Test Parameters - Ametek BROOKFIELD DVNext Operation Instructions Manual

4.5 Test parameters

The Configure Yield Test screen includes several parameters to specify the test method; Spindle, Immersion Mark,
Pre-Shear Speed, Pre-Shear Time, Zero Speed, Wait Time, Run Speed, Torque Reduction, and Temperature. The
required parameters are Spindle, Immersion Mark, Run Speed and Torque Reduction. All other parameters are
optional including those shown below the More/Less bar; Yield Limit, Instructions, Save Path.
Spindle
Spindle Number
A two (2) digit code representing the spindle number used for the test must be selected. See Appendix A for more
information regarding spindles for use with the DVNext Rheometer. Selection of the appropriate spindle code is
important to ensure correct stress calculations. AMETEK Brookfield recommends the use of vane spindles for yield
measurements.
Immersion Mark
Each vane spindle has two (2) immersion marks. The primary immersion mark is located on the spindle shaft.
Normally, the spindle should be inserted so that the sample reaches this mark. If the sample container is too small to
allow the spindle to be inserted to this mark, the secondary immersion mark may be used. This mark appears half-
way down the blades of the vane spindles. See Appendix D for more information regarding spindles and immersion
marks.
Note: Selection of the appropriate immersion mark is important to ensure correct stress calculations.
Figure 4-5
Pre-shear speed and time
An optional Pre-Shear step can be included in the test parameters. The user must supply the pre-shear speed (0.01-
250 RPM) and pre-shear time (1 second-5 minutes 59 seconds).
Pre-shearing is the shearing of sample before measuring its yield properties. This process breaks down the
sample's structure. It is particularly useful if the investigator wants to eliminate previous shear history (e.g., bumping,
transferring) of the sample before testing and observe the structural rebuilding of the sample. This may simulate the
following: ketchup pumped out of a bottle will rebuild after it comes to rest on the French Fries. There are materials
whose measured yield stress will be lower after pre-shearing than if tested without pre-shearing. This may be used
to compare the rate at which different materials rebuild. The yield stress measured in a pre-sheared sample is the
"dynamic yield", while the yield stress measured for an originally undisturbed material is the "static yield". Zeroing
after pre-shearing is performed on the sample is highly recommended for every test. The next section explains how
to do this.
TIP: Set Pre-Shear Speed and Pre-Shear Time to zero if no Pre-Shear is required.
Zero
An optional, but highly recommended, torque Zero step can be included in the test parameters. A zero speed will
cause the rheometer to rotate the motor in the appropriate direction until 0% torque is achieved.
This may be necessary because the spindle sometimes twists a small amount during insertion into the sample.
This results in a small, although possibly significant, torque applied to the sample. Slow zeroing speeds are used to
M19-2101 REVISION 2.0 D V N E X T R H E O M E T E R - O P E R AT I O N A L M A N U A L 54