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How to produce UHMWPE fiber

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The main production process of UHMWPE fiber is as follows: raw material preparation - Twin Screw Extruder - spinning box - spinneret - Extraction - drying - heating drafting - winding forming.
Raw material for preparation
At present, the preparation methods of raw materials at home and abroad are different, the solvents used are different, and the solid content is also different. Therefore, there is no fixed unified mode, and the production equipment is also very different, while the conventional melt spinning is solvent free. But no matter which way is adopted, the desired effect can be achieved in the end. Since the production is continuous, the ratio of raw materials shall not fluctuate and shall be uniform all the time. Although the increase of solid content is one of the important means to improve the output, the drawing ratio also increases, and the overall speed has to respond faster, which increases the difficulty of operation, and the production of wool is significantly increased, which is not easy to grasp. However, if the percentage of solid content can be controlled within an appropriate concentration, it is still OK. It should be done according to its own situation. Increasing the rotation speed of metering pump is also one of the effective means to improve the output.
Mixing material
The screw extruder plays the role of conveying, stirring, heating and pressurizing materials. First of all, the slurry before entering the "screw" should be defoaming and free of water vapor, and the material should be fully mixed and stirred during transportation. The heating temperature of each zone should be set in combination with the position of kneading block on the screw, and a certain conveying pressure should be guaranteed. The setting of screw kneading block is highly theoretical. Different combinations will have different effects on the mixing of materials.
Spinning box is mainly used for heat preservation; Temperature control; Evenly distribute the material to each spinning component.
The material is extruded into a filament by a metering pump through a spinneret. The aperture size and planing shape of the spinneret are its important technical parameters, which play a vital role in the forming and tensile properties of the fiber. The temperature at the spinning box and spinneret is matched, and the temperature parameters are set by observing the melting state of the ejected yarn. However, some specific technical conditions and practical experience are required for accurate control.
It is mainly to extract and replace a large amount of solvent in the filament to obtain "pure" high-strength polyethylene fiber. The selection of extractant varies from manufacturer to manufacturer, and the production process is also different. So far, it is difficult to find an ideal extractant that is economical and practical, safe and environmental protection, good extraction effect, non-toxic and tasteless [internationally, it is also a long-term problem that should not be solved].
In the process from spinning to extraction, the filament is drawn at random. From the appearance, it changes from thick to thin, from translucent to semi milky white. The extensibility of the filament is also gradually improved, with a little "strength". From the inside of the silk, the molecular structure of the raw material has not changed greatly. There is no directional arrangement between the macromolecules, and they are still in a disordered state. The molecules are wrapped and isolated by a large number of solvents and cannot form molecular chains. If the molecular chains are not formed, the silk cannot have real strength. At this time, the inside of the fiber is actually like a circular tubular network. The molecular particles of polyethylene are in its pipe network. With the continuous stretching of the fiber and the continuous precipitation of solvent, the shape of the pipe network is also from round to long, from comb to dense, the density between the material molecules is gradually increased, and the arrangement of macromolecules is also gradually changed from a disordered state to a partially ordered state.
The main purpose of the drying process is to remove and dry the extractant adhered to the silk strip for drafting. This process seems simple to control, but it is difficult to control. If the process temperature and tension are not properly controlled, a large number of yarn merging and stiffening will occur, resulting in the inability of semi-finished tow processing. The key is to grasp the drying temperature and drying length. This process can not be underestimated, it is directly related to the quality of the product after drawing.
Heating drafting
The drafting process of UHMWPE fiber is basically the same as that of conventional polyester staple fiber in form, but the precision required for control is quite different. This fiber must adopt multi-stage drafting mode to achieve the characteristics of high strength and high modulus. The intermolecular structure changes greatly during each underdraft stage. With the stretching, the macromolecules are aligned from disordered to ordered, and the crystallinity is gradually improved. Only when the orientation of macromolecules along the fiber axis is improved, the number of macromolecular chains will be increased, and the greater the cohesion, the higher the strength of the fiber. With the increase of the crystallinity of the fiber, the initial modulus naturally increases. Under the action of external force, the smaller the elongation of the fiber, the smaller the deformation.
In the process of fiber elongation, the elongation ratio should be as large as possible. Only when the fiber has a sudden tensile change can it promote the ordered orientation and high crystallization between macromolecules. The internal crystallization of the fiber occurs at the same time of the formation of high degree of orientation. Due to its high molecular weight and strong resistance to external forces, this fiber can only be hot drawn in production. Therefore, a higher drawing temperature is required to achieve high drawing. The temperature of each drawing stage is different, which is determined according to the state of the filament in the previous process. There is no fixed number, but it must be within the temperature range that the fiber itself can withstand. In production, the temperature generally does not exceed 155 ℃. Otherwise, there will be stiff wires and stiff wires.
Winding forming
Requirements for wire roll forming: the wire barrel shall be free of collapse and burr, and the tow shall be fixed in length and weight. The so-called fixed length and weight is by no means a simple one. The requirements for the length and weight of the tow are very deep, and it is very difficult to accurately grasp them. It is required that all production processes must be normal and stable, and the fiber size can be guaranteed only if it is always uniform. If anyone can really achieve the technical level of fixed length and weight, he will reach the peak in the field of high-strength fibers.