Orientation in extrusion production
DATE：2019/12/5 8:44:54 / READ： / SOURCE：This station
Orientation in extrusion production
The elongated fibrous fillers and macromolecular chains present in the plastic material are largely aligned parallel to the flow direction during flow, and this arrangement is often referred to as orientation. Reason for orientation: If this parallel arrangement is not made, then thin and long cells will inevitably run at different speeds.
This is actually impossible. Of course, for the same reason, the Ta and
When the thermoplastic material between Tm or (T) is subjected to tensile stress, the macromolecular chain also
It will inevitably be arranged in parallel along the flow direction, which is called stretch orientation. The result of the orientation gives the product anisotropy (mechanical properties).
Orientation and de-orientation coexist in shear flow: under the effect of velocity gradient, curled long-chain molecules gradually stretch and straighten along the flow direction to cause orientation; due to the high melt temperature, the molecular thermal movement is intense, so While the macromolecules flow and align, there must be a de-orientation effect. Therefore, analyzing the degree of macromolecule orientation is the result of analyzing the comprehensive balance of these two factors.
In the isothermal flow area, due to the small cross-section of the pipe, the velocity gradient at the pipe wall is the largest, and the melt orientation near the pipe wall is the highest; in the non-isothermal flow area, the pressure of the melt gradually decreases after entering the cavity with a larger cross-section. Therefore, the velocity gradient in the melt also gradually decreases from the maximum value at the gate to the minimum value at the front of the stream. Therefore, the degree of molecular orientation in the front region of the melt is low. When this part of the melt first contacts the mold wall with a lower temperature, it is rapidly cooled to form a frozen layer, that is, a surface with little or no orientation structure. However, the melt near the surface layer still flows, with high viscosity and large speed gradient. Therefore, the melt in this layer (called the subsurface layer) has a high degree of orientation. In addition, the heat loss of the material in the subsurface layer is faster (because the surface layer is very Thin, the time required for thermal conduction is short), so most of the alignment structure of the subsurface layer can be retained. Due to the small velocity gradient, the melt in the central part of the cavity has an orientation range.
The elongated fibrous fillers and macromolecular chains present in the plastic material are largely aligned parallel to the flow direction during flow, and this arrangement is often referred to as orientation. Reason for orientation: If this parallel arrangement is not made, then thin and long cells will inevitably run at different speeds.
This is actually impossible. Of course, for the same reason, the Ta and
When the thermoplastic material between Tm or (T) is subjected to tensile stress, the macromolecular chain also
It will inevitably be arranged in parallel along the flow direction, which is called stretch orientation. The result of the orientation gives the product anisotropy (mechanical properties).
Orientation and de-orientation coexist in shear flow: under the effect of velocity gradient, curled long-chain molecules gradually stretch and straighten along the flow direction to cause orientation; due to the high melt temperature, the molecular thermal movement is intense, so While the macromolecules flow and align, there must be a de-orientation effect. Therefore, analyzing the degree of macromolecule orientation is the result of analyzing the comprehensive balance of these two factors.
In the isothermal flow area, due to the small cross-section of the pipe, the velocity gradient at the pipe wall is the largest, and the melt orientation near the pipe wall is the highest; in the non-isothermal flow area, the pressure of the melt gradually decreases after entering the cavity with a larger cross-section. Therefore, the velocity gradient in the melt also gradually decreases from the maximum value at the gate to the minimum value at the front of the stream. Therefore, the degree of molecular orientation in the front region of the melt is low. When this part of the melt first contacts the mold wall with a lower temperature, it is rapidly cooled to form a frozen layer, that is, a surface with little or no orientation structure. However, the melt near the surface layer still flows, with high viscosity and large speed gradient. Therefore, the melt in this layer (called the subsurface layer) has a high degree of orientation. In addition, the heat loss of the material in the subsurface layer is faster (because the surface layer is very Thin, the time required for thermal conduction is short), so most of the alignment structure of the subsurface layer can be retained. Due to the small velocity gradient, the melt in the central part of the cavity has an orientation range.
Author：admin