Procedure of UHMW-PE (Ultra High Molecular Weight Polyethylene) in Armor Bulletproof Helmet
The main production process of UHMWPE fiber:
Currently, the preparation of raw materials at home and abroad varies, using different solvents and different solids content. Therefore, there is no fixed unified model, the production and production of equipment also varies greatly, while conventional melt spinning is not added solvent. However, 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 cannot fluctuate and requires uniformity at all times. Although the increase in solids content is one of the important means to increase production, but the stretching ratio is also increased, the overall speed of the car are to speed up accordingly, increasing the difficulty of operation, the amount of hairy wire produced compared to significantly more, not easy to grasp. However, if the percentage of solid content can be controlled within the appropriate concentration, it is still possible, therefore, according to their own situation, according to their ability. Increasing the speed of metering pump is also one of the effective means to increase the output.
The screw extruder plays the role of conveying - stirring - heating - pressurization of the material. First of all, the slurry before entering the "screw" to defoam, can not contain water vapor, the material in the process of conveying, to get a full mixing and stirring. The heating temperature of each zone should be set in conjunction with the position of the kneading block on the screw, and to ensure a certain conveying pressure. The setting of the screw kneading block, theoretical, different combinations, the mixing of materials, will have different effects.
The role of the spinning box is mainly insulation; temperature control; uniform distribution of materials to each spinning component.
The material is extruded by the metering pump into a silk strip, which is realized by the spinneret. The size of the aperture of the plate and the shape of the planing surface are its important technical parameters, which play a vital role in the forming and stretching performance of the fiber. The temperature at the spinning box and the spinnerette is matched, and the temperature parameters are set by observing the molten state of the spewed silk. However, some specific technical conditions and practical experience are required for precise control.
The main purpose is to extract and replace a large amount of solvent in the filament to obtain a "pure" degree of high-strength polyethylene fiber. Extractant selection, manufacturers vary, the production process is also different. So far, it is difficult to find a kind of economic and practical, safe and environmentally friendly, good extraction effect, but also non-toxic, tasteless ideal extractant. In the international arena, it is also a long-term problem that should not be solved.
From the spinning to the extraction of this section, the silk strip randomly and constantly stretching, from the appearance of the coarse to fine, from translucent to semi-creamy, the stretchability of the silk is gradually improved, with a little "strength". If you look at the internal silk, the molecular structure of the raw material is not a big change, there is no directional arrangement between the macromolecules, or in a disorderly state, the molecules are wrapped in a large number of solvents isolated, can not form a molecular chain, if the molecular chain can not be formed, the silk can not have real strength. At this time, the internal fiber is actually like a circular tubular mesh, the molecular particles of polyethylene are in its network, with the continuous stretching and thinning of the fiber, the solvent is constantly precipitated, the shape of the network is also from round to long, from comb to dense, the density between the molecules of the material is gradually increased, 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 stuck on the silk strip for drafting. This process is seemingly simple but difficult to control. If the process temperature and tension are not properly controlled, a large number of merging and stiffening will occur, resulting in a semi-finished silk bundle that can no longer be processed. The key is to grasp the drying temperature and drying length. This process should not be underestimated, it is directly related to the quality of the post-drawing product.
The drafting process of UHMWPE fiber is basically the same as that of conventional polyester staple fiber in form, but the required control precision is very different. This fiber must be drafted in multiple stages to achieve high strength and high modulus properties. The intermolecular structure changes considerably during each level of under-drawing. With stretching, the macromolecules move from disordered to ordered, oriented arrangement between them, and the crystallinity gradually increases. Only when the orientation of the macromolecules along the fiber axial direction is increased, the number of macromolecular chains produced will be more, and the holding force will be greater, and the stronger the fiber will naturally be. The crystallinity of the fiber increases, the initial modulus also naturally increases, the smaller the elongation of the fiber under the action of resistance to external forces, and the smaller the deformation.
During the drafting process, the drafting times of fibers should be as large as possible, and the fibers should be allowed to have a sudden stretching change, in order to be more able to promote the orderly orientation and high crystallization among macromolecules. The internal crystallization of the fibers occurs at the same time as the formation of high orientation and the crystallization transformation. Due to the high molecular weight of such fibers and the strong resistance to external forces, the production can only be done by hot stretching process. Therefore, it needs to be equipped with a high stretching temperature in order to achieve high draw. Each level of stretching, the temperature varies, depending on 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 general temperature does not exceed 155 degrees Celsius. Otherwise, there will be stiff and rigid yarns.
Winding and forming
The requirements of silk roll forming are: no collapsed edges, no burrs, fixed length and weight of the silk bundle. The so-called fixed length and weight is not simply a requirement for the length and weight of the silk bundle, it has a very deep connotation, and it is very difficult to grasp accurately. It is a requirement that all production processes must be normal and stable, and that the fibers must always be uniform. If anyone can really achieve the technical level of fixed length and weight, he or she will have reached the top of the field of high strength fiber.