FAQ for Experts. Answers by Experts.

59

What needs to be considered when designing dosing systems?

Simplified time flow of a cycle with tool closing (1), injection unit moves forward (2) , injection (3), holding pressure (4), plastification (5), material intake (6), injection unit moves back (7), cooling (8) and tool opening (9) (image: Motan-Colortronic)

Throughput is not equal throughput – this is especially true for throughput details of injection moulding machines. Even experts can get their wires crossed designing or choosing a suitable synchronous dosing unit with free intake of the main component. …


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58

Why and when is a crystalliser needed?

A fixed bed crystalliser directs a heated air flow through an agitator bin in a defined process to achieve the necessary degree of crystallisation.

Plastics such as PET (Polyethylenterephtalate), PEN (Polyethylennaphthalate) or PLA (Polylactic Acid) can’t be sufficiently processed unless they have been dried prior to processing. PET, for example, is usually dried at 180 °C to achieve a residual moisture content of under 40 ppm. …


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57

What needs to be taken into consideration during initial or refilling of drying bins?

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. …


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56

Avoiding material damage with changing throughputs

Example of a simple logic for temperature reduction in 3 steps according to throughput. For systems with combined automatic air flow regulation the temperature reduction is continuous (Image: Motan-Colortronic)

Changing throughputs for material drying can have serious consequences for the drying process. There are many triggers, for example production interruptions because of tool changes or when only a little material is needed for a job but the dryer used to dry it is too big. …


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55

Stable production with automatic dew point regulation

When processing plastic, the moisture content of the material is a deciding factor for production safety and product quality. Even more important is a defined residual or processing moisture content of the granulate, as this contributes to stable and precisely reproduceable production conditions. …


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54

Can automatic air flow regulation save energy?

The comparison of traditional drying systems with more modern versions illustrates many approaches to saving energy. Particularly air flow regulation, possibly combined with lower temperatures, as well as the use of heat exchangers for regeneration and high temperature applications are valuable additional devices in this context. …


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53

What are the advantages of automatic air flow regulation?

If a drying bin receives more energy than is carried off (through material extraction), the temperature gradient shifts higher, i.e. the material in the bin gets hotter towards the top and can become damaged due to increased dwelling time (image: Motan-Colortronic)

Drying plastics requires a large amount of energy. So, it makes sense to try and find ways of reducing energy consumption where possible – of course, without losing sight of the actual goal: …


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52

When is a return air cooler necessary?

With a return air cooler the air can be cooled to a temperature below the critical area before it flows into the desiccant bed. (Images: Motan-Colortronic)

In issues 50 and 51 we looked at how molecular sieves – also called desiccant beds – operate and how they are regenerated.

 

Specifically at high drying temperatures and/or dry air dryers without automatic air flow regulation the temperature of the return air, and then also the temperature of the active molecular sieve, plays an important role. …


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51

How can re-moisturisation at high air humidity be prevented?

(Picture: Motan-Colortronic)

The following basic principle applies: if plastic granulate is stored in environmental air, its moisture content will adjust to match the moisture present in the air until both moisture contents are the same. …


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50

What is the purpose of molecular sieves?

Now that we have dealt with the basics of dosing, drying and conveying, we will turn to more specific aspects of drying plastics in the next few issues. …


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