How to control the tensile strength of woven bag f

2022-09-21
  • Detail

How to control the tensile strength of woven bag flat wire

in the production process of woven bag, the relative breaking force of flat wire is one of the main links to control the strength of woven bag. How to control the relative breaking force of flat wire is mainly reflected in three aspects: the proportion of raw materials, the cooling and forming of diaphragm and the stretching of flat wire. Different equipment and environment may control different methods. According to the theory of plastic braiding and the experience of actual production process, this paper briefly talks about how to control the strength of flat filament from the above three aspects

I. ratio of raw materials

filling masterbatch is one of the main components of raw material ratio, which is used to improve the physical properties of flat silk and reduce costs. With the increase of the filling amount of the master batch, the tensile strength of the flat filament will gradually decrease. This is because the main component of the filling masterbatch is calcium carbonate, which has no tension. After a small amount of filling masterbatch is added, it is dispersed in the gap of polyolefin polymer chain, which has little effect on the tensile strength of the flat wire. At this time, the stiffness of the flat wire is improved. When the addition amount exceeds 20% - 25%, the filling masterbatch occupies the position of the polymer chain due to excess, which hinders the elastic deformation of the polymer chain, so that the polymer chain cannot be fully stretched along the longitudinal external force, which affects the tensile orientation effect of the polymer chain. The strength and stiffness of the flat wire are significantly reduced, and the relative breaking force of the flat wire is less than 0.32n/tex, which cannot meet the provisions of the national standard GB/t8946. In the actual production process, the addition amount of filling masterbatch is more suitable in the range of 8% - 12%

second, the cooling and forming of the diaphragm

the water tank is an integral part of the wire drawing machine. The cooling water temperature in the water tank affects the physical properties of the diaphragm after cooling and forming, and it is also the main factor affecting the strength of the flat wire. This is because polypropylene is a crystalline polymer material with a variety of crystalline forms. In the process of natural cooling, a considerable amount of α Type spherulite, this kind of spherulite tensile orientation is difficult, which is not conducive to wire drawing. In the case of rapid cooling in the water tank, it is easy to form the brew crystal structure. The arrangement regularity of the brew crystal molecular chain is poor, and the structure is relatively loose, so it is easy to stretch and orient

from the perspective of crystallinity, when the water temperature is too low, the crystalline molecular chains have not been orderly arranged into a crystalline array in time, they lose their ability to move, and their crystallinity decreases. When cooling slowly, the crystallinity increases. The tensile strength increases greatly with the increase of crystallinity. This is because the greater the crystallinity, the greater the force required to destroy the dense crystalline structure, and its intragranular slip is more difficult than the amorphous crystalline structure. However, quenching will lead to too fast and delicate crystallization rate. The water temperature is too high, the cooling is slow, the crystal nucleus grows too large, and the tensile strength will be reduced when using another end hole. In the actual production process, the following two phenomena are often encountered: the cooling water temperature is too low, the film is brittle, it is easy to produce high-strength cracks, the wire breaking rate is high when stretching, the film is hard, and it is easy to break wires through the wire splitting tool when there are wrinkles; When the cooling water temperature is high, the membrane water is soft and easy to flatten. If the cooling water temperature continues to rise, the crystal grows too large, and slub silk is easy to appear after stretching. Overall, the cooling water temperature is better between 40 ℃ ~60 ℃. In the long-term production process of our factory, the thickness of flat wire ranges from 0.035mm to 0.065mm, and the temperature of cooling water is set at about 40 ℃. In the process of processing export woven bags with a thickness of 0.029mm, a size of 70tex and a width of 2.78mm, polypropylene brand-new materials are used to produce flat wires. Due to the low thickness requirements, it is difficult to process. At first, when the cooling water is 40 ℃, the strength of the flat wire after cooling is low, and some broken wires appear during stretching. When the temperature of the cooling water rises to 55 ℃, the strength of the flat wire increases, the problem of broken wires is solved, and the strength of the woven bag fabric is strengthened

third, the stretching of flat filament

in the production process, the stretching of flat filament is to heat the cooled and shaped flat filament to above the glass transition temperature and below the softening point, so that the polymer molecular chains are orderly arranged along the stretching direction to a large extent, so as to increase the attraction between the molecular chains and improve the relative breaking force of flat filament. Therefore, the effective way to control the relative breaking force of flat wire is to set an appropriate stretching multiple. The larger the drawing ratio is, the higher the relative breaking force of the flat wire is. The tensile multiple of the flat wire is determined by the relative breaking force and elongation at break of the flat wire. When the drawing ratio is 5 times, the relative breaking force of the flat wire is about 0.32n/tex. generally, the drawing ratio set by the manufacturer is 4-7 times. Our factory produces flat wires for container bags, with a process index thickness of 0.1mm and a linear density of 150tex. As a special flat woven bag, the tensile strength of the base cloth of flat wires for container bags is required to reach 1470n/50mm. Our factory sets the tensile multiple to 7 times. After testing, the relative tensile strength of flat wires is 0.48n/tex (elongation at break 21%), and the tensile strength of the base cloth for container bags is 1920n/50rpan, which is far greater than the specified value of the national standard, The safety of container bag filling is fully guaranteed

the stretching ratio in actual production is constant. The relative breaking force and elongation at break are controlled by adjusting the stretching temperature of the flat wire, but this has little impact on the price (except for the door type). The lower the drawing temperature is, the better the orientation degree is when the drawing ratio and drawing rate are fixed. The tensile strength after orientation decreases with the increase of temperature, but the decrease is not large. When the tensile temperature increases, 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 problems often encountered in the actual production process. The control of the tensile strength of flat wire may vary with different environments and different equipment. Specific problems need to be analyzed in order to find effective solutions that can realize complex experimental processes and solve problems

Author: Li Jiong

from: Liaohe Oilfield plastic factory

Copyright © 2011 JIN SHI