Under normal circumstances, the main factors affecting the surface brightness of PVC profiles are the three aspects of formula raw materials, mold design and manufacturing, and production technology. The method of improving the surface brightness of PVC profiles generally starts from these three aspects:
1. Optimize formula design to ensure the quality of raw materials
The ratio of stabilizers, processing modifiers and other additives in the formula should ensure good thermal stability and processing fluidity of PVC; the amount of lubricants (especially external lubricants) should be reasonable to reduce extrusion as much as possible. The precipitation phenomenon in the process ensures the good plasticization state of the material. The quality of raw materials should be strictly controlled. It is recommended to choose large-scale, well-equipped and stable quality manufacturers as much as possible to purchase the goods, and to inspect the raw materials after entering the factory.
2. Guarantee the surface brightness of the product from the aspect of mold design and manufacture
The runner structure design of the machine head should ensure that the material flow rate of each part of the die section is consistent as much as possible, the inner rib speed should not be too different from the outer wall (generally not more than 15%), and the thickness should not exceed 2/3 of the outer wall thickness. ; The cavity surface of the mold should achieve sufficient machining accuracy, and the surface roughness should generally be above Ra0.2mm. It is recommended to conduct electroplating treatment on the surface of the shaping die; the water and gas path structure design of the shaping die should ensure sufficient and uniform cooling and adsorption force. It is sufficient, and a “brightness maintaining plate” can be set at the mouth of the stereotype to improve the brightness of the visible surface of the profile; the design of the strain of the stereotype should match the rheological state and production speed of the material as much as possible.
3. Reasonably adjust the extrusion process to improve the surface brightness of the product
In the actual production process, the process temperature, speed and pressure are adjusted according to the plasticization state of the material to ensure good plasticization of the material, and the die temperature is appropriately increased on this basis. If a separate heating zone (generally about 10mm long) is set at the exit of the die forming section to independently control the temperature, it will be more beneficial to improve the surface brightness of the product.