Advanced Warp Knitting

Advanced Warp Knitting

                           Warp knitting is defined as a stitch forming process in which the yarns are supplied to the knitting zone parallel to the selvedge of the fabric, i.e. in the direction of the wales. In warp knitting, every knitting needle is supplied with at least one separate yarn. In order to connect the stitches to form a fabric, the yarns are deflected laterally between the needles. In this manner a knitting needle often draws the new yarn loop through the knitted loop formed by another end of yarn in the previous knitting cycle.
                         

 A warp knitted structure is made up of two parts. The first is the stitch itself, which is formed by wrapping the yarn around the needle and drawing it through the previously knitted loop. This wrapping of the yarn is called an overlap.

                                                    

 The second part of stitch formation is the length of yarn linking together the stitches and this is termed the under lap, which is formed by the lateral movement of the yarns across the needles. The length of the under lap is defined in terms of needle spaces. The longer the under lap, the more it lies at right angles to the fabric length axis. The longer the under lap for a given warp the greater the increase in lateral fabric stability, conversely a shorter under lap reduces the width-wise stability and strength and increases the lengthways stability of the fabric. The length of the under lap also influences the fabric weight. When knitting with a longer under lap, more yarn has to be supplied to the knitting needles.

The under lap crosses and covers more Wales on its way, with the result that the fabric becomes heavier, thicker and denser. Since the under lap is connected to the root of the stitch, it causes a lateral displacement in the root of the stitch due to the warp tension. The reciprocating movements of the yarn, therefore, cause the stitch of each knitted course to incline in the same direction, alternately to the left and to the right. In order to control both the lateral and longitudinal properties, as well as to produce an improved fabric appearance with erect loops, a second set of yarns is usually employed. The second set is usually moved

in the opposite direction to the first in order to help balance the lateral forces on the needles. The length of the under lap need not necessarily be the same for both sets of yarns.

Warp knitting comprises several types of knitted fabrics, including tricot, raschel knits, and Milanese knits. All warp-knit fabrics are resistant to runs and relatively easy to sew. Tricot is very common in lingerie. Milanese is stronger, more stable, smoother and more expensive than tricot and, hence, is used in better lingerie. Milanese is now virtually obsolete. Raschel knits do not stretch significantly and are often bulky; consequently, they are often used as an unlined material for coats, jackets, straight skirts and dresses. The largest outlet for the Raschel Warp Knitting Machine is for lace fabric and trimmings.

Warp knitting offers: 

·         Higher production rates than for weaving.

·         A wide variety of fabric constructions.

·         Large working widths.

·         A low stress rate on the yarn that facilitates careful handling of fibres such as glass, aramide and carbon (particularly when using weft-insertion techniques).

·         Conventional warp knitted structures that can be directionally structured.

·         Three-dimensional structures that can be knitted on double needle bar raschels. With weft insertion, uni-axial, bi-axial, multi-axial and composite structures that can be manufactured on single needle bar raschels.

 Principle of Warp Knitting :

Compound lapping movements are responsible for the production of warp knitted fabric. The compound lapping movement is composed of two separate motion.

·         Swinging motion (backward & forward motion)

·         Shogging motion (the lateral motion or side way movement )

The swinging motion is obtained from the main cam shaft while the shogging motion isobtained from the pattern wheel or pattern drum provided at one side of the machine.

The no. of pattern wheels or no. of endless  chain links will be equal to the no. of guide bars used. The lateral movement of the guide bars along the needle bars or parallel to the needle baris called a shogging motion. The amount of yarn supplied to the guide bar for a definite number of courses iscalled run-in or amount of yarn required (inch ) to 480 courses ( 1 rack ) is termed as run-in.

The ratio of Run-in between two guide bars is termed as
Run-in ratio: Run-in ratio is related to the loop length & structure of fabric & thus the appearance & knitting performance

                                              Warp Knitting Categories

Automotive textiles

•     Sportswear

•     Outerwear

•     Nets

•     Plush fabrics

•     Blankets

•    Shoe fabrics

•    Terry fabrics

•    Medical textiles

                                                

WARP KNITTING MACHINE

RASCHEL MACHINES

The principle of knitting in Raschel is identical to tricot knits. The significant differences between tricot and raschel are that Raschel knitting machinery utilizes latch needles rather than spring bread needles. Fabrics ranging from fine laces to heavy blanket and even carpets can be produced. Interested surface effects and three dimensional effects can also be produced. Spun and filament. Yarns of all counts and deniers can be used.

History of Raschel Machine

In 1855 German warp knitters used warp rib machines made by Red gate to knit lace stoles, which was sold under the name of Raschel Felix. Wilhelm Barfuss began to build his latch needle rib machine which he named Raschel machines. Until the mid-fifties, the Raschel industry tended to be small employing slow, cumbersome but versatile coarse-gauge universal Raschels. Modern specific purpose Raschels date from 1956 when a 12-barRaschel machine led to the development of the Raschel lace industry.

There are now:

Single needle bar Raschels for simple and multi-bar dress and elastic laces and trimmings and curtain nets. High-speed standard Raschels for simple structure such as suitings, versatile multi-purpose Raschels for fancy fabrics, weft insertion and jacquard Raschels and double needle bar Raschels for plush, scarves.

RASCHEL KNITTING MOVEMENT

RASCHEL CROCHET KNIT

Diagram Of A Knitted Net

Advanced warp knitting Technologies

Two next generation technologies are introduced in the field warp knitting. The HKS3-M knitting machine complies continuous thread supervising, utilizing the scanning system and Protechna, an independent thread stabilization system for loose threads, and the roll-ups. It works on the base of specific and constantly variable selection of stitch range, featuring continuous winding tension and tremendously uniform package structure excluding complicated gear-wheel changes. With record speeds, the HKS 2-3 E is the fastest machine for warp knitting. “Speed despite electronic guide bar control” is the slogan of the RSE 5 EL raschel machine, speed of nearly 1800 rpm despite electronic guide bar control, makes it the fastest raschel machine in the world. It is 60 percent faster then the previous model RS (E) 4 EL, with exceptional flexibility in material selection and patterning. This enable the machine to convert not only polyamide and polyester, but also fine cotton yarns into textiles with major designs and filigree structures. Dynamic servo motors, the newest electronic control systems opened extreme probabilities for produces and designers of advanced lingerie lace, with an entirely new patterning system. The ground-breaking design of the pattern guide-bars includes a fine wire to which the latest created thread-carriers equipped with changeable needles are attached. The two elements jointly make a string bar. Each of these string bars is connected at one end to a servo motor, which conducts the racking movement. A damper filled with gas at the other end takes care of string tension over the complete racking range. The strings pass via guide sections that can hold up to eight strings. All the pairs of guide sections create one unit.

The Benefits of this new technology are the following:-

• It allows pattern guide bar-racking movements up to 180mm – comparing with 47mm in the past.

• Additional pattern guide bars and racking rows in the machine space.

• Shorter, so more stable pattern thread carriers.

• Maximum pitch accuracy.

• Self-regulation of racking travel.

• Speedier machine

At present, two machines are equipped with this new technology, 'Fascination Lace FL 20/16' and 'Textronic Lace TL 66/1/36'. The Textronic TL 66/1/36 attains a speed up to 350 rpm and Fascination Lace FL 20/16 reaches up to 700 rpm. The machines that comply with the above mentioned features, such as flexibility, speed, low-maintenance and better communication, are highly recommended to enhance production quantity and quality.

“2010 can rightly be called the ‘Year of warp knitting’ as demand for warp knitting machines continued to grow from the beginning of 2010 due to huge consumption for warp knitted fabrics in domestic market”, revealed Mr Shewale who is currently the Product Head – Warp Knitting with A.T.E. Enterprises Private Limited and is responsible for Karl Mayer business in India              

One more informative session this caught the attention of the stakeholders and industry leaders of the textile sector at the ‘International Conference on Manmade Fibre Textiles’ was the presentation by Mr Kishore Shewale who spoke on ‘Warp Knitting Technology for Innovative Textile Applications’??

Giving details about the technology he said, “Warp knitting is by far the most versatile and a high productive fabric production system in textile industry. Although this industry is present in India since many decades, it is not widely known or popular like other fabric forming processes such as weaving and circular knitting.

“Warp knitted fabrics can be produced in various structures such as rigid and elastic, open or closely knit structures, in flat or tubular or also in 3 dimensional form. The fabric widths can go up to 6.6 meters or even in multiple of this width if it is a net structure. Warp knitted fabrics are often mistaken as woven or circular knitted fabrics though there is a distinct difference in the fabric structure and characteristics.

“Warp knitting machines are mainly classified in two sections or groups – Tricot and Raschel. Basic knitting elements on the Tricot machines are guides, needle, tongues and compound sinker and those on the Raschel machines are guides, needles, tongues, stitch comb bar and knock over comb or trick plate.

“The complete knitting cycle due to one revolution of main shaft or 1 rpm of the machine, which forms a loop in vertical direction, which is known as ‘Course’ – similar to pick in woven fabric can be divided in to four different movements of guide bar, swing –in, overlap, swing–out and under lap”.

Providing an overview of the warp knitting industry, he informed, “Indian warp knitting industry is scattered in different pockets like Mumbai, Surat, Delhi, Ludhiana and Amritsar mainly producing 2 bar and 3 bar tricot fabrics. The main application areas are ladies dress material and saree, lingerie and outerwear, furnishing fabrics, shoe fabrics, automotive fabrics, agro textiles and interlinings.

Warp Knitted Medical Implantable Textiles

Implants which are commonly used include vascular grafts, ligaments, heart valve components, hernia mesh fabrics and adhesion barriers. For example when aortic aneurysms occur, a catheter is inserted into an artery in the groin in order to deliver the implanted polyester graft to the aortic wall where it is attached by small positioning hooks. For example, in one patented internal hernia product, a hernia repair is achieved by using a knitted polypropylene mesh patch in conjunction with an underlay patch that is put on the inside of the abdominal wall and another patch on the outside of the abdominal wall and the knitted polypropylene mesh patch connector joins the two patches together while plugging the rupture in the wall.

 In some applications, knitted polyester vascular and cardiovascular grafts possess a tricot fabric with a velour surface which is designed to promote tissue growth. In this application, reverse locknit is a popular structure.

Other examples of support products include compressive bandages which are used on arms or legs in addition to graduated compressive bandages made on either tricot, raschel or crochet machines.

Warp Knitted Fabrics – Automotive

Table 5: Automotive Applications of Selected Warp Knitted Fabrics

Automotive Applications for Tricot Terry and Velour

Headliners

Seats

Seat backs

Door panels

Sun visors

Columns

Seat pockets

Arm rests

3.5.1 Warp Knit Bandage Products

In recent years a range of 2 bar warp knitted inelastic and elastic compressive bandage products have become more prominent. When required, it is also possible to produce and use both 3 and 4 bar tricot and/or multi-bar raschel based fabric products.

3.5.2 Inelastic Warp Knitted Flat Bandages

As noted previously, it is possible to produce inelastic bandage or primary dressing products on tricot and raschel machines. In Table 7, a tricot laid-in fabric construction using an open chain stitch is documented in construction “A.” Construction “B” in Table 7 documents a modification of the laid-in tricot construction shown in “A” in that it uses a closed half tricot stitch on the front bar in order to connect wales together. Construction “C” in Table 7, documents a simple mesh fabric design that can be produced on a tricot machine. Construction “D” illustrates a raschel fabric with a reasonably long laid-in back bar fabric construction using a chain stitch on the front bar whereas Construction “E” is a similar laid-in fabric but uses a closed half tricot stitch. Raschel construction “F” illustrates a similar fabric to “E” but with a longer lay-in to give a heavier, less open fabric compared to “E.” All fabrics in Table 7 knit with 100% spun cotton yarns

Emerging Technologies in Warp Knitting

Technological Emergence

In 2003, the new generation machines in the warp knitting were displayed at ITMA, Birmingham. The machines were equipped with individual motors to feed thread, fabric take-up and rolling-up, with all easy navigation. All machines had network systems with latest computers. The computer merges a motion control and a PLC for machines sequence control.

The user can operate knitting machine through Internet and intranet communication. Among the others, one computer is using ALC's 'ProCad' software, which guarantees well-organized pattern creation and error free online connection to machines. In addition, ALC software PROFAB and PDA computer also presents output data management facilities.

Two next generation technologies are introduced in the field warp knitting. The HKS3-M knitting machine complies continuous thread supervising, utilizing the scanning system and Protechna, an independent thread stabilization system for loose threads, and the roll-ups. It works on the base of specific and constantly variable selection of stitch range, featuring continuous winding tension and tremendously uniform package structure excluding complicated gear-wheel changes.

With record speeds, the HKS 2-3 E is the fastest machine for warp knitting. “Speed despite electronic guide bar control” is the slogan of the RSE 5 EL raschel machine, speed of nearly 1800 rpm despite electronic guide bar control, makes it the fastest raschel machine in the world. It is 60 percent faster then the previous model RS (E) 4 EL, with exceptional flexibility in material selection and patterning. This enable the machine to convert not only polyamide and polyester, but also fine cotton yarns into textiles with major designs and filigree structures.

Dynamic servo motors, the newest electronic control systems opened extreme probabilities for produces and designers of advanced lingerie lace, with an entirely new patterning system. The ground-breaking design of the pattern guide-bars includes a fine wire to which the latest created thread-carriers equipped with changeable needles are attached. The two elements jointly make a string bar. Each of these string bars is connected at one end to a servo motor, which conducts the racking movement. A damper filled with gas at the other end takes care of string tension over the complete racking range. The strings pass via guide sections that can hold up to eight strings. All the pairs of guide sections create one unit.

The Benefits of this new technology are the following:-

§  It allows pattern guide bar-racking movements up to 180mm – comparing with 47mm in the past.

§   Additional pattern guide bars and racking rows in the machine space.

§   Shorter, so more stable pattern thread carriers.

§   Maximum pitch accuracy.

§   Self-regulation of racking travel.

§   Speedier machine.

At present, two machines are equipped with this new technology, 'Fascination Lace FL 20/16' and 'Textronic Lace TL 66/1/36'. The Textronic TL 66/1/36 attains a speed up to 350 rpm and Fascination Lace FL 20/16 reaches up to 700 rpm.

The machines that comply with the above mentioned features, such as flexibility, speed, low-maintenance and better communication, are highly recommended to enhance production quantity and quality.

FULL  JACQUARD ADVANCED KNITTING

In computer design pattern fist, the single jersey computerized jacquard knitting machine can weave many kind of jacquard fabric the single jersey computerized jacquard knitting machine.

Driving device system: designed scientifically for modern knitting machine. Each part of it is calculated carefully to the highest precision and processed strictly according to technological requirements. it can assure running steadily with lowest noise.

Gearing device: completely soaking in oil bath runs quickly with minimum loss and lowest noise.

Both weft and warp knitting can incorporate the jacquard mechanism to produce multi coloured designs. The jacquard punched-card technique used in weaving can also bead apted to knitting. Cards control the selection or inhibition of the needles to produce the pattern. Another technique for controlling the individual needles to produce the various types of knits and designs utilizes electronic or electromagnetic devices. A third means is the use of a strip of film encoded in a boxed fashion. The film is divided into successive opaque and transparent squares that act similarly to the holes in the jacquard card or paper tape. A lens directs light through the moving film to phototransistors to select the particular needles for each stitch

The SFJ202-T is a full jacquard machine developed especially for economical knitting of collars and other trimmings, as well as full-width panels and even shaping. Its twin-carriage configuration features our renowned Knitran® cam systems and has full tandem knitting capability for increased flexibility and high productivity.

The SFJ also features advanced knitting technology such as a new electromagnetic direct needle selection system, top tensions with one-touch threading and belt-drive with variable knitting width. A full safety cover is also included for noise suppression, dust-proofing and operator safety. The SFJ202-T offers high cost-performance suitable for the production of a vast assortment of knitted items.

                                                     

                     

The SFJ202-T is a full jacquard machine developed especially for economical knitting of collars and other trimmings, as well as full-width panels and even shaping. Its twin-carriage configuration features our renowned Knitran® cam systems and has full tandem knitting capability for increased flexibility and high productivity.

The SFJ also features advanced knitting technology such as a new electromagnetic direct needle selection system, top tensions with one-touch threading and belt-drive with variable knitting width. A full safety cover is also included for noise suppression, dust-proofing and operator safety. The SFJ202-T offers high cost-performance suitable for the production of a vast assortment of knitted items.

Tandem capability and shaping

Combine for great flexibility The SFJ202-T features twin carriages, each with a single Knitran® system. While both carriages can be used together along the entire width of the needle bed for knitting wide panels in double system mode, the carriages can be separated into two single-Knitran® cam systems for knitting two identical pieces simultaneously. Furthermore, shaping capability allows two identically shaped pieces to be knit as well, without wasting materials through cut-loss. Tandem operation in the SFJ thereby allows the machine to support a variety of production methods, significantly increasing the versatility and productivity of the machine.

Increased accuracy in needle selection Needle selection on the SFJ202-T is performed using electromagnetic direct selection. This allows quicker, more accurate needle selection as compared to conventional solenoid-actuated types, resulting in higher productivity and better quality assurance. Improved quality control with the top tension device The top tension device employs a convenient one touch threading system for quick and easy setups. When knots are detected during knitting, the top tension automatically adjusts machine operation according to the situation. The machine stops for large knots, while small knots cause the machine to simply slow down to a preset speed adjustable by 10 levels. The top tension device thus serves as an effective quality control sensor.

Increased opportunities with stitch presser technology Shima Seiki’s patented stitch presser unit features a special motor drive system which allows the pressers to carry out individual on/off adjustments in both knit and transfer, in either direction. In addition to providing better control for knock overs, these pressers gently hold down the fabric for improved consistency and control.