Viscoelastic

The term ‘viscoplastic’ describes a rheological behaviour in which materials undergo plastic deformation under mechanical stress, whilst exhibiting high internal resistance. Although the material yields, it does not flow freely like a liquid, but only sluggishly. Viscoplastic materials require a minimum stress to flow. Below this stress, they remain largely dimensionally stable or deform only very slowly. Above this stress, permanent deformation sets in. Once the stress is removed, the material does not return to its original shape.

In process engineering, viscoelastic consistencies are frequently found in pastes, slurries, doughs, polymer compounds, suspensions with a high solids content, and certain chemicals. Viscoelastic consistencies can also develop during vacuum mixing and drying or contact drying.

This viscoelastic behaviour places particular demands on mixing, kneading, conveying and dosing. High torques, robust mixing tools and a suitable geometry are required to achieve homogeneous mixing. At the same time, the energy input must be carefully controlled so as not to compromise the product structure and quality.

Viscoelastic materials cannot be clearly classified as either solids or liquids. However, they must be capable of being processed in the equipment from which they are discharged as the final product. This is often achieved using amixon vacuum contact dryers, from which the material is discharged as a free-flowing powder.