Leno Fabric Weaving Techniques
  • Leno Fabric Weaving Techniques





    Fabric can be defined as any structure obtained by combining textile fibers to form a thin, flexible and robust texture with a smooth surface and a constant thickness. The basic qualities determined as smooth surface, thinness, flexibility, durability and covering feature vary considerably depending on the fabric structure. There are three basic fabric making methods: weaving, knitting and felting.

    These features of the fabric are also shaped by the unique qualities of the fibers, which are the building blocks of the fabric, and the yarns formed by combining the fibers. On the other hand, the yarn density and the binding of the yarns or the knitting order are also the determining factors in the transformation of the yarn properties to the fabric properties. Knowing the properties of these structures is very important in terms of both production and use.

    In general, according to the structure of woven fabrics;

    1. Simple woven fabrics
    2. It is examined in two main groups as woven fabrics with complex structure.

    On the other hand, woven fabrics:

    1. Normal woven fabrics,
    2. Cross (leno) woven fabrics,
    3. Looped fabrics,
    4. triaxial fabrics,
    5. hand weaving,
    6. narrow textures,
    7. It is possible to examine in seven main groups, including three-dimensional weaving structures.

    Standard structure weaving is a traditional textile surface formed as a result of two separate yarn groups known as weft and warp intersecting with each other at a 90° angle and making connections by passing under and over each other in accordance with the prescribed knitting pattern.






    Leno structure or leno fabrics, It belongs to the group of complex fabrics. In addition to the standard warps positioned parallel to each other, there are leno warps in the structure.

    Weaving surfaces referred to as leno or rotary power are; They are sparsely woven but solidly structured textile surfaces created by the up and down movement of the warp threads, as well as by moving them diagonally.

    In Leno woven fabrics Side-by-side leno warp threads do not remain parallel to each other when connecting with the weft, but are also connected to each other by crossing them. It is these crossings of warp threads that give the fabric its sparse but durable structure.

    In leno fabrics, the unit structure consists of two warp threads and one weft thread.. From these two warp threads to the straight one fixed warp or standard warp, if the warp making the binding action cross warp or rotary warp It called. What are impacted teeth? When one or more teeth fails to grow in the correct position and is therefore held below the normal gum line, it is called an impaction. This can be complete, such as completely unerrupted (buried) third molars (wisdom teeth) or partial when just part of the tooth is visible in the mouth. Why are impactions important? For best function and appearance the teeth should grow in a healthy alignment. When one or more teeth is impacted, this can affect the function of that tooth but also the function and appearance of other teeth. Whether all impactions should be treated is still controversial and your dentist and oral and maxillofacial team can explain the advantages and disadvantages or treatment for you, which is usually surgical.

    In standard woven fabrics while the warp threads are connecting with the weft threads in an upright position, in leno fabrics these warp pairs are twisted by taking parallel weft threads between them.

    If one of the warp yarns used in leno fabrics moves straight and the other moves diagonally, such weaves ''half leno braid (gauze)'', if both warps move diagonally, also ''full leno weave'' It called. What are impacted teeth? When one or more teeth fails to grow in the correct position and is therefore held below the normal gum line, it is called an impaction. This can be complete, such as completely unerrupted (buried) third molars (wisdom teeth) or partial when just part of the tooth is visible in the mouth. Why are impactions important? For best function and appearance the teeth should grow in a healthy alignment. When one or more teeth is impacted, this can affect the function of that tooth but also the function and appearance of other teeth. Whether all impactions should be treated is still controversial and your dentist and oral and maxillofacial team can explain the advantages and disadvantages or treatment for you, which is usually surgical.

    Traditional gauze used as medical bandage (gauze) It is produced with plain weave and half leno connection and it is called by this name because it was first produced in the Gaza region.






    In the production of leno fabric, the entire surface of the woven fabric can be created with leno connections, and a rich patterning variety can be offered by using it together with existing woven weaves.

    Thanks to the elegant appearance and durable performance of leno woven fabrics, their use as clothing dates back to ancient times. Thanks to the developments in fiber and fabric production technology, leno fabric is used in many areas other than clothing due to its excellent structural stability.

    Leno fabrics;

    • In women's and men's tops,
    • In home textile,
    • In packaging and burlap production,
    • In agricultural textiles,
    • In the construction industry,
    • In geotextile applications,
    • In medical textiles
    • automobile upholstery
    • It has an increasing usage area in technical textiles.

    Leno Weaving Techniques

    1. Framed systems,
    2. Comb systems,
    3. jacquard systems,
    4. circular leno systems,
    5. Disc systems

    There are five types.

    1-Frame systems

    Framed systems have an important place in the production of leno fabric, and the positive aspects of the system are minimum wear problems, easy assembly and working with all kinds of yarns.






    The working principle of framed systems using steel wire leno power is as follows;

    In the system consisting of two full powers (left and right powers) and half power between them, the right and left powers are attached to separate frames. The middle power is mounted in such a way that one foot is passed through the right power and the other foot is passed through the left power, and the middle power is mounted in such a way that it can move within the right and left forces. The rotating power thread is passed through the eye of the middle power. In the space between his left and right power is also his elemental power. When the frames on which the right and left forces are attached move respectively, the rotating warp is activated.

    In the first position, the mouthpiece is closed. The basic warp shown in red is between the left and right strength. The rotating warp shown in blue has been passed through the middle power eye.





    In the second case, the left force is lifted up and the middle force connected to it is also lifted up and the mouthpiece is opened from the right of the basic warp.

    In the third case, the power on the right is lifted up, and the middle power, which is connected to it, is lifted up and the mouthpiece is opened from the left of the basic warp. Thus, a cross from right to left is formed on the fabric surface.

    The negative side of weaving machines that weave leno fabric using leno power is their production speed limited to 150-200 rpm. The main reason for this is that the return movement of the leno power is provided by springs.





    With the trade name PosiLeno to increase production speed in systems using Leno power. positive leno system developed. In this system, it consists of two separate movable shafts, one half shaft rotating in the positive direction, and rotary power tools. The positive drive of the half shaft is provided by the movement of the weaving shaft controlled by a shaft, dobby or eccentric.

    The movement of the weaving shafts is transformed according to the optimum flow of the rotary weaving power with the half shaft by means of two specially developed drive arms and connecting rods. With this system, there is no need for assemblies to mount the rotary springs under the weaving shafts.






    With this system, a 100% increase in speed is achieved compared to conventional leno systems. A wide variety of patterns are woven with high flexibility. Again, one of its most important advantages is that it can be mounted on normal fabric weaving machines with very small investments.

    2-Card systems

    Weaving of leno fabrics can be woven in existing weaving machines using leno powers as well as with leno weaving machines specially developed by companies such as Dornier, Itema-Sulzer, Picanol and Vuts.

    The advantage of leno weaving machines developed to weave only leno fabric is that they operate at higher production speeds than the system using leno power.

    In Leno looms, a second reed is added to the back of the weaving reed. In this comb, one comb tooth remains intact, while the second tooth is cut in half. The height of the half-cut tooth determines the maximum level at which the mouthpiece can be opened. Frames have been eliminated in these benches. Machines are simpler looking. Half a tooth has an eye on its end. During the drawing-in process, the basic warp is passed over this strength eye. The rotary warp is in a free state between two full reed teeth. With the right and left movement of the comb, the rotary warp makes its cross movement by passing over the half reed tooth. Crosses are formed on the fabric surface. Carrying the weft in these looms is also possible with all weft transport systems. (air and water jet, projectile and hook) can be realized.

    Working with carded systems, the ITEMA-Sulzer leno weaving machine is a mixture of warp knitting machine and weaving machine. In this machine, just like in warp knitting machines, there is a guide plate, additionally a mesh comb and a normal toothed comb. There are two separate warp threads. in blue color the thread shown is the movable "leno" thread. in red color shown is the warp thread which is fixed. The leno yarn, shown in blue, passes through the rearmost guide plate and the empty part of the mesh comb. Afterwards, both warp threads are drawn together in the same reed tooth.






     1.in position The cross threads in blue are drawn into the holes of the tilt bar, and the plain warps in red are drawn into the perforated reed. Straight warps drawn into the mesh reed are positioned to form the continuous upper shed. The cross threads were brought down by the tilting rod to form the shed and weft registration was carried out.

    in 2nd position After the weft is thrown, the tilt bar moves up and the eye comb moves down. This movement continues until the cross thread comes out of the first gap of the eye comb.

    3.in position When the cross floss comes out of the cavity of the eye comb tooth, the tilt bar slides to the side. The lateral movement of the tilt bar is sufficient to allow the cross thread to pass over the flat warp and pass to the other side of the reed tooth.

    in 4nd position After completing its side movement, the tilt bar starts to move down and the eye comb starts to move up.

    5.in position On the other hand, when the cross warps are lowered, the shed is formed and the weft is ready for insertion. After weft insertion, the system repeats the movement in the opposite direction.

    In this system, the leno yarn (blue color) moves from the left and right of the fixed yarn (red color) in the mesh comb, allowing the nozzle to be opened. Both yarns pass through the normal toothed comb.






    Developed by Dornier ''Easyleno'' The mechanism is actually a mouth opening mechanism. This mechanism can be used in both air-jet and rapier weaving machines. As in normal weaving machines, weft and warp intersect each other at a ninety degree angle in weaving machines that weave leno fabric.





    In this mechanism, there are normal combs and two eyed combs. The comb (blue) in the middle with its eyes facing down makes lateral movements to the right and left. The other gray comb, located at the back and with its eyes facing upwards, moves up and down. The rearmost comb is connected to the frontmost normal comb by a lever. Thanks to this arm, the comb will compress the weft into the fabric, while the gray eyed comb moves down and brings the warp threads to the same level.

    There are two types of yarn in the Leno weaving machine. leno thread, one of which is moving (red thread) the other is fixed thread (blue colored thread). The fixed thread passes through the eyes of the blue comb in the middle. The blue comb moves only laterally during production. Leno thread (moving red thread) passes through the rearmost gray comb. The gray mesh card only moves up and down during production. The fixed thread (blue) always stays under the weft thread. On the other hand, the active red leno thread is always on the weft thread.

    Easyleno weaving machines can work at high speeds with high warp densities.









    In the air jet weaving machine developed by VUTS, there are holes in the frames instead of the forces.






    The first layer warp threads passing through the holes on the frame make vertical movement. The second layer warp threads pass through the needles on the guide plate. The guide plate oscillates to the left and right. The warp threads in the second layer form the leno structure by connecting with the other warp threads.









    The warp threads passing through the guide plate are seen in the lower shed, and the warp threads passing through the holes in the frame are seen in the upper shed. After the weft is thrown, the warp threads are aligned and the tambourine stroke is made.





    3-Jacquard systems

    Jacquard systems are not a system in their own right, they are the adapted version of the reed rotary power system to jacquard mechanisms. Since there is no frame in this system, the forces are connected to the mallion threads from the top and to the springs from the bottom. The movement is given by the jacquard mechanism. It is preferred because of the wide pattern obtained and the reduction of the tension on the warp threads.








    4-Circular leno systems

    Circular weaving machines are similar in appearance to circular knitting machines. Circular leno weaving machines are multi-phase weaving machines developed for the production of tube fabrics used in the sack and packaging industry. It is the weaving machine in which the shuttles follow a circular shuttle path, one after the other, through a wavy shed.




    In circular weaving machines The warp threads come from bobbins lined up on creels on both sides of the machine. The warp threads are fed to the weaving elements from the underside and the fabric is woven by forming a connection with the weft carried by 4 or 6 shuttles in the weaving zone.

    Weft threads, on the other hand, are inside the shuttles as wound on the bobbins and continuously move circularly in the wave-shaped mouthpiece formed in the sleeve.

    circular weaving machines, It is a weaving machine with an all-round circulating system that saves kinetic energy and ensures that the shuttles move without shaking and does not require back and forth movement. Thus, the weft thread does not need to change direction during threading. The number of shuttles increases depending on the diameter. More than one weft is thrown at the same time. Shedding, weft throwing, tuffing processes occur continuously.

    The movement of the weft carrier shuttles is mechanically or electromagnetically controlled. In the mechanical system, the shuttles are moved by the thrust of the friction elements placed under the warp elements. In electromagnetic control, there is no contact between the shuttle and the drive elements.

    The movement of the weft carriers is provided by the rotation of the electromagnetic blocks placed at the back. Electromagnets attract the mining shuttles and follow the circular path of the magnets in the shuttles. Circular weaving machines have weft carriers that carry much more weft threads than shuttles of normal weaving machines. Weft threads are changed outside the shed. For this purpose, all frames are brought to the lower nozzle position.

    Compression of the weft is carried out with lamellas or needle system that makes an oscillating motion instead of a comb. The needle system or the oscillating lamellas reaches the end of the warp threads after the shuttle completes its movement and compresses the weft thread to the fabric line.

    In circular weaving machines The woven fabric is pulled from the middle upper part of the machine and wrapped in a separate winding unit located on the right side.

    It is possible to produce with polypropylene, polyethylene, jute and other yarns. The most important advantage of this type of weaving machines is the insertion of a high amount of weft despite low shuttle speeds.








    5-Disc leno edge systems

    Disc systems are systems used on fabric edges. In woven fabrics, an edge is created to prevent the warp threads from scattering from the edges. Leno weaving edge application is one of the most used techniques in edge formation.

    Leno edge is obtained by crimping at least two outermost warp threads on top of each other. The warp threads curled on each other take the ends of the weft threads between them and provide a stable structure. After the leno edge is formed, the floor is separated from the fabric with the help of scissors and a resistor. It is very important to minimize the yarn consumption during the edge formation as the leno which is separated from the fabric by cutting is discarded. For this, the weft yarns must create the least possible fringing after the width of the fabric.






    In the system, while the discs rotate, they also rotate the warp threads around each other. Here, the yarns are not separated from each other as the basic and rotating warp yarns, but both yarns rotate.



    Posted by %AM, 27% 310%2019 09%:%Jul in Weaving

Leno Fabric Weaving Techniques