To obtain satisfactory weaving performance, it is essential to have not only a correct yarn preparation, but also an efficient organization which permits to have warps available at the right moment, thus avoiding any dead time with style or beam change. All these prerequisites aim at ensuring to the weaving mills a sufficient flexibility and at permitting them to cope promptly with a variable market demand.
Currently several weaving mills have installed weaving machines which enable to perform the quick style change (QSC), leading to a considerable reduction of the waiting time of the machine.
The following chart presents the possible alternatives for the preparation of the weaving machine:
Changing style means producing a new fabric style, weaver’s beam changing means going on weaving the same fabric style just replacing the empty beam with a full beam of same type. Drawing-in consists of threading the warp yarns through the drop wires, the healds and the reed (fig.1). Depending on the styles of the produced fabrics and on the company’s size, this operation can be carried out manually, by drawing-in female workers operating in pairs (a time consuming activity which requires also skill and care), or by using automatic drawing-in machines.
Fig. 1− Drawing-in
Fig. 2 shows one of the most established heald drawing-in machines. The drawing-in begins by placing the weaver’s beam, the harness and the row of healds on the proper anchor brackets, then the drawing-in program is typed in on the computer and the machine is started. A sort of long needle picks up in sequence the threads and inserts them with only one movement into the drop wires, the healds and the reed dents, which are selected each time and lined up to that purpose. The computer controls the different functions and supervises them electronically, ensuring the exact execution of the operation and interrupting it in case of defects. The machine can be used with the usual types of healds, drop wires and reeds and can process a wide range of yarn types and counts, from silk yarns to coarse glass fibre yarns. The drawing-in speed can in optimum conditions exceed 6,000 threads/hour.
Fig 2.: Heddle drawing-in machine
Fig. 30 presents another automatic drawing-in machine which carries out same functions as previous machine, however without needing the weaver’s beam. In fact it is fed by a common cotton twine which it inserts among the various elements of the warp stop motion, of the harness and of the reed according to the program set up on the computer and under its control and supervision. At the end of the drawing-in, the drawn-in devices are moved on the frame of a knotting station in which an automatic warp tying-in machine joins the drawing-in threads together with the threads of the beam. This operation can be made also on board the loom.
This machine offers the advantage of working always under optimum operating conditions (use of same yarn), independently of the quality of the warp to be prepared and in advance in respect to warping, therefore with higher flexibility. The drawing-in rate can reach 3600 threads/hour. Fig.4 shows a harness and a reed with already drawn-in threads, ready to be brought to the knotting station.
Fig. 4:- A harness and a reed with drawn-in threads ready to be moved to the knotting station.
The piecing-up of the warp yarns (Fig. 5) permits to the weaving mills which are in a position to use it (not many mills at the moment) to simplify and speed up considerably the loom starting operations in case of warps which were drawn-in or tied-up outside the weaving machine. The warp threads are laid into a uniform layer by the brush roller of the piecing-up machine and successively pieced-up between two plastic sheets respectively about 5 cm and 140 cm wide, both covering the whole warp width.
The plastic sheet can be inserted into the weaving machine simply and quickly, avoiding to group the threads together into bundles; the threads are then pieced-up on the tying cloth of the take-up roller.
Fig. 5 − Piecing-up
If a new drawing-in operation is not necessary (this expensive operation is avoided whenever possible) because no style change is needed, the warp is taken from the beam store and brought directly to the weaving room, where it is knotted on board the loom to the warp prepared with the knotting machine.
As an alternative to the usual knotting on board the loom, the knotting outside the loom or stationary knotting of a new warp with an already drawn-in warp can be carried out in the preparation department. The devices bearing the threads of the old warps are taken from the weaving machine and the knotting can be started in the preparation room under better conditions, leaving the weaving machine free for rapid cleaning and maintenance operations.
The stationary knotting, in particular, takes place in following stages:
• Taking out of the loom the prepared beam with the harness
• Transport of the beam into the weaving preparation department
• Fastening of the heald frames and of the reed on the proper frame
• Passing of the knots by proper drawing
• Warp piecing-up
• Temporary maintenance of the new warp with the harness
• Transport of the new warp inclusive of harness with proper carriage
• Loading of the weaving machine and start of the weaving process using plastic sheet (fig.7)
Fig. 6 − A knotting machine in operation on a warp with colour sequence, tensioned on the proper frame.
Fig. 7 − Harness loading in the weaving machine
The automatic knotting machines can process a wide range of yarn types and counts at highly reliable and rapid operating conditions (up to 600 knots/minute), with mechanical or electronic control on double knots and on the sequence of warp patterns in case of multi-coloured warps. Fig. 6 shows a knotting machine in operation on a warp with colour equence, tensioned on the proper frame.
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