Weaving Report, Molefe

8/3/2019 Weaving Report, Molefe

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WEAVING

Dimpo .A. Molefe Student ID: T0000576

Weaving Report

Part one: Yarn Preparation for Weaving

Weaving is a textile craft in which two distinct sets of yarns or threads, called the warp and

weft 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. See figure 1 below.

Figure 1: Warp and Weft interlacement

Since the fabric consists of warp and the weft, there are several stages that must be undertaken

on warp yarn compared to weft yarn. This is because warp yarn during the weaving process

experience higher frictional forces since there are thousands of them in the weavers beam,

while the weft yarn experience less force or not at all since during the process only one yarn is

inserted per fabric width. Therefore, warp yarn must be prepared according to the following

stages: beam warping, sizing and waxing, drawing in or tying in and fabric manufacture.

These steps will be carried with a purpose of improving yarn strength by coating, lay down

fibers (hairness reduction) and frictional force (abrasion resistance).

Warping

There are three times of warping: beam or direct warping, sectional or indirect warping

and ball warping.

Direct warping is used for the production of the grey and the mono-color fabrics. For fabric

with one color dyeing can be done yarn before weaving or on the fabric after weaving. Here,

the warpers beams are prepared first from cones range 500-600 (means yarn in this beam are

equal to the number of cones), the cones are situated at the creel. These beams are then taken

to produce weavers beam (beam with thousands of yarns in a beam could be up to 5000

threads) ready for weaving. In a warpers beam threads are loosely packed while in weavers
http://upload.wikimedia.org/wikipedia/commons/c/c7/Kette_und_Schu%C3%9F.jpghttp://www.ft.tul.cz/index.cgi?sou=akce/oslavy_50_let/seznam.htm


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beam are closely packed because beams have the

same size. In preparing the weavers one need a

number of warpers beams for example, if you want

to create weavers beam with 4800 threads from

warpers beam with 400 threads that means 12

warpers beams will be needed. The white and

green structure below is called a beam where by the

green part is called flanges that give a support to the

drum and prevent yarn slippage. White part is the

supported yarn. See figure 2

Figure 2: Beam structure

The expanding comb in a direct beam has the aim of placing all threads on a width

corresponding to the beam width and the aim of maintaining them in order and without

entanglements, while pressure roller (coated with hard cardboard) are responsible forincreasing winding thickness of the yarn on the beam by moving the pressure roller

backwards, thus opposing the resistance offered by the pressure at the set value.

Sectional warping is used forproduction of warp pattern (mixed colors) fabrics, for example

in a creation of stripes and checks materials. See figure 3 below. In the production of such

fabrics only yarn that needs to be dyed before weaving process, fabric can never be dyed. In

sectional warping before preparing weavers beam the warp section laying (sections of

different colors) on the cone drum with one sliding flange must be prepared first. The warp

section with the minimum width of 4mm can have a minimum of 12-24 threads dependingyarn fineness, for maximum end of 480 -560 threads the section width could be up 150mm.

Section drum is prepared by wounding different sections according to need of the fabric, for

example, first section is wound up the sliding cone to make layers, when enough layers are

being made the second one starts wounded, etc. The layers are made in such a way that they

are sliding according to the slope of the cone drum, which means that the second layer must

wound few (mm) to the left from where first layer was wounded see figure 4 below.

a. b.

Figure 3: a. represent strips, b. represent checks
http://www.furnishingfabrics.com/bijapur-as-1092.html


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Figure 3: warp yarn wounded according to section of colors

After section laying preparation the yarn can be transferred to the weavers beam ready for

weaving which can have the 5000 threads.

Leasing rod framewhich during warping separates the threads into various layers, so that they

can go through the subsequent expanding comb without mutual crushing. It serves also

tocreate the room necessary to insert the leasing strings for the sizing operation.

Ball warping is used for production of fabrics such as denim (jeans garment). Cross winding

of yarn around the beam is applied with an aim of increasing dye up take during yarn dyeing

and to avoid breakage during unwinding balls which take place during dyeing. This kind of

warping is called rope form where by 500 to 600 threads are wound around the beam. The

balls are then taken for dyeing and the dyed yarn is stored in tabs (see figure 4 below) which

will be then ready for re-beaming.

Figure 4: storage tabs

Re-beaming involves re-opening of the rope in single yarn and finally wind on a warper beam

for sizing and repair of the damage to yarn due to wet processing is also done at this stage.

Sizing

In this process warper beams are combined to complete the total ends required for one width

and yarn is coated with a chemical formulation (natural chemicals like starch, synthetic,

wetting agents, etc) to withstand friction and stresses during weaving.

Figure 5: Sizing machine: 1 Size vat; 2 Hot air oven; 3 Drum drying machine; 4 Waxing device; 5 Beaming


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Drawing

Drawing-inconsists of threading the warp yarns through the drop wires, the healds and the

reed. Depending on the styles of the produced fabrics and on the companys size, this

operation can be carried out manually (done by hands) see figure 6 below.

Figure 6: Drawing-in

Fabric manufacturing

Figure 7: Schematic diagram for fabric manufacture

There are three motion looms that are involved during the fabric manufacture, primary

motion, secondary motion and auxiliary motion.

Primary motion:

Primary motion consists of three parts, shedding (involves cam, dobby and jacquard), picking

(shuttle, shuttleless) and beat up (crank).

Shedding is a function of weaving involving the lifting of harnesses containing warp ends in

order to provide a shed opening for filling (weft) insertion and to control design. There are

severak types of shedding which are as follows:

Cam Shedding involves the following:

- Employs circular profiled cams to lift the harnesses

- Usually 6- 8 harnesses

- High loom speeds

- Lifting plan relatively easy to change

- Plain, simple twill and satin weaves


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Dobby Shedding:

- Employs a chain of wooden bars with pegs inserted or plastic paper with holes inserted or

computer controls

- Usually 8 - 24harnesses

- More complex twill and satin weaves

- Small geometric figuresand spot weaves

- Pattern stripes

- Slower loom speeds than cam shedding

- Lifting plan more difficult to change

Jacquard Shedding:

- Employs cardboard cards with holes inserted, plastic paper with holes, or computer controls

- Individual warp ends or groups of warp ends are lifted without the use of harnesses

- Design capability is virtually unlimited

- Can produce very large design repeats

- Slowest loom speeds

- More expensive fabrics

Above figures show the complex fabric produced by jacquard design. The flowers seen on the

computer are created on a computer by a program called design scope victor and then weaved

by this systim there is no printing here.

Picking is the method of passing the weft threads which traverses across the fabric through

shed and the inserted weft is known as pick. On the basis of the system used for weft insertion

(picking) modern used called shuttle less and old days used are shuttle (more details about

differences will discussed in part of this report), the weaving machines can be divided into:

A) machines with mechanical weft insertion system:

-by rigid rapiers

- by flexible rapiers

- by projectiles

B) machines with non-mechanical weft insertion

system:- by jets of compressed air


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- by jets of compressed ?? water

Furthermore the machines can be divided into:

A) mono-phase weaving machines (inserting one weft at a time)

B) multi-phase weaving machines (inserting several wefts at a time) but which is still under

research.

Beating up is the process of pushing the pick into the ready woven fabric at a point known as

fell of the cloth. Functions of the reed (see figure above)

- Keep ends parallel and in the same position

- Beat the filling yarn into the fabric

- Provide some control for filling insertion

Implications of increased beat-up

- Filling density

- Warp tension

- Fabric structure and properties

Secondary Motion:

Secondary motion constists of too mechanisms, let off and take up.

Let- off Motion the motion which delivers warp in the weaving area at the required rate and

at a suitable constant tension by unwinding it from a flanged beam called let-off motion. Also

it is divided into two segments negative and positive.

Negative let offthe warp is pulled off the beam and the tension is related by the slippage in a

braking system (friction between chain or rope and beam ruffle) and pull of the warp is totally

against the friction force against let off motion (simple non- automatic mechanism). In a

positive let off, the beam is driven through positive mechanism where there is no slippage takeplace and the tension is controlled by mechanism driving the warp beam, which allows a

certain loss of motion whenever tension increases (automatic control).

Take-up Motionthe motion which withdrawals fabric from the weaving area; at the constantrate that will give the required spacing and winds the fabric onto a roller is called take up

motion. Positive take up is also divided into wheel take up and positive take up.

Auxiliary Motion:

It is responsible for stopping the machine (stop whole process) whenever there is a yarn

breakage by dropping the heald wires that hold the yarn.


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Part Two: Difference parts (types) of Looms.

In weaving a fabric there are so many stages that have to be followed, although in part one

some of looms were discussed but not in details because it was discussing about the whole

process of manufacturing the fabric from beam warping making to completely woven fabric.

Therefore, this part will focus in details on each and every loom. The main types of looms to

focus on are as follows, looms responsible for shedding and those responsible for picking

(weft insertion).

Shedding Motion

Shed involves dividing warp threads into two sheets, thus providing the path for weft

insertion and this is done by raising and lowering frames. This is the area where basic

functions of weaving are performed. Shedding are divided into three (types)parts, cam,

dobby and jacquard shedding where by these can work with different speeds and produce

different type fabrics. Shedding size is very important because it allows a secured weft

insertion. Shedding opening is determined by means of weft insertion (because there are

different ways) and beat up.

Cam shedding is used for designing simple fabrics that have limited number picks about 8 to

10 picks and also limited number heald shafts about 8 to 12. It is called cam shedding because

heald shaft motion for shed opening is created by cam. The motive cams convert the rotary

motion of the main shaft of the weaving machine into the reciprocating the motion of theheald flames. The cam shedding mechanism can be operated by means of positive or negative

action. In positive action, heald shafts are both raised and lowered by cam (see figure 1

below) system of shedding mechanism and in negative action, heald shafts are either raised

or loweredby the mechanism, but are returned by action of some external device, such as

springs. Each cam is connected to its own heald shaft.

Figure 1: Conjugated cams with roller lever

Dobby shedding are used for the production of plain or flat fabrics, that is of fabrics

characterized by

maximum 28-32 heald hafts in the weave repeat. Dobbies can be divided into partsaccordingto the working principle, Hattersley dobbies and rotary dobbies.The Hattersley dobbies are


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dobbies which control the movement of the heald frames through rodsand rocker levers. The

rotary dobbies attain the raising and lowering of the heald frame throughrotating members.

According to the raising motion of the heald frames there are dobbies with positive drive

dobbies with negative drive.

Figure 2: Rotary dobby

Jacquard shedding is used for designs that require the production of drawn shapes, whereby

it is necessary for warp threads to be separately controlled. There is no limit to the number of

picks (can be greater than 5000). Jacquard machines are made in a wide variety of sizes to

control from 100 to 2000 or warp threads. When a high number of independent lift is required

two or three jacquard machines is placed side to side.

Figure 3: Jacquard machine with deck

Picking (Weft insertion)

Picking involves insertion of transverse thread called 'weft' into the space created by the

division of warp sheets. Weft insertion is divided into parts shuttle used in old days and

shuttleless modern used. A shuttle (see figure 4) is a tool designed to neatly and compactly

store weft yarn while weaving. Shuttles are thrown or passed back and forth through the shed,

between the yarn threads of the warp in order to weave the weft.

The simplest shuttles, known as "stick shuttles", are made from a flat, narrow piece of wood

with notches on the ends to hold the weft yarn. More complicated shuttles incorporate

bobbins. Shuttle moves continuously left to right and right to left, and produces closed

selvedge (see figure 1 in part 1) still to be discussed below. The flying shuttle (replaced hand

operation) was one of the key developments in weaving that helped fuel the Industrial

Revolution. It was controlled by a lever and only one weaver had control of this motion. Asprior to this invention weaver used to weave by hand and could only weave a fabric no wider


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than an arms length. If this length exceeded the maximum, two people would do the task of

one but now the flying shuttle can weave much wider than an arms length at much greater

speeds.

Figure 4: wooden shuttle

Shuttleless looms have been developed to overcome the inherent problems created by the

dynamics of the picking mechanism on the conventional Fly Shuttle Looms and make use of

entirely different methods of weft insertion. Air Jet, Water Jet, Rapier, Gripper (Projectile)

and Multi-Phase are the various types of Shuttleless Weaving Machines named after the

method employed for weft insertion.

Projectile looms use a projectile (figure 5) to carry the fill yarn across the weave. Guide teeths

(see figure 6) is the path where by projectile with a gripped yarn move along to provide

control of projectile and it has a gap used to release weft yarn. The projectiles work in

sequence, that is they are launched in succession. They run therefore one after the other,

describing in the space a continuous, endless route, as if they would be stuck on a conveyor

belt.
http://upload.wikimedia.org/wikipedia/commons/9/91/Shuttle_with_bobin.jpg


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Fig. 5: Projectiles Fig.6: guide teeth

Fig. 7 below shows the projectile conveyor chain (shuttle return chain), the projectile

(shuttle) with its back clamp to seize the yarn (thread grippers), the cutting tool (scissors) toseparate the inserted weft from the bobbin and the strap which, through twisting, launches the

projectiles.

Fig. 7:

Rapierloomsare divided into single and double where by double rapier also divided intorigid (rod) and flexible (belt). Single rapier is used to weave small width fabrics since only

one rod travel from one end of the fabric to other end during weft insertion.In double rapier, here the taking rapier holds the weft tight between a clamp, which is pressed

by a spring, and the underlying fixed part. In the middle of the shed, when the rapiers cross

each other, the tapered end of the receiving rapier penetrates into the sliding channel of the

carrying rapier and, during the back motion, hooks the weft thread and slips it off from its

position under the clamp of the bearing carrier. In other double can be called rapier exchange.

The rods (fig. 8)have the advantage that the support and the rapier move along the shed

without any contact with the warp, which fact is important especially when delicate yarns are

to be processed the rods are rigid supports. The belts (fig. 9)are flexible supports made of

composite material, which are equipped in the middle with a series of shaped holes through

which they mesh, like a chain, with the driving toothed wheel. The manufacturers have

mounted on the reed bracket small shaped pins which create a slide guide for the belts ;this guide prevents any anomalous movement of the belts, thus ensuring a stable and exact

motion of the rapiers, at any height and speed. Their shape has been designed in order to

minimize their interference with the warp threads.


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Fig. 8: Rigid rod Belt flexible

Air-jet looms is apply for cam shedding and dobby shedding. The air jet weaving machines

are the weaving machines with the highest weft insertion performance. The air jet weaving

machines require air ducts capable of maintaining an effective air flow on the whole

weaving width. To obtain this, the machine manufacturers prefer today to use the system

with profiled reed, in which the air and the thread are guided through a tunnel-shaped reed

(fig. 10).In the air jet weaving machines, the impulse causing weft launch is provided by a main

nozzle (fig. 11), but the jet of compressed air, being blown in a room of same kind, looses

very quickly its own energy. Consequently, if the weft has to be transported along reasonable

widths, the use of additional gears, that is of secondary or auxiliary (or relay) nozzles (12) is

necessary; these, besides pushing the weft forward, have also the task of keeping it inside the

guide channel.

Fig. 12: relay nozzle Fig. 11: main nozzle

Water- jet looms manufacture of light and medium weight fabrics with standard

characteristics and in water repellent fibre materials, primarily multi-filament synthetic yarns.

Fig. 13 shows how the machine operates. The weft yarn, which is fed from cone 7, is drawn-

off by a feeding and measuring device 2 and then passes through a tension regulator 3 and

a weft clamp 4. When the insertion has to take place, the weft clamp loosensits hold and the

thread inserted inside a nozzle 1is struck by a jet of pressurized water and launched

through the shed at high speed. After the insertion has taken place, while the weft is hold

flat by the threads which are moved by the leno mechanisms 5, the thermal knives 14 enter

into action on the launch side to cut the weft, and on the opposite side to trim the fabric.The water is conveyed by a pump 8, provided with a filter, the piston of which is controlled

by a cam 10 producing the phases of water suction from the container 9 and of water supply

to nozzle1. The sequence of the launch phases is the following: the pump 8 enters into action

and the initial water jet serves only to straighten the residual small piece of weft, from nozzle

1 to thermal knife 14. The yarn flight forms a so-called flight angle, leaving clamp 4 open to

permit to the pressurized water jet to insert the weft thread into the shed. The clamp opening

time varies according to reed width and to loom running speed. On yarn exit from the shed,

there is an electrical feeler or an infrared sensor which checks the presence of the weft end

and makes the machine to stop in case of absence of the weft.


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Fig. 13: Process of water jet.

Weaving Report, Molefe

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