FAQ for Experts. Answers by Experts.

64

What is the purpose of a level control in the collection bin for loss-in-weight systems?

With level control a specified fill level of the collection bin can be set. For this, the load cell (red) continuously monitors the content. (Image: Motan-Colortronic)

There are two customary methods of adjusting the throughput of the dosing system to the throughput of the extruder. Usually, a signal of the extruder that in linear to the extruder rotational speed is used. …


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63

Why does a loss-in-weight system need seperate refilling?

On the left a material loader installed on a refilling hopper. On the right and in the middle material loaders with controlled outlet flaps for direct refilling (image: Motan-Colortronic)

Differential dosing scales are gravimetric removal scales (loss-in-weight doseres), that measure the weight loss of the dosing station continuously. The complete dosing station, including dosing bin with material, the dosing device and the motor are installed on a load cell. …


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62

How does the resolution of a load cell influence dosing accuracy?

Modern load cells are available with different resolutions and maximum loads depending on the demands (image: Motan-Colortronic)

The load cells of gravimetric dosing systems need to master a balancing act – on the one hand they need to measure large throughput rates of up to multiple tons an hour, while on the other be able to measure extremely small amounts of a few hundred grams an hour precisely. …


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61

How does the dosing order affect the dosing results with a gain-in-weight dosing system?

When dosing a very fine, free-flowing component it can be helpful to dose the coarser component first (image: Motan-Colortronic)

First a quick reminder: with gain-in-weight dosing systems the components are dosed separately, one after the other – in batches or asynchronously – into the weigh bin where the weight increase in the bin is measured. …


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60

What needs to be considered when dosing very small amounts?

Throughput does not equal throughput – the motto of the previous issue of mo’s corner where we looked at the maximum throughput of a dosing unit, also applies when dosing very small amounts, such as when dosing colour Masterbatch. …


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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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