Drying Solution

A dehumidifying dryer is a plastics auxiliary machine that dries resin using air that has had its moisture stripped out by a desiccant before it is heated. Because the air is extremely dry typically −40 °C dew point; it pulls moisture out of the pellet from the inside, not just off the surface.

It is a closed-loop system. Air circulates continuously between the dryer and a drying hopper: dry hot air goes into the hopper and passes up through the resin, picks up moisture, returns to the dryer, is filtered and cooled, gives up its moisture to the desiccant, is reheated, and goes back into the hopper. Because the loop is sealed from the factory floor, the drying result does not change when the weather does.

Many engineering plastics absorb water from the air into the polymer itself. When that wet resin is melted, the water flashes to steam inside the barrel and either shows up as a visible defect on the part or chemically attacks the polymer chain — permanently weakening it. Drying is a process requirement, not a finishing touch.

There are two separate problems, and they need different machines:

• Surface moisture sits on the outside of the pellet. Any warm air will drive it off. Non-hygroscopic materials like PP, PE and PS only have this.
• Internal moisture is absorbed into the polymer structure. Only very dry air will pull it back out, because the moisture moves from the pellet to the air only when the air is drier than the pellet. This is what a dehumidifying dryer is for.

Dew point is the temperature at which air becomes saturated and water starts to condense out of it. The lower the dew point, the less moisture the air is carrying. Air at −40 °C dew point is exceptionally dry, which is what gives it the capacity to pull moisture back out of a pellet.

−40 °C became the industry benchmark because it is dry enough for essentially every hygroscopic resin while still being economical to produce. Chasing an ultra-low dew point below that does not dry most materials any faster; it just makes the desiccant and the regeneration heater work harder and raises your power bill. PET is the usual exception, where slightly lower dew points are sometimes specified.

What matters as much as the number is its stability. A dryer that averages −40 °C but spikes to −10 °C every time it switches desiccant beds is producing inconsistent material, and inconsistent material shows up as scrap on some shots and not others- which is much harder to diagnose than a consistent fault.

Typically 2 to 6 hours at the material’s specified drying temperature, with dry air at −40 °C dew point. Nylon and PET sit at the longer end; ABS and PMMA at the shorter end. The drying time is set by the resin supplier, and the hopper is then sized so the material spends that long inside it.

The three variables interact: temperature, time and dew point. If any one of them is wrong, the other two cannot compensate. Running hotter to dry faster risks thermal degradation and discolouration. Running longer than needed at temperature causes over-drying problems in some materials. The correct approach is to hold dew point and temperature at the specified values and size the hopper for the specified time.

The drying hopper is the insulated vessel that holds the resin while it dries. The dryer produces the dry hot air; the hopper is where the drying actually happens. They are separate items and are sized separately and one dryer can serve several hoppers.

A proper drying hopper is not just a bin with a pipe on it. It has an air diffuser cone that spreads the incoming air evenly across the full cross-section, insulation to hold temperature and cut energy loss, and a geometry that produces true mass flow which means material moves down as a plug, so every pellet gets the same residence time. A poorly designed hopper produces channeling, where some material rushes through under-dried while other material sits too long and degrades.

Any sector that processes engineering plastics. In practice the heaviest users are automotive components, electrical and white goods, rigid and flexible packaging film and sheet, medical plastics, PET bottle and preform production, consumer durables, technical compounding, and PET and engineering-plastic recycling.

The common thread is not the industry but the material. A toy manufacturer running nylon gears has the same drying requirement as an automotive tier-one running the same nylon. Conversely, a packaging plant running only PP film may never need a dehumidifying dryer at all.

Measure two things: the dew point of the air going into the hopper, and the residual moisture in the resin coming out of it. Everything else i.e., the temperature display, the fact that the machine is running, the fact that it is warm tells you nothing about whether the material is dry.

A dew point sensor with an alarm on the process air line is the single most useful instrument you can add to an existing installation. For the material itself, a Karl Fischer titration to ISO 15512 is the reference method; a halogen moisture balance is cheaper and less precise but adequate for shift-level spot checks. Check on material changeover and after any dryer stoppage, not just on a fixed schedule.

If you have never measured either, and you process hygroscopic material, there is a reasonable chance your dryer is not doing what you assume it is.

Yes, and on multi-machine installations it usually should be. Drying, conveying and dosing are one material flow, and splitting them across unconnected controllers creates the gaps where material sits exposed, gets mixed up, or is fed under-dried.

A fully integrated line looks like: central or standalone dryer → drying hopper → vacuum loader or conveying system → dosing/blending unit → machine throat. Integration lets material move from hopper to machine without ambient exposure, prevents a machine drawing from a hopper that has not completed its drying cycle, and gives you one control point for the whole material path.

For plants that want visibility rather than just control, drying data: dew point, process temperature, return temperature, alarm history; is the most useful quality record in the material path, because it is the evidence that a batch was processed correctly. Aerodry supplies turnkey systems with operation and production data management software for single-window control across large machine counts.

Everything on this list. A dryer quoted on throughput alone is a guess, and a guess that under-delivers costs far more than the price difference between two correctly sized options.

Material data

• Polymer type and grade for every material to be dried
• Filler content, if any (glass, mineral, talc)
• Bulk density
• Virgin, regrind, or blend and the blend ratio
• Supplier’s specified drying temperature, time and target residual moisture

Process data

• Throughput in kg/hr, per machine
• Process type: injection moulding, extrusion, blow moulding, compounding, film line
• Number of machines to be served
• Shift pattern and running hours
• How many grades run simultaneously, and how often grades change

Site data

• Available floor space and headroom
• Power supply available (phase, voltage, connected load headroom)
• Distance from dryer location to machines
• Compressed air and cooling water availability
• Ambient conditions if unusual (very hot, very humid, dusty, coastal)

Yes. Aerodry exports plastics auxiliary equipment and complete systems, with export packing and crating to international shipping standards, documentation support, and commissioning assistance.

For export enquiries, the same material and throughput data applies, plus destination port, power supply standard at site (voltage, phase, frequency), any local certification requirement, and site ambient conditions: high-humidity coastal and high-temperature sites affect cooling specification.