Brookfield DV-III Ultra Rheometer - Manual (Page 61)

Brookfield Engineering Laboratories, Inc. Page 61 Manual No. M98-211-E0912
An Example of the Bingham Model at Work
A manufacturer of drilling fluid applies the
Bingham Model to ensure the quality of their
product. Results from a recent batch, shown
in Figure VI-50, showed that the yield stress
and plastic viscosity were both below the
pass/fail criteria, which would cause the fluid
to insufficiently hold-up the cuttings. The
shipment was cancelled and the root-cause
of the problem was identified.
Drilling Fluid
Plastic Viscosity (
η
) = 6621 cP
Yield Stress (
€
t
o
) = 166.4 dynes/cm 2
IV.7.4 The Casson Model
€
t = t
o
+ h
D (
€
t
= shear stress,
€
t
o
= yield stress, η = plastic viscosity, and D = shear rate)
What does it tell you?
The Casson model provides parameters similar to that of the Bingham model. However, unlike
the Bingham model, it was developed for materials that exhibit non-Newtonian flow after yielding.
The Casson model indicates the product’s yield stress (
€
t
o
) which is the amount of shear stress
required to initiate flow, and the product’s plastic viscosity,
η
, which is the viscosity of the product
after it yields.
Figure IV-51