Viscometer

Rotational Rheology and Viscosity Fundamentals

Viscometers determine fluid thickness by placing a sample under controlled mechanical shear and recording the resulting resistance.

Dynamic Viscosity (η) = Shear Stress (τ) / Shear Rate (γ̇)

       Applied Rotational Force (F) ---------------->
    +-------------------------------------------------------+  Moving Boundary (Velocity v)
    |   Fluid Layers Sliding in Shear (dv/dy Gradient)      |
    +-------------------------------------------------------+  Stationary Boundary (v = 0)
                               Gap Height (y)

• Shear Stress (τ = F / A): The frictional force applied per unit contact area parallel to fluid motion, expressed in Pascals (Pa) or N/m².
• Shear Rate (γ̇ = dv / dy): The velocity gradient across the shearing gap, expressed in reciprocal seconds (s¹).
• Dynamic Viscosity (η): The ratio of shear stress to shear rate, quantified in Centipoise (cP) or Pascal-seconds (Pa·s), where 1 mPa·s = 1 cP = 10³ Pa·s.
• Kinematic Viscosity (ν = η / ρ): Gravity-driven flow resistance relative to fluid density (ρ), expressed in Centistokes (cSt) or mm²/s.

Digital Rotational Viscometry (ViscoQT Family)

Digital rotational systems calculate dynamic viscosity by rotating an immersion spindle inside a fluid sample at a regulated speed, measuring the fluid drag that opposes the drive shaft.

       [ Digital Torque Transducer / Calibrated Sensor Spring ]
                                  |
                                  v
       [ Stepper Motor (Stepless Variable Speeds: 0.1 to 250 RPM) ]
                                  |
                                  v
       +------------------------------------+
       |          Rotating Spindle          |
       |  (Fluid drag creates counter-torque|
       +------------------------------------+
       |~~~~~~~~~~~~ Test Sample ~~~~~~~~~~~|

Couette Flow Principle

Operating on Couette flow mechanics between concentric boundaries, dynamic viscosity (η) is calculated through the Margules equation:

η = [ M / (4 π L Ω) ] × [ (1 / R_i²) - (1 / R_o²) ]

Where M is the measured retarding torque, Ω is angular velocity in rad/s, L is effective spindle length, and R_i and R_o represent the spindle and container radii.

ViscoQT Operating Specifications

The digital ViscoQT Family pairs with interchangeable rotor sets (LV sets for low-viscosity liquids; RV, HA, and HB sets for dense formulations):

• Viscosity Range: 5 mPa·s up to 320,000,000 mPa·s (320M cP).
• Rotational Speed Range: 0.1 to 250 RPM (model-dependent stepless selection).
• Measurement Accuracy: ±1.0% of full scale range.
• Repeatability: ±0.5% of full scale range.
• Test Standards: ASTM D2196, ISO 2555, ISO 3219.

Dial-Reading Viscometry (ViscoQT DR-100)

For workshop verification and routine bench testing where digital interfaces are unnecessary, analog dial instruments calculate fluid drag through direct mechanical spring deflection.

       [ Mechanical Pointer / Calibrated Dial Scale ]
                             |
                             v
       [ Multi-Speed Gear Drive (6 / 12 / 30 / 60 r/min) ]
                             |
                             v
       +--------------------------------------------+
       |   Selectable Cylindrical Rotors (No. 1–4)  |
       +--------------------------------------------+

Mechanical Deflection Principle

The ViscoQT DR-100 drives interchangeable immersion rotors (Rotors No. 1 through 4) through a fixed-step gear train. Fluid resistance twists an internal beryllium-copper spring, driving a pointer along a calibrated dial scale.

• Viscosity Range: 10 to 100,000 mPa·s (cP).
• Selectable Speeds: 6, 12, 30, and 60 r/min.
• Accuracy: ±5.0% of full scale for Newtonian standards.
• Target Applications: Workshop checks for mineral oils, paints, adhesives, and varnishes.

High-Shear Cone and Plate Method (QualiCAP™ Series)

Cone and plate viscometers evaluate fluid flow under elevated shear conditions, simulating application processes such as roller coating, brushing, and spray atomization.

                 \  Inverted Cone Spindle (Angle θ ≤ 2°) /
                  \                                     /
                   \                                   /
             -------+---------------------------------+-------
             =================================================
                    Flat, Rapid-Equilibrium Thermal Plate

Uniform Shear Rate Geometry

A shallow metal cone (θ ≤ 2°) rotates above a flat, temperature-controlled plate, holding a micro-sample under 1 mL. Because gap clearance increases proportionally with distance from the center apex, the shear rate remains uniform across the entire sample area:

Shear Rate (γ̇) = Ω / θ

Dynamic viscosity (η) is derived from measured torque (M) and cone radius (R):

η = (3 M θ) / (2 π R³ Ω)

QualiCAP™ Operating Specifications

• Viscosity Range: Up to 1,500,000 mPa·s (cone spindle dependent).
• Speed Range: Continuous adjustment from 5 to 1,000 RPM.
• Measurement Accuracy: <2.0% of full scale.
• Sample Volume: Micro-samples under 1 mL with fast temperature stabilization.
• Test Standards: ASTM D4287, ISO 2884-1, BS 3900.

Krebs-Stormer Consistency Method (KS-Series)

The Krebs-Stormer method is the standard test format for architectural paints, coatings, and printing inks.

                  Synchronous Motor Drive (Locked at 200 r/min)
                                       |
                                       v
                            +--------------------+
                            | Offset Paddle Rotor|
                            +--------------------+
                            |~~~~ Paint Sample ~~|

Fixed-Speed Torque Conversion

The KS-Series Krebs Stormer Viscometer rotates a standardized paddle rotor at a regulated speed of 200 r/min ± 0.1 r/min (ASTM D562). Motor resistance converts directly into three standard industrial metrics:

• Krebs Units (KU): 40.2 to 141.0 KU (coatings industry consistency scale).
• Dynamic Viscosity: 27 to 5,250 cP (mPa·s).
• Gram Load: 32 to 1099 gm (equivalent driving weight value).
• Accuracy and Repeatability: ±1.0% of full scale with ±0.5% repeatability.
• Test Standard: ASTM D562.

Non-Newtonian Flow Characterization

Rotational and cone-and-plate viscometers characterize how fluid formulations respond under variable shear rates and mechanical agitation:

       Shear Stress (τ) vs. Shear Rate (γ̇)           Apparent Viscosity (η) vs. Shear Rate (γ̇)

  τ |     / Bingham Plastic (Yield Point τ0)     η | \
    |    /                                         |  \ Shear-Thickening (Dilatant)
    |   /   / Dilatant                             |   \----------------- Newtonian (Constant)
    |  /   /                                       |    \
    | /   /-- Newtonian                            |     \ Shear-Thinning (Pseudoplastic)
    |/  /                                          |      \
    +------------------------ γ̇                    +------------------------- γ̇

• Newtonian Fluids: Viscosity remains constant across all rotational speeds (water, calibration standard oils, pure solvents).
• Pseudoplastic (Shear-Thinning): Viscosity drops as rotational speed increases (coatings, lotions, polymer solutions). Governed by the Ostwald-de Waele formulation: 
  τ = K · γ̇ⁿ (where n < 1)
• Dilatant (Shear-Thickening): Viscosity increases under elevated agitation (dense mineral slurries, starch suspensions, where n > 1).
• Bingham Plastics: Materials require a threshold yield stress (τ₀) before deformation begins (drilling fluids, toothpastes, greases). Governed by the Herschel-Bulkley formulation: 
  τ = τ₀ + K · γ̇ⁿ
• Thixotropic Materials: Viscosity decreases over time under sustained spindle rotation, rebuilding structure once agitation ceases.

Product Specifications and Compliance Matrix