Material blockage is a common problem affecting production efficiency and product quality during the operation of micro particle underwater pelletizers in plastics machinery. A comprehensive approach involving process control, equipment optimization, operational procedures, and raw material management is necessary to achieve stable pelleting.
Process control is the core element in preventing blockage. The key to underwater pelleting is delivering sufficient thermoplastic through the die orifice to maintain the resin melting temperature while the melt is in contact with water several hundred degrees cooler. Improper sequence of resin, cooling water, and cutter activation can easily lead to blockage. For example, if the resin begins to flow before the water reaches the die surface, or if the water reaches the die head before the polymer flows, it can cause die freezing or resin smearing. Therefore, it is essential to strictly follow the sequence of "water first, then resin delivery, and finally the cutter" to ensure uniform die head temperature and avoid localized overheating or undercooling. Furthermore, process fluctuations such as unstable extruder output or low bulk density of recycled material can lead to inconsistent polymer flow, resulting in random die freezing. Using a continuous screen changer instead of a sliding screen changer can reduce flow interruptions and air trapping, ensuring continuous polymer flow.
Optimizing the micro-particle underwater pelletizer is key to improving its anti-clogging capability. Die design directly affects pelleting stability. Compared to barrel heaters, oil heating systems can apply heat evenly over a larger area, reducing the risk of localized die freezing, especially suitable for high-output production lines or materials with narrow melting temperature ranges. The design of the die insulation layer is also crucial; for example, using a vacuum-gap "hollow" die can reduce heat loss and maintain stable die orifice temperature. The gap between the pelletizer blade and the die needs precise control; too small a gap can lead to blade wear or die orifice scratches, while too large a gap may result in incomplete cutting and material blockage. Regularly checking and adjusting the pelletizer blade to ensure its sharpness and rotational stability is an important measure to prevent material blockage.
Proper operating procedures are essential to avoid human error. The startup phase is a high-risk period for material blockage; operators must closely monitor the synchronization of resin, water, and the cutter. For example, preheating the die to a suitable temperature in advance prevents resin from contacting a cold die and causing instantaneous solidification; slowly increasing the extruder speed prevents sudden increases in resin flow from impacting the die orifice. During production, the die head and pelletizing chamber must be cleaned regularly to prevent oligomers and impurities from settling and forming "wall adhesion," which reduces the flow area of the die orifices. When switching to high melt index products, the die and pelletizing water temperatures should be increased in advance to mitigate blockages caused by low melt index product residue, followed by a temperature reduction and switchover according to the plan.
Raw material management is fundamental to reducing blockages. The purity and uniformity of raw materials directly affect the pelleting effect. Impurities such as metals and sand mixed in the raw materials can easily clog the die orifices or scratch the die surface. Therefore, a high-precision screen should be installed at the raw material inlet, and its integrity should be checked regularly to prevent damage that could allow impurities to enter. Furthermore, the moisture and viscosity of the raw materials must be strictly controlled. Excessive moisture may cause particle adhesion, while abnormal viscosity may lead to poor flow. Pre-drying or adding additives to adjust raw material properties can reduce the risk of blockages.
Die maintenance is crucial for extending equipment life. After prolonged use, the inner walls of the die orifices may become rough due to wear or corrosion, increasing resin flow resistance. Regularly polishing the mold to restore its smoothness reduces resin residue and clogging. Simultaneously, check the temperature uniformity of all areas of the mold. If oil valve blockage causes localized temperature abnormalities, clean or replace oil circuit components promptly to ensure overall mold performance stability.
Environmental control is an auxiliary means to ensure stable equipment operation. Micro particle underwater pelletizers are sensitive to ambient humidity and temperature. High humidity environments may cause short circuits in electrical components or condensation in the mold, thus affecting pelleting quality. The workshop needs to be equipped with dehumidification equipment and a constant temperature system to maintain a suitable production environment. In addition, operators must wear anti-static clothing and gloves to avoid static electricity or grease contamination of the die head and pelletizing blade, ensuring equipment surface cleanliness.
Intelligent monitoring is the future direction for improving anti-clogging capabilities. By installing sensors and online detection systems, key parameters such as die head temperature, resin flow rate, and pelletizing blade speed can be monitored in real time, providing early warnings of clogging risks. For example, when the die head temperature fluctuates beyond the set range, the system automatically adjusts the heating power or issues an alarm; when the resin flow rate abnormally decreases, the extruder speed is automatically reduced to avoid die orifice overload. By combining big data analytics and machine learning algorithms, process parameters can be further optimized to achieve intelligent control of the granulation process, fundamentally reducing the occurrence of material blockage problems.
