Air jet Loom

Jet Weaving
Prof. Dr. Emel Önder
&
Ass.Prof.Dr.Omer Berk Berkalp

General Considerations
• In jet picking, the weft yarn is inserted by means of a fluid
known as jet.
• The fluid used in jet-weaving may be air or water.
• The relative velocity between the jet and the weft thread
produces a force on the weft which results in its insertion in
the shed.
• The air jet weaving machines are supplied with compressed
air from a central compressor in the weave room or are
equipped with individual built -in compressors.
• The water jet weaving machines are equipped with individual
injection pumps to pressurize water supplied from the water
main; waste water is discharged into a drain.

• To achieve acceleration of
either compressed air or
pressurized water together
with the leading end of the
weft yarn a nozzle is used.

• The mass of insertion medium to be accelerated is very small,
relative to the shuttle, rapier or projectile weaving machines,
which allows high running speeds.
• Mass of the fluid is about 1.5g.
• Unlike the rapier or projectile insertion systems, there are not
many mechanically moving parts to control and insert the
weft yarn.
• Technical requirements of the fluid are important:
temperature, humidity, impurity content,etc.

• As the tractive force applied to the weft is not very
high, it must be prepared for picking by a metering
device.
• In the majority of the jet weaving machines the
picking system is fitted only on one side of the
machine (single-sided picking) and
• The picking system is fixed firmly to the machine
frame so that the beat-up mechanism carries only
the reed and/or the air duct.

The weaving process
1 cross wound cone, 2 guide eye
and 3 tensioner, 7 metering
device (measures the necessary
pick length of the weft thread). 9
holders to retain the weft thread
after picking, 10 nozzle. The
water or air are supplied to
through tube T
A — the reed, B — the warp
sheet, C — the woven fabric, D
— the weft cutter, E and F — the
leno weave serving to reinforce
the fabric selvedges

The weaving process
The passage of the warp through a jet loom (Elitex air-jet loom)
The weft-insertion medium
does not require support.
The passage of the warp
through the machine can be
modified, so that a
substantial saving in floor
space will be achieved.
The cloth roller is situated
under the warp at the back
of the loom as illustrated.
This makes servicing of the
warp, weft, and cloth from
the back alley easier.

The tractive force in the weft thread
• If the weft thread was merely surrounded by the air or
liquid during the picking and if its velocity was the
same as that of the picking medium it would be
completely tensionless.
• The weft thread would then curl and snarl on itself
across the shed and its insertion would be rather
uncertain.
• Therefore, a tractive (drag) force is needed to produce
the necessary tension in the weft thread and to maintain
that tension for the whole duration of the pick.

• In the jet picking systems this tractive force on the weft thread
results from the friction between the air or liquid and the surface
of the weft thread.
• This explains why the velocity of the picking medium must be
greater than that of the weft thread.
• The level of friction developed in a flowing medium is dependent
on
the square of the velocity difference,
the viscosity of the medium,
the roughness and length of the weft thread and,
in the water jet insertion systems, the wetting property of the weft
yarn.

• Initial velocity of air- 200-300 m/s, initial velocity of water- 40-60 m/s,
initial velocity of weft yarn- 20-30 m/s.
• The higher the viscosity the higher the tractive force .
• As the viscosity of the air is very low, high relative velocities must be used
in the air jet picking systems.
• Viscosity is largely dependent on the temperature of the medium. For
example, the viscosity of water at 0 0C is 0.017 g cm-1 s-1 while at 100 0C
it is as low as 0.0028 g cm-1 s-1.
• In the jet picking systems the tractive force on the weft thread is the
higher the rougher the surface of the weft yarn.
• Considering the low viscosity of the employed picking medium, air-jet
picking systems are designed mainly for the spun weft weaving. However,
they have become suitable to insert filament yarns with some
developments in main nozzle design.

The water jet picking system
• The weft insertion on a water-jet weaving
machine is divided into three phases:
Acceleration of the water in the pump prior to its
injection into the nozzle.
Jet outlet from the nozzle.
Flow in the free environment in different forms:
Compact
Split
Atomized

The injection pump
The water is
incompressible.
When the water is
supplied into a pump
cylinder, it is accelerated
by a spring loaded piston
and the fed through a
piping to the main nozzle.

The main nozzle
The advantage of this type of nozzle is its
simplicity. Its disadvantage is a considerably
higher consumption of water and water
leakage between individual picks.
Open nozzle, no
moving parts.
Fv=constant

Bernoulli’s equation
• The pressure in a moving fluid depends on its speed.
• In particular, since an incompressible liquid’s flow rate is
greater in a constraint region than the rate in a region of a
larger cross section, the pressure is low in the constraint
region. This produces a vacuum effect to accelerate the weft
yarn.
• Similarly, the pressure exerted by the moving air is less than
the pressure of stationary air. The stationary weft yarn is
pushed towards the moving air.
tconsvghP tan
2
1 2
=++ ρρ

Flow in the free environment
A — compact, B — split, C —
atomized. The most suitable for
the weft insertion is the compact
portion of the flow and possibly
also the split portion.
Cp :jet front and Cu :weft front
At tX, the relative speed vR = vp -
vu becomes negative. Beyond
this point tX, the weft thread is
likely to curl and snarl

The timing diagram
A water jet is capable of maintaining its concentration and thus its force over
a greater distance than an air jet, but there are no means readily available to
assist the jet as it traverses the loom.
The weft thread is braked by the reed. The axis of the water jet is more or
less parallel with the fabric fell. The reed moving forward towards the
fabric runs into the wet weft thread, which adheres to it, and is braked by it
and prevented from contracting in the length.

The working conditions
• The water quality:
– Mechanical impurities must be filtered
– Must not contain sediment forming additives (Fe, Mg, Ca, Si)
– Hardness:5-10 in German scale
– Must be harmless biologically and hygienically.
• The working conditions:
– Operating temperature of water: 16-24 0C
– Operating pressure of water:0.5-1.5 kg/cm2
• Design modifications of weaving machine:
– The machine should be provided with an anti corrosive protective
finish or the machine parts (i.e. Reed, temples, healds) should be
made of corrosion resisting steels.

The working conditions
• Water extraction and final drying
– The cloth may contain a great amount of water.
– It is achieved through a cloth squeezing or a suction and then drying.
– Such a system consumes 2 to 3 kW energy and unwelcome source of
additional heating in the weaving room.
– The waste water is usually removed into a drainage system.
• Working speeds:
– The width and speed of water jet looms have been gradually
increased.
– The modern water jet weaving machines can have a speed of around
1500ppm while the maximum reed width is 3 m and the WIR is
1800m/min.

AIRAIR--JET WEAVINGJET WEAVING
• Air jet weaving is a type of weaving in which the weft yarn
is inserted into the warp shed with compressed air.
• The air-jet weaving machine combines high performance
with low manufacturing requirements.
• It has an extremely high weft insertion rate.
• Due to its exceptional performance, air-jet machines are
used primarily for the economical production of standard
fabrics, covering a wide range of styles.
• Meanwhile, more and more special fabrics are also
covered: heavy cotton fabrics such as denim, terry fabrics,
glass fabrics, tire cord,etc.

• High productivity
• Low initial expenses
• High WIR
• Simple operation and reduced hazard because of few
moving parts
• Reduced space requirements
• Low noise and vibration levels
• Low spare parts requirement
• Reliability and minimum maintenance
TheThe advantagesadvantages ofof airair--jetjet weavingweaving machinemachine::

Air jet pickingAir jet picking
• Air-jet picking is governed by the same rules and
relationships as described before for the water-jet
picking.
• However the viscosity of air is hundred times lower than
the viscosity of water. Thus, it may lose its integrity
easily.
• Therefore, a higher air jet speed is required to produce
the necessary tractive force.
• Moreover, different types of insertion configurations are
designed.

Insertion ConfigurationsInsertion Configurations
• Three different systems have been used mainly
on commercial air-jet weaving machines:
1. Single nozzle, confuser guides and suction unit at the
exit side
2. Multiple nozzles with guides
3. Multiple nozzles with profiled reed
• Although all three systems have been used in commercial
looms, the System3 is the most common and standard
configuration in the market.

Insertion ConfigurationsInsertion Configurations
• The main nozzle applies the necessary driving force to initiate
the insertion of predetermined length of weft yarn.
• The air jet flying in a free space entrains (becomes mixed)
with the environmental air and loses its velocity on a
relatively short distance.
• The integrity of the air is preserved by either a confuser or a
tunnel (profiled) reed.
• Buckling of the leading end of the weft is prevented by
applying a constraint at the insertion side of the machine and
by maintaining the projection velocity by a series of back-up
jets. This system is precisely timed and back-up nozzles are
progressively opened.

System1:Single nozzle, confuser guides and suction
unit at the exit side
•Air jet guide ducts (also known as confuser) is formed by a series of ribs (flat
metal plates). They are located on the raceboard in front of the reed and
penetrate between the warp ends during the picking.
•The confuser keeps the initial concentration of the air as much as possible.
•The leading end of the weft is stretched by a suction device

The disadvantage of this system is the weaving width limitation due to
the lack of additional back-up nozzles to keep the air velocity high
enough.
Elitex, 190 cm, 1200 ppm, WIR 1920 m/min
Air duct is conically expanded in the picking direction so that air molecules
in the outer fringes of the jet can be deflected back into the main stream.

The main nozzle
The compressed air is continuously fed
to the jet nozzle. The center barrel of the
nozzle is then made to move outwards by
a cam system, and this creates a gap
through which the pressurized fluid will
be forced.
The air V enters the nozzle
body 1 and flows through
milled grows A round the
nozzle core B in whose orifice
the weft thread is threaded in
the direction of u. The core is
tightened in the body by nut C.
It is an open nozzle without
any inside closures.

System2:Multiple nozzles with guides
• In addition to the main nozzles and air guide
ducts, auxiliary nozzles are also used. They
are located at certain intervals and they
inject (blow) the air sequentially in groups in
the direction of yarn movements.

System 3:Multiple nozzles with profiled reed
+
stretching
nozzle

System 3:Multiple nozzles with profiled reed
• The profiled reed wires are used and the weft yarn is fed in to
the reed tunnel via the main nozzle.
• The main nozzle (sometimes the main and tandem nozzle
combination) provides the initial acceleration, where the relay
nozzles provide high air velocity across the shed.
• Profiled reed provides guidance for the air stream and
separates the weft yarn from warp sheets.
• Relay nozzles are located at certain intervals, say 50 mm,
however, last four nozzles at the exit side are spaced closer,
say 25 mm.
• Additional nozzles increase the air consumption.

The air jet weaving
machines are supplied
with compressed air
maintained from a central
source.
The preparation of the air
before its distribution of
the air to the individual
weaving machine
through a valve system:
•Filtering
•Compressing
•Cooling
•Drying
•Air tank
•Weaving Machine

Weft insertion in air jet picking
The air flow from the nozzle.
The air flow through the shed.
The weft motion.
• The transporting medium has a complicated motion.
• Air flow in weft insertion is unsteady, turbulent, and can be
either compressible or incompressible depending on the
velocty( for air velocities above 100 m/s, compressibility
should be taken into account).

1.The air flow from the nozzle :
• The initial driving force applied to the weft is:
• Fd = driving force
• C = coefficient of friction between air and yarn
• d = yarn diameter
• l = yarn length in the jet subjected to jet pressure
• v = air velocity in the jet
• ρ =air density
( ) 2/2
ρπ lvdCFd =

1.The air flow from the nozzle :
• (Cπd) depends on yarn characteristics:
• The hairiness and roughness influence C
• The yarn linear density and the material influence diameter d
and its circumference.
• Air requirement per pick increases with linear density.
• The density of the air is also very significant and air requirement
is gravimetrically specified, i.e. g/min. This is particularly
important when machines are to be operated in elevated and
high temperature environments.
( ) 2/2
ρπ lvdCFd =

3. The weft motion through the shed:
• The equation of weft motion is
TFSv
dx
dm
ma =+++ 2
• The force acting on the moving thread is proportional to:
( )wa VVld −×××× µρ

Performance of Yarns in Air-jet Weft Insertion
• Air-jet weaving machines are ideal for cost effective
production of bulk fabrics with a wide range of styles.
• Air-jet machines can handle both spun ( natural, synthetic
or blended) yarns and continuous filament yarns.
• Textured yarns are especially suitable, however
monofilament yarns are not suitable.
• A wide range of fabrics from gauze fabrics to dense, heavy
cotton fabrics, from patterned dress fabric to ribbon fabrics
can be woven on air-jet weaving machines .
• The factors that essentially determine whether a yarn is
suitable for the air-jet weft insertion are its count, structure
and twist.

Yarn Count (Ne) Twist Multiple Structure Acceleration (m/sq.sec)
10/1 4 RS 968
10/1 4 OE 865
13/1 4 RS 1189
13/1 4 OE 1083
16/1 4 RS 1258
16/1 4 OE 1235
Table 8.4. Acceleration of open end OE and ring spun (RS) yarns 10
milliseconds after the yarn insertion.

Air jet Loom

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