Resin Dryers: What do they do, and how do they work? The basics

If you know anything aboutplastics processing, you know that it begins with resin pellets. There are many different types of plastic resins that offer a wide range of different physical and chemical characteristics.

These differences in characteristics make every resin unique. The environment and seasonal changes also play a role making a resin behave differently from location to location, or season to season.

Plastics get wet?

Believe it or not, some plastic resins actually get wet; not just on the outside but deep down at the molecular level. Some plastic resins actually have polarity that attracts water molecules that bond with the polymer on a molecular level. These are known ashygroscopic resins.

Plastic resins that don’t attract moisture – or essentially only get wet on the surface – are called非血糖树脂.

Even small amounts of moisture in hygroscopic resins, detectable only with instruments, can lead to quality problems when plastic resins are molded into parts.

问题包括：

Cosmetic/appearance problems:Plastics that should be clear appear cloudy or have opaque streaks.
Strength or performance problems:一个例子是polyethylene terephthalate (PET), a plastic widely used for water bottles. If PET resin is thoroughly dried before it is molded into bottles, the bottles can be very thin-walled, yet very strong and leak-resistant. If not, they’ll break or leak easily.

塑料树脂如何干燥

两种最受欢迎的树脂干衣机是hot-air dryers和干燥剂干燥机s.

Hot-Air Dryers

热空气干燥机pull ambient air from the surrounding environment, heat it with a heating element, and then pass it through a hopper filled with plastic resin. The hot air picks up the moisture from the resin pellets and carries the moisture out of the hopper. Hot air dryers are typically used only for non-hygroscopic materials that collect moisture only on the surface… like dew on your windshield or water droplets on a raincoat.

To dry hygroscopic resins that bind water at a molecular level, a hot-air dryer probably won’t be enough.

Desiccant Dryers

For these materials, a干燥剂干燥机is needed. Desiccant dryers are “the gold standard” for preparing materials. They also use hot air like hot-air dryers, but they have another important ingredient: desiccant.

干燥剂是吸附或接收水分的材料。一个很好的例子是放置在鞋盒或电子产品中以收集水分并防止损坏的数据包。我们都看到了我们购买的产品中“不吃”的小包。

In desiccant dryers made by Conair, desiccant is formed into the shape of a continuously rotating wheel. A closed loop of air moves from the dryer, through the hopper to collect moisture, then back through the desiccant wheel, which removes the moisture, leaving the air stream dry and ready to recirculate.

车轮会不断旋转，以便虽然其中一部分是从过程空气中去除水分，但另一部分正在加热（或再生）以从干燥剂中去除该水分。因此，干燥车轮的作用像一种海绵，不断地接替，然后通过再生去除水。

A closed-cycle desiccant dryer provides an airflow that has a very low moisture content so it provides far better, more consistent drying performance for hard-to dry hygroscopic resins – regardless of location or season.

The Drying Process with Desiccant Dryers

To the right is a schematic of the drying process. Dry air, marked in red (1), leaves the desiccant wheel and is heated before being passed into the base of the resin hopper.

As it flows upward through the hopper, the air absorbs water before circulating out of the hopper into the return-air circuit, where it is cooled and passed through the desiccant wheel, where it gives up its moisture. A separate circuit (2) heats ambient air and passes it through the wheel to regenerate the desiccant.

Finally (3), the regenerated desiccant must be cooled (so it can absorb moisture again). This is accomplished using cooled air returning from the drying hopper.

Once the plastic resin is properly dried, it can be molded or extruded into high-quality parts.

Every Application is Unique

Hopefully this basic explanation was an education that helps you better understand the importance of properly drying resin prior to processing, or at least was a refresher on why your process does or does not require desiccant drying.