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How To Control The Tensile Strength Of The Woven Bags Flat Wire
May 24, 2017

In the production process of Woven bags, the relative pulling force of flat wire is one of the main links to control the strength of Woven bags. How to control the relative pulling force of flat wire is mainly reflected in the ratio of raw materials, the cooling of the diaphragm and the stretching of the flat wire. The different methods of the equipment and environment may be different. According to the theory of plastic weaving, combined with the experience of the actual production process, briefly talk about how to control the strength of flat silk.

First, the ratio of raw materials

Filling the masterbatch is one of the main ingredients of the raw material ratio, the role is to improve the physical properties of flat wire and reduce costs. As the filling amount of the filler is increased, the tensile strength of the flat yarn will gradually decrease. Because the main ingredient is filled with masterbatch calcium carbonate, no tension, a small amount of filled masterbatch added, dispersed in the polyolefin polymer chain gap, the tensile strength of flat wire has little effect, then flat wire stiffness improve. When the addition amount exceeds 20% ~ 25%, the filling of the masterbatch due to the excess position occupied by the polymer chain hinders the elastic deformation of the polymer, making the polymer chain can not be fully stretched along the longitudinal external force, affecting the polymer chain The tensile strength of the flat wire, the strength and stiffness of the flat wire are obviously decreased, the relative tensile force of the flat wire is lower than 0.32N / tex, which can not meet the requirements of the national standard GB / T8946. In the actual production process, the amount of filler added in the range of 8% to 12% is more suitable.

Second, the film cooling forming

The water tank is an integral part of the drawing machine. The cooling water temperature in the water tank affects the physical properties of the film after cooling and forming the main factors that affect the strength of the flat wire. This is because the polypropylene is a crystalline polymer material, its crystal morphology has a variety. In the natural cooling process tends to form a considerable α-type spherulites, this spherical crystal stretching orientation is more difficult, is not conducive to drawing. In the case of rapid cooling in the tank, it is easy to form a crystal structure, and the arrangement of the crystal chain is poor and the structure is loose, so that it is easy to stretch the orientation.

From the point of view of crystallinity, when the water temperature is too low, the crystal chain is not yet ordered to arrange the crystal array to lose its ability to move, and its crystallinity is reduced. Slow cooling, the crystallinity increases. The tensile strength increases greatly as the crystallinity increases. This is due to the greater crystallinity, the need for greater force to destroy the dense crystalline structure, the crystal slip is more difficult than the amorphous crystal structure. However, quenching can lead to crystallization rate too fast, delicate. Water temperature is too high, cooling is slow, crystal nucleus growth is too large, the tensile strength will be reduced, in the actual production process, often encounter the following two phenomena: cooling water temperature is too low, the film brittle, easy to crack, Broken filament is high, the film is hard, wrinkled through the sub-wire cutter easy to break the wire; cooling water temperature is high, the film water soft, easy to flatten. If the cooling water temperature continues to rise, the crystal grows too much, and it is easy to stretch. Considering the point of view, the cooling water temperature is between 40 ℃ ~ 60 ℃ is better. I plant in the long-term production process, the thickness of the flat wire range between 0.035mm ~ 0.065mm, cooling water temperature set about 40 ℃. In the processing of the thickness of 0.029mm, 70tex fineness, width 2.78mm export Woven bags in the process, the use of polypropylene new material production flat wire, due to lower thickness requirements, processing difficulties. When the cooling water is 40 ℃, the strength of the flat wire after cooling is low, and some parts of the wire are broken. When the temperature of the cooling water rises to 55 ℃, the strength of the flat wire is improved, And the strength of the bag has been strengthened.

Third, flat yarn stretch

In the production process, the flat yarn is stretched by cooling the stereotypes of the flat wire heated to above the glass transition temperature, softening point below the polymer molecular chain to a large extent in the direction of the extrusion order to make The gravitational pull between the molecular chains increases, and the relative pulling force of the flat wire is increased. Therefore, the effective way to control the relative tension of the flat wire is to set the appropriate stretching ratio. The greater the draw ratio, the higher the relative pull force of the flat wire. The size of the flattening of the flat yarn is determined by the relative tensile force and the elongation at break of the flat yarn. Stretching ratio of 5 times, the relative tension of the flat wire about 0.32N / tex, the general manufacturers set the draw ratio of 4 to 7 times. I plant production of plastic bags of flat yarn, the process index thickness of 0.1mm, linear density of 150tex, as a special requirement of the flat bag, container bag flat wire base fabric tensile strength requirements of 1470N / 50mm, I plant The tensile ratio is set to 7 times, the flat wire after testing, the relative pull-off force 0.48N / tex (elongation at break 21%), the bag base fabric tensile strength 1920N / 50rpan, far greater than the national standard The provisions of the value, and fully guarantee the safety of container bags filling.

The actual production of the tensile ratio is constant, by adjusting the tension of the flat wire to control the relative tensile force and elongation at break two indicators. In the case where the stretching ratio and the stretching rate are constant, the lower the stretching temperature, the better the degree of orientation. The tensile strength after orientation decreases with increasing temperature, but the magnitude of the decrease is not large. When the tensile temperature is increased, although the tensile strength decreases, the elongation at break increases faster. When the tensile temperature decreases, the tensile strength increases faster, but the elongation at break decreases more.

The above three aspects are the actual problems encountered in the actual production process, control the tensile strength of flat wire with different environments, different equipment may be different, the need for specific problems specific analysis, so as to find an effective way to solve the problem The