Flow behaviour

Flow behaviour is determined by the physical properties of a material, including viscosity (resistance to flow) and shear stress (the stress acting on the material). Depending on the type of material, there are different types of flow behaviour.

Types of flow behaviour

Type	Description	Examples
Newtonian flow	Constant viscosity, independent of shear stress.	Water, thin oils
Shear-thinning flow	Viscosity decreases with increasing shear stress.	Paints, printing inks
Shear-thickening flow	Viscosity increases with increasing shear stress.	Starch-water suspensions
Plastic flow	Material only flows once a certain shear stress is exceeded.	Toothpaste, mayonnaise

Flow behaviour has a direct influence on the processing and quality of materials. It plays a decisive role in various industries, including plastics and elastomer processing.

Applications of flow behaviour

Industry	Applications	Importance of flow behaviour
Plastics processing	Extrusion, injection moulding	Influences shaping and surface quality
Paint and coatings industry	Production and application of paints	Ensures an even coating
Oil and gas industry	Transport of crude oil and gases	Enables efficient flow in pipelines

Flow behaviour is measured using various methods and instruments that analyse viscosity, shear stress and other parameters.

Measuring methods

• Rheometer: measures viscosity and other flow-related properties at different shear stresses and temperatures.

• Capillary viscometer: determines the flow rate of a material through a narrow capillary.

• Rotational viscometer: measures the dependence of viscosity on torque and rotational speed.

• Temperature: higher temperatures generally reduce the viscosity of a material.

• Pressure: for many materials, higher pressure increases flowability.

• Composition: additives and fillers change the flow behaviour to achieve specific properties.

• Higher product quality: even distribution and processing of the material.

• Increased efficiency: reduced material and energy consumption in production.

• Optimised process control: minimisation of production errors and downtime.

• Material complexity: non-Newtonian materials react differently to changes in temperature and pressure.

• Measuring accuracy: precise measurements are difficult for highly viscous or strongly shear-thinning materials.

• Costs: highly specialised measuring instruments and adjustments require investment.

Feature	Newtonian flow	Non-Newtonian flow
Viscosity	Constant	Varies with shear stress
Examples	Water, thin oils	Paints, starch-water suspensions
Measurability	Simple	Complex
Processing	Independent of processing parameters	Dependent on shear stress and temperature

• Why is flow behaviour important? It influences the processability and quality of the end product in numerous industries.

• How is flow behaviour optimised? By adjusting processing temperatures, using additives and precise process control.

• What is the difference between viscosity and flow behaviour? Viscosity is one aspect of flow behaviour and describes the resistance to flow.

• What role do additives play in flow behaviour? Additives can increase or decrease viscosity to adapt the material to specific applications.

Flow behaviour is an essential factor in the processing of liquids, melts and viscoelastic materials. Precise control and analysis of this behaviour enables the manufacture of high-quality products and optimises industrial processes. Whether in plastics and elastomer processing, food production or the chemical industry, understanding flow behaviour is crucial to success.