Die surface hot pelleting system-water ring/underwater cutting
Spray water pelletizer, suitable for most polymers except those with low or viscous melt viscosity. This type of equipment is also known as the water ring pelletizer, the molten polymer from the hot mouth die, is cut into pellets by a rotating knife rotating on the ground die surface. The water flows in a spiral, and after the grain is cut, it is thrown into the water stream for initial cooling. The grain water slurry is discharged into the grain slurry tank to be further cooled and then fed into a centrifugal dryer to remove water.
The underwater pelletizer is similar to the spray pelletizer and the spray pelletizer, except that it has a smooth water flow through the mold surface and is in direct contact with the mold surface. The size of the cutting chamber should be just large enough to allow the cutter to freely rotate across the die surface without restricting the flow of water. The molten polymer is cut from the mouth mold and rotary knife, and the pellet is passed through the temperature-controlled hose out of the granulating chamber and into the centrifugal dryer. In the dryer, the water is drained back into the storage tank, cooled and recycled; The grain is removed by centrifugal dryer. The underwater pelletizer needs to use a die with uniform heat distribution and special insulation facilities. Electric heating is used for small granulator; Large cutting knives need to use oil heat or steam heated die. Process water is routinely heated to higher temperatures, but should not be hot enough to cause harmful effects on the free flow of pellets. Underwater granulators are also suitable for most polymers. The way water flows over the die surface is a major advantage when used for slicing polymers with low viscosity or adhesion, but for some polymers such as nylon and some brands of polyester this feature may cause the die to freeze.
Comparison of the characteristics of water ring and underwater granulation,
Water ring cutting: The water ring granulation production method means that the strip material extruded by the extruder is immediately cut by the rotating blade, and thrown to the high-speed rotating water ring, and then the water takes the grain to the water separator to dehydrate, dry and then sent to the material cooling device to cool down, that is, the finished product. This production method is suitable for mixing and granulating polyolefin.
Underwater cutting: The underwater pelleting production method means that the strip material extruded by the extruder is immediately cooled into the water, and then cut into pellets, and then sent to the centrifugal dryer by circulating water to dehydrate and dry. This kind of cutting method is more suitable for the double screw extruder mixing raw material cutting, used for mass production
Because they are cut in the molten state and water acts as a sound barrier, the noise emission is low. Compared with the cold cutting system, the number of times to change the grain cutter is less.
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