and made of synthetic rubber. The thickness of apron is about 1mm.
ü Lower aprons are larger and made of same material as that of uppers.
ü Aprons are used to support the material which is being drafted and ultimately to reduce the variation in the material i.e. material will be uneven.
ü When a drafting force is applied, there is a chance of variation. So to reduce this variation, aprons are provided.
ü 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.
4. PRESSURE ARM:
ü 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.
ü The top rollers are well pressed on bottom rollers by applying pressure through pressure arm.
ü Pressure depends upon raw material and volume.
ü Adjustment of pressure may be same for each roller or vary from zone to zone (Main, back or front zone).
ü In pressure arm springs are used and somewhere pneumatic pressure is given.
ü By applying more pressure, there are chances of fiber damaging while less pressure cause slippage, which will increase U%age of roving.
ü In cotton material, more the moisture content more will be the arm pressure required. More moisture content in slier is due to,
· More moisture content in cotton (8.9).
· More R.H% (58-63).
5. CRADLE ASSEMBLY:
ü It consists of
ii. Top apron
iii. Steal roller
v. Cradle spring
ü It supports the material during drafting and reduces the variation due to drafting force.
ü Spacer size change the distance between the aprons (bottom &top). For coarse material, bigger size spacer is used.
ü Change of spacer size affect the U%age.
ü Flyer is used to wind the roving on bobbin and to impart twist into the roving by revolving around the bobbin at a speed 700-1300 rpm.
ü Flyer inserts twist. Each flyer rotation creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate.
ü Turns per metre (twist) =
ü 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.
ü 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.
ü 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.
ü 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.
ü If we use high precision flyers, it will result in the form of following advantages:
i. Dynamic flyers ensure excellent yarn quality and free from fluff accumulation and fibre chocking.
ii. Flyers are made from quality aluminum alloy, polished stainless steel tubes and steel parts.
iii. Computer generated aerodynamic profile ensures minimum air turbulence and noise.
iv. To facilitate well twisted roving false twisters are specially designed and manufactured.
v. Minimum vibrations in flyer are kept by high precision balancing at all rated speeds.
vi. To maintain constant pressure, Pressers are made of heat treated special grade steel.
vii. Higher return on investment on flyers.
ü In Simplex machine two condensers are used in the drafting arrangement.
ü The purpose of these condensers is to bring the fiber strands together.
ü It is difficult to control, Spread fiber masses in the drafting zone and they cause unevenness.
ü In Addition, a widely spread strands leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving.
ü The size of condensers should be selected according to the volume of the fiber sliver.
8. TOP AND BOTTOM CLEANERS
ü 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.
ü If this process keep happening the drafting capability of the rollers are effected through contact area and lose grip.
ü Hence tow aprons are used to clean each and every roller during drafting. In this machine two top and bottom cleaners are also used for the cleaning purpose.
9. BOBBIN RAIL
ü 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.
ü Since the diameter of the packages increases with each layer, the length of the roving per coilalso will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after each completed layer.
"A continuous slightly twisted strand of fibers (sliver) is known as roving." The objective of roving is to reduce the sliver in a suitable size for spinning. It is winded on bobbin which is fitted at the top of the bobbin gear. Different size of roving is winded on different color bobbin.
The term hank is very extensively used in connection with roving. "Hank roving is number of hanks in one pound weight and one hank in one pound at length 840 yard". Let one pound roving have 756 yards then hank roving will be, H.R=756/840=0.9. Range of hank roving is 0.4 to 3.0.
Spinning mill where drafting in ring is PK255, there hank roving are coarser and where drafting is PK225 the hank roving will be finer. Drafting system on simplex is SKF-PK1500.
HANK ROVING DECISION:
Hank roving decision factors are,
1. Simplex machine limits: Draft range of simplex is 4-12
2. Sliver grains: As sliver grain increases, coarser will be hank roving.
3. Count required to spun: Coarser count require coarser hank roving and vice versa.
4. Drafting system at ring: Range of draft at ring.
5. Simplex production: Balance production means if ring's required bags are 60 then simplex must
produce 62 bags.
6. Actual efficiency of machine: 85% to 88% should be our simplex production efficiency.
Drafting is “the reduction of weight per unit length” of sliver. Amount of draft applied depends upon the required count of roving. The basic principle of drafting is the difference of surface speeds between the front and back pair of rollers. Due to drafting on simplex, fibers are straighten, compact and parallel to each other.
The drafting zone is inclined at an angle of 150 due to which fibers pass freely from drafting zone towards the simplex bobbin. This prevents the breakage of roving being formed. The drafting range on simplex is 5-20.
The speed of drafting rollers on simplex is slower than that of drawing frame as there is a chance of breakage of roving at high speed. 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.
The drafting system used in this machine is 4/4. 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.
i. Back zone (break draft)
ii. Main zone (major/main draft)
iii. Front zone (tension draft)
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 an optimum draft the fiber orientation is very important factor. To achieve good draft fibers has to be straightened and parallel, this is done by break draft.
In roving frame, draft level often has its over and upper levels/limits of drafting. The drafting is done in between this limits, if not, each of the case tends to transfer high masses through the nips. Always the break draft kept in low level because it only improves the evenness of the sliver.
Break draft depends upon,
AFFECT ON B.D
Volume of the material
More volume of the material requires more preparation of the material and more will be the break draft
Type of the material
i.e. cotton, polyester, PC, PV etc.
More the moisture content more will be the break draft and vice versa.
If rollers are close then we apply more break draft.
More the length of fiber more will be the break draft and vice versa.
If PC blends are, 65:35 & 52:48 then in 65:35 we apply more B.D.
In PV break draft is more as compared to PC.
Approximate draft ranges are
Break draft (back zone)
1.13 to 1.35
Main draft (main zone)
5 to 9
Tension draft (front zone)
1.01 to 1.02
Sliver g/y =65
Hank roving = 9
Total draft = 10
1.20*8.16*1.018 =10 Or 1.25*8.0*1.018 = 10 Or 1.28*7.9*1.018 =10
Main draft is the drafting zone the real drafting is taken place. In here a draft in high magnitude is taken place. For good fiber control many methods are used such as aprons, pressure bars etc.
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.
Total Draft = = (Break draft) × (major draft) × (tension draft)
Total Draft =
e.g. Total Draft = = 4
We can achieve our objectives by applying draft in different zones as per requirement. It is very important factor which contribute a vital role in controlling the variation.
In back zone, draft is applied only for the preparation of strand i.e. sliver or roving to be drafted. However if break draft is in access, then U% will be more and if tit will be lowered then there may un-drafted material will be produced. So it should be accurately given by considering back zone setting, volume of the material, fiber length, roller setting, moisture content, type of the material and blending ratio.
Main draft means, the maximum draft to achieve the drafting objective. With the result of maximum draft there are chances of variation. So to overcome this variation; cradle, aprons and bars are provided. As we know that in cotton material, there are short fibers in drafting zones which are called as floating fibers. So this provision of cradle, apron and bars will support the material to minimize variation
As we discussed already that objective of drafting is achieved by differential of roller speed, so it should be noted that roller speed also affect the evenness of the material. More differential of roller speed will result in more draft and more slippage of rollers. This slippage will be on both sides i.e. in mechanical system and between the fibers. So to achieve good results, one should try his best to give minimum draft in provided range at Simplex.
It should be done by considering the length of fibers. We know that if a fiber is gripped in both the nips of rollers i.e. front & behind; then there are chances of fiber breakage which result more variation in the material and its strength. Now the question is, which setting is recommended for cotton of staple length 1.o8 inches (30mm). S o far the general setting recommended, (which may not acceptable to every technician for each machine), is given in table (1). However just to start, nearest setting should be done and then do the trial for U%age of the material as well as complete spin test.
NIP TO NIP DISTANCE
ROLLER SETTING AND DRAFTING ARRANGEMENT:
In case of Cotton, fibers are of different length (0.5-1.4//). The roller setting is done by considering 2.5% of the fibers (staple length). In different zones the roller setting are as follows,
Staple length + Margin
Back zone setting
(nip to nip)
=Staple length +23 mm
Main zone setting
(nip to nip)
Staple length +20 mm
Front zone setting
(nip to nip)
Staple length +6.5 mm
In BACK ZONE setting is wider and draft is on lower side. It can’t be exceeded up to a limit otherwise there will be more unevenness.
In MAIN ZONE setting is wider but in spite of wider setting, draft is very high. We can give high draft in this zone because extra support in the form of cradle assembly bar and bottom apron is provided. It controls unevenness and in spite of more draft with wider setting, variation doesn’t increase. However one must try his best to apply draft on lower side.
In FRONT ZONE as draft is minimum, so there will be minimum speed differential. This is the main reason that in F.Z setting is too much close. Fiber gripped in both the nips will not break up due to minimum speed differential (draft).
BACK ZONE SETTING
Fiber neither gripped in front nor back pair of rollers.
More floating fibers
As drafting force is less
As most of the fibers are gripped either in back or front pair of rollers.
As most of the fibers are gripped either in back or front pair of rollers.
In this case fibers are gripped in one pair of roller less draft results in less/undrafted material. So we have to apply more draft.
“Binding of fiber strand by revolving it about its own axis is known as twisting.”
As roving is winded on bobbin and in ring department, it is gradually un-winded; so in this process stress on turning bobbin is applied, which result roving breakage, if sufficient twist is not applied. So we can say that following are the twisting objectives,
i. Twisting is done to give some strength to roving so that it can withstand forces of winding, unwinding, transportation and handling of roving during the subsequent process.
ii. To prepare a roving package with minimum breakage at simplex.
iii. To avoid slippage of fibres due to roving tension.
iv. To minimize stress and strain effects on yarn quality parameters.
After drafting, material came out from the nip of the front roller and this form of material is called roving. So one end is gripped between two roller’s nip and other end enters in flyer cap. This roving then passes through the flyer leg and flyer presser. The insertion of the twist is done by the flyer when flyer rotates the twist in sliver is achieved. Suppose 1 inch roving comes out from front roller nip and flyer turns 1 revolution then it means that in one inch roving , twist/turn is 1 i.e. TPI is 1. Further it can be understand by following table,
LENGTH RECEIVED (inch)
TPI(Turns per inch)
ü Flyer inserts twist to the roving. The twist level depends upon two factors,
® flyer speed
® delivery speed
ü The relationships between the twist and above factors are given below.
ü 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.
TWIST MULTIPLYER (TM):
It is an empirical factor which is calculated by knowing hank roving and TPI.
FACTORS EFFECTING TM:
1. Hank roving:
The relationship between hank roving and TM is illustrated by the following table,
Above table shows that if roving is coarser then we apply less TM and vice versa. It will apply on all roving (PC, PV, Carded, Combed).In coarser roving, number of fibres are more due to which more resistance between the fibres. Hence we need less twist to hold the roving strand together.
2. Staple length:
Roving TM will be reduced as staple length increases. Chances of slippage of fibres are more in case of short staple fibres and vice versa.
3. Machine speed:
More speed of the machine results in more stress/pull on roving, hence required more TM and vice versa.
4. Moisture content:
More the moisture content, lesser will be the applied TM and vice versa.
Roving TM depends upon the material in following way,
Short fibres provide resistance for stretching of material.
6. Flyer speed:
For more flyer speed, apply more roving TM to decrease breakage. To increase production increase flyer speed but breakage will also increase. So increase roving TM slightly up to a limit where breakage rate reduces to minimum.
EXCESSIVE TM EFFECTS:
A. Un-drafted material on ring:
Un- drafted material in ring results in,
· More U%age in yarn.
· More yarn breakages at ring.
· Less production at ring, As breakage will increase due to excessive TM.
· More chocking of pneumophil pipe.
B. Low production at Simplex:
Front roller delivery is reduced, so production will low; as TM increases with decrease in front roller delivery..
C. Wear of top rollers:
Due to more TM harder will be the roving, due to which top rollers wear out at ring.
LOWER TM EFFECT:
· Thin places due to stretching.
· More breakage at simplex.
· More breakage during un-winding.
Flyer is the actual mean of twisting of roving. It is in U-shape. Flyer guides the roving to wind on bobbin and give certain amount of pressure by pressing. Flyer presser is paddle shaped and it controls placing of each coil on bobbin. Roving coming from front roller enter through flyer cap into the flyer right hollow leg. This leg is designed in such a way that roving should not throw out through the slot.
Then roving after pressing twice around the presser arm: starts winding on bobbin. On other side there is solid leg which balances the flyer. By increasing the flyer speed production of the machine increases and vice versa. Flyer speed can be changed by changing the motor pulley. Previously range of flyer sped was 700-1000 rpm. Now-a-days it is up to 1500 rpm.
i. FLYER SPEED:
By increasing flyer speed, production also increases. We increase front roller delivery when increase flyer speed. Front roller delivery automatically increased with the increase in flyer speed and vice versa.
ii. HANK ROVING:
With the increase in hank roving (finer), production decreases and vice versa. Following table shows this phenomenon.
0.5 (420 yards/lb i.e. coarser)
1 (840 yards/lb i.e. finer )
iii. ROVING TM:
If we increase roving TM, front roller delivery will decreases resulting in decrease in production and vice versa.
iv. MACHINE EFFICIENCY:
With the increase in efficiency production increases as working time of the machine increases with increase in efficiency.
The down time of the machine is 4 hours and may be consumed as follows,
CAUSE OF MACHINE STOPAGE
Replacement of broken belt etc.
Worker slackness (more doffing time)
The level of twist is somewhat very important in 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.
3. BOBBIN WINDING
After preparation of a twisted strand (roving) there is requirement to wind it on a bobbin; because it is easy to transport in next department and easy to creel on machine. Therefore the problem to be solved is, How to place this roving on bobbin at exactly the same rate as it is delivered from the front rollers?
For winding of roving, there are two systems,
i. FLYER LEAD SYSTEM:
In this system, flyer wraps the roving upon bobbin due to more flyer speed.
ii. BOBBIN LEAD SYSTEM:
In this system, bobbin winds roving around it self due to more speed with respect to flyer. At present time all frames are made with this system due to its advantages over flyer lead system.
Why we use bobbin lead system?
Draw backs in flyer lead system:
Ø Maximum speed at start of the winding. So, when it is revolving with maximum speed, rollers speed also increased to maximum.
Ø More variation (U %) will occur due to maximum speed of flyer.
Ø There will also be variations within the package, which is called CVb.
CVb =Variation of U% between the package.
Ø There are limitations and problems of flyer speed increasing.
Advantages of bobbin lead system:
Ø No change in flyer speed.
Ø No change in roller speed.
Ø Bobbin speed is changing with the insertion of each layer.
Ø There will be no stretch or pull on roving due to maximum bobbin speed as flyer is revolving with the same speed.
CONE DRUM MECHANISM:
Two cone drums are designed in such a way that smaller end diameter is 3.5 inches and bigger end diameter is 7 inches. Top cone drum is driven through shaft and at start belt will be on bigger side of the top cone drum. So, bobbin speed will be more. After completion of a layer as diameter of the bobbin increases, surface speed of the bobbin will also be more. Hence to maintain winding rate equal to delivery rate, belt is shifted towards smaller diameter which will reduce the bobbin speed which is our objective.
Winding can be achieved by maintaining bobbin speed differential with flyer same as in case of roller drafting speed differential is maintained between two successive pair of rollers. At each instant, this difference should be maintained to wind the delivered length of roving. So, for this objective bobbin speed must be continuously reduced in a precisely controlled manner after insertion of each layer. So, cone drum speed reducing drive pass through a compound gear box which reduce precisely speed of bobbin and maintained the required speed differential. So, it is called differential box.
SOLUTION OF WINDING PROBLEM
As already indicated, it is requirement of winding that the delivered material must be winded on bobbin at same rate as that of delivery rate. It is fact that delivery is continuous from the front roller. Also after insertion of 1st layer of roving on bobbin, there will be change in bobbin diameter.
Now problem will occur when diameter of bobbin will increase with the winding of every layer on bobbin. So, to achieve winding rate equal to delivery rate continuously, bobbin speed will be reduced accordingly.
If, diameter of front roller=D= 1//
Front roll delivery rate=π×D×N=3.14×1//×100=314///min
Now, to maintain the winding rate same as front roll delivery,
If, diameter of bobbin=D= 2//
Winding rate to maintain=314///min
Winding rate= π×D×N=3.14×2//×50=314///min
Hence, delivery rate= Winding rate
Hence bobbin speed reduction after insertion of each layer results in equal rate of winding and front rollers delivery.
Winding is the process by means of which roving is drawn from front rollers to the flyer and wound on bobbin. If rate of winding is more as compared to the rate of winding, then there will be more tension and vice versa. However this difference should be very miner, otherwise winding of roving can’t possible.
Diameter of front roller=D= 1//
Speed of front roller =N=150 rpm
Front roll delivery rate=π×D×N=3.14×1//×150=471///min
Diameter of bobbin=D=1.99//
Bobbin speed=N=75 rpm
Winding rate= π×D×N=3.14×1.99//×75=469///min
Received material=471///min and Winded material=469///min.
2// will remain in between front roller nip and flyer cap which result in looseness of the roving. Similarly if winding rate is more as compared to delivery rate, then roving will be too tight resulting in stretching/strain or pull of roving. This tension will be observed between flyer cap and front roller nip. Unfortunately there is no precise way of measuring the tension. It only depends upon personal experience and judgment. If oscillation is more between front roller nip and flyer cap then tension is less and vice versa. More tension result in more stretch and ultimately roving will break or more long thin places generated in yarn. With the result of too slackness, the ends will gradually move down until they will snarl and break at the top of the flyer.
The most difficult problem is to keep the tension of the roving constant. It must be kept in mind that diameter of the bobbin increases by a flexible material (roving), so it will not be accurate. When there is space between coils or layers, then increase in diameter will not be uniform, consequently variation in winding of roving occur, which results in tension variation.
NOTE: more tension is dangerous as it create long thin places which are difficult to remove. While less tension result in accumulation of roving on flyer cap and ultimately break the roving which doesn’t affect quality of yarn.
FACTORS AFFECTING ROVING TENSION:
¾ Flyer speed
¾ Hank roving
¾ Moisture content in roving
BUILDING OF A PACKAGE:
“The system in which we build up the yarn package is called building motion”
In this system, bobbin rail goes up and down, consequently, after each cycle package length is decreased. In this way conical shape bobbin is prepared. “The system in which bobbin rail reverse earlier after each successive layer is called reversal motion”. Each additional layer requires a slow speed of bobbin rail. This function is done by shifting of strap on cone drum (from larger diameter to smaller diameter) which will decrease the speed of bobbin rail.
In coarse hank rovings, there will be fewer coils per inch on the bobbin and vice versa. Hence bobbin will be filled earlier for coarse hank rovings and vice versa.
Layer completion time (seconds)
Since bobbin length is fixed, therefore, there will be only change in coils per inch occur as hank roving changes. So by changing bobbin rail speed we will achieve our objective of winding.
For the same hank roving, increase in bobbin rail speed causes decrease in coils per inch and vice versa. If coils per inch are more then pitch (distance between two coils) of coil will be less and vice versa. We conclude that, when bobbin rail goes up and down more rapidly then coils per inch will decrease.
In winding process there are several aspects has to be achieved. The buildup motion consists of several sub categories.
Ø To shift the spindle rail according to the diameter increase
Ø To reverse the trail motion direction at the top and bottom
Ø 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.
I. Cone drum mechanism
II. Reversing mechanism
III. Buildup mechanism
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.
Ø Fibre to fiber 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.
Ø 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.
Ø 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.
Ø 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.
Ø 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.
Ø 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.
Ø It is advisable to keep the break draft (pre-draft) as low as possible, because lower break draftalways improves roving evenness. .
Ø Centrifugal tension is created at the bobbin surface as the layers are being wound and is createdby 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.
Ø 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.
Ø FACTORS AFFECTING ROVING STRENGTH are as follows:
® The length, fineness, and parallelization of fibres
® The amount of twist and compactness of the roving
® The uniformity of twist and linear density.
Ø 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
Ø 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.
Ø 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.
Ø 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 deliversa product that is sensitive in both winding and unwinding. The following parameters are very important in speed frame. They are
Bottom roller setting
Top roller setting
condensers and spacers
Twist in the roving
Creel and creel draft
Drawframe sliver and can
Ø 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
36s to 40s
24s to 30s
14s to 24s
0.7 to 0.8
36s to 40s
24s to 36s
36s to 45s
24s to 36s
36s to 40s
24s to 36s
16s to 20s
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.
Ø With 4 over 4 drafting system, the total draft can be up to 13, whereas in the case of 3 over 3 drafting system, the draft can not be more than 11.
Ø The Roving thickness and Roving hairiness (yarn hairiness) will be less with 4 over 4 drafting system compared to 3 over 3 drafting system.
Ø 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 up to the nip, lapping on the front bottom or top roller will be less.
Ø 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.
Ø 4/4 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 3 rd 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 and55 mm for synthetic fibres(44 to 51mm)
Ø 3/3 drafting system is good for fibres longer than 51 mm. 30 or 32 mm bottom roller diameters will be used with this system.
Ø Feed hank depends upon the total draft in speed frame. The drafts mentioned in the above table can be considered as a guide line.
Ø 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.
Ø 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" clasimat faults (long thin faults). Therefore the breakage rate in spinning will increase.
Ø 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.
Ø Some times draw frame coiling is a very big problem with synthetic fibres. If kinks (bend or twist in wire/sliver) IN are formed in the sliver, the kink has to be removed before entering the draft zone.
Ø Kinks in the drawframe sliver depends upon
® drawframe delivery speed
® delivery can diameter
® 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.
Ø 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 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.
Ø The roving tension depends on the delivery rate and the difference between peripheral speeds of flyer and the bobbin.
Ø 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 peripheral speeds of flyer and the bobbin, the roving tension will be tight.
Ø 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
Ø 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.
Ø 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.
Ø 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.
Ø 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.
® 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 analyzed 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 ringframes.
® 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, surface 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 speedframe. Sometimes, higher Twist will also reduce the surface cuts.