If you know anything about the processing of plastic products, you are aware that it starts with the raw material of plastic or resin. There are many different types of plastic resins that offer a wide range of different physical and chemical properties.
This difference in properties makes each resin unique. Environment and seasonal changes also play a different role in resin behavior from place to place or season to season.
Do plastics contain moisture?
Believe it or not, some plastic resins for use in plastic injection molding machines actually contain moisture. Not just on the outside, but deep down at the molecular level. Some plastic resins actually have polarity, which attracts water molecules that bind to the polymer at the molecular level. These resins are known as hygroscopic resins.
Plastic resins that do not absorb moisture—or essentially only hold moisture on the surface—are called non-hygroscopic resins.
Even small amounts of moisture in hygroscopic resins, detectable only by instrumentation, can lead to quality problems when molding plastic resins.
Moisture problems in plastic raw materials are:
Appearance problems: Plastics that should be clear appear cloudy or have opaque streaks.
Strength or performance issues: An example involves polyethylene terephthalate (PET), a plastic widely used for water bottles. If the PET resin is fully dried before being molded into the bottles, the bottles can be very thin-walled, yet very strong and leak-resistant. If not, they easily break or leak.
How to dry plastic resin
Hopper dryer hot air plastic materials
Hot air dryers draw air from the environment, heat it with a heating element, and then pass it through a funnel filled with plastic resin. The hot air absorbs the moisture from the resin pellets and removes the moisture from the funnel. Hot air dryers are typically only used for non-hygroscopic materials that collect moisture only on the surface…such as dew on your windshield or water droplets on a raincoat.
A hot air dryer will probably not be enough to dry hygroscopic resins that bind water at the molecular level.
In our dryers, the dryer takes the form of a constantly rotating wheel. A closed loop of air moves through the dryer, through the hopper to collect moisture, then through the dryer wheel, which removes the moisture, leaving the air stream dry and ready for recirculation.
The wheel rotates continuously so that, while one part removes moisture from the process air, another part is heated (or regenerated) to remove that moisture from the desiccant. Therefore, the dryer wheel acts like a kind of sponge, constantly absorbing water and then getting rid of it through regeneration.
A closed-cycle dryer provides airflow that has very low humidity, thus providing much better and more consistent drying performance for difficult-to-dry hygroscopic resins – regardless of location or season. .
Drying process with a hopper dryer
As the material flows upward through the hopper, the air absorbs water before circulating through the hopper into the return air circuit, where it cools and passes through the dryer cycle, where it removes its moisture from gives hands A separate circuit heats the ambient air and passes it through the wheel to regenerate the dry matter.
Once the plastic resin has dried properly, it can be molded or extruded into high quality parts.
SEHD low consumption hopper dryer can be used to dry most non-hygroscopic materials such as PS, PP, ABS, etc. The maximum drying temperature can reach 160 degrees Celsius. Uniform temperature of the hopper with less heat loss In addition, several components are available as options that can recycle hot air and filter iron impurities in the material, which can also be installed on the floor with a floor stand.
Advantages of hopper dryer
The design of the self-blower structure reduces the difference between the inlet air temperature and the heater temperature to ensure a stable inlet air temperature.
To increase the lifespan of the blower, use a heat insulation blower.
The heating tank uses a double-layer insulation structure, which can not only reduce power consumption, but also prevent the environment from overheating.
All material contact surfaces are made of stainless steel to eliminate material contamination.
They are equipped with a magnetic base.
All series are equipped with temperature protection.
With the overheat function, when the drying temperature exceeds the set deviation value, the main power supply will be automatically cut off.
All series are equipped with a one-week timer and intermittent operation as standard.
All series are equipped with microcomputer control and communication interface.
The maximum drying temperature can reach 160 degrees Celsius.
Compared to the standard SHD hopper dryer test, the drying effect of the SEHD increased by an average of 60%, while the power consumption decreased by 40%.
The difference between a hopper dryer and a dehumidifier
A hopper dryer is used to dry plastic materials while a dehumidifier is used to absorb water from the air.
A dryer blows high-temperature air into a drum, which is then rotated by a fan.
Hopper dryer is a tool used to absorb moisture from plastic materials.
We hope this basic tutorial will help you better understand the importance of proper resin drying before processing, or at least why your process may or may not require a dryer.
Each application is unique – a resin that never needs to dry in one city may need to dry all or part of the year if used in another. If you are not sure if your resin needs drying, refer to the resin manufacturer’s information (usually printed on the resin container label). As always, contact our experts with all of your application/processing requirements questions to ensure you have the right equipment to maintain component quality.