A plastic dryer, also known as a plastic dehumidifier, is crucial for processes carried out by companies that transform plastics.

These are specific machines designed to eliminate moisture present in plastic granules during their processing.

Here are the key factors that influence the drying process and the various types of dehumidifiers available.

Plastic dehumidification: key criteria

Drying plastic granules is essential to preserve the material’s properties, enhance the final product’s aesthetics, reduce processing times, and minimize the risk of production defects.

Therefore, the outcome of dehumidification depends on various factors related to the characteristics of the plastic material, external conditions, and the drying process methods.

When exposed to heat, thermoplastic materials, including plastic granules, become malleable. These materials are divided into hygroscopic thermoplastics, which absorb moisture both internally and externally, and non-hygroscopic thermoplastics, which retain moisture only on the surface.

This distinction is crucial in selecting the most suitable dryer for a plastic processing company.

Other factors influencing the effectiveness of the drying process include:

The temperature at which air becomes saturated with moisture. Precise control of the dew point prevents condensation during drying.

  • Type and shape of the material.

These influence the drying strategies used.

  • Airflow rate.

When adjustable according to material specifications, it allows for more precise and efficient drying.

  • Set temperature.

This affects the dehumidifier’s performance and can alter material properties, especially for advanced materials like bioplastics.

  • Drying time.

If too long, it can cause thermal, physical, or chemical degradation of the material and affect the organization of production processes.

  • Initial and final humidity.

Measuring the humidity at the beginning of the process and establishing the desired final moisture content is essential to set the drying parameters correctly.

Choosing the ideal dryer must balance all these factors.

Types of plastic dryers

Given the numerous factors to consider when choosing a dryer for your project, there are many possible machinery alternatives.

Here are some possible systems:

  • Hot air ovens.

A costly manual system is suitable for small quantities of material. It offers limited control over the process and does not guarantee optimal results.

  • Hot air dryers.

Allow continuous drying and can be installed either on the machine or at the side. However, they have high energy costs, are influenced by environmental conditions, and are suitable only for non-hygroscopic materials.

  • Vacuum dryers.

Offer a continuous drying process, reduce processing times, and do not subject the material to harmful stress. However, they are suitable only for small production runs and have high purchase costs.

  • Compressed air dehumidifiers.

Allow continuous drying, require little space, and can be installed at the side of the machine. They are effective only for small production runs, generate high indirect costs, and offer limited process control.

  • Microwave dryers.

Expose the plastic to material degradation risks, making them unsuitable for industrial use.

  • Infrared dehumidifiers.

Allow continuous drying and accelerate the process. Suitable only for large production cycles, they have high costs and energy consumption, and control is complicated with a risk of material contamination.

  • Molecular sieve dryers.

Allow a continuous drying process, can be installed on the machine or at the side, and have no limits on production quantities. However, their dew point is inconsistent, and the molecular sieves degrade quickly, requiring frequent replacements.

  • Rotor dryers.

Offer innovative features compared to traditional solutions. The wheel, the central element of the system, rotates thanks to a stepper motor, and the air passes through it in three phases: through dehumidification, the air is dried, heated to the desired temperature, and used to dry the plastic granules. Then, the regeneration of hot air is generated by a chamber and a dedicated fan. Finally, the cooling of the shape occurs, which is then cooled and returned to the first drying section.

The rotor dryer is considered the most innovative tool. For example, the one proposed by VISMEC company is a compact machine that requires little maintenance and features a wheel with a honeycomb structure that replaces traditional molecular sieves.

Additionally, these dryers offer: a drying temperature of up to 180°C without the use of cooling water, a constant and adjustable dew point down to -50°C, which enables a 40% reduction in energy consumption.

The rotor dryer is also equipped with MPM (Material Protection Management), a system designed to protect the material from excessive wetting and degradation, and SLS (Safety Loading System), a safety system that prevents non-dehumidified material from reaching the processing machine.

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