ABS Blow Molding
ABS blow molded products are widely used in fields such as car tail fins, car side foot pedals, high-end craft flower pots, water purification equipment purifiers, cosmetic packaging containers, etc., with an annual growth rate of 8-10%.
Drying Plan for Raw Materials by Blow Mold Suppliers
Blow mold suppliers are usually able to customize or design high-precision blow molding molds based on customer requirements through technical reference, material selection, and a series of subsequent treatments. The selection range of plastic blow molding raw materials is diverse, with different properties. Some of the plastics have extremely strong water absorption, which seriously affects the accuracy of subsequent processing. Especially during ABS blow molding processing, it is often necessary to dry the material in an environment of 60 ℃ for two hours. So blow mold suppliers need to undergo drying treatment before officially putting the raw materials into use.
Drying Process of Plastic Raw Materials
Blow mold suppliers will thoroughly dry some noncrystalline plastics with strong water absorption, such as polyvinyl alcohol (PVA), polyvinylidene chloride (PVDC), and polyacrylonitrile (PAN). The following are the specific drying steps:
Step 1:
The plastic-specific drying equipment is equipped with a heater inside, and blow mold suppliers can use energy heating elements such as electricity or gas in the equipment for heating. Manufacturers adjust the temperature inside the drying equipment by adjusting the power of the heater until it reaches the appropriate temperature for plastic drying.
Step 2:
Blow mold suppliers can control the amount and direction of air entering and exiting the dryer through a built-in fan. For plastic dryers, blow mold suppliers need to appropriately control the size of the air inlet and outlet, as well as the speed and direction of the airflow, to ensure that the air temperature inside the dryer is uniform and the final humidity of the dried raw materials is appropriate.
Step 3:
After the above two steps are completed, the inside of the dryer will gradually become high temperature and low humidity, and the plastic particles inside the machine will be exposed to the air, absorbing their moisture. The drying process is constantly repeated, and the internal air is constantly circulating. The air inside the plastic is continuously absorbed to obtain plastic raw materials with an appropriate drying degree.
Factors Affecting Plastic Drying
When drying raw materials, blow mold suppliers should not only thoroughly dry them, but also avoid excessive drying, which may lead to material degradation. The following are several important factors that affect the drying of plastic raw materials:
Temperature
The key factors that separate water molecules from plastic raw materials are the drying temperature and the amount of heat. When the temperature reaches a critical value, the binding force between water molecules and polymer chains will decrease at a very fast rate, and the water inside the plastic will be carried away by dry, high-temperature air. When considering the drying temperature, blow mold suppliers mainly consider the inlet temperature, outlet temperature, and the temperature difference between the two. The inlet temperature is not the temperature set by the manufacturer on the equipment, but rather the temperature measured to reach the appropriate drying material. This temperature usually needs to be measured by the supplier at the inlet position. The blow mold suppliers need to control the temperature difference between the outlet and inlet within 15-20 ℃. If it exceeds this range, it is easy to cause the material in the lower part of the barrel to dry normally, but the material temperature in the upper part is far from enough, and the moisture is not dried, which slows down the drying efficiency and slows down the overall process.
Hot Air Flow
In the dryer, the dry hot air will transfer heat to the particles in the drying silo, and with the help of high temperature, the moisture on the surface of the particles will be removed, and the dried moisture will be sent back to the dryer. In this process, only a sufficient temperature and size of airflow can ensure that the material can be heated to the appropriate drying temperature, and the airflow also needs to be maintained for a certain period. In general, the higher the drying airflow speed set by the blow mold suppliers, the higher the relative velocity between the material and airflow. This will greatly shorten the drying process time, but it will produce a certain amount of dust. Therefore, for certain environmental considerations, the airflow speed cannot be too fast.
Drying Time
Plastic raw materials often require a certain amount of time to absorb heat and evaporate water vapor into the surrounding environment. Different materials have different properties and require different drying times. Therefore, blow mold suppliers need to have a detailed understanding of the specific material they need to use, and the time required to achieve effective drying at appropriate temperatures and dew points. In the actual processing process, blow mold suppliers cannot guarantee that the plastic dried each time can be fully utilized or sufficient at once. However, they generally do not want the plastic to be dried or heated for more than 24 hours to prevent the plastic from decomposing or changing color due to prolonged heating.
Dew Point&Humidity
Dew point generally refers to the temperature at which saturated water vapor condenses and condenses in the air. When the relative temperature is 100%, the temperature of the surrounding environment is the dew point temperature. The lower the dew point temperature is below the temperature of the surrounding environment, the less likely it is to condense, and the higher the dryness of the air. In addition, the dew point is generally not affected by temperature, but by pressure. During the operation of the dryer, the first step is to reduce the dew point, and then lower the relative humidity by heating the air. At this time, the air is relatively dry and the pressure is low. After heating, the water molecules in the plastic particles gradually diffuse towards the surrounding air. Both humidity and dew point can indicate the moisture content in the air. If the moisture content in the air is lower and the humidity is lower, it indicates a significant difference between the dew point and the current temperature.
Common Drying Devices for Blow Molding Molds
Blow mold suppliers need to use certain drying devices for drying, and each device is suitable for different drying conditions. Suppliers need to choose the device based on specific application scenarios and material types.
- Far Infrared Preheating and Drying Device
The main principle of the far-infrared preheating and drying device is to conduct heat through radiation. Therefore, even if plastic raw materials are heated in a deeper barrel, there will be no uneven heating of the upper and lower parts. This device not only greatly shortens the drying time of blow mold suppliers, and accelerates the subsequent processing process, but also avoids the risk of uneven heating, which will not cause the decomposition of overheated plastics and the inability of undercooled plastics to dry. This device can also achieve continuous preheating and drying for blow mold suppliers.
- Blast dDrying Oven
When producing small batch parts or conducting prototype blow molding, blow mold suppliers can use an air drying device. The principle of this device is mainly to put plastic raw materials into the oven tray and open the air-blowing oven. By heating the air, the hot air exchanges heat with the raw materials in the tray, taking away the moisture in the raw materials and drying them. The principle of hot air drying hopper and blast drying box is the same, but this method is mainly applied to the production process of plastics. But if the humidity of the external air is too high, this drying method cannot be used.
- Dehumidification and Drying Device
When the blow mold supplier uses a dehumidification and drying device to dry the materials, plastic particles are static and stacked in the material barrel. After molecular sieve dehumidification and heating, the hot air flows from bottom to top and passes through the plastic particle layer. The molecular sieve after moisture absorption can be reused after heating and regeneration. The drying process of a dehumidifying air drying device mainly relies on the difference in water vapor pressure between the surface of plastic particles and the hot air. The drier the hot air, the greater the difference, the faster the drying speed, and the higher the efficiency. The standard for measuring the dryness of hot air is called dew point. Generally speaking, the lower the humidity of the air, the lower the dew point. In general, blow mold suppliers should control the dew point temperature of the hot air flow in the dehumidifying air dryer to be below -30 ℃.
- Vacuum Drying Device
In addition, blow mold suppliers sometimes use hollow drying devices for drying, which can place plastic raw materials in a depressurized environment for drying, achieving the goal of water evaporation. The vacuum drying device has a low drying temperature, high drying rate, and pollution prevention, but the drying batch is small, the investment is large, and the energy consumption is high.
Blow mold suppliers dry plastic raw materials mainly to improve product quality and production efficiency. By using plastic drying equipment, the moisture in plastic particles can be uniformly and effectively removed, and the plastic raw materials can also reach a certain usage temperature. Therefore, the drying treatment of raw materials by blow mold suppliers is a crucial step that cannot be ignored.
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