Moisture in thermoplastic pellets used in Large Scale Additive Manufacturing (LSAM) can cause porosity and poor surface finish. It's critical to dry these using desiccant dehumidifying dryers, which are energy-efficient and versatile, reducing drying
Background:
Thermoplastic pellets are typically manufactured with a certain level of moisture content, which can range from 0.1% to 0.5% by weight. Moisture in thermoplastic pellets can lead to a variety of issues during LSAM, including porosity, poor surface finish, and dimensional instability. Therefore, it is critical to dry thermoplastic pellets before using them in LSAM.
Note that not all thermoplastics need to be dried before processing. Polymers like polypropylene (pp) and high-density polyethylene (HDPE). These types of polymers are typically referred to as ‘non-hygroscopic polymers’.
Drying your thermoplastic pellets:
CEAD uses the drying systems of Vismec, an Italian company that specializes in the design and production of vacuum pumps and compressors, and dryers for a variety of industries. Their products are known for their efficiency, reliability, and durability.
There are several methods for drying thermoplastic pellets. However, the dryers provided by CEAD are so-called desiccant dehumidifying dryers.
Desiccant dehumidifying dryers are a type of drying system that uses desiccant material (for instance silica gel) to remove moisture from plastic pellets. Here are some key features and benefits of desiccant dehumidifying dryers:
- How it works: The drying process begins by exposing the moist pellets to a stream of hot, dry air. The air passes through a desiccant material, which absorbs moisture from the air. As the desiccant material becomes saturated with moisture, it is regenerated by passing a stream of hot, dry air over it. The moisture-laden air is then exhausted from the system.
- Low dew point: Desiccant dehumidifying dryers are capable of achieving very low dew points, which can be critical in applications where even small amounts of moisture can cause problems.
- Energy-efficient: These dryers are typically more energy-efficient than other types of dryers because they use less energy to heat the air. Additionally, because they use a desiccant material to absorb moisture, they don't require as much energy to evaporate moisture from the pellets.
- Versatility: Desiccant dehumidifying dryers can be used with a variety of materials, including plastic pellets, resins, and other hygroscopic materials.
- Reduced drying time: Compared to other drying systems, desiccant dehumidifying dryers can often dry materials more quickly, which can increase production efficiency.
- Prevents defects: By removing moisture from materials, desiccant dehumidifying dryers can help prevent defects such as bubbles, voids, and surface imperfections in the finished products.
Overall, desiccant dehumidifying dryers are a reliable and effective way to dry materials, particularly in applications where low dew points are required.
Effect of moisture content while printing:
The moisture content of thermoplastic pellets can have a significant impact on the quality of printed parts. When pellets with high moisture content are used inheatingd up in the barrel of the extruder, the moisture can evaporate, leading to porosity in the printed part. This can result in reduced strength, poor surface finish, and dimensional instability. Depending on the moisture content in the pellets, it could also result in dangerous situations where the material can ‘explode’ out of the extruder with excessive force.
Optimal Moisture Content:
The optimal moisture content for thermoplastic pellets varies depending on the specific material and printing process being used. However, as a general rule, it is recommended that thermoplastic pellets be dried to a moisture content of less than 0.1% by weight before use in LFAM.
Conclusion:
In conclusion, the drying of thermoplastic pellets is critical to ensure high-quality parts in LFAM. The moisture content of the pellets can have a significant impact on the quality of the printed part, and therefore, it is recommended that pellets be dried to a moisture content of less than 0.1% by weight before use. There are several methods for drying thermoplastic pellets, including desiccant drying, vacuum drying, and hot air drying, and the optimal drying method will depend on the specific material and printing process being used. Proper drying of thermoplastic pellets is essential for successful LFAM and to achieve the full potential of this rapidly growing technology.