Most engineering plastics and plastic alloy pellets contain different degrees of moisture, and the moisture content is distributed on the surface of the plastic pellets and inside the plastic pellets. If the plastic pellets are not well dried, the intrinsic quality and appearance quality of the plastic products are Influential and cause processing difficulties. The intrinsic quality of plastic products is characterized by a significant decrease in various performance indexes, an increase in internal stress, easy cracking, and hydrolysis and degradation of the polymer; appearance quality is characterized by yellowing of the product, generation of bubbles, edulis, silver, and stripes, and The transparency has dropped. Due to the presence of moisture, the apparent viscosity of the plastic melt fluctuates irregularly during the injection molding and extrusion molding process, and the melt sticks to the flow path, sometimes causing severe flow, which makes it difficult to form. For most engineering plastics and plastic alloys, strict drying is especially important! Especially for recycled plastics, after washing, granulation and other regeneration processes, the moisture content is greatly exceeded, and strict drying is required. 1, convection dryer For drying non-hygroscopic materials, a hot air dryer can be used because moisture is only loosely constrained by cohesion and is therefore easy to remove. In such machines, the air in the environment is absorbed by the fan and heated to a specific drying temperature of the material, and the passing drying hopper heats the material and removes moisture by convection. The non-dehumidifying gas dryer is used to dry the hygroscopic material, essentially having three drying sections. In the first section, moisture only evaporates on the surface of the material being dried. In the second drying section, the evaporation point is inside the material, the drying speed is slowly lowered, and the temperature of the material to be dried rises. In the last paragraph, the moisture absorption balance with the dry gas is reached. At this stage, all temperature differences between the inside and outside are eliminated. If at the end of the third stage, the material being dried does not release moisture, this does not mean that it does not contain moisture, but only establishes a balance between the rubber particles and the surrounding environment. In drying technology, the dew point of air is often used as a means of bringing moisture to the air. It represents the temperature at which the load is saturated and the moisture is condensed. The lower the dew point of the air used for drying, the lower the residual moisture content obtained and the lower the drying speed. The heat for drying is transferred to the colloidal particles by convection together with the dehumidified air. Just like hot air drying, this is a convection drying process. The criterion for judging dehumidified air drying is a method for preparing a dehumidified gas. In the dry state, air flows through the adsorbent (usually a molecular sieve) which absorbs moisture from the process gas and provides dehumidified gas for drying. In the regenerated state, the molecular sieve is heated by the hot air to the regeneration temperature. Gas collection through the molecular sieve removes moisture and brings it to the surrounding environment. Another possible method of generating a dehumidified gas is to decompress the compressed gas. The benefit of this approach is that the compressed gas in the supply network has a lower pressure dew point. After the pressure is released, the dew point in the range of -20 ° C is reached. If a lower dew point is required, a membrane or adsorption dryer can be used to further reduce the pressure dew point prior to pressure release. The energy required to dry the colloidal particles consists of two types, one is the energy required to heat the material from the storage temperature to the drying temperature, and the other is the energy required to evaporate the water. The amount of specific gas required for the material can be determined based on the flow of energy required for drying and the temperature at which the drying gas enters and exits the drying hopper. In dehumidified air drying, the energy required to produce the dehumidified gas must be additionally calculated. In adsorption drying, the regenerated molecular sieve must be heated from the dry process temperature (about 60 ° C) to the regeneration temperature (about 200 ° C). To this end, it is common practice to continuously feed the heated gas through a molecular sieve to the regeneration temperature until it reaches a certain temperature as it leaves the molecular sieve. Theoretically, the energy necessary for regeneration consists of heating the molecular sieve and the energy contained in the water, the energy required to overcome the adhesion of water to the molecular sieve, and the energy necessary to evaporate the water and heat the water vapor. The dew point obtained by adsorption is related to the temperature and water carrying capacity of the molecular sieve. Generally, a dew point of ≤ 30 ° C can achieve a moisture carrying capacity of 10% of the molecular sieve. In order to prepare a dehumidified gas, the theoretical energy demand value calculated from the energy is 0.004 degrees/m3 of dehumidification gas. However, in practice this value must be slightly higher because the calculation does not take into account fan or heat loss. By contrast, the specific energy consumption of different types of dehumidification gas generators is determined. To this end, it is assumed that the energy consumption is between 30% and 50% of the rated energy required. Therefore, the specific energy consumption that can be used for desiccant drying is between 0.04 kWh/kg and 0.12 kWh/kg, depending on the material and initial moisture content. In practice, 0.25 kWh/kg and higher can also be achieved, depending on the dryer operating mode and the complexity of the drying operation. 2, vacuum drying Vacuum drying has also entered the field of plastics processing through machines developed by Maguire. This continuously operated machine consists of three small chambers mounted on a rotating conveyor. At position 1, the small cavity is filled with colloidal particles, and then the gas heated to the drying temperature is sent to the heated colloidal particles. When the gas outlet reaches the drying temperature and the cycle time is used up, the vessel is moved to position 2 where there is vacuum. The vacuum lowers the boiling point of the water, so the moisture enters the water vapor state earlier. Therefore, the water diffusion process is accelerated, and there is a greater pressure difference between the inside of the colloid and the surrounding air. Therefore, staying in position 2 for 20-40 minutes, and some extremely hygroscopic materials staying for 60 minutes is sufficient for drying. The container is then moved to position 3 and the dried material can be removed. In dehumidification gas drying and vacuum drying, the same amount of energy is used to heat the plastic because both methods are carried out at the same temperature. But in vacuum drying, gas drying does not consume energy, but energy is used to create a vacuum. The specific energy consumption required to create a vacuum is related to the amount of material used. 3, infrared dryer Another method of drying the colloidal particles is an infrared drying process. In convection heating, the heat flowing into the colloidal particles is limited by the heat transfer of the gas to the colloidal particles and the low thermal conductivity of the colloidal particles. Drying with infrared light, the molecules are directly converted to thermal vibrations, which means that the heating of the material is faster than in convection drying. As an additional acceleration force, in addition to the local pressure difference between the ambient air and the moisture in the colloidal particles, there is a reverse temperature gradient compared to convective heating. The greater the temperature difference between the process gas and the heated particles, the faster the drying process. The infrared drying time is usually between 5 and 15 minutes. This infrared drying process has been designed as a transfer tube concept. The colloidal particles are transported and circulated along a threaded tube on the inner wall. There are several infrared heaters in the center of the tube. In infrared drying, energy consumption between 0.035 kWh/kg and 0.105 kWh/kg can be used. Achieve stable residual moisture Finally, it should be reminded that infrared drying and vacuum drying are new technologies used in plastic processing to reduce stagnant time and energy consumption. However, in recent years, great efforts have been made to improve the efficiency of drying conventional dehumidification gases. There is no doubt that innovative drying processes have their prices. When making investment decisions, an accurate cost assessment should be conducted, taking into account not only the cost of procurement but also the pipeline, energy, space requirements and maintenance. 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