Weaving motion beat up

Chapter 5:Beat-up Mechanisms

Prof.Dr. Emel Önder

Ass.Prof.Dr.Omer Berk BerkalpTEK332E Weaving Technology II, E.Önder &Ö.B. Berkalp

1

Beat-up Motion

The third primary weaving motion is performed by the beat-upmechanism (sley mechanism).

The main function of the beat-up mechanism is thereciprocating motion of the reed.

During weaving the reed performs the following functions:

1.

2.

3.

It holds the warp ends at given distances thus determines the warpdensity and fabric width precisely.

Together with the race board and other guiding

elements, it guidesthe

weft carrier across the warp sheet.

The principal and most important function of the reed is to beat-upevery inserted weft thread to the fabric fell.

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2

Beat-up MotionThe motion of the sley

approximates to simpleharmonic.

It should dwell as long aspossible at the rear deadcenter to leave the largestpossi ble sectio n of the anglefor the weft inse rtio n.

On th e ot he r ha nd , it

sh ou ld be at- up th e we ft toth e fa br ic fe ll st ro ng ly inor

der

to

ob

tain

th

e d

esi

red

p i c k d e n si t y.


Rearmost position of the reed during weft insertion

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Beat up position of the reed

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Loom timing

The timings of most of the events in the loom cycle aregoverned by the position of the reed and thus the sley.

For example, the reed must be on its way towards the back ofthe loom before the shed is large enough to admit the shuttle.This determines the timing of the picking mechanism which isdirectly related to the position of the reed and sley.

Some others are related to it indirectly. For example. the timingof the weft break stop motion is related to the flight of the weftcarrier, which is governed by the position of the reed.

The timings on the weaving machine are stated in relation tothe angular position of the crankshaft (main shaft) whichoperates the sley.

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Four-link sley

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Loom timing

Crank cycle0 = front90 = bottom180 = back270 = top

Opp. Crank cycle0 = front90 = top180 = back270 = bottom


Loom timing

The path traced out by the axis of the crank pin iscalled the ‘crank circle’.

The arrow on the crank circle shows the usualdirection of rotation of the crankshaft.

When the crank and crank arm are in line, and the sley

is in its most forward position.

The crank circle is graduated in degrees from thispoint in the direction of rotation of the crankshaft.

Any timing can be stated in degrees, as, for example,‘healds level at 3000’.

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Loom timing

Looms are provided with a graduated disc on the crankshaftand a fixed pointer to make settings in relation to the angularposition of the crankshaft.

With the reed in its most forward position, the disc is adjustedso that the pointer is opposite to 00 on the graduated scale.

The loom may then be turned

to any desired position manually,the disc turning with it and the pointer remaining vertical andindicating the angular position of the crank shaft.

In modern looms with microprocessors, the main shaftposition is displayed on a screen, but the setting principleremains same.

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Types of beat-up mechanisms

There are several types of mechanisms used forachieving the required motion of sley.They are mainly divided

into two:

link-type beat-up

mechanismsFour-link

Six-link

Multi-link

cam operated beat-up

mechanism.

special mechanisms

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1

1

The motion of the sley

Factors Affecting the Motion

When the sley is operated by crank and crankarm, andits motion approximates

to simple harmonic.

The extent to which it deviates from simple harmonicmotion has practical significance and is governed bythe following factors:

a. the radius of the arc along which the axis of

the

swordpinreciprocates,

b. the relative heights of

the swordpin and crankshaft,

and

c. the length of the crank

in relation to that of the crankarm


1

2

Factors Affecting the Motion

The normal arrangement: The axis of the

crankshaft is on a line passing throughthe extreme positions of the axis of theswordpin, and the reed is vertical at beatup.


Factors affecting the sley motionThe swordpin travels along an arc of a circle centered upon therocking shaft.

This modifies the movement of the swordpin and hence of the reed, but,since the radius of the arc (length of the sley sword) is large (about 0.75m),thus, the effect is small enough to be neglected.

Relative heights of the swordpin & crankshaft

Raising or lowering the crankshaft from its normal position affects

both theextent and the character of the motion of the swordpin.

Moving the crankshaft 10 cm up or down from its normal position;

increases the distance moved by the swordpin by about 8%.

increases the swordpin’ s velocity as it approaches its most forwardposition and to decrease it as it approaches its most backward position.

The result is increasing the effectiveness of beat-up and of allowing moretime for the passage of the weft carrier.

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Sley eccentricity, e = r/l

The ratio r/l, where r is the radius of the crank circleand l is the length of the crank arm, is called the sley-eccentricity ratio ,e.The larger it is, the greater is the deviation

from simpleharmonic motion.If e increases then,

more time is available for shuttle passagemore effective beat up (beat up force increases)BUTmechanical problems occur on loom parts.

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Motion of the sleyThe displacement of theswordpin is expressed as afraction of its totaldisplacements for a halfrevolution of the

crankshaft

Crankshaft is in the normalposition.

The curves for the second halfwill be the mirror images ofthose for the first half.

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Motion of the sleyWith simple harmonic motion (corresponding to e=0 and indefinitelylong crankarms), the swordpin attains its maximum velocity and exactlyhalf its maximum displacement at 900 and again at 2700.

With a finite value of e, with any arrangement possible in practice if thesley is crank-driven, the swordpin attains its maximum velocity and halfits maximum displacement earlier on its backward movement and lateron its forward movement.

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17EccentricityRatio (e)

Positions of Crankshaft at HalfMaximum Displacement

0.0 0 0

0.2 0 0

Sley eccentricity, e = r/lAs the sley-eccentricity ratio increases

the sley remains longer nearer its most backward position, and more timeis available for the passage of the shuttle.

increases the maximum attainable velocity of the sley around beat-up.

We may summarize the advantages of a high sley eccentricity

ratio as follows:

(a) it facilitates the passage of the shuttle; and

(b) it tends to increase the effectiveness of beat up.

The effects of altering the sley-eccentricity ratio within thepracticable limits are, however, greater than those obtained byaltering the height of the crankshaft.

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Sley eccentricity, e = r/lThe disadvantages of a high sley-eccentricity ratio:

A high value implies rapid acceleration and deceleration of thesley around beat-up.

It increases the forces acting on the swordpins, crankpins,cranks, crankarms, crankshaft, and their

bearings, andindirectly on the loom frame.

A high sley-eccentricity ratio will therefore demand morerobust loom parts and a more rigid loom frame in order toprevent excessive vibration and wear, so that, for a givenstandard of performances the loom will cost more.

T

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For this reason, most loom

makers tend to avoid eccentricityratios greater than about 0.3. However, there are exceptions.


A. SaurerB. RűtiC. PicanolD. Prince (water-jet)E. DobcrossF. Northrop


In general, the forces involved in accelerating and decelerating the sley will beproportional to the effective mass of the sley and the square of its velocity.

For given sley eccentricity ratio, its

velocity will be proportional to theproduct of the loom speed and the length of the cranks.

A is a typical automatic loom for weaving cotton and spun rayon fabrics and Bis a non-automatic loom for weaving heavy woolen industrial blankets.


Geometry of the sleyAccommodation of

20 heald shafts isachieved partly by

The

Saurer

cotton

loomwith less no.of

healdshafts.

fairly long crankarms,which give a ratherlow

eccentricity ratio.

The

cran

k

s

h

a

ft

posi

tion

i

s

The

crank

shaft

is

normal, and the reed has

aslight f

orward inclination atbeat

-up

above its normalposition,

which w

ouldlie on the dotted

line.

Th e wo o le n a

ndworsted

l oom to Th e reed is vertical at beat-up.

control u p to 28 h ealdshafts. The

cr

ank islonge

r.A h eavy, wide lo om

with a reed space

of

The

reed

has

afor

ward inclination at

beat

-up, and thecran

kshaf

t position isnor

mal.

5.33 m. Its very high

eccentrici

ty ratio(0.54) is practicable

because the loomspeed is only

65pic

ks/min.

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22

Link-type sley mechanisms (for shuttle weavingand some type of jet machines)

The sley does not remain at an absolute dwell at the rear deadcenter position during picking.The six-link

mechanisms give

considerably larger

picking anglesthan four-link

mechanisms.C: It is used in the

production of

heavy-weight

home furnishingfabrics.

Link x moves from

position x1 to

position x2 so that it

passes throughbeat-up position xp

twice within one revolution of crank 2.

This link dwells for

a longer time in the

area of position x2,

whichcorresponds to the rear dead center of the reed, so that an adequately largepicking angle is provided for the shuttle flight through the warp

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3Link-type sley mechanisms:The four-link mechanism: for lower working

widths, a long connecting rod; for larger

working widths a shorter connecting rod

The six-link mechanisms

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Multi link mechanisms These mechanisms are suitable for the heavy-duty weaving machines of large working

widths.

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Cam operated mechanisms (for most of theshuttleless weaving machines)

To achieve high loom speeds on shuttleless weaving machines;

the mass of the sley should be reduced to a minimum

the distance through which it reciprocates should

be as low as possible.

In order to minimize the weight of the sley, heavy partsassociated with picking are mounted on the loom frame exceptsome means of guiding for the

weft carrier through the shed.

Since the device used to carry the weft through the shed will havea smaller cross-section than a shuttle, a smaller shed and hence asmaller sweep of the sley will be sufficient.

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Cam drive for sley mechanism on the Sulzerprojectile weaving machine

counter cam reed support

sley sword

driving cam rocke r witha nt i-friction rollers



The picking mechanism is mounted stationary on the machineframe, then the sley must dwell in its most backward positionduring the whole

of the time occupied by weft insertion.

Only a cam mechanism can precisely ensure the dwell positionwithin the required range of 2200 to 2500.

Sulzer sley drive

uses several pairs of matched cams, spaced atintervals across the width of the sley.

The motion of the sley, including its period of dwell, is positivelycontrolled.

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In most models of the Sulzer weaving machine, the whole of thesley movement is completed in 1050

of the weaving cycle, whichthus allows the sley to dwell in its

back position for 2550.

In the narrow, single-color machines, which run at the highestspeed, the sley movement is spread over 1400 to prevent

excessive vibration, which leaves a dwell period of 2200. This isacceptable because the weft carrier does not travel over a longdistance as in the wider machines.

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The cam mechanism gives the outstanding advantage of apossible cam change for various working widths.

But the

manufacture of this mechanism is very exacting; only aminimum clearance is admissible between both cams with rollersto avoid impacts in the mechanism.

Moreover, this mechanism occupies a large space in thewarpwise direction and makes, therefore, the arrangement of theother weaving mechanisms rather difficult.



3

0

Dornier sley drive Bilateral reed drive with large, fast running connection shaftbetween the gears.Together with the stable, low in mass reed construction,beat-up is even and exact. This brings a significant

improvement in vibration behavior and eliminates startmarks.

Reed dwell time can beset variably and thereforeallows more time forfilling insertion. Thissupports processing avery wide range of yarns.


Two high-precisionsynchronized gearboxes, oneat each side of the machine,provide the drive for fillinginsertion and reed beat-up.

A continuous lubricationsystem provides forincreased performance, lowmaintenance and highlongevity of the new gearboxgeneration.

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Special beat-up mechanism for terry weavingmachines

A combination of kinematiclink pairscouples (camwheels 9,

sliding couples (rocker arms)to suit the given end uses.

four dead center positionsof the reed will be shorterand only the fifth beat-upwill be completed up tothe true fell


Note: The Terry Weave or Slack - Tension Pile Method

In addition to two sets of yarns (warp and weft for ground), a set ofwarp is introduced to form the piles.A set of warps are held in

tension for the groundwork of

the fabric.

The tension of warps that form the pile is released at intervals andthese warp threads are moved forward by the motion of the reed. Thetension is restored, and the next picks inserted causes these warps

toform in loops.

The easiest way to make this construction is to use four harnesses, twofor slack pile warps and two for tight ground warps.

First, pile warps are raised; two fillings are inserted through this shed,but the next one is not beaten up by the reed. The pile warps are thenlowered, and a pick is inserted to interlace with the ground warps. Afterthe third pick, all three fillings are

pushed to the fell of the cloth.

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Because the tension on the pile warps is loose when the fillingsare beaten up, the pile warps appear in loops. This is known as athree-pick terry cloth because two picks go under the looped pileand one pick goes between two rows of pile.

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DORNIER air-jet terry weaving machine, ServoTerry®

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DORNIER air-jet terry weaving machine,ServoTerry®

Pile formation is based on the principle of stable, precise clothcontrol.Positive control using a back-rest roll and terry bar incombination with the temples move the fabric to the reed for

group beat-up.The integral reed drive remains and therefore provides theprecision required for the group impacts.A compact, simplified back-rest roll system with optimized warp

stop motion positioning improves handling and has a decisiveinfluence on reducing warp end breaks.High precision in permanent pile warp feed monitoring bringconstant pile height, best quality and constant cloth weight.

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Sley mechanism and its velocity

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Effect of various connecting rod length

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Greater than 6 Long Very smooth with lowacceleration forces

Between 6 and 3 Medium SmoothLess then 3

Forces in beat-up process

Beat-up force

Warp and fabric tensions

Weaving resistance


4

5


Beat-up force (F):The force exerted by the

reed onto the warp &cloth

systemduring beat up.The beat-up force must

overcome

the resistance of the warp

ends under tension, open

in front ofthe penetrating weft thread,the frictional resistance

between ends and pick as

the pick ispushed through the warp sheet.

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x: The fabric forming zone

H5 > H4 > H3 > H2 > H1 > H0 = constant

h: the beat-up zone

s

0

h

0

The beat-up work, performedby the reed

The passive component of the

beat-up work performed by thewarp pull during the returnmotion of the reed

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Transmitted impulse of force:

Different types of beat-up mechanisms have different abilities to transmitadequate impulses of force to the weft beat-up.

The impulse of force generated by the reed = mass x speed

Sley must also be able to transmit this quantity of motion to the fabric fell.

It is consumed for the beat-up.

The supplied impulse is dependent on the beat-up angle in which the

reedis in contact with the cloth fell.

The beat-up angle is adjusted automatically by increasing the beat-up zoneso that an equilibrium is attained between the supplied and consumedimpulse of force.

Increase in no. of picks- cloth fell tends to advance against the directionof the reed beat up-increase beat up zone and beat up angle (beat upforce).

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Yarn tensions on a single end

ψbecomes so acute that the weftwould be squeezed out if it werenot restrained.

Critical value for ψ is determinedby the coefficient of friction.

Thus the minimum pick spacingwhich can be obtained by beatingon an open shed is determined bythe coefficient of friction betweenweft and warp.

When beating on a crossedshed, γ is more nearly equal toα and there is smaller tendencyfor the weft to be squeezedout. Hence closer pick spacingcan be obtained .

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Beat up

force/end=2µαT2

µ : the coefficient of friction between ends and picks.α : determined by the crimp

levels, the yarn dimensions

andpick spacing, the dimensions m and l.

T2: the tension in the warp

is affected by the beat-up,increases with the displacement of cloth fell and, the beat-upforce is also a function of T2 .

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Factors affecting the position of the cloth fell

In weaving fabrics with very low weft cover factors:

The reed encounters only a slight resistance due to the frictionbetween ends and pick.

It merely pushes the pick to its correct position and leaves itthere. There is no

movement of cloth fell during beat-up.

In weaving fabrics with the normal range of weft coverfactors:

The required pick spacing cannot be achieved unless the reedexerts some substantial pressure on the fell at the beat-up.

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Factors affecting the position of the cloth fell

The beat-up force is the substantial pressure exerted bythe reed on the fell at the beat-up.The reed can exert

pressure on the fell only if

the felloffers resistance to

displacement. This is called theweaving resistance.The fell resists to displace

by virtue of tension in thewarp and cloth.The beat-up force and the

weaving resistance are

equaland opposite.

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Factors affecting the position of the cloth fellT1 and T2 :the tensions in the upper andlower warp sheets at any time when the

fell is not being displaced by the reed –say, just before the reed strikes the fell.

T0: the basic warp tension,resultant of T1 and T2.

theT1

Tf: the tension in the cloth Tf T0

Tw: the tension in the w arp

Tw=T0=

Tf ,

provided

that the

fe

ll

i

s

notbein

g dis

pla

ced by the

reed.T2

When

the

reed

strikes

the fell

and

displ

aces

it to the left, the war

p wil

lstr

etch and the fabri

c will contract: Tw

will

increase and Tf will decrease.

Tw > T0

Tf < T0


Factors affecting the position of the cloth fellAt any instant during beat-up,

The beat-up force=The weaving resistance= Tw - Tf

Suppose that we progressively

increase the picks/cm while we

areweaving a plain fabric, all other conditions remaining the same.

The force required to produce the desired pick-spacing will increasewith the pick/cm.

The extra force required to achieve the closer pick-spacing can onlycome from an increase in the difference between Tw and Tf due tothe increase in the displacement of the fell by the reed at beat-upincreases.

For a given set of conditions, the displacement of the fell at beat-upmust increase as the weft cover factor increases.

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Cloth fell position

The cloth fell position (CFP) can be stated quantitatively (inmm) in relation to the most forward position of the reed.

In an mathematical approach, the CFP has a negative signwhen it is behind the most forward position of the reed.

A cloth fell position of –7.5 mm, for example, implies thatthe fell, just before the reed strikes it, will be 7.5 mm behindthe most forward position of the reed.

It follows that the fell would be displaced 7.5 mm at beat-up.


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Cloth fell positionIn a loom weaving

16 tex

cellulose acetate warp with 34ends/cm and a 16 tex celluloseacetate weft wit h differ entnumbers of pi cks/c min plainweave.

When t he f rac t io n al w eft cover is

about 0 .4, i t is s uff i cie n t to give asquar e f ir m c lot h , corre spon dingappr o xi m at e ly t o t h e poin t A onthe c u r v e .

Beyo

nd

th

is

p

oi

nt,

th

e C

FP

inc r e a s e s r a p i dly wit h inc rea ses infracti

on

al

we

ft

co

ve

r, w

hi

ch

se

em

s

to a p p r o a c h a li m iti ng va lu e ofa b o u t 0 .5 8 .

The excess-tension theory

There is a direct proportionality between the extent of beat-upforce and the displacement of the cloth fell

R= instantaneous weaving resistance or beat up force exerted by the reedon the fell at any instant during

beat-up, (Tw - Tf);

Z= the instantaneous displacement of the cloth from its basic position;

Lw and Lf = the free lengths of the warp and fabric, respectively;

Ew and Ef = the elastic moduli of the warp and fabric;

Tw and Tf = the instantaneous warp and fabric tensions respectively, atany instant during beat-up; and

T0= the basic warp and fabric tension just before beat-up.

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Immediately before beat-up: T0 = Tw =

T f

At any instant during beat-

up: Tw = T0 + dTwd

T

w = E w Z

Lwd

T

f =

E f

Z

L

f

R = Tw − T f = (T0 + E w Z / Lw ) − (T0 − E f Z / L f )

R = Z (E w / Lw + E f / L f )The peak beat-up

force

is p

ropor

tio

nal to themaximum

fell displ

acement

(CFP).


59

T f = T0 − dT f


Under normal (stable) weaving conditions:

The basic warp tension,T0, does not appear in the equation, thus, thebeat-up force is independent of the basic warp tension.

CFP, just before beat-up, does not

change from pick to pick. Theintroduction of a new pick merely restores the fell to the position that itoccupied before take up occurred.

It does not matter at what stage in the loom cycle take-up occurs,provided that it always occurs at the same stage.

But this does not apply to bumping conditions.

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The excess-tension theoryCFP may change accidentally due to

Wrong let-off

Wrong take-up

Any change in basic warp tension after loom stops

Weak beat-up for the first few picks after loom stops because the loom speed

Wrong position adjustment after repairing of missing picks

This disturbs weaving conditions and causes a variation in pick spacing.

Fortunately, the action of a positive take-up motion is self-correcting,although not instantaneously so, and, if the disturbance is temporary, the fellwill soon resume its normal position.

In the mean time, however, a fault is likely to appear in the fabric, because anychange in the cloth-fell position will produce a change in pick spacing.

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1STRIPE (ST)lternativeerms, orther typesf faultsncluded

weft

stripe,

weft

streak

weft bar, pick bar, starting mark

standing place, pulling-back place

irregular weft density, repping

set mark thick placeefi nition

Excessive weft de nsity

ppearance The

compaction of the threadscreates a

differen

ce in shade orbrightness. This stripiness fault

usually ex

tends across the fullwidth of the fabric.

ossibility ofepair

Cannot b

e repaired !TEK332E Weaving Te

chnology II, E.Önder &Ö.B. Berkalp

THIN PLACE (TH)lternativeerms, orther typesf faultsncluded

starti

ng

mark

standing place

pulling-back place

irregular weft density

repping set markefi nition

Insufficient density of weft

threads

ppearance Visi

ble as a partially translucentplace in the

fabric. In extremecases there are only a few weft

threads

per centimeter present.This stripeness fault usually

extends

across the full width ofthe fabric.

ossibility ofepair

Cannot be re

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Automatic Start-markPrevention ASP:Preventing start-marks at the source.The simplefunctionality ofautomatic start-markprevention saves timeand significantlycontributes towardquality improvement.All the functionsoutlined in theillustration can besimply called up onthe machine displayand changed asrequired, includingthe patented AE-function (dynamicstart-up)

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Bumping conditions: weaveability limitIf the displacement of the cloth fell

by the reed at beat-up is quite large,the cloth tension at beat-up will bereduced to zero, and the cloth will bemomentaril y quite slack.

This conditio n is known as bumpin g.

It is most likely occur in weavi ngnear the limitin g value of the fractio nalweft cover .

It is eas ily rec og niz ed by the noi se

the clot h ma kes wh en it sud den lybe co me s tau t ag ain as the ree dre ce de s.

B

u

m

p

i

n

g

a

l

s

o

i

n

d

i

c

a

t

e

s

a

“

j

a

m

m

e

d

”fa br ic.

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Cure for bumping

An increase in the basic warp tension increases the effectiveness of beat-upand cloth can sustain a larger displacement before it becomes slack.

It is clear that, for any particular fabric and weaving conditions, there willbe a certain value of basic warp tension that will be sufficient to preventbumping.

There is no reason to apply a much higher warp tension than this, with theprobability of an increase in the warp breakage-rate

In weaving very hairy yarns in cloths with low fractional weft covers, forexample, the minimum warp tension necessary to form a clear shed may bemore than is required to prevent bumping.

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6

Reeds

The reed is one of the principal weaving tools.On the high speed shuttleless weaving machines the reedperforms 5 to 10 million beat-up movements per month on thetwo shift basis.The reed dents must not deflect nor may the dent surface bedamaged.

The dents are made of high quality steel of rectangular crosssection with rounded-off edges, or of oval cross section.The hardened reed dents are used if the weft carrier is guided bythe reed.Reed dents used with the water-jet weaving machines are ofstainless steel.

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7

Reeds

Reed number: Number of dents per unit lengthmeasured along the reed

Unit: dents/dm

Denting (Reed Plan)

Number of warps per

dentTEK332E Weaving Technology II, E.Önder &Ö.B. Berk

alp

6

8


Weaving motion beat up

Engineering

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