How to Choose a Mold Temperature Controller for an Extrusion Line: Configuration Guide and Applications
15/10/2026
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How to Choose a Mold Temp
Choosing the right plastic dryer starts with one question:
What plastic material are you processing?
Different plastic resins react to moisture differently. Materials such as PET, PA, PC and PBT can absorb moisture from the surrounding air and normally require controlled drying before processing. Other plastics, such as PP and PE, generally absorb much less internal moisture and may only need drying when surface moisture or storage conditions make it necessary.
Using the wrong drying method can lead to silver streaks, bubbles, poor surface quality, reduced mechanical properties and unstable processing.
In this guide, we explain how to choose a plastic dryer based on material type, drying method, production capacity and actual processing requirements.
For buyers who need a quick answer:
| Material | Typical Moisture Sensitivity | Common Drying Solution |
|---|---|---|
| PET | Very high | Dehumidifying dryer |
| PA / Nylon | Very high | Dehumidifying dryer |
| PC | High | Dehumidifying dryer |
| PBT | High | Dehumidifying dryer |
| TPU | High | Dehumidifying dryer |
| ABS | Moderate | Hopper dryer or dehumidifying dryer |
| PMMA | Moderate | Hopper dryer or dehumidifying dryer |
| PS | Low | Hopper dryer when required |
| PP | Low | Usually no intensive drying; hopper dryer when required |
| PE | Low | Usually no intensive drying; hopper dryer when required |
This table is a general selection reference.
The exact drying temperature, residence time and acceptable moisture content should always be confirmed according to the resin grade and material manufacturer’s processing recommendations.
Plastic pellets can be exposed to moisture during:
Storage
Transportation
Bag opening
Material handling
Recycling
Long-term exposure to humid factory air
When wet resin enters an injection molding machine or extrusion line, the combination of moisture and processing temperature can create quality problems.
Common symptoms include:
Silver streaks or splay
Bubbles and voids
Poor transparency
Rough surface appearance
Material degradation
Reduced strength
Dimensional instability
Unstable molding conditions
Higher scrap rates
Proper drying helps provide more consistent material conditions before processing.
However, simply heating every material is not the correct solution.
The dryer must match the moisture behavior of the resin.
Understanding this difference is one of the most important steps when choosing plastic drying equipment.
Hygroscopic plastics can absorb moisture into the pellet itself.
Typical examples include:
PET
PA / Nylon
PC
PBT
TPU
These materials normally require more than simple surface heating.
A dehumidifying dryer supplies dry heated air and helps remove moisture from inside the resin.
Materials such as:
PP
PE
PS
normally absorb much less moisture internally.
If these materials have been stored correctly, intensive dehumidifying drying may not be necessary.
However, drying may still be useful when:
Pellets have surface condensation
Regrind is being processed
Storage conditions are humid
Material has been washed
Production quality requires tighter moisture control
This is why selecting a dryer only according to the plastic name is not enough.
The actual condition of the material also matters.
For most plastic processors, the selection normally starts with two major categories:
Special applications may also require additional equipment such as PET crystallizers or integrated drying and conveying systems.
A hopper dryer uses heated air to remove moisture from plastic pellets.
It is commonly installed directly above an injection molding machine, extruder or material feeding system.
Hopper dryers are widely used because they are:
Simple
Compact
Easy to operate
Relatively economical
Suitable for continuous material preparation
They are commonly used for general-purpose plastics and applications that do not require extremely low-moisture drying air.
A hopper dryer may be suitable when:
The resin has relatively low moisture sensitivity
Surface moisture is the main problem
Production volume is moderate
Extremely low dew point is not required
A simple machine-side drying solution is preferred
A dehumidifying dryer removes moisture from the drying air before sending the heated dry air through the resin.
This creates a more controlled drying environment.
It is particularly suitable for hygroscopic engineering plastics such as:
PET
PA
PC
PBT
TPU
For these materials, heating alone may not provide sufficiently stable drying.
Consider a dehumidifying dryer when:
You process hygroscopic materials
Product quality requirements are high
Stable drying conditions are important
The factory operates in a humid environment
Production runs continuously
You process engineering plastics
Low and stable material moisture is required
The easiest way to understand the difference is this:
A hopper dryer mainly provides heat.
A dehumidifying dryer provides controlled dry air plus heat.
| Comparison | Hopper Dryer | Dehumidifying Dryer |
|---|---|---|
| Main function | Heated-air drying | Dry-air dehumidifying and drying |
| Equipment cost | Lower | Higher |
| System complexity | Simple | More advanced |
| General-purpose plastics | Suitable | Usually unnecessary |
| Hygroscopic plastics | Limited depending on application | Preferred |
| Humidity control | Limited | Better controlled |
| Drying consistency | Standard | Higher |
| Typical materials | PP, PE, PS, some ABS | PET, PA, PC, PBT, TPU |
Therefore, the cheapest dryer is not necessarily the most economical solution.
If insufficient drying creates high reject rates, the cost of poor-quality production can quickly exceed the difference in equipment price.
PET is highly sensitive to moisture during processing.
For stable PET processing, a dehumidifying dryer is generally the appropriate choice.
Important parameters include:
Incoming moisture condition
Required final moisture content
Drying temperature
Drying time
Dew point
Material throughput
Percentage of recycled material
Some PET applications may also require crystallization before drying.
This is especially relevant when amorphous PET material needs to be processed at elevated drying temperatures.
For these applications, the drying system may include:
Material storage → crystallization → dehumidifying drying → conveying → processing
PET crystallization should be treated as a separate process consideration rather than simply choosing a larger dryer.
PA, commonly called nylon, can absorb moisture rapidly from the surrounding environment.
A dehumidifying dryer is therefore commonly used.
However, the dryer is only one part of the solution.
After drying, nylon should also be protected from excessive exposure to humid ambient air.
The complete material route should be considered:
Storage → Drying → Conveying → Machine Hopper → Processing
For a factory processing nylon continuously, a closed material handling system can help reduce moisture regain after drying.
PC is another moisture-sensitive engineering plastic.
Insufficient drying can contribute to:
Surface defects
Processing instability
Reduced product quality
Problems in transparent components
A dehumidifying dryer is generally preferred when production requires consistent material conditions.
The selected system should provide:
Stable drying temperature
Adequate residence time
Controlled dry air
Reliable material handling after drying
ABS normally requires less demanding drying conditions than PET or nylon, but moisture can still create visible molding defects.
Depending on the production environment, either a hopper dryer or dehumidifying dryer may be suitable.
A hopper dryer can often meet general molding requirements.
Consider a dehumidifying dryer when:
Factory humidity is high
Material has been exposed to air for long periods
Surface appearance is critical
Recycled ABS is used
Production consistency requirements are high
PBT and TPU are moisture-sensitive materials and normally benefit from controlled dehumidifying drying.
For these materials, drying parameters can vary considerably between grades.
This is especially true for TPU.
Always verify the resin supplier’s recommended:
Drying temperature
Drying time
Maximum moisture content
Do not use one fixed drying setting for every grade.
PP and PE generally have very low moisture absorption compared with materials such as PET, nylon or PC.
In many normal production conditions, intensive drying is unnecessary.
However, drying may still be required if:
Pellets contain surface moisture
Material has been stored outdoors
Condensation has occurred
Recycled or washed material is being processed
The factory environment is very humid
In these situations, a hopper dryer can often provide a simple solution.
Choosing the correct dryer technology is only half of the selection process.
You also need the correct capacity.
A useful starting calculation is:
Required Material Capacity = Hourly Material Consumption × Required Drying Time
Suppose an injection molding line consumes:
30 kg/h
and the resin requires:
4 hours of drying
The theoretical drying capacity is:
30 × 4 = 120 kg
Therefore, the hopper must hold at least enough material to maintain the required drying residence time while production continues.
In real production, additional capacity may be needed.
Consider:
Actual resin bulk density
Peak consumption
Production fluctuations
Material change frequency
Number of machines
Continuous production requirements
Safety margin
Do not choose dryer capacity based only on injection molding machine tonnage.
Actual resin consumption is more important.
Imagine a factory processing PC at 25 kg/h.
The material requires approximately four hours of drying according to its processing requirements.
The theoretical required material capacity would be:
25 kg/h × 4 h = 100 kg
The factory should then evaluate:
Whether additional capacity is required for production fluctuations
Whether a dehumidifying dryer is needed
Whether automatic material conveying is required
Whether one dryer will serve one or multiple machines
Whether the material could absorb moisture again during conveying
This method is more reliable than choosing a dryer simply because another factory uses the same model.
Machine-side dryers are often suitable for:
One or several machines
Smaller factories
Frequent material changes
Independent production cells
A centralized drying system becomes more attractive when a factory operates:
Many injection molding machines
Multiple production lines
Large material consumption
Continuous automated production
A central system can integrate:
Material storage
Drying
Dehumidifying
Conveying
Dust collection
Distribution
Central control
The goal is not simply to install larger equipment.
It is to control the complete material preparation process.
Before requesting a quotation, prepare the following information.
PET, ABS, PC, PA, PBT, TPU, PP, PE or another material.
Different grades of the same resin may require different drying conditions.
This determines the actual throughput requirement.
Residence time directly affects hopper capacity.
Follow the material manufacturer’s recommendation.
High-performance applications may require tighter moisture control.
For example:
Injection molding
Extrusion
Blow molding
PET processing
Recycling
Consider whether the dryer will:
Serve one machine
Serve several machines
Connect to an automatic loader
Become part of a central conveying system
A cheaper dryer can become expensive if unstable drying increases scrap or production downtime.
Hopper capacity must be matched with hourly consumption and drying time.
Different polymers have very different moisture behavior.
Properly dried hygroscopic resin can absorb moisture again before entering the processing machine.
Drying effectiveness depends on:
Temperature
Air dryness
Airflow
Residence time
Material condition
Excessive temperature can also damage some materials.
A larger machine is not automatically better.
Oversizing can increase:
Capital cost
Energy consumption
Material residence time
Space requirements
Correct sizing is more important than maximum size.
Before choosing your dryer, answer these questions:
What plastic material are you processing?
Is it hygroscopic?
What is the material grade?
How many kilograms per hour are consumed?
What drying time is required?
What drying temperature is recommended?
What final moisture content is required?
Is recycled material used?
How humid is the factory environment?
How many processing machines need material?
Is automatic conveying required?
Is centralized drying required?
Does production operate continuously?
Once these parameters are known, dryer selection becomes much more accurate.
There is no single best dryer for every plastic. Hopper dryers are commonly used for general-purpose drying, while dehumidifying dryers are better suited to hygroscopic materials such as PET, PA, PC, PBT and TPU.
A hopper dryer mainly uses heated air. A dehumidifying dryer first reduces the moisture content of the drying air and then heats it, providing more controlled drying for moisture-sensitive plastics.
PET is highly moisture-sensitive during processing, so controlled dehumidifying drying is generally used. Some PET materials may also require crystallization before high-temperature drying.
ABS is normally dried before processing when it has absorbed or accumulated moisture. Depending on the application and humidity conditions, either a hopper dryer or dehumidifying dryer may be used.
PP and PE absorb relatively little internal moisture. They often do not require intensive drying when stored correctly, although drying can help remove surface moisture or condensation.
A basic calculation is:
Hourly resin consumption × required drying time = theoretical material capacity.
Additional capacity can then be added according to production fluctuations and safety requirements.
At minimum, provide:
Material type + material grade + hourly consumption + drying requirements + processing method.
This allows the manufacturer to recommend a more appropriate dryer configuration.
The correct plastic dryer should not be selected by price, hopper volume or machine size alone.
A better selection process starts with:
Material → Moisture Requirement → Drying Method → Consumption → Residence Time → Capacity → Conveying Method
For general-purpose materials, a hopper dryer may provide a simple and economical solution.
For hygroscopic engineering plastics, a dehumidifying dryer normally provides more stable moisture control.
For larger automated factories, drying should also be considered together with material storage, conveying and centralized control.
Wensui provides plastic drying and dehumidifying equipment as part of its plastic auxiliary equipment solutions.
If you need help selecting a drying system, provide:
Plastic material + hourly consumption + processing method + required drying conditions
so the equipment configuration can be evaluated according to the actual production requirement.
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