Time Tests and the Test of Time – The Jenike Direct Shear Tester
It’s been over fifty years since Andrew Jenike published Bulletin 123, which summarized how he used a direct shear cell tester to measure the flow properties of powders and then used the results to design reliable hoppers, bins, and silos.
Other shear cell testers exist, most notably the Schulze annular ring shear tester. Annular shear cells have the advantage of having unlimited strain, and because the powder is displaced within a narrow annulus, the state of shear during a test is approximately the same throughout the sample. The same cannot be said for torsional shear cell testers, in which a sample is placed in a cylinder and then rotated against itself. Let’s face it. There’s no displacement at the center, and to assume that an average is near the extremes requires ignoring mechanics.
A client once asked me if he could operate his ring shear tester at 650°C. I told him that he could, but he would have to then purchase another tester. Obtaining flow properties at conditions at which the bulk material is being handled is critical. Therefore, we measured the cohesive strength, wall friction, and compressibility of samples of his materials using a custom built direct shear cell tester, one that can be used at temperatures up to 1000°C. We have testers that can be operated in other extreme conditions, including subzero temperatures and high relative humidity. We’ve tested radioactive materials, and sadly, that particular tester will reside permanently in a nuclear waste disposal facility.
The flow properties of some bulk materials change with time, which is why we conduct “time tests”, where we keep a sample consolidated over a period of time to simulate storage at rest. Jenike’s test methods developed in the 1960s are still used today. Andrew Jenike’s test methods and design methods have indeed withstood the test of time.