Plastic drying refers to removal of water vapor and other volatile substances in plastic raw materials under temperature that plastic is continuously heated without deformation. This process is called drying.
Proper drying of moisture-sensitive plastics is critical for them to perform as intended in application. Poorly dried plastics are likely to cause silver streaks during injection molding process, and may also cause hydrolysis of plastics, causing cracking and strength reduction of plastic parts, which are worthy of attention of on-site technicians.
Reasonable selection of correct dryer is very important for final drying effect. Following are some suggestions for selection of dryers that author has summarized over years for your reference.

1. Determine size of dryer according to amount of materials required for plastic processing, unit is kg/hour, that is, how much plastic needs to be consumed for each sale. It is necessary to ensure that consumption of plastic is less than processing capacity of dryer, and leave a margin of about 20% to ensure that plastic is fully dried.

 

2. Pay attention to temperature setting of several points
a. Temperature at inlet of drying hopper.
Inlet temperature of hopper should be drying temperature recommended by resin manufacturer, and hose connection at inlet should be ensured.
b. Temperature at outlet of drying hopper.
Need to know what temperature of air coming out of hopper is. Outlet temperature should not be same as inlet temperature, but it should not be too low. It is recommended that outlet temperature is about 20 degrees higher than ambient temperature of workshop.
c. Air temperature at desiccant inlet.

 

Certain types of desiccant significantly reduce drying capacity at temperatures above 65 degrees Celsius, so it is recommended that the temperature at desiccant inlet be controlled at around 55 degrees.

3. If you want to use a drying temperature higher than 82 C, you need to connect water line to "aftercooler".

 

4. Check amount of air dryer will circulate.
5. When delivering air to dryer hopper, it should be forced to deliver air to the lowest point where plastic pellets are. Drying air naturally flows upwards and does not circulate to bottom of drying hopper.

 

6. Hose leading to drying hopper should be insulated; return air hose should not be insulated.
7. Reheater coil should have resistance measurement and monitoring functions to ensure normal operation of heater.

 

8. Hopper feeder should be piano hinged with a first-level locking mechanism.
9. All gaskets on the entire drying mechanism should be of high quality, durable, and work like those on a refrigerator door, automatically sealing when touched.
10. Fine powder, volatiles and oil filters should be configured.
11. All filters on dryers or aftercoolers shall have differential pressure indicators with visual or audible alarms to notify maintenance personnel when to clean filters.
12. Controller of dryer should be user-friendly and easy to view.
13. All cone angles of hoppers, spreader cones, etc. should be 60° (included angle).

 

This is to avoid funnel flow and ensure flow collection. If material is funneled, resin will pass through center of hopper faster and not get proper residence time at drying temperature. Additionally, resin on the sides of hopper will stay for long periods of time until hopper is completely emptied, causing excessive drying.

14. Dryer should have a dew point reading.

 

15. If conditions permit, vacuum dryers can be considered, which are currently the most energy-efficient options on market.

 

16. If factory has maintenance problems, membrane compressed air dryers can be considered because they are easy to maintain. Membrane has a long service life and low filtration requirements, and filter may only need to be replaced once a year.