Tuesday, 30 September 2008
Efficiency of Warping Department
The following will calculate the efficiency of a warping machine:
Let Speed in m/min= 300
Set length (m) = 18000
Yarn length on cone/cheese (m)= 54000
Number of Ends/beam= 500
end breaks/400 ends/ 1000 m = 3
Time to mend a warp break (seconds) = 35
Time to change a beam (seconds) = 500
Time to change a creel (seconds) = 3000
Time loss due to miscellaneous causes/1000 m (seconds)= 25
Running time R (s) = 1000x60/300 = 200
R is the uninterrupted running time in meters
Breaks/running ends in beam/1000 m = 3x500/400 = 3.75
Stoppage time /1000 m
(a) to mend breaks (s)= 3.75x35 =131 s
(b) to change a beam (seconds) = 500x1000/18000 = 28 s
(c) to change a creel = 3000x1000/54000 = 56 sec
(d) Miscellaneous time = 25 seconds
Therefore, S, the total stoppage time per 1000 meters (s)= 131+28+56+25 = 240 s
Therefore total efficiency = Rx100/(R+S)= 200x100(200+240) = 45.5 %
Expected Production per shift of 8 hours (m) = (300x60x8x45.5)/100 = 65,500 m
Causes of Low efficiency or Low productivity
1. Increase in End breakage rate
The machine efficiency at warping is highly sensitive to the end breakage rate
2. Improper utilisation of magazine creel
If the creel boy does not keep the magazine creel ready to be used by the time the package in the running creel are over, the efficiency will fall.
3. Reduction in Average Set-length
Lower set lengths reduce the machine efficeincy at warping
4. Number of Tenters per Machine
The number of tenters per machine determine the time to mend an end break. This is because by the time the warper finds a broken end on the beam, the creel boy brings the other end of the broken yarn from the creel
5. Stops due to Machine Breakdown, shortage of cones etc.
If the stops due to machine breakdown, shortage of empty beams or cones/cheeses etc. are high, the actual efficiency of the machine will be lower than calculated.
Monday, 29 September 2008
Process Control in Warping
Warping is the process of winding together on a beam a specified number of warp ends from Creel. The creel is a convenient rack for holding spools, cones or cheeses while the yarn is withdrawn to the warp beam.
The following are the process control parameters in a warping department:
1. Minimising End breaks.
2. Quality of warping beam
3. Control of productivity
Importance of Minimising end breaks:
The stoppage of the machine due to an end break is likely to deteriorate the quality of the beam due to three reasons:
1. The rubbing of the beam by the drum which stops abruptly.
2. Owing to the difficulty in finding the broken end, there is a possibility of incorrect mending. It may lead to lappers during sizing.
3. There is some loss in the extensibility of broken end when the machine is stopped, it increases the probability of breakage in weaving and sizing.
The following points should be noted to improve the quality of warping beams:
1. condition of beam flanges:
If the beam flanges are damaged, the unwinding of yarn near the flanges will not be satisfactory. This will cause difficulties in sizing and weaving.
2. Stop Motions and Breaks:
Proper stopping of the warping machine after an end break ensures that the broken end on the beam can be traced easily.
3. condition of the driving drum:
On most warping machines the beam is driven by fricitonal contact with the driving drum. In order to get a package of the correct density, the pressure between the drum and the warper's beam has to be kept at fairly high level.
4. Barrel Diameter of the Beam
Beams of small barrel diameter give rise to high unwinding tension at sizing, particularly when the beam is about to become empty.
5. Cuts in Accessories in the path of yarn
Drop pins of stop motion, guide rollers, reed denting etc. should bot have any grooves.
6. Creel Fans
Fluff accumulated on the machine, particularly at thread guides, causes tension variations in the yarn. This fluff can pass on to the beam.
7. Length Measuring Motion
The length measuring motion should be accurate, otherwise estimation of beam count would be wrong and subsequently will give incorrect values of size percent which is commonly determined from the weights of yarns on the warper's and the size beams.
8. Density of the Beam
The beam should be firm, inadequate pressure between the beam and the drum causes soft beam. Adequate pressure should be maintained by making suitable mechanical adjustments.
Control of Productivity
The productivity at warping depends upon the machine efficiency and machine speeds. The speed is governed by the mechanical condition of the machine and its design. Machine efficiency depends on several factors, such as the breakage rate, the time taken to mend the machine stop, set length, length of yarn on supply package etc.
Friday, 26 September 2008
Q: Why cotton system of spinning is called so ?
Ans: Because it was initially developed for spinning cotton fibres.
Q: How fiber length affects spinning ?
Ans: A longer fiber can be spun to a finer counts and gives a better spinning performance. In general, the longer the fiber, the higher the yarn tenacity. Too long a fiber gives processing problems specially in carding. Productivity also increases because the yarn spun from a longer fiber needs a lower twist.
Q: What should be the min. number of fibres in the yarn cross section for better spinning performance.
Ans: It should be around 85 for 38 mm and 68 for 51mm fibre
Q: How finer fiber affects spinning performance.
Ans: A fiber fiber can allow spinning of finer yarns. It also leads to more even yarns. Also low twist is required because of greater interfiber friction. However it can lead to excessive neps at carding.
Q: How finer fiber affects the fabric.
Ans: Fabrics produced from finer fibers drape better. They also have a soft "sheen". It usually produces softer fabrics.
Q: What is the formula to calculate the number of fibres in a yarn cross section.
Ans: N = (5315/fiber denier)/ yarn count (Ne)
Q: What is the min fiber strength needed for spinning ?
Ans:0.6 to 0.7 grams/denier
Q: What is crimp. How does it affect spinning.
Ans: It is defined as the weaviness of a fiber. It increases the interfiber friction which helps in spinning process. It also produces yarns and fabrics haveing a greater bulk and a softer feel.
Q: How crimp is measured.
Ans: Crimp is measured in arcs/inch
Q: What will happen if crimp is lower? If crimp is higher ?
Ans: A lower level of crimp than recommended can lead to problems such as lap licking, higher cylinder loading, card web breaking and roller lapping. A higher level of crimp will lead to excessive neps.
Thursday, 25 September 2008
Q: what is the object of aprons.
Answer: The object of aprons is to contol the floating fibres to the possible extent and help to produce regular and stronger yarns with greater drafts.
Q. What is the importance of gap between the two aprons.
Answer: The aprons are not be too far apart or too close. Wider gap fails to control the floating fibre movement. If the gap is less, the pressure between the aprons more. The front-roller-gripped fibres suffer undue strain and the result is the formation of the defect known as 'crackers'
Q. What are the top roller cots or coverings. What is their importance.
Ans: the top rollers of draw frames, speed frames and ring frames, are made of metals. These are usually covered with a convenient cushioning material called as cots.
Q. What is the importance of the top roller cots.
Ans: These are needed to avoid the fibres getting crushed or damages, and also to give a proper grip on the fibres when they are being drafted.
Q. What are the requirements of a good cot.
Ans: A good cot is expected to have unifrom quality and performance, capable of being buffed to precise limits. It should have anti-lap up, oil-resistant, antistatic, trouble-free and temperature properties. It must possess good resilience in order to provide the required degree of cushion and must not contribute to end breaks. It should withstand channeling action and any tendency for flute marding when top rollers are left standing under weight or pressure.
Q. What is the hardness of the cot. what is its importance.
Ans: A shore hardness of 60 deg to 90 deg is preferred. A harder surface would give rise to greater roller slip. A softer surface will lead to more roller lapping.
Q. Why top roll surfaces are grooved.
Ans: The object of grooving is to minimise the lap-up tendency, besides reduction of fly accumulation on top cleaners. The grooving also prevents surface distortions.
Q. What is the object of roller weighting.
Ans: In any pair or rollers, the bottom roller is positively driven while top roller is driven with the grip of the bottom roller. Normally the top rollers themselves fail to exert sufficient pressure and have to be assisted by some suitable external devices. Such devices are known as "roller-weighting devices"
Q. What is roller setting ? What is its importance ?
Ans: The distance between the centres of two pairs of rollers is called roller setting. If the pairs of rollers are set too wide apart, there will be plucking of the fibres instead of even attenuation, and the material that comes forward is full of thick and thin portions. On the other hand, if they are set too close, drafting becomes difficult and many of the long fibres get gripped by both the pairs momentarily. The fibres get either damaged or broken.
Tuesday, 23 September 2008
FAQs in Cotton Spinning
Q. What are the objects of ring spinning
Answer: There are three objects of ring spinning:
1. To draw the roving to the desired degree of fineness.
2. To impart sufficient twist to the emerging strand of fibres to from continuous yarn
3. To wind up the spun yarn into some convenient package form.
Q. What is the object of twist in Ring frame
Ans: The object of twist is to form a yarn with sufficient strength.
Q. Why every spinner wants to produce a yarn with as low twist as possible
Ans: Imparting twist consumes power, it also leads to low production. Also in untwisted from strength of yarn is about 30% more than in twisted state. Cloth manufactured bya low twist yarn tends to be fuller, stronger and more durable, Also dye absorption is better in low twisted yarns.
Q. How fiber length is related to twist
Ans: Longer the fiber, lesser is the amount of twist required. Frictional force increases with greater fibre length and as such there is more clinging power.
Q. How is fiber diameter is related to twist.
Answer: finer the fiber, more is the surface area available for clinging, thus more is the clinging power, hence lesser is the amount of twist required.
Q. How yarn diameter is related to twist ?
Ans: Coarser the yarn, more are the number of fibres per cross section and thus lesser is the required twist.
Q. How twist is related to yarn contraction ?
Ans: When twisted, the fibres take helical shape, that is, they get bent. Owing to this bending, there is a reduction in the length actually delivered from the front roller nip. This reduction in length is called contraction.
Q. What are the directions of twist ?
Ans: There are two popular ways in which yarn is twisted. Right Hand Twist is formed when the spindle revolves in clockwise direction as viewed from top. RH twist is also called, warp way, Z-way or twist way. The Left Hand twist is fromed when the spindle revolves in Anti clock wise direction. LHT is also called weft-way, S-way, reverse way etc.
Q. What are the various conventions of twist directions used in cloth.
Answer: A cloth is supposed to be best if woven with warp twisted right way and weft twisted left way.
Q. Why we avoid S-twist on ring frames.
Ans: It is often difficult to get left hand piecers to attend the machine with S-way twisting.
Q. Why over twisted yarn is not preferred ?
Answer: When overtwisted, the yarn becomes unbalanced. The yarn contracts excessively and becomes poor in strength. the yarn becomes hard, stiff and wiry. It has a harsh feel and dull appearance. It caused a lot of trouble in weaving.
Q. Why overtwisted yarns sometimes are needed.
Ans: Overtwisted yarns are manufactured for some special purpose. 'crepes' and 'voils' are woven with overtwisted yarns.
Thursday, 11 September 2008
Q. What is a comber
Answer: Comber is a machine where short fibres below a certain predetermined length can be easily separated out.
Q. What are the objects of combing
Ans: After combing the fibres are more or less uniform, well straightened or parallelised and free of neps and particles of trash that escaped carding.
Q. What will happen if carded material is presented as such to comber.
Ans: Majority of the fibre hooks in a carded sliver are trailing. Hooks can be straightened out by comber needles provided they are presented in leading position. If the trailing hooks are presented as such, they behave like short fibres and escape into noil.
Q. How we can make majority hooks (trailing) from card sliver to present as leading hooks to comber.
Ans: In order to make the major hooks take the leading position, there should be even passages or even reversals between the card and the comber.
Q. What is lap preparation for comber
Ans: 'Lap preparation' can be taken as a general term which includes all the passages between the card and the comber.
Q. What is backward feed
Ans: On conventional combers the feed usually takes place when the nippers are going backwards. This is known as backward feed.
Saturday, 6 September 2008
Q: What is the object of a speed frame
Ans: The object of a speed frame process is to reduce the sliver bulk to a diameter suitable enough fro the ring spinning frame to spin yarn.
Q : Why twist is required at the speed frame
Answer: Minimum twist is required to see that 1. The roving comes from the front roller nip on to bobbin through the flyer bore without being broken. b. The roving is nicely wound on to the bobbin. 3. that it does not suffer any creel stretch during unwinding in the next machine creel.
4. that the next machine can easily break the twist in the break draft zone.
Q. What is the function of paddle.
Ans: the paddle helps to produce compact and regularly built bobbins.
Q. How come the paddle always keeps pressed against the bobbin.
Answer: The paddle always keeps pressed against the bobbin due to the centrifugal force of the vertical solid bar.
Q. Why the threading slot is in the curved form.
Answer: This helps to prevent air drafts from entering the tube and disturbing the roving inside it. Besides it prevents liberation of fly.
Q: What causes winding of the twisted roving on the bobbin.
Ans: The differential surface speed between presser paddle and bobbin surface are responsible for winding of the twisted roving on the bobbin. Which is caused by differences in the flyer speed and bobbin speed.
Q: Why bobbin speed is reduced as the package diameter increases
Ans: As the diameter grows, bobbin surface speed increases although the revolutions per minute is constant. Therefore, bobbin speed is reduced in order to maintain the constant difference between the speeds of bobbin surface and paddle.
Q: What is 'flyer leading' and 'bobbin leading' case. Which is used in existing Speed frames.
Answer: S/F in which the flyer speed is higher than the bobbin surface speed is called 'flyer leading'. S/F in which the bobbin speed is higher than the flyer speed is called 'bobbin leading'. 'Bobbin Leading' case is used in existing S/F.
Friday, 5 September 2008
FAQ in Cotton Spinning-6
Q. What type of hooks are there in the card web ?
Answer: Bulk of the fibres in the card web are found to have hooks at their rear ends, and they are termed as trailing hooks.
Q. What type of hooks are removed at the drawframes.
Answer: Hooks are preferentially removed when they are presented in the drafting field in trailing direction.
Q. What is doubling. How does this affect regularity of a sliver.
Answer: Doubling is feeding more slivers together into the drafting zone. It improves the uniformity of sliver.
Q. Why we cannot offer a high draft in one go.
Ans: The resistance offered by the disorderly state often results in a greater unevenness in the drawing material.
Q. What can be the drawbacks of excessive parallelisation.
Ans: Slivers with high parallelisation become soft and their withdrawl from cans at later stages results in excessive creel breakages.
Q. What is roller slip
Ans: Top rollers are no positively driven. They are made to bear against the bottom fluted rollers with a suitable weighting arrangement. The motion transmission to the top roller is through the bulky sheet of fibres. Thus the speed of top roll is not the same as botton roll. This fall in speed of top roller is termed as roller slip.
Q. what will happen due to roller slip
Answer: The roller slip produces characteristic drafting waves or unevenness characeristics.
Q. What is a drafting wave
Answer: The irregular motion of short fibres between pairs of rollers give rise to a wave like formation that is known as drafting wave.
Q. What is the principle applied in roller setting over 44 drafting system.
Front and second pair= effective length + 1/8 "
2nd and Third pair= eL+ 1/8"+1/8"
3rd and Back Pair= eL+1/8"+1/8"+1/8"