Mastering Resin Drying: Boosting Quality and Efficiency in Plastics Manufacturing ??

Resin drying systems are used to remove moisture from plastic resin pellets before they enter the processing stage. Excess moisture can lead to defects in the final product, decreased mechanical properties, and processing challenges. Overdried material similarly can lead to processing challenges and rejected parts. Effective system design is critical to achieve desired drying outcomes while minimizing energy consumption and operational costs.

Depending on where in the supply chain that the defective products are found, the costs to the molder can be enormous -- especially if the defective products are delivered to customers leading to a product recall. Even in the best case scenario (in which the defects are detected immediately) the parts must be remolded reducing the efficiency of the operation, and the poor quality parts must be discarded or, if feasible, granulated then reprocessed.

Resin Drying System Components:

A typical resin drying system consists of several key components:

Desiccant Dryers: Desiccant dryers are responsible for dehumidifying the air used in the drying process. They utilize moisture-absorbing desiccant materials, such as silica gel or molecular sieves, to reduce the humidity of the process air which is then sent to the drying bins.

Drying Bins: Drying bins serve as temporary storage for resin pellets during the drying process. The bins are sized based upon the required drying residence time for the material and are equipped with heaters to heat the air before it passes through the resin.

Controls and Monitoring: System control and monitoring equipment, such as temperature and humidity sensors, PLCs (Programmable Logic Controllers), and HMI (Human-Machine Interface) panels, ensure the proper functioning of the drying system and allow for real-time adjustments. The ability to measure and track the temperature and humidity in the drying system is also critical for monitoring system performance and for troubleshooting. In some cases it may also be necessary to monitor the moisture content of dried resins in real-time to guarantee the proper moisture level prior to molding.

System Design Considerations:

Effective resin drying system design requires careful consideration of various factors:

Resin Properties: Different resin types have varying moisture sensitivity levels and will release moisture at varying temperatures. Understanding the specific requirements of the resin being processed is essential for proper equipment selection and for setting appropriate drying conditions.

Some resins (PET for example) need exceptionally high drying temperatures that require the return air to pass through a water-cooled heat exchanger before the moisture can be removed via the desiccant bed.

Throughput Requirements: The system's capacity should align with production needs. Overall the system must be able to provide dried resin at the throughput required, without the risk of delivering under-dried or over-dried material. In order to make that happen, each drying bin must be sized to provide sufficient drying time at the throughput required. The desiccant dryer similarly must be sized to provide the required volume of dry air to the bins.

Energy Efficiency: Efficient drying systems should minimize energy consumption. At its most basic level, the efficiency is increased by ensuring adequate insulation on warm surfaces.

When material usage rates vary frequently, a Variable Frequency Drive (VFD) may be utilized at the desiccant dryer to modulate the quantity of dry air produced in sync with the drying requirements to improve energy efficiency.

Similarly the dry air volume delivered to the bin and air temperature can be modulated according to the material throughput, in order to reduce power consumption and to prevent over-drying. Some resins (Nylons for example) are especially sensitive to over-drying and benefit from additional valving to guarantee constant dewpoint process air.

Conclusion:

Resin drying is an indispensable part of the plastics manufacturing process, influencing product quality and production efficiency. Careful system design and component selection are essential to achieving consistent, high-quality resin pellets and minimizing energy consumption. With the right resin drying system design, manufacturers can enhance their competitiveness and meet the growing demands of their industries.

Interested in talking to the experts at Motan about your own resin conveying needs? Check out our website at https://www.motan-group.com/us/ for more information, and you can reach out to me directly and I will get you into contact with a Motan representative in your area.