In order to improve the quality of finished products, some manufacturers have purchased expensive underwater pelletizers, but have found that the moisture content of the particles still cannot be reduced. Is there no difference between expensive underwater pelletizers and cheaper ones? Actually, it’s just a blind spot in the production process.
In the production of plastic granulation, the main pelletizing methods used include: cooling strand pelletizing, water ring pelletizing, and underwater pelletizing. The pelletizing method affects the surface moisture of plastic particles and the water content directly affects the quality of the finished particles. Among these pelletizing methods, the water content of underwater pelletizing is relatively difficult to control.
So what are the factors that affect the water content of underwater pelletized products?
1. Impact of pelletizing blades
During the application process, the pelletizing blade may experience wear. When the blade is worn to a certain extent, the cut particles will carry some burrs. The water adsorbed by these burrs is difficult to remove in the subsequent dehydration process, resulting in high water content.
2. The impact of filter screens
The application time of the filter screen is too long, resulting in excessive head pressure and screen changing pressure. When the material comes out of the mold, the pressure is instantly released and swells, which can easily wrap water in the material and vaporize to form voids. The water contained in the material cannot be discharged through subsequent drying.
3. The head pressure is too low
The too small head pressure reduces the density of the material extruded from the die, and water seeps into the particles during the conveying process, making it difficult for these seeped water to be released during the dehydration process.
4. Dehydrator mismatch
Unmatched dehydrators are prone to short dewatering distances and shortened particle climbing distances during the dewatering process, resulting in the inability to smoothly remove moisture.
5. The temperature of the water tank is too low
Everyone is aware that the efficiency of hot water dehydration is relatively higher than that of cold water. Even with the use of cooling strand pelletizing, the most effective dehydration method is to blow hot air. This is why the moisture content of the granular material is high when the machine is first started, because when the water in the water tank enters the circulation system, the temperature needs to be lowered due to the low temperature of the system pipeline, and then the temperature is increased by the heat carried out by the granular material from the granulator.
The low water temperature in the water tank not only affects the dehydration efficiency of the dehydrator, but also affects the mold temperature due to the low water temperature, resulting in high head pressure.
6. The temperature of the water tank is too high
If the temperature of the water tank is too low, it is not good. If the temperature of the water tank is too high, it is good. Practice has shown that too high a temperature of the water tank is not good. An excessively high temperature of the water tank slows down the cooling speed of the particles, which can easily form pits on the surface of the particles. At the same time, excessive water temperature can cause the particles to swell, and as the particles gradually cool and contract, the water will be wrapped in the material.
7. The water volume in the water tank is too low
A low water volume in the water tank can easily slow down the water circulation process, prolong the soaking time of particles in the water, and inevitably lead to water infiltration, resulting in a high water content of the particles.
8. Unstable feeding
Unstable feeding can easily cause significant differences in particle size, and excessive size differences can lead to high moisture content in large particle materials.