Coneplates

Coneplates refer to a geometry used in rheometers to measure the flow and deformation behavior of liquids and soft solids. The setup consists of a rotating or oscillating cone positioned above a flat plate, with a small, well-defined gap between the surfaces. A sample is placed in the gap, and rheological properties are inferred from the torque and rotational motion.

In operation, either the cone or plate is driven to rotate, while the other surface remains stationary. The cone’s small angle creates a gap that increases linearly with radius, producing a nearly uniform shear rate across the sample. For a rotating cone, the shear rate is approximately the angular velocity divided by the tangent of the cone angle. The instrument measures torque and speed (or stress and strain in oscillatory tests) to determine viscosity and, for non-Newtonian materials, the viscoelastic moduli. Temperature control is often integrated to ensure stable conditions.

Geometry and typical values are defined by the cone angle and cone radius. Cone angles are small, often in the range of about 0.5 to 4 degrees, and radii commonly span tens of millimeters. The gap at the plate centre is essentially zero and grows with radius, giving a well-characterized shear field. Because only a small volume of sample is required, coneplates are efficient for testing expensive or scarce materials, while enabling precise, repeatable measurements over wide shear rates and frequencies.

Applications include polymer melts, paints, coatings, cosmetics, and food products. Advantages include uniform shear and rapid equilibration; limitations involve evaporation effects for volatile liquids and limitations for extremely high-viscosity samples or highly elastic materials.