Photocoupler

Although the drying of plastic granules is a straightforward process, there are situations where complete drying may not be achieved. Several factors can influence the effectiveness of the drying process:

1. The first step in the drying process involves removing moist air, leaving only a minimal amount of residual moisture. After that, the air is heated to lower its relative humidity. At this point, the dry air has a low vapor pressure, which helps draw moisture out of the particles. As the temperature rises, water molecules within the granules become more mobile, allowing them to escape and move into the surrounding air.

When inspecting the dryer, it's crucial to pay attention to the air filters and hoses. A clogged filter or a collapsed hose can significantly reduce airflow, impacting the dryer’s performance. Additionally, a damaged filter can contaminate the desiccant, reducing its ability to absorb moisture effectively.

2. Heat plays a vital role in breaking the bond between water molecules and hygroscopic polymers. Once the temperature reaches a certain threshold, the attraction between water and the polymer chains weakens, allowing the moisture to be carried away by the dry air. This thermal energy is essential for efficient moisture removal.

To ensure optimal performance, the drying temperature should be monitored at the silo inlet. This helps account for any heat loss that occurs as the air travels through the hose. If the air entering the silo is too cool, it could indicate issues such as improper controller settings, insufficient insulation, or failures in the heater element, contactor, thermocouple, or control system.

3. In the drying environment, the process of heat absorption and moisture diffusion to the surface of the particles takes time. Therefore, resin suppliers typically recommend specific drying times based on the material type, temperature, and dew point. These guidelines help ensure that the granules are properly dried without over-processing.

4. Dry hot air circulates through the silo, transferring heat to the particles and removing moisture from their surfaces. The moisture is then returned to the dryer for further processing. For this to work efficiently, there must be enough airflow to maintain the required drying temperature and ensure the resin remains at that temperature long enough for proper drying.

If the granules are not adequately dried, the dry silo should be checked for sufficient space to allow adequate drying time. Effective drying time refers to the period during which the particles are exposed to the correct temperature and humidity levels. If the residence time is too short, the drying process will not be successful. The size, shape, and density of the pellets or crushed materials also play a role in determining how long they remain in the silo, affecting overall drying efficiency.