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When using automatic compounding systems for the mixing process, some manufacturers often fail to pay attention to the details, resulting in defective products. This article summarizes several aspects of the mixing process that should be taken into account for manufacturers' reference.
Here is the list of contents
Preparation of raw materials
High-speed mixing machine to determine the amount of material
The choice of high-speed mixer discharge temperature
PVC resin should have uniform granularity, proper relative molecular mass range, porous inside, quality should be in accordance with national standards, and loose resin should be used. The water content of resin shall meet the production requirements, otherwise it will increase the difficulty of vapor discharge at high speed mixing.
Various additives, especially lead salt stabilizer and soap stabilizer, the particles should be extremely fine, and the content of active ingredients should be stable and meet the standard of first-class products. The water content of the additives should be low, otherwise it should be pre-dried.
High-speed mixer charging volume should be able to ensure the premise of mixing temperature, try to improve production efficiency. The volume of the material is less than 50% of the empty volume of the mixer, frictional heat generation is smaller. When reaching the preset mixing temperature, such as 120 ℃, it takes more than 15 minutes; when the amount of material accounted for 50-70%, to reach the temperature is only 8-10 minutes; the amount of material in more than 70%, the mixing effect began to become worse, the speed of heating is no longer obvious, the mixer motor current is too large. Therefore, the amount of material added to control the empty volume of the mixing chamber is 50-70% is appropriate.
The results show that the PVC resin particles under strong mixing, material temperature below 50 ℃, PVC agglomerates of powder particles and larger particles are rubbed, the impact of particle crushing becomes smaller, when the apparent density of the dry mix does not change and resin particles become smaller. Material temperature above 80 ℃ to about 120 ℃, the expansion of PVC resin particles become larger, particle size tends to be uniform, the average size of the particles and unmixed PVC resin particles similar; at the same time, because the particles absorb the additives, the apparent density of the dry mix rapidly increased. Material temperature above 120 ℃, the resin particle size decreases while the apparent density of the dry blend is still increasing, under the microscope can be seen in part of the particles or the surface layer of the particles become translucent, indicating that the pores within the particles in the reduction, the internal structure tends to tighten.
Resin particles become larger and uniform is conducive to the flow of dry mix, beneficial to the transport; performance density increases, conducive to the improvement of extrusion yield and reduce the amount of exhaust, to improve the denseness of the product. At the same time, the material temperature above 100 ℃, is conducive to the exclusion of water vapor in the material, so the high-speed mixing temperature is generally set at 110-130 ℃.
The use of liquid stabilizer, while the material moisture content is very low, the hot mix temperature can be set at a lower temperature range, such as 105 ℃, but not less than 90 ℃. The use of solid stabilizers or material moisture content is slightly higher, the hot mix temperature should be 120-125 ℃; additives containing processing modifiers to promote plasticization and internal lubricants, the hot mix temperature can be lower limit. Auxiliaries have delayed plasticization, reduce friction of lead salts and external lubricants more, it is appropriate to take the upper limit. However, in actual operation, special attention should be paid to the difference between the temperature displayed by the meter and the actual material temperature, and the meter display should be corrected regularly to avoid quality accidents.
Zhangjiagang Chenxing Machinery Co., Ltd has many years of experience in producing plastic machinery and equipment, and always takes the enterprise purpose of being the model of the industry and creating first-class products of plastic machinery, and insists on providing more detailed technical support and service for domestic and foreign customers with the business purpose of integrity first and service first. If you are interested in our products, welcome to contact us!
