What needs to be taken into consideration during initial or refilling of drying bins?
Mo explains specific aspects of drying
If there is going to be a complete material change in a drying system, or if a drying bin needs to be refilled, there are certain rules that need to be considered.
A quick reminder: Drying systems are usually designed so that a certain range of different materials with a specific throughput range can be dried reliably and safely. As long as you remain within this processing window, you are safe.
However, if a different material that wasn’t considered in the design needs to be processed, or the throughput is going to change, there are a few things that need to be considered.
- Is the staying time of the material in the drying bin long enough for the required throughput?
- Is there enough air flow in the bin?
- Can the dryer adsorb the necessary amount of water and regenerate in time?
- Can the dryer reach the required drying temperature?
- Can the material even be dried using this drying technology? In this context bear in mind that some drying methods are not suitable for some plastics.
Firstly, a few relevant guide values need to be collected for the material that is going to be dried. This includes recommended residual moisture, specific bulk density, drying temperature and drying time. These values are usually provided by the material manufacturer.
It is also beneficial to determine the initial moisture of the material. As long as the material is taken directly from the previously unopened original packaging, this is not necessary. However, it is also a good idea to determine the staying time of the material at environmental conditions. With this it is possible to make a rough estimate of how quickly re-moisturisation will occur for a material in the worst cast (e.g. when it is exposed to (humid) environmental air due to disruption).
The safest way is to ask the provider of the drying systems for advice when drying a material/throughput not considered in the design. They can usually give a definitive answer on whether it is possible based on the material parameters and processing data.
What needs to be considered for initial filling of empty drying bins: The required staying time of the material in the bin needs to be adhered to. Material must not be removed for processing any sooner. Only once the full staying time is over there is enough sufficiently dried material in the lower part of the bin to change over to continuous operation.
Would you like to see how a drying bin can be used within the drying process? Find out more on www.motan-colortronic.com