Analysis of granulation technology of the hottest

2022-08-17
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Analysis of polymer material granulation technology

most polymers must be mixed before being made into final products, and then granulated to become marketable raw materials. There are many different granulator designs, but all granulators can be divided into two categories: cold pelletizing system and die surface hot pelletizing system. The main difference between the two is the time arrangement of the granulation process. The cold granulation system cuts particles from the cured polymer at the end of the processing process; In the die surface hot grain system, when the molten polymer appears from the die, it is pelleted, and the granular material is cooled downstream. The two pelletizing systems have their own advantages and disadvantages

cold pelletizing system

cold pelletizing system includes die, cooling area (air cooling or water cooling), drying area (if water cooling is used) and pelletizing chamber. There are two types of cold pelletizing systems, namely, tablet granulator and strip granulator

the molten polymer in the pelletizer passes through a belt die or roller mill from the mixing equipment and is rolled into a certain thickness of polymer sheet. The flakes are solidified and cooled over a distance during transportation, and then cut into round or square pellets in a bin with a pelletizer

pellet granulation is the oldest method for manufacturing pellets, which can be used for various polymers from nylon to PVC It is reported that the accuracy is quite good, and the granulation capacity can reach 1843.69kg/h. this is a cold granulation method, and the noise emission is higher than that of granulation from molten polymer. The service life of coagulated polymer cutter is short, and the generation of powder is often a problem. For some polymers, some "particle chain" phenomena can be seen

the use history of bar granulator is almost as long as that of tablet granulator. It includes die, cooling section (water bath or blower), drying section (if water cooling is used) and pelletizer. Extrude the molten polymer with an extruder or gear pump and form strips through a horizontally installed die (the modern die is precision machined and evenly heated to produce strips with stable quality). After the strip is discharged from the mouth, it is cooled by blower or air/vacuum facilities, or by water bath. If water cooling is used, the strips need to pass through a drying section, blow out the moisture with forced ventilation, and then send the strips to the pelletizing chamber. Using the shearing action of a pair of fixed knives and rotary knives, the strip is accurately cut into the required length

the diameter of granular material is 3.175 mm, the length is 3.175mm, and the edges and corners are clear

the traditional method of drawing the strip is to stretch the strip through the cooling section (the most commonly used is water bath), sometimes causing the strip to fall or inconsistent size. This is most common in polymers with poor melting strength, such as polypropylene, polyester and nylon. When the strip falls, the material is scrapped, so the operator should pay close attention. If the strips are not drawn uniformly, the downstream granular materials need to be screened

the strip forming method of other modes does not need to be closely monitored by the operator. The method is to use the slotted feeding conveyor driven by the motor to support and divide the strip from the die to the pelletizer. This kind of strip conveyed by rotary force is relatively uniform in size, and will not fall, so it is less scrapped. Some of these methods can make its production capacity reach 6803.89 kg/h, while the stretching method is only about 1814. High performance carbon fibers and composites are the dominant varieties in Shandong Province 37 kg/h, because the operator can only take care of a limited number of items. The strip production line has the advantages of low cost, simple operation and convenient cleaning. This has its advantages for color mixing, because the replacement of two batches of different colors must thoroughly clean the equipment. However, the disadvantage of the strip making method is that the cooling section needs to occupy space, and its length can be determined according to the temperature of the polymer, which can be directly connected to the requirements of 8 single ended imitations

die surface hot cutting system

there are three basic types of die surface hot cutting system, namely, air flow granulator, water spray (water ring) granulator and underwater granulator. Although such systems can have different designs, typical systems include die, cutting room, electric rotary blade cutter, cooling medium and drying particles without oil source (if water cooling is used)

The die is an important part of the hot granulation system on the die surface. It is installed vertically or horizontally and is usually heated by oil, steam or barrel or belt electric heaters. Electric heating is usually used for smaller die; But larger dies are usually heated with steam or oil. The die structure material has different materials, but no matter what kind of material or heating medium is used, the die orifice diameter must be uniform; There should be enough heat to maintain the temperature of the polymer during the whole extrusion process; The pelletizer must be tough and smooth against the rotating die surface - these are necessary to produce uniform pellets

when the molten polymer is extruded from the die, the granulator rotates at a high speed to cut it into pellets. Typically, the pelletizer is either in contact with or very close to the die surface. After the pellets are cut, they are thrown away from the knife by centrifugal force and transported to the cooling medium. The size, shape, material and installation method of the granulator can be different. In some systems, the pelletizer has a spring load to automatically adjust the spacing between the pelletizer and the die; Some systems must manually adjust the distance between the pelletizer and the die. Because the service life of the cutter depends on the centering accuracy of the cutter the first mock examination, the abrasiveness of the polymer and the aggressiveness of the operator, it is desirable to cut polymer pellets in the molten state

pneumatic granulator is recommended for polymers sensitive to heat and long residence time, such as PVC, TPR and XLPE. The pelletizing rate is as high as 4989.52kg/h, and the flow diameter of polymer from the extruder to the pelletizing chamber should be kept as short as possible, and the least heat should be used. When the polymer is extruded through the die, the rotating force of the die surface will cut it into pellets. After the pellets are cut, they are immediately thrown away from the rotary knife and captured by the forced circulating air in the specially designed pelletizing chamber. The air flow preliminarily quenches the surface of the granular material, and takes it out of the pelletizing chamber and sends it to the cooling area

fluidized bed dryers are often used to cool granular materials. The granular material slides down an adjustable slope, and the circulating fan blows through the granular material. Adjusting the inclination angle of the inclined plane can prolong or shorten the residence time of the granular material in the dryer. Another common cooling method is to unload the pellets from the pelletizing chamber and send them to a water tank, and then use a fluidized bed dryer or centrifugal dryer to remove water

water spray granulator is applicable to most polymers except polymers with low melt viscosity or viscosity. This kind of equipment is also called water ring granulator, and the granulation rate reaches 13607.77 kg/h

the molten polymer is extruded from the hot die and cut into pellets by the rotary knife rotating on the die surface. This sweet granule system is characterized by its specially designed water jet pelletizing chamber. The water flows in a spiral until it flows out of the sweet grain chamber. After the granular material is cut, it is thrown into the water flow for preliminary quenching. The granular slurry is discharged into the granular slurry tank for further cooling, and then sent to the centrifugal dryer to remove water

underwater granulator is similar to pneumatic granulator and water spray granulator, except that it has a steady water flow through the mold surface and is in direct contact with the mold surface. The size of the pelletizing chamber is just enough to enable the pelletizer to rotate freely across the die surface without restricting the water flow. The molten polymer is extruded from the die, and the granular material is cut by the rotary knife. The granular material is brought out of the pelletizing chamber by the temperature adjusted water and enters the centrifugal dryer. In the dryer, the water is discharged back to the storage tank, cooled and recycled; The pellets are removed by centrifugal dryer. The underwater granulator needs to use the die with uniform heat distribution and special insulation facilities. Small size pelletizing and then remove the servo valve knife using electric heating; Large grain cutters need to use oil heated or steam heated die. The process water shall be heated to the maximum temperature under normal circumstances, but its heat shall not be enough to cause harmful effects on the free flow of granular materials. Underwater granulator is used for most polymers, and some models can reach the granulation capacity of 22679.62kglh. When used for granulation of low viscosity or adhesive polymers, the way water flows through the die surface is a great advantage, but for some polymers such as nylon and some brands of polyester, this feature may cause the die to freeze. Other advantages are: because the particles are cut in the molten state, and the water acts as a sound barrier, the noise emission is low; Compared with the cold cutting system, the number of times to replace the cutter is less

centrifugal force granulator

centrifugal force granulator only uses or only needs the minimum amount of heat for the die, not the hot die surface granulator, and because it is a granulator for molten polymer, it is not a cold cutting system, but its own class. This kind of granulator is characterized by the use of cylindrical die, and the extrusion holes are distributed along its circumference. The molten polymer is fed under atmospheric pressure. The extrusion pressure is formed by the depth of melt on the rotor, rotor speed and the relative density of polymer. With the cylindrical die rotating at a high speed with its mandrel, the centrifugal force makes the molten polymer flow evenly to each orifice on the die. When the polymer flows out of the extrusion hole, the rotating die will flow out of the strip to the pelletizer. The pelletizer can be fixed, and it often rotates very slowly on the two turntables in the form of "band saw". Such slow rotation helps to make the wear of the pelletizer uniform and maintain low temperature. After cutting the pellets, due to its own momentum, the pellets are thrown into a silo along a straight track for cooling by spraying water, and then dried by a method similar to that used by other hot mold granulators

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