The main factors affecting the extrusion process of low foaming hard PVC profiles
DATE：2019/11/2 8:47:16 / READ： / SOURCE：This station
The main factors affecting the extrusion process of low foaming hard PVC profiles are extrusion temperature, residence time and extrusion pressure.
1 extrusion temperature
In order to ensure that the material is plasticized uniformly in the extruder, the melt is dense, and a good foam is obtained, the control of the extrusion temperature is important.
When the extrusion temperature is low, the nucleation is less, the bubbles are less, and the foam density is large; when the temperature rises to a certain value, the materials are uniformly mixed, the plasticization is good, the gas increases in solubility from the melt and the number of nucleation increases. Therefore, a good low-density foam can be obtained; when the temperature continues to rise, the viscoelasticity of the material is reduced, the cells can be enlarged by colliding with each other, and the gas diffuses from the inside to the outside of the melt, and the amount of gas in the melt is reduced. Thereby, the density of the foam is increased; when the temperature exceeds a certain value, the internal pressure of the melt is too large, which may cause the melt to rupture.
Therefore, in the feeding section, in order to prevent premature decomposition of the blowing agent, a lower temperature should be employed: in the compression section and the metering section, in order to dissolve a large amount of the blowing agent and to promote the decomposition of the gas in the PVC melt, Higher temperatures should be used; at the die, to prevent excessive foaming and maintain pressure distribution within the head, proper temperature reduction is required.
2 stay time
The length of time that the material stays in the extruder barrel and die is affected by the material properties of the system and the feed rate. The residence time is too short, the foaming agent is not sufficiently decomposed, and the density of the final product is large; the residence time is too long, and the foaming agent is excessively decomposed in the barrel. The reduction in the amount of foaming that can continue to decompose at the die can also result in an increase in the density of the foam. Therefore, the dwell time should be controlled to an appropriate value.
3 extrusion pressure
Extrusion pressure control is the key to foaming success. In general, increasing the extrusion pressure has a positive effect on reducing the cell diameter and increasing the number of bubbles. In addition, the screw speed, the length of the mold flow path and the compression ratio all have an effect on the foaming process. Experiments have shown that increasing the rotational speed in a certain range of screw speeds can increase the melt pressure, which is advantageous for the foaming process.
1 extrusion temperature
In order to ensure that the material is plasticized uniformly in the extruder, the melt is dense, and a good foam is obtained, the control of the extrusion temperature is important.
When the extrusion temperature is low, the nucleation is less, the bubbles are less, and the foam density is large; when the temperature rises to a certain value, the materials are uniformly mixed, the plasticization is good, the gas increases in solubility from the melt and the number of nucleation increases. Therefore, a good low-density foam can be obtained; when the temperature continues to rise, the viscoelasticity of the material is reduced, the cells can be enlarged by colliding with each other, and the gas diffuses from the inside to the outside of the melt, and the amount of gas in the melt is reduced. Thereby, the density of the foam is increased; when the temperature exceeds a certain value, the internal pressure of the melt is too large, which may cause the melt to rupture.
Therefore, in the feeding section, in order to prevent premature decomposition of the blowing agent, a lower temperature should be employed: in the compression section and the metering section, in order to dissolve a large amount of the blowing agent and to promote the decomposition of the gas in the PVC melt, Higher temperatures should be used; at the die, to prevent excessive foaming and maintain pressure distribution within the head, proper temperature reduction is required.
2 stay time
The length of time that the material stays in the extruder barrel and die is affected by the material properties of the system and the feed rate. The residence time is too short, the foaming agent is not sufficiently decomposed, and the density of the final product is large; the residence time is too long, and the foaming agent is excessively decomposed in the barrel. The reduction in the amount of foaming that can continue to decompose at the die can also result in an increase in the density of the foam. Therefore, the dwell time should be controlled to an appropriate value.
3 extrusion pressure
Extrusion pressure control is the key to foaming success. In general, increasing the extrusion pressure has a positive effect on reducing the cell diameter and increasing the number of bubbles. In addition, the screw speed, the length of the mold flow path and the compression ratio all have an effect on the foaming process. Experiments have shown that increasing the rotational speed in a certain range of screw speeds can increase the melt pressure, which is advantageous for the foaming process.
Author：admin