The Development and Future of Circular Knitted Fabric
Prof. Wolfgang Schäch, Reutlingen.
Machine technology and clothing in changing times
The original function of clothing as a means of protection from cold, heat, damp, injury and other unwanted influences has broadened out over the history of man's development. Directly usable materials provided by nature such as fur and leather were unable to fulfil the whole range of needs and were not available in unlimited quantities.
This resulted in a situation where man sought methods of processing animal and vegetable fibres using manual skills to create textile materials to be used for clothing and also to manufacture products used in everyday living, for instance as coverings, sacks or nets. Evidence has been found that the manufacture of woven and hand knitted fabrics using simple tools made of wood or bone was known back in prehistoric times.
The variety of fibrous materials occurring in nature in terms of both structure and colour permitted the production of garments with different appearances and external effects, which allowed the wearer to achieve a certain level of individuality and so attract the attention of others. Human vanity was one of the motivating forces which drove mankind to devote part of its powers of creativity and manual skills to the manufacture of clothing with a high prestige value and beneficial external effects. Clothing was the most important and in many cases the only possession of the simple man, and not the consumer article it has come to be today. History shows that serious arguments frequently ensued over the clothing of the dead.
The growing population created a growing demand for clothing, and it was this need that provided the driving force behind the mechanized production of clothes. The development of technologies designed for the manufacture of textiles did not occur in isolation, but always within the context of the technology generally available and known at a certain time. A weaving loom can, on principle, be built entirely of wood and is capable of production without metal parts. Its development did not depend on the invention of metal extraction and metal processing.
Given this background, it is easy to understand how mechanization of the stitch-forming process using metal tools such as needles and sinkers etc. only become possible when precision mechanics achieved a certain technical standard as a result of the equally important construction of clocks and scales.
The invention of the automatically operating latch needle simplified the stitch-forming process considerably, as it permitted the elimination of needle presses to close the needle head. This development formed the underlying basis for the further development of knitting technology with individually movable and controllable needles already more than 150 years ago.
Modern knitting machine production
To the present day, the further development of flat and circular knitting machines and their operating elements has always moved forward hand in hand with the latest available manufacturing technology available in the field of precision mechanics, such as for example NC and CNC controlled machining centres. These paved the way for production of high machine gauges with narrow tolerances, as well as the mass production of machines with a high density of feeders. From the very beginning, knitting machines have always been "high-tech" products, to coin a modern term, which in contrast to many other technical products were always required to be adaptable at short notice due to their close ties with the world of fashion and the changing spirit of the age.
With the series manufacture of computationally optimized cams, for the first time it was possible to reduce the dynamic forces created during the stitch-forming process. This development laid the foundation for higher working speeds, smoother running and lower wear, resulting in a longer life for machines and their components. Still today, this technological progress remains the state of the art.
The use of compound needles and relative movement technology - developed to the series stage and successfully marketed already for a number of years by Mayer & Cie. - or a combination of both in circular knitting machines would have been inconceivable without the capability for precision machining, as here at least two or three cams are required to run in precise coordination with each over a large number of knitting systems in order to achieve the required degree of harmony in the stitch forming process with minimal stress on the yarn to produce an even, appealing fabric appearance.
Electronic engineering paving the way for automation
Another factor which has brought about a marked improvement in terms of patterning possibilities, user convenience, operating reliability and production monitoring is the introduction of electronic controls in all the components of the circular knitting machine. This has set the stage for the development of automation in circular knitting machines and "just-in-time" production, as presented for example by Mayer & Cie. for the first time at the ITMA '99 with its MCTmatic System. This new technical concept for primarily mechanical-electrical automation has now been developed to the series stage.
Market development
The quantity of knitwear required to cover the global requirement for clothing as protection against the elements is covered to some degree by the circular knitting machine capacity available in the world today. In principle, the market for essentially necessary clothing textiles is saturated. But despite this, changing fashions and the value of clothing as a status symbol amongst all age groups as well as additional requirements in the sport and fitness sector give rise to the expectation of further demand for special, highly application-oriented circular knitting capacity for special, flexible and high quality requirements.
In addition, in the field of technical textiles extensive areas of application already exist which are set to increase demand for circular knitted fabrics as these sectors continue to develop. However, here further developments in other fields of textile technology mean that for example flat knitted, warp knitted and woven fabrics as well as non-woven and composite materials must be considered as competing or complementing products.
What are the underlying strengths of circular knitting technology?
Of all the technologies used in the manufacture of textile materials in the form of yarded fabric, circular knitting technology offers the shortest set-up times - even in machines equipped with a large number of feeders - as it processes the yarn directly off the bobbin. As a result, it has this lowest stored yarn supply requirement compared to other fabric producing techniques. Orders can be completed at extremely short notice and even small quantities can be economically manufactured. Circular knitting technology is the most cost-effective method of manufacturing fashion fabrics.
The circular knitting machine is capable of processing a wide spectrum of different yarn and fibre types without special modification - including for example fibre yarns made from wide-ranging fibre materials or fibre blends as well as differently constituted filament yarns on one and the same machine.
It is equally possible to process different yarns and fibres in one and the same product, either using a mixture of feeders or plating technology to introduce several different threads.
Given the right technical configuration, it is possible to process yarns over a wide yarn thickness range on one machine. This capability, coupled with a wide machine adjustment range, provides scope for the achievement of a wide quality spectrum.
The continuous stitch-forming process which takes place using circular knitting technology and gentle thread deflection mean a consistent, low level of stress on the yarn, resulting in fewer yarn-related machine stoppages. The resulting effect is that of optimum utilization.
As regards wearing comfort, the elasticity and formability of circular knitted fabric offer a number of decisive advantages which are appreciated beyond the world of clothing and fashion also in the field of technical knitted fabrics used a wide range of applications.
Fabric variety
Simple single jersey, rib and interlock fabrics made of fibre or filament yarns will always be the basic staple products of the circular knitting industry, and will continue to satisfy a certain underlying demand, also to a high standard of quality.
As the quality of life continues to improve and with it the desire for more individual clothing, different demands are made with regard to design and quality. More versatile products become necessary and the produced quantities per product are forced downwards. It is precisely the advent of the leisure society and the many possibilities for sport and other activities that are creating the demand for fashionable and functional products which has to be satisfied at short notice.
The timely manufacture of this type of product calls for a highly flexible machine outfit covering a wide range of patterning possibilities and short set-up times. However, it is only by ensuring fast availability and adherence to deadlines that it is possible to guarantee good sales and the necessary returns.
Available technology
Needle selection
A proven technology is the combination of high performance with needle selection of needles featuring different butt configurations in conventional single jersey machines, single jersey machines using the relative movement technology and rib machines (8-cam technology). Modern machines operate with between 2 and 6 needle tracks for needle selection in the cylinder and 2 tracks in the dial. An additional channel in each controls the working butt to set the stitch length. In every phase of their movement, the needles are positively guided through closed tracks.
Knitting patterns are reset by exchanging cam parts for miss-knit, tuck, knit and supporting functions. Using combined quick-clamping and centering devices, cams can be exchanged with the required speed and precision. In these high-speed, extremely productive machines, a wide range of constructions can be produced which differ in terms of their appearance and physical and physiological properties. Circular knitted fabrics for normal and sportswear as well as for technical applications are highly productive.
For small quantities and/or large pattern repeats up to a maximum of the cylinder periphery, single jersey and rib jacquard machines with electronically controlled individual needle selection are ideal. Although their working speed is somewhat lower, they require only minimal set-up times and offer the greatest patterning flexibility.
Thread/yarn selection
Circular knitting machines are able to process different fibres/yarns in one and the same product. The simplest way in which this is done is by processing different yarns made of different fibre materials or with a differing yarn structure at different feeders. This is a technique which can be used in any standard machine. The maximum pattern height corresponds to the number of feeders in the machine.
A second possibility is to feed two different threads to one feeder. Here, one of the threads, the ground thread, is covered by the other one, known as the plating thread. In this case, for example in a single jersey fabric, on the technological face side the plating thread is positioned at the top while the ground thread is on the technological reverse side. For reliable plating, the machine must be suitably equipped. This equipment includes plating yarn feeders, needles with plating head, two yarn supply devices per feeder and, in single jersey machines, in some cases also differently shaped knockover/holding-down sinkers with a different movement sequence.
Thread changing devices / striping attachments at every feeder permit different threads to be processsed in any optional sequences independently of the number of feeders. In most striping attachments, there are four threads available for optional selection.
The selection is programmed with the aid of electronics. The movements executed for lay-in, lay-out, trapping and cutting of the changing threads are generally mechanically controlled.
With the striping attachment, it is not only possible to create optional patterning effects or generate optional areas with different characteristics, but also repeats fashioned to the required length to facilitate subsequent processing or making up. Another possibility offered by striping attachments is to shorten the time taken to change articles at the machine. If, for instance, only threads 1 and 2 of the four possible threads are required for the current article, the threads for the following article can be previously placed at positions 3 and 4, where they are ready for use in the next article with minimum delay.
Processing elastane yarns
Although it is possible to process core spun elastane yarns on standard machines, special devices are required for processing naked elastane yarns. Most elastane yarns for circular knitting machines are naked yarns processed using the plating technique. A special feed device (elastane feed wheel) is therefore required for this type of thread, which ensures that the thread is fed towards the stitch-forming process at a defined and constant degree of elongation.
Circular knitted fabrics containing elastane give rise to problems in as far as the side crease created when winding up a tube of circular knitted fabric is fixed within a short period and can no longer be removed, meaning that the usable fabric width for cutting is reduced to half the circumference of the tube.
Newly developed fabric open devices used on circular knitting machines cut and open out the fabric tube directly after knitting, and wind it up over its entire width up to 160 cm without distortion. This all takes place automatically within the machine, so eliminating the fabric crease problem.
Plush fabrics
Plush fabrics can be manufactured on circular kniting machines in a whole range of variations such as plain plush, striped plush or jacquard plush making use of colour or high-low techniques. Compared to other textile plush and velour producing technologies such as woven or raschel plush, circular knitting machines provide short set-up times coupled with high production output and top quality. The facility for subsequent shearing of the terry loops and the achievement of soft, dense surface properties open up a wide range of applications for both fashions and home textiles, and also in the automotive sector.
Variable fabric width. Scope for adjustment to the market.
Circular knitting machines are long-lived investment goods and should be designed to allow adjustment to changing market requirements over an extensive service lifetime. Particularly in the case of circular knitted fabrics for the technical sector which are required in high quantities while meeting precise specifications, cutting waste represents a major cost factor. As the working diameter of the circular knitting machine and also the stitch density of the available machine cannot be changed, a defined fabric specification necessitates also a fixed fabric width.
Outlook
Classical and fashion wear
The increase in the world's population at a rate of currently 2% will result in further growth in the basic requirement for textiles and circular knitted fabric.
The development of a middle class in Asia, particularly in heavily populated India and China, is giving rise to growing purchasing power. This is exercising a positive knock-on effect on the clothing sector. In these countries, too, the trend is moving away from traditional values and towards the western lifestyle. Uniforms and saris are becoming the exception rather than the rule on the streets. The young and midlife segments of this emerging middle class are moulding their behaviour and habits increasingly on the western model, driving the market with increased demand for high-quality fashion clothing and a marked move towards brand name consciousness. The local textile industry is unable to satisfy these exacting demands either in terms of variety, quantity or quality, nor has it created brand names with the attraction or prestige to compete with the established brand names of the West. As a result, the development and production of this type of article will remain for a long time to come in the managerial hands of the West, with Asian countries offering a positive future outlook as growing export markets.
In terms of business wear, the trend is moving towards a softening of conventional / conservative styles towards greater comfort and casual designs. The casual shirt with no tie, naturally elastic, comfortable and made of high-quality circular knitted fabric, is a first step in this direction. We may look forward to tremendous untapped future potential being opened up in the future in the field of circular knitted fabric for business wear.
Sport, leisure and special-purpose wear
Increasing life expectancy will continue to grow in the future, accompanied by ever greater purchasing power, some of which will flow into the sport, leisure and wellness sector. Here, elastic, comfortable, easy-wear knitted single jersey, rib, inter-lock, laid-in, plush and plated based knitted fabrics offer ideal physiological, physical and also fashion conditions for a whole range of applications.
Product liability and ever more stringent legal requirements relating to accident prevention will give rise to a growing requirement for protective clothing. Circular knitting technology with its flexibility for processing different fibres and yarns is practically predestined as the ideal method of manufacturing fabrics intended for this type of application.
Medical textiles
Although representing a niche market in terms of their quantity, medical products require a long development and testing period as well as demanding a consistently high standard of quality. Growing life expectancy and new fields of application, for example in transplant technology, will open up interesting scope for future growth also in this specialized field.
Home and car textiles
Circular knitted fabrics are used in the modern home environment as bedding textiles, upholstery covers and decor fabrics. Demand is oriented around the number of households, changing lifestyles and habits and the rising standard of living. Although this differs considerably in different countries, in general terms here too, increases may be expected.
Plush
Extreme demands are made on textiles and knitted fabrics used for upholstery in the automotive sector, not only in terms of quality but also when it comes to ensuring a reliable, continuous source of supply. The worldwide demand for automobiles has not yet reached saturation point and a further increase in production will be accompanied by greater demand for circular knitted fabric. Due to the high quality demands in place in this sector, these fabrics will still require the development and production "know-how" of the West, and will continue to be produced under western management for the foreseeable future.
New types of circular knitted products
The processing of ceramic and metal fibres or threads has previously been largely the province of weaving technology in the production of non-elastic grilles or sieves and so on. The processing of these materials using textile technologies is set to assume growing importance in the future. The reasons are various: In terms of their technical application, they offer better resistance to high temperatures. Increasing electric smog will call for more widespread electrical shielding measures in the future. Circular knitting technology offers ideal conditions for the manufacture of electrically conductive, elastic and formable surfaces from electrically conductive threads.
Today, knitted wire fabrics may still be considered niche products used, for example, in applications such as high temperature-resistant elastic suspension systems for catalytic converters in cars or as washable filters for use in kitchen extractor fans. However, in future they will gain increasingly in market significance, also in combination with other textile threads due to the easy combinability of elasticity, high temperature resistance and shielding properties they offer.
Market proximity
Today's circular knitting technology is capable of processing a wide range of different fibres and threads to create a variety of products with differing properties, combining short set-up times with extreme efficiency. Given its wide application spectrum, circular knitting technology is ideally placed to process new materials into new products in the future, and so to provide the market with textile materials to meet its changing demands.
In the clothing sector, its comfortable wearing properties and the flexibility which enable it to respond to the headlong pace of the fashion world place circular knitwear at the forefront of changing trends.
Interesting potential for further growth is certain to emerge from the home wear and automotive textile sectors, not only because of the expanding market in these areas, but also by taking over from previously used textile processes. And in the case of new-style products making use of ceramic or metal fibres or threads, the future significance of circular knitting production techniques is something it is only possible to speculate on. However, one thing may be predicted with some certainty even today: The possibilities offered by circular knitting have already expanded far beyond the limits envisaged only a few years ago.
[ 01.01.2003 ]
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Circular knitting machine of 1939.
Single-Jersey produced with Relanit 1.6 E.
Relanit 1.6 E - Full jacquard electronic capability with the 3-way technique.
Relanit 3.2
OVJA 1.6 ETR, Full electronic with individual needle selection, transfer und striping.
MCTmatic: Automatic setting of the quality wheel and belt tension.
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