What Are The Granulation Methods Of The Granulation Production Line? What Are Their Advantages And Disadvantages?
There are many different pelletizing production line designs on the market, but all pelletizing production lines are divided into two categories: cold pelletizing system and die face hot pelletizing system. The main difference between the two is the time arrangement of the pelletizing process. Each of these two pelletizing systems has its own advantages and disadvantages. Let's take a look at it with Kelongweier!
Cold cutting system
The cold pelletizing system includes a die, a cooling zone (air-cooled or water-cooled), a drying zone (if water-cooled) and a pelletizing chamber. There are two types of cold pelletizing systems, namely flake pelletizers and strip pelletizers.
a: The polymer melted by the tablet granulator flows from the mixing equipment through a belt die or roller mill to form a polymer flake with a certain thickness. The flakes are solidified and cooled for a certain distance during transportation, and then cut into round or square pellets with a pelletizer in a bin.
Tablet pelletizing is a particularly old method of making pellets and can be used for various polymers from nylon to polyvinyl chloride. Advantages: large output. It is reported that the accuracy is quite good, the granulation capacity can reach 1843.69kg/h. This is a cold pelletizing method, and the noise emission is higher than that of pelletizing from molten polymer. The solid-state cutting polymer cutter has a short life and the generation of powder is often a problem. For some polymers, some "particle chaining" phenomena can be seen.
b: The use history of strip pelletizers is almost as long as that of tablet pelletizers. Including die, cooling section (water bath or blower), drying section (if water cooling is used) and pelletizing knife. The polymer melted by a machine or gear pump passes through a horizontally installed die to form a strip (modern die is precisely machined and heated uniformly to produce a strip of stable quality). After the strip is discharged from the mouth, it is cooled by a blower or air/vacuum facility, or cooled by a water bath. If water cooling is used, the strips need to pass through a drying section, with forced ventilation to blow off the moisture, and then the strips are sent to the cutting room. Using the shearing action of a pair of fixed knives and rotating knives, the strips are accurately cut to the required length. The diameter of the pellets is 3.175 mm, the length is 3.175 mm, and the edges and corners are clear.
c: The traditional method of drawing strips is to stretch the strips through the cooling section (a water bath is commonly used), which sometimes causes the strips to fall or have inconsistent dimensions. This is common in polymers with poor strength in the molten state, such as polypropylene, polyester, and nylon. When the strip falls, the material is scrapped, so operators need to pay close attention. If the strips are drawn inconsistently, the downstream pellets need to be screened.
In other modes, the sliver forming method does not need to be closely monitored by the operator. The method is to use a slotted feed conveyor driven by a motor to support and divide the sliver from the die to the pelletizer. The size of the strip conveyed by the rotating force is relatively uniform, and it will not fall and therefore has less scrap. Some of these methods can make the production capacity up to 6803.89 kg/h, while the stretching method is only about 1814.37 kg/h, because the operator can only take care of a limited number of strips.
The strip production line is inexpensive, easy to operate, and easy to clean. This has its advantages for pigment compounding, because the replacement of two batches of different pigments requires thorough cleaning of the equipment. However, the disadvantage of the method of making rods is that the cooling section takes up space, and its length is determined according to the temperature requirements of the polymer.
Die face hot cutting system
There are three basic types of die surface hot cutting system, namely spray granulator, water spray (water ring) granulator and underwater granulator. Although this type of system can have different designs, a typical system includes a die, a cutting chamber, an electric rotary blade, a cooling medium, and a method of drying pellets (if water cooling is used).
The die is an important part of the die surface thermal granulation system. It is installed vertically or horizontally, and is usually heated by oil, steam, or drum-type or belt-type electric heaters. Electric heating is usually used for smaller dies; however, larger dies are usually heated by steam or oil. Die structure materials have different materials, but no matter what material or heating medium is used, the diameter of the die orifice must be uniform; there must be enough heat to maintain the temperature of the polymer during the whole process; the pelletizing knife rotates oppositely The die surface needs to be tough and smooth-these are needed to make uniform pellets.
When the molten polymer is passed through the die, a pelletizing knife rotating at a high speed cuts it into pellets. The typical situation is that the pelletizer is 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 pelletizing knife can be different. In some systems, the pelletizing knife has a spring applied load to automatically adjust the spacing between the pelletizing knife and the die; while some systems need to manually adjust the spacing between the pelletizing knife and the die. Since the life of the cutting knife depends on the accuracy of the knife-die centering, the abrasiveness of the polymer and the aggressiveness of the operator, it is advisable to cut the polymer pellets in the molten state.
a: The spray granulator is recommended for polymers that are sensitive to heat and long residence time, such as polyvinyl chloride, TPR and cross-linked polyethylene. The cutting rate is as high as 4989.52kg/h. The flow path of the polymer from the machine to the cutting chamber should be kept as short as possible, and a small amount of heat should be used. When the polymer passes through the die, the rotational force of the rotation of the die surface cuts it into pellets. After the pellets are cut, they are thrown away from the rotating knife and captured by the forced circulation of air in the specially designed pelletizing chamber. The air stream initially quenches the surface of the pellets and takes it out of the pelletizing chamber to the cooling zone.
Fluidized bed dryers are often used to cool the pellets. The pellets slide down an adjustable slope, and the circulating fan blows air through the pellets. Adjusting the inclination angle of the inclined plane can extend or shorten the residence time of the pellets in the dryer. Another common cooling method is to discharge the pellets from the cutting chamber into a water tank, and then use a fluidized bed dryer or a centrifugal dryer to remove water.
b: Water jet granulator, suitable for most polymers except those with low melt viscosity or viscosity. This type of equipment is also called a water ring pelletizer, with a pelletizing rate of 13607.77 kg/h.
The molten polymer is cut into pellets from the hot die by a rotating knife rotating on the surface of the die. The characteristic of this sweet grain system is its specially designed water jet cutting chamber. The water flows in a spiral around the cause until it flows out of the sweet grain chamber. After the pellets are cut, they are thrown into the water stream 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 water.
c: The underwater granulator is similar to the spray granulator and the water jet granulator. The difference is that it has a steady stream of water flowing through the mold surface, and it is in direct contact with the mold surface. The size of the pelletizing chamber is just enough to allow the pelletizing knife to rotate freely across the die surface without restricting water flow. The molten polymer cuts the pellets from the die and the rotating knife, and the pellets are taken 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 water.
The underwater pelletizer needs to use a die with uniform heat distribution and special insulation facilities. The small pelletizer uses electric heating; the large pelletizer requires oil-heated or steam-heated die. Process water is heated to a higher temperature under normal circumstances, but its heat should not be enough to cause harmful effects on the free flow of pellets. Underwater pelletizers are used for most polymers, and some models can reach a pelletizing capacity of 22679.62kglh. When used for cutting low-viscosity or adhesive polymers, the way water flows through the die surface is a big advantage, but for some polymers such as nylon and certain brands of polyester, this feature may cause the die to freeze . Other advantages are: because the pellets are cut in the molten state, and the water acts as a sound barrier, the noise emission is lower; compared with the cold-cutting system, the number of replacement of pellet cutters is less.
Kelongweier adheres to the brand belief of "Let technology and art achieve industrial intelligent manufacturing" and the core value concept of "Doing flat double extrusion automation". The core products include parallel twin-screw intelligent equipment, stretch pelletizing, filling, Blending modified water ring eagerly cutting, air-cooled die surface eagerly cutting, underwater pelletizing, continuous mixing and extrusion production line, to provide customers with an overall solution for the intelligent production environment based on rubber and plastics, and is committed to creating, energy-saving, stable and intelligent Manufacturing application scenarios.