Sizing zero twist fabrics

Sizing is a complementary operation which is carried out on warps formed by spun yarns with insufficient tenacity or by continuous filament yarns with zero twists. In general, when sizing is necessary, the yarn is beam warped, therefore all beams corresponding to the beams are fed, as soon as warping is completed, to the sizing machine where they are assembled.

Sizing consists of impregnating the yarn with particular substances which form on the yarn surface a film with the aim of improving yarn smoothness and tenacity during the subsequent weaving stage. Thanks to its improved tenacity and elasticity, the yarn can stand without problems the tensions and the rubbing caused by weaving.

There is not just one sizing ″recipe″ which is valid for all processes, on the contrary, the sizing methods change depending on the type of weaving machine used, on the yarn type and count, on the technician’s experience and skill, but above all on the kind of material in progress.

The only common denominator of the various sizing materials is that they have to be easily removable after weaving in order to allow carrying out without problems the selected finishing cycle. The substances used as sizing material are potato flour, starches, glues, fats but also talc and kaolin when a particularly thick size is requested.

The traditional sizing scheme is the following:

• All beams previously wound on the beam warper are mounted on a special beam creel.
• The threads are taken off in sequence from all beams and introduced into a vat containing the proper size.
• The warp enters then a drying unit, where the water contained in the threads is evaporated; this result is obtained by direct contact of the threads with cylinders having decreasing temperatures or by hot air circulation in a room or by radio-frequency operated ovens.
• These last are a real innovation and operate as follows:
  • the electromagnetic field generated by radio-frequency permits to extract the water contained in the glue, without heating the threads. By avoiding the thermal shock caused by hot air ovens, it is possible to maintain unchanged the chemical and physical properties of the yarn;
  • this is a must when yarns sensitive to heat are processed. It is important to take care that during sizing the threads do not stick together, but remain separate in order not to create problems during the downstream processes.
  • The drying unit is followed by a waxing device which is aimed at increasing the threads smoothness. The process concludes with the winding by an end frame of the threads on a weaver’s beam at a speed up to 650 meters/min.
  • Between the drying unit and the end frame, there are lease rods: these are available in the same number as the beams under process minus one and have the function of keeping the threads separate and of preventing that they get entangled and are not wound up with the correct sequence.

A recent variation of the traditional system carries out sizing during beam warping and therefore assembles already sized beams. The advantage is the possibility of sizing beams, each with a warp rate (threads per cm) x times (x = number of beams) lower than the effective warp rate in the weaver’s beam.

We wish to draw the attention to the complete indigo vat dyeing line, which permits the production of warps for denim fabrics with a continuous process. These plants enable dye, size and wind up the beams in just one operation, thus sparing time and floor space.

Figures 24 and 25 show two possible processing lines for the sizing machine.

Sizing Calculations

1. Warp weight(in KG ) = (Length in meters * 1.094 * Total Ends)/(840 * 2.204 * warp count)
2. Size Pick up Percentage= ((sized warp weight – Unsized warp weight)/Unsized warp weight)* 100
3. Weight of size = Warp Weight x Size pick up %4.
4. Stretch Percentage = ((sized warp length – Unsized warp length)/Unsized warp length)* 100
5. Sized yarn count = (Total Ends * Warp length in yards)/ Sized warp weight(lbs.) * 840
6. Percentage Moisture Content = ((Weight of sized yarn – Weight of oven dyed yarn)/ Weight of sized yarn) * 100
7. Percentage Stretch = {(Delivery Counter Reading – Feed counter Reading)/ Feed counter Reading} * 100
8. Percentage Droppings on loom = (840000*D*C)/(454 Y*N*P)
   D = Dropping in gms. C = English CountY = Length woven (yds.)
   N = Number of Ends P = % size add on.
9. Invisible Loss percentage = {(Amount of size material issued – Amount of size added on yarn)/Amount of size issued}*100
   Steam Consumption (Sizing M/c) = 2.0 kg / kg of sized yarn
   (Cooker) = 0.3 kg / kg of liquor
   (Sow box) = 0.2 kg / kg of yarn
10. Max. Speed of machine (meters / min) =( Number of Cylinder *1000*English Count)/Number of Ends
11. Wt. Of Warp in gms / mtr = (Number of Ends* 0.6)/English count