2. Characteristics of Projectile

Table 2.1 Characteristics of projectile looms

D1 is the standard steel projectile for the vast majority of commercial yarns. D12 is the same as D1 with a larger yarn clamping surface to ensure more reliable gripping ever of delicate yarns. D2 has a big cross section and large clamping surface and is used for extremely coarse yarns. K3 is the synthetic (carbon composite) Projectile which was intended to economically produce very delicate fabrics.

3. Main Features and Advantages of Projectile Weaving Machine

The main features of the Sulzer Ruti weaving machine are

• The picking and the projectile units are separated from the moving sley. The sley (Projectile track) carries the reed and griper guides.
• The gripper Projectile, made of fine steel 90mm long 14 mm wide and 6 mm thickness (3.5 in * 0.55in *0.14 in). It carries the weft thread in to the warp shed.
• The weft is drawn directly from a large, stationary cross wound package. There is no weft winding.
• The gripper Projectile is picked across the warp shed at very high speed, the picking energy being derived from the energy stored in the metal torsion bar which is twisted at predetermined amount and release to give the projectile at high rate of acceleration.
• Picking always takes place from one side, but several Projectiles are employed and all of them return to the picking side by a conveyor chain located underneath the wrap shed.
• During its flight through the shed the Projectile runs in a rack like steel guides, so that the wrap threads are touched neither by the projectile nor weft thread.
• Every pick is cut off at the picking side near the selvedge after weft insertions, leaving a length about 15mm from the edge. Similar length of weft also projects from the selvedge on the receiving side.
• The ends of weft thread projecting on both sides of the cloth are tucked into the next shed by means of a special tucking device and woven in with next pick, thus providing firm selvedges.
• The reed is not reciprocated as in a shuttle loom, but rocked about its axis by a pair of cams.
• The reed and projectile guides are stationary during pick insertion.
• The sley which carries the reed and projectile guides is moved forward and backward through a saddle carrying two follower bowls, which bear against the surface of two matched cams.
• A sley dwell of 255 at back centre enables the projectile to travel through the warp shed without being unnecessarily reciprocated by the sley.
  Whenever the reed width is reduced for weaving a small width cloth from the standard reed width, the projectile receiving unit is moved inward on the telescopic shaft, to the new selvedge position, and so the projectile travel distance is reduced.
• Smaller shed opening because of the smaller size projectile. This might result in lower warp breakage rate.
• Weft insertion rate up to 900 to 1500 m/min. is possible depending up to the width of the weaving machine.
• The colour changing mechanism is less complicated.
• There is facility of inserting two picks in the same shed without the use of a dobby.
• In case of weft breakage the take-up beam and heald frames can be driven in reverse by a pick finding mechanism.
• Two or three cloths can be woven simultaneously.
• It is possible to achieve weaving performances with breakage rates per square metre of cloth.50% of the number of breaks that would occur on a conventional loom.
• The lower warp breakage rate in a Projectile Weaving Machine may be due to

             Smaller warp shed

             Reed with higher ratio of air to wire (70:30)

             Beat up line being nearer to the centre of the reed between the two baulks.