Blending and dosing with maximum accuracy

The mixing process has undergone substantial improvement in the past few years owing to the many innovations launched by machinery producers. Moulded plastics are usually a mix of two or more materials, with the masterbatch and other additives blended with raw plastic material prior to the moulding process. There are many types of blenders/mixers and dosing units available that can be used for this purpose with a growing number aimed at achieving enhanced accuracy.

Motan-Colortronic placed its latest generation of its Minicolor V dosing and mixing equipment series into the spotlight at this year's NPE. The letter 'V' stands for volumetric. The disc dosing technology, suitable for small and micro quantities, represents the consistent addition to the Motan Minicolor G (gravimetric) screw dosing systems. The distinguishing feature of the new disc dosing unit is its high, consistent and sustainable repeatability. This is essential with direct dosing of microbatch and masterbatch, or when dealing with micro quantities of additives on a plastics processing system.
The Minicolor V disc dosing equipment series is used in injection moulding and in extrusion. This applies to applications where it is imperative that deviations in the prescribed dosing quantities are categorically avoided thereby ensuring no visible, measurable and functional divergences in the end product.

Attention to details
Excellent results have been achieved with refined disc dosing for the chemical, pharmaceutical and foodstuffs industries, as well as in the automobile sector. Every single detail counts, but first and foremost is the highest possible dosing constancy, together with maximum dosing accuracy, particularly in the case of translucent components. Precision is based on and depends on several criteria (parameters), all constantly and reciprocally influencing each other: CNC milled and ground disc geometries – with accuracies in the μm area; computer-generated cavity diameters and radii; continuously variable drive technology; microprocessor control and regulation; not a single grain of granulate can trickle through uncontrolled; and safe material change-over, without transfer of material residues.

The disc dosing technology has been systematically refined. In the meantime, constant repeatability accuracy of up to 1% has been established. To save on space, Minicolor V is mounted between the machine hopper and the feed throat of the plastics processing machine, directly on the entry flange. Up to two granular additive components can be fed into the free-flowing stream of the main material synchronously – via a stainless steel cruciform.

In the downstream processing step, all components are blended automatically and homogeneously. The dosing time is adjusted using the closed-looped control in relation to the screw-back time of the injection moulding machine or the screw speed of the extruder. The dosing unit can be calibrated simply and quickly. It is equally uncomplicated and fast to clean the equipment.

The Minicolor V disc dosing series is available in six different versions. The unit models with DD discs are equipped with special cutting technology, which if required can cut a plastic granule in half. Assuming a bulk density of 0.6 kg per litre, additive throughputs of 0.05 to 10.6 kg/h can be achieved. The models with DT discs operate using a wiper system and achieve additive throughputs of 0.37 to 340 kg/h. The selection of the relevant dosing disc is predetermined by the respective dosing disc and the dosing behaviour of the individual components. For higher additive throughputs, the Minicolor V equipped with a wiper is appropriate. For super fine dosing with small additive throughputs a DD disc with dosing knife should be used.

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