Why is it important to properly remove moisture from polymer resins before molding or extruding?
Moisture in polymer resin can lead to a variety of processing issues and faulty parts that exhibit aesthetic or functional problems.
What is the difference between hygroscopic and non-hygroscopic materials?
Hygroscopic materials absorb moisture down to their molecular level; moisture interacts with the polymer chains and must be heated to reach the surface, where further heat removes it. Non-hygroscopic resins do not have a natural affinity for moisture and retain water only at their surface, making them easier to dry.
What are the four primary factors critical to properly drying polymer resins?
- Drying temperature
- Dew point
- Airflow
- Residence time
Why is understanding the initial moisture of polymer resin so important?
Many material suppliers will specify drying times and temperatures based on a resin’s presumed moisture. Processors should measure material moisture prior to processing to avoid over drying or under drying material and causing processing or part problems. It is always good practice to refer to the material supplier’s technical data for specific information related to your process and your material properties.
What is the difference between humidity and dew point?
Humidity, absolute or relative, refers to the amount of water vapor in the air. Absolute humidity is the actual amount of water vapor in the air, while relative humidity is the amount of water vapor in relation to the air’s temperature. Dew point, however, is the temperature to which air must be cooled for it to become saturated. As air temperature drops to the dew point (or the dew point rises to the air temperature), relative humidity increases.
What are the types of resin drying machines available?
- Hot air
- Compressed air
- Desiccant bed
- Desiccant wheel
- Vacuum
When is a central resin drying system most appropriate?
There are two types of processors for whom central resin drying is ideal:
- Processors who use a wide range of resins and change materials and colors frequently
- Processors who need to keep floor space open near their molding and extrusion machines or do not have enough space to locate equipment near the process machine.
When is a press-side or portable resin drying system most appropriate?
Processors who typically have fewer than 10-20 molding or extrusion machines and low throughput requirements can comfortably rely on press-side or portable resin drying systems.
When is it time to replace desiccant beads?
Every two years is recommended. Desiccant beads, made with 30% clay binder, break down faster with repeated heating and cooling cycles. As beads break down, dust forms, which can contaminate resin. If you can crush desiccant beads with your fingers, that indicates it is time to replace them. Replace desiccant in a dryer when the dew point of process air of -40º F or below cannot be maintained.
When is it time to replace a desiccant wheel?
Desiccant wheel warranties often range up to five years. Actual usable life can reach 15 years (or longer) because desiccant wheels are made of 100% pure molecular sieve material. Routine maintenance schedules can maintain desiccant wheel performance and extend useful service life.
How often should dryer filters be replaced?
Filters should be checked regularly. If the material is clean with minimal dusting filters should be replaced every six months. If you are processing dusty resin and/or regrind, develop a custom schedule based on your process. Inspect frequently and replace when the filter shows signs of wear. High glass content tends to be dusty. When drying materials with long glass fibers, a cyclone separator might be required between the drying hopper and the dryer to maximize dust removal and stop continued blockages of the filter and dryer.
What’s the difference between a moisture analyzer and a dewpoint sensor?
A moisture analyzer senses the moisture of the material coming out of the drying hopper right before the process. Dewpoint sensor units typically are a standard part of the dryer and monitor the moisture of the dryer air going into the drying hopper to dry the material.
