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Rheological properties of polymer
by：CSSSLD
2021-02-03
In the region of the secondary shear rate, injection molding processing rheological properties of pseudoplastic fluid performance is: the deformation of shear stress and flow need change with shear rate, and increase exponential rule, the deformation and flow of viscous resistance, namely, the apparent viscosity of the liquid change with shear rate, and the exponential law.
This phenomenon is called the shear thinning effect of pseudoplastic fluid.
Since most thermoplastic polymer are pseudoplastic fluid rheological properties, so the polymer melt in injection molding occurs shear thinning effect is a common phenomenon.
according to the nature of the change of viscosity, polymer melt into Newton type and non-newtonian type two kinds big. For Newton type melt, can use Newton describe the rheological properties of the rule of shear flow. In fluid mechanics, fluid shear stress in the flat circular tube and flow occurs in the form of laminar flow and turbulent flow in two forms. Laminar flow, the flow of the liquid is according to the flow layer on a number of parallel to each other, the same layer between each point at the same speed with each other. If the increased flow, make it beyond a certain threshold, then flow into a turbulent.
belong to liquid dilatability is mainly some polymer with high solid content slurry and with the structure of the gel polymer liquid or suspension, under high shear rate of PVC paste flow behavior is similar to this kind of liquid. As used in the pseudoplastic fluid shear stress changes, the change of the shear rate much faster than the change of the shear stress, the flow of the liquid and swelling behavior is the opposite. The viscosity of the fluid is not a constant, he will change with the shear rate and shear stress.
turbulence, the size of the liquid velocity at every point and direction of change with time. Laminar flow and turbulent flow with liquid Reynolds number, greater than 4000 is turbulent. Due to the injection molding of polymer melt Reynolds number is generally far less than 2100, so they can be laminar flow form as a liquid. Ideal laminar flow can be as a thin layer of adjacent layers of liquid along the sliding direction of external force, the liquid layer has a flat plane, parallel to each other each other, and each layer of the sliding velocity of each point are equal, but due to the influence of wall friction, sliding speed difference between each layer.
due to the long chain structure of the macromolecular and winding, the flow of the polymer melt behavior than low molecular liquid complex. In a broad range of shear rate, the liquid flow is directly proportional to the shear stress and shear rate no longer, the melt viscosity is not a constant, and the rheological behavior of polymer melt not obey Newton flow law. Usually the flow law of flow behavior does not obey Newton flow type called a non-newtonian flow, with the flow behavior of liquid known as non-newtonian fluid.
polymer molding methods must be implemented by the deformation and flow of the polymer, so also produced the corresponding injection molding processing of polymer rheology such a discipline. It mainly studies the polymer under the action of external force produced by mechanical phenomena such as stress, strain and strain rate with itself, the relationship between the viscosity and the factors that affect these relationships. Rheological properties of polymer in forming process is mainly refers to the shear viscosity change with shear stress or plastic shear strain and produce change.
in injection molding, only a minority of the viscosity of the polymer melt is not sensitive to shear rate, in addition to the often put their approximate as Newtonian fluid, the vast majority of other polymer melts is characterized by non Newtonian fluid. Apparent viscosity characterization of Newtonian liquid under the action of external force, the ability to resist shear deformation. Because of non-newtonian fluid flow laws is more complex, apparent viscosity except related to the nature of the fluid itself as well as the temperature, also because of the influence of shear rate, which means that the size of the external force and its role in time also can change the stand of fluid viscosity.
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according to the nature of the change of viscosity, polymer melt into Newton type and non-newtonian type two kinds big. For Newton type melt, can use Newton describe the rheological properties of the rule of shear flow. In fluid mechanics, fluid shear stress in the flat circular tube and flow occurs in the form of laminar flow and turbulent flow in two forms. Laminar flow, the flow of the liquid is according to the flow layer on a number of parallel to each other, the same layer between each point at the same speed with each other. If the increased flow, make it beyond a certain threshold, then flow into a turbulent.
belong to liquid dilatability is mainly some polymer with high solid content slurry and with the structure of the gel polymer liquid or suspension, under high shear rate of PVC paste flow behavior is similar to this kind of liquid. As used in the pseudoplastic fluid shear stress changes, the change of the shear rate much faster than the change of the shear stress, the flow of the liquid and swelling behavior is the opposite. The viscosity of the fluid is not a constant, he will change with the shear rate and shear stress.
turbulence, the size of the liquid velocity at every point and direction of change with time. Laminar flow and turbulent flow with liquid Reynolds number, greater than 4000 is turbulent. Due to the injection molding of polymer melt Reynolds number is generally far less than 2100, so they can be laminar flow form as a liquid. Ideal laminar flow can be as a thin layer of adjacent layers of liquid along the sliding direction of external force, the liquid layer has a flat plane, parallel to each other each other, and each layer of the sliding velocity of each point are equal, but due to the influence of wall friction, sliding speed difference between each layer.
due to the long chain structure of the macromolecular and winding, the flow of the polymer melt behavior than low molecular liquid complex. In a broad range of shear rate, the liquid flow is directly proportional to the shear stress and shear rate no longer, the melt viscosity is not a constant, and the rheological behavior of polymer melt not obey Newton flow law. Usually the flow law of flow behavior does not obey Newton flow type called a non-newtonian flow, with the flow behavior of liquid known as non-newtonian fluid.
polymer molding methods must be implemented by the deformation and flow of the polymer, so also produced the corresponding injection molding processing of polymer rheology such a discipline. It mainly studies the polymer under the action of external force produced by mechanical phenomena such as stress, strain and strain rate with itself, the relationship between the viscosity and the factors that affect these relationships. Rheological properties of polymer in forming process is mainly refers to the shear viscosity change with shear stress or plastic shear strain and produce change.
in injection molding, only a minority of the viscosity of the polymer melt is not sensitive to shear rate, in addition to the often put their approximate as Newtonian fluid, the vast majority of other polymer melts is characterized by non Newtonian fluid. Apparent viscosity characterization of Newtonian liquid under the action of external force, the ability to resist shear deformation. Because of non-newtonian fluid flow laws is more complex, apparent viscosity except related to the nature of the fluid itself as well as the temperature, also because of the influence of shear rate, which means that the size of the external force and its role in time also can change the stand of fluid viscosity.
more excellent articles: injection molding product development process, click directly.
http://www。 csssld。 cn//html/2017/Info_0416/552。 HTML
nantong on suye's official website: http://www. csssld。 Cn / /
more wonderful articles, immediately search: changshu da plastic products factory smoothly
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