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The velocity distribution and the end effect

by:CSSSLD     2021-01-23
Because the crystallinity can influence the performance of the injection molding processing, therefore often adopt the method of heat treatment industry for the phase transformation of amorphous phase, is not so stable crystalline structure into the crystalline structure of the stability and small grain into the large grain size, etc. , thus improving has crystallization tendency of polymer molding plastic parts performance. In the process of polymer molding, due to the shear force and tensile force, polymer orientation effect will happen. Orientation is divided into two kinds: one kind is the macromolecular polymer melt and its additives in shear flow along the direction of motion. A flow orientation; Another kind is under the action of tensile force, macromolecule or microcrystalline structure arranged along the loading direction, become stretch orientation.

add pipe or mouth mold straight part, appropriate to reduce the length of the molding pressure and molding temperature, the extrudate properly speed of traction or stretching, etc. , can reduce or eliminate the negative influence of end effect. In the process of forming, the polymer will happen some physical and chemical changes. In some conditions, for example, polymer crystallization or change the crystallinity, molecular orientation by external force, in some cases, the polymer degradation or crosslinking reaction can also occur.

the total rate of polymer crystallization, subject to the limit of the crystal nucleus formation and crystal growth rate, its general change to start slowly, and then quickly reach the maximum, then gradually slow down to zero. With polymer crystallization tendency, will appear in the process of forming crystalline structure, should be determined by forming the cooling rate. As for crystalline structure after the onset of the crystallinity, the crystallization condition of each part are consistent, to a large extent depends on the control cooling conditions.

in the forming process of the physical and chemical changes, can lead to mechanical, optical and thermal properties of the polymer, and other changes in the nature. Understanding of crystallization of polymers during processing, the phenomenon such as orientation, degradation and crosslinking of the characteristics of physical and chemical changes and the influence of molding process conditions for them, and according to the requirements of the product performance and use, to control the physical and chemical changes, the molding and application of polymer has very important practical significance.

according to the characteristics of the state of aggregation, the structure of the polymer into crystalline and amorphous two kinds. Crystalline polymer its crystallization degree available crystalline region of quality scores - in the polymer Crystallinity is measured. When polymer cooling from high temperature to the melting point, if it is a local chain segment has become orderly arrangement, and its size has been able to make the crystal growth, spontaneously orderly arrangement is the size of the particles become crystal billet.

when fluid flow from the storage tank, fill to catheter does not belong to the steady flow, the fluid each the size of the particle movement speed and direction at any time change, thus the speed distribution curve is very flat and in a straight line, only a very thin layer of liquid layer close to the pipe wall, its slowed sharply, to pipe wall is zero. Entrance effect and export expansion effect usually is unfavorable for plastic molding, especially in the processing of plastic injection molding, extrusion molding and wire drawing process, may lead to deformation and distortion product, reduce the dimensional stability of plastic parts, and may cause stress in the plastic parts, reduce the physical and mechanical properties of plastic.

the molecular main chain of the movement to stop, so the pattern of the crystal growth and the growth of the crystal will then stop, then, who has not yet started to crystalline molecules to disorder or an amorphous state in the polymer, which constitute the amorphous region of the polymer. In the process of crystal nucleus formation, if foreign substances exist in the melt, will greatly improve the rate of crystal nucleus formation. When the temperature drops, because the molecular chain segments activity increased resistance and make the crystal growth rate drops.

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