The combination of using plastic and ground granules imposes evaluations and choices on automatic mixing

In the production of recycled polymeric compounds or in the reuse of waste from its plastics processing activity, be it molding, blow molding, extrusion or thermoforming, the reuse of the grinds requires careful evaluation in the context of the final recipes.

Plastic grinds can be added to the main polymer to improve fluidity, reduce the price, modify the DSC, raise or lower the Izod, modify the module or simply reuse the processing scraps that are generated in daily activity.

In order to introduce a plastic grind into the main melt, it is necessary to use a dispenser that can simulate a recipe designed to meet the aesthetic and qualitative needs of the polymer we have need.

In this case, we use a dispenser that has the function of making the mixing principle automatic in the doses that we consider appropriate in order to carry out our work.

There is no doubt that this operation could also be carried out by hand, inserting the established quantity of ground into the hopper, but this activity requires constant presence of a human resource that performs an easily automatable operation.

The dosers we will talk about today are those defined as volumetric and gravimetric

Generally speaking, they are both plants that are responsible for continuously releasing in the plastic melt the chosen percentage of ground that we have established in our recipe.

The volumetric dispenser, as the word says, once loaded, senses what the mass in volume of material to release may be that the operator has previously established for make the compound.

This calculation, to be set in the dispenser, is the result of a preventive series of tests that lead to calculate the correct volume of ground to mix with the material first main.

It is a real calibration of the dosing device used for the material to be measured, through timing exercises, weighing and graphical representation of the results.

This is a critical step that requires skill to ensure that the timer settings entered into the mixer control deliver the correct volume of each material based on the tempo.

The operating principle instead of gravimetric dosers works on the value of the weight of the material to be introduced, then automatically calculates the quantity of ground that the machine operator has set, without having to resort to machine calibration work.

What are the practical differences, between the two systems, in the dosage and problems using the regrind?

We can say that a volumetric dispenser is set to calculate and enter a certain volume of material that is always constant, this is feasible, expressing a certain precision, if the grind used it is always composed of uniform and constant material.

But as we know the regrind used, especially if it derives from post-consumer recycling, can have a certain dimensional and density instability, probably putting the system in crisis dosage.

The problem is obviously reduced if the grind that comes from production waste is uniform and constant, so as to give a certain correct repetition to the calculation of the machine that performs on the volume of plastic.

The gravimetric dosers, on the other hand, use the weight value to check practically every calculated dose, in fact, the machine notices the differences between one recall and another of material, correcting the differences during the next recall.

All the variations of flow rate, mass, time are calculated by the gravimetric doser in order to express the maximum precision and adherence to the recipe set automatically.

Automatic translation. We apologize for any inaccuracies. Original article in Italian