1. The compression ratio of the single screw extruder screw is suitable between 1:2-1:3, preferably 1:2.5, and the optimal length to diameter ratio of the three-stage screw is 25. A good screw design can avoid material decomposition and cracking caused by intense friction. Assuming the screw length is L, the feed section is 0.3L, the compression section is 0.4L, the metering section is 0.3L, and the gap between the screw barrel and the screw is 0.1-0.2mm. The honeycomb plate at the head of the machine needs to have 1.5-5mm holes, using two 400 hole/cmsq filters (approximately 50 mesh). When extruding transparent shoulder straps, a higher horsepower motor is generally required to prevent the motor from stalling or burning out due to overload. Generally, PVC or BM screws are available, but short compression section screws are not suitable.
2. The molding temperature depends on the materials of different manufacturers, and the higher the hardness, the higher the extrusion temperature. The processing temperature increases by 10-20 ℃ from the feeding section to the metering section.
3. If the screw speed is too fast and the friction is overheated due to shear stress, the speed setting should be controlled between 12-60rpm, and the specific value depends on the screw diameter. The larger the diameter, the slower the speed. Each material is different and attention should be paid to the technical requirements of the supplier.
4. Before use, the screw needs to be thoroughly cleaned, and PP or HDPE can be used for cleaning at higher temperatures. Cleaning agents can also be used for cleaning.
5. The design of the machine head should be streamlined and there should be no dead corners to ensure smooth material flow. The bearing line of the mold sleeve can be appropriately extended, and the angle between the mold sleeves is designed to be between 8-12 °, which is more suitable to reduce shear stress, prevent eye droppings during the production process, and stabilize the extrusion amount.
6. TPU has a high coefficient of friction and is difficult to shape. The length of the cooling water tank should be longer than other thermoplastic materials, and TPU with high hardness is easier to form.
7. The core wire must be dry and free of oil stains to prevent bubbles from occurring due to heat. And ensure the best combination.
8. TPU belongs to the category of easily hygroscopic materials, which quickly absorb moisture when placed in the air, especially when ether based materials are more hygroscopic than polyester based materials. Therefore, it is necessary to ensure a good sealing condition. Materials are more prone to moisture absorption under hot conditions, so the remaining materials should be quickly sealed after packaging. Control the moisture content below 0.02% during processing.
Post time: Aug-30-2023