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If you are a rheometrist, please take my 5-minute survey here: https://forms.gle/Pr9VHfbNcaGNpW87A
Contact me directly by email or Linkedin profile if you would like to talk about using 3D-printed tools in your lab (not for sale, but for testing and collaboration).
See more design and implementation details below.
Like a drill bit for a drill, a rheometer needs a tool attached to interact with fluid and measure the complex viscosity. Some tools are better than others overall, and some tools are best for specific applications.
This project combined optimized design with 3D printing and fluid mechanics to redesign the "4-arm vane" and cylindrical DIN rotor into a tool with a fractal cross section to generate a much more homogeneous shear stress profiles without causing excessive sample displacement when loading. This enables accurate measurement data even for "very" complex fluids.
This is paired with a custom-designed separable cup to facilitate loading and cleaning of these "very" complex fluids.
Example design of the cup: it is composed of two parts connected by custom acme threads for fluid-tight seals. Depending on the printer you use to fabricate it, it may require additional sealant between the threads.
Six lower arms grip onto the native Peltier plate of the DHR rheometer, centering the cup.
The vane itself is composed of a back coupling to the rheometer's M14 shaft with a light interference fit (~ 50 µm overlap), and a threaded insert, and the front fractal section with a uniform cross-section.
Printing tolerances with our Form2 are marginally able to produce the right fit on the coupling, but can be thrown off by variations as small as printing in a different orientation. As long as approaches are consistent, however, a vane can be printed, washed (but not UV cured), and immediately used on the rheometer with a new sample, producing reliable rheological flow data.
After design, vanes were printed by stereolithography using a Form2 3D printer.
After printing, tools were mounted onto the rheometer shaft and the runout was assessed using a Keyence laser profilometer (projecting a blue line here to create a surface map).
The maximum point of the projected profile was tracked while rotating the vane many times to extract the runout at that height. This test was then repeated for different heights and then coupling designs.
Following this, with multiple design iterations varying the coupling size, coupling type, material, and finishing steps, principal component analysis (PCA) was performed to extract the most significant and optimized coupling designs. The inner diameter of the printed vane and the type of threaded insert were found to be the most significant parameters to ensure low runout.
We selected an embedded nut as the best inserted coupling for this application.
As-printed threads worked well, but only for 2-3 attachments before the plastic threads began to wear.
Finally, measurements could be made using the printed tools. Here, a measurement was made on ketchup still in the bottle. This demonstration shows the main advantage of the fractal-like structure: it minimizes sample displacement, allowing measurement of the ketchup properties as they have aged on the shelf for days to months. In comparison, other measurement tools would disrupt and change this structure when loading the tool into the dispensing bottle, leading to false measurements of disturbed samples.
For more information
For more information
The full article is freely accessed here: https://arxiv.org/abs/1910.10785
Downloadable printing files may be accessed as supplementary files to our original paper: https://sor.scitation.org/doi/10.1122/1.5132340
If you're interested in licensing this technology, contact me or see here: https://tlo.mit.edu/technologies/fractal-vane-rotors-rheology-measurements-yield-stress-fluids
Please contact me via my Linkedin or at rheo3D (at) mit.edu if you have interest in developing a similar tool for your specific needs.
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