Laray Viscometer Automated

The IGT Laray viscometer is designed to measure the viscosity of most viscous materials, especially of varnish, (high) viscous oils and paste printing inks.

Viscosity is the internal friction of a liquid in motion. In everyday terms the thickness of the fluid. The viscosity η (Pa.s) is generally defined as the ratio of shear stress σ (Pa) to shear rate ϒ (1/s). In a graph this ratio can form a straight or curved line.

With the Laray viscometer, the shear rate can be calculated from the fall time of the rod and the shear stress can be calculated from the weights used. The Laray automated viscometer is equipped with calculation software. This program, puts the shear rate and the shear stress in a graph. The viscosity is the reciprocal of the slope of the line.

The viscosity can only be calculated with this program when the ratio between shear stress and shear rate is a straight line. This is true for a Newtonian liquid and a Bingham plastic. A Newtonian liquid gives a straight line through the origin, η = σ/ ϒ.

A Bingham plastic needs a minimum stress, the yield stress σ0 to initiate the flow. In the graph in Excel format you can notice when the liquid is a Bingham plastic when the straight line does not go through the origin but crosses the X-axis at a certain point (η = (σ-σ0) / ϒ). This point is the yield stress. You can find this value in the calculations.

Software

The built-in software is Android based and has been programmed in such a way that the use is very intuitive and easy. It is ready to use as soon as the Main Menu has appeared on the screen.

Method of operation

• The nip between the rod and cup is filled with the ink to be tested.
• After releasing the rod, it passes two sensors. The first sensor starts the measurement, the second one stops it.
• The speed at which the rod falls down is dependent on the weight placed on top of it.
• After the test, data can be reviewed and transferred to a PC by means of a USB stick.

Standards

The falling rod test method, as well as the instrument itself, have been standardised according to ISO 12644 and DIN 53222.