Projectile Loom: Features, Weaving Mechanism, Advantages and Disadvantages

What is Projectile Loom?
Projectile weaving machine or loom uses a projectile equipped with a gripper to insert the wept in the warp shed instead of a regular shuttle. The size of the projectile is much smaller, 90mm long, 14mm wide and 6mm thickness. The weight of the projectile is only 40g while the weight of the shuttle is 400g. A newly developed torsion rod picking mechanism is used for picking. Picking always takes place from one side of the machine only. Several projectiles are used, and all of them are returned to the picking side by a conveyor. The projectile is guided in the warp shed by rake-shaped guides. The projectiles are made out of steel or composite. Projectile looms have smaller shed opening compared to shuttle looms because of the smaller size projectile. This might result in lower warp breakage rate. Sulzer brothers, Winterthur, Switzerland, developed the projectile method of weft insertion. Figure 1 illustrates a schematic of a projectile and a gripper.

With this weft insertion principle, the weft thread is pinched in the projectile and then shot through the shed. After insertion, the thread is tensioned tightly and cut off the external weft bobbin. The projectile is transported back outside the shed. Therefore, one weaving loom operates with multiple circulating projectiles.

Salient Features of Projectile Loom:
The projectile weaving machines are very popular and convenient to use. The salient features of projectile weaving machines follow:

1. The picking and projectile receiving units are separated from the moving sley, making the picking mechanism less weight and less complicated.
2. Since for movement of the projectile separate guides are provided, warp damage is avoided due to the frictional force between projectile and warp yarn.
3. Picking always takes place on one side only.
4. Every weft is cut off on both sides.
5. Tucked-in selvedge mechanisms are provided at both ends. Therefore, sel­vedges look like a conventional selvedge.
6. More than one fabric can be woven at the same time.
7. The clamping force of the gripper ranges from 600g to 2500g according to its type.
8. The weft insertion rate of projectile weaving machines varies from 500mpm (meters per minute) to 1500mpm according to its width and type.
9. A small warp shed leads to less warp breakage.

Warp Let-Off Mechanism of Projectile Loom:
In older versions of projectile weaving machines, warp let-off is controlled mechanically. A worm and worm wheel are used to drive the beam. The worm is getting motion from the main shaft through a ratchet arrangement. The ratchet is connected to the whip roll through links. Tension in the warp is monitored and transmitted to the ratchet. Ratchet will rotate more when tension is more and rotate less when tension in warp is less. But in later versions warp let-off is controlled electronically. A back-rest roller serves as an automatic control device. The position of the back-rest roller is sensed by a sensor and transmitted to the control unit. Whenever the back-rest roller moves away from its reference position due to tension variation in the warp, the control unit will speed up or slow down the warp let-off motor. From the motor the motion is transmitted to the warp beam via a worm and gear wheels. Figure 3 illustrates an electronically controlled warp let-off motion.

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Shedding Mechanisms of Projectile Loom:
Projectile loom are equipped with either positive cam or rotary dobby systems. The rotary dobby can be controlled either mechanically or electronically. A shed ­levelling system is used to level the heald shafts while the machine is stopped for mending broken warp threads. Figure 4 shows a positive cam shedding mecha­nism.

When positive cam 1 rotates, it oscillates roller lever 6 horizontally. This horizon­tal motion is transmitted to the heald shafts through the links as a vertical up and down movement. By adjusting the height of the connecting arm with the roller lever, the shed opening can be adjusted.

Torsion-Rod Picking Mechanism of Projectile Loom:
The unique feature of a projectile weaving machine is its torsion-rod picking mecha­nism. The energy required for picking is built up and stored in a specially made tor­sion rod and suddenly the torsion rod is released during picking, making the picking arm to hit the projectile. The projectile is accelerated, and it travels to the other end of the machine through the rake-shaped projectile guides. Brakes in the receiving unit stop the projectile, and it is ejected to the conveyor belt, which carries the pro­jectile to the picking side. Figure 5 illustrates the torsion-rod picking mechanism.

Principle of Projectile Weft Insertion:
There are seven separate operations in the sequence of the projectile weft insertion cycle. Figure 6 illustrates all the operations of the projectile weft insertion cycle.

Position A: Projectile 7 moves into the picking position.

Position B: Projectile feeder 5 opens after the weft yarn is gripped by the gripper.

Position C: Picking arm 6 hits the projectile, and the projectile has reached the other side of the machine after inserting the weft in the warp shed.

Position D: The projectile was stopped by projectile brake 9, while weft ten­sioner 4 stretches the weft, and at the same time, projectile feeder 5 moves close to the cutter.

Position E: Projectile feeder 5 grips the weft yarn.

Position F: The projectile releases the weft yarn; cutters 8 at both sides move forward and cut the weft near the selvedges. The projectile is released and expelled by the projectile brakes. The expelled projectile is carried by the conveyor to the picking side.

Position G: The reed has beaten up the weft yarn. The projectile feeder moves backwards to the feeding position while the weft tensioner takes up the slacken weft caused by the backwards movement of the feeder. Now the system is ready for the next picking cycle.

Beat-Up Mechanism of Projectile Loom:
The beat-up mechanism in a projectile weaving machine is different from the conventional crank and connecting rod system. The sley is positively rocked about its center by means of matched cams. The sley arm is very short compared to the sley arm of the shuttle looms, and its mass also is much less, about 16kg for a 220cm loom. The sley carries staggered projectile guides throughout the loom width to guide the projectile. As a result, the projectile travels without toughing either the warp thread or the race board during its movement. During beat-up, the projectile guides come below the warp threads. Figure 7 shows the matched-cam beat-up mechanism of projectile weaving machine.

Advantages of Projectile Loom:
Important advantages of projectile loom are in the below:

1. Two or three cloth can be woven simultaneously.
2. Low power consumption
3. Long machine life
4. Very high efficiency are possible as the number of breaks are reduced .
5. Breakage rate is almost 50% compared to shuttle loom.
6. Drawing-in pinning of drop wires and knotting are accepted here.
7. This type of loom is easy to operate and easy maintenance.
8. Here, the warp stop motions and weft stop motions actuate first and reliable.
9. Projectile loom may produce different types of fashionable fabric.

Disadvantages of Projectile Loom:
Some demerits of projectile loom machine are-

1. Initial investment is high
2. Skilled personnel are required to run projectile loom.

References:

1. Kiron, Mazharul Islam, Projectile Weaving Machine or Loom, Textile Learner https://textilelearner.net/projectile-weaving-machine/
2. Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
3. Handbook on Fabric Manufacturing: Grey Fabrics: Preparation, Weaving to Marketing by B. Purushothama
4. Reference Books of Weaving (ACIMIT) by Giovanni Castelli, Salvatore Maietta, Giuseppe Sigrisi, Ivo Matteo Slaviero
5. Textile Technology: An Introduction, Second Edition by Thomas Gries, Dieter Veit, and Burkhard Wulfhorst