MACHINERY | MIXERS
Above: A new abrasion wear testing approach has been devel- oped at the Bulk Solids Innovation Centre at Kansas State University
This stretching of the flowing material is orderly, and all material is stretched the same,” claims Luker. He says that each set produces 1,000-times better mixing than a typical single-screw metering section and the cumulative effect of the seven sets creates very good distributive mixing. Luker points to experiments that he says prove
that the mixer is mixing at the level of small molecules, such as water. “When we processed undried PMMA (a hygroscopic material with typical levels of 0.3% entrained water vapour), we did not see any bubbles in the extrudate. The mixing is so good that the water vapour is unable to agglomer- ate into water droplets; we’re keeping the water vapour inside the material,” he says. Similar results have been found with PET, he says, which is even more hygroscopic. The Randcastle laboratory continues to run experiments to evaluate potential benefits of the mixer for hygroscopic polymers, which could include eliminating the need for drying of resin pellets. Molecular-level mixing is also important for carbon nanotubes, graphene, conductive materials, or other compounds where it is crucial to have even mixing throughout the material, says Luker. Work carried out at Randcastle has shown that carbon nanotubes can be mixed well to the 1-micron scale. Luker sees the Molecular Homogenizer being used as a standalone mixing device. However, he says it could also potentially be employed at the end of a twin-screw extruder to further homogenise the melt.
Assessing wear Researchers at the US Kansas State University (K-State) Bulk Solids Innovation Center recently developed a test for measuring abrasive wear of equipment used to handle dry bulk materials. “Compounds are often abrasive, so they wear out mixer components very quickly,” says Todd W
50 COMPOUNDING WORLD | November 2021
Smith, who manages the centre. “Conveying of the compounded materials is difficult because they are so abrasive, causing expensive outages and repair. Exotic wear-resistant metals and coatings are available, but they are expensive, often doubling or tripling the price of the component. And there are many wear-resistant options, so it is hard to know which one to use.” After hearing complaints from compounders and other bulk solid material users and finding that available methods were not relevant for this specific need, the researchers developed a testing device and method, says Smith. “The new Abrasive Wear Tester lets us evaluate the relative abrasive- ness of various compounds, as well as the wear resistance of various metals, coatings, plastics, and ceramics. It is relevant for equipment manufactur- ers who build mixers and conveying equipment for compounds and masterbatch. And it is relevant for the companies who are doing the compounding.” Smith says that in the standard configuration of
the three-body abrasive wear test, a test sample coupon (such as metal, coated metal, or plastic) is placed in the test chamber, fresh powder (or other bulk solid material) is continually fed into the abrasion point, and a device rubs the bulk solid against the coupon. The speed and force of the abrasion can be varied and the wear upon the coupon is determined by measuring the depth of wear after a predetermined time. The test is useful for comparing materials of construction for equipment such as conveyors, bins, chutes, and mixers, says Smith. He says that, in addition to comparing materials, the tester can also give an indication of how long equipment will last under abrasive conditions. “In most cases, this is done by first establishing a baseline for a known application. For example, if a mixer or conveying component is known to last for a certain amount of time, then K-State’s Abrasive Wear Tester is set up to measure the wear using that application’s materials for both the sample coupon and the abrasive bulk solid. Then any changes to either the coupon or the bulk solid can be compared to the base line,” he says.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.zeppelin-systems.com �
www.mixaco.com �
www.reliancemixers.com �
www.plasmec.it �
www.promix-solutions.com �
www.readco.com �
www.randcastletechnology.com �
https://bulk-solids.k-state.edu
www.compoundingworld.com
IMAGE: KANSAS STATE UNIVERSITY
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