Detailed Explanation of the Main Classification of Plastic Granulator

The granulator is a very important plastic machine. There are many types of granulators and a wide range of applications. In the chemical industry, the granulator is widely used for various materials whose melting point (softening point) is within 300 °C and needs to be condensed and granulated. Such as: partial anhydride, stearic acid, maleic anhydride; phenolic resin, petroleum resin, sulfur, paraffin, rosin, asphalt, modified resin and other resin products; hot melt adhesive, synthetic soap, urea, additives, rubber and plastic additives products, etc.

In industrial production, many polymers must be mixed and mixed before being made into the final product, and then granulated to become a saleable raw material. The power required by the granulator is proportional to the extrusion volume and exponentially related to the size of the filter screen. There are many granulator equipment, but in general, it can be divided into two types of granulator systems: cold cutting system and die surface hot cutting system. The main difference between the two is the time arrangement of the pelletizing process. Cold pelletizing systems, which are pelletized from solidified polymer at the end of the process, while hot die-face pelletizing systems are pelletized as the molten polymer emerges from the die, and the pellets are pelletized downstream. cool down. Both pelletizing systems have their advantages and disadvantages.

Cold Pelletizing System: A cold pelletizing system consists of a die, cooling zone (air or water cooling), drying zone (if water cooling is used) and a pelletizing chamber. There are two main categories of cold pelletizing systems, namely flake pelletizers and strip pelletizers.

The strip production line is inexpensive, easy to operate, and easy to clean. This has advantages for color compounding, since the change of two different color batches requires a thorough cleaning of the equipment. However, the disadvantage of the strand making method is that the cooling section takes up space, the length of which is determined by the temperature requirements of the polymer.​

​Underwater granulator is similar to airflow granulator and water jet granulator, the difference is that it has a smooth water flow through the die surface and is in direct contact with the die surface. The size of the pelletizing chamber is just enough to allow the pelletizing knife to rotate freely across the die face without restricting the flow of water. The molten polymer is extruded from the die, and the pellets are cut by the rotary knife, and the pellets are carried out of the pelletizing chamber by the temperature-regulated water and enter the centrifugal dryer. In the dryer, the water is drained back to the storage tank, cooled and recycled; the pellets are passed through a centrifugal dryer to remove moisture.

The molten polymer is extruded from a hot die and cut into pellets by a rotary knife that rotates on the die face. The special feature of this pelletizing system is its specially designed water jet pelletizing chamber. The water flows around in a spiral until it flows out of the almond chamber. After the pellets are cut, they are thrown into the water flow for preliminary quenching. The pellet water slurry is discharged into the pellet slurry tank to be further cooled, and then sent to a centrifugal dryer to remove moisture.

Strand granulators have been around for almost as long as tablet granulators. Includes die, cooling section (water bath or blower), drying section (if water-cooled) and pelletizer. The molten polymer is extruded using an extruder or gear pump to form strands through a horizontally mounted die (modern dies are precision machined and uniformly heated to produce strands of consistent quality). Once the strands are discharged from the die, they are cooled with a blower or air/vacuum facility, or with a water bath. If water cooling is used, the strands are passed through a drying section where forced air is used to remove the moisture, and then the strands are sent to the pelletizing chamber. Using the shearing action of a pair of stationary and rotating knives, the strip is cut to the desired length precisely.

The traditional method of drawing strips by pelletizers is to stretch the strips through a cooling section (the most commonly used is a water bath). The process of drawing the strips will also make mistakes, such as the strips falling or the size is inconsistent. This phenomenon is common in polymers with poor melt strength, such as polypropylene, polyester, and nylon. Because of this, we should pay great attention during the operation process. Once the strip material falls, it will be scrapped. If the strip is inconsistent, the downstream pellets need to be sieved with the vibrating screen in the plastic auxiliary machine. So we have to be very careful when choosing a granulator!

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