Granulation - cold cutting system
The cold granulation system consists of a mold, a cooling zone (air-cooled or water-cooled), a drying zone (if water-cooled), and a granulation chamber. It is divided into two categories, namely sheet granulator and strip granulator.
1) Sheet pelletizing machine will melt the polymer from the mixing equipment through the belt die or roll mill, and roll into a certain thickness of polymer sheets. During transportation, the pieces are solidified and cooled for a distance, and then cut into circles or squares in the barrel with a pelletizing knife.
Sheet granulation is the oldest method of granulation and can be used for a variety of different polymers, from nylon to polyvinyl chloride. The method has the advantages of high yield, good granulation precision, good granulation performance and higher noise than the melt polymer cutting method. The curing polymer tool has a short service life and usually has the problem of producing powder. Some "particle chains" can be seen in some polymers.
2) The use history of strip granulator is almost as long as that of sheet granulator. The structure includes a mouth mold, a cooling section (water bath or blower), a drying section (if water cooling is used), and a grain cutter. The molten polymer is formed into strips by a machine or gear pump through a horizontally mounted die (modern dies are precisely machined and evenly heated to produce a strip of consistent quality). After the strip is discharged from the mouth, it is cooled with a blower or air/vacuum device or water bath. If water cooling is used, the strip passes through a drying section where the water is blown away by forced ventilation before the strip is sent to the cutting chamber. Using the shearing action of a pair of fixed and rotating knives, the strip is precisely cut to the desired length, and the corners of the particles are clear.
This method is suitable for most polymers, and has the advantages of low production cost and simple operation, but it requires a large space. The traditional method of wire drawing is to stretch the strip through a cooling section (most commonly a water bath cooling), which sometimes causes the strip to fall off or have inconsistent dimensions. This is most common in polymers with poor strength in the molten state, such as polypropylene, polyester, and nylon. When the strip is dropped, the material is scrapped, so pay close attention, if the strip tensile is not consistent, you need to screen downstream particles.
Slicing in other modes can be done without close monitoring by using a motor-driven slotted feed conveyor that supports and splits the strip from the mold to the pelletizer. The strip transported by rotating force is relatively uniform in size, less affected by the strength of the molten state of the material, and will not fall, so it is less scrapped.
The strip production line has the advantages of low cost, convenient operation and easy cleaning. This has its advantages for color mixing, because replacing two batches of different colors must be thoroughly cleaned. However, the disadvantage of the strip method is that the cooling section takes up space, and the length of the cooling section is determined by the temperature requirements of the polymer.
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