Powders fool people. At first glance, they look dry, clean, and easy to handle. However, anyone who’s worked on a plant floor knows the truth. Powders stick. They clump. They form bridges. They clog hoppers and hold up production.

Ultimately, this isn’t just about friction. It’s about shear—the internal resistance a powder shows when you try to make it move. In short, shear is what decides whether material flows freely or locks into place. If you understand it, you stay ahead of the problems. If you don’t, you lose time and money.

Before the 1950s, bulk solids handling was trial and error. You fixed blockages with hammers, air blasts, or worse. Every operator had their tricks. None of it was predictable.

Then Andrew Jenike stepped in. He created a shear tester that gave hard data, cohesion, internal friction, and flow resistance. Finally, engineers had a way to measure what was really happening inside the bin.

That changed everything. Jenike’s method turned powder handling into real engineering, laying the foundation for many of today’s best practices in powder handling and processing. And his shear cell became the foundation of flow design.

Shear happens when particles slide past each other. Think of pushing a stack of paper. At first, it resists. Push harder, and the sheets shift. In powders, it’s more complicated. Tiny forces, such as moisture, van der Waals, and electrostatics, hold particles together. Even a small change in humidity or vibration can throw everything off. Some powders flow easily, like sand. Others, like fine pharma blends, resist movement with surprising strength. And that resistance can change overnight. That’s why shear testing is regularly done to stay in control of the flow properties, especially when combined with broader flow and flowability testing.

Shear affects everything.

In pharma, poor flow leads to bad dosage. Some tablets end up too strong. Others, too weak. That means recalls, fines, and risk.

In food, powders that clump hold up mixing. A silo jam can stop production cold.

In 3D printing, flow inconsistency ruins prints. Layers fail. Voids form. Waste increases.

Even in mining or cement, unstable flow can be detrimental to the production process. When a bridge inside a silo collapses, the sudden surge can wreck conveyors or possibly spark a dust explosion.

The Jenike shear cell is still the standard. It compresses a sample, then applies lateral force until it fails. You run it at different loads and plot a yield locus, a curve that shows how shear strength changes with consolidation. From that, you get the flow function. If the curve is steep, expect trouble. If it’s flat, the material flows.

Other methods add to the picture:

• Ring shear testers rotate the sample, useful for long-term storage or slow flow.

• Uniaxial testers compress and release the powder. They’re quick but not as detailed.

In some cases, engineers or lab technicians also test wall friction, how powders interact with the bin surface. That’s critical for hopper design.

Yes, it happens. A powder that flows just fine during testing may clog after a week in the silo. Why? Research shows that shear cell size significantly impacts measured flowability; the effect of shear cell size on measured flowability should be considered when comparing lab results to plant performance.

• Time consolidation locks particles together.

• Vibration compacts the bed slowly over time.

• Humidity turns a dry blend into a sticky mess.

Good labs know this. They test powders under real-world conditions, humidity control, vibration exposure, or added time under load. Some even use powder rheometers to simulate what happens during mixing or conveying.

The point is clear: test what the powder will actually face, not just what fits in the cell.

Once you understand the shear behavior, you can act:

• Add flow aids like colloidal silica to reduce friction.

• Use mass-flow hoppers to avoid stagnant zones and bridging.

• Apply anti-caking agents to stop moisture absorption.

Fine-tune the process too:

• In milling, slow the rotor to reduce fines that make the powder more cohesive.

• With pneumatic systems, adjust air velocity to avoid over-shearing the product.

Real-time sensors help catch problems early.

• Load cells detect compaction.

• Near-infrared probes monitor changes in moisture and cohesion.

Catch it early, fix it fast. That’s the goal.

Powders are evolving. Nanomaterials, specialty alloys, and engineered blends don’t behave like anything you’ve tested before. So the tools are changing too.

• X-ray tomography shows how particles rearrange during flow.

• Machine learning predicts behavior from past test data.

• Industry 4.0 brings sensors into hoppers and feeders, tracking flow in real time.

Still, the core issue hasn’t changed. Powders don’t act like solids or liquids. They fall in between. That’s where mistakes are made. Shear testing bridges the gap. It tells you when a powder will flow, when it won’t, and what to do about it. It’s not a luxury. It’s the baseline.