Explanation of the "plasticity" of the production process of PVC products
1. The effect of plasticization on product performance:
The performance of PVC products is closely related to the degree of plasticization. The plasticization degree is not good, the products are brittle, and the mechanical properties cannot meet the requirements. The plasticizing degree is too high, the products will appear yellow line, the mechanical properties are not qualified, and the plasticizing degree is in PVC products. It is very important during the processing.
1). When the degree of plasticization is 60%, the tensile strength is the highest;
2). When the plasticization degree is 65%, the impact strength is the highest;
3). When the degree of plasticization is 70%, the elongation at break is the highest;
It is most suitable for the plasticizing degree of the material for producing the water supply pipe to be 60-65%. Because it can reflect two properties of tensile strength and impact strength in this range.
2. The effect of temperature on plasticization:
When the polymer material is lower than 80 °C, it can not be melted, it is in a glass state, and the material in the glass state is hard and brittle. In the glass state, the material cannot be processed; when the temperature rises to 160 °C, the material is in high elasticity. State, but the material still can't flow in this area, it can only make the material soft and viscoelastic; if it can achieve PVC melt processing and has fluidity, the temperature should be between 160-200 °C, but for any Stabilizer, when the temperature is higher than 200 °C, it is heated for a long time, and the material is decomposed again.
Therefore, when controlling the degree of plasticization, the temperature can only be controlled between 160-200 °C. In the temperature range of 40 ° C, the plasticization is better when the temperature of the PVC is set between 170 and 180 ° C.
3. Ways to improve the degree of plasticization:
1). By increasing the temperature of the fuselage and screw.
2). When the screw rotation speed is normal, increase the feeding speed of the feeder to increase the plasticizing degree.
3). Increase the speed of the extruder at the rated speed of the extruder and in the case of feeding.
4). Give the dry powder a good ripening period (12-48h)
The role of the ripening period:
1). Eliminate static electricity and reduce pollution
2), increase the apparent density
3). Improve the degree of plasticization
4). The low molecular weight polymerization is evenly dispersed to prevent extrusion instability.
5). Improve the degree of plasticization by reducing the temperature of the merging core.
4. How to judge the degree of plasticization:
1). Determine the plasticization degree by the host current (65/132 production line as an example, the host current is 46-52A, our company is suitable for low-calcium products, 45-50A. The premise is: screw speed 16~22r /min, the feed is full and matches the screw speed, the temperature setting matches the screw speed and the host current);
2). Observing the plasticizing degree of the material through the vacuum venting hole of the main machine (that is, the material is filled with more than 60% in the middle of the screw screw groove, the powder in the spiral groove is in the state of bean curd and the material at the bottom of the groove is flattened);
3). Determine the degree of plasticization by the viscoelasticity of the melt material of the die die (this method is more suitable for just starting);
4). Determine the degree of plasticization by the melt pressure and melt temperature of the combined core (the disadvantage is that if the instrument fails or the merging core sensor is dead by the coke, the accuracy of the test result will be affected)