More energy efficient injection moulding

Tex Plastics continued investment in new desiccant dryers makes for lower energy consuming more efficient injection moulding.

28th June 2021

How do low energy rotor wheel dryers make injection moulding more efficient?

This desiccant bed dryer is a machine for the general drying of all hygroscopic materials, i.e. a material which will adsorb water vapor from the air. All polycarbonate resins are hygroscopic and must be thoroughly dried prior to processing. Moisture in the raw polymer granules can cause issues with the mould quality and finish. Dehumidifying of plastics resin is utilised to minimise or eliminate problems that may be caused by too much or too little moisture in a plastic material during processing. The new dryers utilise the latest technology to deliver a highly efficient drying system with a minimum of 40% energy saving, self-adjusting throughput and material protection features.

What are the four basic parameters of the plastic granules drying process?

The drying process has four basic parameters that help produce dry, warm pellets.

  1. The first, and most important, is temperature. The temperature controls the rate at which the resin pellets come to equilibrium with the surrounding air. It is generally accepted that the higher the temperature, the faster the polymer dries. There are, of course, limits, as some materials can be overdried, damaging the resin or causing premature melting.
  2. Second on the list is dewpoint, a measure of humidity in the drying air. It tells you how well the dryer is taking moisture out of the air. It dictates how readily water vapor in and around the polymer will vaporise into the ambient air.
  3. The third parameter is drying time, sometimes referred to as residence time. This is the time during which the polymer is exposed to the drying air at the prescribed temperature and dewpoint. Because plastic pellets do not conduct heat well, sufficient time must be allowed for each pellet to reach temperature. Once properly heated, moisture is released to migrate to the surface of the pellet where the warm, dry air removes it from the hopper.
  4. The fourth parameter is airflow. Simply stated, airflow is the rate at which a volume of air passes through the hopper. It brings heated air from the dryer into the hopper and takes moisture out of the hopper. This number is expressed in cubic feet/minute, referred to in shorthand as “cfm.” Airflow is usually calculated relative to resin throughput (lb/hour), but airflow is not dependent on resin throughput.

Why is drying the raw materials important?

Drying is essential for many materials –often even non-hygroscopic materials perform better having been through a dryer. The extent to which moisture affects the quality of a moulded part is determined by the specific plastic resin being processed and the intended purpose of the part. Improper or incomplete drying of the raw material will create problems, whether during processing or when the product is in use, or worse – both.

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