Reduced unit costs, simplified storage and greater speed and flexibility when changing colours are all factors which favour in-house colouring.
Appropriate peripherals are necessary for optimum material mixing and dosage. For the simplest applications, a volumetric dosage system is sufficient. In combination with an adapted plasticising system - generally screws with rhombus-shaped mixing elements are used - excellent, reproducible colouring results can be achieved.
Rhombus-shaped mixing elements ensure homogenous mixture of the melt, preventing the formation of colour streaks. Moreover, through optimum homogenisation it possible to reduce the proportion of additives, lowering material costs.
Rohmbus-shaped mixing elements are available for screws with diameters starting at 30 millimetres and a L/D ratio greater than 20. A further option for improving the mixing effect in the melt is the use of nozzles with a static mixing section.
For greater dosing accuracy and process reliability, gravimetric dosage systems are available as well as volumetric ones. Through the precise weighing of the compound components, high demands with regard to colouring results, colour fidelity and the relevant tolerances can be met.
Precise colouring of plastics requires comprehensive process and applications engineering consulting from the material and machine manufacturers. Our AT department is also a competent contact in this respect.