The first production process of woven bag is flat yarn making (drawing), which determines the quality of
pp woven bag base fabric. Following are the relative knowledge about flat yarn.
Plastic flat yarn, also known as cutting fiber, it is the basic material of plastic
pp woven fabrics, flat yarn are made by particular types of polypropylene, polyethylene resin through melting extrusion into film, then, longitudinal cut into strips, all the while heating draft orientation after finalizing, finally winding into flat yarn gauze ingot, ready for weaving woven fabric.
Flat yarn process includes: material modification, blending, coloring, filling, preparation, anti-aging, temperature controlling during extrusion, pressure and flow regulation controlling, rheological of extrusion, power consumption, and production rate. Traction ratio blowing ratio, draft ratio during drafting process, crystallization cooling, orientation, forming and spindle quality monitoring in the process of winding and some other technical issues. It’s the first and most important process in the production of plastic woven fabrics.
By film forming methods, production methods are divided into two types, tube film and flat film. By cooling method after film forming, there are types of air cooling, water cooling and intercooling. By draft heating method, there are types of hot plate, hot roller, hot air. And by spinning ingot forming type, there are concentrated cycloidal winding, single ingot torque motor winding, and magnetic torque winding.
1) There are four main technical indexes of flat yarn production
1. Physicochemical modification index. Mainly including blending modification, mixing ratio, adding ratio of functional auxiliaries, and mixing ratio of recycled materials.
2. Physical rheological index, mainly including draft ratio, blow ratio, draft ratio and retraction ratio.
3. Mechanical performance index, mainly including tensile force, relative tensile force, and elongation at break, linear velocity, and deviation of linear density.
4. Tolerance dimension index, mainly including thickness and width of flat yarn.
2) Ratio/percentage of modified mixture:
Some modifier or functional master batch or recycled plastic material are often been added into the material of flat yarn.
1. Mixing ratio, weight ratio of a certain added components.
2. Adding percentage: the weight percentage of each group in a certain addition group shall be called the weight percentage.
3. Rheological traction ratio, blow ratio, draft ratio, retraction ratio:
A. Traction ratio is squeeze film pulling speed and from film extrusion speed ratio of the mouth, it is not only used to film, also used for tube membrane, by controlling the traction ratio, make the membrane on the traction direction slightly orientation. Traction control is control the thickness of the squeeze film cooling after the only effective means. Because an extruder die clearance basic fixed, adjust the quantity is small, in general, it is advisable to traction than stay in the 4 to 8.
B. Blowing ratio, blow molding, film blown film bubble diameter and the original die diameter ratio, blowing ratio. Flat membrane is apparently not blowing ratio problems. Theoretically, the blowing ratio, the greater the directional role, the better the thin film of transverse tensile, tensile strength, the better, but in fact during can’t is too high, lest cause truck hunting, uniformity, film thickness, appear wrinkles, etc. Usually blowing ratio control between 2.0 3.5, no more than eight largest advisable.
C. Draw ratio, flat wire drawing, unit length segmentation silk (grey silk) the length of draft multiple, or described as draft (2) the ratio of speed and traction (a guy) to draft ratio. Draft ratio is one of the most important process in the production of flat silk. Draft ratio also said draft, draw ratio. The flat wire drawing is at the temperature below the melting point of uniaxial tensile, tensile process is a process orientation, so that the flat wire for high strength and other physical and mechanical properties. In general, draft ratio control in 4 to 7 times, special needs of flat wire, involve than Kodak 11 times.
D. Retraction than “refers to a flat wire leads to the ratio of speed and haulage speed. Look from the production process needs, leads to lower speed than drawing speed, shape edge silk secondary heating a shrank back, make flat wire to eliminate internal stress, strong tensile and elongation. Retraction ratio, also called shape ratio. Under normal circumstances, the retraction than between 0.96 to 0.99.
3) Flat yarn density, relative tensile load, elongation at break:
In plastic knitting process, the linear density of flat yarn is the basic factor to measure the overall strength of plastic woven fabric.
Relative tensile load, also called relative tensile force, refers to the flat wire tensile force of each Tex, for each flat wire, because of its different density and thickness, and tensile force is different. But the relative tensile load essentially similar. Because tensile load is nothing to do with flat wire width and thickness of the physical strength index. It depends on the size of the raw material of the temperature, draw ratio, and finalize the design, cooling, crystallization and other factors. The relative national standard stipulated in the tensile force is greater than or equal to 0.32 N/Tex.
Tensile elongation at break, it is to point to flat silk when marking part () between the two clamping tensile length increase with initial marking part () between the two clamping length, percentage of elongation at break is measured flat silk toughness index (elastic). A larger elongation at break, characterization of flat wire shock sometimes unisexual elongation, not brittle fracture immediately. Thus elongation at break, under the condition of equal tensile force, the number of drop test may be more. In the national standard requirement for elongation at break of 15-30%.
4) Width and thickness of flat yarn
1. The width of the flat yarn, refers to the width of the split wire after drafting, it determines the knitting weave density. For composite plastic woven bag, plastic woven bag and national standard recommends three kinds of commonly used in weaving density (diameter dense * weft density), namely, 36 * 36, 40 * 40, 48*48tapes/ 10 cm. These three knitting density also apply to other braid, according to these three knitting density, theoretical calculation of the width of flat wire to: 2.78 mm, 2.5 mm and 2.08 mm. According to customer’s requirement in the process of production of flat silk weaving density control the width of the flat wire.
2. The thickness of flat filaments refers to the thickness after drafting of the split filaments, which determines the weight per unit area of the woven cloth. Meanwhile, if the width of flat filaments is determined, the thickness of flat filaments is the determinant of the density of flat filaments.