Ring Spinning:
Ring Spinning Technology is a simple and old technology, but the production and quality requirements at the present scenario put in a lot of pressure on the Technologist to select the optimum process parameters and machine parameters so that a good quality yarn can be produced at a lower manufacturing cost.
Figure : Ring Frame
Points to be Considered in a Ring Frame
- Draft distribution and settings
- Ring and travellers
- Spindle speed
- Twist
- Lift of the machine
- Creel type
- Feed material
- Length of the machine
- Type of drive
Raw material characteristic plays a major role in selecting the above said process parameters in Ring Frame. Technical information and guidelines are given below based on the learnings from personal experience and discussions with Technologists. This could be used as a guideline and can be implemented based on the trials taken at site. Some of this information can be disproved in some other applications, because many of the parameters are affected by so many variables. A same machine or raw material cannot perform in the same way in two different factories. This is because of the fact that no two factories can be identical.
Drafting The break draft should depend upon the following,
- Fibre type
- Fibre length
- Roving T.M
- Main draft
- Main Draft Zone
Mostly for cotton fibers, short cradles are used in the top arm. Front zone setting is around 42.5 mm to 44 mm depending upon the type of drafting system. The distance between the front top roller and top apron should be around 0.5to 0.7mm when correct size top roller is used. This is normally taken care of by the machinery manufcturer. If a technician changes this setting, this will surely result in more imperfections, especially with karded count the impact will be more. Therefore when processing cotton fibres, care should be taken that the front zone setting should be according to the machinery.
Ring & Traveller
Ring diameter, flange width and ring profile depends upon the fibre, twist per inch, lift of the machine, maximum spindle speed, winding capacity etc.
Operating speed of the traveller has a maximum limit, because the heat generated between ring and traveller should be dissipated by the low mass of the traveller within a short time available.
If the cotton combed yarn is for knitting, traveller speed will not be a limiting factor. Since yarn TPI is less, the yarn strand is not strong enough. Therefore the limiting factor will be yarn tension. Following points to be considered
1) For 12s to 24s , 42mm ring with 180 mm lift can be used
2) For 24s to 36s, 40 mm ring with 180 lift can be used
3) For 36s to 60s , 38 mm ring with 170 mm lift can be used
4) For 70s to 120s, 36 mmring with 160 mm lift can be used.
5) If winding is a problem, it is better to go for reduced production with bigger ring dia.
6) Anti-wedge ring profile is better, because of better heat dissipation
7) Elliptical traveller should be used, to avoid start-up breaks in hosiery counts
8) Special type of travller clearer can be used to avoid accumulation of fibre on the traveller as traveller with waste does not perform well during start-up.
For polyester/cotton blends and cotton weaving counts yarn strength is not a problem. The limiting factor will be a traveller speed. For a ring diameter of 40 mm, spindle speed upto 19500 should not be a problem. Rings like Titan(from Braecker), NCN(bergosesia) etc, will be able to meet the requirements.
For spindle speeds more than 20000 rpm, ORBIT rings or SU-RINGS should be used. As the area of contact is more with this rings, with higher speeds and pressure, the heat produced can be dissipated without any problem. Normal ring and traveller profile will not be able to run at speeds higher than 20000 to produce a good quality yarn.
ORBIT rings will be of great help, to work 100% polyester at higher spindle speeds. Because, of the tension, the heat produced between ring and traveller is extremely high. But one should understand, that ,the yarn strength of polyester is very high. Here the limiting factor is only the heat dissipation. Therefore ORBIT RINGS with high area of contact will be able to run well at higher spindle speeds when processing 100% polyester.
While running 100% cotton, the fibre dust in cotton, acts like a lubricant. All the cottons do not form same amount of lubricating film. If there is no fibre lubrication, traveller wears out very fast. Because of this worn out or burn out travellers, microwelding occurs on the ring surface,< which results in damaged ring surface, hence imperfections and hairiness increases in the yarn.
Lubrication is good with west african cottons. It may not be true with all the cottons from West africa. In general there is a feeling, cottons from Russia, or from very dry places, lubrication is very bad. If the fibre lubrication is very bad, it is better to use lighter travellers and change the travellers as early as possible.
Traveller life depends upon the type of raw material, humidity conditions, ringframe speeds, the yarn count, etc. If the climate is dry , fibre lubrication will be less while processing cotton.
Traveller life is very less when Viscose rayon is processed especially semi dull fibre, because of low lubrication.
Traveller life is better for optical bright fibres.
Traveller life is better for Poly/cotton blends, because of better lubricatiion between ring and traveller.
Because of the centrifugal force excerted by the traveller on the yarn, the particles from the fibre fall on the ring where the traveller is in contact. These particles act like a lubricating film between ring and traveller.
Rubber Cots and Apron
For processing combed cotton, soft cots (60 to 65 degree shorehardness) will result in lower U%, thin and thick places
There are different types of cores (inner fixing part of a rubber cot)available from different manufacturers. Aluminium core, PVC core etc. It is always better to use softer cots with aluminium core.
When softer cots are used, buffing frequency should be reduced to 45 to 90 days depending upon the quality of the rubber cots, if the mill is aiming at very high consistent quality in cotton counts.
If the lapping tendency is very high when processing synthetic fibres for non critical end uses, It is better to use 90 degree shore harness cots, to avoid cots damages. This will improve the working and the yarn quality compared to working with 83 degree shore hardness.
If rubber cots damages are more due to lapping, frequent buffings as high as once in 30 days will be of great help to improve the working and quality. Of course one should try to work the ring frame without lapping.
The basic reasons for lapping in the case of processing synthetic fibre is
End breaks
Pneumafil suction
Rubber cots type
Fibre fineness
Oil content(electrostatic charges)
Department temprature and humidity
Almost all the lappings orginate after an end break. If a mill has an abnormally high lapping problem the first thing to do is to control the end breaks,
After doffing
During speed change
During the maximum speed by optimising the process paramters.
It is obvious that fine fibres will have a stronger tendency to follow the profile of the roller. Therefore lapping tendency will be more.
If the fibre is fine, the number of fibres in the cross section will be more, therefore lapping frequency will be more.
If the pressure applied on the roller is more, then lapping tendancy will be more. Hence fine and longer fibres will have more tendency for lapping because of high top roller pressure required to overcome the drafting resistance.
If the pneumafil suction is less, the lapping tendency will be more both on top and bottom roller. But the pneumafil suction depends on the fan diamater, fan type, fan speed, duct design, length of the machine, profile of the suction tube etc. If any one of the above can be modified and the suction can be improved, it is better to do that to reduce the lapping.
The closer the setting between the suction nozzle and the bottom roller, the higher the suction efficiency and lower the lapping propensity
Higher roving twist will reduce the lapping tendency to some extent. Therefore it is better to have a slightly higher roving twist, provided there is no problem in ringframe drafting, when the lapping tendency is more
With Softer rubber cots lapping tendency will be more due to more surface contact.
The most minute pores, pinholes in the rubber cots or impurities in the cots can cause lapping.
Therefore the quality of buffing and the cots treatment after buffing is very important. Acid treatment is good for synthetic fibres and Berkolising is good for cotton.
Electrostatic charges are troublesome especially where relatively large amount of fibre are being processed in a loose state e.g drawframe, card etc.Lapping tendency on the top roll increases with increasing relative humidity. The frequently held opinion is that processing performace remains stable at a steady absolute relative humidity, i.e. at a constant moisture content per Kg of dry air.
Twist:
The strength of a thread twisted from staple fibres increases with increasing twist, upto certain level. Once it reaches the maximum strength, further increase in twist results in reduction in yarn strength
Coarser and shorter fibres require more Twist per unit length than finer and longer fibres
Twist multiplier is a unit which helps to decide the twist per unit length for different counts from the same raw material.This is nothing but the angle of inclination of the helical disposition of the fibre in the yarn. This is normally expressed as TWIST PER INCH = TWIST MULTIPLIER * SQRT(Ne)
If the two yarns are to have the same strength, then the inclination angles must be the same
For 40s combed knitting application, if the average micronaire of cotton is 3.8 and the 2.5% span length is around 29 mm, Twist multiplier of 3.4 to 3.5 is enough . If the average micronaire is around 4.3, it should be around 3.6 to have better working in Ring frame.
- Cotton combed knitting T.M. = 3.4 to 3.6
- Cotton combed weaving T.M. = 3.7 to 3.8
- Cotton carded knitting T.M. = 3.8 to 4.0
- Cotton carded weaving T.M. = 3.9 to 4.2
The above details are for cottons of 2.5% span length of 27 to 30 mm and the average Micronaire of 3.7 to 4.4. For finer and longer staple, the T.M. will be lower than the above.
In general for processing polyester/viscose , the T.M. is as follows
- 51 mm, 1.4 denier fibre : T.M. = 2.7 to 2.9 for knitting application
- 51 mm, 1.4 denier fibre : T.M. = 2.9 to 3.1 for weaving application
- 44 mm, 1.2 denier fibre : T.M. = 2.9 to 3.0 for knitting application
- 44 mm, 1.4 denier fibre : T.M. = 3.0 to 3.1 for knitting application
- 38 mm, 1.2 denier fibre : T.M. = 3.1 to 3.3 for knitting application
Others
The following ROVING parameters will affect the ring frame process parameters
- Roving T.M.
- Bobbin weight
- Bobbin height
Now we can explain:
Higher the roving T.M., wider the back bottom roller setting or higher the break draft in ring frame
For combed material the creel height should be as low as possible in ringframe
Very long creel heights in ringframe, lower roving T.M. and heavier roving package will result in many long thin places in the yarn.(especially in combed hosiery counts)
In general 16 x 6 " bobbins are used. This helps to increase the spare rovings per machine with higher creel running time. Therefore one should aim at increasing the bobbin weight as well as increasing the number of spare rovings in the ring frame.
Normally 6 row creels are used in modern ring frames. Six row creels will accomodate more spare rovings compared to 5 row creels.(around 150 rovings for 1000 spindle machine.) Creel height should be as low as possible for cotton combed counts. Spare rovings will improve the operators efficiency.
Shorter machines are always better compared to longer machines. But the cost per spindle will go up.
For cotton , polyester/cotton blends, poly/viscose(upto 44mm length), number of spindles upto 1200, should not be a problem. But maintenance is more critical compared to shorter machines.
For synthetic fibres with very high drafting resistance, it is better to use shorter machines, because the load on break draft gears and on second bottom rollers will be extremely high. If long machines are used and the maintenance is not good for such application, the bearing damages, gear damages, bottom roller damages etc. will increase. This will result in coarse counts, higher count C.V., long thin and thick places.
Four spindle drive is always better compared to Tangential belt drive. Because small variation in machining accuracy of bolster , spindle beam etc will affect the spindle speeds, thereby the twist per inch. Waste accumulation between contact rollers, bent contact rollers, damaged contact rollers, oil spilling from any one spindle etc. will affect the spindle speeds and thereby TPI. The spindle speed variation between spindles in a 5 year old ring frame will be very high in case of tangential belt ? drive compared to 4 spindle drive.
Noise level and energy consumption will be low in 4 spindle drive compared to Tangential belt drive
Compared to Contact rollers, Jockey pully damages are nil. I have worked with 20 year old ring frames with Jocky pulleys, but the variations in spindle speed between spindles is very less compared to a 5 year old ring frame with Tangential belt drive. I have made this comment based on my personal experience.
When processing coarse counts at higher speeds, the air current below the machine is a big problem with 4 spindle drive . This is due to the more running parts like tin rollers and jockey pullyes. This will lead to more fluff in the yarn, if humidification system is not good enough to suck the floating ,fluff.
If spindle speeds is high for cotton counts, every end breaks will result in more fluff in the department due to the free end of the yarn getting cut by the traveller when the distance between traveller and the bobbin with the yarn is less. Higher the delay in attending the end break , higher the fly liberation. If the number of openings of return air system for a ring frame is less and the exhaust air volume is not sufficient enough, then fly liberation from an end break will increase the end breaks and thereby will lead to multiple breaks. End break due to a fly entering the traveller will get struck with the traveller and will result in heavier traveller weight and that particular spindle will continue to work bad.
Multiple breaks are very dangerous, as it will result in big variation in yarn hairiness and the ring frame working will be very badly affected due to heavier travellers because of the fluff in the traveller.
Dry atmosphere in ring frame department will result in more yarn hairiness, more fly liberation and more end breaks
It is a good practice to change spindle tapes once in 24 months. Worn out spindle tapes will result in TPI variations which is determinetal to yarn quality.
