Test parameters and turbulence are two key factors to consider when preparing to test with a rotational viscometer. The spindle, speed setting, and temperature of the product are some of the parameters that can impact test results. Additionally, turbulence in the sample’s flow during a test will distort viscosity readings. Knowing how to manage these two factors can significantly contribute to the accuracy of your testing.
The first key to accurate viscosity testing is maintaining consistent test parameters. Following are the parameters that need to be exactly the same for every test you run:
Two common scenarios that utilize viscosity testing are quality control and product development. In each of these situations, there are strategies relating to the two key factors discussed above which you can use to ensure that the testing is accurate.
When a quality control test shows that the viscosity of a product is outside its usual range, the question arises: is there something wrong with the product, or is the viscometer not working properly? There are steps you can take to answer this question.
First, check that the flow is non-turbulent, and that the test parameters are exactly the same as the tests you’ve run on previous batches. If your instrument is capable of saving test parameters for future use, do so. If not, keep a list beside the instrument detailing the test parameters that are to be used for each product your company tests.
A temperature control accessory (sometimes called a thermostatic accessory) may be necessary if the product is hotter or colder than room temperature during testing. This accessory will keep the product at a consistent temperature for each test you run. In the unlikely instance that the product is at room temperature during testing, but you notice that there is a significant change in viscosity with only a degree or two difference in temperature, you might also want to consider using a temperature control accessory to maintain precisely consistent parameters.
If the test parameters were consistent with previous tests, you can do either or both of the following, depending on your instrument’s capabilities. First, if the viscometer has the capability, run a zero setting. The zero setting simulates a test without the spindle attached. Think of it almost like a “re-set” button. Once that’s done, test the product again.
If you’re still getting an unusual result, follow the viscometer’s calibration procedure, using a standard calibration oil.
Once you’ve ruled out an instrument fault, you can be assured that an aberration in the test result is due to the product itself, and take the appropriate action to resolve the situation.
As with quality control testing, it’s also important to ensure non-turbulent flow and consistent test parameters during testing in the product development stage. Doing so allows you to monitor the effects of formulation adjustments to your product. If the flow was smooth and the test parameters were consistent with previous tests, you’ll know that any changes to the product’s viscosity were a result of changes to the formula.
When you’re doing R&D (research and development), you don’t always know what the test parameters ought to be. You may need to determine your own test parameters for use during product development. If so, here are some things to consider for each of the parameters:
Accurate viscosity testing isn’t as tricky to do as it might sound. If you clearly difine the test parameter for each product, most instruments will give repeatable results. Some viscometers let you save test parameters on the instrument, so it’s even easier to prepare and run a test. Even if your instrument doesn’t have this capability, most viscometers are still pretty user-friendly, and it shouldn’t be too difficult to manually input the parameters for each test.
'Til next time!
P.S. If you need help choosing the right instrument, spindles, or parameters for your test, contact us and tell us about your product and testing needs.
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