FUTURE OF YARN AND FABRIC FORMATION

Prof. Dr. G. EGBERS

The Former Director of ITV-Denkendorf, GERMANY

1. Introduction

If one reviews the increase in productivity and quality over the last 15 years, in yarn and fabric production terrific improvements can be seen. The production of a carded ring yarn 30 tex requires only 1,2 operator minutes per kg, and the production of 100 m cotton fabric only 0,2 operator hours, for the generation before us an unbelievable development. But there are also major improvements being made with regard to yarn and fabric quality. In 1982, 50% of all carded cotton ring yarns had a CV = 17,5%; in the meantime this number was reduced to 15,4%. The yarn quality, which 1982 only 5% of all yarn manufactures achieved, is today achieved by 20% of all spinners. New developments in spinning – new drafting systems and compact spinning - will lead to further improvements.

The fabric quality was also improved considerably. If a company like Levi Strauss allowed 100 points per 1.000 m fabric in 1982, they request less than 40 points today.

What has driven the industry to these improvements?

1.      Engineers always work toward improvements.

2.      Yarn quality requirements in weaving (Fig. 1). In earlier days warp yarn required higher strength than weft yarns. Weft yarns were even spun with lower twist. Today, it is the weft yarn, that feels the impact of speed. Fig. 1 shows, how filling speed increases the yarn tension. We need therefore better yarns for modern weaving.

2. Conditions, which allowed to make these improvements

What are the conditions that allowed us to make these improvements? First of all, developments in the area of microprocessors allowed us to make big steps in quality improvements and productivity gains. They enabled us, to control quality online as well as machine settings. They were the prerequisite for automation. Another important factor is the improvement in the precision machines can be manufactured. Precision components for cards, open-end machines, looms and preparation equipment lead to better machines and allowed for higher speeds and improved quality. Rotor spinning is a good example how automation improved quality and allowed to run speeds as high as 150.000 rpm. Therefore, it is the combination of developments achieved in different industrial areas that counts for the productivity increases in the textile industry.

3. Trends in yarn manufacturing

The most important processes in yarn manufacturing are carding and the spinning process as such. Of course, all the other processes are important as well for yarn quality. For instance, due to the super performance of modern auto leveller draw frames the yarn uniformity was improved to a degree, that USTER had to reconsider their statistics. But it can’t be expected, that draw frames will be improved much with regard to the auto leveller quality or to production speed.

Carding is the quality controlling process. With regard to card sliver quality and production speed a lot has been achieved during the last 15 years (Fig. 2). Very often it is forgotten that the function of the card chute is a major contributor to the sliver uniformity. The more consistant the chute works, the more consistant the carding elements are being stressed, which means the card flats can be set much closer, giving a superior card sliver. I will try to explain, why the card mat uniformity is so important: Assume for a moment, our average mat weight would be 450 g/m. If the mat weight momemtarily increases by 20% - what is just normal for older chutes-, the card sees a mat weight of 540 g/m and the sliver weight is changed from 5,0 g/m to 6,0 g/m what everybody would consider to be a big chance. The neps will increase for this part of the sliver dramatically.

A today’s card is a high precision machine. Each component is precision built. This allows to set the card flats very close to the cylinder – as close as 6/1000 inch. The precision of flat setting is the reason, why Trützschler has gone from 4 to 6 setting points. Their diagram demonstrates what this means (Fig. 3) Rieter tries to improve carding quality by an integrated card wire grinding system (Fig. 4). They claim not only quality gains, but also cost reduction.

Which productivity increases in cardingdo we expect for the next 5 years, if one considers a production of 80 kg/h as state of the art for cotton? I expect more than the 100 kg/h, which one could extrapolate from Fig. 5. For carded cotton I expect an increase to about 180 kg/h, which would relate to 200 to 210 kg/h for polyester. Sensors for card web quality, flat setting, wire sharpness and wire condition as well as for sliver uniformity are prerequisites for this productivity increase. It is extremely important to control the condition of the card, even more than today, since only few cards will produce the material needed.

In combing – without discussing all details – 2010 production rate will be almost 80 kg/h for an 8 head comber (Fig. 6). (Why: heavier laps – wider laps) If

In spinning two trends can be seen clearly:

·        Quality improvements in ring spinning due to the introduction of compact spinning, and

·        Productivity increases in open-end as well as in air jet spinning.

The pressure to reduce cost forces all yarn manufacturers to search continuously for opportunities to save cost. If one analyses the yarn manufacturing for typical cotton yarns (Fig. 7) it is very obvious that the raw material is the biggest cost contributor, independently from the spinning system. A yarn manufacturing process that gives us the opportunity to reduce raw material costs is therefore of special interest to the industry. The development of open-end spinning is a good example for this trend. We believe compact spinning is another opportunity to reduce raw material cost.

Compact spinning is a modified ring spinning process that can be used in short staple spinning as well as in long staple spinning. If one wants to explain the principle of compact spinning it is useful to start with fibre spreading in a modern double apron drafting system (Fig. 8). The roving is drafted in the back zone by a draft of around 1,2, whereby the twist is taken out of the roving, and the roving is getting wider. The main draft in the front zone will cause a further fibre spreading, even though the aprons control the fibres. The fibres will be spread over a width of about 4 mm, as they leave the front roll nip. Some fibres are even pushed further out, thus causing insufficient incorporation of these fibres into the yarn. They might even been sucked into the pneumafil, in general about 1% of all fibres, not taking ends down into account. The higher the total draft, the more fibres will go into the pneumafil.

The yarn itself has only a diameter of about 0,2 mm, which means that the 4 mm wide fibre bundle has to be narrowed down to 0,2 mm (Fig. 9). The tension, under which each individual fibre is twisted into the yarn, depends on the position of the fibre in the fibre bundle. The tension is the higher the further the fibre is away from the yarn core. It varies greatly and causes the fibre migration, which means, an individual fibre might be with the front part in the centre of the yarn and with the tail in the yarn sheet area. This is the reason why the twisted yarn has such a high yarn strength. But 4 mm are a pretty wide fibre array. A width of 1,5 mm would already be enough to create migration. Wider fibre spreading increases the yarn hairiness as well as the pneumafil waste and reduces the yarn strength.

It is therefore obvious to compact the spreaded fibres prior to imparting twist and without disturbing the drafting process. A way to achieve this, is called “pneumatic compacting”, which gave the spinning system the name.

Fig. 10 shows the principle of a compact spinning drafting system, which was developed by ITV Denkendorf and which is licensed to Zinser, Ebersbach / Germany. I am not showing different machine designs, since I only want to discuss the principle and the basic advantages of compact spinning. Central part of this new spinning system is the compacting zone, which follows the regular drafting. The top exit roller drives a perforated apron, on which the fibres are compacted on their way from the actual drafting system to the additional pair of rollers (Fig. 11). Since there is only a narrow zone of about 1 mm width under vacuum, the fibres are compacted to a tight bundle and then twisted. This eliminates completely the most critical point in the yarn path, the spinning triangle (Fig.12).

4. Principle advantages of compact spinning

Principally, the following advantages can be achieved processing cotton (similar advantages will be found, processing manmade fibres or wool):

·        Because of the improved fibre incorporation into the yarn, the yarn strength increases by about 10% for coarser yarns and 15% for finer yarns (Fig. 15). The strength increase is the higher, the finer the yarn.

·        As an alternative, the yarn twist can be reduced by 20% to 25% without loosing strength, compared to regular ring yarns. This will, of course, increase the production accordingly. Thus, if the front roll speeds allows to run faster, one will gain the production. In the lab we reduced twist of a carded cotton yarn Ne 20 to a degree, that led to 40 m/min delivery speed.

·        The yarn hairiness is reduced by 70% under equivalent production conditions (Fig. 14). The yarns look therefore more even. The appearance of carded cotton yarns is close to conventional combed yarns. This has tempted people to try to replace combed yarns by carded yarns.

·        The draft in spinning can be increased considerably, without the danger of loosing fibres as explained.

·        The resistance against scuffing – important for weaving – increases by the factor of 2.

·        Therefore, the size add-on in sizing can be reduced by 30%. This alone compensates the increased investment cost for the compacting zone of the ring frame, if one has a vertical process.

·        The ends-down in ring spinning are reduced by about 50%, even at very low twist levels.

·        Using the same twist level as for conventional yarns, cheaper cotton can be used.

·        In worsted spinning, much finer yarns can be spun from the same wool.

·        Since the yarn is not hairy, the lint contamination of the ring frame is remarkably reduced, since most fibres are spun into the yarn. If one has to clean the machine every day now, one has to do it in compact spinning only once a week.

·        The pneumafil waste is reduced by 1% to 1,5%.

Another advantage, which I think, is the most intriguing, is the possibility to produce fabrics, which can’t be copied using other yarns.

·        The fabrics, made from compact yarn, have higher strength, much better lustre, and much better pattern definition (Fig. 15). Knitted fabrics for instance, have either a very clear structure or high lustre and – with reduced yarn twist – much softer hand.

At the moment, compact spinning is still in the start-up phase. Rieter is sold-out for 2000 and 2001, Suessen has sold more than 100.000 spindles, and Zinser has started to sell machines in September 2000. We expect that the quality of the present ring spun cotton yarns will be considered inferior in 5 years from today, except of course, if one tries to compensate the advantages of compact yarns by using superior, more expensive cottons. But still, the much-reduced hairiness even after winding can’t be compensated using the best raw materials, and the advantages in sizing and further advantages downstream will still remain. 

5. Nonconventional spinning systems

With regard to nonconventional spinning systems, two main questions have to be answered:

1.      What is really the ultimate rotor speed and delivery speed in rotor spinning?

2.      What market share might Murata get with their Vortex spinning (MVS)?

There are physical/geometrical limits in rotor spinning, which are related to the interdependence between rotor speed and rotor diameter. The higher the speed, the smaller the rotor, the more difficult to get the fibres into the rotor. The limit is calculated to be at around 180.000 rpm. The specialist knows of course, that any speed increase has an impact on yarn quality and that the range of products, which can be made from such yarns, is narrowing with speed. If one considers this “rotor speed trap”, it makes more sense to try to increase the yarn speed at a given rotor speed. This means we have to develop new spinning elements such as rotors, nozzles and twist stops.

The answer to the second question, the MVS question, seems to be simple: Murata is selling MVS-machines, even though only to US companies, or Asian companies that have the US market as a target. The fun of MVS spinning is the fact that carded cotton yarns can be spun. MVS is not a false-twist air jet technology (Fig. 16), and the machines run at about 350 m/min. Even though they might be able to do so, most companies don’t run 100% carded cotton today. There are two main reasons for this: 

1.      It is not possible to spin yarns coarser than, let us say, Ne 12 (50 tex).

2.      For coarser yarns cotton is used with a relative high amount of short fibres. This leads to a fibre loss of 6% to 8% total. This increases manufacturing costs to a critical level and reduces yarn evenness to a degree, that it is more difficult to weave these yarns.

Working with MVS machines one has to realize that the machine is not very flexible. The setting of the twist stop pin (Fig. 17) is very critical and depends on fibre quality very heavily. To set a machine takes about one day. Any wear of the pin will change the yarn characteristics.
There are some speculations, that MVS might replace conventional air jet machines (MJS) one day. In this respect, it is interesting to see that most companies spin synthetics, blends or combed cotton on MVS machines for same or similar end uses, where people use MJS yarns today. If I would be asked as head of development of a textile machine company, what speed potential I would see for the MVS system, I would predict a delivery speed of about 500 m/min.

6. Developments in Weaving

What carding is for spinning, warp preparation is for weaving. Warp yarns have to be sized normally, a process, which costs around 0,80 DM/kg. Even though a lot of specialists believed, that there were no major chances to improve sizing, the pre-wetting technology is a quantum leap in warp preparation. The size add-on can be reduced by 30% to 40%. This results in a cost reduction in weaving, which we did not see since shuttle-less looms were introduced, replacing the old shuttle looms.

Pre-wetting (Fig. 17) can in principal be done on all sizing machines that have two size boxes. The first size box is filled with hot water, the second with size liquor. All yarns are sized in one box, but with wet split. Such a system is not at optimum, but it works. It is of advantage, to have a very short distance between the water-box and the size-box. This experience stimulated the machine companies to design new size boxes with integrated pre-wet sections. This allows using pre-wetting also in those cases, where only one size box is used today. The newly developed size-boxes don’t need much more space than an old one.

If one now combines pre-wetting and compact spinning, then the size add-on can be reduced by about 50%.There are a lot of details, that have to be observed, if one wants to use this technology successfully.

7. Economics of pre-wetting

The following table, demonstrates the advantages of pre-wetting for a company that has two sizing machines, working on a two shift basis, which supply warps for 240 rapier looms (500 picks/min) and 80 high speed air jet looms (850 picks/min). The total cost is reduced by 1,1 Mio DM per year, which is equivalent to 1,5% more profit. It is very obvious that even in mature technologies major improvements can be made. 

8. State of development in weaving and expected productivity potentials

The productivity of weaving machines was increased over the last decade by a degree, which nobody really expected. On the other hand, we don’t have an universal loom any longer. Specific market sectors did evolve for the different weaving technologies:

·        Air-jet and water-jet looms for bulk products in staple fibre and filament weaving respectively.

·        Rapier looms for fashion fabrics and special industrial fabrics, like air bags, belting.

·        Sulzer looms for heavy denims and super wide products, especially industrial products.

The Sulzer projectile loom is a “speciality machine” today and basically competitive only, if double panels are woven. If one compares water jet and air jet looms installed (Fig. 18) it is from a European stand point interesting to see, that more water jet looms are installed than air jet looms, but that US and European companies are going for the more versatile air jet loom.

If one looks at the distribution of jet weaving technology world wide, water-jet looms have bigger market share that air-jet looms. Air-jet looms are dominating in Europe and in US. One can expect that the air-jet weaving speed limit is around 3.000 m/min for 190 cm wide looms. The equivalent figure for rapier weaving is 1.500 m/min. It does not make much sense to give equivalent figures for projectile weaving, since more or less only double panel looms are being used.

9. Multiphase weaving

A new weaving technology is on the horizon again: multi-phase weaving. The question if this technology will gain a major market share, has still to be ans-wered. But a new area in weaving has begun, independently, what happens to the Sulzer company.

The multiphase weaving machine, introduced into the market by Sulzer under the name M 8300, combines all features of a modern weaving machine with a new weft insertion technology. To make it easier to understand the difference between multiphase weaving and conventional weaving, the three phases of conventional weaving should be remembered (Fig. 19).

1.      The warp yarns are forming a shed.

2.      The weft yarn is inserted by a shuttle, projectile, with water or with air.

3.      The weft is beaten to the panel by the reed.

These three steps are consecutive and require the movement of heavy components with high accelerations, leading to the speed limits discussed. The machine elements have to be moved over relatively large distances:

·        The heavy harnesses move about 100 mm up and down,

·        the rapiers move around 1.000 mm into and out of the warp,

·        the reed is moved back and forth by about 80 mm.

In multiphase weaving the three steps are made continuously by the so-called weaving rotor, the heart of the new machine (Fig. 20). There are no back and forth movements any longer.

The warp yarns are loaded on the guide teeth of the rotor, forming a shed while the rotor is rotating. The shed is moved forward, forming four sheds at the same time. In each shed a yarn is blown by air simultaneously. This is the reason why the productivity of multiphase weaving is three times that of conventional air-jet weaving. The productivity potential is much higher.

The weft is blown by air of moderate pressure. Since 4 yarns are inserted simultaneously, the total weft insertion speed is extremely high, 5.700 m/min at the moment. The limitation is more due to the quality of the package built than due to the air-jet nozzles.

If a yarn is forming the upper or the lower shed is determined by laying bars similar to those being used in warp knitting.

The main advantages of this new weaving technology – other than high
speed  – are:

·        Continuous process,

·        low air consumption for the weft insertion, since the air speed is constant,

·        weaving cost reduction of 30%,

·        low linting,

·        low yarn / yarn friction,

·        considerable noise reduction (10 dB (A)),

·        machine integrated air condition, which reduces the relevant energy cost around 50%,

·        much increased warp length, since the warp beam diameter can be increased to 1.600 mm, compared with 1.100 or 1.250 mm today,

·        Integrated quick style change (from Genkinger).

Of course, there are not only advantages, but also problems, that have to be solved. Major experience is needed in warp preparation. The size formula has to be modified towards better yarn / metal friction.

In order to achieve the same weaving efficiency as in modern air-jet weaving the stop level has to be reduced by 70% to 80%. Those companies that have the M 8300 have experienced an excellent performance. The latest results at ITV Denkendorf with optimised warps and weft packages are unbelievable 0,5 total stops per 100.000 picks!

A disadvantage is of course the low flexibility of this machine. Small lots of fashion fabrics can’t be produced, and you can’t produce all fabrics. But for bulk products, where manufacturing cost plays a major role, the M 8300 would be a very good option. We estimate that 65% of these products could be manufactured on the M 8300. First attempts are being made to run filament yarns on the M 8300. This technology may work for Taslan yarns. It is of course very obvious that staple fibre yarns are causing much less problems than filament yarns. It is a pity that the M 8300 was introduced at a time, where world wide sales of weaving machines were at a record low.

10. Developments in the area of auxiliary equipment

It would be interesting of course to discuss developments in peripherical areas of spinning and weaving. This would refer to equipment for air filtration, air conditioning, waste water recycling, card wire and harness developments, new rings, travellers, rotors and navels in spinning and laser stop motion in weaving, material handling, testing equipment, fabric inspection systems as well as online monitoring systems, and, finally information systems for planning, and scheduling of departments, plants and companies. There is not time enough, to stress all these areas, but I am ready to answer any questions about such topics during the discussion.

Once again, I would like to thank you for inviting me to give this paper at such an esteemed audience, and I would like to thank especially Prof. Kadoglu  for arranging this visit and Kirmen Spinning for sponsoring my participation.

Thank you so much for paying attention.

Tab. 1 Savings due to pre-wetting