Grinding Particle Size Distribution (Sieve Analysis)

Particle size distribution describes the range and spread of particle sizes produced when raw ingredients are ground, typically by hammer mill, before mixing and pelleting or extrusion, measured by passing a sample through a stack of progressively finer sieves and weighing what remains on each, and it is a foundational process variable because nearly every downstream quality attribute, pellet durability, starch gelatinization efficiency, nutrient digestibility, mixing uniformity, depends partly on how finely and how consistently the mash was ground before it ever reaches conditioning. Finer, more uniform grinding generally improves pellet binding and durability (more particle surface area for binding compounds to act on) and can improve digestibility for some ingredients, but over-fine grinding increases energy cost and processing time without further quality benefit past a certain point, so mills target a particle size distribution appropriate to the specific formulation and target species, larval and early juvenile diets typically requiring finer, more uniform grinding than coarser grow-out feeds to match smaller mouth gape and digestive capacity. A wide particle size distribution, a mix of very fine and very coarse particles rather than a tight, consistent range, can cause segregation during subsequent handling (finer particles settling differently than coarse ones in storage bins or during pneumatic conveying), introducing formulation inconsistency between batches even when the original ground mash met its average target specification. Hammer mill screen size, hammer condition, and throughput rate are the main controllable process variables determining the resulting particle size distribution for a given raw material.