Conveying attrition is shaped by particle strength, relative velocity and where impacts occur. Reviewing those drivers together helps explain why a change that protects one product can create wear or breakage elsewhere in the line.
Air Velocity and Particle Velocity Are Different
The conveying gas accelerates particles through drag. Particles normally move more slowly than the gas, and the difference depends on size, density, shape, concentration and pipeline orientation. A large dense granule responds more slowly to a bend than a fine low-density particle and may strike the outer wall more directly.
Increasing blower airflow generally raises gas velocity and eventually particle velocity, but the relationship is not one-to-one. Pressure expansion along a positive-pressure line also changes the gas profile. The correct analysis therefore considers local actual velocity and material response rather than applying one inlet value to the entire route.
Collision Energy Rises with Velocity
As particle velocity increases, more energy must be dissipated during impact. For many friable products, a modest velocity increase can produce a disproportionately larger amount of fines or breakage. The exact relationship and any threshold are material-specific.
Representative impact or conveying tests should use the actual product grade and agreed damage criterion. Published values for a similarly named material can help rank risk but should not become a contractual limit without compatibility evidence.
Particle Size Changes Both Inertia and Strength
Larger particles of the same density carry more mass and tend to resist changes in direction. They may therefore hit bends or vessel walls more severely. At the same time, larger particles can contain more cracks, pores or weak interfaces.
Smaller fragments may follow the gas more readily, but they can increase dust load, filtration demand and segregation. As material degrades, its aerodynamic behavior changes. This feedback means the product leaving the line may not convey like the original feed if it is recycled.
Impact Angle Controls the Stress Mechanism
A near-normal impact creates rapid deceleration and high internal stress, often promoting fracture in brittle particles. A shallow impact can encourage sliding, abrasion or edge chipping. Neither condition is universally safe; the relevant failure mechanism depends on the product and surface.
Bend radius, pipe bore, particle inertia and upstream flow determine the trajectory. A long-radius bend can reduce abrupt direction change for one material while allowing another particle class to slide along the outer wall. Selection should therefore use product-specific evidence and consider the exit trajectory into the next section.
Target Surface Changes the Collision
Rigid metal surfaces deform little and can return or transmit impact energy differently from resilient linings. Elastomers or flexible hose may reduce peak impact for some products, but they must also meet abrasion, chemical, temperature, hygiene and contamination requirements.
A worn or deposited surface changes behavior again. Product buildup may temporarily cushion impact while creating restriction or cross-contamination. Component inspection and controlled test conditions are essential when comparing surface options.
Solids Concentration and Repetition Matter
At higher concentration, particle-to-particle contact may shield some wall impacts but introduce compression, rubbing and chipping. At lower concentration, more particles may encounter the wall at high relative velocity. The net result is material- and regime-dependent.
Damage is cumulative. Count bends, distance and handling cycles separately. Five passes through a compact loop can be more severe than one plant transfer even when the total distance appears similar.
Convert the Driver Matrix into Control Priorities
Rank each driver by sensitivity and controllability. Blower speed and airflow may be adjustable; pipe bore, bend geometry and receiver entry are physical; particle strength and temperature may come from the upstream process. Prioritize changes that reduce the dominant damage mechanism while preserving stable transport.
Attrition control works best when material friability, particle impacts, gas velocity and route geometry are assessed together. Record both the product-quality criterion and the stable transport window in the design basis.
Glossary
Attrition driver: Material, flow or component variable that changes the severity or type of particle damage.
Collision energy: Kinetic energy that must be dissipated when a particle strikes another particle or surface.
Cumulative exposure: Total number and severity of conveying events experienced across all handling cycles.
Impact angle: Angle between particle trajectory and the surface it strikes.
Particle lag: Difference between gas velocity and the lower velocity of conveyed particles.
Target surface: Component surface against which a particle impacts, slides or rebounds.
Trajectory: Path followed by a particle through a bend, fitting or receiver entry.