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Looms & Weaving


Weaving


Weaving is a textile craft in which two distinct sets of yarns or threads, called the warp and the
filling or
weft (older woof), are interlaced to form a fabric or cloth. The warp threads run lengthways
on the piece of cloth, and the weft runs across from side to side, across the bolt of cloth


Weaving is done by intersecting the longitudinal threads, the warp, i.e. "that which is thrown
across", with the transverse threads, the
weft, i.e. "that which is woven".





 
Warp and weft in plain weaving
 

The way the warp and filling threads interlace with each other is called the weave. The majority of
woven products are created with one of three basic weaves:
plain weave, satin weave, or twill.

Woven cloth can be plain (in one colour or a simple pattern), or can be woven in decorative or
artistic designs, including
tapestries. Fabric in which the warp and/or weft is tie-dyed before
weaving is called
ikat.

The ancient craft of handweaving, along with hand spinning, remains a popular craft. The majority
of commercial
fabrics in the West are woven on computer-controlled Jacquard looms. In the past,
simpler fabrics were woven on
dobby looms, while the Jacquard harness adaptation was reserved
for more complex patterns. Some believe the efficiency of the Jacquard loom, with its
Jacquard
weaving
process, makes it more economical for mills to use them to weave all of their fabrics,
regardless of the complexity of the design.

 

Process

An Indian weaver preparing his warp

 
 
A woman weaving with a
manual loom


In general, weaving involves the interlacing of two sets of threads at right angles
to each other: the warp and the weft. The warp are held taut and in parallel order,
typically by means of a loom, though some forms of weaving may use other methods.
The loom is warped (or dressed) with the warp threads passing through
heddles on
two or more harnesses. The warp threads are moved up or down by the harnesses
creating a space called the
shed. The weft thread is wound onto spools called bobbins.
The bobbins are placed in a
shuttle that carries the weft thread through the shed.
The raising and lowering sequence of warp threads gives rise to many possible
weave structures:

 

Both warp and weft can be visible in the final product. By spacing the warp more closely, it can
completely cover the weft that binds it, giving a warpfaced textile such as rep weave. Conversely,
if the warp is spread out, the weft can slide down and completely cover the warp, giving a
weftfaced textile, such as a
tapestry or a Kilim rug. There are a variety of loom styles for hand
weaving and tapestry. In tapestry, the image is created by placing
weft only in certain warp areas,
rather than across the entire warp width.


Loom is a device used to weave cloth. The basic purpose of any loom is to hold the warp threads
under
tension to facilitate the interweaving of the weft threads. The precise shape of the loom and
its mechanics may vary, but the basic function is the same.


The major components of the loom are the warp beam, heddles, harnesses, shuttle, reed and
takeup roll. In the loom, yarn processing includes shedding, picking, battening and taking-up
operations.


 

  • Shedding. Shedding is the raising of the warp yarns to form a shed through which the filling
    yarn, carried by the shuttle, can be inserted. The shed is the vertical space between the
    raised and unraised warp yarns. On the modern loom, simple and intricate shedding
    operations are performed automatically by the heddle or heald frame, also known as a
    harness. This is a rectangular frame to which a series of wires, called heddles or healds, are
    attached. The yarns are passed through the eye holes of the heddles, which hang vertically
    from the harnesses. The weave pattern determines which harness controls which warp
    yarns, and the number of harnesses used depends on the complexity of the weave. Two
    common methods of controlling the heddles are
    dobbies and a Jacquard Head.


     
  • Picking. As the harnesses raise the heddles or healds, which raise the warp yarns, the shed
    is created. The filling yarn in inserted through the shed by a small carrier device called a
    shuttle. The shuttle is normally pointed at each end to allow passage through the shed. In a              
    traditional shuttle loom, the filling yarn is wound onto a quill, which in turn is mounted in the
    shuttle. The filling yarn emerges through a hole in the shuttle as it moves across the loom.
    A single crossing of the shuttle from one side of the loom to the other is known as a pick.
    As the shuttle moves back and forth across the shed, it weaves an edge, or selvage, on
    each side of the fabric to prevent the fabric from raveling.


     
  • Battening. As the shuttle moves across the loom laying down the fill yarn, it also passes
    through openings in another frame called a
    reed (which resembles a comb). With each
    picking operation, the reed presses or battens each filling yarn against the portion of the
    fabric that has already been formed. The point where the fabric is formed is called the fell.             
    Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.

With each weaving operation, the newly constructed fabric must be wound on a cloth beam. This   
process is called taking up. At the same time, the warp yarns must be let off or released from the
warp beams. To become fully automatic, a loom needs a filling stop motion which will brake the
loom, if the weft thread breaks.  An automatic loom requires 0.125 hp to 0.5 hp to operate.

From 1942 the faster and more efficient shuttleless Sulzer Looms and the rapier looms were        
introduced. Modern industrial looms can weave at 2000 weft insertions per minute. Today,
advances in technology have produced a variety of looms designed to maximize production for
specific types of material. The most common of these are air-jet looms and water-jet looms.


Projectile and rapier looms eliminated the need to take the bobbin/pirn of thread through the
shed;


Dobby Loom is a type of floor loom that controls the whole warp threads using a device called
a dobby.
Dobby is short for "draw boy" which refers to the weaver's helpers who used to control the
warp thread by pulling on draw threads.


A dobby loom is an alternative to a treadle loom. Each of them is a floor loom in which every warp  
thread on the loom is attached to a single shaft using a device called a
heddle. A shaft is
sometimes known as a harness, but this terminology is becoming obsolete among active weavers.
Each shaft controls a set of threads. Raising or lowering several shafts at the same time gives a
huge variety of possible gaps or '
sheds' through which the shuttle containing the weft thread can
be thrown.

A manual dobby uses a chain of bars or lags each of which has pegs inserted to select the shafts
to be moved. A computer assisted dobby loom uses a set of solenoids or other electronic devices
to select the shafts. Activation of these solenoids is under the control of a computer program. In
either case the selected shafts are raised or lowered by either leg power on a dobby pedal or
electric or other power sources.


On a treadle loom, each foot-operated treadle is connected by a linkage called a tie-up to one or
more shafts. More than one treadle can operate a single shaft. The tie-up consists of cords or
similar mechanical linkages tying the treadles to the lams that actually lift or lower the shaft.


On treadle operated looms, the number of sheds is limited by the number of treadles available. An
eight shaft loom can create 254 different sheds. There are actually 256 possibilities which is 2 to
the eighth power, but having all threads up or all threads down isn't very useful. However, most
eight shaft floor looms have only ten to twelve treadles due to space limitations. This limits the
weaver to ten to twelve distinct sheds. It is possible to use both feet to get more sheds, but that is
rarely done in practice. It is even possible to change tie-ups in the middle of weaving a cloth but
this is a tedious and error-prone process, so this too is rarely done.


With a dobby loom, all 254 possibilities are available at any time. This vastly increases the number
of cloth designs available to the weaver. The advantage of a dobby loom becomes even more      
pronounced on looms with 12 shafts (4094 possible sheds), 16 shafts (65,534 possible sheds), 
or more. It reaches its peak on a
Jacquard loom in which each thread is individually controlled.


Another advantage to a dobby loom is the ability to handle much longer sequences in the pattern.
A weaver working on a treadled loom must remember the entire sequence of treadlings that make
up the pattern, and must keep track of where they are in the sequence at all times. Getting lost or
making a mistake can ruin the cloth being woven. On a manual dobby the sequence that makes up
the pattern is represented by the chain of dobby bars. The length of the sequence is limited by the
length of the dobby chain. This can easily be several hundred dobby bars, although an average
dobby chain will have approximately fifty bars.


A computer controlled dobby loom (Computer-Dobby) takes this one step further by replacing the
mechanical dobby chain with computer controlled shaft selection. In addition to being able to
handle sequences that are virtually unlimited, the construction of the shaft sequences is done on
the computer screen rather than by building a mechanical dobby chain. This allows the weaver to
load and switch weave drafts in seconds without even getting up from the loom. In addition, the
design process performed on the computer provides the weaver with a more intuitive way to
design fabric; seeing the pattern on a computer screen is easier than trying to visualize it by
looking at the dobby chain.


Dobby looms expand a weavers capabilities and remove some of the tedious work involved in     
designing and producing fabric. Many newer cloth design techniques such as
network drafting
can only reach their full potential on a dobby loom.


Historical Note: Dobby looms first appeared around 1843 -- roughly forty years after M. Jacquard  
invented the Jacquard device that that can be mounted atop a loom to lift the individual heddles
and warp threads.


Jacquard loom

 



The Jacquard loom is a mechanical loom, invented by Joseph Marie Jacquard in 1801, that
simplifies the process of manufacturing textiles with complex patterns such as
brocade, damask,
and
matelasse. The loom is controlled by punched cards with punched holes, each row of which   
corresponds to one row of the design. Multiple rows of holes are punched on each card and the
many cards that compose the design of the textile are strung together in order. It is based on
earlier inventions by the Frenchmen
Basile Bouchon (1725), Jean Baptiste Falcon (1728) and
Jacques Vaucanson (1740).


Principles of Operation

Each hole in the card corresponds to a "Bolus" hook, which can either be up or down. The hook
raises or lowers the harness, which carries and guides the
warp thread so that the weft will either
lie above or below it. The sequence of raised and lowered threads is what creates the pattern.
Each hook can be connected via the harness to a number of threads, allowing more than one
repeat of a pattern. A loom with a 400-hook head might have four threads connected to each
hook, resulting in a fabric that is 1600
warp ends wide with four repeats of the weave going
across.

The term "Jacquard loom" is a misnomer. It is the "Jacquard head" that adapts to a great many
dobby looms such as the "Dornier" brand that allow the weaving machine to then create the
intricate patterns often seen in
Jacquard weaving.

Jacquard looms, whilst relatively common in the textile industry, are not as ubiquitous as dobby
looms which are usually faster and much cheaper to operate. However unlike jacquard looms they
are not capable of producing so many different weaves from one
warp. Modern jacquard looms
are controlled by computers in place of the original punched cards, and can have thousands of
hooks.

The threading of a Jacquard loom is so labor-intensive that many looms are threaded only once.  
Subsequent
warps are then tied in to the existing warp with the help of a knotting robot which ties
each new thread on individually. Even for a small loom with only a few thousand
warp ends the
process of re-threading can take days.


Importance to Computing

The Jacquard loom was the first machine to use punched cards to control a sequence of
operations. Although it did no computation based on them, it is considered an important step in
the
history of computing hardware. The ability to change the pattern of the loom's weave by simply
changing cards was an important conceptual precursor to the development of
computer
programming
. Specifically, Charles Babbage planned to use cards to store programs in his
Analytical engine.


Noveltex supplies all kinds of silk fabrics woven by shuttle loom,
rapier loom and projectile loom, including Dobby and jacquard silk
fabrics, for both apparel and home furnishing purpose.

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