The material strips discharged by the water ring pelletizer from the pelletizing template are immediately cut into pellets by the rotating cutter. Therefore, the PP plastic melt must be cuttable, which affects the temperature of the extruder, the speed of extrusion, and the connecting body. The temperature, the melt pressure, the temperature of the discharging template, the number of holes of the discharging template, the temperature of the cooling water, the pressure of the cooling water and the uniformity of the mixing of the raw materials are all required. In these nine conditions, the conditions are suitable. When the water ring pelletizer is made of PP with high melt index, the equipment can operate normally and produce qualified PP plastic particles.
Polypropylene (PP) is a general-purpose thermoplastic resin with excellent mechanical properties, heat resistance, chemical resistance, and low price, so it has been widely used. PP granulation can adopt processes such as strand cutting and hot cutting with water ring die surface. The hot pelletizing of the water ring die surface has the characteristics of high pelletizing efficiency, small footprint, smooth and beautiful pellets, but the high melt index PP has low viscosity and easy adhesion, which has always been a problem in the pelletizing process.
Because PP is in the molten state, the melt index will change greatly under the small difference in temperature. Therefore, if the process is not well mastered, the water ring pelletizer is used to cut the pellets. It is easy to cause the quality of the plastic particles to lose control, and the particles will interact with each other. Adhesion and agglomeration will block the water ring pelletizing cover in serious cases and cause production interruption. Therefore, adopting the correct cutting process of the water ring pelletizer is the key to the normal operation of the PP water ring pelletizer.
The strips discharged from the pelletizing template by the water ring pelletizer are immediately cut into pellets by the rotating cutter. Therefore, the plastic melt must be cuttable, which is the most basic requirement to ensure the normal progress of the pelletizing process. But in order to ensure this most basic requirement, the temperature of the extruder, the speed of extrusion, the temperature of the connecting body, the melt pressure, the temperature of the discharging die plate, the temperature of the cooling water, the pressure of the cooling water, and the ratio of raw materials are mixed. The uniformity is required. Under suitable conditions, the water ring pelletizer can ensure the normal operation of the equipment when the water ring pelletizer is made of PP with high melt index.
1. Extruder temperature When the extruder temperature is too high, it will cause the melt index to increase and the melt viscosity to decrease. The extruded melt is easy to stick, which is not conducive to pelletizing. When the extruder temperature is low, PP plastic Poor melting, increased viscosity, increased mold release expansion rate, and no problem in pelletizing, but the outer diameter of the pellets becomes larger, the shape is rough, and the appearance quality of the pellets deteriorates, so it is very important to find the appropriate temperature first. Through experiments, it is known that the extruder adopts the process of high temperature in the feed section and gradually lower temperature at the discharge end, which is well compatible with the problems of raw material plasticization and excessive temperature at the discharge port. The specific actual temperature is adjusted according to the actual situation according to the different extruder and material formula.
2. Extrusion speed of the extruder The plastic extruder is an important part of these links. The different design of the extruder screw will affect the plasticization of the raw material. The frictional heat of the screw is different at different speeds. Affect the temperature of the raw material at the exit of the extruder, thereby affecting the melt index of the raw material. A high temperature will cause the pellets to stick, so the appropriate extrusion speed is also a factor that affects the normal pelletizing of the PP water ring pelletizer.