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Preparing For Change

Yarn preparation faces questions as to what the future holds.

By William Oxenham

W hen addressing the question “What will yarn preparation look like in the future?” there are two different approaches. The first is the safer approach of looking at possible progressions and developments in the existing technology, then predicting where this will lead in the future. The second approach is not to be restricted by today’s technology. Starting only with the premise of needing to translate bales of fiber into a strand, which is suitable to feed into a spinning machine. In the present article, it is hoped to combine aspects of both of these approaches. Thus not only will possible developments in processing stages be discussed, but also in some cases the need (or techniques adopted) for the process may be questioned. An inherent assumption is also that the properties of the fibers used will not radically change in the foreseeable future.

There is no doubt that the current trend for greater use of monitoring and control devices will continue, as will the development in off-line testing equipment. This can be a double-edged sword. While these systems provide data on the process and product that was not previously available, they also provide the challenge of how to use the data. There are obvious benefits in using data on fibers to optimize bale lay-down, or to determine drawframe performance by monitoring sliver regularity. Unfortunately, there is presently a surfeit of results and the channelling of data (preferably obtained from both on-line and off-line sources and collated into usable information) to the appropriate individual, is a necessity, if these systems are to have any long-term usefulness.

One of the major concerns expressed by spinners is that the current grading of cotton does not reflect the ultimate quality of the yarn. Some spinners would prefer less effectively ginned fiber, if this caused less fiber damage.

Opening

figure1_959A historical overview of the offerings by different machinery makers clearly shows that there has been a rationalization in units used for opening and cleaning. Whereas, in the past there seemed to be a multitude of apparently different concepts for opening and cleaning fibers. A cursory perusal of the current offerings of machinery makers shows that there essentially seems to be a few core components that can be modified to cater for different demands in terms of opening and/or cleaning. An example of this is the Cleanomat/Tuftomat (Figure 1) unit offered by Trützschler, where the basic design can be altered in terms of number of rollers, roller covering and use of trash removal (mote knives) or “plain” under-screen. By using the correct combination, it is claimed that optimum opening and cleaning can be achieved with minimum fiber damage.

It is hard to foresee any major developments in bale opening systems, which are presently available for either batch or continuous processing. Even in “batch” processing (normal bale lay-down), it is currently possible to process almost 200 bales and up to three different bale groups. Similarly the use of multimixers will be the integral component for efficient fiber blending. With current production rates potentially well in excess of 1,000kg/hour, it is believed that future developments may be aimed at improving quality rather than productivity.

Recent developments that will continue to grow in importance are:

• Fine Particle Cleaners (dedusting units): the successful use of high-speed spinning machines (rotor, jet and vortex) requires that the feedstock is cleaner. For example, in rotor spinning, fine dust particles in the feed lead to rotor deposits that not only reduce processing efficiency, but can also result in moir — defects in the fabric. Similarly with jet/vortex spinning, the presence of fine trash particles in units incorporating small holes to twist the fibers could result in excessive wear and/or blocked channels that would in turn change product and process quality.

• Foreign Parts Detection (metal, foreign fibers, etc.): as the feed to the opening process becomes more automated, there is little opportunity for visual inspection and thus automatic detection and elimination of unwanted material at an early stage is now a critical component of an opening line. There are distinct benefits to early detection and removal of unwanted fibrous material since later processing stages open up and spread out these “foreign fibers.” This can result in the contamination of many yarn packages. Developments in automation coupled with advances in image processing will further improve the efficiency of these units.

Carding

figure2_960High-production carding currently equates to throughputs of about 100kg/hour (maximum 120kg/hour) for a meter-wide card. If developments in other carding technologies such as nonwovens are considered, there is no doubt that further improvements in processing speed will be achieved in cotton cards. This may however necessitate developments in the output from the card, such as dual doffers or some alternative output format to the current sliver. This latter approach, which is used in woolen processing, has been the subject of several research projects and includes the possibility of spinning directly from the card.

While there has been continuous improvement in carding technology and in associated process and product control, these seem to have come of age and rather than simply being “crowd-pullers” at machinery shows, they now present an alternative approach to maintaining high quality in carding. Multiple liquor-in rolls have been tried in the past, and this approach is being promoted by Trützschler and is claimed to give better fiber opening. Other manufacturers have incorporated modifications to the feed/liquor-in region aimed at better cleaning and minimum fiber damage.

Recent machinery exhibitions have unveiled several interesting developments from different card manufacturers, each of which leads to a minor improvement. However, if these could be integrated into one unit there is potentially a major change in the control of the carding process. These developments include both new and established ideas:

• integrated flat grinding has been available for several years;
• automatic measurement of flat setting is now available;
• motorized flat setting (Figure 2) is a possibility;
• an integrated cylinder grinding system (Figure 3) was recently made available. This consists of a grind-stone mounted under the cylinder which traverses the cylinder at intervals calculated by software (based on production and “ experience values”);
• autolevelling systems and the monitoring of sliver regularity is almost a standard accessory; and
• automatic nep counting at the doffer is an established technology but this now forms the basis of “intelligent grinding management.” Data from the automatic nep sensor can provide a useful indication of appropriate times to grind the flats (i.e. when there is an unacceptable increase in the level of neps).

It is thus evident that it is possible to measure sliver quality in terms of uniformity and neps and, furthermore, the factors primarily responsible for sliver quality (i.e. the condition of the card clothing and flat setting) can be adjusted. Thus, rather than grinding and adjusting card settings on a fixed time interval, it is now potentially possible to make these adjustments when the quality of the sliver approaches some predefined limit.

The possibility of incorporating a drafting head between the card and the coiler unit is not new and has been the basis of earlier autolevelling systems and also an approach to eliminating drawframe passages. A drawback of these systems was that they operated at very low drafts and this could result in grouping of fibers, which became evident in subsequent drawing processes. The recently introduced IDF (integrated drawframe) from Trützschler is claimed to overcome the earlier limitations by operating at significantly higher drafts between two and three. Indeed it is claimed that significant improvements in fiber straightening (resulting in greater fiber length and yarn strength) (Figure 4) can be achieved at drafts greater than two.

There are differences of opinion over the use of an integrated drafting system as an alternative to a drawframe passage (since this reduces the doubling and hence blending potential of the processing line). However, this approach may become a standard feature of “cards of the future” should double doffers become a necessary requisite for higher productivity.

The other technology, that may re-emerge, is the use of a direct link between card and drawframe. While this has been proposed several times previously, any future balance in production levels of cards and drawframes may re-establish interest in this approach.

Figure4_962

Combing

figure3_961Combing preparation is potentially totally automated, including the transfer of laps to the comb, and it is unlikely that any major developments will be seen in this area. Unless there is a radical departure from the current design of combing machines, it is unlikely that they will make any significant increases in speeds beyond 400 nips/minute. An area where improvements may be seen is the automatic setting of the comb to achieve some preset quality standards.

The use of imaging systems on the combed web can be used to assess not only the nep and trash particle content, but potentially could also determine fiber length and fineness. The data from these sensors could be part of a system that self-adjusts the comb settings and thus yields consistent quality.

Drawing

Drawframe speeds have peeked at about 1,000m/min. Autolevelling systems are available from all drawframe manufacturers, as is the possibility of automatic can change and the potential of a material handling (can transport) system. It is likely that there may be greater use of rectangular cans (originally promoted by Rieter with their CUBI can system), since these not only provide better use of the available space under modern spinning frames, but also offer easier handling in an automated transport system. The relative advantages and disadvantages of reducing drawframe passages are still the subjects of debate, but it is likely that there will be a move to the use of integrated drawing systems where two drawframes are essentially combined into one unit.

Systems of this type were proposed almost 50 years ago by Toyobo (Figure 5) for cotton spinning and more recently by Sant’Andrea Novara and OKK for worsted processing and it seems logical that such a set-up should figure in a drawing line of the future. As mentioned earlier, the old idea of linking several cards to a drawframe may also reappear if production levels can be matched. The drawframe of the future may also be “smarter” than today, where it responds to data input from previous machines and/or integrated sensing systems. Potentially the machine may optimize draft, ratch, and production speed based on values of fiber properties (obtained from high-volume tests) and regularity of the final sliver.

figure5_963

Roving Frame

There has been a question mark over the future of the roving frame for the last 40 years, but it still forms the feedstock for ring spinning. There is, however, current renewed interest in the use of higher drafts on the ring frame and this leads to the possibility of using heavier feedstock. Thus, it is possible to eliminate the roving frame and use a lightweight sliver to feed the ring frame. A further route to improving the total efficiency of the ring spinning process is to utilize heavyweight rovings in terms of both roving count and package size and weight (up to 5 kg). The use of heavy rovings offers several advantages:

• the production of the roving frame is greatly increased;
• automatic doffing of the roving frame is a well-developed technology;
• automatic transport of rovings and creeling of ring frame is easier to perform than the transport of sliver cans; and
• space requirement at the ring frame is significantly less than with sliver feeds.

As indicated above there is unlikely to be any major increases in productivity of the machines utilized in spinning preparation and likely benefits will probably be achieved by increases in the throughput weights rather than speed. The possibility of shortened processing routes should not be discounted for certain types of yarn, but while direct spinning from the card may be an interesting research topic, it is extremely unlikely to be of any commercial significance. The greater availability of cheaper and more powerful microprocessors; cheaper and more sophisticated imaging systems; cheaper variable speed motors and drivers; and access to more data on fiber and sliver quality will inevitably result in smart, more integrated machines, which automatically respond to compensate for changes in quality.


Editor’s Note: William Oxenham is professor, associate department head and graduate administrator in the Department of Textile and Apparel Technology and Management in the College of Textiles at North Carolina State University. Oxenham earned his bachelor’s degree and doctorate at the University of Leeds, England.
April 2000



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