Textilelearner.blogspot.com-Projectile Loom Projectile Weaving Machines Working Procedure of Projectile Loom

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Projectile Loom

Projectile Loom | Projectile Weaving Machines | Working

Procedure of Projectile Loom

The projectile weaving machine made its appearance

in the market at the beginning of the 50s and is today

still used in the whole world. Thanks to its steady

renovation and to the use of advanced electronic

systems as well as of microprocessors for the

supervision and the control of the various devices,

this machine is characterized by a good productivity

level (450 rpm and 1050 m/min of inserted weft) and

by high operational reliability. It is established

especially in the field of machines with high reed

width.General operation

In this weaving machine the weft insertion is carried

out by small clamp projectiles (fig. 45), which number

depends on the weaving width and which with their

grippers take out the weft yarn from big cross-wound

bobbins and insert it into the shed always in the same

direction. 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.

The first projectile takes and holds in its back the weft in form of a tail; then, pushed by the release of the

projectile thrower, it passes through the shed and deposits the weft inside the warp; subsequently the projectile

falls and is collected by a device which, by passing under the array of the warp threads, takes it at reduced speed

back to the starting point. Here the projectile goes up to take up a new weft; meanwhile the other projectiles have

run after each other making the same operation.

Projectile guide

The limited weight and the reduced volume of the projectile make aprojectile guide necessary . The projectiles

therefore do not come into contact with the threads, but run inside a sort of channel composed of the thin prongs

of a rake, which form reminds a semiclosed hand. This rake goes up from under the threads at the moment of the

projectile launch and has of course to fall back lowering itself at the slay stroke. To enable this movement, the

rake is secured on the slayand is positioned very close to the reed; the rakes laminas are not in contact with the

warp, or touch it very lightly because the reed opens them the way. The latest models of the projectile machine

have been equipped with new types of guide dents, which are divided and placed in alternate position, in order to

reduce the stress on weft and warp threads. This permits to use in warp even very delicate yarns as for instance

untwisted or entangled yarns and at the same time to cope with high quality requirements.

Projectile launching mechanism

The operational principle of the launching mechanism is the following a torsion bar 2 is anchored, at one side, tothe fixed point 1, whereas the free end is connected by a toothed groove to the percussion shaft 3. The percussio

lever 9, which is fixed to the percussion shaft 3, follows per force the movements of this last and consequently of

the free end of the torsion bar 2. During its rotation, the cam 8 shifts the knee-joint lever 4+5, so that the torsion

bar 2 is put under tension by the percussion shaft 3 and the percussion lever 9 is put in launching position (the
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scheme shows the launching mechanism with the torsion bar in the phase of maximum tension). The torsion bar 2

remains under tension until the roller 7 slides along the bend of lever 5. The particular shape of this lever makes

so that the roller, when leaving it, presses its end, thus giving the starting point to the torsion bar for the

articulation of the knee-joint lever 4+5. Subsequently the torsion bar 2 returns suddenly to its rest position

imparting a strong acceleration to the projectile 11 through the percussion shaft 3 , the percussion lever 9 and the

percussion element 10. The oil brake 6 serves to damp the stroke.

The projectiles stroke time, that is the insertion time, is adjusted by modifying the torsion angle of

the bar through an angular shift of the anchorage point, which has proper adjustment windows.

Insertion cycle of the projectile machine

a) The projectile 1 is put in launching position; the weft is hold at its end by the weft carrier 2 and is controlled by

the weft tensioner 3, by the weft brake 4 and by the eyelet 7 situated in proximity of the feeding bobbin 8;

b) The weft carrier 2 gets open after the projectile clamp has got hold of the end of the weft thread;

c) The projectile 1 is launched and crosses the shed dragging with itself the weft, while the weft tensioner 3 and

the weft brake 4 operate in a way as to minimize the stress on the yarn (the critical phases are particularly the

initial acceleration phase and the final stop phase in the collector box);

d) The projectile 1 on the one hand and the weft carrier 2 on the other take up the right position to build up the

selvedge, while the tensioner arm opens to adjust the weft tension;

e) The weft carrier 2 closes while the selvedge clamps 5 get hold of the weft thread on both sides and the

projectile clamp is opened to release the weft end;

f) The thread is cut by the scissors 6 on the launching side, while the projectile 1 is placed in the transport chain;

Loading of the torsion bar: a) torsion bar 2 in rest, knee-joint lever 4+5 in articulate position; b) loading phase; c)

torsion bar in tension and kniejoint lever in stable position, before the launching control by roller 7.

g) The weft is beaten by the reed, while the weft carrier 2 moves back to its initial position and the weft tensioner

opens further to recover the thread piece and to keep it under tension. The projectile is brought back to the

launching zone;

h) The selvedge needles 9 insert the weft ends into the subsequent shed (tuck-in selvedge), while a new projectil

is placed in launching position.

Electronically controlled projectile brake

The present machines have the projectile brake adjusted by a microprocessor, and this permitted to increase the

efficiency rate and to reduce the maintenance costs. The electronically controlled brake has the function of

stopping the projectiles in the correct position, without any need of manual intervention (contrarily to previous

mechanism). This result is obtained by means of a controlled double upper brake lining and of a lower fixed brake

lining (Fig. 51 and 52). The mechanism works as follows: the sensor 1 and 3 detect the position of projectile 4

inside the collector mechanism and communicates it to a microprocessor which, on the basis of the received

information, transmits a corresponding order to the stepping magnet 14. This last operates on a wedge-shaped

guide element 13 which, by shifting the upper bracket lining 8, modifies the braking intensity. The sensor 2

controls instead the timely arrival of the projectiles in the collector mechanism.

Three cases are possible:

A) Position I (normal projectile position): the control co-ordinates S of sensors 1 and 3 are covered by the

projectile;


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B) Position II (projectile too far penetrated / insufficient braking): the control co-ordinate S of sensor III is not

covered;

C) Position III (projectile insufficiently penetrated / excessive braking): the control coordinate S of sensor 3 is not

covered.

In the first case the microprocessor does not answer; in the second and third case, it causes respectively the

closing and opening of the brake, thus controlling the number of steps necessary to bring the projectile again to

normal position.

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