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Since the enhancement method of plastic materials

by:CSSSLD     2021-01-23
Dynamic pressure maintaining enhancement technique modification principle is: through the change of the holding pressure, macromolecular chain under the action of shear force field, highly orientation along the flow direction, and generate a lot of crystal, so that the tensile strength of the plastic products to achieve a substantial increase. Dynamic pressure autofrettage technology, dynamic pressure maintaining enhancement technique is only suitable for injection molding products processing modification, the enhancement in the process of injection molding and extrusion and pressure molding available stretch enhancement technique. Dynamic pressure maintaining enhancement technology refers to the pressure in the process of plastic injection molding stage, using dynamic pressure maintaining equipment for special purpose, to implement the dynamic change of the holding pressure holding stage, so as to improve the tensile strength of a plastic products enhance method. Dynamic pressure maintaining enhancement technique is mainly done by dynamic pressure device.

pressure frequency, increase pressure frequency, the tensile strength decreased. Under the high pressure frequency, the distance the piston moves back and forth is reduced, thus melt flow in the cavity is shortened, the shear flow induced by the orientation. A piston moving back and forth rapidly, on the other hand, half cycle of shear flow induced molecular chain orientation is for the second half of the cycle to freeze the opposite flow, thereby reducing orientation degree, resulting in a decline in mechanical properties. Therefore, in the actual operation process, to increase the original molecular orientation and generally adopting low pressure frequency.

the melt temperature, melt temperature rising, the tensile strength increases, high melt temperature on the one hand, reduce the melt viscosity, molecular chain of mobile ability improved, another, delayed the melt to freeze time, increase the effective dynamic pressure maintaining time, these are conducive to the cavity pressure and shear orientation. With the increase of the holding time, the tensile strength increases. Long the holding time increase the number of dynamic pressure maintaining phase dynamic pressure, the pressure maintaining more fully, it is helpful to reduce the flaws in parts, improve the mechanical properties.

in the process of general injection molding processing, through an appropriate adjustment of the process conditions, can have the effect of increasing plastic products crystallinity and orientation degree, thus enhancement effect to a certain extent, this is a very simple and practical enhancement modification methods. With the increase of injection pressure, the plastic products orientation degree increased rapidly, its crystal type also can be made of spherulite crystal type into a lot of type string of jingjing. As a result, the tensile strength was almost linear increase. In addition, in the process of extrusion molding, by pushing extrusion pressure, also can achieve the goal of autofrettage. The autofrettage principle as well as the formation of crystal orientation degree and string. The specific process control for high injection pressure and lower speed. Appropriate to melt temperature. When the melt temperature is too high, the stretch in the molecular chain of orientation was going to be easy solution, thus unfavorable to orientation of crystallization, when the melt temperature is too low, low molecular chain activity, also does not favor the orientation of crystallization. Melt temperature in the low temperature area is a best value, now form a series of crystal and stretched straight chain crystal the most likely, the enhancement effect is best.

the higher the cooling temperature, the slower cooling rate, the crystallization rate increases, the crystallinity increased, the tensile strength also increase accordingly. This is mainly because the cooling speed is reduced, the melt in the crystallization temperature area to stay for a long time, can be used for the crystallization of the opportunity to increase, thereby increasing the crystallinity. In addition, slow cooling can be beneficial to the formation of crystal type, but also to improve the tensile strength.

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